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Excessive Rainfall Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1014Z Sep 21, 2014)
 
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Abbreviations and acronyms used in this product
 
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


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

...VALID 12Z 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
45 WSW ENV 35 SSW DPG 20 WSW MLF 45 SW SGU VGT 30 NNE DRA
20 ENE TPH 60 NW TPH 25 ESE NFL 30 E LOL 25 ESE B23 45 WSW ENV.

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 30 S BPG
35 ESE 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
30 W GDP ALM 20 N SRR 45 N ROW 55 ENE ROW 15 E HOB 20 WNW INK
30 SE GDP 30 W GDP.


NEVADA INTO WESTERN UT
~~~~~~~~~~~~~~~~~~~~~~

AXIS OF HIGHLY ANOMALOUS PWS (3.5-4.0 STANDARD DEVIATIONS ABOVE
NORMAL PER THE SREF/GEFS) WILL CONTINUE TO PULL NORTHWARD INTO THE
AREA EARLY IN THE PERIOD AHEAD OF THE MID/UPPER LEVEL LOW
CURRENTLY ACROSS CENTRAL CA. MEANWHILE...LARGE-SCALE FORCING
(UPPER DIVERGENCE/DIFFLUENCE AND DEEP-LAYER ASCENT) WILL CONTINUE
TODAY AHEAD OF THE MID/UPPER LEVEL LOW...ALLOWING FOR MORE
WIDESPREAD SHOWERS/TSTMS AND SOMEWHAT ATYPICAL AREAL-AVERAGE
RAINFALL FOR THE TIME OF YEAR (GENERALLY .25 TO .75 INCH). THE
RELATIVELY DRYER LOW LEVELS/HIGH-BASED NATURE OF THE CONVECTION
WILL TEND TO LIMIT RAINFALL EFFICIENCY/RATES...WHILE ALSO CAPPING
MUCAPES AROUND 500-1000 J/KG. THIS WILL LIMIT THE THREAT/COVERAGE
OF ANY EXCESSIVE RAINFALL...THOUGH LOCALIZED AMOUNTS OF 2-3"
WITHIN A FEW HOURS AS PER THE HIGH RESOLUTION GUIDANCE COULD LEAD
TO RUNOFF ISSUES GIVEN THE CURRENT FFG.


WEST TEXAS INTO NEW MEXICO AND SOUTHEASTERN ARIZONA
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

RATHER STAGNANT PATTERN ACROSS THE AREA DURING THIS PERIOD...WITH
LITTLE SHIFT IN THE FEATURES ALOFT WHILE THE FAVORABLE
THERMODYNAMIC PROFILE REMAINS IN PLACE. ONCE AGAIN...LARGE-SCALE
FORCING WILL BE LACKING UNDERNEATH THE BROAD UPPER
RIDGE...HOWEVER...PERSISTENT WEAK 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 AGAIN BY
THE PERSISTENT E-SE (UPSLOPE) LOW-LEVEL FLOW AND MOISTURE
TRANSPORT. PWS WILL REMAIN BETWEEN 2 AND 3 STANDARD DEVIATIONS
ABOVE NORMAL ACROSS THE AREA...WITH THE WESTWARD EXTENT (SECONDARY
PW AXIS) ACROSS SE ARIZONA/WESTERN NEW MEXICO AIDED BY THE UPPER
LEVEL MOISTURE TRANSPORT NORTH OF T.S. POLO. WPC UTILIZED A
MULTI-MODEL BLEND WITH THE QPF...INCORPORATING SOME OF THE HIGHER
RESOLUTION DATA THAT APPEARS TO BE VERIFYING BETTER IN THE NEAR
TERM (NSSL WRF...WRF-ARW...AND SSEO MEAN)...WHICH MAINTAINS DECENT
CONTINUITY FROM THE PREVIOUS WPC FORECAST AND ALIGNS WELL WITH THE
REFORECAST DATA FROM THE 00Z 09/20 CYCLE. 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 GIVEN THE RELATIVELY LOW 1-3 HR FFG...WILL MAINTAIN A
FLASH FLOOD THREAT.

THE MODERATE RISK AREA (SOUTHEAST NM AND A SMALL PORTION OF WEST
TEXAS) WAS DRAWN TO ACCOUNT FOR THE EXPECTED HIGHER RAINFALL
TOTALS COMPARATIVELY SPEAKING...WHILE ALSO ACCOUNTING FOR 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.

HURLEY