875  
FXUS63 KLOT 200931  
AFDLOT  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL  
331 AM CST THU FEB 20 2020  
   
SHORT TERM
 
 
325 AM CST  
 
THROUGH FRIDAY...  
 
A FINAL REINFORCING PUSH OF ARCTIC AIR IS SETTLING IN ACROSS THE  
REGION EARLY THIS MORNING IN THE WAKE OF A SCOURING TROUGH AXIS  
CLEARLY EVIDENT IN SIMPLE RGB WATER VAPOR IMAGERY. A GLANCE AT  
LOW-LEVEL WATER VAPOR (CHANNEL 10) LOOPS SHOW THE GOES-16 ABI  
PICKING UP SURFACE FEATURES ACROSS MUCH OF THE UPPER MIDWEST AND  
NORTHERN GREAT PLAINS--A SURE SIGN OF THE BONE-DRY NATURE OF THIS  
INCOMING AIRMASS. INDEED, WE'VE BEEN ABLE TO FIND A FEW RAOBS FROM  
THIS EVENING SAMPLING 0.03 TO 0.04 INCH PWATS AT BISMARCK,  
ABERDEEN, AND MINNEAPOLIS. THIS DRY AIRMASS WILL CONTINUE TO  
OVERSPREAD OUR AREA TODAY, AND DEWPOINTS ARE CREEPING DOWN BELOW 0  
AT THIS TIME. BEHIND THIS LAST REINFORCING FRONTAL PUSH,  
TEMPERATURES TODAY WILL BE SOME 5 TO 10 DEGREES COOLER THAN THEY  
WERE ON WEDNESDAY, AND A PERSISTENT 10-15 MPH WIND WILL MAKE IT  
FEEL LIKE IT'S IN THE TEENS AND SINGLE DIGITS.  
 
THE INCOMING COLDER AIRMASS IS STARTING TO SATURATE UP DOWNWIND OF  
THE THE LAKE ACROSS PARTS OF WEST-CENTRAL MICHIGAN, AND THERE DOES  
APPEAR TO BE SOME LAND-BREEZE/CONVERGENT ZONE SETTING UP FROM  
MUSKEGON TO HOLLAND BASED ON SURFACE OBSERVATIONS AND STREAMLINE  
ANALYSIS. HI-RES GUIDANCE IS IN GENERALLY GOOD AGREEMENT KEEPING  
THIS MAIN CONVERGENT ZONE WELL TO OUR NORTHEAST, BUT THINGS DO  
LOOK TO BRIEFLY SATURATE UP A BIT MORE ACROSS PARTS OF PORTER  
COUNTY THIS MORNING. WHILE LAKE-INDUCED ELS ARE FORECAST TO BUILD  
UP TO AROUND 6 KFT, THE SATURATED DEPTH WILL BE EXTREMELY THIN  
(PROBABLY ABOUT 1 KFT OR LESS) CAPPED OFF BY THE AFOREMENTIONED  
VERY DRY AIRMASS ALOFT LEADING TO SOME LIKELY NOTABLE DRY AIR  
ENTRAINMENT OF ANY SHOWERS THAT ATTEMPT TO DEVELOP. THIS,  
COMBINED WITH DEWPOINT DEPRESSIONS IN EXCESS OF 10-15 F DON'T SEEM  
TO SUPPORT MUCH IN THE WAY OF LAKE EFFECT SNOW SHOWERS TODAY, AND  
HAVE REMOVED THE LOW MEASURABLE PRECIPITATION CHANCES AS A RESULT  
AND REPLACED WITH FLURRIES FOR THIS MORNING THROUGH THE MID-  
AFTERNOON.  
 
