MESOSCALE PRECIPITATION DISCUSSION 0871
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
609 PM EDT SAT OCT 07 2017

AREAS AFFECTED...WESTERN KY, WESTERN TN, & SOUTHEAST IN

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

VALID 072208Z - 080408Z

SUMMARY...SHOWERS AND THUNDERSTORMS ARE EXPECTED TO DEVELOP/EXPAND
IN COVERAGE OVER THE NEXT SEVERAL HOURS.  HOURLY RAIN TOTALS TO
2.5" WITH LOCAL AMOUNTS TO 4" ARE EXPECTED.

DISCUSSION...THE COMBINATION OF AN APPROACHING FRONTAL BOUNDARY
AND HURRICANE NATE'S MOVEMENT TOWARDS THE CENTRAL GULF COAST HAS
ALLOWED PRECIPITABLE WATER VALUES TO RISE TO 2-2.25" ACROSS THE
AREA PER RAP FORECASTS, WHICH IS WELL ABOVE AVERAGE FOR EARLY
OCTOBER.  A JET STREAK ALOFT IS APPARENT ON SATELLITE IMAGERY NEAR
THE MID-MISSISSIPPI AND LOWER OH VALLEYS, INDUCED BY THE
APPROACHING UPPER TROUGH AND NATE'S OUTFLOW JET.  INFLOW AT 850
HPA IS CONVERGENT OUT OF THE SOUTH-SOUTHWEST AT 30-45 KTS PER VAD
WIND PROFILES, NEAR THE MAGNITUDE OF THE 850-400 HPA MEAN WIND. ML
CAPE VALUES OF 500-1500 J/KG EXIST IN THIS REGION. SHOWERS AND
THUNDERSTORMS HAVE BEGUN TO DEVELOP HERE, WITH AN INCOMING LINE TO
THE WEST ALONG THE PROGRESSIVE COLD FRONT.

EFFECTIVE BULK SHEAR 40-55 KTS ALONG WITH THE UNIDIRECTIONAL FLOW
WITH HEIGHT SHOULD ALLOW FOR LINEAR, TRAINING CONVECTIVE SEGMENTS
WITH POSSIBLE EMBEDDED MESOCYCLONES, BOTH OF WHICH SHOULD RAMP UP
RAINFALL TOTALS.  THERE IS A STRONG SIGNAL WITHIN THE MESOSCALE
GUIDANCE FOR LOCAL AMOUNTS OF 4".  ONCE CIN DEVELOPS AROUND
SUNSET, CONVECTION SHOULD BE ABLE TO TAP INTO AN ADDITIONAL 500
J/KG ALOFT WHICH SHOULD RAMP UP COVERAGE AND RAIN RATES.  HOURLY
RAIN TOTALS UP TO 2.5" ARE EXPECTED.  VERY LITTLE PRECIPITATION
HAS FALLEN OVER THE PAST COUPLE WEEKS, SO HEAVY RAIN RELATED
ISSUES ARE EXPECTED IN HILLY AND URBANIZED AREAS.

ROTH

ATTN...WFO...ILN...IND...LMK...MEG...OHX...PAH...

ATTN...RFC...LMRFC...OHRFC...

LAT...LON   39738487 39098433 37048586 35858733 35328816
            34978880 34738998 35129033 37438832 38918669