Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 282049
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
249 PM CST SAT FEB 28 2015

.UPDATE..

MONITORING UPSTREAM TRENDS WITH AREA OF LIGHT TO MODERATE SNOW
MOVING NORTHEAST ACROSS KANSAS/NEBRASKA/MISSOURI AT THIS TIME. FOR
THIS AFTERNOON...MADE MINOR CHANGES TO POPS WITH THIS SNOW LIKELY
REACHING THE FAR SOUTHWEST PORTION OF THE CWA BY THE 22-23Z TIME
FRAME AND THEN ANTICIPATED TO SPREAD ACROSS MUCH OF NORTHERN
ILLINOIS AND NORTHWEST INDIANA BY THIS EVENING. PER LATEST RADAR
TRENDS AND SHORT TERM GUIDANCE DID INCREASE TOTALS FOR THIS
EVENING WITH A DUSTING UP TO AN INCH OF SNOW LIKELY ALONG AND
NORTH OF INTERSTATE 88...AND 1 TO 2 INCHES SOUTH BY AROUND
MIDNIGHT TONIGHT.

RODRIGUEZ

&&

.SHORT TERM...
320 AM CST

THROUGH SUNDAY...

MAIN FORECAST CONCERN OVER THE WEEKEND WILL BE DEALING WITH SNOW
CHANCES AND AMOUNTS TONIGHT THROUGH THE DAY SUNDAY.

TODAY...HIGH PRESSURE IS CENTERED OVER THE UPPER OHIO VALLEY AND
WILL SHIFT EAST ACROSS THE MID ATLANTIC COAST WHILE A POTENT TROUGH
DIGS SOUTH ACROSS THE WEST COAST AND CLOSES OFF LATER TODAY.
MEANWHILE...A NORTHERN STREAM CLIPPER IS PROGGED TO DIVE INTO THE
NORTHERN PLAINS THIS EVENING AND ACROSS THE UPPER MIDWEST SUNDAY.
AHEAD OF THESE SYSTEMS...THE BAROCLINIC ZONE WILL WAVE NORTH WITH
BROAD AND PERSISTENT WARM ADVECTION OVERSPREADING THE FORECAST AREA
THIS AFTERNOON WITH INCREASING CLOUD COVER. A LEAD WAVE WILL RESULT
IN PRECIPITATION OVERSPREADING THE REGION LATE THIS EVENING AND
EARLY OVERNIGHT PRODUCING LIGHT ACCUMULATIONS ACROSS THE CWA...BUT
ESPECIALLY SOUTH OF I-80 WHERE 1-3 INCHES IS POSSIBLE BY AROUND
DAYBREAK. NORTH OF I-80 WOULD ONLY EXPECT A DUSTING. WHILE MUCH OF
THE AREA MAY SEE A LULL IN PRECIPITATION VERY EARLY SUNDAY BEFORE
THE NORTHERN STREAM WAVE MOVES ACROSS THE REGION...THE FAR SOUTHERN
TIER OF COUNTIES IN PARTICULAR COULD SEE MORE STEADY SNOW CONTINUING
JUST NORTH OF THE BAROCLINIC ZONE. THE MAIN UNCERTAINTY RESIDES IN
EXACTLY WHERE THIS WILL SET UP...WITH MODELS TRENDING SOUTH OVER THE
PAST 24 HOURS. BASED ON THE LATEST PROJECTIONS/MODEL CONSENSUS...AN
ADVISORY MAY STILL BE NEEDED FOR THE SOUTHERN TIER OF COUNTIES IN
THE FORECAST AREA...HOWEVER SHOULD SOUTHWARD TRENDS CONTINUE THEN WE
MAY SKATE BY WITHOUT ANY HEADLINES. EVEN WITH THE UNCERTAINTIES IN
THE LOCATION...THERE REMAIN OTHER LIMITING FACTORS WITH THIS
SYSTEM...INCLUDING A RELATIVELY SHALLOW DGZ...NO STRONG SIGNAL FOR
MESOSCALE BANDING THIS FAR NORTH...AND BEING A MORE PROLONGED LIGHT
SNOW SHOULD HELP MITIGATE ANY IMPACTS. THE LATEST STORM TOTAL
FORECAST CALLS FOR UP TO 2 INCHES NORTH OF I-80...AND 2 TO 5 INCHES
SOUTH...THOUGH SOUTHERN PORTIONS OF FORD/IROQUOIS/BENTON COUNTIES
MAY SEE 4 TO 6 INCHES. BOTTOM LINE IS THAT WE CONTINUE TO TAPER SNOW
TOTALS IN THE NORTH...AND WILL WAIT ANOTHER CYCLE BEFORE WE ISSUE
HEADLINES FOR THE SOUTH...MAINLY DUE TO UNCERTAINTIES IN THE TRACK.

