Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 251905
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
205 PM CDT FRI JUL 25 2014

.DISCUSSION...
324 AM CDT

SYNOPSIS...A TRICKY UNSETTLED FORECAST IS EXPECTED TODAY THROUGH
SUNDAY. THEN THINGS QUIET DOWN FOR THE BEGINNING OF THE WORK WEEK.
SATURDAY WILL BE THE WARMEST DAY IN THE FORECAST WITH HIGHS NEAR
90.  TEMPS THEN FALL TO BELOW NORMAL SUNDAY AND SLOWLY BEGIN TO
CLIMB BACK TO NEAR 80 BY LATE NEXT WEEK.

TODAY AND TONIGHT...
AN UPPER LEVEL HIGH IS OVER THE SOUTHWEST U.S. AND SOUTHERN PLAINS
WHILE LOW PRESSURE IS OVER THE ALBERTA/SASKATCHEWAN BORDER.  THE
HIGH WILL SLOWLY RETROGRADE THROUGH MONDAY AFTERNOON TO OVER THE SW
U.S. WHILE THE LOW PASSES OVER LAKE MICHIGAN SUNDAY EVENING.  AT THE
SURFACE HIGH PRESSURE IS OVER THE OHIO RIVER VALLEY AND IT WILL MOVE
OFF THE ATLANTIC COAST TONIGHT.  THERE ARE TWO SURFACE LOWS...ONE
OVER THE NORTHERN PLAINS AND THE SECOND CO-LOCATED WITH THE UPPER
LEVEL LOW OVER THE ALBERTA/SASKATCHEWAN BORDER.

CONVECTION IS ONGOING OVER WEST CENTRAL MINNESOTA AND IOWA VERY
EARLY THIS MORNING. THE STORMS WILL BE MOVING INTO A MORE STABLE
ENVIRONMENT AND THE LOW LEVEL JET WILL ALSO BE WEAKENING AS IT
PUSHES EAST. THERE IS HIGH CONFIDENCE THAT THE STORMS OVER IOWA WILL
WEAKEN AS THEY APPROACH THE CWA...BUT EXPECTING SHOWERS AND A COUPLE
OF STORMS TO REACH THE I-39 CORRIDOR BY MID MORNING. SOME GUIDANCE
MEMBERS SUGGEST SHOWERS AND STORMS COULD LINGER INTO THE MID
AFTERNOON HOURS BUT THINKING THEY WILL DISSIPATE BY THE EARLY
AFTERNOON.

HIGH CLOUDS WILL BE OVERHEAD AND MAY LIMIT HEATING A BIT...AS SUCH
LEFT HIGH TEMPS TODAY IN THE UPPER 70S.

MULTIPLE ROUNDS OF STORMS ARE EXPECTED WITH THE SECOND ROUND
SPREADING SOUTH THIS EVENING. THE LOW OVER THE PLAINS WILL WEAKEN AS
IT PUSHES EAST AND FORM AN OPEN TROUGH. THE LOWS WARM FRONT WILL
APPROACH THE REGION TONIGHT AND EXPECTING STORMS AHEAD OF IT. THE
NOSE OF THE LOW LEVEL JET WILL ALSO BE OVER NORTHWEST IL THIS
EVENING PROVIDING ADDITIONAL LIFT.  CAPE WILL BE LIMITED WITH
MODEL SOUNDINGS SHOWING SHALLOW AREAS OF CAPE AT 1000 J/KG OR LESS.
PWAT VALUES WILL BE AROUND 1.9 INCHES SO TORRENTIAL DOWNPOURS ARE
THE MOST LIKELY HAZARD.

SATURDAY...
THE PLAINS LOW/TROUGH MOVES OVER THE MIDWEST WITH SATURDAY
HAVING THE BEST CHANCE FOR SEVERE WEATHER ESPECIALLY SOUTH OF I-88.
PWAT VALUES REMAIN HIGH AROUND 1.8 INCHES IN THE MORNING AND THEN
INCREASE TO 2-2.3 INCHES SOUTH OF I-80 SATURDAY AFTERNOON.  CAPE
VALUES WILL BE MUCH MORE HEALTHY IN THE 3000 J/KG RANGE ESPECIALLY
ALONG AND SOUTH OF THE I-80 CORRIDOR.  EXPECTING STORMS TO FIRE
ALONG THE LOWS COLD FRONT SATURDAY AFTERNOON AND EVENING WITH THE
CHANCES OF SHOWERS AND STORMS INCREASING AS YOU HEAD SOUTH.  SOME OF
THESE STORMS MAY BE SEVERE WITH TORRENTIAL DOWNPOURS.  HAIL AND WIND
LOOK TO BE THE MAIN SEVERE THREATS.

SATURDAY WILL FEEL UNPLEASANT TO MANY WITH HIGHS IN THE UPPER 80S
AND HIGH DEWPOINTS.  MAX HEAT INDICES WILL BE IN THE 90S...WITH MID
TO UPPER 90 HEAT INDICES EXPECTED SOUTH OF I-80.

SUNDAY...
THE LOW OVER CANADA DRIFTS SOUTHEAST MOVING OVER WISCONSIN SUNDAY.
ADDITIONAL THUNDERSTORMS ARE POSSIBLE NORTH OF THE I-80
CORRIDOR...WITH THE BEST CHANCES ALONG THE IL/WI STATE LINE. THE
STORMS PUSH EAST OF THE CWA IN THE EVENING. COOLER AIR ASSOCIATED
WITH THE LOW ALSO SPREAD SOUTH WITH HIGHS ON SUNDAY ONLY EXPECTED TO
GET INTO THE LOW TO MID 80S.  OVERNIGHT LOWS WILL BE AROUND
60...EXCEPT FOR DOWNTOWN WHICH WILL BE IN THE LOW 60S.

