Area Forecast Discussion
Issued by NWS Chicago, IL

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831
FXUS63 KLOT 220710
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
210 AM CDT FRI MAY 22 2015

.UPDATE...
759 PM CDT

ONLY MINOR ADJUSTMENTS HAVE BEEN MADE TO THE GOING FORECAST. A
SOMEWHAT WEAK UPPER WAVE...BUT AT EDGE OF A STRONG POLAR LOBE
WITH -37C OBSERVED AT 500MB IN ONTARIO...IS MOVING SOUTHEAST
ACROSS CENTRAL LAKE MICHIGAN. AN ASSOCIATED SURFACE COLD FRONT IS
DRAPED WEST-TO-EAST ACROSS CENTRAL WI AND ACCELERATING DOWN THE
WESTERN SHORE OF LAKE. CONVERGENCE WITH THIS FRONT AND THE STEEP
LAPSE RATES ALOFT AS SAMPLED BY THE 00Z GRB SOUNDING HAVE AIDED IN
SCATTERED SHOWERS ACROSS EASTERN WI AND CENTRAL LAKE MI EARLY
THIS EVE. THESE ARE STRUGGLING WITH VERY DRY AIR EVIDENCED BY THE
GRB SOUNDING AND JUST THE NATURE ON SATELLITE AND RADAR MOSAIC
LOOPS. IT IS POSSIBLE FAR NORTHEAST ILLINOIS AND NORTHWEST INDIANA
GET GRAZED WITH SOME SPRINKLES BETWEEN 10 PM AND 2 AM. A MORE
NOTEWORTHY FEATURE WILL BE THE TEMPERATURE DROP BEHIND THE
FRONT...SINCE READINGS ARE LIKELY TO ONLY SLOWLY FALL UNTIL FROPA
AND THEN SHARPLY DROP...ESPECIALLY NEAR THE LAKE FRONT. READINGS
SHOULD BE IN THE 40S NEAR THE LAKE FRONT WITHIN 1-2 HOURS AFTER
FROPA...AND 40S ARE FORECAST AREAWIDE FOR DAYBREAK ON FRIDAY.

MTF

&&

.SHORT TERM...
247 PM CDT

THROUGH SATURDAY...

HIGH PRESSURE IS OVER THE PLAINS AND SPREADING ACROSS CENTRAL AND
SOUTHERN IL.  EARLY MORNING CLOUDS HAVE CLEARED NICELY AND
TEMPERATURES ROSE QUICKLY IN RESPONSE TO THE AMPLE SUNSHINE.  A WEAK
LOW PRESSURE TROUGH AND COLD FRONT ARE OVER THE NORTHERN END OF LAKE
MICHIGAN AND THE FRONT WILL SLIDE DOWN THE LAKE OVERNIGHT. WHILE A
FEW LIGHT RAIN SHOWERS ARE EXPECTED WITH FRONT OVER THE
LAKE...THINKING IT WILL BE TOO DRY FOR PRECIP TO FALL OVER THE LAND
BASED CWA.  WINDS BECOME NORTH BEHIND THE FRONT LATE TONIGHT INTO
FRIDAY MORNING.

WINDS DROP OFF QUICKLY AS HIGH PRESSURE BUILDS OVERHEAD. FLOW WILL
BE OFF THE LAKE AND EXPECTING WINDS AROUND 10 MPH ALONG THE LAKE
FRIDAY.  AREAS WELL AWAY FROM THE LAKE WILL GET INTO THE MID 60S TO
AROUND 70...WHILE AREAS ALONG THE LAKE WILL ONLY BE IN THE 50S TO
LOW 60S.  OUTSIDE OF CHILLIER TEMPS ALONG THE LAKE...EXPECTING A
BEAUTIFULLY SUNNY DAY. OVERNIGHT LOWS WILL VARY FROM THE LOW 40S TO
AROUND 50.

THE HIGH SHIFTS EAST SATURDAY BUT EXPECTING ANOTHER DRY DAY WITH
INCREASING CLOUD COVER.  THE NEXT LOW FORMS OVER THE CENTRAL PLAINS
TOMORROW BUT THE UPPER LEVEL RIDGE REMAINS OVER THE MIDWEST.
THINKING THE DRY AIR WILL KEEP THE REGION PRECIP FREE THROUGH
SATURDAY AFTERNOON. SOUTH WINDS ARE EXPECTED AND A WEAK LAKE BREEZE
IS POSSIBLE. THINKING THE LAKE BREEZE WILL HUG THE SHORE AND
PROBABLY ONLY PUSH OVER LAND OVER LAKE COUNTY IL.  AS SUCH KEPT
DAYTIME HIGH TEMPS IN THE 60S ALONG THE LAKE BUT EXPECTING ALL OTHER
REGIONS TO CLIMB INTO THE MID 70S. IF CLOUD COVER IS SLOWER THAN
FORECAST...COULD SEE A FEW SITES REACH 80...BUT DECIDED TO GO THE
SAFER ROUTE AND BET ON INCREASING CLOUD COVER. HAVE MEDIUM-HIGH
CONFIDENCE IN HIGH TEMPS FOR SATURDAY.

