Quantitative Precipitation Forecast
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FOUS30 KWBC 292102
QPFERD

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

...VALID 21Z MON SEP 29 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 SW PGD 20 WNW SRQ 35 NW PIE 45 S CTY
35 SSW 40J 40 S TLH 25 SW AAF PAM 20 SSE BGE 20 NE MGR 15 SW HXD
15 ENE SSI 30 SE SGJ 15 E VRB 20 ENE PBI.


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 EACH DAY ACROSS THE PENINSULA.  THIS AREA WAS REFINED
BASED ON RECENT RADAR TRENDS.


NORTHERN HIGH PLAINS
~~~~~~~~~~~~~~~~~~~~
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.


ROTH/HURLEY
$$





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