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000
FXUS63 KLOT 110249
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
949 PM CDT MON MAR 10 2014

.DISCUSSION...
948 PM CDT

WATER VAPOR IMAGERY THIS EVENING SHOWS OUR NEXT WEATHER SYSTEM OF
INTEREST NOW MOVING ACROSS NEVADA. THIS SYSTEM IS EVEN PRODUCING
LIGHTNING STRIKES ACROSS PORTIONS OF SOUTHERN IDAHO AT THIS TIME.
THE NEW 00 UTC NAM IS CURRENTLY ROLLING IN AND IS VERY CONCERNING
FOR MOST OF NORTHERN ILLINOIS TUESDAY NIGHT. IT TRACKS THE LOWER
LEVEL CIRCULATION FARTHER NORTH ACROSS NORTHEASTERN MISSOURI AND
CENTRAL ILLINOIS TUESDAY NIGHT. THIS WOULD RESULT IN A MUCH MORE
FAVORABLE TRACK FOR HEAVY SNOW INTO NORTHERN ILLINOIS...INCLUDING
THE CHICAGO METRO AND RFD AREAS. ALSO GIVEN THE GLOBAL MODELS HAVE
SLOWLY BEEN INCHING NORTHWARD WITH THIS SYSTEM...I CANNOT DISCOUNT
THE NAM SOLUTION. THIS SYSTEM SHOULD HAVE A LOT GOING FOR
IT...WITH ALL MODELS EVEN INDICATING SOME UPPER LEVEL JET COUPLING
ACROSS THE REGION IN CONJUNCTION WITH GOOD FGEN SETTING UP IN
CONJUNCTION WITH THE LOWER/MID LEVEL CIRCULATION.
THEREFORE...HEAVY SNOW...MAYBE EVEN WITH CONVECTION...IS POSSIBLE
TUESDAY NIGHT AS THE MAIN FORCING SETS UP ACROSS THE AREA.

IN SPITE OF ALL THIS...HOWEVER...RATHER THAN SHIFTING THE WATCH
NORTHWARD TO INCLUDE NORTHERN ILLINOIS...I WOULD LIKE TO SEE THE NEW
00 UTC GLOBAL GUIDANCE BEFORE MAKING ANY MAJOR CHANGES TO THE GOING
HEADLINES...TO ENSURE THAT A FARTHER NORTH SOLUTION IS THE WAY TO
GO. AS IT STANDS...THE NAM IS THE FARTHER NORTH WITH THIS SYSTEM.
NOW THAT THE MAIN MID/UPPER LEVEL SYSTEM IS ONSHORE ACROSS THE
WESTERN CONUS...THE 00UTC RAOBS SHOULD BE SAMPLING IT NOW...SO THE
NEW GLOBAL GUIDANCE THIS EVENING SHOULD BEGIN TO GET A BETTER HANDLE
ON THE SYSTEM.

KJB

&&

.PREV DISCUSSION...
322 PM CDT

WHILE A WINTRY PRECIP EVENT LOOMS IN THE SHORT TERM...THE AREA WILL
BE ON A BIT OF A TEMPERATURE ROLLER COASTER RIDE INTO EARLY NEXT
WEEK.

SYNOPSIS...AFTERNOON WATER VAPOR IMAGERY SHOWS A FAIRLY ZONAL FLOW
PATTERN ACROSS MUCH OF NORTH AMERICA THOUGH IT IS DISRUPTED BY A LOW
AMPLITUDE TROUGH MOVING EAST ACROSS WESTERN AND CENTRAL ONTARIO. ONE
OF THE THE MAIN FEATURES OF CONCERN HOWEVER IS A TROUGH MOVING INTO
THE PACIFIC NORTHWEST. THIS WILL BRING PRECIP TO THE AREA TOMORROW
AND TOMORROW NIGHT. TO THE WEST...A RIDGE AXIS TRAILS THIS TROUGH OFF
THE WEST COAST WITH A CLOSED UPPER LOW SPINNING EASTWARD SOUTH OF
THE ALEUTIANS. ANOTHER TROUGH REMAINS CUTOFF OVER NORTHERN MEXICO
AND SOUTHERN TEXAS. AT THE SURFACE...LOW PRESSURE ASSOCIATED WITH THE
ONTARIO TROUGH IS MOVING ACROSS WESTERN ONTARIO WITH A COLD FRONT
TRAILING IT ACROSS THE NORTHERN PLAINS. HIGH PRESSURE IS STRETCHED
ACROSS THE GULF COAST STATES.

