Quantitative Precipitation Forecast
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FOUS30 KWBC 200049
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
848 PM EDT TUE JUL 19 2016

...VALID 01Z WED JUL 20 2016 - 12Z WED JUL 20 2016...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 SE EAU 20 WSW ARR OLY 15 WSW MDH 25 E COU 10 NNE FFL AUM FCM
10 WNW OEO 25 SE EAU.



20/0100Z UPDATE...

WPC ADJUSTED THE SLIGHT RISK AREA OVER THE MID MS VALLEY AND
DOWNGRADED THE SLIGHT RISK OVER THE ERN CAROLINAS TO A SEE TEXT.

MOST CONVECTIVE HEAVY RAIN WILL GRADUALLY DISSIPATE ACROSS PARTS
OF THE SOUTHEAST WITH THE LOSS OF HEATING BUT ONE AREA COULD STILL
PERSIST A BIT LONGER TO POSE LOCAL RUNOFF ISSUES. UPPER TROUGH
GRADUALLY SWINGING OFF THE MID-ATL SEABOARD WITH FAVORABLE UPPER
JET DYNAMICS IS ALLOWING A CLUSTER OF SHOWERS/STORMS TO SPREAD
SOUTH AND EAST FROM SERN VA INTO ERN NC. THIS WOULD BE ROUND TWO
FOR ERN NC IF THE ACTIVITY CAN HOLD ON... EARLIER DIURNAL
CONVECTION WAS NEAR A PRE-FRONTAL/LEE SIDE TROUGH. FELT THE MINOR
DOWNGRADE WAS APPROPRIATE BASED ON A VARIETY OF HI-RES GUIDANCE
AND GLOBAL MODELS SUGGESTING THE ACTIVITY SHOULD DAMPEN AND BE
EXTREMELY LOCALIZED.

A MESO CONVECTIVE HEAVY RAIN CLUSTER CONTINUES TO PLUNGE SOUTH
ACROSS NERN MO/WEST CENTRAL IL. SOME OF THE HI-RES GUIDANCE
INDICATES THE LEADING EDGE OF THE MOST IMPOSING CONVECTION/RAIN
GRADUALLY INTERACTING WITH A STATIONARY LONE CELL NEAR THE STALLED
FRONTAL ZONE OVER SRN IL. THIS COULD ALLOW THE ENTIRE BLOB TO
BECOME STATIONARY AND ENHANCE LEADING TO LOCALLY HEAVY RAIN AND
RUNOFF ISSUES DESPITE FFG VALUES NOT BEING EXTREMELY LOW. WPC ALSO
KEPT THE NRN PERIPHERY OF THIS SLIGHT RISK AREA OR ACROSS ERN
IA/SWRN WI AND SERN MN. UPSTREAM NEAR NERN ND/NWRN MN A VERY SMALL
CLUSTER OF STORMS IS BEGINNING TO ACCELERATE SOUTH AND EAST TOWARD
THE NRN PORTION OF THE SLIGHT RISK AREA. ENOUGH INSTABILITY
REMAINS PRESENT AND ONCE THE GREAT PLAINS LOW LEVEL NOCTURNAL JET
DEVELOPS AND ENHANCES THE POTENTIAL FOR BETTER ORGANIZATION
REMAINS POSSIBLE. THE HI-RES GUIDANCE DOES NOT OFFER MUCH
CONFIDENCE IN THIS AREA... WHETHER OR NOT THIS THINKING WILL
OCCUR... BUT WITH THE POTENTIAL AND CHANCE TO KEEP SOME
CONTINUITY... WPC WILL KEEP AN ELONGATED SLIGHT THREAT.

MUSHER

19/1500Z UPDATE...

