Hail Cannon Report
San Luis Valley, CO 2008
Wendy A. Ryan1
Nolan Doesken2
Colorado Climate Center
Department of Atmospheric Science
Colorado State University
Fort Collins, CO 80523-1371
December 2008
1. Wendy Ryan, Research Associate II, wendy.ryan@colostate.edu 970-491-8506
2. Nolan Doesken, State Climatologist, nolan@atmos.colostate.edu, 970-491-3690
I. Introduction
This report describes observed precipitation patterns in the
San Luis Valley of Colorado during the growing season of
2008. A weather modification permit was granted by the
Colorado Water Conservation Board to Southern Colorado
Farms (SCF) near Center, Colorado. SCF operates hail
cannons in and near large irrigated fields with center pivot
irrigation systems. The permit was
granted with the condition that
careful monitoring of rainfall and
hail be performed to provide public information and documentation on
the possible impacts of hail cannon operations. The permit allowed for
hail cannon operation during the primary growing season for this region
from June 15th through September 15th. This is also the time of year
with the highest probability for hailstorms. This report summarizes
available climate data collected in the San Luis Valley for the 2008 growing season.
II. Geography
The San Luis Valley is a large intermontaine
valley located in south-central Colorado
surrounded by the Sangre de Cristo Mountain
Range to the east and the San Juan and La
Garita Mountain Ranges to the west. There
are five counties that are partially or totally
included in the San Luis Valley: Alamosa County, Saguache County, Rio Grande County,
Conejos County, and Costilla County. Southern Colorado Farms is located in south central
Saguache County. The valley floor covers approximately 3,200 square miles and sits at an
average elevation of 7,500 feet. Although the valley itself is arid, the surrounding mountains’
2
snowmelt provides surface runoff and groundwater recharge to support extensive irrigated
farming in the valley. The Rio Grande is the predominant river basin encompassing much of the
southern and western reaches of the valley. The north portion of the valley is a closed basin.
The central portion of the San Luis Valley is extensively irrigated. Alfalfa, potatoes, barley,
spinach, and lettuce are primary high-value crops in this region. Some of these crops are very
sensitive to hail. Climatic risks to agriculture include freeze damage, wind damage, hail damage
and limited available irrigation due to periodic drought and lowering ground water levels.
III. Climatology
The majority of Colorado is described as semi-arid. Only the high terrain of the Rocky
Mountains typically receives more than 20” of precipitation annually. The San Luis Valley is the
driest contiguous area in the state. Figure 1 shows the 30-year climate average (1971-2000) for
annual precipitation for Colorado. The San Luis Valley is shaded in the deepest orange (<9”),
with most of the valley averaging between 7 and 8” rain and melted snow per year. Precipitation
increases dramatically with elevation in almost every direction, with much of the surrounding
mountains receiving 20-48 inches of precipitation annually.
3
San Luis Valley
Figure 1: Colorado annual precipitation (1971-2000) from PRISM.
There are strong seasonal patterns in the precipitation that falls in this area. Figure 2 shows the
average precipitation each month (rain and the melted water content of snow) at the long-term
weather station at Colorado State University’s San Luis Valley Research Center near Center,
Colorado compared to the average monthly precipitation in the mountains observed at the Wolf
Creek Pass 1E weather station. The Wolf Creek Pass and Center weather stations are less than
40 linear miles apart, and depict both the wettest and driest stations in southern Colorado,
respectively.
4
Center and Wolf Creek Pass Average Precipitation
30-year averages
6
Center 4SSW
Wolf Creek Pass 1E
Precipitation (inches)
5
4
3
2
1
0
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Figure 2: Center and Wolf Creek Pass 30-year average precipitation.
At high elevations, significant amounts of precipitation fall from mid-summer through the winter
months into the early spring with a distinct late spring/early summer dry season. In the center of
the San Luis valley at elevations around 7,500 feet, there is only one short wet season from July
into September. This occurs when wind speeds above mountain top level are light and moisture
associated with the North American Monsoon circulation drifts northward fueling frequent
afternoon thundershowers. This is also the primary hail season. There is high year to year
variability in precipitation throughout the southern Rocky Mountain region.
5
IV. Data
This study documents rain and hail patterns observed in southern Colorado during the 2008
growing season. All available precipitation data from sources in south central Colorado were
assembled. Data used in this study come from five networks. Southern Colorado Farms (SCF)
operated an extensive network of rain gauges and hail pads during the period between 15 June
and 15 September as a requirement of their weather modification permit. Daily rainfall amounts
were recorded as well as hail occurrence and size at 19 of their fields located near Center, CO.
Agro Engineering (AGRO), an agricultural consulting firm in the San Luis Valley, provided
daily precipitation totals at five locations scattered around the Valley equipped with automated
tipping bucket rain gauges. The National Weather Service (NWS) Cooperative Observer
Program (CO-OP) has eleven stations in the San Luis Valley. The Community Collaborative
Rain, Hail, and Snow Network (CoCoRaHS) had 33 stations in the valley during the summer of
2008 that reported. The CoCoRaHS stations did not all have complete data for the whole
summer, but what data were available were utilized. Several stations were operated by the
Center Conservation District in the area immediately east and south east of Southern Colorado
Farms. Lastly, the Colorado Agricultural Meteorological Network (CoAgMet) has five stations
with automated rain gauges in the Valley. In total, 74 stations were identified with daily
measurements of precipitation for all or part of the 2008 season. Fifty-two stations had complete
data (100%), while the remaining 22 stations were missing some data. Station data were utilized
even if it was not serially complete because each daily rainfall report did provide additional
detail for spatial rainfall patterns on any given day. The observation times of all stations were
obtained to avoid any confusion in data analysis. Precipitation reports are shown for the day that
the precipitation occurred (i.e. if the observation time is 0700, the data were shifted to the
previous day when that is when precipitation occurred).
