Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 262201
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
501 PM CDT THU MAR 26 2015

.SHORT TERM...
226 PM CDT

THROUGH FRIDAY...

MAIN CONCERN IN THE SHORT TERM IS LAKE EFFECT PRECIP THIS EVENING
INTO FRIDAY. AN UPPER LEVEL TROUGH CURRENTLY OVER THE CENTRAL CONUS
SHIFTS EAST WITH ITS AXIS MOVING THROUGH THE REGION FRIDAY MORNING.
AT THE SURFACE AN ELONGATED REGION OF LOW PRESSURE IS OVER THE
APPALACHIANS AND IT MOVES OVER THE ATLANTIC OCEAN FRIDAY AFTERNOON.
HIGH PRESSURE IS OVER MANITOBA AND IT MOVES OVER THE REGION FRIDAY
EVENING.

AS THE HIGH MOVES CLOSER...WINDS BECOME NORTH DOWN THE LAKE
RESULTING IN FAVORABLE CONDITIONS FOR LAKE EFFECT PRECIP.  GUIDANCE
SLOWS THE VEERING OF THE WINDS SO PUSHED BACK THE ARRIVAL OF LAKE
EFFECT PRECIP.  THERE IS LESS SHEAR IN THE FORECAST SOUNDINGS WHICH
SUGGESTS IT SHOULD BE EASIER TO CREATE A SINGLE BAND OF LAKE EFFECT
PRECIP.  HAVE HIGH CONFIDENCE IN THE AREAS ALONG THE LAKE SEEING
SOME SNOW...BUT MEDIUM CONFIDENCE IN THE TIMING AND LOCATION OF THE
BAND. ALSO HAVE MEDIUM CONFIDENCE IN SNOW TOTALS AND WENT MIDDLE OF
THE ROAD FOR SNOW AMOUNTS AT THIS TIME.

FOR THE IL SHORE...EXPECTING LAKE EFFECT PRECIP TO PUSH ON SHORE
AROUND OR AFTER 10PM WITH THE BEST CHANCE FOR PRECIP AFTER MIDNIGHT.
 THINKING THE MAJORITY OF PRECIP WILL FALL AFTER 3AM WITH THE AREA
OF SNOW SLOWLY SHIFTING EAST.  WINDS SHOULD TURN NORTH ENOUGH TO
PUSH THE SNOW OVER NW INDIANA ARND 10AM.  THE INITIAL PRECIP MAY
FALL AS A RAIN/SNOW MIX AS WE WILL BE AROUND FREEZING AT THE SFC AND
LACKING SATURATION IN THE DGZ...BUT WE SHOULD MOISTEN UP NICELY
LEADING TO A QUICK TRANSITION OVER TO SNOW.  NOT EXPECTING ANY
SIGNIFICANT OR IMPRESSIVE SNOW TOTALS...BUT THINKING UP TO A HALF OF
AN INCH OF NEW SNOW WILL FALL.  LATEST MODEL RUNS ARE HINTING AT
ENHANCED PARAMETERS FOR LAKE EFFECT SNOW ALONG THE IL SHORE BUT DO
NOT WANT TO JUMP ON THAT BANDWAGON JUST YET SO BUMPED SNOW TOTALS UP
A BIT TO TREND IN THE DIRECTION OF THE LATEST GUIDANCE.

FOR THE IN SHORE...ALSO EXPECTING THE BAND TO REACH LAND AROUND 10
PM AND INTENSITY TO PICK UP AFTER MIDNIGHT.  SOME MODELS FEATURE A
RIBBON OF CONVERGENCE THAT COULD LEAD TO A BAND OF MODERATE
SNOWFALL...BUT ONCE AGAIN STILL A BIT TOO SOON TO GET TOO SPECIFIC.
SNOW WILL SLOWLY SHIFT EAST OVER NW INDIANA THROUGH FRIDAY MORNING.
SOUNDINGS FEATURE QUITE A BIT OF FORCING...BUT SLIGHTLY BELOW THE
DGZ...SO WENT A BIT CONSERVATIVE WITH SNOW AMOUNTS.  THINKING THE
LONGER FETCH AND TIME UNDER THE BAND WILL LEAD TO AROUND AN INCH OF
NEW SNOW. LOCALLY HIGHER TOTALS ARE CERTAINLY POSSIBLE IF A SINGLE
BAND OF SNOW FORMS.

COLDER AIR SINKS SOUTH AS WELL FRIDAY MORNING WITH HIGHS ONCE AGAIN
WELL BELOW NORMAL IN THE LOW TO MID 30S. HIGH PRESSURE MOVES
OVERHEAD FRIDAY AFTERNOON WITH SKIES CLEARING AND NORTH WINDS
DIMINISHING. A CHILLY NIGHT IS EXPECTED WITH CLEAR SKIES AND WEAK
WINDS. LOWS WILL BE IN THE TEENS WITH A LOW AROUND 20 DOWNTOWN.

JEE

&&

.LONG TERM...
226 PM CDT

FRIDAY NIGHT THROUGH THURSDAY...

