Area Forecast Discussion
Issued by NWS Chicago, IL

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482
FXUS63 KLOT 050746
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
146 AM CST FRI FEB 5 2016

.UPDATE...
910 PM CST

ONLY SOME MINOR CHANGES TO THE GOING FORECAST. HAVE BEEFED UP THE
FLURRY MENTION AND ADDED A SLIGHT CHANCE OF MEASURABLE SNOW
SHOWERS TO THE GRIDS/FORECAST. EVENING SOUNDING FROM DVN FEATURED
VERY IMPRESSIVE LAPSE RATES FROM THE SURFACE UP TO NEARLY 500MB
WITH RESPECTABLE MOISTURE ABOVE 850MB. LAST LIGHT VISIBLE IMAGERY
DID SHOW THE SOMEWHAT CONVECTIVE NATURE TO THE CLOUDINESS OVER
IOWA AND HAVE SEEN SOME OF THE SNOW SHOWERS BRIEFLY KNOCK VSBY
DOWN TO 1-2SM. RECENT OBSERVATIONAL TRENDS SUGGEST THAT MUCH OF
THE REFLECTIVITY OVER N IL IS VIRGA WITH MOST SNOW OBS NORTH OF
THE WI BORDER. EVEN SO...GIVEN THE FAIRLY FAVORABLE LOOKING
SOUNDING AND WEAK SHORTWAVE TROUGH MOVING ACROSS THE REGION THINK
SOME BRIEF SNOW SHOWERS CAPABLE OF A QUICK COATING OF SNOW WILL
REMAIN A THREAT...ESPECIALLY NORTH OF I-80 CLOSER TO THE STRONGER
FORCING.

OTHER THAN THE TWEAKS FOR SNOW SHOWERS/FLURRIES...REMAINDER OF THE
FORECAST IN GOOD SHAPE AND NO CHANGES WERE MADE AT THIS TIME.

IZZI

&&

.SHORT TERM...
234 PM CST

THROUGH SATURDAY...

ANOTHER WEAK CLIPPER SYSTEM IS CURRENTLY SHIFTING EASTWARD ACROSS
THE UPPER MIDWEST AND UPPER GREAT LAKES REGION. THIS SYSTEM WILL
DRIVE ANOTHER FRONTAL BOUNDARY ACROSS THE AREA THROUGH THIS EVENING.
AHEAD OF THIS BOUNDARY...THERE COULD BE A FEW LIGHT FLURRIES THIS
EVENING...PARTICULARLY ACROSS NORTH CENTRAL ILLINOIS AS SOME MODEST
ISENTROPIC UPGLIDE SETS UP. HOWEVER...NO ACCUMULATION IS EXPECTED.

A SURFACE RIDGE OF HIGH PRESSURE WILL BUILD OVER THE AREA ON FRIDAY.
SO...IT WILL BE DRY DURING THE DAY...BUT CLOUDY AS SOME HIGHER
CLOUDS MOVE OVER THE REGION. TEMPERATURES ONCE AGAIN LOOK TO TOP OUT
NEAR 30 NORTH AND INTO THE LOW TO MID 30S SOUTH. WARMER CONDITIONS
ARE EXPECTED ON SATURDAY AS SOUTHWESTERLY FLOW SETS UP IN THE WAKE
OF THE DEPARTING SURFACE RIDGE AXIS. THIS SHOULD ALLOW TEMPERATURES
TO GET INTO THE LOW 40S SOUTH AND THE MID TO UPPER 30S NORTH.

KJB

&&

.LONG TERM...
302 PM CST

SATURDAY NIGHT THROUGH THURSDAY...

