Area Forecast Discussion
Issued by NWS Chicago, IL

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS63 KLOT 300828
AFDLOT

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

.SHORT TERM...
234 PM CST

THROUGH SATURDAY...

THE MAIN FOCUS DURING THIS PERIOD WILL BE WITH THE POTENTIAL FOR
SOME ACCUMULATING LAKE EFFECT SNOW ACROSS PORTIONS OF NORTHWESTERN
INDIANA TONIGHT INTO FRIDAY MORNING.

LOW PRESSURE NOW ACROSS THE EASTERN GREAT LAKES REGION...DROVE A
COLD FRONT ACROSS THE AREA THIS MORNING...AND HAS SINCE CONTINUED TO
PRODUCING GUSTY NORTHWEST WINDS ACROSS THE REGION THROUGH THE
AFTERNOON. WATER VAPOR IMAGERY THIS AFTERNOON INDICATES THE NEXT
SHORT WAVE DISTURBANCE NOW DIGGING SOUTHWARD OVER LAKE SUPERIOR.
THIS DISTURBANCE IS EXPECTED TO RACE SOUTHWARD ACROSS SOUTHERN LAKE
MICHIGAN THIS EVENING...AND AS IT DOES SO...IT COULD PRODUCE ENOUGH
LIFT TO SQUEEZE OUT A FEW FLURRIES...SO I HAVE ADDED THE MENTION TO
THE FORECAST THROUGH MUCH OF THE EVENING.

OTHERWISE...IT APPEARS THAT LAKE EFFECT SNOW SHOWERS WILL CONTINUE
TO DEVELOP OVER SOUTHERN LAKE MICHIGAN TONIGHT...AND AS THE BOUNDARY
LAYER FLOW OVER LAKE MICHIGAN BEGINS TO BACK NORTHERLY...IT APPEARS
THAT SOME BANDS OF LAKE EFFECT SNOW WILL BEGIN TO IMPACT PORTIONS OF
NORTHWESTERN INDIANA OVERNIGHT TONIGHT THROUGH FRIDAY MORNING. LAKE
INDUCED EQUILIBRIUM LEVELS ARE EXPECTED TO RESIDE AROUND 5,000
FEET...AND DUE TO THE COLD LOWER LEVEL ATMOSPHERE...THIS SHOULD BE
HIGH ENOUGH TO RESIDE WELL INTO THE DENDRITE GROWTH ZONE.
THEREFORE...SOME EFFICIENT SNOWFALL LOOKS TO RESULT IN SOME
ACCUMULATING POTENTIAL...ESPECIALLY ACROSS PORTIONS OF PORTER COUNTY
INDIANA IN MY AREA...WHERE SOME ISOLATED AREAS COULD GET A COUPLE
INCHES. THESE LAKE EFFECT SNOW SHOWERS WILL COME TO AN END BY EARLY
AFTERNOON AS THE FLOW BEGINS TO SHIFT WESTERLY IN RESPONSE TO A AN
AREA OF SURFACE HIGH SHIFTING SOUTHEASTWARD TOWARDS THE OHIO
VALLEY.

A BRIEF WARMING TREND LOOKS TO BE ON TAP LATE FRIDAY NIGHT AND
SATURDAY AS THIS HIGH SHIFTS OVER THE OHIO VALLEY...SETTING UP A
WEST SOUTHWESTERLY FLOW OF WARMER AIR OVER THE AREA. THIS SHOULD
ALLOW TEMPERATURES TO WARM WELL INTO THE 30S AREA-WIDE.

KJB

&&

.LONG TERM...
328 PM CST

SATURDAY NIGHT THROUGH THURSDAY...

THE MAIN FOCUS DURING THIS PERIOD WILL BE WITH THE INCREASING
POTENTIAL OF A DECENT ACCUMULATING SNOWFALL EVENT ACROSS AT LEAST
PORTIONS OF MY AREA SATURDAY EVENING THROUGH SUNDAY.

