Talking points for “Utility of GOES Imagery in Forecasting / Nowcasting Severe Weather”.
1. Title
2. Learning Objectives – The key to this training session is gaining an understanding of the
utility of GOES satellite imagery in combination with other datasets (i.e. NWP output,
surface and upper air data, radar etc.) in severe weather forecasting / nowcasting. The
learning objectives are listed in a roughly chronological order going from assessing model
output in the 1-2 day period leading up to the event, to the day of the event itself, to hours
before the event, to while the event is unfolding. The role of observational data becomes
increasingly important as we get closer to the time of the event.
3. The first learning objective will be to assess model performance. This pertains to comparing
observational data to NWP output to gain confidence in one model solution versus another.
4. In the situation where the position error of a feature of interest (i.e. 500 mb trough) is carried
along from the previous run, a comparison with observational data can be made to determine
which model solution is more correct in terms of location of the feature of interest.
5. We will focus in on a case where various models had different solutions the day before a
potential severe weather event. Comparison with observational data can be used to show
which of the model solution(s) are outliers and therefore be treated with less confidence
relative to other model solutions. In this case, the potential severe weather event is forecast
to occur on April 23 over the Great Plains. The trough responsible for the potential severe
weather episode is investigated as it moves through the western US. We will be looking at
various model forecasts of 500 mb height from the 0000 UTC 22 April model runs, water
vapor imagery from 0045 – 1215 UTC 23 April 2007 is overlaid. GFS, NAM and UKMET
500 mb height forecasts show model solution divergence beginning over Nevada by 0600
UTC and becoming more evident by 1200 UTC. The UKMET is fastest (furthest southeast),
the NAM is the slowest (furthest northwest) and the GFS is in between. The low center
circulation does appear to be further southeast in the water vapor imagery by 1200 UTC,
however this is subtle so we look for more evidence of that in other data. Overlay the GOES
winds in the vicinity of 500 mb at 0915 UTC to compare the GOES winds with the winds
from the 3 model runs. Determine which of the model(s) fits the data better and which
model(s) do not. Comparison between GOES winds and model output is particularly useful
far from the 00 and 12 Z upper air times. The frame at 1215 UTC displays the observed 500
mb plots. Compare the plotted data with the height/wind data from the 3 models. The NAM
appears too slow with the trough, it should be further southeast. The GFS is better but still
some disagreement with the Flagstaff observation which suggests the trough is slightly
further southeast. The UKMET has the best agreement with the Flagstaff and Grand
Junction observations. Keep in mind, this trend in position of the 500 mb trough has been
present in previous model runs as well (not shown for April 21 runs) with the NAM being
slower, the UKMET faster and the GFS in between. Noticing this trend would yield greater
confidence in the UKMET in terms of position of the 500 mb trough, with slightly less
confidence in the GFS and less confidence in the NAM forecast for the late
afternoon/evening of April 23 in the Plains.
6. The second learning objective is air mass identification. Sometimes there are signatures in
the visible satellite imagery that can be used in tandem with surface and upper air data to
delineate different air masses / boundaries.
7. In this example, GOES visible imagery shows a boundary between an unstable air mass to
the south and a stable air mass to the north. The boundary is a warm front that was
reinforced by an earlier MCS outflow boundary. The cloud streets to the south of the
boundary characterize an unstable air mass. The orientation of the cloud streets are parallel
to the surface winds. The stable wave clouds to the north of the boundary characterize a
stable air mass. The orientation of the stable wave clouds are perpendicular to the wind at
inversion top level.
8. GOES visible imagery 1302 – 1932 UTC 11 May 2000. METARs may be toggled on/off
with the “11May00” check box in the controls frame. For this case we will be focusing on
Iowa. In the animated imagery we observe the development of a region of cloud streets
moving northeast, with a region of stable wave clouds to the northeast. If we toggle on the
METARs we can detect a low pressure area associated with the cloud fields discussed above
moving to the northeast. A warm front exists northeast of the low, and a cold front extends
southwest of the low. Note the movement of the unstable cloud streets towards the northeast
as the southwest flow moves in.
