Area Forecast Discussion
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000
FXUS63 KLOT 312114
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
314 PM CST SAT JAN 31 2015


.SHORT TERM...
312 PM CST

THROUGH SUNDAY NIGHT...

THE MAJOR WINTER STORM TO IMPACT THE REGION TONIGHT THROUGH SUNDAY
NIGHT IS BY FAR THE PRIMARY FOCUS...WITH THE FOLLOWING MAIN
CONCERNS:
-POSSIBILITY OF PTYPE ISSUES ACROSS MY FAR SOUTH TONIGHT INTO EARLY
SUNDAY...WHICH COULD PRODUCE A STRONG GRADIENT IN ACCUMULATING SNOWS
OVER...OR JUST SOUTH OF MY AREA.
-PERIODS OF MODERATE TO HEAVY SNOW OVER THE NORTHERN HALF TO 2/3RDS
OF MY AREA TONIGHT THROUGH SUNDAY EVENING.
-POSSIBILITY OF A STRONGER SYSTEM...WHICH WOULD RESULT IN STRONGER
NORTHEAST WINDS OVER THE AREA SUNDAY AND SUNDAY EVENING. THIS COULD
PRODUCE BLIZZARD CONDITIONS...WITH WHITE OUT CONDITIONS OVER PORTIONS
OF NORTHERN ILLINOIS.

AT THIS TIME WE HAVE CHOSEN TO HOLD OFF ON ISSUING A BLIZZARD
WARNING FOR ANY OF THE AREA. HOWEVER...FUTURE SHIFTS MAY NEED TO
CONSIDER ONE IF THE WINDS CONTINUE TO LOOK AS STRONG. ONLY CHANCES
TO GOING HEADLINES WAS TO EXTEND THROUGH 06 UTC MONDAY FOR MY
WESTERN CWA AND THROUGH 12 UTC MONDAY FOR MY EASTERN CWA.

WATER VAPOR IMAGERY THIS AFTERNOON CONTINUES TO SHOW A VERY
IMPRESSIVE PLUMB OF MOISTURE STREAMING NORTH-NORTHEASTWARD ACROSS
THE PLAINS AND INTO THE MIDDLE MISSOURI AND MISSISSIPPI VALLEYS DOWN
STREAM OF A SOUTHWESTERN CONUS TROUGH. IN FACT...THIS MORNINGS
SOUNDING OUT OF KOAX INDICATED PWATS UP AROUND 0.64 INCHES...WHICH
IS VERY IMPRESSIVE FOR THIS TIME OF YEAR. MEANWHILE...OUR MAIN
WEATHER MAKER FOR THE NEXT DAY IN AND HALF...IS NOW NOTED AS A
POTENT SHORTWAVE DIGGING SOUTHEASTWARD IN THE NORTHERN STREAM ACROSS
MONTANA. THIS SYSTEM WILL HAVE ACCESS TO A GOOD AMOUNT OF THIS
MOISTURE CURRENTLY MOVING INTO THE REGION.

CYCLOGENESIS IS EXPECTED TO RAMP UP ACROSS THE PLAINS TONIGHT AS THE
AFOREMENTIONED DISTURBANCE SHIFTS OVER THE HIGH PLAINS. INCREASING WARM
ADVECTION/ISENTROPIC ASCENT DOWNSTREAM SHOULD CONTINUE TO DRIVE THE
PRECIPITATION SHIELD TO OUR WEST-SOUTHWEST OVER THE REGION BY MID
EVENING. AS MENTIONED ABOVE...PRECIP TYPES LOOK TO BE AN ISSUE...AT
LEAST THROUGH THIS EVENING ACROSS MY FAR SOUTHERN COUNTIES...MAINLY
SOUTH OF PONTIAC TO RENSSELAER LINE. WARMER AIR INITIALLY...WILL
LIKELY ALLOW THIS PRECIP TO START AS SOME LIGHT RAIN...AND THIS
INITIAL PERIOD OF RAIN COULD GET FARTHER NORTH THEN THE ABOVE
MENTIONED LINE. HOWEVER...AS THE LOW DEVELOPS TO OUR SOUTHWEST THIS
EVENING SURFACE WINDS ACROSS NORTHERN PORTIONS OF THE AREA WILL
SWITCH OUT OF THE EAST NORTHEAST AS THE COLD FRONT TO OUR NORTH SAGS
SOUTHWARD. THIS SHOULD RESULT IN A QUICK TRANSITION TO SNOW FOR
AREAS ALONG AND NORTH OF INTERSTATE 80. HOWEVER...WELL SOUTH OF THE
INTERSTATE...WARMER BOUNDARY LAYER TEMPERATURES COULD BE SLOWER TO
ERODE...POSSIBLY LEADING TO MORE RAIN THAN SNOW THIS EVENING. AS
SUCH...CONFIDENCE ACROSS MY SOUTHERN CWA IS LOW WITH TIMING OF
TRANSITION TO SNOW.

