Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 030049
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
849 PM EDT WED SEP 02 2015

...VALID 01Z THU SEP 03 2015 - 12Z THU SEP 03 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...



01Z UPDATE...

...SOUTHWEST U.S...

ACTIVITY ACRS THE SOUTHWEST U.S. WITHIN DECENT MONSOONAL PLUME HAS
STRUGGLED TO BECOME ORGANIZED TO ANY LARGE EXTENT OWING PARTLY TO
RATHER LOW SBCAPES..ONLY MODEST SFC DPS...AND LOWERING PWS BEHIND
MID LEVEL CIRC LIFTING NEWD ACRS NE AZ.  LATEST EXPERMENTAL HRRR
RUNS SHOW POTNL FOR SOME ISOLD HEAVIER STORMS AHEAD OF MID LEVEL
VORT DURING THE EVENING AS IT LIFTS TOWARD THE 4 CORNERS
REGION..BUT SYSTEM WILL BE MOVING INTO INCREASINGLY DRIER LOW
LEVEL ENVIRONMENT.   THERE IS ALSO POTNL FOR SOME STORMS DVLPG
NEWD FROM NRN MEX INTO SE SECTIONS OF AZ AND SW NM DURING THE
REMAINDER OF THE OVERNIGHT PD WITH HI LEVEL MSTR FROM TD 14-E
PSBLY COMING INTO PLAY. OTHERWISE...BELIEVE OVERALL EXCESSIVE
RAINFALL THREAT HAS DIMINISHED FOR A LARGE PORTION OF THE
SOUTHWEST..THOUGH SOME ISOLD RUNOFF ISSUES STILL CAN`T BE RULED
OUT.


...UPPER MISSISSIPPI VALLEY / WESTERN GREAT LAKES...

THUNDERSTORMS PRODUCING HEAVY RAIN RATES WILL OCCUR AHEAD OF A
COMPACT MID LEVEL TROUGH...BUT ALSO IMMEDIATELY BEHIND THE TROUGH
IN AN AREA OF ENHANCED LOW LEVEL INFLOW. THE TROUGH WILL TRACK
FROM THE VICINITY OF THE MN/WI BORDER THIS MORNING TO LOWER
MICHIGAN BY THURSDAY MORNING...WITH THE LEADING THUNDERSTORM
ACTIVITY MIGRATING ALONG A LOOSELY DEFINED WARM FRONT FROM THE
WESTERN END OF LAKE SUPERIOR DOWN TO LOWER MICHIGAN. THE TRAILING
ACTIVITY WILL REDEVELOP EASTWARD AND SOUTHEASTWARD FROM THE
MINNEAPOLIS AREA TOWARD NORTHERN INDIANA. MANY OF THE MODEL
FORECASTS WERE THOUGHT TO NOT BE PROGRESSIVE ENOUGH...AND LIKELY
DISPLAY A SLIGHT NORTHWARD BIAS TO THEIR QPF. WPC PREFERRED THE
00Z SPC WRF...WHICH SHOWED SOME AGREEMENT WITH THE NSSL WRF AND
ECMWF.

GENERALLY THE SHORT WAVELENGTH OF THE MID LEVEL TROUGH...ALONG
WITH REASONABLY STRONG DOWNDRAFT CAPE...SHOULD PROMOTE FORWARD
PROGRESSION...AND ACT AGAINST FLASH FLOODING...ALTHOUGH
PRECIPITABLE WATER VALUES NEAR 1.5 INCHES WILL SUPPORT BRIEF
STRONG RAIN RATES. THE GREATEST CONCERN FOR FLASH FLOODING MAY BE
WITH THE NARROW BANDS OF CONVECTION WHICH FORM ON THE TRAILING
SIDE OF THE TROUGH...IN THE BETTER LOW LEVEL INFLOW. ONE SUCH BAND
HAD SET UP WEDNESDAY MORNING IN WESTERN WISCONSIN WHERE RADAR
ESTIMATED MORE THAN AN INCH IN AN HOUR WAS FALLING AT 1430Z. PER
RECENT DRY WEATHER AND RELATIVELY LARGE FLASH FLOOD GUIDANCE
VALUES REQUIRING ABOUT 2.5 INCHES IN 3 HOURS...THE FLASH FLOOD
THREAT IS NOT VERY PRONOUNCED...BUT ISOLATED FLASH FLOODING COULD
OCCUR.




BURKE/SULLIVAN
$$





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