Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 220743
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
341 AM EDT FRI MAY 22 2015

...VALID 12Z FRI MAY 22 2015 - 12Z SAT MAY 23 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 ENE ATS 10 WNW ROW 50 ENE 4CR 25 WNW TCC 10 WNW DHT DUX
20 WSW PPA 45 SSE HHF 30 NE CSM 15 SSE SWO 25 S OKM 15 NE AQR
15 SE GLE 30 SW RPH 45 E HOB 25 ENE ATS.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 NW GLD 30 WSW AKO 25 SE CYS 35 S TOR 20 SW AIA 25 ENE OGA
10 NNW MCK 35 S MCK 25 NW GLD.


...PORTIONS OF THE CENTRAL HIGH PLAINS...

A SHORTWAVE LIFTING NE FROM THE BROAD UPPER TROUGH BASE IS
ENHANCING THE UPPER DIFFLUENCE AND BROAD SCALE UPPER DIVERGENCE
FROM THE CENTRAL ROCKIES AND CENTRAL PLAINS EARLY THIS MORNING. AS
A RESULT A NEWLY-FORMED WARM CONVEYOR BELT (WCB) IS NOTED PER THE
SATELLITE TRENDS...WITH THE UPTICK IN WAA FORCING (STRENGTHENING
LOW-LEVEL INFLOW AND MOISTURE TRANSPORT ALONG WITH DEEPENING
ISENTROPIC ASCENT) ALLOWING FOR MORE WIDESPREAD AREAS OF FROM THE
CENTRAL ROCKIES INTO THE CENTRAL PLAINS EARLY THIS MORNING. DEEP
LAYER INSTABILITY DURING THIS PERIOD WILL BE MINIMAL (MUCAPES
GENERALLY 400-500 J/KG AT BEST)...HOWEVER WITH THE MODEST PW AND
850-700 MB MOISTURE TRANSPORT ANOMALIES (1-2 STANDARD DEVIATIONS
ABOVE THE NORM)...EXPECT MODERATE RAINFALL TOTALS...ESPECIALLY
EARLY THIS MORNING...AS AREAL-AVERAGE AMOUNTS RANGE BETWEEN .25 TO
.75 INCH ACROSS MUCH OF THE AREA.

LATER IN THE PERIOD (00-12Z SAT)...THE UPPER LEVEL PATTERN BECOMES
EVEN MORE AMPLIFIED AS THE DEEP UPPER LOW SHIFTS INTO THE 4
CORNERS REGION WHILE THE DOWNSTREAM RIDGE BUILDS (HEIGHTS RISE
ACROSS THE EASTERN PLAINS AND MID/UPPER MS VLY). THE INCREASE
UPPER LEVEL DIFFLUENCE ALONG WITH 850 MB S/SW FLOW INCREASING TO
40-50 KTS WILL AGAIN BOOST THE S-N LOW-MID LAYER MOISTURE
TRANSPORT AND MODEST DEEP LAYER INSTBY (MUCAPES 500-1000 J/KG)
INTO THE CENTRAL PLAINS OVERNIGHT. THE BIG QUESTION FROM A QPF
STANDPOINT HOWEVER IS HOW MUCH OF THE HEAVIER NOCTURNAL CONVECTION
LIFTING N-NE FARTHER AWAY FROM THE SURFACE FRONTAL ZONE WILL GET
INTERCEPTED BY THE BETTER THERMODYNAMICAL PROFILES (HIGHER INSTBY
AND PWS) FARTHER SOUTH -- AS IS TYPICALLY THE CASE WITH MADDOX
SYNOPTIC TYPE HEAVY RAINFALL EVENTS. HOWEVER GIVEN THE UPSLOPE
FLOW CONTRIBUTION AND RELATIVELY LOW FFG (1 TO 1.5 INCHES IN 3
HOURS)...EVEN MINIMAL INSTABILITY COULD LEAD TO POTENTIALLY
EXCESSIVE SHORT TERM RAINFALL RATES AND THUS RUNOFF ISSUES.


...SOUTHERN ROCKIES INTO THE SOUTHERN PLAINS...

