🚀 go-pugleaf

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1207 PM CST WED FEB 13 2013

DISCUSSION...
329 AM CST

ANOTHER DAY OF QUIET WEATHER IS IN STORE BEFORE PRECIP CHANCES
RETURN ALONG WITH COLDER TEMPS...FOLLOWED BY MORE UPS AND DOWNS IN
TEMPS AND A SEEMINGLY MORE ACTIVE WEATHER REGIME FOR NEXT WEEK AS A
HIGH AMPLITUDE BUT FAIRLY PROGRESSIVE PATTERN SETS UP. EARLY MORNING
SATELLITE IMAGERY SHOWS A SOMEWHAT SPLIT FLOW OVER THE MISSISSIPPI
RIVER VALLEY AND WESTERN GREAT LAKES. ONE UPPER LOW IS NOTED IN THE
NORTHERN STREAM OF THE FLOW OVER WESTERN ONTARIO WITH A SOUTHERN
STREAM WAVE MOVING INTO THE LOWER OHIO VALLEY. A FLAT RIDGE IS OUT
OVER THE EASTERN PACIFIC WITH AN UPPER LOW OVER WESTERN ALASKA. THE
FLOW IN BETWEEN IS ZONAL WITH SEVERAL EMBEDDED WAVES TRACKING
EASTWARD THROUGH IT WHICH WILL BE KEY PLAYERS IN OUR UPCOMING PRECIP
CHANCES AND COLD PUSH. AT THE SURFACE...WEAK HIGH PRESSURE IS SPREAD
ACROSS THE LOCAL AREA WITH A WEAK LOW OVER THE GULF COAST STATES IN
CONJUNCTION WITH THE OHIO VALLEY UPPER WAVE. SEVERAL LOWS ARE SPREAD
ACROSS CANADA WITH ONE NEARING JAMES BAY AND ANOTHER OVER CENTRAL
ALBERTA WHICH WILL BE AFFECTING US LATER ON TONIGHT AND THURSDAY.

TODAY...TEMPS WILL BE THE FIRST ISSUE TODAY WITH A BALANCE BETWEEN
FAIRLY LIGHT WEST-SOUTHWEST WINDS AND APPROACHING MID LEVEL CLOUD
COVER DETERMINING HOW MUCH WARMING WE SEE. MODEST WARM ADVECTION
WILL BE UNDERWAY ALOFT WITH H85 TEMPS COMING UP TO AROUND -2C AND
H92 TEMPS UP TO AROUND 0 OR +1C. CLOUD COVER LOOKS TO INCREASE FROM
NORTHWEST TO SOUTHEAST WITH THE NORTHWEST HALF TO TWO-THIRDS OF THE
AREA HAVING AT LEAST SOME MID/HIGH CLOUD BY EARLY AFTERNOON. COOLEST
TEMPS WILL OCCUR FAR NORTH WHERE CLOUDS AND SNOW COVER WILL LIMIT
WARMING...WITH CENTRAL AREAS BEING AROUND 40 AND SOUTHERN AREAS
LIKELY IN THE UPPER 40S. THE CENTRAL AREAS FROM CHICAGO BACK TO
LASALLE COUNTY WILL LIKELY BE THE WILDCARD AREAS WITH A POTENTIAL
FOR WARMER THAN FORECAST HIGHS BUT WITH THE FAIRLY COLD START...LATE
MORNING/MIDDAY CLOUD COVER ARRIVAL AND ONLY A LIGHT WEST-SOUTHWEST
WIND HIGHS AROUND 40 SEEM REASONABLE.