HIGH PRESSURE SITS OVER THE REGION FRIDAY NIGHT AND SATURDAY BEFORE
SHIFTING SOUTHEAST OV THE OHIO VALLEY SATURDAY EVENING.  UPPER LEVEL
TEMPS SLOWLY WARM SATURDAY BUT STILL LOOKING AT BELOW NORMAL TEMPS
WITH HIGHS IN THE UPPER 40S AND LOWS IN THE 20S.

THE NEXT UPPER LEVEL TROUGH MOVES OVER SW CANADA SATURDAY AFTERNOON
AND THEN PASSES OVER THE REGION SUNDAY AFTERNOON AND EVENING.  THE
SFC LOW ASSOCIATED WITH THE TROUGH PASSES OVER ONTARIO SUNDAY AS
WELL...AND GUIDANCE IS MUCH MORE CONSISTENT WITH THE LOW/S TRACK
OVER ONTARIO.  GUIDANCE DOES DIFFER WITH THE SPEED OF THE LOW AND
ITS COLD FRONT...WITH THE EURO BEING QUICKER WITH THE LOW YET SLOWER
WITH THE COLD FRONT.  THE NAM AND GFS WERE ON THE SAME PAGE TIMING
WISE SO LEANED HEAVILY IN THEIR DIRECTION.  THEREFORE HAVE PRECIP
MOVING IN SUNDAY MORNING AND PUSHING EAST OF THE CWA SUNDAY EVENING.
FORECAST SOUNDINGS INDICATE THE INITIAL PUSH OF PRECIP MAY BE A MIX
OF SNOW AND SLEET WITH A NICE WARM NOSE ALOFT. PRECIP THEN
TRANSITIONS TO RAIN. FOR HIGH TEMPS...WENT A BIT ON THE COOLER SIDE
SINCE THERE WILL BE AMPLE CLOUD COVER. HAVE HIGH TEMPS IN THE 40S
AND THE GUSTY SOUTHWEST WINDS WILL CERTAINLY MAKE IT FEEL BRISK.

A WEAK SURFACE RIDGE QUICKLY SLIDES PAST MONDAY WITH THE NEXT WEAK
LOW MOVING OVER CENTRAL WI MONDAY NIGHT INTO TUESDAY MORNING.
GUIDANCE IS A BIT MORE PERSISTENT WITH PRECIP BUT THE EURO IS STILL
THE ONLY MODEL BRINGING PRECIP OVER THE CWA. THEREFORE CAPPED POPS
IN THE SLIGHT CHANCE RANGE.  HIGH TEMPS MONDAY AND TUESDAY WILL BE A
BIT MORE SEASONAL IN 50S AND MAYBE AROUND 60 TUESDAY AWAY FROM THE
LAKE.

THE MODELS DISAGREE WITH THE TIMING OF THE PATTERN MID TO LATE NEXT
WEEK WITH A BROAD HIGH MOVING OVERHEAD MID WEEK WITH ANOTHER LOW
PRESSURE SYSTEM LATE IN THE WEEK.  THE LOW WILL BRING ANOTHER CHANCE
OF RAIN AND TEMPS LOOK TO BE AT LEAST AROUND NORMAL IF NOT ABOVE
NORMAL WITH A RELATIVELY ZONAL PATTERN ALOFT.

JEE

&&

.AVIATION...

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

* MVFR CIGS AND SNOW SHOWERS POSSIBLE OVERNIGHT

* NORTHERLY WINDS TURNING NORTHEAST FRIDAY AFTERNOON

IZZI

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

LOW END VFR CIGS CONTINUE TO STREAM IN FROM THE NORTHWEST THIS
AFTERNOON. EXPECT CIGS TO HOVER ABOVE 3000 FT FOR MOST LOCATIONS
THROUGH THE AFTERNOON. WINDS HAVE BEEN VARIABLE BETWEEN 280 AND
340 DEGREES THIS AFTERNOON...BUT HAVE GENERALLY SETTLED AROUND
310-320 DEGREES. EXPECT GUSTS TO 20 KT OR SO. WINDS WILL
GRADUALLY SHIFT TO NORTHERLY THIS EVENING...AND EVEN NORTHEASTERLY
CLOSER TO THE LAKEFRONT. FOCUS SHIFTS TO LAKE EFFECT SHOWER
POTENTIAL OVERNIGHT. MOISTURE REMAINS RATHER SHALLOW THIS
EVENING...BUT OVERNIGHT IT LOOKS LIKE MOISTURE...LOW LEVEL
INSTABILITY...AND HIGHER INVERSION HEIGHTS WOULD SUPPORT A PERIOD
OF SNOW SHOWERS AFTER MIDNIGHT THROUGH DAYBREAK. NOT SUPER
CONFIDENT AS TO HOW ORGANIZED THE SHOWERS WILL BE...BUT
ORD...MDW...AND GYY ARE ALL SUSCEPTIBLE. WAS DEBATING ON A TEMPO
WHICH MAY BE MORE HOW IT PLAYS OUT...BUT WANTED TO KEEP THINGS
SIMPLE WITH THE MVFR -SHSN MENTION DURING THE MOST LIKELY TIME
PERIOD. BEST LIFT IS BELOW THE DENDRITIC GROWTH ZONE...THUS THE
LOWER CONFIDENCE IN RINGING OUT SNOW AND IT MAY NOT BE QUITE AS
EFFICIENT. EITHER WAY...MVFR CONDITIONS ARE EXPECTED OVERNIGHT.

