Area Forecast Discussion
Issued by NWS Chicago, IL

Home | Current Version | Previous Version | Text Only | 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 260741
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
241 AM CDT SUN OCT 26 2014

.DISCUSSION...
236 AM CDT

//SHORT TERM//
THROUGH SUNDAY NIGHT...FOR THE REMAINDER OF THE NIGHT
AND INTO SUNDAY MORNING...AND INDEED THROUGH MUCH OF THE DAY ON
SUNDAY...CLEAR SKIES AND LIGHT WINDS WILL BE THE MAIN FEATURE AS SFC
HIGH PRESSURE SLIDES ACROSS THE AREA BEFORE SETTLING INTO THE OHIO
VALLEY SUNDAY AFTERNOON.  OVERNIGHT...THE CLEAR SKIES AND LIGHT
WINDS SHOULD ALLOW FOR AMPLE RADIATIVE COOLING...WITH TEMPS DROPPING
INTO THE MIDDLE TO UPPER 30S BY DAYBREAK...EXCEPT FOR THE CHICAGO
AREA URBAN HEAT ISLAND...WHICH SHOULD ONLY DROP INTO THE LOWER 40S.
A FEW SHELTERED...LOW LYING LOCATIONS COULD EVEN SEE TEMPERATURES
DROP INTO THE LOWER 30S AS DEWPOINTS CONTINUE TO SLOWLY DROP INTO
THE UPPER 20S BY DAYBREAK.  AFTER SUNRISE...TEMPERATURES SHOULD
CLIMB RAPIDLY UNDER AMPLE SUNSHINE AND A DRY AIRMASS.  THE ONE
CONCERN WILL BE TEMPERATURES ALONG THE LAKE FRONT.  THE WEAK
PRESSURE GRADIENT AND DIFFERENTIAL HEATING BETWEEN THE LAND AND LAKE
MICHIGAN SHOULD ALLOW FOR A LAKE BREEZE TO DEVELOP.  THE MAIN
QUESTION REGARDING THE LAKE BREEZE WILL BE TIMING SINCE IF IT FORMS
LATE ENOUGH IN THE AFTERNOON...LAKEFRONT LOCATIONS COULD SEE
TEMPERATURES REACH INTO THE MIDDLE 60S...BEFORE DROPPING OFF AS THE
BOUNDARY PUSHES INLAND.  AS FOR THE REMAINDER OF THE
CWA...TEMPERATURES WILL STILL BE ABOVE SEASONAL NORMAL LEVELS...
THOUGH NOT QUITE AS HIGH AS SATURDAY...WITH HIGHS EXPECTED TO REACH
INTO THE UPPER 60S TODAY.

SUNDAY EVENING INTO SUNDAY NIGHT...AS THE HIGH CONTINUES TO BUILD
TO THE EAST...LOW PRESSURE WILL DEVELOP OVER THE CNTRL PLAINS
WHILE A DEEPER LOW DEVELOPS OVER THE SRN CANADIAN ROCKIES. THE
DEVELOPING SFC LOW OVER THE CNTRL PLAINS WILL SET A STRONG PATTERN
OF WARM ADVECTION...WITH A WARM FRONT DEVELOPING FROM THE LOW
CENTER OVER THE NE/IA BORDER INTO THE LOWER OHIO VALLEY BY EARLY
SUNDAY EVENING. AHEAD OF THE WARM FRONT...STRENGTHENING SELY WINDS
WILL DEVELOP OVERNIGHT AS THE WARM FRONT SLOWLY LIFTS NORTH. WARM
ADVECTION AND ISENTROPIC LIFT NORTH OF THE WARM FRONT WILL BRING
INCREASING CLOUD COVER THROUGH THE EVENING AS WELL AS INCREASING
CHANCES FOR PCPN. THE STRONGEST FORCING WILL BE IN THE PATH OF THE
SFC LOW AS IT TRACKS NEWD THROUGH IA AND INTO SWRN WI BY EARLY
MONDAY MORNING. WHILE THE CWA WILL SEE INCREASING CLOUD
COVER...THE BEST CHANCES FOR ANY PCPN WILL BE NORTH OF THE IL/WI
BORDER IN THE ZONE OF STRONGEST ISENTROPIC LIFT...THOUGH THE NRN
TIER COUNTIES COULD POSSIBLY SEE SOME LIGHT SHOWERS. WITH THE
INCREASING WARM ADVECTION AND CLOUD COVER OVERNIGHT...TEMPERATURES
SHOULD REMAIN RELATIVELY MILD...WITH OVERNIGHT LOWS IN THE LOWER
TO MIDDLE 50S.

