Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 181418
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1017 AM EDT MON AUG 18 2014

...VALID 15Z MON AUG 18 2014 - 12Z TUE AUG 19 2014...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
90 SW OLS 105 WSW OLS 110 W OLS 75 SSE YUM 60 S NYL 60 SW NYL
50 S IPL 40 S NJK 20 WSW NJK 20 NE TRM 15 W EED 35 NW IFP
30 SE HND 15 ENE LSV 25 W SGU 40 E SGU 45 N GCN 25 NNE FLG
25 ESE INW 30 SE SJN 55 NE SAD 15 NE SAD 20 SE SAD 40 ENE DUG
95 SE DUG 80 NE MMHO 90 SW OLS.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 E MLJ 15 S WRB 30 SE LSF 60 SE MEI 35 SSE TVR 45 W MLU
30 N ELD 35 WNW LLQ 35 SE SGT UTA 30 SW MKL 40 N MSL 30 NNW MDQ
30 NE MDQ 25 WSW RHP CEU 10 E MLJ.


1400 UTC UPDATE

THE ELONGATED SLIGHT RISK AREA THAT STRETCHED FROM THE TN VALLEY
INTO THE SOUTHERN APPALACHIANS AND SOUTHERN MID ATLANTIC WAS
SEPARATE INTO TWO DISTINCT AREAS.  THIS WAS TO REFLECT CONVECTION
POTENTIAL IN THE TWO SEPARATE STREAMS OF SHORTWAVE ENERGY MOVING
WEST TO EAST---WITH A MINIMUM IN ACTIVITY EXPECTED  IN BETWEEN.
THE NORTHEASTERN VORT MOVING FROM WV INTO SOUTHERN VA WILL ENHANCE
UVVS ALONG THE STATIONARY FRONTAL BOUNDARY OVER THE SOUTHERN MID
ATLANTIC.  WITH PW VALUES ABOVE AVERAGE---HEAVY TO ISOLATED
EXCESSIVE RAINFALL AMOUNTS POSSIBLE LATE THIS AFTERNOON INTO THIS
EVENING AS CONVECTION IS EXPECTED TO CONTINUE TO ENHANCE.

FARTHER TO THE SOUTHWEST---THE SLIGHT RISK AREA WAS ALSO EXPANDED
SOUTHWARD TO REFLECT FUTURE MOVEMENT OF CONVECTION AHEAD OF THE
TWO VORTS---ONE ACROSS THE UPPER TN VALLEY AND ONE OVER THE LOWER
MS VALLEY---THAT SHOULD CONTINUE TO ENHANCE CONVECTION ACROSS A
LARGE AREA FROM FAR SOUTHEAST AR/FAR NORTHEAST LA---EASTWARD
THROUGH LARGE PORTIONS OF MS---AL AND NORTHWEST GA.  MOIST
WESTERLY LOW LEVEL FLOW WILL SUPPORT POTENTIAL FOR TRAINING AND/OR
BACK BUILDING OF CELLS WITH BOTH AREAS OF CONVECTION.  IN AREAS OF
TRAINING---1 TO 2" OF RAIN IN AN HOUR POSSIBLE.

OVER THE SOUTHWEST---THE PREVIOUS SLIGHT RISK AREA WAS EXPANDED
SLIGHTLY WESTWARD TO INCLUDE FAR SOUTHEAST CA WHERE MUCH ABOVE
AVERAGE PW VALUES WILL PUSH INTO THIS PERIOD.

NO CHANGES IN THINKING ACROSS THE UPPER MS VALLEY FROM THE
PREVIOUS ISSUANCE.

ORAVEC


PREVIOUS DISCUSSION

...PORTIONS OF THE LOWER MISSISSIPPI VALLEY...TENNESSEE
VALLEY...LOWER OHIO VALLEY...AND MID ATLANTIC...