A COMPLEX WEATHER PATTERN WILL BE IN PLACE ACROSS THE CONUS DURING
THIS PERIOD. OVERALL...THE MAIN DISTURBANCE OF INTEREST IS NOW
EJECTING EAST-NORTHEASTWARD ACROSS THE NORTHEASTERN PACIFIC ALONG
THE EASTERN PERIPHERY OF AN UPPER LOW SOUTH OF THE ALEUTIANS. THIS
FEATURE WILL MOVING ONSHORE ACROSS THE BRITISH COLUMBIA COAST BY
FRIDAY MORNING...THEN IS EXPECTED TO DIG SOUTHEASTWARD ALONG THE
NORTHEASTERN PERIPHERY OF AN UPPER LEVEL RIDGE IN PLACE ACROSS THE
WESTERN CONUS. THE MAIN COMPLEXITIES WITH THIS SYSTEM...IS IF AND
HOW MUCH OF THE SOUTHERN STREAM ENERGY...EMANATING FROM THE
SOUTHWESTERN CONUS TROUGH...GETS TAPPED INTO BY THIS DIGGING SYSTEM.

MODEL GUIDANCE HAS FLIPPED FLOPPED A BIT OVER THE PAST COUPLE OF
RUNS ON HOW FAR NORTH THE ACCOMPANYING PRECIPITATION SHIELD WILL GET
SATURDAY NIGHT INTO SUNDAY. IT APPEARS ONE OF THE MAIN KEYS THAT
WILL PLAY A ROLE IN HOW FAR NORTH THE SNOWFALL ENDS UP GETTING
ACROSS ILLINOIS WILL BE THE TIMING OF COLDER AIRMASS/COLD FRONTAL
PASSAGE EXPECTED ON SATURDAY NIGHT. A MUCH COLDER AIRMASS IS
EXPECTED TO SPILL IN ACROSS THE NORTHERN CONUS AHEAD OF A STOUT 1044
MB HIGH BUILDING SOUTHWARD OUT OF SOUTHERN MANITOBA SATURDAY
NIGHT...AND THIS SHOULD SET UP A GOOD BAROCLINIC ZONE POTENTIALLY
RIGHT ACROSS THE HEART OF MY CWA SATURDAY NIGHT INTO SUNDAY. AT THE
SAME TIME...ISENTROPIC ASCENT AND MOISTURE TRANSPORT WILL RAMP UP TO
OUR SOUTHWEST IN ADVANCE OF THE APPROACHING DISTURBANCE. THIS SHOULD
RESULT IN A LARGE AREA OF SNOWFALL DEVELOPMENT IN THE COLD AIR ACROSS
MISSOURI AND WEST CENTRAL ILLINOIS BY SATURDAY AFTERNOON. IT APPEARS
THIS SNOWFALL WILL GRADUALLY DEVELOP NORTHWARD ACROSS ILLINOIS BY
SATURDAY EVENING...AND MAY END UP IMPACTING MOST OF MY AREA TO SOME
DEGREE OVERNIGHT SATURDAY AND INTO SUNDAY. IT APPEARS THAT A DECENT
BAND OF FRONTOGENESIS COULD SET UP SOMEWHERE NEAR THE I-80 CORRIDOR
INTO SUNDAY MORNING AS A DEFORMATION AXIS TRIES TO DEVELOP WITH THE
925-850 MB LAYER AHEAD OF THE APPROACHING COLD AIRMASS. THIS COULD
RESULT IN SOME AREAS OF HEAVIER SNOW. HOWEVER...CONFIDENCE ON WHERE
EXACTLY THIS ENHANCED MESOSCALE FORCING SETS UP IS LOW AT THIS
TIME...GIVEN THIS SYSTEM IS 60+ HOURS AWAY. IT DOES APPEAR THAT MOST
AREAS MAY SEE AT LEAST SOME LIGHT SNOW ACCUMULATIONS...BUT THE
POTENTIAL OF A FEW TO SEVERAL INCHES OF SNOW ACCUMULATION IS
CERTAINLY A POSSIBILITY.

