Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 010916
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
316 AM CST SUN MAR 1 2015

.SHORT TERM...
315 AM CST

THROUGH MONDAY...

MID LEVEL BAROCLINIC ZONE IS DRAPED ACROSS DOWNSTATE ILLINOIS AND
INDIANA THIS MORNING WITH SNOW NORTH OF THE FRONT STRETCHING UP TO
NEAR THE I-80 CORRIDOR...THOUGH THE STRONGEST RADAR RETURNS ARE
ALONG AND JUST SOUTH OF OUR SOUTHERN CWA BOUNDARY IN EAST CENTRAL
ILLINOIS. FARTHER NORTH...LOW STRATUS DECK AND FOG HAS BEEN
EXPANDING EAST ACROSS IOWA AND NORTHERN ILLINOIS WHERE HIGH CLOUDS
ARE NOT IN PLACE ALLOWING TEMPS TO RADIATE...AND A FEW SITES ARE
REPORTING A FEW FLURRIES UNDER THESE LOW CLOUDS. WATER VAPOR
IMAGERY SHOWS A COUPLE SUBTLE WAVES...THE FIRST LIFTING
NORTHEAST OF THE CWA OVER MICHIGAN...AND THE SECOND LIFTING ACROSS
NORTHERN MISSOURI EARLY THIS MORNING. AS THIS SECOND WAVE MOVES
ACROSS THE REGION THIS MORNING...THE BETTER SNOW TO OUR SOUTH
SHOULD LIFT FARTHER NORTH PRODUCING MODEST ACCUMULATIONS ACROSS
OUR SOUTHERN COUNTIES. OUTSIDE OF A FEW LINGERING FLURRIES...SNOW
SHOULD BE DONE NORTH OF I-80...WITH UP TO 2 INCHES POSSIBLE DOWN
THROUGH THE ILLINOIS/KANKAKEE RIVER VALLEYS...AND 2 TO 4 LOCALLY 5
INCHES DOWN THROUGH FORD/IROQUOIS/BENTON COUNTIES. SNOW SHOULD
BEGIN TO SHIFT TO OUR EAST AS MID LEVEL TROUGH MOVES ACROSS THE
REGION. DRY WEATHER WILL PREVAIL THE REST OF THE EVENING THROUGH
THE DAY MONDAY AS HIGH PRESSURE BUILDS ACROSS ILLINOIS BY MIDDAY
MONDAY.

DEUBELBEISS

&&

.LONG TERM...
315 AM CST

MONDAY NIGHT THROUGH SATURDAY...

SURFACE HIGH WILL SHIFT TO THE MID ATLANTIC COAST LATE MONDAY NIGHT
WHILE SHORTWAVE ENERGY EJECTS ACROSS THE PLAINS AHEAD OF A DEEP
TROUGH OVER THE WEST COAST. IN RESPONSE...SURFACE LOW WILL BEGIN TO
DEEPEN OVER THE PLAINS MONDAY NIGHT INTO EARLY TUESDAY LIFTING
ACROSS THE MID MISSOURI VALLEY BY MIDDAY TUESDAY. THERE ARE NOTABLE
DIFFERENCES BETWEEN MODELS WITH RESPECT TO THE SURFACE LOW TRACK AND
MAGNITUDE TUESDAY...LIKELY DUE TO PHASING ISSUES WITH A NORTHERN
STREAM SYSTEM MOVING ACROSS THE CANADIAN PRAIRIES. THE NAM IN
PARTICULAR IS A NORTHERN OUTLIER WHILE THE GFS AND ECMWF HAVE BEEN
SOMEWHAT CONSISTENT WITH A LOW TRACK ACROSS EAST IOWA INTO LOWER
MICHIGAN...THOUGH HAVE INCHED SOUTH FROM PREVIOUS RUNS //SEEMINGLY A
COMMON TREND THIS WINTER// AND ARE SLOWER TO DEEPEN THE LOW. THIS
HAS RESULTED IN SOME CHANGES IN THINKING. FOR ONE...THE THERMAL
RIDGE AND HIGH PWAT AIR WILL NOT ADVANCE AS FAR INTO THE
CWA...MAKING FROZEN P-TYPE MORE OF A CONCERN...AND SOME
AREAS...ESPECIALLY NORTHERN COUNTIES IN THE CWA MAY SEE LITTLE RAIN
THIS EVENT AND LIGHT SNOW ACCUMULATIONS ON THE FRONT END OF THE
SYSTEM. OVERALL...QPF AMOUNTS APPEAR LESS WITH A WEAKER AND QUICKER
SYSTEM PUSHING ACROSS THE REGION...IN ADDITION TO AN INCREASING
SIGNAL FOR THE DRY SLOT TO PUSH OVERHEAD ON THE BACKSIDE OF THE
SYSTEM RESULTING IN PRECIP TRANSITIONING TO DRIZZLE OR FREEZING
DRIZZLE.

