Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 042055
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
454 PM EDT SAT JUL 04 2015

...VALID 21Z SAT JUL 04 2015 - 12Z SUN JUL 05 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 NW ELD 20 SW GLH 10 NNW CBM 30 SE MQY 30 NNE CSV 25 SSE 1A6
20 E 1A5 10 WNW LGC 35 NNE GZH 35 NNE MOB 10 S BTR 35 E CWF
15 NW POE 35 S SHV 10 N GGG 10 SE SLR 15 NW PRX 15 W DEQ
25 NW ELD.


...NORTHEAST TEXAS THROUGH THE SOUTHEAST STATES AND INTO EASTERN
TENNESSEE...

IN KEEPING UP WITH THE TRENDS...WPC PUSHED THE SLIGHT RISK OF
EXCESSIVE RAINFALL SOUTHWARD AT 21Z. THROUGH EVENING...MOST
ACTIVITY WILL BE CONCENTRATED ALONG THE OUTFLOWS / CAPE GRADIENT
RUNNING FROM NORTHEAST TEXAS THROUGH LA AND SOUTHERN AR INTO
CENTRAL/SOUTHERN MS/AL. BROAD SCALE CONFLUENT 850-700 MB FLOW
SHOULD REMAIN IN PLACE...PUMPING IN AIR FROM A CAPPED...UNSTABLE
SOURCE REGION OVER EAST TEXAS. BROAD MID LEVEL TROUGHING
STRETCHING ACROSS THE SOUTHEAST STATES...AS WELL AS A MORE FOCUSED
VORTICITY MAXIMUM IN EASTERN OKLAHOMA...WILL MAINTAIN A FAVORABLE
BACKGROUND ENVIRONMENT OF LIFT AND SUFFICIENT MID LEVEL LAPSE
RATES.

FARTHER NORTH AND EAST...EARLY MORNING CONVECTION HAD STABILIZED A
ZONE RUNNING ACROSS NORTHERN MS/AL/GA AND FAR SOUTHERN TN. IT IS
UNLIKELY THAT SIGNIFICANT SURFACE BASED OR NEAR-SURFACE BASED
INSTABILITY WILL DEVELOP IN THOSE AREAS...BUT MID LEVEL HEIGHT
FALLS WILL TRACK IN THAT DIRECTION...WITH A WELL DEFINED 600 MB
LOW FORECAST OVER NASHVILLE BY SUNDAY MORNING. AHEAD OF THIS
FEATURE...FLASH FLOOD GUIDANCE VALUES ARE ESPECIALLY LOW ACROSS
EASTERN TENNESSEE...WHERE MODELS ALSO HAVE A CONSISTENT SIGNAL FOR
MODERATE RAINFALL LATER TONIGHT...LIKELY ROOTED IN THE MID LEVELS.
GIVEN THE WELL DEFINED MODEL SIGNAL AND WET ANTECEDENT
CONDITIONS...WE KEPT THE SLIGHT RISK OF EXCESSIVE RAINFALL IN
PLACE FROM NORTHERN AL INTO PARTS OF TN/GA/ FAR WESTERN NC.

FOR AREAS FARTHER SOUTH AND WEST...PLEASE REFER TO MESOSCALE
PRECIPITATION DISCUSSIONS NUMBERS 302 AND 304 FOR DETAILS.


...ARIZONA AND NEW MEXICO...

WITH AMPLE MONSOONAL MOISTURE IN PLACE...THE UPPER LEVEL
DEFORMATION AREA BETWEEN AN UPPER HIGH CENTER DRIFTING OVER THE
FOUR CORNERS REGION AND CYCLONIC FLOW EXTENDING INTO SOUTHERN
CA...IS EXPECTED TO ACCENTUATE THE POTENTIAL FOR DIURNAL ACTIVITY
ALONG THE MOGOLLON RIM INTO THE WHITE MOUNTAINS. THIS WILL RAISE
THE POTENTIAL FOR LOCALLY HEAVY RAINS/FLASH FLOODING. PLEASE READ
MESOSCALE PRECIPITATION DISCUSSION NUMBER 303 FOR A DETAILED
DISCUSSION...VALID THROUGH EARLY SATURDAY EVENING.


