Area Forecast Discussion
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FXUS63 KLOT 301757
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1157 AM CST FRI JAN 30 2015

.UPDATE...
1112 AM CST

HAVE ISSUED A WINTER STORM WATCH FOR THE ENTIRE CWA FROM SATURDAY
EVENING UNTIL EARLY MONDAY. LOOKING AT A LONG DURATION MODERATE
SNOW EVENT. ENERGY FROM A SOUTHERN STREAM WAVE FROM A SOUTHWEST
CLOSED LOW WILL INTERACT WITH A NORTHERN WAVE DIVING SOUTHEAST
TOWARD THE REGION FROM THE NORTHERN PLAINS. THIS WILL RESULT IN
INTENSIFYING WARM ADVECTION/ISENTROPIC ASCENT IN ADVANCE OF AN
INITIALLY WEAK SURFACE LOW OVER THE SOUTHERN PLAINS SUNDAY NIGHT.
AT THE SAME TIME...COLDER AIR WILL OOZE SOUTHWARD AS STRONG ARCTIC
HIGH PRESSURE SPREADS SOUTHEAST FROM THE CANADIAN PRAIRIES.
LOOKING AT LONG PERIOD OF WARM ADVECTION DRIVEN SNOWS STARTING
SATURDAY EVENING...FOLLOWED BY THE DEFORMATION AXIS OF THE
STRENGTHENING SURFACE AND MID LEVEL LOWS LINGERING INTO LATE
SUNDAY. IF SYSTEM AND 850 MB LOW TRACK CONTINUES NORTHWARD SHIFT
ON GUIDANCE...HAVE CONCERN THAT PARTS OF SOUTHERN CWA MAY FLIRT
WITH MARGINAL THERMAL PROFILES SATURDAY EVENING. HOWEVER...LATEST
GUIDANCE SUGGESTS PRIMARILY ALL SNOW EVENT FOR THE ENTIRE
CWA...WITH RATIOS IMPROVING AS COLDER AIR OOZES SOUTHWARD.
FINALLY...ON SUNDAY NIGHT...IMPROVING THERMODYNAMICS AND NORTH-
NORTHEAST FLOW DOWN THE LENGTH OF LAKE MICHIGAN SHOULD RESULT IN
LAKE ENHANCEMENT TRANSITIONING TO TRUE LAKE EFFECT INTO THE
SOUTHEAST HALF TO THIRD OF THE CWA.

DESPITE LONG DURATION SNOWS...HAZARD POSED BY THIS STORM IS LIKELY
TO BE MAGNIFIED BY STRENGTHENING PRESSURE GRADIENT SUNDAY MORNING
INTO SUNDAY NIGHT. DURING THIS TIMEFRAME...SNOW WILL BE
INCREASINGLY FLUFFY...SO BLOWING SNOW DUE TO NORTHEAST WIND GUSTS
OF 30-35 MPH COULD COMBINE WITH FALLING SNOW TO RESULT IN NEAR
BLIZZARD CONDITIONS IN OPEN AREAS AND ON THE IMMEDIATE LAKEFRONT.
CONVERGENT LAKE BAND COULD ALSO RESULT IN EVEN SLIGHTLY STRONGER
WINDS ON THE LAKE FRONT SUNDAY NIGHT INTO EARLY MONDAY
MORNING...KEEPING THE THREAT OF SIGNIFICANTLY REDUCED VISIBILITY
GOING THERE.

OVERALL...HAVE HIGHEST CONFIDENCE IN GREATER THAN 8 INCH SNOW
AMOUNTS IN 24 HOURS ROUGHLY ALONG/SOUTHEAST OF A LINE FROM
WINTHROP HARBOR TO DIXON. NORTHWEST OF THAT LINE...INCLUDING THE
ROCKFORD METRO...POTENTIAL EXISTS FOR GREATER THAN 6 INCHES...BUT
BLOWING/DRIFTING SNOW IS LIKELY TO CAUSE SIGNIFICANT TRAVEL
IMPACTS ON SUNDAY AS PEOPLE HEAD TO GATHERINGS FOR THE BIG GAME.

