Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 282349
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
649 PM CDT SAT MAR 28 2015

.SHORT TERM...
242 PM CDT

THROUGH MONDAY...

REST OF TODAY AND TONIGHT BROAD MIDLEVEL HEIGHT RISES/SUBSIDENCE
WILL CONTINUE TO PROVIDE QUIET WEATHER CONDITIONS ALTHOUGH
UNSEASONABLY COLD CONDITIONS PERSIST AT THE SURFACE WITH A DEEP
UPPER LEVEL TROUGH CENTERED OVER THE EASTERN GREAT LAKES DRIVING
COLD AIR AS FAR AS THE DEEP SOUTH. ON THE BACK EDGE OF THE THIS
SYSTEM...POTENT VORT MAX WILL DROP INTO THE NORTHERN PLAINS THIS
EVENING AND TONIGHT WITH ATTENDANT SURFACE COLD FRONT PUSHING INTO
NORTHERN ILLINOIS LATE SUNDAY AFTERNOON. OUT AHEAD OF THE
FRONT...STRONG LOW LEVEL JET AROUND 50-60 KT WILL TRANSPORT A NARROW
CORRIDOR OF 0.8 INCH PWATS AND A WARM NOSE WITH LAYER MAX TEMPS OF
2-5C WHICH WILL RESULT IN PRIMARILY RAIN FOR THIS SYSTEM. THE
MAIN CONCERN FOR ANY MIXED/WINTRY PRECIP WILL BE CONFINED TO THE
FIRST COUPLE HOURS AT ONSET OF PRECIP WHERE ANTECEDENT DRY AIR MAY
RESULT IN DIABATIC COOLING OF THE COLUMN WHICH WILL ALLOW FOR
SLEET/FREEZING RAIN AND POSSIBLY A FEW FLAKES. WARMING OF THE
COLUMN SHOULD BE FAIRLY RAPID THOUGH WHICH WILL HELP MITIGATE ANY
BRIEF IMPACTS FROM WINTRY P-TYPE. VERY MODEST UPRIGHT INSTABILITY
ROOTED BETWEEN 600-700MB WILL MOVE ACROSS THE REGION MIDDAY AND
COULD RESULT IN A FEW BRIEFLY HEAVIER SHOWERS. PRECIPITATION WILL
MOVE INTO THE WESTERN PORTION OF THE FORECAST AREA BY MID MORNING
AND EXITING EAST BY LATE AFTERNOON. BEHIND THE FRONT...EXPECT MOST
PRECIP TO END...HOWEVER AS THE MAIN UPPER WAVE MOVES OVERHEAD AND
COLD ADVECTION RESULTS IN STEEP LOW LEVEL LAPSE RATES AND SHALLOW
SATURATION MAINLY BELOW 850 MB...CANNOT RULE OUT A FEW SPRINKLES.

ALSO OF CONCERN SUNDAY WILL BE THE MAGNITUDE OF WINDS. A TIGHT
PRESSURE GRADIENT COUPLED WITH A RIBBON OF 6-7MB/3HR PRESSURE FALLS
WILL RESULT IN WINDY CONDITIONS ACROSS THE REGION. BOTH NAM AND GFS
SOUNDINGS SHOW THE POTENTIAL FOR AT LEAST 30-40 MPH WIND GUSTS AND
POSSIBLY A FEW ISOLATED GUSTS TO 45 MPH. A LITTLE UNCERTAIN ABOUT
LOW LEVEL LAPSE RATES AND THE EFFICIENCY OF MIXING WITH THE EXPECTED
CLOUD COVER AND WARMING MID-LEVELS SO WILL HOLD OFF A WIND ADVISORY
FOR THE TIME BEING...BUT WILL GO AHEAD AND ISSUE AN SPS TO HIGHLIGHT
THE CONCERN.

HIGH PRESSURE BUILDS BACK OVER THE MID MISSISSIPPI VALLEY SUNDAY
NIGHT WITH WINDS DIMINISHING AND A RETURN TO DRY CONDITIONS. RIDGE
AXIS SHIFTS EAST ACROSS THE FORECAST AREA DURING THE DAY MONDAY.
TEMPERATURES SHOULD BE NEAR NORMAL WITH MORNING LOWS IN THE LOW TO
MID 30S AND AFTERNOON HIGHS IN THE LOW TO MID 50S.