Hail data were also available from certain stations in the CoCoRaHS and SCF networks. Hail
was observed qualitatively by human observers and quantitatively using foil-wrapped squares of
Styrofoam called “hail pads”. Craters left by the impact of stones, makes it easy to count the
number, hardness, size and severity of stones from each storm. Figure 3 shows the distribution
of the various stations in the five networks.
6
Figure 3: 2008 San Luis Valley observing networks.
V. Rainfall Summary
The following table summarizes the station data used for the 2008 season. The table provides
the latitude, longitude, station/field name, type of network, percent days with missing data, total
precipitation observed between 15 June and 15 September 2008, and the number of days with
Trace precipitation amounts.
7
Table 1: Station information and 2008 precipitation summary.
Latitude
37.7770
37.7060
37.5447
38.1005
37.7060
37.3905
37.7067
37.8288
37.2551
37.1417
37.4795
37.4879
37.4997
37.5363
37.7510
37.7636
37.7925
37.7349
37.7796
37.7930
37.8365
37.8222
37.7637
37.7778
37.7620
37.9943
37.9802
37.6812
37.6735
37.6792
37.3900
37.6518
37.7455
37.7498
37.7414
37.7203
37.7922
37.5770
37.6130
37.5216
37.5459
38.4026
37.6282
38.2361
37.4417
37.4389
37.4722
37.7067
37.9867
37.6742
37.7333
37.1742
37.5811
38.0858
37.4297
37.8074
37.8225
37.8211
37.8354
37.8353
37.7792
37.7788
37.7922
37.7923
37.8060
37.7907
37.7862
37.8057
37.7933
37.7635
37.8214
37.8348
37.7559
37.7698
Longitude
-106.0656
-105.8622
-106.0380
-106.0055
-106.2312
-105.5570
-106.1440
-106.0380
-105.9640
-105.6110
-105.8548
-105.8902
-105.8044
-105.9655
-106.1082
-106.0933
-105.9277
-105.9179
-105.9100
-105.8916
-105.9105
-105.8922
-105.9647
-105.9460
-105.9284
-105.7005
-105.6890
-106.3550
-106.4001
-106.2917
-105.3361
-105.5794
-105.8761
-105.9102
-105.9100
-105.9186
-106.3409
-106.1004
-106.0936
-106.1613
-106.1217
-106.4157
-106.6728
-106.1000
-105.8614
-105.8614
-105.5047
-106.1444
-105.6867
-106.3247
-105.5119
-105.9392
-106.1872
-106.1444
-106.0317
-105.9651
-105.9825
-105.9649
-105.9824
-105.9651
-106.0193
-106.0023
-106.0192
-105.9932
-106.0190
-106.1034
-106.1203
-106.0729
-106.0570
-106.0741
-106.0567
-106.0633
-106.0581
-106.0382
Name/Field
Agro_Center
Agro_Mosca
Agro_Office
Agro_Saguache
Agro_West
BLA01
CTR01
CTR02
LJR01
SAN01
Alamosa 1.2 NE
Alamosa 1.6 NW
Alamosa 4.1 ENE
Alamosa 6.9 NW
Center 0.1 ESE
Center 1.2 NE
Center 10.3 ENE
Center 10.5 E
Center 11.1 E
Center 12.2 ENE
Center 12.4 ENE
Center 12.7 ENE
Center 8.0 E
Center 9.1 ENE
Center 9.9 E
Crestone 0.2 WSW
Crestone 1.2 SSE
Del Norte 0.25 NW
Del Norte 2.6 W
Del Norte 3.3 E
Fort Garland 5.8 ESE
Great Sand Dunes 7.0 SSW
Hooper 0.1 ESE
Hooper 1.8 W
Hooper 1.9 W
Hooper 2.8 SW
La Garita 5.6 WSW
Monte Vista 2.4 E
Monte Vista 3.6 NE
Monte Vista 4.1 S
Monte Vista 2.7 SSE
Sargents 0.3 NE
South Fork 4.1 SW
Villa Grove 8.2 W
Alamosa2S_coop
AlamosaWSO_coop
Blanca_coop
Center4SSW_coop
Crestone1SE_coop
DelNorte_coop
Great_Sand_Dunes_coop
Manassa_coop
Monte Vista_coop
Saguache_coop
Waverly_coop
6
9
10
11
12
13
14
15
18
19
21
22
24
25
26
29
30
36
38
8
Type
agro
agro
agro
agro
agro
coag
coag
coag
coag
coag
coco
coco
coco
coco
coco
coco
coco
coco
coco
coco
coco
coco
coco
coco
coco
coco
coco
coco
coco
coco
coco
coco
coco
coco
coco
coco
coco
coco
coco
coco
coco
coco
coco
coco
coop
coop
coop
coop
coop
coop
coop
coop
coop
coop
coop
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
Traces
0
0
0
0
0
0
0
0
0
0
2
0
9
3
0
3
0
0
0
0
0
0
0
0
0
3
14
6
3
6
0
7
1
2
2
1
16
7
5
5
4
9
2
7
18
21
10
0
15
13
2
9
11
9
4
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
%Missing
6
0
0
0
0
0
0
0
0
0
42
57
22
3
0
0
0
0
0
0
0
0
0
0
0
19
0
0
42
3
49
0
92
89
87
87
2
26
5
0
2
16
32
10
0
0
6
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Total
Precipitation
4.97
2.98
1.06
3.37
2.03
2.59
2.40
2.83
3.41
2.41
1.52
1.62
2.39
2.95
2.32
4.24
3.19
3.03
4.87
5.11
5.57
4.71
4.60
4.61
4.50
3.22
4.51
4.83
