Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 021823
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
123 PM CDT TUE JUN 2 2015

.SHORT TERM...
310 AM CDT

THROUGH WEDNESDAY...

FAIRLY ACTIVE FLOW IN PLACE ACROSS THE PLAINS AND UPPER
MIDWEST...BUT MUCH QUIETER IN OUR REGION EARLY THIS MORNING. SURFACE
HIGH PRESSURE REMAINS IN CONTROL...LARGELY CENTERED TO OUR
NORTH...WITH THE RIDGE AXIS STRETCHED FROM NORTHERN LOWER MICHIGAN
INTO THE LOWER MISSISSIPPI VALLEY.

ACTIVE CONVECTION IN THE PLAINS DRIVEN BY VORT MAXES RIDING ALONG
THE NORTHERN EDGE OF THE UPPER RIDGE WILL REMAIN TO OUR WEST FOR A
COUPLE OF DAYS AS THE RIDGE AXIS SHIFTS EASTWARD AND UPPER LEVEL
HEIGHTS CONTINUE GRADUALLY INCREASING. AS THIS OCCURS...DEBRIS/HIGH
CLOUD COVER WILL DRIFT CLOSER EACH DAY. WE MAY ALSO HAVE SOME FAIR
WEATHER CUMULUS AS WELL. THEREFORE TODAY WILL FEATURE MOSTLY
SUNNY SKIES...THEN WEDNESDAY MOSTLY SUNNY TO PARTLY CLOUDY
CONDITIONS. SURFACE HIGH PRESSURE WILL DRIFT EAST SOME TODAY...AND
MORE SO ON WEDNESDAY...BUT STILL INFLUENCING THE AREA TO KEEP ANY
MOISTURE RETURN FROM GULF WELL WEST. THE NET EFFECT OF THIS TO
ALLOW A WARMER AIR MASS TO INVADE THE REGION...AND ALSO ALLOW
SURFACE FLOW TO VEER FROM NORTHEASTERLY TO SOUTHEASTERLY.
THEREFORE THE GENERAL WARMING TREND CONTINUES EACH DAY...WITH
TYPICAL LAKE COOLING (OF SOME 6-8F FROM INTERIOR COOK COUNTY)
GIVEN THE SYNOPTIC EASTERLY FLOW OVER THE COLD LAKE.

KMD

&&

.LONG TERM...
310 AM CDT

WEDNESDAY NIGHT THROUGH MONDAY...

A BIT MORE COMPLICATED EVOLUTION TO UNFOLD FOR THE WEEKEND AS
SHORTWAVE ENERGY PROPAGATING AHEAD OF THE CUTOFF LOW OFF THE
PACIFIC...AND WITH GUIDANCE MIXED ON HANDLING SMALLER SCALE VORT
MAXES AND HOW/WHERE THEY WILL PROGRESS THROUGH THE REGION HAS
PREVENTED ANY DEFINITIVE DECISIONS ON BEST TIMING OF PRECIPITATION
CHANCES. GENERALLY CHANCES WILL BE INCREASING FRIDAY AND INTO THE
WEEKEND. THURSDAY MORNING STARTS OFF WITH DECAYING CONVECTION ONCE
AGAIN FROM THE PLAINS...BUT AS COMPARED TO DAYS PAST...SOME OF THE
LIFT...BOTH ALOFT AND FROM LEVEL ISENTROPIC LIFT/MOISTURE
TRANSPORT...MAY SNEAK INTO OUR WESTERN AREAS THURSDAY MORNING.
UPPER LEVEL HEIGHTS REMAIN HIGH ON THURSDAY TO PRECLUDE MUCH
FARTHER EASTWARD PROGRESSION OF ANY SHOWERS/STORMS AS THE NAM
SUGGESTS.

A SIMILAR SCENARIO UNFOLDS INTO FRIDAY...WITH THE PRECIPITATION
SHIELD GETTING CLOSER TO THE AREA BUT STILL LIKELY IN A DECAYING
STATE. FRIDAY AFTERNOON SHORTWAVE ENERGY WILL LIKELY BE IN THE
REGION...AND WITH AN UPPER LOW MOVING EAST THROUGH
ONTARIO/QUEBEC...HIGH PRESSURE BEHIND IT WILL BE SENDING A COLD
FRONT TOWARD THE AREA WHICH WILL HELP TO FOCUS PRECIPITATION CHANCES
FRIDAY AND FOR THE WEEKEND. THESE COMBINED FACTORS MAY BE ENOUGH
TO TRIGGER SOME THUNDERSTORMS AS WELL COMBINED WITH AFTERNOON
INSTABILITY. ALL OF THIS DEPENDENT ON CLOUD COVER FROM ANY NEARBY
MORNING CONVECTION. THEREFORE HAD TO HANG ONTO WISHY-WASHY 50 POPS
FOR FRIDAY FROM THE SMART BLEND INITIALIZATION...THOUGH THIS SEEMS
A DECENT DAY/EVENING TO HAVE A CHANCE FOR STORMS.

THINGS GET MORE MUDDLED FOR SATURDAY AS WE NEED TO SEE HOW QUICKLY
THE COLD FRONTAL BOUNDARY SINKS THROUGH AND IF IT REMAINS IN THE
AREA. THE SAME GOES FOR SUNDAY AS NORTHERN PACIFIC ENERGY ATTEMPTS
TO PHASE WITH SOME OF THE ENERGY FROM THE STILL CUTOFF LOW IN THE
WEST...AND BRING A A COLD FRONT WITH IT. SO HAVE HIGHER POPS FOR
SUNDAY THAN SATURDAY AT THIS POINT IN TIME...BUT CONFIDENCE ON THE
WEEKEND FORECAST CERTAINLY ON THE LOWER SIDE UNTIL TIMING BECOMES A
BIT MORE CLEAR.

