FXUS63 KIWX 281635
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
1135 AM EST SAT NOV 28 2009
.AVIATION.../18Z TAFS/
VFR CONDITIONS WILL PREVAIL THROUGH THE MAJORITY OF THE PERIOD AS
SFC HIGH PRESSURE COMBINED WITH UPPER LEVEL RIDGING BRINGS EXCELLENT
FLIGHT CONDITIONS TO THE REGION. POCKETS OF MVFR VIS RESTRICTIONS
ARE POSSIBLE AROUND DAWN GIVEN LL MOISTURE ADVECTION WITH GOOD
RADIATIONAL COOLING. A SFC TROUGH WILL SAG INTO THE REGION BY DAWN
SUN...WITH DETERIORATING FLIGHT CONDITIONS EXPECTED TO ENTER THE
NW. THIS TROUGH WILL SLOWLY PUSH SOUTH ACROSS THE FA THROUGH THE
DAY...SUPPORTING A TREND TO LOW END MVFR CIGS WITH IFR VIS IN
AREAS. RAIN CHANCES WILL INCREASE BY LATE MORNING ASSOCIATED WITH
THIS TROUGH AND AN ASSOCIATED UPPER LEVEL IMPULSE.
A SECONDARY CONCERN TONIGHT WILL BE LL WIND SHEAR AS 1-5 KFT FLOW
INCREASES IN RESPONSE TO THE APPROACHING UPPER WAVE. 25 TO 35
KNOTS OF SHEAR MAY BE POSSIBLE FROM SFC TO 1.5-2.5 KFT AT THE
TERMINALS LATE THIS EVENING INTO THE OVERNIGHT. WILL DEFER MENTION
TO NEXT TAF ISSUANCE GIVEN THE PERIOD.
&&
.PREV DISCUSSION... /ISSUED 408 AM EST SAT NOV 28 2009/
SHORT TERM /TODAY THROUGH SUNDAY NIGHT/...
A POTENT UPPER LEVEL RIDGE OVER THE CENTRAL CONUS WILL BUILD EAST
TODAY AND ALLOW FOR A WELCOME REPRIEVE TO THE COOL AND CLOUDY
CONDITIONS OF LATE FOR SATURDAY. A SHORTWAVE NOW OVER SOUTHEASTERN
ALBERTA WILL STEADILY MOVE SOUTH AND EAST...PROVIDING OUR NEXT
WEATHER MAKER FOR LATE SUNDAY AND SUNDAY NIGHT.
A BEAUTIFUL DAY IS ON TAP TODAY AS ABOVE MENTIONED UPPER RIDGE
BUILDS EAST...WITH STRONG WARM ADVECTION UNDER WESTERLY LOWER TROP
FLOW. WITH A MAJORITY OF THE UPPER LEVEL MOISTURE ALONG THE H25 JET
AXIS...AND WITH THIS AXIS REMAINING NORTH OF OUR AREA TODAY...EXPECT
LITTLE IN THE WAY OF HIGH CLOUDINESS. ALSO...EXPECT A PRETTY STRONG
LLEVEL INVERSION GIVEN COLUMN-DEEP SUBSIDENCE ALONG WITH THE RAPID
WARMING ALOFT...WHICH WILL PRECLUDE ANY LLEVEL CLOUDS. THE RESULT
WILL BE A MSUNNY DAY. ONLY EXPECT MIXING TO AROUND H95 WHICH SHOULD
YIELD HIGHS IN THE UPPER 40S OVER NORTHEASTERN AREAS TO THE LOWER
50S IN THE SOUTHWEST...STILL MORE THAN 5F ABOVE NORMAL.
WEAK COLD FRONTAL BOUNDARY NOW OVER THE EASTERN DAKOTAS WILL BEGIN
SETTLING TOWARDS THE REGION TONIGHT. WITH THE SURFACE WARM FRONT
NORTH AND EAST OF THE CWA...EXPECT GRADUALLY MOISTENING CONDITIONS
UNDER LLEVEL SOUTHWEST FLOW. THIS IS A DECENT FOG SCENARIO WITH
MOISTURE INCREASING WITH HEIGHT IN THE LOWEST LEVELS. WHILE
SOUTHWEST WINDS WILL LIKELY LIMIT THE POTENTIAL FOR DENSE FOG...AND
MAY ALLOW FOR SOME STRATUS DEVELOPMENT...WILL TAKE THE FOG ROUTE AT
THIS POINT AND ADD PATCHY FOG TO THE GRIDS. TEMPS WILL BE HIGHER
GIVEN LESS DECOUPLING AT THE SURFACE...INCREASED LLEVEL
MOISTURE...AND MUCH HIGHER AFTERNOON TEMPERATURES. INHERITED LOWS
IN THE UPPER 30S LOOK VERY REASONABLE AND ONLY MADE A FEW MINOR
TWEAKS...MAINLY TO DROP TEMPS IN THE EAST SLIGHTLY GIVEN LIGHTER
WINDS HERE...ALONG WITH CLEAR SKIES...AT LEAST THROUGH THE EVENING.
COLD FRONT MOVES INTO THE REGION ON SUNDAY...EXITING SUNDAY NIGHT.
