Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 200254
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
954 PM CDT SUN APR 19 2015

.UPDATE...
809 PM CDT

STEADY RAIN WILL CONTINUE MUCH OF THE EVENING ACROSS NORTHERN
ILLINOIS. MID-LEVEL DRY SLOT WILL PIVOT ACROSS EAST-CENTRAL
ILLINOIS AND NORTHWEST INDIANA THIS EVENING WITH RAIN TAPERING TO
A LIGHT DRIZZLE FOR THESE AREAS...BEFORE SHOWERS SPREAD BACK IN
FROM THE WEST OVERNIGHT. ADDED PATCHY FOG TO THE GRIDS THIS
EVENING AND TONIGHT AS SATURATED TO NEAR SATURATED CONDITIONS ARE
IN PLACE THIS EVENING. SUSPECT VISIBILITY WILL BEGIN TO IMPROVE AS
WEST WINDS INCREASE AFTER MIDNIGHT TONIGHT.

BMD

&&

.SHORT TERM...
319 PM CDT

THROUGH MONDAY NIGHT...

AFTER ANOTHER WARM EARLY AFTERNOON ACROSS MUCH OF THE REGION RAIN IS
BEGINNING TO SPREAD NORTHWARD ACROSS SOUTHERN SECTIONS OF THE CHICAGO
METRO AREA AS OF THIS WRITING. THIS ACTIVITY WILL CONTINUE TO
OVERSPREAD THE REGION THROUGH THE AFTERNOON AND EVENING...WITH
TEMPERATURES LIKELY TO DROP BACK INTO THE UPPER 50S AND LOW 60S IN
THE RAIN.

THE MID-LEVEL DISTURBANCE...AND THE ASSOCIATED SURFACE SYSTEM WILL
QUICKLY SHIFT NORTHWARD OVER LOWER MICHIGAN OVERNIGHT...AND IT
APPEARS THAT THE RAIN WILL BECOME MORE SHOWERY AND INTERMITTENT OR
POSSIBLY JUST SOME DRIZZLE LATER THIS EVENING AND INTO THE EARLY
MORNING ACROSS MUCH OF THE AREA AS THIS INITIAL MID LEVEL
DISTURBANCE SHIFTS NORTH OF THE AREA AND SOME DRIER MID LEVEL AIR
SHIFTS OVER THE SOUTHEASTERN HALF OF MY AREA. SOME ADDITIONAL RAIN
SHOWERS ARE POSSIBLE AGAIN EARLY MONDAY WITHIN A REGION OF MID LEVEL
DEFORMATION AND RAP AROUND MOISTURE ASSOCIATED WITH THE DEEPENING
LOWER AND MID LEVEL LOW OVER THE UPPER GREAT LAKES REGION AND
SOUTHERN CANADA.

CONDITIONS SHOULD DRY OUT MONDAY AFTERNOON...WITH ONLY A SMALL
CHANCE OF AN ADDITIONAL SHOWER DEVELOPING AS COLDER AIR ALOFT
STEEPENS THE LOWER LEVEL LAPSE RATES. THE MAIN STORY DURING THE
AFTERNOON WILL BE THE WINDS. WINDS ARE EXPECTED TO INCREASE OUT OF
THE WEST-NORTHWEST DURING THE DAY AS STOUT SURFACE PRESSURE
GRADIENT SETS UP OVER THE REGION AS THE SURFACE LOW DEEPENS TO
AROUND 985 MB ACROSS ONTARIO MONDAY AFTERNOON. MODEL SOUNDINGS
SUGGEST GOOD AFTERNOON MIXING TO AROUND 850 MB SHOULD ALLOW FOR
GUSTS OF AROUND 30 KT AT TIMES...ESPECIALLY DURING THE AFTERNOON.
THESE WIND GUSTS SHOULD ABATE MONDAY EVENING...BUT STRONG WINDS
LOOK TO DEVELOP AGAIN ON TUESDAY. SEE LONG TERM DISCUSSION FOR
MORE INFO ON TUESDAY`S WINDS.

KJB

&&

.LONG TERM...
319 PM CDT

TUESDAY THROUGH SUNDAY...

