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Moderate Mid-Atlantic Rain Event of 12 March 2013
By
Richard H. Grumm and Charles Ross
National Weather Service State College, PA
1. Overview
A fast moving 500 hPa trough (Fig. 1) brought a surge of high precipitable air into the MidAtlantic region (Fig. 2) as the trough moved eastward. The surge of moisture produced a
widespread precipitation event over the eastern United States with some locally heavy rainfall in
portions of eastern Pennsylvania, New York and New Jersey (Fig. 3). Several locations in
northeastern Pennsylvania received over 48 mm of rainfall. The combination of the rain and
snow melt in New York State produced some rises on rivers and streams with 2 points in the
Delaware Basin reaching flood stage1.
As the trough moved eastward, it allowed a surge of warm air into the eastern United States. 911 March 2013 were unseasonably warm. The 30-day temperature trace at Middletown, PA
shows the surge of warm air ahead of the trough. High temperatures were 1 above normal on
the 9-10-11 of March (Fig. 4). The warm air contributed to snow melt in over Pennsylvania and
New York.
As with many rainfall events, most of the rainfall occurred in short period of time. The rain
arrived in the west around 0000 UTC 12 March with most of the accumulating rainfall by 0600
UTC 12 March in western Pennsylvania and Ohio (Fig. 5a). As the frontal system moved
eastward, the north-south bands of rain moved eastward (Fig. 5a-d). The period of heaviest
rainfall in Pennsylvania was between 1200-1800 UTC 12 March 2013 (Fig. 5c) where 32 to 48
mm of rainfall occurred in this 6-hour period.
Forecasts from the NCEP SREF from 08 to 10 March show that the SREF was able to predict the
surge of strong low-level winds (Fig. 6) and high PW air (PW: Fig. 7) into the eastern United
States. The PW data is 6-hour later to show the strong south to north moisture surge and the
advancing frontal system across the region. The frontal orientation and the strong v-winds
implied a Maddox-Synoptic system moving across the Mid-Atlantic region. Outside of tropical
events, Maddox-Synoptic (Maddox et al. 1979) systems produce many of the heavier rainfall
events in the Mid-Atlantic region. This event was relatively modest as it lacked +3 to +5PW
anomalies. The PW surge was well within the climatologically normal realm for this event.
The strong frontal system in the SREF (Fig. 6&7) indicated potentially strong synoptic scale
forcing. Not surprisingly, the SREF produced an axis of south to north rain over the region. Most
of Pennsylnvania and New York were covered by the 12.5mm contour. Several shorter-range
1
Based on MARFC gages minor flooding was observed at Cooks Falls and Walton, NY both in the Delaware basin.
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SREFs produced pockets of 25 mm or more QPF and each individual member 25mm contours
varied spatially over the region. There was a trend to focus higher QPF amounts in northeastern
Pennsylvania (Figs. 8a-i). This was easier to evaluation in the probability forecasts of 25mm or
more QPF (Fig. 9). No members forecast 50 mm or more QPF, however several SREF member
predicted over 40 mm of QPF (Fig. 10). The SREF slightly under predicted the maximum QPF
but did relatively well with predicting a moderate rainfall event when compared to observed
rainfall (Fig 3).
Shorter range SREF QPFs (Fig. 11) show the mean QPF and the 50 mm contours. Only in a few
forecast cycles did any SREF members predict 50mm or more QPF, at the 4% level. The 25mm
contour in northeast Pennsylvania was predicted in the SREF from 11/1500 and 11/2100 UTC
with 1 members indicating over 50 mm in northeast Pennsylvania at 11/500 (Fig. 11e). The
probability of 25mm or more QPF on 12 March (Fig. 12) from the shorter time scale SREFs
show a convergence of solutions emphasizing 25mm or more QPF in northeastern Pennsylvania
and New York but with very short lead-times.
These data show that a fast moving short-wave brought a brief surge of above normal PW into
the Mid-Atlantic region. The PW values were only about 1 above normal (Fig. 2) indicative of
a good but not extreme rainfall event. The pattern was a well-known pattern associated with
many moderate and heavy rainfall events, a Maddox-Synoptic pattern with a surge of strong
southerlies and moisture ahead of an advancing frontal system.
