Streator got lucky and missed out on this storm.
Current forecast discussion says no snow accumulation points south and east of the Chicago area.
And little to no ice accumulation in this area.
Just a glaze of ice on sidewalks and roadways.
There also a dry slot to form and cut off precipitation over this area by morning.
As of right now,no accumulations are expected in this area.
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000
FXUS63 KLOT 212131
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
331 PM CST SAT DEC 21 2013
.DISCUSSION...
331 PM CST
...WINTER STORM...THROUGH TOMORROW AFTERNOON...
HEADLINE NOTES...WILL ALLOW THE FREEZING RAIN ADVISORY TO EXPIRE AT
4PM FOR EAST CENTRAL ILLINOIS COUNTIES.
THE WINTER WEATHER ADVISORY FROM LASALLE COUNTY TO CHICAGO WILL BE
LEFT AS IS TO EXPIRE AT 10PM. HOWEVER...THE EVENING SHIFT MAY NEED
TO CONSIDER EXTENDING AT LEAST PARTS OF THE ADVISORY TO SUNDAY
MORNING PENDING TRENDS WITH SLEET/FREEZING RAIN OR DRIZZLE
THIS EVENING FOLLOWED BY LIGHT SNOW ACCUMULATIONS LATE TONIGHT
THROUGH SUNDAY MORNING.
THE WINTER STORM WARNING AND NORTHERN PORTION OF THE WINTER WEATHER
ADVISORY (LAKE AND KANE) WILL NOW BE STARTED AT 6PM AS MOST
SIGNIFICANT IMPACTS ARE NOT EXPECTED UNTIL LATER THIS EVENING.
DETAILS...
INTERESTINGLY ENOUGH...GUIDANCE CONTINUES TO BE SPLIT ON EVOLUTION
OF THIS SYSTEM EVEN AT THIS LATE HOUR...WITH THE 18Z NAM SHIFTING
SOUTHEAST WITH TRACK OF UPPER LEVEL AND SURFACE LOW CLOSER TO
GFS/ECMWF SOLUTIONS. HOWEVER...THE OVERALL THEME REMAINS CONSISTENT
IN FOCUSING THE HEAVIEST SNOWS INTO NORTH CENTRAL AND PORTIONS OF
FAR NORTHEASTERN ILLINOIS DESPITE THIS CONTINUED VARIANCE.
THE WARM CONVEYOR BELT PRECIPITATION WILL CONTINUE TO STREAM INTO
AREAS PRIMARILY ALONG AND SOUTH OF MENDOTA TO CHICAGO LINE INTO
EARLY THIS EVENING...BUT JUST SKIRTING THE NORTHERN CWA. THERMAL
PROFILES ARE QUITE COMPLEX...WITH A WARM NOSE OF OVER 4C EVIDENT ON
A RECENT ORD AIRCRAFT SOUNDING JUST BELOW 800 MB. AS THE
PRECIPITATION WORKS ITS WAY NORTH...THIS WILL COOL SOME WITH
SATURATION BUT STILL ENOUGH TO AT LEAST PARTIALLY MELT ICE CRYSTALS.
SO AREAS WEST OF CHICAGO ARE IN LINE FOR SLEET OR FREEZING
RAIN/PLAIN RAIN THIS EVENING WHERE IT IS LIKELY TO REMAIN ABOVE
FREEZING/INCLUDING DOWNTOWN CHICAGO. ICE ACCUMULATIONS POSSIBLY UP
TO ONE TENTH OF AN INCH IN SOME AREAS WILL RESULT IN HAZARDOUS ROAD
CONDITIONS. FARTHER SOUTH AND EAST...THE ENTIRE COLUMN WILL REMAIN
ABOVE FREEZING RESULTING IN PLAIN RAIN CONTINUING. FAR
SOUTHEASTERN PORTIONS OF THE AREA COULD SEE SOME NUISANCE TYPE
PONDING AND SMALL STREAM FLOODING. THE OTHER CONCERN IS FOR AREAS
OF FOG...LOCALLY DENSE...CONTINUING INTO THE MID OR LATE EVENING
NORTH OF A PNT TO GYY LINE.
IN THE WINTER STORM AND NORTHERN PORTION OF WINTER WEATHER ADVISORY
AREA...WITH HEAVIEST PRECIP REMAINING SOUTH INTO THE EVENING...ONLY
ANTICIPATING LIGHT SNOW AND SLEET ACCUMULATIONS INTO THIS EVENING.
