Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 010947
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
347 AM CST SUN FEB 1 2015

.SHORT TERM...
347 AM CST

THROUGH MONDAY...

HAVE BEEN SWAMPED THIS MORNING AND AM RUNNING BEHIND...SO GOING TO
KEEP DISCUSSION BRIEF THIS MORNING AND JUST HIT THE IMPORTANT
CHANGES. THE BIGGEST CHANGES TO GOING FORECAST IS THE UPGRADE TO
A BLIZZARD WARNING FOR PORTIONS OF NE IL/CHICAGO METRO AND TO
LOWER SNOW AMOUNTS AND ADD MIXED PRECIP BACK INTO GRIDS FAR SE
CWA.

GUIDANCE HAS CONTINUED TO TREND NORTH AND STRONGER WITH THE TRACK OF
THIS SYSTEM AND COMPARING GUIDANCE WITH SFC OBS AND BEST SFC
PRESSURE FALLS IT WOULD SEEM TO SUPPORT THE FARTHER NORTH TRACK THAT
THE RAP IN PARTICULAR HAS LATCHED ONTO. THE SOMEWHAT DEEPER LOW
ALONG WITH THE VERY STRONG ARCTIC HIGH SPREADING SOUTHEAST WILL
RESULT IN VERY STRONG WINDS DEVELOPING THIS AFTERNOON. INCREASING
LOW LEVEL COLD AIR ADVECTION AND SFC HEIGHT RISES FAVOR PRETTY GOOD
MIXING IN THE BOUNDARY LAYER...WHICH IS WHAT ALL MODEL FORECAST
SOUNDINGS ARE ADVERTISING. TAKING EVEN THE BEST CASE SCENARIO AND
ONE OF THE WEAKEST MODELS BUFKIT MOMENTUM TRANSFER VALUES SUPPORT
4-7 HOURS OF WIND GUSTS BETWEEN 35-40 MPH LATER THIS AFTERNOON AND
EVENING...WITH MORE AGGRESSIVE GFS/RAP SUPPORTING EVEN STRONGER
WINDS OVER A LONGER DURATION. SNOW HAS BEEN WET THUS FAR BUT WITH
TIME SHOULD SEE THE TRANSITION TOWARD DRIER/MORE BLOWABLE SNOW THIS
AFTERNOON FROM NORTH TO SOUTH AS THE COLUMN COOLS AND THE SNOW
LIQUID CONTENT DECREASES. BIGGEST UNCERTAINTY REVOLVES AROUND
REGARDING UPGRADE TO BLIZZARD WARNING WAS THE SNOW LIQUID CONTENT
AND PROBABILITY AND CONFIDENCE IS CERTAINLY HIGHER THE FARTHER NORTH
FROM I-80 THAT YOU GET...BUT EVEN AS FAR SOUTH AS I-80 FELT FAIRLY
CONFIDENT THAT WHITE OUT CONDITIONS COULD DEVELOP LATE THIS
AFTERNOON AND ESPECIALLY THIS EVENING. FARTHER WEST ACROSS NORTH
CENTRAL ILLINOIS FEEL THAT A BLIZZARD WARNING COULD EASILY BE
JUSTIFIED...BUT IN COORDINATION WITH MKX/DVN HAVE OPTED TO HOLD OFF
FOR NOW AS SNOW INTENSITY COULD BE DECREASING AS WINDS PICK UP.
QUITE POSSIBLE DAY SHIFT MAY NEED TO RE-ACCESS THIS AND AN UPGRADE
TO BLIZZARD WARNING FOR RFD AND POINTS WEST COULD OCCUR ON THE DAY
SHIFT.

