721
FXUS63 KLOT 281445
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
845 AM CST SAT FEB 28 2026
KEY MESSAGES
- A PERIOD OF SNOW MAY LEAD TO LOCALLY SLIPPERY TRAVEL THIS
AFTERNOON, MAINLY ON UNTREATED ELEVATED ROADWAYS NEAR AND
NORTH OF I-90.
- THE POTENTIAL FOR ACCUMULATING SNOW SUNDAY NIGHT CONTINUES TO
TREND PRIMARILY SOUTH OF THE AREA.
- OUR ANTICIPATED PATTERN CHANGE TOWARD WARMER AND WETTER
CONDITIONS REMAINS ON TRACK THROUGH THE FIRST HALF OF MARCH.
UPDATE
ISSUED AT 845 AM CST SAT FEB 28 2026
A NARROW BAND OF RADAR RETURNS INDICATIVE OF SNOW STRETCHES
FROM NORTHERN SOUTH DAKOTA THROUGH SOUTHERN MINNESOTA, FAR
NORTHEASTERN IOWA, AND SOUTHERN WISCONSIN. SURFACE DEW POINT
DEPRESSIONS OF 15 TO 20 DEGREES AND CLOUD BASES OF 7000 TO 8000
FEET BENEATH THE RADAR RETURNS EAST OF THE MISSISSIPPI RIVER ARE
INDICATIVE OF A WEDGE OF DRY LOW-LEVEL AIR, WHICH HAS THUS FAR
RENDERED ALL LOCAL RADAR RETURNS TO VIRGA. INDEED, RADAR
REFLECTIVITY RETURNS FROM KMKX AND AND KDVN CONTINUE TO EXHIBIT
THE CLASSIC DOUGHNUT-SHAPE, AS THE RADAR BEAM SAMPLES THE
CONCENTRIC OUTER-EDGE OF WHERE SNOW IS SUBLIMATING INTO THE
WEDGE OF DRY AIR.
AS THE MORNING PROGRESSES, CONTINUED SUBLIMATION OF SNOWFLAKES
SHOULD GRADUALLY WHITTLE AWAY AT THE DEPTH OF THE LOW-LEVEL DRY
LAYER. INDEED, HAVE ALREADY NOTED THE TOP OF THE DRY LAYER FALL
FROM AROUND 600 TO 700 MB IN THE PAST FEW HOURS IN AMDAR
SOUNDINGS FROM MDW. SUCH A PROCESS CAN ALSO BE INFERRED ACROSS
FAR NORTHERN IOWA, WHERE BROKEN CLOUDS NEAR 3500 FEET HAVE
DEVELOPED IN TANDEM WITH REPORTS OF SNOW REACHING THE GROUND.
AND, HAVE NOTED A VERY MODEST "SHRINKING" IN THE DONUT HOLE
SHAPE IN RECENT KMKX REFLECTIVITY DATA PARTICULARLY ON ELEVATED
RADAR ELEVATION ANGLES. AS A RESULT, THERE APPEARS TO BE A
SOMEWHAT BRIEF (2 TO 4 HOUR) WINDOW WHERE SNOW MAY ULTIMATELY
REACH THE GROUND FROM LATE MORNING THROUGH EARLY AFTERNOON AS
THE PEAK IN FORCING TRAVERSES ALONG THE ILLINOIS AND WISCONSIN
STATE LINE. THE INHERITED FORECAST CARRYING LIKELY (>55%) POPS
GENERALLY ALONG AND NORTH OF IL-176 HANDLES SUCH A POSSIBILITY
WELL.
WITH A SOMEWHAT LIMITED TIME WINDOW FOR SNOW, A RESIDUAL DRY
LOW-LEVEL AIRMASS, AND MARGINAL SURFACE TEMPERATURES NEAR
FREEZING, STILL SUSPECT THAT SNOW MAY STRUGGLE TO ACCUMULATE
WHERE IT DOES REACH THE GROUND. ACCORDINGLY, THE INHERITED
FORECAST FOR UP TO ABOUT AN INCH OF SNOW NEAR THE WISCONSIN
STATE LINE REMAINS QUITE APPROPRIATE. OF COURSE, THERE REMAINS A
POSSIBILITY (IMPLIED 40 TO 45% CHANCE OR SO GIVEN THE
AFOREMENTIONED POPS) THAT SNOW NEVER ACTUALLY REACHES THE GROUND
LOCALLY.
