National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS63 KLOT 102211
AFDLOT

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

.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 22Z...

* FOG POTENTIAL WITH MVFR CONDITIONS REMAINS POSSIBLE LATE TONIGHT
  INTO TUESDAY.

* SLIGHT POSSIBILITY FOR MVFR CEILINGS EARLY TUESDAY MORNING.

RODRIGUEZ/IZZI

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

HIGH LEVEL CLOUD COVER IS CURRENTLY OVERHEAD AS SOUTHWEST WINDS
PERSIST EARLY THIS AFTERNOON. THESE GENERAL CONDITIONS ARE
EXPECTED THROUGH THIS AFTERNOON AS A FRONT APPROACHES FROM THE
NORTHWEST. EXPECT THIS FRONT TO PUSH THROUGH THE TERMINALS EARLY
THIS EVENING WITH WINDS TURNING TO THE WEST/NORTHWEST...WHILE ONLY
MID/HIGH LEVEL CLOUD COVER CONTINUE TO STREAM OVERHEAD. SURFACE
PATTERN RELAXES WHILE THE FRONT PUSHES ACROSS THE TERMINALS AND
ANTICIPATE WINDS TO BE ON THE LIGHTER SIDE...BEFORE TURNING TO THE
NORTHEAST AND REMAINING THIS DIRECTION THROUGH THE REMAINDER OF
THE FORECAST PERIOD. WITH SOME INCREASE IN MOISTURE TODAY AS WELL
AS LIGHTER WINDS AND COOLER CONDITIONS MOVING BACK OVERHEAD...FOG
DEVELOPMENT IS POSSIBLE WITH A SLIGHT POSSIBILITY FOR LOW CLOUDS
DEVELOPING TONIGHT. HAVE CONTINUED MENTION OF BOTH POSSIBILITIES
IN THE TAFS...WITH CONFIDENCE HIGHER WITH REGARDS TO FOG
POTENTIAL. HAVE LEFT OUT ANY PRECIP MENTION FOR ORD AT THE END OF
THE FORECAST PERIOD AT THIS TIME...BUT WITH CHANCES FOR RAIN/SNOW
AND THEN ALL SNOW RAPIDLY INCREASING DURING THAT TIME.

RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* HIGH CONFIDENCE WITH FOG DEVELOPMENT TONIGHT...MEDIUM CONFIDENCE
  WITH MVFR CONDITIONS.

* LOW CONFIDENCE WITH MVFR CEILING POTENTIAL.

* HIGH CONFIDENCE IN ALL OTHER ELEMENTS

RODRIGUEZ/IZZI

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

TUESDAY NIGHT...RAIN/SNOW CHANGING TO ALL SNOW DURING THE EVE AND
                PERSISTING OVERNIGHT.
WEDNESDAY...SLGT CHC OF SNOW. MVFR LIKELY IN THE MORNING. GUSTY
            WINDS NEAR DUE NORTH IN DIRECTION.
THURSDAY-FRIDAY...VFR LIKELY.
SATURDAY...SLGT CHC OF SNOW DURING THE NIGHT.
SUNDAY...SLGT CHC OF RAIN/SNOW.

MTF/RODRIGUEZ

&&

.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.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO