Quantitative Precipitation Forecast
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FOUS30 KWBC 281403
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1002 AM EDT SUN AUG 28 2016

...VALID 15Z SUN AUG 28 2016 - 12Z MON AUG 29 2016...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
105 W APF 100 W APF 95 SSW SRQ 15 W PIE 10 NW VDF 35 S BOW
50 WSW FPR 10 N COF 35 ENE COF.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 E KOPM 25 NW KOPM 15 E NQI 45 NNW RBO 25 SE AUS 30 SSW PSN
25 S GGG 15 NNE IER 10 WSW MCB BIX 10 NNW KVKY 25 NNE CYD.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
85 S DMN 50 SSW DMN 40 NW SVC 70 WNW TCS 50 NNW TCS 10 NNE ABQ
25 E E33 25 NE SKX 35 ESE CQC 50 SW TCC 20 ESE TCC 20 WSW EHA
25 SSW GCK DDC 25 W P28 20 E WWR 45 W CSM 35 N MDD 35 S FST
55 S MRF 65 SW MRF.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 WSW CWNH 35 ENE CYSL.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
CXGM 35 ESE BHB 20 SSE BHB 25 ENE BGR 35 NNW WVL 20 NE BGM
10 ENE AGC 15 W HLG 20 SW YNG BUF CWQP CTCK.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 ESE CWDV 40 WSW CMX 20 NNW VOK 10 NW AEL MML 20 ESE KGWR
30 SSW RDR 15 ENE CXMD.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 NNW RPD 20 SE RNH FCM BBB 20 SW FFM 20 ESE JKJ 20 SW BJI GPZ
15 NNE CDD 20 NNW RPD.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
70 W KEY 65 NW KEY 30 W TMB 15 NNW TMB BCT 25 E BCT.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 SW KBQX 15 SSW PSX 15 NNW 5R5 20 SSW JAS 10 W POE AEX
20 ENE BTR 15 ESE NEW 25 SW 9F2.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
E38 60 ESE MMCS 25 ENE LRU 20 E DMN SVC 20 WNW TCS 20 ESE TCS
45 NE TCS 40 W 4CR 20 ENE 4CR 55 WSW CVS 15 S CVN 40 WNW LBB
15 S HOB 15 NW INK 25 NE E38 E38.