HIGH PRESSURE WILL GRADUALLY TRANSLATE EAST ACROSS THE REGION
MIDWEEK THROUGH FRIDAY BRINGING A RETURN TO DRY WEATHER BUT ALSO
COLD CONDITIONS. TEMPERATURES MAY NOT WARM MUCH ON WEDNESDAY AND MAY
EVEN COOL THROUGH THE AFTERNOON WITH COLD ADVECTION THROUGH THE
DAY...AND H85 TEMPS FALLING BACK TO AROUND -19C LATE WEDNESDAY
EVENING. BY THURSDAY NIGHT...THE RIDGE AXIS SHIFTS TO OUR EAST
AND NON-DIURNAL TRENDS MAY BE POSSIBLE AGAIN WITH STEADY OR WARMING
TEMPS OVERNIGHT. ANOTHER CLIPPER SYSTEM IS PROGGED TO IMPACT THE
NORTHERN GREAT LAKES FRIDAY INTO SATURDAY. WHILE IT SHOULD BRING
WARMER TEMPS LOCALLY...IT LOOKS LIKE WE CONTINUE TO SEE DRY WEATHER
DESPITE PASSAGE OF A COLD FRONT FRIDAY NIGHT INTO SATURDAY WITH
PRIMARILY AN INCREASE IN MID/HIGH LEVEL CLOUDINESS.

DEUBELBEISS

&&

.AVIATION...

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

* MVFR CIG/VIS POTENTIAL THIS MORNING...WITH IFR/LIFR JUST OFF TO
  THE WEST/NORTH OF ORD.

* MVFR CIGS PROBABLE THIS AFTERNOON.

RATZER

//DISCUSSION...UPDATED 09Z...

AREA OF CLEARING OVER EASTERN IOWA AND NORTHWEST/NORTH CENTRAL IL
HAS FILLED IN WITH IFR/LIFR STRATUS AND FOG OVER THE PAST COUPLE
OF HOURS. NORTHERN EDGE OF MID/HIGH CLOUD DECK JUST ABOUT OVER ORD
AND WILL LIKELY KEEP AREAS SOUTH OF ORD VFR/HIGH-MVFR WITH WARMER
SURFACE TEMPS...WHILE AREAS FROM ORD NORTH/WEST LIKELY TO MAINTAIN
IFR/LIFR CONDITIONS IN STRATUS AND FOG. ORD CURRENTLY REPORTING
SCT085 ON 1-MIN ASOS SO POTENTIAL FOR RADIATIONAL COOLING TO BRING
LOWER CIGS/VIS INTO OR EARLY THIS MORNING. CONFIDENCE LOW ON JUST
WHERE THE MID/HIGH CLOUD EDGE WILL BE WITH RESPECT TO ORD. MDW/GYY
SHOULD HAVE A GREATER PROBABILITY OF REMAINING ABOVE IFR.

RATZER

PREVIOUS DISCUSSION FROM 06Z...

AREA OF LIGHT SNOW WHICH OVERSPREAD THE TERMINALS DURING THE
EVENING IS JUST ABOUT OVER AT 06Z...WITH CONDITIONS TRENDING BACK
TO VFR IN MOST AREAS. IR SATELLITE IMAGERY HAS DEPICTED AN AREA OF
CLEARING OVER EASTERN IOWA AND NORTHWEST IL OVER THE PAST FEW
HOURS...THOUGH DOES APPEAR TO BE FILLING IN WITH PATCHY MVFR DECK
WHICH IS EXPECTED TO EXPAND EAST ACROSS THE TERMINALS DURING THE
PREDAWN HOURS. RELATIVELY MOIST SURFACE CONDITIONS WITH SMALL
TEMP/DEW POINT SPREADS...SO IF SKIES DO CLEAR FOR A TIME EARLY
THIS MORNING THERE COULD BE SOME MVFR FOG DEVELOPMENT WITH LIGHT
WINDS. THIS WOULD BE MOST LIKELY WEST OF CHICAGO...PRIOR TO
AFOREMENTIONED MVFR DECK EXPANDS EAST BEHIND DEPARTING HIGHER
CLOUDS.

ON SUNDAY...IT APPEARS ADDITIONAL LIGHT SNOW WILL REMAIN JUST OFF
TO THE SOUTH OF THE TERMINALS ACROSS CENTRAL IL/IN. LIGHT
SOUTHEAST WINDS TO BECOME LIGHT SOUTHWEST DURING THE MORNING...
THEN EXPECTED TO SHIFT WEST-NORTHWEST AS COLD FRONT PASSES SUNDAY
EVENING. SOME GUIDANCE INDICATES A BRIEF PERIOD OF GUSTS AS LAPSE
RATES STEEPEN BEHIND THE FRONT SUNDAY EVENING...THOUGH GRADIENT
WEAKENS OVERNIGHT AS HIGH PRESSURE RIDGE QUICKLY BUILDS EAST BY
MONDAY MORNING. ANY LINGERING MVFR STRATUS EXPECTED TO CLEAR OUT
DURING THE EVENING AS WELL.

