Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 260546
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1246 AM CDT SAT JUL 26 2014

.DISCUSSION...
656 PM CDT

MAIN FORECAST UPDATES WERE TO REMOVE POPS THIS EVENING...AND THEN
SHIFT HIGHEST POPS TO THE SOUTHERN THIRD OF THE CWA AFTER MIDNIGHT
TONIGHT.

DEPARTING WAVE TO THE EAST THIS PAST AFTERNOON HAS ALLOWED FOR
DRIER CONDITIONS TO REMAIN IN PLACE EARLY THIS EVENING ACROSS ALL
OF NORTHERN ILLINOIS AND NORTHWEST INDIANA...WITH LATEST RADAR
MOSAIC SHOWING LITTLE OR NO PRECIP OVER THE ENTIRE REGION AT THIS
HOUR. WHILE WEAK FORCING ALOFT WILL REMAIN IN PLACE OWING TO WEAK
MID LEVEL IMPULSES APPROACHING FROM THE WEST A LACK OF SURFACE
FOCUS IN A HIGHLY CAPPED ENVIRONMENT...12-16C 700MB TEMPS PER RAP
ANALYSIS...WILL LIMIT ANY DEVELOPMENT THIS EVENING. OUTSIDE OF A
STRAY SPRINKLE OR LIGHT SHOWER...THIS EVENING WILL REMAIN MOSTLY
DRY AND SO HAVE DROPPED POPS DURING THIS PERIOD. WARM FRONT TO THE
SOUTHWEST WILL SLOWLY MOVE NORTH NORTHEAST OVERNIGHT WHILE
INCREASING LLJ AND WAA HELP DEVELOP SOME SHOWERS AND THUNDERSTORMS
AFTER MIDNIGHT. THE BULK OF THIS PRECIP WILL LIKELY REMAIN
CONFINED TO AREAS ALONG AND SOUTH OF INTERSTATE 80 AS IT SLIDES
EAST SOUTHEAST WITH THE VEERING LLJ...WITH THE STRONGEST STORMS
PRODUCING BRIEF HEAVY DOWNPOURS.

CURRENT CLEAR SKIES OVER NORTHEAST ILLINOIS AND NORTHWEST INDIANA
WILL QUICKLY BECOME CLOUDY ONCE AGAIN THIS EVENING...AS STRATUS
DECK SPREADS EAST AND MID LEVEL CLOUDS DEVELOP OVERNIGHT.

RODRIGUEZ

//PREV DISCUSSION...

254 PM...FORECAST CONCERNS INCLUDE THUNDERSTORM CHANCES AND
TIMING THROUGH SUNDAY EVENING...HIGH TEMPS THIS WEEKEND AND THEN
MUCH COOLER TEMPS EARLY NEXT WEEK.

CONFIDENCE REGARDING CONVECTIVE TRENDS OVER THE NEXT 12 TO 18
HOURS IS FAIRLY LOW. A WEAK UPPER WAVE IS MOVING EAST/SOUTHEAST
ACROSS SOUTHERN WISCONSIN WHICH MAY ALLOW ISOLATED ACTIVITY TO
DEVELOP OVER THE NEXT FEW HOURS. ISOLATED ACTIVITY OVER WESTERN IL
APPEARS TO BE ON THE TRAILING EDGE OF THE WAVE PUSHING ACROSS
SOUTHERN IL BUT ALSO ALONG AN INSTABILITY AXIS EXTENDING INTO
EASTERN IA. SHORT TERM/HI RES GUIDANCE SUGGESTS JUST ISOLATED
COVERAGE THROUGH EARLY THIS EVENING THEN DRY THROUGH LATE EVENING
AND POSSIBLY INTO THE OVERNIGHT HOURS.

AS LOW LEVEL MOISTURE RETURNS TONIGHT ANOTHER WAVE CURRENTLY OVER
EASTERN SOUTH DAKOTA MAY AID THUNDERSTORM DEVELOPMENT OVERNIGHT
TOWARD SUNRISE AND PERHAPS OVER THE EASTERN CWA DEPENDING ON
WHEN...AND IF...ANYTHING DOES DEVELOP...THEN EXIT TO THE SOUTHEAST
QUICKLY SATURDAY MORNING. OPTED TO MAINTAIN LIKELY POPS FOR THIS
TIME PERIOD BUT THERE IS LITTLE CONTINUITY IN THE MODELS AND ITS
POSSIBLE MUCH OF THE OVERNIGHT COULD END UP DRY.

