142
FXUS63 KLOT 050930
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
330 AM CST FRI MAR 5 2021
SHORT TERM
205 AM CST
THROUGH SUNDAY...
METEOROLOGICAL SPRING CONTINUES ITS QUIET START THROUGH THE
WEEKEND. LAKE BREEZE POTENTIAL AND HOW MUCH OF AN AREA NEAR THE
LAKE THIS WIND SHIFT KEEPS COOLER IS REALLY THE ONLY ITEM OF
NOTE. TEMPERATURES WILL BE A TAD ABOVE NORMAL AND START MAKING
LARGER STRIDES ABOVE EARLY MARCH CLIMATOLOGY ON SUNDAY.
HIGH PRESSURE OF 1030 MB IS CENTERED OVER WISCONSIN AND SPRAWLED
INTO NORTHWEST AND NORTH CENTRAL ILLINOIS THIS MORNING. MAINTAINED
TO THE IMMEDIATE EAST OF THIS FEATURE IS BOUNDARY LAYER FLOW FROM
THE NORTHWEST TODAY. FORECAST PROFILES FROM HIGH-RESOLUTION
MODELS DO VARY ON THE MIXED BOUNDARY LAYER DEPTH THIS AFTERNOON,
WITH THE NAM MORE PRONOUNCED AND KEEPING A LAKE BREEZE OUT OF
NORTHEAST ILLINOIS WHILE THE HRRR IS MUCH LESS SO AND ALLOWS
INTRUSION TO A LITTLE WEST OF I-294. LAST WARM SEASON THE HRRR
WAS AT TIMES TOO AGGRESSIVE ON LAKE BREEZES AND EVEN ITS PROFILES
INDICATE ~10 KT OF FLOW TODAY, WHICH USUALLY RETARDS A LAKE
BREEZE TO NEAR THE SHORE. SO HAVE KEPT THE TURN OF THE WINDS FOR
CHICAGO TO LATE AFTERNOON WITH HIGHS MID 40S, WHILE NORTHWEST
INDIANA WILL HAVE MORE OF AN ONSHORE COMPONENT THROUGH THE DAY
WITH HIGHS UPPER 30S TO POSSIBLY LOWER 40S. SOME UPPER 40S ARE
LIKELY IN THE SOUTHERN CWA. PATCHY SHALLOW FOG POTENTIAL MAY BE
PRESENT AGAIN TONIGHT OVER NORTH CENTRAL ILLINOIS, BUT WITH
LITTLE OF IT MATERIALIZING THIS MORNING, DON'T SEE TONIGHT BEING
ANY MORE OF A THREAT.
THROUGH SATURDAY THERE WILL BE LITTLE MOVEMENT IN THE LONG WAVE
PATTERN THAT IS PRIMARILY HELD UP BY A STOUT SUB-500 DAM LOW AT
500 MB OVER EASTERN QUEBEC. NORTHWEST FLOW THAT HAS LITTLE ACTING
ON IT TO BE AGEOSTROPHIC WILL CONTINUE OVER OUR FORECAST AREA AND
AND SURFACE HIGH PRESSURE UNDERNEATH. WITH A SLIGHT EASTWARD
INCHING OF THE HIGH ON SATURDAY, THIS WILL ALLOW AN ONSHORE TURN
OF THE WINDS NEAR THE LAKE WITH HIGHER CONFIDENCE THAN TODAY, AND
KEEP LAKESIDE AREAS IN THE 30S.
SUNDAY WILL START TO SEE MOVEMENT IN THE MID/UPPER LEVEL PATTERN,
WITH HEIGHTS BUILDING AND LOWER TROPOSPHERIC WARM ADVECTION. THE
925 MB TEMPERATURES ARE FORECAST TO WARM FROM -1C TO 3C IN THE
MORNING TO 5C TO 9C BY LATE DAY. THE SURFACE WIND DIRECTION
REMAINS MORE SOUTH-SOUTHEAST TO DUE SOUTH, WHICH TYPICALLY DOES
NOT MEAN TEMPERATURES RACING AWAY THIS TIME OF YEAR (LIKE THEY
MAY THE FOLLOWING DAYS), BUT AT LEAST JUMPING INTO THE 50S FOR
MOST LOCATIONS. THE EXCEPTION WILL BE NEAR THE LAKE IN ILLINOIS
WHERE THE DIRECTION SHOULD PROVIDE SOME DEGREE OF COOLING.
MTF
LONG TERM
330 AM CST
SUNDAY NIGHT THROUGH THURSDAY...
