FXUS63 KIWX 262022
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
322 PM EST THU NOV 26 2009
.SHORT TERM...
TONIGHT THROUGH FRIDAY
SHARP UPPER TROUGH IS BEGINNING TO SLOWLY EJECT NE FROM THE
FA...WITH DEFORMATION PRECIP CONTINUING TO SHIFT EAST. ONE FINAL
BAND OF PRECIP CONTINUES TO ADVECT ACROSS THE WESTERN FA...LIKELY
BECOMING MODIFIED BY LONG FETCH FLOW OVER LK MI. ANOTHER MID LEVEL
IMPULSE IS CLEARLY EVIDENT ON WATER VAPOR...PUSHING SE ACROSS WESTERN
ONTARIO. THIS FEATURE IS EXPECTED TO PHASE WITH THE GREAT LAKES UPPER
LOW AND HELP SUPPORT VIGOROUS CYCLOGENESIS OVER THE NE CONUS. TEMPS
WERE GENERALLY HOLDING IN THE UPPER 30S WITH FEW LOW 40S PRESENT OVER
THE FAR NW ZONES WITH FLOW VEERING NW BEHIND THE ADVECTING SFC
TROUGH. MAIN CONCERN IN THE PERIOD IS PRECIP CHANCES THIS EVENING
AND EVENTUAL CLEARING ON FRI. HAVE TAILORED FORECAST TO NAM AND
LOCAL WRF PROGS...GIVEN LAKE MI RESPONSE WITH CAA...AND GENERAL GOOD
CONTINUITY WITH THERMAL AND MOMENTUM PROGS.
TONIGHT...UPPER TROUGH AND SFC REFLECTION WILL CONTINUE TO PROPAGATE
EAST THROUGH THIS EVENING...SUPPORTING SHOWER CHANCES ACROSS THE
CENTRAL AND EASTERN FA AS THE SFC TROUGH AND LL DEFORMATION ZONE
PUSHES EAST ACROSS THE REGION. CAA WILL SUPPORT H85 T FALLS DOWN TO
AROUND -7C...SUPPORTING MARGINAL DELTA T/S AROUND 13 C BY LATE
TONIGHT. FLOW IS EXPECTED TO CONTINUE TO VEER TONIGHT WITH NEGATIVE
THETA-E ADV SUPPORTING LL RH FALLS. NAM H85 RH PROGS UPSTREAM LK MI
FALL TO AROUND 30 PERCENT COINCIDENT WITH THE COLDEST THERMAL FIELDS
ALOFT...SUPPORTING AN UNFAVORABLE ENVIRONMENT FOR THE PRODUCTION OF
PRECIP. IN ADDITION...INVERSION HEIGHTS WILL CONTINUE TO FALL AND
WITH LK INDUCED CAPES ONLY PROGGED AT AROUND 200 J/KG IN NAM AND WRF
BUFR PROGS...HAVE DECIDED TO LIMIT POPS TONIGHT IN THE NW...WITH A
LOWERING TREND THROUGH THE NIGHT. HAVE OPTED ALSO TO KEEP THE TREND
TO SCT SKY COVER IN THE SW TOWARD DAWN AS DRY AIR CONTINUES TO ADV
INTO THE AREA. COOLEST READINGS ARE EXPECTED IN THE SW WHERE THE
HIGHEST POTENTIAL FOR SCT-BKN CLOUD COVER IS.
FRI...SFC HIGH PRESSURE WILL BEGIN TO BUILD INTO THE AREA WITH UPPER
LEVEL RIDGING AND HEIGHT RISES EXPECTED AHEAD OF THE NEXT SYSTEM.
WAA AND BACKING FLOW WILL GRADUALLY SUPPORT THE DEPLETION OF PRIMARY
AND SECONDARY LK CLOUDS...BUT AT A SLOW PACE. MOST NORTHERN AREAS
WILL LIKELY SEE AMPLE CLOUD COVER THROUGH THE DAY PERIOD. STRONG
SUBSIDENCE INVERSION WITH WEAK MIXING WILL ONLY OFFER HIGHS INTO THE
LOWER 40S AT BEST.