TONIGHT THROUGH THURSDAY...THE SURFACE LOW OVER WESTERN ONTARIO
WILL CONSOLIDATE SOMEWHAT AND TRACK TO SOUTHERN QUEBEC TONIGHT. THIS
WILL DRAG THE ATTENDANT COLD FRONT ACROSS THE AREA OVERNIGHT
BRINGING A SHIFT TO NORTHERLY WINDS. GIVEN THE FLAT UPPER FLOW THIS
FIRST PUSH OF COLD AIR WILL NOT BE TERRIBLY STRONG. AS A RESULT MOST
AREAS WILL REMAIN ABOVE FREEZING IN THE MID 30S OVERNIGHT. TUESDAY
BECOMES MORE CHALLENGING AS THE WESTERN UPPER TROUGH PROGRESSES
EASTWARD. A NORTHERN JET STREAM IS FORECAST TO DEVELOP OVER THE TOP
OF THE UPPER RIDGE EXTENDING UP THE NORTH AMERICAN WEST COAST THEN
DIVE SOUTHEAST ACROSS WESTERN CANADA. MEANWHILE...A SOUTHERN JET
ROUNDING THE BASE OF THE WESTERN TROUGH WILL CONTINUE EASTWARD INTO
THE CENTRAL AND SOUTHERN ROCKIES. THE NORTHERN JET WILL BECOME
DOMINANT WITH A TROUGH AXIS DROPPING SOUTHEAST ACROSS CENTRAL CANADA
TUESDAY WHICH WILL HAVE SOME DEGREE OF PHASING WITH THE EASTWARD
MOVING WAVE ACROSS THE ROCKIES. THE TROUGH WILL DEEPEN AS IT CROSSES
THE MID AND UPPER MISSISSIPPI RIVER VALLEY AND THEN THE LOCAL AREA
WEDNESDAY. SURFACE LOW PRESSURE WILL BEGIN TO STRENGTHEN ACROSS THE
CENTRAL HIGH PLAINS INTO TUESDAY AS THE WESTERN TROUGH APPROACHES.
THE MID LEVEL THERMAL GRADIENT WILL BEGIN TO TIGHTEN FROM NORTHERN
NEBRASKA ACROSS NORTHERN IOWA AND SOUTHERN WISCONSIN AS THE UPPER
TROUGH BEGINS TO DEEPEN WHICH WILL LEAD TO A BAND OF PRECIPITATION
WHICH WILL TRACK SOUTHWARD WITH TIME THROUGH THE DAY. THE SURFACE
LOW WILL THEN STRENGTHEN ACROSS THE LOWER OHIO VALLEY AND TRACK
NORTHEAST TUESDAY NIGHT...WHICH WILL LEAD TO A NORTHEASTWARD
EXPANSION OF PRECIP ACROSS THE REMAINING FORECAST AREA DURING THE
EVENING.