HERE IT WILL BE SOMEWHAT BORDERLINE FOR ALL SNOW WITH A LESS
PRONOUNCED WARM LAYER GRADUALLY COOLING WITH TIME TO BELOW FREEZING.
THE FARTHER SOUTH AND EAST IN THIS AREA YOU GO CAN EXPECT MORE OF A
THREAT FOR LIGHT ICE ACCUMULATIONS DUE TO THE POTENTIAL FOR FULL
MELTING OF ICE CRYSTALS.
DURING THE OVERNIGHT HOURS...A PRONOUNCED MIDLEVEL DRYSLOT WITH THE
UPPER SYSTEM CLEARLY EVIDENT ON W/V IMAGERY WILL ENVELOP THE
SOUTHEASTERN HALF TO TWO THIRDS OF THE AREA. THIS WILL CUT OFF THE
STEADIER PRECIPITATION AND RESULT IN PERIODS OF LIGHT RAIN AND
DRIZZLE/FZDZ...WITH POSSIBLY SOME LIGHT SLEET MIXED IN. AT THIS TIME
IS ALSO WHEN THE TROWAL FEATURE/DEFORMATION AXIS WILL MOST GREATLY
IMPACT NORTH CENTRAL AND FAR NORTHEASTERN ILLINOIS. GUIDANCE
CONTINUES TO SUGGEST STRONG MIDLEVEL FRONTOGENESIS AND LIFT THROUGH
THE DENDRITIC GROWTH ZONE...SO PERIODS OF HEAVY SNOW ARE LIKELY WITH
SNOWFALL RATES OCCASIONALLY IN EXCESS OF 1 INCH PER HOUR.
AGAIN...TRENDS WILL NEED TO NEED TO BE MONITORED CLOSELY FOR THE
TRAJECTORY OF THE HEAVIEST BANDING. THIS IS THE TIME OF THE MOST
SIGNIFICANT IMPACTS AND WHEN ROAD CREWS COULD HAVE TROUBLE KEEPING
UP WITH THE SNOW ACCUMULATIONS. WE ARE ALSO CONCERNED THAT THE QPF
THE MODELS ARE SHOWING UNDER THE DRY SLOT COULD BE A STEADIER
DRIZZLE AND THUS FREEZING DRIZZLE FOR AREAS BELOW FREEZING. THIS
COULD NECESSITATE THE EXTENSION OF THE WINTER WEATHER ADVISORY FROM
LA SALLE COUNTY TO CHICAGO AS MENTIONED ABOVE. THOUGH NOTE THAT THE
CITY ITSELF SHOULD REMAIN ABOVE FREEZING AND MITIGATE IMPACTS.
FINALLY...INTO SUNDAY MORNING...THE DEFORMATION AXIS WILL PIVOT
ACROSS THE NORTHERN CWA. THE BIG QUESTION IS HOW PRONOUNCED THE DRY
SLOT IS AT THAT TIME...WITH THE GFS MUCH MORE BULLISH THAN THE OTHER
MODELS IN RETURNING SATURATION TO AREAS CLOSE TO CHICAGO. THIS WILL
IMPACT HOW MUCH SNOW FALLS DURING THE MORNING SOUTHEAST OF THE
HEAVIEST SNOW AXIS IN OUR CWA WHEN THERMAL PROFILES ARE FINALLY
SUPPORTIVE OF ALL SNOW FOR MOST OF THE AREA. AT THIS TIME...HAVE
LEANED TOWARD THE DRY SLOT MAKING IT TOUGH FOR MUCH ACCUMULATION IN
THE CITY AND POINTS JUST SOUTH...BUT IF THE GFS SOLUTION COMES TO
FRUITION...AMOUNTS COULD BE A BIT HIGHER THAN CURRENTLY FORECAST. ON
THE OTHER HAND...WITH THE BEST FORCING STILL TO THE NORTH AND
DEPARTING NORTHEAST...WOULD NOT EXPECT ANY HEAVY SNOWFALL RATES.
THE OVERALL IDEA IN FORECAST SNOWFALL AMOUNTS REMAINS VERY SIMILAR
TO PREVIOUS FORECASTS...HIGHEST IN THE 6 TO 8 INCH RANGE NORTH OF A
WOODSTOCK TO DIXON LINE AND QUICKLY TAPERING TO THE SOUTHEAST...WITH
LESS THAN INCH IN DOWNTOWN CHICAGO AND LITTLE OR NO ACCUMULATION
POINTS SOUTH AND EAST.