15Z UPDATE...
NO CHANGES AT THIS TIME TO PREVIOUS EXCESSIVE RAINFALL OUTLOOK AND
REASONING.  SULLIVAN


MINNESOTA/WISCONSIN
~~~~~~~~~~~~~~~~~~~
A WARM FRONT ADVANCES INTO CENTRAL MN AHEAD OF A SHORTWAVE MOVING
NEAR THE CENTRAL US/CANADIAN BORDER, WHICH HAS STARTED TO BECOME
CONVECTIVELY ACTIVE IN NORTHEAST SD.  PRECIPITABLE WATER VALUES
RISE ABOVE 1.5" AS LOW-LEVEL INFLOW BECOMES INCREASINGLY CYCLONIC
AFTER 12Z, WITH WINDS EVENTUALLY RISING TO 40+ KTS AT 850 HPA.  A
CAP APPEARS TO BE BUILDING, USING THE 9C ISOTHERM AT 700 HPA AS A
GUIDE.  THE INGREDIENTS APPEAR TO EXIST FOR AN ORGANIZED
CONVECTIVE COMPLEX, PERHAPS ONE OF THE QUASI-LINEAR VARIETY WITH
AN ASSOCIATED COLD POOL FORMING DURING THE AFTERNOON AND EVENING
HOURS ACROSS WEST-CENTRAL MN.  BUT WHERE DOES IT GO FROM THERE?
SOME OF THE MESOSCALE GUIDANCE TRENDED NORTHWARD WHILE THE
GFS/NAM/ECMWF GUIDANCE TRENDED SOUTH.  WHILE NORMALLY A
COMBINATION OF FORWARD PROPAGATING CONVECTIVE VECTORS (WHICH POINT
EASTWARD) AND 1000-500 HPA THICKNESS PATTERN (WHICH POINT SOUTH TO
SOUTH-SOUTHEAST) WOULD BE USED FOR FORWARD PROPAGATION, THE
DEGREE/BREADTH OF INSTABILITY INDICATES THAT MERELY FOLLOWING THE
FORWARD PROPAGATING VECTORS SHOULD SUFFICE.  THIS IDEA CAN BE
REVISITED IN LATER FORECASTS.  WPC MOVES THE COMPLEX EASTWARD WITH
TIME ACROSS MN, RESEMBLING A SLIGHTLY SOUTHWARD ADJUSTED
COMPROMISE OF THE 00Z GFS/00Z NAM/00Z ECMWF SOLUTIONS OR A
COMPROMISE OF THE 12Z/00Z WRF NSSL RUNS.  THE 00Z CANADIAN
REGIONAL APPEARS TO BE A LOWER PROBABILITY ALTERNATIVE SCENARIO
FOR THIS COMPLEX`S EVOLUTION, WITH ITS USUAL NORTHWARD BIAS IN
FULL DISPLAY.  BOTH MARGINAL RISK AND SLIGHT RISK AREAS WERE ADDED
HERE.  LOCAL AMOUNTS IN THE 3-5" RANGE ARE INDICATED BY THE
MESOSCALE GUIDANCE, WHICH COULD FALL QUICKLY AS AVAILABLE MOISTURE
SUPPORTS HOURLY RAIN RATES TO 1.75" WERE CELLS MERGE/TRAIN.


LOWER MS VALLEY & WESTERN GULF COAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A SURFACE TROUGH/850 HPA CIRCULATION INTERACTS WITH PRECIPITABLE
WATER VALUES OF 2-2.25" TO LEAD TO HEAVY RAINS ACROSS PORTIONS OF
LA AND THE LOWER TO MIDDLE TX COAST.  THE MAIN CHALLENGE HERE
CONTINUES TO BE WITH HOW FAR NORTH THE HEAVIER CONVECTIVE BANDS
WILL DEVELOP, WHICH MOVED FAIRLY FAR INLAND ACROSS LA ON SATURDAY.
DIFFERENTIAL HEATING ALONG THE SYSTEM`S NORTHERN FRINGE WILL
LIKELY SUPPORT SOME HEAVIER RAIN BANDS INLAND ACRS PARTS OF THE TX
COAST INTO LA DURING DAYTIME HEATING (ROUGHLY 15Z-03Z).  CLOSER TO
THE LOW-LEVEL CIRCULATION, ONSHORE FLOW SHOULD FOCUS HEAVY RAIN
NEAR THE COAST, PARTICULARLY IN THE 06Z-15Z TIME FRAME.  HOURLY
RAIN RATES COULD REACH 3" WHERE CELLS MERGE OR WITHIN SHORT
TRAINING BANDS.  THE MESOSCALE GUIDANCE SHOWS POCKETS OF 3-6" OF
RAIN NEAR THE LA AND UPPER TX COAST, WHICH IS CLOSE TO THE RADAR
ESTIMATES FROM THE SATURDAY ACTIVITY.  A LARGER SLIGHT RISK AREA
WAS DEPICTED TODAY WHEN COMPARED TO SATURDAY AS SATURDAY`S
RAINFALL LED TO SOME REDUCTION IN THE FLASH FLOOD
GUIDANCE/INCREASE IN SOIL SATURATION ACROSS PORTIONS OF LA.


FLORIDA
~~~~~~~
AN AXIS OF ABOVE NORMAL MOISTURE NEAR THE SOUTHERN PERIPHERY OF
SUBTROPICAL RIDGE IN THE VICINITY OF AN OCCASIONALLY CONVECTIVE
LOW PRESSURE AREA MOVING THROUGH THE FL STRAITS WILL TO LEAD TO
THUNDERSTORMS ACROSS PORTIONS OF THE SOUTHERN PENINSULA.  THE
DEGREE OF HEAVY RAINFALL IN FL DEPENDS ON IF THE SURFACE LOW GETS
BETTER ORGANIZED UNDER A REGIME OF WEAKENING VERTICAL WIND SHEAR
AS THE UNDO INFLUENCE OF AN UPPER LOW WITH ITS NORTH BEGINS TO
RECURVE OUT OF THE PICTURE...SEE TROPICAL WEATHER OUTLOOKS FROM
THE NHC ON ITS POTENTIAL FOR TROPICAL CYCLONE DEVELOPMENT.  SOME
LIGHT NORTH TO NORTHEAST VERTICAL WIND SHEAR IS EXPECTED THUS RAIN
PATTERN OVER FL (OUTSIDE THE KEYS) SHOULD CONTINUE TO BE DOMINATED
BY ENHANCED EASTERLY FLOW WITHIN A VERY MOIST AIRMASS -- CLOSER TO
THE COAST IN THE 06Z-15Z PERIOD AND DUE TO SEA BREEZE CIRCULATIONS
WHICH SHOULD FOCUS ACTIVITY IN SOUTHWEST FL BETWEEN 15Z-03Z.
LOCAL AMOUNTS IN THE 3-5" RANGE ARE INDICATED BY THE MESOSCALE
GUIDANCE, WHICH SEEMS PLAUSIBLE.  MAINTAINED THE MARGINAL AND
SLIGHT RISK AREAS HERE.


