Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 220735
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
335 AM EDT FRI SEP 22 2017

...VALID 12Z FRI SEP 22 2017 - 12Z SAT SEP 23 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 E SGU 45 W SGU 45 SSE ELY 15 E ENV 45 W OGD 15 E HIF
25 WNW PUC 45 W 4HV 40 SW BCE 30 E SGU.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 E BJI BFW ARV 10 W RRL 30 ENE EAU 10 WSW OEO 15 WSW DXX
35 SSW ABR 30 SW FAR 20 E BJI.


...CENTRAL PLAINS / SOUTHERN HIGH PLAINS / SOUTHWEST TEXAS...

WE INTRODUCED A SLIGHT RISK OF EXCESSIVE RAINFALL OVER THE
SOUTHERN HIGH PLAINS...ESPECIALLY EASTERN NEW MEXICO AND SOUTHWEST
TEXAS.

PEAK HEATING ALONG A SSW-NNE ORIENTED FRONT AND TROUGH...COMBINED
WITH STRENGTHENING LOW LEVEL INFLOW...SHOULD PROMOTE THUNDERSTORMS
IN NEBRASKA AND FROM CO/KS DOWN THROUGH EASTERN NEW MEXICO. DEEP
LAYER FLOW FROM THE SOUTH-SOUTHWEST WILL FAVOR TRAINING...AS WILL
FRONTOGENESIS / BANDED FORCING NEAR THE FRONT AND IN THE IMMEDIATE
POST-FRONTAL ENVIRONMENT / ESPECIALLY NEBRASKA.

THE ACTIVITY IN NEW MEXICO...HOWEVER...COULD BE PARTICULARLY
HEALTHY AND LONGER LIVED INTO THE NIGHTTIME HOURS...AS A
PRONOUNCED SHORTWAVE TROUGH ROUNDS THE BASE OF THE LARGE WESTERN
U.S. TROUGH...PUSHING THROUGH ARIZONA...AND ENHANCING THE DEEP
LAYER ASCENT OVER NEW MEXICO. AT THE SAME TIME...PER 500-200 MB
RELATIVE HUMIDITY FIELDS FROM THE GFS...THIS VERY DEEP WESTERN
U.S. TROUGH MAY BEGIN TO TAP INTO MID AND HIGH LEVEL MOISTURE
EMANATING FROM A TROPICAL WAVE ALONG THE WEST COAST OF MEXICO.
THIS INFLUX OF HIGH LEVEL MOISTURE SHOULD BOOST PRECIPITABLE WATER
VALUES AND MAKE FOR A MORE EFFICIENT RAINFALL PROCESS. THE PATTERN
ALSO FEATURES A STRONG MERIDIONAL COMPONENT TO THE DEEP LAYER
FLOW...WHICH COULD ALLOW FOR TRAINING FROM SOUTH TO NORTH...AND A
RISK OF FLASH FLOODING OVER SOUTHWEST TEXAS...EASTERN NEW MEXICO
AND ADJACENT CO/KS/OK FRIDAY NIGHT. NOTE THAT A COUPLE OF HI-RES
MODELS...WRF-ARW AND NSSL WRF...PRODUCE SPOTTY 4-INCH TOTALS IN
NEW MEXICO DURING DAY 1.


...UPPER MIDWEST...

EARLY FRIDAY MORNING THUNDERSTORMS WERE BREAKING OUT IN A WARM
ADVECTION REGIME ACROSS CENTRAL MINNESOTA / SURFACE WARM
FRONT...NORTHERN MINNESOTA / ELEVATED WARM FRONT...AND NORTHEAST
SOUTH DAKOTA / NOSE OF THE PLAINS LOW LEVEL JET. MODELS ARE IN
AGREEMENT...EXPECTING AN MCS TO RIDE NEAR AND NORTH OF THE SURFACE
WARM FRONT THROUGH MIDDAY...CROSSING CENTRAL MN INTO NORTHERN
WISCONSIN. OTHER CLUSTERS OF STORMS WILL OCCUR FARTHER NORTH IN A
MORE ELEVATED FASHION. THE MCS COULD STRUGGLE TO BE MAINTAINED BY
AFTERNOON AS LARGE SCALE FORCING
FAVORS RE-ORGANIZATION BACK TO THE WEST. A FRONTAL WAVE OF LOW
AMPLITUDE BUT OCCURRING BENEATH ENERGETIC UPPER FLOW...IS EXPECTED
TO FORM ACROSS THE CENTRAL PLAINS AND LIFT NORTHEASTWARD. THIS
SHOULD PROMOTE ELEVATED CONVECTION IN THE ZONE OF 850-600 MB LIFT
ACROSS EASTERN SOUTH DAKOTA INTO MUCH OF NORTH DAKOTA AND WESTERN
MINNESOTA. A FEW SURFACE-BASED / WARM-SECTOR STORMS ARE ALSO
POSSIBLE. WHEREVER CLUSTERS OF STORMS FORM NEAR THE WARM
SECTOR...OR ALONG OUTFLOWS AND THE WARM FRONT...PERIODS OF
TRAINING COULD BOOST RAINFALL TOTALS TOWARD EXCESSIVE VALUES.
OVERALL...THE EVENTS MAY BE DISPERSED ACROSS A BROAD AREA...AND
WITH LITTLE PERSISTENT FOCUS IN THE MODELS...WE WILL MAINTAIN ONLY
MARGINAL RISK PROBABILITIES.

BURKE
$$




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