TONIGHT AND THURSDAY...THE CLIPPER TAKING SHAPE OVER ALBERTA THIS MORNING
WILL RACE SOUTHEASTWARD THROUGH THE DAY WITH THE SURFACE LOW
REACHING CENTRAL MINNESOTA LATER THIS EVENING. A MORE FOCUSED PUSH
OF WARM ADVECTION WILL MOVE ACROSS THE AREA FROM WEST TO EAST FROM
AS EARLY AS LATE EVENING THROUGH THE OVERNIGHT BRINGING SOME
DEEPENING SATURATION AND A PUSH OF WEAK ASCENT. THIS MAY TRIGGER
SOME LIGHT PRECIP ACROSS THE NORTHERN QUARTER TO THIRD OF THE CWA
TONIGHT. PRECIP TYPE WILL BE PROBLEMATIC WITH A DECENT WARM WEDGE OF
AIR PUSHING IN BELOW H85. FORECAST SOUNDINGS SHOW SOME VARIATION AND
PROFILES WILL BE CHANGING DURING THE PERIOD WHERE PRECIP IS
POSSIBLE. THE WARM WEDGE ITSELF WILL BE WARM ENOUGH TO SUPPORT
MELTING FAVORING FREEZING RAIN BUT THE LOWEST LEVELS ARE DRY ENOUGH
TO SUPPORT WET BULB COOLING WHICH WOULD STILL YIELD AN ABOVE
FREEZING LAYER BUT ONE MORE FAVORED FOR PARTIAL MELTING AND SLEET.
SFC TEMPS WILL BE KEY AS WELL BUT THEY DO LOOK TO WARM
OVERNIGHT...HOPEFULLY ABOVE FREEZING FOR AREAS THAT SEE
PRECIP....BUT THEY WILL LIKELY BE BELOW AS PRECIP WOULD START. WILL
CARRY A VARIETY OF PRECIP TYPES TONIGHT STARTING WITH SLEET AND
FREEZING RAIN TRANSITIONING TO A MIX OF RAIN...SNOW...AND FREEZING
RAIN DEPENDING ON TIME AND LOCATION AND OF COURSE SURFACE TEMP.
COLDER AIR WILL START TO ARRIVE TOWARD DAYBREAK RESULTING IN
INCREASING CHANCES FOR SNOW TO MIX IN OVER TIME. MAY NEED TO
INCREASE POPS ABOVE THEIR CURRENT CHANCE VALUES FOR THE FAR NORTH AS
WELL. LOW PRECIP CHANCES CONTINUE ACROSS THE NORTHERN THIRD TO HALF
OF THE AREA THURSDAY MORNING WITH MORE OF A RAIN SNOW TO SNOW
SCENARIO AS COLDER AIR SPILLS IN AND WINDS BECOME GUSTY. POPS MAY
CONTINUE THURSDAY AFTERNOON AND EXPAND SLIGHTLY SOUTHWARD AS COLDER
AIR ARRIVES AND THE MAIN UPPER TROUGH APPROACHES. A LULL IS POSSIBLE
LATE IN THE DAY DEPENDING ON HOW QUICKLY THE MAIN TROUGH ARRIVES.
OVERALL DO NOT HAVE VERY HIGH CONFIDENCE IN POP TRENDS DURING THE
DAY. TEMPS SHOULD WARM SOUTH DURING THE MORNING BUT AM THINKING THAT
CENTRAL AND NORTHERN AREAS WILL LOSE A FEW DEGREES DURING THE DAY AS
H85 TEMPS FALL TO AROUND -7C FROM AROUND -1C TO START THE DAY.
SOUTHERN AREAS WILL LIKELY SEE FALLING TEMPS BUT THIS MAY OCCUR
LATER IN THE AFTERNOON.

