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 280817
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
317 AM CDT THU MAY 28 2015

.SHORT TERM...
312 AM CDT

THROUGH THURSDAY NIGHT...

FOR THE REMAINDER OF THE OVERNIGHT HOURS...QUIET CONDITIONS WILL
PREVAIL AS HIGH PRESSURE CENTERED OVER SOUTHERN ONTARIO BRIDGES AN
OLD FRONTAL TROUGH ACROSS THE OHIO VALLEY TO MERGE WITH THE
SUBTROPICAL RIDGE OVER THE SERN CONUS.  MOSTLY CLEAR SKIES AND LIGHT
AND VARIABLE WINDS WILL PERSIST THROUGH THE NIGHT AS TEMPS DROP INTO
THE UPPER 50S TO LOWER 60S.

THROUGH THE MORNING HOURS...THE HIGH PRESSURE WILL SHIFT TO THE EAST
AS A MULTI-CENTERED TROUGH DEVELOPS OVER THE PLAINS.  A NRN STREAM
SHORTWAVE WILL LIFT OUT OF THE DAKOTAS THIS MORNING...LIFTING
QUICKLY TO SWRN ONTARIO BY EARLY THIS EVENING.  THE SFC REFLECTION
OF A SRN STREAM SHORTWAVE DEVELOPING OVER THE WRN CENTRAL PLAINS
WILL BE MUCH LESS PROGRESSIVE...REMAINING IN WRN KS BY THIS EVENING.
 THE TREND FOR THE DAY TODAY WILL BE FOR INCREASING SELY
WINDS...THOUGH SPEEDS WILL REMAIN UNDER 10MPH.  THE SUBTROPICAL
RIDGE EXTENDING FROM THE SERN CONUS THROUGH THE TEXAS GULF COAST
ALONG WITH ONGOING CONVECTION OVER THE SRN PLAINS WILL PREVENT ANY
SIGNIFICANT RETURN FLOW OF LOW LEVEL MOISTURE TODAY...WITH DEWPOINTS
REMAINING IN THE LOW TO MIDDLE 50S UNDER MOSTLY SUNNY SKIES.  AMPLE
SUNSHINE AND RELATIVELY DRY AIR SHOULD ALLOW TEMPERATURES TO REACH
INTO THE MIDDLE 80S ACROSS THE AREA.  THE POSSIBLE EXCEPTION TO THE
WARMING WILL BE THE LAKE MICHIGAN COASTAL AREA.  A WEAK PRESSURE
GRADIENT AND LIGHT SELY SYNOPTIC SCALE WINDS...COMBINED WITH
DIFFERENTIAL HEATING BETWEEN THE STILL COOL LAKE MICHIGAN WATER AND
THE WARMER LAND WILL LIKELY ALLOW FOR A LAKE BREEZE TO FORM.  THERE
IS STILL SOME QUESTION AS TO THE TIMING OF THE LAKE BREEZE
DEVELOPMENT AND HOW FAR INLAND THE BOUNDARY WILL PENETRATE...BUT
CURRENT THINKING IS THAT SFC WINDS SHOULD BECOME ELY ALONG THE IL
SHORE AND NLY-NWLY ALONG THE INDIANA SHORE...BRINGING COOLER AIR
INLAND.  ALSO ANTICIPATE THAT THE BOUNDARY MAY PUSH INLAND INTO
NERN IL...BUT THIS WILL LIKELY NOT UNTIL JUST BEFORE THE PERIOD OF
MAX HEATING.  SO...WHILE THE INLAND LOCATIONS WILL LIKELY SEE TEMPS
IN THE MID 80S...THE COOLING INFLUENCE OF THE DEVELOPING LAKE BREEZE
SHOULD LIMIT TEMPS ALONG THE LAKEFRONT TO THE MIDDLE 70S BEFORE
DROPPING OFF THROUGH THE LATE AFTERNOON AND EARLY EVENING.

