711
FXUS63 KLOT 151939
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
139 PM CST FRI NOV 15 2024
KEY MESSAGES
- WHILE PATCHY DENSE FOG CANNOT BE RULED OUT TONIGHT, NO
IMPACTFUL WEATHER IS EXPECTED THROUGH SATURDAY NIGHT.
- PERIODS OF RAIN ARE EXPECTED MONDAY AFTERNOON THROUGH TUESDAY
MORNING.
- ANOTHER SYSTEM WILL MOVE IN WEDNESDAY THROUGH THURSDAY WITH
ADDITIONAL CHANCES FOR PRECIPITATION.
- A COLDER AIR MASS WILL SETTLE IN LATE NEXT WEEK WITH MORNING
LOW TEMPERATURES AT OR BELOW FREEZING.
DISCUSSION
ISSUED AT 139 PM CST FRI NOV 15 2024
THROUGH SATURDAY NIGHT:
A SURFACE HIGH PRESSURE SYSTEM CONTINUES TO SLOWLY MOVE THROUGH THE
REGION, AND IS LEADING TO NEARLY CALM WINDS. DIURNAL MECHANICAL
MIXING BELOW THE INVERSION IS HELPING ERODE CLOUDS ESPECIALLY WITH
WESTWARD EXTENT, ALLOWING FOR TEMPERATURES TO WARM INTO THE LOWER
50S. BASED ON SATELLITE TRENDS, FEEL THAT MUCH OF OUR AREA HAS A GOOD
SHOT TO SEE AT LEAST BRIGHTER SKIES IF NOT A FEW HOLES IN THE CLOUDS
BEFORE SUNSET, THOUGH AREAS IN NORTHWESTERN INDIANA MAY VERY WELL
REMAIN DECIDEDLY CLOUDY.
TONIGHT, THE CENTER OF THE SURFACE HIGH WILL BEGIN TO SHIFT EAST OF
OUR AREA ALLOWING FOR SURFACE TO LOW-LEVEL (950MB) FLOW TO EVER-SO-
GRADUALLY INCREASE FROM THE SOUTHEAST. AS A RESULT, THE REMNANT
STRATUS DECK INITIALLY POSITIONED NEAR NORTHWESTERN INDIANA WILL BE
POISED TO "SLOSH" BACK NORTHWESTWARD OVER THE REST OF OUR AREA
OVERNIGHT AND INTO TOMORROW. DEPENDING ON HOW LONG IT TAKES FOR
STRATUS TO RETURN, CERTAINLY CAN'T RULE OUT PATCHY DENSE FOG
DEVELOPING OWING TO RESIDUAL LOW-LEVEL MOISTURE TRAPPED BENEATH THE
INVERSION AT LEAST BEFORE WINDS START TO INCREASE. FOR NOW, WILL
HOLD OFF ON INTRODUCING ANY FOGS IN THE GRIDS IN FAVOR OF WATCHING
OBSERVATIONAL TRENDS.
ALSO TONIGHT, A LEAD UPPER-LEVEL SHORTWAVE TROUGH EMBEDDED IN
AGGREGATE TROUGHING ACROSS THE WESTERN US WILL EJECT INTO THE
NORTHERN PLAINS, SUPPORTING THE DEVELOPMENT OF A LOW PRESSURE
SYSTEM. AS THE SURFACE HIGH ACROSS THE GREAT LAKES SHIFTS EASTWARD
AND THE SURFACE LOW DEEPENS IN THE NORTHERN PLAINS, THE LOW-LEVEL
PRESSURE GRADIENT ACROSS OUR AREA WILL BECOME INCREASINGLY PACKED
SUPPORTING INCREASING SOUTHEASTERLY WINDS AFTER DAYBREAK SATURDAY.
INCREASING WAA SHOULD HELP STRENGTHEN THE LOW-LEVEL INVERSION,
EFFECTIVELY TRAPPING LOW CLOUDS IN PLACE ACROSS OUR REGION. AS A
RESULT, WILL ADOPT A CONSERVATIVE APPROACH TO TEMPERATURES AND
FORECAST HIGHS IN THE LOWER 50S TOMORROW.