THURSDAY EVENING THROUGH FRIDAY...THINGS GET MORE INTERESTING
THURSDAY EVENING. THERE IS SOME DISAGREEMENT WITH HOW SHARP THE MAIN
TROUGH AXIS WILL BE AND WHEN EXACTLY IT ARRIVES...WITH GOOD
AGREEMENT ON A SECONDARY UPPER TROUGH AXIS TRAILING BEHIND. WILL
NEED TO WATCH THIS BECAUSE A SHARPER MAIN TROUGH WOULD LIKELY LEAD
TO SNOW CHANCES INCREASING DURING THE EVENING. THE SECOND TROUGH
BRINGS ANOTHER PUSH OF COLD AIR AND GOOD CHANCES FOR A BAND OF SNOW
STARTING EARLY THURSDAY NIGHT. TIMING HAS BEEN A BIT OF AN ISSUE
WITH A SLOWER PROGRESSION POSSIBLE AS WELL. FRIDAY MORNING WILL BE
ANOTHER POTENTIALLY TRICKY PERIOD WITH THE NEW NAM AND ECMWF
SUGGESTING A SURFACE PASSING OVER SOUTHERN LAKE MICHIGAN. THIS WOULD
PRESENT A SHORT WINDOW OF POTENTIAL LAKE ENHANCEMENT FRIDAY MORNING.
THE NAM IS ALSO MUCH MORE EXCITED ABOUT PRECIP AMOUNTS WITH THIS
SERIES OF WAVES THURSDAY NIGHT AND FRIDAY PAINTING OVER THREE TENTHS
LIQUID ACROSS THE NORTHERN HALF OF THE AREA. WILL CONSIDER THIS AN
OUTLIER FOR NOW. OVERALL EXPECT THAT AROUND AN INCH OF ACCUMULATION
WILL BE POSSIBLE ACROSS THE NORTHEAST SECTIONS OF THE CWA WITH
LESSER AMOUNTS GOING WEST AND SOUTH. LIGHT SNOW MAY LINGER THROUGH
FRIDAY WITH ANOTHER WAVE POSSIBLY TRANSITING THE NOW MASSIVE
LONGWAVE TROUGH CENTERED OVER THE WESTERN LAKES. BRISK NORTHWEST
WINDS WILL BE IN PLACE FRIDAY AS TEMPS ONLY REACH THE MID 20S NORTH
TO AROUND FREEZING SOUTH.

SATURDAY THROUGH MONDAY...THE BIG UPPER TROUGH WILL CONTINUE TO BE
SPREAD ACROSS THE EASTERN HALF OF NORTH AMERICA SATURDAY WHILE A BIG
UPPER RIDGE DEVELOPS OVER WESTERN NORTH AMERICA. THE COLDEST AIR
WILL BE OVER THE AREA SATURDAY MORNING WITH H85 TEMPS OF -18 TO -20C
WITH A NORTHWEST BREEZE CONTINUING IN THE MORNING THEN EASING AS
HIGH PRESSURE BUILDS FROM THE WEST. DESPITE THE AMPLITUDE OF THE
PATTERN THE UPPER TROUGH IS FAIRLY SWIFT TO MOVE EASTWARD THROUGH
THE DAY LEADING TO SLIGHT WARM ADVECTION ALOFT...BUT ANY WARMING
AFFECTS THIS WOULD HAVE WILL LIKELY BE NEGATED BY POOR MIXING WITH
THE RIDGE MOVING OVERHEAD. EXPECT HIGHS TO STRUGGLE TO REACH 20
NORTH AND BE HELD TO THE MID 20S SOUTH BUT HAVE A SUSPICION THIS
COULD BE A BIT OPTIMISTIC..THOUGH THE INCREASED MID FEBRUARY SUN
ANGLE WILL HELP THINGS. WARM ADVECTION WILL CONTINUE SUNDAY AS THE
UPPER RIDGE APPROACHES FROM THE WEST. TEMPS WILL BE WARMER BUT AM
NOT CLEAR ON HOW MUCH WITH GUIDANCE DIFFERING ON LOW LEVEL WIND
DIRECTION AND THE SPEED WITH WHICH THE UPPER RIDGE ARRIVES. WITH
SUNSHINE AND PRESUMABLY AN INCH OR LIKELY LESS OF SNOW  COVER FOR
THE BULK OF THE AREA WILL STICK WITH MILDER READINGS IN THE 30S FOR
NOW. AN UPPER TROUGH WILL BE DIGGING INTO THE PLAINS MONDAY PUSHING
THE UPPER RIDGE AXIS TO THE EAST WHILE THE ATTENDANT SURFACE LOW
TRACKS ACROSS THE UPPER MISSISSIPPI RIVER VALLEY. SOUTHERLY LOW
LEVEL FLOW SHOULD ALLOW FOR A MILD DAY WITH HIGHS NEAR 40 NORTH TO
THE MID 40S SOUTH.

