Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 290151
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
851 PM CDT TUE OCT 28 2014

.DISCUSSION...
850 PM CDT

FOR EVENING UPDATE...

ONLY MINOR CHANGE MADE TO GOING FORECAST THIS EVENING WAS TO SLOW
THE CLEARING OF CLOUD COVER ACROSS THE FORECAST AREA OVERNIGHT.

SUB-995 MB SFC LOW LIFTING SLOWLY AWAY TO THE NORTHEAST ACROSS
ONTARIO THIS EVENING...WITH CYCLONIC WEST-NORTHWEST LOW LEVEL FLOW
IN ITS WAKE ACROSS THE UPPER MIDWEST. SOME DECREASE IN CLOUD COVER
HAS TEMPORARILY OCCURRED ACROSS PORTIONS OF NORTHERN IL EARLY THIS
EVENING...THOUGH GOES WATER VAPOR IMAGERY SHOWS ANOTHER STRONG VORT
DIGGING SOUTHEAST ACROSS THE UPPER MISSISSIPPI VALLEY...WITH A
FAIRLY SOLID AREA OF CLOUD COVER AND EVEN A FEW SPRINKLES NOTED OVER
PARTS OF SOUTHEAST MINNESOTA AND FAR WESTERN WISCONSIN. WITH
APPROACHING VORT AND EXTENSIVE UPSTREAM CLOUD COVER IN CONTINUED LOW
LEVEL COLD ADVECTION REGIME...WOULD EXPECT THAT CURRENT DEVELOPING
HOLES IN CLOUDS WOULD FILL IN AS THE NIGHT WEARS ON.

OTHERWISE...TEMP AND WIND TRENDS OF GOING FORECAST APPEAR REASONABLE
AND HAVE MADE NO OTHER SIGNIFICANT CHANGES EXCEPT FOR SKY COVER.

RATZER

&&

.PREV DISCUSSION...
300 PM CDT

BELOW NORMAL TEMPS WILL CHARACTERIZE THE REST OF THE WEEK WITH AN
INFLUX OF MUCH COLDER AND WELL BELOW NORMAL AIR ARRIVING
FRIDAY/SATURDAY BEFORE THINGS MODERATE EARLY NEXT WEEK. THE CLOSED
UPPER LOW THAT HELPED PUSH A COLD FRONTAL BOUNDARY ACROSS THE REGION
THIS MORNING IS NOW CENTERED OVER LAKE SUPERIOR AND TRACKING
EASTWARD. RATHER LOW AMPLITUDE UPPER RIDGING IS MOVING EASTWARD
ACROSS THE WESTERN U.S. AND CANADIAN ROCKIES WITH A SERIES OF LARGER
SCALE TROUGHS OFF THE WEST COAST. OF NOTE IS A WAVE EMBEDDED WITHIN
THE FLOW OVER CENTRAL BRITISH COLUMBIA WHICH WILL CROSS THE AREA AND
SET THE STAGE FOR THE BIG COOL DOWN FRIDAY. AT THE SURFACE...BROAD
LOW PRESSURE IS OVER SOUTHERN ONTARIO WITH THE COLD FRONT THAT
PASSED THIS MORNING NOW WELL TO THE EAST.