BY SUNDAY AFTERNOON...SYSTEM SNOWS WILL EXIT TO THE NORTH AS THE
SURFACE LOW MOVES TO THE EASTERN GREAT LAKES. A NORTHERN STREAM
TROUGH MOVING OVERHEAD COULD KEEP SOME LIGHT SNOW GOING...WITH
LITTLE OR NO ACCUMULATION ANTICIPATED. AS COLDER AIR ARRIVES WITH
GUSTY NORTH/NORTHWESTERLY WINDS...THERE COULD BLOWING AND DRIFTING
SNOW IN OPEN AREAS OF NORTH CENTRAL AND FAR NORTHEASTERN ILLINOIS.
ALSO...ANY REMAINING MOISTURE ON ROADS AND SIDEWALKS COULD
QUICKLY FREEZE LATER IN THE AFTERNOON.
RC
FOR THE EXPENDED FORECAST PERIOD...FROM MONDAY NIGHT THROUGH
SATURDAY...INCLUDING THE CHRISTMAS HOLIDAY...
THE SENSIBLE WEATHER REMAIN LARGELY BENIGN FOR THE EXTENDED FORECAST
PERIOD...WITH THE PRIMARY CONCERNS BEING TEMPERATURE TRENDS AND THE
CHANCE FOR SOME LIGHT SNOW FROM TUESDAY EVENING THROUGH THURSDAY
MORNING. FOR THIS PERIOD...THE LARGER SCALE MODELS ARE IN VERY GOOD
AGREEMENT ON A VERY HIGH AMPLITUDE...QUICKLY PROGRESSIVE PATTERN OVER
NORTH AMERICA. WHAT THIS WILL TRANSLATE INTO TO NORTHERN ILLINOIS
AND NORTHWEST INDIANA WILL BE A ROLLER COASTER RIDE OF A TEMPERATURE
TREND WITH DIPS TO WELL BELOW ZERO FAHRENHEIT TO COMPARATIVELY MILD
HIGHS...THOUGH EVEN THE HIGHEST OF THE HIGHS WILL STILL BE BELOW
SEASONAL NORMALS.
FOR MONDAY...THE DAY WILL START OUT ON THE COOLER SIDE AS A DEEP
UPPER TROUGH DIGS INTO THE MISSISSIPPI VALLEY AS HIGH PRESSURE
BUILDS ACROSS THE NORTHERN PLAINS AND SPREADS EASTWARD. THERE WILL
ACTUALLY BE LITTLE DIURNAL TEMPERATURE CHANCE ON MONDAY WITH HIGHS
ONLY A COUPLE DEGREES HIGHER THAN THE MORNING LOWS AS THE REGION
SITS UNDER PERSISTENT STRONG COLD ADVECTION. THE COLDEST CONDITIONS
OF THE PERIOD WILL COME FOR TUESDAY MORNING AS THE CENTER OF THE
HIGH SLIDES INTO MISSOURI WHILE THE UPPER LEVEL PATTERN AMPLIFIES
FURTHER WHILE THE LONGWAVE PATTERN WAVELENGTH DECREASES. THE
BUILDING RIDGE WILL EXTEND FROM THE SOUTH HIGH PLAINS TOWARD HUDSON
BAY...SETTING UP A PATTERN THAT WILL DRAW COLD ARCTIC AIR INTO THE
REGION. ADDITIONAL COOLING WILL BE AIDED BY CLEARING SKIES AND
WEAKENING WINDS...WHICH WILL PERMIT SOME RADIATIONAL COOLING TO
COMPLEMENT THE ADVECTIVE COOLING. ALSO...A WEAK PRESSURE GRADIENT
WILL REMAIN IN PLACE AS THE CENTER OF THE HIGH WILL SETTLE INTO
MISSOURI. AIR TEMPERATURES EXPECTED TO DROP WELL BELOW ZERO OVER
PORTIONS OF THE CWA NORTH OF A LINE FROM CHICAGO TO PONTIAC...WITH
SOME OF THE LOW LYING...SHELTERED AREAS DROPPING AS LOW AS
-10F...EVEN THE EXPECTED RELATIVELY LIGHT WINDS OF 5-10KT WILL BE
SUFFICIENT TO GENERATE WIND CHILL READING OF -20F TO -25F.
LOCATIONS SOUTH OF THE CHICAGO TO PONTIAC LINE ARE EXPECTED TO
REMAIN SLIGHTLY WARMER WITH LOW IN THE SINGLE DIGITS ABOVE ZERO...SO
WIND CHILL READING WILL "ONLY" BE IN THE -10F TO -15F RANGE.
