681
FXUS63 KLOT 271908
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
208 PM CDT THU MAR 27 2025
KEY MESSAGES
- SCATTERED SHOWERS AND STORMS ARE EXPECTED TO DEVELOP ACROSS
THE REGION OVERNIGHT. A FEW STORMS WILL PRODUCE PEA TO NICKEL
SIZE HAIL.
- FRIDAY WILL BE WARM AND BREEZY WITH HIGHS IN THE 70S AND
SOUTHWESTERLY WINDS GUSTING 30 TO 40 MPH.
- RAIN AND/OR THUNDERSTORMS POSSIBLE AT TIMES OVER THE WEEKEND
WITH A SUBSTANTIAL TEMPERATURE GRADIENT STALLED ACROSS
NORTHERN ILLINOIS.
DISCUSSION
ISSUED AT 208 PM CDT THU MAR 27 2025
THROUGH FRIDAY NIGHT:
RAP-MESOANALYSIS DATA AUGMENTED BY OBSERVATIONS DEPICT A BROAD
REGION OF LOW SURFACE PRESSURE ALONG THE LEE SIDE OF THE ROCKY
MOUNTAINS WELL TO THE WEST OF A SURFACE HIGH PRESSURE SYSTEM
CENTERED OVER THE CAROLINAS. A BROAD WARM FRONTAL ZONE EXTENDS
EASTWARD FROM THE REGION OF LOW PRESSURE FROM THE DAKOTAS
THROUGH THE MIDDLE MISSISSIPPI RIVER VALLEY. SHOWERS AND A FEW
THUNDERSTORMS CONTINUE TO FESTER ALONG THE TERMINUS OF A REMNANT
LOW-LEVEL JET AND WITHIN A REGION OF PERSISTENT MID-LEVEL
FRONTOGENESIS ACTING UPON THE BROAD WARM FRONTAL ZONE, MAINLY
FROM NORTHWESTERN MO INTO CENTRAL IL. OUR AREA HENCE REMAINS
CLOUDED OVER, LEADING TO MUTED TEMPERATURES AND LIGHT WINDS.
TONIGHT, THE BROAD REGION OF LOW PRESSURE WELL TO OUR WEST WILL
CONSOLIDATE AND SHIFT EASTWARD INTO THE NORTHERN PLAINS. AS THIS
OCCURS, LOW- TO MID-LEVEL SOUTHWESTERLY FLOW WILL INCREASE ACROSS
THE MID-MISSISSIPPI RIVER VALLEY, FACILITATING THE NORTHEASTWARD
ADVECTION OF A RESERVOIR OF STEEP MID-LEVEL LAPSE RATES (AN
ELEVATED MIXED LAYER, OR EML) NORTHEASTWARD INTO THE GREAT
LAKES. AS THE WARM FRONTAL ZONE SHARPENS AND LOW-LEVEL JET
REINTENSIFIES OVERNIGHT IN OUR GENERAL REGION, ISENTROPIC
SURFACES WILL BECOME INCREASINGLY SLOPED ALLOWING FOR EFFICIENT
UPGLIDE. WHILE CONFIDENCE IN SHOWERS AND STORMS DEVELOPING IS
HENCE HIGH (>90% CHANCE IN OUR GENERAL REGION), EXACTLY WHERE
CARRIES LOWER CONFIDENCE (40-60% AT ANY GIVEN POINT) OWING TO
DIFFERENCES AMONGST MODEL SUITES AND THE RATE AT WHICH THE BASE
OF THE EML MOISTENS. GLOBAL GUIDANCE SUCH AS THE EPS/GEFS FAVORS
THE AXIS OF SHOWERS AND STORMS EXTENDING FROM SOUTHEASTERN IOWA
TO CENTRAL INDIANA, WHILE HIGH-RES GUIDANCE SUMMARIZED BY THE
HREF FAVORS THE AXIS FURTHER TO THE NORTH FROM EASTERN IOWA TO
LAKE MICHIGAN. THIS IS A FAIRLY TYPICAL SOURCE OF FORECAST
UNCERTAINTY WITH CONVECTION ALONG A NORTHEASTWARD-ADVANCING EML
PLUME AND INTENSIFYING LOW-LEVEL JET, AND CAN BE PRONE TO
SIZABLE FORECAST ERRORS IN OBSERVED LOCATIONS OF STORMS.
