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Excessive Rainfall Discussion
 
(Latest Discussion - Issued 0033Z Mar 27, 2017)
 
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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
833 PM EDT SUN MAR 26 2017

...VALID 01Z MON MAR 27 2017 - 12Z MON MAR 27 2017...
...REFERENCE AWIPS GRAPHIC UNDER...DAY 1 EXCESSIVE RAINFALL...


MARGINAL RISK OF RAINFALL EXCEEDING FFG TO THE RIGHT OF A LINE FROM
20 WSW GLE 10 S OKM 30 ENE FSM 15 NW LRF 10 N PBF 15 SW TXK LNC
20 NNE 05F 25 ESE 7F9 20 WSW GLE.


...OKLAHOMA / TEXAS / ARKANSAS...

RETURNING MOISTURE AND HEIGHT FALLS AHEAD OF A VIGOROUS DEEP LAYER
SHORTWAVE TROUGH HAD YIELDED CONVECTIVE INITIATION IN CLUSTERS
FROM CENTRAL OKLAHOMA DOWN TO ABOUT THE LATITUDE OF WACO TEXAS.
THE 00Z FORT WORTH SOUNDING REVEALED A VERY SHALLOW SURFACE
MOISTURE LAYER...BUT SUFFICIENTLY MOIST LAYER AT THE TOP OF THE
BOUNDARY LAYER TO SUPPORT STRONG UPDRAFTS...PERHAPS NOT TRULY
SURFACE BASED. OVERNIGHT THE WARM SECTOR / CAPE AXIS WILL EXPAND
NORTH AND EASTWARD...WITH CAPE VALUES CLIMBING AS LOW LEVEL
MOISTURE IS ADVECTED TOWARD SOUTHEAST OKLAHOMA AND WESTERN
ARKANSAS. THIS SHOULD SUPPORT CONTINUED CLUSTERS OF STORMS WITH A
MIXTURE OF CONVECTIVE MODES...INCLUDING THE POSSIBILITY OF LOCAL
UPSCALE GROWTH PER RECENT STORM PREDICTION CENTER MESOSCALE
DISCUSSION.

WHETHER OR HOW THIS EVENT WILL TRANSLATE INTO A FLASH FLOOD THREAT
WILL BE DIFFICULT TO PINPOINT WITH MUCH SPECIFICITY. THE 12Z
HI-RES MODELS HAD SHOWN AN EMPHATIC SIGNAL FOR UPSCALE GROWTH AND
A COLD POOL FOCUSING RAINFALL WITHIN THE BROAD LOW LEVEL JET NEAR
THE ARKLATEX OVERNIGHT. HRRR RUNS IN THE LATE AFTERNOON BEGAN TO
BACK OFF OF THIS SUGGESTION...AND STORM MODE WAS STILL LARGELY
SUPERCELLULAR AT 00Z. FLASH FLOOD GUIDANCE SUGGESTS AT LEAST 2
INCHES OF RAIN IN AN HOUR OR 2.5 INCHES IN 3 HOURS WILL BE
REQUIRED TO PRODUCE BANKFUL CONDITIONS. STORM MODE AND MARGINAL
PRECIPITABLE WATER MAY BE WORKING AGAINST THIS OCCURRING...BUT
THERE IS STILL SOME CONCERN THAT LOCAL CELL MERGERS AND SOME
UPSCALE GROWTH OF COLD POOLS INTERCEPTING THE LOW LEVEL FLOW COULD
YIELD SPOTTY INTENSE RAINFALL CAPABLE OF EXCEEDING FFG. THE
MARGINAL RISK AREA IS THEREFORE MAINTAINED AND EXPANDED WESTWARD A
BIT TO CAPTURE ONGOING CONVECTION IN THE I-35 CORRIDOR OVER NORTH
TEXAS AS OF 00Z.

BURKE