MESOSCALE PRECIPITATION DISCUSSION 0226
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
400 PM EDT WED MAY 17 2017

AREAS AFFECTED...SE SD...EXT E NEB...W & N IA...S MN...W WI

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 172000Z - 180100Z

SUMMARY...SATURATED SOIL CONDITIONS AND POTENTIAL FOR REPEAT
CONVECTION PARTICULARLY ALONG STATIONARY FRONT IN S MN/W WI LIKELY
TO POSE FLASH FLOOD THREAT.

DISCUSSION...GOES-E WV LOOP DENOTES A MATURE DEEP CYCLONE OVER NE
NEB WITH A FEW SHORTWAVE SPOKES ROTATING THROUGH THE EASTERN
HEMISPHERE SPARKING CONVECTIVE ACTIVITY.  AT THE SURFACE THE DEEP
CYCLONE IS LOCATED JUST WEST OF SUX IN NE NEB WITH A STATIONARY
FRONT EXTENDING NORTH THEN ENE ACROSS SE SD INTO S MN TOWARD MSP
LOCKED INTO PLACE BY FAIRLY IMPRESSIVE COOL CONVEYOR/NORTH
COMPONENT WINDS FROM SFC TO 8H. A SECONDARY SURGE OF SOUTHERLY
WINDS UP TO 25KTS ACROSS CENTRAL AND EASTERN IA CAN BE DEPICTED AS
A SECONDARY WARM FRONT AND IS SCATTERED WITH ACTIVATING CONVECTION
WITHIN UNSTABLE ENVIRONMENT WITH 1000-1500 MLCAPE AND MID 60S TO
ISOLATED 70F SFC TDS. DPVA ON LEAD EDGE OF SHORTWAVE ENERGY
DEPICTED WELL AT LEADING EDGE OF COOLER TEMPS IN WV IS THE
CATALYST FOR CONVECTIVE DEVELOPMENT.  GIVEN THE BROAD AREA OF
ASCENT WITH LIMITED CAPPING AND MODEST INSTABILITY...CONVECTION IS
MORE NUMEROUS WITH CONVECTIVE CORES BUT CORES ARE ALSO GENERALLY A
BIT SMALLER IN SCALE...LIMITING DURATION AND RAINFALL
GENERATION/EFFICIENCY OF THE CONVECTION.  STILL WITH TPWS OF 1.25
INCREASING TO 1.5" ALONG THE STATIONARY FRONT (WHERE MOISTURE IS
TRAPPED)...CELLS ARE LIKELY TO HAVE RATES UP TO 1.25" THOUGH
PRODUCE STREAKS OF 1-1.5" ACROSS N CENTRAL IA.  HOWEVER...WITH
DEEPLY STACKED CYCLONE...CELLS WILL EVENTUALLY BECOME CONFLUENT
INTO THE AXIS OF THE STATIONARY FRONT FROM SE SD ACROSS S
MN...WHILE DECAYING SLOWLY WITH LOSS OF BEST INSTABILITY.  STILL
WITH MERGERS AND OVERRUNNING THE BOUNDARY...RAINFALL TOTALS WILL
BEGIN TO COMPILE ALONG THE BOUNDARY MUCH LIKE THE CURRENT PROCESS
NEAR THE CENTER OF THE UPPER LOW IN SD ATTM WHERE INSTABILITY IS
BEING LIMITED DUE TO ONGOING OCCLUSION PROCESSES AND INCREASE IN
OVERRUNNING COOLER/STABLE AIR.  AS SUCH THE FOCUS OF MOST INTENSE
RAINFALL AND CORES WILL SLOWLY SHIFT EASTWARD FROM SD ACROSS S MN
TOWARD W WI THROUGH THE LATE AFTERNOON HOURS EARLY EVENING AS THE
SECONDARY WARM FRONT AND ASSOCIATED CONVECTION INTERSECT THE
STATIONARY FRONT.  HI-RES CAMS SUGGEST BROAD 2-3" THROUGH 02Z WITH
ISOLATED 3-4" TOTALS POSSIBLE WHERE BEST CORES TRANSECT THE
BOUNDARY. FAIRLY STRONG AGREEMENT IN THE HI-RES CAMS PROVIDES
HIGHER CONFIDENCE IN HI-RES ENSEMBLES SUCH AS THE HREF VER. 2 SSEO
MEAN AND HRRRTLE.  GIVEN FFG VALUES IN THE AREAS RANGE AROUND 2-3
IN 3HRS WITH LOWER VALUES NEAR URBAN CENTERS ARE AREAS AFFECTED
OVER THE LAST TWO NIGHTS ALONG THE MS RIVER IN SE MN/W WI...AS
SUCH FF THREAT IS CONSIDERED LIKELY 

FURTHER SOUTH ALONG THE MO RIVER INTO W IA..STRONG SHORTWAVE
ROUNDING THE BASE OF THE CYCLONE IS PROVIDING STEEPENING LAPSE
RATES AND DPVA FOR VERTICAL ASCENT SPURRING A LARGE CONVECTIVE
OVERTURNING WITH NUMEROUS CONVECTIVE CORES.  SOME N-S LINEAR ROLLS
ARE NOTED IN SATELLITE IR TOPS/RADAR REF PARTICULARLY CLOSER TO
THE SHORTWAVE AXIS ITSELF.  CELLS ARE BIT MORE ISOLATED FURTHER
EAST AND THEREFORE A BIT MORE ROBUST. CONCERNS FOR CELLS ALONG
THESE LINER LINES TO TRACK/REPEAT THROUGH AREAS OF SATURATED SOILS
(MAINLY OVER E NEB/W IA) POSE SOME CONCERN OF EXCEEDING LOWERED
FFG VALUES IN THE AREA PARTICULARLY IN THE 1HR OR 2HR RANGES GIVEN
FAIRLY PROGRESSIVE NATURE.  AS SUCH ISOLATED FF THREAT IS POSSIBLE
WITHIN THIS AREA AS WELL OVER THE LATE AFTERNOON INTO EARLY
EVENING HOURS.   

GALLINA

ATTN...WFO...ARX...DMX...EAX...FSD...MPX...OAX...

ATTN...RFC...MBRFC...NCRFC...

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            41749371 40989423 40469450 40439581 40919618
            41839638 42389696 42979764 43729773 44389688
            45369395