191
FXUS63 KLOT 202328
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
528 PM CST WED FEB 20 2019
SHORT TERM
153 PM CST
THROUGH THURSDAY NIGHT...
WITH THE FREEZING PRECIPITATION THREAT COMING TO AN END ACROSS
THE REGION, THE MAIN FORECAST FOCUS IS WITH THE GUSTY WEST-
SOUTHWESTERLY WINDS EXPECTED TO DEVELOP ACROSS THE AREA THIS
EVENING. GIVEN THE CURRENT OBSERVATION TRENDS, WE SHOULD BE ABLE
TO DROP THE REST OF THE WINTER WEATHER ADVISORY EARLY THIS
AFTERNOON.
SURFACE LOW PRESSURE OVER SOUTHERN MN WILL SHIFT EAST-
NORTHEASTWARD OVER NORTHERN LAKE MICHIGAN THIS EVENING. AS IT DOES
SO, OUR SURFACE WINDS WILL SHIFT FROM THE SOUTH TO THE WEST-
SOUTHWEST AND BECOME GUSTY UP TO 35 MPH THIS EVENING FOLLOWING A
FRONTAL PASSAGE. THESE WIND SPEEDS WILL ABATE LATE TONIGHT INTO
THURSDAY. THE ARRIVAL OF THE FRONTAL BOUNDARY EARLY THIS EVENING WILL
ALSO BRING AN END TO MUCH OF THE DRIZZLE AND FOG THAT IS
CURRENTLY IN PLACE ACROSS THE AREA.
QUIET WEATHER WITH SEASONAL TEMPERATURES IN THE 30S IS EXPECTED ON
THURSDAY AS SURFACE HIGH PRESSURE SETS UP OVER THE AREA. WHILE WE
SHOULD LOSS THE LOW-LEVEL CLOUD COVER TONIGHT, HIGHER LEVEL CLOUDS
LOOK TO RESULT IN PARTLY CLOUDY TO PARTLY SUNNY SKIES DURING THE
DAY THURSDAY.
KJB
LONG TERM
309 PM CST
THURSDAY NIGHT THROUGH WEDNESDAY...
ACTIVE WEATHER WILL CONTINUE FOR THE LONG TERM FORECAST PERIOD. MAIN
CONCERNS WILL FOCUS ON POTENTIAL ICE ACCUMULATION IN FREEZING RAIN
LATE FRIDAY NIGHT INTO SATURDAY MORNING AND THEN STRONG, GUSTY WINDS
LATE SATURDAY NIGHT INTO SUNDAY NIGHT.
QUIET WEATHER WILL CONTINUE INTO THE BEGINNING OF THE LONG TERM
FORECAST PERIOD AS BROAD UPPER RIDING COVERS THE ERN 2/3 OF THE
CONUS. THE NEXT SYSTEM TO IMPACT THE REGION WILL BE A PACIFIC
SHORTWAVE DROPPING SOUTH INTO THE DESERT SOUTHWEST FRIDAY AND THEN
QUICKLY LIFTING OUT OVER THE CENTRAL PLAINS. THE LONG RANGE
GUIDANCE IS IN GOOD AGREEMENT ON THE 500MB PATTERN WITH THIS SYSTEM,
WITH ONLY MINOR DIFFERENCES IN THE TIMING/INTENSITY OF THE UPPER LOW
AS IT LIFTS ACROSS MISSOURI SATURDAY EVENING. UNFORTUNATELY, THE
SAME CANNOT BE SAID FOR THE ASSOCIATED SFC LOW, WITH THE MODELS
SHOWING A FAIR SPREAD, ESPECIALLY FOR THE TRACK OF THE LOW CENTER.
SO, HAVE BASED THE SENSIBLE WEATHER FEATURES AND IMPACTS FROM THIS
SYSTEM ON THE BLENDED SOLUTION, WHICH WILL NEED TO BE REFINED IN
LATER UPDATES. HOWEVER, THE MAIN IDEA IS THAT AS THE SFC LOW LIFTS
NEWD, A WARM FRONT SETTING UP ACROSS THE LOWER OHIO VALLEY FRIDAY
NIGHT WILL EVENTUALLY SURGE NORTH THROUGH THE DAY ON FRIDAY. A RIDGE
OF HIGH PRESSURE WILL REMAIN ACROSS THE UPPER GREAT LAKES, LIMITING
THE NORTHWARD PROGRESSION OF THE SFC BOUNDARY, BUT ABOVE THE
BOUNDARY LAYER, THE MODELS ARE IN GOOD AGREEMENT DEPICTING STRONG
WARM, MOIST ADVECTION. LATEST THOUGHTS ARE THAT A SHALLOW LAYER OF
COLDER, SUB-FREEZING AIR WILL REMAIN IN PLACE ACROSS THE NORTHERN,
PORTIONS OF THE CWA, WHILE WARMER SFC AIR MAY REACH UP TO, ROUGHLY,
THE I-80 CORRIDOR. PCPN SHOULD SPREAD ACROSS THE AREA LATE FRIDAY
NIGHT, WITH THE FREEZING RAIN LIKELY NORTH OF THE I-80 CORRIDOR AND
ALL RAIN TO THE SOUTH. THE SURFACE FREEZING LINE IS THE MAIN
QUESTION MARK AT THIS TIME, AND WILL BE HIGHLY DEFENDANT ON THE
EXACT TRACK AND SPEED OF THE MAIN SFC LOW. CONSEQUENTLY, THERE IS
SOME UNCERTAINTY ON THE COVERAGE AND DURATION OF ICE ACCUMULATION
WITH THE FREEZING RAIN. THIS SITUATION CERTAINLY BEARS WATCHING.