9. GOES visible imagery 1932 UTC 11 May – 0045 12 May 2000. METARs may be toggled
on/off with the “11May00” check box in the controls frame. The stable wave clouds go
away, likely due to a combination of daytime heating and advection of the boundary between
the cloud streets and wave clouds towards the northeast. Convective initiation occurs around
2245 UTC just ahead of the low in the region of the stable wave cloud and cloud streets
boundary. The convergence in this region is maximized. The conditions were favorable for
tornadoes this day so this storm produced a tornado at 2345 UTC, soon after convective
initiation.
10. GOES visible imagery 1300 – 1900 UTC 31 May 1985. METARs may be toggled on/off
with the “31May85” check box in the controls frame. Identify the various air masses /
boundaries across Ohio, Pennsylvania and western New York. A north-south oriented line of
convection is moving through the area during the morning hours, this moves eastward during
the day. The highest dewpoints are immediately east of the cold front, with south/southwest
winds advecting moisture northward. Some regions in northern Ohio transitioned from
stable wave clouds to unstable cloud streets with daytime heating. Clearing is taking place
across much of northern Ohio and into northwest Pennsylvania. In Ohio, there are
indications of a convergence line (a line of enhanced Cu) ahead of the cold front. Note the
transition from southwest winds over much of Ohio to more backed, southerly to
southeasterly winds across northwest PA, western NY extending into Ontario. There is a
region of subsidence in southeast Ohio.
11. GOES visible imagery 1900 – 2354 UTC 31 May 1985. METARs may be toggled on/off
with the “31May85PM” check box in the controls frame. The first thunderstorms in the
region of interest initiate along a pre-frontal trough in northeast Ohio. These thunderstorms
quickly become severe and move eastward towards Pennsylvania. Note that thunderstorms
activity is inhibited south of this line of storms in east central / southeast Ohio (recall the
subsidence observed in the previous slide). Later on, thunderstorms develop on the cold
front. The environment was favorable for tornadoes on this day, there were numerous F3 and
F4 tornado events as well as a F5 tornado from northeast Ohio into northwest Pennsylvania.
12. The third learning objective will deal with identification of changes in the pre-storm
environment.
13. One of the major reasons we see changes in the pre-storm environment are due to Mesoscale
Convective System (MCS) activity. Monitoring MCS activity for potential effects on later
convection is particularly important because NWP output can struggle with this, meaning
that monitoring observational data is that much more important. Whenever we observe an
MCS we should be thinking of its consequences on potential future convective activity. The
first step is to identify the region that has been stabilized by the outflow from the MCS. The
next step is to identify the boundary between the stable air mass you just identified and the
potential unstable air mass, thunderstorms often develop along MCS outflow boundaries.
Finally, the outflow boundary should be monitored for new convective development, or the
interaction between a storm that develops in the warm sector and the MCS outflow boundary.
The interaction can be favorable for a period of time or unfavorable depending on storm
motion, instability, moisture depth, shear etc.
14. Example of MCS and its effects on later convective development. GOES visible imagery
from 1415 – 2215 5 May 2008. METARs may be toggled on/off with the “5May08” check
box in the controls frame. Early in the loop we see a MCS in Kansas that leads to a well
defined outflow boundary that moves southwest. Around 1900 UTC we can trace the
outflow boundary as the line of cloud streets to the southwest of the boundary, and stable
wave clouds to the northeast of the boundary. Around 2030 UTC we see convective
initiation occurring along the MCS outflow boundary. There were numerous reports of large
hail with these thunderstorms with the largest report being 4.25” in diameter.
15. GFS forecast CAPE from 1200 UTC 24 May 2008, overlays are surface wind
(GFS24May_Wind), dewpoint (GFS24May08_Td), 500 mb height and wind
(GFS24May08_500), temperature (GFS24May_T), QPF (GFS_24May08_QPF), CIN
(GFS24May08_CIN). At 500 mb we see a low over Wyoming that is forecast to move north
during the day, a shortwave trough associated with this system is forecast to move
northeastward across the plains during the day. At the surface we see a cold front / dryline
forecast to move eastward, in response to the shortwave trough. Note the dewpoints and
CAPE in the warm sector with CAPE values ranging from 4000 J/Kg in OK/KS to 3000 J/Kg
in NE and lesser values further north in South Dakota. CIN values by 0000 UTC suggest
convection initiation likely along the dryline / front from SD to NE to KS with more CIN
further south in OK and TX.
