Quantitative Precipitation Forecast
Issued by NWS

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000
FOUS30 KWBC 211336
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
935 AM EDT SUN SEP 21 2014

...VALID 15Z SUN SEP 21 2014 - 12Z MON SEP 22 2014...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
25 E ONO 25 W IDA 20 NNE FIR 15 SSE U28 20 W PGA 50 NW GCN
60 S SGU 10 E DRA 55 SW P68 65 W AWH 25 E ONO.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 E RTN 35 NNW TCC 35 NNE CVN PVW 35 ESE LBB 40 S BPG 50 E FST
25 SSE E38 45 WNW MRF 45 E MMCS 25 E LRU 40 SSW LRU 60 ESE DUG
40 SSW DUG 15 NW FHU 20 NW SAD 35 S GUP 20 SSW GNT SAF 25 W RTN
30 E RTN.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
45 N HOB 20 NW ODO 40 NW PEQ 45 SE ALM 20 N ALM 20 N SRR
45 N ROW 55 ENE ROW 45 N HOB.


GREAT BASIN AND VICINITY
~~~~~~~~~~~~~~~~~~~~~~~~
AN AREA OF HIGHLY ANOMALOUS PRECIPITABLE WATER VALUES (PWS) --
3.5-4.0 STANDARD DEVIATIONS ABOVE NORMAL/NEAR THE 99TH PERCENTILE
FOR LATE SEPTEMBER PER THE RAP/SREF/GEFS GUIDANCE (1-1.25") --
WILL CONTINUE TO PULL NORTHWARD INTO THE AREA EARLY IN THE PERIOD
AHEAD OF THE MID- TO UPPER-LEVEL LOW CURRENTLY ACROSS CENTRAL CA.
LOW-LEVEL INFLOW AT 700 HPA IS FORECAST BY RECENT RAP RUNS TO BE
IN THE 20-25 KT RANGE ACROSS SOUTHERN ID, MUCH OF UT, AND EASTERN
NV WHICH WOULD BE SUFFICIENT TO ORGANIZE CONVECTION ACROSS THE
WEST.  SOME DRY AIR IN LOW LEVELS (OUTSIDE OF EASTERN NV WHICH HAS
MOISTENED UP DUE TO RECENT RAINS) PER REGIONAL 12Z SOUNDINGS
SHOULD ALLOW CONVECTION TO REMAIN PROGRESSIVE -- CELL TRAINING
WOULD BE THE FLASH FLOOD/EXCESSIVE RAINFALL THREAT.  EXPECTATIONS
FROM DAYTIME HEATING ALONG WITH RECENT RAP GUIDANCE INDICATES CAPE
VALUES OF 1000+ J/KG IN POCKETS ACROSS UT AND NV THIS AFTERNOON
AND EVENING.  FARTHER NORTH IN SOUTHERN ID, BUILDING INSTABILITY
COULD BE A PROBLEM DUE TO EXTENSIVE CLOUD COVER WITHIN AN AREA OF
DIFFLUENCE TO THE NORTHEAST OF THE UPPER LOW.  EVEN THOUGH NOT
INCLUDED IN THE AREA (DUE TO LESSER AMOUNTS OF MOISTURE AND MORE
LIMITED/BRIEFER PERIODS OF STRONGER LOW-LEVEL INFLOW), AREAS JUST
OUTSIDE THE EASTERN SIDE OF THE SLIGHT RISK AREA IN SOUTHWEST WY,
EASTERN UT, AND WESTERN CO COULD SEE SOME LOCALIZED FLASH FLOODING
THOUGH THUNDERSTORM ACTIVITY MAY NOT BE AS ORGANIZED.  RAINFALL
RATES UP TO 1.5" AN HOUR ARE SUPPORTED BY THE AVAILABLE MOISTURE,
WITH MESOSCALE GUIDANCE INDICATING LOCAL AMOUNTS OF 2-4" BEING
POSSIBLE.


WEST TEXAS INTO NEW MEXICO AND SOUTHEASTERN ARIZONA
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A RATHER STAGNANT PATTERN IS EXPECTED THIS PERIOD WITH LITTLE
SHIFT IN THE EXPECTED FLOW PATTERN.  PERSISTENT UPPER-LEVEL
DIFFLUENCE BETWEEN THE CLOSED UPPER HIGH ACROSS WRN MEXICO AND THE
FASTER WESTERLIES/HEIGHT FALLS DROPPING INTO THE MID MS VLY WILL
ALLOW FOR THE DEVELOPMENT OF MORE ORGANIZED CONVECTION...AIDED BY
PERSISTENT E-SE (UPSLOPE) LOW-LEVEL FLOW AND MOISTURE TRANSPORT.
PWS WILL REMAIN BETWEEN 2 AND 3 STANDARD DEVIATIONS ABOVE NORMAL
ACROSS THE AREA FOR LATE SEPTEMBER -- IN THE 1.75-2" RANGE -- WITH
THE WESTWARD EXTENT (SECONDARY PW AXIS) ACROSS SE ARIZONA/WESTERN
NEW MEXICO AIDED BY SOME UPPER-LEVEL MOISTURE TRANSPORT NORTHEAST
OF A WEAKENING T.S. POLO.  AREAL AVERAGE AMOUNTS RANGE BETWEEN
0.50-1.5 INCHES OVER MUCH OF THE AREA...HOWEVER...PER THE
AFOREMENTIONED 4KM GUIDANCE...LOCALIZED AMOUNTS OF 3-5+ INCHES ARE
EXPECTED (ESPECIALLY INTO ERN NM), WHICH MAINTAINS A FLASH FLOOD
THREAT.  THE MODERATE RISK AREA (SOUTHEAST NM AND A SMALL PORTION
OF WEST TEXAS) REMAINS TO ACCOUNT FOR THE EXPECTED HIGHER RAINFALL
TOTALS AND THE LOWER FFG IN THAT REGION. THE LATEST SSEO 40KM
NEIGHBORHOOD PROBABILITIES OF QPF EXCEEDING THE FFG REFLECT
THIS...WITH PROBS ABOVE 50 PERCENT NOTED IN THE MODERATE RISK
AREA.

ROTH/HURLEY
$$





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