Quantitative Precipitation Forecast
Issued by NWS

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FOUS30 KWBC 271248
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
847 AM EDT SAT SEP 27 2014

...VALID 12Z SAT SEP 27 2014 - 12Z SUN SEP 28 2014...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 E LLJ 20 WNW DLN 10 SSW BTM 10 E BTM 30 E BTM 20 WSW BZN
30 SSW BZN 30 NE RXE 40 SE U78 25 NNE FIR 30 ESE FIR 45 WNW VEL
45 W VEL 35 ENE PUC 25 NNE U28 U28 25 SW U28 4HV 25 SW 4HV
30 E BCE 40 S BCE 35 NNW GCN 10 E FLG 30 WNW SOW 35 SSE SOW
45 N SAD 25 N SAD 45 NNE DMA 20 SE CGZ 20 SSW GYR 70 WNW LUF
40 ESE EED 15 N IFP 15 ENE LSV 70 WNW SGU 80 S ELY 30 ESE ELY
20 SSW ENV 40 NNW ENV 20 SW 77M 15 ENE BYI 35 E SUN 30 E LLJ.


...WESTERN U.S...

THINGS ARE UNFOLDING AS EXPECTED ACROSS THE WESTERN STATES...AS
THE LARGE AND DEEP MID/UPPER LEVEL TROF WAS CLOSING OFF A MID
LEVEL CENTER OVER CA...WITH DOWNSTREAM RAINFALL INCREASING IN
COVERAGE AND INTENSITY. THE LATEST MODEL RUNS CONTINUE TO BE IN
VERY GOOD AGREEMENT IN TAKING THIS CLOSING H5 LOW ONLY SLOWLY
EASTWARD INTO CENTRAL NV BY SUNDAY MORNING...BUT WITH SUBSTANTIAL
HEIGHT FALLS MAKING IT WELL INTO THE ROCKIES BY THAT SAME TIME.
THIS VERY DYNAMIC SYSTEM AS PER THE SUBSTANTIAL HEIGHT
FALLS...INCREASINGLY FAVORABLE UPPER DIVERGENCE AND...AT LEAST
THRU THE SOUTHERN GREAT BASIN...A MODESTLY STRONG SOUTHERLY LOW
LEVEL JET...WILL LEAD TO A WIDESPREAD RAINFALL...SOME OF IT
HEAVY...FROM AZ NORTHWARD INTO WESTERN MT. GREATER INSTABILITY AND
DEEPER MOISTURE THRU THE SOUTHERN GREAT BASIN WILL SUPPORT
STRONGER CONVECTION BASED NEARER TO THE SURFACE...AND CAPABLE OF
ANCHORING ITSELF ALONG COLD POOLS. FARTHER NORTH...FROM NRN UT/NE
NV AND NORTHWARD...CONVECTION WILL BE ROOTED FARTHER ALOFT...BUT
SHOULD BE PERSISTENT AND REPETITIVE OWING TO SUSTAINED DEEP LAYER
LIFT DURING JET COUPLING. THE WIDTH AND INTENSITY OF CONVECTIVE
ELEMENTS HERE SHOULD BE LIMITED COMPARED TO THE WARMER/MORE
UNSTABLE ENVIRONMENT TO THE SOUTH...BUT IN BOTH AREAS LARGELY
UNIDIRECTIONAL AND UNCHANGING WIND PROFILES WILL ALLOW FOR
TRAINING AND POTENTIAL FLASH FLOODING.

FROM THE DESERT SOUTHWEST INTO THE SOUTHERN GREAT BASIN..ISOLATED
1+ INCH RAINFALL AMOUNTS IN AN HOUR OR TWO AND LOCAL 2-3 INCH
EVENT TOTALS ARE LIKELY...WHILE THE LONGER DURATION EVENT FARTHER
NORTH IS LIKELY TO LEAD TO AREAL AVERAGE 0.50-1.50+ INCH AMOUNTS
OVER A RATHER LARGE AREA. WE EXPANDED THE SLIGHT RISK AREA JUST
SLIGHTLY EAST TO INCLUDE MORE OF UTAH...ESPECIALLY FOR THE
SATURDAY EVENING PERIOD. HEADING INTO SUNDAY...HOWEVER...THE
FAVORABLE PW PLUME OVER THE SOUTWHEST MAY BECOME PINCHED OFF AND
SEPARATE FROM THE FORCING...AND FORCING ITSELF WILL BECOME LESS
PRONOUNCED AS THE LOW BECOMES FULLY CLOSED. MODELS DO SHOW SOME
INDICATION OF HEAVY RAIN POTENTIAL OVER WESTERN NM/CO ON
SUNDAY...BUT THE LIMITING FACTORS CAUSED US TO STOP SHORT OF
EXPANDING THE RISK AREA THIS FAR EAST.


...FLORIDA...

A BROAD REGION OF DEEP AND RICH MOISTURE HAD CONTRIBUTED TO
LOCALLY HEAVY RAINFALL AND SOME FLASH FLOODING IN RECENT DAYS. THE
CENTRAL AXIS OF THIS MOISTURE PLUME AND ASSOCIATED 850-700 MB
CONVERGENCE WILL DRIFT WEST TODAY INTO THE GULF OF MEXICO AND WILL
BRUSH ACROSS THE FLORIDA PANHANDLE. THIS WESTWARD SHIFT MAY REDUCE
AREAL COVERAGE...BUT COULD CAUSE EVENTS TO BECOME EVEN MORE
FOCUSED ALONG THE IMMEDIATE WEST COAST OF THE PENINSULA AND NEAR
THE COAST OF THE PANHANDLE. AN AXIS OF 925 MB CONVERGENCE IS
FORECAST TO PERSIST ACROSS THE NORTHERN PENINSULA...ALONG THE
NORTH SIDE OF GRADIENTS ASSOCIATED WITH A REMNANT LOW LEVEL
BOUNDARY. EASTERLY LOW LEVEL WINDS OF 10-15 KNOTS WILL ALSO
ENHANCE CONVERGENCE ALONG THE WEST COAST SEA-BREEZE...WHILE
PROVIDING INFLOW FROM THE WARM LAND-BASED CAPE SOURCE REGION.
INTENSE LOCAL RAINFALL MAY AGAIN BE CAPABLE OF EXCEEDING 3 TO 4
INCHES IN 2 TO 3 HOURS. SSEO TOOLS INDICATE THAT THE PROBABILITY
OF RAINFALL EXCEEDING 3-HOUR FLASH FLOOD GUIDANCE WITHIN 40 KM OF
A POINT WILL PEAK ABOVE 50 PERCENT BETWEEN 22-02Z ALONG THE WEST
COAST OF THE CENTRAL AND NORTHERN PENINSULA.

TERRY/BURKE
$$




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.