Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 300056
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
856 PM EDT WED MAR 29 2017

...VALID 01Z THU MAR 30 2017 - 12Z THU MAR 30 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
40 WSW MSO 40 SSE P69 35 NNW SNT 30 NW SUN 30 NNE MUO 25 NE EUL
25 E BKE 30 W BKE 25 SSW PDT ALW 10 NNE LWS 25 W MLP 20 ESE MLP
40 WSW MSO.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 NNE KGVX 40 N JAS 25 SSW MWT 35 SSW SGF 45 NNE JLN TOP
15 WNW AFK 20 W FOD 15 E MCW 25 ENE DEH DLL 15 SW MKE 20 SE UGN
10 E MDW 15 NW IKK 10 WSW BMI 15 NNE SPI 15 SW SPI 20 NNW ALN
25 WNW CGI 15 NE NQA 40 ENE GWO 35 E JAN 35 WSW HBG 10 NNW MSY
25 WNW KEIR.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 SE KXIH 30 NW LCH 30 NNE IER BQP TVR 30 N MCB 20 NW HDC
10 W P92 30 WSW SRN.


...WESTERN-CENTRAL GULF COAST...LOWER-MID MISSISSIPPI VALLEY...

2245 UTC UPDATE...

HAVE MADE SIGNIFICANT CHANGES TO THE DAY 1 EXCESSIVE RAINFALL
OUTLOOK...BASED ON THE COMPOSITE OF RADAR/SATELLITE/OBSERVATIONAL
DATA AND TRENDS...ALONG WITH THE TRENDS IN THE GUIDANCE PER THE
18Z RUNS AND THE LAST SEVERAL RUNS OF THE HRRR. ROBUST UPPER-LEVEL
DYNAMICAL SUPPORT WITHIN A DIFFLUENT PATTERN ALOFT AHEAD OF THE
TROUGH...BOOSTED BY THE JET STREAK ROUNDING THE TROUGH BASE...IS
FIRING AN EXPANDING AREA OF CONVECTION ACROSS EAST TX AND WESTERN
LA ON THE SOUTHERN PERIPHERY OF THE WARM CONVEYOR BELT EAST OF THE
DRY LINE (ALONG AND EAST OF THE LIMITING STREAMLINE).
MEANWHILE...THE THERMODYNAMIC PROFILE IS RESPONDING QUITE NICELY
TO THE INCREASING EXIT REGION FORCING...AS THE LATEST SPC
MESOANALYSIS DEPICTS AVAILABLE MIXED LAYER CAPES OF 1000-2000 J/KG
IN THIS ENVIRONMENT WITH SSW 850 MB INFLOW OF 40-50 KTS FROM THE
GOMEX...WHICH IS NEARLY PERPENDICULAR AND OF THE SAME IF NOT
GREATER IN MAGNITUDE AS THE MEAN 850-300 MB FLOW (SUPPORTIVE OF
CELL TRAINING). PW VALUES ARE EXPECTED TO RISE QUICKLY TO 1.5+
INCHES THIS EVENING OVER THE UPPER TX COAST AND ACROSS
WESTERN-CENTRAL LA IN RESPONSE TO THE INCREASINGLY-FAVORABLE
DYNAMICAL/THERMODYNAMICAL PROFILE AS WELL AS THE UPSCALE GROWTH OF
THE CONVECTION. FOR THESE REASONS...HAVE SCALED BACK ON THE
PREVIOUS SLIGHT RISK AREA...FOCUSING ON THE EXPANDING MCS OVER
EASTERN TX...MUCH OF LA...AND FAR SOUTHWEST MS...WHERE ISOLATED
HOURLY RAINFALL RATES OF 2-2.5" HAVE OCCURRED UNDERNEATH THE MORE
INTENSE CELLS.

FARTHER NORTH...HAVE LEFT THE MARGINAL RISK IN PLACE...AS DESPITE
THE FAVORABLE (POSITIVE) MOISTURE ANOMALIES...CONVECTION CURRENTLY
REMAINS UNORGANIZED/SCATTERED AT BEST GIVEN (AT LEAST TO SOME
DEGREE) THE OBSTRUCTION (DISRUPTION) FROM THE AFOREMENTIONED MCS
TO THE SOUTH. STILL...EXPECT THE CONVECTION TO BECOME BETTER
ORGANIZED LATER THIS EVENING TOWARD THE MID MS VALLEY AS THE
DYNAMICAL SUPPORT INCREASES (AS THE THE NORTHERN AND SOUTHERN
UPPER JET STREAKS BECOME BETTER PHASED). NEVERTHELESS...GIVEN THE
MORE LIMITED DEGREE OF DEEP-LAYER INSTABILITY TO WORK
WITH...ANTICIPATE THAT ANY EXCESSIVE SHORT-TERM RAINFALL RATES AND
RUNOFF ISSUES NORTH OF LA TO BE ISOLATED.


...NWRN US...

GUIDANCE HAS REMAINED REASONABLY CONSISTENT OVERALL WITH MASS
FIELDS AND INDICATIONS THAT LEAD IMPULSES RIDING ALOFT OVER AN
ENHANCED PLUME OF ERN PACIFIC MOISTURE WILL SUPPORT A PERIOD OF
MODERATE TO HEAVIER PCPN SPREAD INLAND FROM THE PAC NW TO THE NRN
INTERMOUNTAIN WEST/ROCKIES TODAY. AN 50+ KT WSWRLY LLJ WILL FEED A
PLUME UPWARDS OF 1.25" PWS INTO THE WA/OR/NWRN CA COASTLINE AND
LATEST STLT PASSES SHOW SOME EMBEDDED .25"/HOUR RAINFALL RATES
WITH WAVE DEVELOPMENT OFFSHORE IN THE MAIN MOISTURE PLUME WITH
LONG FETCH CONNECTION WELL BACK TO THE NORTH OF HAWAII. THIS MAY
TRANSLATE TO SOME LOCALLY TERRAIN ENHANCED LIQUID AMOUNTS WED OF
1-3+ OVER COASTAL RANGES INLAND TO THE CASCADES AND TO A LESSER
EXTENT THE BLUE...SAWTOOTH...AND BITTEROOT RANGES WHERE SOME
RUNOFF ISSUES ARE POSSIBLE. HEIGHT FALLS WITH STRONGER EPAC
SHORTWAVE TROUGH APPROACH ARE EXPECTED TO SWEEP INTO THE PAC NW
LATER WED INTO THU...PROVIDING STRONG DYNAMICS AND CONTINUED
UNSETTLED CONDITIONS AS THE DEEPER MOISTURE CUTS OFF/SHIFTS SEWD.

HURLEY/SCHICHTEL
$$





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