335 AM CDT
THE MAIN FORECAST CONCERNS WILL BE THE POTENTIAL FOR FROST ACROSS MY
WESTERN COUNTIES TONIGHT. AND A WIDESPREAD FREEZE FOR MY WESTERN AND
SOUTHERN COUNTIES SATURDAY NIGHT.
IT WILL CONTINUE TO BE A BREEZE DAY ACROSS THE AREA TODAY AS
COLDER AIR CONTINUES TO FILTER SOUTH ACROSS THE AREA. HOWEVER...IT
APPEARS THE WINDOW FOR ADVISORY CRITERIA WINDS HAS PASSED.
THEREFORE...I WILL END THE ADVISORY FOR ALL BUT LAKE AND PORTER
INDIANA. THESE AREAS WILL LIKELY CONTINUE TO EXPERIENCE LOW END
ADVISORY FORCE WINDS OFF THE LAKE THROUGH MID TO LATE MORNING...SO
I HAVE EXTENDED THE ADVISORY THROUGH 18 UTC FOR THESE TWO
NORTHWEST INDIANA COUNTIES.
PRECIPITATION WILL END FOR ALL BUT THE NORTHWEST INDIANA COUNTIES
AND THE ADJACENT ILLINOIS COUNTIES...WHERE LAKE EFFECT SHOWERS MAY
CONTINUE. THE COLD AIR MASS IS SETTING UP A FAVORABLE THERMODYNAMIC
ENVIRONMENT ACROSS LAKE MICHIGAN FOR LAKE EFFECT RAIN SHOWERS.
SURFACE TO 850 DELTA T'S WILL RUN BETWEEN 18 TO 20 DECREES
CELSIUS. THIS SHOULD RESULT IN LAKE INDUCED EL'S IN EXCESS OF
15,000 FT LATE TODAY AND THIS EVENING. OUR LOCAL WRF MODEL
INDICATES THAT THE WINDS ACROSS THE LAKE WILL VEER FROM THE
NORTHWEST TO THE NORTH LATER TODAY AS SURFACE HIGH PRESSURE ACROSS
THE PLAINS BUILDS EAST. THIS LOOKS TO SET UP GOOD BOUNDARY LAYER
CONVERGENCE ALONG THE NORTHWEST INDIANA COUNTIES INTO TONIGHT.
THIS WOULD LIKELY SHIFT ANY BAND OF LAKE EFFECT SHOWERS WESTWARD
ACROSS MY NORTHWEST INDIANA COUNTIES BY THIS EVENING. I SUSPECT THAT
THESE LAKE INDUCED SHOWERS MAY CONTINUE INTO SATURDAY
MORNING...AND COULD ALSO SHIFT BACK ACROSS PORTIONS OF
NORTHEASTERN ILLINOIS. HOWEVER...THE THERMODYNAMIC ENVIRONMENT
WILL QUICKLY BECOME LESS FAVORABLE FOR SHOWERS ON SATURDAY AS WARMER
MID LEVEL TEMPERATURES LOWER INVERSION HEIGHTS.
FARTHER WEST AWAY FROM THE LAKE...FROST WILL BE THE MAIN
CONCERN...ESPECIALLY SATURDAY NIGHT. ALTHOUGH THERE WILL LIKELY BE A
DECK OF STRATO CU THAT DEVELOPS ACROSS THE AREA THIS
AFTERNOON...SKIES SHOULD QUICKLY CLEAR ACROSS NORTH CENTRAL ILLINOIS
THIS EVENING. AT THE SAME TIME WINDS WILL BE ABATING AS THE SURFACE
HIGH BUILDS EAST ACROSS THE UPPER MISSISSIPPI RIVER VALLEY. THIS
SHOULD ALLOW MY NORTH CENTRAL ILLINOIS COUNTIES TO DROP INTO THE 30S
TONIGHT. THIS WOULD POTENTIALLY SET THE STAGE FOR AREAS OF FROST IN
THESE AREAS. HOWEVER...DUE TO UNCERTAINTIES ON HOW QUICKLY THE WINDS
WILL DIE OFF...I DECIDED TO HOLD OFF ON FROST HEADLINES FOR NOW.
THE SURFACE HIGH WILL BUILD EAST SOUTHEASTWARD ACROSS NORTHERN
ILLINOIS ON SATURDAY AND SATURDAY NIGHT. TEMPERATURES WILL LIKELY
REMAIN IN THE MID 50S IN MOST AREAS ON SATURDAY...AND WITH THE
SURFACE HIGH OVERHEAD SATURDAY NIGHT...THE POTENTIAL IS THERE FOR A
WIDESPREAD FREEZE FOR PORTIONS OF NORTH CENTRAL ILLINOIS AND THE
WESTERN SUBURBS OF CHICAGO. A FREEZE WATCH MAY BE NEEDED IN THE
FUTURE DURING THIS PERIOD.
