Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 252100
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
300 PM CST WED FEB 25 2015

.SHORT TERM...

THROUGH THURSDAY NIGHT...

300 PM...FORECAST CONCERNS/CHALLENGES ARE SNOWFALL AMOUNTS THRU
THURSDAY MORNING AND LAKE EFFECT POTENTIAL/AMOUNTS OVERNIGHT THRU
THURSDAY EVENING.

SNOW CONTINUES TO OVERSPREAD NORTHWEST IL REDUCING VISIBILITIES TO
UNDER A MILE AT TIMES AND THIS WILL CONTINUE MOVING EAST/SOUTHEAST
ACROSS THE REST OF THE AREA DURING THE MID/LATE AFTERNOON. WITH
TIME...THE BEST FORCING SAGS SOUTH ACROSS THE SOUTHERN CWA INTO
CENTRAL IL THIS EVENING THUS EXPECT AMOUNTS TO BE HEAVIEST ACROSS
THE SOUTHWEST CWA WHERE STORM TOTAL 2-4 INCHES ARE POSSIBLE...
WITH LESSER AMOUNTS TO THE NORTH...IN THE 1-3 INCH RANGE. CHANGES
TO THIS EVENING WERE TO INCREASE TO CAT POPS AND ALSO BUMP UP QPF
AMOUNTS SOME...GENERALLY IN THE ONE TO TWO TENTHS RANGE. THE NET
AFFECT OF THIS IS THAT STORM TOTAL AMOUNTS ARE NOW ON THE HIGHER
END OF THE ABOVE RANGES. ITS POSSIBLE SOME AREAS IN THE SOUTHWEST
CWA MAY REACH 4 INCHES...BUT CONFIDENCE IS LOW ENOUGH TO HOLD OFF
ON ANY ADVISORIES FOR THOSE SOUTHWEST COUNTIES WITH AN SPS
CURRENTLY OUT HIGHLIGHTING THESE HIGHER AMOUNTS.

WHILE THE BULK OF THE ACCUMULATING SNOW WILL LIKELY FALL THIS
EVENING...THERE WILL LIKELY REMAIN VERY LIGHT SNOW/FLURRIES THRU
MUCH OF THE NIGHT INTO THURSDAY MORNING...AS IT FINALLY ENDS FROM
THE NORTHWEST MIDDAY/EARLY THURSDAY AFTERNOON.

HOWEVER...NORTHEAST WINDS HAVE ALREADY ALLOWED SOME LAKE EFFECT
SNOW TO DEVELOP ACROSS SOUTHEAST WI AND THIS NORTHEAST FLOW WILL
FIRST ADD SOME LAKE ENHANCEMENT THIS EVENING AND THEN TRANSITION
TO LAKE EFFECT SNOW SHOWERS OVERNIGHT INTO THURSDAY MORNING.
THERMAL PROFILES SHOW A FAIRLY GOOD SET UP FOR LAKE EFFECT AND
HIGH RES GUIDANCE WOULD SUGGEST A POSSIBLE LAKE EFFECT PLUME
AFFECTING LAKE COUNTY IL OVERNIGHT...THEN EASTERN COOK COUNTY
THURSDAY MORNING AS IT SHIFTS INTO NORTHWEST INDIANA. BUT
CONFIDENCE REGARDING DURATION AND LOCATION IS FAIRLY LOW. AREAS
NEAR THE LAKE MAY END UP WITH AN ADDITIONAL 1-2 INCHES OF LAKE
EFFECT OVERNIGHT INTO THURSDAY MORNING. AS THE BAND SHIFTS INTO
NORTHWEST INDIANA THURSDAY AFTERNOON...DECENT CONVERGENCE SETS UP
BY THURSDAY EVENING SO SOME CONCERN THAT IF A BAND CAN PERSIST FOR
ANY LENGTH OF TIME...ADDITIONAL ACCUMULATION WOULD POSSIBLE...
MAINLY EAST OF GARY.

AFTER TEMPERATURES REACHED THE LOWER/MID 20S NORTH TO NEAR 30
SOUTH TODAY...THEY WILL FALL THROUGH THE TEENS THIS EVENING AND
POSSIBLY REMAIN STEADY IN THE LOWER/MID TEENS ACROSS THE SOUTH AND
NEAR THE LAKE OVERNIGHT...FALLING INTO THE SINGLE DIGITS ACROSS
THE NORTHWEST CWA BY MORNING. BUT NOT MUCH RECOVERY IS EXPECTED
FOR THURSDAY HIGHS...HANGING OUT MAINLY IN THE TEENS.

