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 18Z...
* 010-040 WINDS GUSTING TO AROUND 20 KT CONTINUING THROUGH THE
AFTERNOON.
* SCT-BKN 030-035 CLOUDS NEXT HOUR OR TWO WITH DECREASING COVERAGE
CONTINUING THROUGH MID AFTERNOON.
MDB
//DISCUSSION...UPDATED 18Z...
NORTH-NORTHEAST WINDS CONTINUE AHEAD OF HIGH PRESSURE WHICH WILL
BUILD IN FROM THE WEST TONIGHT. WINDS CONTINUE TO GUST TO AROUND
20 KT ACROSS THE CHICAGO METRO CLOSER TO LAKE MICHIGAN WITH
AROUND 25 KT AT GYY. LAKE EFFECT CLOUDS CONTINUE FROM THE CHICAGO
TERMINALS EASTWARD BUT COVERAGE IS STARTING TO SCATTER AND EXPECT
THIS TREND TO CONTINUE WITH THE MOST ABUNDANT COVERAGE CLOSE TO
THE ILLINOIS SHORE AND ACROSS NORTHWEST INDIANA. WINDS WILL
DIMINISH THIS EVENING AS THE HIGH DRAWS CLOSER WITH LITTLE IN THE
WAY OF CLOUD COVER EXPECTED TO PERSIST INTO THE EVENING. NEXT
ISSUE WILL BE POTENTIAL FOR FOG DEVELOPMENT. EXPECT THAT RFD AND
DPA HAVE THE BEST CHANCE FOR AT LEAST PATCHY FOG OVERNIGHT. THE
AIRMASS THAT IS BUILDING INTO THE AREA IS DRIER BUT WITH FAIRLY
WET GROUND AND GOOD RADIATIONAL COOLING EXPECTED FOG SHOULD
DEVELOP. ALTERNATIVELY...DEW/FROST MAY QUICKLY DEVELOP AND
PRECLUDE MUCH FOG FROM FORMING. IF UPSTREAM OBS FROM THIS MORNING
ARE ANY INDICATION FOG WILL DEVELOP LATE TONIGHT. WILL CARRY MIFG
FOR NOW AT RFD/DPA BUT IFR FOG IS POSSIBLE. ORD/MDW/GYY SHOULD SEE
LITTLE IF ANY FOG DEVELOPMENT WITH WARMER OVERNIGHT TEMPS.
MDB
//ORD AND MDW CONFIDENCE...UPDATED 18Z...
* MEDIUM-HIGH CONFIDENCE IN WINDS 010-030 CONTINUING WITH HIGH
CONFIDENCE THAT THE CHANCE FOR WINDS TO TURN MORE NORTHERLY
TOWARD 350-360 LATE AFTERNOON IS LOW.
* HIGH CONFIDENCE IN CEILING FORECAST.
MDB
//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...
SUNDAY NIGHT THROUGH FRIDAY...VFR.
JEE
&&
.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.
&&
$$