THE ONLY SIGNIFICANT CHANGE MADE TO THE OVERNIGHT OUTLOOK WAS TO
ACCOUNT FOR THE ONGOING CONVECTION ACROSS WESTERN/CENTRAL IA.
WHILE THE LEADING CONVECTIVE LINE HAS BEEN PROGRESSIVELY MOVING
INTO CENTRAL IA...ADDITIONAL THUNDERSTORMS CONTINUE TO DEVELOP IN
ITS WAKE ACROSS THE NORTHWESTERN IA WITH A GENERAL WEST-EAST
ORIENTATION. RECENT HOURLY RATES PER MESONET DATA REMAIN IN THE
0.75 TO 1.00 INCH RANGE. WHILE THERE MAY NOT BE A WIDESPREAD
THREAT FOR FLASH FLOODING...THIS EARLY ROUND OF CONVECTION WILL
EFFECTIVELY LOWER FFG VALUES ACROSS THE REGION. DIFFICULT TO SAY
HOW LONG THIS ACTIVITY WILL PERSIST GIVEN THE LIMITED INSTABILITY
POOL BASED ON RECENT RAP OBJECTIVE ANALYSES. HOWEVER...THERE SEEMS
TO BE SOME SORT OF WEST-EAST BOUNDARY THE CONVECTION IS FIRING
ALONG WHILE IN THE PRESENCE OF 1.75 TO 2.00 INCH PWATS.

RUBIN-OSTER


PREVIOUS DISCUSSION...

...CENTRAL PLAINS/MID-UPPER MS VALLEY...

THE MODELS INDICATE ACTIVITY IN NEBRASKA TRANSLATE DOWNSTREAM INTO
MN/IOWA AS THE LOW-MID LEVEL WARM FRONT AND ZONE OF 850-700 MB
WARM/MOIST ADVECTION AND CONVERGENCE SPURS CONVECTIVE DEVELOPMENT
TODAY AND TONIGHT.
LOCALLY HEAVY RAINFALL IS INDICATED AS THE GFS SHOWS PRECIPITABLE
WATER (PW) MAXIMA OF 2 INCHES INTO SOUTHEAST MN/ECMWF UP TO 2.25
INCHES NEAR THE SOUTHERN MN/WI BORDER.
THE HIGH RES WRF ARW AND NMMB/NAM CONUS NEST ALSO SHOW MAXIMA
DEVELOPING WITHIN THE WARM ADVECTION ZONE AND MOISTURE POOL IN
EASTERN IOWA...SUPPORTED BY THE NAM 300 MB DIVERGENCE SLIDING
SOUTHEAST OVERNIGHT FROM SOUTHEAST MN INTO EASTERN IOWA...AND THE
ECMWF INCREASING PW VALUES TO 2 INCHES. MANUAL PROGS BLENDED THE
GFS/NAM AND HIGH RES CONVECTIVE ALLOWING MODELS 00Z WRF
ARW/NMMB/NSSL WRF.  THE 00Z CANADIAN REGIONAL GEM MOVED THE PRECIP
EAST FASTER ACROSS WI/IL AND WAS GIVEN THE LEAST WEIGHTING AS AN
OUTLIER. A SLIGHT RISK OF EXCESSIVE RAINFALL WAS INDICATED AS THE
POSSIBILITY EXISTS OF MORE THAN ONE ROUND OF STORMS PLUS THE HIGH
RES CONVECTIVE ALLOWING ENSEMBLES SHOW POTENTIAL FOR 3-6 INCHES OF
RAIN FOR THE 24 HOUR PERIOD.


...SOUTHERN MID-ATL/SOUTHEAST...

AN UPPER-LEVEL TROUGH WILL DRIVE A SURFACE COLD FRONT THROUGH THE
SOUTHERN MID-ATL STATES INTO THE SOUTHEAST... WHILE BECOMING
QUASI-STATIONARY OR STALL. PRECIPITABLE WATER (PW) VALUES
GENERALLY 1.5 TO 2 INCHES WILL POOL OUT AHEAD AND INVOF OF THIS
FRONTAL ZONE...WHICH  LIKELY YIELDING SCATTERED TO NUMEROUS
SHOWERS/STORMS WITH THE MOST WIDESPREAD ACTIVITY TUE AFTN/EVENING
ACROSS SERN VA INTO ERN NC/NORTHEAST SC...WHERE THE SEA BREEZE
SHOULD AID DEVELOPMENT OF SHOWERS.  WITH THE 850 MB TROUGH
PROGRESSING SOUTH...THE ACTIVITY SHOULD MOVE SLOWLY SOUTH TONIGHT.
MANUAL PROGS BLENDED CONTINUITY WITH THE GFS/HIGH RES WRF
ARW/NMMB/NSSL WRF.  THE HIGH RES MODELS SHOW 1-2 INCHES WITH
LOCALLY HIGHER MAXIMA SO A SLIGHT RISK OF EXCESSIVE RAINFALL WAS
MAINTAINED.


PETERSEN
$$




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