SOUTHERN ROCKIES/CENTRAL AND SOUTHERN PLAINS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A SHORTWAVE SHOULD TRACK SLOWLY EASTWARD TOWARD THE AZ/NM BORDER
REGION THIS EVENING WITH MODELS IN GOOD AGREEMENT TIMING-WISE.
BROADER DIURNAL THUNDERSTORM COVERAGE IS EXPECTED ACROSS THE
SOUTHERN ROCKIES AND FROM WESTERN TX INTO SOUTHWEST KS WHERE THERE
MESOSCALE GUIDANCE AGREEMENT FOR LOCAL AMOUNTS IN THE 3-6" RANGE.
A SLIGHT RISK OF EXCESSIVE RAINFALL HAS BEEN ADDED FOR PORTIONS OF
SOUTHERN NM AND WESTERN TX WHERE THE HIGHEST PRECIPITATION AND THE
LOWEST FLASH FLOOD GUIDANCE VALUES ARE EXPECTED TO OVERLAP.


NORTHEAST
~~~~~~~~~
A WEAKENING SHORTWAVE AND ASSOCIATED FRONTAL ZONE ARE EXPECTED TO
BE ACCOMPANIED BY A BAND OF SHOWERS AND THUNDERSTORMS ACROSS THE
NORTHEAST DURING DAYTIME HEATING ON SUNDAY.  PRECIPITABLE WATER
VALUES OF 1.5-2" ARE EXPECTED NEAR THIS BOUNDARY/FRONT ALOFT.
WHILE AREAL AVERAGE AMOUNTS SHOULD BE GENERALLY LIGHT TO MODERATE,
POCKETS OF HEAVY RAINFALL SHOULD BE POSSIBLE NEAR AND WITHIN THE
CONVERGENT CYCLONIC FLOW NEAR THE SURFACE FEATURE.  LOCAL AMOUNTS
IN THE 2-4" RANGE SHOULD BE POSSIBLE, GIVEN ENOUGH INSTABILITY
BUILDS ACROSS THE PERIOD, WHICH IS A BIGGER QUESTION MARK THE
FARTHER EAST YOU GO IN NEW ENGLAND.  MAINTAINED THE MARGINAL RISK
FOR EXCESSIVE RAINFALL IN THIS AREA.

ROTH
$$





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