OTHER BIG CHANGE TO FORECAST WAS TO ADD SLEET AND THEN DRIZZLE TO
THE FAR SOUTHEAST CWA. SFC TEMPS HAVE BEEN A BIT WARMER AND THE
FARTHER NORTH TRACK OF THE SFC LOW SHOULD KEEP LOW LEVEL WAA GOING
INTO EARLY AFTERNOON WITH AT LEAST THE THREAT OF MIXED
PRECIP...POSSIBLY TRANSITIONING OVER TO JUST DRIZZLE/SNIZZLE AS MID
LEVEL DRY SLOT OVERSPREADS THAT AREA REMOVING ICE NUCLEI FROM THE
CLOUDS LATE THIS AFTERNOON INTO THIS EVENING. THE WETTER SNOW SOUTH
OF I-80 SHOULD RESULT IN LESS SEVERE AND LESS IMPACTFUL
BLOWING/DRIFTING SNOW. GIVEN THE MARGINAL TEMPS AND POTENTIAL MIX
PRECIP HAVE CUT BACK ON ACCUMS IN THE FAR SOUTHEAST COUNTIES OF THE
CWA.

ACCUMULATING LAKE EFFECT POTENTIAL ACTUALLY LOOKS SOMEWHAT LESS
IMPRESSIVE THAN IT DID LAST NIGHT...AND IT WAS ALREADY LOOKING
MARGINAL. SOME SYSTEM SNOWS SHOULD LINGER INTO THIS EVENING BUT LAKE
CONTRIBUTIONS LOOK MINOR WITH LOW INVERSION HEIGHTS AND DECREASING
BOUNDARY LAYER RH AS THE THERMODYNAMICS IMPROVE EVER SO SLIGHTLY.
ANY LAKE ENHANCEMENT TO SNOW TOTALS SHOULD END UP BEING TRIVIAL.

FINALLY...GOING SNOWFALL TOTALS LOOK RIGHT ON TARGET AND MADE VERY
FEW CHANGES OTHER THAN IN SE AS NOTED ABOVE. A RESPECTABLY LARGE
SWATH OF A FOOT OR MORE OF SNOW STILL LOOKS LIKELY AND PROBABLY
CENTERED RELATIVELY CLOSE TO THE I-80 TO I-88/290 CORRIDORS.
ACTUALLY THINKING THAT MAX SNOWFALL TOTALS IN THE CWA COULD END UP
BEING ON THE HIGH END OF THE 10-14 INCH RANGE WITH LOCALIZED TOTALS
POTENTIALLY PUSHING A FOOT AND A HALF IF THE DEFO BAND IS INDEED AS
IMPRESSIVE AS SOME OF THE GUIDANCE WOULD SUGGEST. WHILE SNOWFALL
TOTALS WILL BE VERY IMPRESSIVE OVER MOST OF THE CWA...IT IS
IMPORTANT TO REMEMBER THE BLIZZARD WARNING IS ISSUED NOT FOR
SNOWFALL AMOUNTS BUT RATHER FOR VISIBILITY AND WINDS. THE CRITERIA
FOR BLIZZARD WARNING IS 3+ HOURS OF LESS THAN 1/4SM VSBY IN FALLING
AND/OR BLOWING SNOW ALONG WITH SUSTAINED WINDS OR FREQUENT GUSTS
OVER 35 MPH.

IZZI

&&

.LONG TERM...

MONDAY NIGHT THROUGH SATURDAY...

134 AM...FORECAST CONCERNS INCLUDE A CHANCE OF LIGHT SNOW MONDAY
NIGHT INTO TUESDAY...THEN A BETTER CHANCE FOR ACCUMULATING LIGHT
SNOW TUESDAY NIGHT INTO WEDNESDAY MORNING.

A RIDGE OF HIGH PRESSURE WILL BE MOVING SOUTHEAST OF THE AREA
MONDAY EVENING AS A WEAK WAVE MOVES ACROSS THE REGION MONDAY NIGHT.
FAIRLY LIGHT QPF FROM ALL THE MODELS WITH THIS WAVE BUT PLENTY COLD
ENOUGH FOR THE LOW QPF AMOUNTS TO POTENTIALLY FLUFF UP TO A HALF
INCH MONDAY NIGHT. WHILE TEMPS BY THIS TIME WILL LIKELY BE IN THE
SINGLE DIGITS OR LOW TEENS...CLOUD COVER AND WEAK WARM AIR ADVECTION
MAY ALLOW TEMPS TO HOLD STEADY OR RISE A FEW DEGREES OVERNIGHT.

