Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 221410
AFDLOT

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

.SHORT TERM...
227 AM CDT

THROUGH FRIDAY NIGHT...

CONDITIONS WILL REMAIN RELATIVELY QUIET ACROSS THE REGION.  THE MAIN
ISSUE WILL BE THE PASSAGE OF A COLD FRONT MOVING INTO FAR NERN IL
EARLY THIS MORNING.  THE COLD FRONT IS SURGING THROUGH THE SRN TIP
OF LAKE MICHIGAN...BUT IS MAKING SLOWER PROGRESS INLAND THAN
PREVIOUSLY ANTICIPATED.  HOWEVER...THE LATEST RADAR IMAGERY DEPICTS
THE BOUNDARY VERY WELL AND IT HAS MOVED INLAND INTO LAKE AND COOK
COUNTIES AND IS APPROACHING ORD/MDW IN IL...AND IS BEGINNING TO MOVE
ONSHORE INTO NWRN INDIANA.  THE MAIN IMPACT WILL BE TO TURN WINDS
NELY AND BRING SOME COOLER AIR INLAND.  THERE HAD BEEN SOME SCT
SHOWERS KICKED OFF BY THE FRONT...BUT THEY ARE MOVING INTO SWRN
LOWER MICHIGAN AND NO PCPN IS EXPECTED INTO NERN IL/NWRN IN.

FOLLOWING THE FROPA...HIGH PRESSURE WILL BUILD SOUTH ACROSS THE
GREAT LAKES FROM CANADA...BRINGING CLEAR SKIES AND DIMINISHING
WINDS...ALONG WITH A VERY SLACK PRESSURE GRADIENT.  UNDER AMPLE
SUNSHINE...DIFFERENTIAL HEATING BETWEEN LAND AND COOL LAKE MICHIGAN
WATERS SHOULD ALLOW FOR LAKE BREEZE DEVELOPMENT THIS AFTERNOON.
WHILE MUCH OF THE REGION SHOULD BE ABLE TO WARM INTO LOW 70S...THE
LAKE BREEZE MOVING INLAND SHOULD LIMIT TEMPS ALONG THE LAKE TO THE
LOWER TO MIDDLE 50S AND LOCATIONS A LITTLE FURTHER INLAND WILL
LIKELY SEE HIGHS ONLY IN THE LOWER 60S.

KREIN

&&

.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 14Z...

* EASTERLY WINDS THROUGH THE DAY UP AROUND 10 KT AT TIMES THIS
  AFTERNOON.

KJB

//DISCUSSION...UPDATED 14Z...

HIGH PRESSURE WILL SHIFT DOWN LAKE MICHIGAN THROUGH THE DAY...AND
THIS WILL RESULT IN AN EASTERLY FLOW AT THE TERMINALS THROUGH
THE DAY. WIND SPEEDS WILL LIKELY BE IN THE 7 TO 10 KT RANGE FOR
MUCH OF THE MORNING. HOWEVER...A STRONGER PUSH OF WIND OFF THE
LAKE THIS AFTERNOON COULD PUT SPEEDS UP IN THE 10 TO 12 KT RANGE
FOR A PERIOD AT THE EASTERN TERMINALS. OTHERWISE...VFR CONDITIONS
ARE EXPECTED THROUGH THE PERIOD.

KJB

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* HIGH WITH ALL FORECAST ELEMENTS.

KJB

//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 14Z...

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