DEUBELBEISS

&&

.LONG TERM...
242 PM CDT

MONDAY NIGHT THROUGH SATURDAY...

A CLIPPER SYSTEM WILL DIG ACROSS THE UPPER MIDWEST AND WESTERN
GREAT LAKES MONDAY NIGHT. THE GFS AND ECMWF HAVE COME IN MUCH
BETTER AGREEMENT ON SURFACE LOW TRACK FROM 24 HOURS AGO WITH THE
GFS SHIFTING SOUTH MORE IN LINE WITH THE EUROPEAN. THE NAM IS A
NORTHERN OUTLIER. WITH THE EXPECTED SURFACE TRACK...MOST LIKELY
EXPECT TO SEE PRECIPITATION STAY NORTH OF THE FORECAST AREA MONDAY
NIGHT...AND ANYTHING FORMING ALONG THE COLD FRONT DURING THE DAY
MONDAY SHOULD DEVELOP TO OUR SOUTH/SOUTHEAST. WE DO GET A BRIEF
REINFORCING SHOT OF COLDER AIR THAT WILL SLOW OUR WARNING
TREND...BUT 60S STILL APPEAR FAVORABLE FOR ESPECIALLY WEDNESDAY
AND POSSIBLY THURSDAY DEPENDING ON FROPA TIMING. BROAD UPPER LEVEL
RIDGE WILL BUILD ACROSS THE MID SECTION OF THE COUNTRY WEDNESDAY
WHILE LOW PRESSURE MOVES EAST ACROSS THE CANADIAN PRAIRIES. 850MB
TEMPS ARE PROGGED TO WARM TO AROUND 10C WHICH SHOULD TRANSLATE TO
SURFACE TEMPS IN THE 60S...AND IF ANYTHING FEEL FORECAST TEMPS
FOR WEDNESDAY MAY BE TOO LOW AT THE MOMENT. A COLD FRONT IS
PROGGED TO PUSH ACROSS THE REGION THURSDAY THOUGH THERE ARE
SIGNIFICANT TIMING DIFFERENCES BETWEEN THE MODELS WHICH WOULD
IMPACT TEMPS. ANOTHER COOLDOWN LOOKS POSSIBLE LATE IN THE WEEK
INTO NEXT WEEKEND WITH BOTH THE GFS AND ECMWF TRACKING A DEEP LOW
ACROSS THE OHIO VALLEY PULLING COLDER AIR INTO THE UPPER MIDWEST
AND BRINGING ANOTHER CHANCE OF SNOW TO NORTHERN ILLINOIS.

DEUBELBEISS

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 00Z...

* STRONG SOUTHERLY WINDS DEVELOP EARLY-MID MORNING SUNDAY
* CHANCE OF LLWS EARLY SUNDAY MORNING
* PERIOD OF SNOW/GRAUPEL/SLEET POSSIBLE AT ONSET OF PRECIP LATE
  SUNDAY MORNING
* PERIOD OF RAIN THROUGH EARLY-MID AFTERNOON SUNDAY W/MVFR CIGS
  AND VSBY

IZZI

//DISCUSSION...UPDATED 00Z...

HIGH PRESSURE WILL MOVE OFF TO THE EAST TONIGHT ALLOWING LAKE
INFLUENCED EAST WINDS TO TURN SOUTHEAST THIS EVENING. FAST MOVING
STORM SYSTEM WILL RESULT IN WINDS BECOMING SOUTHERLY AND
INCREASING PRIOR TO SUNRISE. WINDS AROUND 2000FT AGL WILL INCREASE
TO 50-60KT BY EARLY-MID MORNING SUNDAY AT BASE OF SHARP INVERSION
POSSIBLY RESULTING IN SOME LLWS REPORTS SUNDAY MORNING THOUGH
SUSPECT TURBULENCE MAY BE MORE OF AN ISSUE THAN LLWS SO HELD OFF
ON INCLUDING LLWS IN TAFS FOR NOW. WINDS WILL QUICKLY INCREASE TO
20-25KT WITH GUSTS OF 33-38KT PRIMARILY FROM 190-200 BETWEEN
12-15Z WITH GUSTS IN THE NEIGHBORHOOD OF 35KT LIKELY TO CONTINUE
THROUGH THE LATE MORNING BEFORE PERHAPS EASING SLIGHTLY EARLY IN
THE AFTERNOON THOUGH LIKELY REMAINING NEAR/SLIGHTLY ABOVE 30KT.
BAND OF PRECIPITATION WILL MOVE ACROSS THE TERMINALS LATE SUNDAY
MORNING THROUGH MID AFTERNOON WITH PRECIP POTENTIALLY STARTING AS
A PERIOD OF SNOW...SLEET...OR POSSIBLY SOME GRAUPEL GIVEN THE
STEEP MID-LEVEL LAPSE RATES AND STRONG LOW LEVEL JET WITH SOME
CONVECTIVE ELEMENTS WITHIN THE PRECIP BAND. WARMING TEMPS SHOULD
RESULT IN FAIRLY QUICK CHANGE OVER TO RAIN AFTER ONSET OF PRECIP.
SOME SHOWERS COULD ACCOMPANY COLD FRONT MOVING THROUGH THE REGION
EARLY SUNDAY EVENING WITH WINDS SHIFTING TO NORTHWEST BEHIND THE
FRONT AND GRADUALLY EASING.

