Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 220101
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
800 PM EST SAT JAN 21 2017

...VALID 01Z SUN JAN 22 2017 - 12Z SUN JAN 22 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
180 W ACV 130 W CEC 65 WNW CEC 10 WNW CEC 40 SE CEC 30 W O54
30 WSW O54 45 N UKI 25 ENE STS 10 ESE LVK 45 NNW PRB 20 SE PRB
40 SW BFL 10 WSW SDB NTD 40 NNW NSI 70 SSW LPC 110 SW VBG.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 WNW KIKT 20 NE BVE 15 ESE HEZ 20 S MLU 15 E BAD TXK
25 NE MWT 20 SSW JBR 30 SE OLV 25 NW 1M4 15 NE 8A0 30 WSW CAE
50 S MYR 50 E NRB 10 S 40J 50 SSW AAF.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
90 SW O87 60 SW O87 30 S O87 25 NNW UKI 10 ESE UKI APC
10 ENE PAO 15 N WVI 20 SE SNS 25 NNE 87Q SBP 15 ESE SMX
10 SSE LPC 30 SW LPC 50 SW XVW 85 WSW VBG.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 ENE ATL HQU 15 ESE AGS 10 ENE JYL 15 SSE TBR 20 SSW VDI
15 NW DQH 20 E ABY 25 WSW OZR 30 NNE MOB 15 SSE HBG 20 NNE PIB
20 ENE NMM 25 SE TCL 10 ENE ATL.


LOWER MS VALLEY/SE U.S..

CONVECTIVE COVERAGE IS EXPECTED TO CONTINUE TO EXPAND ACROSS THE
SOUTHEAST INTO THE OVERNIGHT. SYNOPTIC FORCING WILL INCREASE AHEAD
OF A STRONG SHORTWAVE CURRENTLY LOCATED OVER AR/LA AND MOVING
NORTHEASTWARD. UPPER LEVEL DIVERGENCE IS ALSO EXPECTED TO INCREASE
IN THE LEFT EXIT REGION OF THE SUBTROPICAL JET. SOUTHERLY FLOW
WILL CONTINUE TO INCREASE AS WELL...ADVECTING MOISTURE AND
INSTABILITY BACK NORTHEAST INTO PORTIONS OF SOUTHERN/CENTRAL
MS/AL/GA. PRECIPITABLE WATER VALUES WILL GENERALLY BE RUNNING 1-2
STANDARD DEVIATIONS ABOVE NORMAL...PLENTY FOR HEAVY RAINFALL
RATES. OVERALL EXPECT CONVECTION TO BECOME PRETTY PROGRESSIVE AS
WE HEAD THROUGH THE NIGHT WHICH SHOULD LIMIT THE OVERALL FLASH
FLOOD THREAT. ALTHOUGH SOME CELL MERGERS THIS EVENING ACROSS
LA/AR/MS MAY LEAD TO AN ISOLATED FLASH FLOOD THREAT. CONVECTION
SHOULD INCREASE OVERNIGHT WHERE BOTH SYNOPTIC ASCENT AND THE LOW
LEVEL MOISTURE CONVERGENCE OVERLAP ACROSS AL/GA....EVENTUALLY INTO
SC. HEAVY RAINFALL TODAY ACROSS A PORTION OF THIS REGION HAS
RESULTED IN SATURATING SOILS AND LOWERED FLASH FLOOD GUIDANCE.
THUS THIS ADDITIONAL CONVECTION...AND POSSIBILITY OF 1-3 INCHES OF
ADDITIONAL RAINFALL...MOVING OVER THESE SAME AREAS MAY RESULT IN
AN INCREASED FLASH FLOOD THREAT OVERNIGHT. ALTHOUGH AS OF NOW
WOULD EXPECT MAINLY JUST MINOR FLOODING ISSUES TO POTENTIALLY
ARISE...WITH THE PROGRESSIVE NATURE OF CONVECTION PREVENTING MORE
WIDESPREAD SIGNIFICANT ISSUES. NONETHELESS...FEEL THE INCREASING
CONVECTIVE COVERAGE COMBINED WITH HEAVY ANTECEDENT RAINFALL
JUSTIFIES THE UPGRADE TO A SLIGHT RISK FOR PORTIONS OF
SOUTHERN/CENTRAL MS/AL/GA FOR THE POTENTIAL OF MAINLY MINOR FLASH
FLOOD ISSUES OVERNIGHT.

CHENARD

...PREVIOUS DISCUSSION...

...CALIFORNIA...

THE NEXT ATMOSPHERIC RIVER QUICKLY ORGANIZES BACK OFFSHORE AND
APPROACHES SATURDAY NIGHT...WITH THE INITIAL ONSLAUGHT OF HEAVIER
RAINFALL AIMED AGAIN AT NORTHERN CALIFORNIA. ONCE AGAIN A DEEP AND
AMPLIFYING TROUGH WILL BRING THE RIVER ONSHORE...ALTHOUGH WITH
STEADY PROGRESSION THERE WILL NOT BE TERRIBLY LONG RESIDENCE TIME
OF THE ENHANCED MOISTURE FLUX AT ANY ONE LOCATION. CERTAINLY THERE
WILL BE CAUSE FOR CONCERN IN FLOOD-PRONE
AREAS...HOWEVER...ESPECIALLY GIVEN THE RECENT EXTENDED STRETCH OF
WET WEATHER...AS ONCE AGAIN MODERATE PW AND MOISTURE FLUX
ANOMALIES WILL DEVELOP...SUPPORTING HEAVY 1-HOUR AND 3-HOUR RAIN
RATES. A CONSENSUS QPF APPROACH MATCHES REMARKABLY WELL TO THE
GEFS REFORECAST DATA BASED ON ANALOG CASES...INDICATING AREAL
AVERAGE AMOUNTS 1.5 TO 2.5 INCHES THROUGH SUNDAY MORNING IN THE
FAVORED COASTAL TERRAIN AND NORTHERN SIERRAS / SHASTA`S. THE EVENT
WILL WORK DOWN INTO SOUTHERN CALIFORNIA TOWARD DAY 2.

BURKE
$$





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