Area Forecast Discussion
Issued by NWS Chicago, IL

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129
FXUS63 KLOT 062029
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
229 PM CST SAT FEB 6 2016

.UPDATE...
932 AM CST

FOR MORNING UPDATE...

AFTER MOSTLY CLEAR SKIES EARLY THIS MORNING ACROSS MUCH OF THE
FORECAST AREA...AN AREA OF STRATUS WAS SPREADING ACROSS NORTHERN
IL ESPECIALLY NORTH OF THE I-88 CORRIDOR AND WILL MAKE FOR CLOUDY
OR MOSTLY CLOUDY SKIES FOR THESE LOCATIONS TODAY. GUIDANCE
SUGGESTS EXTENSIVE AREA OF LOWER CLOUDS WITHIN WEAK LOW LEVEL
MOIST AXIS OVER IA WILL CONTINUE TO MOVE SLOWLY EASTWARD AND
AFFECT MAINLY NORTHERN HALF OR SO OF THE CWA. RELATIVELY SHALLOW
NATURE OF CLOUD DECK AS INFERRED FROM VISIBLE SATELLITE IMAGERY
AND RAP SOUNDINGS...COMBINED WITH PASSAGE OF MID-LEVEL SHORT WAVE
TROUGH SHOULD PRECLUDE ANY PRECIPITATION AND HAVE REMOVED FLURRIES
FROM MORNING FORECAST. HAVE ALSO DECREASED CLOUD COVER ACROSS
SOUTHERN COUNTIES OF THE CWA THROUGH MUCH OF THE AFTERNOON. OTHER
ELEMENTS OF THE FORECAST...INCLUDING TEMPERATURES...APPEAR TO BE
ON TRACK. UPDATED GRIDS/ZFP AVAILABLE.

RATZER

&&

.SHORT TERM...
327 AM CST

THROUGH SUNDAY...

AN UPPER LEVEL TROUGH AND VORT STREAMER SLIDE SOUTHEAST THROUGH THE
REGION THIS MORNING WITH SCATTERED FLURRIES ALSO SHIFTING SOUTHEAST.
THE FLURRIES ARE STRUGGLING RIGHT NOW...AND NOT EXPECTING ANY
ACCUMULATION.  SOUTHWEST WINDS USHER IN WARMER AIR WITH HIGHS AROUND
40. LOCATIONS SOUTH OF I-80 SHOULD SEE SOME SUN TODAY...AND THE SUN
SHOULD HELP TEMPS RISE INTO THE LOW TO MID 40S.

THE NEXT SYSTEM MOVES OVER NORTHERN WISCONSIN BY LATE SUNDAY
AFTERNOON.  THE VORT STREAMER ASSOCIATED WITH THE UPPER LEVEL LOW
MOVES OVER NW IL SUNDAY AFTERNOON AND COULD KICK OFF LIGHT RAIN
SUNDAY AFTERNOON.  THE GFS IS MORE BULLISH THAN THE OTHER MODELS
REGARDING PRECIP SUNDAY...SO ONLY HAVE A SLIGHT CHANCE OF RAIN.
CONFIDENCE IS LOW IN THE OCCURRENCE AND EXTENT OF RAIN SUNDAY
AFTERNOON...BUT HAVE HIGH CONFIDENCE THAT ANY PRECIP THAT FALLS WILL
BE RAIN. HIGH TEMPS SUNDAY WILL BE IN THE LOW TO MID 40S.

JEE

&&

.LONG TERM...
229 PM CST

SUNDAY NIGHT THROUGH SATURDAY...

