851 PM CDT
MADE SOME MINOR TWEAKS TO OVERNIGHT FORECAST GRIDS. GIVEN OVERCAST
SPREADING WELL BACK TO WEST AND NOT EXPECTED TO BREAK OVERNIGHT AND
TEMPERATURES ALREADY COOLING SLIGHTLY SLOWER THAN IN PREVIOUS
GRIDS...BUMPED MIN T UP A FEW DEGREES ACROSS THE AREA. REGARDING
LAKE EFFECT POTENTIAL...PARAMETERS LOOK DECENT ON FCAST SOUNDINGS
AND THINKING THERE WILL BE GOOD LAKESHORE CONVERGENCE ONCE PRECIP
MAKES IT DOWN TO NE IL...BUT WINDOW IS SHORT LIVED BEFORE WINDS OVER
LAKE GO MORE NNW AND SHIFT LAKE EFFECT FARTHER EAST THURSDAY
MORNING. THEREFORE...TIGHTENED UP POP GRADIENT IN COOK COUNTY TO
KEEP LIKELY POPS CONFINED TO FAR EASTERN COOK AND SCALED BACK CHANCE
WORDING TO LOWER END CHANCE FOR AREAS FARTHER INLAND IN COOK AND
LAKE. ALSO SLOWED ARRIVAL OF SLIGHT CHANCE POPS FOR AREAS
GENERALLY WEST OF A MCHENRY TO AURORA TO STREATOR LINE UNTIL
CLOSER TO DAYBREAK IN ASSOCIATION WITH AN UPPER LEVEL TROUGH
APPROACHING FROM THE WEST.
RC/MDB
//PREV DISCUSSION...
321 PM CDT
MAIN CONCERN FOR THE NEXT FEW DAYS WILL FOCUS ON LAKE EFFECT RAIN
SHOWERS DEVELOPING TONIGHT AND THEN TRANSITIONING TO TEMPERATURES
FOR THE NEXT FEW DAYS.
FOR THE REMAINDER OF THE AFTERNOON AND TONIGHT...THE STRONG COLD
FRONT HAS CLEARED CWA AND IS APPROACHING THE OHIO VALLEY. A MUCH
COOLER AIRMASS HAS OVERSPREAD OVER THE REGION AS PREVAILING
NORTHERLY WINDS SET UP OVER THE MIDWEST AND GREAT LAKES REGIONS.
SOME LIGHT RAIN MAY LINGER OVER THE FAR SOUTHERN COUNTIES THROUGH
THE EVENING...PERHAPS BEING ENHANCED BY A STRONG JET STREAM DIRECTLY
OVERHEAD.
OVERNIGHT TONIGHT AND INTO TOMORROW...THE MAIN PCPN CONCERN WILL
FOCUS ON LAKE EFFECT RAINSHOWERS OVER FAR NERN IL/NWRN INDIANA. HAVE
MADE LITTLE CHANGE TO THE GOING FORECAST IN THIS RESPECT AS THE
LATEST MODEL RUNS REMAIN RELATIVELY CONSISTENT WITH A NORTHERLY
FETCH OF COOLER AIR TO PERSIST THROUGH LATE THURSDAY AFTERNOON. AS
LAKE WATER TEMPS REMAIN RELATIVELY WARM COMPARED SFC TEMPS...AND SFC
TO 850MB DELTA-T OF 14-15C...THE LOW LEVEL ENVIRONMENT WILL BE
CONDUCIVE TO LAKE EFFECT PCPN. WILL ALSO MAINTAIN THE SLIGHT CHANCE
FOR THUNDER OVER FAR SRN LAKE MICHIGAN...ESPECIALLY FOR
THURSDAY...WHEN THE THE COOLEST AIR ALOFT...ASSOCIATED WITH A
PASSING UPPER TROUGH...WILL BE OVER LAKE MICHIGAN. WHILE THE ACTUAL
CHANCES FOR THUNDER WILL BE LOW...THE STEEP LAPSE RATES WILL AT
LEAST BE CONDUCIVE TO OCCASIONAL LOCALLY HEAVIER SHOWERS MIXING WITH
SOME GRAUPEL.
BY THURSDAY NIGHT...THE UPPER TROUGH WILL PASS TO THE EAST AND LOW
LEVEL FLOW WILL BEGIN TO BACK MORE WESTERLY...SHIFTING THE FOCUS OF
ANY REMAINING LAKE EFFECT SHOWERS OVER LOWER MICHIGAN AND NRN
INDIANA. NWRN PORTER COUNTY SHOULD BE THE ONLY PORTION OF THE LOCAL
CWA WHICH MAY SEE SOME PCPN LINGERING INTO THURSDAY EVENING.
THE FORECAST ELEMENT OF CONCERN WILL SHIFT TO TEMPERATURES...
