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 270825
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
225 AM CST FRI FEB 27 2015

.UPDATE...
827 PM CST

LAKE EFFECT SNOW IS STARTING TO WIND DOWN AS DRIER AIR MASS
ADVECTS INTO THE AREA ALLOWING FOR A WEAKENING OF THE BROKEN LES
BAND THAT HAD PERSISTED ALL DAY. AS PROGRESSIVELY DRIER AIR
CONTINUED TO FILTER IN TONIGHT AND EVENTUALLY ONSHORE COMPONENT TO
FLOW WEAKENS WOULD ANTICIPATE LES TO END IN PORTER COUNTY LATER
THIS EVENING OR JUST PAST MIDNIGHT. GIVEN EXPECTATIONS AND RECENT
RADAR TRENDS MAY SHORTEN THE DURATION OF THE LAKE EFFECT SNOW
WARNING IN THE NEXT HOUR OR TWO IF NOT CANCEL IT OUTRIGHT.

ELSEWHERE CLOUDINESS OVER SOUTHERN PORTIONS OF THE CWA IS LIKELY
TO SLOWLY DISSIPATE AND MOVE OUT LEAVING SKIES FAIRLY CLEAR ACROSS
THE AREA. CENTER OF THE HIGH PRESSURE IS STILL HUNDREDS OF MILE TO
OUR NORTHWEST BUT WITH FRESH SNOW PACK WOULD EXPECT GRADIENT TO BE
WEAK ENOUGH FOR WINDS TO FURTHER DECOUPLE OVERNIGHT...ESPECIALLY
WITH HIGH GROWING CLOSER IN TIME. SUSPECT THAT THE WIND CHILL
ADVISORY WILL BE HARD PRESSED TO VERIFY MOST AREAS WITH THE
TYPICALLY COLDER VALLEYS LIKELY SEEING WINDS GO CALM...LIKELY KRPJ
AND KFRD ALREADY HAVE OR WINDS TO STAY UP ENOUGH TO KEEP TEMPS
FROM TANKING. THE TOOTHPASTE IS OUT OF THE PROVERBIAL TUBE SO NOT
PLANNING ANY CHANGES TO THE WIND CHILL ADVISORY SINCE A FEW
LOCATIONS COULD TAG ADVISORY FOR AN HOUR OR TWO AND IT WILL BE
VERY COLD.

IZZI

&&

.SHORT TERM...

THROUGH SATURDAY...

243 PM...LAKE EFFECT IS NOW ORGANIZING INTO A SINGLE BAND AS
WINDS TURN MORE NORTHWEST ACROSS NORTHEAST IL AND THIS BAND IS
SHIFTING TO THE SOUTHEAST AND WILL BE OUT OF COOK COUNTY IN THE
NEXT HOUR OR SO. WILL BE EXPIRING LAKE COUNTY IL FROM THE WARNING
AND FOR NOW WILL LET COOK COUNTY RIDE UNTIL 6 PM...BUT IF CURRENT
TRENDS CONTINUE...IT PROBABLY WILL BE CANCELED EARLY.

HI RES GUIDANCE IS IN REASONABLE AGREEMENT THAT THE LAKE EFFECT
BAND WILL SHIFT INTO PORTER COUNTY BY EARLY/MID EVENING...SO
EXPECTED AMOUNTS IN NORTHERN LAKE COUNTY INDIANA ARE A BIT
UNCERTAIN BUT WITH RATES OF 1-2 INCHES PER HOUR IN THE BAND...ITS
POSSIBLE SOME ISOLATED AMOUNTS OF 3 TO 6 INCHES WILL BE POSSIBLE.
MORE CONFIDENCE WITH AMOUNTS INTO NORTHERN PORTER COUNTY AS THE
BAND REMAINS THERE FROM MID EVENING THROUGH THE OVERNIGHT HOURS
WITH LOCALLY 4 TO 7 INCHES...PERHAPS MOSTLY NEAR THE LAKE. THE
BAND THEN BEGINS TO SHIFT OUT OF THE LAKE TOWARD MORNING. SO NOT
PLANNING ANY CHANGES TO THE WARNING END TIME FOR EITHER LAKE OR
PORTER COUNTIES...THOUGH CONFIDENCE REGARDING WHEN EXACTLY PRECIP
ENDS IS A BIT UNCERTAIN.

