Area Forecast Discussion
Issued by NWS Chicago, IL

Home | Current Version | Previous Version | Text Only | 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 260919
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
419 AM CDT THU MAR 26 2015

.SHORT TERM...
219 AM CDT

THROUGH TONIGHT...
IR IMAGERY EARLY THIS MORNING DISPLAYS THE CHANNEL OF MOISTURE
POSITIONED ACROSS THE MID-MISSOURI VALLEY STRETCHING NORTHEAST
THROUGH LOWER MICHIGAN. REGIONAL RADAR MOSAIC ALSO SHOWS THE BULK
OF THE PRECIP OVER SOUTHERN IL/CENTRAL IN...WITH SOME SHOWERS
LINGERING ACROSS THE SOUTHERN FORECAST AREA INTO A PORTION OF
NORTHWEST INDIANA. DRY AIR WILL CONTINUE TO SLIDE SOUTHEAST ACROSS
THE REGION...WITH SOME THINNING IN THE CLOUDS LATER THIS MORNING.
GUIDANCE HAS BEEN INDICATING THAT ANY THINNING OF THE SOLAR SHIELD
WOULD BE BRIEF...AS WINDS WILL BE TURNING NORTHERLY LATER THIS
AFTERNOON ALLOWING LAKE MOISTURE TO DEVELOP AND ADVECT ACROSS
NORTHERN IL/NORTHWEST IN. MIXING WILL INCREASE LATER THIS
MORNING...WITH AN INCREASE IN THE LOW LEVEL GRADIENT...THIS SHOULD
ALLOW FOR SOME GUSTS BETWEEN 20 AND 25 MPH.

500MB TROUGH AXIS WILL ARRIVE THIS AFTN COUPLED WITH AN UNSEASONABLY
COOL THERMAL TROUGH IN THE LOW LEVELS. THE COMBINATION WILL LIKELY
LOCK SFC TEMPS THIS AFTN IN THE LOW/MID 40S...AND POSSIBLY IN THE
UPR 30S CLOSER TO LAKE MICHIGAN. WINDS WILL STEADILY TURN NORTHERLY
LATE THIS AFTN/EARLY EVENING...WITH THE LAKE SFC-850MB TEMP GRADIENT
INCREASING AS A RESULT OF THE ANOMALOUS THERMAL TROUGH ADVECTING
SOUTH ACROSS THE WESTERN GREAT LAKES. THIS WILL LIKELY ALLOW LAKE
MOISTURE TO INCREASE...WITH SOME LAKE INDUCATED RAIN SHOWERS
BECOMING MIXED WITH SNOW...THEN TRANSITIONING TO ALL SNOW LATE
TONIGHT. HI-RES LOCAL GUIDANCE HAS DONE A DECENT JOB DEPICTING THIS
FROM RECENT CYCLES. SOME LIGHT ACCUMS WILL BE POSSIBLE...HOWEVER
THIS WILL HINGE UPON WHEN PRECIP TRANSITIONS TO ALL SNOW. EXPECT ANY
ACCUMS TO BE LESS THAN 1 INCH AND MORE LIKELY LESS THAN 0.5...MAINLY
FOR AREAS ADJACENT TO LAKE MICHIGAN.

LAKE CLOUDS WILL LIKELY HELP TO KEEP SFC TEMPS A FEW DEGREES WARMER
IN THE LOW/MID 20S TONIGHT CLOSER TO LAKE MICHIGAN...WHILE LOCATIONS
ALONG AND WEST OF MENDOTA TO CRYSTAL LAKE WILL DIP TO AROUND 20 FOR
OVERNIGHT LOWS.

BEACHLER

&&

.LONG TERM...
331 AM CDT

FRIDAY THROUGH WEDNESDAY...

AN AMPLIFIED UPPER LEVEL FLOW PATTERN ACROSS NORTH AMERICA WILL ACT
TO DRIVE THE HEART OF AN UNSEASONABLY COLD AIRMASS SOUTHWARD ACROSS
THE GREAT LAKES REGION ON FRIDAY. THE COLD AIRMASS IS PROGGED TO
FEATURE NEAR -15 DEGREE CELSIUS TEMPERATURES AT 850 MB  AND -8 TO -
10 925 MB TEMPERATURES. THIS WILL LIKELY RESULT IN SURFACE
TEMPERATURES STRUGGLING TO GET INTO THE LOW TO MID 30S ACROSS MUCH
OF THE AREA. IN ADDITION TO THE COLD...SOME LINGERING LIGHT LAKE
EFFECT SNOW SHOWERS COULD LINGER INTO FRIDAY...ESPECIALLY ACROSS
NORTHWESTERN INDIANA.

A CANADIAN SURFACE RIDGE IS EXPECTED TO MOVE OVERHEAD BY SATURDAY
MORNING...AND THIS SHOULD ALLOW TEMPERATURES LATE FRIDAY NIGHT TO
DROP INTO THE TEENS IN MOST AREAS OUTSIDE OF CHICAGO. IN SPITE OF A
GOOD AMOUNT OF SUNSHINE ON SATURDAY...WITH THE SURFACE HIGH
OVERHEAD...HIGH TEMPERATURES WILL ONLY LIKELY BE ABLE TO CLIMB INTO
THE MID TO UPPER 30S IN MOST AREAS.

THE WEATHER PATTERN BEGINS TO CHANGE FOR THE SECOND HALF OF THE
WEEKEND AS A SIGNIFICANT NORTHERN PACIFIC WAVE IS FORECAST TO SHIFT
EASTWARD ONSHORE ACROSS THE PACIFIC NORTHWEST. THE SYSTEM IS
EXPECTED TO MOVE ATOP THE WESTERN CONUS RIDGE AND SHIFT OVER THE
GREAT LAKES REGION BY SUNDAY EVENING. SOME GUSTY SOUTHWEST WINDS AND
A PERIOD OF LIGHT RAIN IS POSSIBLY SUNDAY AS THIS SYSTEM IMPACTS THE
GREAT LAKES REGION.

