Quantitative Precipitation Forecast
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000
FOUS30 KWBC 112313
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
612 PM EST THU JAN 11 2018

...VALID 2312Z THU JAN 11 2018 - 12Z FRI JAN 12 2018...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 ESE BCB 15 SE ROA MTV 20 ESE UKF 15 S MRN 15 N GSP
10 WNW CEU 30 WNW CEU 15 SW 1A5 10 SSW 1A5 25 W AVL 20 N AVL TNB
10 ESE PSK 15 ESE BCB.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 NW IER 25 NNE BAD 35 NW ELD 15 ESE M89 25 W PBF 30 SE M19
25 NNE BYH CIR PAH 30 W HOP 45 SSW CKV 35 NW MSL 35 N HKS AEX
25 NW POE 25 NW IER.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 W JHW 25 E BUF 20 E CWQP 10 E GTB 35 E GTB 40 NW GFL
25 E UCA 20 SSW UCA 25 NNW IPT 10 E LBE 20 NW 48I 25 SSW CRW
20 ENE HTS 15 WNW PKB 10 SE YNG 15 W JHW.


...LOWER TO MID MISSISSIPPI VALLEY...

AS OF 23Z WATCHING A CONVECTIVE LINE STRETCHING FROM SOUTHERN AR
INTO WESTERN LA STEADILY PROGRESSING OFF TO THE EAST. THE
PROGRESSIVE NATURE OF THE LINE IS GENERALLY KEEPING RATES AT OR
BELOW 0.5" IN AN HOUR...WITH ISOLATED 1" AN HOUR TOTALS NEAR THE
TX/LA BORDER CLOSER TO THE GULF COAST. THESE VALUES ARE GENERALLY
BELOW FFG AND THUS NOT CURRENTLY POSING MUCH OF A FLASH FLOOD
RISK. SHOULD CONTINUE TO SEE THIS CONVECTION MOVE OFF TO THE EAST
THROUGH THE EVENING HOURS...SUPPORTED BY ROUGHLY 200-500 J/KG OF
MUCAPE AND STRONG SYNOPTIC ASCENT. PWAT VALES AROUND 1.5-2 SD
ABOVE AVERAGE ALSO ARE SUPPORTIVE OF LOCALLY HEAVY RAINFALL. THE
FURTHER SOUTH YOU GO THE MORE CONVECTIVE IN NATURE THE ACTIVITY
SHOULD BE...BUT FURTHER NORTH THE DURATION SHOULD BE A BIT LONGER
AND FFG IS A LITTLE LOWER. OVERALL THIS IS A MARGINAL EVENT...BUT
CONTINUE TO SEE LOW PROBABILITIES IN BOTH THE HREF AND HRRR TLE OF
2" OF RAIN IN A 3 HOUR PERIOD OVER THE MARGINAL RISK AREA...WHICH
MAY BEGIN TO APPROACH FFG. THUS ONLY MINIMAL CHANGES WERE MADE TO
THIS RISK AREA.

...SOUTHERN APPALACHIANS...

OROGRAPHICALLY ENHANCED RAINFALL CONTINUES INTO PORTIONS OF THE
SOUTHERN APPALACHIANS THIS EVENING. HIGHEST TOTALS THUS FAR HAVE
BEEN CONFINED TO THE FAVORED AREAS OF SOUTHWEST NC. RAINFALL
AMOUNTS OF 2-3" HAVE ALREADY FALLEN IN THIS AREA...WITH AMOUNTS
POSSIBLY AS HIGH AS 4-5" (THE ACCURACY OF THESE GAUGES IS
UNCERTAIN ALTHOUGH THE AMOUNTS ARE PLAUSIBLE). IT LOOKS LIKE THIS
REGION SHOULD SEE SEVERAL MORE HOURS OF OROGRAPHICALLY ENHANCED
RAINFALL WITH AN ADDITIONAL 2" OR SO POSSIBLE BEFORE THE FOCUS
SHIFTS FURTHER NORTH INTO NORTHWEST NC AND SOUTHWEST VA. THE
DURATION OF RAINFALL IN THESE FURTHER NORTH AREAS SHOULD BE
LESS...BUT STILL LOOKING AT AN ADDITIONAL 2" HERE ON TOP OF THE
1-2" THAT HAS ALREADY FALLEN. IN GENERAL RATES ARE NOT THAT HIGH
AND SOILS STARTED OUT DRY...HOWEVER RAINFALL OF THIS MAGNITUDE
STILL MAY BEGIN TO CAUSE SOME FLOODING CONCERNS. THUS WILL
MAINTAIN THE MARGINAL RISK.

...EASTERN OH VALLEY INTO THE LOWER GREAT LAKES...

ADDED IN A MARGINAL RISK WITH THIS UPDATE FROM PORTIONS OF WV
NORTHEAST INTO FAR EASTERN OH...WESTERN PA AND WESTERN NY. A
PRETTY GOOD SIGNAL AMONGST THE HIGH RES GUIDANCE FOR A CORRIDOR OF
MODERATE TO LOCALLY HEAVY RAINFALL ACROSS THIS AREA WITHIN AN AXIS
OF PERSISTENT STRONG LOW LEVEL MOISTURE TRANSPORT. PWAT VALUES
INCREASING TO AROUND OR ABOVE 1.25" WILL BE AROUND RECORD VALUES
FOR THIS TIME OF YEAR. THE COMBINATION OF THIS PERSISTENT MOISTURE
TRANSPORT AND VERY ANOMALOUS PWAT VALUES WILL SUPPORT RAINFALL
TOTALS GENERALLY BETWEEN 1" AND 2.5" WITHIN THE MARGINAL RISK AREA
THROUGH 12Z FRIDAY. A LACK OF INSTABILITY SHOULD KEEP RATES FROM
GETTING TOO HIGH...ALTHOUGH MODEL SOUNDINGS DO SHOW SOME WEAK
ELEVATED INSTABILITY...WHICH SHOULD ALLOW FOR ISOLATED AMOUNTS AS
HIGH AS 0.5"-0.75" WITHIN AN HOUR. BOTH THE HREF AND HRRR TLE ALSO
SHOW GOOD PROBABILITIES OF AMOUNTS EXCEEDING 1" IN A THREE HOUR
PERIOD WITHIN THE RISK AREA. THESE AMOUNTS BEGIN TO APPROACH FFG
OVER THE AREA...AND WHEN COMBINED WITH SNOW MELT AND FROZEN
GROUND...SUGGESTS SOME FLOOD THREAT MAY DEVELOP OVERNIGHT. THE
ACTUAL AREA IMPACTED MAY END UP SMALLER THAN THE MARGINAL RISK
AREA DEPICTED...BUT MADE THE AREA A BIT BROAD TO ENCOMPASS THE
UNCERTAINTY THAT REMAINS WITH REGARDS TO WHERE EXACTLY THE
HEAVIEST RAIN AXIS SETS UP.

CHENARD
$$




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