SEVERAL CHALLENGES SURROUND THIS EVENT...THE FIRST OF WHICH ARE
PRECIP TIMING AND TEMPERATURE TRENDS. DESPITE THE PASSAGE OF THE
COLD FRONT TONIGHT HIGHS TUESDAY LOOK TO BE MILD WITH A RANGE FROM
AROUND 40 NORTH TO THE MID 50S FAR SOUTH. THE INITIAL AREA OF WARM
ADVECTION PRECIP WILL BE TO THE NORTH OF THE AREA THROUGH MUCH OF THE
DAY BUT THEN DEVELOP OR MOVE INTO THE NORTHERN CWA LATE IN THE
AFTERNOON. FORECAST SOUNDINGS SHOW ENOUGH DRY AIR TO ALLOW FOR
EVAPORATIVE COOLING TO THE POINT WHERE RAIN WOULD TRANSITION MIXED
PRECIP THEN QUICKLY TO SNOW. THE STRONGEST FORCING ARRIVES DURING
THE EVENING...ESPECIALLY DURING THE MID AND LATE EVENING AS THE
UPPER TROUGH DEEPENS. GIVEN THE MID LEVEL TEMP GRADIENT AND THE
EVOLUTION OF THE SYSTEM STRONG FRONTOGENETIC FORCING IS EXPECTED
DURING THE MID EVENING INTO THE OVERNIGHT HOURS. THE STRONG FORCING
AND STRENGTHENING OF THE SYSTEM WILL ALLOW FOR THE COLUMN TO COOL TO
PROVIDE A FAIRLY QUICK CHANGE OVER TO SNOW FROM NORTH TO SOUTH
THROUGH THE EVENING. FORECAST CROSS SECTIONS ALSO SHOW THE IDEA OF
AT LEAST LOWERED...IF NOT NEGATIVE STABILITY ABOVE THE ORGANIZED
FGEN ASCENT LEAVING THE POTENTIAL FOR CONVECTIVE BANDING. THE BEST
FORCING DOES MOVE THROUGH QUICKLY WHICH WILL LIMIT HOW MUCH OF THE
0.8 INCH PRECIPITABLE WATER VALUES THAT WILL BE REALIZED BUT THE
SIGNALS FOR BANDING/INTENSE PRECIP ARE CONCERNING. THE LOW TRACK
VARIES AMONG GUIDANCE AND GIVEN THAT THE UPPER FLOW PATTERN WILL BE
EVOLVING/PHASING BETWEEN NOW AND TOMORROW EXPECT TO SEE GUIDANCE
FLUCTUATE FURTHER. THIS WILL ULTIMATELY HELP DICTATE HOW FAR NORTH
MORE SIGNIFICANT PRECIP AMOUNTS WILL OCCUR WITH THE LATEST TRENDS
SHOW A MORE NORTHERLY TRACK PUTTING MORE OF THE AREA AT RISK. IN
TERMS OF AMOUNTS...WITH THINGS TRENDING FURTHER NORTH HAVE INCREASED
SNOW AMOUNTS ACROSS THE AREA. GIVEN ALL OF THE ABOVE THESE MAY
CHANGE FURTHER...WITH TOTAL AMOUNTS HINGING ON HOW QUICKLY A
TRANSITION TO SNOW OCCURS...ESPECIALLY FOR FAR SOUTHERN AREAS. WITH
THE STRENGTH OF FORCING INTENSE SNOWFALL RATES ARE LIKELY WHERE
BANDS FOCUS AND TURN TO SNOW. RIGHT NOW AREAS ALONG AND SOUTH OF
INTERSTATE 80 ARE FAVORED FOR THE GREATEST AMOUNTS. FAR SOUTHERN
AREAS SOUTH OF A PONTIAC TO RENSSELAER LINE WILL BE TRICKY AS THEY
WILL TAKE LONGEST TO CHANGE OVER AND MAY SEE REDUCED AMOUNTS AS A
RESULT.

HEADLINE REASONING...MANY AREAS MAY ULTIMATELY SEE AN ADVISORY LEVEL
EVENT BUT THERE IS SOME POTENTIAL FOR WARNING CRITERIA SNOWS WHICH
COULD FALL IN A SHORT AMOUNT OF TIME. THEREFORE DO NOT FEEL GOING
RIGHT TO AN ADVISORY IS THE BEST OPTION AT THIS POINT. AFTER
COORDINATION WITH NEIGHBORING OFFICES WILL HOIST A WINTER STORM
WATCH FOR THE SOUTHEAST THIRD OR SO OF THE AREA OR FROM PORTER
SOUTHWEST TO LAKE...KANKAKEE...AND LIVINGSTON COUNTIES AND POINTS
SOUTH. DEBATED INCLUDING AREAS A LITTLE FURTHER NORTH FROM THE
SOUTHERN CHICAGO METRO BACK TO OTTAWA/MENDOTA BUT DO NOT HAVE ENOUGH
CONFIDENCE IN ENOUGH OF A NORTHWARD SHIFT WITH UPCOMING RUNS TO DO
THIS AT THIS POINT. OVERALL ITS A MINIMAL CONFIDENCE WATCH.

THE SYSTEM DEPARTS WEDNESDAY WITH SNOW ENDING BUT STRONG NORTHERLY
WINDS WILL LIKELY CAUSE BLOWING SNOW...WITH 30 KT GUSTS POSSIBLE. IT
WILL BE MUCH COLDER WITH HIGHS IN THE 20S. WARMING WILL OCCUR
THURSDAY AS UPPER RIDGING SPREADS WARMER AIR INTO THE
REGION...WITH HIGHS ABOVE FREEZING LOOKING LIKELY.

MDB

THURSDAY NIGHT AND BEYOND...

START TO THE EXTENDED PERIOD WILL BE QUITE DECEIVING AS THE WARMING
WHICH WILL BE ONGOING DURING THAT TIME WILL NOT BE REPRESENTATIVE OF
THE REST OF THE PERIOD...WITH BELOW NORMAL CONDITIONS EXPECTED TO BE
IN PLACE ONCE AGAIN.

