Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 151825
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
125 PM CDT TUE APR 15 2014

.DISCUSSION...
1138 AM CDT

MINOR UPDATES TO SKY COVER AND POP/WX THIS MORNING...TO ACCOUNT
FOR PARTLY SUNNY SKIES WITH SOME ISOL TO SCT FLURRIES THROUGH
EARLY THIS AFTERNOON. LATEST SATELLITE IMAGERY DEPICTING RAPID
STRATOCU DEVELOPMENT ACROSS THE REGION OVER THE LAST HOUR. THIS IS
OCCURRING AS CYCLONIC FLOW REMAINS IN PLACE WHILE LONGWAVE TROUGH
PROGRESSES THROUGH THE REGION...AND LOW LEVEL LAPSE RATES CONTINUE
TO STEEPEN. AS REMAINING SNOW MELTS OVER THE NEXT ONE TO TWO
HOURS...SHOULD OBSERVE ANY HOLES IN THE CLOUD DECK TO FILL WITH
SKIES BECOMING MORE PARTLY SUNNY WITH POSSIBLE BUT BRIEF OVERCAST
SKIES THIS AFTERNOON. RADAR IS SHOWING SOME LIGHT RETURNS AS
CU/STRATOCU FIELD CONTINUES TO BUBBLE...AND WOULD NOT BE OUT OF
THE QUESTION FOR SOME MOISTURE TO BE SQUEEZED OUT ESPECIALLY NEAR
BETTER LOW LEVEL CONVERGENCE. HAVE INCLUDED THE MENTION OF
FLURRIES IN THE GRIDS...BUT THIS SHOULD LIKELY PEAK OVER THE NEXT
COUPLE OF HOURS BEFORE DIMINISHING INTO THE REST OF THE AFTERNOON.

RODRIGUEZ

//PREV DISCUSSION...
329 AM CDT

AFTER 72 HOURS OF A WHIRLWIND OF WEATHER ACROSS THE AREA...INCLUDING
GOLF BALL SIZE HAIL...TEMPERATURES NEAR OR REACHING 80...HOURLY
TEMPERATURE CHANGES OF 15 TO 20 DEGREES IN BOTH DIRECTIONS SUNDAY
NIGHT...RAINFALL IN EXCESS OF AN INCH IN PLACES...TEMPERATURES
THEN IN THE 30S AND 20S...AND LATE SEASON SNOW OF ONE TO EVEN TWO
INCHES...THE PATTERN NOW LOOKS TO QUIET MIDWEEK. THE FORECAST
CHALLENGES ARE NOW MAINLY ON TEMPERATURES...AS WELL AS
PRECIPITATION CHANCES THURSDAY AND FRIDAY. THE THREAT OF HIGH
IMPACT WEATHER IS LOW THROUGH THE NEXT WEEK.

TODAY...
A DOME OF LOW TROPOSPHERIC HEIGHTS AND COLD AIR IS CENTERED ACROSS
HUDSON BAY AND INTO QUEBEC AND A REMINISCENT SIGNATURE OF THIS PAST
DECEMBER-FEBRUARY. AN EXTENDING LONG WAVE TROUGH DROPS ALL THE WAY
DOWN THE MISSISSIPPI RIVER VALLEY EARLY THIS MORNING AND IS PUSHING
EAST. ANONYMOUSLY COLD AIR OF -12C TO -14C AT 850MB OBSERVED ON
UPSTREAM SOUNDINGS LAST EVE HAS MOVED SOUTH OVER LAKE MICHIGAN
AND GENERATED CONCENTRATED LAKE EFFECT SHOWERS INTO FAR EASTERN
COOK COUNTY AND FAR NORTHWEST INDIANA SINCE LATE LAST EVE. WOULD
NOT BE SURPRISED IF DAYBREAK FOUND SOME NEAR THREE INCH TOTALS ON
GRASSY SURFACES IN PARTS OF LAKE COUNTY INDIANA JUST SIMPLY FROM
THE AROUND 5-6 HOUR DURATION OF THE 1-2SM SNOW. THANKFULLY FOR
RUSH HOUR GOERS IN THESE AREAS THIS MORNING...THIS SHOULD
DISSIPATE IN INTENSITY BETWEEN 5 AND 7 AM AS DRIER AIR CONTINUES
TO MOVE IN AND HAVE ALREADY SEEN THAT ON RADAR TRENDS. SOME
LINGERING LIGHT AND LESS ORGANIZED SNOW SHOWERS MAY BE SEEN THIS
MORNING IN THESE LAKE ADJACENT AREAS. IN ADDITION...CANNOT RULE
OUT A FEW FLURRIES THROUGH EARLY AFTERNOON IN OTHER AREAS AS THE
TROUGH PASSES AND FINGERS OF COLD AIR CUMULUS/STRATOCUMULUS
CONTINUE.