3.36
3.99
1.94
5.49
0.67
1.00
1.43
2.17
4.39
2.15
3.54
5.16
3.11
3.14
4.29
4.07
2.20
1.90
2.64
2.40
4.50
4.66
6.81
3.70
4.47
1.96
1.94
3.67
3.13
3.23
3.09
3.39
5.19
5.16
4.48
4.72
3.35
5.54
5.50
4.90
4.77
5.16
3.64
3.98
4.18
4.72
Local Precipitation Analysis
In order to understand the variability in precipitation data within the valley, several
comparisons are presented for the local NWS CO-OP stations in the valley that have established
long-term statistics to other nearby observing stations. The CO-OP stations that will be
presented are: Alamosa, Center, and Monte Vista. The second figure for each station shows
accumulated precipitation anomaly graphs. These illustrate the temporal pattern of precipitation
trends by calculating the monthly precipitation departure from a common averaging period
(1971-2000) and graphing those anomalies cumulatively starting in 1996 at the three CO-OP
stations. Wet periods result in a positive trend while dry periods produce a negative trend.
Alamosa
Figure 4 shows cumulative daily precipitation totals and long term cumulative average
rainfall for the June 15 – September 15 summer period for the Alamosa WSO airport weather
station along with data from Alamosa 6.9W (CoCoRaHS) and Alamosa 2S (NWS CO-OP). The
long term daily average data for Alamosa WSO are plotted for reference. It is clear that
precipitation around Alamosa is variable. The Alamosa 6.9NW was 96% of the normal
precipitation for the airport. Alamosa 2S was 72% of normal. The Alamosa WSO was 62% of
normal. Figure 5 shows the cumulative monthly precipitation departure from normal since the
mid 1990s. Alamosa data show a recent dry period since the beginning of 2008 following what
had been two consecutive wetter than average years.
9
Alamosa, CO Accumulated Precipiation from 15 June to 15 Septebmer 2008
3.5
Alamosa 6.9NW (CoCoRaHS)
3
Alamosa 2S (COOP)
Alamosa WSO (COOP)
Cumulative Precipitation (in)
2.5
Alamosa WSO Cumulative 30 year
normal precip
2
1.5
1
0.5
0
6/15/2008 6/25/2008
7/5/2008
7/15/2008 7/25/2008 8/4/2008
8/14/2008 8/24/2008 9/3/2008
9/13/2008
Date
Figure 4: Cumulative precipitation for selected Alamosa stations for summer
Alamosa
Accumulated
Precipitation
Departureis1996-2008
2008. The
Alamosa
normal cumulative
precipitation
shown for reference.
2
Accumulated Precipitation Departure (in)
1
0
-1
-2
-3
-4
-5
-6
-7
Ja
n9
Ju 6
l-9
Ja 6
n9
Ju 7
l-9
Ja 7
n9
Ju 8
l-9
Ja 8
n9
Ju 9
l-9
Ja 9
n0
Ju 0
l-0
Ja 0
n0
Ju 1
l-0
Ja 1
n0
Ju 2
l-0
Ja 2
n0
Ju 3
l-0
Ja 3
n0
Ju 4
l-0
Ja 4
n0
Ju 5
l-0
Ja 5
n0
Ju 6
l-0
Ja 6
n0
Ju 7
l-0
Ja 7
n0
Ju 8
l-0
8
-8
Figure 5: Accumulated precipitation anomaly graph from 1996-2008 for
Alamosa WSO.
10
Center
Figure 6 shows the cumulative daily precipitation and long term averages for the Center 4SSW
CO-OP as well as data from surrounding stations including: Center02 (CoAgMet), Center 1.2NE
(CoCoRaHS), and Center 0.1ESE (CoCoRaHS). Center02, 4SSW and 0.1ESE show some
agreement while the 1.2NE station showed much higher precipitation than the rest. The 1.2NE
station was 140% or normal mostly as a result of being hit hard by two strong storms.. Center 2
was 93% of normal. Center 4SSW was 79% of normal. Center 0.1 ESE was 76% of normal.
Figure 7 illustrates the accumulated monthly precipitation departure from normal for Center
4SSW. As was the case for Alamosa, following predominantly above average precipitation in
2006 and 2007, since the beginning of 2008 the Center 4SSW station has received below normal
precipitation.
Center, CO Accumulated Precipitation from 15 June to 15 September 2008
4.5
CTR02 (CoAgMet)
4
Center 1.2 NE (CoCoRaHS)
Cumulative Precipitation (in)
3.5
Center 4SSW (COOP)
3
Center 0.1ESE (CoCoRaHS)
2.5
2
Center 4SSW Cumulative 30 year normal
precip
1.5
1
0.5
0
6/15/2008 6/25/2008
7/5/2008
7/15/2008 7/25/2008 8/4/2008
8/14/2008 8/24/2008 9/3/2008
9/13/2008
Date
Figure 6: Cumulative precipitation for selected Center stations for summer 2008.
