810
FXUS63 KLOT 111918
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL
218 PM CDT SUN MAY 11 2025
KEY MESSAGES
- SUMMER-LIKE WARMTH WILL PREVAIL THROUGH THE MIDDLE OF THE
WEEK, THOUGH LOCATIONS NEAR LAKE MICHIGAN WILL REMAIN COOLER
ON MOST DAYS. NEAR-RECORD TEMPERATURES ARE EXPECTED ON
THURSDAY.
- ISOLATED TO SCATTERED SHOWERS AND STORMS ARE EXPECTED MONDAY
THROUGH THURSDAY, THOUGH MANY HOURS AND AREAS WILL REMAIN DRY.
- THERE IS A THREAT FOR SEVERE WEATHER THURSDAY AFTERNOON AND
EVENING, CONTINGENT ON THUNDERSTORMS DEVELOPING.
DISCUSSION
ISSUED AT 218 PM CDT SUN MAY 11 2025
THROUGH MONDAY NIGHT:
PER RECENT GOES-19 WATER VAPOR IMAGERY AND RAP-ANALYZED SURFACE
FIELDS, A SURFACE HIGH PRESSURE SYSTEM IS PARKED OVER THE GREAT LAKES
REGION BETWEEN A SPRAWLING UPPER-LEVEL LOW ALONG THE GULF COAST AND
AN UPPER-LEVEL RIDGE ARCING ALONG THE US/CANADIAN BORDER. SUNNY
SKIES, LIGHT WINDS, LOW HUMIDITY VALUES, AND TEMPERATURES WARMING
INTO THE 70S ARE THUS MAKING FOR A BEAUTIFUL DAY. WITH NOT MUCH
EXPECTED TO CHANGE IN THE SURFACE- TO UPPER-LEVEL PATTERN IN THE
NEXT 12 HOURS, TONIGHT WILL BE SIMILARLY TRANQUIL WITH LIGHT WINDS,
MOSTLY CLEAR SKIES, LOW HUMIDITY VALUES, AND OVERNIGHT LOWS IN THE
UPPER 40S TO LOWER 50S.
TOMORROW, A PACIFIC TROUGH DIVING ALONG THE WESTERN US COAST WILL
ENCOURAGE THE GULF COAST LOW PRESSURE SYSTEM TO LIFT EAST-
NORTHEASTWARD TOWARD THE OHIO RIVER VALLEY. WITH FORECAST SOUNDINGS
DEPICTING APPRECIABLE DEPTH TO THE RESIDUAL DRY LOW-LEVEL AIRMASS IN
THE GREAT LAKES, IT WILL TAKE TIME FOR MOISTURE ADVECTION VIA WEAK
EAST TO SOUTHEASTERLY FLOW TO AFFORD GRADUALLY INCREASING CLOUDS
FROM LATE MORNING TO EARLY AFTERNOON. ACCORDINGLY, DO THINK
AGGRESSIVE DIURNAL HEATING WILL AFFORD HIGHS IN THE THE UPPER
70S TO LOWER 80S, SAVE FOR COOLER READINGS EAST OF I-294 IN THE
SHADOW OF LAKE MICHIGAN. MOST GUIDANCE DOES ADVERTISE A "SLUG"
OF PWATS >1" PUSHING INTO THE LOWER GREAT LAKES BY TOMORROW
EVENING, WHICH SHOULD BE ACCOMPANIED BY ISOLATED TO SCATTERED
SHOWERS AND STORMS. FOR NOW, 20 TO 30% POPS REMAINS APPROPRIATE
FOR THE AFTERNOON AND EVENING HOURS (IN OTHER WORDS, MANY AREAS
WILL STAY DRY).