16. As in previous slide, except this is the NAM forecast 1200 UTC 24 May 2008. We show the
NAM forecast here as well, which depicts a similar scenario to the GFS. Of particular
interest is the magnitude of the CAPE in the warm sector in NE and KS – a large region in
the 3000 to 4000+ J/Kg range.
17. GOES 10.7 um IR imagery during the overnight and morning hours of 24 May 2008. Note
the MCS over Kansas and Nebraska during the overnight hours. The MCS stabilizes a large
area in its wake. This will have a profound effect on the CAPE forecast, particularly over
Nebraska and Kansas. Overlays (24MAYGFS00Z_QPF and 24MAYNAM00Z_QPF) are the
GFS and NAM QPF forecasts respectively, from the 00Z run. The GFS had the majority of
the QPF too far northwest while the NAM also had this problem as well as a lack of QPF
with the MCS over Kansas. The models typically do not have a good handle on MCS’s, and
in particular the effects on future convective development. This is where monitoring
observational data is critical for anticipating effects on convection later in the day. Refer
back to slides 16 and 17 (the 12Z NAM and GFS forecasts) and show the 24May_METAR
overlay to see where the models were overestimating CAPE.
18. SPC Mesoanalysis of SBCAPE at 0000 UTC 25 May 2008 and (toggle) MLCAPE. CAPE
values are significantly lower than forecast in the warm sector across Kansas and Nebraska.
South of the MCS in Oklahoma, CAPE values are in the 3000 – 5000 J/Kg range.
19. GOES visible imagery from 1545 – 2310 UTC 24 May 2008. MCS outflow boundaries can
be seen across Kansas and Oklahoma. A storm initiates along the dryline / MCS outflow
boundary intersection in Oklahoma, we will look at this in more detail in the next slide. The
convection in Nebraska is weak (just one severe weather report – 0.75” hail) and storms do
not develop in Kansas. Supercells do develop in South Dakota close to the 500 mb low,
where 500 mb temperatures are much colder than further south. The MCS had a significant
influence on the warm sector and subsequent distribution of severe weather reports which
were primarily confined to South Dakota and Oklahoma.
20. GOES visible imagery from 1445 – 2202 UTC 24 May 2008 centered over northern
Oklahoma. Outflow from the MCS stabilized the area of north central to northeast
Oklahoma, northward into Kansas. The outflow boundary intersects the dryline in northwest
Oklahoma where convective initiation occurs. CAPE values in this region were in the 30004000 J/Kg range. The initial storm moves into the stable air (note the stable wave clouds)
and dissipates, however, an outflow boundary from this storm intersects the MCS outflow
boundary to cause additional convective initiation. The later storm propagates along the
MCS boundary and produces a EF2 tornado.
21. Now we will look at a short case study to analyze changes in the pre-storm environment.
The case is from 5 July 2000. We begin by looking at NWP output. The image shows
CAPE from the 1200 UTC run of the Eta model. Advance the frames to inspect the various
forecast times at 3 hour increments. Also make use of the overlays in the controls frame,
these include the 1200 UTC run Eta model fields of 500 mb wind, surface dewpoint, MSLP,
surface temperature and surface wind. Our forecast area is northeast Colorado. 500 mb
winds show southwest flow in the 25-30 knot range over the forecast area. MSLP and
surface winds show pressure falls taking place to the west during the day with a broad low
pressure area across Colorado and Wyoming by 0000 UTC. Winds across northeast
Colorado are forecast to be easterly at 1800 UTC and become more southeast, then
south/southeast by 0000 UTC in the forecast area. Forecast temperature and dewpoint fields
show relatively high dewpoints in the morning to mid-day hours (in the northeast/easterly
flow regime). Forecast temperatures reach the mid-90’s by 2100 UTC and the corresponding
dewpoints drop dramatically at this time, likely in response to mixing out the moisture. This
leads to the most unstable air mass in place in the late morning to early afternoon hours
across the forecast area.
