984
FXUS63 KLOT 122352
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
652 PM CDT MON MAY 12 2025
KEY MESSAGES
- SUMMER-LIKE WARMTH AWAY FROM THE LAKE EXPECTED THROUGH
MIDWEEK. THERE IS A CHANCE FOR NEAR-RECORD TEMPERATURES ON
THURSDAY.
- CHANCE FOR SHOWERS AND STORMS THROUGH TUESDAY EVENING, THOUGH
MANY HOURS AND AREAS WILL REMAIN DRY.
- THERE IS A THREAT FOR SEVERE WEATHER THURSDAY AFTERNOON AND
EVENING, CONTINGENT ON STORMS DEVELOPING.
DISCUSSION
ISSUED AT 237 PM CDT MON MAY 12 2025
THROUGH TUESDAY NIGHT:
WATER VAPOR SATELLITE IMAGERY IS SHOWING THE UPPER LEVEL LOW IN
THE LOWER MISSISSIPPI VALLEY SLOWLY LIFTING NORTHWARD AND
WARPING LONGITUDINALLY. IT IS PROJECTED TO CONTINUE TO TRACK
NORTHEASTWARD ALONG A MEMPHIS TO INDIANAPOLIS LINE. THIS TRACK
WILL KEEP THE BETTER FORCING AND INSTABILITY WELL EAST OF THE
FORECAST AREA. THAT BEING SAID, MODELS ARE SUGGESTING A LOBE OF
HIGHER VORTICITY TO PIVOT AROUND THE LOW THIS EVENING AND
THROUGH THE OVERNIGHT WITH A SLUG OF HIGHER MOISTURE CONTENT.
HOWEVER, GUIDANCE IS ALL OVER THE PLACE ON WHETHER THE SHOWERS
WILL BE FOCUSED MORE AROUND INTERSTATE 39 AND FOX VALLEY
CORRIDOR, WHILE OTHERS BRING IT INTO THE CHICAGO METRO. WHILE
THE EXPECTATION IS FOR THE MOISTURE TO MOVE FROM SOUTHEAST TO
NORTHWEST (ALONG THE CYCLONIC TRACK), THERE IS LOWER CONFIDENCE
ON EXACT COVERAGE OF SHOWERS. ADDITIONALLY LAPSE RATES ALOFT ARE
FAIRLY MARGINAL AROUND ONLY 6C/KM, SO THE RISK FOR THUNDER
DEVELOPING WAS CAPPED AT A SLIGHT CHANCE
SHOWER COVERAGE OVERNIGHT WILL BE MONITORED, BUT WITH CLOUD
COVER BUILDING IN TEMPERATURES SHOULD ONLY COOL INTO THE LOW TO
MID 60S. MODEL SOUNDINGS ARE PROJECTING A STOUT INVERSION OVER
THE AREA. WINDS WILL DIMINISH, BUT REMAIN AROUND 5 TO 10 MPH.
COMBINE THAT WITH THE WARMER TEMPERATURES, AND THE CHANCE FOR
FOG ON LAND IS LOW. HOWEVER, WITH THE COOLER LAKE, THE
TEMPERATURE DIFFERENCE COULD BE ENOUGH TO HAVE SOME PATCHY FOG
OVER THE WATER AND POTENTIALLY ALONG THE IMMEDIATE SHORELINE.
