Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 260255
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
955 PM CDT FRI JUL 25 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 03Z...

* MVFR CIGS PROBABLY DEVELOPING TONIGHT
* SMALL THREAT OF SHRA/POSSIBLE TSRA LATE TONIGHT/EARLY SATURDAY
  MORNING
* WIND SHIFT TO EAST WITH LAKE BREEZE POSSIBLE SATURDAY AFTERNOON

IZZI

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

UPPER LEVEL DISTURBANCE PUSHING SOUTHEAST OF THE REGION SHOULD
ALLOW FOR GENERALLY DRY CONDITIONS THROUGH THE EVENING INTO THE
START OVER THE OVERNIGHT HOURS. INCREASING MOISTURE SURGING INTO
THE REGION LATE TONIGHT INTO EARLY SATURDAY COULD RESULT IN SCTD
SHRA/TSRA DEVELOPING WITH LATEST MODEL GUIDANCE SUGGESTING THE
BEST CHANCES WILL BE SOUTH OF CHICAGO AND ROCKFORD.

WINDS HAVE BEEN BACKING TO THE SOUTH AND EVEN SOUTHEAST OVER NW IL
AND IA AS DEVELOPING WARM FRONT TAKES SHAPE. ANTICIPATE THIS TREND
TO CONTINUE EAST INTO CHGO TERMINALS THIS EVENING WITH WINDS
PROBABLY BECOMING MORE SOUTHERLY AND POSSIBLY EVEN A BIT EAST OF
DUE SOUTH...THOUGH SPEEDS EXPECTED TO BE LIGHT. VERY LOW
CONFIDENCE IN WIND DIRECTION TOMORROW THOUGH SOME SORT OF WESTERLY
COMPONENT SEEMS PROBABLE...HOWEVER AM CONCERNED THAT SPEEDS COULD
BE LIGHT ENOUGH TO ALLOW LAKE BREEZE TO FORM.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* MEDIUM CONFIDENCE IN CIGS FORECAST THROUGH PERIOD
* MEDIUM CONFIDENCE IN TERMINALS REMAINING DRY THROUGH PERIOD
* LOW CONFIDENCE IN WIND DIRECTION SATURDAY

IZZI

//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.

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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