SNOW SHOULD FALL AT A GOOD RATE OVERNIGHT TONIGHT ACROSS MUCH OF MY
AREA AS A BAND OF 850 MB FRONTOGENESIS SETS UP ACROSS NORTHERN
ILLINOIS. THIS SNOWFALL TONIGHT ALONE COULD PRODUCE 2 TO 5 INCHES OF
SNOW BY EARLY SUNDAY MORNING ACROSS MUCH OF THE AREA.

MODEL GUIDANCE CONTINUES TO SUGGEST A MUCH MORE ORGANIZED SYSTEM
DEVELOPING OVER THE AREA DURING THE DAY SUNDAY...WITH THE UPPER
SHORT WAVE TOUGH FORECAST TO SHARPEN OVER THE MID MISSISSIPPI VALLEY
AND THUS RESULTING IN MORE ROBUST DYNAMICS SUPPORTIVE OF A STRONG
LOWER LEVEL CIRCULATION. THIS A STRONGER SOLUTION WILL NOT ONLY
SUPPORT MORE SNOWFALL...BUT ALSO STRONGER NORTHEASTERLY WINDS. AS
SUCH...WIND SPEEDS COULD BECOME AN ISSUE...POSSIBLY BECOMING STRONG
ENOUGH TO RESULT IN NEAR BLIZZARD TO BLIZZARD CONDITIONS. I WILL NOT
UPGRADE TO A BLIZZARD WARNING WITH THIS PACKAGE...BUT IT MAY NEED TO
BE CONSIDERED IF A STRONGER SOLUTION WITH A DEEPER SURFACE SYSTEM
MATERIALIZES. EITHER WAY...THIS LOOKS TO BE A HIGH IMPACT STORM FOR
MUCH OF THE AREA. THE 850 MB LOW IS SET TO TRACK ACROSS CENTRAL
ILLINOIS BY LATE SUNDAY AFTERNOON...THIS AGAIN COULD PUT THE SNOW TO
RAIN LINE FAIRLY CLOSE TO MY FAR SOUTHERN COUNTIES...POSSIBLY
LEADING TO A SHARPE SNOW ACCUMULATION GRADIENT OVER MY FAR SOUTH...OR
JUST OUTSIDE OF MY AREA TO THE SOUTH.

THE TRACK OF THE 850 AND 700 MB LOWS WOULD SUGGEST PERIODS OF HEAVY
SNOW ACROSS MUCH OF NORTHERN ILLINOIS/NORTHWESTERN INDIANA THROUGH
THE DAY TOMORROW...WITH STRONG MID LEVEL FRONTOGENESIS SETTING UP
WITHIN A DEVELOPING DEFORMATION ZONE. AS SUCH SNOW RATES IN EXCESS
OF AN INCH PER HOUR ARE CERTAINLY POSSIBLE AT TIMES TOMORROW. SNOW
SHOULD CONTINUE INTO SUNDAY EVENING...BEFORE GRADUALLY TAPERING OFF
ACROSS MY WESTERN AREAS BY MIDNIGHT MONDAY MORNING.
HOWEVER...SNOWFALL MAY CONTINUE ACROSS PORTIONS OF  MY EASTERN
CWA...WITH SOME POSSIBLE LAKE ENHANCED SNOWS CONTINUING. AS
MENTIONED IN PREVIOUS DISCUSSIONS...INVERSION HEIGHTS DO NOT GET
VERY HIGH...BUT THE FACT THAT THEY WILL STILL BE WITHIN THE
DENDRITIC GROWTH ZONE...WOULD SEEM TO SUPPORT AT LEAST SOME MINOR
ADDITIONAL ACCUMULATIONS INTO MONDAY MORNING. GIVEN THIS...I HAVE
MADE THE CHANGES HIGHLIGHTED ABOVE TO THE GOING WINTER STORM WARNING.