KREIN


//MEDIUM TERM//
MONDAY THROUGH TUESDAY...
THE WEEK KICKS-OFF WITH VERY MILD TEMPERATURES...AS TEMPS MAY TAG
80 DEGREES ACROSS PORTIONS OF THE FORECAST AREA. HOWEVER AS CAN BE
EXPECTED WITH VERY ANOMALOUS CONDITIONS...THE POTENTIAL EXISTS FOR
THUNDERSTORMS IN THE LATE AFTERNOON/EVENING TIMEFRAME MONDAY. MID-
LVL RIDGING OVER THE GREAT LAKES WILL BEGIN TO FLATTEN EARLY
MON...AS A ROBUST 500MB TROUGH DIGS INTO THE ROCKIES. SFC FLOW
WILL BE TURNING SOUTHWESTERLY AND MAY BACK FURTHER TO THE SOUTH BY
MIDDAY MON. THIS WILL ALLOW A WARM FRONTAL BOUNDARY TO LIFT
NORTH...ALLOWING STEADY ADVECTION OF MUCH WARMER/MOIST AIR INTO
THE REGION. DEW POINTS WILL PUSH INTO THE 50S...AND POSSIBLY NEAR
60 DEG BY MID- AFTN MON. GUIDANCE HAS BEEN RELATIVELY CONSISTENT
WITH SUGGESTING THE LLVLS WILL BECOME CAPPED SO NOT EXPECTING MUCH
WEATHER PRIOR TO 21Z MON. THEN THE SFC SHUD WARM ENOUGH TO
DISSOLVE THE CAP...WITH STRONG 0-3KM SHEAR DEVELOPING BY EARLY
EVE. CAPE DOESN`T LOOK TO BE TOO FAVORABLE WITHIN THE ENVIRONMENT
LATE AFTN/EARLY EVE...ALTHOUGH MUCAPE COULD NEAR 1000J/KG. LAPSE
RATES WILL STEEPEN...AND COULD SUPPORT A FEW MARGINALLY SEVERE
HAIL.

PWAT VALUES WILL STEADILY INCREASE IN EXCESS OF 1"...NEARING 1.5" BY
LATE MON AFTN/EVE. WHILE IT APPEARS LIKELY THAT STORMS WILL BE
PROGRESSIVE GIVEN THE STRENGTHENING LLVL FLOW...THE MOISTURE RICH
ENVIRONMENT AND MARGINAL 850MFLUX COULD WARRANT A FEW STORMS
PRODUCING MODERATE TO BRIEF HEAVY DOWNPOURS. OVERNIGHT MON WITH
CONTINUED CHANCES OF PRECIP/STORMS...STEADILY SHIFTING EAST BY TUE
MORNING...THE CLOUDS WILL LIKELY KEEP TEMPS MILD MON NIGHT IN THE
MID/UPR 50S TO PERHAPS ARND 60 IN THE SOUTHEAST CWFA.

