Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 270813
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
213 AM CST TUE JAN 27 2015

.SHORT TERM...
258 PM CST

TONIGHT THROUGH TUESDAY...
WEAK CLIPPER HAS PRODUCED SOME LIGHT SNOW ACROSS NORTHERN IL THIS
AFTERNOON. LATEST RADAR IMAGERY SUGGESTS THE BACK EDGE OF THE
PRECIP BEGINNING TO WORK EAST ALONG I-39. WITH CONSIDERABLE DRY
AIR AT THE SFC...NOT ALL PRECIP HAS BEEN ABLE TO REACH THE SFC.
THE SLIGHTLY STEADIER SNOW WAS LOCATED ACROSS FAR NORTHEAST
IL...MAINLY OVER LAKE/MCHENRY COUNTIES. MOST HI-RES GUIDANCE
INDICATES THE LIFT/OMEGA WILL QUICKLY DISSIPATE ARND 00Z...WHICH
SUGGESTS WE MAY BE ABLE TO END THE LIGHT SNOW EARLIER. IT IS
POSSIBLE THAT WITH SOME WEAK LLVL CONVERGENCE THAT SOME
FLURRIES/LGT SNOW MAY LINGER TO 3Z...BUT THIS IS A LOW CONFIDENCE
SCENARIO. THE OTHER LINGERING CONCERN IS THE POSSIBILITY FOR
PATCHY FZDZ. WITH THE LACK OF GOOD SATURATION...THINK AT MOST THIS
WILL END UP AS A PATCHY FZDZ.

CLOUDS WILL LIKELY REMAIN LOCKED IN THRU THE OVERNIGHT
PERIOD...DESPITE THE CLEAR SKIES THIS AFTN ACROSS CENTRAL IOWA. THE
LACK OF MIXING WILL PERSIST THRU TUE MORNING...ANTI-CYCLONIC FLOW
WILL STEADILY MIX IN DRY AIR TUE MIDDAY. THIS MAY PROVIDE SOME
BREAKS IN THE CLOUD COVER BY EARLY AFTN. LLVL FLOW WILL TURN
NORTHEASTERLY...WHICH COULD HOLD TEMPS IN THE LOW 30S. IF CLOUDS CAN
THIN EARLIER IN THE DAY...TEMPS MAY BE ABLE TO WARM AN ADDTL DEGREE
OR TWO GIVEN THE LACK OF SNOW PACK.

SFC RIDGE WILL BE OVERHEAD TUE NGT...WITH DRY CONDS PERSISTING.
TEMPS SHUD EASILY RADIATE INTO THE MID-TEENS.

BEACHLER

&&

.LONG TERM...
258 PM CST

WEDNESDAY THROUGH MONDAY...
MID-LVL RIDGING WILL SLIDE EAST ACROSS THE CENTRAL PLAINS WED...WITH
A ROBUST MID-LVL THERMAL RIDGE OF 10 TO 14 DEG C LIFTING NORTHEAST
INTO A PORTION OF THE MID-MISSOURI VALLEY. THIS WILL LIKELY SET THE
STAGE FOR POTENTIALLY A MILD WED AFTN/EVE...AS TEMPS COULD WARM INTO
THE UPR 30S TO POSSIBLY THE LOW 40S ALONG THE SOUTHERN CWFA. LLVL
MOISTURE WILL BE SLOW TO ADVECT NORTH...HOWEVER GUIDANCE SUGGESTS
THAT AS THE BETTER MID-LVL VORT ARRIVES PRECIP SHIELD WILL INCREASE.
EQUALLY LATE WED NGT/EARLY THUR A DRY SLOT IS BEING PROGGED TO
DEVELOP. WITH THE LACK OF STRONG LLVL FORCING...IT IS POSSIBLE THAT
PARCELS REMAIN SMALL MORE IN THE FORM OF DRIZZLE. WILL MAINTAIN A
RAIN/SNOW MIX...BUT FEELING IS THAT ENOUGH WARM AIR WILL BE IN PLACE
TO PUSH THIS OVER TO LGT RAIN.

