327 PM CDT
MAIN CONCERN FOR THE REMAINDER OF THE AFTERNOON AND INTO THE EVENING
WILL FOCUS OF THE SCATTERED SHOWERS THAT DEVELOPED THIS AFTERNOON.
AFTER SKIES CLEARED OUT EARLIER TODAY...SUNSHINE AND COLD AIR ALOFT
GENERATED VERY STEEP LAPSE RATES...QUICKLY TRIGGERING SCATTERED
SHOWERS OVER NRN IL. GIVEN THE STRONG INSTABILITY AND COLD AIR
ALOFT...OCCASIONAL GRAUPEL WILL BE POSSIBLE WITH THE STRONGER
SHOWERS. SHOWERS SHOULD DISSIPATE AROUND SUNSET.
AFTER SUNSET...AS SKIES CLEAR OUT AND SFC HIGH PRESSURE BUILDS
ACROSS THE CWA...WINDS WILL QUICKLY BECOME LIGHT AND VARIABLE. WITH
A DRY AIRMASS IN PLACE...AND DEWPOINTS IN THE LOW 30S...TEMPERATURES
ACROSS MUCH OF THE AREA WILL ALSO DROP INTO THE LOWER 30S.
THUS...FROST IS LIKELY TONIGHT FOR MUCH OF THE CWA. IMMEDIATE
LAKEFRONT AND LOCATIONS AWAY FROM HEAVILY URBANIZED AREAS WILL BE
MOST PRONE TO FROST.
BEGINNING TOMORROW...THE REGION WILL BE IMPACTED BY A SERIES OF
NORTHERN STREAM SHORTWAVES WHICH WILL BRING PERIODS SHOWERS TO AT
LEAST PORTIONS OF THE CWA OVER THE NEXT SEVERAL DAYS.
THE FIRST IN THE SERIES OF THESE SYSTEMS WILL TRACK ACROSS SOUTHERN
CANADA...DRAGGING A WEAK COLD FRONT ACROSS THE AREA FRIDAY AFTERNOON
AND EVENING. WITH THE STRONGEST FORCING LIKELY TO BE WELL TO THE
NORTH...THE NORTHERN TIER COUNTIES WILL BE MOST SUSCEPTIBLE TO ANY
PCPN. BY FRIDAY NIGHT...THE FOCUS OF PCPN WILL TRANSITION TO LAKE
EFFECT RAIN SHOWERS FOR LAKE AND PORTER COUNTIES IN NWRN INDIANA AND
OVER LAKE MICHIGAN. AS THE COLDEST AIR ASSOCIATED AN UPPER TROUGH
MOVES ACROSS THE LAKE FRIDAY NIGHT...THERE WILL ONCE AGAIN BE A
SLIGHT CHANCE FOR SOME THUNDER TO ACCOMPANY THE HEAVIER LAKE EFFECT
SHOWERS. BY SATURDAY MORNING...THE UPPER TROUGH WILL SHIFT OFF TO
THE EAST AS A RIDGE BUILDS ACROSS THE MISSISSIPPI VALLEY AND INTO
THE UPPER MIDWEST. EVEN COOLER AIR WILL OVERSPREAD THE AREA BY
SATURDAY MORNING. TEMPERATURES ARE EXPECTED TO DROP INTO THE UPPER
20S TO LOWER 30S ACROSS ALL OF THE CWA...WITH THE EXCEPTION OF THE
IMMEDIATE LAKE FRONT AND DOWNTOWN CHICAGO. LOCATIONS WEST OF THE
FOX VALLEY AND NORTH OF I-80 MAY SEE TEMPERATURES DROP INTO THE
UPPER 30S...SO A FREEZE WARNING MAY BE REQUIRED FOR THE NORTHWESTERN
PORTIONS OF THE CWA. THE REMAINDER OF SATURDAY AND INTO SATURDAY
NIGHT SHOULD BE QUIET. THE NEXT UPSTREAM SYSTEM SHOULD MOVE ACROSS
THE UPPER MISSISSIPPI VALLEY BY SUNDAY MORNING. THE TRACK OF THIS
SYSTEM SHOULD BE MORE SOUTHERLY THAN THE PREVIOUS...WITH THE MAIN
SFC LOW TRACKING ALONG THE WISCONSIN BORDER. THUS SHOWERS SHOULD BE
MORE WIDESPREAD WITH GRAUPEL LIKELY AGAIN SUNDAY AND SUNDAY NIGHT.