As shown here, the NCEP SREF correctly predicted the relative timing, orientation, and pattern
of the precipitation shield. In areas of heaviest rainfall it may have slightly underestimated the
precipitation, though at least 1 member did predict in excess of 50 mm of QPF in close proximity
to the close 48 mm contour in Figure 3. The SREF forecasts indicated the axis of heavier QPF
quite well and as forecast length decreased, the forecast region of heavier rainfall converged
toward where most of the heavier precipitation was observed.
The pattern and the SREF QPF probabilities correctly indicated that this was not likely a high
flood threat event. The two points in New York which reached flood stage likely had some
contribution due to snowmelt. Most locations remained well below flood levels. Without a
contribution from snow melt or frozen ground, it is often difficult to get serious flooding impacts
when rainfall is below 75mm over much of Pennsylvania.
2. Acknowledgements
The MARFC for flood, snow melt contributions in New York State, and rainfall data.
3. References
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Doty, B.E. and J.L. Kinter III, 1995: Geophysical Data Analysis and Visualization using GrADS.
Visualization Techniques in Space and Atmospheric Sciences, eds. E.P. Szuszczewicz and
J.H. Bredekamp, NASA, Washington, D.C., 209-219.
Maddox,R.A., C.F Chappell, and L.R. Hoxit. 1979: Synoptic and meso-alpha aspects of flash
flood events. Bull. Amer. Meteor. Soc., 60, 115-123.
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Figure 1. GFS 00-hour forecasts of 500 hPa heights (m) and 500 hPa height anomalies in 24 hour intervals from a) 0000 UTC 9 March through f) 0000 UTC
14 March 2013. Return to text.
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Figure 2. As in Figure 1 except for precipitable water (mm) and precipitable water anomalies. Return to text.
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Figure 3. Stage-IV QPE (mm) for the period of 0000 UTC 12-13 March 2013. Return to text.
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Figure 4. Middletown, PA observed high and low temperatures for the period of 12 February through 12 March 2013. The high
temperature trace is read and the low temperature trace is blue. The thick warm color line is the climatological mean and the thick
blue line is the climatological minimum. Dashed lines show 1 standard deviation intervals of the climatic mean.
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Figure 5. As in Figure 3 except for 6-hour rainfall amounts (mm) valid for the 6-hour periods ending at a) 0600 UTC, b) 1200 UTC, d) 1800 UTC 12
March and d) 0000 UTC 13 March 2013. Return to text.
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Figure 6. SREF forecasts of 850 hPa winds (kts) and v-wind anomalies valid at 0600 UTC 12 March 2013 from SREF initialized at a) 2100 UTC 8 March, b)
0300 UTC 9 March, c) 0900 UTC 9 March, d) 1500 UTC 9 March, e) 2100 UTC 9 March, f) 0300 UTC 10 March, g) 0900 UTC 10 March, h) 1500 UTC 10 March,
and i) 2100 UTC 10 March 2013. Return to text.
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Figure 7. As in Figure 6 except SREF precipitable water and PW anomalies valid at 1200 UTC 12 March 2013. Return to text.
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Figure 8. As in Figure 7 except for SREF accumulated QPF valid for the 24 hour period 0000 UTC 13 March 2013 showing the ensemble mean QPF
(mm: shaded), each members 25mm contour (thin colored lines) and the ensemble mean 25mm contour (thick black). Please note the 8 March
2013 SREF did not cover the entire forecast range. Return to text.
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Figure 9. As in Figure 8 except for the probability of 25 mm or more QPF. The thick black contour is the ensemble mean 25mm contour. Return
to text.
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Figure 10. As in Figure 9 except for SREF forecasts of 40 mm of QPF. Return to text.
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Figure 11. As in Figure 8 except total QPF valid from 0000 UTC 12 March through 1200 UTC 13 March 2013 with 50mm contour from each members for
SREF initialized at a) 0900 UTC 10 March, b) 2100 UTC 10 March, c) 0300 11 March, d) 0900 UTC 11 March, e) 1500 UTC 11 March and f) 2100 UTC 11
March 2013. Return to text.
