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AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1100 AM CDT SAT MAY 11 2013

.DISCUSSION...
349 AM CDT

MAIN FORECAST CHALLENGES/CONCERNS ARE WITH PRECIP CHANCES AND
TRENDS TODAY...SOME COLDER NIGHTS WITH POSSIBLE FROST AHEAD...AS
WELL AS THE WARM UP NEXT WEEK.

IN THE NEAR TERM...STUBBORN STRATUS DECK CONTINUES TO LINGER
ACROSS PORTIONS OF NORTHEAST ILLINOIS AND NORTHWEST INDIANA EARLY
THIS MORNING. ALTHOUGH THIS STRATUS WILL CONTINUE TO SHIFT
SOUTHEAST THIS MORNING...IT WILL DO SO RATHER SLOWLY WITH LATEST
RAP GUIDANCE AND DISTANCE SPEED TOOL HAVE THIS CLOUD COVER EXITING
A PONTIAC TO CHICAGO LINE OVER THE NEXT COUPLE OF HOURS WITH AREAS
ACROSS EAST CENTRAL ILLINOIS AND NORTHWEST INDIANA OBSERVING THIS
STRATUS AT LEAST THROUGH AROUND SUNRISE. AS SOON AS THESE LOW
CLOUDS EXIT...ATTENTION TURNS TOWARDS AN INCREASE IN CLOUD COVER
FROM THE APPROACHING SYSTEM TO THE NORTHWEST. MID/HIGH LEVEL CLOUD
COVER CAN BE OBSERVED PROGRESSING ACROSS EASTERN IOWA ND CENTRAL
WISCONSIN THIS MORNING...ALONG AND JUST AHEAD MID LEVEL TROUGH AND
ATTENDANT SURFACE TROUGH. THIS MID LEVEL WAVE WILL HELP STEER THIS
SURFACE TROUGH AND ASSOCIATED COLD FRONT SOUTHEAST THROUGH EASTERN
IOWA AND CENTRAL WISCONSIN THIS MORNING WITH THE ONGOING SHOWERS
OVER WESTERN WISCONSIN EXPECTED TO WORK THEIR WAY TOWARDS NORTHERN
ILLINOIS THROUGH MID MORNING. GUIDANCE HAS NOT BEEN OVERLY EXCITED
WITH PRECIP DEVELOPMENT INITIALLY THIS MORNING...WITH LITTLE IF ANY
QPF DEVELOPMENT ACROSS NORTHWEST/NORTHERN ILLINOIS THROUGH THE 15Z
TIME FRAME. LATEST SHORT TERM GUIDANCE CONTINUES TO SHOW THIS
TREND EVEN WITH SUCCESSIVE RUNS THIS MORNING...AND AM STARTING TO
BELIEVE THIS. FORCING ALONG THIS TROUGH/FRONT IS RATHER WEAK AT
THIS TIME AND CONTINUES THIS TREND THROUGH THE 15Z TIME FRAME AS
THIS SYSTEM AND PRECIP WORK THEIR WAY ACROSS NORTHERN
ILLINOIS...AND SO HAVE LOWERED POPS DURING THIS TIME FRAME TO LOW
CHANCE POPS PRIMARILY AROUND THE ROCKFORD AREA. ITS NOT UNTIL MORE
TOWARDS THE 16-17Z TIME FRAME THAT BETTER DEVELOPMENT IS
EXPECTED...WITH AREAS IN NORTHEAST ILLINOIS LIKELY OBSERVING LIGHT
RAIN SHOWERS. THIS IS IN RESPONSE TO A MUCH STRONGER AND MORE
DEFINED VORT MAX DIGGING SOUTHEAST ALONG THIS TROUGH/FRONT MOVING
SOUTHEAST ACROSS NORTHERN ILLINOIS TOWARDS MID DAY...WITH THIS
SYSTEM THEN CONTINUING SOUTHEAST WITH LIGHT SHOWERS THEN LIKELY TO
CONTINUE DEVELOPING INTO EAST CENTRAL ILLINOIS AND NORTHWEST
INDIANA THROUGH THE EARLY AFTERNOON. ALL IN ALL...THIS PRECIP
SHOULD BE LIGHT WITH AREAS OBSERVING LESS THAN A TENTH OF AN INCH
OF RAINFALL WITH THUNDER NOT EXPECTED DUE TO LACK OF INSTABILITY.

