Area Forecast Discussion
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FXUS63 KLOT 072042
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
242 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...
241 PM CST

LONG TERM...

MONDAY NIGHT THROUGH SUNDAY...

FORECAST CONCERNS THROUGH THE EXTENDED PERIOD INCLUDE SNOW
SHOWERS ACROSS THE FORECAST AREA INTO WEDNESDAY...LAKE EFFECT SNOW
ACROSS PARTS OF NORTHWEST INDIANA...AND COLDER TEMPERATURES
THROUGH PERIOD.

DEEP CLOSED UPPER LOW DRIFTS SLOWLY SOUTHEAST FROM THE WESTERN
GREAT LAKES TO THE UPPER OHIO VALLEY THROUGH MID-WEEK...WITHIN
MASSIVE LARGE SCALE UPPER TROUGH ACROSS EASTERN NORTH AMERICA.
DEEP AND PERSISTENT NORTH-NORTHWESTERLY FLOW WEST OF THE TROUGH
AXIS PRODUCES AN INFLUX OF COLD ARCTIC AIR WITH 850 MB TEMPS
DROPPING INTO THE -15 TO -20 C RANGE AND WHICH LINGERS THROUGH
NEXT WEEKEND. STEEP LOW LEVEL LAPSE RATES AND A SERIES OF MID-
LEVEL VORTICITY MAXIMA WILL SET THE STAGE FOR PERIODIC SNOW
SHOWERS...ESPECIALLY FROM MONDAY NIGHT THROUGH EARLY WEDNESDAY
AFTER WHICH THE STRONG VORTICITY CHANNEL SHIFTS OFF TO THE EAST
AND MODELS INDICATE SUBSTANTIAL DRYING OF THE LOW-MID LEVELS BY
WEDNESDAY NIGHT. INTERMITTENT SNOW SHOWERS APPEAR FAIRLY LIKELY
WITHIN THIS REGIME ESPECIALLY EAST...WITH COVERAGE AND INTENSITY
MODULATED BY SMALLER AMPLITUDE SHORT WAVES/VORT MAXIMA ROTATING
THROUGH THE FLOW. WHILE LOW LEVEL LAPSE RATES AND INSTABILITY ARE
STRONGER MONDAY NIGHT...A STRONGER PUSH OF LOW LEVEL COLD AIR
ARRIVES TUESDAY WITH FORECAST SOUNDINGS FROM THE NAM/GFS/ECMWF ALL
INDICATING WEAK FORCING WITHIN A FAIRLY DEEP (200 MB) SATURATED
ISOTHERMAL PROFILE IN THE -10 TO -20 C DENDRITIC GROWTH ZONE FROM
EARLY TUESDAY MORNING INTO TUESDAY EVENING. THUS WHILE HIGHEST
POPS IN THE EXTENDED PERIOD ARE IN THE MONDAY NIGHT-EARLY TUESDAY
PERIOD...LIGHT ACCUMULATIONS WILL LIKELY CONTINUE INTO TUESDAY
AFTERNOON OR EVENING ACROSS THE EASTERN HALF OF THE CWA. MODEL QPF
GENERALLY RANGES FROM 0.05-0.10 INCHES MON NGT/TUESDAY... AND 0.05
INCHES OR LESS TUES NIGHT AND WEDNESDAY WITH LOWEST AMOUNTS
FARTHER WEST. SNOW TO LIQUID RATIOS INCREASING TO NEAR 20 TO 1
WOULD SUGGEST THE POTENTIAL FOR AS MUCH AS 2-3 INCHES OF
ACCUMULATION (OUTSIDE OF LAKE EFFECT AREAS) ACROSS THE EASTERN CWA
OVER ABOUT A 36 HOUR PERIOD...LESS TO THE WEST.

WITH COLD NORTH-NORTHWEST LOW LEVEL FLOW...THE LAKE SNOW BELT
REGION OF EASTERN LAKE AND PORTER COUNTIES WILL SEE LAKE EFFECT
SNOW DURING THE PERIOD...WITH THE FETCH FAVORABLE MAINLY EAST OF
GARY AS WINDS VEER MORE NORTHERLY. LAKE-INDUCED INSTABILITY RAMPS
UP QUICKLY DURING THE EVENING WITH EQUILIBRIUM LEVELS OF 8000-9000
FT...WEAKENING A BIT OVERNIGHT INTO TUESDAY AS LOW LEVELS COOL AND
STRENGTHEN INVERSION NEAR 850 MB. CONTINUED COOLING OF THE COLUMN
LEADS TO INCREASING INSTABILITY AGAIN LATER TUESDAY AFTERNOON INTO
WEDNESDAY...THOUGH GUIDANCE GENERALLY MAINTAINS THE STRONGEST LOW
LEVEL CONVERGENCE JUST EAST OF THE CWA FROM NORTHEAST PORTER INTO
LA PORTE AND BERRIEN COUNTIES. RISING MID-LEVEL HEIGHTS AND
SUBSIDENCE ALONG WITH WEAKENING FLOW/CONVERGENCE AND BACKING OF
LOW LEVEL WINDS TO A MORE WESTERLY DIRECTION SHOULD GRADUALLY
REDUCE ACCUMULATIONS WEDNESDAY AFTERNOON AND NIGHT. SEVERAL INCHES
OF ACCUMULATION DO APPEAR POSSIBLE BY THAT TIME MAINLY ACROSS
NORTHEAST PORTER COUNTY. LOW LEVEL WINDS EVENTUALLY BACK MORE
WESTERLY BY THURSDAY ENDING LIGHTER LAKE SNOW SHOWERS IN PORTER
COUNTY.

UPPER TROUGH SLOWLY DRIFTS EAST THROUGH THE END OF THE WEEK AND
NEXT WEEKEND...WITH SURFACE HIGH PRESSURE EVENTUALLY MOVING ACROSS
THE WESTERN LAKES LATE SATURDAY INTO SUNDAY. ARCTIC AIR WILL KEEP
TEMPERATURES BELOW NORMAL DURING THE TUESDAY-SUNDAY PERIOD HOWEVER
AS WE REMAIN IN NORTHWEST FLOW ALOFT BETWEEN EAST COAST TROUGH AND
DOWNSTREAM OF RIDGING ACROSS THE CENTRAL CONUS. TEMPS THROUGH THE
PERIOD GENERALLY EXPECTED TO SEE LOWS IN THE SINGLE DIGITS AND
HIGHS IN THE TEENS TO LOW 20S. SUB-ZERO MORNING WIND CHILLS ARE
EXPECTED PARTICULARLY WEDNESDAY AND THURSDAY MORNINGS.

RATZER

&&

.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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