Quantitative Precipitation Forecast
Issued by NWS

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FOUS30 KWBC 010759
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
358 AM EDT SAT AUG 01 2015

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


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
15 SSW TLH 25 WNW GNV 10 NNE OCF 20 SW VVG 20 NNW BKV
30 WSW CTY 35 SW 40J 20 SE AAF 15 WSW AAF 15 SSW TLH.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
35 SSW AMA 15 S DUX 10 W HHF 30 NW CSM 20 SE HBR 20 SSE FDR
40 SSE CDS 25 SSW CDS 35 SSW AMA.


...SOUTHERN PLAINS...

DEEP MOISTURE AND INSTABILITY FROM THE MONSOONAL FLOW OVER THE
SOUTHWEST IS TRANSPORTED INTO THE SOUTHERN PLAINS ON A
STRENGTHENING LOW LEVEL SOUTHERLY FLOW. THE MOISTURE AND
INSTABILITY SHOULD FEED DEVELOPING CONVECTIVE COMPLEXES ALONG AN
ELEVATED BOUNDARY EXTENDING ACROSS NORTH TX AND PORTIONS OF
SOUTHWEST OK...WHICH MAY PRODUCE HEAVY TO EXCESSIVE RAINFALL.

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 OP THE LOW LEVEL JET.
FOR NOW...A MORE CONSERVATIVE APPROACH WAS USED FOR QPF. IT SHOULD
BE NOTED THAT SOME OF THE HIGH RESOLUTION GUIDANCE (ESPECIALLY THE
00Z REGIONAL GEM...00Z WRF ARW AND NAM CONEST) PRODUCE AMOUNTS IN
EXCESS OF 3 INCHES. THE HIGH MOISTURE CONTENT OF THE AIRMASS MAKES
THAT PLAUSIBLE...SO A SLIGHT RISK WAS RETAINED FOR THIS AREA.


...SOUTHWEST/GREAT BASIN/CA...

DEEP MOISTURE AND INSTABILITY IN THE MONSOONAL FLOW ACROSS THE
SOUTHWEST AND GREAT BASIN CONTINUES...WHICH FEEDS DEVELOPING
CONVECTION ACROSS THE REGION. THERE IS A MULTI MODEL SIGNAL THAT A
SHORT WAVE TRACKING OUT OF NORTHWEST MEXICO CROSSES AZ ON ITS WAY
INTO SOUTHERN AND WESTERN NV. THE LIFT ASSOCIATED WITH THE SHORT
WAVE COULD ALLOW MORE ORGANIZATION OF CONVECTION...AND GIVEN THE
EXPECTED MOISTURE PROFILES...LOCALLY HEAVY TO POSSIBLY EXCESSIVE
RAINFALL IS POSSIBLE.

HIGH MOISTURE CONTENT AIR (WITH PRECIPITABLE WATER VALUES TOPPING
OUT NEAR 1.75 INCHES ACROSS PORTIONS OF AZ) AND MARGINAL
INSTABILITY SHOULD AGAIN COMBINE TO PRODUCE AT LEAST SCATTERED
CONVECTION NM/AZ INTO PORTIONS OF NORTHERN CA AND MUCH OF NV.
INITIALLY...THE CONVECTION SHOULD BE TIED TO THE TERRAIN...WHERE
LOCAL UPSLOPE ACROSS PORTIONS OF NM/SOUTHERN CO SHOULD HELP FOCUS
INSTABILITY AND MOISTURE. ACROSS THE TERRAIN OF NM AND AZ...AREAS
OF 0.25 TO 0.50 INCHES OF QPF ARE EXPECTED. FOR THIS MOST
PART...THESE VALUES ARE BELOW THE ONE AND THREE HOUR FLASH FLOOD
GUIDANCE NUMBERS.

THERE IS A MULTI MODEL CONSENSUS THAT A DECENT SHORT WAVE TRACKS
OUT OF NORTHWEST MEXICO ACROSS AZ INTO SOUTHERN AND CENTRAL
NV...MAINLY AFTER 01/18Z. THE SHORT WAVE SHOULD PRODUCE ENOUGH
LIFT TO SUPPORT MORE ORGANIZED CONVECTION ACROSS NORTHWEST AZ INTO
PORTIONS OF SOUTHERN AND CENTRAL NV AND NEARBY EAST CENTRAL CA.
WHILE THE BASIN AVERAGE QPF VALUES SHOULD BE LESS THAN 0.50
INCHES...THE HIGH MOISTURE CONTENT AIR (WITH PRECIPITABLE WATER
VALUES BETWEEN THREE AND FOUR STANDARD DEVIATIONS ABOVE THE MEAN)
SUGGEST THAT LOCAL HIGHER AMOUNTS ARE POSSIBLE...AND SOME HIGH
RESOLUTION SOLUTIONS (SUCH AS THE 00Z WRF ARW AND 00Z NAM CONEST)
SUGGEST LOCAL 2-3 INCH AMOUNTS. SINCE IT IS NOT CLEAR WHERE THESE
AMOUNTS WILL OCCUR...A SEE TEXT WAS ISSUED FOR MUCH OF WESTERN
AZ/SOUTHERN AND CENTRAL NV. SHOULD THE FOCUS FOR CONVECTION BECOME
CLEARER LATER TODAY...THIS COULD BE UPGRADED TO A SLIGHT RISK.


...FL...

A WEAKENING FRONTAL BOUNDARY PROVIDES LOW LEVEL CONVERGENCE AND A
FOCUS FOR DEVELOPING CONVECTION ACROSS FL DURING DAY 1. THE
ABUNDANCE OF MOISTURE IN THE COLUMN...AS WELL AS SLOW CELL MOTION
DUE TO A WEAK STEERING FLOW...SUGGESTS THAT CONVECTION THAT
DEVELOPS IN BEST LOW LEVEL CONVERGENCE WILL PRODUCE HEAVY TO
EXCESSIVE RAINFALL OVER PORTIONS OF NORTHWEST FL.

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.

HAYES
$$




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