Quantitative Precipitation Forecast
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FOUS30 KWBC 150003
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
803 PM EDT THU SEP 14 2017

...VALID 01Z FRI SEP 15 2017 - 12Z FRI SEP 15 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 NNW RQE 55 NNW INW 15 W FLG 50 NW PRC 55 NNE IGM 15 SSE SGU
SGU 30 NW SGU 75 NW SGU 55 SW ELY 20 SSW EKO 40 WSW TWF
25 ENE SUN 25 WNW S14 25 N WYS 40 NNW COD 30 W SHR 20 WSW IDV
HLD 35 S BVR 45 E VEL 35 N HDN 10 N 20V 15 SSE GUC 10 N E33
35 SE FMN 25 NNW RQE.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
45 WNW CMX 25 E BFW 10 NNE MZH 15 SSW PWC 20 N PKD 20 WNW FOZ
30 SSW CWCH 20 ESE CWDV 15 SW CXCA 45 E CWEC 30 NNW P59
45 WNW CMX.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
VSF 15 NNW CEF BAF 15 W HFD OXC 10 E HPN 10 SSE EWR SMQ
20 SW 12N 15 SSW MPO 30 SW AVP 25 ENE SEG 35 NNE UNV 25 S ELZ
ELZ 20 N ELZ DSV 10 NW PEO 25 NNE PEO 25 NE FZY 20 ESE GTB
20 S SLK 15 SW MPV 20 WNW LEB VSF.


15/01UTC UPDATE...

FOR THIS UPDATE...SOME SMALL ADJUSTMENTS WERE MADE TO PREVIOUS
MARGINAL RISK AREAS TO ACCOUNT FOR CURRENT RADAR/SATL TRENDS.
ACROSS THE GT BAINS AND NRN ROCKIES...EXPANDED MARGINAL RISK
SLIGHTLY NEWD INTO SRN MT BASED ON TRENDS OF BOTH THE HRRR AND
HRRR EXPERIMENTAL WITH EXPECTATION OF INCREASING ISENTROPIC LIFT
OVER FRONTAL BNDRY OVERNIGHT AS S/WV LIFTS NEWD INTO WY BY FRI
MRNG.  LOCAL 6 HR AMOUNTS IN EXCESS OF AN INCH COULD TRANSLATE TO
SOME VERY ISOLD RUNOFF ISSUES IN STEEPER TERRAIN OR POOR DRAINAGE
AREAS BUT FOR MOST AREAS NORTH OF THE FRONT...RAINFALL WILL BE
PRIMARILY STRATIFORM AND LONGER DURATION..LIMITING A TRUE FLASH
FLOOD THREAT THERE.  FARTHER SOUTH SOME LINGERING WEAK INSTABILITY
THROUGH PARTS OF UT INTO WRN CO THROUGH THE EARLY OVERNIGHT COULD
LEAD TO SOME BRIEF HEAVIER DOWNPOURS...BUT PROGRESSIVE NATURE OF
ACTIVITY SHOULD LIMIT ANY ORGANIZED FF THREA.   ACROSS THE
NORTHEAST HI RES GUIDANCE SHOWS A VERY SHORT TERM THREAT FOR ISOLD
HEAVIER CONVECTION THROUGH THE EARLY OVERNIGHT..SO HAVE MAINTAINED
MARGINAL RISK THERE.  PREVIOUS FORECAST REASONING FOR NRN MN IS
UNCHANGED.     SULLIVAN