RC/KJB

&&

.SHORT TERM...
1128 AM CST

TONIGHT THROUGH SATURDAY...

WITH HIGH PRESSURE OVERHEAD...MINIMAL CLOUD COVER COVERS MUCH OF
THE REGION THIS AFTERNOON. THE EXCEPTION BEING NORTHWEST
INDIANA...WHICH REMAINS UNDER LAKE EFFECT CLOUDS AND FLURRIES.
TEMPERATURES HAVE SLOWLY WARMED INTO THE MID/UPR 20S...WITH A FEW
LOCATIONS SOUTH OF PONTIAC/WATSEKA POSSIBLY TOUCHING 30 DEGREES
LATER THIS AFTERNOON.

SFC RIDGE WILL STEADILY SLIDE EAST OVERNIGHT...WITH LIGHT LLVL FLOW
TURNING WESTERLY TO SOUTHWESTERLY. MINIMAL CLOUD COVER OVERNIGHT
SHOULD ALLOW TEMPS TO STEADILY RADIATE INTO THE MID/UPR TEENS.

SATURDAY...
MAIN FOCUS WILL BE ON TIMING OF MOISTURE RETURNING ALONG WITH THE
DEVELOPING WINTER STORM. FORTUNATELY IT APPEARS THE TIMING WILL BE
AFTER THE SATURDAY PERIOD. LLVL FLOW WILL REMAIN
SOUTHWESTERLY...WITH STEADY SATURATION FROM ALOFT TO THE SFC.
THERMAL TEMPS ALOFT WILL RISE TO ARND 0DEG C BY MIDDAY...BUT AS
MOISTURE ARRIVES ALOFT...EXPECT TEMPS TO SLOWLY COOL. SOUNDINGS
STILL ADVERTISE SOME DRY AIR IN THE MID LEVELS. TEMPS COULD WARM
INTO THE LOW/MID 30S...POSSIBLY BRIEFLY TOUCHING 40 DEGREES IN THE
FAR SOUTHERN CWFA BEFORE CLOUDS THICKEN WITH MOISTURE ARRIVAL.

BEACHLER

&&

.LONG TERM...
313 AM CST

SATURDAY THROUGH THURSDAY...

ALL EYES IN THE LONG TERM ARE ON THE COMPLEX WEEKEND STORM SYSTEM
WHICH LOOKS LIKELY TO BRING SHOVEL-ABLE SNOWFALL TO THE CWA SATURDAY
NIGHT AND SUNDAY. MAIN SHORTWAVE ENERGY RESPONSIBLE FOR THE
DEVELOPING STORM SYSTEM THIS WEEKEND IS RELATIVELY COMPACT SHORTWAVE
ABOUT 700 MILES WEST OF THE BRITISH COLUMBIA COAST. THIS SHORTWAVE
IS FORECAST TO MOVE ONSHORE THIS EVENING AND THEN DIVE SOUTHEAST
INTO THE NORTHERN ROCKIES AND HIGH PLAINS BY SATURDAY
EVENING...WHILE WHILE PHASING WITH SHORTWAVE ENERGY CURRENTLY OVER
INTERIOR ALASKA.

