Quantitative Precipitation Forecast
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FOUS30 KWBC 021410
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1009 AM EDT THU JUL 02 2015

...VALID 15Z THU JUL 02 2015 - 12Z FRI JUL 03 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
70 NW LOL 15 NNE LOL 35 W P68 65 S ELY 40 NW SGU 35 SW SGU
30 ENE LSV VGT 15 WSW DRA 55 W DRA 60 N IYK 40 NNW IYK 30 NE PTV
35 NNE MAE 35 NE MOD 10 ENE BAB 35 NE CIC 50 ENE RDD 40 SSW AAT
40 S AAT 70 NW LOL.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 ESE FLP 45 SSE PAH 10 SSW GLW 35 SSE 1A6 20 N GRD 10 E AHN
25 E ANB 35 SSW 1M4 35 SE SGT 25 SE MLC 10 NNE CHK END
10 SSE GCM 15 ESE FLP.


...MARYLAND / DELAWARE / NEW JERSEY...

IN THE NEAR TERM A LOW AMPLITUDE SHORTWAVE APPROACHING THE MID
ATLANTIC COAST WILL PRODUCE DEEP CONVECTION WHERE LOW LEVEL WARM
ADVECTION COINCIDES WITH WEAKLY DEFINED MID LEVEL FRONTOGENESIS.
STRONG THUNDERSTORMS OVER SOUTHERN MD AND DE SHOWED SOME POTENTIAL
FOR TRAINING...AND WITH PW VALUES ABOVE 1.85 INCHES PER RAP
SOUNDINGS INSTANTANEOUS RAIN RATES WILL BE QUITE HEAVY. AT 10AM
RADAR ESTIMATED 1.0 TO 1.6 INCHES OF RAIN IN AN HOUR OVER SOUTHERN
MD. PER RAP FORECASTS...LIFT WILL BE SUSTAINED IN THIS REGION
THROUGH ABOUT 18Z. CELL MOTIONS WILL REMAIN MODERATELY PACED...AND
THE AXIS OF NEW CELL GROWTH MAY SLIDE SOUTH AND EAST OVER
TIME...HELPING TO DISTRIBUTE THE RAINFALL. BUT SMALL SCALE
EPISODES OF TRAINING OVER 1-2 HOURS COULD YIELD EXCESSIVE RAINFALL
FOR SOME LOCATIONS IN SOUTHERN MD...MUCH OF DE...AND FAR SOUTHERN
NJ.


...QUASI-STATIONARY FRONTAL ZONE FROM OKLAHOMA TO TENNESSEE AND
THE WESTERN CAROLINAS...

THE LARGE SCALE PATTERN FEATURES AN H5 RIDGE REMAINING INTACT FROM
THE SOUTHERN ROCKIES NORTHWESTWARD INTO THE PACIFIC NORTHWEST AND
A DOWNSTREAM H5 TROF PERSISTING OVER THE EASTERN HALF OF THE
NATION. THIS PATTERN PUTS THE AREA FROM THE PLAINS INTO PARTS OF
THE MID MS AND TN VALLEYS IN A WESTERLY TO NORTHWESTERLY FLOW
REGIME WITH SEVERAL EMBEDDED SHORTWAVES...WHICH WILL REMAIN
CONDUCIVE FOR CONVECTIVE CLUSTERS CAPABLE OF PRODUCING AT LEAST
MODERATE TO LOCALLY HEAVY RAINFALL. OCCASIONAL POOLING OF PWS TO
NEAR OR ABOVE 1.75 INCHES EXPECTED. A QUASI-STATIONARY SURFACE
BOUNDARY WILL ACT TO DEFINE THE INSTABILITY AXIS. MODEL CAPE
FORECASTS SUGGEST THAT INSTABILITY MAY BECOME INCREASINGLY LIMITED
TO THE WARM SECTOR ALONG THE EASTERN PORTION OF THE FRONT WHERE
ONGOING CONVECTIVE SHIELD PRECIPITATION AND AN AMPLIFYING
SHORTWAVE WILL OVERTURN THE ATMOSPHERE NEAR THE SOUTHERN
APPALACHIANS THROUGH MIDDAY. SOME RECOVERY...AND SLIGHT NORTHWARD
TRANSPORT OF MOISTURE MAY OCCUR AGAIN OVERNIGHT AS ANOTHER SHARPLY
DEFINED SHORTWAVE ARRIVES IN EASTERN TN. A COMPLICATING
FACTOR...THOUGH...WILL BE THE INFLUENCE OF CONVECTIVE
OUTFLOWS...SUCH AS ASSOCIATED WITH A CONVECTIVE SYSTEM OVER
ARKANSAS THIS MORNING. THE REMNANT COLD POOL MAY PROMOTE UPSCALE
GROWTH AND INTERCEPTION OF INFLOW WHEN STORMS REFORM ALONG IT FROM
CENTRAL AR TO WESTERN TN / NORTHERN MS LATER IN THE AFTERNOON.