THIS TROUGH/FRONT WILL PUSH THROUGH THE ENTIRE CWA BY LATE THIS
AFTERNOON WITH ANY PRECIP EXITING SOUTHEAST OF THE AREA. CLOUD
COVER MAY TRY TO LINGER OVER THE CWA INTO THE EVENING BUT AM
EXPECTING A CLEARING TREND TONIGHT AS MOSTLY CLEAR SKIES ARE
EXPECTED. THESE CLEAR SKIES COINCIDING WITH A MUCH COLDER AIRMASS
IN PLACE WILL PROVIDE NIGHT TIME LOWS TONIGHT IN THE 30S...WITH
NORTHERN ILLINOIS OBSERVING LOW TO MID 30S. WITH THESE COLDER
TEMPS...PATCHY FROST WILL BE POSSIBLE MAINLY ACROSS NORTHWEST
ILLINOIS. ALTHOUGH...DUE EXPECT SUSTAINED SURFACE WINDS TO LIMIT
MOST FROST DEVELOPMENT TONIGHT. ALTHOUGH A WARMING TREND WILL BE
STARTING SUNDAY NIGHT...IT DOES APPEAR AS IF ANOTHER COLD NIGHT
WILL BE LIKELY. THIS WILL BE ESPECIALLY THE CASE AS A SURFACE
RIDGE AXIS MOVES OVERHEAD AND WINDS DROP OFF...AND SO HAVE ONCE
MADE MENTION OF FROST SUNDAY NIGHT WITH MOST AREAS ACROSS
NORTHEAST ILLINOIS AND NORTHWEST INDIANA LIKELY OBSERVING AT LEAST
PATCHY FROST. AREAS ACROSS FAR NORTHERN ILLINOIS WILL HAVE TO
CONTINUE TO BE MONITORED SUNDAY NIGHT AS THIS AREA IS WHERE I
ANTICIPATE THE COLDEST TEMPS IN THE LOWER 30S TO BE LOCATED.

HAVE CONTINUED THE WARMING TREND FOR NEXT WEEK STARTING MONDAY BUT
WITH TUESDAY AND WEDNESDAY STILL APPEARING TO BE RATHER
WARM...WITH 80 DEGREE WEATHER STILL APPEARING LIKELY BOTH OF THOSE
DAYS. THERE WILL BE A BRIEF WINDOW FOR SHOWERS/THUNDERSTORMS
MONDAY NIGHT AS THE WAA WING LIFTS NORTHEAST...BUT DONT ANTICIPATE
MUCH IN TERMS OF ANY PROLONGED PERIOD OF PRECIP DURING THAT TIME.
THERE DOES STILL APPEAR TO BE CHANCES FOR SHOWERS/THUNDERSTORMS
ONCE AGAIN BY THE WEDNESDAY/THURSDAY TIME FRAME...BUT WITH
GUIDANCE CONTINUING TO DIFFER WITH REGARDS TO THIS SYSTEM
EVOLUTION. WILL CONTINUE TO MONITOR LATER MODEL RUNS AS A MORE
ACTIVE WEATHER PATTERN COULD POSSIBLY EVOLVE LATER THIS WEEK.

RODRIGUEZ

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* PRECIP HAS PUSHED EAST OF TERMINALS.
* MVFR CIGS ARND 1600-1800FT AGL...IMPROVE TO ARND A 3KFT AGL DECK
  MIDDAY.
* WINDS CONTINUE TO SHIFT FROM SW TO NW BY 18Z. SPEEDS INCREASE TO
  ARND 20KT AND GUSTS BTWN 29-32KT.
* PSBL BREAK IN 3KFT AGL CIGS THEN CLOUDS INCREASE WITH PSBL VCSH
  OR -SHRA LATE THIS AFTN/THRU EARLY EVE.
* VFR CIGS RETURN OVERNIGHT.

BEACHLER

//DISCUSSION...UPDATED 12Z...

PRECIPITATION COVERAGE HAS STEADILY DIMINISHED THIS MORNING...AS
THE MOISTURE SLOWLY SLIDES EAST. IT APPEARS THAT PRECIP MAY
ACTUALLY SLIDE JUST NORTH/SOUTH OF ORD/MDW. HAVE OPTED TO REMOVE
TEMPO GROUP AT THIS TIME...AND HELD ONTO JUST A VCSH. LOCAL
GUIDANCE SUGGESTS THAT PRECIP COVERAGE MAY INCREASE LATER THIS
MORNING/EARLY AFTERNOON AS THE FRONTAL BOUNDARY SLIDES SOUTHEAST
OF MDW. VISIBLE IMAGERY INDIDCATES CLOUDS LINGER TO THE WEST OF
THE FRONT...WITH SFC OBS REPORTING CIGS ARND 1200-1400FT AGL. HAVE
PUSHED CIGS DOWN TO ACCOUNT FOR THIS LATER THIS MORNING. WITH
FROPA EXPECTED LATER THIS MORNING...WINDS WILL SHIFT FROM SW TO NW
AND RAPIDLY INCREASE. GUSTS TO 30 KT STILL LOOK ON TRACK...WITH A
FEW GUSTS EXCEEDING 30 KT AT TIMES. CIGS WILL LIFT TO ARND
1500FT...THEN WITH ANOTHER UPPER LEVEL SYSTEM SLIDING SOUTHEAST
ACROSS MINNESOTA...A BRIEF PERIOD OF SCT CLOUDS WILL QUICKLY FILL
BACK IN AND BECOME BKN/OVC LATE THIS AFTN. IT IS POSSIBLE THAT A
BRIEF SHOWER MAY ACCOMPANY THE UPPER LEVEL SYSTEM AS IT APPROACHES
THE TAF SITES.

