🚀 go-pugleaf

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1252 PM CDT THU MAY 9 2013

.DISCUSSION...
354 AM CDT

IN THE NEAR TERM...CLOSED MID-LEVEL CIRCULATION WAS LOCATED NEAR
SIOUX FALLS EARLY THIS AM...WITH ADDITIONAL SHORT WAVE ENERGY AND
ASSOCIATED CONVECTIVE CLUSTERS OVER OKLAHOMA/KANSAS. UPPER LOW IS
EXPECTED TO OPEN UP AND PHASE WITH SOUTHERN ENERGY INTO A POSITIVE
TILT TROUGH WHICH WILL MOVE SLOWLY EAST ACROSS THE REGION THROUGH
FRIDAY. WEAK SURFACE LOW PRESSURE OVER NORTHEAST KANSAS WILL DEEPEN
SLIGHTLY IN THE PROCESS...AND MOVE TO SOUTHEAST IA/WESTERN IL BY
THIS EVENING. SOUTHERLY 25-35 KT LOW LEVEL JET AND ASSOCIATED
MOISTURE TRANSPORT CURRENTLY FOCUSED INTO OK/KS/WESTERN MO WILL
GRADUALLY VEER INTO IL DURING THE DAY...AFFECTING OUR CWA
PARTICULARLY FROM LATE MORNING THROUGH THIS AFTERNOON/EARLY
EVENING. WITH SURFACE LOW PROGGED ACROSS CENTRAL/NORTHERN IL THIS
AFTERNOON AND EVENING...EFFECTIVE WARM FRONT DEVELOPS WEST-EAST
ACROSS THE SOUTHERN HALF OF THE CWA. FORECAST SOUNDINGS INDICATE
BETWEEN 500-1200 J/KG MLCAPE IN THE WARM SECTOR ALONG/SOUTH OF THE
FRONT...WHILE MID LEVEL LAPSE RATES FARTHER NORTH REMAIN MARGINAL
BUT LIKELY SUFFICIENT FOR OCCASIONAL THUNDER THERE. WHILE CLOUD
COVER AND PRECIP COVERAGE MAY LIMIT SFC/NEAR SFC BASED
DESTABILIZATION SOMEWHAT...PRESENCE OF 30-40 KT MID LEVEL FLOW AND
25-35 KT 0-6 KM BULK SHEAR DOES SUPPORT ORGANIZED CONVECTION. LINE
SEGMENTS WITH ATTENDANT SEVERE WIND/HAIL THREAT ARE EXPECTED TO BE
THE MAIN SEVERE WEATHER THREAT...THOUGH BACKED LOW LEVEL FLOW
NEAR/ALONG THE WARM FRONT COULD SUPPORT MINIMAL TORNADO POTENTIAL
PARTICULARLY IF LESS CLOUD COVER/MORE INSTABILITY WERE TO OCCUR.
MORE WIDESPREAD ISSUE IS LIKELY TO BE POTENTIAL FOR RAINFALL AMOUNTS
IN EXCESS OF 1.0 INCHES WITH RAIN/STORMS AS PWATS INCREASE TO AROUND
1.35 INCHES BY LATE AFTERNOON/EVENING. HEAVIER RAIN AND
THUNDERSTORMS SHOULD GRADUALLY MOVE OFF TO THE EAST/SOUTHEAST OF THE
CWA LATER TONIGHT...AS SFC LOW AND COLD FRONT MOVE THROUGH AND AXIS
OF BEST LOW LEVEL MOISTURE TRANSPORT VEERS ACROSS IN/OH.

SHOWERY WEATHER WILL LIKELY CONTINUE INTO FRIDAY HOWEVER...AS SLOW
MOVING UPPER TROUGH TRAVERSES THE FORECAST AREA. COOLER AIR WILL
FILTER IN AS WELL...WITH TEMPS FALLING FROM TODAYS UPPER 60S-MID 70S
TO LOWER-MID 60S NORTH TO SOUTH...AND 50S ALONG LAKE MICHIGAN.

