Quantitative Precipitation Forecast
Issued by NWS

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
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 201850
QPFERD

EXCESSIVE RAINFALL DISCUSSION...CORRECTION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
249 PM EDT SAT SEP 20 2014

...VALID 18Z SAT SEP 20 2014 - 00Z MON SEP 22 2014...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
45 SW CDS 10 S DYS 10 ENE E29 35 S 6R6 100 SW 6R6 65 S MRF
50 SE MMCS HMN 15 WSW 4CR 50 WNW CVS 40 NW PVW 45 SW CDS.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 NW 9BB 30 SW DPG 15 N CDC 45 WSW SGU 30 NE DRA 20 WSW TPH
NFL 40 WSW WMC 35 NE WMC 20 NW 9BB.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 SSE PKV 20 SSE NGP 25 ESE BRO 10 SW MMMA 50 W MFE
10 ESE MMNL 55 NNW ALI 25 SSE PKV.


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 AND EASTERNMOST CA SO FAR
TODAY.  PRECIPITABLE WATER VALUES (PWS) RISE INTO THE 0.75-1"
RANGE, WHILE SEEMINGLY LOW, ARE FOUR SIGMAS ABOVE AVERAGE AND LIE
CLOSE TO RECORD VALUES 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 WHERE CELLS MERGE AND/OR TRAIN.  THE 12Z
NAM CONEST IS ADVERTISING AMOUNTS PREVIOUSLY UNSEEN WITHIN THE
MESOSCALE QPF OUTPUT DURING THE WARM SEASON ACROSS CENTRAL NV AND
THE SIERRA NEVADA -- WITH LOCAL AMOUNTS OF 4" INDICATED IN BOTH
AREAS.  LOCAL AMOUNTS OF 2-4" ARE CONSIDERED POSSIBLE HERE.  THE
BUCKLED TOPOGRAPHY AND POTENTIALLY HARD SOILS ACROSS THIS ARID
REGION COMBINED WITH THE EXPECTED RAINFALL COULD CAUSE FLASH
FLOODING/DEBRIS FLOWS.  COORDINATION WITH SAB/NESDIS REINFORCES
THE IDEA OF FLASH FLOOD POSSIBILITIES IN THIS REGION.  THE SLIGHT
RISK OF EXCESSIVE RAINFALL REMAINS.


CENTRAL IL
~~~~~~~~~~
LATER 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 12Z SOUNDINGS SHOULD ALLOW THE CONVECTION TO REMAIN
FORWARD PROPAGATING, TO THE EAST-SOUTHEAST AT 20+ KTS PER THE 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.  THERE IS
A WEAK SIGNAL WITHIN THE MESOSCALE GUIDANCE FOR LOCAL 2-4" RAINS
BETWEEN NORTHERN MO AND CENTRAL IN INTO THIS EVENING.  FFGS ARE
RELATIVELY LOW IN THIS REGION, SO MAINTAINED A SEE TEXT AREA IN
THIS REGION FOR THE POSSIBILITY OF REPEATING CONVECTION AS A
COURSE OF LEAST REGRET.


SOUTHEAST NEW MEXICO & TEXAS
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
ODILE`S REMNANT CIRCULATION PERSISTS AT THE LOW- AND MID-LEVELS --
CURRENTLY ENTERING NORTHWEST TX.  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 SOUTHERN 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 SOUTHERN 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
NOT EXPECTED TO BE WIDESPREAD, SO ELIMINATED THE MODERATE RISK
FROM THIS REGION DUE TO THIS EXPECTATION.  DEEPER INSTABILITY AND
HIGHER CAPE VALUES DURING THE AFTERNOON AND EVENING LEAD TO
LESS-ORGANIZED, PULSE-TYPE THUNDERSTORM ACTIVITY WITH MORE
PROGRESSIVE OUTFLOW BOUNDARIES.  WHILE THE GUIDANCE GRADUALLY
WEAKEN ODILE`S REMNANT CIRCULATION, 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.  THERE REMAIN SIGNALS IN THE MESOSCALE GUIDANCE FOR
TWO AREAS OF POTENTIAL EXCESSIVE RAINFALL -- SOUTHEAST NM INTO
WESTERN TX, AND DOWN ACROSS SOUTHERN TX.  SPLIT THE SLIGHT RISK
INTO TWO PIECES BECAUSE OF THIS SIGNAL.


SOUTHERN FL/SOUTHEAST COAST
~~~~~~~~~~~~~~~~~~~~~~~~~~~
A BROAD UPPER LEVEL TROUGH WITH CONVECTIVE FRONTAL WAVES --
INCLUDING A STRENGTHENING AND INCREASINGLY DOMINANT COASTAL LOW
WELL OFFSHORE NORTHEAST FL/GA -- WILL FOCUS 25-35 KTS OF LOW-LEVEL
INFLOW NEAR SOUTH-CENTRAL FL TODAY 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, STRONGEST IN NC, 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.  THE
BEST SIGNAL WITHIN THE GUIDANCE FOR HEAVY RAINFALL IS THE NC
COAST.  CONSIDERING THE UNCERTAINLY REGARDING QPF AMOUNTS IS
HIGHER THAN USUAL IN GA/SC/NC, SO HAVE INCLUDED THESE AREA WITHIN
A SEE TEXT REGION RATHER THAN A SLIGHT RISK.

ROTH
$$





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