PREVIOUS DISCUSSION...UPDATED 12Z...

PESKY MVFR CIGS HAVE EXPANDED NORTH SOME IN THE PAST COUPLE HOURS
AND THEIR SOUTHEASTWARD PROGRESS HAS SLOWED GREATLY. GOES IMAGERY
SUGGESTS THAT THE CLEARING LINE IS AROUND 5SM NW OF ORD AND
INCHING TOWARD THEM...SO HAVE OPTED TO MAINTAIN A TEMPO FOR MVFR
CIGS 12-13Z. GIVEN SLOWED PROGRESS AM GROWING MORE CONCERNED THAT
MDW COULD BE STUCK IN MVFR CIGS FOR A COUPLE MORE HOURS...BUT EVEN
IF SO ONCE THE COLD FRONT BLASTS THROUGH LATER THIS MORNING WILL
CERTAINLY GO VFR AT THAT TIME.

SHOWERS HAVE BEEN INCREASING IN COVERAGE AND DEVELOPING
SOUTHWESTWARD ALONG THE FRONT FROM WISCONSIN SOUTH INTO EASTERN
IOWA EARLY THIS MORNING. ANTICIPATE THESE SHRA TO MAINTAIN STEADY
STATE OR POSSIBLY INCREASE IN COVERAGE/INTENSITY THIS MORNING AS
THEY MOVE EAST TOWARD AND THROUGH THE TERMINALS. EXPECT VFR CIGS
WITH SHRA THROUGH BRIEF MVFR VSBY POSSIBLE WITH THE HEAVIER RAIN
WITH RAIN LIKELY TO LAST LESS THAN 45 MINS IN ANY ONE GIVEN
LOCATION. BEHIND THE FRONT SKIES CLEAR OUT WITH JUST A FEW- SCT
HIGH BASED FLAT CU POSSIBLE MUCH OF THE AFTERNOON WITH STRONG
NORTHWEST WINDS DEVELOPING. SOUDNINGS SUPPORT GUSTS TO AND
OCCASIONALLY SLIGHTLY OVER 30KT LATE MORNING THROUGH THE
AFTERNOON. SECONDARY UPPER LEVEL DISTURBANCE OVER CENTRAL MN IS
LIKELY TO PIVOT SOUTHEAST TOWARD THE AREA TOWARD EVENING WITH VERY
COLD AIR ALOFT RESULTING IN STEEPENING OF LOW LEVEL LAPSE RATES
AND RESULTANT DEEPENING OF THE CUMULUS WITH ISOLD SHRA (POSSIBLY
WITH SOME GS) POSSIBLE THIS EVENING. WINDS WILL EASE A BIT BY
EARLY EVENING BUT MORE NOTICEABLE DECREASE IN WINDS/GUSTINESS WILL
BE AS SKIES CLEAR OUT MID-LATE EVENING.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* MEDIUM CONFIDENCE IN CIGS.
* HIGH CONFIDENCE IN WIND SPEEDS/GUSTS.
* LOW CONFIDENCE IN PRECIP POTENTIAL THIS EVENING.
* MEDIUM/HIGH CONFIDENCE IN THINNING CLOUDS AND VFR CONDS
  DEVELOPING AFT 4Z SUN.

BEACHLER

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

SUNDAY NIGHT AND MONDAY...VFR.

TUESDAY...VFR.

WEDNESDAY...CHANCE SHRA/TSRA.

THURSDAY THROUGH RIDAY...A PERIOD OR TWO OF SHRA/TSRA POSSIBLE.

