Area Forecast Discussion
Issued by NWS Chicago, IL

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS63 KLOT 280847
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
347 AM CDT SAT MAR 28 2015

.SHORT TERM...
306 AM CDT

THROUGH TONIGHT...

SURFACE HIGH PRESSURE UNDER DRY NORTHWEST UPPER FLOW TODAY WILL
OFFER A SUNNY SKY AND LITTLE IN THE WAY OF SENSIBLE WEATHER. A LAKE
BREEZE IS EXPECTED TO DEVELOP AND SPREAD INLAND A COUPLE TIERS OF
COUNTIES EARLY TO MID AFTERNOON. THIS WILL STUNT WARMING SOME AND
MAYBE EVEN LEAD TO A DROP BY A COUPLE DEGREES FOR PLACES NEAR THE
LAKE SHORE.

THE LOW-LEVEL AIR MASS WILL MODIFY SOME TODAY AND WITHOUT AS STRONG
OF A LAKE ADVECTIVE COMPONENT IN THE WIND SPEED...TEMPERATURES
SHOULD RESULT AROUND 5F HIGHER. THE LIGHT ONSHORE FLOW DURING LATE
MARCH ON AVERAGE RESULTS IN ABOUT A 6-7 DEGREE DIFFERENCE BETWEEN
THE FAR DOWNTOWN CHICAGO AND THE FAR OUTLYING METRO AND AM NEAR THAT
IN THE FORECAST FOR TODAY...ABOUT 38-39 OUTLYING TO 34 DOWNTOWN.
TAGGING 40 IS EXPECTED TOWARD THE I-39 CORRIDOR.

THE DRY AIR MASS TODAY AWAY FROM THE LAKE MODIFIED AIR COULD RESULT
IN DEW POINTS FALLING INTO THE SINGLE DIGITS DURING PEAK MIXING
EARLY TO MID AFTERNOON.

MTF

&&

.LONG TERM...

SUNDAY THROUGH SUNDAY NIGHT...

MAIN CONCERNS ARE WITH STRONG SOUTHWEST WINDS AND RAIN SHOWERS
AHEAD OF AN APPROACHING COLD FRONT. PART OF STRONG UPPER WAVE/VORT
MAX MOVING ONTO PAC NW COAST AS NOTED ON W/V IMAGERY THIS MORNING
WILL DIVE SOUTHEASTWARD TOWARD THE AREA. IN ADDITION...ROBUST LOW
LEVEL JET OF 50+ KT WILL FOCUS A NARROW AXIS OF STRONG MOISTURE
TRANSPORT...WITH WAA/ISENTROPIC ASCENT ALSO AIDING IN PRECIP
BLOSSOMING. FAIRLY STEEP LAPSE RATES ALOFT COULD RESULT IN BRIEF
PERIODS OF MODERATE INTENSITY SHOWERS. THERE IS SOME CONCERN THAT
PRECIP COULD START AS LIGHT SNOW OR A MIX AT ONSET IN PARTS OF THE
NORTHERN CWA...AIDED BY WET BULBING OF INITIALLY DRY COLUMN...BUT
RAPID WARMING OF THE BOUNDARY LAYER SHOULD CAUSE ANY INITIAL
FROZEN PTYPE TO GO OVER TO RAIN. DEPARTURE OF EXPANSIVE HIGH
PRESSURE TO THE SOUTHEAST AND APPROACH OF COLD FRONTAL TROUGH
TRAILING FROM LOW PRESSURE NEAR OR NORTH OF LAKE SUPERIOR WILL
RESULT IN FAIRLY IMPRESSIVE ISALLOBARIC PRESSURE FALLS. THUS
SOUTH-SOUTHWEST WINDS WILL BECOME QUITE STRONG...WITH GUST SPEEDS
UP TO ~40 MPH SUPPORTED BY MODEL SOUNDINGS. THE STRONG WINDS WILL
COUNTERACT HIGHS IN THE MID TO UPPER 40S TO MAKE FOR A RAW DAY.

HAVE BUMPED UP POPS A BIT MORE WITHIN THE CATEGORICAL RANGE FROM
THE LATE MORNING THROUGH EARLY AFTERNOON...THEN A TRAILING UPPER
WAVE SHOULD KEEP SOME SHOWER ACTIVITY GOING INTO THE NORTHEAST
HALF ESPECIALLY OF THE CWA IN THE LATE AFTERNOON AND POSSIBLY
EARLY EVENING DEPENDING ON PATH OF THE SHORT WAVE. WINDS WILL TURN
WEST AND THEN DIMINISH BEHIND THE COLD FRONTAL PASSAGE...WITH
CLEARING SKIES AND LOWS FALLING INTO THE LOWER 30S.

MONDAY THROUGH FRIDAY...