DEUBELBEISS

&&

.LONG TERM...
320 AM CST

SUNDAY NIGHT THROUGH FRIDAY...

HIGH PRESSURE WILL ALLOW CLOUDS TO CLEAR OUT SUNDAY NIGHT AND FOR
SOME SUNSHINE ON MONDAY...BUT A MORE POTENT SYSTEM CONTINUES TO BEAR
WATCHING FOR TUESDAY. DEEP TROUGHING OVER THE WEST COAST WILL INCH
EAST ACROSS THE INTERMOUNTAIN WEST EARLY NEXT WEEK WITH A LEAD WAVE
EJECTING OVER THE PLAINS RESULTING IN A DEEPENING SURFACE LOW
PROGGED TO TRACK FROM THE CENTRAL PLAINS MONDAY NIGHT AND ACROSS THE
MID/UPPER MISSISSIPPI VALLEY TUESDAY. MANY OF THE FORECAST DETAILS
HINGE ON THE TRACK...BUT SO FAR MODELS SEEM TO BE FOCUSED ON A TRACK
ACROSS OR JUST WEST/NORTH OF THE CWA. THIS SHOULD RESULT IN THE WARM
SECTOR LIFTING NORTH ACROSS ILLINOIS. MODELS CONTINUE TO HINT AT
50-60KT LOW LEVEL JET ADVECTING AROUND +5C H85 THERMAL RIDGE AND 1.0
INCH PWATS ACROSS CENTRAL/NORTHERN ILLINOIS TUESDAY AFTERNOON. AT
THE SURFACE...WARM/MOIST ADVECTION WILL FIGHT AGAINST OUR SNOWPACK
BUT COULD SEE TEMPERATURES PUSHING THE 40 MARK. AS PREVIOUSLY
MENTIONED...RAPID MELTING/RUNOFF REMAINS A CONCERN TUESDAY GIVEN THE
ANOMALOUSLY HIGH PWAT AIR/HIGH QPF AND MID 30 DEWPOINTS WHICH SHOULD
EAT AWAY AT THE SNOW. P-TYPE MAY BE A CONCERN MAINLY AT THE ONSET
WITH THE WARM AIR OVERRIDING OUR BELOW FREEZING SURFACE TEMPS...BUT
TYPICALLY FIND THAT MODELS ARE TOO SLOW AND UNDER-DO THE STRENGTH OF
THE WARM ADVECTION DOWN LOW SO WILL CONTINUE TO MONITOR BUT FREEZING
MAY BE SOMEWHAT LOCALIZED. OTHERWISE ANY FROZEN PRECIP TYPES EARLY
SHOULD TRANSITION TO ALL RAIN FROM MID MORNING TO EARLY AFTERNOON.
PRECIP MAY CHANGE BACK TO SNOW ON THE BACKSIDE TUESDAY EVENING/NIGHT
BUT DO NOT ANTICIPATE ANY ACCUMULATIONS. COLD HIGH PRESSURE MAKES
ITS WAY BACK INTO THE REGION WEDNESDAY WITH H85 TEMPS BOTTOMING OUT
AROUND -20C WEDNESDAY NIGHT WHEN SUB ZERO LOWS ARE ONCE AGAIN
POSSIBLE. MODELS DO HINT AT ANOTHER BRIEF WARMUP FRIDAY INTO
SATURDAY.

DEUBELBEISS

&&

.CLIMATE...

TEMPERATURES ARE FORECAST ONCE AGAIN TO BE CLOSE OR BREAK THE
FOLLOWING DAILY RECORDS THROUGH THE END OF THE MONTH.

ROCKFORD...

SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* LIGHT SNOW OVERSPREADS ORD/MDW AFT 2Z...WITH A PERIOD OF
  STEADIER SNOW WITH VSBYS REDUCTION TO 2SM POSSIBLY AROUND 1SM
  FOR AN HOUR UNTIL 6Z.

