Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 052346
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
546 PM CST FRI FEB 5 2016

.SHORT TERM...
232 PM CST

TONIGHT THROUGH SATURDAY...

LOW CLOUDS CONTINUE TO SCATTER-OUT FROM NORTHWEST TO SOUTHEAST
THIS AFTERNOON AS WEAK SURFACE HIGH PRESSURE MOVES INTO THE REGION
IN THE WAKE OF THIS MORNINGS WEAK COLD FRONT. HIGH CLOUDS WERE
ALREADY BEGINNING TO SPREAD ACROSS THE AREA FROM THE WEST...AHEAD
OF THE NEXT DISTURBANCE OVER THE PLAINS. EXPECT THAT TEMPS WILL
FALL OFF INTO THE 20S WITH SUNSET...THEN HOLD NEARLY STEADY
OVERNIGHT AS CLOUDS THICKEN. GUIDANCE IN CLOSE AGREEMENT WITH
TEMPS AND DID NOT STRAY MUCH FROM MET/MAV BLEND.

ANOTHER WEAK CLIPPER SYSTEM WILL MOVE ACROSS THE AREA TONIGHT
INTO SATURDAY MORNING...KICKING A WEAK SHORT WAVE OVER THE MID-
MISSOURI VALLEY NORTHEAST ACROSS THE REGION AHEAD OF IT TONIGHT.
UPSTREAM 12Z RAOBS FROM THIS MORNING DEPICT FAIRLY DRY AIR BELOW
ABOUT 650 MB AND MODEL SOUNDINGS AND TIME-HEIGHT DEPICTIONS
INDICATE THAT LOWER LEVELS MAY STRUGGLE TO WITH GENERALLY WEAK
FORCING FOR ASCENT. REGIONAL RADAR MOSAIC AND SURFACE OBS DO
INDICATE LIGHT SNOW OCCURRING ACROSS WESTERN IA AT THIS
TIME...THOUGH MODELS ERODE THIS PRECIP WITH TIME AS IT TRIES TO
SPREAD EAST. THUS WHILE MID/HIGH CLOUDS WILL THICKEN THIS
EVENING...NO GUIDANCE PRODUCES MEASURABLE PRECIP FROM THE
APPROACHING SYSTEM AND IT APPEARS THAT ANYTHING MORE THAN A FEW
FLURRIES IS UNLIKELY. TIMING FOR FLURRIES APPEARS TO BE MAINLY
AFTER MIDNIGHT TONIGHT THROUGH EARLY SATURDAY MORNING.

MID-LEVEL TROUGH AXIS MOVES OFF TO THE EAST OF THE FORECAST AREA
SATURDAY AFTERNOON...WITH ASSOCIATED SURFACE TROUGH WASHING OUT
ACROSS THE CWA AND BECOMING INDISTINCT. T-SECTS INDICATE SKIES
WILL BECOME PARTLY SUNNY ESPECIALLY ACROSS THE SOUTHERN PARTS OF
THE CWA. MODEST SOUTHWEST WINDS MAINTAIN WARM ADVECTION THROUGH
THE DAY AND 925-950 MB TEMPS SUPPORT AFTERNOON HIGHS IN THE MID-
UPPER 30S FAR NORTH...AND IN THE LOWER 40S ALONG AND SOUTH OF THE
I-80 CORRIDOR. PREFERRED THE SLIGHTLY WARMER MAV GUIDANCE FOR
SATURDAY MAX TEMPS.

RATZER

&&

.LONG TERM...
239 PM CST

SUNDAY NIGHT THROUGH FRIDAY...