The Center 4SSW CO-OP normal cumulative precipitation is shown for
reference.
11
Center Accumulated Precipitation Departure 1996-2008
3
Accumulated Precipitation Departure (in)
2
1
0
-1
-2
-3
-4
Ja
n9
Ju 6
l-9
Ja 6
n9
Ju 7
l-9
Ja 7
n9
Ju 8
l-9
Ja 8
n9
Ju 9
l-9
Ja 9
n0
Ju 0
l-0
Ja 0
n0
Ju 1
l-0
Ja 1
n0
Ju 2
l-0
Ja 2
n0
Ju 3
l-0
Ja 3
n0
Ju 4
l-0
Ja 4
n0
Ju 5
l-0
Ja 5
n0
Ju 6
l-0
Ja 6
n0
Ju 7
l-0
Ja 7
n0
Ju 8
l-0
8
-5
Figure 7: Accumulated precipitation anomaly graph from 1996-2008 for
Center 4SSW.
Monte Vista
Figure 8 shows the cumulative daily precipitation and long term averages for the Monte Vista
CO-OP as well as data from surrounding stations including: Office (Agro), Monte Vista 3.6NE
(CoCoRaHS), Monte Vista 4.1S (CoCoRaHS), and Monte Vista 2.7 SSE (CoCoRaHS). Once
again, substantial variations in precipitation are noted in the area. The Agro station which was
farthest from the CO-OP was only 31% of normal. Monte Vista 3.6NE was 104% of normal.
Monte Vista 4.1S was 151% of normal. Monte Vista 2.7SSE was 91% of normal. The CO-OP
station was 131% of normal. There is some question if the Agro Engineering station was
operating correctly all summer.
Figure 9 provides the accumulated monthly precipitation departure from normal time series.
Monte Vista does not show the recent dryness that characterized Center and Alamosa, although
it was drier than average in the spring of 2008.
12
Monte Vista, CO Cumulative Precipitation from 15 June to 15 September 2008
6
Office (Agro)
MV 3.6 NE (CoCoRaHS)
Cumulative Precipitation (in)
5
MV 4.1S (CoCoRaHS)
MV 2.7 SSE (CoCoRaHS)
4
3
MV (COOP)
Monte Vista 2W Cumulative 30 year normal
precip
2
1
0
6/15/2008 6/25/2008 7/5/2008 7/15/2008 7/25/2008 8/4/2008 8/14/2008 8/24/2008 9/3/2008 9/13/2008
Date
Figure 8: Cumulative precipitation for selected Monte Vista stations for summer 2008. The
Monte Vista COOP normal cumulative precipitation is shown for reference.
Monte Vista Accumulated Precipitation Departure 1996-2008
13
Accumulated Precipitation Departure (in)
11
9
7
5
3
1
-1
-3
Ja
n9
Ju 6
l-9
Ja 6
n9
Ju 7
l-9
Ja 7
n9
Ju 8
l-9
Ja 8
n9
Ju 9
l-9
Ja 9
n0
Ju 0
l-0
Ja 0
n0
Ju 1
l-0
Ja 1
n0
Ju 2
l-0
Ja 2
n0
Ju 3
l-0
Ja 3
n0
Ju 4
l-0
Ja 4
n0
Ju 5
l-0
Ja 5
n0
Ju 6
l-0
Ja 6
n0
Ju 7
l-0
Ja 7
n0
Ju 8
l-0
8
-5
Figure 9: Accumulated precipitation anomaly graph from 1996-2008 for
Monte Vista.
13
VI. Total Summer Precipitation
Precipitation over the entire San Luis Valley (Figures 10-12) was lower during the 2008
summer (June 15 – September 15) than during the prior two summers. In the immediate vicinity
of Center and Southern Colorado Farms summer 2008 precipitation varied from around 3.00” at
the drier locations up to 5.50”. While lower than the past two summers, the Center locations
were again among the higher rainfall amounts observed anywhere in the Valley.
Figure 10: Summer 2006 precipitation summary.
14
Figure 11: Summer 2007 precipitation summary.
Figure 12: Summer 2008 precipitation summary.
Figure 13 compares growing season precipitation totals for each of the SCF and surrounding
CoCoRaHS stations in Center for 2006-2008. This graph illustrates some of the interesting local
15
features of both spatial variability and year to year differences. For example, the fields at SCF
that were wettest in 2007 were driest in 2006 and even drier in 2008. Fields 21 and 22,
curiously, have received generous and similar precipitation amounts (around 6.00” in each of the
three summers).
PPT_2006
PPT_2007
PPT_2008
Center, CO Stations Multi-Year Comparison
8
7
Precipitation (in)
6
5
4
3
2
1
0
E
E
E
E
E
E
E
E
E
E
E
ES .2 N EN 0.5 1.1 EN EN EN 8.0 EN 9.9
1 er
3 r 1 r 1 .2 .4 .7 er
1
.
.
er 10 te te
r
12 12 12 nt
r 9 nt
nt er en en ter ter ter Ce nte Ce
te
C
C en en en
en Ce ent
e
C
C
C
C
C
C
6
9
10
11
12
13
14
15
18
19
21
22
24
25
26
29
30
36
38
1
0.
Station
Figure 13: Summer total precipitation summary for Center and surrounding
stations for 2006-2008.
