Quantitative Precipitation Forecast
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FOUS30 KWBC 040052
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
852 PM EDT FRI JUL 03 2015

...VALID 01Z SAT JUL 04 2015 - 12Z SAT JUL 04 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
35 NE TUP 35 WNW CHA 25 NW RHP 15 S 1A5 20 ENE GVL 15 WSW FTY
30 ENE NMM HKS 10 SSE MLU 25 E OSA 20 SE AQR 20 NNE FSM
20 WNW NQA 35 NE TUP.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 WSW IAD 10 ESE BCB 20 ENE GEV 40 NNW AVL 30 NNW OQT 20 N BNA
35 SSE CIR PAH 30 ENE M30 35 E OWB 30 NE LEX 40 WNW HTS
25 SSW HLG AGC 20 SW DUJ 25 N FIG 30 WNW IPT 10 SW SEG 15 SW CXY
15 WSW IAD.



...KENTUCKY TO PENNSYLVANIA/WESTERN MARYLAND AND THE VIRGINIAS...

HEATING HAD CONTRIBUTED TO EARLIER DEVELOPMENT OF MODERATE
INSTABILITY OVER KENTUCKY WITHIN OTHERWISE SATURATED VERTICAL
PROFILES WITH POOR MID LEVEL LAPSE RATES. BROAD LIFT WITHIN
CYCLONIC FLOW IN THE EASTERN U.S. TROUGH HAD BEEN VERY EFFICIENT
AT WRINGING OUT CONVECTIVE PRECIPITATION FROM THESE PROFILES WITH
THE INFUSION OF HEAT AT THE SURFACE. THOUGH INDIVIDUAL CELL
CLUSTERS WERE OF RELATIVELY SMALL SCALE...THEY WERE PLENTIFUL IN
NUMBER...WITH DEEP WESTERLY FLOW PROMOTING TRAINING. THIS BEHAVIOR
MAY CONTINUE ACROSS WESTERN AND CENTRAL KY THROUGH THE EVENING
HOURS...ALTHOUGH WITH GRADUALLY DIMINISHING INTENSITY AS BOUNDARY
LAYER HEATING CEASES AND DEEP LAYER ASCENT BEGINS TO PASS EAST OF
THE INSTABILITY GRADIENT...AND INTO EASTERN KY.

AREAS FROM EASTERN KY INTO THE MID ATLANTIC STATES WERE
COOLER...WITH PROFILES THAT WERE MORE STABLE TO SURFACE BASED
PARCELS...BUT STILL WITH ABUNDANT MOISTURE AND MOST UNSTABLE CAPE
VALUES THAT WILL BE NON-ZERO WHEN THE MID LEVELS ARE FORCIBLY
LIFTED. PER THE GFS...DEEP LAYER ASCENT WILL CONTINUE TO INCREASE
THROUGH 06-09Z WITHIN THE SLIGHT RISK AREA OUTLINE FROM EASTERN KY
INTO PARTS OF WV/PA/MD/VA. PW VALUES MEASURED ABOVE 1.5 INCHES IN
00Z SOUNDINGS...AND RISING ABOVE 1.6 INCHES OVERNIGHT...WILL
PROMOTE EFFICIENT RAINFALL. THERE WILL BE POTENTIAL FOR FLASH
FLOODING WHEREVER LOCAL TERRAIN ENHANCEMENT AND/OR TRAINING TAKES
PLACE...ESPECIALLY WITH THIS REGION HAVING BEEN WET IN RECENT
WEEKS...AND WITH FLASH FLOOD GUIDANCE NUMBERS RUNNING LOW.


...LOWER MISSISSIPPI VALLEY ACROSS TO NORTHERN GEORGIA...

BY EARLY EVENING A PROGRESSIVE MCS WAS PASSING SOUTH OF THE AREAS
HARDEST HIT BY FLOODING IN NORTHERN MISSISSIPPI. ELSEWHERE STABLE
POCKETS OF AIR HAD GROWN ACROSS MUCH OF TENNESSEE...AND IN THE
WAKE OF AN MCS WHICH TRACKED THROUGH GA/SC. CLUSTERS OF CONVECTION
AND SOME TRAINING HAD BEEN NOTED WHERE STRONGER SURFACE HEATING
TOOK PLACE FRIDAY IN PARTS OF TX/OK/AR AND AL. AFTER A BRIEF BREAK
FROM LARGE SCALE ORGANIZATION...ANOTHER UPSWING APPEARS POSSIBLE
LATE FRIDAY NIGHT. A SHORTWAVE TROUGH DIVES INTO THE BASE OF THE
LARGER SCALE EASTERN U.S. TROUGH...AND MODELS DEPICT A SWATH OF
MODERATE TO LOCALLY HEAVY RAINFALL WITHIN THE CONFLUENT 850-700 MB
FLOW REGIME THAT HAS TAKEN UP RESIDENCE FROM SE OK/NE TX ACROSS
ADJACENT PARTS OF AR/LA INTO NORTHERN MS/AL/GA AND EXTREME
SOUTHERN TN. GIVEN THE SUBTLE NATURE OF THE INSTABILITY GRADIENTS
AND MID LEVEL FORCING MECHANISMS...THE SSEO MEAN HAD DONE A GOOD
JOB FRIDAY OF PRESENTING A MORE COHERENT PICTURE THAN ANY OF THE
INDIVIDUAL COMPONENT MODELS. THE 12Z SSEO MEAN PAINTS THE HEAVIEST
SWATH OF RAIN ALONG THE AR/LA BORDER AND INTO CENTRAL MISSISSIPPI
OVERNIGHT. THIS IS CONSISTENT WITH THE 12Z GFS...AND JUST SLIGHTLY
SOUTH OF THE 12Z ECMWF.


