Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 292035
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
235 PM CST THU JAN 29 2015

.SHORT TERM...
234 PM CST

THROUGH SATURDAY...

THE MAIN FOCUS DURING THIS PERIOD WILL BE WITH THE POTENTIAL FOR
SOME ACCUMULATING LAKE EFFECT SNOW ACROSS PORTIONS OF NORTHWESTERN
INDIANA TONIGHT INTO FRIDAY MORNING.

LOW PRESSURE NOW ACROSS THE EASTERN GREAT LAKES REGION...DROVE A
COLD FRONT ACROSS THE AREA THIS MORNING...AND HAS SINCE CONTINUED TO
PRODUCING GUSTY NORTHWEST WINDS ACROSS THE REGION THROUGH THE
AFTERNOON. WATER VAPOR IMAGERY THIS AFTERNOON INDICATES THE NEXT
SHORT WAVE DISTURBANCE NOW DIGGING SOUTHWARD OVER LAKE SUPERIOR.
THIS DISTURBANCE IS EXPECTED TO RACE SOUTHWARD ACROSS SOUTHERN LAKE
MICHIGAN THIS EVENING...AND AS IT DOES SO...IT COULD PRODUCE ENOUGH
LIFT TO SQUEEZE OUT A FEW FLURRIES...SO I HAVE ADDED THE MENTION TO
THE FORECAST THROUGH MUCH OF THE EVENING.

OTHERWISE...IT APPEARS THAT LAKE EFFECT SNOW SHOWERS WILL CONTINUE
TO DEVELOP OVER SOUTHERN LAKE MICHIGAN TONIGHT...AND AS THE BOUNDARY
LAYER FLOW OVER LAKE MICHIGAN BEGINS TO BACK NORTHERLY...IT APPEARS
THAT SOME BANDS OF LAKE EFFECT SNOW WILL BEGIN TO IMPACT PORTIONS OF
NORTHWESTERN INDIANA OVERNIGHT TONIGHT THROUGH FRIDAY MORNING. LAKE
INDUCED EQUILIBRIUM LEVELS ARE EXPECTED TO RESIDE AROUND 5,000
FEET...AND DUE TO THE COLD LOWER LEVEL ATMOSPHERE...THIS SHOULD BE
HIGH ENOUGH TO RESIDE WELL INTO THE DENDRITE GROWTH ZONE.
THEREFORE...SOME EFFICIENT SNOWFALL LOOKS TO RESULT IN SOME
ACCUMULATING POTENTIAL...ESPECIALLY ACROSS PORTIONS OF PORTER COUNTY
INDIANA IN MY AREA...WHERE SOME ISOLATED AREAS COULD GET A COUPLE
INCHES. THESE LAKE EFFECT SNOW SHOWERS WILL COME TO AN END BY EARLY
AFTERNOON AS THE FLOW BEGINS TO SHIFT WESTERLY IN RESPONSE TO A AN
AREA OF SURFACE HIGH SHIFTING SOUTHEASTWARD TOWARDS THE OHIO
VALLEY.

A BRIEF WARMING TREND LOOKS TO BE ON TAP LATE FRIDAY NIGHT AND
SATURDAY AS THIS HIGH SHIFTS OVER THE OHIO VALLEY...SETTING UP A
WEST SOUTHWESTERLY FLOW OF WARMER AIR OVER THE AREA. THIS SHOULD
ALLOW TEMPERATURES TO WARM WELL INTO THE 30S AREA-WIDE.

KJB

&&

.LONG TERM...
358 AM CST

COMING SOON.

&&

.AVIATION...

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

* NORTHWEST WINDS GUSTING TO AROUND 25 KT OR SO THROUGH AT LEAST
  MIDNIGHT...TAPERING SOME OVERNIGHT.

* MVFR CIGS PERSISTING INTO THE EVENING...LIFTING TO VFR EITHER
  OVERNIGHT OR INTO FRIDAY MORNING.

* FLURRIES THIS EVENING REDUCING VSBY TO MVFR.

KMD

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

MAIN AVIATION CONCERN IS WITH GUSTY NW WINDS THIS AFTERNOON AND
TONIGHT. WE HAVE HAD A HARD TIME REALIZING DEEPER MIXING WITH THE
SOLID MVFR CLOUD DECK IN PLACE. WE HAVE SEEN OCCASIONAL 30 KT
GUSTS ON 1-MINUTE ASOS OBSERVATIONS...BUT IN GENERAL SUSTAINED
WINDS HAVE BEEN IN THE MID TO UPPER TEENS WITH GUSTS INTO THE MID
20S. EXPECT THESE WINDS TO REMAIN IN PLACE THIS AFTERNOON AND
EVENING AS A SECOND WAVE OF COLD AIR ADVECTION ENSUES TONIGHT.

