181
FXUS63 KLOT 091242
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
642 AM CST TUE FEB 9 2010
DISCUSSION
349 AM CST
SHORT TERM (TODAY THROUGH WEDNESDAY)...
OVERALL MADE VERY FEW CHANGES TO GOING FORECAST THIS MORNING AS
THINGS GENERALLY RIGHT ON COURSE.
POWERFUL UPPER LOW CONTINUES TO PIVOT SOUTH-SOUTHEASTWARD ACROSS
WESTERN IOWA EARLY THIS MORNING WITH TEXTBOOK BAROCLINIC LEAF
PATTERN DEVELOPING TO THE EAST OF THE CLOSED LOW. IMPRESSIVE REGION
OF UPPER LEVEL DIVERGENCE APPARENT OVER WI/MN WITH DEVELOPING
DEFORMATION ZONE. UPPER LOW STILL PROGGED TO GRADUALLY TURN MORE
EASTWARD TODAY MOVING ACROSS DOWNSTATE ILLINOIS AND INTO THE EASTERN
OHIO VALLEY BY WEDNESDAY MORNING.
AS UPPER LOW MAKES ITS TURN EASTWARD TODAY REALLY LOOKING FOR FAIRLY
CONTINUOUS SNOW ACROSS MOST OF THE CWA AS WE TRANSITION FROM THE
WARM CONVEYOR BELT INTO THE DEFORMATION ZONE THIS AFTERNOON. THE
EXCEPTION MAY BE OVER SOUTHERN 1/3 OR SO OF THE CWA WHERE CLOSER
PROXIMITY TO THE MID LEVEL DRY INTRUSION MAY RESULT IN SNOW BECOMING
MORE INTERMITTENT.
OBVIOUSLY SYNOPTICALLY FORCING WILL BE QUITE STRONG AS THIS VIGOROUS
SYSTEM MOVES ACROSS THE REGION...THE LIMITING FACTOR FOR MORE
IMPRESSIVE SNOWFALL RATES WILL BE THE RELATIVE LACK OF QUALITY
MOISTURE RETURN INTO THIS SYSTEM. PRECIPITABLE WATER VALUES PROGGED
TO REMAIN AT OR BELOW ONE THIRD OF AN INCH...WHICH IS ACTUALLY
"NORMAL" FOR THIS TIME OF YEAR. UPSTREAM MIXING RATIOS ARE BETWEEN
1.5-2.0 G/KG WITH GARCIA METHOD ONLY SUPPORTING 12 HOURLY SNOWFALL
RATES OF 3-4 INCHES...WHICH IS IN LINE WITH MODEL QPF. WHILE
SYNOPTIC SNOWFALL IS NOT GOING TO BE ALL THAT HEAVY WITH SNOWFALL
RATES GENERALLY LESS THAN A HALF INCH PER HOUR...IT WILL BE A LONG
DURATION EVENT WHICH WILL ALLOW TOTALS TO PILE UP. DID BROADEN THE
FORECAST SNOWFALL RANGE A BIT TO 5-10 INCHES ACROSS WESTERN AND
SOUTHERN PORTIONS OF THE CWA.
WHILE SYNOPTIC SNOWS WILL BE MOSTLY FAIRLY LIGHT...STEEPENING
LOW/MID LEVEL LAPSE RATES WITH THE APPROACH OF THE UPPER LOW SHOULD
RESULT IN INCREASINGLY FAVORABLE SET UP FOR LAKE ENHANCEMENT TO THE
SNOWFALL. FIRST OVER NORTHEAST ILLINOIS THIS AFTERNOON SHIFTING INTO
NORTHWEST INDIANA THIS EVENING AS LOW LEVEL FLOW BACKS. WHILE LAKE
INDUCED INSTABILITY IS NOT PROGGED TO BE OVERLY IMPRESSIVE...VERY
HIGH INVERSION HEIGHTS IN THE PRESENCE OF STRONG SYNOPTIC SCALE LIFT
COULD ALLOW FOR SOME BANDS OF HEAVY LAKE ENHANCED SNOW TO DEVELOP
THIS AFTERNOON AND EVENING. LOCAL LAKE EFFECT DECISION TREE ACTUALLY
SUGGESTS THAT SNOWFALL RATES OF 1-2" PER HOUR CAN BE EXPECTED.
DURATION OF FETCH SHOULD BE FAIRLY SHORT FOR NORTHEAST ILLINOIS SO
WHILE SNOWFALL COULD BE HEAVY FOR A TIME LATER TODAY...SNOWFALL
TOTALS SHOULDNT GET TOO FAR OUT OF HAND ASSUMING THE LOW LEVEL FLOW
BACKS AS QUICKLY AS MODELS SUGGEST.
