🚀 go-pugleaf

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1141 AM CST SUN DEC 16 2012

DISCUSSION...
823 AM CST

MADE SOME MINOR TWEAKS TO GOING GRIDS/FORECAST FOR TODAY.
FIRST...ADJUSTED RAIN CHANCES TO CHICAGO METRO INTO NW INDY ENDING
FROM WEST TO EAST THIS MORNING. CANNOT RULE OUT SOME PATCHY LIGHT
DRIZZLE INTO THE AFTERNOON BUT CHANCES LOOK LOW SO KEPT OUT OF THE
GRIDS.

MODEST COLD AIR ADVECTION SHOULD CONTINUE THROUGH THE DAY AND
GIVEN THE OVERCAST SKIES WOULD EXPECT IT TO BE SUFFICIENT TO KEEP
TEMPS STEADY OR SLOWLY FALLING THROUGH THE DAY. AFTERNOON TEMPS
SHOULD FALL INTO THE 30S WESTERN CWA AND LOWER 40S EAST.

IZZI

//PREV DISCUSSION...

330 AM...FORECAST CONCERN NOW SHIFTS TO POTENTIAL WINTER STORM TO
AFFECT THE REGION WEDNESDAY NIGHT THROUGH FRIDAY MORNING...AND ITS
NUMEROUS CHALLENGES.

IN THE SHORT TERM...SURFACE LOW PRESSURE ACROSS CENTRAL WI WILL
CONTINUE TO SLOWLY LIFT NORTHEAST TODAY AND TONIGHT. AREA OF
SHOWERS DEVELOPED ACROSS FAR NORTHERN IL EARLY THIS MORNING AS A
WEAK WAVE ROTATED AROUND THIS SYSTEM. STILL A CHANCE FOR SOME
SHOWERS/DRIZZLE THIS MORNING BUT WILL BE LIFTING NORTHEAST THROUGH
THE MORNING WITH THIS AFTERNOON LOOKING MAINLY DRY. TEMPERATURES
RANGE IN THE UPPER 40S TO THE LOWER 50S CURRENTLY WITH A WEAK COLD
FRONT CROSSING INTO WESTERN IL. NOT MUCH COLDER AIR BEHIND THIS
FRONT BUT TEMP TRENDS TODAY STILL A LITTLE TRICKY. HIGHS ACROSS
WESTERN AREAS LIKELY TO BE THIS MORNING THEN STEADY OR SLOWLY
FALLING TEMPS THIS AFTERNOON. TEMPS MAY CLIMB A FEW DEGREES
FURTHER EAST BEFORE BEGINNING TO FALL DURING THE AFTERNOON.

LOW PRESSURE DEVELOPING OVER THE SOUTHERN PLAINS TODAY ALONG THE
SOUTHERN END OF THE COLD FRONT WILL MOVE ACROSS THE OHIO VALLEY
MONDAY AND INTO THE MID ATLANTIC MONDAY NIGHT...WHILE DEEPENING.
HAD APPEARED 24 HRS AGO THIS LOW WOULD TRACK SLIGHTLY FURTHER
NORTHEAST AND ABSORB THE CURRENT LOW. AS HIGH TEMPERATURES REACH
THE UPPER 30S TO LOWER 40S ON MONDAY...PRECIP SHOULD INITIALLY BE
ALL LIQUID AND WITH JUST A FEW HUNDREDTHS OF AN INCH POSSIBLE
ACROSS THE SOUTHEAST CWA. DEPENDING ON HOW FAST THIS PRECIP EXITS
THE AREA MONDAY NIGHT...COULD BE A MIX WITH SOME LIGHT SNOW BEFORE
ENDING BUT NOT EXPECTING ANY SNOW ACCUMULATION.

A RIDGE OF HIGH PRESSURE QUICKLY MOVES ACROSS THE REGION/WESTERN
LAKES LATE MONDAY NIGHT/EARLY TUESDAY MORNING WITH FLOW TURNING
SOUTHERLY TUESDAY. A WEAK LOW SHIFTS EAST ACROSS THE CENTRAL
PLAINS AND IS WEAKENING AS IT MOVES ACROSS SOUTHERN WI/NORTHERN IL
TUESDAY AFTERNOON. DEPENDING ON ITS EXACT TRACK... WINDS SHOULD
TURN SOUTHERLY OVER MUCH OF THE AREA AIDING WARMER TEMPS IN THE
40S. THUS ANY PRECIP WITH THIS SYSTEM LIKELY TO BE RAIN THOUGH A
FEW FLAKES MAY MIX IN EARLIER IN THE MORNING.

