MESOSCALE PRECIPITATION DISCUSSION 0879...CORRECTED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
718 PM EDT SUN OCT 08 2017

CORRECTED FOR GRAMMAR

AREAS AFFECTED...SOUTHERN APPALACHIANS

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

VALID 082313Z - 090513Z

SUMMARY...TROPICAL DEPRESSION NATE IS EXPECTED TO ALLOW FOR HOURLY
RAIN TOTALS TO 2" WITH LOCAL AMOUNTS TO 4" OVER THE NEXT SEVERAL
HOURS.

DISCUSSION...SATELLITE IMAGERY REVEALS THAT THE CIRCULATIONS
ASSOCIATED WITH NATE ARE DECOUPLED DUE TO VERTICAL WIND SHEAR,
WITH THE MID-LEVEL CIRCULATION MOVING INTO NORTHERN GA WITH
WARMING CLOUD TOPS WHILE THE SURFACE CIRCULATION LINGERS BEHIND
ACROSS SOUTHERN TN. RECENT RAINS ARE CAUSING A WEAK COLD AIR
DAMMING SIGNATURE ACROSS NORTHERN GA AND THE WESTERN CAROLINAS IN
RECENT SURFACE OBSERVATIONS -- AN IDEA THAT IS REINFORCED BY THE
MU AND ML CAPE FIELDS IN THE REGION.  CIN IS BEGINNING TO DEVELOP
PER SPC MESOANALYSES.  WITH ITS DEVELOPING CONNECTIONS TO A
BAROCLINIC ZONE ON INFRARED IMAGERY AND ITS INCREASINGLY ELONGATED
APPEARANCE, EXTRATROPICAL TRANSITION IS UNDERWAY.  PRECIPITABLE
WATER VALUES OF 2-2.5" EXIST HERE PER RAP ANALYSES.  INFLOW IS
CONVERGENT AT 850 HPA AT 25-50 KTS PER VAD WIND PROFILES, LEADING
TO UPSLOPE FLOW ALONG SOUTH TO SOUTHEAST FACING TOPOGRAPHY, WHICH
IS IMPORTING MU CAPE VALUES OF 500-1000+ J/KG INTO THE REGION. 

THE MESOSCALE GUIDANCE HAS A GOOD SIGNAL FOR LOCAL AMOUNTS OF 4"
ACROSS THE MOUNTAINS OF SOUTHWEST VA AND THE WESTERN CAROLINAS --
THE HRRR RUNS APPEAR HIGHLY INFLATED WHEN COMPARED TO THE
REMAINDER OF THE GUIDANCE.  FOR THE FIRST FEW HOURS, HOURLY RAIN
TOTALS UP TO 2" ARE POSSIBLE.  AFTER 02Z, PRECIPITATION IS
EXPECTED TO BECOME MORE STRATIFORM WITH DECREASING RATES AS
INSTABILITY IS FORECAST TO SIGNIFICANTLY ERODE.  THIS IDEA IS
SUPPORTED BY THE 18Z SSEO NEIGHBORHOOD PROBABILITIES.  IT APPEARS
TO TAKE UNTIL 04-05Z FOR THE STRONGER BOUNDARY LAYER MOISTURE
CONVERGENCE INTO THE MOUNTAINS TO WEAKEN, SO USED A SIX HOUR
WINDOW AS A PRECAUTION.

ROTH

ATTN...WFO...CAE...FFC...GSP...JKL...MRX...RAH...RLX...RNK...

ATTN...RFC...LMRFC...MARFC...OHRFC...SERFC...

LAT...LON   37558203 37368173 37278155 37418042 36877988
            35638040 34778083 34098192 34078290 34178342
            34838387 35548366 36858303 37328232