TOTAL STORM ACCUMULATIONS LOOK TO TOP OUT NEAR A FOOT IN MANY
AREAS...WITH SOME POSSIBLY GETTING A COUPLE MORE INCHES THAN THIS.
IT APPEARS SLIGHTLY LIGHTER AMOUNTS ARE EXPECTED ACROSS NORTH
CENTRAL ILLINOIS. OVERALL CONFIDENCE IS BECOMING HIGHER IS GETTING
HEAVY SNOW...ESPECIALLY ACROSS THE NORTHERN HALF TO 3/4 OF MY AREA.
CONFIDENCE ON TOTAL SNOW AMOUNTS IS A BIT LOWER ACROSS MY CENTRAL
ILLINOIS COUNTIES...DUE TO THE POSSIBILITY FOR SOME MIXING ISSUES.

KJB

&&

.LONG TERM...
312 PM CST

MONDAY NIGHT THROUGH SATURDAY...

THE START OF THE FORECAST PERIOD WILL BE MARKED WITH EXITING
SNOWFALL WITH THE DEPARTING WINTER STORM...WHILE LAKE EFFECT SNOW
SHOWERS PERSIST NEAR THE LAKE ON MONDAY. WITH THE DEPARTING UPPER
LEVEL TROUGH AND ASSOCIATED SURFACE LOW...LOW LEVEL FLOW WILL
CONTINUE TO BACK MORE TO THE NORTH AND NORTHWEST. HOWEVER...THE
EXTENT OF THIS VEERING THROUGHOUT THE DAY WILL DETERMINE THE
PLACEMENT/DURATION OF THESE LINGERING SNOW SHOWERS WITH SOME
GUIDANCE KEEPING THE POSSIBILITY FOR LAKE EFFECT SNOW SHOWERS INTO
ILLINOIS DURING THIS TIME. EVEN IF THIS WERE TO OCCUR...NOT OVERLY
CONCERNED WITH TOO MUCH ADDITIONAL SNOWFALL DURING THIS TIME WITH
DEPARTING SYNOPTIC LIFT AND MODEST INVERSION HEIGHTS. SHIFTING HIGH
PRESSURE ACROSS THE REGION WILL ALLOW FLOW TO CONTINUE BACKING AND
ANY LINGERING SNOW SHOWERS TO PUSH FURTHER EAST LATER IN THE DAY AND
INTO MONDAY EVENING. APPROACHING SPEED MAX MONDAY NIGHT WILL HELP
STEER ANOTHER AREA OF LIGHT SNOW TOWARDS THE CWA AND DO THINK IT
WILL REACH NORTHERN ILLINOIS...BUT IT SHOULD BE DIMINISHING WITH
DISJOINTING LARGE SCALE SUPPORT AND WITH LITTLE ACCUMULATION
EXPECTED. TEMPS IN THE SINGLE DIGITS ARE LIKELY MONDAY NIGHT...WITH
INCREASING CLOUD COVER AND WHILE THE SURFACE RIDGE QUICKLY SHIFTS TO
THE SOUTHEAST.

ACTIVE WEATHER PATTERN WILL PERSIST THROUGH MID WEEK AS NORTHWEST
FLOW USHERS IN AN ADDITIONAL MID/UPPER LEVEL SYSTEM. THIS APPEARS TO
BE MORE OF A VIGOROUS SYSTEM WITH ACCUMULATING SNOW APPEARING TO BE
A POSSIBILITY LATE TUESDAY AND TUESDAY NIGHT. PRECIP SHOULD EXIT
WEDNESDAY MORNING...AS LARGE UPPER LEVEL TROUGH DIGS SOUTH ACROSS
THE REGION. STRONG PUSH OF COLDER AIR WILL OCCUR AND HELP WITH
ADDITIONAL LAKE EFFECT SNOW SHOWERS ON WEDNESDAY AS WELL AS MUCH
COLDER LOW TEMPS...WITH BELOW ZERO TEMPS APPEARING LIKELY WEDNESDAY
NIGHT AND THURSDAY NIGHT.