ELSEWHERE, TODAY LOOKS RATHER BANAL WITH INCREASING CLOUD COVER
AND GRADUALLY INCREASING EAST TO NORTHEASTERLY FLOW. HIGHS WILL
STALL GENERALLY NEAR 40 ALONG THE I-88/I-80 CORRIDORS AND RISE
TO AROUND 50 NEAR US-24.
UPDATED PRODUCTS WILL BE SENT SOON.
BORCHARDT
DISCUSSION
ISSUED AT 316 AM CST SAT FEB 28 2026
THROUGH MONDAY:
WE ARE MONITORING A NARROW BAND OF SNOW APPROACHING THE REGION
THAT CURRENTLY EXTENDS FROM SOUTHWEST NORTH DAKOTA ACROSS SOUTH
DAKOTA INTO SOUTHWEST MINNESOTA. THIS FEATURE IS ASSOCIATED
WITH A FRONTOGENETICAL RESPONSE TO DIVERGENCE ALOFT IN THE LEFT
EXIT REGION OF AN UPPER LEVEL JET STREAK. THE FGEN LAYER
APPEARS TO RESIDE WITHIN 850-750MB WHICH IS SITUATED BENEATH A
RATHER DEEP LAYER OF SATURATION WITHIN THE DGZ PAIRED WITH
FAIRLY STEEP LAPSE RATES WITHIN THAT LAYER, INDICATIVE OF
EMBEDDED LOCALLY HIGH SNOWFALL RATES OF 1"+ PER HOUR. THE KEY
FORECAST CHALLENGE IS WHETHER THIS FEATURE WILL MAINTAIN ITS
EAST SOUTHEASTWARD PROGRESSION INTO PORTIONS OF NORTHERN
ILLINOIS AND WHETHER IT CAN OVERCOME PRONOUNCED LOW-LEVEL DRY
AIR HERE LOCALLY. 00Z GUIDANCE HAD LARGELY MAINTAINED THE IDEA
THAT THIS BAND WOULD BEGIN TO TREND MORE EAST THAN SOUTHEAST
THROUGH THE MORNING KEEPING ACCUMULATIONS LARGELY NORTH OF THE
WISCONSIN STATE LINE. HOWEVER, THE CURRENT POSITION OF THE SNOW
BAND HAS REMAINED MOSTLY SOUTH OF THESE EARLIER SOLUTIONS, MORE
IN LINE WITH THE 0Z ARW AND NOW LIKELY BEING PICKED UP BY THE
RECENT 06Z NAMNEST WHICH BRING THE SNOW ACROSS PORTIONS OF
NORTHERN ILLINOIS.
AS A RESULT, IT FELT PRUDENT TO NUDGE UP SNOWFALL AMOUNTS (~0.5
TO 1") NEAR AND NORTH OF A ROCKFORD TO EVANSTON LINE (HIGHEST
TOWARD THE WISCONSIN STATE LINE). IT REMAINS LOWER CONFIDENCE
AS TO WHETHER THIS WILL LEAD TO TRAVEL IMPACTS HERE LOCALLY WITH
PAVEMENT TEMPERATURE OBSERVATIONS STILL ABOVE FREEZING AFTER AN
UNSEASONABLY WARM FRIDAY. THUS, WITH THIS IN MIND AND DAYTIME
TIMING WITH FAIRLY STRONG LAST DAY OF FEBRUARY SUN, SUSPECT
THAT ANY ACCUMULATIONS WOULD BE MAINLY CONFINED TO GRASSY AND
UNTREATED ELEVATED SURFACES (INCLUDING BRIDGES AND OVERPASSES).