NORTHWEST INDIANA WILL BE A BIT OF A DIFFERENT STORY WITH A LONGER
DURATION OF FAVORABLE LAKE FETCH MUCH OF TONIGHT...PARTICULARLY OVER
PORTER COUNTY. GIVEN THE SET UP TOTALS OF UP TO A FOOT AND A HALF
STILL SEEM ON TARGET FOR NORTHEAST PORTER COUNTY. WEDNESDAY MORNING
RAPIDLY RISING MID LEVEL HEIGHTS AND LOWERING INVERSION HEIGHTS
SHOULD RESULT IN DIMINISHING INTENSITY OF THE LAKE EFFECT SNOW WHILE
SOME FURTHER BACKING OF THE WINDS SHOULD PUSH WHAT IS LEFT OF THE
LAKE EFFECT INTO IWX'S CWA.
LAST BUT FAR FROM LEAST OF OUR PROBLEMS WILL BE THE INCREASINGLY
STRONG NORTHWEST WINDS TONIGHT. A SURFACE LOW IN NORTHERN
MISSISSIPPI IS PROGGED TO LIFT NNE INTO EASTERN INDIANA/WESTERN
OHIO LATER TODAY. AS THE LOW MOVES INTO AN INCREASINGLY FAVORABLY
DIFFLUENT UPPER FLOW ITS PROGGED TO UNDERGO A PERIOD OF RAPID
INTENSIFICATION...DEEPENING ABOUT 10MB IN 12 HOURS. THIS SHOULD
RESULT IN AN INCREASINGLY TIGHT PRESSURE GRADIENT FOLLOWED BY
STRONG PRESSURE RISES AS THE LOW CONTINUES TO SLOWLY DEEPEN AS IT
RAPIDLY ACCELERATES EASTWARD. THE STRONG PRESSURE RISES AND COLD
AIR ADVECTION SHOULD KEEP LOW LEVEL LAPSE RATES STEEP AND ALLOW
30-35KT MEAN BOUNDARY LAYER WINDS TO BE TRANSPORTED TO THE SURFACE
IN GUSTS LATE TONIGHT INTO WEDNESDAY MORNING.
FAIRLY CONFIDENT THAT WE WILL SEE A SEVERAL HOUR PERIOD LATE TONIGHT
INTO EARLY WEDNESDAY MORNING WHERE WE WILL MEET THE WIND CRITERIA
FOR A BLIZZARD OVER OUR SOUTHEASTERN CWA. CONFIDENCE IS A BIT LOWER
IN THE "BLOW-ABILITY" OF THE SNOW THAT FALLS TODAY. GENERALLY EXPECT
A FAIRLY LIGHT/FLUFFY SNOW THAT SHOULD BE EFFICIENTLY BLOWN AROUND
BUT ENOUGH UNCERTAINTY EXISTS TO JUST GO WITH A BLIZZARD WATCH FOR
NOW. DUAL HEADLINE FOR WINTER STORM WARNING/BLIZZARD WATCH SEEMED
PRUDENT TO HEIGHTEN THE AWARENESS THAT THE POTENTIAL EXISTS FOR A
TRUE GROUND BLIZZARD IN OPEN/RURAL AREAS LATE TONIGHT INTO WED
MORNING WITH TRAVEL POTENTIALLY BECOMING NEARLY IMPOSSIBLE. DAY
SHIFT SHOULD HAVE A BETTER IDEA AS TO THE CHARACTER (IE. THE
"BLOW-ABILITY") OF THE SNOWFALL AND ALSO HAVE ANOTHER RUN OF THE
MODELS TO LOOK AT BEFORE MAKING A DECISION ON WHETHER TO UPGRADE TO
A BLIZZARD WARNING.
LONG TERM (WEDNESDAY NIGHT ONWARD)...
ONLY MINOR CHANGES WERE MADE TO THE EXISTING EXTENDED FORECAST.
LOW TEMPERATURES THURSDAY AND FRIDAY ARE SOMEWHAT LOWER THAN
GUIDANCE NUMBERS DUE TO THE ANTICIPATED FRESH SNOW...DECREASING
CLOUDS...AND LIGHT WINDS. HIGHS ALSO WERE TWEAKED DOWNWARD A
BIT...BUT NOT QUITE AS MUCH. A QUICK SHOT OF A LITTLE MORE SNOW IS
POSSIBLE ON FRIDAY AS AN UPPER LEVEL SHORTWAVE AND WEAK SFC LOW
RACE THROUGH THE AREA...THOUGH AT THIS TIME IT APPEARS THAT MOST
OF THIS ACTIVITY MAY BE TO OUR SOUTH.
