Area Forecast Discussion
Issued by NWS Chicago, IL

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246
FXUS63 KLOT 051746
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1146 AM CST FRI FEB 5 2016

.UPDATE...
947 AM CST

FOR MORNING UPDATED...

FEW MINOR TWEAKS TO SKY COVER GRIDS AND TO ADD SOME FLURRIES
ACROSS EASTERN PARTS OF THE CHICAGO AREA THIS MORNING.

MID-LEVEL SHORT WAVE TROUGH NOTED ACROSS FAR NORTHEAST IL AND
SOUTHERN LAKE MICHIGAN AT MID-MORNING...WITH FLURRIES BEING
REPORTED BENEATH DEEPER CLOUDS SEEN IN VISIBLE SATELLITE IMAGERY.
THESE SHOULD CONTINUE TO PULL OFF TO THE EAST THROUGH NOON...WITH
DECREASING CLOUD COVER FROM THE NORTHWEST AS DRIER LOW LEVEL AIR
SPREADS IN ON NORTHWEST WINDS AND SUBSIDENCE BEHIND MORNING SHORT
WAVE. IN ADDITION TO THE ADDITION OF FLURRIES MENTIONED ABOVE HAVE
DECREASED SKY COVER ESPECIALLY ACROSS NORTH CENTRAL IL LATE THIS
MORNING AND THIS AFTERNOON. HIGH CLOUDS WILL INCREASE AND THICKEN
LATER THIS AFTERNOON/EVENING. OTHERWISE...NEAR TERM OF FORECAST IN
GOOD SHAPE THROUGH THE REMAINDER OF THE DAY.

RATZER

&&

.SHORT TERM...
259 AM CST

THROUGH SATURDAY NIGHT...

A FEW FLURRIES EAST OF I-39 WILL CONTINUE EAST EARLY THIS MORNING
WITH LITTLE TO NO ACCUMULATION EXPECTED. THE CLOUD COVER IS LEADING
TO WARMER THAN EXPECTED TEMPS AT MOST LOCATIONS.  THE UPPER LEVEL
TROUGH IS OVER THE CENTRAL OHIO VALLEY WITH A RIDGE OVER THE PLAINS.
THE RIDGE AND ASSOCIATED SURFACE HIGH MOVE OVER THE REGION TODAY
RESULTING IN TEMPS AT OR WARMER THAN WHAT THEY WERE THURSDAY.
THINKING IT WILL REMAIN CLOUDY TODAY. STRATUS IS SPREADING OVER THE
REGION AND THE UPPER LEVEL THERMAL TROUGH ASSOCIATED WITH THE
STRATUS REMAINS OVERHEAD. FORECAST SOUNDINGS ALSO SUGGEST THAT THE
COLUMN WILL REMAIN MOIST ENOUGH FOR CLOUD COVER.

A SHORTWAVE TROUGH AND VORT STREAMER MOVE THROUGH THE REGION LATE
TONIGHT INTO SATURDAY MORNING. THINKING THE LIFT ASSOCIATED WITH THE
VORT STREAMER WILL BE ENOUGH TO PRODUCE FLURRIES LATE TONIGHT
THROUGH SATURDAY MORNING. NO ACCUMULATION IS EXPECTED ESPECIALLY
SINCE CONFIDENCE IS LOW IN THE COVERAGE AND PERSISTENCE OF THE
FLURRIES. THE STREAMER WILL ALSO BE SCOOTING THROUGH...WHICH SHOULD
TRANSLATE TO TRANSIENT FLURRIES TOO.

SOUTH WINDS AND WARM AIR ADVECTION KICK IN SATURDAY RESULTING IN
HIGHS FROM THE MID 30S ALONG THE IL/WI STATE LINE TO LOW TO MID 40S
SOUTH OF I-80. SATURDAY AFTERNOON SHOULD BE DRY BUT CLOUDY.
OVERNIGHT LOWS WILL BE IN THE UPPER 20S.

JEE

&&

.LONG TERM...
259 AM CST

SUNDAY THROUGH THURSDAY...

THE NEXT SYSTEM MOVES OVER THE REGION MONDAY AND THE SURFACE LOW
SHOULD BE VERTICALLY ALIGNED WITH THE UPPER LEVEL LOW.  THE TRICKY
PART WILL BE IF THERE WILL BE PRECIP SUNDAY AS THE UPPER LEVEL LOW/S
VORTICITY STREAMERS ROTATE THROUGH. DECIDED TO INCLUDE LOW END
SLIGHT CHANCE TO CHANCE POPS FOR LIGHT PRECIP THROUGH THE DAY.  THE
BETTER CHANCES WILL BE ALONG THE IL/WI STATE LINE CLOSER TO THE
PARENT LOW AND FORCING. TEMPS WILL BE INCREASING TO ABOVE FREEZING
SUNDAY SO HAVE PRECIP BEGINNING AS SNOW BECOMING RAIN BY MID DAY.
THERE IS A DECENT CHANCE THAT SUNDAY MAY BE DRY...SO HAVE HIGH
CONFIDENCE IN TEMPS SUNDAY BUT LOW CONFIDENCE IN PRECIP CHANCES.