VII. Radar and Hail Pad Analysis
Radar data were gathered for each day that the hail cannons were fired. In the following
samples, radar animations are added to allow the reader to track the storms as they developed
and passed the Center area. The radar parameter that will be displayed is the vertically
integrated liquid (VIL) water. An abnormally high VIL is an indication that hail is present in the
clouds. The radar data resolution are 1km by 1 degree in azimuth. The time period of data
collection was from approximately 2 hours prior to the cannons being fired to 2 hours post
cannon firings. The radar data were examined and are displayed on two spatial scales: one
16
zoomed directly into the Southern Colorado Farms fields, the other took a wider view to show
development and movement of storms across the entire San Luis Valley region. The radar times
are in displayed in Greenwich Mean Time (GMT/UTC). This is six hours later (i.e. add 6 hours
to) Mountain Daylight Time. Daily precipitation maps are shown for all available stations in the
valley for each event. Figure 14 shows the field locations on the farm.
Figure 14: Southern Colorado Farm fields and Center CoCoRaHS station
locations.
To view the radar loop, hold the Control key while clicking the hyper link. The images will
automatically begin to loop. The time (GMT) is given on the right hand panel of the image.
18 June 2008
On this date, only one cannon on field 17 was fired from 15:30 to 16:00 MDT (21:30 – 22:00
GMT). Hail was only observed on Field 15. No hail was observed at any of the surrounding
CoCoRaHS stations. Light rain amounts were reported on fields 6, 13, 14, 18, and 19.
17
Link to field zoomed radar data
Link to San Luis Valley radar data
The radar images zoomed into the SCF local area indicate that there was some potential present
on the farms with this storm. Looking at the zoomed out version of the radar data, the storm
appears to have strengthened somewhat as it moved to the SE. Analysis of other nearby stations
indicates that as the storm moved to the SE rainfall increased, but was not heavy. A precipitation
map for this day is shown in Figure 15. The precipitation at SCF ranged from 0.00-0.10” while
the Great Sand Dunes CoCoRaHS station reported 0.21” from the same storm.
Hail pad analysis indicates Field 15 likely experienced minimal hail. The dents on the hail pad
were primarily from large rain drops and not hail.
Figure 15: Precipitation summary for 18 June 2008
18
25 June 2008
One cannon on Field 30 was fired from 15:46-16:06 MDT (21:46-22:06 GMT). No hail was
observed at any SCF fields or CoCoRaHS stations. Precipitation from this storm was very light
and fairly localized (Figure 16).
Link to field zoomed radar data
Link to San Luis Valley radar data
From the radar data covering the valley, the storm approached from the northwest. The
precipitation signature from this storm mostly broke up as it reached the Center area and SCF.
Small amounts of precipitation were measured on 7 of the fields as well as downwind at Hooper.
It is indiscernible whether the storm breakup was due to the cannon being fired or if it was just
the natural progression of the storm moving across the valley.
Figure 16: Precipitation summary for 25 June 2008
19
28 June 2008
Two cannons were fired on fields 9 and 11 from 16:19-16:25 MDT (22:19-22:25 GMT). No hail
was observed at SCF or at any of the CoCoRaHS stations in the vicinity. Light precipitation was
measured on 11 of the fields (Figure 17).
Link to zoomed radar data
Link to San Luis Valley radar data
The radar data indicate that the storm approached from the southeast and then quickly dissipated
at approximately the time the cannons were firing. The Center CoCoRaHS stations reported no
precipitation as they were not in the direct path of the storm. With this fairly unusual direction
of propogation, there are no data available in the downwind direction of SCF (in this case to the
northwest).
Figure 17: Precipitation summary for 28 June 2008
20
29 June 2008
All cannons except field 38 were fired from 18:22-18:41 MDT (24:22-24:41 GMT). Hail was
reported on 5 of the SCF fields (6, 9, 10, 13, and 14) as well as 11 of the surrounding CoCoRaHS
stations in Center and Hooper. Precipitation was reported on all fields as well as the majority of
surrounding stations from multiple networks. The heaviest observed rains were east and south of
SCF (Figure 18).
Link to zoomed radar data-30June08 Midnight to 0300GMT
Link to San Luis Valley radar data-29June through Midnight GMT
Link to San Luis Valley radar data-30June through 0300GMT
The radar data show the storm approaching from the north heading southward. The radar
indicates hail was likely already present in the storm before reaching SCF. The radar-derived
hail potential decreased as the storm propagated southward. The stations to the South of the
farms in Monte Vista did receive both rainfall and small amounts of hail.
21
Figure 18: Precipitation summary for 29 June 2008
Hail pad analysis indicated that the only fields to actually receive hail were 6, 10 and 14 with the
other hail pads showed mostly evidence of heavy rain and large rain drops (Figure 19). Some of
the surrounding Center and Hooper stations reported pea to grape sized hail.
FLD 6
FLD 14
FLD 10
FLD 13
Figure 19: Hail pad photos by field for 29 June 2008.
22
FLD 9
2 July 2008
One cannon on the North Ranch was fired from 15:49-16:16 MDT (21:49- 22:16 GMT). No hail
was reported on any SCF fields or surrounding CoCoRaHS stations.
Precipitation was reported
on 5 of the fields (6, 9, 10, 11, and 12) with very small amounts noted (Figure 20).
Link to zoomed radar data
Link to San Luis Valley radar data
The radar data show a storm with hail potential approaching from the north and propagated
southward toward the NE sectors of the farms. At the time the cannon began to be fired, the
storm hail potential appeared to decrease. More rainfall was reported at stations to the south of
SCF.