500MB PATTERN TRIES TO TRANSITION TOWARDS QUASI-ZONAL. THIS WILL
PROVIDE A RELATIVELY ACTIVE SETUP TOWARDS THE UPCOMING WEEKEND. THE
MID-WEEK SHORTWAVE WILL SLIDE EAST BY THUR NGT...WITH LIKELY A DRY
END TO THE WEEK. TEMPS WILL BE MILD AGAIN THUR...THE CHALLENGE IS
HOW WARM. CURRENT THINKING IS THAT WITH FROPA LIKELY IN THE MORNING
THUR THAT MAX TEMPS MAY OCCUR PRIOR TO DAYBREAK...MAINLY IN THE UPR
30S. POSSIBLY ARND 40 IN THE SOUTHERN CWFA. THEN WITH COLD AIR
ADVECTING IN FROM THE NORTHWEST...TEMPS WILL STEADILY COOL THUR AFTN
INTO THE LOW/MID 30S. DRY AIR MOVES IN THUR NGT WITH SFC RIDGING AND
SHUD REMAIN IN PLACE THRU MUCH OF FRI.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* PERIOD OF LIGHT SNOW TAPERING OFF TO SNIZZLE DURING THE PRE-DAWN
  HOURS...WITH IFR/LOW-MVFR CIG/VIS.

* CIGS EXPECTED TO IMPROVE TO SOLID MID-HIGH RANGE MVFR SHORTLY
  AFTER SUNRISE...SCATTERING TO VFR BY MID-AFTERNOON.

* LIGHT SE WINDS TO BECOME NE THROUGH SUNRISE...INCREASING TO
  AROUND DURING THE DAY.

RATZER

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

ELONGATED/SHEARED MID-LEVEL DISTURBANCE CONTINUES TO PROPAGATE
SOUTHEASTWARD ACROSS THE FORECAST AREA AT MIDNIGHT...PRODUCING AN
AREA OF LIGHT SNOW AND SOME FREEZING DRIZZLE ACROSS SOUTHEAST
WISCONSIN AND NORTHEAST IL/NORTHWEST INDIANA. EXTRAPOLATION OF
RADAR FEATURES...WHICH COINCIDES WITH IR COLDER CLOUD TOPS AND AND
MODEL FORECAST OF SHEARED MID-LEVEL CIRCULATION...SUGGESTS MORE
ORGANIZED PRECIPITATION SHOULD END BY 10Z OR SO FOR THE CHICAGO
TERMINALS AND A COUPLE OF HOURS EARLIER FOR RFD. FORECAST
SOUNDINGS DO DEPICT LOW LEVELS REMAINING VERY MOIST AND CAPABLE OF
PRODUCING LIGHT FREEZING DRIZZLE/FLURRIES (SNIZZLE) AND AT LEAST
PATCHY IFR CIGS THROUGH SUNRISE OR SO...BEFORE INCREASING NORTH-
NORTHEAST BOUNDARY LAYER WINDS REALLY BEGIN TO DRY OUT THE LOWER
LEVELS. CONCURRENT WITH THAT...THERE SHOULD BE A STEADY
IMPROVEMENT IN CIG/VIS AND EVENTUALLY SCATTERING TO VFR IS
EXPECTED BY EARLY-MID AFTERNOON.

AS FOR WINDS...WEAK SURFACE LOW/TROUGH ACROSS IL WILL MOVE OFF TO
THE SOUTHEAST ACROSS THE OHIO RIVER THIS MORNING...ALLOWING LIGHT
SOUTHEAST (OR CALM/VARIABLE AT RFD) WINDS TO BACK TO THE NORTHEAST
AND EVENTUALLY INCREASE TO AROUND 10 KT LATER THIS MORNING. WEAK
HIGH PRESSURE RIDGE THEN MOVES INTO THE REGION TONIGHT ALLOWING
LIGHT WINDS TO VEER TO THE SOUTHEAST AGAIN.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* MEDIUM-HIGH CONFIDENCE IN ORGANIZED PRECIP ENDING PRIOR TO
  SUNRISE.

* HIGH IN WIND TRENDS.

* MEDIUM-LOW WITH CIG/VIS TRENDS REMAINDER OF OVERNIGHT/EARLY
  MORNING HOURS.

RATZER

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

WEDNESDAY...VFR THEN CHANCE FOR LIGHT RAIN OR DRIZZLE WEDNESDAY
NIGHT AND POTENTIAL FOR MVFR/IFR.