SATURDAY NIGHT THROUGH SUNDAY...
RELATIVELY QUIET FOR SAT NGT AS A SOUTHERN STREAM MID-LVL TROUGH
SLOWLY SLIDES EAST...WITH THE NORTHERN STREAM IN TRANSITION.
UPSTREAM OF THE GREAT LAKES REGION WILL BE WEAK HEIGHT RISES WHICH
WILL LIKELY DELAY PRECIP ARRIVAL FOR SUN DUE TO GREATER SUBSIDENCE
IN THE LOWER LEVELS. BY DAYBREAK SUN A SHORTWAVE WILL BE SLIDING
SOUTH FROM CENTRAL CANADA INTO THE NORTHERN PLAINS AND QUICKLY SLIDE
EAST BY MIDDAY SUN TO THE UPPER MIDWEST...WITH A SFC WAVE PRODUCING
A LEE-SIDE FRONTAL BOUNDARY. GUIDANCE IS ENHANCING THIS BOUNDARY AS
IT CLIPS NORTHERN IL MIDDAY SUN...INDICATING STEADY MOISTENING IN
FROM THE TOP/DOWN AND POSSIBLY BRINGING SOME LIGHT PRECIP TO THE
FORECAST AREA. FORTUNATELY A PUSH OF WARMER AIR FROM THE SOUTH
THROUGH THE MORNING/MIDDAY SUN WILL LIFT SFC TEMPS INTO THE UPPER
30S TO POSSIBLY THE MID 40S ACROSS THE KANKAKEE VALLEY. SO ANY LIGHT
PRECIP THAT FALLS WILL BE AS LIGHT RAIN AT THE ONSET.

WITH COLDER AIR STEADILY ADVECTING SOUTH AS THE VORT MAX ARRIVES
OVER CENTRAL WISC...LAPSE RATES WILL STEEPEN AND SHOULD BEGIN TO
BRING A LIGHT RAIN/SNOW MIX IN THE EVE HOURS. AT THIS TIME QPF
REMAINS VERY LOW...AND ANY LIGHT SNOW THAT WERE TO FALL WOULD
STRUGGLE TO ACCUMULATE AT THE ONSET. HOWEVER AS COLD AIR CONTINUES
TO ADVECT ACROSS THE REGION LATE SUN...PERHAPS A DUSTING WILL OCCUR
BY DAYBREAK MON FOR AREAS NORTH OF I-80.

MONDAY THROUGH THURSDAY... MID-LVL VORT MAX WILL BE STUBBORN TO
DEPART THE REGION AS IT SAGS SOUTH ACROSS NORTHERN IL MON...AND
EVENTUALLY SLIDES EAST EARLY TUE MORNING. SFC GRADIENT WILL BEGIN TO
DIMINISH AS THE LOW SLIDES OVERHEAD EARLY MON...BUT ONCE THE
SHORTWAVE PUSHES EAST THE GRADIENT RETURNS AND WINDS INCREASE FROM
THE NORTHWEST. 850MB THERMAL TROUGH OF -9 TO -12 DEG C SLIDES
OVERHEAD FROM THE NORTHWEST AND SHOULD KEEP SFC TEMPS IN THE 30S
FROM THE CONSIDERABLE SOLAR SHIELDING MON...THEN EVEN COLDER AIR
ARRIVES ALOFT TUE WITH TEMPS STRUGGLING TO WARM BEYOND THE 20S FOR
HIGHS. FLOW WILL BE TURNING NORTHERLY ALONG THE BACK SIDE OF THE
DEPARTING TROUGH TUE...WHICH WOULD ALLOW FOR SOME LAKE EFFECT PRECIP
TO DEVELOP AND LIKELY KEEP CONSIDERABLE CLOUDINESS FOR AREAS
ADJACENT TO LAKE MICHIGAN...ESPECIALLY NORTHWEST INDIANA.

