Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 060649
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
249 AM EDT WED MAY 06 2015

...VALID 06Z WED MAY 06 2015 - 12Z THU MAY 07 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 N 5R5 20 WNW VCT 20 ESE SSF 30 WNW HYI 10 SSE GRK 25 NW CNW
20 NNW 7F9 35 ESE BPG 25 NNW MDD 15 WSW LBB 20 E PVW 15 NW CDS
10 NNW HBR TIK 10 NW LBR 40 ENE OCH 15 WSW JAS 20 NNE EFD
10 N 5R5.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 ENE CWEI 15 SSW KRUG 20 ESE BIS MBG 40 NW HON 25 ENE HON
15 SW OTG 10 NE CBF 20 WSW AFK 25 SW HJH 15 WSW HDE 30 S IEN
20 WNW RCA 35 SE K20U 40 ENE CYEN 30 ENE CWEI.



...SOUTHERN PLAINS...

WITHIN A BROAD DEVELOPING REGION OF FAVORABLE GULF INFLOW...A
CONCENTRATED FLASH FLOOD THREAT HAD MATERIALIZED IN THE TEXAS HILL
COUNTRY. THE EVENT...ALTHOUGH SMALL SCALE...MAY PERSIST OWING TO
STRONG INFLOW OF A VERY MOIST AND SUFFICIENTLY UNSTABLE AIRMASS.
MID/UPPER LEVEL FORCING WILL VERY GRADUALLY SLIDE EASTWARD...BUT
WILL NOT ENTIRELY DISSIPATE...AND THERE ARE SOME MODEL SIGNALS FOR
HEAVY RAIN TO EITHER CONTINUE OR REDEVELOP FARTHER INTO EAST /
SOUTHEAST TEXAS DURING THE DAY.

MEANWHILE...A LARGER AREA OF MODERATE TO HEAVY RAINS WILL
ACCOMPANY SOMEWHAT STRONGER HEIGHT FALLS OVERSPREADING CENTRAL AND
EASTERN OK AND NORTH TX THIS MORNING. THE FLASH FLOOD RISK IN
SOUTHWEST OKLAHOMA HAD BEEN ENABLED BY WETTING RAINS EARLIER IN
THE DAY. OTHERWISE...THIS EVENT WAS RELATIVELY PROGRESSIVE...WITH
BROAD SCALE LIFT SIMPLY RAINING OUT THE AVAILABLE WATER IN THE
COLUMN RATHER EFFICIENTLY. THERE IS SOME CHANCE...SEEN
PARTICULARLY IN THE HRRR...THAT TRAINING AND/OR MERGING OF
CONVECTIVE CLUSTERS COULD RESULT IN A HEIGHTENED RISK OF EXCESSIVE
RAINFALL IN SOUTHERN OK / NORTH TX DURING THE EARLY MORNING HOURS.

LATER TODAY THROUGH TONIGHT...EXPECT ALSO A DRYLINE CONVECTIVE
EVENT. THOUGH PLACEMENT OF THE DRYLINE EVENT VARIES IN THE
MODELS...WPC FAVORED A COMBINATION OF THE 00Z NSSL WRF AND GFS
WITH THE 12Z ECMWF...ALL OF WHICH POINT TO CONVECTION POSSIBLY
GROWING UPSCALE AFTER INITIATING IN FAR SOUTHWEST TEXAS UP TO NEAR
THE CAPROCK IN THE AFTERNOON. ANY SUCH CONVECTION COULD ROLL OVER
AREAS WHICH RECEIVED VERY HEAVY RAIN BOTH IN TX AND OK OVER THE
PAST TWO NIGHTS...THEREFORE WE STRETCHED A SLIGHT RISK OF
EXCESSIVE RAINFALL ACROSS SW TX TO THE RED RIVER VALLEY AND DOWN
INTO SE TX TO CAPTURE SOME OF THE MORE LIKELY SCENARIOS IN WHICH
EXCESSIVE RAIN WILL BE POSSIBLE.


...NORTHERN / CENTRAL PLAINS...

THERE IS A STRONG MODEL SIGNAL FOR ORGANIZED CONVECTION TO ROLL
THROUGH CENTRAL AND EASTERN NE AND PERHAPS NORTHERN KS THIS
AFTERNOON/EVENING. WITH THE LOW IN COLORADO OPENING AND
EJECTING...STRONG HEIGHT FALLS WILL PASS THROUGH NE COINCIDENT
WITH AN INCREASE OF SOUTHERLY INFLOW. THE HIGH RESOLUTION MODELS
AS WELL AS THE GFS 27 KM OUTPUT HAVE BEEN CONSISTENT FROM RUN TO
RUN IN INDICATING HEAVY RAIN. THERE IS ALSO A REASONABLY
STRONG...ALTHOUGH MORE NARROW...QPF SIGNAL IN THE WESTERN DAKOTAS
WHERE AN INVERTED LOW LEVEL TROUGH WILL SET UP AND INTERCEPT
INCREASINGLY MOIST SOUTHEASTLY INFLOW. THOUGH THERE MAY BE A BREAK
IN BETWEEN...WE STRETCHED A SLIGHT RISK AREA ACROSS FROM
CENTRAL/EASTERN NE UP THROUGH WRN SD/ND. PRECIPITABLE WATER VALUES
REACH 3 STANDARD DEVIATIONS FROM CLIMATOLOGY IN THE WESTERN
DAKOTAS TODAY. IN FACT...THE 1.0 TO 1.20 INCH VALUES PREDICTED
THERE WOULD BE RECORDS FOR THE DATE PER THE SPC SOUNDING
CLIMATOLOGY PAGE. FORECAST SOUNDINGS INDICATE GREATER INSTABILITY
TODAY COMPARED TO WHEN THIS ANOMALOUS MOISTURE PLUME PASSED
THROUGH THE CENTRAL ROCKIES ON TUESDAY.


...NEVADA / UTAH...

PERSISTENT UPPER LEVEL DIFLUENCE WILL SET UP OVER NORTHERN NV AND
WESTERN UT TODAY AS A STRONG CLOSED LOW DIGS TOWARD CALIFORNIA AND
AN ANTI-CYCLONICALLY CURVED JET STRENGTHENS OVER THE NORTHERN
ROCKIES. DEEP LAYER ASCENT WILL COMBINE WITH STRONG HEATING AND
SUFFICIENT MOISTURE / CAPE VALUES OF A FEW HUNDRED J/KG PER THE
NAM/GFS AND SREF / TO PRODUCE WIDESPREAD CONVECTION. THE LIMITING
FACTOR WILL BE A RELATIVELY DRY SUB-CLOUD LAYER AND PRECIPITABLE
WATER VALUES ONLY 0.50 INCHES AT MOST. STILL...THE LARGE SCALE
ASCENT COULD PROMOTE SOME PERIODS OF TRAINING TO BOOST RAIN TOTALS
LOCALLY...WITH THE HIGH RESOLUTION MODELS INDICATING POTENTIAL FOR
0.75 INCH OR GREATER EVENT TOTALS.

BURKE
$$





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