FXUS63 KLOT 221847
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1247 PM CST TUE DEC 22 2009
.DISCUSSION...
1015 AM CST
...NEAR TERM UPDATE...
JUST A FEW TWEAKS TO NEAR TERM FORECAST THIS MORNING TO ACCOUNT FOR
LATEST RADAR TRENDS REGARDING MORNING SNOW...AND CHANCES FOR LIGHT
FREEZING RAIN/DRIZZLE THIS AFTERNOON AND EVENING.
12Z UPPER AIR ANALYSIS INDICATES THAT SHORTWAVE RESPONSIBLE FOR
OVERNIGHT AND MORNING SNOW IS ON ITS WAY OUT OVER EASTERN INDIANA AT
THIS HOUR...WITH LOW LEVEL BAROCLINIC ZONE AND 850 WAA OVER THE CWA
AND ASSOCIATED ISENTROPIC LIFT BEING THE PRIMARY FORCING FOR
REMAINING SNOW THIS MORNING. SHORT TERM MODEL GUIDANCE INDICATES
THAT GOING IDEA OF LIGHT SNOW LIFTING NORTH ACROSS NORTHERN TWO OR
SO TIER OF COUNTIES LATE THIS MORNING AND AFTERNOON IS ON TRACK.
STILL EXPECT TO SEE A DOWNWARD TREND IN INTENSITY WITH THIS AREA OF
SNOW...BUT VERY MINOR AMPLITUDE SHORTWAVE ANALYZED OVER IOWA AT 12Z
WILL RIPPLE THROUGH THE FORECAST AREA THIS AFTERNOON...LIKELY ADDING
JUST A TOUCH OF RISING MOTION TO OVERALL PICTURE AND KEEPING SNOW
JUST ABOVE THE FLURRY LEVEL. AT ANY RATE...DON'T EXPECT ANYTHING
MORE THAN PERHAPS AN ADDITIONAL TENTH OF TWO OF SNOW AT THE MOST FOR
THOSE LOCATIONS THAT SEE SNOW LATE THIS MORNING AND AFTERNOON.
ATTENTION THIS AFTERNOON AND EVENING THEN TURNS TO LIGHT PRECIP AND
QUESTIONS OF PRECIP TYPE ACROSS THE FORECAST AREA. WARM AIR
ADVECTION LOOKS TO START CRANKING UP ACROSS THE SOUTHERN FORECAST
AREA THIS EVENING. MODELS ARE SPITTING OUT SEVERAL TENTHS OF AN
INCH OF QPF ACROSS MAINLY AREAS TO THE SOUTH OF I-88. FORECAST
SOUNDINGS INDICATE THAT FREEZING DRIZZLE OR LIGHT FREEZING RAIN ARE
THE PROBABLE PRECIP TYPE THIS EVENING AND OVERNIGHT...THOUGH A FEW
SNOWFLAKES ARE CERTAINLY POSSIBLE...ESPECIALLY BETWEEN I-80 AND
I-88.
UPDATED FORECAST PRODUCTS AND GRIDS OUT SHORTLY.
BOXELL
&&
.AVIATION...
1244 PM CST
1800 UTC TAFS...SHORT TERM CONCERNS ARE IFR CIGS AND/OR VSBYS
ACROSS THE LOCAL TERMINALS WITH LONGER TERM CONCERNS TIMING AND
TYPE/S/ OF PCPN WED MORNING.
IR SATELLITE SHOWS MULTIPLE CLOSELY SPACED LOW AMPLITUDE SHORT
WAVES TRACKING FROM THE UPPER MIDWEST ACROSS THE SOUTHERN
GRTLKS...UPPER OH VALLEY TO THE JERSEY SHORE. STILL ONE UPSTREAM
SHORT WAVE OVR NORTHERN MN BUT WITH UPPER RIDGING POKING NORTHWARD OVR THE
MN/DAKOTAS BORDER IN RESPONSE TO SHARP UPPER TROF ROTATING OVR THE
DESERT SW THIS UPPER MIDWEST SHORT WAVE TO PASS INTO THE WRN GRTLKS
N OF THE LOCAL TERMINALS.
LAST SHORT WAVE TO AFFECT TERMINALS NOW CROSSING OVR ERN WI AND
NE IL...DAMPENING OUT IN THE PROCESS AND SHOWING CONTINUED WARNING
OF TOPS SO EXPECT ANY ACCUMULATING -SN AND VSBY REDUCTIONS
ASSOCIATED WITH IT TO END 19-20Z. PLENTY OF LOW LEVEL MOISTURE
REMAINS IN PLACE SO MVFR TO PREVAIL WITH ONLY OCNL VERY LIGHT
SN/FLURRIES REST OF AFTERNOON AND TONIGHT.