SATURDAY NIGHT, INCREASING LOW-LEVEL MOISTURE VIA AN INTENSIFYING
LOW-LEVEL JET AHEAD OF AN APPROACHING, BUT WEAKENING, COLD FRONT
SHOULD SUPPORT THE DEVELOPMENT OF A FEW ELEVATED WARM-SECTOR SHOWERS
(20% CHANCE), PRIMARILY NEAR THE MISSISSIPPI RIVER. A QUICK PEAK AT
FORECAST SOUNDINGS SUGGESTS THAT A CLAP OF THUNDER OR TWO CANNOT BE
RULED OUT, GIVEN FORECAST ELEVATED LFCS AND STEEP MID-LEVEL LAPSE
RATES WILL ALLOW FOR THEORETICAL PARCEL TRACES TO TERMINATE NEAR OR
JUST ABOVE THE -20C LEVEL. FOR THIS REASON, DID TOSS IN A SLIGHT (10
TO 15%) CHANCE FOR A THUNDERSTORM BETWEEN MIDNIGHT AND DAYBREAK
SUNDAY MORNING, FOCUSED ACROSS NORTHWESTERN ILLINOIS WHERE COVERAGE
OF SHOWERS SHOULD BE HIGHEST (AND SPC HAS THEIR "DAY 2" THUNDER
LINE).
BORCHARDT
SUNDAY THROUGH FRIDAY:
MUCH OF THE FORECAST AREA WILL LIKELY BE DRY ON SUNDAY WITH
HIGH TEMPERATURES IN THE UPPER 50S TO LOW 60S. HOWEVER, WITH
LINGER MOISTURE IN THE AREA AND THE PASSING COLD FRONT PROVIDING
JUST ENOUGH LIFT, THERE IS THE POTENTIAL FOR SOME RAIN IN THE
AFTERNOON/EVENING THOUGH MAINLY FOR AREAS SOUTH AND EAST OF
I-55.
THE NEXT UPPER LEVEL DISTURBANCE MOVES NORTHEASTWARD FROM EL
PASO TO ONTARIO ON MONDAY. RAIN CHANCES INCREASE IN THE LATE
MORNING AND INTO THE AFTERNOON AS THE WARM FRONT MOVES
NORTHWARD. THE WAVE ITSELF WILL SLOWLY WEAKEN AS IT APPROACHES
IOWA AND BECOMES MORE VERTICALLY STACK OVER THE SURFACE LOW
IN THE EARLY EVENING. HOWEVER, AS THIS OCCLUDED LOW MOVES OVER
THE REGION, MORE WIDESPREAD RAIN CAN BE EXPECTED MONDAY NIGHT.
RAIN WILL LINGER TUESDAY MORNING, POTENTIALLY TRANSITIONING INTO
MORE DRIZZLE THAN ACTUAL RAIN AFTER DAYBREAK, AS THE LOW
CONTINUES TO WEAKEN AND MOVE TO THE NORTHEAST.
A BROADER, LONGER WAVE THAT IS PROJECTED OVER THE PACIFIC
NORTHWEST WEDNESDAY WILL CROSS OVER THE ROCKIES TUESDAY INTO
WEDNESDAY. THERE IS STILL SOME UNCERTAINTY WITH MODELS ON THE
EXACT PATH, TIMING, AND WHETHER OR NOT THERE IS ANY PHASING WITH
THE PREVIOUS WAVE FROM MONDAY/TUESDAY'S RAIN. NEVERTHELESS, A
DEEP SURFACE LOW IS EXPECTED MOVE OVER THE REGION TO PROVIDE
THE NEXT CHANCE FOR RAIN. THE POPS FROM THE NBM DID NOT LOOK
UNREASONABLE AND GIVEN THE UNCERTAINTY IN THE EXACT TRACK OF
THE LOW THEY WERE LEFT AS IS IN THE FORECAST. HOWEVER, ON THE
BACKSIDE OF THE UPPER LOW, 850 MB TEMPERATURES WILL LIKELY DROP
BELOW FREEZING. CURRENTLY SURFACE TEMPERATURES WILL LIKELY STAY
ABOVE FREEZING SO THE PRECIP TYPE WAS KEPT AS RAIN, BUT WITH
GUIDANCE TRENDING SLIGHTLY COLDER IN THE COLUMN THERE IS THE
SLIGHT CHANCE (15 PERCENT OR LESS) FOR SOME SNOW FLAKES TO BE
MIXED IN FOR AREAS CLOSER TO THE WISCONSIN BORDER OR DOWNWIND
OF LAKE MICHIGAN ON WEDNESDAY NIGHT. GIVEN THAT THIS WINDOW IS
STILL 6 DAYS OUT, CONFIDENCE REMAINS IN BETTER CHANCES FOR RAIN
AND LOWER ON EXACT TIMING AND ANY FROZEN PRECIP.