THE CORE OF THIS SPRAWLING SURFACE HIGH WILL BEGIN TO BUILD  
OFF TO OUR SOUTHWEST LATER THIS EVENING AND OVERNIGHT, AND WINDS  
WILL RESPOND BY SLOWLY BACKING AROUND TO THE SOUTHWEST. THERE  
LOOKS TO BE A PERIOD LATER THIS EVENING WHEN WINDS MAY BRIEFLY GO  
LIGHT AND VARIABLE, ALLOWING SOME OF TYPICAL COLD SPOTS TO DROP  
QUICKLY INTO THE SINGLE DIGITS. SURFACE FLOW DOES LOOK TO  
GRADUALLY TICK UPWARDS OVERNIGHT AS THE PRESSURE GRADIENT  
TIGHTENS, HOWEVER, AND THIS MAY END UP KEEPING TEMPERATURES FROM  
REALLY BOTTOMING OUT.  
 
FOR FRIDAY, WE'LL BEGIN TO PICK UP SOME ADDITIONAL FLOW OFF THE  
SURFACE AND BUFKIT SOUNDINGS LOOK SUPPORTIVE OF MIXING OF SOME 30  
MPH GUSTS TO THE SURFACE THROUGH THE LATE-MORNING AND AFTERNOON  
HOURS, ESPECIALLY NORTH OF I-80. WHILE WE'LL LIKELY BE STARTING  
OFF FROM A FAIRLY COOL POINT IN THE MORNING, THE BREEZY SOUTHWEST  
WINDS AND LIKELIHOOD OF MAXIMIZED MIXING SUPPORTS GOING ABOVE  
BLENDED GUIDANCE FOR HIGHS, MORE TOWARDS STATISTICAL OUTPUT, WITH  
SOME UPPER 30 TO 40 DEGREE READINGS NOT OUT OF THE QUESTION.  
 
CARLAW  
 

 
   
LONG TERM
 
 
325 AM CST  
 
FRIDAY NIGHT THROUGH WEDNESDAY...  
 
THE LONG TERM PORTION OF THE FORECAST APPEARS SOMEWHAT MORE  
UNSETTLED AS BROAD CYCLONIC MID-LEVEL FLOW BECOMES MORE  
ESTABLISHED ACROSS THE CENTRAL AND EASTERN CONUS, ALTHOUGH THE  
QUIESCENT AND DRY STRETCH DOES LOOK TO CONTINUE THROUGH THE  
WEEKEND.  
 
SATURDAY--AND ALSO LIKELY MUCH IF NOT ALL OF SUNDAY--ARE SHAPING  
UP TO BE PRETTY STELLAR DAYS ACROSS THE AREA AS LOW-LEVEL WEST TO  
SOUTHWEST FLOW CONTINUES TO NUDGE A WARMER AIRMASS OVERHEAD. ASIDE  
FROM SOME OCCASIONAL TUFTS OF HIGH CIRRUS, SATURDAY IS LOOKING  
ESSENTIALLY CLOUDLESS WITH A STRONG MIXING POTENTIAL. LOCAL 925  
MB TEMPERATURE CLIMATOLOGY INCORPORATING NO SNOWPACK UPSTREAM  
CONSERVATIVELY SUPPORTS HIGHS ON SATURDAY IN THE MID 40S, WITH A  
SMATTERING OF 50 DEGREE READINGS WITHIN THE REALM OF  
POSSIBILITIES. SUNDAY HAS THE POTENTIAL TO BE EVEN WARMER,  
ALTHOUGH THERE ARE STILL SOME LINGERING QUESTIONS ABOUT HOW MUCH  
HIGH CLOUD COVER WILL GET TOSSED OVERHEAD THROUGH THE AFTERNOON  
AHEAD OF OUR NEXT WEATHER DISTURBANCE. THE LATEST ECMWF ENSEMBLE  
SUPPORTS WIDESPREAD LOWER 50 DEGREE HIGHS ACROSS MUCH OF THE AREA,  
WHICH IS MORE OR LESS IN LINE WITH THE AFOREMENTIONED LOCAL 925  
MB CLIMATOLOGY RESEARCH. HAVEN'T QUITE BIT OFF ON THIS YET, BUT  
CONTINUE TO TREND THE FORECAST HIGHS INTO THE 75TH TO 85TH  
PERCENTILE OF AVAILABLE BLENDED GUIDANCE FOR BOTH SATURDAY AND  
SUNDAY.  
 