HIGH PRESSURE BUILDS ACROSS THE MIDWEST TONIGHT AND THEN MOVES
ACROSS THE AREA ON FRIDAY. WINDS WILL SLOWLY DIMINISH OVERNIGHT
BUT LIKELY REMAIN IN THE 5-10 MPH. THIS COMBINED WITH TEMPS
DROPPING WELL BELOW ZERO AWAY FROM CHICAGO WILL RESULT IN WINDS
CHILLS 20 BELOW TO 25 BELOW ZERO ACROSS THE NORTHERN CWA AND INTO
THE 15 BELOW RANGE SOUTH OF I-80. VALUES ARE BIT MARGINAL INTO
CHICAGO AND ALONG THE I-80 CORRIDOR BUT PLAN TO ISSUE A WIND
CHILL ADVISORY OVERNIGHT INTO FRIDAY MORNING GENERALLY ALONG AND
NORTH OF I-80 IN ILLINOIS.

DESPITE THE LIGHT WINDS AND SUNNY SKIES ON FRIDAY AS THE HIGH
SLOWLY MOVES ACROSS THE AREA...THE AIRMASS WILL REMAIN VERY COLD
WITH HIGHS ONLY REACHING THE MID TO PERHAPS UPPER TEENS. TEMPS
WILL LIKELY TANK FRIDAY NIGHT AS THE HIGH SHIFTS EAST AND LIGHT
WINDS TURN SOUTHERLY. SATURDAY WILL BE DRY AND A BIT WARMER WITH
HIGHS IN THE LOWER/MID 20S WITH INCREASING CLOUDS IN THE
AFTERNOON. CMS

&&

.LONG TERM...

SATURDAY NIGHT THROUGH THURSDAY...

THE TIME FRAME WILL START OUT ACTIVE AS A PERIOD OF ACCUMULATING
SNOW IS APPEARING LIKELY SATURDAY NIGHT INTO SUNDAY. STEADILY
INCREASING UPPER LEVEL FLOW OUT AHEAD OF DIGGING TROUGH TO THE
NORTH WILL ALLOW SHORT WAVE ENERGY TO TRAVERSE THE REGION DURING
THIS PERIOD...WHILE ONGOING WAA PERSISTS. THIS SHOULD ALLOW SNOW
TO SPREAD NORTHEAST ACROSS THE CWA DURING THE EVENING HOURS WITH
SNOW LIKELY ACROSS MUCH OF THE CWA AFTER THE MIDNIGHT TIME
FRAME...THEN LIKELY CONTINUING INTO SUNDAY AFTERNOON. MOST
GUIDANCE IN AGREEMENT WITH OVERALL LARGE SCALE SETUP DURING THIS
TIME AND EVEN WITH THIS SNOW SPREADING OVER THE CWA.
HOWEVER...THERE DOES APPEAR TO BE SOME TIMING DIFFERENCES OF THE
ONSET AND TIMING OF BEST SNOWFALL. SO I DO FEEL IT WILL SNOW AND
HAVE LIKELY POPS OVER THE ENTIRE CWA LATE SATURDAY NIGHT INTO
SUNDAY MORNING...BUT DID NOT GO TO CATEGORICAL BASED ON THE
PREVIOUSLY MENTIONED UNCERTAINTIES. ONLY MINOR CHANGES MADE TO THE
CURRENT SNOW FORECAST WITH THE BEST FORCING AND HIGHEST SNOWFALL
TOTALS CURRENTLY EXPECTED TO BE SOUTH OF I80. WHILE MOST OF THE
CWA WILL LIKELY OBSERVE ACCUMULATING SNOWFALL...THE SOUTHERN CWA
COULD APPROACH ADVISORY TYPE SNOW. HOWEVER I WONDER IF MY CURRENT
TOTAL MIGHT BE A LITTLE TOO HIGH...ESPECIALLY WITH THE ANTICIPATED
DRIVING MECHANISMS OF THIS SNOW...BUT THE LONGER DURATION OF THIS
LIGHT TO AT TIME MODERATE SNOW COULD HELP FOR THE CURRENT FORECAST
TOTALS. SYSTEM SNOW WILL DEPART TO THE EAST LATE SUNDAY AND SUNDAY
EVENING...AS HIGH PRESSURE BUILDS ACROSS THE REGION.