NEXT WAVE QUICKLY SHIFTS SOUTHEAST ACROSS THE AREA BY TUESDAY
EVENING WITH QPF AMOUNTS BETWEEN ONE AND TWO TENTHS. THIS HAS BEEN
A FAIRLY CONSISTENT FEATURE ON THE MODELS AND IF THIS MATERIALIZES
AS ADVERTISED...A FEW INCHES OF SNOW WILL BE POSSIBLE. TIMING AND
LOCATION ALSO ARE A BIT UNCERTAIN...EARLIER COULD IMPACT THE TUESDAY
EVENING RUSH...LATER COULD IMPACT THE WEDNESDAY MORNING RUSH. BUT
GIVEN THE POTENTIAL FOR SOME ACCUMULATION...OPTED TO BUMP POPS UP TO
LIKELY FOR TUESDAY NIGHT.

HIGH PRESSURE THEN SETTLES SOUTH ACROSS THE MIDWEST AND LAKES REGION
WEDNESDAY INTO THURSDAY AND WITH IT...SOME VERY COLD AIR. WITH A
DEEP SNOWPACK BY THAT TIME AND DIMINISHING WINDS WEDNESDAY NIGHT
INTO THURSDAY...EXPECT MANY LOCATIONS TO DROP BELOW ZERO FOR LOWS
THURSDAY MORNING. THE AIRMASS MODIFIES/WARMS SOME THURSDAY BUT
STILL EXPECTING LOWS IN THE LOWER SINGLE DIGITS THURSDAY EVENING...
POSSIBLY BELOW ZERO BUT WARM AIR ADVECTION BY MORNING WITH
INCREASING SOUTHERLY WINDS MAY PUT THE BRAKES ON HOW LOW TEMPS FALL
THURSDAY NIGHT. STRONG SOUTHERLY WINDS CONTINUE INTO SATURDAY WITH
WARMING TEMPS...THAT WILL LIKELY BE MUTED SOME BY THE SNOWPACK. CMS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* SNOW THRU THE PERIOD. VISIBILITIES GENERALLY AROUND 3/4SM...WITH
  OCNL PERIODS OF VIS AS LOW AS 1/4SM POSSIBLE ESPECIALLY THIS
  AFTERNOON.

* STRONG NORTHEAST WINDS SUNDAY...GUSTING UP TO 35 KT.

* BLOWING SNOW SUNDAY AND SUNDAY NIGHT.

* IFR/LIFR CIGS THRU THE PERIOD.

KREIN

//DISCUSSION...UPDATED 06Z...

LONG DURATION SNOW EVENT UNDERWAY AS LOW PRESSURE OVER KANSAS
MOVES EAST TO SOUTHERN INDIANA BY SUNDAY EVENING AS IT SLOWLY
STRENGTHENS. MOISTURE STREAMING NORTH FROM THE GULF WILL ALLOW
THIS SYSTEM TO PRODUCE MODERATE SNOW THROUGH SUNDAY EVENING...
BEFORE SLOWLY TAPERING OFF LATE SUNDAY EVENING AND EARLY MONDAY
MORNING. VISIBILITIES WILL LIKELY FLUCTUATE FROM TIME TO TIME
BUT PREVAILING VIS LIKELY TO BE AROUND 1/2SM FOR MUCH OF THE
EVENT.

AS THE GRADIENT STRENGTHENS SUNDAY MORNING...NORTHEAST WINDS
WILL INCREASE UP TO 20KTS WITH GUSTS 30-35KTS FOR MUCH OF THE
AFTERNOON AND EVENING. THESE STRONG WINDS WILL PRODUCE BLOWING
AND DRIFTING SNOW THAT MAY REDUCE VISIBILITIES UNDER 1/2SM AT
TIMES. THE WINDS WILL TURN MORE NORTHERLY SUNDAY EVENING AND
THEN BEGIN TO DIMINISH EARLY MONDAY MORNING. CMS

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* HIGH FOR SNOW/VIS THRU THE PERIOD.