...UTAH / NEVADA...

THE GREATEST DEEP LAYER LIFT OVER THE WEST COINCIDED WITH A SMALL
NORTHWARD MOVING VORTICITY MAXIMUM IN NEVADA...BUT ALSO COINCIDED
WITH EXTENSIVE MID AND HIGH LEVEL CLOUD COVER. ARRIVAL OF THE LIFT
WITH THIS FEATURE WILL BE SOMEWHAT OUT OF PHASE WITH THE DIURNAL
DEVELOPMENT OF CONVECTION OVER NORTHERN NEVADA...WHICH HAD ALREADY
BEGUN IN A LOOSELY ORGANIZED FASHION. AT MID AFTERNOON IT APPEARED
A MORE COHESIVE THREAT FOR FLASH FLOODING MAY EXIST IN
UTAH...WHERE STRONGER HEATING HAD BROUGHT MIXED LAYER CAPE VALUES
UP TO AROUND 1000 J/KG. EARLY CONVECTIVE CELLS WERE SLOW
MOVING...AND AS THE VORTICITY MAXIMUM LIFTS THROUGH
NEVADA...SOUTHWESTERLY 700 MB WINDS WILL INCREASE INTO WESTERN /
SOUTHWESTERN UTAH...PROVIDING SOME IMPETUS FOR SUSTAINED INFLOW AT
CLOUD BASE...AND PERHAPS EVEN SLOWER MOVEMENT. PRECIPITABLE WATER
VALUES WERE NEAR OR JUST ABOVE 1.00 INCHES THROUGHOUT THIS REGION.


...NORTH DAKOTA AND MINNESOTA...

SYNOPTIC FEATURES...INCLUDING DIFLUENT UPPER LEVEL FLOW IN ADVANCE
OF A MEDIUM WAVELENGTH TROUGH...WILL OVERLAP FAVORABLY WITH
INSTABILITY AND LOW LEVEL INFLOW TO SUPPORT CONVECTION WELL INTO
THE NIGHT ACROSS ND AND NORTHERN MN. THE PRE-CONVECTIVE
ENVIRONMENT WILL BE CHARACTERIZED BY A BROAD RIBBON OF
PRECIPITABLE WATER VALUES AROUND 1.25 INCHES...INCREASING ABOVE
THAT MARK WHERE MOISTURE IS POOLED NEAR THE APPROACHING
THUNDERSTORMS LATER TONIGHT. THE RAP FORECASTS MOST UNSTABLE CAPE
VALUES TO REMAIN PRETTY RESPECTABLE...AT GREATER THAN 1500 J/KG
EVEN AT 06Z...AS A 30 KNOT LOW LEVEL JET KEEPS THE LOWER
ATMOSPHERE MIXED. INDIVIDUAL CELLS AND LINE SEGMENTS SHOULD BE
PROGRESSIVE...BUT THERE IS POTENTIAL FOR SOME BACKWARD PROPAGATION
INTO THE LOW LEVEL INFLOW...AND BROAD SCALE LIFT MAY ALLOW FOR A
PERIOD OF REDEVELOPMENT ALONG OUTFLOWS AND SOME TRAINING TO BOOST
RAINFALL TOTALS. THE HIGH RESOLUTION MODELS HAVE A SIMILAR SIGNAL
TO ONE ANOTHER...PRODUCING LOCAL RAINFALL AMOUNTS ABOVE 2 INCHES
OVERNIGHT IN MAINLY NORTHEAST ND AND NORTHWEST MN. THIS SUGGESTS
RATES COULD EXCEED THE 1 OR 3 HOUR FLASH FLOOD GUIDANCE IN THAT
REGION.

BURKE/PEREIRA
$$





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