Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 270334
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
934 PM CST MON JAN 26 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 03Z...

* PERIODS OF LIGHT SNOW AND FREEZING DRIZZLE CONTINUING INTO THE
  OVERNIGHT...WITH FREEZING DRIZZLE POSSIBLY PERSISTING UNTIL
  ~13-14Z.

* PREDOMINANTLY IFR CIGS EXPECTED UNTIL ABOUT 13Z...BUT THERE WILL
  BE OCCASIONAL IMPROVEMENT TO MVFR...ESPECIALLY THIS EVENING.

* MVFR VSBY...WITH OCCASIONAL IFR VSBY AT LEAST THROUGH 07Z.

* NORTHEAST WINDS AROUND 10 KT BY MID TUESDAY MORNING.

RC

//DISCUSSION...UPDATED 03Z...

HAVE TRENDED MORE PESSIMISTIC IN THE TAFS REGARDING THE END TIME
OF PRECIPITATION OVERNIGHT. AN ELONGATED UPPER LEVEL DISTURBANCE
WILL REMAIN OVER THE AREA THROUGH THE NIGHT...PROVIDING FORCING
FOR MAINLY LIGHT PRECIP BUT ALSO BURSTS OF OCCASIONALLY MODERATE
SNOW SLIDING SOUTHEAST. THESE BURSTS OF SNOW WILL RESULT IN IFR
VSBY AND MAYBE A TENTH OR TWO OF ACCUMULATION. WITH
TIME...SOUNDINGS SUGGEST A MORE PRONOUNCED LOSS OF ICE CRYSTALS IN
THE CLOUDS OVER NORTHEAST IL AND NW INDIANA BY ABOUT 10Z...BUT
ENOUGH LIFT AND LOW LEVEL MOISTURE TO LIKELY KEEP AT LEAST PATCHY
FREEZING DRIZZLE GOING UNTIL THE 12Z- 14Z TIMEFRAME. THE CIG
FORECAST IS TRICKY...AS MOST OF NORTHERN IL HAS IFR CIGS BUT THERE
ARE POCKETS OF LOW MVFR IN NORTHEAST ILLINOIS. EXPECT ORD TO DROP
BACK DOWN TO IFR BUT WILL NEED TO MONITOR THIS.
FINALLY...INCREASED NORTHEAST WIND SPEEDS TO AROUND 10 KT FOR
ORD/MDW/GYY BY MID TUESDAY MORNING. SPEEDS SHOULD DIMINISH BY THE
EARLY TO MID AFTERNOON AS CIGS CONTINUE TO GRADUALLY IMPROVE.


FROM 00Z...

DIFFICULT AVIATION CONDITIONS THIS EVENING INTO THE OVERNIGHT AS A
WEAK LOW PRESSURE AREA DIVES SOUTHEAST AND AN UPPER LEVEL
DISTURBANCE REMAINS OVER THE REGION. LIFT FROM THE UPPER
DISTURBANCE BUT NO SNOW CRYSTALS IN THE CLOUDS WILL KEEP
OCCASIONAL TO STEADY FREEZING DRIZZLE GOING AT RFD AND DPA AT
LEAST THROUGH THE MID EVENING. FOR THE CHICAGO TERMINALS...THE
CLOUDS STILL HAVE SNOW CRYSTALS IN THEM...BUT MIXING WITH FREEZING
DRIZZLE HAS ALREADY BEEN OCCURRING. CONFIDENCE IS LOWER ON
DURATION AND EXTENT OF FREEZING DRIZZLE LATER THIS EVENING...SO
HAVE CARRIED A TEMPO GROUP IN THE TAF FOR NOW. LEFT OUT FZDZ OUT
OF THE GYY TAF...BUT BASED ON TRENDS MAY NEED TO INCLUDE IT. THE
FREEZING DRIZZLE IS LIKELY TO CAUSE ICY CONDITIONS ON ROADWAYS.

THE OTHER CONCERN IS CIGS AND VSBY. MOIST LOW LEVELS HAVE ENABLED
COVERAGE OF IFR CIGS TO INCREASE...WITH LOWEST BASES AT NORTH
CENTRAL IL TERMINALS INCLUDING RFD. EXPECTING TEMPORARY IFR TO
BECOME PREVAILING AT ORD LATER THIS EVENING...BUT HAVE LOWER
CONFIDENCE IN MDW AND GYY...AND HOW LONG LOWER CIGS WILL PERSIST
INTO TUESDAY MORNING. THEY ARE MOST LIKELY TO PERSIST THROUGH PART
OF THE MORNING AT RFD/DPA. WINDS WILL BECOME NORTHEAST ON
TUESDAY...AND SPEEDS COULD BE CLOSE TO 10 KT AT ORD/MDW/GYY. ANY
REMAINING LOWER CIGS ON TUESDAY SHOULD ERODE BY THE EARLY
AFTERNOON.

RC

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* MEDIUM IN PRECIP TRENDS.

* MEDIUM-HIGH IN WIND TRENDS.

* MEDIUM IN CIG/VSBY TRENDS.

RC

//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...
216 PM CST

LOW PRESSURE OVER THE UPPER MIDWEST WILL DROP SOUTH TOWARDS THE
TENNESSEE VALLEY TODAY AND TONIGHT...BUT WEAKENING WHILE DOING SO.
THIS WEAKENING TREND ALONG WITH HIGH PRESSURE BUILDING ACROSS THE
CENTRAL GREAT LAKES TONIGHT WILL HELP MAINTAIN OVERALL LIGHTER
WINDS IN PLACE. THIS WILL CONTINUE ON TUESDAY AND TUESDAY NIGHT AS
THE CENTER OF THE HIGH PASSES OVER THE LAKE. THIS HIGH WILL THEN
SHIFT TO THE EAST WEDNESDAY INTO WEDNESDAY NIGHT AS LOW PRESSURE
SHIFTS EAST THROUGH THE CENTRAL PLAINS. EXPECT SOUTHERLY WINDS TO
INCREASE OUT AHEAD OF THE LOW DURING THIS PERIOD...AND ESPECIALLY
WEDNESDAY NIGHT WHEN SPEEDS APPROACHING 30KT WILL BE OBSERVED.

RODRIGUEZ

&&

.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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