Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 211144
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
644 AM CDT TUE OCT 21 2014

.DISCUSSION...
218 AM CDT

BELOW AVERAGE TEMPERATURES THE NEXT COUPLE OF DAYS WILL GRADUALLY
GIVE WAY TO A BOUT OF INDIAN SUMMER OVER THE WEEKEND.

WATER VAPOR IMAGERY SHOWS AN AMPLIFYING UPPER TROUGH OVER THE
EASTERN CONUS THIS MORNING WITH LAST EVENING`S UPPER AIR ANALYSIS
SHOWING A POCKET OF SUB-FREEZING 850MB TEMPS ADVECTING SOUTH INTO
THE WESTERN GREAT LAKES REGION. THE CHILLY AIR MOVING OVER THE
RELATIVELY MILDER LAKE WATER IS CURRENTLY RESULTING IN A MARGINAL
LAKE EFFECT SHOWER SET-UP WITH SCATTERED LIGHT SHOWERS OR SPRINKLES
SHOWING UP OVER SOUTHERN LM INTO NW IN. LOW LEVEL FLOW WILL VEER TO
MORE NORTHEASTERLY DIRECTION TODAY AND SEND SOME OF THE LAKE EFFECT
CLOUDINESS AND POTENTIALLY SPRINKLES/LIGHT SHOWERS INTO EXTREME NE
IL THIS MORNING. RELATIVELY LOW INVERSION HEIGHTS AND SOMEWHAT WEAK
INSTABILITY MAKE THE CHANCES OF MEASURABLE PRECIP LOW AND HAVE KEPT
POPS IN THE LOWER END OF THE CHANCE CATEGORY. CLOUDINESS SHOULD BE
MOST PREVALENT TODAY NEAR THE LAKE WITH BETTER INCREASINGLY SUNNY
SKIES WELL INLAND. CLOUD COVER SHOULD KEEP HIGHS STRUGGLING INTO THE
LOWER 50S IN NE IL WHILE MID OR EVEN UPPER 50S ARE POSSIBLE OUT
TOWARD MENDOTA AND FAR SOUTHWESTERN CWA WHERE MORE SUN CAN BE
EXPECTED.

LOW CONFIDENCE IN THE EXTENT OF LAKE CLOUDINESS TONIGHT...WHICH
WOULD PLAY A ROLE IN LOW TEMPS. MORE CLOUDS NEAR THE LAKE WOULD
RESULT IN LOWS A COUPLE DEGREES WARMER THAN CURRENTLY FORECAST AND
VICE VERSA IF MAINLY CLEAR. SUNNY SKIES ARE EXPECTED WEDNESDAY AS
TRANSIENT UPPER RIDGE BUILDS INTO THE AREA BETWEEN DEPARTING DEEP
UPPER TROUGH/LOW AND THE NEXT STRONG NORTHERN STREAM SHORTWAVE
SLATED TO ARRIVE IN OUR AREA LATER THURSDAY. NOT LOOKING FOR MUCH OF
A CHANCE OF SUBSTANTIAL WARMING WEDNESDAY WITH A STILL SOMEWHAT COOL
EASTERLY LOW LEVEL FLOW AND ONLY WEAK LOW LEVEL WARM AIR ADVECTION.

BY THURSDAY SHOWER CHANCES WILL BE ON THE INCREASE AS SHARP NORTHERN
STREAM TROUGH TRACKS SOUTHEAST INTO THE WESTERN LAKES. LACK OF
RETURN FLOW SHOULD RESULT IN LIMITED MOISTURE FOR THE SYSTEM...BUT
FAIRLY STRONG FORCING SHOULD ALLOW FOR A PERIOD OF SHOWERS ACROSS
THE CWA THURSDAY AFTERNOON OR EVENING. NOT MUCH COOLING BEHIND THIS
SYSTEM FRIDAY...THEN A FAST MOVING WEAK CANADIAN COLD FRONT SHOULD
BRING A BRIEF COOL DOWN SATURDAY BEFORE MORE SUBSTANTIAL WARM AIR
ADVECTION SUNDAY INTO MONDAY LIKELY SENDS TEMPERATURES NEAR IF NOT
INTO THE 70S ACROSS THE CWA. MEDIUM RANGE MODELS DO SHOW A
PROGRESSIVE LONG WAVE TROUGH MOVING ACROSS THE CONUS BY EARLY NEXT
WEEK WITH COLD FRONT LIKELY TO ARRIVE LATER MONDAY OR TUESDAY
BRINGING AN END TO OUR BRIEF BUT POTENTIALLY IMPRESSIVE WARM UP.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 12Z...

