Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 020053
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
852 PM EDT SAT AUG 01 2015

...VALID 01Z SUN AUG 02 2015 - 12Z SUN AUG 02 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


AFTER LOOKING AT THE 00Z RAOBS..AND RECENT SATELLITE AND RADAR
IMAGERY/TRENDS..PREVIOUS OUTLINED THREAT AREAS FOR POTENTIALLY
EXCESSIVE RAINS STILL APPEAR GOOD..SO SEE NO REASON TO DEVIATE
FROM THE EARLIER ISSUANCE.  THE NORTHERN FL PENINSULA STILL LOOKS
TO BE MOST FAVORED FOR MORE ORGANIZED HEAVY TO LOCALLY EXCESSIVE
RAINS..CONCENTRATED VICINITY OF THE LOW/MID LEVEL SHEAR AXIS AND
IN A PERSISTENT AND RATHER DEEP LAYERED ONSHORE FLOW REGIME.
PREVIOUS DISCUSSION FOLLOWS...

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 N AAF TLH 20 NNW 40J 35 NNE CTY 15 ENE OCF 10 N GIF 30 N PGD
10 WNW SRQ 30 WSW PIE 70 SE AAF 45 WSW AAF 25 N AAF.

...FL...

THE SLIGHT RISK AREA IN FLORIDA WAS EXPANDED SOMEWHAT...TO INCLUDE
AREAS FARTHER SOUTH INTO THE TAMPA BAY AREA AND OVER THROUGH THE
CENTRAL PART OF THE PENINSULA. THE EXPECTATION IS THAT VERY HIGH
RAIN RATES ARE THE MAIN CONCERN...RATHER THAN PARTICULARLY
EXCESSIVE RAIN TOTALS. THE MODEL TRENDS HAVE BEEN TOWARD LESSER
EVENT TOTALS...AS CONVECTION WILL BE PRONE TO FORMING ALONG THE
COAST AND RADIATING OUT...QUICKLY PROPAGATING EAST THROUGH THE
MIXED BOUNDARY LAYER OVER THE PENINSULA...AND PROPAGATING MORE
SLOWLY WEST INTO THE BETTER INFLOW. WHILE THE POSSIBLITY FOR
EXTREME RAIN TOTALS...MORE THAN 5 INCHES POSSIBLE THROUGH
SUNDAY...REMAINS IN TACT NEAR THE COAST...THE OVERALL EVENT SHOULD
BE CHARACTERIZED MORE BY UNUSUALLY HIGH SHORT TERM RAIN RATES
GIVEN SUCH ANOMALOUS PW VALUES EXCEEDING 2.25 INCHES AT TIMES.


...PREVIOUS FL DISCUSSION...

A SLOWING FRONTAL BOUNDARY SHOULD BECOME QUASI STATIONARY ACROSS
PORTIONS OF THE SOUTHEAST STATES INTO THE WESTERN FL PANHANDLE.
THE FRONT SERVES TO FOCUS LOW LEVEL CONVERGENCE AND
INSTABILITY...WHICH TAPS DEEP TROPICAL MOISTURE (WITH PRECIPITABLE
WATER VALUES OF 2.25+ INCHES) TO PRODUCE CONVECTIVE CLUSTERS NEAR
THE FRONT...STRETCHING FROM ACROSS SOUTHEAST GA ACROSS NORTHERN FL
AND A PORTION OF THE WESTERN FL PANHANDLE. THE MID LEVEL STEERING
CURRENT IS FAIRLY WEAK...SUPPORTING SLOW CELL MOVEMENT ALONG THE
FRONT OVER THE ABOVEMENTIONED LOCATIONS. THE BEST CONCENTRATION OF
CONVECTIVE CLUSTERS IS EXPECTED ACROSS THE EASTERN FL PANHANDLE
ACROSS PORTIONS OF THE WEST COAST OF THE PENINSULA. OVER THIS
AREA...1.50 TO 3.00 INCHES OF QPF WAS PLACED...WITH THE HIGHEST
AMOUNTS BETWEEN KCTY AND KBKV.

