🚀 go-pugleaf

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1138 AM CST THU FEB 14 2013

DISCUSSION...
1059 AM CST

FOR MORNING UPDATE...

ONLY MINOR TWEAKS TO GOING FORECAST...MAINLY WITH RESPECT TO
TIMING/PLACEMENT OF LIGHT PRECIP THROUGH THE DAY.

MORNING WATER VAPOR IMAGERY AND UPPER AIR ANALYSIS DEPICTS FAIRLY
DECENT MID LEVEL SHORT WAVE TROUGH TRACKING EAST ACROSS WI AND FAR
NORTHERN IL...WITH ASSOCIATED SURFACE LOW MOVING OVER CENTRAL LAKE
MICHIGAN AT 16Z. REGIONAL RADAR MOSAIC INDICATES PRECIP LARGELY
NORTH OF THE IL/WI BORDER AND ACROSS LAKE MICHIGAN AND LOWER
MICHIGAN. SOME VERY LIGHT RETURNS NOTED ALONG THE WI BORDER AND
ALONG/NORTH OF ROUGHLY A RFD-ORD LINE ALONG SOUTHERN PERIPHERY OF
MID-LEVEL VORT INFLUENCE...WITH SOME --RA OR --SW REPORTED IN A
COUPLE OF SPOTS. THIS AREA OF PRECIP SHOULD CONTINUE TO MOVE EAST
OVER LAKE MICHIGAN THROUGH MIDDAY WITH THE VORT ITSELF. BASED ON
THESE TRENDS...HAVE TIGHTENED UP THE SOUTHERN EDGE OF THE LOW POP
GRADIENT AND HAVE MENTIONED JUST SLIGHT CHANCE OF LIGHT RAIN/SNOW
ACROSS AREAS NORTH/NORTHEAST OF I-90 IN ILLINOIS THROUGH MIDDAY.

VISIBLE SATELLITE INDICATES A LITTLE BIT OF CLEARING...OR AT LEAST A
DECREASE IN THE OVERCAST ACROSS NORTHEAST IA AND WESTERN WI BEHIND
THE LEAD SHORT WAVE...THOUGH STRATOCU WAS OBSERVED DEVELOPING IN THE
LOW LEVEL COLD ADVECTION IN THAT REGION. THUS WHILE A STRAY FLURRY
OR RAIN DROP CANT BE RULED OUT...IT APPEARS THAT THE EARLY/MID
AFTERNOON HOURS SHOULD BE DRY. THE NEXT SYSTEM TO WATCH IS ANOTHER
CLIPPER CURRENTLY MOVING SOUTHEAST FROM THE DAKOTAS...WITH AN AREA
OF LIGHT SNOW FROM SOUTH DAKOTA/SOUTHWEST MINNESOTA INTO NORTHWEST
IA AT THIS TIME. GUIDANCE APPEARS REASONABLE IN SPREADING THIS
SOUTHEAST INTO WESTERN IL BY EARLY THIS EVENING...WITH SOME LIGHT
ACCUMULATING SNOW EXPECTED FOR PARTICULARLY THE SOUTHWEST 2/3 OR SO
OF THE WFO LOT CWA. MORE ON THAT THIS AFTERNOON.

OTHERWISE...REMAINDER OF NEAR TERM FORECAST APPEARS IN GOOD SHAPE
WITH TEMPS 35-42-ISH AND BLUSTERY WINDS VEERING MORE WEST-NORTHWEST
LATER THIS AFTERNOON.

