Quantitative Precipitation Forecast
Issued by NWS

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000
FOUS30 KWBC 241340
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
940 AM EDT WED JUN 24 2015

...VALID 15Z WED JUN 24 2015 - 12Z THU JUN 25 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
10 NE DPA 30 WSW ASW 10 NW AID 10 NNE BMG FOA 10 WNW CPS
35 N COU 10 WSW FNB 15 W FET 15 SSW SPW 10 S PDC 10 NE DPA.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 S LWD 10 SE RDK 15 NNW ADU 15 WNW MIW 10 N DVN 10 ESE C75
15 WSW CMI 15 SW TAZ 10 ESE UIN 20 S LWD.


...NEBRASKA / IOWA / ILLINOIS / MISSOURI / INDIANA...

CONCERNS FOR EXCESSIVE RAINFALL THIS PERIOD WILL BE FOCUSED WITHIN
THE SLIGHTLY ELEVATED FRONTAL ZONE FROM 925-850 MB ACROSS SOUTHERN
IOWA/ FAR NORTHERN MISSOURI / WEST-CENTRAL ILLINOIS...AND
EXTENDING INTO ADJACENT PARTS OF NEBRASKA AND INDIANA. THE 00Z
CYCLE OF MESOSCALE MODELS PRODUCED UNUSUALLY HIGH RAIN TOTALS
ACROSS THE BOARD. IN FACT...THE SSEO MEAN...AN AVERAGE OF SEVERAL
MODELS...PREDICTS 3 INCHES OF RAIN IN EASTERN IOWA THROUGH 12Z
THURSDAY. INDIVIDUAL MODELS PREDICT SMALLER SCALE...COUNTY
LEVEL...TOTALS OF 5 TO 7 INCHES. GIVEN THE OVERALL CONSISTENCY OF
THE PLACEMENT AND INTENSITY OF THE RAIN IN OUR PREFERRED MODELS
FOR THIS EVENT /WRF ARW---NMMB---NSSL WRF AND ECMWF / A MODERATE
RISK OF EXCESSIVE RAINFALL IS FORECAST OVER MUCH OF SOUTHERN IOWA
/ FAR NORTHERN MISSOURI / WEST-CENTRAL ILLINOIS.

IN THE 15Z UPDATE THE SLIGHT AND MODERATE RISK AREAS WERE EXPANDED
WESTWARD...AND THE MODERATE RISK AREA WAS DROPPED SLIGHTLY
SOUTHWARD...ALL BASED ON OBSERVATIONAL TRENDS AND HRRR CAPE
FORECASTS. ONGOING ELEVATED CONVECTION THIS MORNING WAS FRACTURED
AND SHOULD NOT ENTIRELY INHIBIT THE NORTHWARD TRANSPORT OF
UNSTABLE AIR THROUGH NEBRASKA AND WESTERN IOWA. THE CONVECTION WAS
EXTENSIVE ENOUGH...HOWEVER...THAT THERE ARE NO QUESTIONS ABOUT HOW
FAR NORTHEAST THE UNSTABLE AIR WILL BE ABLE TO
DEVELOP...ESPECIALLY WITH THE HRRR NOW KEEPING THE CAPE AXIS MORE
NARROW AND CONFINED THROUGH EARLY EVENING. WPC TRIMMED THE EASTERN
PORTION OF THE MODERATE RISK TO REMOVE INDIANA AND EASTERN
ILLINOIS...AS INFLOW WILL BE MORE FOCUSED ON THE SOUTH AND WEST
SIDES OF THE CONVECTION TODAY/TONIGHT. THESE AREAS DO REMAIN
WITHIN THE SLIGHT RISK AREA AS THE EVENT WILL MIGRATE IN THAT
DIRECTION BY THURSDAY MORNING.