KMD

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* EASTERLY WINDS OF 9-10 KT THROUGH THE AFTERNOON WITH SPORADIC
  GUSTS EARLY THIS AFTERNOON.

* ANOTHER LAKE BREEZE TURNING WINDS EASTERLY ON WEDNESDAY
  AFTERNOON.

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

A HIGH PRESSURE RIDGE REMAINS ANCHORED ACROSS THE LOCAL AREA. THIS
HAS PROVIDED DEVELOPMENT OF A LAKE BREEZE THAT TURNED WINDS
EASTERLY AT ORD AND MDW. THESE WINDS WILL CONTINUE THROUGH THE
AFTERNOON WITH SOME UNDULATION LIKELY...INCLUDING SPORADIC GUSTS
AROUND 15 KT EARLY THIS AFTERNOON. WIND SPEEDS WILL SHOW A GRADUAL
DIMINISHING DURING DUSK.

THE WEATHER REGIME ON WEDNESDAY IS FAVORABLE AGAIN FOR A LAKE
BREEZE DEVELOPMENT...THOUGH A LATER MORE TRADITIONAL PASSAGE TIME
THAN TODAY AND NOT AS SUPPORTIVE FOR 10 KT WINDS.

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* MEDIUM-HIGH IN WINDS THIS AFTERNOON AND MEDIUM-HIGH IN TIMING
  OF DIMINISHING BELOW 10 KT.

* MEDIUM-HIGH IN WINDS AND TIMING OF SHIFT ON WEDNESDAY
  AFTERNOON.

//OUTLOOK FOR ORD/MDW FOR 00Z THURSDAY-12Z TUESDAY...UPDATED 12Z...

* WEDNESDAY NIGHT AND THURSDAY...DRY/VFR. SOUTHEAST WINDS.
* FRIDAY...CHANCE OF SHRA/TSRA. MVFR LIKELY. NORTHEAST WINDS.
* SATURDAY...SLIGHT CHANCE OF SHRA. MVFR POSSIBLE. NORTHEAST
  WINDS.
* SUNDAY...CHANCE OF SHRA/TSRA. SOUTH WINDS.
* MONDAY...SLIGHT CHANCE OF SHRA/TSRA. GUSTY WEST WINDS.

MTF/CMS

&&

.MARINE...
122 PM CDT

A PERIOD OF QUIET WEATHER SETTING UP FOR LAKE MICHIGAN AS A SERIES
OF HIGH PRESSURE SYSTEMS CROSS THE GREAT LAKES REGION.  AS OF
TUESDAY AFTERNOON...HIGH PRESSURE IS CENTERED OVER LAKE HURON WITH A
RIDGE AXIS EXTENDING SOUTHWEST ACROSS SOUTHERN LAKE MICHIGAN AND
THEN TO THE LOWER MISSISSIPPI VALLEY WHILE LOW PRESSURE DEVELOPS IN
THE LEE OF THE ROCKIES.  LITTLE CHANCE IS EXPECTED TO THE PATTERN
THROUGH TOMORROW AFTERNOON WITH GENERALLY LIGHT WINDS WITH A
GENERALLY SOUTHERLY FETCH.  THE EXCEPTION WILL BE THE SOUTHERN LAKE
MICHIGAN NEARSHORE WATERS WHERE THE WEAK PRESSURE GRADIENT
ASSOCIATED WITH THE RIDGE IN PLACE WILL SET UP ONSHORE FLOW DUE TO
LAKE BREEZE FORMATION.  BY WEDNESDAY EVENING...THE HIGH WILL PUSH
ACROSS NEW ENGLAND AS A COMPLEX TROUGH OF LOW PRESSURE EXTENDS FROM
JAMES BAY...THROUGH THE UPPER MISSISSIPPI VALLEY...TO A DEEPENING
LOW PRESSURE CENTER OVER THE SOUTH HIGH PLAINS.  THIS WILL MAINTAIN
THE SOUTHERLY FETCH OVER LAKE MICHIGAN WITH WINDS INCREASING IN
RESPONSE TO A STRENGTHENING GRADIENT OVER THE LAKE.  HOWEVER...EVEN
WITH THIS STRENGTHENING GRADIENT...WINDS SHOULD STILL ONLY BE IN THE
10 TO 20 KT RANGE.  THE NORTHERN STREAM SYSTEMS...OVER CANADA WILL
BE MUCH MORE PROGRESSIVE THAN SYSTEMS OVER THE CENTRAL PLAINS...AS
THE LOW PRESSURE OVER CANADA QUICKLY MOVES TO NERN CANADA...WHILE AT
THE OTHER END OF THE TROUGH...LOW PRESSURE REMAINS NEARLY STATIONARY
OVER WRN KS.  THE NRN SYSTEM WILL DRAG A COLD FRONT ACROSS NRN LAKE
MICHIGAN BY THURSDAY EVENING.  ANOTHER AREA OF HIGH PRESSURE
BUILDING OUT OF SOUTHERN ONTARIO AND ACROSS THE UPPER GREAT LAKES
WILL HELP PUSH THE COLD FRONT DOWN THE LENGTH OF THE LAKE...CLEARING
THE SOUTHERN TIP OF THE LAKE BY FRIDAY EVENING.  THIS HIGH WILL VERY
SLOWLY SAG TO THE EAST AND SOUTH...KEEPING PREVAILING EASTERLY WINDS
OVER THE LAKE INTO THE WEEKEND...BEFORE VEERING TO SOUTHERLY BY
SUNDAY AS THE TROUGH OVER THE WESTERN PLAINS FINALLY LIFTS OUT
TOWARD THE UPPER MISSISSIPPI VALLEY.

KREIN

&&

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

$$

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