GUIDANCE REMAINS STEADFAST IN DIGGING STRONG SHORT WAVE INTO THE
REGION AND AMPLIFYING UPPER TROUGH ACROSS THE FRIDAY NIGHT AND
SATURDAY. AS ADVERTISED EARLIER...SHARP SURFACE COLD FRONT IS
EXPECTED TO PUSH THROUGH DURING THE MORNING/MIDDAY HOURS...WITH
TEMPS LIKELY FALLING INTO THE 50S BEHIND THE FRONT DURING THE
AFTERNOON. UNSEASONABLY COOL HIGH PRESSURE BUILDS ACROSS THE PLAINS
AND MISSISSIPPI VALLEY SATURDAY NIGHT...SETTING THE STAGE FOR A
CHILLY MOTHERS DAY. 850 MB TEMPS IN THE NEGATIVE SINGLE DIGITS
PORTEND AFTERNOON HIGHS STRUGGLING TO GET TO/ABOVE 60 ESPECIALLY
ACROSS NORTHEAST IL/NORTHWEST IN. LOWS WILL LIKELY DIP INTO THE 30S
IN SOME NORTHERN PARTS OF THE CWA SATURDAY NIGHT AND AGAIN SUNDAY
NIGHT. LOOKS LIKE ENOUGH GRADIENT/WIND TO PREVENT PATCHY FROST
DEVELOPMENT BEHIND THE FRONT SATURDAY NIGHT...THOUGH THERE COULD BE
SOME FROST IN COLDER MORE SHELTERED AREAS LATE SUNDAY NIGHT.

AS QUICKLY AS WE COOL DOWN OVER THE NEXT COUPLE OF DAYS...GUIDANCE
CONTINUES TO INDICATE THAT THE DEEP UPPER TROUGH WILL BE
PROGRESSIVE. UPPER RIDGING AND STRONG WARM ADVECTION LOOKS TO PUSH
OUR TEMPS BACK FIRMLY INTO THE 60S MONDAY...AND QUITE POSSIBLY THE
80S ESPECIALLY WEST BY TUESDAY AS 850 MB TEMPS APPROACH +20 C. WEAK
SLOW MOVING COOL FRONT SAGS ACROSS THE AREA WEDNESDAY TEMPERING THE
WARM-UP A BIT POTENTIALLY ACROSS THE NORTH...ALONG WITH THE NEXT
CHANCE OF SHOWERS/STORMS.

RATZER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* SHOWERS WITH ISOLATED/SCATTERED TSRA MID/LATE AFTERNOON.
* SHOWERS THIS EVENING...ENDING OVERNIGHT.
* LIGHT SOUTHEASTERLY WINDS BECOMING EAST BY EARLY EVENING THEN
  NORTH BY LATE EVENING...WITH SOME GUSTS POSSIBLE OVERNIGHT.
* MVFR CIGS BY EARLY EVENING WITH IFR/LIFR CIGS DEVELOPING DURING
  THE EVENING...IMPROVING TO MVFR FRIDAY MORNING. CMS

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

LINE OF SHRA/TSRA LIFTING NORTH ACROSS CENTRAL IL HAS BEGUN TO
WEAKEN AS ADDITIONAL TSRA LIFT NORTHEAST ACROSS EASTERN IL. WHILE
THIS ACTIVITY IS WEAKENING...HAVE ADJUSTED TIMING...A LITTLE
EARLIER...AS SOME SHOWER ACTIVITY WILL LIKELY REACH THE TERMINALS
BY MID AFTERNOON. ADDITIONAL SHOWERS AND PERHAPS ISOLATED TSRA
WILL CONTINUE TO DEVELOP/SPREAD NORTH ACROSS THE AREA THROUGH
EARLY THIS EVENING AS AN UPPER WAVE LIFTS NORTH. APPEARS THE BEST
THUNDER COVERAGE WILL REMAIN SOUTHEAST OF THE TERMINALS AND FOR
NOW HAVE MAINTAINED VCTS BUT TRENDS WILL NEED TO BE MONITORED FOR
UPDATES. AS AN AREA OF SURFACE LOW PRESSURE MOVES ACROSS THE AREA
LATE TONIGHT INTO THE EARLY OVERNIGHT HOURS...ADDITIONAL SHOWERS
WILL BE POSSIBLE.

THIS SURFACE LOW...AND THE LOCATION OF THE WARM FRONT AHEAD OF IT
THIS AFTERNOON WILL MAKE WIND DIRECTIONS PROBLEMATIC. SOUTHERLY
WINDS TO THE I-80 CORRIDOR LOOK ON TRACK BUT AT MDW/ORD...WINDS ON
ONE MINUTE DATA HAVE BEEN LIGHT WESTERLY TO LIGHT EASTERLY...AS
WELL AS CALM. WHILE GRADIENT REMAINS WEAK...APPEARS AS THE SURFACE
LOW APPROACHES...SOUTHEASTERLY WINDS WILL LIKELY PREVAIL AND THEN
SHIFT MORE EAST THEN NORTHEAST THIS EVENING BUT CONFIDENCE
REGARDING WINDS THROUGH THIS EVENING REMAINS LOW.

