Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 211859
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 PM EDT THU AUG 21 2014

...VALID 18Z THU AUG 21 2014 - 00Z SAT AUG 23 2014...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
CWBZ 10 SSW CMSB 15 E CWFQ 30 N 1V4 15 NE 1V4 15 SSE 1V4 LEB
VSF 15 S RUT 20 SSW RUT 10 ESE GFL GFL 10 NW GFL 15 WSW GFL
10 NNE SCH ALB 50 N MSV 20 SSE BGM 25 SW BGM 10 E ELM 15 S PEO
PEO 20 SSW FZY 15 E FZY GTB 15 NNE GTB 20 S OGS 10 ESE OGS MSS
CWBZ.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
35 E HEI 15 SSE HEI 10 E 2WX 65 WSW 2WX 50 SSE MLS MLS
25 SE JDN 60 NW JDN 50 SW CWVN 15 SSW CWVN 20 SE CWAQ 10 E ISN
20 ENE KS25 15 SSE KHZE 35 E HEI.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 ENE IND 15 WSW MQB 20 SE CNC 10 SSW DSM 15 E AMW 15 SE MRJ
35 WSW MKG 10 NNW TOL 10 NW BJJ 20 E PHD AFJ 15 NE MGW
25 SSW 2G4 10 SSE EKN 30 NNE LWB 20 NNE BKW 20 NNW I16 25 SE HTS
35 WNW HTS 15 SSE ILN 10 NNW HAO 15 ENE IND.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 NNE BIL 40 WSW BIL 15 S LVM 20 SSE BZN 35 SSE HLN 20 WNW HLN
40 NNE 3DU 40 S 8S0 30 SSW CTB 25 ESE CTB 55 N GFA 40 SSW HVR
50 NNE LWT 35 ENE LWT 15 NNE BIL.


MID MS VALLEY/MID WEST---TOWARD THE UPPER OH VALLEY/CENTRAL
APPALACHIANS


OVERALL---NO BIG CHANGES MADE TO THE PREVIOUS SLIGHT RISK AREA
DEPICTED FROM THE MID MS VALLEY TOWARD THE UPPER OH VALLEY/CENTRAL
APPALACHIANS REGION.
AN ACTIVE CONVECTIVE PATTERN EXPECTED IN THE VICINITY OF A FRONTAL
BOUNDARY AND ASSOCIATED AXIS OF ABOVE AVERAGE PW VALUES---1 TO 2
STANDARD DEVIATIONS ABOVE THE MEAN---STRETCHING FROM THE MID MS
VALLEY/LOWER LAKES TOWARD THE UPPER MS VALLEY THIS PERIOD.
CONFIDENCE HAS DECREASED WITH RESPECT TO THE DETAILS OF THE TIMING
OF AREAS OF CONVECTION AS THERE IS LARGE MODEL TO MODEL
DIFFERENCES AND LARGE RUN TO RUN DIFFERENCES---ESPECIALLY IN THE
HI RES GUIDANCE WHICH OFTEN WILL DEPICT THESE ORGANIZED CONVECTIVE
REGIONS BETTER.  MOIST WEST SOUTHWESTERLY FLOW INTO THIS BOUNDARY
AND ENHANCED UVVS ASSOCIATED WITH SHORTWAVES MOVING ALONG THE
SOUTHERN EDGE OF THE WESTERLIES WILL SUPPORT ADDITIONAL CONVECTIVE
DEVELOPMENT ALONG THIS FRONT.  THERE IS POTENTIAL FOR TRAINING OF
CELLS IN A GENERAL WEST NORTHWEST TO EAST SOUTHEAST DIRECTION THIS
PERIOD---SUPPORTING HEAVY TO ISOLATED EXCESSIVE RAINFALL AMOUNTS.
ALONG WITH THE DIFFERENCES IN TIMING AMONG THE MODELS---THERE IS
DIFFERENCES LATITUDE WISE WITH THE MAX QPF AXES.  THE FARTHER
SOUTHWARD OVERALL AXIS OF THE NAM WAS FAVORED -ALTHOUGH AMOUNTS
WERE INCREASED GIVEN TRAINING POTENTIAL.  WHILE THERE IS A LOT OF
DIFFERENCES IN QPF AXES---THERE IS A SIGNAL FOR POTENTIAL OF VERY
HEAVY RAINFALL TOTALS IN THE HI RES GUIDANCE.  IN AREAS OF
TRAINING---ISOLATED TOTALS OF 1-2"+ IN AN HOUR AND TOTALS OF 3-5"+
POSSIBLE.