THURSDAY...CHANCE OF LIGHT SNOW OR LIGHT RAIN/SNOW MIX/ MVFR
LIKELY/IFR POSSIBLE.

FRIDAY...NORTH WINDS. PRIMARILY VFR.

SATURDAY AND SUNDAY...CHANCE OF LIGHT SNOW SATURDAY NIGHT INTO
SUNDAY. IFR POSSIBLE.

RC

&&

.MARINE...
213 AM CST

MARINE CONCERNS ON LAKE MICHIGAN ARE A PERIOD OF STRONG SOUTH WINDS
WEDNESDAY AFTERNOON AND NIGHT...THEN A SHIFT TO STRONG NORTH TO
NORTHWEST WINDS THURSDAY AFTERNOON INTO EARLY FRIDAY...WITH THE
POTENTIAL FOR A PERIOD OF NORTHWEST GALES ESPECIALLY THURSDAY
AFTERNOON AND THURSDAY EVENING.

IN THE NEAR TERM...RELATIVELY QUIET WEATHER ACROSS THE LAKE EARLY
THIS MORNING AS A WEAKENING SURFACE TROUGH OVER ILLINOIS AND THE
LOWER OHIO VALLEY CONTINUES TO MOVE OFF TO THE SOUTHEAST...ALLOWING
WEAK HIGH PRESSURE TO SETTLE ACROSS THE AREA FROM THE NORTH TODAY.
LOOKING TO THE WEST...AN AREA OF LOW PRESSURE DEVELOPING IN THE LEE
OF THE CANADIAN ROCKIES WILL SLIDE SOUTHEAST INTO THE PLAINS
THROUGH TONIGHT...THEN WILL MOVE SLOWLY EAST TOWARD LAKE MICHIGAN
WEDNESDAY AND WEDNESDAY NIGHT. IN RESPONSE TO PRESSURE FALLS AHEAD
OF THE LOW...THE GRADIENT WILL TIGHTEN ACROSS LAKE MICHIGAN
WEDNESDAY WITH SOUTH WINDS RAMPING UP INTO THE 30 KT RANGE BY LATE
AFTERNOON AND EVENING. WINDS WILL DIMINISH BRIEFLY EARLY THURSDAY
MORNING AS THE LOW PRESSURE CENTER AND COLD FRONTAL TROUGH CROSS THE
LAKE...BEFORE WINDS SHIFT TO THE NORTH-NORTHWEST AND INCREASE
QUICKLY BACK INTO THE 30-35 KT RANGE THURSDAY AFTERNOON. FORECAST
SOUNDINGS INDICATE THE POTENTIAL FOR GALES THURSDAY AFTERNOON AND
EVENING IN THE STRONG PRESSURE RISES AND COLD ADVECTION BEHIND THE
DEPARTING LOW AND COLD FRONT. THESE STRONG WINDS WILL CONTINUE INTO
EARLY FRIDAY...BEFORE DIMINISHING AS A BROAD AREA OF HIGH PRESSURE
SPREADS INTO THE AREA BY FRIDAY EVENING. THE HIGH WILL SLOWLY MOVE
OFF TO THE EAST ON SATURDAY...WITH A WEAK LOW EXPECTED TO PASS
ACROSS THE NORTHERN LAKES SATURDAY NIGHT AND TRAIL A COLD FRONT
ACROSS LAKE MICHIGAN THROUGH SUNDAY.

FOR THE ILLINOIS AND NORTHWEST INDIANA NEARSHORE WATERS SMALL CRAFT
ADVISORY CONDITIONS LOOK TO DEVELOP WEDNESDAY AFTERNOON AND CONTINUE
THROUGH THURSDAY MORNING...WITH A BRIEF BREAK BEFORE HIGH WIND/WAVE
CONDITIONS DEVELOP AGAIN BY EARLY THURSDAY AFTERNOON. HIGH WAVES
WOULD LIKELY LINGER THROUGH MUCH OF FRIDAY...ESPECIALLY ALONG THE
INDIANA SHORE EAST OF GARY.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...FREEZING RAIN ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-
     ILZ010-ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-
     ILZ022-ILZ023-ILZ032-ILZ033-ILZ039 UNTIL 6 AM TUESDAY.

IN...NONE.
LM...NONE.
&&

$$

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