ESPECIALLY FOR FRIDAY MORNING AND SATURDAY MORNING. MUCH OF THE
LINGERING LOW LEVEL CLOUD COVER SHOULD FINALLY CLEAR OUT THURSDAY
NIGHT AND INTO THE WEEKEND. THIS WILL ALLOW TEMPERATURES TO RADIATE
INTO THE LOWER 30S FOR MIN TEMPS FRIDAY MORNING AND SATURDAY
MORNING. DO NOT ANTICIPATE ANY SGFNT CHANCES FOR PCPN THROUGH
SATURDAY AS THE MAIN TRACK OF SHORT WAVE ENERGY WILL BE THROUGH THE
UPPER GREAT LAKES.
THE NEXT CHANCE FOR ANY PCPN WILL NOT COME UNTIL SUNDAY. THE LONGER
TERM MODELS ARE ADVERTISING A STRONG SHORT WAVE TO DROP OUT OF
CANADA AND INTO THE UPPER MISSISSIPPI VALLEY. THE LATEST 12Z RUNS OF
THE GFS AND ECMWF ARE RELATIVELY CONSISTENT WITH THE TIMING OF THE
SYSTEM...THOUGH THE GFS IS TRENDING QUITE A BIT DEEPER.
HOWEVER...THE STRENGTH DIFFERENCES WILL LIKELY HAVE LITTLE IMPACT ON
THE SENSIBLE WEATHER FORECAST. SINCE THE MAIN FORCING FROM THE
SYSTEM SHOULD BE OVER WISCONSIN AND NORTHERN LAKE MICHIGAN...WILL
ONLY CARRY SLIGHT CHANCE POPS FOR SUNDAY AT THIS TIME. FOR
TEMPERATURES...EXPECT HIGHS TO BE RELATIVELY CONSISTENT THROUGH
SATURDAY WITH HIGHS IN THE LOWER TO MIDDLE 50S. THERE SHOULD BE A
GRADUAL WARMING TREND SETTING UP BY EARLY NEXT WEEK. WITH THE UPPER
TROUGH MOVING OFF TO THE EAST...AN UPPER RIDGE IS EXPECTED TO BUILD
OVER THE UPPER MISSISSIPPI VALLEY AND INTO THE MIDWEST. SO...BY
EARLY NEXT WEEK...TEMPERATURES MAY REBOUND BACK INTO THE UPPER 50S
TO LOWER 60S.
KREIN
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 06Z...
* LAKE EFFECT SHOWERS AND MVFR CIGS NEARBY...MOST LIKELY
SOUTHEAST OF TERMINALS TOWARD GYY...BUT CLOSE TO MDW.
LENNING
//DISCUSSION...UPDATED 06Z...
LATEST RADAR IMAGES SHOWING SHOWERY LAKE EFFECT BANDS FORMING
NORTH OF THE GYY AREA AND WORKING ONSHORE AS ANTICIPATED. WINDS
AROUND THE PERIMETER OF THE LAKE ARE INDICATING A CONVERGENCE
TOWARD THE RELATIVELY WARM LAKE WATERS...THUS PROVIDING CONTINUED
LOW LEVEL SUPPORT FOR THIS SHOWER ACTIVITY...WHILE AN APPROACHING
UPPER LEVEL TROUGH WILL BE PROVIDING THE LARGE SCALE SUPPORT.
ACTIVITY SHOULD BE DIMINISHING THIS AFTERNOON AS THE MID LAKE
CONVERGENCE WEAKENS. A SURFACE RIDGE WORKING IN FROM SOUTHWEST OF
THE AREA WILL ALLOW WINDS TO TURN NORTHWEST LATER TODAY...AND
LIKELY GO LIGHT AND VARIABLE OVERNIGHT INTO FRIDAY MORNING.
LENNING
//ORD AND MDW CONFIDENCE...UPDATED 06Z...
* HIGH CONFIDENCE THAT ANY NEAR TERM MVFR WOULD BE SHORT LIVED.
* MEDIUM CONFIDENCE THAT SHOWERS AND MVFR CIGS WILL STAY SOUTH
AND EAST OF TERMINALS TODAY.
* HIGH CONFIDENCE IN GENERAL NORTHERLY WIND DIRECTION
TODAY...SLOWLY TURNING NORTHWEST.
LENNING
//OUTLOOK FOR ORD/MDW FOR 12Z FRIDAY-12Z WEDNESDAY...UPDATED 00Z...
FRIDAY...VFR. SLIGHT CHANCE -SHRA.
SATURDAY...VFR. WX NIL.
SUNDAY...VFR. SLIGHT CHANCE -SHRA.
MONDAY...VFR. WX NIL.
TUESDAY...VFR. WX NIL.
TRS
&&
.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.
&&
$$