A HIGHLY AMPLIFIED UPPER LEVEL PATTERN WILL CONTINUE INTO THE LONGER
TERM FORECAST PERIOD WITH A STRONG NORTHERN STREAM SHORTWAVE
DROPPING FROM THE UPPER MISSISSIPPI VALLEY SUNDAY NIGHT ACROSS LAKE
MICHIGAN AND INTO LOWER MICHIGAN MONDAY.  AN ASSOCIATED COLD FRONT
WILL PUSH ACROSS THE REGION LATE SUNDAY NIGHT INTO MONDAY WITH
BLUSTERY CONDITIONS DEVELOPING THROUGH THE DAY WITH NWLY WINDS
GUSTING TO 25 TO 30MPH AT TIMES.  STRONG COLD ADVECTION SHOULD BEGIN
IN EARNEST MONDAY NIGHT AS THE UPPER LOW MOVES SLOWLY TOWARD THE ERN
GREAT LAKES AND UPPER RIDGING BUILDS OVER THE PAC NORTHWEST.  THE
UPPER FLOW PATTERN SHOULD CONTINUE TO INCREASE IN AMPLITUDE INTO
MIDWEEK WHILE SHOWING LITTLE PROGRESSION.  THIS WILL SET UP THE NEXT
ROUND OF COLDER CONDITIONS FOR THE REGION AS A PERSISTENT FETCH OF
COLD AIR OUT OF THE ARCTIC WILL OVERSPREAD THE REGION.  BY
TUESDAY...HIGH TEMPS SHOULD ONLY BE IN THE UPPER TEENS TO MIDDLE
20S.  OVERNIGHT LOWS WEDNESDAY AND THURSDAY MORNING SHOULD GENERALLY
BE IN THE SINGLE DIGITS ACROSS THE AREA...WITH TEMPS ARND 10-12F
OVER THE SERN PORTIONS OF THE CWA AND DOWNTOWN CHICAGO.  WIND CHILL
READINGS SHOULD BE LOWEST WEDNESDAY MORNING AS WINDS ARND 10 MPH
PERSIST OVERNIGHT...DRIVING WIND CHILLS DOWN TO -10 TO -15F.  BY
THURSDAY...THE PATTERN IS EXPECTED TO BREAK DOWN A BIT WITH THE
UPPER RIDGE OVER THE WRN CONUS FLATTENING IN RESPONSE TO A DEEP
UPPER LOW DROPPING SOUTH OF HUDSON BAY WHICH WILL ALSO HELP THE
UPPER TROUGH TO SHIFT TO THE EAST.  SO...BY LATE IN THE
PERIOD...CONDITIONS SHOULD TREND A LITTLE WARMER...BUT TEMPERATURES
SHOULD STILL BE WELL BELOW NORMAL.

THE GREATEST CHANCE FOR PCPN WILL BE SUNDAY NIGHT INTO TUESDAY AS A
SERIES OF SHORTWAVES DROP SEWD THROUGH THE FAST NWLY FLOW SETTING UP
ACROSS THE REGION.  THE MAY END UP BEING A PERIOD OF RELATIVELY HIGH
POPS AND LOW QPF AS THERE SHOULD BE LITTLE IN THE WAY OF DEEP LAYER
MOISTURE FOR THE SHORTWAVES TO WORK WITH. BY MONDAY AFTERNOON INTO
TUESDAY...PCPN MAY ALSO JUST BE SCT SNOW SHOWERS UNDER CYCLONIC FLOW
ALOFT.  THERE WILL LIKELY BE SOME ACCUMULATION FOR THE PERIOD FROM
SUNDAY NIGHT THROUGH TUESDAY WITH CURRENT INDICATORS SUGGESTING 1 TO
3 INCHES OF SNOW OVER THE 48 HOUR PERIOD.  FROM WEDNESDAY THROUGH
SATURDAY...EXPECT THAT PCPN CHANCES WILL SHUT OFF AS UPPER FLOW
TRENDS TOWARD A BROAD UPPER TROUGH OVER PORTIONS OF THE CONUS EAST
OF THE ROCKIES AND WEAK RIDGING ALONG THE ROCKIES.  SOME LAKE EFFECT
SNOW SHOWERS COULD IMPACT THE ERN SHORES OF LAKE MICHIGAN...BUT THE
LOCAL AREA SHOULD TREND DRY.

KREIN

&&

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

MAIN AVIATION CONCERNS ARE A SHORT DURATION OF MVFR CIGS EARLY
THIS AFTERNOON...AND POTENTIAL FOR GUSTY WEST-SOUTHWEST ON SUNDAY.