RATZER

//PREV DISCUSSION...
330 AM CST

CHANGES ARE ON THE WAY AS AN APPROACHING ALBERTA CLIPPER CROSSES THE
AREA THROUGH TONIGHT. THE REST OF THE PERIOD WILL BE CHARACTERIZED BY
UPS AND DOWNS IN TEMPS AND A POTENTIALLY ACTIVE STORM TRACK BUT
OVERALL CONFIDENCE IS LIMITED IN DETAILS. EARLY MORNING WATER VAPOR
IMAGERY A BROAD UPPER TROUGH WHICH HAS DEVELOPED OVER THE MID
SECTION OF NORTH AMERICA. UPPER RIDGING IS PUSHING INTO THE WEST
COAST WHICH LEAVES A NORTHWESTERLY FLOW SPREADING INTO THE AREA WITH
THE FIRST OF SEVERAL WAVES MOVING INTO WESTERN WISCONSIN. THE NEXT
IS MOVING ACROSS THE WESTERN DAKOTAS WITH ANOTHER MORE SUBTLE WAVE
FROM NORTHERN ALBERTA INTO SASKATCHEWAN. AT THE SURFACE...THE SFC
LOW ASSOCIATED WITH THE FIRST WAVE IS MOVING EASTWARD TOWARD CENTRAL
LAKE MICHIGAN WHILE HIGH PRESSURE RIDGING EXTENDS FROM THE TENNESSEE
VALLEY INTO THE ST. LAWRENCE VALLEY.

TODAY THROUGH FRIDAY...TEMP TRENDS AND PRECIP CHANCES ARE THE MAIN
FOCUS THROUGH FRIDAY. WARM ADVECTION ASSOCIATED WITH THE APPROACHING
CLIPPER CONTINUES TO MOVE ACROSS THE AREA EARLY THIS MORNING WITH
SOME LIGHT PRECIP STILL POSSIBLE ACROSS THE FAR NORTHEASTERN CWA IN
RESPONSE. A PUSH OF MID LEVEL DRY AIR IS BEING PULLED INTO THE
TROUGH AND WILL SPREAD OVER THE AREA OVER THE NEXT FEW HOURS WITH
THE UPPER TROUGH AXIS PASSING AS WELL. COLD ADVECTION COMMENCES
BEHIND THE TROUGH WITH A SOMEWHAT DIFFUSE COLD FRONTAL BOUNDARY
CROSSING THE AREA AND TURNING WINDS WEST-NORTHWEST INTO MID
AFTERNOON WHEN IT EXITS THE AREA. BASED ON  RADAR/SATELLITE TRENDS
THE WESTERN FLANK OF SNOW CURRENTLY FALLING ACROSS THE MINNESOTA
RIVER VALLEY IN SOUTH-CENTRAL MN WILL MAY PIVOT ACROSS THE NORTHERN
CWA FROM MID TO LATE MORNING BUT LATEST NEAR TERM GUIDANCE DOES
SUGGEST THAT THIS WILL BE IN A DIMINISHED STATE. WILL CONTINUE WITH
A FEW HOURS OF SLIGHT/LOW CHANCE POPS IN THE NORTH BASED ON THIS
BUT IT LOOKS LIKE ANY PRECIP WOULD BE VERY LIGHT. SOUNDING PROFILES
WILL COOL THROUGH THE MORNING AND WOULD EXPECT THAT THEY WOULD BE
COLD ENOUGH FOR SNOW BY THE TIME THE WEAK FORCING ARRIVES THOUGH
SOME LINGERING RAIN AND EVEN SLEET IS NOT OUT OF THE QUESTION. ONCE
THE TROUGH AXIS EXITS BY EARLY AFTERNOON THERE WILL BE LITTLE
SUPPORT FOR PRECIP THROUGH THE AFTERNOON THOUGH THE EXCEPTION COULD
BE THE FAR NORTHERN CWA LATE IN THE AFTERNOON. THE DAKOTAS WAVE WILL
BEAR WATCHING AS IT WILL BE PUSHING INTO NORTHERN/CENTRAL IOWA LATE
IN THE DAY WITH THE ASSOCIATED PRECIP SHIELD ACROSS EASTERN IOWA.
THE MAIN FORCING WITH THIS TROUGH IS A BIT DISJOINTED AND THE MAIN
VORT MAX LOOKS TO PASS TO THE SOUTHWEST OF THE AREA BUT THE
ASSOCIATED PRECIP MAY AFFECT THE FAR SOUTHWESTERN CWA THIS EVENING.
HAVE UPPED POPS TO MID/HIGH CHANCE AS THIS WAVE IS CURRENTLY
WELL-ORGANIZED AND PRODUCING A PRETTY GOOD SWATH OF LIGHT SNOW
ACROSS CENTRAL NORTH DAKOTA. GUIDANCE HAS FLUCTUATED QUITE A BIT
WITH RESPECT TO FOCUS FOR PRECIP ACROSS THE REST OF THE CWA. BEYOND
THIS SHORTWAVE THINGS LOOK LESS FOCUSED FOR THE EASTERN CWA. THERE
WILL BE A TROUGH AXIS EXTENDING FROM THE NORTHEAST THAT WILL PHASE
WITH THE DAKOTAS TROUGH AND THIS MAY BE ENOUGH TO BRING SOME LIGHT
SNOW TO MAINLY THE NORTHERN CWA LATE THIS EVENING OR OVERNIGHT THEN
THE SOUTHEAST CWA FRIDAY MORNING. ACCUMULATIONS OVERALL LOOK TO BE
LIGHT...LESS THAN A HALF INCH FOR MOST AREAS UNLESS BETTER PHASING
NOTED ABOVE CAN OCCUR THEN SLIGHTLY HIGHER AMOUNTS COULD OCCUR...BUT
SOUTHWEST AREAS MAY NOW HAVE THE BEST CHANCE FOR AN INCH OR POSSIBLY
A LITTLE MORE DEPENDING ON HOW WELL THE WAVE STAYS IN TACT. OVERALL
CONFIDENCE IN DETAILS IS FAIRLY LOW GIVEN THE LACK OF WELL-ORGANIZED
FORCING THANKS TO THE NUMEROUS SUBTLE TROUGHS.