HIGH PRESSURE WILL THEN APPROACH THE REGION THURSDAY NIGHT INTO
FRIDAY MORNING WITH CLEARING SKIES AND DIMINISHING WINDS. THIS
WILL ALLOW TEMPS TO DROP WELL BELOW ZERO...PERHAPS 10 BELOW IN THE
OUTLYING COLD SPOTS. AND DESPITE THE LIGHTER WINDS...WIND CHILLS
COULD DIP TO ADVISORY LEVELS AS COLD AS 25 BELOW FRIDAY MORNING.
CMS

&&

.LONG TERM...

FRIDAY THROUGH WEDNESDAY...

300 PM...FORECAST CONCERNS INCLUDE POTENTIAL ACCUMULATING SNOW
SATURDAY NIGHT INTO SUNDAY...THEN ANOTHER SNOW OR MIXED PRECIP
EVENT TUESDAY/TUESDAY NIGHT.

HIGH PRESSURE WILL MOVE ACROSS THE REGION FRIDAY INTO FRIDAY
NIGHT KEEPING VERY COLD AIR IN PLACE. HIGHS ON FRIDAY WILL LIKELY
STRUGGLE TO REACH THE LOWER/MID TEENS AND THEN WITH LIGHT WINDS
AND CLEAR SKIES...LOWS SHOULD TANK AGAIN FRIDAY NIGHT AND LIKELY
GO BELOW ZERO AGAIN.

BROAD WARM AIR ADVECTION THEN SPREADS ACROSS THE REGION SATURDAY
NIGHT INTO SUNDAY AND THIS HAS BEEN A FAIRLY CONSISTENT FEATURE
FOR SEVERAL RUNS NOW...THOUGH STRENGTH/THERMAL PROFILES HAVE
VARIED. CURRENTLY APPEARS THE BULK OF THIS PRECIP/EVENT WILL BE
ALL SNOW. WITH QPF AMOUNTS RANGING BETWEEN A QUARTER TO A HALF
INCH...LOOKS LIKE THERE COULD BE A BAND OF SEVERAL INCHES OF SNOW
WITH THIS SYSTEM BY SUNDAY EVENING...BUT STILL SEVERAL DAYS AWAY
SO A BIT EARLY FOR SPECIFIC AMOUNTS/LOCATIONS. BUT DID BUMP POPS
UP TO LIKELY.

HIGH PRESSURE MOVES ACROSS THE REGION MONDAY AND THEN ANOTHER
SIMILAR SYSTEM ARRIVES FOR TUESDAY WITH A SURFACE LOW DEVELOPING
OVER THE OHIO VALLEY TUESDAY NIGHT. THIS SYSTEM SEEMS TO HAVE A
BIT WARMER AIR WITH IT...OR THE POTENTIAL TO HAVE SOME WARMER AIR
INTO THE CWA. HOWEVER...SOUNDINGS/THERMAL PROFILES SUGGEST THE
BULK OF THIS PRECIP WILL ALSO BE SNOW. MAINTAINED A MIX OF RAIN
AND SNOW SOUTH OF I-80 BUT CONFIDENCE IS FAIRLY LOW FROM THIS
DISTANCE. CMS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING RECORDS LATER THIS WEEK...INCLUDING ONE IN ROCKFORD SET
JUST LAST WINTER:

ROCKFORD...

THURSDAY FEB 26TH LOW MAXIMUM: 11 IN 1920
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 20Z...

* SNOW DEVELOPING OVER THE AREA BY LATE AFTERNOON AND CONTINUING
  THROUGH THURSDAY MORNING. IFR VSBY LIKELY WITH MVFR CIGS.
  PERIODS OF LIFR VIS POSSIBLE THIS EVENING.

