Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 191406
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1005 AM EDT SUN APR 19 2015

...VALID 15Z SUN APR 19 2015 - 12Z MON APR 20 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 ESE GSP 20 WSW AND 20 ENE GVL 20 E DNN 10 NNE CHA 15 SW CSV
30 N CSV 20 N SME 10 NW LEX 30 N FFT CVG 20 SSE ILN 30 W 3I2
25 SE HTS 15 WSW I16 10 SSE BKW 25 N LWB 15 NW W99 MRB
20 ENE FDK MTN 10 ESE BWI NYG 30 ENE FVX 20 N TDF BUY VUJ UZA
30 ESE GSP.



...SPINE OF THE APPALACHIANS EXTENDING EASTWARD TO NEAR RALEIGH TO
BALTIMORE...

IN THE 15Z UPDATE WE EXPANDED THE SLIGHT RISK AREA JUST SLIGHTLY
NORTH AND EAST BASED ON SSEO MEAN PRECIPITATION FORECASTS AND THE
NORTHWARD EXTENT OF THE SREF MOST UNSTABLE CAPE 500 J/KG BY 12Z
MONDAY. THIS EXPANSION ENCOMPASSES PARTS OF WV AND MD...INCLUDING
THE RELATIVELY LOWER FLASH FLOOD GUIDANCE WHICH EXTENDS UP THE
URBAN CORRIDOR FROM WASHINGTON D.C. TO BALTIMORE.

PREVIOUS DISCUSSION...
SOUTHERN STREAM SHORTWAVE ENERGY LIFTING NORTHEASTWARD OUT OF THE
LOWER MS VALLEY WILL CROSS THE TN VALLEY AND THE SOUTHERN/CENTRAL
APPALACHIANS BY LATER SUN.  A SIGNIFICANT RESURGENCE OF DEEPER
MOISTURE/HIGHER PWATS OWING TO AN INCREASE IN WARM ADVECTION/LOW
LEVEL JET ENERGY...COUPLED WITH THE LARGER SCALE SHORTWAVE
DYNAMICS AND THE NORTHWARD ADVANCE OF A FRONT..SHOULD HELP FOCUS
HEAVIER RAINS BEGINNING EARLY SUNDAY AND CONTINUING INTO SUNDAY
EVENING ACROSS THE INTERIOR OF THE SOUTHEAST AND ESPECIALLY THE
SOUTHERN/CENTRAL APPALACHIANS WHERE DEVELOPING UPSLOPE FLOW WILL
AID IN RAINFALL PRODUCTION.  THE GLOBAL MODELS LED BY THE
ECMWF/UKMET/NAM AND GFS AS WELL AS THE HIRES MODELS ALL FOCUS
HEAVY RAINFALL AMOUNTS THIS PERIOD FROM NORTHEASTERN GA UP THRU
THE WESTERN CAROLINAS AND INTO WESTERN VA..WITH AN AXIS OF 2-4
INCH TOTALS EXPECTED AND ISOLATED AMOUNTS IN EXCESS OF 5 INCHES
POSSIBLE. THUS..HAVE KEPT THE SLIGHT RISK WITH THE POTENTIAL FOR
SOME FLOODING ISSUES ESPECIALLY IN THE HIGHER ELEVATIONS.


...EASTERN END OF THE TN/OH VALLEYS INTO THE WESTERN FOOTHILLS OF
THE APPALACHIANS...

ARRIVAL OF BROAD SYNOPTIC ASCENT AND TRANSPORT OF LOWER/MIDDLE
LEVEL MOISTURE INTO THIS REGION WILL YIELD WIDESPREAD RAIN THROUGH
EARLY SUNDAY AFTERNOON. AT THE TAIL END OF THIS SYNOPTICALLY
FORCED REGIME ENOUGH HEATING SHOULD TAKE PLACE TO PRODUCE CAPE OF
500-1000 J/KG THIS AFTERNOON DEVELOPING FIRST IN EASTERN TN AND
SPREADING NORTHWARD. THIS WILL SUPPORT A MORE CONVECTIVE
PRECIPITATION REGIME WITHIN THE ENTRANCE REGION OF A JET STREAK
LIFTING TOWARD EASTERN KY/OH BY 00Z. INDIVIDUAL CELL MOTIONS WILL
BE RATHER QUICK...BUT HIGH RESOLUTION GUIDANCE FORECASTS SOME
SW-NE ORIENTED SWATHS OF TRAINING CONVECTION. RECENT HRRR RUNS
GOING OUT THROUGH 00Z AND BEYOND...AS WELL AS THE 00Z SSEO MEAN
24-HOUR PRECIPITATION SHOW A SIGNAL FOR LOCAL 1-2 INCH RAINFALL
AMOUNTS...SOME OF WHICH COULD OCCUR QUICKLY WITH CONVECTION THIS
AFTERNOON/EVENING. GIVEN RECENT WET CONDITIONS AND MARGINALLY LOW
FLASH FLOOD GUIDANCE VALUES IN THIS REGION WE EXPANDED THE SLIGHT
RISK OVER THE APPALACHIANS TO COVER PARTS OF EASTERN TN/KY AND FAR
SOUTHERN OH.


...SOUTHERN AL/GA AND NORTHERN FL...

INTENSE SHORT TERM PRECIPITATION LASTING 1-2 HOURS AT A GIVEN
LOCATION...MAY APPROACH FLASH FLOOD GUIDANCE VALUES...AND WOULD BE
OF PARTICULAR CONCERN IN URBAN AREAS. THROUGH MIDDAY STRONG LOW
LEVEL INFLOW WILL TAP INTO A MODERATELY UNSTABLE ENVIRONMENT OVER
THE NORTHERN GULF...WITH PW VALUES ABOVE 1.75 INCHES EXTENDING
WELL INLAND AND SUPPORTING SHORT TERM RAIN RATES OF AROUND 2
INCHES IN AN HOUR. THIS WILL OCCUR BENEATH STRONGLY DIFLUENT UPPER
FLOW NEARLY CO-LOCATED WITH A MID LEVEL SHORTWAVE AND ASSOCIATED
HEIGHT FALLS. MIXED STORM MODES HAD LED TO A VARIETY OF STORM
MOTIONS AND HENCE CELL MERGERS...BOOSTING RAINFALL LOCALLY. THIS
TYPE OF ACTIVITY MAY BE SHORT LIVED...HOWEVER...AS MID LEVEL
FORCING MECHANISMS WILL REMAIN PROGRESSIVE...AS EVIDENCED BY A
WEAKENING TREND AT THE BACK EDGE OF ONGOING CONVECTION IN FAR SRN
AL / FAR WRN FL PANHANDLE. AN 850-700 MB TROUGH AXIS OVERTAKING
THIS REGION SHOULD ENCOURAGE EASTWARD PROGRESSION...AND BOTH THE
11Z AND 12Z HRRR GROW THIS ACTIVITY UPSCALE INTO A FORWARD
PROPAGATING MCS AFFECTING SOUTHWEST GA AND NORTHERN FL THROUGH
EARLY AFTERNOON. ISOLATED LOCATIONS ARE LIKELY TO SEE RAINFALL
EXCEEDING THE FLASH FLOOD GUIDANCE VALUES OF GENERALLY 2.5 INCHES
IN AN HOUR OR 3 INCHES IN 3 HOURS...AND FLASH FLOODING APPEARS
MORE LIKELY DURING THE EARLY EVOLUTION OF THIS EVENT THROUGH
15-16Z. SEE MESOSCALE PRECIPITATION DISCUSSION NUMBER FOR DETAILS.

BURKE/TERRY
$$




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