Quantitative Precipitation Forecast
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FOUS30 KWBC 211752
QPFERD

EXCESSIVE RAINFALL DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
149 PM EDT SUN SEP 21 2014

...VALID 18Z SUN SEP 21 2014 - 00Z TUE SEP 23 2014...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 E RTN 35 SW CAO 15 ENE CVN 10 W LBB 20 NW SNK BPG 30 SSW ODO
30 WSW PEQ 15 ESE MMCS 25 W MMCS 40 SSW DMN 45 SSW DMN
70 SSW DMN 75 SSW DMN 20 SE DUG 25 ESE OLS 10 S OLS 25 NNW FHU
40 ENE SJN 20 WNW 4SL 15 S CEZ TEX 25 WNW ALS 25 W RTN 30 E RTN.

SLIGHT RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
30 SSW B23 55 W AWH 30 E MUO 45 SE LLJ 10 SSW WEY 40 WSW COD
50 NW LND 40 SW BVR VEL 45 E PUC 10 S PUC 20 WNW 4HV 25 WNW PGA
50 NW GCN 60 S SGU 10 E DRA 55 SW P68 30 SSW B23.

MODERATE RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
55 N HOB 25 NNW HOB 30 W HOB 35 W ATS 25 SSW SRR 15 WSW SRR
20 N SRR 45 N ROW 50 SW CVS 55 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"+) -- WILL
CONTINUE TO PULL NORTHWARD INTO THE AREA EARLY IN THE PERIOD AHEAD
OF THE MID- TO UPPER-LEVEL LOW CURRENTLY ACROSS NORTHWEST NV WHICH
PROGRESSES INTO NORTHWEST WY MONDAY AFTERNOON.  LOW-LEVEL INFLOW
AT 700 HPA IS FORECAST BY RECENT RAP/NAM RUNS TO BE IN THE 20-25
KT RANGE ACROSS SOUTHERN ID, MUCH OF UT, EASTERN NV, SOUTHWEST CO,
AND NORTHWEST WY, 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 SLIGHT RISK AREAS IN WEST-CENTRAL
CO COULD SEE SOME LOCALIZED FLASH FLOODING THOUGH THUNDERSTORM
ACTIVITY MAY NOT BE AS ORGANIZED -- THERE WAS A WEAKER SIGNAL FOR
HEAVY RAINFALL HERE WITHIN THE 12Z MESOSCALE QPF GUIDANCE.
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
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.  INFLOW INTO THE REGION SHIFTS FROM
SOUTHEASTERLY TO MORE SOUTHERLY WITH TIME, WHICH SHOULD SLOWLY
DECREASE THE RISK OF FLASH FLOODING ACROSS THE REGION.  INITIALLY,
WHAT REMAINS OF ODILE OPENS UP INTO A 700 HPA TROUGH AND
RETROGRADES WEST AND NORTHWEST INTO/ACROSS NM, WHICH SHOULD END
THE SIGNIFICANT RAINFALL/FLASH FLOOD THREAT FROM EAST TO WEST
TODAY ACROSS WESTERN TX AS A SUBSIDENCE INVERSION BUILDS IN ITS
WAKE.  PWS WILL REMAIN BETWEEN 2 AND 3 STANDARD DEVIATIONS ABOVE
NORMAL ACROSS WESTERN TX AND NM FOR LATE SEPTEMBER -- IN THE
1.50-1.75" 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 2-5" ARE EXPECTED ACROSS PORTIONS OF NM, WHICH
MAINTAINS A FLASH FLOOD THREAT OVER SATURATED AREAS.  THE MODERATE
RISK AREA (SOUTHEAST NM AND A SMALL PORTION OF WEST TEXAS) HAS
SHRUNK, BUT REMAINS TO ACCOUNT FOR THE EXPECTED HIGHER RAINFALL
TOTALS AND THE SATURATED SOILS IN THAT REGION.

ROTH
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