399
FXUS63 KLOT 180801
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
301 AM CDT SAT APR 18 2026
KEY MESSAGES
- BREEZY TO WINDY CONDITIONS TODAY WITH COLDER WEATHER OVER THE
WEEKEND INTO EARLY NEXT WEEK.
- POTENTIAL (20-30%) FOR SOME GUSTY SHOWERS SUNDAY AFTERNOON.
- FROST/FREEZE CONDITIONS ARE EXPECTED MANY AREAS SUNDAY AND
ESPECIALLY MONDAY MORNING.
DISCUSSION
ISSUED AT 301 AM CDT SAT APR 18 2026
A STRONG COLD FRONT IS SHIFTING ACROSS THE REGION EARLY THIS
MORNING. IN ITS WAKE, BLUSTERY NORTHWEST WINDS WILL GUST TO 30
MPH TODAY. PERSISTENT COLD ADVECTION WILL HOLD HIGHS GENERALLY
IN THE UPPER 40S AND LOWER 50S. LINGERING STRATUS WILL ERODE AND
THIN THROUGH THE AFTERNOON, YIELDING MOSTLY CLEAR SKIES
OVERNIGHT INTO SUNDAY MORNING. SINCE WE'LL REMAIN ON THE
NORTHERN PERIPHERY OF A MODEST MID 1020S MB HIGH ACROSS THE
ARKLATEX, WE'LL LIKELY HOLD ONTO AT LEAST SOME SURFACE FLOW
THROUGH THE NIGHT. THIS SHOULD TEND TO LIMIT THE EXPANSIVENESS
OF THE FROST THREAT, ALTHOUGH WITH TEMPERATURES EXPECTED TO DIP
TO NEAR FREEZING WEST AND NORTH OF THE FOX VALLEY, IT'S POSSIBLE
WE MAY NEED TO CONSIDER A SMALL FROST ADVISORY FOR PARTS OF THE
AREA. WILL DEFER THIS DECISION TO THE DAYSHIFT.
ON SUNDAY, A FAST-MOVING AND FAIRLY ENERGETIC/ROBUST WAVE
EMBEDDED WITHIN BROAD CYCLONIC FLOW WILL DROP ACROSS THE
REGION. AS THIS APPROACHES THROUGH THE AFTERNOON, SURFACE-700 MB
LAPSE RATES ARE FORECAST TO INCREASE SIGNIFICANTLY--TOWARDS 9
C/KM. WITH THE INCREASING IN ATTENDANT FORCING, FORECAST
SOUNDINGS REVEAL SUFFICIENT SATURATION THROUGH THE 700-800 MB
LAYER AND THE DEVELOPMENT OF JUST ENOUGH INSTABILITY TO SUPPORT
PERHAPS WIDELY SCATTERED DIURNALLY-DRIVEN SHOWERS AND HAVE ADDED
SOME LOW-END PRECIP CHANCES TO THE FORECAST TO ACCOUNT FOR
THIS. GIVEN THE LOW WET BULB ZERO HEIGHTS AND PRESENCE OF 0-3 KM
CAPE, SUPPOSE IT WOULDN'T BE ENTIRELY OUT OF THE QUESTION FOR
SOME GRAUPEL IF ROBUST CONVECTIVE ELEMENTS DEVELOP, ALTHOUGH NO
ACCUMULATIONS WOULD RESULT WITH AIR TEMPERATURES IN THE 40S/50S.
ADDITIONALLY, TOP-OF-CHANNEL FLOW AROUND 30 KNOTS SUGGESTS THE
POTENTIAL FOR OCCASIONAL 35 MPH WIND GUSTS (PARTICULARLY NEAR
AND SOUTH OF I-80) IF THIS LEVEL OF MIXING IS REALIZED.
