Quantitative Precipitation Forecast
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000
FOUS30 KWBC 182224
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
624 PM EDT THU MAY 18 2017

...VALID 2224Z THU MAY 18 2017 - 12Z FRI MAY 19 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
35 WNW ITR 40 N LHX 10 W PUB MNH 20 NNW DEN CYS 20 ESE BRX
20 NE TOR 10 WNW AIA 25 ENE SNY 35 SW OGA 35 WNW ITR.

MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 SSE RUE 10 ESE JWY SJT 40 S BPG 15 NNW BPG 50 SSW CDS
35 SE HHF 35 SSW DDC 55 WSW HYS EAR 30 WSW SUX 15 ENE CIN
35 SSW OTM 30 E COU 20 SSW UNO 25 SSE RUE.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 E GCM 10 SW CQB HBR 30 N JWG 15 SSW PTT 25 WSW GBD RSL
25 ENE CNK STJ 15 SSE CDJ 20 ENE DMO 40 W AIZ 20 E JLN 15 E GCM.


...CENTRAL / SOUTHERN GREAT PLAINS...

AN OUTBREAK OF SEVERE THUNDERSTORMS WAS UNDERWAY AS OF 22Z. PLEASE
REFER TO STORM PREDICTION CENTER AND LOCAL WEATHER FORECAST OFFICE
PRODUCTS FOR DETAILS. FLASH FLOODING WILL ACT AS A SECONDARY
THREAT...AT LEAST INITIALLY. CELL MODE WAS DECIDEDLY SUPERCELLULAR
FROM NORTH TEXAS THROUGH WESTERN OKLAHOMA. THE FLOOD RISK THERE
WILL DEPEND ON BRIEF TRAINING OF SUPERCELLS ON LOCAL SCALES
THROUGH THE EVENING HOURS. FARTHER NORTH THE DEEP LAYER FORCING
ASSOCIATED WITH A PRONOUNCED JET STREAK...WILL INTERACT WITH A
LIFTING SURFACE WARM FRONT...TO YIELD VERY WIDESPREAD INITIATION
AND CELL MERGERS...AS WAS ALREADY OCCURRING. WHILE THIS ACTIVITY
WILL ACT UPON STRONG INSTABILITY TO PRODUCE DEEP UPDRAFTS WITH
VERY HEAVY SHORT TERM RAIN RATES...THERE IS EVERY INDICATION FROM
THE MESOSCALE MODELS THAT MERGING AND TRAINING WILL BE RELATIVELY
SHORT-LIVED AT ANY GIVEN LOCATION...AND THAT COMBINED OUTFLOWS AS
WELL AS INCREASINGLY STRONG STEERING FLOW WILL PUSH THE ACTIVITY
TOWARD THE EAST THROUGH 03Z. RAPID ACCUMULATION OF GREATER THAN 2
INCHES OF RAINFALL DURING THAT TIME MAY JUST EXCEED FLASH FLOOD
GUIDANCE IN SOME LOCATIONS.

IF THERE IS A BETTER DEFINED FLASH FLOOD RISK...IT MAY COME
TOGETHER AFTER 02 OR 03Z TONIGHT ACROSS SOUTHERN KANSAS AND
NORTHERN OKLAHOMA. THIS IS WHERE THE NOSE OF THE NOCTURNALLY
ENHANCED LOW LEVEL JET MAY MEET A COMBINED COLD POOL...AND
INCREASED LOW LEVEL FOCUS AS THE SURFACE COLD FRONT STARTS TO MAKE
PROGRESS BEHIND THE INITIAL SHORTWAVE / JET STREAK. THE NAM CONUS
NEST...AND 19Z AND 20Z HRRR POINT TO A POTENTIALLY MORE FOCUSED
HEAVY RAIN EVENT STRADDLING THE OK/KS BORDER FROM ABOUT MEDFORD
AND WELLINGTON EASTWARD.

SOME GUIDANCE ALSO PREDICTS A SWATH OF LOCALLY HEAVY RAINFALL OVER
SOUTHERN AND EASTERN OKLAHOMA AND NORTHWEST ARKANSAS. THIS COULD
OCCUR AS A CONTINUATION OF STORM CLUSTERS MOVING OUT OF WESTERN
NORTH TEXAS...AND AS NEW CELLS ARE POTENTIALLY INITIATED WHEN
DECOUPLING LEADS TO A BOOST IN CONVERGENCE JUST ABOVE THE SURFACE
AT NIGHTFALL. DEEP LAYER SUPPORT WILL BE LESS FAVORABLE ALONG THIS
AXIS...BUT WE DID MAINTAIN SOME CONSERVATIVE QPF AND A MARGINAL
RISK OF EXCESSIVE RAINFALL TO COVER THIS POSSIBILITY.


...CENTRAL HIGH PLAINS / PARTS OF CO/NE/WY...

A MARGINAL RISK AREA WAS MAINTAINED FOR THE RAINFALL COMPONENT TO
THE WRAPPED UP MID LEVEL CYCLONE OVER THE CENTRAL HIGH PLAINS.
SLOW MOVEMENT OF THE CLOSED LOW WILL FOCUS AN AREA OF MODERATE TO
OCCASIONALLY HEAVY RAINFALL...WITH SOME EMBEDDED
CONVECTION...ESPECIALLY THIS EVENING...FROM THE I-25 CORRIDOR IN
COLORADO TOWARD SOUTHEAST WYOMING AND WESTERN NEBRASKA. HI RES
GUIDANCE IS SHOWING HOURLY RATES OF MAINLY 0.25 INCHES OR
LESS...BUT WITH EMBEDDED POTENTIAL FOR 0.50 INCH PER HOUR RATES.
ANY FLASH FLOOD / EXCESSIVE RAINFALL THREAT WILL BE DRIVEN BY
LONGER TERM ACCUMULATIONS ON THE ORDER OF 6 HOURS...ALTHOUGH THE
6-HOUR FLASH FLOOD GUIDANCE VALUES OF 1.00 TO 1.50 INCHES ARE NOT
LIKELY TO BE EXCEEDED AT MORE THAN ISOLATED LOCATIONS.

BURKE/ORAVEC
$$





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