THE UPPER LEVEL LOW CONTINUES ITS MOLASSES SPEED JOURNEY
NORTHEASTWARD ON TUESDAY. BEING ON THE BACKSIDE OF THE LOW, FLOW
ALOFT WILL BECOME WEAKER. THE BETTER COVERAGE FOR SHOWERS
TOMORROW WILL BE DURING THE DAY TIME HOURS AROUND THE I-39
CORRIDOR AND DOWN SOUTH OF INTERSTATE 80 LATER IN THE DAY, AS A
LOBE OF VORTICITY ROTATES AROUND THE LOW. WHILE THERE IS A
CHANCE FOR SHOWERS AND STORMS, THERE WILL BE MANY HOURS AND
AREAS THAT WILL REMAIN DRY. AGAIN, INSTABILITY DOES NOT LOOK
FANTASTIC TOMORROW, BUT AS THESE SHOWERS AND STORMS PULSE, SOME
LIGHTNING, BRIEF DOWNPOURS AND LOCALLY ERRATIC WINDS (AS A STORM
WOULD COLLAPSE) CANNOT BE COMPLETELY RULED OUT. CHANCES FOR
SHOWERS AND STORMS DIMINISH INTO TUESDAY NIGHT. LASTLY, THE
FORECAST TEMPERED HIGH TEMPERATURES TOMORROW. THERE IS A CHANCE
THAT LOCALIZED WESTERN PARTS WILL TOUCH 80, BUT WITH THE
INCREASING CLOUD COVER, THE EXPECTATION IS FOR MORE WIDESPREAD
70S ACROSS MUCH OF THE FORECAST AREA (60S ALONG THE LAKE
SHORELINE).
DK
WEDNESDAY THROUGH MONDAY:
THE FORECAST IN THE LONG TERM PICKS UP ON WEDNESDAY WHEN MILD
SOUTHERLY LOW LEVEL FLOW WILL OVERSPREAD THE REGION AHEAD OF
DEVELOPING PLAINS STORM SYSTEM. THIS SHOULD ALLOW FOR AFTERNOON
TEMPERATURES TO REACH THE LOWER 80S AROUND MOST OF THE AREA. A
BIT OF AN ONSHORE COMPONENT TO THE WIND WILL KEEP CONDITIONS
NOTABLY COOLER NEAR THE IL LAKESHORE. WHILE FORECAST SOUNDINGS
ARE RATHER DRY, A FEW ISOLATED DIURNALLY-DRIVEN SHOWERS COULD
POP UP IN THE AFTERNOON, BUT A MAJORITY OF THE CWA WILL BE
STAYING DRY. EFFICIENT WARM ADVECTION WILL CONTINUE INTO
THURSDAY AHEAD OF THE SYSTEM AND AFTERNOON HIGHS ARE FORECAST
AROUND 90 DEGREES AREA-WIDE. CONDITIONS WILL AGAIN BE A FEW TO
SEVERAL DEGREES COOLER NEAR THE LAKE, ESPECIALLY ALONG THE IL
NORTHSHORE.
THE BIG FOCUS IN THIS FORECAST PACKAGE IS A POTENTIAL FOR
SEVERE WEATHER ON THURSDAY ASSOCIATED WITH THAT PLAINS SYSTEM.
DURING THE DAY ON THURSDAY, A DIGGING UPPER TROUGH WILL EJECT
FROM THE CENTRAL PLAINS UP INTO MN AND AN ASSOCIATED
STRENGTHENING SURFACE LOW WILL FOLLOW SUIT. EXTENDING SOUTHEAST
OF THE LOW TRACK WILL BE A HEAVILY OCCLUDED COLD FRONT THAT WILL
BE MOVING ACROSS OUR AREA DURING THE AFTERNOON AND EVENING.
