Quantitative Precipitation Forecast
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FOUS30 KWBC 050832
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
331 AM EST MON DEC 05 2016

...VALID 12Z MON DEC 05 2016 - 12Z TUE DEC 06 2016...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 SE KBQX 10 NW DWH GLH DCU 25 W CEU 25 W CAE 55 E HXD
10 NNE NRB 70 WNW PIE.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 S KGVX 25 ESE LBX 10 NE EFD 45 E CXO 40 NNE JAS 20 NE TVR
30 ENE JAN 20 NNW GPT 20 NW NSE 30 SW LSF 10 NNE MCN 15 NW JYL
SVN 35 ESE VAD 25 SW 40J 75 SSE AAF.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 SSE KXIH 25 NNE GLS 30 SE JAS 20 SE ACP 25 ENE LFT 25 N 7R3
25 E 7R3 30 NNE GSM 15 S KSPR.


...SOUTHERN U.S AND GULF COAST...

OVERALL EXPECT TO SEE A COMPLEX CONVECTIVE EVOLUTION TODAY...WITH
A FEW AREAS OF POSSIBLE EXCESSIVE RAINFALL DEVELOPING. AS OF EARLY
MONDAY MORNING CURRENTLY HAVE A BROAD SWATH OF STEADY RAINFALL
OVER PORTIONS OF CENTRAL TEXAS DEVELOPING IN THE STRONG WARM AIR
ADVECTION AHEAD OF THE UPPER LOW. THIS INLAND PRECIPITATION IS
DISPLACED WELL NORTH OF THE SURFACE FRONT AND BETTER
INSTABILITY...ALTHOUGH DO NOTE SOME WEAK ELEVATED INSTABILITY.
EXPECT THIS AXIS OF SHOWERS AND EMBEDDED CONVECTION TO GENERALLY
MOVE EASTWARD INTO CENTRAL LA THIS MORNING AND TOWARDS CENTRAL
MS/AL BY THIS AFTERNOON. WOULD NOT EXPECT THIS RAINFALL BE TO BE
ALL THAT INTENSE GIVEN THE LACK OF INSTABILITY AS MENTIONED ABOVE.
HOWEVER WILL CONTINUE A SLIGHT RISK ACROSS PORTIONS OF CENTRAL LA
AND SOUTHWEST MS TO ACCOUNT FOR THIS MORNING CONVECTION...AS
RECENT RAP RUNS CONTINUE TO SHOW SOME ELEVATED INSTABILITY WORKING
NORTH THROUGH THE MORNING HOURS AND RECENT RADAR DOES SEEM TO SHOW
AN UPTICK IN CONVECTIVE INTENSITY WITH THE ACTIVITY STREAMING FROM
EAST TEXAS TOWARDS CENTRAL LA. ALSO AT LEAST A PORTION OF THIS
SLIGHT RISK AREA HAS SEEN SEVERAL INCHES OF RAIN OVER THE PAST FEW
DAYS...WHICH MAY RESULT IN SOME RUNOFF ISSUES SHOULD RATES GET
HIGH ENOUGH. FURTHER EAST INTO AL WILL JUST CARRY A MARGINAL RISK
AS THIS MORNING/AFTERNOON ACTIVITY SHOULD WEAKEN AS IT HEADS INTO
THIS REGION GIVEN THE LACK OF INSTABILITY.

EXPECT MORE INTENSE CONVECTION TO FOCUS CLOSER TO THE GULF COAST
CLOSER TO THE WARM FRONT WHERE THE BETTER INSTABILITY IS
LOCATED...WHICH WILL SLOWLY LIFT NORTHWARD THROUGH THE DAY. CAN
ALREADY SEE THIS CONVECTION FORMING OFF AND NEAR THE TEXAS COAST
THIS MORNING. THE LATEST HRRR AND HIGH RES ARW APPEAR TO BE
HANDLING THIS ACTIVITY BEST AND SUGGEST HEAVY CONVECTION WILL
STREAM NORTHWARD TOWARDS THE FAR SOUTHEAST TX COAST AND INTO
SOUTHERN LA THROUGH THE MORNING HOURS. IMPRESSIVE PRECIPITABLE
WATER VALUES AND LOW LEVEL MOISTURE TRANSPORT SHOULD SUPPORT HEAVY
RAINFALL RATES WITH THIS CONVECTION. THINK THERE IS THE POTENTIAL
FOR LOCALIZED AMOUNTS OF 2-5" ACROSS THIS AREA THROUGH THE MORNING
HOURS. THE POTENTIAL FOR HIGH RATES AND REPEAT CONVECTION THROUGH
THE MORNING HOURS RESULTING IN SOME TRAINING WARRANTS A SLIGHT
RISK ACROSS THE AREA. HOWEVER GIVEN ANTECEDENT RAINFALL OPTED TO
CONTINUE WITH A MODERATE RISK FROM FAR SOUTHEAST TX INTO SOUTHERN
LA. THERE IS CHANCE THE HEAVIEST RAINFALL THIS MORNING WILL REMAIN
EAST OF THE AREAS THAT HAVE RECEIVED THE HEAVIEST ANTECEDENT
RAINFALL...WHICH WOULD LOWER THE FLASH FLOOD RISK. HOWEVER FEEL
THE RISK IS STILL HIGH ENOUGH TO WARRANT THE CONTINUATION OF THE
MODERATE RISK FOR NOW. WILL REASSESS BY MID MORNING.