Figure 20: Precipitation summary for 2 July 2008.
23
3 July 2008
All cannons except Field 15 were fired from 15:57-16:30 MDT (21:57-22:30 GMT). No hail
was reported on any of the SCF fields or surrounding CoCoRaHS stations. Precipitation was
reported on 11 of the fields and many of the nearby stations (Figure 21). Rainfall amounts were
light over most of SCF but heavier to the immediate east.
Link to zoomed radar data
Link to San Luis Valley radar data
The radar data show a small storm with potential for hail production approaching from the north,
propagating southward and expanding eastward. The storm quickly dissipated and the threat of
hail diminished at the about the time that the cannons were fired. The CoCoRaHS stations to the
east of the farms received more precipitation than the farm. Stations farther south in Alamosa
and Rio Grande Counties received no precipitation.
24
Figure 21: Precipitation summary for 3 July 2008.
6 July 2008
One cannon on field 38 was fired briefly from 18:18- 18:30 MDT (24:18- 24:30 GMT). No hail
was reported on any of the fields or nearby CoCoRaHS stations. Precipitation was reported on
every SCF field as well as many nearby stations. Rainfall totals were light to moderate (Figure
22).
Link to zoomed radar data
Link to San Luis Valley radar data
Radar analysis showed only weak reflectivity and no significant potential for hail from this
storm.
25
Figure 22: Precipitation summary for 6 July 2008.
8 July 2008
All cannons except for Field 5 were fired from 15:58-16:45 MDT (21:58- 22:45 GMT).
Subsequently, hail was reported on 10 of the SCF fields (13, 14, 18, 24, 25, 26, 29, 30, 36, and
38). Few CoCoRaHS hail reports were submitted for this date, except for one station in Crestone
well to the northeast which received 3/8” sized hail.
Precipitation was reported on every field
and many of the surrounding sites. Rainfall exceeded 0.30” at several gauges (Figure 23).
Link to zoomed radar data
Link to San Luis Valley radar data
The radar data indicated the storm approaching from the north and propagating southward.
From the appearance of the radar returns the storm was nearly over the farms and producing hail
by the time the hail cannons commenced firing. The apparent severity of the storm then
26
decreased.
Figure 23: Precipitation summary for 8 July 2008.
Hail pads were analyzed from fields 13, 15, 18, 24, 26, 29, 30 and 38. Hail was the heaviest on
fields 13 and 38 consistent with the radar estimates. Figure 24 shows all available hail pads
collected.
27
FLD 30
FLD 13
FLD 15
FLD 18
FLD 24
FLD 26
FLD 29
FLD 38
Figure 24: Hail pads by field for 8 July 2008.
28 July 2008:
All cannons except field 30 were fired from 14:15-15:06 MDT (20:15- 21:06 GMT). Hail was
reported on SCF fields 11 and 12. One CoCoRaHS hail report from Del Norte was also
submitted. Precipitation was reported on all SCF fields and at most of the surrounding
monitoring stations (Figure 25) with moderate rainfall amounts in some locations.
Link to zoomed radar data
Link to San Luis Valley radar data
Radar data indicated a storm approaching from the northwest with potential for hail prior to
reaching the farms. Larger areas had hail potential estimated from radar than actually
experienced hail. For example, fields 6, 9, and 10 experience no hail but radar indicated hail
potential there.
28
Figure 25: Precipitation summary for 28 July 2008.
Hail pad analysis (Figure 26) showed that field 11 received only rain, while field 12 received a
mix of hard and soft hail.
FLD 11
FLD 12
Figure 26: Hail pads by field for 28 July 2008.
29
5 August 2008:
All but 3 cannons were fired from 14:53- 16:24 MDT (20:53- 22:24 GMT). Hail was not
reported on any of the SCF fields or surrounding CoCoRaHS stations. Precipitation was
reported on all but 3 SCF fields (13, 14 and 18), but amounts were light (Figure 27).
Link to zoomed radar data
Link to San Luis Valley radar data
Radar data showed storm development with little movement of individual cells on this day.
There was hail potential as a storm approached from south of the farms, but about the time
cannons were fired the storm weakened in potential for hail.
Figure 27: Precipitation summary for 5 August 2008
30
7 August 2008
Hail was reported on SCF fields 21 and 26. Moderate to locally heavy rains were reported at
most monitoring stations in the Valley (Figure 28). All cannons were fired from 17:30-18:27
MDT (23:30-0:27 GMT). Cannon 30 also fired unintentionally from 19:00-21:00 MDT.
Link to zoomed radar data on 8 August 2008 midnight through 0300GMT
Link to San Luis Valley radar data on 7 August 2008 through midnight GMT
Link to San Luis Valley radar data on 8 August 2008 midnight through 0300 GMT
Radar showed a storm approaching the farm from the south with some hail potential. As the
storm passed over the farm, the hail potential decreased but still produced hail on two of the
fields where radar returns were strongest. Precipitation was received at most of the surrounding
network gages, including those to the north with as much as 2.00” on the farm itself.
31
Figure 28: Precipitation summary for 7 August 2008.
Hail pad analysis (Figure 29) showed that field 21 (information not labeled correctly in photo,
should be 21 not 12) received only rain. Field 26 received hard hail that averaged 0.1” in
diameter.