EARLY NEXT WEEK APPEARS TO BEGIN QUIET...BUT WITH ACTIVE WEATHER
RETURNING THROUGH MIDWEEK. HIGHLY AMPLIFIED PATTERN WITH UPPER
LEVEL RIDGE OVER THE EASTERN US AND A DIGGING TROUGH OVER THE
WESTERN CONUS WILL BE IN PLACE ON TUESDAY...AS DEEPENING SURFACE
LOW APPROACHES THE CWA FROM THE SOUTHWEST. STRONG WARM AIR AND
MOIST ADVECTION IS ANTICIPATED MONDAY NIGHT AND ESPECIALLY
TUESDAY/TUESDAY NIGHT. THIS WILL NOT ONLY PROVIDE THE POTENTIAL
FOR INITIAL VARYING PRECIP TYPE BUT WITH ALSO STEADIER
RAINFALL...AS A BROAD AREA OF PRECIP IS EXPECTED TO ACCOMPANY THIS
SYSTEM. EC AND GFS SIMILAR WITH REGARDS TO WAA...BUT WITH THE GFS
NOT AS ROBUST WITH THE MOISTURE ADVECTION AS THE EC IS APPEARING
TO BE. IF THE EC WERE TO VERIFY...THEN SURFACE DEWPOINTS COULD
APPROACH 50 DEG AND 850MB DEWPOINTS APPROACHING 10-11C. THIS WILL
BE CONCERNING FOR POSSIBLE HYDRO ISSUES...ESPECIALLY WITH THE
ANTICIPATED SNOW THIS WEEKEND. THERMAL PROFILES SUPPORTIVE OF ALL
RAIN ON TUESDAY AND ALTHOUGH I HAVENT INCLUDED THUNDER IN THE
GRIDS AT THIS TIME...WILL NEED TO MONITOR THIS POTENTIAL AS
WELL...ESPECIALLY FOR THE SOUTHERN CWA.

RODRIGUEZ

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING DAILY RECORDS THROUGH THE END OF THE MONTH...INCLUDING
ONE ON FRIDAY IN ROCKFORD THAT WAS SET JUST LAST WINTER:

ROCKFORD...

FRIDAY FEB 27TH LOW MAXIMUM: 15 IN 2014
SATURDAY FEB 28TH LOW: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

FRIDAY FEB 27TH LOW: -6 IN 1897
SATURDAY FEB 28TH LOW: 0 IN 1884

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* NONE.

RATZER

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

HIGH PRESSURE CENTERED OVER THE MID-MISSOURI VALLEY EARLY THIS
MORNING WILL SPREAD SLOWLY EAST-SOUTHEAST ACROSS THE REGION
THROUGH TONIGHT. LIGHT NORTHWEST WINDS WILL BECOME WEST DURING THE
DAY AND SOUTHWEST TONIGHT...WITH SPEEDS GENERALLY LESS THAN 10 KT.
DRY ARCTIC AIR MASS WILL MAKE FOR MAINLY CLEAR SKIES THROUGH THE
PERIOD.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH FOR ALL ELEMENTS.