EXPECT MOSTLY CLEAR SKIES AND LIGHT WINDS OVER MUCH OF THE FA FRI
NIGHT. DRY AIR IN PLACE COMBINED WITH GOOD RATIONALLY COOLING SETUP
WILL SUPPORT LOWS IN THE 20S AT MANY PLACES...TO AROUND 30 IN THE
FAR SW WHERE SFC WINDS MAY BEGIN TO RESPOND TO PRESSURE FALLS WEST
OF THE FA TOWARD DAWN.
&&
.LONG TERM...
SHRT TERM PREFERENCE STILL LIES W/LESS PROGRESSIVE SPLITTING MID LVL
TROUGH DEPICTIONS TO START. THIS FITS WELL W/PRIOR GRIDS AND
SUGGESTS FEW IN ANY CHGS YET FOR SUN AFTN/SUN NIGHT. HWVR WILL AT
LEAST SHADE WRN AREAS DOWN POP WISE MON IN RESPECT OF WRN NEIGHBOR
XPCNS AND COLLABORATION CONSTRAINTS.
OTHERWISE FAR GREATER PROBS MANIFEST TWD END OF THE PD W/CONTD HUGE
MODEL SPREAD RELATED TO HOW POTENT SRN STREAM ENERGY EJECTS OUT AHD
OF IMPRESSIVE NRN STREAM TROUGH DVLPMNT OVR THE NRN PLAINS. HPC
PREFERENCE OF TAKING NRN STREAM HGT FALLS FURTHER W THROUGH THE WRN
US FITS W/CURRENT XPCN OF LEAD SW COMING ONSHORE OVR THE PAC NW THIS
AFTN SPLITTING W/SRN STREAM SW CUTTING OFF OVR NRN MEXICO AND
ULTIMATELY SLWR TO EJECT NE AHD OF POTENT NRN STREAM TROUGH DVLPG
ACRS THE NRN PLAINS MID WEEK. THUS WILL CONT TO RIDE DRY FCST
THROUGH END OF DY7 YET LIKELY ADD A MID RANGE CHC MENTION TOMORROW
IF PLACEMENT OF SRN STREAM WV LIFTING UP THROUGH THE OH VALLEY HOLDS
AS HAS BEEN THE CASE IN SVRL DIFF MODEL CYCLES THE LAST FEW DAYS. WRN
PERIPHERY OF THIS SYS HOLDS THE POTENTIAL FOR SIG SNOW ACCUMULATION
PENDING HOW ENERGY ALOFT PHASES AND HOW QUICKLY MODIFIED ARCTIC AIR
GETS ENTRAINED UNDERNEATH WRN EXTENT OF PCPN SHIELD. CERTAINLY
SOMETHING TO KEEP WATCHING ALTHOUGH THE HIGH LEVEL OF UNCERTAINTY
SHOULD BE STRESSED.
&&
.AVIATION.../18Z TAFS/
UPPER LEVEL VORTEX AND ASSOCIATED SFC TROUGH CONTINUES TO PROGRESS
EAST ACROSS THE REGION WITH LOW END MVFR TO HIGH END IFR CIGS/VIS
SCT ACROSS THE FA. RAIN SHOWERS WILL CONTINUE TO WAIN THROUGH THE
EVENING AS THE UPPER LOW BEGINS TO EJECT NE OUT OF THE FA .
ADVANCING SFC TROUGH NOW ENTERING THE WESTERN FA WILL VEER WINDS
NW AND INCREASE...REMAIN GUSTY THROUGH EVENING AS CAA ENSUES.
EXPECT SCOURING OF REMNANT IFR CIGS AS DRIER AIR WORKS INTO THE FA
BEHIND THE SFC TROUGH. LINGERING LIGHT RAIN OR SNOW SHOWERS WILL
BE POSSIBLE NEAR LAKE MI THROUGH EVENING...WITH PRECIP EXPECTED TO
END TONIGHT. LOOK FOR LINGERING MVFR CIGS INTO FRI...WITH A TREND
TO SCT CIGS BY LATER IN THE DAY.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 4 PM EST FRIDAY FOR LMZ043-046.
&&
$$
SHORT TERM...JC
LONG TERM...HOLSTEN
AVIATION...JC