THAT WAVE WILL GRADUALLY MOVE EAST ALLOWING THE COLDER, DRIER
AIR MASS TO SLOWLY SETTLE IN THROUGH THE END OF THE WEEK.
MORNING LOW TEMPERATURES ARE EXPECTED AT OR BELOW FREEZING FOR
THURSDAY THROUGH SATURDAY. LUCKILY THE DRIER AIRMASS WILL
PREVENT ANY APPRECIABLE PRECIPITATION WITH IT; THOUGH THE
EXCEPTION BEING ALONG THE SOUTHWESTERN EDGE OF LAKE MICHIGAN.
WITH PERSISTENT NORTHWEST FLOW BEHIND THIS SYSTEM, THERE COULD
BE A CHANCE FOR LINGERING LAKE EFFECT PRECIP LAKE IN THE WEEK
NEXT WEEK FOR AREAS IN NORTHWEST INDIANA.
DK
AVIATION /18Z TAFS THROUGH 00Z SUNDAY/
ISSUED AT 1126 AM CST FRI NOV 15 2024
WHILE THE MORNING STRATUS DECK CONTINUES SHIFT EASTWARD TOWARD
LAKE MICHIGAN, RENEWED STRATOCUMULUS DEVELOPMENT IS EFFECTIVELY
CAUSING A CONTINUATION OF CIGS BASED BETWEEN 2500-3000 FEET AT
ALL TERMINALS. WINDS ARE LARGELY 5KT OR LESS THANKS TO AN
APPROACHING SURFACE PRESSURE RIDGE.
TONIGHT, LOW-LEVEL STEERING FLOW WILL GRADUALLY BECOME
SOUTHEASTERLY, CAUSING THE STRATUS DECK TO OUR EAST TO "SLOSH"
BACK WESTWARD. ALL THE SAME, BUILDING MID-LEVEL RIDGING WILL
ENCOURAGE INVERSION HEIGHTS TO CONTINUE BUILDING DOWNWARD. FOR
THIS REASON, WILL ADVERTISE GRADUALLY LOWERING CIGS BACK INTO
THE 1500 TO 2000 FT RANGE OVERNIGHT. FORECAST OMEGA PROFILES
WITHIN THE STRATUS DECK FROM THE HRRR INDICATE AN OSCILLATORY
PATTERN (INDICATIVE OF GRAVITY WAVES RIDING ATOP THE STABLE
LAYER) OVERNIGHT, SUGGESTING THERE MAY BE PERIODIC PERIODS OF
DRIZZLE AND FINE MIST. HOWEVER, DO FEEL THE MARGINAL DEPTH OF
THE STRATUS (1000FT DEEP OR SO) WILL BE QUITE HOSTILE TO
PRECIPITATION GENERATION. SO, WILL WITHHOLD ANY MENTION OF BR IN
THE OUTGOING SET OF TAFS. FINALLY, WHEREVER THE STRATUS DECK
FAILS TO REACH BY DAYBREAK (RFD?), PATCHY DENSE FOG MAY DEVELOP
GIVEN RESIDUAL LOW-LEVEL MOISTURE AND NEARLY CALM WINDS.
TOMORROW, STRATUS IS EXPECTED TO CONTINUE. SOUTHEASTERLY WINDS
WILL INCREASE THROUGHOUT THE DAY WITH GUSTS OF 15-20KT EXPECTED
BY THE END OF THE TAF.
BORCHARDT
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
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