Quantitative Precipitation Forecast
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000
FOUS30 KWBC 201411
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
911 AM EST FRI JAN 20 2017

...VALID 15Z FRI JAN 20 2017 - 12Z SAT JAN 21 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
100 WSW STS 70 W STS 25 SSW UKI 10 NNE APC 35 ENE SNS 45 W BFL
15 ESE SDB 35 NW PSP 30 NE CZZ 60 SSE CZZ 85 S MMTJ 105 SSW NRS
90 SSW NUC.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 NE KVAF 10 WNW KGVX 25 SE LFK 40 E BAD 10 SE GWO 25 WSW EET
20 WNW TOI NPA 10 N KMDJ 15 NNE XCN 15 WSW QT8.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
45 W MRY 20 SSW SQL RHV 25 NNW PRB 40 NNE SBA 10 NNE 3A6
15 NNE EMT 10 N ONT 15 NE RIV 20 SSW PSP 15 N CZZ 25 SSW CZZ
35 SSW NRS 60 WSW NZY.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 SW KVBS ACP 40 SSW HKS 50 SE MEI 35 NNE BFM GAO 35 N KVQT.


1500 UTC UPDATE

NO CHANGES MADE TO THE PREVIOUS EXCESSIVE RAINFALL POTENTIAL
OUTLOOK.

ORAVEC

...CALIFORNIA...

BROAD SCALE CYCLONIC FLOW EXISTS OVER THE WESTERN U.S...ANCHORED
UPSTREAM BY A POWERFUL 160-170 KNOT JET STREAK. A BETTER DEFINED /
DEEPER TROUGH WILL DEVELOP AND MIGRATE INTO CALIFORNIA EARLY TODAY
ALONG THE CYCLONIC SHEAR SIDE OF THIS RATHER STRAIGHT AND RATHER
STRONG JET STREAK. THIS WAVE WILL TAP INTO SUB-TROPICAL MOISTURE
AND PRODUCE DEEP ONSHORE FLOW THROUGH THE COLUMN...WITH 700 MB
U-WIND COMPONENT ANOMALIES OF 3 TO 5 STANDARD DEVIATIONS FROM
CLIMATOLOGY ALONG THE COAST. THIS ALONG WITH STRONG HEIGHT FALLS
AS THE FLOW AMPLIFIES A BIT...WILL PROMOTE SOME HEAVY RAINFALL FOR
COASTAL CALIFORNIA...PROGRESSING NORTH TO SOUTH DURING THE DAY.
RAINFALL RATES WILL LIKELY EXCEED A HALF INCH PER HOUR AT
TIMES...LEADING TO EVENT TOTALS OF 2.0 TO 3.5 INCHES IN THE
FAVORED TERRAIN ALONG THE COAST...AS WELL AS SIMILAR LIQUID
EQUIVALENTS OVER THE SOUTHERN END OF THE SIERRAS. ALONG THE COAST
THE RAINFALL WILL BE FAIRLY EVENLY DISTRIBUTED FROM MONTEREY TO
SAN DIEGO...AS THE SYSTEM WILL REMAIN POTENT BUT PROGRESSIVE.
FLOODING / FLASH FLOODING WILL BE POSSIBLE.


...CENTRAL GULF COAST STATES...

THE NEXT IN A SERIES OF ENERGETIC AND PROGRESSIVE SHORTWAVE
TROUGHS WILL PULL OUT IN THE PLAINS TODAY...ACTING TO TIGHTEN
GRADIENTS AND STRENGTHEN A JET STREAK WITHIN SSW - NNE FLOW OVER
THE WESTERN GULF STATES. THE LOW LEVEL
RESPONSE WILL DRAW MOISTURE AND INSTABILITY RAPIDLY BACK NORTHWARD
OUT OF THE GULF INTO LOUISIANA AND ADJACENT PARTS OF TX / MS. THE
GREATEST MOISTURE FLUX SHOULD BE ORIENTED INTO SOUTHERN LOUISIANA
BY 00-06Z
THE 21ST...WITH WINDS THEN BEGINNING TO VEER AS THE SYNOPTIC FLOW
REGIME REMAINS PROGRESSIVE. THEREFORE...WE FAVORED SOLUTIONS SUCH
AS THE NSSL WRF AND GEM REGIONAL WHICH DEPICT HEAVIER SWATHS OF
RAIN ORIGINATING IN SOUTHERN LOUISIANA AND EXPANDING EASTWARD.
THIS ORIENTATION...AS DEPICTED IN THE DETERMINISTIC WPC
FORECAST...WOULD OVERLAP WITH AREAS THAT SAW HEAVY RAIN ON
THURSDAY...AND WHERE FLASH FLOOD GUIDANCE VALUES HAVE DECREASED.
WE ENCOMPASSED MUCH OF SOUTHERN LOUISIANA AND SOUTHERN MISSISSIPPI
IN A SLIGHT RISK OF EXCESSIVE RAINFALL...BUT WERE ALSO GENEROUS
WITH THE NORTHERN EXPANSE OF THE SLIGHT AND MARGINAL RISK
AREAS...ACCOUNTING FOR UNCERTAINTY AND ACCOUNTING FOR A SECONDARY
SWATH OF HEAVIER RAIN RATES SEEN IN MUCH OF THE HI-RES GUIDANCE
OVER NORTHERN LA / CENTRAL MS. THIS SEEMS TO CORRESPOND TO MID
LEVEL FRONTOGENESIS AND DEEP LAYER Q-VECTOR CONVERGENCE PER THE
GFS AND ECMWF.

BURKE
$$




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