IZZI

&&

.MARINE...
351 AM CDT

STRONG COLD FRONT WILL SWEEP ACROSS THE LAKE TODAY. STRONG PRESSURE
RISES BEHIND THE FRONT WILL LIKELY LEAD TO AN INITIAL BRIEFLY STRONG
SURGE OF NORTHWEST WINDS UP TO 25 OR POSSIBLY EVEN 30KT...BUT
STRONGER COLD AIR ADVECTION LAGS BEHIND THE FRONT A BIT SO STABLE
MARINE LAYER SHOULD ALLOW WINDS TO RELAX OVER THE OPEN LAKE THIS
AFTERNOON AFTER THE INITIAL FRONTAL SURGE. STRONG COLD AIR ADVECTION
REALLY RAMPS UP BY EVENING WITH 850MB TEMPS DROPPING WELL BELOW ZERO
AND UPSTREAM AIR OVER THE LAND LIKELY COOLING AS WELL LEADING TO AN
INCREASINGLY UNSTABLE MARINE LAYER OVER THE LAKE TONIGHT. WHILE THIS
TAKES PLACE...LOW PRESSURE WILL BEGIN DEEPENING FAIRLY QUICKLY AS IT
MOVES FROM LAKE HURON NORTH INTO QUEBEC WITH STRONG PRESSURE RISES
ALSO MOVING ACROSS THE LAKE. COMBINATION OF ALL THESE FACTORS LOOK
TO RESULT IN GALES DEVELOPING TONIGHT...ESPECIALLY NORTHERN MOST
PORTIONS OF THE LAKE WHERE HIGH END GALES ARE POSSIBLE BY LATE
TONIGHT. GALES WILL SLOWLY SUBSIDE SUNDAY...BUT LIKELY LINGERING
INTO SUNDAY AFTERNOON OVER FAR NORTHERN PORTIONS OF THE LAKE. GIVEN
THE HIGH PROBABILITY OF GALES OCCURRING WITHIN 24 HOURS AND HIGH END
GALES BEING FORECAST HAVE OPTED TO GO OUT OF THE GATE WITH A GALE
WARNING FAR NORTH. FOR CENTRAL PORTIONS OF THE LAKE GALES LOOK
PROBABLE BUT THE SET-UP IS MORE MARGINAL SO HAVE OPTED TO JUST GO
WITH A GALE WATCH GIVING THE DAY SHIFT TIME TO GET A LOOK AT LATEST
GUIDANCE BEFORE MAKING A FINAL DECISION.

FOR THE NEAR SHORE HAVE ALLOWED CURRENT SMALL CRAFT ADVISORY TO
EXPIRE AT 4 AM...BUT MAY STILL BE GETTING WAVES CLOSE TO 5 FT EAST
OF BURNS HARBOR BUT WITH BUOYS AND SHIP OBS INDICATING WAVES COMING
DOWN FELT COMFORTABLE ALLOWING IT TO EXPIRE. HAVE HOISTED ANOTHER
SCY FOR THIS AFTERNOON THROUGH SUNDAY FOR WINDS FOR THE ILLINOIS
SHORE AND FOR WINDS THEN WAVES ALONG THE INDIANA SHORE. SET-UP FOR
THE ILLINOIS SHORE IS A BIT COMPLICATED WITH STRONGEST WINDS THIS
AFTERNOON LIKELY RIGHT ALONG THE SHORE WITH INCREASINGLY STABLE
CONDITIONS LEADING TO LIGHTER WINDS FARTHER OFFSHORE. TONIGHT MARINE
LAYER STABILITY WILL FLIP FROM STABLE TO UNSTABLE RESULTING IN
STRONGEST WINDS BECOMING FOCUSED FARTHER OFFSHORE. DURING THE
TRANSITION THERE WILL PROBABLY BE A WINDOW OF TIME THIS EVENING WITH
WINDS BELOW CRITERIA...BUT LIKELY TOO SHORT IN DURATION TO TRY AND
GET CUTE WITH HEADLINES. FOR INDIANA SHORE...MORE STABLE CONDITIONS
TODAY MAY RESULT IN MORE MARGINAL WINDS FOR SMALL CRAFT ADVISORY
THIS AFTERNOON BUT AS MARINE LAYER DESTABILIZES LOOK FOR WINDS TO
RAMP UP TONIGHT TO 30KT WITH WAVES ALSO BUILDING UP DUE TO LONGER
FETCH. LAKE BREEZE LIKELY TO DEVELOP ALONG INDIANA SHORE SUNDAY
AFTERNOON RESULTING IN SHIFT TO LIGHTER NORTHEAST WINDS BUT BY THEN
WAVES SHOULD HAVE BEEN BUILT UP ENOUGH TO REQUIRE SOME TIME TO
SUBSIDE.

IZZI

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ563...MIDNIGHT SUNDAY TO
     3 PM SUNDAY.

     SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 3 PM
     SUNDAY.

     SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 3 PM SUNDAY
.

     GALE WATCH...LMZ366-LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ868-
     LMZ870-LMZ872-LMZ874...MIDNIGHT SUNDAY TO 9 AM SUNDAY.

&&

$$


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