Area Forecast Discussion
Issued by NWS Chicago, IL

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033
FXUS63 KLOT 082025
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
225 PM CST MON FEB 8 2016

.UPDATE...
1128 AM CST

FOR MORNING UPDATE...

HAVE UPDATED TEMPERATURE TRENDS TODAY...WITH READINGS ALREADY
BEGINNING TO FALL FROM MORNING HIGHS. GFS LAMP GUIDANCE SEEMS TO
BE CAPTURING THIS NICELY AND HAVE USED THIS TO DEPICT A SLOW FALL
INTO THE LOWER AND MIDDLE 20S THROUGH LATE AFTERNOON. WINDS ALSO
PICKING UP FROM THE WEST BEHIND SECONDARY COLD FRONT ESPECIALLY
ACROSS THE WESTERN PORTIONS OF THE CWA...WHERE WIND CHILLS WILL
FALL TO THE SINGLE DIGITS AND LOWER TEENS THIS AFTERNOON.
OTHERWISE...FORECAST OF FLURRIES AND SNOW SHOWERS REMAINS
APPROPRIATE FOR THE CURRENT WEATHER REGIME WITH COLD ADVECTION
STEEPENING LOW LEVEL LAPSE RATES AND A SERIES OF MID-LEVEL VORT
CIRCULATIONS HELPING TO MODULATE COVERAGE AND INTENSITY OF
GENERALLY LIGHT SNOW. UPDATED GRIDS/ZFP AVAILABLE.

RATZER

&&

.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 18Z TAFS...

UPPER LEVEL LOW OVER LAKE MICHIGAN EARLY THIS AFTERNOON WILL
CONTINUE TO SLOWLY MEANDER EASTWARD ACROSS THE GREAT LAKES TODAY
AND TOMORROW WITH PINWHEELING UPPER LEVEL DISTURBANCES BRINGING
PERIODIC CHANCES FOR LIGHT SNOW SHOWERS AND FLURRIES TO THE
REGION. ONE OF THESE WAVES IS NOW DROPPING SOUTH INTO CENTRAL
ILLINOIS WHICH SHOULD ALLOW A LULL IN THE SNOW ACTIVITY IN ITS
WAKE THROUGH THE REST OF THE AFTERNOON. ANOTHER WAVE IS PROGGED TO
ROTATE ACROSS THE TERMINALS LATE THIS EVENING AND TONIGHT. FORCING
IS FAIRLY WEAK HOWEVER LOW LEVEL MOISTURE IS FOCUSED WITHIN A
RELATIVELY DEEP SNOW GROWTH ZONE WHICH SHOULD ALLOW FOR EFFICIENT
SNOW PRODUCTION. CONFIDENCE IN THE TIMING DETAILS REMAINS FAIRLY
LOW THOUGH GIVEN THE RATHER BENIGN FORCING. DURING THE DAY
TUESDAY...COLD AIR SPILLING INTO THE REGION WILL RESULT IN
STEEPENING LOW LEVEL LAPSE RATES AND ONCE AGAIN PRIME THE
ATMOSPHERE FOR DECENT SNOW PRODUCTION IF WE REALIZE ANY
FORCING...HOWEVER ANY FORCING CONTINUES TO BE WEAK RESULTING IN
CONSIDERABLE UNCERTAINTY SO FOR NOW WILL JUST INTRODUCE A PROB30
FOR SNOW EARLY TO MID AFTERNOON. WINDS WILL REMAIN OUT OF THE
NORTHWEST THROUGH THE PERIOD...WITH GUSTS INCREASING LATE THIS
AFTERNOON INTO EARLY EVENING. EXPECT CIGS TO REMAIN MVFR THROUGH
THE PERIOD.

BMD

&&

.MARINE...
223 PM CST

LOW PRESSURE CENTERED NEAR LAKE HURON/LAKE ONTARIO EARLY THIS
AFTERNOON WILL VERY GRADUALLY MEANDER TOWARDS LAKE ONTARIO BY
TOMORROW NIGHT WITH MODERATELY STRONG NORTH TO NORTHWEST WINDS
EXPECTED TO BE IN PLACE ACROSS LAKE MICHIGAN. WINDS ARE EXPECTED
TO REMAIN AROUND 30 KT THIS EVENING THROUGH WEDNESDAY
NIGHT...WITH A FEW GALE FORCE GUSTS POSSIBLE MAINLY TUESDAY INTO
TUESDAY NIGHT. FREEZING SPRAY IS ALSO A CONCERN TUESDAY THROUGH
WEDNESDAY EVENING. HIGH PRESSURE WILL BUILD FROM THE UPPER
MIDWEST WEDNESDAY NIGHT INTO THE OHIO VALLEY THURSDAY NIGHT
RESULTING A MODEST TAPERING OF THE WINDS AS THEY BACK TO THE WEST.
ANOTHER COLD FRONT WILL SWEEP ACROSS LAKE MICHIGAN FRIDAY TURNING
WINDS BACK TO NORTHERLY AND PICKING UP ONCE AGAIN. THIS FRONT WILL
USHER IN A BITTERLY COLD ARCTIC AIRMASS WHICH COULD RESULT IN
ADDITIONAL GALES...PARTICULARLY FRIDAY NIGHT...AND FREEZING SPRAY
ACROSS LAKE MICHIGAN.

BMD

&&

.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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