Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 280942
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
342 AM CST SAT FEB 28 2015

.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: -7 IN 1962
SATURDAY FEB 28TH LOW MAXIMUM: 17 IN 1962

CHICAGO...

SATURDAY FEB 28TH LOW: 0 IN 1884

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* PERIOD OF LIGHT SNOW POSSIBLE LATE SATURDAY EVENING/OVERNIGHT.
  MVFR/BRIEF IFR CONDITIONS ASSOCIATED WITH PRECIP.

RATZER

//DISCUSSION...UPDATED 06Z...

HIGH PRESSURE OVER THE AREA EARLY THIS MORNING WILL START SATURDAY
OUT WITH SIMILAR QUIET CONDITIONS AS ON FRIDAY. ONLY A FEW MID-
LEVEL CLOUDS...AND THOSE MAINLY SOUTH OF THE TERMINALS...WILL BE
PRESENT WITH A WEAK DISTURBANCE MOVING THROUGH LARGELY DRY
ATMOSPHERE THROUGH MID-DAY. MOISTURE WILL INCREASE FROM THE SOUTH
LATE IN THE DAY...WITH VFR CEILINGS DEVELOPING AND LOWERING TO
4000-5000 FT AGL BY EARLY EVENING. MODEL FORECAST SOUNDINGS
INDICATE DEEPENING MID-LOW LEVEL SATURATION DEVELOPING MID-LATE
EVENING AS AN UPPER LEVEL DISTURBANCE TRACKS ACROSS THE REGION.
GUIDANCE INDICATES A PERIOD OF LIGHT SNOW BEGINNING 03Z-ISH AND
AND LINGERING PAST MIDNIGHT BEFORE A LULL DEVELOPS AS THE MID-
LEVEL WAVE MOVES AWAY TO THE EAST. ADDITIONAL PERIODS OF LIGHT
SNOW APPEAR LIKELY BEYOND END OF THE CURRENT TAF PERIOD SUNDAY
MORNING- EARLY AFTERNOON...THOUGH THE BEST FORCING/SATURATION
LOOKS TO REMAIN TO THE SOUTH OF THE TERMINALS.

AS FOR WINDS...SURFACE HIGH PASSING SOUTH OF THE TERMINALS EARLY
THIS MORNING RESULTING IN SOUTHWEST WINDS LESS THAN 5 KT BACKING
TO THE SOUTH-SOUTHEAST AFTER SUNRISE...WITH SPEEDS GENERALLY UNDER
10 KT THOUGH THE DAY. LIGHT SOUTHEAST WINDS EXPECTED SATURDAY
EVENING.

RATZER

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* MEDIUM WITH SNOW TIMING AND CIG/VIS IMPACTS.

* HIGH ALL OTHER ELEMENTS.

RATZER

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...IFR LIKELY WITH PERIODS OF LIGHT SNOW.

MONDAY...VFR.

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

WEDNESDAY...MVFR CIGS POSSIBLE.

THURSDAY...CHANCE OF MVFR CIGS EARLY.

IZZI

&&

.MARINE...
205 AM CST

MARINE CONCERNS FOCUS MAINLY ON A COUPLE OF PERIODS OF WINDS IN THE
25-30 KT RANGE...SUNDAY NIGHT...AND AGAIN WITH A GREATER POTENTIAL
FOR A PERIOD OF GALES TUESDAY INTO WEDNESDAY.

HIGH PRESSURE WAS CENTERED ACROSS ILLINOIS...INDIANA AND OHIO EARLY
THIS MORNING. THIS HIGH WILL DEVELOP EASTWARD ACROSS THE NORTHERN
APPALACHIANS TODAY...AND TO THE JERSEY SHORE ON SUNDAY. FARTHER
NORTH...A DEEP LOW WILL MOVE ACROSS FAR NORTHERN ONTARIO AND HUDSON
BAY BUT WILL TRAIL A COLD FRONT AND ASSOCIATED TROUGH SOUTHWARD
ACROSS THE WESTERN LAKES SUNDAY. COLDER AIR RETURNING BEHIND THIS
FRONT AND HIGH PRESSURE BUILDING EAST FROM THE PLAINS WILL RESULT IN
NORTHWEST WINDS INCREASING INTO THE 25-30 KT RANGE SUNDAY NIGHT.
WINDS WILL DIMINISH FAIRLY QUICKLY MONDAY HOWEVER...AS THE HIGH
MOVES QUICKLY ACROSS THE MIDWEST AND GREAT LAKES MONDAY AFTERNOON.

WINDS WILL VEER BACK AROUND TO THE SOUTH-SOUTHEAST MONDAY NIGHT AS
THE HIGH CONTINUES OFF TO THE EAST...AND AN AREA OF LOW PRESSURE
TAKES SHAPE OVER THE CENTRAL HIGH PLAINS. THIS LOW IS EXPECTED TO
DEEPEN WHILE TRACKING EAST ACROSS IOWA AND ILLINOIS ON TUESDAY...AND
NORTHEAST ACROSS LOWER MICHIGAN AND SOUTHWESTERN ONTARIO TUESDAY
NIGHT. SOUTH-SOUTHEAST WINDS WILL INCREASE INTO THE 20-25 KT RANGE
AHEAD OF THE LOW TUESDAY...THEN LIKELY INTO THE 30-35 KT RANGE
TUESDAY NIGHT INTO WEDNESDAY AS COLD AIR AGAIN SURGES IN BEHIND THE
DEPARTING LOW. THE LOW WILL CONTINUE TO DEEPEN OFF TO THE NORTHEAST
INTO QUEBEC WEDNESDAY...AS HIGH PRESSURE BUILDS SOUTHEAST ACROSS THE
PLAINS...HELPING TO MAINTAIN GUSTY NORTHWEST WINDS INTO WEDNESDAY
NIGHT.

SOME MODEL DIFFERENCES REMAIN WITH THE STRENGTH AND TIMING OF THE
PASSAGE OF THE LOW ACROSS THE AREA TUESDAY AND TUESDAY NIGHT...
THOUGH THE SCENARIO IS SIMILAR AMONGST GUIDANCE SOLUTIONS. GALE
HEADLINES MAY NEED TO BE CONSIDERED AS THE TIME APPROACHES AND
GUIDANCE SOLUTIONS CONVERGE ON THE TIMING OF THE GREATEST THREAT.

RATZER

&&

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

$$

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