TONIGHT THROUGH THURSDAY...QUIET WEATHER WILL PREVAIL THROUGH
WEDNESDAY NIGHT. COLD ADVECTION CONTINUES INTO THE AREA THIS
AFTERNOON AND WILL CONTINUE OVERNIGHT. THE PRESSURE GRADIENT WILL
SUPPORT A STEADY THOUGH NOT TERRIBLY STRONG WESTERLY WIND WHICH WILL
KEEP TEMPS FROM BOTTOMING OUT BUT DO EXPECT THEM TO FALL INTO THE
UPPER 30S TO AROUND 40. THE UPPER TROUGH WILL MOVE NORTHEAST INTO
NORTHERN QUEBEC BUT ANOTHER TROUGH AXIS IS EXPECTED TO AMPLIFY AND
SWING ACROSS THE AREA WEDNESDAY. THE BULK OF THE ASCENT AND DEEPER
MOISTURE ASSOCIATED WITH THIS WILL PASS NORTH OF THE AREA SO AM ONLY
EXPECTING SOME INCREASE IN CLOUD COVER ACROSS NORTHERN AREA AND THIS
MAY BE MINIMAL. THE TROUGH WILL INTRODUCE ANOTHER MODEST PUSH OF
COLDER MID LEVEL AIR SO HIGH TEMPERATURES WILL BE COLDER THAN TODAY
WITH READINGS FROM AROUND 50 NORTH TO THE MID 50S FAR SOUTH. WINDS
WILL TURN NORTHWESTERLY BUT BECOME FAIRLY LIGHT LATE IN THE DAY.
THIS WILL SET THE STAGE FOR COLDER TEMPS WEDNESDAY NIGHT WITH 30S
FOR ALL AREAS OUTSIDE THE IMMEDIATE DOWNTOWN AREA. THE WAVE OVER
BRITISH COLUMBIA TODAY WILL MAKE ITS WAY SOUTHEAST ACROSS THE
NORTHERN PLAINS AND ACROSS THE AREA THURSDAY. GUIDANCE CONTINUES TO
BE MIXED WITH REGARD TO PRECIP POTENTIAL THURSDAY BUT A FAIRLY DRY
ATMOSPHERE WILL BE IN PLACE SO DRY CONDITIONS COULD PREVAIL. WILL GO
AHEAD AND CARRY A SLIGHT CHANCE MENTION FOR MOST AREAS FOR NOW. THE
WAVE WILL BRING A PUSH OF WARMER MID LEVEL AIR AHEAD OF IT SO HIGHS
WILL MODERATE INTO THE LOW TO MID 50S.