SO...WHILE THE WIND CHILLS OVER THE NORTHWEST HALF OF THE CWA WILL
LIKELY REACH THE WIND CHILL ADVISORY CRITERIA LEVELS...GIVEN THE
ONGOING WINTER WEATHER...WILL HOLD OFF ON ISSUING ANY TYPE OF
HEADLINE AT THIS TIME.
THE OTHER SIGNIFICANT CONCERN WILL BE THE CHANCES FOR SOME LIGHT
SNOW FOR CHRISTMAS EVE THROUGH CHRISTMAS DAY. FOLLOWING THE PASSAGE
OF THE HIGH PRESSURE OFF TO THE EAST...THE UPPER RIDGE WILL ALSO
PROGRESS TO THE EAST OF THE LOCAL AREA WHILE A BROAD UPPER TROUGH
CARVES OUT OVER THE NORTHERN AND CENTRAL PLAINS WITH A SERIES OF
EMBEDDED SHORTWAVES. WHILE THE SHORTWAVES AND ASSOCIATED SFC
TROUGHS/WEAK COLD FRONTS THROUGH THE PERIOD FROM CHRISTMAS EVE
THROUGH BOXING DAY...WILL PROVIDE AMPLE FORCING FOR GENERATING
PCPN...AND DEEP LAYER COLD AIR IN PLACE WILL GUARANTEE THAT THE PCPN
WILL BE ALL SNOW...THE MISSING INGREDIENT FOR ANY SIGNIFICANT SNOW
WILL BE DEEP LAYER MOISTURE. FROM TUESDAY NIGHT THROUGH
THURSDAY...THE CWA WILL BE CUT OFF FROM ANY GULF MOISTURE BY A RIDGE
OF SFC HIGH PRESSURE EXTENDING FROM THE MID ATLANTIC REGION THROUGH
THE RED RIVER VALLEY. SO...WHILE IT IS LOOKING LIKE THERE SHOULD BE
PERIODS OF SOME LIGHT SNOW FALLING THROUGH THE CHRISTMAS HOLIDAY
PERIOD...ACTUAL ADDITIONAL ACCUMULATIONS SHOULD BE LIGHT.
FOR THE REMAINDER OF THE EXTENDED FORECAST PERIOD...THE ROLLER
COASTER RIDE OF TEMPERATURES WILL CONTINUE AS THE PATTER REMAINS
QUICKLY PROGRESSIVE. TEMPERATURES SHOULD MODERATE SOME ON WEDNESDAY
WITH HIGHS IN THE UPPER 20S TO AROUND 30F AND LOWS THURSDAY MORNING
RANGING FROM THE LOWER TEENS OVER THE ROCKFORD AREA TO THE LOWER 20S
OVER THE SERN PORTIONS OF THE CWA...ANOTHER SHOT OF ARCTIC AIR WILL
INTRUDE ON THE AREA THROUGH THE DAY ON THURSDAY...WITH ONLY A FEW
DEGREES OF WARMING ABOVE MORNING LOWS...WHILE FRIDAY MORNING...
TEMPERATURES SHOULD DROP BELOW ZERO OVER THE NWRN PORTIONS OF THE
CWA...REACHING DOWN TO -5F OVER THE ROCKFORD AREA. HOWEVER...SINCE
THE TRACK OF THE SFC HIGH WILL BE THROUGH IOWA AND ILLINOIS...
LEADING TO LIGHTER WINDS AND LESS OF A WIND CHILL FACTOR. ON THE
OTHER HAND...IF THERE IS MORE SKY CLEARING TO GO ALONG WITH THE
LIGHTER WINDS...THERE MAY BE MORE RADIATIVE COOLING THAN WOULD BE
SUGGESTED AT THIS TIME AND MIN TEMPS FOR FRIDAY MORNING MAY BE LOWER
THAN CURRENTLY ANTICIPATED AND THE CWA COULD BE FLIRTING WITH
ADVISORY CRITERIA WIND CHILLS AGAIN. OTHER THAN THE CHANCE FOR SOME
LIGHT SNOW AROUND CHRISTMAS...NO OTHER PCPN IS EXPECTED THROUGH THE
REMAINDER OF THE EXTENDED FORECAST PERIOD.
KREIN
www.nws.noaa.gov/view/prodsByState.php?state=IL&prodtype=discussion