FLD 26
FLD 21
Figure 29: Hail pads by field for 7 August 2008.
32
16 August 2008
A very severe storm pummeled portions of the San Luis Valley on this day. The storm was a
part of a large weather systems affecting Colorado and parts of adjacent states. All cannons were
fired from 14:15-15:11 MDT (20:15-21:11 GMT). Hail was reported on every field of SCF as
well as at surrounding stations in: Center, Crestone, Del Norte, Hooper, Monte Vista and Villa
Grove. Hail production from the storm was already well-developed prior to the cannons being
fired and the dimensions of the storm were quite large. Crops were severely damaged and some
hail was large enough to break windows and damage vehicles. This hailstorm area and severity
is unusual for San Luis Valley. Rainfall was also widespread and substantial (Figure 30).
Link to zoomed radar data
Link to San Luis Valley radar data
It is clear from the radar data that the storm was already producing hail prior to hitting SCF.
Hail pad analysis (Figure 31 and Table 2) confirmed the severity of hail damage across SCF and
surrounding areas. Figure 32 shows the spatial distribution of hail stone concentrations (number
of stones, size and hardness of stones) from hail pads collected for this storm.
33
Figure 30: Precipitation summary for 16 August 2008.
FLD 38
FLD 6
FLD 12
FLD 13
FLD 10
FLD 15
34
FLD 11
FLD 36
FLD 18
FLD 19
FLD 21
FLD 22
FLD 24
FLD 25
FLD 26
FLD 29
FLD 30
CO-SA-47
CO-SA-15
CO-SA-41
CO-SA-42
CO-SA-43
CO-SA-45
CO-SA-46
Figure 31: Hail pads by field/station for 16 August 2008.
35
CO-SA-40
CO-SA-44
Figure 32: Hail pad stone concentration for 16 August 2008 (stones/sqft).
36
Table 2: Hail summary for 16 August 2008.
Longitude
Latitude
Field
-105.96506 37.80737
6
-105.9825 37.82253
9
-105.96491 37.82111
10
-105.98237
37.8354
11
-105.96507 37.83527
12
-106.01926 37.77915
13
-106.00227 37.77877
14
-106.01917 37.79222
15
-105.99321 37.79228
18
-106.01902 37.80595
19
-106.10335 37.79066
21
-106.1203 37.78623
22
-106.07286 37.80569
24
-106.05697
37.7933
25
-106.07413 37.76352
26
-106.05665 37.82139
29
-106.06329 37.83479
30
-106.05811 37.75593
36
-106.03822 37.76983
38
-106.10817 37.75098 Center 0.1 ESE
-106.093333 37.763611 Center 1.2 NE
-105.92773
37.7925 Center 10.3 ENE
-105.91793 37.73485 Center 10.5 E
-105.91003 37.77962 Center 11.1 E
-105.89163 37.79303 Center 12.2 ENE
-105.91048 37.83649 Center 12.4 ENE
-105.89222 37.82218 Center 12.7 ENE
-105.96467 37.76367 Center 8.0 E
-105.94599 37.77778 Center 9.1 ENE
-105.92842 37.76196 Center 9.9 E
Type
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
COCO
COCO
COCO
COCO
COCO
COCO
COCO
COCO
COCO
COCO
COCO
Concentration
(stones/sqft)
Largest Stone
(in)
Average Stone
Size (in)
Character
1092
0.30
0.15
Hard
1123
880
1090
826
0.20
0.40
0.35
0.40
0.13
0.15
0.15
0.20
Hard
Hard
Hard
Hard
1267
1152
1210
590
970
722
912
3000
835
662
3000
851
0.25
0.30
0.35
0.50
0.75
0.40
0.40
>1.00
0.25
0.30
1.00
0.40
0.10
0.15
0.15
0.25
0.25
0.20
0.20
0.35
0.10
0.18
0.40
0.25
Hard
Hard
Hard
Hard
Hard
Hard
Hard
Hard
Hard
Hard/soft
Hard
hard/soft
2045
533
260
1220
1642
2621
1233
458
773
0.10
0.60
0.40
0.50
0.40
0.25
0.50
0.50
0.50
0.10
0.40
0.10
0.25
0.10
0.10
0.25
0.25
0.25
Hard/soft
Hard
Hard
Hard
Hard
Hard
Hard
Hard
Hard
3 September 2008
The cannons were fired two different times on this day 2 ½ hours apart: 14:00-14:37 MDT
(20:00-20:37 GMT) and 16:35-17:05 MDT (22:35-23:05 GMT). Hail was reported on all SCF
fields as well as the surrounding Center and Hooper CoCoRaHS stations. Rainfall on this date
was concentrated near Center and SCF but with amounts close to 1” in some areas (Figure 33).
Link to zoomed radar data
Link to San Luis Valley radar data
The radar data show the two waves of the storm. In the first wave, the hail was likely already
formed in the cloud well before the storm hit the farms. The second wave formed just west of
the farms and was not as strong, so potential for hail cannon effectiveness may have been greater
in this second episode.
37
Figure 33: Precipitation summary for 3 September 2008.
The hail pads collected on 3 September 2008 (Figure 34 and Table 3) were variable depending
on position on the farms. The radar indicates that during the second wave of the storm hail
potential was greatest on fields: 6, 9, 10, 13, 14, 15, 18 and 38. Hail pad stone densities are
shown in Figure 35.