FOR THURSDAY NIGHT...THE FORECAST FOCUS WILL SHIFT TO INCREASING
PCPN CHANCES.  THE LARGER SCALE PATTERN WILL BE SLOWLY PROGRESSIVE
THROUGH THE EVENING...THOUGH THE NRN STREAM SHORTWAVE WILL TRACK
EAST QUICKER THAN THE SRN STREAM SHORTWAVE THAT WILL BE HINDERED
SOMEWHAT BY THE SUBTROPICAL RIDGE EXTENDING ACROSS THE SERN CONUS.
HOWEVER...THERE WILL BE SOME PROGRESSION TO THE PATTERN...WITH THE
SUBTROPICAL RIDGE RETREATING TO THE EAST...OPENING UP THE GLFMEX AND
INTRODUCING A RETURN FLOW OF MOISTURE ACROSS THE REGION.  LATEST
GUIDANCE SUGGESTS THAT DEWPOINTS WILL REBOUND INTO THE LOWER TO
MIDDLE 60S BY EARLY FRIDAY MORNING OVER MUCH OF THE CWA.  THE NRN
STREAM SYSTEM WILL DRAG A COLD FRONT THROUGH THE UPPER MISSISSIPPI
VALLEY OVERNIGHT TONIGHT WHILE THE SRN STREAM SYSTEM MOVES INTO THE
UPPER OHIO VALLEY.  ISENTROPIC LIFT IN THE WARM SECTOR OF THE SYSTEM
SHOULD BE ADEQUATE TO GENERATE SHOWERS AND THUNDERSTORMS OVER THE
MIDDLE AND UPPER MISSISSIPPI VALLEY TONIGHT AND SPREADING INTO THE
WRN PORTIONS OF THE CWA...GENERALLY ALONG AND WEST OF THE I-39
CORRIDOR INTO THE PRE-DAWN HOURS.  GIVEN SOME TIMING DIFFERENCES OF
THE MAIN SHORTWAVE PATHS AND HOW QUICKLY THE SUBTROPICAL RIDGE WILL
RETREAT WILL IMPACT THE TIMING OF PCPN SPREADING EAST ACROSS THE
CWA.  SO...WHILE THERE IS HIGH CONFIDENCE IN PCPN REACHING THE I-39
CORRIDOR DURG THE PRE-DAWN HOURS...THERE IS A CHANCE THAT SOME
ACTIVITY COULD SPREAD AS FAR EAST AS THE FOX VALLEY AND THE I-55
CORRIDOR BY DAYBREAK...SO HAVE SPREADED SOME LOW POPS A LITTLE
FARTHER EAST THAN PREVIOUSLY ANTICIPATED. AS THE WARM/MOIST
ADVECTION RAMPS UP TONIGHT...OVERNIGHT LOWS WILL BE A BIT HIGHER
THAN THE PAST COUPLE DAYS...WITH LOWS IN THE LOWER TO MIDDLE 60S.

KREIN

&&

.LONG TERM...
247 AM CDT

FRIDAY THROUGH WEDNESDAY...

FRIDAY...
MAIN CHALLENGES FOR FRI WILL BE ON PRECIP TIMING AND COVERAGE.
GUIDANCE HAS INDICATED SOME SLOWING TO THE DEPARTING SFC
RIDGE...WITH MID-LVL HEIGHTS NOT BEGINNING TO FALL UNTIL AFT
DAYBREAK FRI. THE MORE POTENT LOBE OF VORTICITY WILL BE ROUNDING THE
TROUGH AXIS EARLY FRI...THEN FORMING A SFC WAVE FEATURE ACROSS THE
SOUTHERN PLAINS. THE QUASI-STATIONARY BOUNDARY WILL BE ORIENTED FROM
THE SOUTHERN PLAINS NORTHEAST THROUGH THE UPPER MIDWEST. BUT WITH
THE MINOR DELAY IN DEPARTING RIDGE...THIS MAY PROVIDE A WEAK BUCKLE
TO THE GREATER PRECIP COVERAGE ONLY TEMPORARILY FRI MORNING. BY
MIDDAY THE BOUNDARY WILL BE DRIFTING EAST...WITH ABUNDANT LOW LEVEL
MOISTURE ADVECTING NORTH INTO THIS FEATURE. DEW POINTS WILL HOVER IN
THE LOW/MID 60S...AS PWAT VALUES APPROACH 1.5 INCHES. 850MB V-WIND
COMPONENT SUGGESTS WINDS WILL NOT BE TOO STRONG...SO AT THIS TIME
WOULD NOT SUSPECT AS THE SFC WAVE LIFTS NORTHEAST ALONG THE BOUNDARY
GROWTH IN CONVECTION TO BE VERY LARGE. HOWEVER...IT DOES APPEAR TO
BE AN IDEAL SETUP FOR EMBEDDED THUNDER. WITH THE UPSTREAM MID-LVL
VORT STRENGTHENING OVER CENTRAL CANADA...THIS WILL LIKELY ALLOW THE
QUASI-STATIONARY BOUNDARY TO FURTHER ENHANCE. THIS COULD AID IN
PRECIP PRODUCTION WITH THE BOUNDARY SLIDING OVERHEAD FRI
NIGHT.