THE WEATHER PATTERN IS EXPECTED TO CHANGE LATER SUNDAY INTO EARLY
NEXT WEEK AS A HIGH LATITUDE UPPER LEVEL RIDGE BUILDS OVER WESTERN
NORTH AMERICA. THIS WILL ACT TO BUCKLED THE UPPER LEVEL JET STREAM
SOUTHWARD OVER THE GREAT LAKES REGION...AND ULTIMATELY SEND A MUCH
COLDER CANADIAN AIRMASS OUR WAY. MODEL GUIDANCE CONTINUES TO
SUGGEST THAT AS THE MAIN UPPER TROUGH DIGS OVER THE AREA...IT WILL
DEVELOP INTO A CLOSED UPPER LOW...AND BE SLOW TO SHIFT OUT OF THE
AREA. AS A RESULT...IT APPEARS THAT THERE COULD BE PERIODS OF SNOW
SHOWERS AREA-WIDE MONDAY AND POSSIBLY INTO TUESDAY. THIS COULD
RESULT IN MINOR SNOW ACCUMULATIONS. HOWEVER...IT ALSO APPEARS THAT
THIS COLD AIRMASS COULD SET UP A DECENT LAKE EFFECT SNOW EVENT EARLY
NEXT WEEK. THE MAIN QUESTION AT THIS TIME IS WILL ANY OF THIS LAKE
EFFECT SNOW IMPACT NORTHEASTERN ILLINOIS. GUIDANCE REMAINS SOMEWHAT
SPLIT ON WHETHER THE SURFACE LOW WILL PROGRESS FAR ENOUGH SOUTH
INTO THE LOWER GREAT LAKES EARLY NEXT WEEK AS HIGH PRESSURE BUILDS
IN FROM THE WEST. ULTIMATELY THIS WILL DETERMINE IF THE FLOW OVER
LAKE MICHIGAN BECOMES NORTH-NORTHEAST ENOUGH TO RESULT IN SOME LAKE
EFFECT INTO NORTHEAST ILLINOIS. HOWEVER...PORTIONS OF NORTHWESTERN
INDIANA AND THE EASTERN SHORES OF THE LAKE WOULD CERTAINLY BE
FAVORED FOR LAKE EFFECT SNOW SHOWERS AS THE WINDS LIKELY BECOME MORE
NORTHWEST WITH TIME.

KJB

&&

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

WEAK DISTURBANCE MOVING ACROSS THE REGION MAY STILL PRODUCE SOME
FLURRIES OR A BRIEF SNOW SHOWER DURING THE FIRST COUPLE HOURS OF
THIS TAF CYCLE. WEAK COLD FRONT WILL MOVE ACROSS THE TERMINALS
OVERNIGHT AND RESULT IN A WIND SHIFT TO LIGHT NORTHWEST BY
MORNING. RELATIVELY SMALL AREA OF MVFR CIGS EXIST BEHIND THE FRONT
AND WHILE GUIDANCE IS NOT HITTING THE THREAT TERRIBLY HARD...FELT
IT WAS BEST TO HANG ONTO A PERIOD OF MVFR CIGS FRIDAY MORNING.
ASSUMING MVFR CIGS MATERIALIZE THEN WOULD STILL ANTICIPATE A TREND
TOWARD VFR CONDITIONS FRIDAY AFTERNOON. STILL WORTH POINTING OUT
THAT THE CIGS FORECAST FOR LATE TONIGHT AND FRIDAY IS LOW
CONFIDENCE.

IZZI

&&

.MARINE...
143 AM CST

A MORE COMMON MID-WINTER SETUP FOR THE GREAT LAKES WILL ESTABLISH
ITSELF INTO NEXT WEEK...WITH SYSTEMS FROM THE NORTHWEST AND
ASSOCIATED SURFACE COLD FRONTS MOVING ACROSS THE GENERAL REGION.
ONE SUCH WEAKER COLD FRONT IS PASSING ACROSS THE LAKE VERY EARLY
THIS MORNING TURNING WINDS NORTHWEST. THE NEXT LOW PRESSURE WILL
PASS QUICKLY NORTH OF THE GREAT LAKES VERY LATE TONIGHT INTO
SATURDAY MORNING. THIS WILL PROVIDE A TIGHTENING PRESSURE GRADIENT
OVER THE NORTHERN PART OF THE LAKE WITH LIKELY 30 KT GUSTS.

A STRONGER NORTHWEST FLOW SYSTEM WILL DROP DOWN OVER THE WESTERN
GREAT LAKES BY SUNDAY NIGHT AND INTO LOWER MICHIGAN BY MIDDAY
MONDAY. THIS LOW LOOKS TO LIKELY SLOW AS IT DOES. WINDS AHEAD OF
THIS COULD GET INTO THE 25 TO 30 KT CATEGORY OVER THE OPEN WATER
AND NEAR SMALL CRAFT CRITERIA IN THE NEARSHORE. ON THE BACKSIDE OF
THE SYSTEM...COLD ADVECTION WILL VERY LIKELY PROVIDE AT LEAST 30
KT AND POTENTIALLY GALE FORCE GUSTS FOR THE OPEN WATER WITH SMALL
CRAFT CRITERIA IN THE NEARSHORE. THIS RIGHT NOW IS MOST FAVORED
MONDAY NIGHT AND/OR TUESDAY.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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