CIGS WILL LIKELY BEGIN TO FALL INTO MVFR AS PRECIP DEVELOPS AND AS
THE LOW LEVELS SATURATE WITH FLOW OFF THE LAKE...EXPECT CIGS TO
QUICKLY LOWER INTO IFR THIS EVENING AND AS THE SURFACE LOW
APPROACHES...CIGS LIKELY TO DROP INTO LIFR AND POSSIBLY VLIFR WITH
CIGS SLOWLY LIFTING FRIDAY MORNING AS THE LOW SHIFTS EAST. CMS

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* MEDIUM CONFIDENCE REGARDING SHOWERS TIMING/TRENDS.
* LOW CONFIDENCE REGARDING TSRA THIS AFTERNOON INTO THIS EVENING.
* MEDIUM CONFIDENCE REGARDING CIGS THROUGH THE PERIOD.
* LOW CONFIDENCE REGARDING WINDS THIS AFTERNOON...MEDIUM
  CONFIDENCE FOR THE REST OF THE PERIOD. CMS

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

FRIDAY NIGHT...CLEARING SKIES.
SATURDAY...VFR. GUSTY NORTHWEST WINDS.
SUNDAY AND MONDAY...VFR.
TUESDAY...STRONG SOUTHERLY WINDS...OTHERWISE VFR.
WEDNESDAY...CHANCE OF TSRA.

KJB

&&

.MARINE...
208 AM CDT

A COLD FRONT WILL DROP SOUTHWARD DOWN THE LAKE TODAY. IN THE WAKE OF
THIS FRONT...WINDS WILL BECOME NORTH AND INCREASE UP TO 25 TO 30 KT
FOR A PERIOD INTO FRIDAY MORNING. THIS SHOULD RESULT IN SMALL
CRAFT ADVISORY CONDITIONS FOR BOTH THE INDIANA AND ILLINOIS NEAR
SHORE WATERS LATER TONIGHT THROUGH FRIDAY EVENING...AS WAVES
CLIMB ABOVE 6 FT AND NORTHERLY WINDS GUST UP IN THE 25 TO 30 KT
RANGE.

IN ADDITION TO WINDS...A WEATHER DISTURBANCE IS EXPECTED TO RESULT
IN A SURFACE WAVE OF LOW PRESSURE...WHICH SHOULD MOVE ALONG THE
FRONTAL BOUNDARY JUST SOUTH OF THE LAKE TONIGHT. THIS LOOKS TO
RESULT IN PERIODS OF SHOWERS AND THUNDERSTORMS...ESPECIALLY ACROSS
THE SOUTHERN PORTION OF THE LAKE LATER TODAY AND TONIGHT.

THE WINDS SHOULD TO ABATE FOR A PERIOD LATE FRIDAY AND INTO SATURDAY
AS ANOTHER SURFACE RIDGE OF HIGH PRESSURE BUILDS OVER THE LAKE.
HOWEVER...ANOTHER COLD FRONT STILL LOOKS TO TAKE AIM ON THE LAKE
SATURDAY AFTERNOON. THIS WILL ONCE AGAIN LEAD TO A
PERIOD OF STRONGER NORTHWESTERLY WINDS INTO SUNDAY MORNING.

ANOTHER PERIOD OF LIGHT AND VARIABLE WINDS LOOKS TO SET UP AGAIN FOR
LATE SUNDAY AND INTO MONDAY OF NEXT WEEK AS ANOTHER AREA OF SURFACE
HIGH PRESSURE BUILDS ACROSS THE WESTERN LAKES. HOWEVER...ONCE THIS
HIGH SHIFTS EAST MONDAY NIGHT...IT APPEARS THAT A STRONG PRESSURE
GRADIENT WILL SET UP ACROSS THE WESTERN LAKES...AS A POTENT STORM
SYSTEM MOVES EASTWARD ACROSS CANADA. THIS LOOKS TO RESULT IN SOME
STRONG SOUTHERLY WINDS OVER THE LAKE FOR TUESDAY OF NEXT WEEK.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...1 AM FRIDAY TO 4
     AM SATURDAY.

     SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...7 AM FRIDAY TO 4
     AM SATURDAY.

&&

$$


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