NEXT CONCERN IS AROUND MVFR CIGS AND POSSIBLE FLURRIES TONIGHT.
CIGS SHOULD GENERALLY REMAIN ABOVE 1500 FT WITH THE GUSTY WINDS
AND MIXED VERY LOW LEVELS. A WEAKER TROUGH AXIS WILL MOVE THROUGH
THE TERMINALS THIS AFTERNOON...FOLLOWED BY A SHARPER VORT MAX THIS
EVENING. UPSTREAM OBSEVATIONS IN NORTHERN MINNESOTA AHEAD OF THIS
WAVE HAVE BEEN REPORTING SOME FLURRIES AND POSSIBLY EVEN SOME
FREEZING DRIZZLE. AS THIS WAVE MOVES THROUGH THIS EVENING...LOWER
LEVEL TEMPERATURES COOL TO THAT POINT TO SUPPORT SOME FLURRIES
AND POSSIBLE VISIBILITY REDUCTION IF THIS ACTIVITY. CONFIDENCE ON
THIS IS LOW ON SPECIFICALLY IMPACTING ANY PARTICULAR TERMINAL...SO
IT HAS NOT BEEN MENTIONED IN THE TAFS AT THE MOMENT. BUT
CONFIDENCE IS PRETTY HIGH THAT THE MVFR CIGS LINGER THROUGH MUCH
OF THE NIGHT. HIGH PRESSURE BUILDS IN TOMORROW WHICH RESULTS IN
LIGHTER WINDS AND LIKELY SOME SCATTERING OUT OF THE LOW CLOUD
DECK...BUT CONFIDENCE TIMING THE SCATTERING IS NOT VERY HIGH.

KMD

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

* HIGH IN WINDS...MEDIUM ON GUSTS.

* HIGH IN MVFR CIGS ABOVE 1800 FT THROUGH AT LEAST MIDNIGHT. LOW-
  MEDIUM ON SPECIFIC SCATTERING TIME...WHICH WOULD COULD BE
  BETWEEN 6Z AND 9Z BUT MOST LIKELY BE SOME TIME AFTER 12Z.

* LOW ON FLURRIES AND ANY ASSOCIATED VSBY REDUCTION THIS EVENING.

KMD

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

FRIDAY NIGHT...VFR. SOUTHWEST WINDS.
SATURDAY...CHANCE OF SNOW AND IFR DURING THE NIGHT. WEST WINDS.
SUNDAY...CHANCE OF SNOW AND IFR. AT LEAST MVFR CIGS LIKELY.
         NORTHEAST WINDS.
MONDAY NIGHT-WEDNESDAY...CHANCES OF MAINLY LIGHT SNOW. WEST WINDS.

MTF

&&

.MARINE...
153 PM CST

ACTIVE PATTERN LOOKS TO PERSIST THROUGH THE WEEKEND WITH MUCH
COLDER AIR ARRIVING EARLY NEXT WEEK. WITH THE SLOW AND STEADY
DEPARTURE OF TWO LOW PRESSURES OVER THE WESTERN GREAT LAKES THIS
MORNING...THE TWO LOWS ARE NOW CONSOLIDATING OVER NORTHEAST LAKE
HURON. ALONG THE BACKEDGE OF THESE LOW PRESSURES...THE PRESSURE
GRADIENT HAS TIGHTEN AND WAS PRODUCING GALE FORCE WINDS TO 35 KT
FROM THE NORTHWEST. MOST OF THE AFTERNOON WINDS HAVE BEEN HELD TO
AROUND LOW END GALES OR JUST UNDER GALE FORCE...HOWEVER AS THE
AFTERNOON PROGRESSED MIXING HAS BEEN ABLE TO BRING TO THE SURFACE
MUCH STRONGER WINDS. AS A RESULT WILL MAINTAIN THE CURRENT GALE
WARNING THROUGH THIS EVENING. WITH THE STRONGEST GRADIENT OVER THE
NORTHERN HALF OF THE LAKE...PRODUCING GALES TO 40KT AT TIMES...THIS WILL
LIKELY PRODUCE HEAVY FREEZING SPRAY. FURTHER SOUTH THE GALES WILL
LIKELY REMAIN AROUND 35KT AND THE FREEZING SPRAY SHOULD ONLY BE
ALONG THE MODERATE LEVEL AND NOT REQUIRE A HEADLINE.

WAVES WILL CONTINUE TO BUILD EARLY THIS EVENING...WITH THE HIGHEST
WAVES BETWEEN 12-15 FT TONIGHT. HIGH PRESSURE THEN QUICKLY ARRIVES
AND BRINGS LIGHTER WINDS TO THE LAKE BY MIDDAY FRIDAY. THEN HIGH
PRESSURE QUICKLY SLIDES EAST/SOUTHEAST...WITH WINDS TURNING
SOUTHERLY AHEAD OF YET ANOTHER LOW PRESSURE SYSTEM OVER THE
WEEKEND. A FRONTAL BOUNDARY WILL SLIDE SOUTH FROM CANADA
SATURDAY...AND COULD DEVELOP A TIGHT GRADIENT OVER THE LAKE FOR A
PERIOD SATURDAY NIGHT INTO SUNDAY. AT THIS TIME IT LOOKS LIKE
NORTH/NORTHEAST WINDS WILL TOP OUT AROUND 30KT...BUT COULD SEE A
FEW GALE FORCE GUSTS FOR A FEW HOURS EARLY SUNDAY. THEN HIGH
PRESSURE PUSHES OVER THE WESTERN GREAT LAKES SUNDAY NIGHT INTO
MONDAY. UNFORTUNATELY ANOTHER ACTIVE PATTERN LOOKS FAVORABLE FOR
EARLY NEXT WEEK.

BEACHLER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...HEAVY FREEZING SPRAY WARNING...LMZ261-LMZ362-LMZ364-LMZ366-
     LMZ563-LMZ565-LMZ567-LMZ868 UNTIL 3 AM FRIDAY.

     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 UNTIL 3 AM FRIDAY.

&&

$$

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