WITH WARM MID LEVEL TEMPERATURES AND DRIER AIR CAPPING THE
ENVIRONMENT NEAR THE SURFACE FRONT FROM SOUTHERN NEBRASKA TO
CENTRAL MISSOURI...LARGE SCALE CONVECTION IS EXPECTED FARTHER
NORTH...WHERE LOW LEVEL MOISTURE AND THETA-E ADVECTION WILL BE
MAXIMIZED. A LOW AMPLITUDE BUT WELL DEFINED MID LEVEL TROUGH WILL
ALSO CONTRIBUTE TO HEIGHT FALLS AND AN INCREASING AMOUNT OF UPPER
DIFFLUENCE THIS AFTERNOON/EVENING. THERE IS A LIKELIHOOD OF
TRAINING OF CELLS IN A WEST TO EAST DIRECTION ACROSS THE MODERATE
RISK AREA...ESPECIALLY IN THE 0000 TO 1200 UTC THURSDAY TIME FRAME
WHEN THE LOW LEVEL FLOW BECOMES INCREASINGLY ORIENTED WEST TO
EAST. ONE COMPLICATING FACTOR WAS AN ONGOING MCS IN NORTHERN
NEBRASKA WHICH HAD RACED AHEAD OF THE PRIMARY HEIGHT FALLS AND
TROUGH AXIS. THE MCS WAS RELATIVELY SMALL AND HAS SHOWN WEAKENING
TRENDS AS OF 13Z...BUT WARM ADVECTION MAY SUSTAIN SOME SEMBLANCE
OF AN MCS INTO THE AFTERNOON AS IT TRACKS TOWARD WESTERN IOWA.
THIS COULD BE A FACTOR IN DETERMINING TIMING AND FOCUS OF THE
FLASH FLOOD POTENTIAL...WHICH IS OTHERWISE EXPECTED TO INCREASE
DURING THE LOW LEVEL JET CYCLE OVERNIGHT. WITH ABOVE AVERAGE PW
VALUES ALONG THE ELEVATED FRONTAL ZONE...AND AN OVERALL FAVORABLE
PATTERN...WIDESPREAD HEAVY PRECIPITATION APPEARS LIKELY. EXPECT
SHORT TERM PRECIPITATION AMOUNTS OF 1-2" AND ISOLATED TOTALS OF
5"+ POSSIBLE.


...HIGH PLAINS OF WYOMING / SOUTH DAKOTA / FAR WESTERN NEBRASKA...

ALTHOUGH NOT A TRADITIONAL FRONTAL PASSAGE...THE PASSAGE OF A MID
LEVEL TROUGH AND ASSOCIATED SURFACE REFLECTION WILL RESULT IN A
SLIGHT ENHANCEMENT OF UPSLOPE FLOW TODAY AND
TONIGHT...SUPERIMPOSED ON AN 850-700 MB BAROCLINIC ZONE IN WHICH
MOST UNSTABLE CAPE VALUES ARE FORECAST TO PERSIST NEAR OR ABOVE
1000 J/KG. THIS SETS THE STAGE FOR ISOLATED AFTERNOON
THUNDERSTORMS AND AN INCREASE OF THUNDERSTORM COVERAGE AND
INTENSITY EARLY THURSDAY MORNING AHEAD OF AN APPROACHING UPPER
LEVEL TROUGH. IT IS POSSIBLE THAT APPRECIABLE COVERAGE WOULD HOLD
OFF UNTIL JUST BEYOND THIS OUTLOOK PERIOD...AFTER 12Z THURSDAY.
THE HIGH RESOLUTION MODELS...HOWEVER...ARE UNANIMOUS IN SIGNALING
AT LEAST ISOLATED TO SCATTERED ACTIVITY PRIOR TO THAT TIME...WITH
SOLUTIONS SUCH AS THE GEM REGIONAL AND NAM CONEST INDICATING
SMALLER SCALE HEAVY SWATHS OF PRECIPITATION OVER THE BLACK
HILLS...ESPECIALLY EARLY THURSDAY MORNING. WITH PRECIPITABLE WATER
VALUES ABOVE 1 INCH...AND FLASH FLOOD GUIDANCE ON THE LOW SIDE...A
LOW END RISK OF FLASH FLOODING DOES APPEAR TO EXIST...AND MAY
BECOME MORE PRONOUNCED ON THURSDAY.

BURKE/ORAVEC
$$





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