Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 300836
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
336 AM CDT TUE SEP 30 2014

.DISCUSSION...
332 AM CDT

MAIN FORECAST CONCERNS/CHALLENGES ARE WITH CLOUD COVER AND TEMPS
TODAY...AND THEN INCREASING CHANCES FOR SHOWERS AND THUNDERSTORMS
LATE WEDNESDAY NIGHT INTO THURSDAY AND THURSDAY NIGHT.

COLD FRONT NOW SOUTH OF THE CWA EARLY THIS MORNING AS LOW STRATUS
HAS MOVED OVER MUCH OF THE REGION...WHILE TEMPS CONTINUE TO FALL
INTO THE 40S AND 50S UNDER A STEADY NORTHEAST WIND. WITH ISOLATED
SHOWERS NOW EAST OF THE CWA EXPECT DRY CONDITIONS TODAY BUT WITH
THIS STRATUS LIKELY HANGING AROUND FOR SOME TIME THIS MORNING.
GUIDANCE APPEARING TO BE TOO QUICK SCATTERING OUT THESE CLOUDS
THIS MORNING AND TRYING TO INDICATE THERE WILL BE HOLES BY 12Z.
WITH THIS NOT A LIKELY SCENARIO HAVE GONE MORE PESSIMISTIC WITH
TRENDS THIS MORNING AND DONT HAVE ANY REAL CLEARING UNTIL LATE
MORNING/MIDDAY. MOST AREAS WILL LIKELY OBSERVE A SCATTERING TREND
INTO THE AFTERNOON...BUT WITH AREAS NEAR THE LAKE HOLDING ONTO
THESE CLOUDS FOR MUCH OF THE DAY. DID LOWER HIGH TEMPS AS WELL AS
SLOWED TEMP TREND THIS MORNING...WITH IT POSSIBLE FOR LOCATIONS IN
FAR NORTHEAST ILLINOIS AND NORTHWEST INDIANA NOT MAKING IT OUT OF
THE 50S TODAY.

QUIET BUT COOL NIGHT TONIGHT AS BOUNDARY LAYER FLOW VEERS AND ANY
LINGERING CLOUD COVER COMING OFF THE LAKE PUSHES NORTH INTO
WISCONSIN LATER THIS EVENING...AND MOST LOCATIONS OBSERVING CLEAR
TO PARTLY CLOUDY SKIES. FAIRLY ENERGETIC VORT MAX CURRENTLY
LIFTING NORTH THROUGH THE CENTRAL PLAINS WILL CONTINUE NORTH INTO
THE NORTHERN PLAINS TODAY INTO TONIGHT. AS THIS OCCURS...UPPER
LEVEL RIDGING WILL BE BRIEF TONIGHT AS RIDGE AXIS SHIFTS TO THE
EAST AND WE QUICKLY TRANSITION TOWARDS A SOUTHWEST FLOW PATTERN.
THIS WILL ALLOW FOR A PERIOD OF WAA GOING INTO WEDNESDAY WITH
TEMPS REBOUNDING BACK INTO THE 70S FOR MOST LOCATIONS. MADE
MINIMAL CHANGES TO GOING FORECAST HIGHS ON WEDNESDAY AS
UNCERTAINTY WITH APPROACHING MID/HIGH LEVEL CLOUD COVER COULD PLAY
INTO THE EXTENT OF WARMING THAT OCCURS.

