FXUS63 KIWX 142340
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
640 PM EST MON DEC 14 2009
.AVIATION...
SFC COLD FRONT CONTINUES TO PUSH SE ACROSS THE FA...WITH A SLIGHT
IMPROVEMENT IN FLIGHT CONDITIONS PER VIS BEHIND THE FRONT. TEMPORARY
VIS RESTRICTIONS IN -DZ EXPECTED RIGHT ALONG THE SFC FRONT AS
LIFT INTERACTS WITH LINGERING MOISTURE. -DZ WILL END POST FRONTAL
WITH CIGS HANGING AROUND 1 KFT THROUGH MUCH OF THE PERIOD GIVEN A
CAA REGIME WITH A GROWING INVERSION AND HAVE CARRIED LOW END MVFR
CIGS THROUGH MUCH OF THE PERIOD AT BOTH TERMINALS. DO EXPECT A
WEAK LAKE RESPONSE WITH LAKE EFFECT SNOW SHOWERS ACROSS THE FAR
NW LATER IN THE PERIOD...HEAVIEST IN MI WITH THE LOWEST FLIGHT
RESTRICTIONS THERE. CONTINUED -SN MVFR VIS RESTRICTION AT
SBN...BUT ADJUSTED TIME FOREWORD GIVEN BUFR FORECAST THERMAL
PROFILES. WINDS WILL VEER NW AND INCREASE THROUGH MORNING...WITH
GUSTS EXPECTED GIVEN SFC PRESSURE GRADIENT AND FLOW ALOFT.
&&
.PREV DISCUSSION... /ISSUED 325 PM EST MON DEC 14 2009/
SHORT TERM...THIS AFTERNOON THROUGH TUESDAY NIGHT...
MAIN FOCUS OF SHORT TERM LIES WITH AREA OF SFC LOW PRESSURE
CURRENTLY CENTERED OVER CWA AND NW LOW LVL FLOW BEHIND IT. AREAS OF
DRIZZLE AND FOG HAVE PERSISTED OVER FAR NRN INDIANA AND SOUTHERN
LOWER MICHIGAN AS BETTER LOW LVL FLOW AND MIXING HAS REMAINED
SOUTH. STRONG MIXING HAS ALLOWED SRN CWA TO BREAK OUT OF CLOUDS AND
TEMPS HAVE ABSOLUTELY SOARED INTO THE LOW 50S THIS AFTERNOON. COLD
FRONT WILL PUSH THROUGH WITH WK FORCING JUST ENOUGH TO CONTINUE LOW
CHANCE POP WORDING THOUGH EXPECTING MAINLY DRIZZLE DURING FROPA.
CAA BEGINS IN EARNEST TONIGHT WITH H85 TEMPS DROPPING NEARLY 20
DEGREES IN THE NEXT 24 HRS. OBVIOUS ISSUES LIE WITH FRIGIDNESS OF
COLD AIR AND AMOUNT OF LAKE EFFECT SNOW. CAA TONIGHT AND TOMORROW
WILL RESULT IN FALLING TEMPS FROM NOW UNTIL WED MORNING WITH ANY
DIURNAL RISE TUESDAY DOUBTFUL. GOING TEMP GRIDS IN GOOD SHAPE WITH
ONLY MINOR CHANGES MADE TO TREND LOWS TUE NIGHT DOWN...ESPECIALLY IN
SW CWA WHERE SOME CLEARING IS POSSIBLE.
AS FAR AS LAKE EFFECT...NOT EXPECTING A PARTICULARLY ROBUST EVENT
GIVEN LOW INVERSION HEIGHTS AND SUBSTANTIAL SYNOPTIC LOW LVL DRYING
TMRW AFT/EVE. FETCH OF 290-300 FAVORABLE FOR A MULTI-BAND EVENT
WITH H85 TEMPS DROPPING TO -12C TO 15C RESULTING IN DELTA T/S NEAR
20 BY MIDDAY TUE. THIS SAID...DGZ WON/T FALL INTO AREA OF LIFT
UNTIL MIDDAY TUE BUT EXPECT A GOOD 12 HRS OF LIGHT SNOWFALL TO
RESULT IN A FEW INCHES OF SNOW IN BERRIEN AND CASS COUNTIES. WILL
HOLD OFF ON ANY ADVISORY MENTION FOR NOW GIVEN MARGINAL SET UP AND
LOW INVERSION HEIGHTS THOUGH WOULDN/T BE TERRIBLY SURPRISED TO SEE
SEVERAL INCHES OF ACCUMS SOMEWHERE IN BERRIEN OR CASS COUNTY GIVEN
LACK OF LOW LVL SHEAR AND RELATIVELY LONG DURATION. DID BUMP POPS TO
CATEGORICAL TOMORROW AND SLIGHTLY BUMPED UP SNOW AMOUNTS.