BORCHARDT
TUESDAY THROUGH SUNDAY:
GENERALLY SPEAKING, TUESDAY'S WEATHER SHOULD BE FAIRLY SIMILAR
TO MONDAY'S. HOWEVER, WITH THE UPPER LOW ALLUDED TO IN THE SHORT
TERM PORTION OF THE DISCUSSION NOW HAVING A GREATER PRESENCE IN
OUR AREA AND WITH THE ASSOCIATED HUMID GULF AIR MASS LIKELY TO
HAVE FULLY ENVELOPED NORTHERN ILLINOIS AND NORTHWEST INDIANA
PRIOR TO TUESDAY AFTERNOON, PRETTY MUCH ANYWHERE IN OUR FORECAST
AREA WILL BE FAIR GAME FOR DIURNAL CONVECTION TO SPROUT THIS
TIME AROUND. THE GRADUALLY WEAKENING NATURE OF THE UPPER LOW
PAIRED WITH SUBPAR LAPSE RATES ACROSS THE HEIGHT OF THE
TROPOSPHERE DOES LEAD TO SOME QUESTIONS REGARDING WHAT THE EXACT
COVERAGE OF CONVECTION WILL BE ON TUESDAY, BUT THE MORE ABUNDANT
UPPER-LEVEL FORCING DOES SEEM TO POINT TOWARDS A GREATER
COVERAGE OF SHOWERS AND STORMS ON TUESDAY COMPARED TO MONDAY
WITH AT LEAST WIDELY SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS
LOOKING LIKE A GOOD BET BASED ON THE LATEST FORECAST GUIDANCE.
NEGLIGIBLE DEEP LAYER SHEAR WILL CAUSE CONVECTION TO BE SLOW-
MOVING AND PULSE-LIKE ONCE AGAIN, LEADING TO LIGHTNING,
DOWNPOURS, AND GUSTY WINDS BEING THE MAIN THREATS WITH THE MOST
ROBUST CONVECTION. THE ENHANCED AMBIENT VORTICITY ASSOCIATED
WITH THE UPPER LOW AND OUTFLOW BOUNDARIES AT THE SURFACE COULD
OPEN THE DOOR FOR SOME FUNNEL CLOUD FUNNY BUSINESS, AS WELL.
BY WEDNESDAY, THE UPPER LOW IS EXPECTED TO HAVE DEFORMED QUITE
A BIT AND DRIFTED EASTWARD SLIGHTLY IN RESPONSE TO THE CONTINUED
EASTWARD PROGRESSION OF THE DEEP WESTERN CONUS TROUGH.
ACCORDINGLY, THE COVERAGE OF THE NEXT ROUND OF DIURNAL
CONVECTION IN OUR FORECAST AREA ON WEDNESDAY APPEARS THAT IT
WILL BE LOWER COMPARED TO TUESDAY AND STILL SEEMS TO BE BEST
HANDLED BY AREA-WIDE SLIGHT CHANCE AND LOWER-END CHANCE POPS (UP
TO 40%) AT THIS TIME. THE LESSER DEGREE OF CONVECTIVE COVERAGE
SHOULD MEAN THAT MORE SUNSHINE SHOULD BE SEEN, AND THAT SHOULD
TRANSLATE TO MORE WIDESPREAD LOW-MID 80 DEGREE READINGS BEING
OBSERVED ACROSS LOCATIONS WELL INLAND AWAY FROM LAKE MICHIGAN'S
INFLUENCE. THE SUMMER-LIKE WARMTH AND HUMIDITY WILL THEN
CONTINUE INTO THURSDAY, WITH TEMPERATURES EVEN WARMER THAN
WEDNESDAY'S EXPECTED DUE TO THE CONTINUED SOLAR INSOLATION AND
INCREASING WARM AIR ADVECTION. IN FACT, IT'S QUITE POSSIBLE
THAT WE COULD SEE OUR FIRST 90 DEGREE READINGS OF THE YEAR IN
OUR FORECAST AREA ON THURSDAY. IF THAT WERE TO OCCUR, THEN THE
DAILY HIGH TEMPERATURES FOR MAY 15TH IN CHICAGO AND ROCKFORD (91
AND 90, RESPECTIVELY) WOULD POTENTIALLY BE IN JEOPARDY. FOR
ONCE, THESE WARMER TEMPERATURES MAY REACH AT LEAST SOME OF OUR
LAKESIDE LOCALES AS WINDS ON THURSDAY SHOULD BE BREEZY AND FROM
THE SOUTH.
LATE WEDNESDAY INTO THURSDAY, THE WESTERN CONUS TROUGH IS
EXPECTED TO EJECT INTO THE NORTHERN PLAINS AND UPPER MIDWEST.
