Graphic for MPD #0907

MESOSCALE PRECIPITATION DISCUSSION 0907
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
104 AM EDT MON OCT 23 2017

AREAS AFFECTED...EXTREME NORTHWEST AL...MIDDLE TN...WESTERN KY

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

VALID 230500Z - 230930Z

SUMMARY...A BAND OF HEAVY RAIN TRAINING FROM SOUTH TO NORTH MAY
CAUSE SOME FLASH FLOODING CONCERNS LOCALLY OVER THE NEXT FEW HOURS.

DISCUSSION...THE LATEST NON-OPERATIONAL GOES-16 WV CHANNEL SUITE
SHOWS AN INCREASINGLY DIVERGENT MID TO UPPER LEVEL FLOW PATTERN
OVER NORTHWEST AL...CENTRAL/WESTERN TN AND INTO WESTERN KY AS A
SOUTHERN STREAM TROUGH AND ASSOCIATED CLOSED UPPER LEVEL CENTER
DEEPENS OVER THE MID/LOWER MS VALLEY. THE STRONGER FORCING ALOFT
COINCIDING WITH COOLING CLOUD TOPS AND AN INTENSIFYING AXIS OF
HEAVY RAIN WHICH HAS BEEN SEEN TRAINING SOUTH TO NORTH OVER MIDDLE
TN OVER THE LAST COUPLE OF HOURS AND JUST OUT AHEAD OF A
SLOW-MOVING COLD FRONT. ADDITIONAL HEAVY RAINS ARE SEEN ALSO
DEVELOPING OVER NORTHWEST AL AS WELL OVER THE LAST 30 MINUTES
WHICH IS ADVANCING NORTH TOWARD MIDDLE TN.

SURFACE OBSERVATIONS SHOW AN AREA OF LOW PRESSURE DEVELOPING ALONG
THE FRONT OVER WESTERN KY...AND THIS IS HELPING TO ENHANCE THE
SOUTHERLY LOW LEVEL JET ACROSS THE REGION WITH STRONGER MOISTURE
TRANSPORT NOTED OVER THE LAST COUPLE OF HOURS AS A RESULT. IN
FACT...THE FORT CAMPBELL AND NASHVILLE VWP DATA HAS DEPICTING
SOUTHERLY 850 MB WINDS OF 50 TO 55 KTS OVER THE LAST HOUR ALONE.

INSTABILITY PARAMETERS ARE NOT PARTICULARLY FAVORABLE FOR HEAVY
RAINFALL...AS MUCAPE VALUES ARE ONLY ON THE ORDER OF 250 J/KG.
HOWEVER...THE INCREASINGLY FORCED ASCENT THROUGH THE COLUMN IS
COMPENSATING AND AREAS DUAL-POL RADARS ARE SHOWING RAINFALL RATES
OF AS MUCH AS 1.5 INCHES/HR. THE LATEST GPS-DERIVED PWATS ACROSS
THIS REGION ARE ON THE ORDER OF 1.6 TO 1.8 INCHES WHICH IS ALSO
HELPING TO ENHANCE THE RAINFALL EFFICIENCY FOR SOME OF THESE
HEAVIER RATES.

THE 00Z HRRRX ACTUALLY SHOWS A VERY GOOD HANDLE ON THE CURRENT
AXIS OF HEAVY RAINFALL...AND SUPPORTS AS MUCH AS 2 TO 4 INCHES OF
RAIN THROUGH 09Z ACROSS AREAS OF FAR NORTHWEST AL...MIDDLE TN AND
INTO PARTS OF WESTERN KY. THE HEAVIEST RAINFALL WILL BE GENERALLY
IN A RATHER NARROW SOUTH TO NORTH AXIS...BUT WILL BE CAPABLE OF
GENERATING SOME RUNOFF PROBLEMS AND POSSIBLE FLASH FLOODING AS THE
UPPER FORCING OVER THE REGION STRENGTHENS A BIT MORE TOWARD 06Z
AND HELPS TO ENHANCE THE RAINFALL RATES A BIT MORE. WILL CONTINUE
TO MONITOR.

ORRISON

ATTN...WFO...HUN...LMK...MEG...OHX...PAH...

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

LAT...LON   37888763 37788686 36578663 35268690 34688736
            34718807 35758806 36588812 37508787


Last Updated: 104 AM EDT MON OCT 23 2017