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Figure 12. As in Figure 11 except for probability of 25 mm or more QPF in the 24 hour period from 0000 UTC 12 March to 0000 UTC March 2013. Return
to text.
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March 12 - 13, 2013 Preliminary Flood Summary
Above FS
Crest
(ft)NWS State
(ft)
Flood =
10.18
10.0
Delaware
Cooks Falls, New York
Streamflow
College
Case ExamplesBelow FS (ft)
(cfs)
10,400
Flood = 10.0
Category (ft)
Record (ft) (cfs)
10.0 (minor)
20.55
Beaver Kill - (WFO BGM)
3/12/2013
March 12, 2013
3/12/2013
16.0
(moderate)
62,400
Gage & Town/Delaware County
5:30-5:45
PM
5:45 - 6:15 PM
7:45-8:00 PM
18.0 (major)
June 28, 2006
6,360
Flood = 9.5
9.5 (minor)
16.85
Walton, New York
Flood = 9.5
9.60
West Branch Delaware River - (WFO
BGM)
3/12/2013
March 12, 2013
3/13/2013
Gage & Town/Delaware County
8:15-9:00
PM
11:30 PM
9:15PM-2:30AM
14.0
(moderate)
16.0 (major)
28,600
June 28, 2006
Crest Statistics
Flooding 3/12/2013 - 3/13/2013
and crests occurred 3/12/2013
First flood of 1 that occurred in March, 2013
Third flood that has occurred in 2013
Number of Floods Cresting in Minor Range - 2
Number of Floods Cresting in Moderate Range - 0
Number of Floods Cresting in Major Range - 0
MARFC Power Ranking = 2
(Minor = 1 - Moderate = 5 - Major = 10)
Time in EST
Weather Summary
Low pressure moved through southern Canada dragging a slow moving cold front across the MARFC basins with several waves running up the slow moving
front. The last wave of low pressure developed over Virginia early March 12 and move northward producing 1 to 2 inches of rain across eastern PA and
northern New Jersey. Precipitable water values were 1-2+ STD above the mean. Snow melt across the northeast contributed to the flooding with
temperatures and dew points rising into the 50s.
TOP 24-HOUR PRECIPITATION AMOUNTS (Liquid Equivalent and in inches)
3/11/2013 (12 Z) - 3/12/2013 (12 Z)
Amount
Location
3/12/2013 (12 Z) - 3/13/2013 (12 Z)
County
Amount
Location
County
2.20 Apple Orchard Mt, VA IFL
Botetourt
2.17 Phoenicia, NY
Ulster
2.12 Sloan Branch, VA IFLOWS
Botetourt
2.00 Claryville NY , F/P Precip
Ulster
1.75 Big Island, VA
Bedford
1.99 Jim Thorpe, PA 1.1NNE
COCO
Carbon
1.40 Pedlar Dam, VA F/P Precip
Amherst
1.83 Flatbrookville, NJ
Sussex
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1.40 Tinker Creek, VA IFLOWS
Botetourt
1.75 Friedensburg, PA GOES
Schuylkill
1.28 Oriskany, VA IFLOWS
Botetourt
1.75 Tamaqua, PA
Schuylkill
1.27 Waynesboro, VA WTP COOP
1.19 Lexington, VA
1.16 Simmonsville, VA IFLOWS
1.12 Charlottesville, VA 2W
1.09 Blacksburg, VA 0.4N COCO
independent city
1.74 Springtown, PA
Bucks
Rockbridge
1.67 Kresgeville, PA
Monroe
Craig
1.63 Landingville, PA
Schuylkill
Albemarle
1.62 Mahanoy City, PA 4NE DCN
Schuylkill
Montgomery
1.62 Pottsville, PA 1.3WSW CO
Schuylkill
1.08 Daleville, VA IFLOWS
Botetourt
1.61 Beltzville Dam, PA
1.08 Middlebrook, VA IFLOWS
Augusta
1.60 Hamburg, PA F/P Precip
Berks
Montgomery
1.60 Glendon, PA 3.5S COCO
Northampton
1.05 Blacksburg, VA 5.0W COCO
1.04 North Fork, VA IFLOWS
Botetourt
1.60 Pine Grove, PA
Floods by MARFC Basins
Carbon
Schuylkill