Quantitative Precipitation Forecast
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FOUS30 KWBC 230019
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
718 PM EST SUN JAN 22 2017

...VALID 01Z MON JAN 23 2017 - 12Z MON JAN 23 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 NNW CHA OQT 40 WSW TRI 10 NNE VJI 10 WNW HLX 10 SE PSK
10 SSW HSP 20 NNW SHD 15 SSW SHD 15 NE MTV 10 NNE INT 15 ESE JQF
15 ESE UZA 15 SSE GRD WDR RYY 30 SW VPC 20 N ALX 15 SSE EET
10 W TCL 35 E CBM 15 NE 1M4 15 E MDQ 25 NNW CHA.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
65 SW MRY 15 SSE MRY 30 SE SNS 25 ENE PRB 40 E PRB 20 SW BFL
20 SSE BFL 20 S PTV 20 NNW VIS 10 ENE MAE 20 ENE MOD BAB
25 NNE CIC 30 ENE OVE 50 SSW TVL 35 NNE VIS 30 W IYK EDW
30 SW DAG 20 WNW NXP 15 E TRM 20 SSW NJK 90 SSE MMTJ 130 S MMTJ
180 SSW NRS 205 SSW NRS.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 SW NTD 15 SE NTD 10 SW SMO 15 SSE PMD 25 NNE RIV 15 NW PSP
20 SW PSP CZZ 60 S MMTJ 95 SSW NRS 115 S NUC.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 WSW BHM 25 WSW 3A1 30 W CHA 30 NE CHA 25 SW TYS 35 NW AVL
20 W TNB 10 WNW UKF 10 NE IPJ 30 WSW UZA 15 WNW GRD 20 E GVL 47A
20 NE ANB 20 WSW BHM.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 NNE RNM 10 NW CZZ SEE NFG 10 E SNA POC 15 NE ONT 20 NE RIV
20 NNE RNM.


0100 UTC UPDATE...

ACRS THE SOUTHEAST U.S...
STG N/S CONVECTIVE LINE AHEAD OF DEEPENING SFC LOW OVER NRN GA
SHOULD CONTINUE TO MORE RAPIDLY TOWARD AND OFF THE SE COAST OVER
THE NEXT FEW HOURS WHILE MOVING QUICK ENOUGH ACRS THE FL PENINSULA
TO PRECLUDE ANY ORGANIZED EXCESSIVE RAIN THREAT THERE.  MAIN HEAVY
TO PSBL EXCESSIVE RAIN THREAT WILL FOCUS WITHIN EVOLVING COMMA
HEAD BAND TO THE NORTH OF THE SFC LOW WHERE SLOW PIVOTING BAND OF
MDT TO LOCALLY HEAVY RAIN COULD LEAD TO LOCAL 1 TO 2 INCH RAINS IN
SEVERAL HOURS.  THESE AMOUNTS ON TOP OF LOWERING FF GUIDANCE
VALUES..GIVEN LOCALLY HEAVY RAINS SUN AFTN/EVENING COULD LEAD TO
SOME RUNOFF ISSUES...ESPECIALLY NEAR STEEPER TERRAIN INFLUENCES.

ACRS CA...
WHILE BROAD ONSHORE FLOW PATRN WILL MAINTAIN RAIN THREAT THROUGH
MUCH OF THE CA COAST ALONG WITH SNOW THREAT IN THE HIER
TERRAIN...MAIN PW PLUME ALONG ADVANCING COLD FRONT CONTINUES TO
PUSH SEWD INTO SRN CA WHERE THE MORE SIGNIFICANT HEAVY RAIN THREAT
WILL FOCUS FOR THE REMAINDER OF THE OVERNIGHT PD.  PREFRONTAL
RAINFALL AMOUNTS OF BETWEEN 1 TO 2 INCHES WITH LOCALLY HEAVIER
AMOUNTS IN FAVORED UPSLOPE AREAS WILL OCCUR MAINLY BEFORE 06Z.
MODERATELY STG POST FRONTAL WLY FLOW OF 30KTS OR SO SHOULD LEAD TO
ADDITIONAL RAINS OF 1+" MAINLY OVER THE MORE FAVORED WRN FACING
UPSLOPE AREAS..BELOW LOWERING SNOW LEVELS.  SLIGHT AN MDT
EXCESSIVE RAINFALL THREATS WERE ADJUSTED SWD BASED ON THE SWD
PROGRESSION OF EXPECTED HEAVIER RAINS TONIGHT.

SULLIVAN

PREVIOUS DISCUSSION FOLLOWS...



...CALIFORNIA...
...MODERATE RISK OF EXCESSIVE RAINFALL SANTA BARBARA TO LOS
ANGELES...