REGARDLESS OF WHERE STORMS DO DEVELOP, MODEST CONVECTIVE-LAYER
SHEAR OF 20-25KT AND RELATIVELY LOW FREEZING LEVELS NEAR 10KFT
WILL SUPPORT PERIODIC INSTANCES OF PEA TO NICKEL SIZE HAIL, IN
ADDITION TO HEALTHY DOWNPOURS AND FREQUENT LIGHTNING STRIKES.
(NOTE THAT HREF 48-HOUR PMM QPF SUPPORTS A FEW SWATHS OF >1"
RAIN SOMEWHERE IN OUR GENERAL REGION OVERNIGHT).
SHOWERS AND STORMS MAY LINGER BEYOND DAYBREAK ACROSS
NORTHEASTERN OR EASTERN ILLINOIS TOMORROW MORNING UNTIL THE
CONTINUED EASTWARD- ADVANCEMENT OF THE SURFACE LOW TO OUR
NORTHWEST PULLS THE WARM FRONT INTO WISCONSIN. DECREASING
CLOUDINESS WILL ALLOW FOR MIXING HEIGHTS TO QUICKLY BUILD UPWARD
INTO THE REMNANT LOW-LEVEL JET, THOUGH A STRENGTHENING LOW-
LEVEL INVERSION MAY TEND TO LIMIT THE EFFICIENCY WITH WHICH
WINDS CAN MIX TO THE GROUND (E.G. WAA-DRIVEN WINDS). WITH THAT
SAID, FORECAST MIXING PROFILES AMONG HRRR/RAP/NAM3 DATA SUPPORT
FREQUENT GUSTS OF 30 TO 40 MPH. TEMPERATURES WILL ALSO ROCKET
UPWARD TOMORROW, WITH 850MB TEMPERATURES NORTH OF +10C AND AT
LEAST PARTIAL SUNSHINE SUPPORTING HIGHS WELL INTO THE 70S. IN
ALL, TOMORROW WILL LOOK AND FEEL QUITE A BIT DIFFERENT COMPARED
TO TODAY.
WINDS WILL REMAIN BREEZY AFTER SUNSET TOMORROW NIGHT AS
TEMPERATURES ONLY GRADUALLY FALL (OFFSETTING IMMEDIATE
DECOUPLING). OVERNIGHT LOWS WILL FALL TOWARD THE UPPER 50S.
BORCHARDT
SATURDAY THROUGH THURSDAY:
WARM FRONT IS FORECAST TO BE NORTH OF THE AREA SATURDAY
MORNING, WITH THE MAIN FOCUS FOR OVERNIGHT PRECIPITATION TO OUR
NORTH ACROSS IA-WI, ASSOCIATED WITH AN EASTWARD TRACKING SURFACE
WAVE. GUIDANCE IS IN GENERAL AGREEMENT HOWEVER, IN SAGGING THE
FRONT BACK SOUTH AS A LAKE-ENHANCED COLD FRONT DURING THE
AFTERNOON. WHILE SOME DIFFERENCES IN TIMING ARE EVIDENT BETWEEN
THE VARIOUS MODEL ENSEMBLES, THERE IS CONSENSUS INDICATING THIS
"BACK DOOR" COLD FRONT WILL SLIDE DOWN THE LAKE, SHIFT WINDS TO
THE NORTHEAST, AND BRING MUCH COOLER TEMPERATURES (40S ALONG THE
LAKE, 50S INLAND) THROUGH AT LEAST THE I-90 CORRIDOR FROM
NORTHERN IL INTO NORTHWEST IN BY EVENING. SHOWER CHANCES ALSO
INCREASE BY SATURDAY AFTERNOON AS A PAIR OF MID-LEVEL SHORT
WAVES APPROACH THE AREA, ONE FROM THE PLAINS HEADING INTO THE
UPPER MIDWEST, AND ANOTHER FARTHER SOUTH TRACKING INTO THE LOWER
OHIO VALLEY. ENSEMBLES CONTINUE TO SHOW SOME SPREAD WITH THE
AMPLITUDE AND EXACT TRACK WITH THESE DISTURBANCES, THOUGH
GENERALLY FAVOR INCREASE SHOWER POTENTIAL ALONG THE FRONT TO OUR
NORTHWEST (IA/SOUTHWEST WI) AND FARTHER SOUTH INTO PARTS OF
CENTRAL IL/IN. THE WFO LOT CWA APPEARS TO BE IN A PRECIP MINIMUM
BETWEEN THESE TO AREAS OF FOCUS, THOUGH AN OVERALL UPTICK IN
SCATTERED COVERAGE APPEARS LIKELY SATURDAY AFTERNOON.
