Area Forecast Discussion
Issued by NWS Chicago, IL

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773
FXUS63 KLOT 071800
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1200 PM CST SUN FEB 7 2016

.UPDATE...

1045 AM CST

NO BIG CHANGES TO GOING FORECAST. BREEZY AND MILD CONDITIONS ARE
IN PLACE IN THE WARM SECTOR OF THE CLIPPER LOW ALONG THE MN/CANADA
BORDER. BASED OFF PROGGED AND OBSERVED LOWER LEVEL THERMAL
PROFILES...ADJUSTED TEMPS UPWARD A DEGREE OR TWO IN MANY
LOCATIONS...WITH HIGHS AS WARM AS 48-49 FAVORED ALONG/EAST OF
I-55. ALSO MADE ADJUSTMENTS TO SKY COVER TRENDS...WITH A POCKET OF
SOME CLEARING IN THE MID/HIGH CLOUDS ESPECIALLY NORTH OF I-88
THROUGH EARLY AFTERNOON. LOOKING AHEAD TO SNOW SHOWERS TONIGHT
INTO EARLY MONDAY...TREND IS FOR A SLOWER ARRIVAL FROM THE
NORTHWEST AND PERHAPS BEST FOCUS INTO NORTH CENTRAL IL SOUTH OF
I-80. WILL ADDRESS THIS IN THE AFTERNOON FORECAST UPDATE.

RC

&&

.SHORT TERM...
322 AM CST

THROUGH TUESDAY...

ACCUMULATING SNOW TONIGHT THROUGH TUESDAY...PLEASE SEE THE SNOWFALL
TOTAL SECTION BELOW FOR SPECIFIC DETAILS. BELOW ZERO WIND CHILLS
FOLLOW THE SNOW TUESDAY NIGHT.

THE NEXT SYSTEM IS PUSHING INTO MINNESOTA THIS MORNING. A FEW LIGHT
ECHOES ARE ON RADAR...BUT NO PRECIP IS MAKING IT TO THE GROUND.  THE
UPPER LEVEL TROUGH WILL MOVE OVER THE UPPER MIDWEST TODAY AND THE
SURFACE LOW WILL BECOME CENTERED OVER WISCONSIN. WHILE A VORT
STREAMER ASSOCIATED WITH THE TROUGH WILL ROTATE THROUGH THIS
AFTERNOON AND EVENING...FORECAST SOUNDINGS ARE VERY DRY. THEREFORE
LOOKING AT A DRY DAY WITH SOUTHWEST WINDS AND WAA HELPING TEMPS RISE
INTO THE MID TO UPPER 40S.  DEFINITELY ENJOY IT BECAUSE THE PATTERN
WILL BE SHIFTING OVER THE NEXT COUPLE OF DAYS.

THE TROUGH AND SURFACE LOW SLOWLY SHIFT EAST THROUGH EARLY WEEK.
THIS WILL LEAD TO AN EXTENDED PERIOD OF LIGHT SNOW SHOWERS TONIGHT
THROUGH TUESDAY.  THE COLUMN SATURATES LATE THIS EVENING OVER NORTH
CENTRAL IL. PRECIP MAY INITIALLY FALL AS RAIN...BUT EXPECTING IT TO
QUICKLY TURN OVER TO SNOW AS THE COLUMN AND SURFACE COOLS.  SNOW
SPREADS EAST OVERNIGHT AND THERE COULD BE PERIODS OF LOW VISIBILITY
MONDAY DUE TO AN ABUNDANCE OF LARGE SNOWFLAKES. SNOWFALL RATES WILL
VARY...BUT A DEEP DGZ OF 5000-7000 FT WILL LIKELY LEAD TO LARGE
DENDRITES. THE LARGE FLAKES HAVE KNACK FOR REDUCING VISIBILITY
SIGNIFICANTLY...THEREFORE THOSE WITH TRAVEL PLANS MONDAY SHOULD PLAN
EXTRA TIME JUST IN CASE THEY ENCOUNTER POOR VISIBILITY.  STEADY SNOW
CONTINUES TUESDAY WITH HIGHS ONLY IN THE UPPER TEENS TO MID 20S.
GUSTY WINDS COULD RESULT IN AREAS OF BLOWING SNOW TUESDAY ESPECIALLY
IN OPEN AREAS.

