MESOSCALE PRECIPITATION DISCUSSION 0338
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
328 PM EDT WED JUN 20 2018

AREAS AFFECTED...IOWA...EXT NORTHWEST IL

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

VALID 201930Z - 210130Z

SUMMARY...DEEP CYCLOGENESIS WILL LEAD TO SLOW MOVING/STATIONARY
CELLS ALONG THE TROWAL ACROSS SATURATED SOILS LEADING TO LIKELY
FLASH FLOODING WITH 2-4" LIKELY WITH LOCALIZED HIGHER AMOUNTS
POSSIBLE.

DISCUSSION...GOES-16 WV SUITE DEPICTS A NEGATIVELY TILTED MID TO
UPPER LEVEL TROF ACROSS NEB INTO NW MO ATTM.  A STRONG UPSTREAM
90KT 3H JET IS UNDER CUTTING THE TROF AND ROUNDING THE BASE WITH A
NARROW SW-NW SPEED MAX TO 50KTS EXPECTED TOWARD 00Z IN THE
VICINITY OF THE MISSOURI RIVER. SO STRONG DIFFLUENCE BUT ALSO
SPEED DIVERGENCE WILL SUPPORT VERY STRONG CYCLOGENESIS ACROSS
CENTRAL IA.  GIVEN THE STRENGTH OF THE JET AND SHARPNESS OF THE
TROF...THE COLD FRONT WILL BE ACCELERATING EASTWARD QUICKLY...AND
WILL ORIENTED THE WARM CONVEYOR BELT/TROWAL BISECTING IA FROM NEAR
THE QUAD CITIES TO NW IA WITH VERY SLOW/NEAR ZERO CELL MOTION
VECTORS.  CLOUD COVER/MODERATE SHOWERS ACROSS THE SE SD INTO NW IA
HAS SIGNIFICANTLY STUNTED INSTABILITY BUT STRONG INSOLATION IN
CENTRAL IA SUPPORTED 2000-2500 J/KG CAPES GIVEN MID-70S TDS.  

STRONG CONVERGENCE ALONG THE FRONTAL ZONE HAS SPARKED RAPIDLY
DEVELOPING CONVECTION THAT HAS BEEN LIFTING NORTH WITH SOME CELLS
DEVELOPMENT WITHIN THE DEVELOPING TROWAL OVER NW IA AS WELL. 
GIVEN ADVECTION OF THE INSTABILITY THROUGH THE TROWAL AND HIGH LOW
TO MID-LEVEL MOISTURE POOLED ALONG THE FRONT...TOTAL PWS OVER
1.75" HAVE BEEN OBSERVED IN GPS AND BLENDED TPW SUPPORTING MOIST
LOW LEVEL PROFILES FOR EFFICIENT RAINFALL PRODUCTION AND RATES. 
ALONG THE SIDE OF THE DEVELOPING SURFACE LOW...RAP PROPAGATION
VECTORS WILL BE ALIGNED FOR TRAINING/MERGERS WITH 10-15KTS TOWARD
THE NNW SLOWING TO NEAR ZERO NEAR SLB...SUPPORTING THE POTENTIAL
FOR HIGH RATES INITIALLY BUT CONTINUING TO SUPPORT MODERATE TO
HEAVY SHIELD PRECIPITATION FOR A LONGER DURATION INUNDATION
FLOODING CONCERNS AFTER NIGHTFALL. HI-RES CAMS ARE SUPPORTIVE AND
ARE SUGGESTIVE OF 2-4" TOTALS WITH SOME POTENTIAL ISOLATED SPOTS
OVER 6" PSBL.  GIVEN WET ANTECEDENT CONDITIONS FLASH FLOODING IS
CONSIDERED LIKELY ACROSS NW IA TO CENTRAL IA.

FURTHER EAST...NEAR THE TRIPLE POINT IN E IA...CELLS WILL ALSO
SLOW DOWN NEAR/ACROSS THE WARM FRONT INTO N IL...WHILE DURATION
GIVEN SLIGHTLY FASTER FORWARD (EASTWARD) PROPAGATION VECTORS.
HOWEVER LOWERED 1HR FFG VALUES 1.5-2" AND 3HR TO 2-3" STILL REMAIN
POSSIBLE FOR EXCEEDANCE GIVEN THE RAINFALL EFFICIENCY AND FLASH
FLOODING IS POSSIBLE ACROSS E IA INTO NW IL THROUGH THE EVENING
HOURS. 

GALLINA

ATTN...WFO...DMX...DVN...FSD...

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

LAT...LON   43509547 43359443 42979335 42609213 42149088
            41709010 41079077 41329212 41789370 42089496
            42319575 42479641 43369646