Quantitative Precipitation Forecast
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000
FOUS30 KWBC 051023
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
623 AM EDT TUE MAY 05 2015

...VALID 12Z TUE MAY 05 2015 - 12Z WED MAY 06 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 NNE AQR 10 E GYI NFW 20 SSE 7F9 25 NNE JCT 50 NNE 6R6
10 W INK 35 ESE CNM 35 WSW HOB 40 N HOB 35 ESE CVN 50 WSW AMA
30 W DHT 40 W CAO 15 SSW VTP 20 NNE ALS 25 ENE MYP 30 SE CCU
25 ENE CCU 30 E 20V 30 ENE 20V 40 SW PUM 30 W PUM 10 N VDW
20 W IBM 35 WNW OGA 15 ESE OGA 35 SW MCK 50 N GCK 20 SSE DDC
30 NNE WWR 25 SSE AVK 20 ENE WDG 25 ESE PNC 20 SSW BVO 10 NE OKM
20 NNE AQR.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 WSW LBB 40 E LBB 65 S CDS 35 NNW DYS 30 SW SWW 15 NNW ODO
25 S HOB 20 NE HOB 15 WSW LBB.


...WEST TX / OK / ADJACENT PORTIONS OF NM/CO/KS...

A PRONOUNCED THREAT OF ADDITIONAL FLASH FLOODING WILL CONTINUE
THROUGH AT LEAST 15Z...IN A FOCUSED AREA OF WEST TEXAS AND FAR SE
NM TO THE NORTH OF MIDLAND. THIS IS WHERE AN OUTFLOW BOUNDARY HAD
SET UP ORTHOGONAL TO A LOW LEVEL JET OF AT LEAST 35 TO 45 KNOTS.
CELLS WERE RELUCTANT TO PROPAGATE DOWNSTREAM AS THE INSTABILITY
AXIS WAS QUITE NARROW...BUT A VERY PERSISTENT UPPER DIFLUENCE
PATTERN AND DEEP LAYER LIFT WILL SUPPORT REGENERATION OF CELLS ON
THE WESTERN FLANK. PER RAP AND HRRR FORECASTS...THE CONVECTION
THAT WAS GROWING UPSCALE IN SE NM AT 10Z SHOULD REPRESENT THE LAST
BATCH OF PRECIPITATION TO RAKE THIS AREA BEFORE A MID LEVEL
SHORTWAVE TROUGH AXIS FINALLY MOVES THROUGH...BUT NOT BEFORE AN
ADDITIONAL 1-2 INCHES OF RAIN ADDS TO TOTALS THAT WERE IN SOME
CASES 7-PLUS INCHES OVERNIGHT. SEE MESOSCALE PRECIPITATION
DISCUSSION NUMBER 0054 FOR DETAILS.

ELSEWHERE...WE MAINTAINED A BROAD SLIGHT RISK AREA IN PARTS OF
CO/KS/OK/TX/NM TO ENCOMPASS SUSTAINED SOUTHERLY LOW LEVEL FLOW AND
LARGE SCALE UPPER LEVEL FORCING WHICH SLIDES THROUGH THE SOUTHERN
PLAINS IN THE NEXT 24-30 HOURS. WHILE THIS KEEPS CONTINUITY FROM
PREVIOUS FORECASTS AND COVERS THE MODEL CONSENSUS FOR MODERATE TO
HEAVY PRECIPITATION...CONFIDENCE IN ANY SPECIFIC FLASH FLOOD EVENT
IS LOWER THAT IT WAS FOR THE WEST TEXAS EVENT. HEIGHT FALLS WILL
BE MAXIMIZED FARTHER NORTH TOWARD KS/NE...BUT GREATER MOISTURE
DEPTH IS EXPECTED ALONG THE TAIL END OF THOSE HEIGHT
FALLS...SUPPORTING A HEAVY RAIN ENVIRONMENT OVER PRIMARILY OK/TX
DURING THE AFTERNOON AND TUESDAY NIGHT. THE QPF DETAILS APPEARED
BETTER HANDLED BY THE 00Z WRF-ARW AND GEM REGIONAL...AS WELL AS
THE GFS AND 12Z ECMWF. THE MODEL SIGNAL IS NOT PARTICULARLY
HEAVY...BUT WITH STRONGLY MERIDIONAL FLOW AND PW VALUES RISING TO
AROUND 1.5 INCHES WITHIN A PLUME EXTENDING NORTHWARD FROM THE SE
TX COAST...THERE IS POTENTIAL FOR TRAINING CELLS TO PRODUCE MORE
THAN 2 INCHES IN AN HOUR LOCALLY. THE FLASH FLOOD GUIDANCE VALUES
OF ROUGHLY 2.0 TO 2.5 INCHES IN 1 HOUR OR 2.50 - 3.0 INCHES IN 3
HOURS COULD BE EXCEEDED...ESPECIALLY OVER THE FAR EASTERN TX/OK
PANHANDLES INTO WRN OK...AND DEVELOPING FROM NORTH TX INTO
SOUTHERN AND CENTRAL OK WHERE A READY SUPPLY OF RICH MOISTURE AND
MODERATE INSTABILITY MAY BE MORE SUSTAINABLE.


