Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 201947
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
247 PM CDT MON APR 20 2015

.SHORT TERM...
228 AM CDT

THROUGH TUESDAY...
COVERAGE OF RAIN CONTINUES TO DIMINISH EARLY THIS MORNING...WITH
THE LOW PRESSURE POSITIONED OVER SOUTHWEST LOWER MICHIGAN. THE
PRESSURE GRADIENT IS MINIMAL...ALLOWING PATCHY FOG AND LOW CLOUD
BASES TO DEVELOP. FORTUNATELY THIS WILL ONLY BE TEMPORARY...AS
JUST WEST OF THE FORECAST AREA THE GRADIENT QUICKLY INCREASES.
WINDS UPSTREAM ACROSS MN/IA HAVE BEEN GUSTING FROM THE NORTHWEST
BETWEEN 25 AND 35 MPH. AS THE LOW CONTINUES TO LIFT NORTHEAST THIS
MORNING...THE WRAP AROUND MOISTURE OVER NORTHEAST IA WILL PIVOT
EAST AND CLIP THE NORTHERN PORTIONS OF THE FORECAST AREA BEFORE
LIFTING NORTHEAST. DRY AIR REMAINS WELL NORTHWEST OF THE FORECAST
AREA...SO IT LOOKS LIKE THE BULK OF THE MORNING WILL FEATURE
ABUNDANT SOLAR SHIELDING. COLD AIR WILL STEADILY ADVECT SOUTHEAST
ACROSS THE REGION...WITH TEMPS STRUGGLING TO WARM MUCH FROM THE
EARLY MORNING LOWS OF THE MID 50S. ENOUGH DRY AIR SHUD FINALLY
ARRIVE ARND SUNSET TO START THINNING THE CLOUD SHIELD...WHICH WILL
ONLY ALLOW OVERNIGHT LOWS OF THE UPR 30S TO ARND 40.

500MB VORT WILL SLOWLY PUSH EAST ACROSS THE WESTERN GREAT
LAKES...REACHING LOWER MICHIGAN TUE MORNING. THE WEAK RIDGING ACROSS
THE NORTH ATLANTIC WILL SLOW THE DEPARTURE OF THE 500MB TROUGH
AXIS...WHICH WILL MAINTAIN A STEADY NORTHWEST FLOW ACROSS THE
FORECAST AREA. A WEAK EMBEDDED VORT WILL ROTATE SOUTHEAST ACROSS THE
UPPER MIDWEST TOWARDS SOUTHERN WISC...WHICH COULD BRING ANOTHER
PERIOD OF LIGHT SHOWERS TUE AFTN. THE SFC MAY WARM A TOUCH WITH THE
THIN CLOUD COVER...ENOUGH TO CREATE SOME INSTABILITY SHOWERS AS THE
LAPSE RATES SHUD STEEPEN MARGINALLY. HOWEVER AT THIS TIME IT DOES
NOT APPEAR TO BE UNSTABLE ENOUGH TO WARRANT ANY MENTION OF
THUNDER. HIGHS WILL ONCE AGAIN REMAIN UNSEASONABLY COOL IN THE
LOW/MID 50S.

BEACHLER

&&

.LONG TERM...
228 AM CDT

WEDNESDAY THROUGH SUNDAY...
THE PATTERN HAS CHANGED BACK INTO A NORTHWEST FLOW...AS A HIGH
LATITUDE BLOCK DEVELOPS AND MAINTAINS THE 500MB VORT OVER THE
GREAT LAKES/ONTARIO/QUEBEC THRU FRI. ENSEMBLES MAINTAIN MINIMAL
SPREAD AMONGST SOLUTIONS THRU FRI...INDICATING MODEST WEAKENING TO
THE INTENSITY OF THE TROUGH. BY THE WEEKEND THE TROUGH WILL BE
SHIFTING TO THE EAST COAST...WHICH WILL ALLOW A SLIGHTLY LESS
AMPLIFIED FLOW FOR THE GREAT LAKES.

SFC RIDGING IS POISED TO SLIP SOUTHEAST FROM CENTRAL CANADA
WED...AND BRING DRY/COOL WEATHER WED-SUN. THE SOUTHERN STREAM SHUD
REMAIN WELL SOUTH. OVER THE UPCOMING WEEKEND SOLUTIONS INDICATE THE
SOUTHERN STREAM MAY BUCKLE AND LIFT PRECIP NORTH INTO THE OHIO
VALLEY...HOWEVER THIS APPEARS TO BE A LOW CONFIDENCE SCENARIO AT
THIS TIME. DESPITE THE UNSEASONABLY COOL WEATHER FOR MID-WEEK...THE
LESS AMPLIFIED FLOW FOR THE WEEKEND SHUD ALLOW TEMPS TO APPROACH
SEASONAL CONDS ARND 60.