SOUTHERN TIER OF NY--NORTHERN NY INTO NORTHERN NEW ENGLAND

CHANGE TO THE PREVIOUS EXCESSIVE RAINFALL POTENTIAL OUTLOOK HERE
WERE MOSTLY FOR CURRENT RADAR TRENDS.  THE SLIGHT RISK AREA WAS
EXTENDED SOUTHWESTWARD TO CAPTURE THE SLOW MOVING ACTIVITY IN THE
VICINITY OF THE SOUTHERN TIER OF NY STATE. OTHERWISE---SLOW MOVING
CONVECTION AHEAD OF THE SLOW MOVING UPPER VORT AND ASSOCIATED
FRONTAL BOUNDARY MOVING EASTWARD LATE THIS AFTERNOON INTO TONIGHT
FROM THE EASTERN GREAT LAKES INTO THE NORTHERN MID ATLANTIC
POSSIBLE WITH ISOLATED SHORT TERM PRECIPITATION TOTALS OF 1-1.5"+
POSSIBLE.  THE HI RES ARW--NMM---NAM CONEST AND NSSL WRF ARE
SHOWING HEAVY RAIN POTENTIAL LATER THIS PERIOD IN THE VICINITY
SOUTHEAST NY INTO NORTHERN NJ AS THE ABOVE MENTIONED VORT PUSHES
EAST SOUTHEAST DURING THE DAY ON FRIDAY.  LOW CONFIDENCE AT THE
MOMENT---BUT THESE AMOUNTS IF THEY OCCUR MAY PRODUCE RUNOFF ISSUES
ACROSS THESE AREAS.


NORTHERN ROCKIES INTO THE NORTHERN PLAINS

THE MEAN TROF ACROSS THE NORTHWESTERN U.S. WILL AMPLIFY DAY 1 IN
RESPONSE TO SHORTWAVE ENERGY DIVING SOUTHEASTWARD FROM OFF THE
B.C. COAST INTO THE PACIFIC NORTHWEST TONIGHT AND EASTWARD ACROSS
THE NORTHERN ROCKIES FRIDAY.  MODEL CONSENSUS IS FOR TWO PRIMARY
AREAS OF PRECIPITATION WITH THIS AMPLIFYING TROF.  AN INITIAL
BATCH OF PRECIP ASSOCIATED WITH A LEAD SHORTWAVE EJECTING OUT OF
THE MEAN TROF POSITION TONIGHT INTO THE NORTHERN HIGH
PLAINS---EAST NORTHEASTWARD INTO THE REMAINDER OF THE NORTHERN
PLAINS DURING FRIDAY.  THIS WILL BE FOLLOWED BY ANOTHER ORGANIZE
AREA OF PRECIPITATION FORMING UPSTREAM ACROSS THE NORTHERN
ROCKIES/NORTHERN HIGH PLAINS IN RESPONSE TO THE MID TO UPPER TROF
AMPLIFICATION AND STRENGTHENING LOW LEVEL EASTERLY TO
NORTHEASTERLY FLOW. WITH FFG VALUES RELATIVELY LOW ACROSS THESE
AREAS---ISOLATED RUNOFF ISSUES MAY DEVELOP WITH EACH ROUND OF
ORGANIZED PRECIPITATION.

SOUTHWEST---SOUTHERN ROCKIES INTO THE SOUTHERN HIGH PLAINS

TO THE SOUTH OF THE AMPLIFYING UPPER TROF OVER THE NORTHWEST--THE
CLOSED LOW INITIALLY OFF THE SOUTHERN CA COAST WILL BE KICKED
INLAND THROUGH THE SOUTHWEST AND TOWARD THE SOUTHERN
ROCKIES/SOUTHERN HIGH PLAINS.  WIDESPREAD SHOWERS EXPECTED TO
CONTINUE AHEAD OF THIS CLOSED LOW IN A REGION OF WELL DEFINED
UPPER DIFFLUENCE AND ABOVE AVERAGE PW VALUES.  ISOLATED HEAVY TO
EXCESSIVE PRECIPITATION TOTALS POSSIBLE THIS PERIOD AHEAD OF THIS
TROF--ALTHOUGH CONFIDENCE ON PLACEMENT IS LOW.

ORAVEC
$$




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