BASED ON THE LATEST GUIDANCE, EXPECT SOMEWHAT OF A NON-DIURNAL
SURFACE TEMPERATURE TREND, WITH SFC TEMPS RISING THROUGH THE LATE
NIGHT HOURS, AND THEN RISING ABOVE FREEZING DURING THE MORNING HOURS
ALLOWING THE PCPN TO TRANSITION OVER TO ALL RAIN.
THE NEXT AREA OF CONCERN WILL BE STRONG, GUSTY WINDS FOLLOWING THE
PASSAGE OF THE ASSOCIATED COLD FRONT. WHILE THERE ARE SOME
DIFFERENCES AMONG THE MODELS IN THE EXACT TRACK OF THE SURFACE LOW,
THERE ARE SOME STRONG SIGNALS THAT THE SFC LOW WILL CONTINUE TO
DEEPEN AS IT LIFTS NORTHEAST THROUGH THE CENTRAL GREAT LAKES EARLY
SUNDAY. A STRONG PRESSURE RISE/FALL COUPLET WILL ACCOMPANY THE
FRONTAL PASSAGE WITH +/ 20 MB PER 6 HR AND +/- 12 MB PER 3 HR
PRESSURE TENDENCIES INDICTED IN THE LONGER RANGE GUIDANCE. ALSO,
MODEL SOUNDINGS SHOW 50 TO 60 KT WEST-NORTHWEST WINDS AT THE TOP OF
THE MIXED LAYER ON SUNDAY. DEPENDING ON HOW DEEP MIXING MAY OCCUR,
THERE WILL BE A CHANCE FOR WIND GUSTS IN EXCESS OF 45 MPH POSSIBLE
AND A WIND ADVISORY OR HIGH WIND WARNING MAY BE NEEDED. A LARGE
TEMPERATURE SWING IS LIKELY WITH THE PASSAGE OF THIS SYSTEM. AHEAD
OF THE FRONT, TEMPERATURES ARE EXPECTED TO REACH HIGHS RANGING FROM
AROUND 40 F ALONG THE IL/WI BORDER TO THE LOW 50S FOR THE SOUTHERN
PORTIONS OF THE CWA. HIGHS ON SUNDAY SHOULD ONLY BE IN THE LOWER TO
MIDDLE 30S.
YET ANOTHER SYSTEM IS FORECAST TO MOVE ACROSS THE REGION EARLY NEXT
WEEK. AT THIS DISTANCE, THERE ARE STILL LARGE DIFFERENCES IN THE
STRENGTH AND TRACK OF THIS NEXT SYSTEM. WHILE THERE ARE SOME
INDICATIONS THAT ANOTHER ROUND OF SNOW IS POSSIBLE, BUT MODEL SPREAD
IN THE LONG RANGE GUIDANCE IS TOO LARGE TO HAVE ANY CONFIDENCE IN
ANY SPECIFICS.
AVIATION
FOR THE 00Z TAFS...
528 PM...PRIMARY FORECAST CONCERNS ARE GUSTY SOUTHWEST WINDS AND
CIGS THROUGH DAYBREAK THURSDAY.
SOUTHWEST WINDS WILL REMAIN GUSTY THROUGH EARLY THURSDAY MORNING
IN THE 20-25KT RANGE. SPEEDS/GUSTS WILL SLOWLY DIMINISH OVERNIGHT
WITH GUSTS LARGELY OVER BY DAYBREAK. WESTERLY WINDS 10-15KTS WILL
CONTINUE THURSDAY. CIGS ARE SLOWLY LIFTING TO LOW MVFR EARLY THIS
EVENING WITH SOME IFR CIGS BUT THE TREND WILL BE FOR CIGS TO LIFT
THROUGH MVFR THIS EVENING AND BEGIN TO SCATTER OUT OVERNIGHT FROM
WEST TO EAST. FEW/SCT LOW CLOUDS ARE POSSIBLE MAINLY THURSDAY
MORNING ALONG WITH HIGH CLOUDS THURSDAY. CMS
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS UNTIL 9 AM THURSDAY.
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