TRENDS BECOME A BIT MORE CONFIDENT ON SATURDAY AS THE NORTHERN CWA
REMAINS CAPPED BUT INSTABILITY ACROSS THE SOUTHERN CWA/CENTRAL IL
INCREASES BY LATE AFTERNOON FOR EXPECTED THUNDERSTORM DEVELOPMENT.
THE SEVERE THREAT WOULD BE PRIMARILY DAMAGING WINDS BUT WITH
DEWPOINTS SURGING BACK INTO THE 70S...HEAVY RAIN WILL BE POSSIBLE
AND WITH TRAINING OF STORMS OVER THE SAME AREAS...SOME POTENTIAL
FOR FLOODING WILL ALSO BE POSSIBLE. BULK OF THIS ACTIVITY APPEARS
TO REMAIN SOUTH OF THE I-80 CORRIDOR WITH THE ACTIVITY MOVING
SOUTHEAST OF THE CWA SATURDAY NIGHT.

HIGH TEMPERATURES ON SATURDAY WILL BE DEPENDENT ON THUNDERSTORMS...
AND HOW SOON THEY FORM AS WELL AS CLOUD COVER. LOW LEVEL THERMAL
PROFILES WOULD SUGGEST UPPER 80S TO AROUND 90 IS DOABLE BUT MADE
NO CHANGES TO CURRENT FORECAST OF MID/UPPER 80S. WITH LITTLE
CHANGE TO AIRMASS SATURDAY NIGHT...AND LIKELY WET GROUND ACROSS
THE SOUTHERN CWA...COMBINED WITH LIGHT WINDS...FOG DEVELOPMENT
SEEMS LIKELY LATE SATURDAY NIGHT INTO SUNDAY MORNING...PRIMARILY
ACROSS THE SOUTHERN CWA.

LOW PRESSURE WILL MOVE ACROSS THE WESTERN LAKES SUNDAY WITH A
TRAILING COLD FRONT MOVING ACROSS THE AREA SUNDAY MORNING. WINDS
WILL SHIFT WEST/NORTHWEST BEHIND THE FRONT AND FORECAST SOUNDINGS
SUGGEST IT WOULD BECOME QUITE BREEZY/WINDY SUNDAY AFTERNOON. ANY
THUNDERSTORM POTENTIAL WOULD LIKELY BE SHORT-LIVED AND ALONG/AHEAD
OF THE FRONT.

A SECOND COLD FRONT/SURGE OF COLDER AIR WILL THEN MOVE SOUTH
ACROSS THE WESTERN LAKES SUNDAY NIGHT. THIS COULD TRIGGER A FEW
SHOWERS OVERNIGHT BUT BULK OF THIS ACTIVITY SHOULD REMAIN
NORTHEAST OF THE CWA. WINDS WILL SHIFT NORTHERLY BEHIND THIS FRONT
WITH HIGHS ON MONDAY ONLY IN THE LOWER/MID 70S. TEMPS MODERATE
BACK INTO THE UPPER 70S/NEAR 80 BY THE MIDDLE OF NEXT WEEK WITH
PERIODIC CHANCES FOR SHOWERS/THUNDERSTORMS...MAINLY IN THE
AFTERNOON/EARLY EVENING. CMS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* MVFR CIGS LIKELY AT TIMES THROUGH MID-MORNING.
* SMALL THREAT OF SHRA/TSRA THROUGH THIS MORNING.
* POSSIBLE WIND SHIFT TO EAST WITH A LAKE BREEZE LATE THIS
  AFTERNOON.


//DISCUSSION...UPDATED 06Z...

A DIFFUSE LOW-LEVEL TROUGH FROM MN DOWN TO KS CONTINUES TO INCH
EASTWARD. MOISTURE CONTINUES TO SLOWLY INCREASE ACROSS THE AREA
AHEAD OF THIS. WITH THAT INCREASE...2000-3500 FT CIGS ARE
WIDESPREAD ACROSS NORTHERN IA/WI/NORTHERN IL AND EXPECTING THAT
OVER THE TAF SITES THROUGH AT LEAST DAYBREAK AND LIKELY A FEW
HOURS LONGER. THERE IS SOME INDICATION ROCKFORD COULD DROP DOWN TO
NEAR 1000 FT AROUND DAYBREAK. WARM AIR ADVECTION ASCENT MAY BE
ENOUGH PRIOR TO DAYBREAK TO SPARK A FEW SHRA/TSRA BUT MAINLY SOUTH
OF THE TAF SITES. CONVECTION EXPECTED PRIOR TO DAYBREAK ACROSS
PARTS OF SD INTO NW/NC IA IS EXPECTED TO WEAKEN THIS MORNING AS IT
SHIFTS EAST. SO WHILE CANNOT RULE OUT AND SHRA/TSRA TODAY...THE
FORCING IS PRETTY NEBULOUS DESPITE HIGH MOISTURE AROUND. SO HAVE
KEPT THE TAFS PRIMARILY DRY. THE BETTER FOCUS TONIGHT WILL BE
ALONG A WARM FRONT BOUNDARY DRAPED ACROSS CENTRAL IL AND IN.