PRIMARY QUESTIONS ARE FRONTAL TIMING...AND HOW MUCH MOISTURE CAN
RETURN SOUTHEAST OF THE FRONT TO SPAWN SHRAS. NAM IS DOING A BETTER
JOB WITH HANDLING LLEVEL MOISTURE OVER THE CENTRAL PLAINS THAN IT
WAS A DAY AGO...WITH THE GFS ALSO BETTER THAN YESTERDAY...BUT STILL
TOO MOIST. WILL FOLLOW THE NAM/S MOISTURE EVOLUTION...BUT AS FOR
THE TIMING...WILL BLEND OUR PREVIOUS THOUGHTS WITH A SOLUTION
SIMILAR TO THE ECMWF WHICH IS A LITTLE FASTER THAN OUR PREVIOUS
GRIDS...BUT STILL SLOWER THAN THE NAM/GFS. THIS CAPTURES A SOMEWHAT
FASTER OVERALL TREND...BUT MAINTAINS SOME CONSISTENCY AS WELL. FOR
SUNDAY...EXPECT LLEVEL MOISTENING AHEAD OF THE FRONT TO ALLOW FOR
QUICKLY INCREASING CLOUDS WITH POSITIVE DPVA ABOVE THE SURFACE
CONVERGENCE ZONE POPPING SOME SHRAS BY MID/LATE AFTERNOON. BY THE
TIME ENOUGH MOISTURE ARRIVES TO SPAWN PRECIP...THE FRONT MAY HAVE
CLEARED BY NORTHWESTERN ZONES...SO HAVE ONLY KEPT A SCHC POP HERE
AND SOME SPOTS COULD REMAIN DRY. LOWERED HIGHS SLIGHTLY IN A FEW
SPOTS GIVEN EXPECTED AFTERNOON CLOUD COVER BUT GIVEN SOME PARTIAL
EARLY DAY SUN AND MUCH HIGH LOWS THAN THE PREVIOUS NIGHT...HIGHS
NEARING 50 LOOK GOOD.
ON SUNDAY NIGHT...FRONT SETTLES SOUTH AND EAST OF THE CWA WITH
DIMINISHING POPS CHANCES IN THE SOUTHEAST OVERNIGHT. WITH LAKE T/S
AROUND 8C...AND MODEL CONSENSUS SHOWING T85S DROPPING TO AROUND -7C
AFTER MIDNIGHT...ALONG WITH A MIXED LAYER 320 FLOW...EXPECT A LAKE
RESPONSE TO GET GOING...BUT LIKELY NOT UNTIL AFTER MIDNIGHT. BL
TEMPS LOOK MARGINALLY COLD ENOUGH FOR SNOW...SO WILL INCLUDE RASN
MENTION AFTER MIDNIGHT AS WELL. EXPECT LOWS NEAR OR JUST ABOVE THE
FREEZING MARK BY DAYBREAK.
LONG TERM...
MAIN CHANGES EARLY IN THE PERIOD AS LATE WEEK MODEL DISAGREEMENT
STILL PLAGUES DETAILS OF STRONG SYSTEM TO LIFT OUT OF THE SOUTHEAST
IN SECOND HALF OF THE PERIOD. BY 12Z MONDAY MODEL SUITE IN GOOD
AGREEMENT ON SFC FRONT WHICH PUSHED THROUGH EARLIER ON SUNDAY HAS
PROGRESSED TO NEAR THE APPALACHIAN SPINE AS FLOW ALOFT REMAINS
STRONG AND PROGRESSIVE. COOLER AIR FOLLOWING IN ITS WAKE AS UPPER
TROUGH SHIFTS INTO THE GREAT LAKES DROPPING H85 TEMPS TO -7C SETS UP
A SHORT WINDOW FOR A MILD LAKE RESPONSE. DROPPED POPS ASSOC WITH
LLEVEL BNDRY AND ADDED LAKE POPS WHICH SHIFT NORTH AND DECREASE AS
NW WINDS BACK TO WESTERLY AND TEMPS ALOFT INCREASE. ALREADY LOW EQL
LEVELS ARE BELOW GROWTH ZONE AND SHOW MARGINAL MOISTURE KEEPING
RESPONSE ON THE PUNY SIDE...AND THOUGH WET BULBS ARE ABV ZERO ONLY
VERY NEAR SFC WILL HEDGE WITH RAIN/SNOW SHOWER WORDING THOUGH
NEARER 46 DEGREE LAKE LIQUID SHOULD DOMINATE SIMILAR TO RECENT EVENT.
MID TO LATE WEEK MODEL PICTURE IS LARGELY UNCHANGED AS BRIEF UPPER
RIDGING IN WAKE OF EARLY WEEK WAVE IS QUICKLY REPLACED BY NEXT
POTENT TROUGH TO DIG SOUTH OUT OF CANADA WHICH PHASES WITH WAVE
MOVING OUT OF THE DESERT SW LIFTING A POTENTIALLY POTENT SYSTEM
SOMEWHERE THROUGH THE EASTERN CONUS. UNFORTUNATELY THIS CONSISTENCY
IN THE MODELS IS WITH THEIR OWN PREVIOUS RUNS WHICH ARE DISSIMILAR
BETWEEN MODELS. 00Z ECMWF STILL BRINGS UPPER WAVE UP THE OHIO VALLEY
WITH RAIN/SNOW CHANCES FOR THE REGION...WHILE THE GFS PHASES A
FASTER MOVING SOUTHERN WAVE FURTHER SOUTHEAST LEAVING THE CWA DRY.
INTERESTINGLY THE 12Z AND 00Z ECMWF ARE NOW ABOUT 12 HOURS FASTER
THAN LAST NIGHT...WHICH IS TOWARDS THE FASTER GFS WHICH IS JUST OFF
THE MAINE COAST WITH A 978MB LOW BY 12Z THU. GIVEN TIMING SHOWN IN
OP MODELS AND ENSEMBLE MEANS LOW CHC POPS ARE SCOOTED AHEAD BY 12
HOURS THOUGH IT IS ESSENTIALLY NO MORE CLEAR AS TO THE EVENTUAL
TRACK.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&
$$
SHORT TERM...ARNOTT
LONG TERM...LUDINGTON
AVIATION...JC