TEMPS WILL EQUALLY BE A CHALLENGE FRI...GIVEN THE THICK SOLAR
SHIELDING POISED TO LIMIT SFC HEATING. THE ABUNDANT LOW LEVEL
MOISTURE WILL ABSORB ANY HEAT...MAKING IT DIFFICULT TO WARM AND
PERHAPS KEEPING TEMPS A FEW DEGREES LOWER THAN CURRENTLY PROGGED.
HAVE NUDGED TEMPS IN THE FAR NORTHERN CWFA DOWN A COUPLE DEGREES TO
REFLECT THIS INTO THE UPR 70S...MEANWHILE FURTHER SOUTH HAVE HELD
ONTO THE 80 TO LOW 80S RANGE.

SATURDAY THROUGH MIDDLE OF NEXT WEEK... ENSEMBLES HAVE CONTINUED TO
PROG A HIGH AMPLITUDE RIDGE ACROSS WESTERN CANADA AT THE START OF
THE WEEKEND...THEN SLOWLY WEAKENING THIS FEATURE AS THE CENTRAL
CONUS TRANSITIONS INTO A RELATIVELY FLAT WEST-EAST FLOW BY TUE/WED
OF NEXT WEEK. THE MAIN STORY FOR THE WEEKEND WILL BE ON THE TEMPS
ABRUPTLY CHANGEING FROM EARLY SUMMER TO MID-SPRING...WITH A STOUT
FRONTAL BOUNDARY SWEEPING ACROSS THE FORECAST AREA SAT MIDDAY. THIS
WILL BRING MUCH COOLER AIR AS WINDS QUICKLY VEER NORTH/NORTHEAST
AND BLEED THE MUCH COOLER MARINE AIR FROM LAKE MICHIGAN OVER
NORTHEAST IL/NORTHWEST IN SAT/SUN. HIGHS SAT MAY STRUGGLE TO WARM
BEYOND THE UPR 50S ACROSS NORTHEAST IL/NORTHWEST IN...WITH ONLY
LOW 60S ELSEWHERE.

WITH FLOW BECOMING SOMEWHAT FLAT TOWARDS MON/TUE ACROSS THE
CENTRAL CONUS...THIS WILL HELP TO FLUSH THE SFC RIDGE EAST FROM
THE GREAT LAKES REGION. THIS WILL LIKELY ALLOW TEMPS TO SLOWLY
RETURN TO SEASONAL CONDS BY MIDDLE OF NEXT WEEK...HOWEVER
CURRENTLY GUIDANCE INDICATES A DRY STRETCH AS MID-LVL HEIGHTS MAY
BEGIN TO NUDGE UP CLOSER TO TUE/WED. BUT CONFIDENCE IN THE FINAL
FEW PERIODS OF THE EXTENDED ARE CURRENTLY LOW.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 09Z...

* ESELY WINDS AROUND 10 KT THURSDAY AFTERNOON FOLLOWING LAKE
  BREEZE PASSAGE.

* CHANCE OF SHOWERS LATE THURSDAY NIGHT.