RODRIGUEZ

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* NO CONCERNS THROUGH 22Z.

* CIGS QUICKLY LOWER TO MVFR WITH PRECIP ONSET ARND 00-02Z. CIGS
  THEN LOWER TO IFR CONDS ARND 5Z AND LIKELY REMAIN AT IFR THRU
  SUN MIDDAY.

* PRECIP ONSET COULD START AS A RAIN/SNOW MIX...BUT SHOULD QUICKLY
  TRANSITION TO ALL SNOW BY 03Z.

* WINDS WILL START BETWEEN 240-260 DEG AND LIGHT...THEN SLOWLY
  FLIP TO NORTH THEN NORTHEAST BY MIDNIGHT. WINDS WILL INCREASE
  SUN MORNING WITH SPEEDS ARND 16-20KT AND GUSTS APPROACHING 30KT
  BY MID-MORNING SUNDAY.

* VISIBILITIES WITH SNOW WILL FALL TO 1SM THEN FURTHER DIMINISH TO
  AROUND 1/2SM OR POSSIBLY 1/4SM SUN MORNING.

BEACHLER

//DISCUSSION...UPDATED 18Z...

VISIBLE IMAGERY BRIEFLY INDICATED SOME THIN CLOUD COVER OVER FAR
NORTHEAST IL/NORTHWEST IN...BUT WITH INCREASING CLOUDS JUST
SOUTHWEST THIS HAS SINCE THICKENED THE CLOUD COVER OVER THE TAF
SITES. BASES THIS AFTERNOON WILL HOVER ARND 6-8KFT AGL...BUT
UPSTREAM ACROSS WESTCENTRAL IL/NORTHEAST MO...CIGS HAVE LOWERED TO
ARND 3-5KFT AGL. EXPECT LOWER CIGS TO ARRIVE AT THE TAF SITES BY
21-22Z...WITH MVFR CONDS DEVELOPING BY 23-00Z. GUIDANCE HAS
REMAINED CONSISTENT WITH THE PRECIP ONSET BEING FOCUSED ARND
2Z...AND COULD BRIEFLY START AS A RAIN/SNOW MIX. BUT WITH SLIGHTLY
DRIER AIR AT THE SURFACE...PRECIP WILL QUICKLY TRANSITION OVER TO
ALL SNOW WITHIN AN HOUR OR TWO.

VSBYS WILL QUICKLY DIMINISH WITH THE STEADIER SNOW DEVELOPING
LATER THIS EVENING...LIKELY FALLING ARND 1 TO 1 1/2 MILES AND
CLOSER TO 1SM BY MIDNIGHT. WINDS WILL REMAIN LIGHT THROUGH THIS
EVENING...BUT STEADILY TURN NORTHWEST THEN NORTH TO NORTHEAST BY
DAYBREAK SUN. THE BULK OF THE SNOW IS EXPECTED TO OCCUR WITHIN
EARLY SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON...WITH VSBYS
LIKELY DIMINISHING TO 1/2SM AND COULD BRIEFLY REDUCE FURTHER TO
1/4SM BY LATE MORNING SUNDAY. SIMULATANEOUSLY WINDS WILL BE
INCREASING FROM THE NORTHEAST...AS SUSTAINED WINDS INCREASE TO
NEAR 20KT AND GUSTS APPROACH 30KT BY 14-15Z SUN. IT IS POSSIBLE
GUSTS COULD BE EVEN STRONGER BY MIDDAY...AND COULD PROLONG A
PERIOD OF 1/4 TO 1/2SM VSBYS INTO SUN AFTERNOON.

LAKE EFFECT SNOW IS ALSO A CONCERN FOR SUN AFTERNOON AS NORTHEAST
WINDS INCREASE...WHICH WILL LIKELY KEEP IFR TO POSSIBLY LIFR CIGS
NEARBY INTO THE AFTERNOON HOURS.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE ALL ELEMENTS THROUGH LATE AFTERNOON.

* MEDIUM TO HIGH CONFIDENCE IN THE TIMING OF ONSET OF PCPN.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF ACCUMULATING SNOW.

* LOW CONFIDENCE IN THE EXACT ENDING TIME.

