Area Forecast Discussion
Issued by NWS Chicago, IL

Home | Current Version | Previous Version | Graphics & Text | 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 150901
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
401 AM CDT TUE APR 15 2014

.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...
329 AM CDT

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 09Z...

* POTENTIAL FOR A LAKE BREEZE TUESDAY AFTERNOON/EVENING.

BMD

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

HIGH PRESSURE IS SLOWLY BUILDING EAST FROM THE MID-MISSOURI VALLEY
WITH MFVR CIGS AND LIGHT SNOW GRADUALLY ERODING AND SHIFTING EAST OF
THE TERMINALS TONIGHT. THE EXCEPTION WILL BE AT GARY WHERE SOME LAKE
EFFECT SNOW WILL BE AT OR NEAR THE TERMINAL FOR THE NEXT FEW HOURS.
OTHERWISE...VFR CONDITIONS ARE SETTING UP ACROSS THE REMAINDER OF
THE AREA WITH MODEST NORTHWEST WINDS. WINDS WILL BACK TOWARDS THE
WEST TUESDAY AFTERNOON AND DIMINISH SOME...ALLOWING A LAKE BREEZE TO
DEVELOP. WITH WEAK THERMAL CONTRAST BETWEEN THE LAKE AND LAND...AND
AN OPPOSING WEST FLOW...IT REMAINS DOUBTFUL THAT THE LAKE BREEZE
WILL MAKE IT THROUGH ORD/MDW SO FOR NOW WILL HOLD OFF ON ANY
WIND SHIFT BUT IT WILL NEED TO BE MONITORED. HIGH PRESSURE WILL BUILD
OVERHEAD MID TO LAKE EVENING TUESDAY WITH WINDS BECOMING LIGHT AND
VARIABLE OVERNIGHT...THEN BECOMING SOUTHEASTERLY EARLY WEDNESDAY.

BMD

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

* LOW CONFIDENCE THAT A LAKE BREEZE WILL REACH ORD/MDW.
* HIGH CONFIDENCE IN REMAINING FORECAST ELEMENTS.

BMD

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

WEDNESDAY THROUGH THURSDAY...VFR.

FRIDAY...RAIN LIKELY. IFR POSSIBLE.

SATURDAY...MVFR CIGS POSSIBLE.

SUNDAY...CHANCE OF RAIN.

IZZI

&&

.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.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.CHICAGO.GOV
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.