Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 292320
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
719 PM EDT MON SEP 29 2014

...VALID 00Z TUE SEP 30 2014 - 00Z WED OCT 01 2014...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 ENE PBI 30 WNW BCT 20 ENE RSW 15 NW PGD 10 NW PIE 35 WSW CTY
35 SSW 40J 40 S TLH 15 E AAF 15 NE AAF TLH 20 S SSI 30 SE SGJ
15 E VRB 20 ENE PBI.


PORTIONS OF THE CENTRAL AND NORTHERN HIGH PLAINS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
MESOSCALE PRECIPITATION DISCUSSION #401 HAS BEEN ISSUED -- VALID
UNTIL ~03Z -- FOR NORTHEAST CO, WESTERN NE, SOUTHEASTERN-MOST WY,
AND SOUTHWESTERN-MOST SD.  SEE THE MPD FOR MORE INFORMATION ON
SHORT TERM EXCESSIVE RAINFALL CONCERNS IN THIS REGION.

LATER TONIGHT, THE CLOSED MID/UPPER LEVEL LOW CURRENTLY ACROSS THE
GREAT BASIN WILL LIFT E THEN NE INTO THE NORTHERN PLAINS AS
ANOTHER SHORTWAVE TROUGH AND ASSOCIATED UPPER JET STREAK DROPS
INTO THE PAC NW AND NORTHERN INTERMOUNTAIN WEST. THESE TROUGHS
WILL EVENTUALLY PHASE.  THE APPROACHING UPSTREAM JET
AXIS/SHORTWAVE TROUGH WILL CAUSE THE LEAD TROUGH TO TAKE ON A
NEGATIVE TILT UPON LIFTING OUT INTO THE CENTRAL/NORTHERN PLAINS ON
TUESDAY, LEADING TO STRONGER UPPER LEVEL DIFFLUENCE/DIVERGENCE AND
DEEP LAYER Q-VECTOR CONVERGENCE. THE MODELS SHOW THE UPPER
DIVERGENCE MAXIMIZING OVERNIGHT OVER THE WY/NORTHERN CO FOOTHILLS
AND INTO THE NORTHERN HIGH PLAINS.  AT LOW LEVELS...THE PRE-TROUGH
THERMODYNAMIC ENVIRONMENT BECOMES INCREASINGLY FAVORABLE GIVEN THE
INCREASING S-SE LOW-LEVEL AGEOSTROPHIC RESPONSE...THOUGH THE AXIS
OF HIGHEST PWS (ABOVE 1.25 INCHES) ALONG A 40-50 KT LOW LEVEL JET
SHIFTS FARTHER EAST ACROSS THE CENTRAL/NRN PLAINS WHILE BECOMING
MORE DISPLACED WITH THE BEST UVVS/UPPER DIVERGENCE OVER THE
FOOTHILLS AND HIGH PLAINS. AS A RESULT...MODEL PROJECTED MUCAPES
WITHIN THE AXIS OF BEST DYNAMICAL FORCING (AND ANOMALOUS
EASTERLY/UPSLOPE LOW-LEVEL FLOW) ARE GENERALLY BELOW 500
J/KG...THEREFORE THE EXCESSIVE RAINFALL POTENTIAL (SHORT TERM
RAINFALL RATES) WILL BE LIMITED IN THE HIGH PLAINS. AT THE SAME
TIME...THE AFOREMENTIONED ANOMALOUS EASTERLY COMPONENT (NEGATIVE
850 MB U WIND COMPONENT BTWN 4-5 STANDARD DEVIATIONS) ACROSS THE
WY/NORTHERN CO FOOTHILLS AND NORTHERN HIGH PLAINS WILL AGAIN FAVOR
MAXIMUM TERRAIN- ENHANCED RAINFALL TOTALS (AREAL-AVERAGE AMOUNTS
BETWEEN 1-3 INCHES)...EVEN THOUGH THE EXCESSIVE RAINFALL POTENTIAL
WILL BE MITIGATED BY THE LACK (ABSENCE) OF DEEP LAYER INSTABILITY.