WARMER CONDITIONS STILL LOOK TO RETURN TO THE REGION NEXT WEEK AS
THE STORM TRACK LOOKS TO FAVOR SYSTEMS TRACKING EASTWARD ACROSS THE
NORTHERN CONUS. IN FACT...WE COULD SEE TEMPERATURES BACK INTO THE
60S BY THE END OF THE FORECAST PERIOD.

KJB

&&

.AVIATION...

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

* MAINLY VFR CIGS THRU OVERNIGHT.

* NORTHWEST WINDS TURNING NORTH AND GUSTING TO 20KT BY MID-
  MORNING.

* POSSIBLE LAKE EFFECT RAIN/SNOW SHOWERS BECOMING ALL SNOW LATE
  THIS EVENING.

BEACHLER

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

IR IMAGERY EARLY THIS MORNING SHOWS THE BULK OF THE STRATUS CLOUDS
SOUTH OF THE TAF SITES...AND WITH THE FLOW TURNING NORTHWESTERLY
THIS SHOULD HELP TO KEEP THE STRATUS SOUTH OF THE TAF SITES
OVERNIGHT. WINDS WILL SLOWLY TURN NORTHERLY BY MID-MORNING WITH
GUSTS DEVELOPING TO 20KT. CLOUDS MAY BRIEFLY THIN FURTHER LATER
THIS MORNING...HOWEVER WITH COOLER AIR WORKING BACK INTO THE
REGION...STRATUS LAKE CLOUDS MAY DEVELOP AND ALSO PRODUCE SOME
LIGHT RAIN/SNOW LATE AFTN. TEMPS WILL COOL INTO THE LOW 30S LATER
THIS EVENING AND MAY TRANSITION THE PRECIP OVER TO ALL SNOW...WITH
ONLY MINOR REDUCTIONS. GIVEN THE CONFIDENCE IS LOW...WILL HOLD OFF
AT THIS TIME ON MENTIONING THIS WITHIN THE CURRENT TAF BUT WILL
MAINTAIN THE STRATUS CLOUDS AND POSSIBLE MVFR CIGS DEVELOPING.

BEACHLER

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

* HIGH CONFIDENCE IN WIND DIR/SPEED...MEDIUM CONFIDENCE IN
  DURATION OF GUSTS MID-MORNING THROUGH MID-AFTERNOON.

* HIGH CONFIDENCE IN CIGS REMAINING VFR THRU 20Z...MEDIUM
  CONFIDENCE IN MVFR CIGS DEVELOPING AFT 00Z WITH PRECIP.

* MEDIUM CONFIDENCE IN PRECIP TIMING.

BEACHLER

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

FRIDAY...VFR. BREEZY NORTH WINDS TURNING NORTHEAST THROUGH THE
AFTERNOON.

SATURDAY...VFR. LIGHT NORTHEAST WINDS TURNING SOUTHEAST.

SUNDAY...CHANCE RAIN THROUGH THE DAY...POSSIBLY MIXING WITH SNOW
EARLY. MVFR CIGS/VIS POSSIBLE. GUSTY SOUTHWEST WINDS.

MONDAY...VFR. WEST WINDS.

TUESDAY...VFR. SOUTHWEST WINDS.

MDB

&&

.MARINE...
352 AM CDT

A COLD FRONT WILL MOVE SOUTHWARD ACROSS LAKE MICHIGAN TODAY...
RESULTING IN INCREASING NORTHERLY FLOW DOWN THE LAKE. IT APPEARS
THAT NORTHERLY WINDS OF 30 KT WILL DEVELOP LATER THIS AFTERNOON IN
THE WAKE OF THIS FRONT AND CONTINUE THROUGH FRIDAY MORNING AS A
SURFACE RIDGE OF HIGH PRESSURE SHIFTS SOUTHEASTWARD FROM CANADA TO
THE UPPER MIDWEST. THESE STRONG NORTHERLY WINDS WILL LIKELY LEAD TO
LARGE WAVES AND HAZARDOUS CONDITIONS SUPPORTIVE OF A SMALL CRAFT
ADVISORY FOR THE ILLINOIS AND INDIANA NEAR SHORE WATERS
TONIGHT THROUGH FRIDAY NIGHT.

THE SURFACE HIGH WILL MOVE SOUTHEAST OF LAKE MICHIGAN BY SATURDAY
NIGHT AND SUNDAY AS ANOTHER POTENT SURFACE LOW TRACKS EASTWARD
ACROSS SOUTH CENTRAL CANADA. THESE TWO PRESSURE PATTERNS STILL LOOK
TO SET UP AN OPTIMAL SURFACE PRESSURE GRADIENT PATTERN TO SUPPORT A
PERIOD OF SOUTHERLY GALES OVER THE OPEN WATERS OF LAKE MICHIGAN ON
SUNDAY. THE POSSIBILITY EVEN EXISTS FOR SOME HIGHER END GALES OF 40
OR EVEN 45 KT WINDS FOR A SHORT PERIOD ON SUNDAY AS STRONG PRESSURE
FALLS OVERSPREAD EASTERN ONTARIO IN ADVANCE OF THE APPROACHING
SURFACE SYSTEM. A COLD FRONT WILL SWING OVER THE LAKE BY LATE
SUNDAY...RESULTING IN SWIFTING WINDS OUT OF THE WEST-NORTHWEST
SUNDAY NIGHT.

KJB

&&

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

$$

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.