HOWEVER, IF LOCALLY HIGHER SNOWFALL RATES CAN BE ACHIEVED LATE
MORNING INTO EARLY AFTERNOON WHEN THE FGEN SIGNAL IS MAXIMIZED,
A BRIEF (1-2 HR) PERIOD OF PAVEMENT ACCUMULATIONS WOULD BE
POSSIBLE, LEADING TO A GREATER COVERAGE OF SLIPPERY TRAVEL
CONDITIONS. LASTLY WE WILL HAVE TO MONITOR FOR ANY ADDITIONAL
SOUTHWARD ADJUSTMENTS TO THE TRACK OF THE BAND OF SNOW WHICH
COULD INCLUDE MORE OF THE CHICAGO METRO AREA BUT THERE SHOULD BE
A FAIRLY SHARP SOUTHERN EDGE TO THE SNOWFALL.
TEMPERATURES TODAY WILL FEATURE A FAIRLY SIZABLE GRADIENT FROM
NORTH TO SOUTH, WITH LOWER TO MID 30S FOR HIGHS NORTH OF I-88
CLOSER TO THE POTENTIAL BAND OF SNOW. IN CONTRAST, WARMER MID
40S TO AROUND 50 POSSIBLE ARE LIKELY SOUTH OF I-80.
IN THE WAKE OF TODAY'S SNOW SYSTEM THIS EVENING, A LAKE EFFECT
SNOW BAND MAY TRY TO SET UP AND ORIENT INTO NORTHEAST ILLINOIS
TOWARD DAYBREAK SUNDAY. LAKE EFFECT PARAMETERS DON'T LOOK
ESPECIALLY IMPRESSIVE AT THIS TIME BUT SOME HIGH-RES GUIDANCE
SUGGESTS THERE COULD AT LEAST BE A LIGHT DUSTING NEAR THE LAKE
BEFORE IT ENDS IN THE AFTERNOON ON SUNDAY. HAVE MAINTAINED
SLIGHT CHANCES (~20%) NEAR THE LAKE TO ACCOUNT FOR THIS.
MODEL GUIDANCE FOR THE SUNDAY NIGHT SYSTEM CONTINUES TO TREND
FARTHER SOUTH WITH BLENDED GUIDANCE KEEPING THE ACCUMULATING
SNOW LARGELY SOUTH OF THE AREA. HAVE HELD ONTO LOW SNOW CHANCES
SOUTH OF I-80 WITH THIS UPDATE GIVEN THERE HAS BEEN SOME
VARIABILITY IN THE POSITION OF THE BAND THE PAST FEW DAYS.
SUSPECT THIS MAY END UP NOT MUCH MORE THAN FLURRIES GIVEN THERE
WILL BE DRY AIR TO CONTEND WITH AMIDST EXPANDING SURFACE HIGH
PRESSURE OVER THE UPPER MIDWEST AND GREAT LAKES REGION.
COLD AIR ADVECTION PAIRED WITH NORTHEAST WINDS OFF LAKE
MICHIGAN WILL LIKELY KEEP TEMPERATURES IN THE 30S ACROSS THE
AREA ON SUNDAY. AFTER A CHILLY SUNDAY TEMPERATURES THEN TREND
WARMER ON MONDAY WITH HIGHS MAINLY IN THE 40S (UPPER 30S NEAR
THE IL LAKESHORE) AS WE TRANSITION INTO A WARMER AND WETTER
PATTERN, MORE ON THAT BELOW.
PETR
MONDAY NIGHT ONWARD:
A SIGNIFICANT LARGE SCALE WEATHER PATTERN SHIFT IS EXPECTED DURING
THIS COMING WEEK. THE PATTERN WILL TRANSITION TO THE NEGATIVE
PHASE OF THE PACIFIC NORTH AMERICAN (PNA) TELECONNECTION PATTERN,
WHICH IS CHARACTERIZED BY WESTERN CONUS MID AND UPPER LEVEL
TROUGHING AND EASTERN CONUS RIDGING. WHILE THE DAY-TO-DAY
SPECIFICS OF THIS PATTERN REMAIN SOMEWHAT UNCLEAR, THERE IS ABOVE
AVERAGE FORECAST CONFIDENCE THAT THIS PATTERN WILL FAVOR PERIODS
OF ACTIVE WEATHER, INCLUDING NOTABLE RAINFALL AMOUNTS AND
THUNDERSTORMS, ALONG WITH ABOVE AVERAGE TEMPERATURES THROUGH NEXT
WEEKEND. OUR CURRENT FORECAST DOES ADVERTISE AT LEAST SOME LOWER
END CHANCES FOR RAIN EACH DAY TUESDAY THROUGH NEXT WEEKEND. IN
SPITE OF THIS, DO NOT EXPECTED TO BE RAINING CONSTANTLY, AS THERE
WILL BE PERIODS OF DRY TIME.