THE BEST LOW-LEVEL MOISTURE AND INSTABILITY AXIS IS DEPICTED
ALONG/WEST OF THE MISSISSIPPI RIVER SATURDAY AFTERNOON, AHEAD OF
AN AREA OF SURFACE LOW PRESSURE ASSOCIATED WITH THE NORTHERN,
MORE AMPLIFIED SHORT WAVE. THIS IS WHERE THE GREATEST THUNDER
POTENTIAL LOOKS TO BE SATURDAY AFTERNOON/EVENING, THOUGH SOME OF
THIS MAY SPREAD INTO WESTERN PARTS OF IL/LOT CWA IN A
DIMINISHING TREND. CURRENT FORECAST SOUNDINGS ARE NOT VERY
IMPRESSIVE ACROSS OUR WESTERN CWA AT THIS TIME HOWEVER. ENSEMBLE
GUIDANCE CONTINUES TO SHOW CONSIDERABLE SPREAD WITH THE
STRENGTH AND TRACK OF THE AFOREMENTIONED SURFACE LOW AND THE
EASTWARD TIMING OF THE TRAILING COLD FRONT SATURDAY NIGHT INTO
SUNDAY. EPS/CMCE ARE DEEPER AND FARTHER NORTHWEST WITH THE LOW
AND SLOWER WITH THE FRONT, WHILE THE GEFS (AND SREF THROUGH 12Z
SUNDAY) ARE WEAKER AND FARTHER SOUTHEAST INTO IL. OVERALL,
SUNDAY DOES LOOK TO BE RATHER SHOWERY AND PERHAPS THUNDERY
DEPENDING ON WHICH OF THESE SOLUTIONS END UP VERIFYING. HIGHEST
THUNDER POTENTIAL WOULD GENERALLY BE ACROSS OUR SOUTHEASTERN CWA
WITH THE SLOWEST FRONTAL MOVEMENT, OR EVEN EAST/SOUTHEAST OF
THE AREA IN THE CASE OF THE FASTER TIMING. IN EITHER EVENT, THE
STRONGEST INSTABILITY IS PROGGED SOUTH/SOUTHEAST OF THE FORECAST
AREA. SHOWERS PERSIST BEHIND SUNDAY NIGHT INTO EARLY MONDAY
BEHIND THE FRONT AS THE MAIN UPPER LEVEL TROUGH WORKS ACROSS THE
AREA. COLDER AIR WRAPPING IN BEHIND THE DEPARTING LOW, COOLING
THE COLUMN AND ALLOWING A MIX OR CHANGE TO WET SNOW LATER SUNDAY
NIGHT INTO MONDAY MORNING. DEEPER EPS EVEN SUGGESTS A LINGERING
DEFORMATION BAND MAY MAINTAIN THE THREAT OF PRECIPITATION INTO
MONDAY AFTERNOON.
DRY BUT MUCH COOLER CONDITIONS ARE INDICATED LATE MONDAY INTO
TUESDAY, AS HIGH PRESSURE SPREADS BRIEFLY ACROSS THE REGION.
DESPITE THE CONSIDERABLE MODEL SPREAD SEEN WITH THE WEEKEND
SYSTEM, GLOBAL ENSEMBLES CURRENTLY SHOW VERY GOOD AGREEMENT IN
RETURNING TO A WESTERN CONUS UPPER TROUGH/DOWNSTREAM CENTRAL
CONUS UPPER RIDGE BY MID-WEEK, THOUGH THE PATTERN IS PROGRESSIVE
AND BRINGS RAIN AND POSSIBLY THUNDERSTORM CHANCES BACK INTO THE
AREA IN THE LATE TUESDAY INTO WEDNESDAY PERIOD ALONG WITH
WARMER TEMPERATURES.