UPPER LEVEL PATTERN WILL DEAMPLIFY SOME...WHICH WILL KEEP THE COLD
AIR LOCKED TO THE NORTH IN CANADA. OVERALL...THIS WILL RESULT IN A
MUCH MILDER WEEK...THOUGH THERE IS UNCERTAINTY IN THE GUIDANCE IN
HOW WARM CERTAIN DAYS WILL BECOME. THUS STAYED CLOSE TO A GUIDANCE
SMART BLEND FOR TEMPERATURES. MONDAY SHOULD BE A FAIRLY NICE DAY
IN THE MID TO UPPER 50S AND NO LAKE COOLING ANTICIPATED.
DIFFERENCES ALSO CONTINUE ON HANDLING OF A CLIPPER TYPE SYSTEM
MONDAY NIGHT...THOUGH 00Z ECMWF DID TREND NORTH AND 00Z
OPERATIONAL GFS ALSO REMAIN WELL NORTH. MAINTAINED LOWER END
CHANCE AND SLIGHT POPS FOR NOW NORTH OF THE KANKAKEE RIVER. WARMER
END OF GUIDANCE WOULD YIELD AT LEAST MID TO UPPER 60S BY
WEDNESDAY...THEN NEXT FRONTAL SYSTEM COULD ARRIVE WEDNESDAY
NIGHT...WITH A SLOWING TREND ON LAST FEW MODEL CYCLES. ADDED
SLIGHT CHANCE THUNDER WORDING IN SOUTH...AS GFS AND SOME ENSEMBLE
MEMBERS DO BRING AN IMPRESSIVE SURGE OF HIGHER DEWPOINTS
NORTHWARD. UNCERTAINTY THEN REALLY GROWS LATER IN THE WEEK...WITH
SOME POTENTIAL FOR A STRONGER LOW PRESSURE AREA AS PER 00Z
OPERATIONAL ECMWF.

RC

&&

.AVIATION...

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

* LAKE BREEZE AIDING IN WINDS POSSIBLY TOPPING 9 KT THIS
  AFTERNOON.
* 40-45 KT SW WINDS BETWEEN 1000-2000 FT NEAR DAYBREAK SUNDAY
  POSSIBLY CREATING LLWS.

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

HIGH PRESSURE WILL REMAIN DIRECTLY OVER THE AREA THROUGH TODAY
BEFORE SHIFTING EAST TONIGHT. THIS WILL ALLOW FLOW FROM THE
NORTHEAST OR EAST-NORTHEAST TO INCREASE DURING THE EARLY
AFTERNOON...WITH SPEEDS OF 9 KT OR SLIGHTLY OVER POSSIBLE FOR AT
LEAST A COUPLE HOUR WINDOW DURING THE AFTERNOON. SURFACE WINDS
WILL TURN SOUTHERLY TONIGHT AS LOW PRESSURE APPROACHES FROM THE
NORTHWEST. SURFACE SPEEDS SHOULD GRADUALLY INCREASE LATE SATURDAY
NIGHT WHILE LOW-LEVEL JET WINDS INCREASE MARKEDLY ABOVE 1000 FT
OR SO...POSSIBLY RESULTING IN LLWS NEAR DAYBREAK SUNDAY.

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

* MEDIUM IN TIMING AND MAGNITUDE OF LAKE BREEZE. LOW IN DURATION
  OF SPEEDS AT 9+ KT.
* MEDIUM-HIGH IN 40-45KT SW LOW-LEVEL JET WINDS NEAR DAYBREAK
  SUNDAY. LOW IN TRUE LLWS.

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...MVFR CIGS DEVELOPING WITH A PERIOD OF RAIN.

MONDAY...PRIMARILY VFR DURING DAY. CHANCE OF SHRA AT NIGHT.

TUESDAY...CHANCE OF MVFR CIGS EARLY.

WEDNESDAY...VFR.

THURSDAY...CHANCE OF SHRA...OTHERWISE VFR.

MTF/IZZI

&&

.MARINE...
242 PM CDT

WINDS ARE COMING DOWN AS HIGH PRESSURE SLIDES EAST TOWARD THE
WESTERN LAKES.  HOWEVER WAVES WILL REMAIN HAZARDOUS TO SMALL CRAFT
INTO SATURDAY MORNING.  THE HIGH SHIFTS SOUTHEAST OVER THE OHIO
VALLEY SATURDAY EVENING WITH WINDS BECOMING SOUTHWEST TO 30 KT
OVERNIGHT.  THE NEXT LOW PASSES OVER ONTARIO SUNDAY AND WINDS
INCREASE TO GALES ACROSS THE LAKE.  MAX GUSTS OF 45 KT WILL BE OVER
THE NORTHERN END OF THE LAKE...AND WILL ISSUE A GALE WATCH FOR ALL
OF THE OPEN WATERS. GALES ARE POSSIBLE OVER THE NEARSHORE WATERS AS
WELL BUT WILL HOLD OFF ON ISSUING A WATCH AS CONFIDENCE IN NOT HIGH
ENOUGH FOR A WATCH AT THIS POINT.  THE LOWS COLD FRONT SWINGS OVER
THE LAKE SUNDAY EVENING WITH WINDS DIMINISHING AND BECOMING WEST TO
30 KT.  A WEAK RIDGE PASSES OVER THE LAKE MONDAY WITH A SURFACE LOW
MOVING OVER THE LAKE TUESDAY MORNING.  ANOTHER HIGH PRESSURE SYSTEM
REACHES THE WESTERN LAKES MID WEEK THEN A STRONG LOW SLIDES NORTH OF
THE LAKE THURSDAY.

JEE

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 10 AM SATURDAY.

     SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...4 AM SUNDAY TO 10
     AM SUNDAY.

     GALE WARNING...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...10 AM
     SUNDAY TO 4 PM SUNDAY.

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

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.