SOUTHWESTERN U.S. SYSTEM TO MOVE E ACROSS THE SRN ROCKIES OVERNIGHT. MODELS
SHOW DRY MID LEVEL OVERNIGHT WITH SATURATED 2-2.5KM SFC BASED LAYER.
WITH TOPS OF THIS MOISTURE NOT COLD ENOUGH FOR ICE CRYSTAL FORMATION
AND TOO THICK OF A MID LEVEL DRY LAYER FOR ICE CRYSTAL INTRODUCTION TO
SURVIVE FOR SEEDING FROM ABV...EXPECT SOME -FZDZ AS WEAK UVV
STARTS TO INCREASE IN THIS LOW LEVEL SUPER COOLED MOIST LAYER.
AS THE UPPER SYSTEM CONTINUES EASTWARD OUT OVR THE SRN HI PLAINS
DURING THE DAY WED STRONG WAA AND DEEP ISENTROPIC UPGLIDE TO
SPREAD E ACROSS THE MID MS VALLEY AND EVENTUALLY OVER THE LOCAL
TERMINALS. BY 18Z SIGNIFICANT PCPN EXPECT TO HAVE REACHED CHI AREA
WITH MIXED WINTER PCPN TYPES. EXACT TIMING OF DIFFERENT TYPE
TYPICALLY DIFFICULT...ESPECIALLY THIS FAR OUT...AS ALL DEPENDS ON
HOW STRONG AND DEEP MID LEVEL WARMING IS COMPARED TO LOW LEVEL
WARMING THOUGH EXPECT FRESH SNOW COVER TO HELP TO KEEP SFC TEMPS
SUPPRESSED AS OPPOSED TO IF HAD BARE GROUND.
WIND SPEEDS TO GRADUALLY RAMP UP WITH TIME...PRETTY MUCH
REMAINING OUT OF THE E...AS THE SFC LOW DEEPENS WHILE TURNING NE
THEN N FROM THE TX PANHANDLE TO THE MID MO VALLEY BY LATE WED.
TRS
&&
.MARINE...
215 AM...MAIN FORECAST CONCERN REMAINS A STRONG WINTER STORM TO
AFFECT THE LAKES REGION FROM WEDNESDAY THROUGH FRIDAY WITH GALES
EXPECTED TO DEVELOP THURSDAY.
HIGH PRESSURE OVER CENTRAL ONTARIO WILL REMAIN NEARLY STATIONARY
THROUGH THURSDAY MORNING WHILE IT CONTINUES TO STRENGTHEN. NEW
LOW PRESSURE DEVELOPING OVER THE SOUTHERN PLAINS TODAY WILL
SLOWLY LIFT NORTH TO MISSOURI BY THURSDAY EVENING AS IT CONTINUES
TO DEEPEN. THE GRADIENT BETWEEN THE HIGH OVER ONTARIO AND THIS
LOW LIFTING NORTH WILL CONTINUE TO TIGHTEN TONIGHT THRU THURSDAY
MORNING. TRENDS HAVE BEEN IN FAIR AGREEMENT OVER THE PAST FEW DAYS
AND EXPECT GUSTS TO 30KTS TO DEVELOP BY WEDNESDAY AFTERNOON OVER
SOUTHERN LAKE MICHIGAN WITH GALES TO 40KTS BY MIDDAY THURSDAY AND
WILL BE GOING WITH A GALE WATCH STARTING THURSDAY MORNING. FURTHER
NORTH...LOW END GALES OVER NORTHERN LAKE MICHIGAN SEEM REASONABLE
THOUGH TIMING IS A BIT LATER...PROBABLY NOT DEVELOPING UNTIL
THURSDAY EVENING...BUT WILL STILL HOIST A GALE WATCH WITH THIS
FORECAST. AS THE LOW CONTINUES TO LIFT NORTH ACROSS IOWA BY
FRIDAY MORNING AND WISCONSIN FRIDAY NIGHT...IT BEGINS TO SLOWLY
WEAKEN...AND EXPECT WIND SPEEDS TO GRADUALLY RELAX FRIDAY INTO
FRIDAY NIGHT WITH GALES LIKELY ENDING BY MID/LATE MORNING FRIDAY.
CMS
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-
ILZ023...NOON WEDNESDAY TO NOON THURSDAY.
IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011...NOON
WEDNESDAY TO NOON THURSDAY.
LM...GALE WATCH...LMZ080-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ870-LMZ872-
LMZ874-LMZ876-LMZ878...6 AM THURSDAY TO NOON FRIDAY.
GALE WATCH...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
LMZ868...6 PM THURSDAY TO NOON FRIDAY.
SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
LMZ745...MIDNIGHT WEDNESDAY TO 6 AM THURSDAY.
&&
$$
