328 AM CDT
PRIMARY FORECAST CHALLENGE IS LAKE EFFECT POTENTIAL THIS MORNING
FOLLOWED BY TIMING AND ACCESSING THE POTENTIAL IMPACTS OF THE FAST
MOVING NW FLOW CLIPPERS THE NEXT WEEK.
THE LAKE EFFECT MACHINE IS BEGINNING TO CRANK UP EARLY THIS MORNING
WITH WSR-88D MOSAIC SHOWING A BAND OF SCTD SHOWERS LIGHTING OVER THE
WESTERN PORTIONS OF THE LAKE FROM EAST OF DOOR COUNTY SSW TO INLAND
OVER EXTREME SOUTHEAST WI. EXPECT TO SEE A CONTINUED UPTICK IN BOTH
COVERAGE WITHIN THE BAND AND ESPECIALLY IN INTENSITY AS MID-LEVELS
COOL AND EQUILIBRIUM LEVELS CONTINUE TO RISE IN RESPONSE. SERIES OF
ACARS SOUNDINGS OUT OF RFD SHOWS THIS PROCESS IS ALREADY UNDER WAY
WITH UP TO 4C COOLING HAVING TAKEN PLACE IN JUST THE PAST FEW HOURS
BETWEEN 800-600MB. WHAT WE WILL BE LACKING IN THE GIRTH OF THE
POSITIVE (BUOYANT) AREA IN THE SOUNDINGS WE WILL BE MAKING UP WITH
WITH THE DEPTH AS EQUILIBRIUM LEVELS RISE TO OVER 20KFT THIS MORNING
OVER THE LAKE. LAKE INDUCED CAPE VALUES OVER 500 J/KG WITH EL'S
ABOVE THE -20C STILL WOULD SUGGEST A THREAT OF ISOLATED T-STORMS
THIS MORNING NEAR THE LAKE. THE STEEP LAPSE RATES AND LOW FREEZING
LEVELS WOULD ALSO SUPPORT SOME POTENTIAL FOR GRAUPEL THIS MORNING.
LAKE EFFECT SHOULD SHIFT EAST INTO INDIANA THIS MORNING AND THEN OUT
OUR CWA LATER THIS AFTERNOON AS LOW LEVEL FLOW VEERS. GIVEN THE VERY
COLD TEMPS ALOFT HARD TO RULE OUT AN ISOLATED SHOWER...EVEN OUTSIDE
OF THE LAKE EFFECT AREAS...THOUGH WITH LARGE SCALE FORCING SHIFTING
EAST THE THREAT WILL BE MAINLY THIS MORNING. MID/UPPER LEVEL
CLOUDINESS WILL CLEAR OUT QUICKLY THIS MORNING AS TROUGH AXIS SHIFTS
EASTWARD...BUT STEEP LOW LEVEL LAPSE RATES SHOULD ALLOW A HEALTHY
STRATOCUMULUS FIELD TO FILL IN THIS AFTERNOON. WORRIED THAT IT COULD
TAKE SOME TIME FOR THE STRATOCUMULUS TO DISSIPATE AFTER SUNSET BY
WHICH TIME WE COULD ALREADY SEE AN INCREASE IN MID/HIGH CLOUDS AS
WAA ALOFT DEVELOPS IN ADVANCE OF THE NEXT WAVE. THAT MAKES TEMP
FORECAST VERY TRICKY FOR TONIGHT AS SEVERAL HOURS OF CLEAR SKIES
COULD ALLOW SOME AREAS TO DIP BELOW FREEZING...WHILE CONVERSELY MOVE
CLOUDS THAN EXPECTED WOULD LIKELY KEEP TEMPS WARMER THAN WHATS IN
THE GRIDS. FROST/FREEZE THREAT IS NOT ZERO TONIGHT...BUT THERE IS
TOO MUCH UNCERTAINTY TO HOIST ANY SORT OF HEADLINES YET. (NOTE: WE
WILL CONTINUE TO ISSUE FROST/FREEZE HEADLINES UNTIL OCT 31ST OR THE
FIRST HARD FREEZE...WHICH EVER COMES FIRST)
NEXT CLIPPER WILL SWING ACROSS THE REGION FRIDAY. WARM AIR ADVECTION
AHEAD OF IT SHOULD PROVIDE SOME SOME SLIGHTLY MODERATION IN TEMPS
FRIDAY BEFORE THE NEXT QUICK SHOT OF COLD AIR ADVECTION FRIDAY NIGHT
INTO SATURDAY. HAVE MAINTAINED A SLIGHT CHANCE OF SHRA IN THE GRIDS
FRIDAY AFTERNOON IN ADVANCE OF THIS SHORTWAVE. WHILE IT WILL BE
MOISTURE STARVED...WHAT IT LACKS IN MOISTURE IT MAKES UP FOR WITH
COLD AIR ALOFT/STEEP LAPSE RATES AND THAT COULD BE ENOUGH TO
COMPENSATE FOR THE DEARTH OF MOISTURE TO SUPPORT SOME SMALL CHANCE
OF ISOLATED/SCATTERED PM SHOWERS.