THE TRACK OF THESE SHORTWAVES WILL LIKELY BE AFFECTED BY A VIGOROUS
SHORTWAVE PIVOTING AROUND THE HUDSON BAY LOW AND A LARGE CLOSED LOW
DEVELOPING OVER THE SOUTHWEST CONUS AND DROPPING SOUTH INTO NORTHERN
OLD MEXICO. THE COMPLEXITY OF THIS PATTERN LENDS ITSELF TO HIGHER
THAN AVERAGE UNCERTAINTY WITH RESPECT TO THE EVENTUAL EVOLUTION OF
THE WEEKEND SYSTEM...ITS INTENSITY...QPF AMOUNTS...AND PLACEMENT OF
THE HEAVIEST QPF AND SNOWFALL. GIVEN THE NUMBER OF PLAYERS INVOLVED
AND THE FACT THE PRIMARY SHORTWAVE IS STILL OFFSHORE IT IS QUITE
PLAUSIBLE THAT THERE COULD BE ADDITIONAL LARGE SWINGS IN THE
FORECAST MODELS` PREDICTED TRACK/INTENSITY OF THIS SYSTEM...MUCH
LIKE WHAT WAS SEEN IN THE PAST FEW DAYS WITH THE MAIN STORY 24 HOURS
AGO BEING THE BIG SOUTHWARD TRENDS IN THE SOLUTIONS...FOLLOWED BY A
FORECAST TRACK SHIFT OF NEARLY 200 MILES FARTHER NORTH IN THE 00Z
ECMWF TONIGHT VS ITS RUN 24 HOURS AGO.

OK...ENOUGH ABOUT THE UNCERTAINTIES AND ON TO THE CURRENT
EXPECTATIONS OF THE SYSTEM. AS SHORTWAVE DROPS SOUTHEAST INTO THE
NORTHERN ROCKIES LOOK FOR A COLORADO LOW TO DEVELOP SATURDAY...THEN
TRACK EASTWARD ACROSS SOUTHERN ILLINOIS SUNDAY AFTERNOON AND
EVENTUALLY EAST TO THE MID ATLANTIC REGION BY MONDAY MORNING. THE
STRONG SHORTWAVE PIVOTING AROUND THE HUDSON BAY VORTEX AND ITS
ASSOCIATED SURFACE LOW ARE STILL PROGGED TO DRIVE A COLD FRONT SOUTH
ACROSS THE CWA SATURDAY WITH THE FRONT EVENTUALLY STALLING OUT TO
OUT SOUTH SATURDAY NIGHT AND SETTING THE STAGE FOR WHAT LOOKS TO BE
A LONG DURATION WAA SNOW EVENT. LOOKING AT THE 280-295K ISENTROPIC
SURFACES MODELS HAVE UPGLIDE STARTING SAT EVENING AND CONTINUING
THROUGH SUNDAY MORNING WITH WEAK/BROAD DEFORMATION BAND LIKELY TO
KEEP SNOWS GOING THROUGH MUCH OF THE DAY SUNDAY.

LOW/MID LEVEL PARCELS OVER THE AREA SAT NIGHT/SUNDAY MORNING ARE
PROGGED TO HAVE ORIGINATED FROM THE WESTERN GULF...SO THIS SYSTEM
WILL HAVE ACCESS TO MUCH MORE MOISTURE THAN MOST OF OUR SYSTEMS HAVE
HAD THIS WINTER...THOUGH IT STILL WILL BE FEEDING OFF A RECYCLED
CONTINENTAL POLAR AIRMASS FOLLOWING TODAY`S FROPA IN THE GULF.
STRONGEST ASCENT/HEAVIEST SNOWFALL IN THIS EVENING`S RUNS LOOKS TO
BE CENTERED ON SAT NIGHT AND OVER OUR SOUTHERN CWA. CURRENT RUN`S
THERMODYNAMICS FORECAST MOISTURE/OMEGA REALLY POINT TOWARD
SNOW:LIQUID RATIOS NEAR CLIMO (10-12:1) FOR THE MAJORITY OF THE
EVENT WHICH GIVEN LATEST MODEL CONSENSUS/WPC QPF FORECAST WOULD
SUGGEST WIDESPREAD 3-6" AMOUNTS ACROSS THE CWA WITH LOCALLY HEAVIER
AMOUNTS TO NEAR 8 INCHES IN OUR SOUTHERN CWA. GIVEN THE LONG
DURATION OF THE EVENT...WARNING CRITERIA IS 8 INCHES IN 24 HOURS
WHICH IS POSSIBLE BUT GIVEN ALL THE UNCERTAINTIES CONFIDENCE IS NOT
HIGH IN IF AND WHERE THIS WOULD OCCUR SO NO WATCH IS PLANNED AT THIS
TIME.