22. GOES visible imagery during the morning hours and METARs. During the morning hours,
we see the MCS in Nebraska and the outflow associated with it moving to the southwest.
Winds in northeast Colorado are east/northeasterly by 1800 UTC with dewpoints in the upper
50s to 60s, consistent with the Eta forecast up to that time.
23. Now we look later in the day, this is the GOES 10.7 um imagery from 1625 – 2325 UTC 5
July 2000. The MCS in Nebraska can be seen early in the loop, moving east out of the
picture. The outflow boundary can be easily identified in the IR channel since the air mass is
relatively moist compared to its surroundings. The moist air mass will show up as cooler in
the IR imagery, which is a lighter color in this color table. Speed up the loop to watch the
MCS outflow boundary moving from southwest Nebraska into northeast Colorado. Recall
the Eta model had temperatures rising in this region and dewpoints dropping due to mixing.
In reality, we see the moist air mass moving westward, providing for an unstable air mass
and potential enhancement for convection along the outflow boundary. Also, the elevation
rises appreciably across this region - North Platte (2800 feet) to northeast Colorado on the
moist side of the boundary (~4000 feet) – so that the effects of elevated heating will
contribute to higher surface theta-e.
24. GOES visible imagery 1645 5 July – 0202 6 July 2000. We see indications of the MCS
outflow boundary moving westward across northeast Colorado around 2200 UTC as
indicated by a line of cumulus. This continues to move westward, but we lose track of it in
the visible imagery as the cumulus along it dissipates. The early convective development
occurs in southwest Nebraska, along the southern edge of the MCS outflow boundary, as
well as in Wyoming (and later the Nebraska panhandle) as storms initiate there. Keep in
mind, the storms in Wyoming and the Nebraska panhandle have high LCL’s as the
temperature / dewpoint spread was very high in the environment where these storms initiated.
However, we do see an interesting development with a thunderstorm in the south central
portions of the Nebraska panhandle, starting around 0030 UTC. This thunderstorm has a
more impressive overshooting top with it, and begins turning to the right around 0045, these
are indications of a more intense thunderstorm (we’ll look at radar reflectivity in the next
slide). A bit later, around 0115 UTC this storm is looking very intense and has storm scale
features around it, there are cumulus above an invigorated RFD, we will discuss this in more
detail later in this session. For now, we’ll say this signature is associated with an intensifying
thunderstorm. The thunderstorm intensified dramatically as it encountered the more unstable
air mass from the MCS outflow boundary. Also, it may have moved to the right along the
boundary, helping to intensify the storm. The later is hard to say for sure, but the storm
motion is at least a hybrid of right movement due to dynamical effects as well as propagation
along the MCS outflow boundary.
25. KGLD 0.5 degree base reflectivity along with METARs 0036 – 0206 6 July 2000. The MCS
outflow boundary shows up nicely in this loop. Note the observation at Sidney, NE (south
central Nebraska panhandle) before the storm went through (86/64) as well as the
observation in northeast Colorado after the outflow boundary goes through (83/66). At the
elevation of this region (around 4000 feet), this is a very unstable air mass (using
surface/upper data, greater than 4000 J/kg of CAPE), in contrast to the hot/dry air mass the
12Z Eta model was forecasting for this region. The storm from the southern Nebraska
panhandle moves into this unstable air mass (and most likely propagates along the boundary)
and moves southeast into northeast Colorado. Storm reports associated with this storm
around this time include a F3 tornado and softball size hail. Monitoring changes in the prestorm environment (particularly since it contrasted sharply with NWP output) were critical
for this case.
26. GOES water vapor imagery 0845 – 1615 UTC 9 June 2005. In this case, we will be
considering northwest Kansas as the forecast area. On the large scale we see a mid-level low
in the Idaho vicinity and associated trough over the Rockies. Over Kansas we can see
multiple MCS’ during the course of the loop.
27. NAM CAPE / MSLP and wind forecast from the 1200 UTC 9 June 2005 run. The NAM
forecast a surface low to slowly move northward and deepen during the day. East of the
surface low southerly winds are advecting moisture northward, resulting in CAPE values
around 3000 J/Kg by late afternoon in northwest Kansas.