BY FRIDAY...THE PASSAGE OF ALL OF THESE WAVES WILL HAVE AMPLIFIED
THE MAIN LONGWAVE TROUGH CENTERED OVER THE GREAT LAKES. SEVERAL MORE
WEAK WAVES WILL CROSS THE AREA LEAVING THE OPPORTUNITY FOR PERIODIC
FLURRIES AND MAYBE EVEN LIGHT SNOW BUT AT THIS POINT THEY DO NOT
LOOK TO AMOUNT TO MUCH. LAKE EFFECT WILL BE GOING STRONG ON LAKE
MICHIGAN BUT THE BULK IF NOT ALL OF IT LOOKS TO REMAIN JUST EAST OF
PORTER COUNTY. EACH UPPER WAVE MAY HELP TURN THE FLOW MORE NORTHERLY
AT TIMES SO WILL NEED TO KEEP A CAREFUL WATCH FOR THIS TO OCCUR AS
IT COULD RESULT IN A SINGLE BAND OF SNOW MIGRATING TOWARD EASTERN
PORTER COUNTY BUT CONFIDENCE IS LOW IN THIS OCCURRING. WILL KEEP
CHANCE POPS MENTIONED FOR NOW WITH SOME SNOW SHOWERS POSSIBLY
AFFECTING EASTERN PORTER BUT THE HEAVIEST ACTIVITY LOOKS TO BE TO
THE EAST. IN TERMS OF TEMPS...HIGHS MAY OCCUR THIS MORNING BEFORE
TEMPS LEVEL AND PROBABLY COOL A FEW DEGREES THROUGH THE
AFTERNOON...ESPECIALLY NORTH...THANKS TO INCOMING COLD ADVECTION.
WITH THE DRY SLOT COMING OVER...THERE MAY BE ENOUGH SUNSHINE TO
OFFSET THE COOLING FOR SOUTHERN AND MAYBE EVEN CENTRAL AREAS. WINDS
WILL BE GUSTY FROM THE WEST THEN TURN MORE NORTHWESTERLY LATER IN
THE DAY. ANOTHER PUSH OF COLD ADVECTION WILL WORK IN FRIDAY PUSHING
H85 TEMPS BACK TO AROUND -15C DURING THE DAY. EXPECT HIGHS IN THE
MID 20S NORTH TO AROUND FREEZING SOUTH WITH BREEZY NORTHWEST WINDS.