MONDAY THROUGH THURSDAY...
WE REMAIN UNDER THE UPPER LEVEL TROUGH THROUGH NEXT WEEK WITH A
SURFACE HIGH MOVING OVER THE REGION BY MID WEEK.  THERE ARE
OCCASIONAL CHANCES OF SHOWERS AND STORMS BUT NONE OF THOSE CHANCES
LOOK ALL THAT IMPRESSIVE AT THIS POINT.  THE BIGGER STORY WILL BE
ANOTHER EXTENDED PERIOD OF BELOW NORMAL TEMPS...ALTHOUGH
TEMPERATURES WILL BE SLOWLY RISING THROUGH THE END OF THE FORECAST
PERIOD.

JEE

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* SOUTH WINDS GUSTING AROUND 20 KT THIS AFTERNOON.

* POTENTIAL FOR A FEW SCATTERED SHRA THIS AFTERNOON.

* CHANCE OF TSRA INCREASES LATE TONIGHT.

* PERIOD OF MVFR CIG/FOG POSSIBLE EARLY SATURDAY.

* WIND DIRECTION SOMEWHAT VARIABLE SAT MORNING.

RATZER

//DISCUSSION...UPDATED 18Z...

LOW PRESSURE WAS OVER EASTERN NEBRASKA AT MIDDAY...WITH A WARM
FRONT EXTENDING SOUTHEAST ACROSS THE LOWER MISSOURI RIVER VALLEY.
CIRCULATION ASSOCIATED WITH A MID-LEVEL DISTURBANCE/REMNANT MCV
OVER SOUTHERN WI WAS PRODUCING SOME RAIN ACROSS WI...BUT ONLY
SPOTTY SHRA INTO NORTHERN FOR THE MOST PART...WHILE A COMPLEX OF
THUNDERSTORMS CONTINUES TO MOVE SOUTHEAST ALONG THE MISSISSIPPI
RIVER INTO WESTERN/SOUTHERN IL. TERMINALS WILL REMAIN IN AN AREA
OF BROAD MOIST ASCENT INTO TONIGHT...WITH NOCTURNAL INCREASE IN
LOW LEVEL JET AND AN APPROACHING MID-LEVEL WAVE EXPECTED TO
EVENTUALLY SHIFT THE ELEVATED WARM FRONTAL ZONE EASTWARD AND
PRODUCE SCATTERED THUNDERSTORM THREAT OVER THE TERMINALS LATER
TONIGHT. PATTERN IS RELATIVELY MESSY HOWEVER...WITH FAIRLY LOW
CONFIDENCE IN TIMING DETAILS BEYOND THE OVERALL TREND AT THIS
TIME. AT THIS TIME HOWEVER...IT APPEARS THAT THE GREATEST
THUNDERSTORM THREAT WILL BE TOWARD/AFTER MIDNIGHT. LOW LEVEL JET
THEN TO BECOME MORE WEST/NORTHWEST BY SATURDAY
MORNING...DECREASING THUNDERSTORM POTENTIAL OVER TERMINALS AFTER
SUNRISE. SOME POTENTIAL WILL EXIST FOR BRIEF PERIOD OF MVFR
CEILING AND SOME GROUND FOG WILL EXIST EARLY SATURDAY MORNING
ESPECIALLY WHERE ORGANIZED RAINS FALL.

SOUTHERLY SURFACE WINDS GUSTING AROUND 20 KT THIS AFTERNOON IN
RESPONSE TO PRESSURE FALLS ACROSS WI/IA...APPARENTLY ENHANCED OVER
WESTERN IL BY WAKE LOW BEHIND MISSISSIPPI VALLEY THUNDERSTORM
COMPLEX. WINDS DIMINISH TONIGHT AFTER SUNSET AS GRADIENT WEAKENS
WITH APPROACH OF SURFACE TROUGH. WINDS SHOULD SHIFT MORE
WEST/NORTHWEST SATURDAY MORNING AS SURFACE TROUGH/COLD FRONT SAGS
SOUTHEAST ACROSS THE AREA...THOUGH GUIDANCE INDICATES SOME
VARIABILITY IN WIND DIRECTION IN WEAK GRADIENT NEAR THE TROUGH.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* LOW CONFIDENCE IN SHRA THIS AFTN/EVENING. MEDIUM CONFIDENCE IN
  TSRA LATE TONIGHT.

* MEDIUM CONFIDENCE IN WIND TRENDS THIS AFTERNOON/EVENING. LOW
  CONFIDENCE IN WIND DIRECTION DETAILS SATURDAY MORNING.

* LOW CONFIDENCE IN MVFR CIG/VIS DEVELOPMENT LATE TONIGHT/EARLY
  SATURDAY.

RATZER

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

SATURDAY NIGHT...SMALL CHANCE OF TSRA.
SUNDAY...CHANCE OF TSRA.
MONDAY...VFR LIKELY. STRONG NORTH-NORTHEAST WINDS.
TUESDAY...VFR.
WEDNESDAY-THURSDAY...SLIGHT CHANCE OF TSRA.

MTF

&&

.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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