MESOSCALE PRECIPITATION DISCUSSION 0124
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
503 PM EDT THU MAY 03 2018

AREAS AFFECTED...EXTREME EASTERN NEB...IA...SOUTHEAST
MN...SOUTHERN WI...FAR NORTHERN IL

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 032100Z - 040300Z

SUMMARY...SHOWERS AND THUNDERSTORMS WILL BE EXPANDING IN COVERAGE
AS LOW PRESSURE APPROACHES FROM THE SOUTHWEST. THE WET ANTECEDENT
CONDITIONS MAY RESULT IN SOME FLASH FLOODING CONCERNS THROUGH THE
LATE EVENING HOURS.

DISCUSSION...THE LATE-AFTERNOON GOES-16 AIRMASS RGB IMAGERY SHOWS
THE CLASSIC SIGNATURE OF A DEVELOPING MID LEVEL DEFORMATION ZONE
AHEAD OF AN APPROACHING PV ANOMALY ASSOCIATED WITH A STRONG
SHORTWAVE TROUGH. ENHANCED MID LEVEL FORCING/DPVA ASSOCIATED WITH
THIS WILL INTERACT WITH MOIST SOUTHERLY FLOW AHEAD OF A DEEPENING
WAVE OF LOW PRESSURE TO PROMOTE AN EXPANDING AREA OF HEAVY SHOWERS
AND THUNDERSTORMS NEAR AND TO THE NORTH OF A WARM FRONT SLOWLY
ADVANCING NORTHEAST ACROSS THE MIDWEST.

IN FACT...THE LATEST HRRR GUIDANCE FAVORS THE DEVELOPMENT OF A 40
TO 50 KT S/SW LOW LEVEL JET ACROSS THE MID MS VALLEY BETWEEN 00Z
AND 03Z WHICH WILL INTERCEPT THE AFOREMENTIONED FRONT AND FAVOR
STRENGTHENING LOW LEVEL MOISTURE AND INSTABILITY TRANSPORT FOR
MORE ORGANIZED AND LOCALLY FOCUSED CONVECTIVE GROWTH JUST NORTH OF
THE FRONT WHERE DEEP LAYER SHOULD BE MAXIMIZED. ALREADY A NOSE OF
MLCAPE VALUES OF 500 TO 1000 J/KG HAS NOSED UP ACROSS NORTHWEST MO
AND INTO SOUTHERN IA AND IS HELPING TO ALLOW CONVECTION TO BREAK
OUT BACK ACROSS FAR EASTERN NEB AND WESTERN IA AT THIS TIME.

EXPECT RAINFALL RATES OF AS MUCH AS 1.5 INCHES/HR AND STORM TOTAL
AMOUNTS THROUGH 03Z OF AS MUCH AS 2 TO 4 INCHES WITH ISOLATED
HEAVIER AMOUNTS NOT OUT OF THE QUESTION. GIVEN THE WET ANTECEDENT
CONDITIONS...SOME FLASH FLOODING WILL BE POSSIBLE.

ORRISON

ATTN...WFO...ARX...DMX...DVN...EAX...FSD...GRB...LOT...MKX...
MPX...OAX...

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

LAT...LON   44199100 44178958 44018882 43388802 42238812
            41968985 41529160 41049330 40499482 40649592
            41659651 42699619 43339516 43789376 44029253