OUR FIRST FAVORED PERIOD OF RAIN IS LATE MONDAY NIGHT INTO
TUESDAY IN ASSOCIATION WITH INCREASING WARM AIR ADVECTION
(ISENTROPIC UPGLIDE) SETTING UP ACROSS A SURFACE FRONTAL BOUNDARY
DOWNSTREAM OF AN IMPULSE TRAVERSING THE COLORADO ROCKIES. THERE'S
A NON-ZERO CHANCE THAT THE INITIAL RAIN WILL FALL WHILE TEMPERATURES
AND/OR SURFACE WET BULBS OVER PARTS OF THE AREA ARE AT OR JUST
BELOW FREEZING IN THE OVERNIGHT/PRE-DAWN HOURS OF TUESDAY. WITH
EAST-SOUTHEASTERLY FLOW COMING FROM A REGION OF 20S DEW POINTS TO
OUR EAST ASSOCIATED WITH DEPARTING STRONG SURFACE HIGH PRESSURE,
THERE MIGHT BE ENOUGH OF A DELAY IN SURFACE WARMING TO RESULT IN
A BRIEF PERIOD OF FREEZING RAIN. THE PRIMARY ZONE OF INTEREST FOR
THIS LOWER END POTENTIAL WOULD BE NEAR AND NORTH OF I-90 IN FAR
NORTHERN ILLINOIS. EVEN IF A PERIOD OF FREEZING RAIN MATERIALIZES,
FAIRLY MILD ANTECEDENT PAVEMENT TEMPERATURES MAY SERVE TO MITIGATE
TRAVEL IMPACTS. WE'LL HOLD OFF A FEW MORE CYCLES IN TERMS OF
RAMPING UP MESSAGING FOR THE CURRENT SLIGHT/20% CHANCE OF FREEZING
RAIN IN PARTS OF FAR NORTHERN ILLINOIS.
ULTIMATELY, THERE IS A STRONG SIGNAL FOR RAINFALL DURING THE LATE
MONDAY NIGHT AND TUESDAY PERIOD, WITH ROUGHLY 70 TO 90+ PERCENT
OF THE ENSEMBLE MEMBERS PRODUCING RAIN ACROSS A GOOD PORTION OF
THE AREA. THEREAFTER, ENSEMBLE SPREAD INCREASES, PARTICULARLY WITH
THE SPEED AND TIMING OF THE THE NEXT IMPULSE EXPECTED TO SHIFT
INTO THE LOWER GREAT LAKES REGION SOMETIME WEDNESDAY INTO
THURSDAY. THE GEFS AND TO A LESSER EXTENT THE CANADIAN ENSEMBLE
SYSTEM HAVE REMAINED ON THE FASTER SIDE OF THE GUIDANCE ENVELOPE
FOR WEDNESDAY, WHICH WOULD ENTAIL RAINY/INCLEMENT CONDITIONS.
MEANWHILE, IF THE SLOWER SOLUTIONS ADVERTISED BY ABOUT HALF OF THE
ENSEMBLE SUITES (THE ECMWF AND UKMET ENSEMBLES) PAN OUT, A GOOD
CHUNK OF WEDNESDAY COULD BE DRY (ESPECIALLY WITH NORTHWARD EXTENT)
BEFORE RAIN CHANCES INCREASE AGAIN WEDNESDAY NIGHT INTO THURSDAY.
ON EITHER SIDE OF THE FASTER TO SLOWER SPECTRUM WITH RESPECT TO
RAIN TRENDS WEDNESDAY-THURSDAY, TEMPERATURES MAY END UP A GOOD
DEAL COOLER THAN THE OFFICIAL FORECAST IN PARTS OF THE AREA DUE
TO ONSHORE FLOW FROM LAKE MICHIGAN. THIS IS PARTICULARLY THE CASE
ON THURSDAY NEAR THE LAKE IN NORTHEAST ILLINOIS.