THE LOW MOVES OVER THE REGION SUNDAY NIGHT AND GUIDANCE FEATURES
SOME DIFFERENCES IN THE LOWS PATH.  EITHER WAY HAVE HIGHER
CONFIDENCE IN PRECIP SUNDAY NIGHT THROUGH MONDAY.  COLDER AIR MOVES
IN THE WITH THE LOW RESULTING IN LOWS BELOW FREEZING SUNDAY NIGHT.
AS SUCH HAVE RAIN BECOMING SNOW.  INITIAL SNOWFALL TOTALS THROUGH
SUNDAY NIGHT ARE ALL LESS THAN A HALF OF AN INCH AS FORCING LOOKS
MEAGER.

LIGHT SNOW CONTINUES THROUGH TUESDAY NIGHT ESPECIALLY OVER NORTHWEST
INDIANA WHERE LAKE EFFECT SNOW MAY PERSIST INTO WEDNESDAY. THE LOW
AND ITS TROUGH PUSH EAST TUESDAY AFTERNOON...BUT A SECOND
TROUGH/VORT STREAMER PUSHES SOUTH FROM CANADA INTO THE MIDWEST
TUESDAY NIGHT INTO WEDNESDAY. THE BIGGER STORY WITH THE SECOND
STREAMER WILL BE A PUNCH OF COLD AIR...-10 TO -20C AT 850
MB...MOVING OVER THE REGION. IT LOOKS LIKE WE WILL MISS THE COLDEST
AIR ASSOCIATED WITH THE STREAMER...BUT WIND CHILLS TUESDAY
NIGHT/WEDNESDAY MORNING WILL BE AROUND 0 OR SLIGHTLY BELOW ZERO.

HIGH PRESSURE MOVES OVER THE REGION MID TO LATE NEXT WEEK WITH LAKE
EFFECT SNOW FOCUSING EAST OF THE WARNING AREA. TEMPS WILL BE IN THE
20S WEDNESDAY AND THEN AROUND 30 THURSDAY.

JEE

&&

.AVIATION...
FOR THE 18Z TAFS...

MAIN AVIATION CONCERNS ARE LINGERING 1300-1900 FT MVFR BKN CIGS
EARLY THIS AFTERNOON...AND LOW PROBABILITY OF FLURRIES LATER
TONIGHT/EARLY SATURDAY MORNING.

WEAK MID-LEVEL WAVE CONTINUES TO MOVE SLOWLY EAST-SOUTHEAST ACROSS
SOUTHERN LAKE MICHIGAN THIS AFTERNOON...WITH A FEW FLURRIES
LINGERING OVER GYY-VPZ AREAS AND BKN MVFR DECK ERODING FROM THE
NORTHWEST ACROSS OTHER TERMINALS. WHILE SOME HOLES HAVE OPENED UP
ACROSS ORD...VISIBLE SATELLITE TRENDS SUGGEST A COUPLE HOURS OF
BKN MVFR CIGS STILL LIKELY EARLY THIS AFTERNOON. HIGH CLOUDS ARE
ALREADY STREAMING IN FROM THE WEST AHEAD OF THE NEXT DISTURBANCE
WHICH WILL MOVE ACROSS THE AREA TONIGHT AND SATURDAY MORNING. THIS
APPROACHING SYSTEM IS WEAKER THAN THE ONE WHICH BROUGHT LIGHT SNOW
TO THE REGION THIS MORNING...AND MODEL FORECAST SOUNDINGS INDICATE
ATMOSPHERE WILL STRUGGLE TO SATURATE THROUGH A DEEP LAYER. SOME
POTENTIAL FOR A LOWER VFR CEILING IN THE 3500-4500 FT RANGE FROM
THIS EVENING INTO EARLY SATURDAY...AND A FEW FLURRIES CANT BE
RULED OUT...THOUGH NO HIGH-RES GUIDANCE ACTUALLY INDICATES
MEASURABLE PRECIP FOR ANY OF THE TAF SITES. CONFIDENCE IS HIGH
THAT MVFR CIGS WILL SCATTER TO VFR THIS AFTERNOON...AND MEDIUM-
HIGH IN MAINTAINING VFR CONDITIONS THROUGH SATURDAY MORNING.

AS FOR WINDS...NORTHWEST WINDS NEAR 10 KT AT MIDDAY WILL SLOWLY
DIMINISH AND BECOME SOUTHWEST BY MID-LATE EVENING AS WEAK SURFACE
HIGH PRESSURE MOVES ACROSS THE AREA. SOUTH-SOUTHWEST WINDS LESS
THAN 10 KTS PICK UP TO AROUND 10 KTS LATER SATURDAY AFTERNOON.
CONFIDENCE IS HIGH IN WIND TRENDS.

RATZER

&&

.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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