WINDS ARE A CHALLENGE TODAY DUE PARTLY TO THE LIGHT GRADIENT AND
MORNING CLOUD COVER LIKELY TO INHIBIT MIXING TO SOME DEGREE. IT
WOULD APPEAR A LAKE BREEZE WILL DEVELOP BUT HOW FAR INLAND THIS
PROPAGATES IS THE MAIN UNCERTAINTY. HAVE OPTED TO INCLUDE IN THIS
SET OF TAFS BUT NOT MENTION A WIND SHIFT AT ORD UNTIL LATE IN THE
DAY/EARLY EVE...AS ANY LAKE BREEZE ARRIVAL WOULD LIKELY BE LATER.


//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH IN MVFR CIGS OCCURRING THROUGH AT LEAST 12Z AND MEDIUM IN
  BASES REMAINING ABOVE 1500 FT.
* LOW IN ANY SHRA/TSRA THROUGH THE DAY TODAY BUT ANY ARE LIKELY TO
  BE TEMPORARY.
* LOW IN WIND DIRECTION THROUGH MUCH OF THE TAF INCLUDING WHETHER
  AN EASTERLY SHIFT WILL OCCUR AT BOTH AIRPORTS.


//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...CHANCE OF TSRA.

MONDAY...VFR. GUSTY NNE WINDS.

TUESDAY THROUGH THURSDAY...GENERALLY VFR.

MTF/IZZI

&&

.MARINE...
205 PM CDT

SOUTHERLY WINDS WILL CONTINUE TO STRENGTHEN OVER THE LAKE THIS
AFTERNOON AND TONIGHT AS HIGH PRESSURE MOVES OFF THE MID ATLANTIC
COAST WHILE LOW PRESSURE MOVES ACROSS THE MIDDLE AND UPPER
MISSISSIPPI VALLEY. THE SURFACE TROUGH LEADING TO THE INCREASE IN
WINDS WILL WEAKEN AND DISSIPATE SATURDAY. LOW PRESSURE DROPPING
OUT OF THE CANADIAN ROCKIES AND TRACKING ACROSS THE SOUTHERN
CANADIAN PRAIRIES WILL BECOME THE MORE DOMINANT FEATURE TO AFFECT
LAKE MICHIGAN AS IT TRACKS ACROSS LAKE SUPERIOR AND LAKE MICHIGAN
SATURDAY NIGHT. WINDS WILL BECOME WEAKER AND MORE VARIABLE WITH THE
LOW WEAKENING AS IT PASSES ACROSS THE WESTERN GREAT LAKES REGION
SATURDAY NIGHT. A SURGE OF MUCH COOLER AIR WITH PUSH SOUTH DOWN
THE LENGTH OF THE LAKE SUNDAY NIGHT AND MONDAY WITH WINDS BECOMING
NORTHERLY AND INCREASING TO ARND 30KT...WITH A FEW GALE FORCE
GUSTS TO 35 KT POSSIBLE. THE MOST LIKELY PERIOD TO SEE THE GALE
FORCE GUSTS SHOULD BE SATURDAY NIGHT INTO SUNDAY MORNING WHEN THE
COLD ADVECTION FOLLOWING THE PASSAGE OF THE LOW AND AN ASSOCIATED
COLD FRONT WILL BE THE STRONGEST. HIGH PRESSURE WILL QUICKLY BUILD
ACROSS THE PLAINS MONDAY AND SPREAD ACROSS THE UPPER MISSISSIPPI
VALLEY AND WESTERN GREAT LAKES MONDAY NIGHT AND THEN SETTLE INTO
THE OHIO VALLEY BY TUESDAY. ANOTHER WEAK LOW TRACKING
SOUTHEASTWARD ACROSS ONTARIO WILL KEEP GENERALLY NORTHWESTERLY TO
WESTERLY WINDS OVER THE LAKE INTO TUESDAY.

WHILE A GALE HEADLINE WILL NOT BE ISSUED WITH THE STRONG NORTH
WINDS SUNDAY NIGHT AND MONDAY...WINDS AND WAVES WILL LIKELY BE
SUFFICIENT TO NECESSITATE A SMALL CRAFT ADVISORY.

KREIN

&&

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

$$

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