AS WE HEAD THROUGH THE AFTERNOON HOURS WOULD ALSO EXPECT TO SEE
CONVECTIVE COVERAGE INCREASE FURTHER EAST ALONG THE GULF COAST
INTO THE FLORIDA PANHANDLE. RECENT MODEL GUIDANCE CONTINUES TO
SUGGEST THE PLUME OF MAX PRECIPITABLE WATER AND LOW LEVEL MOISTURE
TRANSPORT WILL FUNNEL INTO THE FL PANHANDLE AND SOUTHERN GA THIS
AFTERNOON. THIS MOISTURE PLUME IS THE RESULT OF ENHANCED LOW LEVEL
FLOW IN BETWEEN THE UPPER LOW TO THE WEST AND THE UPPER HIGH OVER
THE SOUTHERN ATLANTIC. IN FACT ANTICIPATE PWAT VALUES TO SURPASS
2" ACROSS THE FL PANHANDLE INTO SOUTHERN GA...WHICH WILL APPROACH
CLIMATOLOGICAL MAX VALUES. MEANWHILE...ALOFT THE FLOW WILL BECOME
INCREASINGLY DIVERGENT IN THE RIGHT ENTRANCE REGION OF THE UPPER
JET. THUS WOULD APPEAR TO BE A GOOD SETUP FOR WIDESPREAD
CONVECTION CAPABLE OF PRODUCING HEAVY RATES. WILL NOT NECESSARILY
SEE A LOT OF BACKBUILDING CONVECTION...BUT EXPECTED WIDESPREAD
COVERAGE SHOULD RESULT IN SOME TRAINING POTENTIAL. THUS WHILE
OVERALL WPC QPF WAS A MULTI MODEL GLOBAL AND HIGH RES
BLEND...PREFERENCE FOR QPF WAS GIVEN TO THE WETTER MODELS ACROSS
THIS REGION...GENERALLY THE HRRR AND OTHER AVAILABLE HIGH RES
MODELS. A MULTI MODEL HIGH RES SIGNAL EXISTS FOR POCKETS OF 2-4"
FROM THE FL PANHANDLE INTO SOUTHERN GA. WILL THUS CONTINUE WITH A
SLIGHT RISK OF EXCESSIVE RAINFALL FROM THE FLORIDA PANHANDLE INTO
SOUTHEAST GA.

AS WE HEAD INTO TONIGHT AND THE UPPER LOW BEGINS TO EJECT INTO THE
LOWER MS VALLEY EXPECT TO SEE ADDITIONAL CONVECTION FORM ALONG THE
COLD FRONT FROM EASTERN LA INTO MS...MOVING INTO AL AND GA
OVERNIGHT. COULD SEE SOME LOCALLY HEAVIER RATES WITH THIS
ACTIVITY. MEANWHILE WILL CONTINUE TO SEE A BROAD AREA OF SHOWERS
AHEAD OF THE UPPER LOW PROGRESS INTO THE MID ATLANTIC AND SOME
WRAP AROUND RAIN ON THE BACKSIDE OF THE LOW FROM AR INTO THE
WESTERN OH/TN VALLEY. OVERALL THE TREND AMONGST ALL THE GUIDANCE
WAS FOR A SLIGHTLY FURTHER EAST LOW TRACK...THUS DID CUT BACK QPF
AMOUNTS SOME ACROSS THE NORTHWEST EDGE OF THE PRECIPITATION SHIELD
TO COME MORE IN LINE WITH THE CURRENT MODEL CONSENSUS. OVERALL
RAINFALL ASSOCIATED WITH THIS ACTIVITY OUTSIDE OF THE SLIGHT RISK
AREAS WILL EITHER LACK SUFFICIENT INSTABILITY OR GENERALLY BE TOO
PROGRESSIVE TO WARRANT ANYTHING MORE THAN A MARGINAL RISK AT THIS
TIME. CAPPED THE NORTHERN EDGE OF THE MARGINAL RISK AT THE
EXPECTED INSTABILITY GRADIENT SUGGESTED BY THE CONSENSUS OF HIGH
RES MODELS.

CHENARD
$$




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