Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 280728
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
228 AM CDT TUE OCT 28 2014

.DISCUSSION...
252 PM CDT

RAIN/THUNDER CHANCES AND COOLER TEMPERATURES WILL BE THE INITIAL
FOCUS OF THE FORECAST THIS PERIOD...WITH OTHER HIGHLIGHTS A SECOND
NOTICEABLE COOL DOWN LATE IN THE WEEK WITH MODERATION EARLY NEXT
WEEK. AFTERNOON WATER VAPOR IMAGERY SHOWS UPPER RIDGING NOW OVER THE
GREAT LAKES WITH A CLOSED UPPER LOW PIVOTING EASTWARD ACROSS THE
NORTHERN PLAINS WITH ITS AXIS EXTENDING DOWN INTO TEXAS. LOW
AMPLITUDE RIDGING IS BUILDING OVER THE WEST COAST IN RESPONSE TO A
CLOSED LOW OFF THE BRITISH COLUMBIA COAST. AT THE SURFACE...HIGH
PRESSURE IS OVER THE EAST COAST WITH AN ELONGATED SURFACE LOW
STRETCHING FROM SOUTHERN MANITOBA TO CENTRAL IOWA BACK INTO THE
SOUTHERN PLAINS.

TONIGHT...THE CLOSED UPPER LOW OVER THE NORTHERN PLAINS WILL MOVE
EASTWARD THIS EVENING WITH A STRENGTHENING UPPER JET TRACKING
NORTHEASTWARD OVER THE GREAT LAKES AHEAD OF IT. THIS WILL ALLOW THE
ELONGATED SURFACE LOW TO THE WEST OF THE AREA TO CONSOLIDATE AND
DEEPEN OVER CENTRAL AND NORTHERN LAKE MICHIGAN INTO TUESDAY MORNING.
THIS WILL IN TURN BRING A COLD FRONT ACROSS THE AREA TONIGHT. WATER
VAPOR SHOWS SEVERAL WAVES EMBEDDED IN THE SOUTHWESTERLY MID/UPPER
FLOW AHEAD OF THE TROUGH THIS AFTERNOON. THE FIRST WAVE IS MOVING
INTO CENTRAL ILLINOIS PRODUCING SCATTERED SHOWERS AND WILL CONTINUE
TO TRACK NORTHEAST ACROSS THE SOUTHERN CWA LATE THIS AFTERNOON.
ANOTHER WAVE NOTED MOVING ACROSS EASTERN KANSAS INTO MISSOURI WILL
TRACK NORTHEAST ACROSS THE AREA EARLY TO MID EVENING WITH YET
ANOTHER WAVE LOOKING TO AFFECT THE AREA OVERNIGHT. DEEP LAYER
MOISTURE CONTINUES TO INCREASE WITH SOUNDINGS SHOWING ELEVATED
INSTABILITY ACROSS THE REGION ABOVE A STOUT LOW LEVEL CAP. EXPECT
THAT SOME SCATTERED SHOWER ACTIVITY WILL AFFECT THE FORECAST AREA IN
CONJUNCTION WITH THE FIRST AND SECOND WAVES...WITH SOME ISOLATED
THUNDER POSSIBLE. THIS WOULD BE TIMED LATE THIS AFTERNOON THROUGH
EARLY EVENING. FROM THAT POINT THE APPROACHING COLD FRONT SHOULD
BECOME MORE INVOLVED IN SHOWER AND THUNDER DEVELOPMENT WITH UPPER
FEATURES SUCH AS THE INCREASING JET MOVING INTO THE AREA. THE FRONT
SHOULD ARRIVE IN THE WESTERN CWA TOWARD MID EVENING WHICH SHOULD
INTRODUCE AN INCREASE IN SHOWER AND THUNDERSTORM COVERAGE INTO THE
EARLY OVERNIGHT. AM THINKING THAT NORTHWESTERN AREAS MAY SEE ONLY
SCATTERED ACTIVITY WITH COVERAGE INCREASING OVER THE CENTRAL CWA
FROM UP NEAR WAUKEGAN SOUTHWEST TOWARD THE MENDOTA AREA WITH
STEADILY INCREASING COVERAGE EAST OF THERE. HAVE REFINED POPS TO
SHOW LOWER POTENTIAL IN THE WEST AND NORTHWEST AND OVERALL DELAYED
THE HIGHEST POPS UNTIL AFTER MIDNIGHT OR SO...KEEPING EVENING VALUES
AT CHANCE OR LOWER. AM NOT EXPECTING ABUNDANT RAINFALL BUT ISOLATED
HEAVIER DOWNPOURS WILL BE POSSIBLE...ESPECIALLY OVERNIGHT SOUTH AND
EAST OF CHICAGO WHERE BEST ORGANIZATION IS EXPECTED. ACTIVITY WILL
BEGIN TO END FROM THE WEST OVERNIGHT AS DRIER AIR STARTS TO SPREAD
IN.