THE NEW WORK WEEK WILL BE A CONTINUATION OF THE DRY AND
INCREASINGLY MILD CONDITIONS, WITH HIGHS IN THE 60S A GOOD BET ON
MONDAY AND TUESDAY. OUR LONG QUIET STRETCH THEN APPEARS LIKELY TO
COME TO AN END IN THE WEDNESDAY-THURSDAY TIMEFRAME, WHEN AT LEAST
ISOLATED THUNDERSTORMS APPEAR POSSIBLE.
THE SYNOPTIC PATTERN IS A GOOD ONE ON MONDAY AND TUESDAY FOR
UNSEASONABLE WARMTH, WITH STRONG POSITIVE MID-LEVEL HEIGHT
ANOMALIES AND PERSISTENT WARM ADVECTION. AT THE SURFACE, ELONGATED
TROUGHING OVER THE HIGH PLAINS AND EXPANSIVE HIGH PRESSURE OVER
THE EASTERN CONUS WILL KEEP SOUTHWEST TO SOUTHERLY WINDS ELEVATED.
THE POSITION OF THE SURFACE HIGH CENTER OVER THE SOUTHEAST AND
RIDGING BACK ACROSS THE GULF STATES WILL BLOCK OFF MOISTURE
TRAJECTORIES. CLIMO OF PROGGED 925 MB TEMPS OF +8 TO +10C OR A BIT
HIGHER AT PEAK HEATING ON MONDAY-TUESDAY SUPPORTS HIGHS IN THE
LOWER TO MID 60S. MONDAY WILL FEATURE BREEZY SOUTHWESTERLY WINDS,
BECOMING CLOSE TO DUE SOUTH-SOUTHWESTERLY AND INCREASING ON
TUESDAY AS THE PRESSURE GRADIENT TIGHTENS. IF THERE'S LESS CLOUDS,
TUESDAY COULD BE A CANDIDATE FOR DEEPER MIXING, MEANING TEMPS
OVERPERFORM A BIT AND DEW POINTS POSSIBLY UNDERPERFORM. WITH WIND
GUSTS UP TO OR OVER 30 MPH, EXTENDED DRY PATTERN OVER AREAS THAT
LOST SNOW COVER EARLIEST COULD YIELD AN ELEVATED FIRE WEATHER
RISK. STILL A FEW DAYS TO MONITOR TRENDS FOR THIS PERIOD.
THE GUSTY SOUTHERLY WINDS WILL INCREASE THROUGH TUESDAY NIGHT,
LIKELY KEEPING TEMPS IN THE LOWER 50S, WELL ABOVE NORMAL HIGHS FOR
THE DATE. BOTH THE GFS AND ECMWF DEPICT A PLUME OF VERY STEEP
MID-LEVEL LAPSE RATES BEING ADVECTED EASTWARD ACROSS OUR AREA.
HAVE SOME LOW POPS INDICATED OVERNIGHT, WHICH WOULD BE ELEVATED
WARM ADVECTION SHOWERS. WITH SUCH STEEP LAPSE RATES, IF PARCELS
CAN OVERCOME THE VERY WARM EML BASE AT 700 MB, WOULD SPELL A NON-
ZERO CHANCE FOR ISOLATED THUNDERSTORMS. WE LOOK TO FINALLY TAP
INTO BETTER BOUNDARY LAYER MOISTURE ON WEDNESDAY, WITH DEW POINTS
GETTING TO 50F OR HIGHER DRAWN NORTHWARD BY SOUTH-SOUTHWEST WINDS
GUSTING UP TO 30-40 MPH. DESPITE MOSTLY CLOUDY SKIES, VERY MILD
START AND STRONG WARM ADVECTION WILL SUPPORT HIGHS AGAIN IN THE
LOW-MID 60S. WHILE WE LOOK TO BE IN THE WARM SECTOR OF TROUGHING
OFF TO THE WEST AND NORTHWEST, SOME UPPER JET SUPPORT COULD HELP
SCATTERED SHOWERS BREAK OUT DURING THE DAY.
UNCERTAINTY INCREASES IN HOW THINGS WILL EVOLVE WEDNESDAY EVENING-
THURSDAY, BUT IN A BROAD SENSE WE SHOULD SEE SURFACE COLD FRONT
MOVE INTO THE AREA AND THEN POSSIBLY STALL OUT DURING THURSDAY AS
WAVES OF ENERGY INTERACT WITH THE FRONT. PWATS OF 150-250% OF
NORMAL COULD SET THE STAGE FOR HEAVY RAINFALL, ESPECIALLY
ASSOCIATED WITH ANY THUNDERSTORMS, WHICH APPEAR QUITE POSSIBLE.
