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[Printable]
085
FXUS63 KLOT 250911
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
411 AM CDT FRI APR 25 2014

.DISCUSSION...
329 AM CDT

SPRING TODAY...GONE TOMORROW AND THROUGH THE WEEKEND (ESPECIALLY FOR
AREAS NEAR THE LAKE).

PAIR OF UPPER LOWS AND ASSOCIATED SURFACE TROUGHINESS WILL SHIFT
EAST OF THE REGION THIS MORNING WITH WESTERLY WINDS LOCKING IN TODAY
AND ADVECTING IN MUCH DRIER AIR MASS. THE AIR MASS ADVECTING IN IS
OF PACIFIC ORIGIN AND WARMED INTO THE LOWER 70S OVER NEBRASKA
THURSDAY AND GIVEN THE ANTICIPATED DEEPLY MIXED BOUNDARY LAYER AND
AMPLE SUNSHINE WOULD EXPECT HIGHS IN THE UPPER 60S/LOWER 70S TODAY.
WESTERLY FLOW SHOULD BE PLENTY STRONG TO KEEP THE MARINE LAYER AND
ASSOCIATED COOLING OFFSHORE ALLOWING WARMTH TO MAKE IT RIGHT UP TO
THE BEACHES TODAY.

WEAK SECONDARY COLD FRONT WILL MOVE ACROSS THE AREA TONIGHT AND
WHILE THE SYNOPTIC PUSH OF COLDER AIR IS WEAK...THE WIND SHIFT TO
NORTHERLY WILL GET AUGMENTED BY LAKE MICHIGAN AND RESULT IN A FAIRLY
PRECIPITOUS FALL IN TEMPERATURES NEAR THE LAKE LATER TONIGHT. WEAK
SHORTWAVE AND ASSOCIATED MID LEVEL MOISTURE COMBINED WITH FAIRLY
STEEP MID LEVEL LAPSE RATES COULD BE ENOUGH TO KICK OFF SOME SPOTTY
LIGHT SHOWERS OR SPRINKLES OVERNIGHT TONIGHT...BUT CHANCES FOR
MEASURABLE PRECIP LOOK LOW.

THE SHIFT IN WINDS OFF THE LAKE TONIGHT WILL MARK THE BEGINNING OF
WHAT LOOKS TO BE A PROLONGED PERIOD OF COLD EASTERLY FLOW OFF THE
LAKE INTO NE IL. LARGE AND DEEP UPPER TROUGH SHOULD TRANSLATE
EASTWARD ACROSS THE ROCKIES AND RESULT IN STRONG SURFACE
CYCLOGENESIS OVER THE PLAINS OVER THE WEEKEND...WHICH WILL RESULT IN
AN STRENGTHENING PRESSURE GRADIENT AND FLOW OFF THE LAKE THIS
WEEKEND. SOME THREAT OF SHOWERS EXISTS SAT NIGHT AS LEAD WAVE
EMANATES NORTHEAST FROM THE DEEP TROUGH...BUT DOES LOOK LIKE WE
COULD EEK OUT A MOSTLY DRY DAY SUNDAY. BY SUNDAY NIGHT THROUGH THE
MIDDLE OF NEXT WEEK THE LARGE/DEEP CUT OFF LOW SHOULD MEANDER
EASTWARD AND SETTING UP WHAT LOOKS TO BE A PREDOMINANTLY WET PERIOD
WITH WAVES OF RAIN AND SHOWERS AND POSSIBLY A THUNDERSTORM OR TWO.
REALLY IMPOSSIBLE TO PICK OUT ANY POTENTIALLY DRY OR EVEN DRIER
PERIODS...SO AM LEFT WITH NO CHOICE BUT TO MAINTAIN POPS THROUGH THE
DAY 7 PERIOD.

TEMPERATURES WILL BE MORE TRICKY...ESPECIALLY SOUTHERN CWA. HOWLING
EASTERLY WINDS OFF THE LAKE SHOULD KEEP TEMPS FAIRLY STEADY IN THE
40S THROUGH THE WEEKEND INTO EARLY NEXT WEEK ALONG THE ILLINOIS
SHORE. FARTHER SOUTH...MEDIUM RANGE MODELS ATTEMPT TO LIFT THE
SYNOPTIC WARM FRONT NORTHWARD INTO OUR SOUTHERN CWA. IF THIS WERE TO
VERIFY THEN A SUBSTANTIAL WARM UP WOULD TAKE PLACE WITH A HUGE TEMP
GRADIENT ACROSS THE CWA...THOUGH THE LIKELIHOOD OF EXTENSIVE
CONVECTION ASSOCIATED WITH THIS SYSTEM CERTAINLY RAISES THE
POSSIBILITY OF THE FRONT GETTING HUNG UP FARTHER SOUTH AND THE BIG
WARM UP FOR OUR SOUTHERN CWA EITHER NOT MATERIALIZING OR TAKING MUCH
LONGER TO DO SO.