* NORTH/NORTHEAST WINDS 10-14 KTS AND GUSTY MID MORNING THRU LATE
  AFTERNOON.
* SLIGHT CHANCE FOR SHRA MID MORNING THRU MID AFTERNOON.
* MVFR CIGS MID MORNING THRU MID AFTERNOON. CMS

//DISCUSSION...UPDATED 12Z...

NO SIGNIFICANT CHANGES TO PREVIOUS FORECAST. NORTHERLY WINDS WILL
INCREASE TO 10-14KTS IN THE NEXT FEW HOURS AND TURN MORE TO THE
NORTHEAST THIS MORNING AND THIS AFTERNOON. GUSTS INTO THE 16-20KT
RANGE WILL ALSO DEVELOP MID MORNING AND CONTINUE INTO THE
AFTERNOON. WINDS WILL QUICKLY DIMINISH BY EARLY EVENING AND TURN
MORE EAST/NORTHEAST TONIGHT.

LAKE EFFECT RAIN SHOWERS CONTINUE TO MOVE SOUTH INTO NORTHWEST
INDIANA AND WILL AFFECT GYY AT TIMES THIS MORNING. AS THE WINDS
TURN MORE NORTHEAST...THESE SHOWERS MAY MOVE FAR ENOUGH INLAND TO
REACH ORD/MDW. HOWEVER...HAVE MAINTAINED A DRY FORECAST GIVEN THE
EXPECTED SHORT DURATION AND ISOLATED COVERAGE.

4-5KFT VFR CIGS WILL LOWER TO MVFR MID/LATE MORNING...WITH MVFR
CIGS ACROSS EASTERN WI AND SPREADING SOUTH. TIMING AND DURATION
WILL LIKELY NEED TO BE ADJUSTED WITH MORNING UPDATES. CMS

//ORD AND MDW CONFIDENCE...UPDATED 12Z...

* HIGH FOR WIND SPEEDS/GUSTS/DIRECTIONS THRU THE PERIOD.
* LOW FOR SHRA MID MORNING THRU MID AFTERNOON.
* MEDIUM FOR MVFR CIGS. CMS

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

* WEDNESDAY NIGHT...DRY/VFR.
* THURSDAY...CHANCE OF SHRA. SOUTH WINDS.
* FRIDAY AND SATURDAY...DRY/VFR. WEST/SOUTHWEST WINDS.
* SUNDAY...DRY/VFR. SOUTH WINDS.
* MONDAY...SLIGHT CHANCE OF SHRA. GUSTY SOUTHWEST WINDS.

&&

.MARINE...

258 AM...LOW PRESSURE NEAR LAKE ONTARIO WILL MOVE OFF THE MID
ATLANTIC COAST WEDNESDAY MORNING THEN DEEPEN AGAIN AS IT MOVES
NORTHEAST ALONG THE NEW ENGLAND COAST WEDNESDAY NIGHT THROUGH
THURSDAY NIGHT. HIGH PRESSURE OVER ONTARIO WILL STRENGTHEN AS IT
MOVES INTO QUEBEC TONIGHT AND WEDNESDAY...WITH A TRAILING WEAKER
RIDGE BUILDING ACROSS THE WESTERN LAKES TODAY AND CROSSING LAKE
MICHIGAN TONIGHT. NORTH WINDS ARE STILL EXPECTED TO INCREASE TO
30 KT WITH A TIGHT GRADIENT BETWEEN THE APPROACHING RIDGE AND THE
DEPARTING LOW BUT SPEEDS WILL PROBABLY DIMINISH A LITTLE FASTER
THAN PREVIOUSLY INDICATED LATE THIS AFTERNOON INTO THIS EVENING.
THE RIDGE WILL BECOME STATIONARY OVER THE EASTERN LAKES WEDNESDAY
NIGHT AND THURSDAY AS IT WEAKENS. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS UNTIL 7 AM WEDNESDAY.

&&

$$

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