WINDS REMAINING NNE ON FRIDAY WITH FLURRIES TAPERING DURING THE
MORNING.

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

* HIGH IN WIND TRENDS TODAY...MEDIUM IN WIND TRENDS TONIGHT/FRIDAY

* HIGH IN CIGS REMAINING VFR THIS AFTERNOON...MEDIUM-HIGH IN
  RETURNING TO MVFR OVERNIGHT

* LOW-MEDIUM CONFIDENCE IN LAKE EFFECT SNOW AND ASSOCIATED IMPACTS

IZZI

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

FRIDAY NIGHT...VFR. NORTH WINDS TURNING NORTHEAST.

SATURDAY...VFR. LIGHT NORTHEAST WINDS TURNING SOUTHEAST.

SUNDAY...CHANCE RAIN THROUGH THE DAY...POSSIBLY MIXING WITH SNOW
EARLY. MVFR CIGS/VIS POSSIBLE. GUSTY SOUTHWEST WINDS.

MONDAY...VFR. WEST WINDS.

TUESDAY...VFR. SOUTHWEST WINDS.

WEDNESDAY...SLIGHT CHANCE OF RAIN. MAINLY VFR.

BEACHLER

&&

.MARINE...
203 PM CDT

MAIN MARINE FORECAST CONCERNS FOCUS ON A COUPLE OF PERIODS OF
STRONGER WINDS...THE FIRST FROM THE NORTH LATE TONIGHT THROUGH
FRIDAY EVENING AND THE SECOND A STRONGER PERIOD OF SOUTH WINDS AND
POTENTIAL GALES SATURDAY NIGHT THROUGH SUNDAY AND THEN BECOMING
WEST AND VERY SLOWLY DIMINISHING SUNDAY NIGHT INTO MONDAY.

LOW PRESSURE WAS LIFTING NORTHEAST THROUGH THE OHIO VALLEY THIS
AFTERNOON...WHILE HIGH PRESSURE WAS PUSHING SOUTHWARD FROM CENTRAL
CANADA. IN ADDITION...A WEAK SURFACE TROUGH WAS PUSHING SOUTH
ACROSS THE LAKE...WITH COLDER AIR AND A TIGHTENING GRADIENT AHEAD
OF THE APPROACHING HIGH STARTING TO SHIFT WINDS MORE TO THE NORTH-
NORTHWEST WITH GUSTS NEAR 30 KT ON THE NORTH END OF THE LAKE. THIS
TROUGH WILL CONTINUE TO MOVE SOUTH DOWN THE LAKE THROUGH THIS
EVENING...WITH WINDS BECOMING NORTHERLY AND INCREASING TO 30 KT
TONIGHT AND SLOWLY EASING TO 25 KT OR SO THROUGH LATE FRIDAY. THIS
NORTHERLY FETCH WILL LEAD TO WAVES BUILDING INTO THE 8 FOOT
RANGE...AND WILL HAVE A SMALL CRAFT ADVISORY IN EFFECT AFTER 06Z
FRI/1 AM CDT FOR THE IL/IN NEARSHORE WATERS. WINDS WILL CONTINUE
TO DIMINISH MORE QUICKLY LATER FRIDAY NIGHT AND SATURDAY...THOUGH
WILL HAVE THE SCA RUN THROUGH 21Z SAT/4 PM CDT AS WAVES SUBSIDE
MORE SLOWLY.

THE SURFACE HIGH WILL CONTINUE TO SPREAD SOUTHEAST ACROSS THE
WESTERN LAKES AND INTO THE OHIO VALLEY BY SATURDAY EVENING...
ALLOWING WINDS TO SHIFT BACK TO THE SOUTH. A DEEPENING AREA OF LOW
PRESSURE IS EXPECTED TO DEVELOP AND MOVE EAST THROUGH MANITOBA AND
INTO ONTARIO SATURDAY NIGHT INTO SUNDAY...TIGHTENING THE GRADIENT
AND INCREASING SOUTH WINDS TO 35-40 KT GALES BY SUNDAY MORNING.
WINDS LOOK TO EAST A BIT LATE SUNDAY AND SHIFT WEST AS THE
TRAILING COLD FRONT MOVES ACROSS THE LAKE. WESTERLY WINDS THEN
CONTINUE TO DIMINISH MONDAY.

SOUTH GALES APPEAR TO BE FAIRLY LIKELY FOR DURING THE DAY
SUNDAY... THOUGH ON DAY 4 STILL A LITTLE BEYOND THE TIME PERIOD
FOR A GALE WATCH. IF FORECAST GUIDANCE CONTINUES TO DEPICT A
SIMILAR SCENARIO WILL LIKELY NEED A GALE WATCH IN THE NEXT DAY OR
SO.

RATZER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...1 AM FRIDAY TO 4 PM SATURDAY.

&&

$$

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