TEMPERATURES WILL BE WELL BELOW NORMAL TODAY WITH THE COLD POCKET
OF AIR AT THE TOP OF THE MIXED LAYER. WINDS TURNING OFF THE LAKE
SHOULD KEEP DOWNTOWN CHICAGO SHY OF 40 DEGREES. WITH THIS
PRONOUNCED COLD AND EVEN SOME AIDED BOUNDARY LAYER COOLING THANKS
TO LIGHT SNOW COVER...A RECORD LOW MAX TEMP IS POSSIBLE TODAY AT
ROCKFORD. SEE THE CLIMATE DISCUSSION BELOW FOR MORE ON THIS.

TONIGHT...
WITH HIGH PRESSURE OVER THE AREA IN THE EVENING IT SETS THE STAGE
FOR A VERY COOL NIGHT...BUT HIGH CLOUDS LOOK TO MOVE INTO NORTHERN
LOCATIONS AT SOME POINT TONIGHT AND MAKE IT TRICKY. HOW QUICKLY
THAT EXPANSION OCCURS DIFFERS AMONG GUIDANCE...BUT GIVEN THICK
CIRRUS ALREADY INTO NORTH DAKOTA EARLY THIS MORNING AND NAM
SIMULATED WATER VAPOR ON THE INCREASE THIS EVE...HAVE OPTED TO
SHOW TEMPS FLAT-LINING IN NORTH CENTRAL IL LATER TONIGHT...AND
THIS COULD EVEN OCCUR IN CHICAGO. LOWS WILL STILL BE WELL BELOW
NORMAL WITH MID 20S TO LOWER 30S.

WEDNESDAY THROUGH FRIDAY...
WITH SUCH A PRONOUNCED COLD AIR MASS AND ASSOCIATED VORTEX OVER
HUDSON BAY/EASTERN CANADA...UPPER RIDGING LOOKS TO BE TEMPERED AS IT
ADVANCES EASTWARD INTO THE AREA. MULTIPLE IMPULSES ARE NOTED FROM
WEDNESDAY NIGHT THROUGH FRIDAY IN THE REGION. THE FIRST WILL BRING A
COOL FRONT INTO THE AREA ON WEDNESDAY NIGHT...BUT THE GULF LOOKS CUT
OFF FOR MUCH PRECIP ALONG THIS INITIAL BOUNDARY. THAT BAROCLINIC
ZONE WILL BE A FOCUS FOR THE NEXT COUPLE IMPULSES TO COME ALONG
LATER THURSDAY INTO FRIDAY. OVER THE PAST 24 HOURS GUIDANCE HAS
TRENDED WEAKER AND FURTHER SOUTH WITH THESE...ESPECIALLY WITH ANY
SURFACE REFLECTION. HAVE OPTED TO MENTION RAIN AS LIGHT IN THE
FORECAST FOR THIS TIME RANGE BECAUSE OF THIS PATTERN.
TEMPERATURES LOOK TO BE A REAL CHALLENGE ON THURSDAY AND
FRIDAY...AND WHILE HAVE COOLED FRIDAY IT STILL COULD CERTAINLY BE
COOLER THAN FORECAST BY QUITE A BIT WITH NORTHEAST FLOW IF LOW
CLOUDS AND LIGHT RAIN ARE INDEED OVER THE AREA.

THIS WEEKEND INTO EARLY NEXT WEEK...
A MORE PROGRESSIVE FLOW PATTERN EVOLVES OVER THE NORTHERN
CONUS WITH SPREAD IN GUIDANCE ON A WEAK SYSTEM OF PACIFIC ORIGIN.
SO HAVE NOT STRAYED MUCH FROM A GUIDANCE BLEND IN POPS WHICH IS
GENERALLY WISE IN THESE SITUATIONS. TEMPERATURES LOOK TO RUN
SLIGHTLY BELOW TO NORMAL IN THIS PERIOD.

