Quantitative Precipitation Forecast
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FOUS30 KWBC 211821
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
220 PM EDT MON JUL 21 2014

...VALID 18Z MON JUL 21 2014 - 00Z WED JUL 23 2014...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 N K7L2 15 SSE BIS BIS 20 N BIS 40 N BIS 25 SW K5H4
10 SSW K5H4 15 ESE K5H4 20 N K46D 30 SE DVL 15 WSW RDR 10 N CKN
15 W VWU 35 WSW CWCH 20 S CWDV 25 S CWEC 45 WNW CMX 15 NNE ASX
25 S SUW 25 NW JMR 20 S ADC 20 ESE FFM 20 WSW FFM 25 E KGWR KGWR
10 WNW K2D5 45 SSW JMS 35 ENE K7L2 20 NE K7L2 15 N K7L2.



...EASTERN ND INTO NORTHERN MN...

THE AREA FROM EASTERN NORTH DAKOTA INTO NORTHERN MINNESOTA
CONTINUES TO BE THE FOCUS FOR POSSIBLE MCS DEVELOPMENT LATER THIS
AFTERNOON AND CONTINUING INTO THE NIGHT AS SHORTWAVE ENERGY COMING
OUT OF THE GREAT BASIN/NORTHERN ROCKIES TURNS EASTWARD.  SURFACE
PRESSURES FALL IN RESPONSE TO THE SHORTWAVE LATER TONIGHT AND
TUESDAY AND A LOW FORMS ALONG A COLD FRONT DROPPING SLOWLY
SOUTHEAST THROUGH THE REGION. AN INCREASING SOUTHWESTERLY LOW
LEVEL JET WILL DRAW MORE MOISTURE INTO THE REGION WITH
PRECIPITABLE WATER VALUES AROUND 2 INCHES POOLING IN VICINITY OF
THE FRONT LEADING TO AN ENVIRONMENT FAVORABLE FOR HEAVY RAINFALL.
SOME 1 TO 2 INCH RAINFALL AMOUNTS IN A COUPLE OF HOURS...WITH SOME
2 TO 3+ INCH TOTALS.  THESE RAINFALL RATES/TOTALS COULD STILL
CAUSE SOME FLOODING PROBLEMS WITHIN THE SLIGHT RISK AREA EVEN IF
THIS IS A FORWARD PROPAGATING SYSTEM.

THE 12Z SUITE OF MODEL GUIDANCE CONTINUED TO BE SPLIT ON THE IDEA
OF WHERE THE AXIS OF HEAVIEST RAINFALL WILL SET UP...WITH THE 12Z
CYCLE EVEN OPENING UP SOME QUESTION ON HOW FAST THE HEAVIEST PCPN
SPREADS EAST. THE 12Z WPC GRAPHICS FOR DAY 1 LARGELY FOLLOWED THE
POSITION OF THE UPPER LEVEL WAVE RUNNING ALONG THE CANADIAN BORDER
FOR TIMING THE BEST PCPN AREA.  THE MODEL AGREEMENT WAS NOT TOO
DISPARATE THERE.  THE DIFFERENCE IN NORTH/SOUTH PLACEMENT
REMAINED.  THE GEM REGIONAL/GFS/UKMET WERE ON THE NORTH SIDE OF
THE GUIDANCE BY 22/06Z.  THE NAM WAS ABOUT AT THE SAME LATITUDE AS
THE ECMWF BUT CERTAINLY SLOWER. THE WPC FORECAST WAS TO STAY A BIT
ON THE SOUTH SIDE OF THE GUIDANCE NEAR THE FRINGE OF THE CAPE.
THIS IDEA HAD THE SUPPORT OF THE HI RES GUIDANCE ALTHOUGH WE DID
NOT FOLLOW THEIR IDEA OF STREAKING HEAVY RAIN EASTWARD AS FAST AS
THE WRF/SSEO.

...SOUTHEAST...

12Z SOUNDINGS SHOWED A MOIST AIRMASS IN PLACE WITH PRECIPITABLE
WATER VALUES APPROACHING 2.25 INCHES IN THE CAROLINAS...AND K
INDEX VALUES OF 35 TO 40 SUGGESTING THE ENVIRONMENT CAN SUPPORT
CELLS WITH INTENSE RAINFALL RATES AND LOCALLY HEAVY RAFL.  SOME
ISOLATED PROBLEMS DUE TO RUNOFF OR PONDING OF WATER MAY BE
POSSIBLE FROM THE CAROLINAS INTO SOUTHWEST VA SINCE ANY CELLS
CAPABLE OF PRODUCING MDT TO LOCALLY HEAVY RAINFALL SHOULD BE
MOVING FAIRLY SLOW GIVEN SPEEDS OF UNDER 10 KTS IN THE STEERING
LAYER.

THINKING IS THAT THE MOST LIKELY TIME FOR PROBLEMS SHOULD BE
CONFINED TO THE PERIOD FROM LATE THIS AFTERNOON INTO THE EARLY
EVENING. THE AREAS OF NORTH CAROLINA INTO FAR SOUTHERN VA ARE
NORTH OF A BOUNDARY WHICH MAY HELP FOCUS ACTIVITY...WHILE A VORT
LOBE MOVING NORTHEAST ACROSS SOUTHERN GA WILL ALSO HELP FOCUS SOME
OF THE CONVECTION.

BANN

$$





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