FXUS63 KIWX 272114
AFDIWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
414 PM EST FRI NOV 27 2009

.SHORT TERM...

TONIGHT THROUGH SATURDAY NIGHT

DEEP UPPER NEGATIVE HEIGHT ANOMALY OVER THE EASTERN US CONTINUES TO 
SUPPORT COLD CONDITIONS ACROSS THE GREAT LAKES TODAY. LAKE EFFECT 
CLOUDS COVER MOST OF THE FA...AS TEMPS STRUGGLE TO REACH 40. SFC 
RIDGE AXIS EXTENDS SOUTH FROM CENTRAL WI INTO THE LOWER MISSISSIPPI 
VALLEY WITH MOSTLY CLEAR SKIES LOCATED OVER MUCH OF THE WESTERN 
MIDWEST. LEE SIDE TROUGH OVER THE PLAINS IS BEGINNING TO PUSH EAST 
AS A MID LEVEL IMPULSE BEGINS TO PUSH EAST ACROSS THE NORTHERN 
ROCKIES. PAC AIRMASS...MODIFIED BY DOWNSLOPE SLOPE FLOW IS 
SUPPORTING TEMPS WELL INTO THE 50S AND 60S ACROSS THE PLAINS...WITH 
WELL MIXED SOUTHERLY FLOW. THIS SYSTEM AND ITS ASSOCIATED ADVECTIONS 
WILL BE THE FOCUS OF THE SHORT TERM PERIOD...AS IT PUSHES EAST. HAVE 
UTILIZED A BLEND OF DETERMINISTIC MODELS FOR GUIDANCE...WITH NO 
STRONG PREFERENCE AT THIS POINT. 

TONIGHT...LK EFFECT CLOUDS WILL CONTINUE TO DEPLETE THROUGH THE 
NIGHT PERIOD...SHIFTING EAST IN THE PROCESS AS BACKING LL WINDS AND 
WAA SUPPORTS A LESSENING LAKE RESPONSE. SFC RIDGE WILL SHIFT EAST 
OF THE FA WITH LIGHT WINDS EXPECTED THROUGH MUCH OF THE 
PERIOD...ALTHOUGH WESTERN AREAS MAY SEE A REPONSE TO THE WIND FIELD 
BY DAWN AS THE SFC PRESSURE GRADIENT TIGHTENS IN RESPONSE TO 
ADVECTING/PROPAGATING SFC LOW PRESSURE. VERY DRY AIRMASS IN PLACE 
COUPLED WITH LIGHT WINDS AND CLEAR SKIES WILL SUPPORT A PERIOD OF 
DECENT COOLING ACROSS MOST OF THE FA WITH TEMPS FALLING IN THE 
20S...MAINLY IN THE EASTERN HALF OF THE FA. ADVECTING CIRRUS MAY 
QUELL T FALLS SOME...BUT NOT EXPECTING A THICK CLOUD DECK AT THIS 
POINT. 

SAT...MILD DAY IN STORE AS A WAA WILL BE THE DOMINATE WEATHER 
PROCESS. PLAINS AIRMASS WILL ADVECT INTO THE REGION ALOFT. 
HOWEVER...HIGHLY SHEARED FLOW UNDER A STRONG LL INVERSION WILL ONLY 
OFFER SHALLOW MIXING. REGARDLESS...TEMPS ARE STILL EXPECTED TO REACH 
THE LOWS 50S OVER MUCH OF THE SW HALF OF THE FA...WITH UPPER 40S IN 
THE NE...ABOVE NORMAL TEMPS FOR LATE NOV. MOSTLY SUNNY SKIES ARE 
EXPECTED WITH CIRRUS LIKELY...ALTHOUGH CIRRUS SHOULD STILL ALLOW 
AMPLE INSOLATION.

SFC LOW AND ASSOCIATED UPPER IMPULSE WILL NEAR THE REGION SAT NIGHT 
WITH INCREASING MID AND HIGH CLOUDS EXPECTED. VERY LIMITED MOISTURE 
FIELDS WILL OFFER DRY CONDITIONS THROUGH THE PERIOD...GIVEN STRONGER 
FORCING FOR ASCENT WELL NORTHWEST OF THE REGION.

&&

.LONG TERM...
SUNDAY THROUGH FRIDAY. INTER/INTRA MODEL CONSISTENCY CONTS WRT NRN 
EXTENSION OF ALBERTA TO EPAC SHORTWAVE STEERING INTO THE WESTERN 
GRTLKS ON SUNDAY. DECENT EPAC/INTR MTN MID LVL MOISTURE FEED 
COMBINED WITH MINIMAL LLVL MSTR POOLING AHEAD OF SFC REFLECTION WITH 
5-6 G/KG SFC-4KFT. MIDLVL SHORTWAVE INTO SRN GRTLKS/NRN IN SUNDAY 
EVENING COINCIDENT WITH 80-100M 7-5H 24 HR HGHT FALLS. HAVE PROVIDED 
SOME ADDNL TIMING WITH MID RANGE CHC POPS SUN AFTN INTO SUN 
NIGHT...WITH INKLING TOWARD GOING SCT/COVERAGE WORDING BUT AS LATE 
DY3/NIGHT WILL AFFORD ADDNL MODEL RUN FOR THAT CONVEYANCE. 

PREFERENCE GOES AWAY FM ECMWF SOLN KEEPING SECOND NRN STREAM ENERGY 
GULF OF AK. HOWEVER...FEEL TRENDS OF GFS/GEFS/GEM GLB IN PHASING NRN 
STREAM INTO BASE OF KSFO TO SOCAL CUTOFF TO FORM DEEP GRTLKS INTO TN 
VLY 5H TROF BY DY6 WITH WEAK FORCING FOR RASN MIX PSBL THU 
TRANSITIONING INTO LOW-MOD LAKE EFFECT SN POTNL DY7 AS TROF 
COMPLETES PHASING AND TRANSITIONS INTO ERN GRLTKS. AS THIS THE FIRST 
INTRO TO POPS/WX LATE IN FCST PD WITH AT LEAST A FAIR AMOUNT OF 
UNCERTAINTY WILL RELEGATE POPS TO LOW CHC. 

&&

.AVIATION.../18Z TAFS/
SFC HIGH PRESSURE CONTINUES TO BUILD ACROSS THE OHIO VALLEY REGION
WITH NW FLOW PREVALENT ACROSS THE GREAT LAKES. COLD THERMAL
FIELDS CONTINUE TO SUPPORT LAKE EFFECT CLOUDS OVER MUCH OF THE
FA...WITH LOW END VFR CIGS THE NORM. WAA WITH BACKING LL WINDS
WILL HELP DEPLETE LAKE CLOUDS THROUGH TONIGHT...WITH CLEARING
EXPECTED LATE. SFC WINDS WILL BACK IN THE PERIOD AND BEGIN TO
INCREASE ON SAT AS SFC LOW PRESSURE PUSHES INTO THE UPPER
MIDWEST.

&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&

$$

SHORT TERM...JC
LONG TERM...MURPHY
AVIATION...JC