Quantitative Precipitation Forecast
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FOUS30 KWBC 020816
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
415 AM EDT SUN AUG 02 2015

...VALID 12Z SUN AUG 02 2015 - 12Z MON AUG 03 2015...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
75 SSE AAF 50 SE AAF 45 SW 40J 15 SW 40J 25 NNW GNV 25 SE GNV
VVG 10 NNW LAL 10 N SRQ 45 WSW SPG 110 W PIE 75 SSE AAF.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 NW TAD 25 WSW TAD 15 W RTN 15 W LVS 15 SE SAF 15 SSW SAF
20 NE AEG AEG 25 W AEG 10 ESE GNT GNT 35 NNW GNT 30 NE GUP
30 NNE RQE 50 N RQE 60 SW CEZ 55 S 4BL 40 SSW 4BL 40 SW 4BL
55 NE PGA 50 SSW 4HV 40 SSW 4HV 30 SW 4HV 15 SW 4HV 4HV 15 E 4HV
20 SW CNY 10 SSE CNY 15 E CNY 25 ENE CNY 20 WSW GJT 10 ENE GJT
10 SW RIL 10 W EGE 10 WNW CCU 30 SE LXV 40 SW FCS 30 NNE VTP
20 NW TAD.


...FL...

DEEP TROPICAL MOISTURE AND INSTABILITY WILL FEED SURGES OF
CONVECTION THAT TRACK ALONG A SURFACE TROUGH FROM THE EASTERN GULF
OF MEXICO ACROSS PORTIONS OF NORTHERN FL DURING DAY 1...PRODUCING
HEAVY TO EXCESSIVE RAINFALL. A SLIGHT RISK AREA WAS PLACED OVER A
PORTION OF THE WEST COAST OF FL IN RESPONSE TO THE THREAT.

THERE IS A LULL IN THE CONVECTION ACROSS PORTIONS OF NORTHERN AND
CENTRAL FL EARLY THIS MORNING...AS THE BEST MEAN LAYER INSTABILITY
REMAINS OFF THE WEST COAST OF THE PENINSULA. THE ACTIVITY SHOULD
REDEVELOP CLOSER TO 02/12Z...AS INSTABILITY INCREASES...AND THE
2.50 INCH PRECIPITABLE WATER PLUME OFF THE WEST COAST SURGES
EASTWARD. THE BEST LOW LEVEL MOISTURE FLUX IS CENTERED AROUND
02/18Z...AND SLOWLY TAILS OFF AFTER THAT TIME. THE BEST CONVECTION
IS EXPECTED BETWEEN 02/12Z AND 03/00Z...AFTER WHICH THE BEST LOW
AND MID LEVEL MOISTURE SHOULD BEGIN TO SLIDE TO THE EAST. THE HIGH
MOISTURE CONTENT OF THE AIR (ABOUT TWO STANDARD DEVIATIONS ABOVE
THE MEAN)...AS WELL AS THE POTENTIAL FOR TRAINING ACROSS PORTIONS
OF THE NORTHWEST PORTION OF THE PENINSULA...INDICATES THAT A BASIN
AVERAGE OF 3 TO 4 INCHES OF QPF SHOULD BE EXPECTED BETWEEN KCTY
AND KBKV.

THERE IS SOME SPREAD ON WHERE THE QPF MAXIMUM OCCURS. THIS SEEMS
TO BE TIED TO THE POSITION OF A SURFACE TROUGH ALONG THE WEST
COAST...AND THE LATITUDINAL DIFFERENCES RESULT IN A LOWER THAN
AVERAGE FORECAST FOR MAXIMUM QPF. IT SHOULD BE NOTED THAT SOME OF
THE 00Z HIGH RESOLUTION GUIDANCE...SUCH AS THE 00Z WRF ARW AND 00Z
REGIONAL GEM...SHOW THE POTENTIAL FOR AN ADDITIONAL 6 TO 9 INCHES
OF RAINFALL WHERE TRAINING OCCURS. LIKE THE DIFFERENCES BETWEEN
THE 00Z GFS/ECMWF...THE HIGH RESOLUTION GUIDANCE ALSO SHOWS SPREAD
ON THE PLACEMENT OF MAXIMUM QPF. GIVEN THE SPREAD IN PLACE...A
SLIGHT RISK AREA WAS PLACED OVER MUCH OF THE WESTERN PORTION OF
THE PENINSULA FROM KTPA NORTHWEST INTO THE BIG BEND AREA.


