Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 080946
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
346 AM CST MON FEB 8 2016

.SHORT TERM...
337 AM CST

THROUGH WEDNESDAY...

THE FORECAST DETAILS AND OVERALL MESSAGE REMAIN SIMILAR FOR THE
UPCOMING LONG DURATION LIGHT SNOW EVENT WITHIN A MORE BLUSTERY
AND COLDER PATTERN. HAVE HONED FURTHER IN ON THIS EVENING THROUGH
TUESDAY MORNING AS A PROBABLE TIME FOR WIDESPREAD LIGHT SNOW WITH
ACCUMULATIONS...WITH TODAY SEEING MORE FLURRIES AND OCCASIONAL
SNOW SHOWERS. WITH THE OVER 30 HOURS EXPECTED OF OFF AND ON
SNOW...ACCUMULATIONS CONTINUE TO LOOK ON THE ORDER OF ONE HALF TO
2.5 INCHES FOR MOST AREAS. IN GENERAL...HIGHER TOTALS LOOK
EAST...ALTHOUGH SNOWFALL TOTALS TEND TO END UP LIKE A WRINKLED
SHEET AND NOT NICE AND SMOOTH /BORROWED THAT FROM A COLLEAGUE/.
FINALLY...PORTER COUNTY INDIANA STILL LOOKS TO HAVE LAKE EFFECT
ENHANCEMENT THAT WILL BRING SNOWFALL TOTALS UP.

ONE OF THE MORE PRONOUNCED COLD CORE UPPER LOWS OF THIS WINTER IS
ROTATING ITS WAY SOUTHEASTWARD ACROSS THE WESTERN GREAT LAKES
EARLY THIS MORNING. LARGE SCALE WATER VAPOR IMAGERY REVEALS THE
UPPER JET MAXIMUM IS STILL ROUNDING THE TOP OF THE WESTERN NORTH
AMERICAN RIDGE WITH THE RIDGE CONTINUING TO BUILD. AS A
RESULT...THE GREAT LAKES TROUGH WILL CONTINUE TO DIG AND PROGRESS
SOUTHEAST THROUGH TONIGHT AS THAT JET HEADS DUE SOUTH OVER THE
PLAINS. IN ADDITION...THE DEEP LOW OFF THE EASTERN SEABOARD WILL
FURTHER KEEP OUR UPPER LOW FROM PROGRESSING QUICKLY
EAST...ASSISTING IN THE BUILDING CHILL AND LONG DURATION LIGHT
SNOW.

THE PRIMARY SURFACE COLD FRONT WILL CLEAR THE AREA SOON AFTER
DAYBREAK WITH TEMPERATURES INCHING DOWNWARD A FEW DEGREES AND THEN
LIKELY NOT TO RECOVER MUCH TODAY...WITH THE AFTERNOON IN THE MID
20S TO LOWER 30S FOR MOST. STEEP LOW-LEVEL LAPSE RATES BEHIND
THIS FRONT ARE ASSISTING IN WIDESPREAD FLURRIES ENTERING NORTHERN
ILLINOIS PER RADAR AND OBSERVATIONS...WITH A SCATTERING OF
EMBEDDED HIGHER REFLECTIVITY AND MORE SNOW SHOWER-ISH ACTIVITY.
AM EXPECTING THIS TO BASICALLY BE THE CASE TODAY ACROSS OUR
AREA...THAT IS FLURRIES MORE OFTEN THAN NOT...WITH OCCASIONAL TRUE
SNOW SHOWERS AND QUICKLY VARYING VISIBILITY. THE COVERAGE OF SNOW
SHOWERS WILL BE MODULATED BY A HANDFUL OF FACTORS...WITH VORTICITY
MAXIMAS PROBABLY THE SIMPLEST TO KEY IN ON...WITH OTHERS BEING
MORE MESOSCALE /E.G. LOW-LEVEL F-GEN/. THESE FACTORS WITHIN SOME
OF THE HIGH-RES HOURLY GUIDANCE THROUGH TODAY WOULD POINT TOWARD
SLIGHTLY BETTER TRUE SNOW SHOWER COVERAGE OVER THE WESTERN AND
SOUTHERN CWA. BUT AGAIN TOUGH TO TIME EXACTLY SO A BROAD
CONSISTENT FORECAST MESSAGE FOR TODAY.