AN UPPER LEVEL RIDGE WILL BUILD EASTWARD ON SUNDAY...SETTING UP WARM
WESTERLY SURFACE FLOW. IT APPEARS A NICE PERIOD OF WARM AND DRY
WEATHER IS SETTING UP FOR THE FIRST WEEK OF OCTOBER. TEMPERATURES
WILL LIKELY BE IN THE 70S AS SOON AS MONDAY.
KJB
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 1920Z...
* NORTHWEST WINDS GUSTING TO 25-28 KT AT TIMES THIS AFTERNOON.
* SCATTERED -SHRA POSSIBLE LATE THIS AFTERNOON.
* SCT-BKN SKIES 3500-4500 FT.
* POTENTIAL FOR LAKE EFFECT SHRA LATER TONIGHT/SATURDAY MORNING.
* POTENTIAL FOR 2000-3000 FT LAKE EFFECT CIGS OVERNIGHT THROUGH
SATURDAY MORNING.
MDB
//DISCUSSION...UPDATED 1920Z...
WEAK UPPER WAVE AND STEEP LAPSE RATES HAVE RESULTED IN SCATTERED
SHOWER DEVELOPMENT ACROSS SOUTHERN WI WHICH ARE QUICKLY MOVING
SOUTHWARD. HAVE ADDED VCSH TO THE ORD/MDW/DPA TAFS FROM 21-00Z AND
IT IS POSSIBLE THAT THESE MAY IMPACT THE TERMINALS FOR BRIEF
PERIODS AND BRING ENOUGH RAIN TO AT LEAST WET THE RUNWAYS.
ACTIVITY WILL DIMINISH WITH SUNSET.
FROM 18Z...
NORTH TO NORTH-NORTHWEST WINDS CONTINUE EARLY THIS AFTERNOON AND
EXPECT THAT GUSTS WILL INCREASE TO AROUND 25 KT OR SLIGHTLY
HIGHER...WITH GUSTS OF 25-30 KT CONTINUING AT GYY. SCT-BKN LOWER
END VFR SKIES WILL CONTINUE THROUGH THE AFTERNOON WITH SKIES WELL
INLAND OF THE LAKE SEEING CLEARING AS THE SUN SETS. AREAS NEAR THE
LAKE AND ACROSS MUCH OF NORTHWEST INDIANA WILL SEE AT LEAST
SCATTERED SKIES CONTINUE THIS EVENING...WITH BROKEN SKIES PROBABLY
PREVAILING AT GYY THANKS TO THE LAKE. LAKE EFFECT SHOWERS WILL
BECOME MORE LIKELY INTO THE EVENING AND ESPECIALLY TONIGHT WITH
CURRENT RADAR MOSAIC SHOWING SOME DEVELOPMENT TRYING TO ORGANIZE
DOWN THE LONG AXIS OF THE LAKE. INITIAL ACTIVITY SHOULD STAY JUST
EAST OF GYY BUT WILL LIKELY DRIFT WESTWARD WITH TIME. MAY BE A
LITTLE SLOW ON THE VCSH MENTION THERE BUT ITS NOT COMPLETELY CLEAR
HOW QUICKLY THE BANDS WILL INTO THE EVENING. CONFIDENCE IS BETTER
IN LAKE EFFECT SHRA EVOLUTION INTO TONIGHT. LOW LEVEL FLOW WILL
BECOME SLIGHTLY EAST OF NORTH WITH CONVERGENCE SETTING UP ON THE
WESTERN SHORE OF THE LAKE. THIS WOULD SUPPORT A WESTWARD MOVEMENT
TO ANY ACTIVITY THIS EVENING AND OVERNIGHT. THIS WILL BRING AT
LEAST THE CHANCE FOR SHRA TO THE ILLINOIS SHORELINE OVERNIGHT INTO
SATURDAY MORNING WITH ACTIVITY POSSIBLY MOVING AS FAR INLAND AS
ORD/MDW. STILL SOME QUESTION IF DEVELOPMENT WILL CONTINUE
OVERNIGHT WITH PARAMETERS WANING A BIT BUT WILL STICK WITH VCSH
MENTION AT ORD/MDW. MVFR CIGS ARE ALSO POSSIBLE THERE...AS WELL AS
DPA. SHRA ACTIVITY SHOULD SHUTOFF BY EARLY AFTERNOON ALLOWING
SCATTERING OF SKIES. FURTHER INLAND...INCLUDING RFD...SKIES WILL
PROBABLY BE MOSTLY CLEAR WITH SOME STRATOCU POSSIBLY DEVELOPING
LATE MORNING. WINDS WILL BE LIGHTER WITH SOME GUSTS TO NEAR 20 KT
POSSIBLE DURING THE AFTERNOON.
MDB
//ORD AND MDW CONFIDENCE...UPDATED 1920Z...