IZZI/LENNING
AVIATION
1200 UTC TAFS...MAIN CONCERN FOR THE FORECAST IS WITH PERSISTENT
SNOWFALL THROUGH THE PERIOD ALONG WITH FALLING CEILINGS AND
VISIBILITIES.
SNOW IS ONGOING THIS MORNING AS UPPER LEVEL SYSTEM CONTINUES TO
PROGRESS SOUTHEAST THROUGH THE REGION. SINCE THE SNOW HAS STARTED
LAST NIGHT...MVFR CEILINGS HAVE BEEN PREDOMINANT ACROSS MUCH OF
THE AREA. LOW MVFR CEILINGS WILL STICK AROUND FOR THE NEXT COUPLE
OF HOURS...UNTIL CEILINGS CONTINUE TO COME DOWN TO IFR CONDITIONS.
THIS WILL BE COINCIDING WITH CONTINUED LIGHT SNOW ALONG WITH
VISIBILITIES HOLDING AROUND 1 MILE FOR MUCH OF THE MORNING. BY THE
EARLY AFTERNOON TIMEFRAME...THINGS REALLY GO DOWN HILL AS LIFR
CONDITIONS WILL BE POSSIBLE. THESE CONDITIONS WILL BE POSSIBLE DUE
TO THE BETTER SYNOPTIC LIFT OCCURRING DURING THIS PERIOD...WITH
LAKE ENHANCEMENT BEGINNING TO TAKE PLACE. I HAVE LIFR CONDITIONS
PERSISTING FOR SOMETIME...BUT FEEL CONFIDENT THATS WHAT THE
PREVAILING CONDITIONS WILL BE AS THE LAKE ENHANCEMENT TO THE SNOW
REALLY RAMPS UP DURING THE LATE AFTERNOON/EARLY EVENING.
CONDITIONS WILL SLOWLY BEGIN TO IMPROVE LATER TONIGHT AS NORTHEAST
ILLINOIS BEGINS TO LOSE LAKE EFFECT ASPECT TO THE SNOW. EVEN
STILL...IFR CONDITIONS ALONG WITH LIGHT SNOW WILL BE POSSIBLE
THROUGH THE EARLY MORNING HOURS ON WEDNESDAY.
EASTERLY WINDS WILL BE INCREASING THROUGHOUT THE DAY ON TUESDAY
AS PRESSURE GRADIENT BEGINS TIGHTEN ACROSS THE REGION. AS AREA OF
LOW PRESSURE MOVES INTO THE AREA THIS EVENING...WINDS WILL
CONTINUE TO INCREASE AS WELL AS WINDS BACKING TO MORE OF A
NORTHEAST DIRECTION. WINDS WILL TURN MORE NORTH/NORTHWEST LATE
TONIGHT WITH LOW MOVING OFF TO THE EAST...BUT WITH HIGHER WIND
GUSTS MAINTAINING AROUND THE TERMINALS THROUGH THE END OF THE
FORECAST PERIOD.
RODRIGUEZ
MARINE
343 AM CST
HIGH PRESSURE OVER WESTERN ONTARIO WILL BRING EAST TO NORTHEAST FLOW
ACROSS THE LAKE TODAY...BUT A DEEPENING LOW PRESSURE SYSTEM MOVING
INTO THE OHIO VALLEY WILL TURN WINDS TO THE NORTH AND THEN NORTHWEST
TOMORROW AND THURSDAY. FREQUENT GALE FORCE GUSTS FROM THE NORTH AND
NORTHWEST ARE ANTICIPATED FROM TONIGHT THROUGH TOMORROW BEFORE THE
LOW BEGINS TO WEAKEN LATE WEDNESDAY. LIGHT NORTHWEST FLOW WILL THEN
PERSIST INTO THE WEEKEND AHEAD OF A RIDGE OF HIGH PRESSURE OVER THE
PLAINS THAT IS VERY SLOWLY MAKING ITS WAY EAST TOWARD THE AREA.
LENNING
LOT WATCHES/WARNINGS/ADVISORIES
IL...WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-
ILZ023-ILZ032-ILZ033-ILZ039 UNTIL 9 AM WEDNESDAY.
IN...WINTER STORM WARNING...INZ001-INZ002-INZ011 UNTIL NOON WEDNESDAY.
WINTER STORM WARNING...INZ010-INZ019 UNTIL 9 AM WEDNESDAY.
LM...GALE WARNING...LMZ080-LMZ669-LMZ671-LMZ673-LMZ675-LMZ743-LMZ744-
LMZ745-LMZ777-LMZ779-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...6
PM TUESDAY TO 9 PM WEDNESDAY.
GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
LMZ740-LMZ741-LMZ742-LMZ868...6 PM TUESDAY TO 4 PM
WEDNESDAY.
SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...3 PM TUESDAY TO 6
PM TUESDAY.
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