REGARDLESS OF EXACTLY HOW THE MID TO LATE WEEK PERIOD EVOLVES,
PRECIPITABLE WATER OF 250-300% OF AVERAGE/NORMAL FOR EARLY MARCH
COULD CERTAINLY SPELL CORRIDORS OF HEAVY RAINFALL AND AN
ASSOCIATED FLOODING THREAT. THE EXTENT (OR LACK THEREOF) OF
EMBEDDED THUNDERSTORMS WILL LIKELY PLAY A ROLE AS WELL. FINALLY,
THE EXCEPTIONALLY MILD AND MOIST CYCLONE WARM SECTORS IN THE
UPCOMING PATTERN MAY ALSO FEATURE A THREAT FOR ORGANIZED STRONG
TO SEVERE CONVECTION WITHIN IN THE GENERAL REGION. NEXT FRIDAY MAY
BE A "DAY TO WATCH" IN THIS REGARD. EVEN AT THIS LEAD TIME, THE
VARIOUS ENSEMBLE SYSTEMS HAVE A STRIKINGLY STRONG SIGNAL FOR A
NORTHWARD SURGE OF ANOMALOUS DEW POINTS IN THE 50S TO POSSIBLY
60F+ IN SPOTS COINCIDING WITH AN APPROACHING COLD FRONT AND
SEASONABLY STRONG WIND FIELDS.
CASTRO/KJB
AVIATION /12Z TAFS THROUGH 18Z SUNDAY/
ISSUED AT 556 AM CST SAT FEB 28 2026
MAIN CONCERN:
- POTENTIAL FOR A PERIOD OF SNOW AND ASSOCIATED VSBY IMPACTS AT
THE NORTHERN ILLINOIS TERMINALS TODAY
THE SOUTHERN EXTENT OF A FAIRLY NARROW SNOW BAND TODAY REMAINS
UNCERTAIN. RECENT UPSTREAM RADAR AND OBSERVATIONAL TRENDS HAVE
BEEN A BETTER FIT FOR NEAR-TERM GUIDANCE THAT SHIFTED A BIT
SOUTH FROM PREVIOUS MODEL CYCLES. THIS STILL PLACES THE NORTHERN
ILLINOIS TERMINALS ON THE SHARP SOUTHERN EDGE DIVIDING LINE
BETWEEN SNOW WITH IMPACTS TO VSBY AND VFR FLURRIES AT MOST. FOR
THIS ISSUANCE, MAINTAINED PROB30 MENTION, THOUGH WITH IFR VSBY
AT RFD AND ORD WHERE THERE'S A BETTER CHANCE FOR A PERIOD OF
HIGHER SNOWFALL RATES. GIVEN MILD PAVEMENT TEMPERATURES GOING
INTO TODAY AND THE FAIRLY STRONG END OF FEBRUARY SUN, PAVEMENT
ACCUMULATIONS WOULD PROBABLY BE LIMITED (A RELATIVELY HIGHER
CHANCE AT RFD).
CIGS SHOULD BUILD DOWN TO A PERIOD OF PREVAILING MVFR AT THE
CHICAGO METRO SITES THIS EVENING DUE TO STRENGTHENING NORTH-
NORTHEAST FLOW. THIS COULD EVENTUALLY YIELD INTERMITTENT LAKE
EFFECT FLURRIES NEAR THE LAKE, WITH LITTLE/NO IMPACTS EXPECTED
IF THEY OCCUR. ONCE WINDS SHIFT EAST OF NORTH THIS MORNING,
THEY'RE EXPECTED TO REMAIN EAST OF NORTH THROUGH SUNDAY. EXPECT
THE STRONGEST WINDS LATE TODAY AND ESPECIALLY THIS EVENING WHEN
GUSTS NEAR THE LAKE MAY REACH AS HIGH AS 20-25 KT AT TIMES.
CASTRO
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY FROM 2 PM THIS AFTERNOON TO 3 PM CST
SUNDAY FOR WINTHROP HARBOR IL TO BURNS HARBOR IN.
SMALL CRAFT ADVISORY UNTIL 3 PM CST SUNDAY FOR BURNS HARBOR TO
MICHIGAN CITY IN.
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