* HIGH CONFIDENCE IN WIND FORECAST.
* MEDIUM-HIGH CONFIDENCE THAT -SHRA WILL MOVE INTO THE AREA
21-22Z...MAY DIRECTLY AFFECT TERMINALS FOR BRIEF PERIODS...BUT
ACTIVITY IS WIDELY SCATTERED.
* HIGH CONFIDENCE IN CEILING FORECAST THIS AFTERNOON.
* MEDIUM CONFIDENCE IN LAKE EFFECT SHRA AT LEAST BEING IN THE
VICINITY OF THE AIRPORT LATE TONIGHT AND SATURDAY MORNING.
* MEDIUM-HIGH CONFIDENCE IN LAKE EFFECT CEILINGS LATE TONIGHT AND
SATURDAY MORNING BUT LOW CONFIDENCE IN THEM BEING BELOW 3000 FT.
MDB
//OUTLOOK FOR ORD/MDW FOR 00Z SUNDAY-12Z FRIDAY...UPDATED 12Z...
SATURDAY NIGHT THROUGH THURSDAY...VFR.
MDB
&&
.MARINE...
143 PM CDT
MARINE FORECAST CONCERNS ARE FOCUSED ON GRADUAL DECREASE IN STRONG
NORTHERLY WINDS ACROSS LAKE MICHIGAN...HIGH WAVES AND ASSOCIATED
STORM/GALE/SMALL CRAFT ADVISORY HEADLINE ISSUES INTO SUNDAY.
LOW PRESSURE CONTINUES TO FILL NEAR TORONTO ONTARIO EARLY THIS
AFTERNOON. THIS LOW WILL CONTINUE TO WEAKEN AS IT DRIFTS EAST ACROSS
UPSTATE NEW YORK THIS EVENING...AND EVENTUALLY REFORMS OFF THE EAST
COAST. AS THIS OCCURS...HIGH PRESSURE OVER WESTERN ONTARIO AND THE
UPPER MIDWEST WILL SLOWLY DRIFT SOUTHEAST ACROSS THE NORTHERN AND
WESTERN GREAT LAKES AND THE MID MISSISSIPPI VALLEY THROUGH SUNDAY
MORNING. THIS WILL ALLOW CONTINUED GRADUAL WEAKENING OF THE SURFACE
PRESSURE GRADIENT ACROSS LAKE MICHIGAN.
AFTER THIS MORNINGS GUSTS IN EXCESS OF 50 KTS...AND WAVES HIGHER
THAN 20 FT PER BUOY AND SHIP OBS...WINDS HAVE SETTLED TO 35-40 KTS
FOR THE MOST PART ACROSS THE OPEN WATERS AND THE SOUTH SHORE WITH
WAVES NOW IN THE 12-15 FOOT RANGE PER LATEST BUOY OBS. THUS HAVE
ALLOWED THE STORM WARNING TO EXPIRE AS OF 1 PM CDT...REPLACED BY A
GALE WARNING WHICH WILL RUN THROUGH 1 AM CDT SATURDAY BASED ON
CONSISTENT MODEL GUIDANCE. WITH EXPIRATION OF GALE WARNINGS
TONIGHT...WILL HAVE TO HOIST SMALL CRAFT ADVISORIES FOR THE ILLINOIS
AND INDIANA NEARSHORE WATERS. LONG NORTHERLY FETCH AND CONTINUED
RATHER GRADUAL DECLINE IN WIND SPEEDS WILL HELP TO MAINTAIN WAVES
WELL ABOVE 4 FT PARTICULARLY ALONG THE INDIANA SHORE INTO SUNDAY
MORNING. WILL LIKELY BE ABLE TO KEEP ILLINOIS SHORE SMALL CRAFT
ADVISORIES A LITTLE SHORTER...WITH A SLIGHTLY MORE FAVORABLE FETCH
FOR ALLOWING WAVES TO SUBSIDE.
WINDS AND WAVES SHOULD BE MUCH LOWER FROM SUNDAY INTO THE MIDDLE OF
NEXT WEEK...AS BLOCKING PATTERN ALOFT ALLOWS HIGH PRESSURE RIDGE TO
LINGER ACROSS THE CENTRAL PART OF THE NATION AND THE WESTERN LAKES.
IN FACT WIND DIRECTION FORECAST BECOMES A BIT UNCERTAIN DUE TO VERY
WEAK GRADIENT DURING THIS PERIOD.
RATZER
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...LAKESHORE FLOOD WARNING...INZ002 UNTIL 4 PM FRIDAY.
LM...GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ744-LMZ745-LMZ777-
LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 1 AM
SATURDAY.
GALE WARNING...NEARSHORE WINTHROP TO WILMETTE HARBORS UNTIL 4 PM FRIDAY.
GALE WARNING...LMZ741-LMZ742-LMZ743 UNTIL 10 PM FRIDAY.
&&
$$
