Quantitative Precipitation Forecast
Issued by NWS

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000
FOUS30 KWBC 170807
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
406 AM EDT SUN SEP 17 2017

...VALID 12Z SUN SEP 17 2017 - 12Z MON SEP 18 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
50 NE CYXZ 20 E CYXZ 40 SSW CWXZ 45 NE SAW 25 ESE VOK 10 E FFL
20 WNW SGF 20 S BVO 20 NE HUT 10 SW AIO 15 NW RGK 10 E BFW
20 WNW CYQT 10 SW CXCA 30 SSW CYGQ.


...SOUTHERN PLAINS AND MIDWEST TO LAKE SUPERIOR...

A NARROW MARGINAL RISK AREA STILL STRADDLES THE COLD FRONT
ADVANCING INTO THE MIDDLE OF THE NATION. GENERALLY THE PATTERN
FAVORS PROGRESSIVE STORM MODES...WITH PROGRESSION ENHANCED BY
OUTFLOW IN SOME CASES. THIS IS WORKING AGAINST THE THREAT OF
EXCESSIVE RAINS...BUT FAIRLY ROBUST PW ANOMALIES FROM 1.0 TO 2.5
STANDARD DEVIATIONS ALONG WITH STEEP LAPSE RATES / MODERATE CAPE
VALUES...WILL SUPPORT SOME LOCALLY HEAVY RAIN RATES ANYWHERE FROM
NORTHEAST OKLAHOMA TO THE U.P. OF MICHIGAN.

OVER THE SOUTHERN PLAINS THERE IS SOME CONNECTION TO MID AND HIGH
LEVEL MOISTURE STREAMING OUT OF THE TROPICS TO THE NORTH OF
PACIFIC TROPICAL STORM NORMA. AN ADVANCED GROUP OF
THUNDERSTORMS...HOWEVER...ROOTED IN THE MID LEVEL MOISTURE WELL
AHEAD OF THE SURFACE COLD FRONT...WILL CONSUME SOME OF THE
AVAILABLE INSTABILITY WHILE MEAN LAYER WINDS AND DRYER LOW LEVEL
AIR ALL PROMOTE QUICK EASTWARD PROGRESSION THROUGH MISSOURI AND
SOUTHERN IOWA. HEIGHT FALLS SWEEPING THROUGH THE NORTHERN PLAINS
AND A TRAILING TROUGH AXIS BRUSHING ACROSS THE SOUTHERN PLAINS
WILL YIELD ADDITIONAL THUNDERSTORM DEVELOPMENT BACK WEST...AS WAS
OCCURRING IN PORTIONS OF KANSAS AT 0030Z. EXPECT MORE OF THIS
ALONG THE SURFACE FRONT IN OK/KS/MO/IA LATE THIS EVENING.
STILL...CORFIDI VECTORS ARE AT A SHARP ANGLE TO THE MEAN CELL
MOTION...SUCH THAT TRAINING MAY NOT BE MUCH OF AN ISSUE EXCEPT FOR
BRIEF TIMES ON SMALL SCALES.

FARTHER NORTH...WIND PROFILES ARE ACTUALLY QUITE SIMILAR UP INTO
THE WESTERN GREAT LAKES...AND WITH GREATER FORCING THERE...IT IS
AGAIN LIKELY THAT STORMS WILL ASSUME A PROGRESSIVE MODE...ONE
REASON THAT WE ARE NOT SEEING ANYTHING PARTICULARLY EXCESSIVE IN
THE HI-RES MODEL QPFS. STILL...WE WILL MAINTAIN THE MARGINAL RISK
TO COVER THE POSSIBILITY OF A FEW INSTANCES OF ENHANCED RAIN RATES
OVER ANY SUSCEPTIBLE BASINS.

BURKE
$$





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