RATZER

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

SATURDAY...VFR THEN SNOW DEVELOPING SATURDAY NIGHT. IFR LIKELY.

SUNDAY...PERIODS OF ACCUMULATING SNOW ENDING BY LATE AFTERNOON.
IFR LIKELY.

MONDAY...VFR THEN CHANCE OF WINTRY MIX AND IFR MONDAY NIGHT.

TUESDAY...RAIN AND IFR LIKELY...POSSIBLY ENDING AS LIGHT SNOW
TUESDAY NIGHT. IFR

WEDNESDAY...MVFR POSSIBLE.

RC

&&

.MARINE...
219 AM CST

MAIN PERIOD OF CONCERN FOR GUSTY 20-30 KT WINDS LOOKS TO BE SUNDAY
NIGHT INTO EARLY MONDAY...AND POTENTIALLY AGAIN ON WEDNESDAY. MUCH
OF LAKE REMAINS ICE COVERED...WITH ONLY THE CENTRAL AND SOUTHERN
PORTIONS WELL AWAY FROM SHORE APPEARING OPEN IN RECENT SATELLITE
DATA.

HIGH PRESSURE CENTERED OVER THE MID-MISSOURI RIVER VALLEY WILL MOVE
EAST-SOUTHEAST ACROSS THE MIDWEST SOUTH OF THE LAKES THROUGH TONIGHT
AND TO THE MID-ATLANTIC REGION BY LATE SATURDAY. MEANWHILE...LOW
PRESSURE WILL MOVE ACROSS HUDSON BAY TODAY...WITH A DEEPER TROUGH
DEVELOPING NORTH OF THE LAKES SATURDAY. THIS WILL RESULT IN WINDS
BECOMING WESTERLY OVER LAKE MICHIGAN TODAY...INCREASING A BIT INTO
THE 20 KT RANGE TONIGHT AS THE GRADIENT TIGHTENS UP BETWEEN THE HIGH
PASSING SOUTH OF THE LAKES AND LOW PRESSURE FARTHER TO THE NORTH.
SATURDAY INTO SUNDAY...WINDS WILL SHIFT TO THE SOUTH-SOUTHWEST AS A
COLD FRONTAL TROUGH APPROACHES FROM THE NORTHWEST. THE FRONT WILL
PASS ACROSS THE LAKE SUNDAY WITH A SHIFT BACK TO THE WEST...BECOMING
NORTHWEST AND BECOMING GUSTY 25-30 KT SUNDAY NIGHT INTO MONDAY
MORNING AS HIGH PRESSURE MOVES IN FROM THE WEST AND BRIEFLY TIGHTENS
THE GRADIENT ONCE AGAIN. THE HIGH WILL MOVE ACROSS THE SOUTHERN
LAKES AND MIDWEST MONDAY WITH NORTHWEST WINDS QUICKLY DIMINISHING
AND EVENTUALLY BECOMING SOUTHEASTERLY MONDAY NIGHT AS THE HIGH
SLIDES OFF TO THE EAST.

MEDIUM-RANGE MODEL RUNS INDICATE LOW PRESSURE WILL MOVE NEAR
SOUTHERN LAKE MICHIGAN TUESDAY OR TUESDAY NIGHT. CURRENT INDICATIONS
ARE THAT SOUTHEAST WINDS WILL INCREASE TUESDAY INTO THE 20 KT RANGE
OR SO...BEFORE BRIEFLY DECREASING AND VEERING NORTH-NORTHWEST BY
EARLY WEDNESDAY AND INCREASING INTO THE 25-30 KT RANGE AS COLDER AIR
ONCE AGAIN SURGES IN.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WIND CHILL ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
     ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022
     UNTIL 9 AM FRIDAY.

IN...LAKE EFFECT SNOW WARNING...INZ002 UNTIL 6 AM FRIDAY.

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.