28. GOES water vapor imagery 1602 – 1845 UTC 9 June 2005, 500 mb Height and Vorticity in
the overlay (9June500). Here we see an approaching shortwave passing through southeast
Colorado moving towards western Kansas. The shortwave aids in large scale upward
motion, enhances the shear profile through a small region of stronger mid-level winds and
aids destabilization through mid-level cooling.
29. GOES visible imagery 1415 – 1845 UTC 9 June 2005. METARs may be toggled on/off with
the “9June05v” check box in the controls frame. Analyze the various air masses /
boundaries. We can see a low pressure center circulation in northwest Kansas, with a dryline
extending south of it. The MCS in north central Kansas produces an outflow boundary that
moves westward. Stable wave clouds exist in the stable region behind the MCS. Cloud
streets exist in the unstable region southwest of the outflow boundary (notice that earlier this
region had stable wave clouds, but became unstable with daytime heating / mid-level
cooling). By 1845 UTC we can see the outflow boundary oriented northwest to southeast,
with the warm sector bounded by the outflow boundary and the dryline to the west. We also
observe east-west oriented lines of cumulus in the warm sector embedded in an area of
ascent, perhaps associated with speed convergence. Disregard the 83/46 observation as this
is bad data (at least the dewpoint observation).
30. GOES visible imagery 1845 – 2302 UTC 9 June 2005. METARs may be toggled on/off with
the “9June05s” check box in the controls frame. Early in the loop we see a few regions
where convective initiation occurs, one along the outflow boundary near the Nebraska
border, the other just west of there in the region of enhanced cumulus discussed earlier, and
the other along the dryline just east of the surface low, at the west end of the east-west line
discussed earlier. Note the observation of 87/65, when the outflow boundary pushes through
this site, the winds back to a more east/southeast direction and increase to 20 kts. The storms
that initiated along the outflow boundary near the Nebraska border move into the stable air
mass and dissipate. The dominant storm is the one that initiated further southwest along the
dryline, ahead of the low and along the east-west oriented boundary.
31. KGLD Goodland, KS 0.5° reflectivity from 1606 – 2256 UTC 9 June 2005. METARs may
be toggled on/off with the “9June05r”. When the radar is in clear air mode early on, the low
pressure center is well defined. The dominant storm mentioned in the previous slide can be
seen to move northeast initially then interacts with the outflow boundary and turns east. This
storm produced a F2 tornado and golfball size hail.
32. GOES visible imagery from 1610 – 2202 UTC May 25 2008. Overlays are METARs
(25May08_METAR) and the AWIPS speed tool (25May08_speed) for tracking the feature of
interest. The feature of interest here is a fast moving cloud field that you can first observe in
southeast Nebraska at the start of the loop, moves northeastward towards Iowa (with areas of
enhanced cumulus associated with it) and is coincident with convective initiation in north
central Iowa. The speed tool overlay is used to track this feature, which is found to be
moving at 54 knots. The feature is most likely a mesoscale jet streak. In the observations,
note that the surface winds veer immediately after the passage of this jet streak. At the point
where thunderstorms initiate in north central Iowa, the winds ahead of the jet streak are more
backed, while behind it are more veered, leading to enhanced convergence associated with
this feature. One of the thunderstorms associated with this jet streak produced an EF5
tornado at Parkersburg, Iowa. This is an example of a feature that can be tracked in the
satellite imagery and monitored carefully for potential convective initiation and a near-storm
environment that is very favorable for severe thunderstorms. There are other signatures in
the satellite imagery (cirrus streaks) that we can observe further north, going into Minnesota.
These signatures are sometimes associated with jet streaks as well.
33. Sounding from Omaha, NE at 1800 UTC 25 May 2008. Fortunately, there was a sounding at
the right place and time to capture the Mesoscale jet streak mentioned in the previous slide.
Given that the feature was moving at 54 knots according to the AWIPS speed tool, this
feature exists somewhere between 400 to 750 mb. The AWIPS cloud height product shows
these clouds to be around 700 to 750 mb. We will use this information to try to locate the
feature in NWP output next.
