FXUS63 KIND 040525
AFDIND
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE INDIANAPOLIS IN
1225 AM EST FRI DEC 4 2009
.AVIATION...DISCUSSION FOR THE 04/06Z TAFS.
VFR EXPECTED THROUGH THE PERIOD. BROAD UPPER TROUGH WILL BE ROTATING
THROUGH THE GREAT LAKES THROUGH THE PERIOD...BUT MAIN FORCING WILL
REMAIN NORTH AND WEST OF THE SITES...SO THE ONLY IMPACT WILL BE A
REDEVELOPMENT OF CLOUD COVER. CLOUD DECK ASSOCIATED WITH MOST RECENT
SYSTEM HAS SCATTERED OUT AS IT PUSHES EASTWARD...AND ALL SITES ARE
NOW VFR. MOSTLY CLEAR SKIES WILL PERSIST OVERNIGHT BEFORE
ENCROACHING STRATUS DECK UNDER UPPER LOW MOVES IN...AND CUMULUS
DEVELOPMENT FILLS IN ANY MAJOR GAPS IN COVERAGE. PROFILES INDICATE
POSSIBILITY THAT CLOUD DECK COULD FLIRT WITH HIGH END MVFR TOMORROW
AFTERNOON...BUT WITH TROUGH WEAKENING AND PULLING NORTHEAST...THIS
SEEMS UNLIKELY. CONVECTIVE CLOUD BASES SHOULD BE AROUND 3.5K FEET AT
LOWEST. WINDS WILL REMAIN AT OR BELOW 10 KNOTS THROUGH THE PERIOD.
&&
.PREV DISCUSSION... /ISSUED 838 PM EST THU DEC 3 2009/
UPDATE...SATELLITE SHOWING BULK OF THE CUMULUS CLOUDS WERE GONE
WEST OF INTERSTATE 65...AND IN FACT THE WHOLE FORECAST AREA SHOULD
SEE PARTLY CLOUDY SKIES AFTER 06Z AT THE WORST...SO UPDATED ZONES TO
REFLECT THIS. THICK CUMULUS DECK ACROSS WESTERN ILLINOIS SHOULD NOT
MAKE IT TO OUR WESTERN COUNTIES UNTIL AROUND 12Z PER THE AWIPS
DISTANCE SPEED TOOL.
PREV DISCUSSION.../ISSUED 317 PM EST THU DEC 3 2009/
ABUNDANT LOW LEVEL MOISTURE CONTINUES TO ROTATE INTO REGION WITH
CYCLONIC FLOW ALOFT. DRIER AIR IS ATTEMPTING TO MOVE INTO THE
FORECAST AREA FROM THE WEST THIS AFTERNOON...BUT CUMULUS HAS
REDEVELOPED OVER EASTERN ILLINOIS UNDER LOW LEVEL COLD ADVECTION.
TEMPERATURES HAD BEEN HELD DOWN MAINLY IN THE MIDDLE AND UPPER 30S
UNDER THE CLOUDS THIS AFTERNOON.
FORECAST CHALLENGES FOCUS ON CLOUDS AND TEMPERATURES OVER THE NEXT
COUPLE DAYS AND IN THE EXTENDED...THE ARRIVAL AND IMPACTS OF A
POTENTIALLY SIGNIFICANT STORM BY THE MIDDLE OF NEXT WEEK. IN THE
SHORT TERM...MODEL CONSENSUS IN DECENT AGREEMENT ON SENSIBLE
WEATHER.
INITIAL FOCUS IS ON THE BREAKUP OF THE CLOUD DECK TONIGHT. MODEL
SOUNDINGS INDICATING DRIER AIR WILL CONTINUE TO MAKE HEADWAY INTO
CENTRAL INDIANA TONIGHT...WHICH SHOULD ENABLE A RISING OF THE
CEILINGS FOLLOWED BY SOME SCATTERING OF THE DECK BY MID EVENING AND
PRIMARILY SOUTH/WEST OF INDY AS SURFACE HIGH PRESSURE RIDGE EXTENDS
INTO THE OHIO VALLEY. HOWEVER...UPPER LEVEL LOW CURRENTLY OVER IOWA
THIS AFTERNOON WILL SLOWLY TRANSITION EAST/NORTHEAST INTO THE
CENTRAL GREAT LAKES BY FRIDAY MORNING. WHILE DEEPER FORCING AND SNOW
SHOWERS ASSOCIATED WITH THIS FEATURE WILL REMAIN NORTH OF THE
FORECAST AREA...THIS WILL LIKELY ENHANCE CLOUD DECK OVER NORTHERN
HALF OF FORECAST AREA LATE TONIGHT AND IN FACT MAY EVEN ALLOW IT TO
EXPAND BACK SOUTH A BIT. THEREFORE...WILL LEAVE MAINLY CLOUDY SKIES
NORTH OF INTERSTATE 70 FOR MUCH OF THE NIGHT. DESPITE THE CLOUDS...
COLDEST NIGHT OF THE SEASON SO FAR SEEM LIKELY AS 850MB TEMPS CRASH
INTO THE -12 TO -10C RANGE.