MAIN FORECAST CONCERNS/CHALLENGES ARE WITH BELOW NORMAL TEMPS
THROUGH THE FORECAST.

LARGE UPPER LEVEL CENTER WILL BE CENTERED ACROSS THE REGION AT THE
START OF THE PERIOD...AND REMAIN SITUATED THROUGH MUCH OF THE WORK
WEEK AS IT SLOWLY MOVES EAST. SEVERAL VORT LOBES ARE ANTICIPATED TO
WRAP AROUND THIS UPPER LEVEL LOW ON TUESDAY AND WITH STEEPENING
LAPSE RATES...EXPECT SKY COVER TO INCREASE THROUGH THE DAY WHILE
SCATTERED SHOWERS BECOME POSSIBLE...ESPECIALLY ACROSS NORTHERN
ILLINOIS. AS THIS OCCURS...LIKELY DEEP MIXING WITH STRONG FLOW ALOFT
WILL ALLOW FOR ANOTHER WINDY DAY. GUIDANCE IS SUGGESTING THAT
ADVISORY CONDITIONS COULD BE REACHED IN THE AFTERNOON...AND WILL
NEED TO CONTINUE MONITORING THIS POTENTIAL. ANY REMAINING PRECIP AND
CLOUD COVER SHOULD EXIT THE AREA TUESDAY NIGHT WITH DRY CONDITIONS
EXPECTED. SOME GUIDANCE DEVELOPS A SWATH OF PRECIP OVER THE CWA LATE
IN THE NIGHT INTO EARLY WEDNESDAY. HOWEVER...A MORE LIKELY SCENARIO
AT THIS TIME WOULD BE FOR DRY CONDITIONS AND SO HAVE LEFT OUT ANY
POPS AT THIS TIME. ONGOING CAA WILL MAKE FOR CHILLY CONDITIONS
TUESDAY NIGHT...WITH LOW TEMPS IN THE 30S. IF PRECIP WERE TO OCCUR
DURING THIS PERIOD...THESE COLDER CONDITIONS COULD SUPPORT THE
POTENTIAL FOR AT LEAST A RAIN SNOW MIX ACROSS NORTHERN ILLINOIS.
EXPECT DRY CONDITIONS WITH BELOW NORMAL TEMPS THROUGH THE REST OF
THE FORECAST PERIOD...WITH FORECAST HIGHS IN THE 50S. COLD NIGHT
TIME LOWS IN THE 30S COULD BECOME AN ISSUE LATE IN THE WORK WEEK AS
HIGH PRESSURE IS ANTICIPATED TO MOVE OVERHEAD...WITH LIGHTER WINDS
AND THE COLD TEMPS POSSIBLY CREATING A SETUP FOR FROST.

RODRIGUEZ

&&

.AVIATION...

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

* WINDS BACKING NORTHWEST LATE THIS EVENING.

* LIGHT RAIN SHOWERS LATE THIS EVENING BECOMING ISOLATED AFTER
  05Z-06Z...THEN A PROBABLE PERIOD OF SHOWERS MONDAY MORNING.

* LIFR CIGS LASTING INTO OVERNIGHT WITH SLOW IMPROVEMENT DURING
  THE DAYBREAK TIME.

* MVFR VISIBILITY LOWERING TO IFR LATE THIS EVENING THEN LIKELY
  IMPROVING SLOWLY PRIOR TO DAYBREAK.

* GUSTY WEST WINDS DEVELOPING MONDAY MORNING WITH MAX GUSTS ARND
  30 KT LATE MONDAY MORNING AND AFTERNOON.