TUESDAY THROUGH THURSDAY...THE SURFACE LOW LIFTS TO JAMES BAY BY
TUESDAY EVENING WITH THE MAIN UPPER TROUGH AXIS NOT SWINGING BY
UNTIL EARLY WEDNESDAY. A STEADY FLOW OF COLD ADVECTION WILL BE
UNDERWAY TUESDAY BEHIND THE FRONT SO HIGHS MAY OCCUR EARLY IN THE
DAY BUT INCREASINGLY SUNNY SKIES MAY OFFSET THE COLD ADVECTION AND
ALLOW FOR STEADIER TEMPS. THERE WILL BE A MODEST INCREASE IN DEEP
LAYER MOISTURE AS THE TROUGH AXIS ROTATES BY WEDNESDAY MORNING SO AN
INCREASE OF CLOUDS MAY RESULT BUT AT THIS POINT ANY SHOWER POTENTIAL
WOULD BE VERY LOW AND WILL NOT HAVE ANY MENTION. LOW LEVEL FLOW WILL
TURN NORTHWESTERLY BUT IT APPEARS ANY LAKE EFFECT SHOWERS WOULD
REMAIN NORTH AND EAST OF THE AREA. THE LARGE SCALE TROUGH WILL
BROADEN OVER MUCH OF EASTERN NORTH AMERICA GOING INTO THURSDAY.
THERE HAS BEEN A CONSISTENT SIGNAL FOR A SHORTWAVE TO TRACK
SOUTHEAST ACROSS THE AREA THURSDAY BUT MOISTURE SHOULD BE MEAGER AND
FORCING NOT TERRIBLY COHERENT. WILL NEED TO WATCH THIS PERIOD FOR
SHOWER POTENTIAL BUT WILL MAINTAIN A DRY FORECAST FOR NOW. HIGHS
WILL BE IN THE 50S WEDNESDAY AND THURSDAY WITH WEDNESDAY BEING THE
COOLEST.

FRIDAY THROUGH THE WEEKEND...MEDIUM RANGE GUIDANCE CONTINUES TO
POINT TO A SHARPENING OF THE LONGWAVE TROUGH FRIDAY AS A STRONG
UPPER WAVE DIGS SOUTHWARD FROM CENTRAL CANADA. THIS IS EXPECTED TO
BRING H85 TEMPS OF NEAR -8C BY FRIDAY NIGHT WITH BREEZY NORTH LOW
LEVEL FLOW. THE TROUGH ITSELF COULD PRODUCE SOME SHOWERS THURSDAY
NIGHT BUT AGAIN THE AIRMASS LOOKS FAIRLY DRY AND THE FORCING QUICK
TO MOVE THROUGH. LAKE EFFECT PRECIP BECOMES A CONCERN WITH THE DUE
NORTH WIND AND VERY COLD AIRMASS BUT HIGH PRESSURE QUICKLY MOVING IN
MAY KEEP FAVORABLE INVERSION HEIGHTS SHORT LIVED. HIGHS FRIDAY WILL
ONLY BE IN THE 40S AND CURRENT FORECAST VALUES COULD BE A LITTLE
OPTIMISTIC...THOUGH SUNSHINE MAY HELP OFFSET THE STRONG COLD
ADVECTION SLIGHTLY. BEYOND THAT SHARP UPPER RIDGING IS EXPECTED TO
BUILD ACROSS THE PLAINS AND MISSISSIPPI RIVER VALLEY AS A DEEP
TROUGH SPREADS INTO THE WESTERN U.S. IT IS STILL NOT CLEAR HOW
QUICKLY THIS WILL SHIFT EASTWARD SO THE SPEED WITH WHICH THE
ACCOMPANYING WARMING TREND OCCURS IS STILL IN QUESTION BUT
MODERATION SHOULD BEGIN BY SUNDAY. HAVE LOW CONFIDENCE BY MONDAY
HAVING SEEN SEVERAL VARIATIONS WITH HOW THE UPPER FLOW PATTERN
EVOLVES OVER THE PAST FEW DAYS...WITH LATEST GUIDANCE SHOWING A
NORTHERN STREAM TROUGH PUSHING THE UPPER RIDGE WITH AN ASSOCIATED
SURFACE LOW OVER SOUTHERN CANADA BRINGING A FRONT ACROSS THE AREA
EARLY NEXT WEEK.

MDB

&&

.AVIATION...

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

* SSW WIND GUSTING TO 25 KT BECOMING WEST AROUND 09Z.

* SCATTERED SHRA WITH POSSIBLE EMBEDDED THUNDER...ESPECIALLY IN
  SOUTHEASTER TRACON AREA.

* WEST WIND ON TUESDAY GUSTING TO 30 KT.