MONDAY SHOULD BE QUIET...BUT ANOTHER SYSTEM IS BEING ADVERTISED BY
THE LONGER RANGE MODELS FOR THE MIDDLE OF NEXT WEEK. WHILE THE
MODELS ARE IN RELATIVELY GOOD AGREEMENT ON TRACK...TIMING AND
STRENGTH OF THE FIRST TWO SYSTEMS...THE GFS AND ECMWF ARE ABOUT
12-18 HOURS OUT OF PHASE AND THE ECMWF HAS MUCH HIGHER AMPLITUDE TO
THE UPPER TROUGH. IN THE ABSENCE OF A GOOD MODEL CONSENSUS...WILL
ONLY CARRY CHANCE POPS. WHILE THERE CERTAINLY SHOULD BE MORE PCPN
FOR MIDWEEK...THE TIMING IS HIGHLY QUESTIONABLE.
KREIN
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 22Z...
* DIURNAL SHOWERS TIL EARLY EVE.
* CHANCES FOR SHOWERS LATE FRIDAY.
SHEA/TRS
//DISCUSSION...UPDATED 20Z...
WEAK INSTABILITY SHOWERS CONTINUE TO ADVANCE TO THE SOUTHEAST FROM
WISCONSIN THIS AFTERNOON. MESOANALYSIS SHOWED ROUGHLY 100 J/KG OF
SURFACE BASED CAPE...COUPLED WITH VERY COLD TEMPERATURES
ALOFT...THE SUFFICIENT DAYTIME HEATING SEEN THIS AFTERNOON...WAS
ENOUGH TO SPARK SCATTERED SHOWERS. CONFIDENCE ON THE CELLS MOVING
WITHIN THE VICINITY OF THE TERMINALS IS PRETTY HIGH...THOUGH
IMPACT WILL REMAIN LOW AS THE ODDS OF THESE SHOWERS MOVING ACROSS
THE TERMINAL IS NOT HAS HIGH. FOR NOW WILL ADD IN THE MENTION OF
VCSH AS TIMING INDIVIDUAL ELEMENTS OF THE CLUSTER WOULD BE
DIFFICULT. CIGS AND VIS SHOULD REMAIN VFR IF IMPACTED...BUT IT
WOULD BE SHORT LIVED. AS THE SUN SETS...THE SHOWERS WILL THEN
QUICKLY FADE. WITH THE COLD TEMPERATURES ALOFT AND THE LOW
FREEZING LEVELS...THERE IS THE CHANCE THAT SMALL GRAUPEL WOULD BE
NOTED WITH THE LIGHT SHOWERS. OTHERWISE...THE LIGHT AND EASTERLY
WINDS ACROSS THE EASTERN TERMINALS SHOULD WEAKEN MORE...TURN
NORTHERLY AND THEN BECOME VARIABLE OVERNIGHT.
SHEA
//DISCUSSION...UPDATED 18Z...
