MESOSCALE PRECIPITATION DISCUSSION 0483
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
151 PM EDT THU JUL 19 2018

AREAS AFFECTED...SOUTHERN MN...NORTHEAST IA...

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

VALID 191751Z - 192330Z

SUMMARY...INCREASING CONVECTION AND COVERAGE WITH SLOWING AND
CONVERGENT CELL MOTIONS POSE LOCALIZED FLASH FLOOD RISK.

DISCUSSION...GOES-16 WV SUITE DEPICTS THE HIGHLY ELONGATED SHEAR
AXIS FROM SE ND TO NW IL WITH A STRONG NORTHWESTERLY JET STREAK
ALONG THE SW PERIPHERY CENTERED THROUGH NEB TO SW IA.  WEAKER BUT
HIGHLY ANTICYCLONICALLY CURVED OUTFLOW ALONG THE NE EDGE OF THE
SHEAR AXIS PROVIDES SOME LARGER SCALE ASCENT.  WV AND GPS TPW
OBS/BLENDED TPW IMAGERY SHOWS STRONG DRY PUNCH ACROSS SE SD INTO
CENTRAL IA WITH VALUES ALREADY RAPIDLY FALLING TOWARD 1.3" IN
CENTRAL IA.  STILL COOL CONVEYOR BELT WITHIN THE SHEAR AXIS AND SE
FLOW ACROSS NE IA AND RETURN MOISTURE FROM THE INNER CORE OF THE
UPPER LOW KEEP THE PWATS IN THE 1.5-1.75" RANGE.  CURRENTLY THOUGH
THE Q-AXIS IS REMOVED TO THE EAST FROM THE BEST
INSTABILITY/HEATING AXIS THAT IS NOSING UP THROUGH WEST CENTRAL IA
GENERALLY COINCIDENT JUST AHEAD OF LOW LEVEL TWIST IN NW IA SEEN
IN VISIBLE IMAGERY.

AT THE SURFACE AN OCCLUDED SFC LOW IS NEAR BIG STONE COUNTY, MN
WITH THE FRONT EXTENDING SSE THEN DUE SOUTH JUST BEHIND THE
INSTABILITY AXIS...WITH SSELY LOW LEVEL FLOW AHEAD AND MID-60S TDS
WITH STRONG 10-15KT DUE WESTERLY FLOW BEHIND SUPPORTS STRONG MST
CONVERGENCE TO DEVELOP DEEP CONVECTION.  GIVEN DEEPER MOISTURE
DEPTH/PROFILES ACROSS SOUTHERN MN CELLS ARE MORE ROBUST AND GIVEN
PROXIMITY TO THE SHEAR AXIS...CELL MOTIONS REDUCE TO NEAR 5KTS AND
ARE GENERALLY CONVERGENT TO THE AXIS RUNNING FAIRLY SIMILAR TO THE
MINNESOTA RIVER.  AN MCV/VORT CENTER TO THE NW IN NE SD IS ALSO
STARTING TO SLIDE SOUTHEASTWARD PROVIDING ADDITIONAL DPVA ASCENT
FOR ADDITIONAL CONVECTION DEVELOP UPSTREAM INTO THIS AXIS AS
WELL...LEADING TO HIGHER PROBABILITIES FOR STATIONARY CELL MOTIONS
OVER THE NEXT FEW HOURS.  GIVEN SELY FLUX INTO THE AREA...THESE
CELLS ARE LIKELY TO MAINTAIN FAIRLY WELL EVEN WITHOUT THE DEEPEST
INSTABILITY (LESS THAN 1000 J/KG MLCAPES).  RATES OF 1-1.5"/HR ARE
LIKELY AND POSSIBLY AS HIGH AS 2" NEAR THE MN/IA BORDER TOWARD AEL
OR AUM WHERE DEEPEST MOISTURE WILL CONTINUE TO RESIDE THOUGH ALSO
BE FASTER MOVING.

THIS AXIS OF HIGHER RAINFALL IS GENERALLY COINCIDES WITH LOWERED
FFG VALUES FROM LAST EVENING'S RAINFALL AND IS SUPPORTED BY THE
BULK OF THE HI-RES CAMS BUT IN PARTICULAR RECENT HRRR, 12Z NMMB
AND GEM REGIONAL RUNS.  WHILE GUIDANCE AND CURRENT INSTABILITY
SUGGEST CONVECTION MAY BE A BIT MORE SCATTERED...THERE IS SOLID
SIGNAL FOR 1.5-3" TOTALS AND FLASH FLOODING CAN BE CONSIDERED
POSSIBLE THROUGH THE NEXT 4-6 HRS IN THIS AREA.

GALLINA

ATTN...WFO...ABR...ARX...DMX...FSD...MPX...

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

LAT...LON   45569500 45249416 44849296 43789140 42819156
            43129361 43649489 44079573 44379612 44869642
            45429605