TUESDAY AND BEYOND...OVERALL PATTERN AGREEMENT IS HIGH AS WE WORK
INTO TUESDAY WITH THE AFOREMENTIONED LONGWAVE TROUGH REACHING THE
AREA. THE MAIN QUESTIONS WILL BE THE DEGREE TO WHICH IT IS PHASED
WITH GUIDANCE THE PAST FEW NIGHTS POINTING TOWARD PRETTY WELL
PHASED. THIS CERTAINLY HAS THE POTENTIAL TO CHANGE AS THE PATTERN
EVOLVES OVER THE PACIFIC OVER THE NEXT FEW DAYS BUT HAVE SEEN SOME
CONSISTENCY THUS FAR. THE END RESULT IS A REORGANIZATION OF THE
UPPER MISSISSIPPI RIVER VALLEY LOW INTO A LOW ACROSS CENTRAL ILLINOIS
OR THE LOWER OHIO VALLEY WHICH QUICKLY WORKS NORTHEASTWARD. BASED ON
THE WARMING LEADING UP TO THE LOW PRECIP WOULD START AS RAIN AND END
AS SNOW AS THE UPPER TROUGH AXIS AND ATTENDANT COLD FRONT PUSH
COLDER AIR INTO THE AREA. STILL TOO EARLY FOR DETAILS BUT THIS IS
THE GENERAL TREND SUPPORTED OVER RECENT SHIFTS. BEYOND THAT THE
TROUGH/RIDGE PARADE LOOKS TO CONTINUE THROUGH THE END OF THE WEEK
RESULTING IN TEMPERATURES SWINGS AS WELL AS THE POTENTIAL FOR
MOISTURE LADEN SOUTHWEST SYSTEMS TO TRACK SOMEWHERE ACROSS THE
REGION.

MDB

&&

AVIATION...

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

* WINTRY MIX OF PRECIP MOVES IN LATE TONIGHT WITH PRECIP CHANGING
  TO A -RASN MIX THURSDAY MORNING.

* CIGS LOWER TO MVFR THURSDAY MORNING.

* GUSTY SW/W WINDS DEVELOP BY MID MORNING THURSDAY. MAX GUSTS ARND
  35 KT POSSIBLE IN THE AFTERNOON.

JEE

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

HIGH PRESSURE THAT WAS OVERHEAD LAST NIGHT HAS WEAKENED WHILE LOW
PRESSURE IS APPROACHING FROM THE NORTHWEST. WINDS ARE A LITTLE
NOISY THIS MORNING BEHIND THE LOW WITH A GENERAL SW DIRECTION AOB
10 KT. EXPECTING VFR CONDITIONS UNTIL THE LOW REACHES THE AREA
LATE TONIGHT.

CIGS WILL BEGIN TO THICKEN AHEAD OF THE LOW WITH VFR CIGS 050-090
CURRENTLY SPREAD ACROSS SOUTH DAKOTA AND MINNESOTA. WHILE THE LOW
WILL PASS NORTH OF THE TERMINALS...PRECIP AND MVFR CIGS WILL
SPREAD SE LATE TONIGHT INTO THURSDAY MORNING. THE VARIOUS GUIDANCE
MEMBERS SHOW A HODGEPODGE OF SOLUTIONS REGARDING PRECIP TYPE AND
PRECIP PERSISTENCE. MAIN ISSUE IS THE MOISTURE CONTENT ASSOCIATED
WITH THE SYSTEM. VARIOUS MODELS INDICATE THERE WILL ONLY BE A
SHALLOW LAYER OF MOISTURE WHICH COULD EITHER RESULT IN PERIODS OF
LIGHT PRECIP...OR NO PRECIP AT ALL DEPENDING ON HOW DEEP THE LAYER
IS. THAT BEING SAID GUIDANCE IS RATHER CONSISTENT THAT LIGHT
PRECIP WILL IMPACT THE TERMINALS ARND DAWN ON THURSDAY WITH A
WINTRY MIX EXPECTED. RFD WILL HAVE THE BEST CHANCE OF SEEING SNOW
WHILE THE OTHER TERMINALS WILL LIKELY SEE A MIX OF FREEZING RAIN
AND ICE PELLETS. LITTLE TO NO SNOW OR ICE ACCUMULATION IS EXPECTED
THROUGHOUT THE DAY.