JEE

&&

.LONG TERM...
202 AM CDT

SATURDAY THROUGH THURSDAY...

SATURDAY THROUGH MEMORIAL DAY...
WEAK SFC RIDGING CENTERED OVER THE EASTERN OHIO VALLEY/MID-ATLANTIC
REGION...WILL CONTINUE TO DRIFT EAST SATURDAY MORNING...WITH LLVL
FLOW TURNING SOUTHEASTERLY TO SOUTHERLY. RETURN FLOW MOISTURE FROM
THE WESTERN GULF WILL BE ALREADY STREAMING NORTH THROUGH THE OZARKS
INTO THE PLAINS SATURDAY. FORTUNATELY HEIGHTS BEGIN TO INCREASE
SLIGHTLY SAT...SO EXPECT MUCH OF THE DAY/AFTN TO REMAIN DRY WITH
STEADILY INCREASING CLOUD COVER FROM SOUTHWEST TO NORTHEAST.

GUIDANCE CONTINUES TO PUMP ADDTL LLVL MOISTURE INTO THE
PLAINS...WITH THE MOIST AXIS EVENTUALLY SHIFTING EAST TOWARDS THE
WESTERN OHIO VALLEY AND GREAT LAKES LATE SAT NGT BUT MORE SO SUN
AFTN. DEW POINTS WILL BE STEADILY RISING SUN...WITH SOUTHERLY
FLOW...THIS WILL SETUP A WARM/HUMID DAY. THERMAL RIDGE OF 10-12 DEG
C WILL BE ADVECTING NORTH ACROSS THE REGION...HOWEVER EXPECT
ABUNDANT SOLAR SHIELDING TO DAMPEN HOW MUCH THE SFC CAN REALIZE THE
WARMTH ALOFT. AT THIS TIME WILL NUDGE TEMPS UP A FEW DEGREES BOTH
SAT AND SUN...WITH TEMPS NEARING THE MID/UPR 70S SUN AND POSSIBLY
ARND 80 IN THE FAR SOUTHERN CWFA. HOWEVER AS ELUDED TO EARLIER...THE
MOISTURE PLUME WILL BE STEADILY INCREASING SUN WITH PWAT VALUES
NEARING 30-40MM OR AROUND 1.5 INCHES. THIS WILL ALSO MAKE IT MORE
DIFFICULT TO WARM THE SFC...BY MOISTENING THE PARCELS.

SUN NGT THE LLVL JET IS PROGGED TO INCREASE FROM THE
SOUTHWEST...WITH GUIDANCE PROGGING A WEAK LOBE OF MID-LVL VORTICITY
LIFTING NORTH ACROSS THE OZARKS. HAVE NUDGED POPS UP TO LIKELY SUN
NGT...WHICH SEEMS TO LINE-UP WELL GIVEN THE ENVIRONMENTAL SETUP.
CURRENT THINKING IS THAT COVERAGE OF CONVECTION COULD BE LIMITED
GIVEN THE MAIN FOCUS WILL BE WELL WEST/NORTHWEST OF THE REGION. SO
ANY THUNDERSTORMS WOULD LIKELY BE EMBEDDED OR SCATTERED AT BEST.

TEMPS SUN NGT WILL REMAIN VERY MILD...IN THE MID/UPR 60S. BUT COULD
SEE A FEW LOCATIONS NOT DIP BELOW 70 ALONG THE KANKAKEE VALLEY.

UNFORTUNATELY CHANCES FOR SHOWERS AND POSSIBLY A THUNDERSTORM
CONTINUES INTO MEMORIAL DAY...HOWEVER AS HAS BEEN THE CASE WITH
OTHER SYSTEMS...THE PATTERN IS SIMILAR AND COULD PRODUCE LIMITED
COVERAGE OF SHOWERS DURING THE DAY. GUIDANCE IS HINTING THAT A DRY
SLOT MAY DEVELOP ACROSS THE SOUTHERN PLAINS AND QUICKLY LIFT
NORTHEAST TOWARDS NORTHERN IL LATE MON AFTN/EARLY EVE. IF THIS CAN
MESH TOGETHER...DRY CONDS MAY END UP DEVELOPING FOR THE SECOND HALF
OF MEMORIAL DAY. WARM MOIST CONDS CONTINUE INTO MON WITH TEMPS
GENERALLY IN THE MID/UPR 70S...BUT WITH DEW POINTS IN THE MID
60S.