THE TROUGH SHIFTS EAST TUESDAY AFTERNOON AND NIGHT LEADING TO A
GRADUAL WEST TO EAST END TO THE SNOW. SNOW WILL LINGER THE LONGEST
OVER PORTER COUNTY INDIANA DUE TO LAKE EFFECT SNOW.

SNOWFALL TOTALS...WEST OF I-39 WILL SEE 1-3 INCHES...THEN 2-4 INCHES
EAST OF I-39. LAKE AND PORTER COUNTIES IN INDIANA WILL HAVE THE
HIGHEST TOTALS OF 4-6 INCHES.  LOCALLY HIGHER AMOUNTS ARE POSSIBLE
ACROSS THE WARNING AREA TO DO MESOSCALE ENHANCEMENTS.

THE OTHER CONCERN IS ARCTIC AIR WILL REACH THE REGION TUESDAY NIGHT
AS THE HEART OF THE TROUGH SITS OVERHEAD.  LOW TEMPS WILL BE IN THE
SINGLE DIGITS AND WIND CHILLS WILL VARY BETWEEN 5 AND 15 BELOW
ZERO.

JEE

&&

.LONG TERM...
322 AM CST

WEDNESDAY THROUGH SUNDAY...

LAKE EFFECT SNOW MAY LINGER OVER NW INDIANA WEDNESDAY...BUT
EXPECTING DRY AND COLD CONDITIONS OTHERWISE. COULD SEE A FEW BREAKS
IN THE CLOUDS AND THE FRESH SNOWPACK COULD RESULT IN COLDER THAN
FORECAST TEMPERATURES.  WEDNESDAY NIGHT ALSO LOOKS COLD WITH WIND
CHILLS BETWEEN 5 AND 10 BELOW ZERO. OVERNIGHT TEMPS COULD BE EVEN
COLDER IF CLOUDS CLEAR OUT AS THE SURFACE HIGH BUILDS IN.

THE REST OF THE WEEK LOOKS DRY WITH ONLY A SLIGHT CHANCE OF LAKE
EFFECT SNOW OVER NW INDIANA.  GUIDANCE DIFFERS GREATLY IN THE UPPER
LEVEL PATTERN. THE GFS SUGGESTS WE WOULD WARM ALOFT THROUGH SATURDAY
WHILE THE ECMWF HOLDS A TROUGH AND ARCTIC AIR OVERHEAD. DID NOT
ADJUST SUPERBLEND TEMPS SINCE THE TEMPS ARE BETWEEN THE TWO
SOLUTIONS.

JEE

&&

.AVIATION...
FOR THE 18Z TAFS...

MAIN AVIATION CONCERN IS WITH PERIODS OF SNOW SHOWERS AND
ASSOCIATED VSBY REDUCTIONS LATE TONIGHT THROUGH MONDAY. UNTIL
THEN...QUIET VFR CONDITIONS WITH GUSTY SOUTHWEST WINDS EASING BY
MID TO LATE AFTERNOON. LOW PRESSURE OVER FAR NORTHERN MINNESOTA
WILL SLOWLY SLIDE SOUTHEAST INTO MONDAY MORNING. A COLD FRONT
TRAILING FROM THE LOW WILL BRING IN FIRST PUSH OF COLD AIR AND
CIGS LOWERING TO MVFR FROM NORTHWEST TO SOUTHEAST IN 06Z-10Z
TIMEFRAME. CANNOT RULE OUT AT LEAST PATCHY HIGHER END IFR CIGS.
AT THE SAME TIME...UPPER LEVEL LOW PRESSURE ASSOCIATED WITH THE
SURFACE LOW WILL WRAP AN UPPER DISTURBANCE OVER THE AREA
OVERNIGHT. THIS SHOULD CAUSE SNOW SHOWERS TO BLOSSOM. PER SOME HI-
RES GUIDANCE WHICH IS SUPPORTED BY OVERALL SETUP...A MORE
ORGANIZED BUT NARROW BAND OF SNOW SHOWERS IS EXPECTED TO MOVE
QUICKLY SOUTHEAST ACROSS THE TERMINALS ROUGHLY IN THE 06Z-14Z
TIMEFRAME. HAVE NARROWED TIME RANGE INHERITED TEMPO GROUPS FOR IFR
VSBY IN SHSN GIVEN EXPECTATION OF A NARROW AND FAIRLY QUICKLY
MOVING BAND OF SHSN. NEXT UPDATE SHOULD BE ABLE TO HONE IN ON THE
TIMING EVEN MORE. LIGHT ACCUMULATIONS OF UP TO A FEW TENTHS OF AN
INCH ARE POSSIBLE.