NE/IA BORDER
~~~~~~~~~~~~
BROAD/STRONG 850 HPA INFLOW AHEAD OF THE HIGH PLAINS SYSTEM INTO A
FRONTAL BOUNDARY OF 25-40 KTS IS EXPECTED TO LEAD TO ORGANIZED
CONVECTION, WHICH SHOULD BE FORWARD PROPAGATING TOWARDS THE EAST
AT ~30 KTS.  EXPECTED INFLOW SHOULD BE ROUGHLY SIMILAR TO THE MEAN
850-400 HPA WIND, WHICH COULD LEAD TO PRECIPITATION EFFICIENCY
(HOURLY RATES UP TO 1.5" IN STRONGER STORMS).  A NARROW AXIS OF
1000-1500 J/KG CAPES ARE FORECAST NEAR THE NE/IA BORDER, WHICH
WOULD LIKELY BE THE INITIATION POINT FOR CONVECTION BEFORE IT
STREAKS EASTWARD.  THE BREADTH OF THE LOW-LEVEL INFLOW COULD LEAD
TO CELL TRAINING FROM EASTERNMOST NE INTO SOUTHWEST IA AFTER
30/18Z.  SINCE THE PRECIPITABLE WATER VALUES REMAIN <1.50", FELT A
SEE TEXT WOULD SATISFY THE EXPECTED CONCERN.  OUTFLOW BOUNDARIES
FROM THE CONVECTION SHOULD FORCE THE COMPOSITE BOUNDARY SOUTHWARD
TOWARDS KANSAS CITY BY EVENING, WHICH FITS IN NICELY WITH THE AREA
DEPICTED WITHIN THE DAY 2 EXCESSIVE RAINFALL OUTLOOK.


SOUTHEAST
~~~~~~~~~
AREAS OF MODERATE TO HEAVY RAINFALL TO CONTINUE INTO THE EVENING
HOURS OVER THIS REGION AS THE UPPER TROUGH -- CURRENTLY PUSHING
THROUGH THE TN VALLEY -- CONTINUES TO PRESS EASTWARD.  ANOTHER 3-6
HOURS OF FAVORABLE DYNAMICAL SUPPORT (UPPER LEVEL DIVERGENCE AND
MORE FOCUSED SOUTHERLY LOW-LEVEL MOISTURE CONVERGENCE) AHEAD OF
THE SHORTWAVE TROUGH WILL MAINTAIN THE WIDESPREAD WARM-TOPPED
CONVECTION...WHILE THE BACK EDGE OF THE HEAVIER RAINFALL GRADUALLY
PUSHES EAST. MAXIMUM OBSERVED RAINFALL REPORTS (2-4+ INCHES)
REMAIN HIGHER THAN THE RADAR ESTIMATES...INDICATIVE OF THE
EFFICIENT WARM RAIN PROCESSES WITH THE DEEP WARM CLOUD LAYER (WET
BULB ZERO HEIGHTS ~14000 FT OR HIGHER) AND HIGH PWS (~2.25" PER
THE 12Z KCHS UPPER AIR SOUNDING AND THE LATEST GPS DATA). CONTINUE
TO EXPECT THE WIDESPREAD CLOUD COVER/LACK OF DIFFERENTIAL HEATING
AND WEAK/MOIST ADIABATIC LAPSE RATES ALOFT TO LIMIT THE RAINFALL
RATES IN AREAS FARTHER NORTH OF THE WARM/STATIONARY
FRONT...HOWEVER HIGHER MUCAPES (~1000 J/KG) ALONG AND SOUTH OF THE
SFC FRONTAL BNDRY CURRENTLY ACROSS NRN FL (NEAR THE SE GA BORDER)
WILL ENHANCE THE EXCESSIVE RAINFALL POTENTIAL ACROSS SE GA/NRN
FL...WHILE ALSO INTO EASTERN PORTIONS OF THE FL PENINSULA GIVEN
THE ENHANCED MOISTURE CONVERGENCE TOWARDS THE EAST COAST WHICH
SHOULD BE FAVORED RAINFALL MAGNITUDE-WISE EACH AFTERNOON/EVENING
DUE TO THE SOUTHWESTERLY LOW-LEVEL WIND FLOW. PER THE HIGH RES
GUIDANCE...ADDITIONAL LOCALIZED AMOUNTS OF 3-4+ INCHES ARE
EXPECTED TUESDAY ACROSS THE PENINSULA.  THIS AREA WAS REFINED
BASED ON RECENT RADAR TRENDS.

ROTH/HURLEY
$$





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