IT LOOKS UNSETTLED HEADING INTO THE MIDDLE OF NEXT WEEK...BUT
CONFIDENCE IS FAIRLY LOW IN THE FORECAST DETAILS. MODELS ARE
NOTORIOUS FOR STRUGGLING IN THEIR HANDLING OF LARGE CUT OFF LOWS AND
THAT MAKES THE PLACEMENT OF KEY SYNOPTIC FEATURES IN THE CURRENT
MODEL SOLUTIONS SUSPECT. IF CURRENT MODELS DID VERIFY THEN THE SFC
LOW WOULD LIFT NORTH OF THE AREA AND WINDS COULD TURN WESTERLY AND
END THE PROLONGED PERIOD OF EASTERLY FLOW BY MID WEEK. PLENTY OF
TIME FOR THIS TO CHANGE SO WITH LOW CONFIDENCE LARGELY STUCK WITH
THE BLENDED GUIDANCE FOR POPS/TEMPS.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* SHOWERS OR DRIZZLE THROUGH THE PREDAWN HOURS.

* PERIODS OF MVFR CIGS INTO EARLY FRIDAY MORNING. BRIEF PERIODS OF
  IFR CIGS POSSIBLE.

* WIND SHIFT TO THE NORTHWEST OVERNIGHT.

* STRONG/GUSTY WEST/NORTHWEST WINDS FRIDAY.

KREIN

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

A BAND OF RAIN ASSOCIATED WITH LOW PRESSURE MOVING THROUGH CENTRAL
ILLINOIS WILL PERSIST UNTIL ARND 07-08Z AT RFD AND 09-10Z FOR THE
CHICAGO AREA TERMINALS. LATEST RADAR IMAGERY SHOWS A SHARP CUTOFF
ALONG THE BACK EDGE OF THE PCPN AS DRIER AIR IS DRAWN AROUND THE
WRN PERIPHERY OF THE LOW. THERE MAY ALSO BE A PERIOD OF MVFR CIGS
IN A CONVERGENCE BAND ALONG AN INVERTED SFC TROUGH AXIS EXTENDING
NORTH FROM THE SFC LOW.

THE SFC LOW IS EXPECTED TO PUSH INTO NRN INDIANA THROUGH THE
MORNING HOURS...WITH WINDS BACKING THROUGH NORTHERLY TO NWLY BY
LATE MORNING. THERE COULD BE A SHORT PERIOD OF LIGHT AND VARIABLE
WINDS DURG THE PRE-DAWN HOURS AS THE INVERTED SFC TROUGH AXIS PASSES
OVER THE TERMINAL AREAS. BY LATE MORNING WIND WILL BECOME STRONGER
AND MORE GUSTY OUT OF THE NORTHWEST AS COLD ADVECTION SETS UP
BEING THE PASSING LOW PRESSURE SYSTEM. THE LATEST HIGH RESOLUTION
SHORT RANGE MODEL GUIDANCE SUGGEST THAT A WEAK SFC RIDGE WILL
BUILD IN BEHIND THE EXITING SYSTEM...ALLOWING WIND TO BACK TO MORE
DUE WESTERLY BY EARLY AFTERNOON...WITH SPEEDS REMAINING ARND
10KT...WITH A FEW HIGHER GUSTS POSSIBLE THROUGH THE REMAINDER OF
THE AFTERNOON.

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* HIGH CONFIDENCE IN PERIODS OF RAIN THROUGH THE PREDAWN HOURS.

* MEDIUM CONFIDENCE IN MVFR CIGS THROUGH THE PREDAWN HOURS...LOW
  CONFIDENCE IN IFR POTENTIAL/TIMING/DURATION.

* MEDIUM CONFIDENCE IN WIND TRENDS THROUGH THE PERIOD.

* MEDIUM TO HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS AFTER
  THE PREDAWN HOURS.

KREIN

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

* SATURDAY...DRY/VFR.
* SATURDAY NIGHT AND SUNDAY...CHANCE OF SHRA.
* SUNDAY NIGHT THROUGH MONDAY NIGHT...SHRA LIKELY. MVFR POSSIBLE.
* TUESDAY THROUGH WEDNESDAY...CHANCE OF SHRA.

&&

.MARINE...
315 AM CDT

LOW PRESSURE OVER THE CENTRAL ILLINOIS AND INDIANA BORDER WITH A
TROUGH AXIS EXTENDING NORTH THROUGH WISCONSIN WILL MOVE EAST
TODAY...WITH THE LOW MOVING TO THE EASTERN GREAT LAKES BY THIS
EVENING...WITH A TROUGH AXIS EXTENDING BACK TO LOW PRESSURE OF
29.7 INCHES OVER NORTHERN LAKE MICHIGAN. HIGH PRESSURE OF 30.0
INCHES IS EXPECTED TO BUILD OUT OF CANADA AND INTO THE UPPER
MISSISSIPPI VALLEY FRIDAY NIGHT. THE HIGH PRESSURE WILL BUILD
ACROSS LAKE MICHIGAN SATURDAY AND SATURDAY NIGHT AS LOW PRESSURE
OF 29.1 INCHES DEVELOPS OVER THE WESTERN PLAINS. THIS LOW WILL
SLOWLY LIFT NORTHEAST INTO SOUTH DAKOTA BY MONDAY NIGHT WITH A
WARM FRONT EXTENDING EAST ACROSS THE MIDDLE MISSISSIPPI VALLEY TO
THE OHIO VALLEY...SETTING UP AN EXTENDED PERIOD OF EAST WINDS OVER
LAKE MICHIGAN FROM SUNDAY NIGHT THROUGH THE END OF THE FORECAST
PERIOD.

&&

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

$$

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