BY LATE MORNING THE MODELS BEGIN TO DISAGREE ON HOW MUCH MOISTURE
WILL BE AVAILABLE. KEPT -RASN GOING THROUGH 00Z AT ORD SINCE
SCATTERED SHOWERS MAY PASS OVER THE TERMINAL THROUGH THE
AFTERNOON. NOTE THAT CIGS WILL LIKELY BE MVFR TOMORROW WITH LITTLE
IMPROVEMENT UNTIL THE COLUMN DRIES OUT.

FOR WINDS...WINDS ALOFT STRENGTHEN WITH 30 KT EXPECTED JUST 018 FT
OFF THE GROUND. SURFACE SW/W WINDS WILL INCREASE FROM LATE MORNING
THROUGH THE AFTERNOON. GUSTS ARND 30 KT ARE LIKELY BY 18Z..AND
COULD EASILY SEE OCNL MAX GUSTS ARND 35 KT IN THE AFTN.

JEE


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

* MEDIUM CONFIDENCE IN PRECIP TYPE...LOW CONFIDENCE IN TIMING OF
  PRECIP TYPE CHANGES AND HOW LONG PRECIP WILL LAST.

* HIGH CONFIDENCE IN CIG TRENDS...MEDIUM CONFIDENCE IN HOW LOW
  CIGS WILL GET. 015 CIGS PSBL.

* HIGH CONFIDENCE IN WIND FORECAST.

JEE

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

* THURSDAY NIGHT...SNOW LIKELY. MVFR LIKELY. IFR POSSIBLE.
* FRIDAY...CHANCE OF SNOW. MVFR POSSIBLE.
* SATURDAY AND SUNDAY...DRY/VFR.
* MONDAY...SLIGHT CHANCE OF RAIN OR SNOW.
* TUESDAY...CHANCE OF SNOW.

&&

MARINE...

306 AM...LOW PRESSURE WILL MOVE ACROSS THE NORTHERN PLAINS TODAY
AND THEN MOVE EAST TONIGHT...CROSSING NORTHERN LAKE MICHIGAN EARLY
THURSDAY AFTERNOON. THE GRADIENT WILL STEADILY TIGHTEN OVER SOUTH
CENTRAL LAKE MICHIGAN LATE TONIGHT WITH SOUTHERLY WINDS INCREASING
TO 25KTS BY THURSDAY MORNING. WINDS WILL SHIFT WESTERLY THURSDAY
MORNING ACROSS SOUTHERN PARTS OF THE LAKE AND INCREASE TO 30KTS.
HOWEVER...SPECIFIC WIND SPEEDS WILL BE DETERMINED BY THE EXACT TRACK
OF THE LOW. ITS POSSIBLE THAT WIND SPEEDS MAY DIMINISH NORTH OF A
LINE FROM MILWAUKEE TO MUSKEGON AS THE LOW APPROACHES/PASSES. IN
ADDITION...IF THE LOW TRACKS A LITTLE FURTHER SOUTH...MORE ACROSS
NORTH CENTRAL LAKE MICHIGAN...THERE COULD BE A BRIEF PERIOD OF
EASTERLY WINDS ACROSS FAR NORTHERN PARTS OF THE LAKE. THE LOW WILL
THEN MOVE NORTHEAST AND SLOWLY WEAKEN THURSDAY NIGHT INTO FRIDAY.
THE TIGHT GRADIENT COMBINED WITH COLDER AIR SPREADING ACROSS THE
REGION WILL ALLOW NORTHWEST WINDS TO INCREASE TO 30KTS. COULD BE A
PERIOD OF LOW END GALES ACROSS THE NORTH HALF OR SO THURSDAY
EVENING ON THE BACK SIDE OF THE LOW BUT CONFIDENCE REMAINS LOW.
NORTHWEST WINDS WILL SLOWLY DIMINISH FRIDAY NIGHT INTO SATURDAY AS
A RIDGE OF HIGH PRESSURE MOVES ACROSS THE LAKES SATURDAY NIGHT. CMS

&&

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

$$