918
FXUS63 KIWX 151700
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
100 PM EDT THU OCT 15 2026
KEY MESSAGES
- SCATTERED RAIN POSSIBLE TODAY, MAINLY WEST OF I-69.
- THERE IS A MARGINAL RISK OF SEVERE STORMS (MAINLY WIND) ALONG
AND SOUTH OF US ROUTE 24 THIS EVENING. CONFIDENCE IN SEVERE
WEATHER IS LOW.
- TURNING MUCH COOLER AND WINDY FOR FRIDAY WITH SOME LAKE EFFECT
RAIN SHOWERS EXPECTED. WATCHING FOR FROST CHANCES, WHICH
APPEAR THE MOST POSSIBLE SUNDAY MORNING, BUT SATURDAY
MORNING'S CHANCES CANNOT BE RULED OUT.
DISCUSSION
ISSUED AT 245 AM EDT THU OCT 15 2026
SURFACE HIGH PRESSURE SLIDES EASTWARD THIS MORNING ACROSS THE
NORTHERN GREAT LAKES. THIS ALLOWED DRIER AIR TO SEEP INTO THE AREA
BEHIND THE SLOWLY SOUTHWARD-MOVING COLD FRONT FROM WEDNESDAY. THIS
FRONT QUICKLY TURNS AROUND INTO A NORTHWARD-MOVING WARM FRONT TODAY
AS A DEEP UPPER LOW FORCES A SURFACE LOW NORTHWARD ALONG THE WESTERN
EXTENSION OF THE BAROCLINIC ZONE DOWN TO THE SOUTHERN PLAINS. SO,
THE ATTENTION TURNS TO THE TIMING OF THE SURFACE WARM SECTOR'S
ARRIVAL TO SEE IF WE CAN GET SURFACE-BASED OR ONLY ELEVATED
CONVECTION. THE GFS STILL HAS AREAS OF LARGE SCALE ASCENT MOVING
THROUGH THE AREA THIS AFTERNOON WHEREAS THE ECMWF APPEARS TO HAVE
MOST OF THE BETTER LIFT MOVING NORTH OF THE AREA. THE DRIER THE LOW
LEVELS CAN GET AND MAYBE LESSER CLOUD COVER BEFORE SUNRISE WOULD BE
BETTER FOR INSTABILITY FORMATION. INDICATIONS IN BOTH THE NAM AND
THE HRRR ARE THAT THE SURFACE WARM FRONT WAITS UNTIL 2 TO 4Z TO GET
INTO OUR SOUTHERN 1 TO 2 ROWS OF ZONES, WHICH WOULD ALLOW A SHORT
TIME PERIOD (1 TO 3 HOURS?) FOR SURFACE-BASED CONVECTION AFTER THAT.
THE MAIN INGREDIENT OF CONCERN IS THE SHEAR, WHICH THE HRRR
INDICATES HAS AROUND 45 KTS OF EBWD SHEAR. NOW, BECAUSE THE LOW
LEVELS UP TO 850 MB ARE ESSENTIALLY SATURATED, LCLS ARE SUB-1000M,
BUT INSTABILITY IS 500 J/KG OR BELOW. SO, PERHAPS THERE COULD BE
SOME SHALLOW SUPERCELLS OR CELLS WITH EMBEDDED ROTATION. WITH THE
MOIST PWATS AROUND 1.8 INCHES, HEAVY RAIN RATES COULD OCCUR, BUT
CELL MOTIONS ARE RATHER FAST LIKELY LIMITING OVERALL FLOOD THREAT;
THAT AND THE FACT THAT WE'VE BEEN DRY FOR SO LONG. THE OTHER
POSSIBILITY WOULD BE A MOISTURE LOADED CORE- COLLAPSING DAMAGING
WIND THREAT, BUT THAT WEAK OF INSTABILITY MAY ALSO LIMIT THAT
THREAT. THE COLD FRONT SLIDES THROUGH OVERNIGHT MEANING THE RAIN
THREAT IS OUT OF THE AREA BY 12Z FRIDAY.
