326 PM CDT
MAIN CONCERNS FOR AFTERNOON FORECAST PACKAGE REVOLVE AROUND
OVERNIGHT LOW TEMPERATURES AND WIDESPREAD FROST LATE TONIGHT INTO
SUNDAY MORNING...BUT OTHERWISE WE WILL BE ENTERING A RATHER TRANQUIL
PERIOD OF WEATHER WITH FEW CONCERNS.
A RIDGE OF HIGH PRESSURE EXTENDS FROM LAKE SUPERIOR SOUTHWEST
TOWARDS THE MID MISSISSIPPI VALLEY THIS AFTERNOON WITH LIGHT
NORTHEASTERLY FLOW IN PLACE OVER MUCH OF THE CWA. THE EXCEPTION IS
ALONG THE LAKE SHORE WHERE GUSTY NNE WINDS CONTINUE TO MOVE OFF THE
LAKE...BUT THESE WINDS WILL CONTINUE TO DIMINISH THROUGH THE EVENING
AS THE PRESSURE GRADIENT SLACKENS. NOT TOO MUCH CLOUD COVER TO SPEAK
OF AWAY FROM THE LAKE. SOME FLAT CU WILL DISSIPATE WITH LOSS OF
DAYTIME HEATING...AND LAKE GENERATED CLOUDS WILL BECOME LESS
FAVORABLE OVERNIGHT AS H85 TEMPS WARM WITH APPROACHING THERMAL RIDGE
ALLOWING INVERSION HEIGHTS TO DECREASE BELOW LAKE LCL HEIGHTS
OVERNIGHT PER NAM BUFR SOUNDINGS.
AFTER MIDNIGHT TONIGHT...THE SURFACE RIDGE AXIS WILL SHIFT EASTWARD
TO THE WESTERN PORTIONS OF THE CWA. THIS WILL SET UP FAVORABLE
CONDITIONS FOR RADIATIONAL COOLING WITH WINDS GOING CALM GENERALLY
WEST OF THE I-355/I-290 CORRIDOR AND SKIES MOSTLY CLEAR. OPTED TO
CONTINUE FORECAST FOR TEMPERATURES BELOW ALL GUIDANCE ACROSS OUR
WEST...AND TOWARDS LOWER END OF THE SPECTRUM FOR THE REMAINDER OF
THE CWA. WITH TEMPERATURES EXPECTED TO FALL INTO THE LOW TO MID 30S
FOR MUCH OF THE CWA...HOISTED A FROST ADVISORY FOR THE ENTIRE
CWA...EXCEPT FOR COUNTIES ALONG THE LAKE. AM A LITTLE UNCERTAIN ON
HOW TO HANDLE LAKE COUNTY ILLINOIS AND PORTIONS OF FAR N/NW COOK
COUNTY. WOULD EXPECT TO SEE LAND BREEZE DEVELOP OVERNIGHT WHICH MAY
ALLOW TEMPERATURES TO DROP A LITTLE FURTHER THAN EXPECTED...BUT FOR
NOW ONLY INCLUDED PATCHY FROST FOR THESE AREAS...AND WILL MONITOR
SHORT TERM TRENDS FOR POTENTIAL UPDATES. FOR THE REMAINDER OF COOK
COUNTY...AS WELL AS LAKE AND PORTER COUNTIES IN INDIANA...NORTHERLY
FLOW OFF THE LAKE SHOULD PROP UP TEMPERATURES ALONG THE
SHORE...AS SHOULD URBAN HEAT ISLAND EFFECTS WHICH WILL KEEP
TEMPERATURES IN THE MID 40S NEAR DOWNTOWN CHICAGO.
BEYOND SUNDAY MORNING...UPPER RIDGE IS EXPECTED TO BUILD ACROSS THE
REGION AND PRETTY MUCH STAY IN PLACE THROUGH THE WEEK. H85 TEMPS
RISE FROM THE LOW SINGLE DIGITS TODAY INTO THE MID TEENS BY MONDAY.
SURFACE TEMPS MONDAY WILL REBOUND INTO THE UPPER 60S AND LOW
70S...AND WILL CONTINUE A SLOW WARMING TREND THROUGH THURSDAY WHEN
TEMPERATURES TOP OUT IN THE MID TO UPPER 70S. MODELS ARE IN DECENT
AGREEMENT THROUGH THE END OF THE WEEK...LENDING TO HIGH CONFIDENCE
IN THE PLEASANT FORECAST THROUGH THE WEEK. GLOBAL ENSEMBLE MEMBERS
AS WELL AS OPERATIONAL GFS/ECMWF SOLUTIONS BEGIN TO DIVERGE FRIDAY
INTO THE WEEKEND ON HOW FAR EAST TO PROGRESS THE UPPER RIDGE. THE
GFS HAS ACTUALLY TRENDED TOWARDS THE ECMWF WHICH IS ON THE SLOWER
END OF THE SPECTRUM...WHICH KEEPS FAIR WEATHER IN THE AREA AT
LEAST LATE INTO THE WEEKEND. GFS ENSEMBLE MEAN HOWEVER INDICATES
POTENTIAL FOR A COLD FRONT TO COME THROUGH THE REGION ON SATURDAY.
KEPT FORECAST DRY THOUGH FRIDAY...BUT INTRODUCED SLIGHT CHANCE
POPS FOR SATURDAY.
BMD
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 00Z...
* NORTH-NORTHEAST WINDS 010-040 DEG CONTINUE TO DIMINISH THIS
EVENING...AND BECOME LIGHT 340-350 LATER TONIGHT.
RATZER
//DISCUSSION...UPDATED 00Z...
