046  
FXUS63 KLOT 191729  
AFDLOT  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL  
1229 PM CDT FRI APR 19 2024  
   
KEY MESSAGES
 
 
- WEST WINDS GUSTING 35-40 MPH WITH AN ELEVATED FIRE DANGER THIS  
AFTERNOON.  
 
- PATCHY FROST POSSIBLE ACROSS THE NORTHWEST CWA TONIGHT.  
 
- MUCH COOLER TEMPERATURES ARE EXPECTED OVER THE WEEKEND WITH A  
THREAT FOR FROST AND SUB-FREEZING TEMPERATURES, PARTICULARLY ON  
SATURDAY NIGHT OUTSIDE OF CHICAGO.  
 
- THE NEXT OPPORTUNITY FOR RAIN WILL ARRIVE MONDAY NIGHT INTO  
TUESDAY.  
 

 
   
UPDATE
 
 
ISSUED AT 1045 AM CDT FRI APR 19 2024  
 
NO BIG CHANGES TO FORECAST THIS MORNING. MAIN ITEMS REMAIN GUSTY  
WEST TO WEST-NORTHWEST WINDS 35-40 MPH, AND LOW DEW POINTS AND  
RELATIVE HUMIDITIES THIS AFTERNOON MAKING FOR ELEVATED FIRE  
DANGER THIS AFTERNOON. WINDS REMAIN SLIGHTLY ELEVATED TONIGHT  
(8-12 MPH) WHICH SHOULD TEND TO LIMIT WIDESPREAD PATCHY FROST  
POTENTIAL TO THE MOST SHELTERED AREAS. DID BUMP TEMPS UP JUST A  
SMIDGE ACROSS OUR NORTHERN CWA THIS AFTERNOON WHERE MOST  
SUNSHINE EXPECTED, BUT OTHERWISE NO SIGNIFICANT CHANGES HERE  
THIS MORNING.  
 
RATZER  
 

 
   
DISCUSSION
 
 
ISSUED AT 201 AM CDT FRI APR 19 2024  
 
THROUGH SATURDAY:  
 
WESTERLY WINDS WILL STEADILY INCREASE AFTER SUNRISE AND ARE  
EXPECTED TO GUST INTO THE 35-40 MPH RANGE THIS AFTERNOON AND  
THEN WILL DIMINISH WITH SUNSET THIS EVENING. DEWPOINTS ARE  
EXPECTED TO DROP INTO THE MID 20S, POSSIBLY LOWER 20S AND THIS  
WILL ALLOW RELATIVE HUMIDITY LEVELS TO DROP INTO THE 25-30  
PERCENT RANGE, RESULTING IN AN ELEVATED FIRE DANGER.  
 
THESE LOWER DEWPOINTS WILL CONTINUE TONIGHT WHICH WILL ALLOW LOW  
TEMPS TO DROP INTO THE MID 30S FOR MOST AREAS BY SATURDAY  
MORNING, WITH SOME LOWER 30S POSSIBLE. THIS PRESENTS THE  
POTENTIAL FOR FROST TO DEVELOP BUT NORTHWEST WINDS MAY REMAIN  
IN THE 10 MPH RANGE FOR MOST OF THE NIGHT WHICH MAY BE TOO  
STRONG FOR FROST TO FORM. MAINTAINED PATCHY FROST MENTION ACROSS  
THE NORTHWEST CWA, ROUGHLY FROM THE FOX VALLEY WEST AND THEN  
NORTH OF I-80. CONFIDENCE IS LOW FOR HOW WIDESPREAD ANY FROST  
WOULD BECOME AND TRENDS WILL NEED TO BE MONITORED LATER TODAY.  
 
SATURDAY WILL STILL BE BREEZY, WITH NORTHWEST WINDS POSSIBLY  
GUSTING INTO THE 20-25 MPH RANGE. WHILE DEWPOINTS WILL GENERALLY  
BE IN THE 20S, HIGH TEMPS LOOK TO BE A FEW DEGREES COOLER,  
PERHAPS ONLY LOWER 50S FOR HIGHS. THUS, RELATIVE HUMIDITY LEVELS  
LOOK TO BE A LITTLE HIGHER, IN ADDITION TO THE EXPECTED LOWER  
WIND SPEEDS, THUS AN ELEVATED FIRE DANGER IS NOT EXPECTED. CMS  
 
SATURDAY NIGHT THROUGH THURSDAY:  
 
