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AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1108 AM CDT FRI MAY 10 2013

.DISCUSSION...
316 AM CDT

OODLES AND OODLES OF FORECAST CHALLENGES THIS MORNING AS BLOCKY
PATTERN CONTINUES TO BREAK DOWN AND TRANSITION TO A HIGHLY AMPLIFIED
BY MORE PROGRESSIVE PATTERN. FORECAST HIGHLIGHTS INCLUDE:
1) STRATUS AND SUBSEQUENT EFFECT ON TEMPS TODAY
2) STRONG COLD FRONT/SCATTERED SHOWERS SATURDAY
3) UNSEASONABLY CHILLY TEMPS THIS WEEKEND
4) RAPID TRANSITION TO UNSEASONABLY "HOT" WEATHER NEXT WEEK
5) MULTIPLE DAYS OF FIRE WEATHER CONCERNS (TO BE ADDRESSED IN FIRE
WX SECTION OF AFD)

FIRST UP ON THE OLE FORECAST PLATTER IS TODAY`S WEATHER. SFC LOW
WILL CONTINUE TO TRACK EAST ALONG I-80 ACROSS NORTHERN INDIANA TODAY
WITH BRISK NNE WINDS OFF THE LAKE LIKELY TO STRENGTHEN THE ALREADY
STOUT FRONTAL INVERSION WHICH SHOULD HELP LOCK IN STRATUS DECK FOR
MUCH OF THE DAY. THE LOW CLOUDS/STRONG NNE WIND COMBO SHOULD DO ONE
HECK OF A NUMBER ON TEMPS TODAY IN THE CHICAGO AREA WITH MUCH OF THE
DAY LIKELY SPENT IN THE 40S...WITH AREAS WELL INLAND REACHING INTO
THE 50S. SOME CLEARING IS EXPECTED THIS AFTERNOON WESTERN CWA WHICH
SHOULD ALLOW TEMPS TO RECOVER BETTER SETTING UP A LARGE GRADIENT
ACROSS THE CWA.

WEAK NARROW RIDGE AXIS MOVES ACROSS THE REGION TONIGHT WITH WINDS
QUICKLY SUBSIDING AND STRATUS BREAKING UP THIS EVENING OVER EASTERN
CWA. WINDS WILL BRIEFLY TURN SOUTHWEST AHEAD OF FACT MOVING/STRONG
COLD FRONT THAT WILL COME BARRELING ACROSS THE CWA ON SATURDAY.
SHOULD BE ENOUGH OF AN OPPORTUNITY FOR HEATING FOR HIGHS WELL INTO
THE 50S NW HALF OF THE AREA AND PROBABLY LOW 60S SE CWA. WHAT WE`LL
BE LACKING IN MOISTURE LOOKS TO BE WELL COMPENSATED FOR IN TERMS OF
STRONG FORCING AND HAVE INCREASED POPS ACROSS THE CWA AND JUST WENT
WITH SCT`D SHOWERS AS IT APPEARS QUITE LIKELY THAT THERE WILL BE AT
LEAST A BROKEN BAND OF SHOWERS ACCOMPANYING THE FRONT. THINK MOST
AREAS COULD END UP SEEING A SHOWER SATURDAY BUT DURATION LOOKS BRIEF
AND SHOULDNT BE A BIG DEAL.

IN THE WAKE OF THE FRONT INCREASINGLY STRONG NORTHWEST
WINDS...LIKELY GUSTING TO 30+ MPH WILL LIKELY RESULT IN AFTERNOON
TEMPS BECOMING STEADY OR EVEN FALLING A FEW DEGREES. SKIES LOOK TO
CLEAR BEHIND THE FRONT BUT EXPECT ENOUGH OF A GRADIENT SATURDAY
NIGHT TO KEEP THE FROST THREAT LOW DESPITE LOWS DIPPING INTO THE 30S
AWAY FROM THE URBAN HEAT ISLAND AND LAKE. SUNDAY SHOULD BE ANOTHER
BREEZY AND UNSEASONABLY COOL DAY WITH HIGHS IN THE 50S AND A BRISK
NORTHWEST WIND THAT IS LIKELY TO TURN IN OFF THE LAKE IN THE
AFTERNOON FROM THE CHICAGO SHORE SOUTHWARD WHICH WILL KNOCK TEMPS
DOWN EVEN A FEW MORE NOTCHES THERE.