STRONGER SYNOPTIC LIFT...SLIGHTLY BETTER LAPSE RATES...AND A MORE
FAVORABLE THERMAL PROFILE FOR DENDRITES ALL ARRIVE EARLY THIS
EVENING FROM NORTH TO SOUTH AS A VORTICITY LOBE ROTATES
SOUTHWARD. THE MODEL GUIDANCE IS IN FAIRLY GOOD AGREEMENT WITH
THIS AND HAVE JUST GONE LIGHT SNOW AREAWIDE. THIS FOR NORTHERN
AREAS WILL LIKELY OVERLAP AT LEAST PART OF THE EVENING COMMUTE
AND A PERSISTENT...THOUGH LIGHT...ACCUMULATION IS LIKELY TO BEGIN
IN THAT TIME. ITS MORE CHALLENGING TO SAY WHEN THIS PERIOD WILL
END...BUT IT LOOKS TO CONTINUE INTO TUESDAY MORNING. WITH
NORTHWEST LOW-LEVEL WINDS HAVING INCREASED ON RE-ENFORCED COLD
ADVECTION...VISIBILITY COULD BE LOW TO QUITE LOW AT TIMES. SO WITH
POSSIBLE TWO COMMUTES LIKELY TO BE DEALING WITH LIGHT ACCUMULATING
SNOW AND SOME VARYING VISIBILITY HAVE GONE AHEAD AND ISSUED AN SPS
TO FURTHER THE MESSAGE.

LOW-LEVEL WINDS WILL TURN OFF THE LAKE IN NORTHWEST INDIANA WITH
LAKE ENHANCEMENT TO THE SNOW LIKELY INTO BOTH LAKE AND PORTER
COUNTY BY LATE TONIGHT...THOUGH THE LONGER FETCH WILL BE POINTED
INTO PORTER COUNTY. EQUILIBRIUM LEVELS ARE FORECAST TO BE AROUND
8000 FT THOUGH WITH A GRADUALLY DEEPENING DENDRITIC GROWTH LAYER.
SO THIS WILL HELP ACCUMULATIONS IN THIS AREA WITH 2 TO 3 INCHES
PRESENTLY FAVORED IN THE FAR NORTHEAST PART OF THE COUNTY BY
TUESDAY EVENING...AND ADDITIONAL AFTER THAT POINT LATE TUESDAY
NIGHT INTO WEDNESDAY...POSSIBLY EVEN A FEW MORE INCHES. WILL NEED
TO MONITOR IF A HEADLINE IS NEEDED...PARTICULARLY IF RATES ARE
MORE ENHANCED...ALTHOUGH THE BETTER LAKE EFFECT SETUP CONTINUES TO
LOOK FURTHER EAST...SO NOT ANTICIPATING IT AT THIS TIME.

TEMPERATURES LOOK TO NOT CLIMB AT ALL ON TUESDAY WITH WIND CHILLS
IN THE SINGLE DIGITS. CYCLONIC FLOW PERSISTS THROUGH WEDNESDAY SO
CONTINUE TO LEAN CLOUDIER THAN GUIDANCE INTO THEN. IF CLOUDS CAN
CLEAR BY WEDNESDAY NIGHT...THAT LOOKS TO BE A PARTICULARLY CHILLY
NIGHT WITH SOME OUTLYING AREAS POTENTIALLY DROPPING TO OR BELOW
ZERO.

MTF

&&

.LONG TERM...
340 AM CST

WEDNESDAY NIGHT THROUGH MONDAY...

THE PATTERN CONTINUES TO LOOK LIKE A COOLER THAN NORMAL ONE IN
THIS TIME PERIOD. THE ELEVATED BAROCLINIC ZONE ON THE WESTERN SIDE
OF THE EASTERN NORTH AMERICAN TROUGH LOOKS TO BE UNSETTLED WITH
SEVERAL RIPPLES SUPPORTING OCCASIONAL LIGHT SNOW
CHANCES...ALTHOUGH THE PLACEMENT OF THAT HAS LARGE SPREAD IN
GUIDANCE AT THIS TIME. AN EVEN MORE ANOMALOUS UPPER LEVEL LOW IS
FORECAST TO DIG INTO EASTERN CANADA BY FRIDAY OR SATURDAY...WITH
THE EC FURTHER SOUTH WITH THIS FEATURE. THIS RESULTS IN SOME
DIFFERENCES IN THE SURFACE PRESSURE FIELDS BETWEEN THE GFS AND
EC...THOUGH THE GENERAL SYNOPTIC PATTERN WITH A STRONG CANADIAN
HIGH TO THE WEST AND A STRONG COLD FRONT PUSHING SOUTH THROUGH THE
GREAT LAKES CAN SUPPORT BETTER LAKE EFFECT POTENTIAL FOR SOME OF
OUR LAKE ADJACENT AREAS...AT THIS TIME MORE SO FAR NORTHWEST
INDIANA. OVERALL THOUGH BECAUSE OF THE NORTHWEST FLOW...THE THREAT
OF WIDESPREAD HIGH IMPACT WEATHER LOOKS LOW AT THIS TIME.