KREIN

//DISCUSSION...UPDATED 00Z...
AS WEAK HIGH PRESSURE SETTLES OVER NRN IL/IN/SRN LAKE
MICHIGAN...WINDS HAVE DROPPED OF TO CALM/LGT AND VRBL. AN AREA OF
SHOWERS IS QUICKLY DROPPING THROUGH ECNTRL WI AND CNTRL LAKE
MICHIGAN WITH AN OUTFLOW BOUNDARY RACING OUT AHEAD. LATEST RADAR
TRENDS SUGGEST THAT THE PCPN IS WEAKENING AND MOVING SELY ENOUGH
THAT IT WILL MISS THE TERMINALS...EVEN GYY. QUIET CONDITIONS
SHOULD PREVAIL THROUGH THE REMAINDER OF THE NIGHT...BUT BY EARLY
MORNING...A DEEPENING TROUGH OVER THE CNTRL/NRN PLAINS WILL HELP
TURN WINDS TO PREVAILING SELY BY DAYBREAK...WITH SPEEDS LESS THAN
10 KT. THE WEAK SELY GRADIENT WILL REMAIN IN PLACE THROUGH THE
DAY...AND SHOULD BE WEAK ENOUGH TO ALLOW FOR A LAKE BREEZE TO
DEVELOP. THE LATEST HIGH RES MODEL GUIDANCE AGREES WITH
CONVENTIONAL WISDOM THAT A LAKE BREEZE SHOULD DEVELOP UNDER THE
EXPECTED PATTERN...WITH WINDS SHIFTING TO JUST SOUTH OF EAST AND
INCREASING TO ARND 10KT.

AS THE SFC TROUGH BEGINS TO MOVE EAST ACROSS THE NORTHERN PLAINS
AND TOWARD THE UPPER MISSISSIPPI VALLEY LAKE THURSDAY
NIGHT...WINDS WILL VEER TO SOUTHERLY. WARM/MOIST ADVECTION UNDER
THE SOUTHERLY FLOW WILL BRING INCREASING LOW AND MID CLOUDS AND A
CHANCE OF SHOWERS BY THE EARLY MORNING HOURS.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* MEDIUM IN LAKE BREEZE WIND SHIFT TIMING AND SPEED/DIRECTION
  FOLLOWING LAKE BREEZE PASSAGE.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

KREIN

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

FRIDAY...PERIODIC SHRA/TSRA. MVFR POSSIBLE. SOUTHWEST WINDS.

SATURDAY...CHANCE SHRA. MVFR POSSIBLE. STRONG NORTH-NORTHEAST
WINDS.

SUNDAY...VFR/WX NIL. NORTHEAST WINDS.

MONDAY...VFR/WX NIL. EAST WINDS.

TUESDAY...VFR/WX NIL. SOUTH WINDS.

KJB

&&

.MARINE...
247 AM CDT

WEAK SFC RIDGE OF HIGH PRESSURE CENTERED OVER EASTERN
ONTARIO...WITH SOME LINGERING INFLUENCE OF DRY AIR ACROSS LAKE
MICHIGAN FOR THE BULK OF TODAY. THE WESTERN GREAT LAKES WILL BEGIN
TO SEE THE SOUTHERLY FLOW THIS AFTERNOON/EVENING...AS WINDS
INCREASE. A SLOW MOVING FRONTAL BOUNDARY ORIENTED OVER THE
SOUTHERN PLAINS STRETCHES NORTH TO JUST WEST OF LAKE SUPERIOR.
THSI BOUNDARY WILL BEGIN TO INCH EAST TOWARDS THE NORTHERN
PORTIONS OF LAKE MICHIGAN FRI MORNING...ALLOWING THE GRADIENT TO
TIGHTEN AND SOUTHERLY WINDS TO INCREASE. THEN THE FRONTAL BOUNDARY
WILL SLIDE SOUTHEAST SLOWLY ACROSS LAKE MICHIGAN...ALONG WITH THE
GRADIENT TIGHTENING BY FRIDAY NIGHT INTO SATURDAY. A STRONG RIDGE
OF HIGH PRESSURE WILL DROP SOUTH FROM CENTRAL CANADA ALONG THE
BACK EDGE OF THE FRONT...HELPING TO INCREASE A PERIOD OF NORTH GALES
SATURDAY FOR THE CENTRAL/SOUTHERN PORTIONS OF LAKE MICHIGAN.
GUIDANCE HAS BACKED OFF A TOUCH ON THE WIND SPEEDS...HOWEVER A
GALE WATCH MAY STILL NEED TO BE ISSUED. THE STRONG WINDS COUPLED
WITH MUCH COOLER AIR WILL EASILY BUILD WAVES FOR THE SOUTHERN HALF
OF THE LAKE SATURDAY. COOL AIR AND NORTH/NORTHEAST WINDS WILL
CONTINUE TO OCCUR SAT NIGHT THRU SUN...LIKELY MAINTAINING LARGER
WAVES ALONG THE IL/IN NEARSHORE WATERS.

BEACHLER

&&

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

$$

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.