THE LOW PRESSURE SYSTEM THAT DEVELOPS IN RESPONSE WILL HELP
ADVECT A MORE PRONOUNCED EML INTO THE MIDWEST AND WILL ALSO
CAUSE KINEMATIC FIELDS ACROSS THE REGION TO STRENGTHEN. THIS
WILL AUGMENT THE PRE-EXISTING WARMTH AND MOISTURE TO FOSTER A
POTENTIAL THREAT FOR SEVERE WEATHER ACROSS THE REGION LATE
THURSDAY INTO EARLY FRIDAY. IT IS THUS NOT SURPRISING THAT AI,
MACHINE LEARNING, AND ANALOG GUIDANCE ALL CONTINUES TO HIGHLIGHT
OUR FORECAST AREA AS BEING UNDER THE GUN FOR POTENTIAL SEVERE
WEATHER DURING THIS TIME. HOWEVER, THIS GUIDANCE ISN'T ALWAYS
PARTICULARLY SKILLFUL IN IDENTIFYING AND ACCOUNTING FOR
POTENTIAL FAILURE MODES SUCH AS CAPPING, SUB-OPTIMAL FORCING,
ETC., AND IT CONTINUES TO LOOK LIKE WE'LL AT LEAST HAVE SOME
DEGREE OF CAPPING AT THE BASE OF THE EML TO CONTEND WITH ON
THURSDAY. THUS, WHILE CONFIDENCE IS RELATIVELY HIGH AT THIS
POINT IN TIME THAT THE PARAMETER SPACE THAT WILL BE IN PLACE
OVER THE REGION LATE THURSDAY WILL LARGELY BE FAVORABLE FOR
SEVERE THUNDERSTORMS, CONFIDENCE IS STILL FAIRLY LOW IN WHETHER
EVERYTHING WILL COME TOGETHER JUST RIGHT FOR THIS PARAMETER
SPACE TO BE FULLY UTILIZED, OR WHETHER WE'LL EVEN SEE STORMS AT
ALL. IT WILL STILL LIKELY BE A FEW MORE DAYS BEFORE WE'LL BE
ABLE TO MORE CLOSELY ASSESS THE FINER SCALE DETAILS OF THIS
SEVERE WEATHER POTENTIAL, SO STAY TUNED FOR ADDITIONAL UPDATES.
OUR WEATHER FOR FRIDAY WILL LARGELY DEPEND ON HOW THINGS PLAY
OUT ON THURSDAY WITH THE LOW PRESSURE SYSTEM'S EVOLUTION. A
STRONG COLD FRONTAL PASSAGE THURSDAY NIGHT/FRIDAY MORNING WOULD
TEND TO FAVOR DRY AND BREEZY CONDITIONS ACROSS THE AREA ON
FRIDAY. ON THE OTHER HAND THOUGH, THE NEARBY PRESENCE OF THE
AFOREMENTIONED UPPER-LEVEL TROUGH COULD STILL SUPPORT SHOWER AND
THUNDERSTORMS CHANCES HERE IF THE COLD FRONT ARRIVES TOO EARLY
OR TOO LATE AND/OR ISN'T ROBUST ENOUGH TO SUFFICIENTLY SCOUR OUT
THE WARMTH AND MOISTURE IN THE AREA. WHILE THERE MAY BE A
REPRIEVE FROM THE WARMER AND STORMIER CONDITIONS THIS COMING
WEEKEND, THE OVERALL WEATHER PATTERN ACROSS THE CENTRAL CONUS
IS EXPECTED TO REMAIN FAIRLY ACTIVE INTO NEXT WEEK. THIS COULD
RESULT IN ADDITIONAL CHANCES FOR SHOWERS AND THUNDERSTORMS IN
OUR AREA DURING THE UPCOMING WORK WEEK.
OGOREK
AVIATION /18Z TAFS THROUGH 00Z TUESDAY/
ISSUED AT 1204 PM CDT SUN MAY 11 2025
THERE ARE NO AVIATION CONCERNS THROUGH THE TAF PERIOD. EASTERLY
WINDS WILL PREVAIL WITH SPEEDS AT OR BELOW 10KT. LOW-END VFR
CIGS MAY DEVELOP TOWARD THE END OF THE 30-HOUR TAF WINDOW AT
ORD/MDW AS LOW-LEVEL MOISTURE INCREASES, THOUGH WILL WITHHOLD
MENTION FOR NOW.
BORCHARDT
LOT WATCHES/WARNINGS/ADVISORIES
IL...NONE.
IN...NONE.
LM...NONE.
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