* HIGH FOR WINDS/GUSTS THRU THE PERIOD.

* HIGH FOR BLOWING SNOW SUNDAY/SUNDAY NIGHT.

KREIN

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

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...IFR VSBY
POSSIBLE.

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.

MDB

&&

.MARINE...
315 AM CST

THE SFC LOW OVER THE PLAINS LOOKS TO BE DEEPENING A LITTLE FASTER
AND LOWER WHILE THE HIGH PRESSURE RIDGING OVER THE UPPER GREAT
LAKES IS TRENDING A LITTLE STRONGER. THIS COMBINATION WITH STRONG
COLD ADVECTION SETTING UP OVER THE LAKE TODAY...HAVE EXPANDED THE
GALE WARNING OVER THE ENTIRE OPEN WATERS OF LAKE MICHIGAN AS WELL
AS EXTENDING IN TIME...STARTING A LITTLE EARLIER...AT 15Z THIS
MORNING AND GOING A LITTLE LATER...TO 09Z TONIGHT. ALSO...HAVE
INCREASED GALES TO 40KT OVER THE SOUTHERN PORTIONS OF THE LAKE
WHERE THE PRESSURE GRADIENT AND PRESSURE FALLS ARE STRONGEST. AS
THE WINDS PICK UP TO GALE FORCE AND MUCH COLDER AIR FILTERS OVER
THE LAKE LATER TODAY...HEAVY FREEZING SPRAY WILL BE LIKELY...SO
HAVE ALSO ISSUED A HEAVY FREEZING SPRAY WARNING FROM 15Z THIS
MORNING TO 09Z TONIGHT. THE COLDER AIR WILL SPREAD OVER THE
NORTHERN PORTIONS OF THE LAKE EARLIER THAN THE SOUTHERN
PORTIONS...SO IT IS POSSIBLE THAT THE HEAVY FREEZING SPRAY
POTENTIAL MAY NOT REACH THE SOUTHERN PORTIONS OF THE LAKE UNTIL
THIS AFTERNOON...BUT WENT WITH ONE SEGMENT TO THE WARNING TO
COINCIDE WITH THE GALE WARNING TIMING. THE LOW SHOULD PUSH EAST
INTO THE MID ATLANTIC REGION BE MONDAY AFTERNOON...WHILE HIGH
PRESSURE SPREADS ACROSS THE MISSISSIPPI RIVER INTO THE WESTERN
GREAT LAKES REGION. THIS WILL LEAD TO SUBSIDING WINDS AND
WAVES...ESPECIALLY AS WEAK HIGH PRESSURE PRESSURE CROSSES THE LAKE
MONDAY NIGHT AND TUESDAY.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WARNING...ILZ005-ILZ006-ILZ011-ILZ012-ILZ013-ILZ014-
     ILZ020-ILZ022 UNTIL 2 PM SUNDAY.

     BLIZZARD WARNING...ILZ005-ILZ006-ILZ011-ILZ012-ILZ013-ILZ014-
     ILZ020-ILZ022...2 PM SUNDAY TO MIDNIGHT MONDAY.

     WINTER STORM WARNING...ILZ003-ILZ004-ILZ008-ILZ010-ILZ019-ILZ021-
     ILZ023-ILZ032-ILZ033-ILZ039 UNTIL MIDNIGHT MONDAY.

IN...BLIZZARD WARNING...INZ001...2 PM SUNDAY TO MIDNIGHT MONDAY.

     WINTER STORM WARNING...INZ001 UNTIL 2 PM SUNDAY.

     WINTER STORM WARNING...INZ002-INZ010-INZ011-INZ019 UNTIL
     MIDNIGHT MONDAY.

LM...GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-LMZ872-
     LMZ874-LMZ876-LMZ878...9 AM SUNDAY TO 3 AM MONDAY.

     HEAVY FREEZING SPRAY WARNING...LMZ080-LMZ261-LMZ362-LMZ364-
     LMZ366-LMZ563-LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-
     LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-
     LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...9 AM SUNDAY TO
     3 AM MONDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 9 AM SUNDAY.

&&

$$

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