...WESTERN UNITED STATES...

MONSOONAL MOISTURE CONTINUES TO SURGE INTO THE SOUTHWEST
STATES...AND PORTIONS OF THE MOISTURE ARE DIVERTED INTO THE GREAT
BASIN AND SOUTHERN PLAINS. THE HIGH MOISTURE CONTENT
AIR...COMBINED WITH MARGINAL INSTABILITY AND LIFT FROM A SHORT
WAVE CROSSING THE SOUTHERN ROCKIES AND GREAT BASIN...IS EXPECTED
TO PRODUCE AN AREA OF SCATTERED TO BROKEN CONVECTION...WHICH COULD
PRODUCE HEAVY TO LOCALLY EXCESSIVE RAINFALL.

THE BEST THRUST OF MONSOONAL MOISTURE SHOULD OCCUR ACROSS NM INTO
THE SOUTHERN ROCKIES AND GREAT BASIN (AS SEEN ON THE LATEST HIGH
AND MID LEVEL LAYERED PRECIPITABLE WATER IMAGES). THERE IS GOOD
MODEL AGREEMENT THAT A SHORT WAVE TRACKS NORTH OUT OF AZ THROUGH
NV AND UT DURING THE AFTERNOON AND EVENING HOURS. THE SYNOPTIC
SCALE ASCENT ASSOCIATED WITH THE SHORT WAVE SHOULD ALLOW CLUSTERS
OF CONVECTION TO BLOSSOM ACROSS WESTERN CO (INCLUDING THE SAN JUAN
MOUNTAINS)...NORTHERN NM AND SOUTHEAST UT. PRECIPITABLE WATER
VALUES HERE SHOULD RANGE BETWEEN TWO AND THREE STANDARD DEVIATIONS
ABOVE THE MEAN...INCREASING THE THREAT FOR FLASH FLOODING. SOME OF
THE HIGH RESOLUTION GUIDANCE SUGGESTS LOCAL 2.00 INCH QPF AMOUNTS
ARE POSSIBLE WITH STORMS THAT TAP THE HIGH MOISTURE AIR...AND
BASED ON WHAT OCCURRED ACROSS WESTERN CO SAT...THIS SEEMS
POSSIBLE.

THERE IS SOME UNCERTAINTY CONCERNING HOW WIDESPREAD THE HEAVY RAIN
THREAT WILL BE...BUT WESTERN CO AND NORTHERN NM SEEM TO BE IN THE
AREAS WITH THE BEST COMBINATION OF LIFT/MOISTURE. WHILE BASIN
AVERAGE QPF AMOUNTS BETWEEN 0.25 AND 0.50 INCHES MAY BE COMMON IN
THE HIGHER TERRAIN...HIGHER AMOUNTS IN AREAS WHERE ONE AND THREE
HOUR FLASH FLOOD GUIDANCE VALUES ARE AN INCH OR LESS WILL CAUSE
PROBLEMS. A SLIGHT RISK AREA WAS ISSUED FOR THIS AREA.

FURTHER WEST...INSTABILITY AND MOISTURE COULD SUPPORT SCATTERED
CONVECTION WITH LOCALLY HEAVY RAINFALL ACROSS PORTIONS OF NV INTO
NORTHERN CA AND WESTERN OR. PRECIPITABLE WATER VALUES FROM
NORTHERN CA/SOUTHWEST OR THROUGH MUCH OF NV SHOULD TOP OUT BETWEEN
TWO AND THREE STANDARD DEVIATIONS ABOVE THE MEAN....AND MARGINAL
INSTABILITY SHOULD INITIATE CONVECTION MAINLY OVER THE TERRAIN.
SOME OF THE MORE AGGRESSIVE HIGH RESOLUTION GUIDANCE (LIKE THE 00Z
NAM CONEST) SUGGESTS THAT LOCAL 1.00+ INCH AMOUNTS ARE POSSIBLE
ACROSS THE TERRAIN OF CENTRAL NV. WITH A SHORT WAVE CROSSING THE
REGION FOR SYNOPTIC SCALE ASCENT...LOCAL QPF AMOUNTS OF THIS
MAGNITUDE ARE PLAUSIBLE. GIVEN THE HIGH MOISTURE CONTENT OF THE
AIR...A SEE TEXT WAS PLACED OVER NV.

HAYES
$$




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