A FAIRLY FLAT...ELONGATED TROUGH ALOFT ALONG WITH AN ASSOCIATED
SLOW-MOVING SURFACE FRONTAL BOUNDARY WILL SET THE STAGE FOR
MULTIPLE ROUNDS OF DIURNALLY-ENHANCED...SLOW MOVING SHOWERS/TSTMS
ACROSS THE OUTLOOK AREA DURING THE PERIOD. THE ACTIVITY WILL BE
AIDED BY THE ROBUST PRE-FRONTAL THERMODYNAMIC ENVIRONMENT...AS
PWATS INCREASING TO 2.00+ INCHES ALONG WITH HIGH WET BULB ZERO
LEVELS (ABOVE 12KFT) ENSURE A DEEP WARM CLOUD LAYER AND THUS
RAINFALL EFFICIENCY. DYNAMICAL SUPPORT FOR DEEP-LAYER LIFT WILL BE
LACKING...AND AS SUCH THE TOTAL EXPECTED RAINFALL ACROSS THE
OUTLOOK AREA WILL AVERAGE UNDER 2 INCHES. HOWEVER...ISOLATED
RAINFALL RATES OF 2-2.5 INCHES WITHIN AN HOUR AND/OR 3-4+ INCHES
WITHIN 3 HOURS WILL LEAD TO SOME SHORT-TERM RUNOFF ISSUES...AS
SOME OF THE HIGHER RESOLUTION/MESOSCALE GUIDANCE INDICATE ISOLATED
24 HOUR AMOUNTS ABOVE 4 INCHES (INCLUDING THE 4KM NAM
CONEST...WRF-ARW...AND NSSL WRF).


...UPPER MISSISSIPPI VALLEY...

AN UPPER TROUGH ACROSS THE NORTHERN PLAINS WILL PUSH SLOWLY E-SE
ACROSS THE UPPER MIDWEST DURING THE PERIOD. AS A RESULT...THE AXIS
OF ANOMALOUS PW VALUES (BTWN 1.5-1.75 INCHES) AND HIGHER LLVL
THETA-E ALONG THE TROWAL ZONE REMAIN ACROSS THE AREA THROUGH EARLY
TUE. THE PRE-FRONTAL LLVL INFLOW NEARLY PARALLEL TO AND AT TIMES
EXCEEDING THE MEAN 850-300 MB FLOW WILL CONTINUE TO ALLOW FOR SLOW
PROGRESSION OF THE CONVECTIVE CLUSTERS...AND AS SUCH ISOLATED
RAINFALL RATES AROUND 2 INCHES WITHIN AN HOUR AND/OR 3-4 INCHES
WITHIN 3 HOURS WILL LIKELY LEAD TO LOCALIZED SHORT-TERM RUNOFF
ISSUES. OTHERWISE...AREAL AVERAGE RAINFALL ACROSS THE OUTLOOK AREA
WILL RANGE BETWEEN 1-1.5 INCHES.


...SOUTHWEST...


DRAWN BY SOUTHERLY FLOW AHEAD OF AN UPPER LOW DROPPING SOUTH ALONG
THE CA COAST... A WEALTH OF MONSOONAL MOISTURE WILL LIFT INTO
ARIZONA TODAY AND ESPECIALLY DURING THE AFTERNOON AND OVERNIGHT.
WHILE DIFFERING SOMEWHAT WITH THE DETAILS (DEPENDING ON THE MODEL
RESOLUTION)...THE GUIDANCE REMAINS FAIRLY CONSISTENT WITH THE
HEAVY RAINFALL SIGNAL ACROSS THIS REGION. AREAL-AVERAGE TOTALS ON
A 20 KM SCALE AREA EXPECTED TO RANGE ANYWHERE BETWEEN .25 AND 1.5
INCHES ACROSS THE OUTLOOK AREA (HIGHEST ALONG AND SOUTH OF THE
MOGOLLON RIM)...HOWEVER...ISOLATED TOTALS OVER 4 INCHES WERE NOTED
ON ALL OF THE HIGHER RESOLUTION MODELS. AS PWATS CLIMB TO 1.5-1.75
INCHES...ISOLATED RAINFALL RATES AROUND 2 INCHES PER HOUR AND/OR
2-4 INCHES WITHIN 3 HOURS WILL LEAD TO LOCALIZED FLASH FLOODING.

FOR FURTHER DETAILS REGARDING ANY ACTIVE MESOSCALE PRECIPITATION
DISCUSSIONS (MPD) WITHIN THE EXCESSIVE RAINFALL OUTLOOK
AREAS...PLEASE REFER TO THE LINK FROM THE WPC HOME PAGE ABOVE THE
TOP NEWS OF THE DAY... OR GO DIRECTLY TO THE MPD PAGE:
WWW.WPC.NCEP.NOAA.GOV/METWATCH/METWATCH_MPD.PHP.

HURLEY
$$





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