IT'S ALONG AND JUST OUT AHEAD OF THIS FRONT THAT WE SEE THE
POSSIBILITY OF SEVERE WEATHER, BUT IT'LL BE VERY SENSITIVE
ENVIRONMENT WITH A CLEAR BUST POTENTIAL. AN IMPRESSIVE
THERMODYNAMIC FIELD WILL OVERSPREAD THE REGION AHEAD OF THE
BOUNDARY WITH MODELS RESOLVING ANYWHERE FROM 2,500 TO 3,500
JOULES OF MLCAPE ATOP OUR CWA DURING THE AFTERNOON AND EARLY
EVENING. SURFACE HIGHS AROUND 90 BENEATH COLD ADVECTION ALOFT
WILL PROVIDE STEEP LAPSE RATES ON THE ORDER OF 8-9 K/KM THROUGH
THE MID LEVELS AND NEAR DRY-ADIABATIC THROUGH THE BOUNDARY
LAYER. SHEAR PROFILES ARE ALSO MORE THAN SUFFICIENT TO SUPPORT
ORGANIZED, SEVERE CONVECTION. HOWEVER, A CAPPING INVERSION, ONLY
MODEST FORCING, AND TONS OF DRY AIR ALL PUT A DAMPER ON THIS
POTENTIAL. THERE ARE DISAGREEMENTS IN HOW MUCH CIN IS MAINTAINED
AHEAD OF THE FRONT, BUT ANYTHING APPRECIABLE MAY BE DIFFICULT
TO OVERCOME IN THIS SETUP. QUICK SURFACE PRESSURE FALLS WILL
GENERATE MODEST DYNAMIC FORCING IN THE LOW LEVELS WHICH MAY HELP
CHIP AWAY AT THE CAP, BUT THE FAR BETTER DEEP LAYER FORCING
WILL BE DISPLACED TO THE NORTH AND WEST NEARER TO THE LOW TRACK.
CONVERGENCE AND FORCING FOR ASCENT ALONG THE FRONT ITSELF
APPEAR PRETTY MEAGER AS WELL. CIN SHOULD GENERALLY LESSEN
THROUGH THE DAYTIME WITH DIURNAL HEATING, SO IT'S POSSIBLE THAT
STORMS MAY HAVE AN EASIER TIME GOING UP WITH EASTWARD EXTENT
ACROSS OUR CWA. THIS WILL BE ESPECIALLY TRUE IF THE EARLIER
SOLUTIONS (NAMELY GFS) CAN VERIFY. FINALLY, POSSIBLY THE BIGGEST
WRENCH IN THIS POTENTIAL IS THE COPIOUS AMOUNTS OF DRY AIR.
FORECAST SOUNDINGS EXHIBIT A TYPICAL "INVERTED-V" BOUNDARY LAYER
AND IT'S POSSIBLE THAT JUST ENOUGH MOISTURE WILL GATHER BENEATH
THE INVERSION TO SATURATE AND REALIZE THE EXPLOSIVE
INSTABILITY. DEEP MIXING THROUGH A DRY BOUNDARY LAYER WILL MAKE
THIS DIFFICULT THOUGH. GUIDANCE IS STRUGGLING WITH THIS
POTENTIAL BASED OFF OF SPLOTCHY AND INCONSISTENT POP AND QPF
OUTPUT. IF STORMS DEVELOP, ALL HAZARDS WILL BE ON THE TABLE BUT
THE BIGGEST CONCERN LOOKS TO BE DAMAGING WIND GUSTS AS THE STEEP
LAPSE RATES AMID SUCH DRY AIR SHOULD BE VERY SUPPORTIVE OF
STRONG CONVECTIVE DOWNDRAFTS. THE SEEMINGLY BEST CHANCE AT
SEEING STORMS ON THURSDAY IS ACROSS OUR NORTH WHERE SLIGHTLY
BETTER MOISTURE AND FORCING WILL BE FOUND, BUT IT'S POSSIBLE THE
WHOLE AREA STAYS QUIET. MORE DETAILS WILL COME INTO FOCUS OVER
THE NEXT COUPLE OF DAYS AS MORE GUIDANCE BECOMES AVAILABLE.
