FXUS63 KIND 120841
AFDIND

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE INDIANAPOLIS IN
340 AM EST SAT DEC 12 2009

.DISCUSSION...
SURFACE ANALYSIS SHOWS HIGH PRESSURE OVER THE EASTERN SEABOARD WITH 
LOW PRESSURE FORMING OVER THE INTERMOUNTAIN WEST. IR SATELLITE LOOP 
SHOWS COME CIRRUS REACHING INTO THE WESTERN COUNTIES. TEMPERATURES 
WERE IN THE LOW 20S WITH DEWPOINTS AROUND 10.

FORECAST FOCUS IS ON POPS AND PRECIPITATION TYPE TONIGHT. MODELS IN 
GOOD AGREEMENT SO WILL USE A BLEND.

TODAY HIGH PRESSURE CONTINUES TO CONTROL THE WEATHER. WITH THE HIGH 
BEING OFF TO THE EAST FLOW WILL BE OUT OF THE SOUTH TO SOUTHWEST AND 
WARM ADVECTION WILL TAKE PLACE. CLOUDS WILL BE ON THE INCREASE 
ADVECTING IN FROM THE SOUTHWEST ADN THIS WILL INHIBIT FULL WARMING. 
WENT FOR HIGHS BETWEEN THE MAV AND MET NUMBERS IN THE UPPER 30S TO 
LOW 40S.

TONIGHT ISENTROPIC LIFT REALLY RAMPS UP AND AN UPPER WAVE MOVES 
THROUGH THE AREA AS DEPICTED BY UPPER LEVEL Q VECTOR CONVERGENCE. 
BASED ON CONDENSATION PRESSURE DEFICITS PRECIPITATION WILL MOVE IN 
FROM THE SOUTHWEST AROUND 0-3Z OR SO AND OVERSPREAD THE AREA AND 
THUS HAVE RAMPED UP POPS FROM SOUTHWEST TO NORTHEAST. SOUNDINGS FROM 
BOTH NAM AND GFS ARE SHOWING THE POSSIBILITY OF A BRIEF PERIOD OF 
FREEZING RAIN SHORTLY AFTER ONSET SINCE PRECIPITATION COULD COOL THE 
COLUMN AS IT SATURATES THE DRIER LOW LEVELS ACROSS THE NORTHERN HALF 
OR SO OF THE AREA. AT THIS TIME IT DOESN/T LOOK LIKE THE COLDER AIR 
AT THE SURFACE WILL BE DEEP ENOUGH FOR SLEET. WARM AND MOIST 
ADVECTION DOES CONTINUE AND SHOULD BRING THE ENTIRE AREA UP TO WARM 
ENOUGH FOR ALL RAIN BY 6Z AND THE BEST FORCING/MOISTURE ARE OVER THE 
ENTIRE AREA FROM 6-12Z AND THUS HAVE GONE CATEGORICAL RAIN DURING 
THIS TIME. FOR SURFACE TEMPERATURES PREFERED THE COOLER MET NUMBERS 
AND USED 3 HOURLY TEMPERATURES RATHER THAN DIURNAL TREND WITH GOOD 
COOLING JUST AFTER SUNSET AND THEN TEMPERATURES INCREASING WITH THE 
WARM MOIST ADVECTION.

FOR SUNDAY MORNING KEPT A CHANCE OF RAIN IN THE EAST AND BROUGHT IN 
SOME LIGHT PATCHY DRIZZLE IN THE WEST BASED ON SOUNDING PROFILES 
DRYING AT THE UPPER LEVELS BUT REMAINING SATURATED IN THE LOWEST 
LEVELS. WENT DRY AFTER 18Z. FOR HIGH TEMPERATURES A MAV/MET AVERAGE 
MATCHED UP WELL WITH H8 TEMPS.

FEW CHANGES MADE AFTER SUNDAY WITH WEAK COLD FRONT MOVING THROUGH 
MONDAY/MONDAY NIGHT RETAINED SLIGHT CHANCES OF RAIN AND A RAIN/SNOW 
MIX LATE OVERNIGHT.

&&

.AVIATION...DISCUSSION FOR 12/06Z TAFS.
VFR CONDITIONS WILL CONTINUE FOR ABOUT THE NEXT 20 HOURS AND THEN 
DROP RAPIDLY TO LOW MVFR OR IFR AS RAIN SPREADS INTO OUR REGION.  

HIGH PRESSURE FROM NORTH CAROLINA TO KENTUCKY WILL CONTINUE TO 
DOMINATE OUR WEATHER AS IT MOVES SLOWLY EASTWARD.  CLEAR SKIES 
SHOULD CONTINUE OVER TAF SITES UNTIL SUNRISE.  BROKEN CLOUDS AROUND 
5 THOUSAND WILL SPREAD INTO THE OHIO VALLEY BY SUNRISE.  BUT MOST 
OF THIS CLOUDINESS SHOULD REMAIN FROM SOUTHERN INDIANA AND SOUTHWARD 
UNTIL MID OR LATE SATURDAY AFTERNOON.  

AN UPPER LEVEL DISTURBANCE WILL SPREAD RAIN ACROSS OUR REGION 
SATURDAY NIGHT AND FLIGHT CATEGORIES.  NAM SHOWS THE MAJORITY OF 
THIS RAIN OCCURRING FROM 03Z TO ABOUT 10Z SUNDAY...BUT LOW MVFR OR 
IFR CIGS WILL LINGER WELL AFTER THAT.

&&

.IND WATCHES/WARNINGS/ADVISORIES...NONE. 

&&

$$

PUBLIC...CP
AVIATION...JH