THE UPPER LEVEL LOW WILL REMAIN OVER THE REGION DURING THE DAY ON
MONDAY...SO ITS CONCEIVABLE THAT THERE WILL BE NO REAL BREAKS IN
-SN/-SHSN. WITH THIS BEING SAID...FOCUS FOR ANOTHER AREA OF
ORGANIZED/HEAVIER SHSN MAY PASS SOUTHWEST OF THE TERMINALS DURING
MONDAY MORNING AND NEXT ROUND NOT TIL TOWARD OR AFTER 00Z. HAVE
MAINTAINED PROB30 FROM PREVIOUS TAF FOR IFR VSBY REDUCTION
POTENTIAL THROUGH MID-LATE MONDAY MORNING GIVEN LOW CONFIDENCE.
WINDS WILL BE WEST-NORTHWEST TO NORTHWEST WITH GUSTS CLOSE TO OR
A BIT OVER 20 KT ON MONDAY. EXPECTING CIGS TO REMAIN MVFR.

RC

&&

.MARINE...
148 AM CST

THE LAKE MICHIGAN WEATHER FROM TODAY THROUGH WEDNESDAY WILL BE
ENTIRELY INFLUENCED BY A STRONG LOW PRESSURE DIVING IN FROM CANADA
LATER TODAY THAT WILL THEN DRIFT EAST OVER THE GREAT LAKES. THE
SOUTHWEST WINDS AHEAD OF THIS WILL BE AROUND OR A TAD ABOVE 30 KT
THIS MORNING OVER THE OPEN WATER...AND SOME 22-25 KT GUSTS IN THE
ILLINOIS AND INDIANA NEARSHORE. AT THIS TIME AM LEANING ON NOT
HAVING A SMALL CRAFT ADVISORY TODAY DUE TO LACK OF DURATION OF
THESE WINDS AND THE CONFIDENCE IN DEGREE OF MIXING BEING LOWER
THAN TYPICAL FOR A FORECAST ONLY 6 TO 12 HOURS FROM NOW. WILL
ASSESS TRENDS THROUGH DAYBREAK THOUGH AND IF THEY ARE OUTPACING
THE FORECAST THEN WILL ISSUE AN ADVISORY.

AS THE NORTHWEST FLOW ON THE BACKSIDE OF THE LOW BEGINS TO WRAP IN
ON MONDAY...SMALL CRAFT CRITERIA IS VERY LIKELY TO BE SEEN IN THE
NEARSHORE. AS FOR THE OPEN WATER...THE POTENTIAL FOR GALES
DEFINITELY EXITS FOR AT LEAST TIMES IN THE MONDAY NIGHT THROUGH
TUESDAY NIGHT WINDOW. THE LOW IS FORECAST TO SLOW DUE TO A VERY DEEP
LOW LIFTING NORTHWARD OFF THE EASTERN U.S. SEABOARD. SO THIS THROWS
CONTINUED UNCERTAINTY ON HOW FAST THE LOW WILL MOVE EASTWARD AND
THUS THE DEGREE OF PRESSURE GRADIENT AND COLD ADVECTION COUPLED OVER
THE OPEN WATERS FOR GALES. WILL NOTE SOME GALES IN THE GLF AND
CONTINUED LIGHT FREEZING SPRAY CHANCES.

MTF

&&

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

$$

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