TROUGH AXIS WILL BE PIVOTING OVERHEAD TUE...WITH A DRY WEDGE WORKING
IN QUICKLY BY MIDDAY TUE AND BRINGING AN END TO THE PRECIP. SFC LOW
WILL CONTINUE TO DEEPEN ACROSS NORTHERN LOWER MICHIGAN TUE
AFTN...SLOWLY LIFTING NORTHEAST INTO ONTARIO/QUEBEC. MUCH
COOLER/DRIER AIR WILL BE ADVECTING BACK INTO THE REGION TUE
AFTN/EVE...AS TEMPS MAY TOP OUT ARND 60/LOW 60S EARLY IN THE DAY
BEFORE BEGINNING TO FALL A FEW DEGREES TUE AFTN INTO THE MID/UPR
50S. THERMAL TROUGH CONTINUES TO SLIDE OVERHEAD TUE NGT...AND WITH
P-CLOUDY SKIES...TEMPS SHUD COOL INTO THE UPR 30S/LOW 40S.

//LONG TERM//
WEDNESDAY THROUGH NEXT WEEKEND...

WILL MOTHER NATURE PROVIDE A TREAT OF DRY WEATHER FRI AFTN/EVE OR
WILL WE BE TRICKED. FROM MID-WEEK INTO THE UPCOMING WEEKEND...THE
PATTERN WILL BE TRANSITIONING TOWARDS A RIDGE/TROUGH SETUP ACROSS
THE CONUS. CURRENT ENSEMBLE PROGS PAINT A HIGH AMPLITUDE RIDGE
DEVELOPING ACROSS THE ROCKIES STRETCHING NORTH INTO THE CANADIAN
ROCKIES WED/THUR...WHILE TROUGHING DIGS INTO THE SOUTHWEST CONUS
AND TROUGHING DIGS INTO THE SOUTHEAST STATES. THEN THE FIRST HALF
OF NEXT WEEKEND THE RIDGE WILL BEGIN TO FLATTEN. A SHORTWAVE WILL
TRAVERSE THE REGION THUR BRINGING A CHC FOR LGT PRECIP THUR/EARLY
FRI.

THERE HAS BEEN SOME CONSISTENCY IN THE LATER PERIODS THAT TEMPS WILL
COOL FRI/SAT OF NEXT WEEK INTO THE 40S FOR HIGHS WITH OVERNIGHT LOWS
IN THE MID 20S/LOW 30S AS A SFC RIDGE ARRIVES.

BEACHLER

&&

.AVIATION...

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

* LLWS LIKELY OVERNIGHT WITH SFC WINDS WNWLY AT ARND 5 KT AND NWLY
  ARND 30-35 KT AT 1500 FT AGL.

* CHANCE FOR AN EASTERLY SURFACE WIND SHIFT WITH A LAKE BREEZE
  SUNDAY AFTERNOON.

KREIN

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

WNWLY WINDS WILL CONTINUE TO DIMINISH TO LGT/VRBL OVERNIGHT AS A
STRONG NOCTURNAL INVERSION FORMS UNDER CLEAR SKIES. WINDS ALOFT AT
THE INVERSION LAYER QUICKLY BECM NWLY 30-35KT...SETTING UP THE
LIKELIHOOD FOR LLWS...SO LLWS HAS BEEN ADDED TO THE FORECAST.
ANTICIPATE THAT WITH CLEAR SKIES AND A DRY AIRMASS IN PLACE...THE
BOUNDARY LAYER WILL QUICKLY BECOME WELL MIXED AND THE POTENTIAL
FOR LLWS SHOULD END BY 12-13Z. AS SFC HIGH PRESSURE BUILDS ACROSS
THE REGION THE REMAINDER OF THE DAY WILL BE CLEAR AND DRY WITH
LIGHT WINDS. THE WEAK PRESSURE GRADIENT SHOULD ALLOW FOR THE
DEVELOPMENT OF A LAKE BREEZE. THERE IS STILL SOME QUESTION AS TO
HOW FAR INLAND THE BOUNDARY WILL PUSH AND HOW STRONG WINDS WILL BE
BEHIND THE BOUNDARY. GIVEN THAT THE WATER-LAND TEMP DIFFERENTIAL
IS NOT THAT GREAT...FEEL THAT THE BOUNDARY WILL BE SLOW TO PUSH
INLAND...LIKELY NOT PUSHING THROUGH ORD/MDW UNTIL 22-23Z. ALSO IN
THE ABSENCE OF A STRONG PUSH BEHIND THE BOUNDARY...WINDS SHOULD
REMAIN LESS THAN 10KT WHILE BACKING TO ELY. OVERNIGHT SUNDAY
NIGHT...THE HIGH PRESSURE WILL SHIFT TO THE EAST AS LOW PRESSURE
MOVES ACROSS THE PLAINS. WINDS WILL TREND TO SELY THOUGH THE
EVENING AND SLY OVERNIGHT. INCREASING WARM ADVECTION THROUGH THE
NIGHT SHOULD BRING INCREASING CLOUD COVER...BUT ANTICIPATE THAT
BASES WILL REMAIN AT THE LOWER END OF VFR THROUGH THE NIGHT.