1500 UTC UPDATE

NORTHEAST PA---SOUTHERN TIER OF NY---EASTERN NY---FAR NORTHERN NJ
INTO FAR WESTERN NEW ENGLAND

FOR THE 1500 UTC UPDATE A MARGINAL RISK AREA WAS ADDED OVER
PORTIONS OF THE NORTHEAST FROM NORTHEAST PA---ACROSS THE SOUTHERN
TIER OF NY STATE---EASTERN NY---FAR NORTHERN NJ AND INTO FAR
WESTERN PORTIONS OF NEW ENGLAND.   HEAVY RAINS HAVE OCCURRED AHEAD
OF THE TROF CURRENTLY MOVING INTO THE EASTERN LAKES/UPPER OH
VALLEY REGION OVERNIGHT---WITH POTENTIAL FOR ADDITIONAL CONVECTION
AND LOCALIZED HEAVY RAINFALL AMOUNTS INTO THIS EVENING AS THIS
UPPER TROF CONTINUES TO PUSH EASTWARD. INSTABILITY WILL INCREASE
AHEAD OF THE TROF THIS AFTERNOON ACROSS EASTERN NY INTO WESTERN
NEW ENGLAND WITH MUCAPE VALUES OF 500-1000 J/KG ACROSS THESE
AREAS.  THIS WILL SUPPORT CONTINUED POTENTIAL FOR LOCALIZED 1-2"+
PRECIP TOTALS AND ISOLATED RUNOFF ISSUES ACROSS THESE AREAS.

ORAVEC




INITIAL DISCUSSION

...GREAT BASIN INTO THE NRN ROCKY STATES...

A COMPACT CLOSED LOW NOW OVER CA WILL LIFT NORTHEASTWARD INTO THE
GREAT BASIN TODAY AND INTO THE NRN ROCKIES BY EARLY MONDAY.
OVERALL...THERE IS STILL GOOD MASS FIELD AGREEMENT WITH THE
EVOLUTION OF THIS FEATURE IN THE LATEST GUIDANCE. WELL DEFINED
UPPER DIFFLUENCE IN AN AXIS OF ABOVE AVERAGE PW VALUES AHEAD OF
THIS CLOSED LOW WILL SUPPORT INCREASING PRECIPITATION COVERAGE
THROUGH THE GREAT BASIN. NRN STREAM HEIGHT FALLS DIVING SHARPLY
SOUTHEASTWARD THROUGH THE PAC NW WILL MEANWHILE STRONGLY AMPLIFY A
NRN STREAM UPPER TROF OVER THE N-CENTRAL GREAT BASIN AS SRN STREAM
SYSTEM APPROACH ENHANCES MOISTURE TRANSPORT INTO THE REGION. LARGE
SCALE LIFT AHEAD OF THESE HEIGHT FALLS COMBINED WITH POST FRONTAL
NORTHEASTERLY FLOW FROM THE NRN HIGH PLAINS INTO THE NRN ROCKIES
WILL SUPPORT SOME MODERATE TO LOCALLY HEAVY PRECIP TOTALS OVER THE
NRN ROCKY STATES. A COMBINATION OF WPC CONTINUITY AND MESO-MODEL
CONSENSUS SEEMED REASONABLY WELL CLUSTERED.A NRN ROCKIES PRECIP
CHANGE OVER TO SNOW WILL OCCUR IN RESPONSE TO LOWERING HEIGHTS
FROM THE AMPLIFYING TROF AND LOWER ATMOSPHERIC COOLING AND WINTER
WEATHER WATCHES AND ADVISORIES ARE ALREADY IN EFFECT. THE WPC
MARGINAL EXCESSIVE RAINFALL RISK COVERS AREAS FROM THE CENTRAL
GREAT BASIN TO THE NRN ROCKY STATES ALONG/SOUTH OF THE
COOLING/STABILIZING FRONT.

...NRN MN...

A STRENGTHENING SURFACE FRONTAL BOUNDARY WILL SINK SLOWLY
SOUTHEASTWARD THROUGH UPPER MS. SOUTHERLY LOW LEVEL FLOW IS
EXPECTED TO STRENGTHEN INTO THIS BOUNDARY THURSDAY AHEAD OF A
FRONTAL WAVE/UPPER IMPULSE. THIS WILL SUPPORT INCREASING PRECIP
CHANCES INTO FRIDAY FROM NRN MN AND FAR UPPER GREAT LAKES INTO
ONTARIO...INCLUDING A SW-NE SWATH OF MODERATE AMOUNTS UPWARDS TO
IN EXCESS OF ONE INCH WITH TRAINING. A WPC CONTINUITY AND
MESO-MODEL CONSENSUS SEEMS REASONABLY WELL CLUSTERED AND OFFERS
SOME MARGINAL EXCESSIVE RAINFALL THREAT.

SCHICHTEL

$$





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