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 14Z...
* LAKE EFFECT SHOWERS THIS MORNING WITH BRIEF MVFR CIGS
SHEA
//DISCUSSION...UPDATED 12Z...
CONSIDERABLE DEVELOPMENT OF LAKE EFFECT RAIN SHOWERS OVER THE
SOUTHERN END OF THE LAKE THIS MORNING SHOULD POSE ONLY MINOR
PROBLEMS FOR ORD/MDW. LATEST TRENDS SHOW THESE BANDS DROPPING
SOUTH OF THESE TERMINAL AREAS OVER THE NEXT COUPLE OF
HOURS...FOCUSING MORE TOWARD GYY. PATCHY MVFR CIGS AROUND 2600FT
ARE ALSO PRESENT WITH THESE SHOWERS...BUT FEEL THAT THESE SHOULD
BE SHORT LIVED BASED ON UPSTREAM REPORTS. WINDS ALREADY HAVE
STARTED BACKING AROUND TO THE NORTHWEST...AND MAY DO SO FASTER
THAN CURRENT TAFS ARE DEPICTING. WIND SPEEDS SHOULD BE RELATIVELY
LIGHT TODAY AHEAD OF AN APPROACHING RIDGE...THEN LIKELY DECOUPLE
TO LIGHT AND VARIABLE OVERNIGHT.
LENNING
//ORD AND MDW CONFIDENCE...UPDATED 14Z...
* HIGH CONFIDENCE THAT -SHRA AND MVFR CIGS WILL BE SHORT AND PUSH
EAST
* MEDIUM CONFIDENCE IN WIND DIRECTIONS
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...
201 AM CDT
SEVERAL UPPER LEVEL DISTURBANCES/CLIPPER SYSTEMS SHOULD AFFECT THE
WEATHER OVER LAKE MICHIGAN OVER THE NEXT FEW DAYS. EACH DISTURBANCE
LOOKS TO PROVIDE AN INCREASE IN THE WINDS AND GOOD CHANCES FOR LAKE
EFFECT/LAKE ENHANCED SHOWERS AND POTENTIALLY SOME THUNDERSTORMS.
THE FIRST UPPER LEVEL DISTURBANCE OF INTEREST IS CURRENTLY
APPROACHING THE AREA FROM THE NORTHERN PLAINS. THIS WAVE WILL PUSH
ACROSS LAKE MICHIGAN LATER THIS MORNING. COLD TEMPERATURES ALOFT
ASSOCIATED WITH THIS DISTURBANCE SHOULD PROVIDE IDEAL THERMODYNAMIC
CONDITIONS FOR ADDITIONAL LAKE ENHANCED SHOWERS AND POTENTIALLY SOME
THUNDERSTORMS TO DEVELOP ACROSS THE WARMER WATERS OF LAKE MICHIGAN
THROUGH THE MORNING HOURS TODAY. THIS ACTIVITY SHOULD DIMINISH DURING
THE AFTERNOON HOURS.
ANOTHER DISTURBANCE WILL RACE SOUTHEASTWARD ACROSS THE LAKE LATER
FRIDAY AND FRIDAY NIGHT. THIS AGAIN LOOKS TO SET UP DECENT
THERMODYNAMIC CONDITIONS FOR LAKE EFFECT
SHOWERS/THUNDERSTORMS...ESPECIALLY ACROSS THE EASTERN HALF OF THE
LAKE. IN ADDITION TO THE THREAT FOR PRECIPITATION...SOUTHWESTERLY
WINDS LOOK TO INCREASE TO 15 TO 20 KT AHEAD OF THE SURFACE LOW
DURING THE DAY ON FRIDAY.
FINALLY...A THIRD A POTENTIALLY STRONGER CLIPPER SYSTEM LOOKS TO
MOVE ACROSS LAKE MICHIGAN SATURDAY NIGHT THROUGH SUNDAY. THIS
DISTURBANCE COULD PRODUCE STRONGER SOUTHERLY WINDS IN THE 20 TO 30
KT RANGE ON SUNDAY AS THE SURFACE LOW APPROACHES FROM THE UPPER
MISSISSIPPI RIVER VALLEY.
KJB
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
UNTIL 10 AM THURSDAY.
&&
$$
