Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 282157
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
457 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 22Z...

* LAKE BREEZE INFLUENCED EASTERLY WINDS INTO EARLY EVENING
* PRECIPITATION DEVELOPING MID-MORNING SUNDAY...COULD INCLUDE A
  MIX OF SLEET/SNOW FOR 1-2 HOURS AT ONSET BEFORE CHANGING TO ALL
  RAIN WITH TEMPERATURES ABOVE FREEZING
* VERY GUSTY SOUTHWEST WINDS SUNDAY...SUSTAINED 20 KT WITH GUSTS
  OVER 30 KT

RATZER/IZZI

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

SURFACE HIGH PRESSURE MOVING ACROSS THE TERMINALS TODAY...WITH
WEAK GRADIENT AND LIGHT WINDS ALLOWING LAKE BREEZE TO DEVELOP AND
PUSH INLAND WITH EAST-NORTHEAST WIND NEAR 10 KT EVENTUALLY
BECOMING LIGHT SOUTHEAST THIS EVENING. MAY BRIEFLY SEE WINDS 10KT+
BUT SHOULD BE SPORADIC/SHORT LIVED.

LOW PRESSURE WILL MOVE ACROSS SOUTHERN CANADA TONIGHT AND
SUNDAY...ALLOWING WINDS TO BECOME SOUTH AND INCREASE ESPECIALLY
TOWARD MORNING. JUST PRIOR TO SUNRISE WINDS IN THE 1000-1500 FT
LAYER INCREASE TO 40+ KTS...THOUGH GUSTY SURFACE WINDS ALSO
DEVELOP WHICH SHOULD RESULT MORE IN A MECHANICAL TURBULENCE
SCENARIO RATHER THAN A SHARP LLWS LAYER. SOUTHWEST WINDS WILL
INCREASE DURING THE MORNING...WITH GUSTS REACHING/TOPPING 30 KTS
BY LATE MORNING AND CONTINUING INTO THE AFTERNOON.

PRECIPITATION IS EXPECTED TO DEVELOP FROM THE WEST SUNDAY
MORNING...AS MOISTURE LIFTS NORTH TOWARD THE CANADIAN LOW. COLUMN
LOOKS TO INITIALLY BE COOL ENOUGH...AT LEAST THROUGH EVAPORATIVE
COOLING...TO SUPPORT A MIX OF SNOW/SLEET DURING THE ONSET OF
PRECIPITATION BEFORE CHANGING TO ALL RAIN AS WARM ADVECTION
OVERWHELMS COLUMN AND SATURATION OCCURS. SURFACE TEMPERATURES
WILL BE RISING INTO THE MID-UPPER 30S DURING THE MORNING AND
AROUND 40 BY EARLY AFTERNOON.

RATZER

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

* HIGH IN LAKE BREEZE WIND TRENDS THIS AFTERNOON.
* HIGH IN PRECIPITATION DEVELOPING BY MID-LATE MORNING SUNDAY. LOW
  IN PRECIPITATION TYPE AT ONSET.
* HIGH IN STRONG GUSTY SW WINDS SUNDAY. LOW IN TRUE LLWS SUNDAY
  MORNING.

RATZER/IZZI

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

SUNDAY NIGHT...MAINLY VFR. WEST WINDS.
MONDAY...CHANCE OF RAIN AND MVFR AT NIGHT. SOUTHWEST WINDS.
TUESDAY...VFR NORTHEAST WINDS.
WEDNESDAY...CHANCE FOR RAIN SHOWERS AT NIGHT.
THURSDAY-FRIDAY...CHANCE OF RAIN. WEST WINDS.

MTF

&&

.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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