34. RUC 00 hour forecast 700 mb isotachs and profiler data at 700 mb valid 18:00 UTC 25 May
2008. Keep in mind, the Omaha sounding at this time showed 50 knots at 700 mb. The
analysis does indicate some indications of a jet streak in the vicinity of Omaha, but is
underestimating it based on the 18Z sounding. It’s good practice to look for a feature you see
in the satellite imagery in other datasets as well (NWP output, profiler, ACARS etc),
although sometimes it may not show up for various reasons. Not all mesoscale features you
see in the models are real, but when you have supporting evidence in observational data it
should be “red flagged” with caution and monitored for potential effects on convection.
35. NAM 500 mb height, vorticity (shaded) and winds forecast from 1200 UTC 25 May 2008. A
vort max is first observed in southeast Nebraska at the 3 hour forecast valid 1500 UTC. This
is where the feature was first observed around this time. By 1800 UTC the feature can be
seen around Omaha. Note the veering of the winds behind this feature as well, consistent
with the response observed in the METARs. The NAM generally seemed to capture this
feature.
36. The last learning objective deals with monitoring the changing near-storm environment
during the nowcast to warning decision making (WDM) time period. At this time period,
NWP output is of least importance, while observational data is of most importance.
37. GOES visible imagery with METARs overlaid 1932 UTC 24 June – 0015 UTC 25 June
2003. At the start of this loop we see a stable air mass characterized by stable wave clouds
and/or stratus with cooler temperatures, south of this air mass we observe unstable cloud
streets and warmer temperatures. As we start the loop we see a thunderstorm initiate along
the boundary in air masses. By 2240 this thunderstorm appears to be weakening
considerably (the overshooting top goes away, and the anvil cirrus becomes thin). However,
this storm puts down an outflow boundary to the west that interacts with the pre-existing
boundary discussed earlier. This storm quickly intensifies and produces a F4 tornado.
Monitoring boundaries and their effects on convective activity is crucial during this period
where significant changes can take place so rapidly.
38. GOES visible imagery 1345 – 2215 UTC 22 July 2007. METARs may be toggled on/off
with the “22July07” check box in the controls frame. An offshore MCS produces an outflow
boundary that propagates westward across north Florida / southern Georgia. Numerous
thunderstorms initiate along the outflow boundary, but are then undercut by the stable air
mass immediately behind the outflow boundary, leading to their dissipation. The south end
of the outflow boundary interacts with a developing sea-breeze, this interaction leads to
additional thunderstorms where a tornado is reported at 1654 UTC as a waterspout moves
ashore. The outflow boundary also interacts with the sea-breeze on the Gulf coast of Florida,
this collision takes place starting around 1900 UTC. Soon after the boundary interaction we
see enhanced thunderstorms where severe wind is reported.
39. GOES visible imagery 1456 – 2341 UTC 16 June 1992. METARs may be toggled on/off
with the “16June92” check box in the controls frame. Identify changes taking place in the
near-storm environment. The early convection in Wisconsin lays down an outflow boundary,
with stable wave clouds on the cold side of the boundary. Note whre the outflow boundary
sets up in northeast Iowa, a storm develops along this boundary around 1930 UTC, travels
eastward along the boundary for a period (a F1 tornado is reported at 2003 UTC), then the
storm moves into the stable side of the boundary and quickly dissipates.
40. Next we will consider cloud features that may be detected in the vicinity of severe storms.
This schematic shows what you might see in a visible satellite image of a supercell, with an
overshooting top, flanking line to its southwest, inflow feeder clouds to the east of the
flanking line an lines of towering cumulus above an invigorated RFD. Here, we will focus
on the lines of cumulus that form above an invigorated RFD and the inflow feeder clouds.
These features coincide with transition to, or intensification of, supercell thunderstorms.
What mechanisms cause these to develop and how they relate to supercell behavior is an area
of research, however we know at this time that when these features are observed the supercell
is undergoing intensification. Note that there are numerous reasons why we may not see
these features (intervening anvil cirrus from nearby storms, high level cirrus over the area,
nighttime, GOES-East versus GOES-West viewing angle etc), but when they are visible,
know the thunderstorm is intensifying.