OVERNIGHT LOWS WILL ALSO BECOME A CONCERN...ESPECIALLY WED NGT AND
THUR NGT. GUIDANCE CONTINUES TO SUGGEST LOWS MAY DIP INTO THE LOW
30S. WITH LIGHT WINDS DEVELOPING...PATCHY FROST MAY DEVELOP AND A
FEW LOCATIONS COULD SEE FREEZING CONDITIONS AS WELL.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* WESTERLY WINDS GUSTING OCCASIONALLY TO AROUND 30 KT THIS
  AFTERNOON AND FREQUENTLY TO 30+ KTS ON TUESDAY AFTERNOON.

* CIGS SLOWLY LIFTING TO ABOVE MFVR BY 21Z-22Z.

* WIDELY SCATTERED LIGHT SHOWERS POSSIBLE THROUGH EARLY EVENING
  AND THEN AGAIN TUESDAY AFTERNOON.


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

LOW PRESSURE WILL MOVE NORTH OF THE GREAT LAKES BY TONIGHT BUT ITS
INFLUENCE WILL CONTINUE ACROSS THE REGION WITH GUSTY WESTERLY
WINDS THIS AFTERNOON AND LIKELY SLIGHTLY STRONGER WINDS ON
TUESDAY. CLOUD BASES WILL CONTINUE TO GRADUALLY LIFT IN THE
CYCLONIC FLOW. GIVEN THE CLOSE-CELLED NATURE OF THE CLOUDS ON
SATELLITE...DO NOT EXPECT A QUICK SCATTERING AT SUNDOWN. CLOUD
BASES WILL BE HIGHER ON TUESDAY GIVEN A GREATER MIXING DEPTH.
SCATTERED RAIN SHOWERS ARE LIKELY ACROSS WISCONSIN ON TUESDAY AND
ARE POSSIBLE DOWN INTO NORTHERN ILLINOIS. BY LATE AFTERNOON...AN
UPPER LEVEL DISTURBANCE WILL MOVE EAST ACROSS CENTRAL ILLINOIS AND
POTENTIALLY BRING SCATTERED SHOWERS AND EVEN POSSIBLY A FEW STORMS
BUT THOSE SHOULD BE SOUTH OF THE TAF SITES.


//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH IN WIND DIRECTION AND MEDIUM-HIGH IN SPEEDS AND GUSTS.

* HIGH IN GRADUAL LIFTING OF CIGS.

* HIGH THAT ANY SHOWERS THIS AFTERNOON AND EARLY EVENING WILL BE
  LIGHT AND VERY BRIEF.


//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...
12Z...

TUESDAY NIGHT...VFR.
WEDNESDAY-THURSDAY...VFR. NORTHWEST WINDS.
FRIDAY-SATURDAY...VFR. WINDS BECOMING NORTHEAST.
SUNDAY...VFR. NNE WINDS.

MTF/KMD

&&

.MARINE...
247 AM CDT

DEEP LOW PRESSURE ALONG THE EAST SIDE LAKE MICHIGAN WILL CONTINUE
NORTH INTO SOUTHWEST ONTARIO TODAY. BEHIND THE LOW...A TRAILING
TROUGH AXIS AND COLD FRONT WILL MOVE OVER THE LAKE BRINGING A
PERIOD OF WEST WINDS TO 30 KT FOR THE NEARSHORE WATERS. ANOTHER
SECONDARY LOW ON THE BACK SIDE OF THIS SYSTEM WILL CREATE A
SIMILAR SETUP FOR TUESDAY. WINDS MAY BE A TOUCH STRONGER WITH THIS
LOW AS IT BRINGS A REINFORCING SHOT OF COLD AIR. RIGHT NOW
CONFIDENCE IS LOW ON GALES...THOUGH WINDS TO 30 KT SEEM A DECENT
BET FOR MUCH OF THE LAKE. HIGH PRESSURE IN THE CANADIAN PRAIRIES
AND EXTENDING SOUTH INTO THE UPPER MIDWEST WITH LOW PRESSURE IN SE
CANADA WILL CREATE A PERIOD OF WNW WINDS ACROSS THE LAKE.

KMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 9 PM MONDAY.

     GALE WATCH...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...9 AM
     TUESDAY TO 10 PM TUESDAY.

&&

$$

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