MEDIUM RANGE MODELS REMAIN IN EXCELLENT AGREEMENT ON PUSHING THE
DEEP TROUGH RESPONSIBLE FOR THE COLD AIR THIS WEEKEND QUICKLY
EASTWARD AS 130+ KNOT JET ROUNDS THE BASE OF THE TROUGH OFF THE PAC
NW COAST AND COMES PLOWING EAST INTO SOUTHWEST CANADA. THIS JET WILL
CONTINUE EASTWARD WITH EXTRAORDINARY 500MB HEIGHT RISES OF OVER 300M
PROGGED TO TAKE PLACE IN UNDER 36 HOURS OVER THE AREA...WITH 150M
HEIGHT RISES MONDAY ALONE. ECMWF/GFS HAVE BOTH BEEN REMARKABLY
CONSISTENT FOR DAYS NOW IN BLASTING 850MB TEMPS OF 20C+ INTO THE
AREA TUESDAY INTO WEDNESDAY. WHILE THE 00Z ECMWF HAS SLOWED DOWN THE
EASTWARD PROGRESSION OF THE RIDGE SLIGHTLY COMPARED TO PREVIOUS RUNS
IT TOO STILL SUPPORTS UNSEASONABLE WARMTH BY TUESDAY AND ESPECIALLY
WEDNESDAY.

MODEL FORECAST 2M TEMPS AND DEWPOINTS BOTH LOOK TO HAVE SOME ISSUES
TUESDAY AND WEDNESDAY WITH VERY SHALLOW MIXING DESPITE STRONG
SOUTHWEST WINDS AND AMPLE SUNSHINE. LOW LEVEL JET WILL BE MORE
WESTERLY THAN SOUTHERLY AND GIVEN THE WEEKEND FRONT MAKING IT SOUTH
INTO THE GULF OF MEXICO THINK MOISTURE RETURN WILL BE VERY LIMITED
TUESDAY. MODEL 2M DEWPOINTS IN THE 60S APPEAR TO BE LARGELY DRIVEN
ON EVAPOTRANSPIRATION...WHICH SHOULD BE WELL BELOW NORMAL GIVEN THE
LATE GREEN UP AND LATE PLANTING OF CROPS. IN ADDITION...THE HIGHER
DEWPOINTS ARE LIKELY A RESULT OF THE VERY SHALLOW MIXING WHICH ALSO
IS SUGGESTING TEMPS MUCH COOLER. MOS GUIDANCE IS MORE HEAVILY
WEIGHTED TOWARD CLIMO 5+ DAYS OUT...SO GIVEN STRONG RUN-TO-RUN AND
MODEL TO MODEL CONSISTENCY FELT COMFORTABLE BUMPING HIGHS UP TUES
AND WED WELL ABOVE GUIDANCE AND BASED THEM LARGELY ON TYPICAL
850/925MB CLIMATOLOGICAL ANOMALIES. THIS FAVORS HIGHS IN THE
MID/UPPER 80S WITH NEAR RECORD HIGHS OF 90F+ NOT EVEN TOTALLY OUT OF
THE REALM OF POSSIBILITIES.

IZZI

&&

.FIRE WEATHER...

UNSEASONABLY STRONG LATE SEASON COLD FRONT WILL SWEEP THROUGH THE
AREA RAPIDLY DURING THE DAY SATURDAY. STRONG NORTHWEST WINDS WILL
LIKELY GUST TO IF NOT OVER 30 MPH BEHIND THE FRONT SATURDAY
AFTERNOON. IN ADDITION...RH VALUES ARE LIKELY TO TUMBLE SATURDAY
AFTERNOON INTO THE 25-35% RANGE. WHILE THERE WILL LIKELY BE SOME
SCATTERED SHOWERS RIGHT ALONG THE FRONT...ANY RAINFALL SATURDAY WILL
LIKELY BE BRIEF AND NOT VERY CONSEQUENTIAL IN TERMS OF WETTING
FUELS. HOWEVER...MOST OF THE AREA GOT BETWEEN ONE THIRD AND THREE
QUARTERS OF AN INCH OF RAIN THURSDAY EVENING WHICH WILL LIKELY LEAVE
ALL BUT THE QUICKEST DRYING FUELS STILL TOO MOIST FOR A SUBSTANTIAL
FIRE RISK SATURDAY.

