FXUS63 KIND 070403
AFDIND
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE INDIANAPOLIS IN
1103 PM EST SUN DEC 6 2009
.AVIATION...DISCUSSION FOR THE 06Z TAFS.
LATEST MODELS ARE MORE IN LINE WITH RADAR TRENDS AND ISENTROPIC
ANALYSIS AND SUGGESTS PRECIP WILL MOVE INTO THE WESTERN TERMINALS BY
06Z AND EASTERN ONES BY 08Z. MOST OF THE UPSTREAM PRECIPITATION IS
IN THE FORM OF SNOW...BUT WOULDN'T BE SURPRISED TO SEE FREEZING
DRIZZLE FOR A TIME BASED ON BUFKIT. CEILINGS WERE FALLING TO MVFR
JUST BEHIND THE ONSET OF THE SNOW...SO WILL MOVE UP MVFR TO 06Z AND
08Z RESPECTIVELY AS WELL. ALSO...WILL MOVE THE END TIME UP A FEW
HOURS CLOSER TO 14Z EASTERN TAF SITES AND 16Z WESTERN ONES BASED ON
SPEED OF THE RESPONSIBLE UPPER DISTURBANCE. MVFR TO CONTINUE THROUGH
THE REMAINDER OF THE TAF PERIOD BASED ON UPSTREAM CONDITIONS AND
MODEL TIME SECTIONS. FINALLY...WINDS WILL NOT BE A FACTOR LESS THAN
10 KNOTS.
&&
.PREV DISCUSSION...
SURFACE ANALYSIS SHOWS LOW PRESSURE FORMING UP FROM THE COLORADO
MOUNTAINS DOWN TO THE TEXAS PANHANDLE WITH HIGH PRESSURE OVER THE
EASTERN US. WATER VAPOR LOOP SHOWS AN ELONGATED UPPER LOW OVER THE
WESTERN HALF OF THE COUNTRY WITH AN UPPER RIDGE OVER THE EAST.
VISIBLE SATELLITE SHOWS SCATTERED TO BROKEN CIRRUS CLOUDS OVER THE
AREA. TEMPERATURES WERE IN THE MID 30S WITH DEWPOINTS IN THE UPPER
TEENS AND WINDS OF 5-10 KTS OUT OF THE SOUTH.
A VERY ACTIVE WEATHER PATTERN IN STORE THROUGH MID WEEK. FORECAST
FOCUS IS FIRST ON POPS AND TIMING FOR SNOW TONIGHT AND MONDAY AND
THEN ON WINDS/PRECIPITATION TYPE/SEVERE POTENTIAL WITH STRONG MID
WEEK SYSTEM.
MODELS ARE IN DECENT AGREEMENT FOR OVERALL PATTERN SO MOSTLY USED A
MODEL BLEND. HOWEVER NAM TIMING FOR THIS FIRST SYSTEM IS SLOWER THAN
GFS/ECMWF/GEM AND THUS WILL FAVOR THE FASTER SOLUTION OF THE GFS.
THE FIRST CHALLENGE FOR THE FORECAST IS THE SHORTWAVE AND WEAK LOW
PRESSURE SYSTEM ASSOCIATED WITH IT THAT WILL SWING THROUGH THE AREA
LATE TONIGHT THROUGH MONDAY MORNING. WHILE THE UPPER SYSTEM DOES NOT
LOOK IMPRESSIVE IN THE H5 CHART IT DOES HAVE GOOD /-30/ UPPER Q
VECTOR CONVERGENCE AS WELL AS SOME WEAK FRONTOGENESIS OVER THE AREA.
WHAT THE SYSTEM LACKS IS A DECENT AMOUNT OF MOISTURE. AS FORCING
INITIALLY ARRIVES THERE IS SOME UPPER LEVEL MOISTURE BUT THE LOW
LEVELS ARE VERY DRY. WHEN THE BEST FORCING IS AROUND /AT 12Z
ACCORDING TO THE GFS/ THERE IS FINALLY SATURATION AT THE LOW LEVELS
AND UP TO AROUND H7 BUT THERE IS DRYING IN THE SNOW GROWTH ZONE.
CURRENTLY THINKING THE BEST CHANCES FOR ANY SNOW FORMING AND MAKING
IT TO THE GROUND WILL BE RIGHT AROUND 12Z ACROSS MOST OF THE AREA.
GUIDANCE ONLY GIVING A SLIGHT CHANCE AT MOST SO DID THINK THE
FORCING WAS ENOUGH TO WARRANT A RAISE OF POPS TO CHANCE...BUT STILL
THINK IT IS A TOSS UP WHETHER OR NOT MOST PLACES RECEIVE EVEN A
TENTH OF AN INCH. UNFORTUNATELY THE TIMING DOES COINCIDE WITH THE
MONDAY MORNING COMMUTE AND WILL MENTION THE POSSIBILITY OF THIS IN
THE HWO. ON A POSITIVE NOTE THE TEMPERATURES ARE COLD ENOUGH DURING
THE TIME OF THE FORCING THAT PRECIPITATION TYPE WILL BE ALL SNOW.