FRIDAY AND SATURDAY...GUIDANCE CONTINUES TO BE RATHER CONSISTENT ON
A STRONG UPPER TROUGH DIGGING STRAIGHT SOUTH FROM NORTHERN CANADA
THURSDAY NIGHT AND FRIDAY. THIS WILL PUSH A RELATIVELY WEAK SURFACE
LOW SOUTHEAST ACROSS THE NORTHERN GREAT LAKES WHICH WILL BE
DEEPENING WITH TIME. A VERY STRONG CANADIAN HIGH BUILDS INTO THE
MID/UPPER MISSISSIPPI RIVER VALLEY AND UPPER GREAT LAKES BEHIND THE
LOW INTO FRIDAY NIGHT. H85 TEMPS ARE STILL FORECAST TO FALL TO
AROUND -8C WITH SOME GUIDANCE TRENDING A LITTLE COLDER. THIS WILL
RESULT IN MUCH COLDER SURFACE AIR SPREADING IN THROUGH THE DAY
FRIDAY WHICH IF TIMING HOLDS WILL LIKELY RESULT IN FALLING TEMPS
THROUGH THE DAY. WHILE IT IS STILL EARLY FOR SPECIFICS DO HAVE A
FEW CONCERNS THAT WILL BEAR WATCHING OVER THE NEXT FEW DAYS GIVEN
THE SYNOPTIC SET UP. FIRST IS PRECIP. THE BULK OF SYNOPTIC PRECIP
APPEARS TO REMAIN TO THE EAST OF THE AREA WITH THE UPPER LOW
CENTER REMAINING JUST TO THE EAST WITH THE DEFORMATION AXIS PRECIP
LOOKING SHORT LIVED...THOUGH ENOUGH COLD AIR COULD ARRIVE ALLOWING
FOR A MIX OF PRECIP TYPES. NEXT IS LAKE EFFECT POTENTIAL. IT WILL
CERTAINLY BE COLD ENOUGH FOR LAKE EFFECT PROCESSES WITH LAKE-H85
DELTA TS OF 18-19 C. ORGANIZATION OF BANDS LOOKS TO BE THE
CHALLENGE WITH WINDS STEADILY COMING AROUND FROM NORTHWEST TO
NORTH WITH SPEEDS POTENTIALLY BEING VERY STRONG THROUGH THE
UNSTABLE LAYER. IN ADDITION...WITH THE STRONG HIGH BUILDING IN
INVERSION HEIGHTS MAY QUICKLY FALL PUTTING AN END TO ANY
MEANINGFUL PRECIP...ESPECIALLY BY THE TIME A DUE NORTH FETCH
FAVORING STRONG CONVERGENCE OVER THE LAKE SETS UP FRIDAY
NIGHT/SATURDAY MORNING. LAKE PRECIP TYPE WILL ALSO BE A CONCERN
AND BE DEPENDENT ON LOW LEVEL TEMPS BUT IF PRECIP CAN OCCUR AFTER
DARK FRIDAY THEN IT COULD BE ALL FROZEN. GIVEN THE TIME RANGE AND
THE POTENTIAL LIMITING FACTORS WILL CARRY LOW CHANCE POPS FOR
AREAS NEAR THE LAKE FAVORED BY A NORTH TO NORTH-NORTHEAST WIND.
ANOTHER CONCERN WILL BE THE POTENTIAL FOR VERY STRONG WIND GUSTS
ALONG THE LAKESHORE...AS WELL AS LARGE WAVES IMPACTING THE
SHORELINE THANKS TO THE LONG FETCH OF NORTH WIND. AGAIN...TOO
EARLY TO PIN DOWN DETAILS BUT THE ABOVE CONCERNS ARE HIGHLIGHTED
GIVEN THE SYNOPTIC EXPECTATIONS. THINGS QUIET DOWN SATURDAY AS THE
HIGH MOVES IN LEAVING HIGHS ONLY IN THE 40S.

SUNDAY INTO EARLY NEXT WEEK...THE SURFACE HIGH SHIFTS EAST SUNDAY
WITH A SHARP UPPER RIDGE BUILDING IN FROM THE WEST BRINGING A PUSH
OF WARMER AIR. A LARGE TROUGH WILL BE OVER THE WEST AND GUIDANCE
CONTINUES TO SHOW THIS SPLITTING WITH A TROUGH TRACKING NORTHEAST
ACROSS THE NORTHERN HIGH PLAINS AND INTO MANITOBA INTO MONDAY. THIS
WILL PUSH THE UPPER RIDGE EAST BUT THE ATTENDANT SURFACE LOW WILL
BRING A COLD FRONT TO THE AREA SOME TIME MONDAY OR TUESDAY. WITH THE
PARENT LOW SO FAR TO THE NORTH THE FRONT MAY SLOW AND STALL NEAR THE
AREA. SUNDAY SHOULD SEE HIGHS MODERATE A BIT WITH HIGHS INTO THE 50S
MONDAY. PRECIP TIMING WILL BE DICTATED BY THE TIMING OF THE EXPECTED
FRONT.

MDB

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* GUSTY WESTERLY WINDS THIS EVENING AND AGAIN WEDNESDAY. CMS

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

GUSTY WESTERLY WINDS WILL DIMINISH THIS EVENING AS THE GRADIENT
SLOWLY WEAKENS BETWEEN DEPARTING LOW PRESSURE ACROSS EASTERN
ONTARIO AND APPROACHING HIGH PRESSURE OVER THE PLAINS. SPEEDS MAY
DIP INTO 7-10KT RANGE OVERNIGHT BUT WILL INCREASE AGAIN WEDNESDAY
MORNING AS THE LOW LEVELS BEGIN TO MIX...WITH GUSTS INTO THE MID
TO UPPER TEEN KT RANGE. AS THE HIGH CONTINUES TO SPREAD SOUTHEAST
OVER THE OHIO VALLEY...GUSTS WILL DIMINISH IN THE AFTERNOON AND
THEN SPEEDS WILL RAPIDLY DIMINISH TO 5 KTS OR LESS WEDNESDAY
EVENING.

