Quantitative Precipitation Forecast
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FOUS30 KWBC 201225
QPFERD

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

...VALID 12Z 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 105 S E38 50 SSW MRF 50 S GDP 30 SE SRR
45 WSW CVS 40 ENE CVN 45 NE PVW 25 SW F05 30 NE ABI 15 SSW 6R9
25 S 3T5 15 SW LBX 20 ENE KBQX 10 N KMZG KOPM 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 ALREADY 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 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 AT 12Z 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.

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 TO LEAD TO LESS-ORGANIZED,
PULSE-TYPE 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 VLY.


FLORIDA/SOUTHEAST COAST
~~~~~~~~~~~~~~~~~~~~~~~
A BROAD UPPER LEVEL TROUGH WITH 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, UNCERTAINLY IS
SOMEWHAT HIGHER, SO HAVE INCLUDED THIS AREA WITHIN A SEE TEXT
REGION.

ROTH/HURLEY
$$




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.