IZZI

//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* LOW-MEDIUM CONFIDENCE IN SNOW/SLEET/GRAUPEL POTENTIAL
* HIGH CONFIDENCE IN PRECIP TIMING
* LOW CONFIDENCE IN POTENTIAL FOR LLWS EARLY SUNDAY MORNING
* MEDIUM-HIGH CONFIDENCE IN WIND SPEEDS/GUSTS SUNDAY

IZZI

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

MONDAY...PRIMARILY VFR.

TUESDAY...PRIMARILY VFR. LAKE BREEZE/NE WINDS DEVELOPING.

WEDNESDAY...PRIMARILY VFR. MODERATE-STRONG SOUTH WINDS POSSIBLE.

THURSDAY...CHANCE SHRA/TSRA IN MORNING...OTHERWISE VFR.

FRIDAY...LOW CONFIDENCE. RAIN/SUB-VFR CONDITIONS POSSIBLE.

IZZI

&&

.MARINE...
149 PM CDT

HIGH PRESSURE OVER THE LAKE HAS BEEN HELPING FOR QUIET CONDITIONS
WITH LIGHT WINDS...BUT EXPECT THIS TO CHANGE TONIGHT AND
ESPECIALLY SUNDAY MORNING AS THIS HIGH SHIFTS TO THE EAST AND A
TROUGH OF LOW PRESSURE APPROACHES FROM THE WEST. LIGHTER SOUTHERLY
WINDS THIS EVENING WILL INCREASE RAPIDLY OVER THE ENTIRE LAKE
OVERNIGHT WITH SOUTH/SOUTHWEST GALES TO 45 KT STILL EXPECTED.
HOWEVER SOUTHERLY FLOW IS APPEARING TO LIKELY APPROACH STORM FORCE
WINDS FOR A PERIOD SUNDAY MORNING THROUGH EARLY SUNDAY AFTERNOON.
WITH A HIGH LIKELIHOOD OF THIS OCCURRENCE...HAVE MAINTAINED THE
CURRENT GALE WARNING IN EFFECT FOR THE ENTIRE LAKE BUT TRANSITION
THE NORTHERN HALF TO A STORM WARNING BY 14Z AND CONTINUE IT
THROUGH 20Z. GALES MAY LINGER A COUPLE OF HOURS BEYOND THIS END
TIME BUT SHOULD BE DIMINISHING AS WELL. GALE WARNING FOR THE SOUTH
HALF REMAINS THE SOME...BUT WITH SOME POSSIBILITY THAT THE GALES
COULD CONTINUE A COUPLE OF HOURS BEYOND THE END TIME TOMORROW
EVENING.

MADE SOME MINOR CHANGES TO THE CURRENT HEADLINES FOR THE
NEARSHORE...PRIMARILY EXTENDING THE GALE WARNING TO 00Z AS WELL.
ALSO...WINDS SHOULD PICK UP PRIOR TO THE GALE WARNING FOR THE
INDIANA NEARSHORE AND SO DID ISSUE AN SCA TONIGHT INTO EARLY
SUNDAY.

RODRIGUEZ

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...4 AM SUNDAY TO 10 AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 7 PM SUNDAY.

     GALE WARNING...LMZ777-LMZ779...4 AM SUNDAY TO 7 PM SUNDAY.

&&

$$

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