MESOSCALE PRECIPITATION DISCUSSION 0700
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
700 PM EDT TUE AUG 15 2017
AREAS AFFECTED...NEBRASKA & NORTHWEST IA
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY
VALID 152259Z - 160459Z
SUMMARY...CONVECTION IS EXPANDING WESTWARD ACROSS NE. HOURLY RAIN
TOTALS UP TO 2" WITH LOCAL AMOUNTS TO 5" SHOULD ENHANCE FLASH
FLOOD CONCERNS.
DISCUSSION...A WARM FRONT HAS MOVED ACROSS SOUTHERN NE AND IS
BEGINNING TO ACT AS THE FOCUS FOR NEW CONVECTION ACROSS CENTRAL
AND SOUTHWEST NE. MEANWHILE, THUNDERSTORMS CONTINUE TO DROP HEAVY
RAINFALL ACROSS CENTRAL AND NORTHEAST NE AND ENTER NORTHWEST IA.
PRECIPITABLE WATER VALUES ARE 1.5-2" PER RAP MODEL INITIALIZATION.
ML CAPE VALUES OF 2000-3500 J/KG ARE BEING IMPORTED INTO THE
BOUNDARY BY SOUTH-SOUTHEAST WINDS OF 20 KTS AT 850 HPA -- NEAR THE
MAGNITUDE OF THE MEAN 850-400 HPA WINDS -- PER VAD WIND PROFILES.
BULK SHEAR OF 25-40 KTS EXISTS IN THE REGION PER SPC MESOANALYSES.
WHILE THE MESOSCALE GUIDANCE IS STRUGGLING WITH THE CONVECTION IN
EASTERN NE NEAR THE NE/IA BORDER, IT APPEARS TO HAVE SOME HANDLE
ON EXPECTATIONS FARTHER WEST ACROSS NE OVER THE NEXT SEVERAL HOURS
BASED ON CURRENT SATELLITE/RADAR TRENDS, WITH A GENERAL SIGNAL FOR
5" THROUGH 05Z. CONVECTION MOVING IN FROM CO/WY SHOULD MERGE WITH
THE BUILDING ACTIVITY ACROSS WESTERN NE WITH TIME. BACKING AND
INCREASING WINDS AT 850 HPA THROUGH 01Z SHOULD CAUSE CONVECTION TO
EXPAND WESTWARD/SOLIDIFY ACROSS WESTERN NE UNTIL THE CO/WY
ACTIVITY MERGES IN. AS WINDS AT 850 HPA INCREASE, BACKBUILDING
BECOMES MORE OF A HEAVY RAINFALL CONCERN. TRAINING IS ALSO
EXPECTED AS STORMS SHOULD MOVE EAST AT 20 KTS PARALLEL TO THE
INSTABILITY GRADIENT AND 1000-500 HPA THICKNESS PATTERN. OF
CONCERN IS CIN DEVELOPMENT OVERNIGHT WHICH SHOULD SHIFT CONVECTION
NORTHWARD TOWARDS THE EASTERN NE/SD BORDER, WHICH COULD ALLOW
FUTURE CONVECTION TO TRACK OVER AREAS HIT HARD TODAY IN NORTHEAST
NE. SOILS ARE AT LEAST PARTIALLY SATURATED DUE TO ABOVE NORMAL
RAINFALL OVER THE PAST COUPLE WEEKS ACROSS MUCH OF NE AND
SOUTHEAST SD. FLASH FLOODING IS AN INCREASING CONCERN IN THIS
AREA.
ROTH
ATTN...WFO...BOU...DMX...FSD...GID...LBF...OAX...UNR...
ATTN...RFC...MBRFC...NCRFC...
LAT...LON 43779711 43029364 41379462 40729642 40729976
40770128 40800246 41620188 42250101 43159948
Last Updated: 700 PM EDT TUE AUG 15 2017