MESOSCALE PRECIPITATION DISCUSSION 0227
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
659 PM EDT TUE MAY 29 2018

AREAS AFFECTED...WESTERN AND CENTRAL IA...SOUTHERN AND CENTRAL MN

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

VALID 292300Z - 300300Z

SUMMARY...CONVECTION TRAINING IN A QUASI UNIDIRECTIONAL FLOW COULD
RESULT IN A FLASH FLOOD THREAT INTO THE EVENING HOURS.

DISCUSSION...REGIONAL RADARS INDICATED NORTH TO SOUTH ORIENTED
LINES OF CONVECTION MOVING SLOWLY EASTWARD ACROSS WESTERN IA INTO
CENTRAL MN LATE THIS AFTERNOON. THE CONVECTION IS ENTRENCHED IN AN
AXIS OF 1000-15000 J/KG OF MLCAPE...WHERE PRECIPITABLE WATER
VALUES RANGE BETWEEN 1.50/2.00 INCHES (WHICH IS ABOUT TWO STANDARD
DEVIATIONS ABOVE THE MEAN). THE MID LEVEL FLOW IS MORE OR LESS
UNIDIRECTIONAL AHEAD OF A SHORT WAVE OVER EASTERN NE (AS SEEN ON
THE GOES-16 MID LEVEL WV LOOP).

RAP SOUNDINGS OVER WESTERN IA INTO CENTRAL MN AREA SHOWING DRY AIR
IN THE MID LEVELS...SUPPORTIVE OF HAIL. SPOTTER REPORTS AND HCA
PRODUCTS OUT OF KMPX INDICATED THAT HAIL AS OCCURRING...WHICH
SHOULD LIMIT THE FLASH FLOOD THREAT IN THE NEAR TERM.
HOWEVER...THE COLUMN IS EXPECTED TO MOISTEN AS THE LINES OF
CONVECTION MOVE SLOWLY EASTWARD. CONVECTION TRAINING IN THIS
ENVIRONMENT COULD POSE FLASH FLOOD THREAT...PARTICULARLY OVER
WESTERN IA INTO SOUTHERN MN...WHERE SOUNDINGS SHOWED THE COLUMN
MOISTENING MORE QUICKLY.

RADAR ESTIMATES OVER IA/MN ARE CURRENTLY BEGIN CONTAMINATED BY
HAIL...BUT AS THE STORMS SLOWLY TRANSFORM FROM HAIL PRODUCERS INTO
A FLASH FLOOD THREAT...LOCAL 2.00/3.00 INCH RAINFALL AMOUNTS ARE
POSSIBLE. THIS IS INDICATED BY THE MOST RECENT HRRR/EXPERIMENTAL
HRRR...WITH THE HIGHEST AMOUNTS FROM WEST CENTRAL IA INTO SOUTH
CENTRAL MN. TRAINING WOULD BE REQUIRED TO INITIAL FLASH
FLOODING...SO AT THIS TIME... FLASH FLOODING IS ONLY CONSIDERED
POSSIBLE.

HAYES

ATTN...WFO...DMX...FSD...MPX...OAX...

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

LAT...LON   45869385 45669317 45139291 44229322 43779335
            42009344 41219356 40959548 43909556 44839536
            45679487