BY WEDNESDAY AFTERNOON...AN UPPER TROUGH IS DIGGING ACROSS THE
CENTRAL PLAINS AS LOW PRESSURE OVER OKLAHOMA TURNS NORTHEAST
BOUND FOR THE GREAT LAKES REGION. THE GENERAL TRACK OF THIS LOW
IS FAIRLY SIMILAR TO 24 HRS AGO...FROM ROUGHLY STL TO GYY TO GRR
FROM EARLY THURSDAY MORNING THROUGH THURSDAY EVENING...THUS
CONFIDENCE IS INCREASING REGARDING THIS TRACK BUT TIMING/SPEED
STILL REMAIN UNCERTAIN AS THESE SYSTEMS TYPICALLY SLOW AS THE
UPPER TROUGH CONTINUES TO DIG. ITS ALSO IMPORTANT TO REMEMBER
THAT A CHANGE IN THIS TRACK OF JUST 50 OR 100 MILES COULD MAKE
FOR HUGE CHANGES TO THE FORECAST.

BUT AS IT LOOKS FROM THIS DISTANCE...WARMER/MORE MOIST AIR WILL
SPREAD NORTH UNDER AND TO THE EAST OF THE TRACK OF THE LOW AND
EXPECT TEMPS IN THE UPPER 30S/LOWER 40S WEDNESDAY NIGHT...PERHAPS
EVEN RISING TEMPS ACROSS THE EASTERN HALF/THIRD OF THE CWA WITH
ALL RAIN. SOMEWHERE ACROSS THE WESTERN HALF/THIRD...THERE WILL BE
A TRANSITION FROM RAIN TO SNOW...TOO EARLY TO SAY WHERE/WHEN. AS
THE LOW CONTINUES NORTH THURSDAY...COLDER AIR WILL SPREAD SOUTH
ACROSS NORTH CENTRAL IL SWITCHING PRECIP OVER TO ALL SNOW...AND
THAT TRANSITION WILL CONTINUE EAST THURSDAY AFTERNOON WITH MUCH IF
NOT ALL THE AREA BEING COLD ENOUGH FOR ALL SNOW BY THE THURSDAY
EVENING RUSH...PROBABLY SOONER. THEN THE QUESTION BECOMES HOW
MUCH QPF WILL STILL BE FALLING AT THAT TIME. A SLOWER ARRIVAL AND
SLOWER SPEED WILL RESULT IN MUCH MORE QPF AVAILABLE WHEN THE COLD
AIR IS IN PLACE. A BIT TOO EARLY TO START DISCUSSING POSSIBLE QPF
AND/OR SNOWFALL AMOUNTS OTHER THAN TO STAY THAT SOMEWHERE ON THE
NORTHWEST SIDE OF THIS SYSTEM...A BAND OF HEAVY SNOW IS LIKELY AND
THAT BAND MAY END UP JUST NORTHWEST OF THE CWA. THE LOW CONTINUES
TO DEEPEN THURSDAY NIGHT WITH THE GRADIENT TIGHTENING AND COLDER
AIR SPREADING ACROSS THE REGION. WINDS GUSTING AS HIGH AS 40
MPH...PROBABLY HIGHER...MAY MAKE FOR SOME ROUGH TRAVEL WITH
POSSIBLE BLOWING/DRIFTING SNOW...WHERE SNOW DOES FALL. WINDS
LIKELY TO STAY UP FOR MUCH OF THURSDAY NIGHT WITH WIND CHILLS
POTENTIALLY NEAR ZERO BY FRIDAY MORNING. CMS

&&

AVIATION...

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

* LOW END MVFR CIGS HANG AROUND UNTIL THE PREDAWN HOURS TOMORROW.

* SW TO W WINDS GUSTING BTWN 15 AND 20 KT THROUGH THE EARLY
  AFTERNOON....THEN GUSTING ARND 15 KT THROUGH THE LATE AFTERNOON.