SATURDAY AND SUNDAY...THE BIG LONGWAVE TROUGH AND THE WESTERN UPPER RIDGE
WILL TRANSLATE EASTWARD SATURDAY. THE CORE OF THE COLDEST AIR WILL
BE RIGHT OVER THE AREA SATURDAY WITH A NORTHWEST BREEZE CONTINUING
BUT LIKELY DIMINISHING SOME THROUGH THE AFTERNOON AS A SURFACE RIDGE
ARRIVES FROM THE WEST. ADDITIONAL WAVES LOOK TO CROSS THE AREA SO
FLURRIES OR SLIGHT POPS MAY NEED TO BE ADDED. WILL NEED TO CONTINUE
TO KEEP AN EYE ON LAKE EFFECT POTENTIAL ACROSS PORTER COUNTY ONCE
AGAIN. THE SURFACE RIDGE WILL SHIFT EAST SATURDAY NIGHT WHILE THE
UPPER RIDGE PUSHES WARM ADVECTION INTO THE AREA FROM THE WEST. RIGHT
NOW AM ONLY EXPECTING AN INCREASE IN CLOUD COVER WITH THE WARM PUSH
SUNDAY. THE UPPER RIDGE WILL BE SHUNTED EASTWARD AS AN UPPER TROUGH
DIGS INTO THE NORTHERN HIGH PLAINS LATER SUNDAY. THIS WILL SHARPEN
THE PUSH OF MILDER AIR FROM THE SOUTHWEST AS THE UPPER FLOW
RE-ORIENTS INTO MONDAY. HIGHS SATURDAY WILL RANGE FROM AROUND 20
NORTH TO THE MID 20S SOUTH BUT REBOUND SUNDAY WITH READINGS IN THE
LOW 30S NORTHEAST TO MID/UPPER 30S SOUTHWEST.

MONDAY AND BEYOND...THE DETAILS OF THIS PERIOD REMAIN MURKY AS
GUIDANCE TRIES TO HANDLE THE INCOMING NORTHERN PLAINS TROUGH.
HOWEVER...THERE CONTINUES TO BE GENERAL AGREEMENT IN THE TROUGH
SPAWNING SFC LOW PRESSURE ACROSS NORTH DAKOTA/NORTHERN MINNESOTA.
THE BIGGER ISSUE HAS BEEN THE HANDLING OF THE DEVELOPMENT LOW
PRESSURE DEVELOPMENT CLOSER TO THE BASE OF THE TROUGH ACROSS THE
SOUTHERN PLAINS INTO THE MID MISSISSIPPI RIVER VALLEY MONDAY. THE
LATEST 00Z GUIDANCE IS IN GOOD AGREEMENT WITH AN ELONGATED SFC LOW
DEVELOPING AND MOVING ACROSS THE LOWER OHIO VALLEY AND MERGING WITH
THE MINNESOTA LOW OVER LAKE HURON TUESDAY MORNING. THIS CONTINUES TO
SUPPORT DECENT POPS ACROSS THE AREA LATER MONDAY/MONDAY
NIGHT...THOUGH THERE HAVE BEEN A FEW RUNS THAT KEPT PRECIP AWAY FROM
THE AREA. STILL EXPECT TO SEE VARIATIONS WITH THE HANDLING OF THE
UPPER TROUGH BEING THE KEY DRIVING FACTOR BUT WILL CONTINUE WITH
DECENT POPS...MAINLY OVER THE SOUTHEAST HALF OF THE AREA BUT IT
WOULD NOT TAKE MUCH OF A SHIFT TO AFFECT THIS DRAMATICALLY. THIS
TROUGH WOULD BRING A SUBSEQUENT COOL DOWN TUESDAY AND WEDNESDAY.
WEAK UPPER RIDGING THEN COMES ACROSS AS ANOTHER BIG TROUGH DIGS INTO
THE WEST...KEEPING THE POTENTIAL FOR ANOTHER LOW TO AFFECT THE AREA
LATE IN THE WEEK.

MDB

&&

AVIATION...

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

* STRONG/GUSTY WESTERLY WINDS THROUGH EARLY EVENING.
* MVFR CIGS THROUGH LATE AFTERNOON.
* CHANCE OF LIGHT SNOW OVERNIGHT INTO FRIDAY MORNING.

