Quantitative Precipitation Forecast
Issued by NWS

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000
FOUS30 KWBC 201341
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
937 AM EDT SAT SEP 20 2014

...VALID 15Z SAT SEP 20 2014 - 12Z SUN SEP 21 2014...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 SW DRT 35 S 6R6 100 SW 6R6 60 SW MRF 50 S GDP 20 SW ROW
45 WSW CVS 35 NW PVW 30 W CDS 25 SW F05 30 NE ABI 15 SSW 6R9
25 S 3T5 15 SW LBX 25 N KBQX 15 SE 2R8 20 ENE PIL 20 E BRO
30 SSE MMRX 30 SSW MMNL 55 SSE MMPG 25 SW DRT.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 ESE AWH 40 SSE ENV 20 WNW CDC 45 WSW SGU 25 NE DRA 25 SE TPH
60 E NFL 25 WNW B23 40 SW AWH 25 ESE AWH.


NV/WESTERN UT
~~~~~~~~~~~~~
MOISTURE RETURNS TODAY AHEAD OF AN UPPER-LEVEL LOW EDGING INTO THE
REGION, WHICH HAS LED TO WIDELY SCATTERED SHOWERS AND
THUNDERSTORMS ACROSS SOUTH-CENTRAL NV EARLY THIS MORNING.
PRECIPITABLE WATER VALUES (PWS) RISE INTO THE 0.75-1" RANGE, WHILE
SEEMINGLY LOW, LIE CLOSE TO THE 90TH PERCENTILE FOR MID- TO
LATE-SEPTEMBER.  HOURLY RAINFALL RATES UP TO 1" ARE POSSIBLE WITH
THIS MOISTURE SUPPLY.  INSTABILITY/CAPE VALUES ARE BOUND TO RISE
TO 1000-2000 J/KG THIS AFTERNOON AND EVENING DUE TO MOSTLY SUNNY
SKIES TODAY.  THE RAP/NAM GUIDANCE SHOW A 850/700 HPA CIRCULATION
MOVING INTO CENTRAL NV WITH TIME, WHICH INCREASES THE MAGNITUDE OF
THE 700 HPA INFLOW INTO NORTHEAST NV AND WESTERN UT -- UP TO 25
KTS PER THE 06Z NAM.  THIS DEGREE OF INFLOW COULD ORGANIZE ANY
CONVECTION THAT FORMS ACROSS THE REGION.  THE MODEL GUIDANCE --
INCLUDING THE 00Z GEFS-BASED AND CLIMATOLOGY-BASED QPF REFORECAST
-- SUGGEST THAT AREAL AVERAGE AMOUNTS OF AN INCH ARE POSSIBLE,
WHICH IMPLIES LOCALLY HIGHER AMOUNTS CLOSER TO 2" WHERE CELLS
MERGE AND/OR TRAIN.  CONSIDERING THE BUCKLED TOPOGRAPHY AND
POTENTIALLY HARD SOILS ACROSS THIS ARID REGION, THIS DEGREE OF
RAINFALL COULD CAUSE FLASH FLOODING/DEBRIS FLOWS.  RECENT
COORDINATION WITH SAB/NESDIS HAS REINFORCED THE IDEA OF FLASH
FLOOD POSSIBILITIES IN THIS REGION.  INTRODUCED A SLIGHT RISK OF
EXCESSIVE RAINFALL HERE.


CENTRAL IL
~~~~~~~~~~
LATE THIS AFTERNOON AND EARLY THIS EVENING, THERE IS A BRIEF
WINDOW WHEN THE LOW-LEVEL INFLOW (WHICH IS SUFFICIENT FOR THE WET
MULTICELL ENVIRONMENT) CONSPIRES WITH A SLOWING SURFACE FRONT AND
INCREASED INSTABILITY DUE TO DAYTIME HEATING TO ELEVATE FLASH
FLOOD CONCERNS.  HOWEVER, SOME DRY AIR IN THE LOW-LEVELS SEEN IN
REGIONAL SOUNDINGS SHOULD ALLOW THE CONVECTION TO REMAIN FORWARD
PROPAGATING, TO THE EAST-SOUTHEAST AT 20+ KTS PER THE 06Z GFS.  IF
CONVECTION GETS TOO FAR REMOVED FROM THE FRONTAL BOUNDARY, A NEW
LINE OF STORMS ALONG THE FRONT ITSELF COULD LEAD TO A SECOND
CONVECTIVE ROUND, INCREASING THE RISK OF FLASH FLOODING.  FFGS ARE
RELATIVELY LOW IN THIS REGION, SO INTRODUCED A SEE TEXT AREA IN
THIS REGION FOR THE POSSIBILITY OF REPEATING CONVECTION AS A
COURSE OF LEAST REGRET.