DECAYING UPPER TROUGH WILL REMAIN JUST WEST OF THE FORECAST AREA ON
FRIDAY...WITH REGION CONTINUING IN CYCLONIC FLOW ALOFT WITH COLD
ADVECTION IN THE LOW LEVELS. THIS WOULD SEEM TO SUGGEST DIURNAL
CUMULUS FIELD SHOULD BECOME WELL ESTABLISHED ACROSS MUCH OF THE
FORECAST AREA BY MIDDAY. STRENGTHENING RIDGE AT THE SURFACE AND
INCREASING DEPTH TO DRIER AIR SHOULD ENABLE CUMULUS TO SCATTER
FRIDAY EVENING WITH SKIES BECOMING PARTLY CLOUDY TO MOSTLY CLEAR FOR
MUCH OF CENTRAL INDIANA. TROUGH AXIS WILL REMAIN OVER REGION FRIDAY
NIGHT...HELD UP AS LARGE AREA OF PRECIPITATION EXPANDS UP THROUGH
THE CENTRAL APPALACHIANS ON THE LESS SIDE OF THE TROUGH. BACK SIDE
OF THE MID/HIGH LEVEL CLOUD SHIELD ASSOCIATED WITH THIS SYSTEM
LIKELY TO GRAZE SOUTHERN COUNTIES LATE FRIDAY NIGHT AND EARLY
SATURDAY.
DEEPER SUBSIDENCE ATTEMPTS TO ADVECT INTO THE OHIO VALLEY SATURDAY
AS AFOREMENTIONED UPPER TROUGH AND ASSOCIATED PRECIPITATION SHIFT
QUICKLY INTO THE MID ATLANTIC REGION. WHILE BEST CHANCE AT SUNSHINE
ACROSS THE REGION WILL EXIST ON SATURDAY...STILL ANTICIPATE SOME
DIURNAL CUMULUS DEVELOPMENT AS BOTH 12Z NAM/OP GFS INDICATING LOW
LEVEL THERMAL TROUGH AXIS WILL LAG BACK ACROSS EASTERN FORECAST AREA
INTO SATURDAY AFTERNOON WITH JUST NEUTRAL ADVECTION NOTED AT 850MB.
FOR THAT REASON ALONE...HAVE HELD ON TO MENTION OF PARTLY CLOUDY
SKIES FOR MUCH OF THE AREA. SKIES WILL BECOME MAINLY CLEAR SATURDAY
NIGHT AS CENTER OF SURFACE HIGH MOVES THROUGH THE OHIO VALLEY AND
RIDGING ALOFT DEVELOPS.
IN THE EXTENDED...FOCUS CONTINUES TO BE ON POTENTIAL SIGNIFICANT
STORM FOR TUESDAY-WEDNESDAY. AFTER A QUIET SUNDAY...WEAK FRONT WILL
MOVE ACROSS THE REGION EARLY MONDAY. HAVE INTRODUCED 20 POPS FOR
ENTIRE FORECAST AREA LATE SUNDAY NIGHT AND EARLY MONDAY AS BOUNDARY
PASSES THROUGH. 12Z OP GFS/15Z SREF BOTH INDICATE POTENTIAL FOR A
LIGHT RAIN/SNOW MIX WITH POSSIBLY ENOUGH COLD AIR FOR MAINLY SNOW
NORTH OF I-70. FOCUS THEN TURNS TO LOW PRESSURE DEVELOPING EAST OF
THE ROCKIES EARLY TUESDAY...AND PROGRESSING QUICKLY INTO THE OHIO
VALLEY TUESDAY NIGHT/WEDNESDAY. MAJORITY OF EXTENDED MODELS
INDICATING LOW PRESSURE WILL AFFECT REGION DURING THE TIME PERIOD
BUT AS IS TO BE EXPECTED AT FIVE TO SIX DAYS OUT...DIFFER ON THE
DETAILS FROM RUN TO RUN AND MODEL TO MODEL. 00Z ECMWF/12Z OP GFS
BOTH FAVORING A LESS AMPLIFIED STORM TRACK THROUGH THE OHIO/
TENNESSEE VALLEYS. THIS TRACK WOULD FAVOR COLDER WEATHER AND
PRECIPITATION TRANSITIONING FROM A WINTRY MIX TO SNOW FROM SOUTH TO
NORTH. 12Z GFS ENSEMBLE MEAN FAVORING A TRACK DIRECTLY THROUGH
CENTRAL INDIANA WITH MOST BUT NOT ALL INDIVIDUAL MEMBERS CLUSTERED
IN THE OHIO VALLEY. 12Z ECMWF SHOWING MAINLY RAIN FOR MUCH OF THE
AREA WITH A RAPIDLY DEEPENING SYSTEM FOLLOWING A LAKE CUTTER PATH
INTO THE GREAT LAKES. AT THIS POINT WITH SO MUCH UNCERTAINTY SEVERAL
DAYS OUT...TRENDED TOWARDS HPC GUIDANCE AND PREVIOUS FORECAST
THOUGHTS INDICATING A RAIN/SNOW MIX SOUTH AND MAINLY SNOW NORTH.
WITH GREATER CONFIDENCE ON TIMING IMPACTS...DID INCREASE TO 40 POPS
TUESDAY NIGHT AND WEDNESDAY. ALSO UNDERCUT TEMPERATURES FOR MUCH OF
NEXT WEEK...WITH MOST LOCATIONS REMAINING IN THE 30S FOR HIGHS
THROUGH THE PERIOD.
TEMPS...GENERALLY LEANED TOWARDS COOLER MET GUIDANCE THROUGH
SATURDAY NIGHT. WITH EXPECTED CLOUDS AND COLD ADVECTION FRIDAY...
ANTICIPATE HIGHS ONLY IN THE MID 30S. SLIGHTLY WARMER WEATHER IS
EXPECTED SATURDAY WITH A LITTLE MORE IN THE WAY OF SUNSHINE...BUT
MUCH OF THE REGION WILL STAY BELOW 40 DEGREES. LOWS IN THE LOWER/MID
20S TONIGHT WILL FALL INTO THE TEENS FOR MANY FOR THE FIRST TIME
THIS SEASON FRIDAY/SATURDAY NIGHTS.
&&
.IND WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
PUBLIC...KOCH
AVIATION...NIELD