FUELS WILL CONTINUE TO DRY ON SUNDAY AND WINDS WILL BE SOMEWHAT
ELEVATED...ESPECIALLY EARLY IN THE AFTERNOON ALONG WITH LOW RH
VALUES IN THE AFTERNOON. AT THIS POINT IT LOOKS LIKE WINDS WILL
REMAIN WELL BELOW RED FLAG THRESHOLDS...THOUGH A SLIGHTLY ELEVATED
GRASS/BRUSH FIRE DANGER WILL EXIST.

BIGGER FIRE DANGER CONCERNS APPEAR TO BE IN THE TUES/WED TIME FRAME.
STILL A FAIR AMOUNT OF UNCERTAINTY IN THE DETAILS...BUT IT DOES LOOK
LIKE STRONG SOUTHWEST WINDS WILL DEVELOP WITH TEMPERATURES SOARING
WELL INTO THE 80S. MODELS LIKELY FAR TOO MOIST IN FORECAST MOISTURE
LEVELS (SEE DISCUSSION SECTION ABOVE FOR DETAILS AS TO WHY) AND
POTENTIAL EXISTS TO MIX FAIRLY DEEPLY WHICH COULD ALLOW DEWPOINTS TO
MIX OUT AND CONDITIONS TO POSSIBLY APPROACH RED FLAG CRITERIA TUES
OR WED. STILL SOME DIFFERENCES IN THE MODELS REGARDING JUST HOW
WARM/DRY/BREEZY TUESDAY WILL BE AND THERE IS ALWAYS UNCERTAINTY IN
FORECASTING NEAR RECORD LEVEL TEMPERATURES SO LATER FORECASTS SHOULD
BE MONITORED AS WE ARE ABLE TO FINE TUNE THE DETAILS BETTER IN TIME.

IZZI

&&

.AVIATION...

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

* IFR CIGS CONTINUING THROUGH EARLY AFTERNOON...MAY NEED TO SLOW
  THE IMPROVEMENT TO LATE AFTERNOON OR EVEN EARLY EVENING.

* WINDS IN THE 350-020 RANGE FAVORING DUE NORTH THROUGH THE
  MORNING WITH NNE BECOMING MORE LIKELY OR MORE FREQUENT THIS
  AFTERNOON.

* DRIZZLE/SPRINKLES/LIGHT RAIN POSSIBLE THROUGH MIDDAY.

MDB

//DISCUSSION...UPDATED 16Z...

NO MAJOR CHANGES TO FORECAST THINKING. CIGS HAVE SHOWED SIGNS OF
VERY SLIGHT IMPROVEMENT OVER THE LAST HOUR BUT EXPECT THAT
ORD/MDW/DPA/GYY WILL BE STEADY OR VERY SLOW TO IMPROVE THANKS TO
PERSISTENT LAKE FLOW AND LOWER CIGS REMAINING UPSTREAM. PRECIP TO
THE NORTH IS WINDING DOWN AND THIS MAY HELP UPSTREAM CIGS TO
IMPROVE SOMEWHAT. STILL NOT CLEAR ON TIMING OF IMPROVEMENT TO MVFR
AT THESE SITES BUT EVEN WHEN IT DOES OCCUR CIGS STILL LOOK TO BE
AT OR MAYBE JUST ABOVE 010 UNTIL SCATTERING/CLEARING CAN OCCUR
THIS EVENING. RFD SHOULD SEE A QUICKER IMPROVEMENT WITHIN THE MVFR
CATEGORY WITH SCATTERING EARLY THIS EVENING AS WELL.
OTHERWISE...WINDS AT ORD/MDW REMAIN NNW BUT STILL THINK THAT
SLIGHTLY MORE NORTH-NORTHEAST DIRECTION WILL BECOME MORE PREVALENT
MIDDAY/EARLY AFTERNOON.

MDB

FROM 12Z...