WE LOOK TO DO IT ALL OVER AGAIN OVER THE WEEKEND WITH ANOTHER SHOT
OF WARM AIR ADVECTION SAT NIGHT INTO SUNDAY AHEAD OF THE NEXT
CLIPPER. MODELS HAVE TRENDED MUCH STRONGER WITH THIS WAVE AND NOW
CLOSE OFF A DEEP TROPOSPHERIC CIRCULATION...THOUGH TEMPS ALOFT LOOK
TO BE MUCH WARMER WITH THIS WAVE RESULTING IN WEAKER LOW/MID LEVEL
LAPSE RATES/INSTABILITY. LIKE ITS YOUNGER BROTHER...THIS CLIPPER
WILL BE LACKING MOISTURE...BUT THE LACK OF MOISTURE AND INSTABILITY
COULD BE COMPENSATED FOR BY THE STRONGER DIFF VORT ADVECTION AND
RESULTANT QG FORCING. HAVE OPTED TO MAINTAIN THE GOING SMALL CHANCE
POPS FOR SUNDAY...BUT THE CHANCES LOOK SLIM AND EVEN IF SHOWERS DO
DEVELOP THEY WOULD BE FAST MOVING...BRIEF...AND RATHER
INSIGNIFICANT. OVERALL THE WEEKEND LOOKS 95%+ DRY AND SEASONABLE.
COULD LITERALLY CUT AND PASTE THE PREVIOUS PARAGRAPH INTO THIS ONE
AND JUST REPLACE THE DAYS OF THE WEEK AS WE DO IT ALL OVER AGAIN
NEXT WEEK. THE BIGGEST DIFFERENCE IS THAT MEDIUM RANGE MODELS ARE
GRADUALLY BREAKING DOWN THE HUDSON BAY VORTEX AND THEREFORE THE NEXT
CLIPPER IS EXPECTED TO TRACK EVEN FARTHER NORTH. THIS COULD RESULT
IN A MORE SUBSTANTIAL WARM UP TUESDAY WITH HIGHS CLIMBING INTO THE
60S...THOUGH HAVE KEPT TEMPS SOMEWHAT CONSERVATIVE IN THE
GRIDS/FORECAST FOR NOW AS ALLBLEND NUMBERS HAVENT QUITE LATCHED ON
TO SUCH OPTIMISM.
IZZI
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 20Z...
* LIGHT DIURNAL SHOWERS
* EASTERLY WINDS THIS AFTERNOON
* CHANCES FOR SHOWERS LATE FRIDAY
SHEA
//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 18Z...
* LOW CONFIDENCE ON EASTERLY WIND DURATION...HIGH ON WINDS
BECOMING LIGHT THIS EVENING
* HIGH CONFIDENCE IN CIG/VIS FORECAST THROUGH THE OVERNIGHT HOURS
* MEDIUM ON PRECIP THIS EVENING
SHEA
//OUTLOOK FOR ORD/MDW FOR 00Z SATURDAY-12Z THURSDAY...UPDATED 12Z...
FRIDAY NIGHT...VFR. SLIGHT CHANCE -SHRA.
SATURDAY...VFR. WX NIL.
SUNDAY...VFR. SLIGHT CHANCE -SHRA.
MONDAY...VFR. WX NIL.
TUESDAY...VFR. WX NIL.
WEDNESDAY...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.
&&
$$