41. Research on inflow feeder clouds sheds some light on their relationship to severe weather. A
statistical study (see Mazur et al 2007 reference on the student guide) of 131 storms that
exhibited persistent storm features looked at the presence of inflow feeder clouds and severe
weather reports within a -30 to +10 time period, as well as mesoscyclone detection from the
MDA. Much like the enhanced-v satellite signature, observing inflow feeder clouds are not
necessary for severe weather occurence. However, if inflow feeder clouds are observed there
is a 77% chance of severe weather within 30 minutes. Combined inflow feeder cloud and
mesocyclone presence indicates a 85% chance of severe weather within 30 minutes.
42. GOES visible imagery 1745 – 2125 UTC 11 June 2001. METARs may be toggled on/off
with the “11June01” check box in the controls frame. A supercell develops in the vicinity of
a low in southwest Minnesota. This storm exhibits inflow feeder clouds around 1955 UTC.
Also note the outflow on the west side of the supercell around this time.
43. GOES visible imagery 1800 UTC 6 June – 0126 7 June 1989. METARs may be toggled
on/off with the “6June89” check box in the controls frame. At 2030 UTC we see a MCS
moving southeastward, producing a outflow boundary that is southeast-northwest oriented
moving westward. A dryline exists from the Texas panhandle just west of Amarillo (81/65 at
2030 UTC) and extends northward into Kansas. Convective initiation is seen along the
dryline in southwest Kansas. This storm interacts with the MCS outflow boundary and
begins moving southeast, at that time inflow feeder clouds can be observed between 2146 –
2316 UTC. This storm was associated with a F3 tornado and 2.0” diameter hail. By 2216
we see new thunderstorm development along the dryline in the northern Texas panhandle.
This storm is slowly intensifying as it moves northeast, the seems to intensify rapidly by
2331 UTC, most likely due to the interaction with the MCS outflow boundary. The new
storm cuts off the inflow from the storm to the north discussed earlier. Afterwards, this
storm continues to intensify and we see a combination of inflow feeder clouds along with
existing clouds in the region becoming enhanced and moving quickly into the storm. This
storm produced a F1 tornado and golfball size hail:
Time (UTC)
21:46
21:58
22:19
23:31
00:30
01:58
02:13
Storm report
F1 tornado
F3 tornado
2.0” hail
2.75” hail
1.75” hail
tornado
F1 tornado
44. GOES visible imagery along with corresponding time matched 0.5 degree base reflectivity
from the Rapid City, SD radar. The storm of interest is coming out of Wyoming into
southwest South Dakota. Inflow feeder clouds become evident by 2145 UTC and persist
until about 2210 UTC. The inflow feeder clouds temporarily go away then come back again
by 2225 UTC and become more enhanced in time. Also note the new storm that initiated to
the east of the original storm, the inflow feeder clouds on the eastern end are likely
associated with the new storm. Starting around 2240 UTC we observe low-level stratus
outflow overtaking the region where inflow feeder clouds existed. The animated imagery
shows outflow moving towards the southwest. This corresponds well with the trends we see
in the reflectivity field as well. Storm reports:
Time (UTC)
Storm report
21:19
tornado
21:25
tornado
22:34
tornado
45. Example showing Towering Cumulus above an invigorated RFD. This is the 5 July 2000
case we analyzed earlier. TCu above an invigorated RFD first appear around 01:15 UTC
with the storm in the south-central part of the Nebraska panhandle. Recall this is the time that
the storm realized the higher dewpoints and probably began to propagate southward along
the MCS outflow boundary. Storm reports with this storm include:
Time (UTC)
Storm report
02:25
1.75” hail
02:45
4.5” hail
03:10
F3 tornado
46. Here we look at an example of lines of towering cumulus that form above an invigorated
RFD. The storm of interest is in eastern Colorado moving southward. The storm seems to
be propagating along the outflow boundary of a previous storm during a period in this loop.
Cumulus form above the RFD just after 0000 UTC 23 July and appear most noticeable
around 0125 UTC. When you observe this signature in the visible imagery, know the storm
is undergoing intensification. There were numerous reports of tornadoes with this storm:
Time (UTC)
Storm report
00:55
tornado
01:10
tornado
01:16
2.75” hail
01:58
tornado
02:00
tornado