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

A SHIELD OF RAIN AND AT TIMES RAIN SHOWERS WILL CONTINUE TO
ADVANCE NORTHWARD ACROSS THE TAF SITES THROUGH MID-EVENING.
VISIBILITY WILL SHOW SOME FLUCTUATIONS IN THIS RAIN...MAINLY
BETWEEN 3SM AND 5SM. AS THE RAIN BECOMES MORE SCATTERED SHOWERS
AFTER 02-03ZZ AND A LIGHTER WIND FLOW NEAR LOW PRESSURE
OCCURS...THE SATURATION IS EXPECTED TO BRING LIFR CONDITIONS. THIS
IS ALREADY BEING OBSERVED UPSTREAM IN CENTRAL AND EASTERN IL.
CONFIDENCE IS HIGHEST IN LIFR CIGS BUT VISIBILITY UNDER 1SM IS
ALSO POSSIBLE...ESPECIALLY AT TAF SITES NOT FAR FROM THE LAKE
INCLUDING ORD AND MDW. ALREADY WEBCAM IMAGERY FROM DOWNTOWN
CHICAGO SHOWS WHAT IS LIKELY PART LAKE ENHANCED SUB 1SM FOG AND
WITH CONTINUED NORTHEAST WINDS THIS EVE...THIS IS POSSIBLE THIS
ROLLS INTO ORD AND MDW IN THE WAKE OF THE SHOWERS.

LATER TONIGHT WESTERLY WINDS WILL BEGIN AND THIS MAY RESULT IN A
GRADUAL IMPROVEMENT BY DAYBREAK. SOON AFTER SUNRISE THE COLD FRONT
IS EXPECTED TO MOVE OVER CHICAGO WITH WESTERLY WINDS INCREASING.
THERE WILL BE LIKELY AN AREA OF SHOWERS TOO IN THE MORNING...BUT
OVERALL CIGS AND VISIBILITY SHOULD BE IMPROVING INTO THE MVFR
CATEGORY. THE PATTERN BEHIND THE COLD FRONT FAVORS GUSTY WINDS
WHICH ARE BEING OBSERVED ACROSS THE PLAINS STATES TODAY. SPORADIC
PEAK GUSTS OF 30 KT ARE EXPECTED BETWEEN 16Z-22Z.


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

* HIGH IN WIND DIRECTION THROUGH THE TAF. MEDIUM-HIGH IN SPEED.

* HIGH IN RAIN TIMING.

* HIGH IN CIGS AND DURATION. MEDIUM IN CIGS ONLY DROPPING AS FAR
  AS 400FT.

* MEDIUM IN VISIBILITY TRENDS AND VISIBILITY DROPPING NO MORE
  THAN TO 1 1/2SM.

* MEDIUM IN CIGS/VISBYS AND SHRA DURING THE MORNING RUSH ON
  MONDAY.


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

TUESDAY...SLIGHT CHANCE OF SHRA AND MVFR. GUSTY WEST WINDS.
WEDNESDAY-THURSDAY...VFR. NORTHWEST WINDS.
FRIDAY-SATURDAY...VFR. WINDS BECOMING NORTHEAST.

MTF

&&

.MARINE...
324 PM CDT

AS A TROUGH OF LOW PRESSURE AND SECONDARY LOW PRESSURE CENTER
MOVE ACROSS THE GREAT LAKES REGION TONIGHT...WINDS WILL LIKELY BE
VARIABLE AT TIMES. THIS WILL ESPECIALLY BE THE CASE OVER THE
SOUTHERN HALF OF THE LAKE WHERE THE LOW PRESSURE SYSTEM IS
EXPECTED TO MOVE THROUGH. IN THE NEAR TERM...EAST NORTHEAST WINDS
WILL PREVAIL OVER THE LAKE WITH THE HIGHEST SPEEDS TO 30 KT
OCCURRING OVER THE NORTHERN HALF AND WHILE 15 TO 25 KT WINDS ARE
BEING OBSERVED OVER THE SOUTH...WITH SPEEDS EXPECTED TO SLIGHTLY
DIMINISH TONIGHT. AS THIS TROUGH/LOW EXIT TO THE EAST ON
MONDAY...STRONGER WESTERLY WINDS WILL DEVELOP. HIGHEST WINDS TO 30
KT WILL OCCUR ALONG THE NEARSHORE WATERS WHILE ONLY 15 TO 25 KT
ARE LIKELY OVER THE OPEN WATERS. A SIMILAR SETUP IS EXPECTED ON
TUESDAY BUT WITH SPEEDS SLIGHTLY HIGHER...AS TO 30 KT WILL LIKELY
PREVAIL FOR BOTH LOCATIONS AND WITH EVEN GALES POSSIBLE ALONG THE
NEARSHORE WATERS DURING THE DAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...11 AM MONDAY TO 9 PM MONDAY.

&&

$$

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