AS ARCTIC AIR SPREADS SOUTHWARD ON THE BACK SIDE OF THE SYSTEM
SUNDAY AFTERNOON AND SUNDAY NIGHT THERE COULD BE SOME LAKE ENHANCED
SNOW THAT COULD TRANSITION TO PURE LAKE EFFECT SNOW SHOWERS SUNDAY
NIGHT. FORECAST SOUNDINGS DO SHOW MODERATELY STRONG LOW LEVEL
INSTABILITY BELOW THE FRONTAL INVERSION...BUT INVERSION HEIGHTS ARE
FORECAST TO ONLY BE AROUND 5-6KFT SO LAKE EFFECT CONVECTION WOULD BE
SHALLOW. CURRENT FORECAST THERMODYNAMICS AND FORECAST OF VERY DRY
AIR ATOP A SOLID INVERSION...IT REALLY DOESNT LOOK TO FAVOR LAKE
EFFECT BEING A BIG PLAYER IN SNOWFALL TOTALS. CAN`T RULE OUT A BIT
OF ENHANCEMENT TO THE SNOWFALL OVER NORTHEAST ILLINOIS SUN AFTERNOON
AND NIGHT...BUT GIVEN THE CURRENT MODEL RUNS THE CONTRIBUTION TO
TOTALS FROM THE LAKE LOOK TO BE TRIVIAL COMPARED TO THE SYNOPTIC
SNOWS.

PATTERN LOOKS TO REMAIN VERY PROGRESSIVE IN THE WAKE OF THE
SYSTEM...SO ARCTIC AIR WILL NOT HAVE TIME TO GET WELL ENTRENCHED
BEFORE WARM AIR ADVECTION DEVELOPS LATER MONDAY IN ADVANCE OF THE
NEXT CLIPPER WHICH THIS EVENING`S RUN HAVE TRACKING ACROSS WISCONSIN
KEEPING US IN THE RELATIVELY DRY WARM SECTOR TUESDAY. ANOTHER SURGE
OF ARCTIC IS PROGGED TO ARRIVE TOWARD MIDWEEK WITH SOME SNOW
POSSIBLY ACCOMPANYING IT. WHILE IT LOOKS TO BE VERY COLD
MIDWEEK...GFS AND ECMWF BEYOND DAY 7 SUGGEST THE PATTERN WILL REMAIN
PROGRESSIVE WITH ARCTIC AIR NOT STICKING AROUND WITH LONG WAVE
TROUGH MIGRATING EAST OUT OF THE AREA.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* NO CONCERNS THROUGH DAYBREAK SATURDAY.

* WINDS REMAIN LIGHT...SLOWLY TURNING WEST/SOUTHWEST WITH SPEEDS
  AROUND 5-7KT.

BEACHLER

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

HIGH PRESSURE OVERHEAD WILL KEEP SKIES MOSTLY CLEAR THIS AFTERNOON
THROUGH THIS EVENING...WITH LIGHT NORTH WINDS ARND 4-6KT. HIGH
PRESSURE WILL STEADILY SHIFT SOUTHEAST...ALLOWING WINDS TO SLOWLY
TURN WEST TO SOUTHWEST BY DAYBREAK SATURDAY. VFR CONDS WILL
PREVAIL THROUGH AT LEAST SATURDAY AFTERNOON. THEN A DEVELOPING
WINTER STORM IS EXPECTED TO SLOWLY LIFT NORTHEAST TOWARDS NORTHERN
IL/NORTHWEST IN SATURDAY NIGHT. THIS WILL BRING A QUICK INCREASE
OF CLOUDS AND MVFR TO POSSIBLY IFR CONDS BY SATURDAY NIGHT. LIGHT
SNOW WILL ALSO DEVELOP...AND MAY BECOME MORE STEADY LATE SATURDAY
NIGHT.