IT IS DIFFICULT TO SEPARATE THE AREAS OF INTEREST AT THIS
TIME...SO A BROAD SLIGHT RISK OF EXCESSIVE RAINFALL IS DRAWN FROM
OKLAHOMA TO THE FAR WESTERN CAROLINAS. GENERALLY...HOWEVER...THE
RISK WILL PEAK EARLIER IN THE DAY WITH EASTWARD EXTENT. FARTHER
WEST IN OK/AR SLOWER CELL MOTIONS AND CONFLUENT 700 MB FLOW
SUGGEST PERHAPS A MORE FOCUSED RISK THIS AFTERNOON AND EVENING.

WPC QPF REMAINED CLOSE TO THE HIGHER RES QPF GUIDANCE OF THE
ARW...NMMB...ECMWF AND GEM REGIONAL. EXPECT SOME 1-2 INCH AREAL
AVERAGE RAINFALL AMOUNTS IN A GENERAL WEST-EAST BAND...WITH SOME
LOCALLY HEAVY TOTALS of 3+ INCHES CERTAINLY POSSIBLE.


...SOUTH CAROLINA...

WE ALSO NOTED SOME COHERENT MODEL SIGNAL FOR HEAVY RAIN ALONG THE
SOUTH CAROLINA COAST / SEA BREEZE. THE SIGNAL WAS STRONG ENOUGH IT
SHOWED UP IN THE SSEO MEAN. CELL MOTIONS WILL NOT BE ESPECIALLY
SLOW...BUT INCREASING WIND FIELDS AHEAD OF THE NORTHERN STREAM
TROUGHING WILL SUPPORT INFLOW THAT COULD SUSTAIN ORGANIZED HEAVY
RAINFALL OVER A SMALL AREA NEAR THE COAST FOR A FEW HOURS THIS
AFTERNOON.


...CALIFORNIA AND NEVADA...

ANOMALOUS MOISTURE AND ADEQUATE MODEL SIGNAL FOR HEAVY RAINFALL
ARE CAUSE FOR CONCERN OVER PARTS OF NV/CA THIS AFTERNOON.
PRECIPITABLE WATER VALUES OF 1.00 TO 1.20 INCHES ARE HIGHLY
ANOMALOUS...REACHING MORE THAN 4 STANDARD DEVIATIONS ABOVE
CLIMATOLOGY FOR CENTRAL AND SOUTHERN NV AND ALONG THE SIERRAS. ON
WEDNESDAY ORGANIZED CONVECTION IN THE SOUTHWEST U.S. WAS
CONCENTRATED WITHIN A PLUME OF DEEP LAYER MOISTURE ROUGHLY
REPRESENTED BY THE 700-300 MB LAYER. FOLLOWING THIS PLUME IN THE
CIRA LAYERED TPW PRODUCT AND IN THE MODELS...EXPECT THAT THE AREA
NOW OUTLINED BY A SLIGHT RISK OF EXCESSIVE RAINFALL WILL SEE A
FAVORABLE COMBINATION OF MOISTURE AND INSTABILITY TO SUPPORT HEAVY
RAINFALL THIS AFTERNOON/EVENING. THE GFS FORECASTS AN INVERTED
TROUGH SLIDING WESTWARD UNDERNEATH THE WESTERN U.S. RIDGE
CENTER...TO REACH THE SIERRAS AROUND 00Z FRIDAY. THIS FEATURE WILL
SERVE TO FOCUS LIFT AND ENHANCED EASTERLY INFLOW NEAR CLOUD BASE
AROUND 600 MB TO PROMOTE CELL REDEVELOPMENT AND TRAINING ALONG
OUTFLOWS. THE MODEL PRECIPITATION FORECASTS ARE NOT ESPECIALLY
HEAVY...BUT DO SHOW SPATIAL SIMILARITY AND POCKETS OF RAINFALL
TOTALING MORE THAN ONE INCH WITHIN THE SLIGHT RISK AREA. WITH THE
ANOMALOUS MOISTURE AND ANY TRAINING...SPOTTY TOTALS GREATER THAN
1.5 INCHES EVEN APPEAR POSSIBLE...AND SHORTER TERM RATES WILL
LIKELY BE HEAVY ENOUGH TO CAUSE FLASH FLOODING IN SUSCEPTIBLE
TERRAIN AND/OR OVER BURN SCARS.

BURKE/TERRY
$$




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