SURFACE HIGH PRESSURE WILL THEN BUILD NEARLY OVERHEAD SUNDAY
NIGHT INTO MONDAY MORNING. THIS WILL SET THE STAGE FOR MORE
ROBUST RADIATIONAL COOLING AND SOMEWHAT MORE WIDESPREAD NEAR TO
SUB- FREEZING TEMPERATURES OUTSIDE OF CHICAGO. WILL LIKELY NEED
A COMBINATION OF FROST ADVISORIES AND FREEZE WARNINGS FOR THIS.
BROAD WARM ADVECTION WILL RE-ESTABLISH ACROSS THE AREA ON MONDAY
AND TUESDAY WITH TEMPERATURES EXPECTED TO PUSH BACK INTO THE
70S ON TUESDAY. SOME GUIDANCE (MAINLY THE GFS) SQUEEZES OUT SOME
SHOWERS--LIKELY UNDER AN INCOMING EML PLUME--AHEAD OF A COLD
FRONT TUESDAY AFTERNOON AND EVENING. FORECAST SOUNDINGS AT THIS
TIME LOOK TOO CAPPED FOR THUNDERSTORM DEVELOPMENT, ALTHOUGH VERY
STEEP LAPSE RATES ALOFT SUGGEST WE'LL NEED TO KEEP AN EYE ON
THIS. THEREAFTER, THERE'S A SIGNAL FOR A MORE ROBUST SYNOPTIC
WAVE AND ASSOCIATED COLD FRONT SWEEPING THROUGH THE UPPER
MIDWEST TOWARDS THE END OF THE WEEK, WHICH COULD BRING THE NEXT
THUNDERSTORM CHANCES TO THE AREA.
CARLAW
AVIATION /06Z TAFS THROUGH 12Z SUNDAY/
ISSUED AT 1227 AM CDT SAT APR 18 2026
FORECAST CONCERNS INCLUDE...
LOW MVFR, POSSIBLE IFR, CIGS OVERNIGHT INTO SATURDAY MORNING.
STRONG/GUSTY NORTHWEST WINDS SATURDAY.
SCATTERED SHOWERS OVERNIGHT.
SCATTERED SHOWERS WILL CONTINUE FOR A FEW MORE HOURS OVER THE
TERMINALS WITH SHOWERS EXTENDING THROUGH DAYBREAK JUST SOUTHEAST
OF THE TERMINALS. THERE IS A SMALL CHANCE FOR THUNDER OVER THE
NEXT HOUR OR SO, BUT ANY ADDITIONAL THUNDER POTENTIAL IS
EXPECTED TO REMAIN SOUTHEAST OF THE TERMINALS.
LOW MVFR CIGS AND PATCHY IFR CIGS HAVE DEVELOPED ACROSS
NORTHWEST IL AND SOUTHERN WI ALONG AND BEHIND AN APPROACHING
COLD FRONT. THESE LOWER CIGS ARE EXPECTED TO SPREAD EAST ACROSS
THE REST OF THE AREA OVERNIGHT. ONLY MEDIUM CONFIDENCE FOR CIG
TRENDS, BUT PREVAILING LOW MVFR CIGS LOOK ON TRACK FOR AT LEAST
A FEW HOURS. CIGS WILL LIKELY BE SLOWLY LIFTING INTO LOW VFR
AFTER DAYBREAK WITH CIGS POSSIBLY SCATTERING OUT DURING THE
AFTERNOON AND MOST LIKELY BY SATURDAY EVENING.
SOUTHWEST WINDS GUSTING INTO THE LOWER 20KT RANGE WILL SHIFT TO
THE WEST/NORTHWEST BEHIND THE COLD FRONT OVERNIGHT WITH GUSTS
INTO THE MID 20KT RANGE. GUSTS WILL INCREASE FURTHER, PERHAPS
INTO THE 30KT RANGE MID/LATE SATURDAY MORNING. SPEEDS AND GUSTS
WILL DIMINISH QUICKLY WITH SUNSET SATURDAY EVENING AND TURN TO
THE SOUTHWEST. CMS
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY UNTIL 10 PM CDT THIS EVENING FOR THE IL
AND IN NEARSHORE WATERS.
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