...SOUTHWEST...

MONSOONAL MOISTURE COMBINING WITH MARGINAL TO MODERATE INSTABILITY
COULD LEAD TO ISOLATED FLASH FLOODING ACROSS PORTIONS OF THE
SOUTHWEST STATES. A LOW LEVEL EAST SOUTHEAST FLOW FROM THE
SOUTHERN PLAINS TRANSPORTS 1.25 PRECIPITABLE WATER AIR INTO
NM...WHILE THE MONSOONAL FLOW BRINGS 1.75 INCH PRECIPITABLE WATER
AIR IN SOUTHERN AZ. MODEL SOUNDINGS SHOWED MARGINAL TO LOCALLY
MODERATE INSTABILITY...WHICH APPEARS TO PEAK ACROSS SOUTHEAST
AZ/SOUTHWEST NM.

THERE IS A MULTI MODEL SIGNAL THAT A WEAK SHORT WAVE RUNNING
WESTWARD AT THE BOTTOM OF THE WESTERN UNITED STATES RIDGE COULD
YIELD A FLARE UP OF DEEP CONVECTION...PERHAPS A SHORT LIVED MCS
ACROSS WESTERN NM AND EASTERN AZ. SIMULATED SATELLITE IMAGERY FROM
THE NAM AND NSSL WRF INDICATE THIS POTENTIAL. WHILE MOST MODEL QPF
OUTPUT ACROSS THIS AREA IS GENERALLY UNDER AN INCH...THE HIGH
MOISTURE CONTENT OF THE AIR COULD RESULT IN HIGHER RAINFALL RATES.


...CALIFORNIA / NEVADA / OREGON...

AN INVERTED MID LEVEL TROUGH WAS PASSING SLOWLY WESTWARD ACROSS
THE SIERRAS...AND INTO FAR NORTHERN CALIFORNIA AND FAR SOUTHERN
OREGON. PRECIPITABLE WATER VALUES TOPPING OUT NEAR 1.25 INCHES
SURROUNDED THE TROUGH AXIS AND EXTENDED BACK INTO NORTHERN
NEVADA...REPRESENTING A STRONGLY ANOMALOUS AIR MASS AT 3 TO 4
STANDARD DEVIATIONS ABOVE THE CLIMATOLOGICAL MEAN. A NWS
COOPERATIVE OBSERVER REPORTED 1.06 INCHES OF RAIN IN ONLY 35
MINUTES FRIDAY EVENING NEAR VERDI NEVADA. THE POTENTIAL IS THERE
FOR VERY HEAVY RAIN RATES...EXCEEDING FLASH FLOOD GUIDANCE
VALUES...ESPECIALLY OVER NORTHERN CALIFORNIA...FOLLOWING THE TRACK
OF THE INVERTED TROUGH AND ASSOCIATED MID LEVEL MOISTURE GRADIENT
REVEALED THROUGH WATER VAPOR IMAGERY. THE SSEO MEAN AND LATE
AFTERNOON RUNS OF THE HRRR PLACE AREAL AVERAGE PRECIPITATION OF
0.25 TO 0.50 INCHES OVER FAR NORTHERN CALIFORNIA...NORTH OF RED
BLUFF. DRIER LOW LEVEL AIR OVER OREGON SHOULD LIMIT THE HEAVY RAIN
POTENTIAL THERE...AND REMNANT CELLS IN NEVADA WILL BE LOSING MID
LEVEL SUPPORT WITH TIME. GIVEN 00Z RADAR TRENDS...CONVECTIVE
COVERAGE OVER CALIFORNIA MAY ALSO WANE AS THE TROUGH MOVES OFF THE
HIGHEST TERRAIN...BUT WHEREVER THUNDERSTORMS DO OCCUR FOR 30-60
MINUTES...LOCAL RAINFALL AMOUNTS COULD EASILY EXCEED ONE INCH.

BURKE/HAYES
$$





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