ENSEMBLES CONTINUE TO FEATURE A HIGH CONFIDENCE IN A HIGH AMPLITUDE
500MB RIDGE ALONG THE WESTERN CONUS EXTENDING NORTH INTO WESTERN
NORTHWEST CANADA...WITH THE DOWNSTREAM TROUGH LINGERING ACROSS THE
GREAT LAKES REGION. THROUGH TIME IT DOES APPEAR THE TROUGH WILL
EXPAND AS THE RIDGE OVER THE WESTERN ATLANTIC BEGINS TO SHIFT
EAST...HOWEVER THIS WILL KEEP AN UNSEASONABLY COOL AIR OVER THE
GREAT LAKES REGION THROUGH THE BULK OF THE EXTENDED PERIODS WITH
PERIODIC CHANCES FOR FLURRIES/LIGHT SNOW.

BEACHLER

&&

.AVIATION...
FOR THE 00Z TAFS...

MAIN FORECAST CONCERNS ARE WITH A LOW PROBABILITY OF MVFR
CEILINGS AND FLURRIES LATE TONIGHT INTO EARLY SATURDAY MORNING.
HOWEVER...HAVE EXCLUDED MENTION OF EITHER IN THE TAFS DUE TO LOW
CONFIDENCE.

MID LEVEL CLOUD COVER CONTINUES TO MOVE ACROSS THE TERMINALS AND
AM EXPECTING VFR CEILINGS THIS EVENING. MVFR CEILINGS JUST TO THE
SOUTH/SOUTHEAST OF THE TERMINALS WILL LIKELY REMAIN TO THE SOUTH.
HOWEVER...AS THE CURRENT HIGH IN PLACE SHIFTS TO THE
EAST...ADDITIONAL UPSTREAM LOWER CEILINGS COULD PUSH TOWARDS THE
TERMINALS. ONCE AGAIN...LOW CONFIDENCE WITH THIS SOLUTION AND HAVE
EXCLUDED ANY MENTION. AN UPSTREAM MID LEVEL DISTURBANCE COULD
PROVIDE SOME FLURRIES TONIGHT BUT WITH LITTLE IF ANY IMPACTS
EXPECTED AT THIS TIME. WESTERLY WINDS WILL BECOME SOUTHWEST THIS
EVENING INTO SATURDAY...WHILE VFR CONDITIONS CONTINUE.

RODRIGUEZ

&&

.MARINE...
104 PM CST

MARINE FORECAST CONCERNS FOCUS ON A COUPLE PERIODS OF STRONGER
FLOW. THE FIRST OF THESE COMES TONIGHT INTO SATURDAY MORNING
ACROSS NORTHERN PARTS OF THE LAKE...AS WEST-SOUTHWEST WINDS
INCREASE TO 25-30 KT IN RESPONSE TO AN AREA OF LOW PRESSURE
PASSING TO THE NORTH OF LAKE SUPERIOR. THE GRADIENT WILL EASE A
BIT BY SATURDAY AFTERNOON AS A WEAK COLD FRONT SAGS ACROSS THE
NORTHERN LAKES. DEEPER LOW PRESSURE WILL TRACK SOUTHEAST ALONG
THIS BOUNDARY SATURDAY NIGHT... RESULTING IN WINDS BACKING MORE
SOUTHERLY AND PICKING UP TO 20-25 KT. THE LOW IS EXPECTED TO MOVE
ACROSS LAKE MICHIGAN ON MONDAY WITH WINDS DECREASING AS THE
GRADIENT AGAIN WEAKENS NEAR THE LOW CENTER. THE LOW WILL MOVE
SLOWLY OFF TO THE EAST-SOUTHEAST MONDAY NIGHT...WHILE HIGH
PRESSURE BUILDS ACROSS THE CANADIAN PRAIRIES AND NORTHERN PLAINS
AND CAUSES THE GRADIENT TO STRENGTHEN AGAIN. NORTH-NORTHWEST WINDS
ARE EXPECTED TO INCREASE TO 30 KT AFTER MIDNIGHT MONDAY NIGHT AND
CONTINUE THROUGH TUESDAY. SOME MODEL FORECASTS SUPPORT MARGINAL
GALES DURING THIS PERIOD.

RATZER

&&

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

$$

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