THE UPPER LOW WILL TRACK ACROSS FAR NORTHERN WI ON FRIDAY AND
AN ENHANCED LOW LEVEL WIND FIELD ON THE SOUTHERN FLANK OF THE
LOW WILL EXTEND OVER OUR AREA. DEEP AND VERY EFFICIENT BOUNDARY
LAYER MIXING SHOULD LEAD TO GUSTY, IF NOT OUTRIGHT STRONG WINDS
OUT OF THE SOUTHWEST DURING THE DAY. AND WITH VERY DRY LOW LEVEL
AIR, THERE ARE QUICKLY-GROWING CONCERNS REGARDING FIRE WEATHER
ON FRIDAY, POSSIBLY A CONSIDERABLE THREAT. THIS MORNING'S 12Z
EURO, FOR INSTANCE, RESOLVES 40 TO 50 MPH GUSTS DURING THE DAY
WHILE MIXING SURFACE RHS DOWN TO 15 TO 20%. IF SOMETHING LIKE
THIS WERE TO VERIFY, WE'D BE TALKING ABOUT EXTREME FIRE WEATHER
CONCERNS FOR FRIDAY. FOLLOWING THURSDAY, TEMPERATURES SHOULD BE
ON A GENERAL COOLING TREND THROUGH THE WEEKEND BUT WILL REMAIN
WARM. THE UPPER LOW STILL HANGING OUT TO OUR NORTH WILL ALLOW
FOR CONTINUED WARM ADVECTION ALOFT AND WE SHOULD LARGELY SEE
LOWER 80S ON FRIDAY WITH HIGHS IN THE 70S FORECAST THROUGH THE
WEEKEND.
DOOM
AVIATION /00Z TAFS THROUGH 06Z TUESDAY/
ISSUED AT 652 PM CDT MON MAY 12 2025
FORECAST CONCERNS INCLUDE...
CHANCE OF SHOWERS, POSSIBLY A THUNDERSTORM TONIGHT.
CHANCE OF SHOWERS, POSSIBLY A THUNDERSTORM TUESDAY AFTERNOON.
IFR/LOW MVFR CIGS OVERNIGHT/TUESDAY MORNING.
POSSIBLE IFR CIGS/VIS TUESDAY EVENING.
SCATTERED SHOWERS AND THUNDERSTORMS CURRENTLY OVER EAST CENTRAL
IL ARE EXPECTED TO MOVE NORTHWEST, BUT REMAIN SOUTH OF THE
TERMINALS THIS EVENING. ADDITIONAL SHOWERS ARE POSSIBLE
OVERNIGHT FOR THE TERMINALS BUT CONFIDENCE IS LOW. WHILE MANY
AREAS WILL REMAIN DRY, MAINTAINED PROB MENTION FOR NOW.
SCATTERED SHOWERS AND A FEW THUNDERSTORMS ARE AGAIN POSSIBLE
TUESDAY AFTERNOON INTO TUESDAY EVENING, WITH THE BEST CHANCES
SOUTHWEST OF THE CHICAGO TERMINALS AND KEPT THE TAFS DRY FOR
THIS TIME PERIOD FOR NOW.
GUIDANCE IS IN FAIR AGREEMENT WITH CIGS LOWERING TO LOW MVFR OR
IFR OVERNIGHT AND THEN QUICKLY LIFTING THROUGH MVFR TUESDAY
MORNING. PREVIOUS FORECAST HAD THESE TRENDS HANDLED WELL. ONLY
CONCERN IS FOR THE POTENTIAL FOR LIFR CIGS AND CONFIDENCE IS
LOW.
FOG IS EXPECTED TO DEVELOP OVER LAKE MICHIGAN TONIGHT INTO
TUESDAY MORNING. SOME OF THIS FOG AND ASSOCIATED LOWER CIGS MAY
DRIFT INLAND A SHORT DISTANCE ON TUESDAY BUT AFTER SUNSET
TUESDAY EVENING, MODELS STEADILY SPREAD THIS INLAND. HAVE CIGS
LOWERING FOR THE NEW 30HR ORD/MDW TAF. LOWER CONDITIONS ARE
POSSIBLE AND TRENDS WILL NEED TO BE MONITORED.
EAST/SOUTHEAST WINDS ARE EXPECTED THROUGH THE PERIOD. CMS
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
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