Quantitative Precipitation Forecast
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FOUS30 KWBC 201428
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1027 AM EDT MON MAR 20 2017

...VALID 15Z MON MAR 20 2017 - 12Z TUE MAR 21 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
85 SW OTH 30 SW OTH 30 WSW RBG 30 SSW SXT 40 SW SIY 10 NNW MHS
25 NE MHS 35 ESE MHS 50 E RDD 30 N BLU BLU 10 E BAB CIC RDD
30 WNW RBL 30 ENE UKI 15 ENE STS 15 SW STS 55 SW UKI.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 E ASW 20 ENE FDY 25 SSW BJJ VTA 20 SE SGH 25 WNW WMO
30 SSE LAF 30 NNW LAF 20 E ASW.


1500 UTC UPDATE

PORTIONS OF THE MID WEST INTO THE UPPER OH VALLEY AND CENTRAL
APPALACHIANS

PRIMARY CHANGE TO THE PREVIOUS EXCESSIVE RAINFALL POTENTIAL
OUTLOOK WAS OVER PORTIONS OF THE MID WEST---UPPER OH VALLEY INTO
THE CENTRAL APPALACHIANS.    THE CURRENT AREA OF ORGANIZED
CONVECTION THAT SUNK SOUTHEASTWARD OVERNIGHT INTO EARLY THIS
MORNING FROM NORTHERN TO EASTERN IL...INTO NORTHERN TO CENTRAL IN
AND INTO SOUTHWEST OH CONTINUES TO SHOW SIGNS OF WEAKENING WITH
WARMING CLOUD TOPS AND DECREASING RADAR RETURNS.  MODEL CONSENSUS
IS FOR ADDITIONAL ELEVATED CONVECTION TO RE-FIRE THIS AFTERNOON
SLIGHTLY TO THE EAST OF THE PREVIOUS COMPLEX AND THEN SINK
SOUTHEASTWARD.  THE PREVIOUS ACTIVITY WAS NOT MODELED VERY
WELL---WITH CONVECTION FARTHER TO THE SOUTH THAN FORECAST.  THIS
SAME BIAS COULD REAPPEAR THIS AFTERNOON INTO THIS EVENING WITH THE
NEXT ROUND AS IT PRESSES SOUTHEASTWARD.  THE PREVIOUS MARGINAL
OUTLOOK WAS EXPANDED TO THE SOUTHEAST TO COVER THE POSSIBLE TRACK
OF THE ADDITIONAL ORGANIZED CONVECTION.  SEVERAL OF THE HI RES
RUNS SUGGEST THE NEW ACTIVITY MAY FIRE OVER NORTHERN INDIANA THAT
RECEIVED SOME HEAVY RAINS FROM THE INITIAL LINE---AND THEN TRACK
SOUTHEASTWARD INTO SOUTHERN OH---FAR NORTHEAST KY AND LARGE
PORTIONS OF WV.  WHILE IT APPEARS THIS CONVECTION SHOULD BE FAIRLY
PROGRESSIVE---THERE COULD STILL BE A PERIOD OF TRAINING OF
CELLS---ESPECIALLY ON THE SOUTHWEST SIDE OF ANY CONVECTION WHERE
THE LOW LEVEL FLOW MAY BE PARALLEL TO LINE OF CONVECTION.  STILL A
LOT OF UNCERTAINTIES WITH THIS NEXT AREA GIVEN THE CURRENT
WEAKENING AREA AND INHERENT MODEL DIFFICULTIES IN MODELING
ORGANIZED ELEVATED CONVECTION.  ISOLATED SHORT TERM PRECIP TOTALS
OF 1"+ POSSIBLE.

NO CHANGES MADE TO THE MARGINAL RISK OVER FAR SW OREGON INTO
NORTHERN CALIFORNIA/

ORAVEC

PREVIOUS DISCUSSION


...NORTHERN CALIFORNIA INTO SOUTHWEST OREGON...

DEEP-LAYER WAA/MOISTURE WITHIN THE INITIAL WARM CONVEYOR BELT
(WCB) EARLY IN THE PERIOD WILL SEGUE TO ANOTHER (MORE MERIDIONAL)
WCB ACROSS THE WESTERN CONUS DURING DAY 1. THIS AS THE UPPER FLOW
BECOMES INCREASINGLY DIFFLUENT AHEAD OF AN AMPLIFYING (REINFORCED)
UPPER TROUGH OFF THE COAST...AS THE UPPER LEVEL JET STREAK ROUNDS
THE TROUGH BASE AND APPROACHES SOUTHERN CA BY THE END OF THE
PERIOD (12Z TUE). THE PERSISTENT BROAD-SCALE QS VECTOR CONVERGENCE
AND ATTENDANT DEEP-LAYER WWA FORCING/MOIST ISENTROPIC ASCENT WILL
GENERATE ADDITIONAL MODERATE-HEAVY PCPN ACROSS NORTHERN CA AND FAR
SOUTHWEST OR...WITH THE HEAVIEST AMOUNTS ONCE AGAIN TIED TO THE
TERRAIN. THIS INCLUDES THE COASTAL RANGES...SHASTA/SISKIYOUS...AND
NORTHERN SIERRA...AREAS THAT WILL BENEFIT THE MOST AT THE LEADING
EDGE OF THE SUBTROPICAL MOISTURE PLUME (PWS AOA 1.0").
AREAL-AVERAGE QPF TOTALS ARE EXPECTED TO RANGE BETWEEN 1-2+" OVER
THE OROGRAPHICALLY-FAVORED RANGES...WITH THE ASSORTMENT OF
HIGH-RES GUIDANCE SUPPORTIVE OF LOCALLY HIGHER AMOUNTS (3-4
INCHES) ACROSS THE AFOREMENTIONED NORTHERN CA-SOUTHWEST OR RANGES.