TUESDAY THROUGH THURSDAY... HIGH AMPLITUDE RIDGING REMAINS ACROSS
WESTERN CANADA/ALASKA...WITH THE DOWNSTREAM TROUGH SLOWLY MODERATING
AND BLENDING INTO THE DAMPENING RIDGE OVER THE ATLANTIC. THEN BY
TUE/WED THE DOWNSTREAM RIDGE WILL CONSOLIDATING INTO A SLIGHTLY
STRONGER RIDGE ACROSS THE SOUTHEASTERN CONUS. THIS PATTERN WILL
LIKELY TRANSLATE INTO A SOUTH/SOUTHWEST FLOW ACROSS THE CENTRAL
CONUS TOWARDS THE MIDDLE OF NEXT WEEK...WITH TEMPS GENERALLY IN THE
UPR 70S TO LOW 80S WITH PERIODIC CHANCES FOR AFTN
SHOWERS/THUNDERSTORMS.

BEACHLER

&&

.AVIATION...

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

* NORTHEAST WINDS ARND 12KT WITH OCNL HIGHER GUST...WITH SPEEDS
  DIMINISHING TO ARND 10KT AND GUSTS SUBSIDING BY ARND 08Z.

* LAKE BREEZE EARLY FRIDAY AFTERNOON WITH WIND SHIFT TO ELY ARND
  10KT.

KREIN

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

A COLD FRONT PUSHING INTO ORD BY ISSUANCE TIME AND CONTINUING TO
QUICKLY PUSH SOUTH THROUGH THE NIGHT. EXPECT A SURGE OF STRONGER
WINDS IMMEDIATELY FOLLOWING THE FROPA...TO ARND 12KT WITH OCNL
GUSTS TO ARND 18KT FOR A COUPLE HOURS. EXPECT THAT NELY WINDS
SHOULD SUBSIDE TO SUSTAINED ARND 10KT FOR REMAINDER OF THE MORNING
HOURS. AS HIGH PRESSURE QUICKLY BUILDS IN BEHIND THE FRONT...A
WEAK PRESSURE GRADIENT WILL SET UP AND WITH LITTLE CLOUD
COVER...RELATIVELY HIGH CONFIDENCE FOR A LAKE BREEZE TO DEVELOP
AND THAT IT WILL MOVE WEST OF ORD/MDW. CONFIDENCE IS A LITTLE
LOWER ON THE EXACT TIMING..BUT MEDIUM FOR TIMING AND SPEEDS... BUT
WOULD ANTICIPATE SPEEDS ARND 10KTS FOR AN HOUR OR TWO THEN SETTLE
BACK UNDER 10KTS BY LATE AFTERNOON.

OTHERWISE...NO SIG WX IS EXPECTED FOR THE PERIOD WITH DRY...
PREVAILING VFR CONDITIONS.

KREIN

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

* HIGH CONFIDENCE IN LAKE BREEZE DEVELOPMENT THIS AFTERNOON... BUT
  MEDIUM FOR TIMING.

* HIGH CONFIDENCE IN ALL OTHE FORECAST ELEMENTS.

KREIN

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

* SATURDAY...DRY/VFR. SOUTH WINDS.
* SUNDAY...SHRA LIKELY/CHANCE OF TSRA. MVFR POSSIBLE. SOUTH WINDS.
* MONDAY AND TUESDAY...CHANCE OF SHRA/TSRA. STRONG/GUSTY
  SOUTHWEST WINDS.
* WEDNESDAY...CHANCE OF SHRA/TSRA. SOUTHWEST WINDS.

&&

.MARINE...
202 AM CDT

BROAD SURFACE RIDGE OF HIGH PRESSURE WILL CONTINUE TO DRIFT
EAST...WITH WINDS SLOWLY TURNING SOUTHERLY ACROSS THE SOUTHERN TIP
OF THE LAKE THIS EVENING AND EVENTUALLY OVER THE ENTIRE LAKE BY
SATURDAY. WARM MOIST AIR WILL THEN LIFT NORTH ACROSS
ILLINOIS...AND REACH LAKE MICHIGAN BY SATURDAY NIGHT INTO MEMORIAL
DAY. THE LOW LEVEL WINDS DO NOT APPEAR TO BE VERY STRONG...SO IT
IS BECOMING POSSIBLE THAT SOME LAKE FOG MAY BEGIN TO DEVELOP
SATURDAY EVENING AND POSSIBLY THICKEN FURTHER FOR SUNDAY INTO
MEMORIAL DAY/MONDAY. AT THIS TIME WILL HOLD OFF ON INCLUDING ANY
FOG IN THE FORECAST...HOWEVER IT APPEARS THE PATTERN IS SETTING UP
TO PRODUCE FOG.

BEACHLER

&&

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

$$

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