THE BEST WAA/MOIST ADVECTION WILL REMAIN JUST TO THE WEST FOR MOST
OF THE DAY WEDNESDAY BUT THIS WILL CHANGE WEDNESDAY NIGHT AS
MID/UPPER LEVEL TROUGH DIGS ACROSS THE CENTRAL PLAINS...AND
STRENGTHENING LLJ BECOMES ORIENTED TOWARDS NORTHERN ILLINOIS. THIS
COINCIDING WITH FAIRLY ENERGETIC MID LEVEL FLOW...DEVELOPING
PRECIP SHIELD SHOULD BEGIN REACHING MOST LOCATIONS IN NORTHERN
ILLINOIS AFTER THE MIDNIGHT TIME FRAME. DESPITE INCREASING
INSTABILITY WEDNESDAY NIGHT...INSTABILITY AXIS DOES APPEAR TO STAY
JUST TO THE WEST/SOUTHWEST OF THE CWA DURING THIS TIME. ALTHOUGH
THIS MAY BE THE CASE...STRENGTHENING LLJ COULD OFFSET ANY LACKING
INSTABILITY AND SO HAVE MAINTAINED CHANCE THUNDER WORDING OVER THE
ENTIRE CWA...WITH THE FAR WEST AND SOUTHWEST AREAS LIKELY
OBSERVING BEST CHANCES FOR THUNDER. MOISTURE WILL CONTINUE TO
INCREASE DURING THIS TIME AND DO FEEL THERE COULD BE SOME PERIODS
OF MORE MODERATE RAINFALL...BUT THIS WONT LIKELY OCCUR UNTIL VERY
LATE IN THE NIGHT AND TOWARDS EARLY THURSDAY MORNING.

BETTER AGREEMENT OBSERVED WITH VARYING MODELS THIS MORNING
REGARDING APPROACHING MID/UPPER LEVEL TROUGH AND ASSOCIATED
SURFACE FEATURE THURSDAY AND THURSDAY NIGHT. SURFACE LOW SHOULD
LIFT RIGHT ALONG THE MISSISSIPPI RIVER AREA INTO SOUTHWEST
WISCONSIN THURSDAY AND THEN INTO THE GREAT LAKES REGION THURSDAY
NIGHT. CONTINUED LARGE SCALE SUPPORT DURING THIS PERIOD WILL ALLOW
FOR A WET DAY THURSDAY INTO THURSDAY NIGHT AS PERIODS OF SHOWERS
AND THUNDERSTORMS ARE LIKELY. A SLOWER DEPARTING TREND WILL OCCUR
THURSDAY NIGHT...AND DID KEEP LIKELY WORDING LONGER INTO THE
NIGHT. ALTHOUGH MOISTURE AND INSTABILITY WILL CONTINUE TO INCREASE
DURING THIS TIME...IT DOES LOOK LIKE THE BEST INSTABILITY WILL
REMAIN SOUTH OF THE CWA. SO AT THIS TIME...AM NOT OVERLY CONCERNED
WITH ANY SEVERE POTENTIAL BUT AM MORE CONCERNED WITH HEAVY
RAINFALL AND POSSIBLE LOCALIZED FLOODING...ESPECIALLY AS THE BEST
OVERALL MOIST ADVECTION OCCURS INTO THURSDAY NIGHT.

RODRIGUEZ

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 06Z...

* CIGS AROUND 1000 FT CONTINUING THROUGH THE OVERNIGHT WITH
  OCCASIONAL LOWERING TO 800-900 FT...ESPECIALLY AT ORD.

* MVFR CIGS EXPECTED TO CONTINUE INTO THE EVENING WITH LIFTING
  DURING THE AFTERNOON.

* NORTHEAST WINDS WILL DIMINISH LATE TONIGHT AND REMAIN NEAR 10 KT
  THIS AFTERNOON.

MDB

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

LOW MVFR CIGS CONTINUE TO BE SPREAD ACROSS THE THE TERMINALS AND
WILL REMAIN IN PLACE OVERNIGHT. SOME PERIODIC LOWERING TO IFR WILL
LIKELY OCCUR BUT CIGS UPSTREAM HAVE IMPROVED SLIGHTLY IN SPOTS
LIKELY BECAUSE OF AN INFLUX OF DRIER AIR. EXPECT THAT THE LOWEST
CIGS MAY BE OCCURRING NOW THROUGH THE NEXT FEW HOURS THEN MAY
START TO LIFT TOWARDS DAYBREAK...WITH STEADIER LIFTING THROUGH THE
MORNING. AM THINKING THAT RFD/DPA MAY SCATTER DURING THE AFTERNOON
AT SOME POINT WITH FLOW OFF THE LAKE KEEPING CLOUD COVER BROKEN AT
ORD/MDW/GYY THOUGH SOME SCATTERING COULD OCCUR. LOW LEVEL FLOW AT
CLOUD LEVEL TURNS SOUTHEASTERLY THIS EVENING WHICH MAY PROMOTE AN
INCREASE IN CLOUD COVER AS WELL AS PUSH IT FURTHER INLAND.
THEREFORE A RETURN TO MVFR CIGS IS POSSIBLE AT DPA/RFD THIS
EVENING. WILL KEEP COVERAGE SCATTERED FOR NOW. NORTHEAST SURFACE
WINDS WILL BE GRADUALLY EASING THROUGH THE REST OF THE NIGHT AND
GENERALLY BE NEAR 10 KT FOR THE MORNING/AFTERNOON BEFORE TURNING
EAST THIS EVENING.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 06Z...