MTF

&&

.AVIATION...
FOR THE 06Z TAFS...

LIGHT REFLECTIVITIES CAN BE SEEN ON RADAR ALONG THE WESTERN IL AND
WI STATE LINES...WITH ONLY A FEW SITES REPORTING FLURRIES. THE
MORE WIDESPREAD SNOW IS ACROSS SOUTHEAST MN AND CENTRAL IOWA
ASSOCIATED WITH THE LOW/S VORTICITY STREAMER. GUIDANCE SUGGESTS
THAT IT WILL TAKE SOME TIME FOR THE COLUMN TO SATURATE AND SNOW TO
REACH THE GROUND...SO PUSHED BACK THE SNOW START TIME BY AN HOUR.
SNOW COULD TAKE EVEN LONGER TO START FALLING ESPECIALLY AT THE
EASTERN TERMINALS. SOME GUIDANCE MEMBERS SUGGEST SNOW WILL NOT
REACH THE GROUND UNTIL THIS EVENING...HOWEVER HAVE LOW CONFIDENCE
IN THOSE MEMBERS. FORCING FROM THE LOW WILL AT LEAST PRODUCE
FLURRIES THROUGHOUT THE DAY. A PERIOD OF MODERATE SNOW AND IFR
VSBY IS PSBL EARLY THIS MORNING. MVFR CIGS WILL ACCOMPANY THE SNOW
SHOWERS.

SOUTHWEST WINDS BECOME GUSTY NORTHWEST WINDS THIS EVENING.

HAVE HIGH CONFIDENCE IN MVFR CIGS AND SNOW FALLING FROM EARLY THIS
MORNING ONWARD. HAVE MEDIUM CONFIDENCE IN PERIODS OF MODERATE SNOW
AND IFR VSBY...BUT LOW CONFIDENCE IN EXACT TIMING. ALSO HAVE LOW
CONFIDENCE IN THE EXACT START TIME OF THE SNOW.

JEE

&&

.MARINE...
301 AM CST

ISSUED A SMALL CRAFT ADVISORY FOR TONIGHT THROUGH EARLY WEDNESDAY
NIGHT FOR THE IL NEARSHORE WATERS...AND INTO THURSDAY MORNING FOR
THE INDIANA NEARSHORE WATERS DUE TO HAZARDOUS WINDS AND WAVES.

A WEAK LOW OVER THE U.P. OF MI WILL DRIFT OVER THE LAKE TODAY AND
REACH THE EASTERN GREAT LAKES LATE THIS AFTERNOON.  WINDS WILL
BECOME NORTH BEHIND THE LOW AND INCREASE TO 30 KT.  HIGH PRESSURE
SINKS SOUTH OVER THE PLAINS TUESDAY NIGHT AND MOVES OVER THE
MISSISSIPPI VALLEY WEDNESDAY EVENING. THE TIGHTENED GRADIENT BETWEEN
THE HIGH AND LOW WILL RESULT IN AN EXTENDED PERIOD OF 30 KT WINDS
THROUGH WEDNESDAY NIGHT. LOW END GALE FORCE GUSTS ARE POSSIBLE LATE
TUESDAY AFTERNOON OVER THE NORTHERN HALF OF THE LAKE...AND THE GALES
REACH THE SOUTHERN END OF THE LAKE TUESDAY NIGHT.  HOWEVER...DO NOT
HAVE ENOUGH CONFIDENCE IN GALES TO ISSUE A GALE WATCH FOR TUESDAY
NIGHT INTO WEDNESDAY.  WINDS DIMINISH AS THE HIGH MOVES OVER THE
LAKE WEDNESDAY NIGHT INTO THURSDAY.

ANOTHER WEAK LOW PASSES OVER THE EASTERN GREAT LAKES THURSDAY NIGHT
AND FRIDAY WHILE HIGH PRESSURE MOVES OVER MINNESOTA FRIDAY NIGHT AND
SATURDAY.  NORTHWEST TO NORTH WINDS INCREASE TO 30 KT LATE IN THE
WEEK.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...MIDNIGHT TUESDAY
     TO 9 AM THURSDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...MIDNIGHT TUESDAY
     TO 3 AM THURSDAY.

&&

$$

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