THE FLASH FLOOD THREAT APPEARS PARTICULARLY PRONOUNCED TODAY ALONG
THE CALIFORNIA COAST FROM MONTEREY TO SAN DIEGO...BUT ESPECIALLY
IN SOUTHERN CALIFORNIA. MULTIPLE HI-RES MODELS PRODUCE HOURLY RAIN
RATES GREATER THAN 0.75 INCHES NEAR AND SOUTH OF SANTA
BARBARA...AND IT IS LIKELY THAT INTENSE SOUTHERLY FLOW IN THE
850-700 MB LAYER WILL COMBINE WITH THE TERRAIN TO BOOST THOSE
HOURLY RATES ABOVE 1.00 INCH FROM MIDDAY INTO THE LATE AFTERNOON
HOURS.
GEFS 850-700 MB ONSHORE FLOW WIND SPEED ANOMALIES ARE MORE GREATLY
FOCUSED ALONG THE SOUTHERN CALIFORNIA COAST AND THE SOUTHERN
SIERRAS TODAY. TOTAL PRECIPITABLE WATER VALUES OF 1.00 INCH AGAIN
PUSH INTO SOUTHERN CALIFORNIA. AREAL AVERAGE PRECIPITATION OF 2 TO
4 INCHES IS A STRONG BET ALONG THE COAST OF CENTRAL/SOUTHERN
CALIFORNIA AND THE SLOPES OF THE SOUTHERN SIERRAS THROUGH MONDAY
MORNING. THIS WILL FALL MORE HEAVILY AND MORE RAPIDLY IN SOUTHERN
CALIFORNIA...WHERE DOWNSCALING OF THE QPF TAKES THE PREDICTED
AMOUNTS UP TO 5 OR EVEN 6 INCHES IN SPOTS.

GIVEN RECENT STORM SYSTEMS IN RAPID SUCCESSION...THE AREA MAY BE
MORE PRONE TO RAPID RUNOFF. IN SANTA BARBARA AND
VENTURA COUNTIES THE NATIONAL WATER MODEL...FORCED BY GFS
QPF...PRODUCES A TRANSITION FROM MUCH BELOW NORMAL STREAM FLOW TO
HIGH FLOW IN ONLY A 3 HOUR WINDOW.


...SOUTHEAST STATES...

A BROAD MARGINAL RISK OF EXCESSIVE RAINFALL IS INDICATED HERE...AS
A DEEP AND GRADUALLY PROGRESSIVE STORM SYSTEM DRIVES LARGE AREAS
OF CONVECTIVELY ENHANCED RAINFALL. IT WAS NOT OBVIOUS WHERE TO
EMBED A HIGHER PROBABILITIES AND A SLIGHT RISK AREA. BY MID
MORNING THE EXTENSIVE CONVECTION NEAR THE GULF COAST MAY HAVE
PLAYED OUT...AND WE WILL SEE A TRANSITION TOWARD MORE PROGRESSIVE
AND FRACTURED MODES OF CONVECTION THIS AFTERNOON AT LOWER
LATITUDES...AND STEADY RAIN WITHIN AN ENVIRONMENT OF LESSER
INSTABILITY FARTHER NORTH. THE LOWER FLASH FLOOD GUIDANCE VALUES
EXIST TO THE NORTH...ESPECIALLY UP INTO THE APPALACHIANS...WHILE
FFG REMAINS ON THE HIGHER SIDE TO THE SOUTH DESPITE RECENT
RAINFALL. ULTIMATELY...THE BALANCE OF THESE FACTORS LED TO
ISSUANCE OF A BROAD SLIGHT RISK...AND ONE THAT WILL LIKELY NEED TO
BE TRIMMED THROUGHOUT THE DAY AS THE SYSTEM EVOLVES. THE AREA OF
PERHAPS GREATEST CONCERN WILL BE SOUTHERN ALABAMA / GEORGIA...AND
FAR NORTHERN FLORIDA...WHERE HEAVY RAIN FELL SATURDAY...AND WHERE
A SECOND ROUND WAS OCCURRING THIS MORNING. ADDITIONAL SCATTERED
THUNDERSTORMS PRODUCING BRIEF BOUTS OF HEAVY RAIN ARE EXPECTED IN
THIS AREA THIS AFTERNOON. FARTHER NORTH...THE 00Z GUIDANCE TRENDED
DEEPER AND STRONGER WITH THE SYNOPTIC LOW AS IT TRACKS TOWARD
NORTHEAST ALABAMA...SETTING UP A STRONG DEFORMATION AREA WHERE
MODERATE RAINFALL AND PERHAPS EMBEDDED CONVECTIVE ELEMENTS MAY
LEAD TO HEAVY AMOUNTS OVER A BIT LONGER DURATION. OBSERVATIONS OF
INCREASED SOIL MOISTURE AND IN-BANK RISES ON STREAMS WERE REPORTED
BY THE LOCAL OFFICE IN HUNTSVILLE.

BURKE
$$




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