FOLLOWING THE EARLY MORNING ACTIVITY ASSOCIATED WITH THE
AFOREMENTIONED SHORTWAVE LIFTING NORTHEAST OF THE CLOSED UPPER
LOW...THERE WILL BE A RELATIVE PERIOD OF TRANQUILITY DURING THE
DAY AS THE UPPER LOW DIGS INTO THE SOUTHWEST AND HEIGHTS BEGIN TO
RISE ACROSS THE SOUTHERN PLAINS. ATTENTION THEN SHIFTS TO THE
POTENTIAL FOR MCS DEVELOPMENT OVERNIGHT...AS THE UPPER LOW PIVOTS
INTO THE 4 CORNERS REGION AND THE UPPER FLOW ACROSS THE SOUTHERN
ROCKIES INTO THE SOUTHERN PLAINS BECOMES INCREASINGLY DIFFLUENT.
THE MODELS SHOW MODEST BROAD-SCALE UPPER DIVERGENCE DEVELOPING
BETWEEN THE TROUGH-RIDGE AXES ACROSS THE SOUTHERN ROCKIES AND TX
PANHANDLE EASTWARD THROUGH THE RED RIVER VALLEY IN NORTH
TX/SOUTHERN OK...THOUGH SUSPECT THE ROBUST UVVS NOTED FROM SOME OF
THE NWP (GFS IN PARTICULAR) ARE INDICATIVE OF THE MODEL DEVELOPING
AN MCS. THE THERMODYNAMIC PARAMETERS ARE INDEED IMPRESSIVE
OVERNIGHT FRI INTO EARLY SAT...AS THE LOW LEVEL S/SSW INFLOW
INCREASES TO 40-50 KTS... MUCAPES CLIMB TO 1000-1500 J/KG...AND PW
ANOMALIES RISE TO AROUND 2 STANDARD DEVIATIONS ABOVE NORMAL. THE
WRF-ARW...WRF-NMMB...AND NSSL-WRF SIMULATED REFLECTIVITY GUIDANCE
SUGGEST A GENESIS REGION ACROSS EASTERN NEW MEXICO ALONG AND NORTH
OF THE SURFACE WARM FRONT BETWEEN 00-06Z...WITH THE ACTIVITY AND
WARM FRONTAL BOUNDARY LIFTING NE/ENE THROUGH 12Z. WPC UTILIZED A
MULTI-MODEL BLEND WITH THE QPF...THE BULK OF WHICH WAS BASED WITH
27KM ECMWF GUIDANCE WHICH WAS SUPPORTED BY THE 00 NSSL-WRF OUTPUT.
AREAL-AVERAGE QPF BETWEEN .25 AND 1.00 INCH WAS NOTED OVER A BROAD
AREA...HOWEVER AS PER THE HIGH RESOLUTION GUIDANCE...LOCALIZED
AMOUNTS BETWEEN 2-4+ INCHES WITHIN A 6 HOUR PERIOD WILL BE
POSSIBLE.


...NORTHEAST OREGON...

AS THE DEEP UPPER LOW PIVOTS INTO THE SOUTHWEST AND 4 CORNERS
REGION DURING THE DAY 1 PERIOD...THE UPPER PATTERN ACROSS THE
ENTIRE WESTERN CONUS WILL REMAIN STRONGLY MERIDIONAL WITH SOMEWHAT
OF A REX-BLOCKING SIGNATURE AS A CLOSED 570 DM 500 MB HIGH FORMS
ACROSS WESTERN CANADA AND EVENTUALLY DROPS INTO THE NORTHERN GREAT
BASIN BY THE END OF THE PERIOD. A SHARPENING DEFORMATION/SHEAR
AXIS AT MID LEVELS DEVELOPS ALONG THE WEST COAST BETWEEN THE 500
MB RIDGE ACROSS THE PACIFIC AND THE AFOREMENTIONED 500 MB HIGH
THAT PINCHES OFF ACROSS WESTERN CANADA AND THE NORTHERN GREAT
BASIN. THIS UNUSUAL DYNAMICAL SETUP ALONG WITH THE ANOMALOUS
THERMODYNAMIC PROFILE (MUCAPES INCREASING TO 1000-1500 J/KG DURING
THE AFTN/EVENING ALONG WITH PWS AOA 0.75 INCH) WILL MAKE FOR
LOCALLY HEAVY/POTENTIALLY EXCESSIVE OROGRAPHICALLY-ENHANCED
RAINFALL ALONG AND NEAR THE BLUE MTNS OF NORTHEAST OREGON. WHAT
MAKES THIS SITUATION UNIQUE IS THE FAVORABLE MOISTURE AND
INSTABILITY PROFILE DESPITE THE NORTHERLY LOW LEVEL FLOW. 24 HOUR
AREAL-AVERAGE RAINFALL AMOUNTS ARE EXPECTED TO RANGE BETWEEN .50
AND 1.00 INCH ACROSS THE AREA PER A MULTI-MODEL
BLEND...HOWEVER...PER THE HIGH RESOLUTION GUIDANCE...LOCALLY
HIGHER AMOUNTS BETWEEN 1-3+ INCHES WITHIN A 3-6 HOUR PERIOD WILL
CAUSE RUNOFF ISSUES GIVEN THE RELATIVELY LOW FFG. THE 00Z NAM
CONEST WAS PARTICULARLY ROBUST... WITH ISOLATED MAXIMA OF 5+
INCHES NOTED.

HURLEY


$$




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