WITH THIS PERIOD 6+ DAYS OUT AND PLENTY OF TIME FOR CHANGES,
INTRODUCED A SLIGHT CHANCE FOR THUNDERSTORMS WEDNESDAY NIGHT-
THURSDAY (I-80 AND SOUTH FOR NOW ON THURSDAY CLOSER TO BOUNDARY).
TEMPERATURES WILL COOL DOWN TO THE NORTH OF THE BOUNDARY ON
THURSDAY, IN PARTICULAR NEAR THE LAKE IF WINDS FLIP TO OUT OF THE
NORTH AND NORTHEAST. THE ACTIVE PERIOD SHOULD CONTINUE THROUGH
THURSDAY NIGHT AND EARLY FRIDAY, FOLLOWED BY MUCH COOLER
CONDITIONS NEXT WEEKEND.
CASTRO
AVIATION
FOR THE 06Z TAFS...
AVIATION FORECAST CONCERNS:
* SOME POTENTIAL FOR A LAKE BREEZE TO SHIFT WINDS NORTHEAST AT
KORD AND KMDW LATE FRIDAY AFTERNOON.
SURFACE HIGH PRESSURE RIDGE CONTINUES TO DRIFT SLOWLY SOUTH ACROSS
WISCONSIN LATE THIS EVENING. ALONG THE SOUTHERN PERIPHERY OF THE
HIGH, NORTHEAST WINDS CONTINUE TO DIMINISH ACROSS THE TERMINALS.
THIS TREND WILL CONTINUE OVERNIGHT, WITH WINDS EXPECTED TO SHIFT
LIGHT NORTH-NORTHWEST DURING THE PRE-DAWN HOURS AS THE RIDGE
SETTLES INTO NORTHWEST ILLINOIS.
SURFACE HIGH PRESSURE WILL REMAIN JUST WEST OF THE TERMINALS
FRIDAY, RESULTING IN RELATIVELY LIGHT NORTHWEST WINDS NEAR 10 KTS
PERSISTING DURING THE DAY. SOME HIGH-RES MODEL GUIDANCE CONTINUES
TO INDICATE THAT A LAKE BREEZE WILL DEVELOP AND BRING WINDS
NORTHEAST AT KGYY BY MIDDAY/AFTERNOON, THOUGH MODELS CONTINUE TO
SUGGEST THAT THE BOUNDARY MAY NOT MOVE THROUGH KMDW/KORD. THIS
APPEARS TO BE DUE TO 10-15 KT SUSTAINED NNW WINDS AT/ABOVE THE TOP
OF THE MIXED LAYER DURING THE AFTERNOON, WHICH COULD BE JUST
ENOUGH TO LIMIT THE INLAND PUSH OF THE LAKE BREEZE FROM THE IL
SHORE. HAVE RELATIVELY LOW CONFIDENCE IN THIS AT THIS TIME, AS ANY
WEAKER FLOW ALOFT WILL LIKELY ALLOW THE BOUNDARY TO MOVE INTO THE
KMDW/KORD TERMINALS AFTER 22-23Z, BUT WITH MOST GUIDANCE KEEPING
IT EAST OF THESE AIRFIELDS WILL LEAVE IT OUT OF THEIR TAFS FOR NOW.
PROVIDED THE LAKE BREEZE DOES NOT MOVE THROUGH KMDW/KORD LATE
FRIDAY, LIGHT NORTHWEST WINDS SHOULD CONTINUE FRIDAY NIGHT, WITH
FLOW EVENTUALLY BECOMING MORE NORTHERLY TOWARD SATURDAY MORNING.
FORECAST SOUNDINGS HINT AT SOME SHALLOW FOG POTENTIAL ACROSS
PARTS OF NORTH CENTRAL IL LATE TONIGHT INTO EARLY FRIDAY MORNING.
NORTHEAST SURFACE WINDS HAVE BROUGHT DRIER AIR INTO KRFD OVER THE
LAST SEVERAL HOURS, WITH 10 DEGREE SURFACE DEW POINT DEPRESSIONS
NOT INDICATIVE OF FOG DEVELOPING ANY TIME SOON. BETTER CHANCES
APPEAR TO BE FARTHER SOUTH/SOUTHWEST OF KRFD. OTHERWISE, VFR
CONDITIONS ARE EXPECTED TO PREVAIL ACROSS THE AREA THROUGH THE
PERIOD.
RATZER
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
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