THE OTHER FACTOR TO CONSIDER WITH THIS EVENT IS THE POTENTIAL FOR
LAKE ENHANCED SNOW SHOWERS LATER SUNDAY AND INTO SUNDAY NIGHT ACROSS
NORTHEASTERN ILLINOIS. AS THE COLDER AIRMASS BEGINS TO SPILL
SOUTHWARD OVER THE AREA ON SUNDAY...WINDS WILL BECOME NORTHEASTERLY
OFF OF LAKE MICHIGAN. THE COLDER AIRMASS...FEATURING 850 MB
TEMPERATURES IN THE TEENS BELOW ZERO CELSIUS...SHOULD ALSO PRODUCE
FAVORABLE THERMODYNAMICS IN THE LOWEST LEVELS OF THE ATMOSPHERE FOR
ENHANCED SNOW SHOWERS LATER SUNDAY AND SUNDAY NIGHT. MODEL SOUNDINGS
INDICATE INVERSION HEIGHTS REACHING UP AROUND 5-6,000 FEET...WHICH
SHOULD EXTEND WELL INTO THE DENDRITIC GROWTH ZONE. THEREFORE...WE CANT
RULE OUT THE POTENTIAL FOR SOME HEAVIER SNOW TOTALS ACROSS PORTIONS
OF NORTHEASTERN ILLINOIS. AT THIS TIME...I HAVE REMAINED A BIT
CONSERVATIVE ON SNOW AMOUNTS ACROSS NORTHERN ILLINOIS...MAINLY DUE
TO THE HIGH UNCERTAINTIES WITH THIS EVOLVING SYSTEM.

FOLLOWING THIS SYSTEM...IT APPEARS THE REGION WILL REMAIN IN AND
ACTIVE WEST/NORTHWESTERLY FLOW PATTERN. THIS COULD SUPPORT A FEW
ADDITIONAL CLIPPER TYPE SYSTEMS WITH SNOW CHANCES AND REINFORCING
SHOTS OF COLD AIR THROUGH THE EXTENDED PERIOD. OVERALL...IT APPEARS
THAT WE WILL REMAIN BELOW TO WELL BELOW AVERAGE FOR TEMPERATURES
NEXT WEEK. A PERIOD OF VERY COLD CONDITIONS COULD ALSO BE IN THE
WORKS FOR THE LATTER PART OF NEXT WEEK...WITH THE POSSIBILITIES OF A
SYSTEM DIGGING SOUTHWARD OVER THE AREA FROM THE HIGH LATITUDES OF
CANADA.

KJB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* GUSTY NORTHWEST WINDS THROUGH EARLY THIS MORNING BACKING TO
  SOUTHWEST THIS AFTERNOON.

KREIN

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

COLD AIR ADVECTION AND A WEAK UPPER DISTURBANCE WILL WORK IN
CONCERT TO PRODUCE SOME FLURRIES AND BRIEF LIGHT SNOW SHOWERS
OVERNIGHT...LIKELY ENDING PRIOR TO SUNRISE. HAVE SEEN A FEW BRIEF
VSBY REDUCTIONS IN THE SNOW SHOWERS IN SE WISCONSIN AND CERTAINLY
POSSIBLE THE SAME COULD OCCUR INTO OUR TERMINALS...THOUGH ANY
VSBY RESTRICTIONS WILL LIKELY BE SHORT LIVED. LOWER END VFR CIGS
SHOULD SCATTER OUT AT SOME POINT FRIDAY MORNING AND NOT
ANTICIPATING ANY MVFR CIGS THROUGH THE PERIOD. NORTHWEST WINDS
WILL GRADUALLY EASE THROUGH THE MORNING HOURS BEFORE GRADUALLY
BACK TO SOUTHWEST FRIDAY AFTERNOON INTO EARLY EVENING BUT WITH
VERY LIGHT SPEEDS.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* MEDIUM TO HIGH CONFIDENCE WIND TRENDS.

* MEDIUM CONFIDENCE IN CLOUD COVER TRENDS.

* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS

KREIN

//OUTLOOK FOR ORD/MDW FOR 12Z SATURDAY-12Z THURSDAY...UPDATED 00Z...

SATURDAY...CHANCE OF SNOW AND IFR DURING THE NIGHT. WEST WINDS.
SUNDAY...CHANCE OF SNOW AND IFR. AT LEAST MVFR CIGS LIKELY.
         NORTHEAST WINDS.
MONDAY NIGHT-WEDNESDAY...CHANCES OF MAINLY LIGHT SNOW. WEST WINDS.

MDB

&&

.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...NONE.
IN...NONE.
LM...GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
     LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-LMZ872-
     LMZ874-LMZ876-LMZ878 UNTIL 3 AM FRIDAY.

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

     HEAVY FREEZING SPRAY WARNING...LMZ261-LMZ362-LMZ364-LMZ366-
     LMZ563-LMZ565-LMZ567-LMZ868 UNTIL 3 AM FRIDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.