MTF

&&

.CLIMATE...

IT IS POSSIBLE A RECORD LOW MAX IS REACHED AT ROCKFORD TODAY WITH
THAT BEING 39 SET IN 1951. WE PRESENTLY ARE FORECASTING A FEW
DEGREES WARMER THAN THIS. THE CHICAGO RECORD OF 34 IN 1928 LOOKS
SAFE AT OHARE AIRPORT.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* POTENTIAL FOR LAKE BREEZE THIS AFTERNOON/EVENING

DZ

//DISCUSSION...UPDATED 18Z...

COMBINATION OF COLD AIR ALOFT AND DAYTIME HEATING HAS LEAD TO
DEVELOPMENT OF OVERALL SHALLOW STRATOCUMULUS FIELD ACROSS THE
AREA. A FEW WEAK RETURNS PAINTING ON RADAR AND FLURRIES HAVE BEEN REPORTED
AT SOME LOCATIONS. FLURRIES TO REMAIN POSSIBLE INTO MID AFTERNOON
UNTIL COLD AIR POOL ALOFT MOVES FURTHER EAST. CLOUDS TO THEN THIN
AND DISSIPATE LATE THIS AFTERNOON INTO EARLY EVENING.

LAKE BREEZE NOT EXPECTED TO PUSH TOO FAR INLAND AS CLOUD COVER TO
MINIMIZE LAND/LAKE TEMPERATURE CONTRAST AND ALLOW REGIONAL FLOW TO
DOMINATE.

AXIS OF A LARGE HIGH PRESSURE AREA STRETCHED OVER MINNESOTA TO
ACROSS MISSOURI AT MIDDAY. AXIS TO MOVE ACROSS THIS EVENING
CAUSING WIND TO BECOME LIGHT AND VARIABLE. WIND TO BECOME SOUTH BY
DAYBREAK WEDNESDAY AND STEADILY INCREASE WITH GUSTS AROUND 30KT BY
AFTERNOON AS NEXT LOW PRESSURE SYSTEM MOVES OUT OF THE PLAINS. DZ

//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* LOW CONFIDENCE LAKE BREEZE WILL MOVE ACROSS ORD/MDW
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS

DZ


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

WEDNESDAY NIGHT...VFR.
THURSDAY...CHC RAIN LATE. MAINLY VFR.
FRIDAY...RAIN. MVFR/IFR PSBL.
SATURDAY...VFR.
SUNDAY...CHC RAIN.
MONDAY...SLT CHC RAIN.

BMD

&&

.MARINE...
237 AM CDT

WINDS WILL CONTINUE TO SLOWLY DIMINISH TODAY AS HIGH PRESSURE BUILDS
OVER THE REGION. WAVES WILL REMAIN ELEVATED THROUGH MID TO LATE THIS
AFTERNOON...THEN SHOULD SUBSIDE ENOUGH TO ALLOW THE SMALL CRAFT
ADVISORY TO EXPIRE. THE RIDGE AXIS WILL MOVE ACROSS LAKE MICHIGAN
THIS EVENING WITH LIGHT WINDS ACROSS MUCH OF THE LAKE. LOW PRESSURE
WILL BEGIN TO TAKE SHAPE LATE TUESDAY INTO WEDNESDAY OVER THE
NORTHERN PLAINS...MOVING OVER WISCONSIN WEDNESDAY NIGHT. SOUTH TO
SOUTHEAST FLOW WILL RAMP UP THROUGH THE DAY WEDNESDAY...AND WHILE
STABLE CONDITIONS OVER THE LAKE WILL HELP KEEP CONDITIONS IN CHECK
OVER THE OPEN WATERS...GUSTS TO AROUND 30 KT WILL ARE STILL
EXPECTED. ANOTHER SMALL CRAFT ADVISORY WILL LIKELY BE NEEDED
STARTING MID MORNING WEDNESDAY AND LASTING THROUGH LATE WEDNESDAY
EVENING.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 5 PM TUESDAY.

&&

$$

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