THE CURRENT MULTI-MODEL CONSENSUS SUPPORTS PRECIPITATION-FREE  
CONDITIONS PREVAILING THROUGH THE DAYTIME ON SUNDAY AND  
POTENTIALLY EVEN THROUGH THE EVENING HOURS. AS SEEMS TO BE TYPICAL  
WITH CLOSED, SOUTHERN-STREAM WAVES, GUIDANCE CONTINUES TO SLOW THE  
OVERALL PROGRESSION WITH EACH RUN, AND HAVE ADJUSTED POPS UNDER  
THE NATIONAL BLEND INTO SUNDAY NIGHT AS A RESULT. WITH NOTABLE  
POSITIVE 500 MB HEIGHT DPROG/DT TENDENCIES NOTED DOWNSTREAM OF OUR  
NEXT INCOMING WAVE, WOULDN'T BE SURPRISED IF THIS SLOWER TREND  
CONTINUED. WHILE THE DETERMINISTIC AND ENSEMBLE GLOBAL GUIDANCE  
REMAINS IN DECENT AGREEMENT REGARDING THE LARGE-SCALE EVOLUTION OF  
THINGS INTO MONDAY AND TUESDAY, SUBTLE WOBBLES IN THE PLACEMENT OF  
THE MAIN VORT MAX (WHICH IS CURRENTLY CHURNING AWAY A FEW HUNDRED  
MILES OFF THE NORTHERN CALIFORNIA COAST) HAVE LED TO FLUCTUATIONS  
IN THE NORTHERN-MOST EXTENT OF THE MAIN REGION OF UPPER DIVERGENCE  
WHICH COULD SET UP SHOP SOMEWHERE IN OR NEAR OUR CWA. AS A  
RESULT, OUTSIDE OF DELAYING THE ONSET OF HIGHER POPS, DIDN'T MAKE  
ANY SWEEPING CHANGES TO THE BLENDED POPS INTO MONDAY AND BEYOND.  
THIS SYSTEM LOOKS RELATIVELY WARM, AND HAVE DEPICTED MOSTLY RAIN  
WITH SOME RAIN/SNOW POTENTIAL ON MONDAY AND TUESDAY MORNINGS.  
 
BEYOND THIS, GUIDANCE INDICATES THE POTENTIAL FOR ANOTHER  
SHORTWAVE/PV ANOMALY TO DROP DOWN THROUGH THE GREAT BASIN AT THE  
EDGE OF THE FASTER MID-LEVEL FLOW WHICH LOOKS TO KEEP THINGS  
UNSETTLED INTO THE MIDDLE AND POSSIBLY END OF NEXT WEEK.  
 
CARLAW  
 

 
   
AVIATION
 
 
FOR THE 06Z TAFS...  
 
THERE ARE NO SIGNIFICANT WEATHER CONCERNS THROUGH THE PERIOD.  
 
NORTHERLY WINDS AND VFR CONDITIONS ARE EXPECTED TO CONTINUE  
THROUGH THE DAY THURSDAY AS A STRONG ARCTIC SURFACE HIGH  
GRADUALLY SAGS SOUTHWARD OVER EASTERN IA TOMORROW AFTERNOON. THE  
WINDS WILL THEN VEER WESTERLY THURSDAY EVENING.  
 
KJB  
 

 
   
LOT WATCHES/WARNINGS/ADVISORIES
 
 
IL...NONE.  
IN...NONE.  
LM...SMALL CRAFT ADVISORY...IN NEARSHORE WATERS UNTIL 3 PM THURSDAY.  
 

 
 

 
 
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