RATZER

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

* LOW IN IFR/LIFR CIG/VIS MOVING INTO ORD/MDW THIS AM...AND IN CIG
  TRENDS INTO SUNDAY AFTERNOON.

* HIGH IN ALL OTHER ELEMENTS.

RATZER

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

MONDAY...VFR.

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

WEDNESDAY...MVFR CIGS POSSIBLE.

THURSDAY AND FRIDAY...MAINLY VFR.

IZZI

&&

.MARINE...
237 AM CST

MARINE FOCUS REMAINS ON A COUPLE PERIODS OF STRONGER WINDS NEAR 30
KT OVER THE NEXT SEVERAL DAYS. THE FIRST ONE IS TONIGHT AS HIGH
PRESSURE BUILDS IN BEHIND A COLD FRONT PUSHING ACROSS THE LAKE. THE
OTHER WILL BE TUESDAY AHEAD OF AN APPROACHING LOW...AND TUESDAY
NIGHT INTO WEDNESDAY AS COLD AIR SURGES INTO THE AREA ONCE AGAIN AS
THE DEEPENING LOW CONTINUES TO MOVE OFF TO THE NORTHEAST. A PERIOD
OF WEST-NORTHWESTERLY GALES ARE POSSIBLE TUESDAY NIGHT.

IN THE NEAR TERM...RELATIVELY QUIET WEATHER WAS ACROSS THE LAKE THIS
MORNING WITH WEAK HIGH PRESSURE RIDGING JUST SOUTH OF THE LAKES FROM
ILLINOIS TO NEW ENGLAND. A COLD FRONT WAS OVER THE UPPER MIDWEST...
AND WILL MOVE SOUTHEAST AND ACROSS THE LAKE THIS EVENING. THE
COMBINATION OF COLD AIR SPREADING IN BEHIND THE FRONT AND STRONG
HIGH PRESSURE BUILDING EAST FROM THE PLAINS WILL TIGHTEN THE
GRADIENT FOR A PERIOD TONIGHT...ALLOWING WEST-NORTHWEST WINDS TO
INCREASE TO 25-30 KT BEFORE DIMINISHING QUICKLY MONDAY MORNING AS
THE HIGH MOVES INTO THE REGION. THE RIDGE WILL MOVE EAST OF THE LAKE
MONDAY AFTERNOON...WITH A TROUGH OF LOW PRESSURE DEVELOPING FROM
MANITOBA INTO THE HIGH PLAINS. LOW PRESSURE WILL DEVELOP OVER THE
PLAINS AND MOVE NORTHEAST ACROSS KANSAS BY EARLY TUESDAY AND MOVING
NEAR SOUTHERN OR CENTRAL LAKE MICHIGAN BY TUESDAY EVENING. WINDS
WILL BECOME SOUTH-SOUTHEAST AHEAD OF THE LOW EARLY
TUESDAY...INCREASING TO 20-25 KT FOR A TIME BEFORE THE GRADIENT
WEAKENS NEAR THE LOW/TROUGH CENTER LATE IN THE DAY. THE LOW WILL BE
DEEPENING AS IT PASSES AND LIFTS NORTHEAST AWAY FROM LAKE MICHIGAN
TUESDAY NIGHT...WITH WINDS VEERING WEST-NORTHWEST AND INCREASING
INTO THE 30 KT RANGE OVERNIGHT AND INTO WEDNESDAY. SOME GUIDANCE
CONTINUES TO SUGGEST A PERIOD OF NORTHWEST GALES POSSIBLE DURING THE
LATE TUESDAY NIGHT/EARLY WEDNESDAY TIME FRAME...THOUGH THERE REMAINS
SOME DIFFERENCES IN THE DETAILS OF THE STRENGTH OF THE LOW. FOR NOW
HAVE MAINTAINED A MENTION OF GALE FORCE GUSTS TUESDAY NIGHT.
WEST-NORTHWEST WINDS LOOK TO REMAIN FAIRLY STOUT THROUGH WEDNESDAY
AND EVEN INTO WEDNESDAY NIGHT...AS HIGH PRESSURE DEVELOPS SOUTHEAST
FROM THE PLAINS TO THE OHIO VALLEY AND KEEPS THE WESTERN LAKES IN A
TIGHTER GRADIENT NORTH/NORTHEAST OF THE HIGH CENTER.

ILLINOIS/INDIANA NEAR SHORE WATERS REMAIN MOSTLY ICE COVERED. IF NOT
FOR LACK OF OPEN WATER...INCREASING SOUTHEAST WINDS LATE MONDAY
NIGHT COULD OTHERWISE LEAD TO SMALL CRAFT ADVISORY CONDITIONS MAINLY
NORTH OF CHICAGO BY TUESDAY MORNING.

RATZER

&&

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

$$

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