AS FAR AS THE 00Z GUIDANCE GOES...THERE IS HIGH FORECAST
CONFIDENCE IN A NON-GFS GENERAL MODEL COMPROMISE...WITH EMPHASIS
ON THE HIGH-RES MEANS (INCLUDING THE HREF... IN-HOUSE BIAS
CORRECTED HIGH-RES ENSEMBLE...AND PARALLEL NBM) GIVEN THE BETTER
SENSITIVITY OVER THE HIGHER TERRAIN. THE GFS WAS A NOTICEABLY WET
OUTLIER OVER FAR NORTHWEST CA AND SOUTHWEST OR...DEPICTING A
POCKET OF AREAL-AVERAGE TOTALS OVER 2 INCHES.

A MARGINAL RISK FOR EXCESSIVE RAINFALL CONTINUES IN EFFECT FROM
12Z MON - 12Z TUE ACROSS NORTHERN CA AND FAR SOUTHWEST
OREGON...INCLUDING THE COASTAL...SHASTA/SISKIYOUS...AND NORTHERN
SIERRA RANGES THEREIN. LOCALIZED TOTALS OF 3-4"...THE BULK OF
WHICH EXPECTED TO FALL WITHIN 12-18 HOURS MON AFTERNOON AND
OVERNIGHT...WILL POTENTIALLY LEAD TO LOCALIZED SHORT-TERM RUNOFF
ISSUES...PARTICULARLY IN AREAS OF MORE RAPID SNOW MELT.


...NORTHERN OHIO VALLEY...

THE SHORTWAVE TROUGH OVER THE EASTERN CONUS EARLY IN THE PERIOD
WILL GIVE WAY TO SHEARED ENERGY/VORT LOBES WITH ENSUING FLATTENING
(ZONAL) FLOW ALOFT. THE DEGREE OF UPPER DIVERGENCE AND DEEP-LAYER
ASCENT BEHIND THE DEPARTING UPPER RIDGE WILL BE TEMPERED SOMEWHAT
BY THE BROAD RIGHT-EXIT REGION FORCING FROM THE STRAIGHT UPPER
LEVEL JET STREAK -- WHICH WOULD FAVOR INCREASED SUBSIDENCE.
BELIEVE THE COMPETING SYNOPTIC FORCINGS ARE RESPONSIBLE FOR THE
CONTINUED MODEL QPF DISCREPANCY...BOTH IN TERMS OF AMOUNTS AND
LATITUDINAL PLACEMENT. MOREOVER...THE MODELS ARE EXHIBITING
DIFFICULTY HANDLING THE CONVECTION BREAKING OUT EARLY THIS AM
ACROSS THE UPPER MIDWEST (FEEDING OFF ELEVATED MUCAPES NEAR 1000
J/KG). BELIEVE THE STEEP MID LEVEL LAPSE RATES (7-8C/ KM BETWEEN
700-500 MB) ARE CHIEFLY RESPONSIBLE...WHICH IS ANOTHER COMPONENT
IN THE EXIT REGION OF A BROAD...STRAIGHT UPPER JET STREAK.

DESPITE THE DIFFERENCES IN THE DETAILS...THE MODEL CONSENSUS IS
FOR MODEST QPF TOTALS FOR MOST AREAS ACROSS MUCH OF THE OH VALLEY
INTO THE WESTERN SLOPES OF THE APPALACHIANS (WITH THE UPSLOPE
WESTERLY LOW-LEVEL FLOW)...BUOYED AT LEAST TO SOME DEGREE BY THE
MODEST MOISTURE ANOMALIES ALONG WITH THE STEEPENING MID LEVEL
LAPSE RATES. PER THE SREF AND GEFS...BOTH PW AND 850-700 MB
MOISTURE FLUX ANOMALIES ARE EXPECTED TO AVERAGE AROUND 2 STANDARD
DEVIATIONS ABOVE NORMAL. HIGHEST TOTALS ARE EXPECTED IN A ROUGHLY
W-E CORRIDOR FROM CENTRAL IN INTO CENTRAL OH... WHERE
AREAL-AVERAGE AMOUNTS ARE EXPECTED TO RANGE BETWEEN 0.50-1.00 INCH
WITH LOCALLY HIGHER AMOUNTS UNDERNEATH THE STRONGEST ELEVATED
CONVECTION.

A MARGINAL RISK FOR EXCESSIVE RAINFALL HAS BEEN HOISTED FROM
NORTHERN AND CENTRAL PORTIONS OF IN EASTWARD INTO CENTRAL OH. AS
NOTED FROM MULTIPLE HIGH-RES CAMS...THE AFOREMENTIONED ELEVATED
CONVECTION DROPPING INTO IN-OH MAY BRING ISOLATED TOTALS AROUND
1.5+ INCHES WITHIN 3 HOURS OR LESS TODAY...CLOSE TO IF NOT
EXCEEDING THE FFG...ESPECIALLY DURING THE MORNING HOURS WHEN THE
WESTERLY LOW-LEVEL INFLOW IS NEARLY PARALLEL TO THE 850-300 MB
MEAN WIND (SUPPORTIVE OF CELL TRAINING).

HURLEY
$$





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