* HIGH CONFIDENCE IN AN EXTENDED PERIOD OF IFR CIGS/VIS...BUT
  LOWER CONFIDENCE IN HOW LOW CIGS/VIS WILL GO AND THE DURATION OF
  THE LOWEST CONDITIONS.

* HIGH CONFIDENCE IN GENERAL WIND TRENDS. MEDIUM CONFIDENCE IN THE
  TIMING OF THE WIND SHIFT FROM SWLY TO NELY. THERE COULD BE A
  SHORT PERIOD OF LGT/VRBL WINDS DURG THE TIMING OF THE WIND
  SHIFT.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...SNOW AND BLOWING SNOW LIKELY THROUGH MIDNIGHT WITH
IFR CIGS/VIS. SNOW TAPERING OF DURG THE LATE NIGHT HOURS...BUT IFR
CONDITIONS STILL POSSIBLE.

MONDAY...CHANCE LINGERING SNOW SHOWERS IN THE MORNING. CHANCE OF
SNOW AGAIN AFTER MIDNIGHT. MVFR CIGS/VIS LIKELY.  IFR POSSIBLE.

TUESDAY...CHANCE SNOW. PERIODS OF MVFR CIGS/VIS LIKELY.

WEDNESDAY...SLIGHT CHANCE SNOW THROUGH EARLY EVENING. PERIODS OF
MVFR CIGS/VIS POSSIBLE.  VFR/WX NIL OVERNIGHT.

THURSDAY...VFR/WX NIL.

FRIDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
156 PM CST

CONFIDENCE HAS INCREASED FOR A PERIOD OF GALES SUNDAY AFTERNOON AND
EVENING...ESPECIALLY FOR SOUTHERN LAKE MICHIGAN. THE SURFACE LOW
EJECTING FROM THE ROCKIES WILL PASS TO THE SOUTH AND EAST OF THE
LAKE ON SUNDAY AFTERNOON AND EVENING. IT IS DURING THIS TIME FRAME
WHEN THE LOW WILL STILL BE STRENGTHENING AND HIGH PRESSURE NOSES
INTO THE PLAINS FROM THE UPPER MIDWEST WHERE THE PRESSURE
GRADIENT WILL BE THE STRONGEST. WINDS NEAR GALE FORCE WILL BE
FOUND ON NORTHERN LOCATIONS...WITH SOUTHERN LAKE MICHIGAN SEEMING A
PRETTY SOLID BET FOR A PERIOD OF GALES. WITH THE STRENGTHENING
LOW...35 TO 40 KT ARE POSSIBLE...NOT ONLY FOR THE OPEN WATERS BUT
FOR THE NEARSHORE WATERS OF ILLINOIS AND INDIANA. WINDS BEGIN
NORTHEAST...THEN TURN NORTHERLY OVERNIGHT SUNDAY INTO MONDAY...THEN
SHIFT NORTHWESTERLY MONDAY AS THE LOW PULLS AWAY. HIGH PRESSURE
WILL THEN SHIFT SOUTH OF THE LAKE MONDAY NIGHT AS WEAK LOW
PRESSURE GRAZES THE NORTHERN LAKE TURNING WINDS SOUTHWESTERLY.
STRONG HIGH PRESSSURE WILL REBUILD IN THE PLAINS ON
WEDNESDAY...WHICH WILL DRIVE A COLD FRONT SOUTH DOWN THE LAKE. THE
HIGH WILL MOVE OVER THE LAKE WEDNESDAY NIGHT THROUGH THURSDAY
EVENING FOR A CALMER PERIOD...BEFORE IT SHIFTS EAST FRIDAY.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ006-ILZ013-ILZ014-ILZ022-ILZ023-ILZ033-
     ILZ039...9 PM SATURDAY TO 6 AM MONDAY.

     WINTER STORM WARNING...ILZ003-ILZ004-ILZ005-ILZ008-ILZ010-ILZ011-
     ILZ012-ILZ019-ILZ020-ILZ021-ILZ032 UNTIL MIDNIGHT MONDAY.

IN...WINTER STORM WARNING...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...GALE WARNING...LMZ080-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ872-LMZ874-LMZ876-
     LMZ878...NOON SUNDAY TO 1 AM MONDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...6 AM SUNDAY TO
     NOON SUNDAY.

&&

$$

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