SOUTHEAST NEW MEXICO INTO WESTERN/CENTRAL/SOUTHERN TEXAS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
ODILE`S REMNANT CIRCULATION HAS WEAKENED AT THE LOW- AND
MID-LEVELS, BUT ITS MOISTURE CONTRIBUTION REMAINS.  THE OVERALL
PATTERN AND THERMODYNAMIC SETUP REMAINS IN PLACE ACROSS THE AREA
TO FAVOR ADDITIONAL CONVECTIVE FORMATION THIS PERIOD WITH AREAS OF
HEAVY AND POTENTIALLY EXCESSIVE RAINFALL. CONTINUED SOUTHEASTERLY
LOW-LEVEL FLOW WILL MAINTAIN FAVORABLE MOISTURE TRANSPORT FROM THE
WESTERN GULF WHICH WEAKENS DURING THE DAY AND INCREASES
OVERNIGHT...WITH THE AREA ALIGNED ALONG THE AXIS OF MAXIMUM PWS
RANGING FROM ~1.5" IN SERN NM TO NEAR 2.5" IN SOUTHEAST TX.  THESE
PWS ARE 2-2.5 SIGMAS ABOVE THE MEAN FOR MID- TO LATE-SEPTEMBER.
THIS DEGREE OF MOISTURE SUPPORTS HOURLY RAIN RATES AS HIGH AS 2"
ACROSS NM AND 3" ACROSS SOUTHEAST TX.  FOR SHORT TERM CONCERNS
ACROSS THE TX BIG COUNTRY, MPD #0393 IS UNDER PRODUCTION AND
SHOULD BE ISSUED BY 14Z, WHICH IS PLANNED TO BE VALID FOR A FEW
HOURS.

THE OVERNIGHT INCREASE IN INFLOW IS LIKELY TO AID MULTI-CELLULAR
ORGANIZATION AND SLOW PROPAGATION INTO THE LOW-LEVEL INFLOW
(INCREASED THREAT FOR CELL TRAINING) DURING THESE TIMES.  USING
LAST NIGHT/THIS MORNING AS A PROXY, THIS SORT OF DEVELOPMENT IS
EXPECTED TO BE FAIRLY LOCALIZED, SO ELIMINATED THE MODERATE RISK
FROM THIS REGION DUE TO THIS EXPECTATION.  DEEPER INSTABILITY AND
HIGHER CAPE VALUES DURING THE DAY LEAD TO LESS-ORGANIZED,
PULSE-TYPE THUNDERSTORM ACTIVITY WITH MORE PROGRESSIVE OUTFLOW
BOUNDARIES.  WHILE THE GUIDANCE GRADUALLY WEAKEN ODILE`S REMNANTS
CIRCULATION NEAR THE SERN NM/WRN TX BORDER...BROAD UPPER-LEVEL
DIFFLUENCE WILL REMAIN IN PLACE IN BETWEEN THE CLOSED UPPER HIGH
OVER NW MEXICO AND THE FASTER WESTERLIES/HEIGHT FALLS MOVING INTO
THE MID-MS VALLEY.


FLORIDA/SOUTHEAST COAST
~~~~~~~~~~~~~~~~~~~~~~~
A BROAD UPPER LEVEL TROUGH WITH CONVECTIVE FRONTAL WAVES -- A
WEAKENING ONE IN THE EASTERN GULF OF MEXICO AND A STRENGTHENING
COASTAL LOW OFFSHORE NORTHEAST FL/GA -- WILL FOCUS 25-35 KTS OF
LOW-LEVEL INFLOW ACROSS CENTRAL FL AND CLOSE TO THE COASTLINE OF
THE SOUTHEAST US FROM THE GA COAST NORTHEAST THROUGH THE COAST OF
THE CAROLINAS.  PWS OF 2" ALONG WITH EXPECTED BOUNDARY LAYER
MOISTURE CONVERGENCE IN BOTH REGIONS COULD FOCUS WET MULTICELLS
WITH HIGH HOURLY RAIN RATES OF UP TO 2.5", GIVEN ENOUGH
INSTABILITY IS PRESENT.  LOCALIZED AMOUNTS OF 3-5" WILL BE
POSSIBLE. GIVEN THE ANTECEDENT HIGH FFG VALUES ACROSS FL, ANY
SHORT-TERM RUNOFF ISSUES ARE LIKELY TO BE ISOLATED AT MOST.  WHILE
FFGS ARE LOWER ALONG THE COAST OF GA AND SC THE BEST POTENTIAL FOR
HEAVIER RAINFALL APPEARS TO BE ACROSS EASTERNMOST NC. UNCERTAINLY
IS SOMEWHAT HIGHER THAN USUAL, SO HAVE INCLUDED THIS AREA WITHIN A
SEE TEXT REGION RATHER THAN A SLIGHT RISK.

ROTH/HURLEY
$$




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