38
FLD 38
FLD 6
FLD 9
FLD 10
FLD 12
FLD 13
FLD 14
FLD 15
FLD 18
FLD 19
FLD 21
FLD 22
FLD 24
FLD 25
FLD 26
FLD 29
FLD 30
FLD 36
CO-SA-47
39
CO-SA-11
CO-SA-40
CO-SA-41
CO-SA-42
CO-SA-44
CO-SA-43
CO-SA-46
Figure 34: Hail pads by field/station for 3 September 2008.
Figure 35: Hail pad stone density for 3 September 2008 (stones/sqft).
40
Table 3: Hail summary for 3 September 2008.
Longitude
-105.96506
-105.9825
-105.96491
-105.98237
-105.96507
-106.01926
-106.00227
-106.01917
-105.99321
-106.01902
-106.10335
-106.1203
-106.07286
-106.05697
-106.07413
-106.05665
-106.06329
-106.05811
-106.03822
-105.91003
-105.89163
-105.91048
-105.89222
-105.96467
-105.94599
-105.92842
Latitude
37.80737
37.82253
37.82111
37.8354
37.83527
37.77915
37.77877
37.79222
37.79228
37.80595
37.79066
37.78623
37.80569
37.7933
37.76352
37.82139
37.83479
37.75593
37.76983
37.77962
37.79303
37.83649
37.82218
37.76367
37.77778
37.76196
Field
6
9
10
11
12
13
14
15
18
19
21
22
24
25
26
29
30
36
38
Center 11.1 E
Center 12.2 ENE
Center 12.4 ENE
Center 12.7 ENE
Center 8.0 E
Center 9.1 ENE
Center 9.9 E
Type
Concentration
(stones/sqft)
Largest Stone
(in)
Average Stone
Size (in)
Character
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
SCF
COCO
COCO
COCO
COCO
COCO
COCO
COCO
500
634
345
288
230
806
720
864
720
519
806
835
922
752
905
864
576
220
540
1296
518
901
377
835
1094
922
0.35
0.35
0.30
0.20
0.30
0.30
0.35
0.40
0.35
0.40
0.35
0.30
0.35
0.40
0.40
0.35
0.25
0.50
0.30
0.25
0.25
0.40
0.40
0.25
0.25
0.25
0.18
0.20
0.15
0.10
0.15
0.20
0.18
0.18
0.18
0.20
0.30
0.20
0.15
0.15
0.20
0.13
0.15
0.35
0.18
0.10
0.10
0.25
0.10
0.10
0.10
0.10
Hard/soft
Hard/soft
Soft
Hard/soft/rain
Hard/soft
Hard
Hard
Hard
Hard/soft
Hard/soft
Hard/soft
Soft
Hard/soft
Hard/soft
Hard
Hard
Hard/soft
Hard
Hard
Hard
Hard
Hard
Hard/Soft
Hard
Hard
Hard
VIII. Conclusions
Over 70 rainfall observing sites were used to monitor storms over the San Luis Valley and the
immediate Southern Colorado Farms area during the 2008 growing season/hail cannon permit
season (June 15 – September 15). Since this study began in 2006, this was the driest summer for
the region. However, for the third year in a row, some of the heavier rainfall amounts observed
over the agricultural portions of the San Luis Valley were observed over Southern Colorado
Farms.
Hail cannons were fired on 13 days for a total of 6.6 hours of usage compared to 17 days with
9.3 hours of total usage in 2006 and 22 days with 15.9 hours of total usage in 2007. It is not
surprising that 2008 was not only the driest year but also had the least amount of hours of hail
cannon usage out of the past three years. To enhance the interpretation of storm behavior for this
study, radar data and estimates of hail potential were included. Also, this year Southern
Colorado Farms provided very complete hail pad documentation to aid in storm analysis.
41
Radar analysis illustrated what the storm conditions were as they approached, crossed and passed
the Farms. Interestingly, in 2008 few of the storms approached from the west. The most
common storm direction this year was moving/propagating from north to south. One notable
example showed a storm headed from southeast to northwest. The strongest storms with the
greatest quantity and areal extent of hail (Aug. 16 and Sep. 3, 2008) both marched systematically
across the area from NW to SE.
There are several instances where the radar shows a reduction in hail potential at approximately
the time when cannons started firing. This was not the case, however, with the two strongest
storms. It is difficult to tell with this limited sample of storms if hail storm weakening for the
smaller storms was directly related to cannon firings or if it is simply the weakening of the storm
as it moves through the valley. Nevertheless, it is an interesting observation that can hopefully
continue to be tracked.
As for assessing rainfall patterns and the potential effects hail cannon use may have, the natural
variability in summer precipitation is so large that direct effects are and will continue to be
difficult to assess. The fact that rainfall has maximized over the Farm on three consecutive years
(but with distinctly different patterns each year) continues to catch the attention of our analysis.
It is possible that this is simply an indirect effect of a higher density observing network over and
around Southern Colorado Farms. Likewise, it is possible that this is and always has been an
area prone to heavier summer rains but data were simply not available before this study to
document this difference. It is also possible that hail cannon activity may result in some local
increase in rainfall.
IX. Acknowledgements
The authors acknowledge the Colorado Water Conservation Board for sponsoring this research
project. Special thanks is also given to the Southern Colorado Farms and Center Extension
Office observers for providing high quality observations of both rainfall and hail events. The
Agro Engineering, CoAgMet, NWS CO-OP and CoCoRaHS networks are also acknowledged
for allowing access to their precipitation data collection efforts in the San Luis Valley.
42