KJB

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

SNOW WILL BEGIN TO OVERSPREAD KRFD WITHIN THE NEXT COUPLE
HOURS...THEN OVER THE EASTERN TERMINALS BY LATE AFTERNOON (~22 UTC).
I HAVE MOVED UP THE TIMING OF ONSET ABOUT AN HOUR AND A HALF TO 2
HOURS AT MOST PLACES BASED ON THE PROGRESSION OF THE SNOW TO THE
WEST. SOME OF THE LATEST AMDAR SOUNDINGS OUT OF KMDW STILL INDICATE
A CORRIDOR OF DRY AIR FROM AROUND 5-7,000 FEET AGL. HOWEVER...IT
APPEARS THAT THIS DRY AIR WILL QUICKLY MOISTEN OVER THE NEXT FEW
HOURS...LIKELY ALLOWING SNOW TO REACH THE GROUND LATER THIS
AFTERNOON IN AND AROUND THE CHICAGO TERMINALS. THE OTHER CHANGE TO
THE NEW TAFS WAS TO HIT THE VISIBILITIES A BIT HARDER. UPSTREAM
OBSERVATIONS INDICATE VERY LOW VISIBILITIES...IN SOME CASES WELL
UNDER A MILE. ALTHOUGH THE LOWEST VISIBILITIES UNDER A MILE IN THE
SNOW WILL LIKELY REMAIN TO THE SOUTHWEST OF THE TERMINALS...IT DOES
APPEAR THAT VISIBILITIES OF 1 TO 2 MILES WILL BE A GOOD BET OVER THE
AREA...ESPECIALLY THIS EVENING DURING THE PEAK OF THE SNOWFALL.
LIGHTER SNOW WILL LIKELY LINGER INTO THURSDAY MORNING FOR THE
EASTERN TERMINALS NEAR LAKE MICHIGAN DUE TO LINGERING LAKE EFFECT
SNOW SHOWERS. HOWEVER...SNOW SHOULD COME TO AN END AT KRFD AFTER
MIDNIGHT TONIGHT. ELSEWHERE...CONDITIONS WILL IMPROVE BY THURSDAY
AFTERNOON AS THE LAKE EFFECT THREAT SHIFTS INTO NORTHWESTERN
INDIANA.

KJB

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* MEDIUM-HIGH IN SNOW TIMING.
* MEDIUM-HIGH IN MVFR CIGS AND IFR VIS OCCURRENCE...LOW ON HOW
  LONG IFR OR LIFR WILL LAST.

KJB

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

THURSDAY NIGHT...MVFR CIGS POSSIBLE.
FRIDAY THROUGH SATURDAY...VFR.
SUNDAY...SNOW...ACCUMULATIONS POSSIBLE.
MONDAY...SLT CHC SNOW LATE.
TUESDAY...CHANCE OF RAIN OR SNOW.

KB

&&

.MARINE...
230 PM CST

WITH NEARLY SOLID ICE COVERAGE OVER THE NORTHERN PORTIONS OF LAKE
MICHIGAN...NORTH OF A LINE FROM STURGEON BAY WISCONSIN TO POINT
BETSIE MICHIGAN...WAVES HAVE BEEN OMITTED FROM THE OPEN WATERS
FORECAST. ALSO...WITH EXTENSIVE ICE COVERAGE OVER THE NEARSHORE
WATERS OF SOUTHERN LAKE MICHIGAN...WAVES HAVE BEEN OMITTED FROM
THE NEARSHORE FORECAST.

A QUIETER PATTERN IS SETTING UP FOR THE LAKE AS A SERIES OF ARCTIC
HIGH PRESSURE SYSTEMS BUILD OUT OF CANADA...SAG THROUGH THE PLAINS
AND TO THE SOUTH OF THE GREAT LAKES. THE FIRST ARCTIC HIGH IS
CURRENTLY BUILDING OUT OF CANADA AND WILL SPREAD ACROSS THE PLAINS
THURSDAY AND THURSDAY NIGHT WITH THE CENTER OF THE HIGH MOVING
THROUGH THE OHIO VALLEY FRIDAY NIGHT AND SATURDAY. AS THIS HIGH
PUSHES OFF THE EAST COAST SUNDAY...A WEAK TROUGH OF LOW PRESSURE
AND AN ASSOCIATED WEAK COLD FRONT WILL PUSH ACROSS THE LAKE.
ANOTHER ARCTIC HIGH IS EXPECTED TO DROP OUT OF CANADA LATE SUNDAY
AND TAKE A MORE NORTHERLY TRACK...WITH THE CENTER OF THIS MOVING
ACROSS THE GREAT LAKES REGION MONDAY NIGHT AND TUESDAY.

KREIN

&&

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

$$

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