KREIN

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

* HIGH CONFIDENCE IN SURFACE WINDS THROUGH EARLY SUNDAY AFTERNOON.
  MEDIUM CONFIDENCE IN TIMING OF THE LAKE BREEZE AND WIND SPEED
  BEHIND THE LAKE BREEZE.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN

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

MONDAY...SHRA LIKELY MAINLY DURING THE EVE WITH A CHANCE OF TSRA.
         SW WINDS.
TUESDAY...CHANCE OF SHRA DURING THE MORNING WITH A SLIGHT
          CHANCE OF TSRA. W WINDS.
WEDNESDAY...VFR. W WINDS.
THURSDAY...CHANCE OF SHRA. W WINDS TURNING N.
FRIDAY...SLIGHT CHANCE OF SHRA. NE WINDS.

MTF

&&

.MARINE...
217 AM CDT

A FEW ACTIVE PERIODS SETTING UP ACROSS THE GREAT LAKES REGION OVER
THE NEXT FEW DAYS...AS WEAK RIDGING CENTERED OVER THE OHIO VALLEY
SHIFTS EAST BY THIS EVENING. THIS WILL ALLOW FLOW TO TURN
SOUTHEASTERLY TO SOUTHERLY MON. A DEVELOPING TROUGH OF LOW
PRESSURE STRETCHING FROM THE CENTRAL PLAINS NORTH INTO THE
NORTHERN PLAINS WILL SLOWLY CONSOLIDATE INTO A LOW ACROSS LOWER
MICHIGAN TUE MORNING. THE GRADIENT IS POISED TO INCREASE ACROSS
THE NORTHERN TIER AND SOUTHERN TIER OF LAKE MICHIGAN...WITH GUSTS
NEARING 25KT AND POSSIBLY A FEW GUSTS TO 30KT MON NGT. IT IS
POSSIBLE SMALL CRAFT CONDS COULD DEVELOP MON...BUT WITH MUCH
WARMER/MOIST AIR FLOWING ACROSS THE SLIGHTLY COOLER LAKE THE WIND
GUSTS COULD BE SLIGHTLY DIMINISHED.

THEN THE LOW IS EXPECTED TO DEEPEN AS IT LIFTS NORTH ACROSS
EASTERN LAKE SUPERIOR TUE MIDDAY...WITH A TIGHT GRADIENT
DEVELOPING ONCE AGAIN ACROSS THE ENTIRE LAKE AND PRODUCING WEST TO
NORTHWEST WINDS NEAR BETWEEN 25 TO 30 KT TUE EVENING/WED MORNING.
HIGH PRESSURE THEN SLOWLY BUILDS BACK INTO THE REGION WED/THUR
WITH LIGHTER WEST/NORTHWEST WINDS DEVELOPING.

BEACHLER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 10 AM 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.