BEACHLER

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

HIGH PRESSURE OVERHEAD CONTINUES TO DRIFT EAST THIS
AFTERNOON...WITH A VERY LIGHT GRADIENT AND WINDS LESS THAN 6KT
FROM THE SOUTH. WINDS ARE EXPECTED TO REMAIN LIGHT FROM THE
SOUTHEAST...STARTING TO TURN MORE SOUTHERLY OVERNIGHT AND THEN
SOUTHWEST AROUND DAYBREAK SUNDAY. LIGHT SNOW ACROSS THE CENTRAL
PLAINS THIS AFTERNOON IS FORECAST TO STEADILY LIFT NORTHEAST
TOWARDS NORTHERN IL/NORTHWEST IN AIRFIELDS. CIGS WILL STEADILY
LOWER TONIGHT...WITH GUIDANCE INDICATING CIGS WILL LOWER TO A
PERIOD OF MVFR WITH LGT SNOW BETWEEN 3Z TO 7Z. THERE COULD BE A
BRIEF MOMENT WITH CIGS DIPPING TO IFR CONDS OR NEAR IFR CONDS
BETWEEN 3-6Z IN THE STEADIER SNOW. MOISTURE BEGINS TO PIVOT EAST
BEFORE DAYBREAK WITH SOME LINGERING FLURRIES THRU DAYBREAK...THEN
SNOW SHOULD END WITH WINDS TURNING SOUTHWEST AND CIGS SLOWLY LIFT
BACK TOWARDS VFR CONDS.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN ALL ELEMENTS THROUGH 00Z.

* HIGH CONFIDENCE IN WINDS AFT 00Z THRU SUN MIDDAY.

* MEDIUM/HIGH CONFIDENCE IN CIGS AND TIMING OF SNOW.

* MEDIUM CONFIDENCE IN VSBYS WITH LGT SNOW BTWEEN 3-6Z.

BEACHLER

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

SUNDAY NIGHT...MVFR CEILINGS MAINLY EARLY.

MONDAY...VFR. CHANCE OF SNOW AFTER MIDNIGHT.

TUESDAY...RAIN...FREEZING RAIN...OR SNOW. IFR PROBABLE.

WEDNESDAY...MVFR CIGS POSSIBLE.

THURSDAY AND FRIDAY...MAINLY VFR.

RATZER

&&

.MARINE...
249 PM CST

VISIBLE SATELLITE IMAGERY TODAY SHOWS THAT MUCH OF THE LAKE IS ICE
BOUND EXCEPT FOR A NARROW CORRIDOR FROM THE SOUTH CENTRAL PORTION TO
JUST NORTHWEST OF MANISTEE HARBOR. THE ICE IS LIKELY TO FURTHER
EXPAND THROUGH MONDAY NIGHT AS A COLD AIR MASS REMAINS OVER THE LAKE.
SOUTH-SOUTHWEST WINDS WILL REACH 20-25 KT AT TIMES THROUGH SUNDAY
AFTERNOON OVER THE CENTRAL AND NORTHERN PORTIONS OF THE LAKE. A COLD
FRONT WILL THEN CROSS THE LAKE SUNDAY EVENING...WITH A BRIEF PERIOD
OF NORTHWEST WINDS UP TO 30 KT ON THE SOUTHERN PORTION OF THE LAKE.
ANOTHER LARGE HIGH PRESSURE WILL APPROACH ON MONDAY...RESULTING IN
DIMINISHING WINDS. THE HIGH WILL SHIFT EAST ON MONDAY NIGHT INTO
TUESDAY AS LOW PRESSURE APPROACHES FROM THE CENTRAL PLAINS...RESULTING
IN SOUTHERLY WINDS PICKING UP TO 20 TO 25 KT BY TUESDAY MORNING.
MOST MODEL GUIDANCE HAS TRENDED WEAKER WITH SYSTEM OVERALL. THIS
WOULD MAKE TOP END NORTHWEST WIND SPEEDS TO 30 KT OVER THE CENTRAL
AND SOUTHERN PORTION OF THE LAKE MORE LIKELY THAN GALES TUESDAY
NIGHT AND WEDNESDAY BEHIND THE LOW. IF THE LOW IS STRONGER...GALES
WOULD STILL BE POSSIBLE. YET ANOTHER EXPANSIVE HIGH PRESSURE AREA
WILL MOVE TO THE MID MISSISSIPPI VALLEY BY THURSDAY...WITH
INCREASING SOUTHWEST WINDS AS THE HIGH SLIDES SOUTHEAST THURSDAY
NIGHT.

RC

&&

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

$$

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