THERE IS REMARKABLE CONSISTENCY AMONG THE VARIOUS 00Z
REGIONAL/GLOBAL SOLUTIONS PLACING 3.00 TO 4.00 INCHES OF QPF IN
THE ABOVEMENTIONED LOCATIONS. SOME OF THE 00Z HIGH RESOLUTION
MODEL SOLUTIONS PLACED MAXIMUM NEAR 8 INCHES (INCLUDING THE 00Z
WRF ARW/NMMB AND 00Z REGIONAL GEM..WHICH WAS CLOSER TO 11 INCHES
OF QPF) IN THIS AREA...OR JUST OFFSHORE. THESE AMOUNTS COULD BE
PLAUSIBLE...GIVEN THE DEEP MOISTURE IN PLACE AND SLOW
CELL/CLUSTER MOVEMENT. HOWEVER...SINCE THERE IS SOME SPREAD AS TO
WHETHER THE HIGHEST QPF AMOUNTS OCCUR JUST OFFSHORE OR ON LAND
OVER NORTHWEST FL...A MORE CONSERVATIVE APPROACH WAS USED FOR THE
WPC QPF. IN ANY EVENT...THE POTENTIAL FOR HIGH RAINFALL RATES AND
SLOW CELL MOTIONS NECESSITATE A SLIGHT RISK AREA FOR PORTIONS OF
NORTH FL.


...SOUTHWEST/GREAT BASIN...

MOISTURE AND INSTABILITY WERE SOMEWHAT TYPICAL FOR THE MONSOON
SEASON PER REGIONAL 12Z SOUNDINGS. DRY LOW LEVEL AIR EXTENDED UP
THROUGH A FAIR DEPTH IN SOUNDINGS FROM AZ TO NV...WHICH WILL CUT
DOWN ON PRECIPITATION EFFICIENCY...ALTHOUGH ENHANCED MID AND HIGH
LEVEL MOISTURE WILL LEND 0.75 TO 1.25 INCH PRECIPITABLE WATER TO
THUNDERSTORMS FORMING ON THE HIGH TERRAIN. A SHEAR AXIS AT THE
WESTERN PERIPHERY OF THE MID LEVEL RIDGE EXTENDED ACROSS WESTERN
NV NEAR THE CA BORDER...DOWN INTO CENTRAL AZ. AN EMBEDDED
SHORTWAVE TROUGH WILL LIFT NORTHWARD TODAY OUT OF AZ TOWARD
SOUTHERN NV. LIFT ASSOCIATED WITH THE SHORT WAVE COULD ALLOW FOR
GREATER ORGANIZATION OF CONVECTION...AND GIVEN THE EXPECTED
MOISTURE PROFILES...ISOLATED HEAVY RAINFALL. THE MODEL QPF SIGNAL
IS THAT OF AN AVERAGE DAY IN THE WESTERN U.S...WITHOUT MUCH
SPECIFIC FOCUS. SOME HIGH RESOLUTION SOLUTIONS (SUCH AS THE 00Z
WRF ARW AND 00Z NAM CONEST) SUGGEST LOCAL AMOUNTS ABOVE 2
INCHES...BUT AGAIN THIS IS TOWARD THE LOWER END OF THE VALUES THAT
THOSE MODELS TYPICALLY GENERATE. THE FLASH FLOOD THREAT SHOULD BE
ON SMALL SCALES AND DEPENDENT ON BRIEFLY INTENSE DOWNPOURS SETTING
UP OVER PLACES THAT ARE MORE SUSCEPTIBLE.


...SOUTHERN HIGH PLAINS...

EARLY MORNING CONVECTION ACROSS NORTH TX SHOULD PRODUCE AN
MCV...WHICH CROSSES NORTH TX INTO SOUTHWEST OK THIS MORNING INTO
THE AFTERNOON. THE MCV SHOULD PROVIDE SUFFICIENT SUPPORT FOR
ADDITIONAL CONVECTION IN ITS PATH INTO THE AFTERNOON HOURS.
ADDITIONAL CONVECTION IS EXPECTED TO DEVELOP ACROSS NORTHEAST NM
THIS AFTERNOON AND EVENING...WHICH SHOULD FOLLOW THE SAME PATH AS
THE CONVECTION THIS MORNING...AS THE MID LEVEL RIDGE REMAINS IN
PLACE. AS THE LOW LEVEL FLOW INCREASES AGAIN ACROSS NORTH
TX/WESTERN OK/WESTERN KS AFTER 02/00Z...ADDITIONAL CONVECTION
COULD DEVELOP ON THE NOSE OF A LOW LEVEL JET NEAR 02/06Z ACROSS
NORTH TX...WHICH MOVES INTO SOUTHWEST OK. WHILE THERE IS SOME
MODEL COMMONALITY AMONG 00Z MODEL SOLUTIONS HERE...IT IT NOT CLEAR
IF A FULL BLOWN MCS DEVELOPS IN THE PRESENCE OF THE LOW LEVEL
JET...AS UPPER SUPPORT WILL BE LACKING...AND INFLOW OVERNIGHT WILL
COME FROM DRIER SOURCE REGIONS TO THE SOUTH OF THE SEMI-PERMANENT
WEAK FRONTAL ZONE.

BURKE/HAYES/TERRY
$$





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