MESOSCALE PRECIPITATION DISCUSSION 0441
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
700 PM EDT THU JUL 12 2018

AREAS AFFECTED...SOUTHEASTERN SD...NORTH CENTRAL NEB...

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 122300Z - 130400Z

SUMMARY...UPSCALE DEVELOPING COMPLEX EMERGING FROM SAND HILLS INTO
LONG-TERM SATURATED ENVIRONMENT WITH 2-4" TOTALS PSBL THROUGH 06Z
WITH FLASH FLOODING LIKELY.

DISCUSSION...GOES-16 WV SUITE DEPICTS A SHEARING MID-LEVEL
SHORTWAVE EXITING OUT OF NE CO INTO WESTERN NEB WITH A NICE
ANTICYCLONIC CIRRUS SHIELD OVER SD INTO N MN INDICATIVE TO A
FAIRLY TIGHT ISOTACH GRADIENT RIGHT ENTRANCE REGION OF THE 3H JET
(80KT MAX IN ONTARIO).  THESE FEATURES PROVIDE EXCELLENT UPPER
LEVEL DIVERGENCE/DPVA FOR BROAD SCALE ASCENT AND EVENTUAL
STRENGTHENING OF LOW LEVEL INFLOW.

CIRA LPW PRODUCT EXCELLENTLY DEPICTS THE CONFLUENCE OF LOW LEVEL
MOISTURE STREAMS WHILE WHERE SFC TO 850MB DIRECTED TOWARD THE
DEVELOPING SURFACE WAVE BUT EVENTUALLY VEERING ACROSS THE SAND
HILLS.  WHILE THE 850-7H LAYER SHOWS IT INTERSECTING WITH
LINGERING MID-LEVEL MOISTURE POOLED ALONG THE NEB/SD BORDER. 
STRONG CONVERGENCE ALONG BOTH BOUNDARIES HAS DEVELOPED TWO LINES
OF DEEP CONVECTION WITH NEW CELLS FILLING IN BETWEEN.  AT THE
INTERSECTION...NEW CELLS OVER THE NORTHERN SAND HILLS IN CHERRY TO
KEYA PAHA COUNTY ARE RAPIDLY COOLING IN EXCESS OF -80C DRIVEN BY
VERY UNSTABLE ENVIRONMENT BEING TAPPED (SBCAPES OVER 5000 J/KG). 
TOTAL PW VALUES IN EXCESS OF 1.75" WILL SUPPORT HEAVY RAINFALL
EVEN THOUGH SOME WILL BE LOST TO HAIL GENERATION...THE FLUX
LOADING SHOULD SUPPORT RATES IN EXCESS OF 2-2.5"/HR.

STRONG DOWNDRAFTS DUE TO THE EXTREME INSTABILITY MAY DISRUPT SOME
INFLOW GIVEN WEAKER 850MB WINDS CURRENTLY BUT AND OVERALL MEAN
CELL MOTION SHOULD BE PARALLEL TO THE SFC BOUNDARY/MOISTURE POOL
INTO SE SD SUPPORTING SOME TRAINING OF CELLS IN THE SHORT TERM. 
THIS THREAT SHOULD SUPPORT TOTALS OF 2-3" IN 2-3HRS POSING
POSSIBLE FLASH FLOODING INITIALLY.

AS THE EVENING PROGRESSES...FLASH FLOODING WILL BECOME MORE LIKELY
AS THE LLJ WILL STRENGTHEN AND VEER.   THE MST CONVERGENCE WILL
SUPPORT FURTHER UPSTREAM DEVELOPMENT IN THE SAND HILLS THAT WILL
TRACK TO THE NORTHEAST AFTER 02Z AS WELL.  WHILE THIS IS MORE
LIKELY TO SET UP CONVECTION SOUTH AND EAST OF THE INITIAL
CONVECTION THERE IS SUFFICIENT UNCERTAINTY THAT ANY OVERLAP ADDING
A POTENTIAL ADDITIONAL 2-4" WOULD CLEARLY LEAD TO LIKELY FLASH
FLOODING CONDITIONS OVER SATURATED SOILS WHERE 30 DAY AHAPS ARE
300% PERCENT OF NORMAL  THOUGH LAST 14 DAYS ARE A BIT DRIER IN SD
THERE THEY ARE OVER 300% IN NORTHEAST NEB.
GALLINA

ATTN...WFO...FSD...LBF...OAX...UNR...

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

LAT...LON   44059712 43929665 43409660 43059669 42789708
            42569799 42459869 42429963 42650060 43130062
            43479931 43679869