DEPARTING LONGWAVE TROUGH WILL MAKE WAY FOR BRIEF UPPER LEVEL
RIDGING ACROSS THE AREA THURSDAY NIGHT INTO FRIDAY. BACKING
WINDS/WAA WILL SPREAD WARMER TEMPS ALOFT OVER THE REGION AS
SOUTHERLY WINDS...OUT AHEAD OF MID/UPPER LEVEL TROUGH AND ATTENDANT
SURFACE LOW...USHER IN SLIGHTLY ABOVE NORMAL TEMPS ON FRIDAY.
ALTHOUGH ANTICIPATE THIS TO BE RATHER BRIEF AS THE AFOREMENTIONED
MID/UPPER LEVEL TROUGH AND SURFACE LOW DROP EAST/SOUTHEAST AND SWING
A COLD FRONT THROUGH THE AREA LATE IN THE DAY FRIDAY. THERE ARE SOME
SUBTLE DIFFERENCES WITH THE INITIAL EXTENT OF THIS COLDER AIR...BUT
OVERALL A COLDER TREND WILL CONTINUE THROUGH THE WEEKEND INTO EARLY
NEXT WEEK WITH BELOW NORMAL TEMPS ONCE AGAIN BACK IN PLACE.

PRECIP CHANCES TO START THE PERIOD ARE MARGINAL WITH ANY DEVELOPMENT
LIKELY TO REMAIN MINOR. WITH THE EXCEPTION OF THE COLDER AIR...MODEL
VARIABILITY SHOWS ITSELF BY EARLY NEXT WEEK WITH CONFIDENCE AT
PRECIP CHANCES DURING THIS PERIOD LOW. NONETHELESS...IT DOES APPEAR
AS IF THERE WILL BE SOME POTENTIAL FOR PRECIP SUNDAY AND SUNDAY
NIGHT...OF WHICH WOULD LIKELY BE SNOW.

RODRIGUEZ

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* WINDS BECOMING NE AROUND 10KT TUESDAY
* RAIN/SNOW DEVELOPS TUESDAY EVENING...CHANGING TO WET SNOW
* CIGS/VSBY TRENDING DOWN TO MVFR AND POSSIBLY IFR TUESDAY EVENING

IZZI

//DISCUSSION...UPDATED 00Z...

SURFACE TROUGH/WEAK COLD FRONT WILL SAG SOUTHWARD ACROSS THE
REGION TONIGHT WITH WEAK PRESSURE GRADIENT IN VICINITY OF THIS
TROUGH ALLOWING WINDS TO GO LIGHT/VARIABLE. ADDED BOUNDARY LAYER
MOISTURE FROM SNOW MELT AND THE LIGHT WINDS COULD ALLOW FOR SOME
LIGHT GROUND FOG TO DEVELOP TONIGHT...PARTICULARLY AT THE RURAL
AIRPORTS. EXTENSIVE HIGH CLOUDINESS AND LATE ARRIVAL OF BETTER
PUSH OF COLDER AIR COULD LESSEN THE THREAT OF FOG DEVELOPMENT
TONIGHT AND GIVEN MODERATELY LARGE TEMP/DEWPOINT SPREADS NOW HAVE
OPTED TO BACK OFF ON LIGHT FOG MENTION IN THE TAFS. IN
ADDITION...MODELS CONTINUE TO STRUGGLE WITH BOUNDARY LAYER TEMPS
AND SUBSEQUENT RH THANKS TO THEIR POOR HANDLING OF THE TEMPS OVER
MELTING SNOW COVER.

DEVELOPING LOW PRESSURE TO THE SOUTHWEST OF THE AREA TUESDAY
AFTERNOON WILL RESULT IN INCREASING NORTHEAST WINDS TUESDAY
AFTERNOON AND ESPECIALLY TUESDAY EVENING. AS LOW PRESSURE REALLY
BEGINS TO STRENGTHEN TUES EVENING LOOK FOR NORTHEAST WINDS TO
BECOME QUITE GUSTY...POSSIBLY IN EXCESS OF 25KT TUESDAY NIGHT.
PRECIPITATION IS LIKELY TO DEVELOP TUES EVENING AT ORD...PROBABLY
STARTING OUT AS RAIN BEFORE COLUMN COOLS ENOUGH FOR A FLIP OVER TO
WET SNOW. CONDITIONS COULD BE CONSIDERABLY LOWER THAN TAFS ARE
ADVERTISING...BUT GIVEN SOME UNCERTAINTIES IN PRECIP TYPE AND
TIMING HAVE OPTED TO ERR ON THE LIGHTER SIDE FOR NOW AND WILL
ALLOW LATER SHIFTS TO HIT PRECIP HARDER.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* HIGH CONFIDENCE ON VSBY REMAINING VFR THROUGH TONIGHT...MEDIUM
  CONFIDENCE IN VFR VSBY TUESDAY
* MEDIUM-HIGH CONFIDENCE IN WIND FORECAST THROUGH PERIOD
* LOW-MEDIUM CONFIDENCE IN PRECIP TYPE/INTENSITY TUESDAY EVENING
* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS

IZZI

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

WEDNESDAY...MVFR CIGS.