THE EXIT OF RAIN SHOWERS TO THE EAST HAS PROVED TO BE A BIT OF A
CHALLENGE WITH RESPECT TO THE WIND FORECAST THIS AFTERNOON. A LAKE
BOUNDARY HAS MOVED ACROSS THE TERMINALS AND PULLED WINDS AROUND TO
THE EAST THIS AFTERNOON. SYNOPTICALLY WINDS SHOULD BE OUT OF THE
NORTHEAST AND NO GUIDANCE INDICATED THAT A LB SHOULD FORM
TODAY...NOR IS IT REALLY FAVORABLE FOR THOSE CONDITIONS. SUSPECT
WINDS WILL REMAIN EASTERLY FOR THE NEXT FEW HOURS BEFORE REALLY
WEAKENING OVERNIGHT. OVERALL GUSTY CONDITIONS WITH THE BREEZE WERE
ALL LOCATED WITH THE LEADING EDGE OF THE BOUNDARY...AND SHOULD NOW
JUST REMAIN IN THE 7 KT RANGE WITH DIRECTIONS REMAINING NEARLY
EASTERLY...WITH SOME VARIANCE FROM NORTHEAST TO EAST. SHOWER
ACTIVITY FROM THIS MORNING HAS ENDED AND SHIFTED EAST...AND
SUBSIDENCE IN THE WAKE OF AN EXITING VORT HAS HELPED TO CLEAR
SKIES OUT FOR A SHORT TIME BEFORE A ROBUST CU FIELD DEVELOPED.
DAYTIME HEATING AND DEEP MIXING WILL ALLOW BASES TO CONTINUE TO
RISE THROUGH THE AFTERNOON...AND REMAIN VFR. CHANCES FOR PRECIP
INCREASE TOMORROW BEYOND THE TAFOR AS ANOTHER FRONT MOVES CLOSE.
SHEA
//ORD AND MDW CONFIDENCE...UPDATED 22Z...
* HIGH IN LGT VRB WIND THIS EVE AND OVERNIGHT.
* HIGH IN VFR THRU TONIGHT AND FRI.
* MEDIUM IN SCT SHRA DISSIPATION AROUND 00Z.
TRS
//OUTLOOK FOR ORD/MDW FOR 00Z SAT-12Z THU...UPDATED 12Z...
FRI NIGHT...VFR. SLIGHT CHANCE -SHRA.
SAT...VFR. WX NIL.
SUN...VFR. SLIGHT CHANCE -SHRA.
MON...VFR. WX NIL.
TUE...VFR. WX NIL.
WED...VFR. SHRA POSSIBLE.
LENNING
&&
.MARINE...
254 PM CDT
RIDGE OF HIGH PRESSURE WILL BUILD INTO THE WESTERN GREAT LAKES
REGION THIS EVENING AND CONTINUE OVERNIGHT...GRADUALLY DRIFTING
EAST. AS THE RIDGE DRIFTS EAST EARLY FRIDAY MORNING...WINDS WILL
TURN SOUTHWESTERLY OVER LAKE MICHIGAN. A DEVELOPING LOW PRESSURE
SYSTEM WILL THEN SLIDE EAST/SOUTHEAST ACROSS THE NORTHERN PLAINS AND
ARRIVE ACROSS THE WESTERN GREAT LAKES REGION FRIDAY NIGHT/SATURDAY.
SOUTHWEST WINDS AHEAD OF THIS FRONTAL BOUNDARY AND LOW PRESSURE
SYSTEM WILL INCREASE TO 15 TO 25 KT...THEN DECREASE SATURDAY
AFTERNOON. THEN YET ANOTHER STRONGER LOW PRESSURE SYSTEM IS POISED
TO ARRIVE ACROSS THE GREAT LAKES REGION SUNDAY...AND BRING INCREASED
WINDS TO POSSIBLY 30KT FOR MANY PORTIONS OF THE LAKE SUNDAY. THIS
MAY CREATE SMALL CRAFT CONDITIONS FOR THE NEARSHORE WATERS OF
ILLINOIS/INDIANA SUNDAY FROM INCREASED WINDS.
BEACHLER
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...FROST ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
ILZ011-ILZ012-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-
ILZ039...1 AM FRIDAY TO 7 AM FRIDAY.
IN...FROST ADVISORY...INZ010-INZ011-INZ019...1 AM FRIDAY TO 7 AM
FRIDAY.
LM...NONE.
&&
$$
