Quantitative Precipitation Forecast
Issued by NWS

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983
FOUS30 KWBC 162138
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
537 PM EDT SAT SEP 16 2017

...VALID 2137Z SAT SEP 16 2017 - 12Z SUN SEP 17 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
45 N CWCJ 10 SSE ARV T08 25 S CMY 30 NE IRK 25 ESE PPF
15 ESE SWO 15 S SWO 20 NNW PWA 15 NE AVK 25 SSE SLN 30 NE SLN
15 E BIE 10 SSE SLB 15 SE 8Y2 10 NE HZX 40 N CWDV.


...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. IT IS ANTICIPATED THAT
HEIGHT FALLS SWEEPING THROUGH THE NORTHERN PLAINS AND A TRAILING
TROUGH AXIS BRUSHING ACROSS THE SOUTHERN PLAINS WILL YIELD
ADDITIONAL THUNDERSTORM DEVELOPMENT BACK WEST...ALONG THE SURFACE
FRONT IN OK/KS/MO/IA 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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