Area Forecast Discussion
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000
FXUS63 KLOT 260314
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
914 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 03Z...

* SNOW/SNOW SHOWERS CONTINUING THROUGH MID TO LATE THURSDAY
  MORNING. IFR VSBY LIKELY...WITH OCCASIONAL LIFR VSBY OVERNIGHT
  INTO POSSIBLY THURSDAY MORNING IF/WHEN HEAVIER LAKE EFFECT SNOW
  SHOWERS DIRECTLY IMPACT TERMINALS.

* NORTHEAST WINDS GRADUALLY BECOMING MORE NORTHERLY ON
  THURSDAY...WITH AT LEAST OCCASIONAL GUSTS OF 15-20 KT THURSDAY
  MORNING THROUGH THURSDAY AFTERNOON.

* MVFR CIGS WITH OCCASIONAL IFR CIGS IN HEAVIER SNOW AND TIMING
  OF CIG IMPROVEMENTS ON THURSDAY.

RC

//DISCUSSION...UPDATED 00Z...

A LOW PRESSURE SYSTEM OVER WESTERN MISSORI WILL WEAKEN AS IT
SLIDES EAST TONIGHT BUT AN UPPER LEVEL DISTURBANCE OVER THE AREA
WILL KEEP LIGHT SNOW GOING THROUGH MUCH OF THE NIGHT AT THE
EASTERN TERMINALS. BASED ON OBS TRENDS...HAVE TIMED TEMPO LIFR
VSBY FROM NOW THROUGH MID-LATE EVENING HOURS AT TAF SITES.
NORTHEAST WINDS FROM LAKE MICHIGAN ARE ALSO RESULTING IN LAKE
ENHANCEMENT ALONG THE LAKESHORE...INCLUDING GYY...WHERE 1/2SM VSBY
IN MODERATE SNOW WAS OCCURRING AS OF THIS WRITING. AS SYSTEM SNOW
SLIDES SOUTHEAST OVERNIGHT...CONCERN SHIFTS TO DURATION AND
INTENSITY OF LAKE EFFECT SNOW INTO NORTHEAST IL AND THEN NW
INDIANA THROUGH THURSDAY. GUIDANCE SUGGESTS POTENTIAL FOR DECENT
LAKE EFFECT SNOW BAND OR BANDS TO BE NEAR ORD/MDW THROUGH EARLY TO
MID THURSDAY MORNING...THEN GRADUALLY SLIDING EAST AS WINDS TURN
MORE NORTHERLY. HAVE NOT GONE LOWER THAN 1SM VSBY FOR ANY TAF SITE
DURING EXPECTED TIME OF LAKE EFFECT SNOW...BUT WILL NEED TO
MONITOR TRENDS FOR POSSIBLE INCLUSION OF LIFR AGAIN. ALSO SOME
UNCERTAINTY WITH HOW QUICKLY THE BAND WILL SHIFT EAST.

CIGS WILL BE PREDOMINANTLY MVFR...BUT HEAVIER SNOW HAS BEEN
RESULTING IN PERIODIC IFR. CIGS SHOULD IMPROVE TO VFR FROM WEST TO
EAST ON THURSDAY...WITH EXCEPTION OF GYY...WHERE LAKE EFFECT SNOW
COULD LINGER INTO THE LATE AFTERNOON HOURS. WINDS WILL TURN MORE
NORTHERLY THEN NORTH-NORTHWEST WITH TIME ON THURSDAY...BUT EXACT
DIRECTIONS WILL BE CONTROLLED BY ORIENTATION OF LAKE EFFECT
CONVERGENCE...SO THERE WILL BE VARIABILITY IN DIRECTIONS ON
THURSDAY MORNING. GUST SPEEDS CLOSER TO THE LAKE ARE EXPECTED TO
BE IN THE 15-20 KT RANGE.

RC

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* HIGH IN PREDOMINANTLY IFR VSBY AND MVFR CIGS TONIGHT INTO
  THURSDAY MORNING...LOW IN EXACT DURATION OF IFR VSBY AND CIG
  IMPROVEMENT TIME ON THURSDAY.

* MEDIUM-HIGH IN OCCASIONAL LIFR VSBY OVERNIGHT...LOW IN LIFR VSBY
  LINGERING INTO THURSDAY MORNING.

* MEDIUM IN OCCASIONAL IFR CIGS IN HEAVIER SNOW
  OVERNIGHT...ESPECIALLY AT MDW.

* MEDIUM-HIGH IN WIND TRENDS.

RC

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

FRIDAY...VFR.

SATURDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE SATURDAY NIGHT.

SUNDAY...LIGHT SNOW LIKELY...IFR POSSIBLE.

MONDAY...VFR THEN LIGHT SNOW AND IFR POSSIBLE MONDAY NIGHT.

TUESDAY...SNOW LIKELY...IFR POSSIBLE.

RC

&&

.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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