BKN/OVC 4-6KFT CIGS MAY LOWER INTO THE 3-4KFT RANGE LATER THIS
EVENING AND OVERNIGHT BUT WITH SOME HOLES SHOWING UP OVER SOUTHERN
WI...CONFIDENCE REGARDING HOW PREVAILING BKN CIGS REMAIN OVERNIGHT
IS LOW...BUT SHOULD REMAIN VFR. CMS

//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* HIGH FOR WINDS THRU THE PERIOD. CMS

//OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z...

* THURSDAY...SLIGHT CHANCE OF SHRA. LIGHT WEST WINDS.
* FRIDAY...SLIGHT CHANCE OF SHRA. STRONG/GUSTY NORTH WINDS.
* SATURDAY...DRY/VFR. NORTHEAST WINDS.
* SUNDAY...SLIGHT CHANCE OF SHRA. SOUTH WINDS.
* MONDAY...CHANCE OF SHRA. GUSTY SOUTH WINDS.

&&

.MARINE...
345 PM CDT

DEEPENING LOW PRESSURE CONTINUES TO MOVE NORTHEAST TOWARDS
SOUTHEAST ONTARIO THIS AFTERNOON...WHILE COLDER AIR FILTERS ACROSS
THE LAKE BEHIND THIS SYSTEM. DESPITE THIS LOW MOVING TOWARDS JAMES
BAY TONIGHT...DO EXPECT A FAIRLY TIGHT SURFACE PATTERN TO REMAIN
OVER THE LAKE. WINDS TO 30 KT WILL BE LIKELY ACROSS THE ENTIRE
LAKE TONIGHT...WITH GALE FORCE GUSTS REMAINING A POSSIBILITY AS
WELL. THERE DOES APPEAR TO BE A SMALL WINDOW LATER THIS AFTERNOON
INTO THE EVENING...CONSISTING OF A COUPLE OF HOURS...WHEN MORE
PREVAILING GALES MIGHT BE OBSERVED. THIS DURATION WILL ONCE AGAIN
BE SHORT...AND WITH GUSTS MORE LIKELY TO BE OBSERVED. SO HAVE NOT
ISSUED ANY GALE HEADLINE FOR THIS EVENING...BUT HAVE CONTINUED
GALE FORCE GUST MENTIONING IN THE GLF. WITH THE LOW FURTHER
DEPARTING TO THE NORTHEAST AND HIGH PRESSURE BUILDING NEAR THE
REGION ON WEDNESDAY...DO EXPECT DIMINISHING WINDS ACROSS THE LAKE.
THIS DIMINISHING TREND WILL LIKELY CONTINUE INTO THURSDAY...BEFORE
ATTENTION SHIFTS TOWARDS POSSIBLE STRONG WIND EVENT ON FRIDAY. LOW
PRESSURE WILL MOVE ACROSS THE GREAT LAKES REGION FRIDAY...WHILE
MUCH COLDER AIR AND STRONG HIGH PRESSURE BUILD IN BEHIND IT. THIS
WILL SET THE STAGE FOR POTENTIALLY VERY STRONG NORTHERLY WINDS
OVER THE ENTIRE LAKE. THIS SYSTEM WARRANTS CLOSE MONITORING AS
HIGH END GALES ARE APPEARING A DISTINCT POSSIBILITY...WITH THE
POTENTIAL FOR STORM FORCE WINDS ALSO THERE.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...INDIANA NEARSHORE WATERS UNTIL 10 AM
     WEDNESDAY.

     SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 4 AM WEDNESDAY.

&&

$$

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