BEACHLER


//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE IN ALL ELEMENTS THROUGH 18Z SATURDAY.

* MEDIUM CONFIDENCE IN TIMING OF MVFR AFTER 22Z SATURDAY.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z...

SATURDAY NIGHT...SNOW. IFR CIGS/VIS LIKELY.

SUNDAY...SNOW THROUGH THE DAY...TAPERING OFF OVERNIGHT. MVFR
CIGS/VIS LIKELY. PERIODS IFR CONDITIONS POSSIBLE.

MONDAY...VFR/WX NIL EARLY. SLIGHT CHANCE SNOW OVERNIGHT. MVFR
CIGS/VIS LIKELY.

TUESDAY AND WEDNESDAY...CHANCE OF SNOW. PERIODS OF MVFR CIGS/VIS
LIKELY.

THURSDAY...VFR/WX NIL.

KREIN

&&

.MARINE...
230 AM CST

A PROGRESSIVE...ACTIVE PATTERN WILL CONTINUE FOR LAKE MICHIGAN FOR
THE NEXT SEVERAL DAYS. WINDS ARE SLOWLY DIMINISHING OVER THE LAKE
AND WILL LET THE GALE AND HEAVY FREEZING SPRAY WARNINGS EXPIRE AT
300 AM. HOWEVER...WITH LAKE MICHIGAN STILL UNDER A RELATIVELY
STRONG PRESSURE GRADIENT...A SMALL CRAFT ADVISORY WILL BE ISSUED
FOR BOTH THE ILLINOIS NEARSHORE WATERS AS WINDS ARE STILL ARND 30
KT EARLY THIS MORNING...BUT SHOULD DROP OFF TO 10-15KT BY MID DAY.
RESIDUAL WAVE ACTION FROM THE PERSISTENT NORTHERLY WINDS SHOULD
KEEP WAVES ABOVE 4 FT THROUGH THIS AFTERNOON. AS THE AXIS OF HIGH
PRESSURE MOVES ACROSS THE LAKE THIS EVENING A BRIEF PERIOD OF
RELATIVELY MILD CONDITONS WILL SET UP...BUT THE HIGH WILL QUICKLY
SETTLE INTO THE OHIO VALLEY TONIGHT AS LOW PRESSURE TRACKS ACROSS
THE UPPER GREAT LAKES REGION. THIS SYSTEM WILL DRAG A COLD FRONT
ACROSS THE LAKE SATURDAY. FOLLOWING THE PASSAGE OF THE COLD
FRONT...STRONG HIGH PRESSURE WILL BUILD ACROSS THE CNTRL PLAINS
AND UPPER GREAT LAKES SATUDAY NIGHT AND SUNDAY WHILE LOW PRESSURE
DEVELOPS OVER THE LOWER OHIO VALLEY SUNDAY AFTERNOON. AN EXTENDED
PERIOD OF NELY WINDS OF 25-30 KT WILL BEGIN FOLLOWING THE FRONTAL
PASSAGE AND PERSIST INTO EARLY NEXT WEEK.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ003-ILZ004-ILZ008-ILZ010-ILZ011-ILZ019-
     ILZ020-ILZ021-ILZ032-ILZ039...6 PM SATURDAY TO MIDNIGHT
     MONDAY.

     WINTER STORM WATCH...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014-ILZ022-
     ILZ023-ILZ033...9 PM SATURDAY TO 6 AM MONDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...9 PM
     SATURDAY TO 6 AM MONDAY.

LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 PM FRIDAY.

&&

$$

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