* HIGH CONFIDENCE IN CIGS HOVERING AROUND 1000 FT OVERNIGHT.
  MEDIUM CONFIDENCE IN OCCASIONAL LOWERING BELOW 1000
  FT...ESPECIALLY AT ORD.

* MEDIUM-HIGH CONFIDENCE IN MVFR CONTINUING THROUGH THE DAY...HIGH
  CONFIDENCE IN BASES LIFTING DURING THE AFTERNOON. SCATTERING IS
  POSSIBLE.

* HIGH CONFIDENCE IN WIND TRENDS.

MDB

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

WEDNESDAY...VFR. SOUTHEAST WINDS.

THURSDAY...TSRA LIKELY...MVFR POSSIBLE. SOUTH WINDS TURNING
SOUTHWEST LATE.

FRIDAY...SLIGHT CHANCE SHRA...MVFR POSSIBLE. BREEZY WEST WINDS.

SATURDAY...VFR. WEST WINDS.

SUNDAY...SLIGHT CHANCE SHRA. WEST-SOUTHWEST WINDS.

RATZER

&&

.MARINE...
257 AM CDT

STRONG NORTHERLY WINDS WILL GRADUALLY DECREASE IN SPEED INTO THE
AFTERNOON AS HIGH PRESSURE RIDGING MOVES ACROSS LAKE MICHIGAN. THE
PRESSURE GRADIENT WILL TIGHTEN UP SOMEWHAT WEDNESDAY AS THE RIDGE
SHIFTS EAST AND LOW PRESSURE OVER THE CENTRAL HIGH PLAINS TRACKS
NORTH TO MANITOBA BY WEDNESDAY AFTERNOON. THIS WILL ALLOW WINDS TO
SHIFT TO THE SOUTHEAST TONIGHT. WILL CONTINUE WITH THE SMALL CRAFT
ADVISORY THROUGH THIS AFTERNOON. STEADY SOUTH TO SOUTHEAST WINDS
WILL CONTINUE INTO THURSDAY WHEN LOW PRESSURE DEVELOPS OVER THE
TEXAS/OKLAHOMA PANHANDLE AND TRACKS NORTHEAST TO THE U.P. OF
MICHIGAN THURSDAY NIGHT. FORECAST MODELS HAVE STRUGGLED WITH THE
TRACK AND INTENSITY OF THIS SYSTEM THOUGH THERE HAS BEEN VERY
GENERAL AGREEMENT IN THE LOW TRACKING NORTHWEST OF THE LAKE AND
DEEPENING WHILE DOING SO. WHILE SPECIFICS ARE STILL UNDETERMINED
THE STAGE WILL BE SET FOR A PERIOD OF STRONGER WINDS ACROSS THE
LAKE...STARTING OUT SOUTHERLY THEN TURNING WESTERLY AS A COLD
FRONT PASSES THURSDAY NIGHT. SEVERAL OTHER MORE SUBTLE SURFACE
TROUGHS MAY CROSS FRIDAY INTO SATURDAY ALLOWING WINDS TO FLUCTUATE
BETWEEN WEST AND NORTHWEST. A PERIOD OF GALES STILL LOOKS
POSSIBLE...PRIMARILY AFTER THE PASSAGE OF THE MAIN FRONT AS COLDER
AIR SPREADS IN. WIND SPEEDS WILL GRADUALLY EASE GOING INTO SUNDAY.

MDB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 7 PM TUESDAY.

&&

$$

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