Quantitative Precipitation Forecast
Issued by NWS

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000
FOUS30 KWBC 190746
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
246 AM EST THU JAN 19 2017

...VALID 12Z THU JAN 19 2017 - 12Z FRI JAN 20 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
50 SSE KXIH 25 S GLS LVJ 20 ESE CXO 45 NNE JAS BQP 30 NNE MKL
20 NNE BWG 20 W EKQ 35 WSW TYS 25 NNE 47A 10 SSE VPC 25 ESE ANB
MXF 35 N CEW 20 NNW ECP 35 WSW PAM 50 E KVOA.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
40 S SBA SBA 25 NNW OXR 10 NW 3A6 15 NNE POC 15 NNE ONT
25 NNE RIV 20 WNW PSP 15 W PSP 30 NNE RNM 20 N CZZ 20 SSW CZZ
40 S MMTJ 50 SW NRS.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
60 WNW CEC 25 NW CEC 30 NE ACV 25 SSW O54 30 NNE STS 10 WNW LVK
10 N WVI 20 NW MRY 85 SW SQL 85 SW SFO.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 SSE MEI 15 ESE BTR 25 SW HEZ 40 SSE OLV 40 NW MDQ 25 NW 4A9
15 WNW EET 15 SSE MEI.


...SOUTHEAST U.S...

A LARGE UPPER TROUGH WILL PIVOT OVER THE PLAINS...BRINGING A
NEGATIVELY TILTED SHORTWAVE UP THROUGH THE LOWER
MISSISSIPPI...TOWARD THE TENNESSEE VALLEY. WATER VAPOR LOOPS
REVEALED A WELL DEFINED SHORTWAVE TROUGH UPSTREAM OVER
MEXICO...WITHIN THE PLUME OF MID-UPPER LEVEL MOISTURE HAVING A
CONNECTION TO THE TROPICAL EASTERN PACIFIC. THIS CONNECTION
SUPPORTS MODEL PRECIPITABLE WATER VALUES THAT PLUME/POOL TO NEAR
1.75 INCHES. AS THE FORCING ARRIVES EARLY TODAY...EXPECT
RAIN/THUNDERSTORMS TO EXPAND IN COVERAGE AND BECOME BETTER
ORGANIZED FROM LOUISIANA TO SOUTHERN TENNESSEE. FOR A SEVERAL HOUR
PERIOD THE WINDS THROUGH A DEEP LAYER WILL BE FAIRLY
UNIDIRECTIONAL. MEAN 0-6 KM WINDS DO NOT CHANGE MUCH...COMING FROM
ABOUT 210 DEGREES...BETWEEN 12-21Z. THIS COULD LEAD TO
TRAINING...AND ALTHOUGH CAPE WILL BE WEAK...UPDRAFTS SHOULD BE
FAIRLY ROBUST GIVEN THE INCREASING DEEP LAYER ASCENT...AND WILL BE
VERY EFFICIENT GIVEN PW ANOMALIES 2.5 TO 3.0 STANDARD DEVIATIONS
AND MODERATELY STRONG 850-700 MB MOISTURE TRANSPORT. CONCERN IS
GREATEST ALONG AN AXIS FROM SOUTHWEST THROUGH CENTRAL MS TO
NORTHERN AL AND SOUTHERN TN. WPC QPF SIDED A LITTLE MORE TOWARD
THE GLOBAL MODEL CONSENSUS GIVEN THE TIME OF YEAR AND LIKELIHOOD
OF WEAK COLD POOLS...BUT THE NSSL WRF...NCEP WRF NMM...AND NAM
CONUS NEST AT 00Z ALSO SUPPORTED THIS APPROACH TO SOME
DEGREE...AND ALL SUGGEST THAT THE FLASH FLOOD GUIDANCE VALUES OF
ABOUT 1.5 INCHES IN 1 HOUR OR 2.0 TO 2.5 INCHES IN THREE HOURS MAY
BE ACHIEVED TODAY. HENCE AN UPGRADE TO SLIGHT RISK IN COORDINATION
WITH SOME OF THE LOCAL OFFICES.


...CALIFORNIA...

A PROGRESSIVE...FULL LATITUDE TROUGH WAS MOVING INLAND OVER THE
WEST. EARLY TODAY MODERATE RAINFALL WILL OCCUR OVER COASTAL
SOUTHERN CALIFORNIA BEFORE THE CONNECTION TO SUB-TROPICAL MOISTURE
PINCHES OFF. OBSERVED RAINFALL EXCEEDING A QUARTER INCH PER HOUR
COULD LEAD TO RAPID RUNOFF OR FLASH FLOODING IN SOME SENSITIVE
LOCATIONS...INCLUDING BURN SCARS.

BY FRIDAY MORNING THE NEXT FRONTAL SYSTEM WILL BEGIN TO IMPACT
NORTHERN CALIFORNIA FROM MENDOCINO DOWN TO AROUND MONTEREY. VERY
STRONG 12-HOUR HEIGHT FALLS IN THE LEFT EXIT REGION OF A 170 KNOT
JET STREAK WILL LIKELY MEAN SOME
CONVECTIVE ENHANCEMENT TO THE RAINFALL COMING INTO NORTHERN
CALIFORNIA AT THE TIME...WITH POTENTIAL FOR RAPID RUNOFF OR SOME
FLOODING CONCERNS ALONG THE COAST. ENHANCED MOISTURE CONTENT /
FLUX LOOKS TO BE RELATIVELY SHORT-LIVED...SO WE WILL INTRODUCE
ONLY A MARGINAL RISK AT THIS TIME...BUT WILL NEED TO WATCH TO SEE
IF THE VERY STRONG FORCING PRODUCES GREATER INSTABILITY THAN
CURRENTLY SEEN IN THE MUCAPE FIELDS FROM THE HI-RES MODELS.

BURKE
$$




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