Quantitative Precipitation Forecast
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FOUS30 KWBC 051858
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 PM EDT TUE MAY 05 2015

...VALID 18Z TUE MAY 05 2015 - 00Z THU MAY 07 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 WSW RPH 10 SSE CSM 15 WSW HUT 30 SSW EMP 10 ESE GCM
45 SE MLC 15 W 3T1 25 ESE ACT 15 NW 05F 20 WSW RPH.



...PORTIONS OF THE SOUTHERN AND CENTRAL PLAINS...

MAINTAINED A BROAD SLIGHT RISK AREA IN PARTS OF NORTHERN TX ACROSS
THE RED RIVER INTO EASTERN OK AND A SMALL PORTION OF SOUTHEAST
KS...MAINLY FOR THE EXPECTED NOCTURNAL CONVECTION AND HEAVY
RAINFALL THREAT OVERNIGHT MON INTO EARLY TUE. THE HIGHLY AMPLIFIED
TROUGH-RIDGE SETUP WILL ONCE AGAIN SET THE STAGE FOR STRONG UPPER
LEVEL DIFFLUENCE/DIVERGENCE DOWNSTREAM OF THE TROUGH
AXIS...COUPLED WITH THE ENHANCED (ANOMALOUS) LOW LEVEL MOISTURE
TRANSPORT AND S-N ADVECTION OF HIGHER PW VALUES (WHICH WILL TAP
THE SUBTROPICAL JET STREAM). 850 MB MOISTURE FLUX ANOMALIES ARE
EXPECTED TO CLIMB TO NEAR 3 STANDARD DEVIATIONS ABOVE NORMAL ALONG
THE AXIS OF A 50KT 850 MB LLJ... WHILE PW VALUES CLIMB BETWEEN 1.5
AND 1.75 INCHES. THE JUXTAPOSITION OF FAVORABLE DYNAMICAL FORCING
AND THERMODYNAMIC PROFILES SUPPORT A CONTINUATION OF THE EXCESSIVE
RAINFALL THREAT FROM THE PREVIOUS FORECAST...HOWEVER...A SLIGHT
RISK WAS MAINTAINED GIVEN THE CONTINUED N-S SPREAD WITH THE
HEAVIER QPF AMONG THE MODELS (INCLUDING THE HIGH-RES). THIS IS
SOMEWHAT COMMON AMONG MADDOX SYNOPTIC TYPE EVENTS...ESPECIALLY
INTO LATE SPRING WHERE DEEP LAYER INSTABILITY WILL OFTEN CONFINE
THE HEAVIER RAINFALL ON THE SOUTHERN EDGE OF THE GUIDANCE SPREAD.
THE WILD CARD HERE WILL BE THE DEGREE OF DEEP-LAYER
INSTABILITY...AS THE SLOWLY-DECAYING MCS DEBRIS FROM OVERNIGHT
ALONG WITH THE EXTENSIVE SYNOPTICALLY-DRIVEN CLOUD COVER AHEAD OF
THE TROUGH HAS THUS FAR LIMITED THE AIRMASS RECOVERY AND THUS
SURFACE-BASED INSTABILITY. REGARDLESS...THE SIGNAL IS CERTAINLY
THERE FOR EXCESSIVE RAINFALL POTENTIAL OVERNIGHT... AS MUCAPES
CLIMB BETWEEN 1000-2000 J/KG WITH THE INCREASING LLJ. IN
ADDITION...AS THE S-SSW LLJ STRENGTHENS TO ~50 KTS...THE
ORIENTATION AND SPEED RELATIVE TO THE MEAN WIND WILL CAUSE
CONSIDERABLE UPWIND PROPAGATION AND AS A RESULT A LARGE N-S
COMPONENT TO THE CORFIDI VECTORS. AS A RESULT...TRAINING OF CELLS
WILL BECOME LIKELY AFTER 00Z.


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

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. LIGHT UPSLOPE FLOW SHOULD PERSIST THIS AFTERNOON NEAR AND
NORTH OF THE PALMER DIVIDE...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 LATE THIS AFTERNOON INTO
EARLY EVENING...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 FOCUS
THERE...AND WITH LARGELY MERIDIONAL FLOW...SOME TRAINING OF CELLS
FROM SOUTH TO NORTH COULD PRODUCE A FLASH FLOOD RISK.


...SOUTHWEST SD/NORTHEAST WY...

UPSLOPE WILL DEVELOP INTO SW SD INTO NORTHEAST WY. 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...SOME OF WHICH MAY PRODUCE LOCALIZED SHORT TERM RUNOFF
ISSUES.

HURLEY
$$





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