KREIN

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

A DEEPENING LOW SYSTEM WILL MOVE FROM EASTERN WISCONSIN INTO
THE UPPER GREAT LAKES OVERNIGHT...WITH A COLD FRONT TRAILING TO
THE SOUTHWEST. A BAND OF SHOWERS CONTINUES AHEAD OF THE
FRONT...ALONG A STRONG LOW LEVEL JET. LATEST RADAR TRENDS INDICATE
THAT THE INDIVIDUAL PCPN ELEMENTS ARE TRACKING TO THE
NORTHEAST...WITH THE STRONG MID LEVEL FLOW...BUT THE OVERALL EWD
PROGRESSION OF THE SYSTEM IS RELATIVELY SLOW. THE GREATEST
COVERAGE OF PCPN EXTENDS SOUTH OF A LINE FROM CHICAGO TO PEORIA.
AT 06Z...THERE IS NO THUNDER OVER THE CHICAGO AREA AIRSPACE...WITH
ANY LIGHTNING WELL TO THE NORTH OVER NERN WI...WITH THE STRONGER
FORCING ASSOCIATED WITH THE LOW CENTER...OR WELL TO THE
SOUTH...WITH THE NRN EXTENT OF THE THUNDER NEAR SPRINGFIELD INVOF
AN UPPER LEVEL JET MAX. WHILE THERE COULD STILL BE A CHANCE FOR
SOME ISOLD TS OVERNIGHT...THESE CHANCES ARE LOW.

SWLY WINDS ARE STRENGTHENING IN ADVANCE OF THE COLD FRONT...WITH
GUSTS TO 25KT LIKELY FOR THE NEXT FEW HOURS. THERE SHOULD BE A
BRIEF LULL IN THE WINDS AS THE FRONTAL TROUGH PASSES ACROSS THE
REGION WHILE DIRECTION VEERS TO WLY. EXPECT THAT WINDS WILL PICK
UP AGAIN SHORTLY AFTER THE FROPA AS THE COLD ADVECTION AND
PRESSURE RISES INCREASE WITH THE LOW CENTER TRACKING TO THE
NORTHEAST. THE LATEST MODEL GUIDANCE AND SATELLITE IMAGERY TRENDS
SUGGEST THAT A MID LEVEL DRY SLOW WILL MOVE OVER THE AREA BY EARLY
MORNING. UNDER CLEARING SKIES...MIXING SHOULD INCREASE AND EXPECT
THAT THE REMAINDER OF THE DAY SHOULD BE QUITE BREEZE WITH WLY
WINDS GUSTING TO ARND 30 KT...OR EVEN SLIGHTLY HIGHER AT TIMES.

KREIN

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

* MEDIUM TO HIGH CONFIDENCE IN WIND TRENDS.

* HIGH IN PCPN TRENDS. LOW ON WHETHER ANY VCTS/TSRA WILL OCCUR.

* HIGH THAT IF ANY MVFR CONDITIONS OCCUR IT WILL BE WITHIN RAIN
  ONLY AND BRIEF.

KREIN

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

WEDNESDAY...VFR. W WIND.
THURSDAY...MAINLY VFR. SW WIND.
FRIDAY...MAINLY VFR. N WIND.
SATURDAY...MAINLY VFR. SE WIND.
SUNDAY...SLIGHT CHANCE OF SHRA. SE WIND.

MTF

&&

.MARINE...
214 AM CDT

LOW PRESSURE HAS BEEN SLUGGISH TO LIFT NORTHEAST...AND EARLY THIS
MORNING WAS JUST PUSHING EAST ACROSS CENTRAL LAKE MICHIGAN. THIS
LOW WILL THEN LIFT NORTHEAST AND DEEPEN. A TRAILING FRONTAL
BOUNDARY WILL PUSH EAST ACROSS THE LAKE BY DAYBREAK OR SHORTLY
AFTER DAYBREAK...WITH WINDS TURNING WEST AND INCREASING. SURFACE
OBSERVATIONS WEST OF THE FRONT HAVE BEEN GUSTING FROM THE WEST TO
25-30KT. AS THE LOW CONTINUES TO LIFT NORTHEAST...BY MIDDAY THE
GRADIENT TIGHTENS FURTHER ACROSS THE NORTHERN SECTIONS OF THE LAKE
AND COULD PRODUCE A PERIOD OF GALES TO 35KT EARLY THIS AFTN. BY
LATE THIS EVENING THE GRADIENT WILL CONTINUE TO DIMINISH...WITH
HIGH PRESSURE BUILDING INTO THE MID-MISSOURI VALLEY. THIS WILL
KEEP THE LAKE IN A WEST/NORTHWEST FLOW...WITH WINDS GENERALLY
REMAINING 15-25 KT OVERNIGHT INTO DAYBREAK WED.

WINDS REMAIN GENERALLY WESTERLY AND CONDITIONS GRADUALLY RELAX
THROUGH THE REMAINDER OF THE WEEK UNDER THE INFLUENCE OF AN
APPROACHING RIDGE UNTIL ANOTHER LOW CROSSES THE LAKE THURSDAY
NIGHT. COLD NORTHERLY FLOW THEN DEVELOPS FOR FRIDAY AND MOST OF
SATURDAY. THIS WILL LIKELY PRODUCE LARGER WAVES FOR A LONGER
PERIOD OF TIME ACROSS THE CENTRAL/SOUTHERN PORTIONS OF THE LAKE
GIVEN THE COLD AIR SLIDING SOUTH ACROSS THE WARMER LAKE SURFACE.

BEACHLER

&&

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

&&

$$

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