WEAK SURFACE TROUGH WAS ALONG THE MISSISSIPPI RIVER AT MIDDAY.
SOUTHWEST FLOW ABOVE THE SURFACE WAS HELPING TO ADVECT AN AREA OF
LOW LEVEL MOISTURE AND MVFR CEILINGS ACROSS FAR NORTHERN IL...WITH
NORTHERN IL TERMINAL SITES GENERALLY ALONG THE SOUTHERN PERIPHERY
OF THE MORE SOLID CLOUD COVER. BASED ON VISIBLE SATELLITE TRENDS...
A BRIEF 1-3 HOUR PERIOD OF MVFR CIGS IN THE 1500-2000 FT RANGE
WILL LIKELY AFFECT ORD/DPA/MDW/RFD...WITH GYY EXPECTED TO REMAIN
SCATTERED AT BEST. RFD WILL BE CLOSER TO THE MORE WIDESPREAD CLOUD
COVER TO THE NORTH AND WEST THOUGH IT APPEARS THAT RFD WILL ALSO
SCATTER OUT. WINDS THEN LOOK TO BACK SLIGHTLY MORE SOUTH-SOUTHWEST
THIS EVENING...IN RESPONSE TO SURFACE PRESSURE FALLS ASSOCIATED
WITH LOW PRESSURE MOVING SOUTHEAST INTO THE NORTHERN PLAINS.
EXTENSIVE AREA OF IFR/LIFR OVER IA EXPECTED TO LIFT MORE NORTHEAST
THAN EAST OVERNIGHT...WITH GUIDANCE KEEPING IL/NW IN TERMINALS
VFR WHILE ERODING AND SHIFTING IFR CIGS NORTHEAST ACROSS WI.

AFOREMENTIONED LOW PRESSURE TRACKS ACROSS THE NORTHERN GREAT LAKES
REGION THROUGH SUNDAY...WITH A GRADUAL TIGHTENING OF THE GRADIENT
AND INCREASING SOUTH-SOUTHWEST WINDS OVERNIGHT. STRONG LOW LEVEL
INVERSION IS EXPECTED TO LIMIT GUSTINESS LATE TONIGHT...THOUGH
WINDS LIKELY GUSTING 20+ KTS FROM THE WEST-SOUTHWEST SUNDAY AS
PACIFIC COLD FRONT MOVES ACROSS THE REGION TRAILING THE LOW.
FORECAST SOUNDINGS FROM VARIOUS MODELS MAINTAIN CONSIDERABLE DRY
AIR IN THE LOW-MID LEVELS WITH VFR CONDITIONS EXPECTED AND MINIMAL
PRECIP THREAT.

RATZER

&&

.MARINE...
119 AM CST

A WEAK BUT DEEPENING LOW PRESSURE JUST NORTH OF LAKE SUPERIOR EARLY
THIS MORNING WILL QUICKLY SCOOT EAST THROUGH TODAY. MORNING WIND
GUSTS ACROSS THE NORTHERN THIRD TO HALF OF THE LAKE SHOULD BE AROUND
30 KT ASSOCIATED WITH THIS. SOUTHWEST WINDS WILL RE-INCREASE TO THAT
MAGNITUDE TONIGHT AS DEEP LOW PRESSURE BEGINS TO APPROACH FROM THE
SOUTHERN CANADIAN PROVINCES. THE WINDS ACTUALLY WILL EASE A TAD
SUNDAY AFTERNOON AND MORE SO SUNDAY NIGHT AS THE WARM ADVECTION
AHEAD OF THIS LOW WILL NOT BE PARTICULARLY STRONG.

HIGH UNCERTAINTY EXISTS ON HOW FAST THIS NEXT LOW WILL MOVE INTO
LOWER MICHIGAN ON MONDAY AFTERNOON OR EVENING. BEHIND IT THE
PRESSURE GRADIENT AND COLD ADVECTION MAY BE ENOUGH FOR AT LEAST
OCCASIONAL GALES MONDAY NIGHT INTO TUESDAY AND TUESDAY
NIGHT...ALTHOUGH THAT SIGNAL IS A BIT LESS THAN IT WAS 24 HOURS
AGO...LIKELY BECAUSE THE LOW HAS SLOWED IN MODEL GUIDANCE. THERE
MAY BE SOME LIGHT FREEZING SPRAY TUESDAY NIGHT AS A SECOND COLD
PUSH MOVES OVER THE LAKE...MAINLY OVER NORTHERN AND EASTERN
PORTIONS.

MTF

&&

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

$$

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