THURSDAY THROUGH SATURDAY...VFR PROBABLE.

SUNDAY...SLIGHT CHANCE OF -SN.

IZZI

&&

.MARINE...
230 PM CDT

FOLLOWING THE PASSAGE OF A WEAK COLD FRONT...A SHORT PERIOD OF
RELATIVE CALM IS EXPECTED FOR LAKE MICHIGAN FOLLOWED BY A PERIOD
OF ACTIVE PERIOD IS SETTING UP FOR LAKE MICHIGAN FOR THE FOLLOWING
FEW DAYS.

RELATIVELY LIGHT WEST WINDS WILL BECOME MORE LIGHT AND VARIABLE AS
HIGH PRESSURE BUILDS ACROSS THE LAKE. A DEEPENING LOW PRESSURE
SYSTEM IS EXPECTED TO TRACK FROM THE SOUTHERN PLAINS BY TUESDAY
MORNING THROUGH THE OHIO VALLEY ON WEDNESDAY. IN THE MEAN TIME
POLAR HIGH PRESSURE WILL BUILD INTO THE UPPER GREAT LAKES. THE
DEEPENING LOW PASSING SOUTH OF THE LAKE AND POLAR HIGH PRESSURE TO
THE NORTH WILL LEAD TO A PERIOD OF STRONG COLD ADVECTION AND A
STRENGTHENING PRESSURE GRADIENT. ANTICIPATE THAT NORTH WINDS
SHOULD INCREASE TO GALE FORCE OVER THE SOUTH HALF OF THE LAKE AND
THE NEARSHORE WATERS BY LATE WEDNESDAY EVENING...IN PARTICULAR
RESPONSE TO THE APPROACHING DEEPENING LOW AND STRENGTHENING
PRESSURE GRADIENT. AS THE COLD ADVECTION SETS UP...WINDS WILL
STRENGTHEN TO GALE FORCE OVER THE NORTHERN PORTIONS OF THE LAKE AS
WELL. AS THE HIGH SAGS OVER THE NORTHERN PORTION OF THE LAKE LATE
WEDNESDAY EVENING...WINDS WILL DROP BELOW GALE FORCE. ANOTHER HIGH
WILL SPREAD ACROSS THE GREAT LAKES REGION LATE WEDNESDAY NIGHT AND
EARLY THURSDAY...BRINGING A LULL TO THE WINDS. A CLIPPER TYPE
SYSTEM IS THEN EXPECTED TO DROP OUT OF NORTHERN ALBERTA AND TRACK
ACROSS THE UPPER GREAT LAKES ON FRIDAY. THIS WILL BRING A PERIOD
OF STRENGTHENING SOUTH TO SOUTHWEST WINDS. WHILE THE SOUTH TO
SOUTHWEST WINDS WILL BE BRISK...DO NOT EXPECT MORE GALES AT THIS
TIME. SO...EVEN THOUGH THE LAKE REMAINS MOSTLY ICE-COVERED...THE
WARMING SETTING UP BEFORE THE GALES AND THE PERIODS OF STRONG
WINDS WILL ALLOW THE ICE TO BECOME MORE BROKEN UP AND WILL LIKELY
SHIFT AROUND THE LAKE. LATEST VIS SATELLITE IMAGERY AND COASTAL
WEBCAMS SHOW OPEN WATER IN THE ILLINOIS NEARSHORE WATERS NORTH OF
NORTHERLY ISLAND...SO WILL REINTRODUCE WAVES TO THAT PORTION OF
THE NEARSHORE WATERS.

KREIN

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...WINTER STORM WATCH...ILZ023-ILZ032-ILZ033-ILZ039...10 PM TUESDAY
     TO 1 PM WEDNESDAY.

IN...WINTER STORM WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...10 PM
     TUESDAY TO 1 PM WEDNESDAY.

LM...GALE WARNING...LMZ080-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-
     LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ870-LMZ872-
     LMZ874-LMZ876-LMZ878...MIDNIGHT WEDNESDAY TO 9 PM WEDNESDAY.

     GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
     LMZ868...3 AM WEDNESDAY TO 4 PM WEDNESDAY.

&&

$$

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