LOW CEILINGS PERSIST THIS MORNING...BUT WITH CEILINGS HAVING SINCE
RISEN TO IFR CEILINGS AROUND 700FT AND DONT EXPECT MUCH OF ANY
IMPROVEMENT FROM THESE IFR CEILINGS THROUGH MUCH OF THE MORNING.
ALTHOUGH THE SHOWERS HAVE EXITED THE TERMINALS AND DONT EXPECT ANY
FURTHER DEVELOPMENT...FOG AND SOME PATCHY DRIZZLE REMAINS AND IS
HELPING TO REDUCE VIS TO 2SM-4SM THIS MORNING. DO EXPECT AN
IMPROVEMENT WITH THIS FOG AND VIS WITH ANY VIS RESTRICTIONS LIKELY
BECOMING LIMITED THROUGH MID TO LATE MORNING. HAVE IFR CEILINGS
LIFTING TO MVFR BY 20Z THIS AFTERNOON BUT WITH CONFIDENCE LOW AT
THIS TIME...AS ITS POSSIBLE THAT THE TERMINALS COULD SEE THIS IFR
EVEN LONGER INTO THE DAY. SO HAVE MAINTAINED THE PESSIMISTIC TAFS
WITH THIS SLOW IMPROVEMENT INTO LATER THIS AFTERNOON. CEILINGS
SHOULD IMPROVE OVERNIGHT WITH VFR CONDITIONS EXPECTED THROUGH THE
REMAINDER OF THE FORECAST PERIOD...WITH A CHANCE OF BRIEF SHOWERS
TOWARDS THE END OF THE FORECAST PERIOD FOR ORD. EXPECT NORTHERLY
WINDS TO BECOME MORE NORTHEAST LATER THIS MORNING AS GUSTS ALSO
INCREASE.

RODRIGUEZ

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

* HIGH CONFIDENCE IN IFR CIGS CONTINUING THROUGH EARLY AFTERNOON
  WITH LOW-MEDIUM CONFIDENCE IN NEEDING TO EXTEND IT LATER THROUGH
  THE AFTERNOON.

* HIGH CONFIDENCE IN WIND DIRECTION 350-020...MEDIUM CONFIDENCE
  FAVORING 350-360 THROUGH THE MORNING THEN FAVORING 360-020 THIS
  AFTERNOON.

* HIGH CONFIDENCE THAT DRIZZLE/SPRINKLES/LIGHT RAIN WILL BE SPOTTY
  IN COVERAGE.

MDB

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

SATURDAY NIGHT...VFR.

SUNDAY...VFR.

MONDAY...VFR.

TUESDAY...VFR.

WEDNESDAY...CHANCE TSRA LATE.

THURSDAY...CHANCE TSRA.

RODRIGUEZ

&&

.MARINE...
431 AM CDT

AS AN AREA OF LOW PRESSURE CONTINUES TO SHIFT EAST THROUGH
NORTHERN ILLINOIS AND THE SOUTHERN GREAT LAKES THIS MORNING...A
TIGHT PRESSURE GRADIENT REMAINS OVER MUCH OF THE NORTHERN TWO
THIRDS OF THE LAKE. THIS IS RESULTING IN SOME FAIRLY STRONG
NORTHERLY WINDS WITH TO 30 KT WINDS BEING REPORTED IN THESE SAME
AREAS...WITH EVEN OCCASIONAL GALES TO 35 KT OCCURRING OVER THE
MIDDLE PORTIONS OF THE LAKE. EXPECT THESE NORTHERLY WINDS TO
PERSIST THROUGH MID DAY...BEFORE A SLOW DIMINISHING TREND IS
LIKELY LATER THIS AFTERNOON AND EVENING. AFTER A NIGHT OF LIGHTER
WINDS TONIGHT...NEW LOW PRESSURE WILL DEVELOP ACROSS ONTARIO AND
SHIFT EAST ON SATURDAY. EXPECT WESTERLY WINDS TO INCREASE
THROUGHOUT THE DAY AS THEY TURN MORE NORTHWEST. THEN A PERIOD OF
NORTHWEST WINDS TO 30KT CAN EXPECTED SATURDAY NIGHT INTO SUNDAY
PRIMARILY FOR THE NORTHERN HALF OF THE LAKE...WITH WINDS THEN
DIMINISHING ONCE AGAIN SUNDAY INTO SUNDAY NIGHT ACROSS THE ENTIRE
LAKE.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ366-LMZ565-LMZ567-LMZ669-LMZ671-LMZ673-LMZ868-
     LMZ870-LMZ872-LMZ874 UNTIL 3 PM FRIDAY.

     SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 AM SATURDAY.

&&

$$


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