JEE

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

THE WEAK LOW IS OVER NORTHERN LAKE MICHIGAN AND SLOWLY MOVING NE.
DRY AIR OVER IOWA HAS REMAINED IN IOWA...SO DESPITE THE GUSTY
WINDS THE LOW CIGS HAVE HUNG AROUND. GIVEN THE DAMP
ENVIRONMENT...THINKING GUIDANCE MAY HAVE BEEN RIGHT ALL ALONG
KEEPING CIGS IN THE MVFR RANGE THROUGH TONIGHT. AS SUCH EXTENDED
CIGS ARND OVC020 THROUGH THE PREDAWN HOURS TOMORROW. 10Z IS A
LITTLE QUICKER THAN WHAT GUIDANCE SUGGESTS BUT EXPECTING THE WINDS
TO TURN NORTHWEST TOMORROW MORNING WHICH WILL HELP BRING DRIER AIR
INTO THE REGION. VFR CLOUDY CONDITIONS ARE EXPECTED TOMORROW. THE
ONLY OTHER QUESTION IS WITH WINDS TOMORROW. GUIDANCE VARIES
BETWEEN NORTH AND NORTHEAST WINDS...BUT WIND SPEEDS WILL BE 5 KT
OR LESS. AS SUCH WENT WITH N WINDS...BUT THERE IS A POSSIBILITY OF
WINDS FLOPPING OVER TO NE ESPECIALLY AT MDW AND ORD IN THE
AFTERNOON.

JEE


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

* HIGH CONFIDENCE IN ALL FORECAST TRENDS.

* MEDIUM CONFIDENCE IN TIMING OF CIG IMPROVEMENT.

JEE

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

MONDAY NIGHT...VFR.

TUESDAY...SLGT CHC RA/SN SHOWERS. BRIEF MVFR POSSIBLE.

WEDNESDAY...VFR...THEN RA DVLPG WEDNESDAY NGT. IFR POSSIBLE.

THURSDAY...RAIN CHANGING TO SNOW WITH IFR LIKELY. BECOMING WINDY.

FRIDAY...STRONG GUSTY NW WINDS. VFR.

SATURDAY...VFR.

RATZER

&&

MARINE...
305 AM CST

LOW PRESSURE OVER WISCONSIN WILL CONTINUE TO LIFT NORTHEAST ACROSS
UPPER MICHIGAN THROUGH TONIGHT...BEFORE SLOWLY FILLING ACROSS
EASTERN ONTARIO ON MONDAY. AN OCCLUDED FRONT EXTENDING SOUTHEAST
FROM THE LOW WILL LIFT ACROSS THE NORTHERN PART OF LAKE MICHIGAN
THIS MORNING...WITH WINDS SHIFTING TO THE WEST-SOUTHWEST ACROSS THE
ENTIRE LAKE BY AFTERNOON. GUSTS OF 20-25 KTS WILL BE POSSIBLE OVER
THE SOUTHERN AND CENTRAL PARTS OF THE LAKE...IN THE STRONGER
GRADIENT SOUTH OF THE RETREATING LOW. WEAK HIGH PRESSURE RIDGING
WILL THEN SPREAD ACROSS THE LAKE MONDAY NIGHT WITH LIGHTER NORTHWEST
WINDS. A WEAK LOW WILL MOVE ACROSS THE LAKE TUESDAY...THOUGH WITH
WINDS GENERALLY LESS THAN 15 KTS.

ATTENTION IS THEN FOCUSED ON A MAJOR LOW PRESSURE SYSTEM WHICH IS
FORECAST TO DEVELOP ACROSS THE SOUTHERN PLAINS MID-WEEK...AND LIFT
NORTHEAST ACROSS IL AND NORTHERN INDIANA THURSDAY AND INTO LOWER
MICHIGAN THURSDAY NIGHT. THE LOW IS EXPECTED TO BE DEEPENING
STRONGLY AS IT MOVES THROUGH THE MIDWEST...WITH WINDS INCREASING TO
GALE FORCE AND BACKING FROM NORTHEAST TO NORTHWEST BEHIND THE LOW.
HIGH GALES ARE LIKELY LATE THURSDAY INTO FRIDAY...WITH THE POTENTIAL
FOR STORM FORCE GUSTS. IT IS IMPORTANT TO NOTE THAT THIS STORM
SYSTEM IS STILL 5-6 DAYS AWAY AT THIS POINT...AND COULD EVOLVE
DIFFERENTLY THAN CURRENT MODEL GUIDANCE INDICATES. HOWEVER...
GUIDANCE IS IN RELATIVELY GOOD AGREEMENT WITH THE STRENGTH AND TRACK
OF THE LOW AT THIS TIME.

RATZER

&&

LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$