BY MONDAY AFTERNOON THE SYSTEM SHOULD BE MOVING OUT RAPIDLY AND BE
REPLACED BY A QUICK SHOT OF HIGH PRESSURE FOR MONDAY NIGHT AND INTO
TUESDAY. TUESDAY AFTERNOON IS WHEN THE NEXT ROUND OF PRECIPITATION
SHOULD BEGIN TO ARRIVE. ISENTROPIC LIFT STARTS TO RAMP UP BY TUESDAY
MORNING BUT CONDENSATION PRESSURE DEFICITS INDICATE SATURATION WILL
NOT BE REACHED ANYWHERE IN THE FORECAST AREA BEFORE 18Z. AFTER THIS
BROUGHT IN HIGHEST CHANCES OF RAIN IN THE SOUTH WHERE THE ISENTROPIC
LIFT IS MAXIMIZED.
TUESDAY NIGHT LOOKS INTERESTING. A NEGATIVELY TILTED H8 TROUGH
SWINGS OUT OF THE CENTRAL PLAINS WHILE IT/S ATTENDANT SURFACE LOW
ZIPS FROM WESTERN OR CENTRAL OKLAHOMA TO THE NORTHERN
ILLINOIS/INDIANA BORDER AND DEEPENS. THIS SHOULD PUT INDIANA BRIEFLY
IN THE WARM SECTOR WITH A LOW LEVEL JET OF 45-65 KTS TO THE SOUTH.
WARM SECTOR HOWEVER WILL NOT BE PARTICULARLY WARM THIS FAR NORTH AND
EVEN ELEVATED INSTABILITY IS BARELY DISCERNIBLE. AT THIS POINT THING
SEVERE POTENTIAL WILL STAY TO THE SOUTH BUT DO THINK WITH SYSTEM
THIS DYNAMIC THAT THUNDER IS NOT OUT OF THE QUESTION SO ADDED A
SLIGHT CHANCE OF THUNDER BACK IN. AS FAR AS OVERALL POPS ARE
CONCERNED...STRENGTH OF ALL FACTORS PREVIOUSLY MENTIONED AS WELL AS
GOOD MOISTURE FEED WARRANT RAISING POPS TO 90. COLD AIR DOES NOT
ARRIVE IN GFS/ECMWF/GEM/NAM UNTIL AFTER 12Z SO PRECIP TYPE SHOULD BE
ALL RAIN.
WEDNESDAY CONTINUES THE FUN. MAJORITY OF MODELS ARE BRINGING IN THE
THE COLD AIR HARD AND FAST SOMEWHERE BETWEEN 12 AND 18Z AND THE
DEPTH OF IT LOOKS LIKE THE CHANGE OVER BETWEEN RAIN AND SNOW WILL BE
RAPID. WITH THE UNCERTAINTY OF EXACTLY WHERE IN THIS WINDOW THE COLD
AIR WILL ARRIVE HAVE INCLUDED RAIN OR SNOW DURING THIS TIME BEFORE A
CHANGE OVER TO ALL SNOW BY 18Z. BEST FORCING IS MOVING OUT AS THE
COLD AIR ARRIVES AND THUS DO NOT EXPECT MUCH IN THE WAY OF SNOW
ACCUMULATIONS...RIGHT NOW LOOKING AT HALF AN INCH OR LESS. AS THE
SURFACE LOW MOVES OFF TO THE NORTHEAST IT CONTINUES TO STRENGTHEN
AND THE PRESSURE GRADIENT ACROSS THE AREA TIGHTENS WITH PRETTY MUCH
UNIDIRECTIONAL WINDS QUITE A WAYS UP. THIS WILL LEAD TO STRONG WINDS
AND HAVE CURRENTLY INCLUDED GUSTS UP TO 35 KTS. BUFKIT IS SHOWING
POTENTIAL FOR EVEN HIGHER GUSTS AND THE STRENGTH OF THESE GUSTS WILL
NEED TO BE EVALUATED WITH SUBSEQUENT FORECASTS. THESE WINDS SHOULD
STICK AROUND THROUGH WEDNESDAY NIGHT BEFORE FINALLY DROPPING OFF
SOME ON THURSDAY MORNING AS HIGH PRESSURE BUILDS CLOSER.
ON SHORT TERM TEMPS...WHILE WE HAVE BEEN RUNNING BELOW GUIDANCE THE
PAST COUPLE OF DAYS...THINK THAT TREND IS ABOUT DONE NOW WITH
INCREASING CLOUD COVER AND NEUTRAL TO WARM ADVECTION. MAV AND MET
NUMBERS WERE VERY SIMILAR FOR TONIGHT AND MONDAY AND USED AN AVERAGE.
DID NOT DEVIATE FROM HPC DAYS 5-7 WITH GENERALLY ZONAL FLOW.
&&
.IND WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
PUBLIC...CP
AVIATION...MK
UPDATE...JP