RATZER
AVIATION /18Z TAFS THROUGH 00Z SATURDAY/
ISSUED AT 1220 PM CDT THU MAR 27 2025
KEY MESSAGES FOR THE 18Z TAFS:
- VFR CLOUD COVER THIS AFTERNOON WITH A FEW ISOLATED LIGHT
SHOWERS AND SPRINKLES.
- A PERIOD OF MORE SUBSTANTIAL SHOWERS AND THUNDERSTORMS
OVERNIGHT, WITH IFR CIGS AND VSBYS.
- LOW CLOUDS CLEAR BY MID FRIDAY MORNING, THEN SOUTHWEST WINDS
BECOME INCREASINGLY GUSTY (UP TO AROUND 35 KT) THROUGH THE
AFTERNOON.
AN AREA OF VFR CLOUD COVER BASED IN THE 6-8,000 FT RANGE
CONTINUE TO STREAM ACROSS THE AREA EARLY THIS AFTERNOON. THERE
ARE ALSO SOME ISOLATED SHOWERS, THOUGH MOST OF THESE ARE
EXPECTED TO REMAIN SOUTHWEST OF THE MAIN CHICAGO TERMINALS.
OTHERWISE, EXPECT LIGHT (10 KT OR LESS) SOUTH TO SOUTHWEST
WINDS TO BACK MORE SOUTHEASTERLY INTO THIS EVENING AS A WARM
FRONT BEGINS TO APPROACH THE AREA FROM THE SOUTH.
THE WARM FRONT WILL LIFT NORTHWARD ACROSS THE TERMINAL AIRSPACE
AROUND DAYBREAK FRIDAY MORNING. AS IT BEGINS TO MOVE INTO THE
AREA AFTER MIDNIGHT, A PERIOD OF SHOWERS AND THUNDERSTORMS ARE
LIKELY (60%+ CHANCE) TO DEVELOP AND MOVE ACROSS THE TERMINALS.
CURRENT BEST TIMING FOR THESE STORMS LOOK TO BE IN THE 08-12Z
TIMEFRAME. THE ONLY CHANGE FOR THE NEW SET OF TAFS WAS TO
CONVERT THE PROB30 TO A TEMPO GROUP FOR THESE STORMS.
OTHERWISE, SHOULD SEE SOME LOWER CIGS AND VSBYS WITH THESE
SHOWERS AND STORMS, WITH IFR CONDITIONS FAVORED.
ONCE THE WARM FRONT LIFTS NORTH OF THE AREA AFTER DAYBREAK
FRIDAY, EXPECT THE LOW CLOUDS TO SCATTER OUT FOR THE DAY, WITH
VFR CONDITIONS RETURNING. THE ONLY OTHER NOTE FOR FRIDAY WILL BE
THE INCREASING SOUTHWESTERLY WINDS THROUGH THE DAY. EXPECT WINDS
TO GUST UP AROUND (OR EVEN A BIT ABOVE) 35 KT, ESPECIALLY DURING
THE MID AND LATE AFTERNOON HOURS.
KJB
MARINE
ISSUED AT 208 PM CDT THU MAR 27 2025
THURSDAY NIGHT INTO FRIDAY, A SEASONABLY STRONG LOW PRESSURE
SYSTEM WILL MOVE FROM THE NORTHERN PLAINS TOWARD THE GREAT LAKES
CAUSING A SURFACE WARM FRONT TO LIFT NORTHWARD THROUGH THE
REGION. BEHIND THE FRONT, SOUTHWESTERLY WINDS WILL INCREASE IN
MAGNITUDE WITH GALE FORCE GUSTS IN EXCESS OF 35 KT POSSIBLE,
STARTING FRIDAY AFTERNOON AND LASTING THROUGH EARLY SATURDAY
MORNING. SINCE WATER TEMPERATURES REMAIN COLD (LEADING TO
STABILITY OVER THE LAKE), THE THREAT FOR GALE FORCE WINDS WILL
BE WITHIN THE FIRST 2 TO 3 MILES OF THE LAKESHORE. A GALE WATCH
REMAINS IN EFFECT FOR THE ILLINOIS AND A PORTION OF THE
NORTHWESTERN INDIANA NEARSHORE FRIDAY AFTERNOON THROUGH EARLY
SATURDAY MORNING.
NWS CHICAGO
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...GALE WATCH FROM FRIDAY AFTERNOON THROUGH LATE FRIDAY NIGHT FOR
THE IL AND IN NEARSHORE WATERS.
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