WE'RE IN FOR A QUIESCENT STRETCH OF WEATHER THROUGH THE WEEKEND  
AND THE START OF THE WORK WEEK AS A SPRAWLING SURFACE HIGH BUILDS  
ACROSS THE CENTRAL CONUS. WHILE THE CORE OF THE HIGH PRESSURE  
WON'T EVER BUILD DIRECTLY OVERHEAD, IT LOOKS LIKE THE GRADIENT  
WILL RELAX SUFFICIENTLY ON SATURDAY NIGHT INTO SUNDAY TO YIELD AN  
EFFECTIVE RADIATIONAL COOLING SETUP, ASSUMING A REGION OF HIGH  
CLOUD COVER ASSOCIATED WITH AN UPPER JET STREAK THINS AND  
DIMINISHES AS MODELED. WITH DEWPOINTS IN THE LOW TO MID 20S, A  
POTENTIAL FOR SUB-FREEZING TEMPERATURES EXISTS, PARTICULARLY FOR  
OUTLYING AREAS WEST AND NORTH OF CHICAGO. NO HEADLINES JUST YET,  
BUT IT'S POSSIBLE WE'LL NEED TO CONSIDER FREEZE WATCHES FOR THIS  
PERIOD.  
 
WE'LL STEP INTO A BRIEF WARMING TREND MONDAY AND TUESDAY AS THE  
LOW-LEVEL FLOW TURNS SOUTHWESTERLY. A SLIGHTLY ELEVATED FIRE  
DANGER MAY EVOLVE ON MONDAY WITH BREEZY SOUTHWESTERLY WINDS AND  
AFTERNOON RH VALUES DIPPING INTO THE 30 TO 35 PERCENT RANGE. THE  
NEXT PRECIPITATION CHANCES ARRIVE MONDAY NIGHT INTO TUESDAY AS A  
FAIRLY ROBUST UPPER VORT APPROACHES, DRIVING A NOTABLE INCREASE IN  
WARM ADVECTION ACROSS THE REGION. INSTABILITY AND OVERALL  
MOISTURE QUALITY/DEPTH DON'T LOOK PARTICULARLY IMPRESSIVE,  
HOWEVER, WITH ACTIVITY LIKELY IN THE FORM OF SCATTERED SHOWERS.  
 
A REINFORCING SHOT OF COOLER AIR WILL ARRIVE IN THE WAKE OF A COLD  
FRONT TUESDAY NIGHT AND WEDNESDAY BEFORE HIGH TEMPERATURES ONCE  
AGAIN WARM BACK TOWARDS AND INTO THE 60S--AT LEAST AWAY FROM THE  
LAKE IN NORTHEAST ILLINOIS WHERE PERSISTENT ONSHORE FLOW WILL HOLD  
TEMPERATURES IN THE 50S. THEREAFTER, WHILE TIMING AND AMPLITUDE  
DIFFERENCES ARE EVIDENT, THERE SEEMS TO BE A CONSISTENT SIGNAL IN  
THE DETERMINISTIC AND ENSEMBLE SUITE OF A LARGE TROUGH DEVELOPING  
ACROSS THE GREAT BASIN TOWARDS THE END OF NEXT WEEK, WITH EMBEDDED  
SHORTWAVES SHUTTLING EAST ACROSS THE CENTRAL CONUS INTO THE  
WEEKEND WHICH COULD BRING THE NEXT ROUNDS OF SHOWERS AND STORMS TO  
THE REGION.  
 
CARLAW  
 

 
   
AVIATION /18Z TAFS THROUGH 00Z SUNDAY/
 
 
ISSUED AT 1229 PM CDT FRI APR 19 2024  
 
THE SOLE FORECAST CONCERN FOR THIS TAF PERIOD IS THE GUSTY  
WEST-NORTHWEST WINDS THIS AFTERNOON. GUSTS ARE GENERALLY  
EXPECTED TO REMAIN AROUND 30 KTS THIS AFTERNOON, BUT  
OCCASIONALLY HIGHER GUSTS BETWEEN 30 TO 35 KTS ARE POSSIBLE.  
WHILE GUSTS WILL DIMINISH SOMEWHAT THIS EVENING, FORECAST  
SOUNDINGS SHOW THAT THE ATMOSPHERE MAY REMAIN MIXED OVERNIGHT SO  
EXPECT AT LEAST PERIODIC GUSTS AROUND 20 KTS TO PERSIST  
OVERNIGHT AND THROUGH SATURDAY. OTHERWISE, EXPECT FEW TO SCT  
VFR CLOUDS THIS AFTERNOON TO GRADUALLY INCREASE TO BKN VFR  
CEILINGS SATURDAY AFTERNOON.  
 
YACK  
 

 
   
LOT WATCHES/WARNINGS/ADVISORIES
 
 
IL...NONE.  
IN...NONE.  
LM...SMALL CRAFT ADVISORY UNTIL 7 PM CDT THIS EVENING FOR THE IL  
AND IN NEARSHORE WATERS.  
 

 
 

 
 
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