HIGH PRESSURE CONTINUES TO BUILD IN FROM THE NORTHWEST EARLY THIS
EVENING...INDUCING NORTH-NORTHEAST WINDS ACROSS THE TERMINALS.
GRADIENT CONTINUES TO WEAKEN AS THE HIGH APPROACHES...WITH WINDS
EXPECTED TO DECOUPLE THIS EVENING AND REMAIN LESS THAN 10 KTS
THROUGH SUNDAY. WITH RELATIVELY LIGHT NORTHWEST WINDS ON SUNDAY
AND SURFACE RIDGE JUST TO THE WEST OF CHICAGO...THERE IS SOME
CONCERN THAT WINDS COULD TURN NORTH-NORTHEAST AGAIN WITH A LIGHT
LAKE BREEZE IN THE AFTERNOON. GUIDANCE IS NOT INDICATING
THIS...EVEN HIGH RESOLUTION LOCALLY RUN WRF...THUS CONFIDENCE IS
LOW IN THIS OCCURRING. EXPECT GYY WILL HAVE THE GREATEST POTENTIAL
FOR A MORE NORTHERLY COMPONENT AND HAVE INDICATED THIS IN THE KGYY
TAF.
OTHERWISE...MID-LEVEL WARMING AND LOWERING OF INVERSION OVER LAKE
MICHIGAN HAS RESULTED IN RAPID DECREASE IN LAKE-INDUCED CLOUD
COVER THIS AFTERNOON. AS FLOW ABOVE BOUNDARY LAYER IS PROGGED TO
BECOME SLIGHTLY NORTHEAST OVERNIGHT THERE IS SOME SLIGHT CHANCE OF
SOME PATCHY STRATOCU...THOUGH VERY LOW PROBABILITY OF CEILINGS.
SOME LIGHT GROUND FOG ALSO A POSSIBILITY MAINLY WEST OF CHICAGO
CLOSER TO THE SURFACE RIDGE AXIS. HAVE MAINTAINED MIFG MENTION IN
THE RFD AND DPA TAFS...THOUGH RECENT SUNNY AND BREEZY CONDITIONS
ARGUE AGAINST SIGNIFICANT VISIBILITY RESTRICTIONS. DEW/FROST
DEPOSITION IS PERHAPS MORE LIKELY THAN ANY SIGNIFICANT GROUND FOG
SUNDAY MORNING.
RATZER
//ORD AND MDW CONFIDENCE...UPDATED 00Z...
* HIGH CONFIDENCE IN ALL ELEMENTS.
RATZER
//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...
MONDAY THROUGH FRIDAY...VFR.
RATZER
&&
.MARINE...
246 PM CDT
WINDS ARE CONTINUING TO SLOWLY DIMINISH ACROSS THE LAKE THIS
AFTERNOON AS HIGH PRESSURE SPREAD FROM LAKE SUPERIOR SOUTHWARD INTO
IOWA AND MISSOURI SLOWLY DRIFTS EAST AND WEAKENS SLIGHTLY. SPEEDS
WILL REMAIN IN THE10 TO 20 KT RANGE NORTH THIS EVENING WITH 15 TO 25
KT ACROSS THE SOUTH HALF BUT THESE WILL DIMINISH TO 10 TO 15 KT
NORTH AND 10 TO 20 KT SOUTH TONIGHT. SPEEDS WILL REMAIN STEADY
ACROSS THE NORTH HALF SUNDAY BUT THERE MAY BE A SLIGHT INCREASE TO
THE 15-20 RANGE ACROSS THE SOUTH DURING THE DAY. DIRECTION WILL
REMAIN NORTH TO NORTHEAST INTO SUNDAY MORNING BUT SHOULD TURN
NORTH TO NORTHWEST AFTER THAT. WITH THE PERSISTENT NORTH TO
NORTHEAST WINDS WAVES WILL BE SLOW TO SUBSIDE ACROSS THE SOUTH END
OF THE LAKE. WILL NEED TO EXTEND THE SMALL CRAFT ADVISORY THROUGH
SUNDAY MORNING. THIS MAY NEED TO RUN LONGER FOR THE INDIANA
NEARSHORE IF WINDS PICK UP SLIGHTLY SUNDAY AFTERNOON AND KEEP
WAVES UP. GENERALLY LIGHT WINDS WILL THEN BE IN PLACE AS THE HIGH
PARKS OVER THE LAKE LATER SUNDAY AND REMAINS THERE THROUGH THE
EARLY PART OF NEXT WEEK. A VARIABLE NORTHERLY DIRECTION SHOULD
PREVAIL INTO TUESDAY BUT SHIFT TO A STEADIER SOUTHERLY DIRECTION
TUESDAY. SPEEDS WILL THEN PICK UP WEDNESDAY AS THE PRESSURE
GRADIENT INCREASES BUT THIS INCREASE LOOKS TO BE RATHER MODEST
WITH THE ABSENCE OF ANY SIGNIFICANT LOW PRESSURE SYSTEMS AFFECTING
THE REGION THROUGH THE WEEK.
MDB
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...FROST ADVISORY...ILZ003-ILZ004-ILZ005-ILZ008-ILZ010-ILZ011-
ILZ012-ILZ013-ILZ019-ILZ020-ILZ021-ILZ022-ILZ023-ILZ032-
ILZ033-ILZ039...2 AM SUNDAY TO 8 AM SUNDAY.
IN...FROST ADVISORY...INZ010-INZ011-INZ019...2 AM SUNDAY TO 8 AM
SUNDAY.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
UNTIL 10 AM SUNDAY.
&&
$$