THE AFOREMENTIONED UPPER LOW IS SQUEEZED NORTHEASTWARD OUT AHEAD OF
A DIVING UPPER LOW FROM CANADA. ON IT'S BACK SIDE IS A STRONG 1040
MB SURFACE HIGH INDICATIVE OF RELATIVELY COLD AIR THAT ITS BRINGING
WITH IT. THIS BRINGS IN A COUPLE OF HAZARDS THAT WE'LL GET TO
DESCRIBING HERE INCLUDING LAKE EFFECT RAIN, GUSTY WINDS, AND
POTENTIALLY A FROST CHANCE. FOR THE LAKE EFFECT RAIN, THE LAKE NEEDS
TO GET SOME INSTABILITY GOING FIRST AS WELL AS LOW LEVEL CONVERGENCE
AND A RETURN OF LOW LEVEL MOISTURE BEHIND THE COLD FRONT. NORTHWEST
WIND CONVERGENCE COMBINES WITH THESE FEATURES AROUND 12Z FRIDAY AND
WOULD EXPECT THE INTENSITY OF LAKE ENHANCEMENT TO INCREASE THROUGH
AROUND 18Z WHEN THE VIGOROUS VORT MAX SWINGS THROUGH. GIVEN LAKE
TEMPS OF 62 DEGREES, BUFKIT NAM SOUNDINGS INDICATE 15 TO 25 DEGREE
DELTA T VALUES WITH TALL LAKE INDUCED INVERSIONS DURING THE
AFTERNOON. HOWEVER, THERE ARE INDICATIONS THAT DRY AIR BEGINS TO
WORK INTO THE LOW LEVELS DURING THE EVENING HOURS AFTER THE LOW
LEVEL TROUGH MOVES THROUGH AND TRAJECTORIES GO MORE NORTHERLY. LOW
LEVEL MOISTURE MOVES OUT OF THE AREA AND THERE ARE INDICATIONS THAT
RAIN SUBSIDES BY 12Z SATURDAY, BUT COULD SEE LAKE EFFECT CLOUDS
LINGERING SATURDAY MORNING, ESPECIALLY IN THE WEST. THEN, NORTHWEST
WINDS SWINGING THROUGH FRIDAY EVENING GUST BETWEEN 30 AND 40 MPH,
HIGHEST ALONG THE SURFACE TROUGH, WHICH COULD BRING DOWN A STRAY 45
MPH GUST. NOW, THE COLD AIR COMING IN FRIDAY NIGHT HAS 850 MB TEMPS
DOWN TO -2C 12Z SATURDAY MORNING BEFORE WARMING ENSUES. THE PRESSURE
GRADIENT SLACKENS OVERNIGHT INTO EARLY SATURDAY MORNING AND CLOUD
COVER ALSO DISSIPATES OVERNIGHT BRINGING SOME QUESTIONS ABOUT HOW
SCATTERED OUT CLOUDS CAN BE EAST OF US-31. GIVEN FORECAST LOWS
SECURELY IN THE 30S FRIDAY NIGHT, WE'LL HAVE TO WATCH FOR FROST
CHANCES THEN, BUT WIND AND CLOUD COVER COMPLICATE CHANCES. A DRY DAY
CONTINUES ON SATURDAY AND SURFACE HIGH PRESSURE OVERHEAD CONTINUES
TO KEEP THE AREA CALM WIND-WISE. WHICH ALLOWS A SECOND OPPORTUNITY
FOR FROST SATURDAY NIGHT AS THE CORE OF THE COLD AIR LIFTS
NORTHEASTWARD. FORECAST LOWS DIP DOWN INTO THE 30S AGAIN, BUT AN
INCREASED GRADIENT ATTEMPTS TO ENTER FROM THE NORTH. THIS APPEARS TO
BE THE ONLY COMPLICATION FOR ANOTHER FROST ATTEMPT SATURDAY NIGHT.
LOOKING AHEAD, EVEN OVER THE NEXT 2 TO 3 DAYS, ANOMALOUS HIGH
PRESSURE BUILDING NEAR GREENLAND CAUSING BLOCKING TO BUILD PEAKS
DURING THE 16TH TO 21ST OF OCTOBER. THIS IS ABOUT THE TIME THAT THE
NAO/AO DIPS NEGATIVE. MEANWHILE, THE AFOREMENTIONED BAROCLINIC ZONE
HAS PUSHED EASTWARD POTENTIALLY STALLING ALONG THE EASTERN SEABOARD
AND FORMING AN UPPER LOW OR CONTINUING TO PUSH EASTWARD. EITHER WAY,
THIS ALLOWS A SPRAWLING AREA OF HIGH PRESSURE TO REMAIN ACROSS THE
AREA UNTIL AT LEAST AROUND THURSDAY OF NEXT WEEK AND POTENTIALLY
EVEN LONGER KEEPING DRY AIR OVERHEAD.
AVIATION /18Z TAFS THROUGH 18Z FRIDAY/
ISSUED AT 1259 PM EDT THU OCT 15 2026
LOW PRESSURE OVER FAR NORTHERN MO THIS AFTERNOON SLOWLY LIFTS
NORTHEAST THROUGH THE TAF PERIOD. DISORGANIZED AREA OF SHOWERS
AHEAD OF A WARM FRONT IS SLOWLY APPROACHING FROM THE SW. THE
INHERITED PROB30 -TSRA REMAINS ON TRACK. QUESTIONABLE
INSTABILITY LIMITS CONFIDENCE IN THUNDER AT BOTH KSBN AND KFWA.
A PERIOD OF IFR TO EVEN LIFR CEILINGS ARE FAVORED AT KSBN AS THE
LOW'S CENTROID MOVES NEAR THE TERMINAL. WIND VEERS AND QUICKLY
INCREASES IN SPEED DURING THE OVERNIGHT. LAKE EFFECT RAIN
SHOWERS OCCUR JUST BEYOND THIS TAF PERIOD.
IWX WATCHES/WARNINGS/ADVISORIES
IN...NONE.
OH...NONE.
MI...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 11 PM THIS EVENING TO 11 AM EDT
FRIDAY FOR LMZ043-046.
GALE WARNING FROM 11 AM FRIDAY TO 2 AM EDT SATURDAY FOR LMZ043-
046.
DISCUSSION...ROLLER
AVIATION...BROWN
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