LONG TERM...
..WEDNESDAY THROUGH MONDAY...
RATHER ZONAL FLOW AT BEGINNING OF LONG TERM PERIOD STILL LOOKS TO
BECOME BUCKLED BY WEEKEND WITH GOOD CHANCE FOR COLD AIR INTRUSION
THIS WEEKEND INTO EARLY NEXT WEEK. GRIDS HAVE OVERALL IDEA WELL IN
HAND AND ONLY SOME MINOR ADJUSTMENTS NEEDED BASED ON LATEST MEDIUM
RANGE MODELS AND GUIDANCE.
HIGH PRESSURE WILL BE MOVING OVER THE AREA ON WEDNESDAY. WESTERLY
FLOW AND DELTA T VALUES STILL AROUND 13 TO 15C SUGGEST A FEW LIGHT
LAKE EFFECT SNOW SHOWERS OR FLURRIES STILL POSSIBLE WITH LAKE
CLOUDS. FLOW WILL BE WESTERLY AND DEPTH OF MOISTURE BECOMING VERY
SHALLOW SO POPS CONFINED TO MAINLY BERRIEN...CASS AND ST. JOSEPH
COUNTIES. ACCUMS LITTLE OR NONE BY THIS TIME PERIOD. HIGH CONTINUES
TO BUILD IN DURING THE DAY SO REMOVED PCPN FROM AFTERNOON.
SEVERAL WEAK AND POORLY HANDLED SHORT WAVES TO MOVE THROUGH THE MEAN
FLOW FROM WED NIGHT THROUGH THIS WEEKEND BEFORE STRONGER WAVE DROPS
OUT OF CANADA AND HELPS DIG EASTERN CONUS TROUGH. THIS WILL ALLOW
MUCH COLDER AIR TO MOVE SOUTH WITH SUCCESSIVE SHORT WAVES ENHANCING
THE COLD AIR THROUGH MONDAY. DETAILS REMAIN UNCERTAIN WITH MODEL
DIFFERENCES IN TIMING...LOCATION AND CONTINUITY. PREFERENCE LIES
WITH COMPROMISE OF GFS AND ECMWF ALONG WITH GFS ENSEMBLES...SIMILAR
TO HPC GUIDANCE. THIS LEADS TO BASICALLY FLURRIES IN THE FRIDAY
THROUGH MONDAY TIME FRAME AWAY FROM LAKE. DEPENDING ON STRENGTH AND
TRACK OF MAIN SHORT WAVE/CLIPPER SYSTEM THIS WEEKEND COULD NEED TO
EXPAND POPS FOR LIGHT SNOW.
THE COLD AIR WILL CERTAINLY BRING LAKE EFFECT SNOW SHOWERS ONCE
AGAIN BUT TIMING OF SHORT WAVES AND WIND TRAJECTORIES MAKE IT
DIFFICULT TO PIN DOWN ANY PERIOD OR LOCATION FOR BEST SNOWFALL.
GIVEN THE AGREEMENT IN MODELS OF ARCTIC SURGE SNOW SHOWER
POSSIBILITY LOOKS HIGH FOR THE PERIOD BUT LOW FOR ANY SPECIFIC 12
HOUR WINDOW AT THIS TIME RANGE. HAVE ADDED BROAD LOW CHANCE POPS TO
TYPICAL LAKE EFFECT AREAS ACROSS THE NORTH AND THIS CAN BE REFINED
AS MODEL DETAIL GROWS.
SEASONABLE MID DECEMBER TEMPERATURES EXPECTED MOST OF REMAINDER OF
THIS WEEK. COULD SEE HIGHS A LITTLE WARMER ON THURSDAY DEPENDING ON
AMOUNT OF CLOUDS AND DEGREE OF WARM AIR ADVECTION AND MIXING AHEAD
OF WEAK SHORT WAVE. THIS WAVE LIKELY TO BRING FIRST INITIAL SHOT OF
COLDER AIR BY FRIDAY. HAVE CONTINUED WITH COOLER THAN GUIDANCE TEMPS
FROM FRIDAY THROUGH MONDAY AS GFS MEX NUMBERS TREND TOWARD CLIMO AND
ARE USUALLY TOO WARM IN COLD AIR ADVECTION SITUATIONS.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...SMALL CRAFT ADVISORY FROM 10 PM THIS EVENING TO 1 AM EST
WEDNESDAY FOR LMZ043-046.
&&
$$
SHORT TERM...SIMPSON
LONG TERM...LASHLEY
AVIATION...JC