PAW

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

A LOW PRESSURE CENTER OVER CENTRAL LAKE MICHIGAN WILL CONTINUE
MOVING TO THE EAST. SUSTAINED WINDS AND GUSTS WILL DIMINISH FROM
LATE AFTERNOON THROUGH THE EVENING AS IT MOVES AWAY. MVFR CIGS
ASSOCIATED WITH THIS LOW WILL IMPROVE TO VFR LEVELS ALSO FROM LATE
AFTERNOON THROUGH THE EVENING. THEN AN UPPER LEVEL WAVE MOVING
SOUTHEAST FROM THE DAKOTAS WILL MOVE ACROSS IL OVERNIGHT. AT THIS
TIME IT APPEARS THAT PRECIPITATION ASSOCIATED WITH THIS WAVE WILL
REMAIN MOSTLY WEST AND SOUTHWEST OF ALL THE TERMINALS...THOUGH
HAVE RETAINED THE PROB30 FOR LIGHT SNOW IN THE TAFS UNTIL THE
EXACT TRACK OF THE PRECIPITATION BECOMES MORE CLEAR.

PAW


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

* HIGH CONFIDENCE IN WIND TREND.
* MEDIUM CONFIDENCE IN MVFR CIGS TIMING.
* LOW CONFIDENCE IN SNOW POTENTIAL OVERNIGHT/FRIDAY MORNING.

PAW

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

* FRIDAY NIGHT AND SATURDAY...MVFR POSSIBLE.
* SUNDAY...DRY/VFR.
* MONDAY...CHANCE OF RAIN/SNOW. MVFR POSSIBLE.
* TUESDAY...GUSTY WEST WINDS. DRY/VFR.
* WEDNESDAY...DRY/VFR.

&&

MARINE...

309 AM...LOW PRESSURE OVER WESTERN WI EARLY THIS MORNING WILL MOVE
EAST ACROSS CENTRAL LAKE MICHIGAN LATE THIS MORNING. SOUTHERLY
WINDS OVER THE SOUTHERN HALF OF THE LAKE WILL TURN SOUTHWESTERLY
THEN SHIFT WESTERLY BEHIND A TRAILING COLD FRONT LATE THIS
MORNING. SPEEDS WILL BE INCREASING AS THE LOW APPROACHES WITH
30KTS EXPECTED FROM MID MORNING INTO THIS EVENING. OVER THE NORTH
END OF THE LAKE...SOUTHERLY WINDS WILL BECOME LIGHT AND VARIABLE
AND THEN SHIFT NORTHEAST LATER THIS MORNING AND BECOME NORTH WHILE
RAPIDLY INCREASING TO 30KTS DURING THE EARLY TO MID AFTERNOON. THE
STRONGEST GRADIENT WILL MOVE ACROSS THE NORTHERN HALF OF THE LAKE
JUST BEHIND THE LOW LATER THIS AFTERNOON AND EARLY THIS EVENING.
THUS THERE COULD BE A PERIOD OF LOW END GALES. CONFIDENCE REMAINS
LOW REGARDING HOW PREVAILING THEY MAY BECOME SO FOR NOW...PLAN TO
MAINTAIN CURRENT GALE GUST WORDING BUT THIS WILL NEED TO BE
MONITORED THIS MORNING. HIGH PRESSURE WILL BUILD ACROSS THE PLAINS
FRIDAY AS THE LOW MOVES NORTHEAST OVER QUEBEC. THIS WILL MAINTAIN
A NORTHWEST GRADIENT ACROSS THE WESTERN LAKES WHICH WILL SLOWLY
BEGIN TO DIMINISH SATURDAY INTO SATURDAY EVENING AS THE RIDGE
CONTINUES EAST. LOW PRESSURE IS EXPECTED TO MOVE ACROSS THE
NORTHERN PLAINS SUNDAY NIGHT AND ACROSS THE UPPER LAKES MONDAY.
THIS WILL TURN WINDS SOUTHERLY SUNDAY AND DEPENDING ON HOW STRONG
THE LOW BECOMES...COULD BE UP TO 30KTS. A TRAILING COLD FRONT WILL
MOVE ACROSS THE LAKE MONDAY NIGHT WITH NORTHWEST WINDS TO 30 KTS
TUESDAY AND PERHAPS AS HIGH AS LOW END GALES. CMS

&&

LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 10 PM THURSDAY.

&&

$$