343
AWUS01 KWNH 171959
FFGMPD
MNZ000-IAZ000-NEZ000-SDZ000-180200-
MESOSCALE PRECIPITATION DISCUSSION 0178
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
358 PM EDT SUN MAY 17 2026
AREAS AFFECTED...SOUTHEAST SD...EASTERN NEB...WESTERN IA...FAR
SOUTHWEST MN...
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE
VALID 172000Z - 180200Z
SUMMARY...INCREASING AVAILABLE MOISTURE TO SUPPORT HIGHER RAINFALL
EFFICIENCY OVER THE NEXT FEW HOURS (UP TO 2"/HR). PROGRESSIVE
NATURE MAY BE A LIMITING FACTOR, BUT CELLS WILL MOVE INTO A BIT
MORE PRONE TO FF DUE TO RECENT RAINS (ESP. SOUTH).
DISCUSSION...19Z SURFACE ANALYSIS DEPICTS THE VERY DYNAMIC
ENVIRONMENT IN PLACE ACROSS THE PLAINS THIS AFTERNOON (GIVEN BROAD
SOUTHWESTERLY FLOW ALOFT). THE SOUTHERN STREAM SHORTWAVE LAST
EVENING THAT HAS PROGRESSED INTO THE GREAT LAKES HELPED TO
REINFORCE A TIGHT MOISTURE GRADIENT ALONG THE PRIMARY WEST TO EAST
FROM FROM A WEAK WAVE IN E IA BACK ACROSS CENTRAL IA TO A SURFACE
WAVE NEAR AN STRONG CLUSTER OF THUNDERSTORMS WITH A HISTORY OF
HAIL AND FORWARD PROGRESSION. CIRA LPW AND RAP ANALYSIS SHOWS A
TIGHT, ENHANCED MOISTURE PLUME ALONG AND SOUTH OF THE BOUNDARY
GENERALLY DENOTED BY AGITATED CU FIELD (NE NEB, INTO CENTRAL IA)
OPPOSED BY NORTH WHERE TRANSVERSE BANDING SHOWS THE GREATER
STABILIZED AREA THAT IS A BIT DRIER AS WELL ACROSS FAR NW IA INTO
SW MN. ENHANCED TDS IN THROUGH 850MB ALONG WITH SLIGHTLY BACKED
FLOW FOR SOLID MOISTURE FLUX TRANSPORT TOWARD THE SURFACE LOW
ALONG/AHEAD OF MAIN COLD FRONT NE OF O'NEIL, NEB.
SOLID LOW LEVEL DIRECTIONAL CONVERGENCE HAS AIDED MAINTENANCE OF
THE CLUSTER WITH STRONG DEEP LAYER MOISTURE CONVERGENCE SIGNALS
DENOTING THE FLUX. AS THE CLUSTER REACHES THE DEEPER MOISTURE
AXIS, EXPECTATION IS BOTH INCREASED MOISTURE LOADING TO THE
UPDRAFTS HELPING TO BROADEN DOWNDRAFTS AS WELL AS INCREASE
RAINFALL EFFICIENCY. RAPID REFRESH GUIDANCE INCLUDING THE HRRR
AND WOFS SOLUTIONS DENOTE THIS UPTICK IN THE NEXT HOUR OR SO WITH
SUB-HOURLY INTENSE RATES EXPECTED; WITH 15-MINUTE HRRR TOTALS OVER
1-1.25" WHILE 5-MINUTE RATES IN THE WOFS OVER .5", AS HIGH AS .75"
CONSISTENTLY ACROSS SE SDAK. DEEP LAYER STEERING AND COLD FRONTAL
PUSH ARE LIKELY TO LIMIT RESIDENCY TIME BUT SOME EASTWARD
DEVELOPMENT ALONG THE FRONTAL/THETA-E AXIS MAY BREAK OUT
ADDITIONAL DOWNSTREAM CELLS TO HELP WITH SOME REPEATING TO REACH
HIGHER REQUIRED TOTALS TO INDUCE WIDELY SCATTERED INCIDENTS OF
FLASH FLOODING (2-3" IN 1-3HRS).
FURTHER EXPANSION OF THE CONVECTION TOWARD THE SOUTH ALONG AND
NORTH OF THE STRONGER 995MB SURFACE LOW ALONG THE NEB/KS WILL COME
AS EMBEDDED SHORTWAVE IN THE DEEPER SOUTHWESTERLY FLOW APPROACHES
AND UPPER-LEVEL DIFFLUENCE INCREASES INTO A DEVELOPING NORTH-SOUTH
JET STREAK PLACING MUCH OF THE AREA OF CONCERN IN FAVORABLE
DIVERGENCE/OUTFLOW ENVIRONMENT ALOFT IN THE RIGHT ENTRANCE OF SAID
JET STREAK.
HYDROLOGICALLY, MUCH OF THE AREA REMAINS IN SOLID DROUGHT WITH
0-40CM RATIOS IN THE 20-30%, THOUGH SCATTERED ACTIVITY LAST NIGHT
DID WET A FEW AREAS, ESPECIALLY SOUTH AND EAST ACROSS E NEB AND
THROUGH THE MISSOURI RIVER VALLEY. AS NOTED, ABOVE THE
PROGRESSIVE NATURE WILL LIKELY LIMIT THE OVERALL COVERAGE OF FLASH
FLOODING, BUT THE SHEAR INTENSITY WITH SOME REPEATING AND POSSIBLE
INTERSECTION WITH THOSE WETTER UPPER SOILS, SUGGEST WIDELY
SCATTERED FLASH FLOODING IS POSSIBLE THIS EVENING.
GALLINA
..PLEASE SEE WWW.WPC.NCEP.NOAA.GOV FOR GRAPHIC PRODUCT
ATTN...WFO...FSD...GID...OAX...
ATTN...RFC...KRF...MSR...NWC...
LAT...LON 44499698 44179587 43629534 42319568 41069591
40489702 40519934 40929935 41569836 42459794
42909829 43449867 44209800
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