...EASTERN CO / WESTERN KS / FAR SW NE...

UPSLOPE INTO THE HIGHLANDS OF FAR NORTHEAST NM AND SOUTHERN CO
WILL BE LIMITED TO THE EARLY MORNING HOURS DURING THE DIURNAL
MINIMUM OF INSTABILITY. STILL...INCREASING MID/UPPER
LIFT...WORKING WITH PW VALUES OF 0.75 INCHES TO NEAR 1.0
INCH...WILL PROMOTE WIDESPREAD RAINFALL TO FURTHER SATURATE THE
GROUND ABOVE WHAT CONVECTION HAD ACCOMPLISHED MONDAY NIGHT. DURING
THE AFTERNOON...LIGHT UPSLOPE FLOW SHOULD PERSIST NEAR AND NORTH
OF THE PALMER DIVIDE AT LEAST DURING THE 18-21Z PERIOD...WHILE
MIGRATION OF THE SYNOPTIC TROUGH THROUGH THIS REGION WILL
GRADUALLY ENCOURAGE VEERING OF LOW LEVEL FLOW...WITH A SURFACE
TROUGH AXIS MIGRATING OUT TOWARD KANSAS AND FAR NORTHEAST CO BY
00Z. WHILE THE STRENGTH AND PERSISTENCE OF THE UPSLOPE IS NOT
IDEAL FOR HEAVY RAIN...OTHER FACTORS...SUCH AS ANTECEDENT
RAINFALL...PW VALUES OF 0.75 INCHES ALL THE WAY WEST OF I-25...AND
PASSAGE OF THE COLDEST MID LEVEL TEMPERATURES THROUGH CENTRAL
COLORADO THIS AFTERNOON...SUGGEST A RISK OF FLASH FLOODING. AS
NOTED BY THE NWS BOULDER FORECAST OFFICE...THE PREDICTED PW VALUES
WOULD BE A RECORD FOR THE DATE.

THOUGH ANTECEDENT CONDITIONS ARE NOT AS RIPE ON THE EASTERN PLAINS
AND OVER ADJACENT KS/NE...LOW LEVEL MOISTURE TRANSPORT WILL FOCS
THERE...AND WITH LARGELY MERIDIONAL FLOW...SOME TRAINING OF CELLS
FROM SOUTH TO NORTH COULD PRODUCE A FLASH FLOOD RISK.


...WESTERN NE / SOUTHWEST SD...

UPSLOPE WILL DEVELOP INTO WESTERN NE AND SW SD / THE BLACK HILLS.
PW VALUES DO BECOME ANOMALOUSLY HIGH AT THIS LONGITUDE AS THE 0.75
INCH VALUES COME CLOSE TO RAPID CITY BY TUESDAY EVENING. THIS
WOULD BE OF GREATER CONCERN EXCEPT THAT THE MODEL QPFS ARE QUITE
TAME FOR NOW...LIKELY OWING TO WEAK INSTABILITY. STILL...A HEAVY
RAIN THREAT COULD DEVELOP SHOULD HEATING AND DEEP LAYER LIFT PROVE
SUFFICIENT TO BOOST INSTABILITY AND SUPPORT HEAVIER CONVECTIVE
RAIN RATES. WILL WATCH THE MODEL CAPE AND QPF TRENDS FOR A
STRONGER SIGNAL...AND POSSIBLE INTRODUCTION OF A SLIGHT RISK OF
EXCESSIVE RAINFALL OVER THIS REGION.

BURKE
$$




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