743
FXUS63 KIWX 151819
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
219 PM EDT THU MAY 15 2025
KEY MESSAGES
- STRONG TO SEVERE STORMS ARE LIKELY THIS EVENING INTO THE EARLY
OVERNIGHT (8 PM THROUGH 2 AM EDT). ALL HAZARDS POSSIBLE.
- ANOTHER ROUND OF SHOWERS AND STORMS IS EXPECTED LATE FRIDAY
AFTERNOON INTO FRIDAY EVENING. A FEW STORMS COULD BECOME
SEVERE.
- WARM TEMPERATURES THROUGH FRIDAY WILL GIVE WAY TO COOLER AND
DRIER CONDITIONS THIS WEEKEND.
DISCUSSION
ISSUED AT 218 PM EDT THU MAY 15 2025
HIGH END SEVERE THREAT (ALL HAZARDS) REMAINS IN PLAY THIS EVENING
INTO THE EARLY OVERNIGHT (8P-2A EDT) AS ANY CONVECTION ALONG AN
INCOMING DRYLINE WILL HAVE 35-40 KNOTS OF DEEP LAYER SHEAR AND 2000-
3000 J/KG OF MLCAPE TO WORK WITH. THE LOW LEVEL JET ALSO INCREASES
THIS EVENING WITH 0-3 KM STORM-RELATED HELICITY PUSHING 250-300
M2/S2 FOR A TORNADO THREAT. THERE WILL ALSO BE SUFFICIENT CAPE IN
THE HAIL GROWTH ZONE/EML WITH SUPERCELLS FOR LARGE HAIL, WITH ANY
ORGANIZATION INTO SEGMENTS SUPPORTING A WIND DAMAGE THREAT MID-LATE
EVENING.
EXPECTATIONS ARE STILL FOR CONVECTIVE INITIATION (SCATTERED DISCRETE
SUPERCELLS) IN NE IL BETWEEN 21-00Z, LIKELY CONGEALING INTO
QUASI-LINEAR SEGMENTS OR CLUSTERS WITH EASTWARD PROGRESSION
INTO THE LOCAL AREA THEREAFTER. CAPPING AT THE BASE OF AN EML,
AND MORE FAVORABLE DEEP ASCENT AND LOW LEVEL CONVERGENCE LIFTING
THROUGH WI AND MI, BRINGS INTO QUESTION STORM EVOLUTION/CHANCES
FOR AREAS SOUTH OF THE US 30 CORRIDOR. MUCH HIGHER CONFIDENCE
IN STRONG TO SEVERE STORMS BREAKING THROUGH THE CAP AND TRACKING
EAST THROUGH NORTHERN ZONES AS WEAK HEIGHT FALLS/COOLING ALOFT
CLIPS THE LOWER GREAT LAKES.
DRIER AIR BRIEFLY FILTERS IN BEHIND THE FRONT LATER TONIGHT INTO
MOST OF THE DAY FRIDAY WITH HIGHS ONCE AGAIN WELL INTO THE 80S.
MOISTURE DOES RETURN NORTHWARD LATE FRIDAY INTO FRIDAY EVENING IN
ADVANCE OF A SECONDARY COLD FRONT AND MID LEVEL SHORTWAVE (70-80 KT
500 MB JET) ARRIVING FROM THE MID MS VALLEY. THIS SHOULD BE ENOUGH
TO GENERATE A ROUND OF SHOWERS AND STORMS MAINLY FRIDAY EVENING WITH
DEEP FORCING, MOISTURE QUALITY, AND DEEP LAYER SHEAR MAGNITUDES
FAVORABLE FOR SCATTERED STRONG TO SEVERE STORMS. INSTABILITY
MAGNITUDES ARE LACKING WHEN COMPARED TO THIS EVENING HOWEVER WITH
THE PRIMARY MOISTURE/INSTABILITY RESERVOIR LIKELY SUPPRESSED CLOSER
TO THE OH RIVER. DRY AIR ON LEADING EDGE WITH A SUB-CLOUD INVERTED-V
PROFILE AND HIGH DCAPE VALUES MAY SUPPORT GOOD DOWNDRAFT POTENTIAL
AND LOCALIZED WIND DAMAGE IF MORE ROBUST CELLS DEVELOP, ALONG WITH A
HAIL THREAT GIVEN LINGERING STEEP MID LEVEL RATES.
DRY AND COOLER WEATHER WILL FILTER IN BEHIND FRIDAY NIGHT'S WAVE IN
TIME FOR THE WEEKEND, WITH SATURDAY ALSO BREEZY. RAIN CHANCES
EVENTUALLY RETURN TOWARD THE MIDDLE OF AS THE NEXT WESTERN CONUS
UPPER TROUGH SLOWS OR CUT-OFF OVER THE MIDWEST.
AVIATION /18Z TAFS THROUGH 18Z FRIDAY/
ISSUED AT 126 PM EDT THU MAY 15 2025
A STRONG UPPER LEVEL JET STREAK WILL NOISE INTO THE SOUTHERN
GREAT LAKES REGION TONIGHT. THE PRIMARY UPPER LEVEL LOW LINGERS
WELL BACK TO THE WEST ACROSS THE NORTHERN PLAINS, BUT INCREASING
LARGE SCALE LIFT AT THOSE NOSE OF THIS JET COUPLED WITH MODERATE
TO STRONG SURFACE BASED INSTABILITY SHOULD LEAD TO CONVECTIVE
INITIATION ACROSS NORTHEAST ILLINOIS LATE THIS AFTERNOON,
EVENTUALLY SHIFTING INTO NORTHWEST INDIANA AFTER 00Z. HAVE
GENERALLY MAINTAINED IDEA OF PREVIOUS TAF TIMING OF BETTER
CONVECTIVE TRENDS AT KFWA AND KSBN WITH A 3 TO 4 HOUR WINDOW OF
PREVAILING THUNDER. GIVEN MODERATE TO STRONG INSTABILITY AND
AMPLE SHEAR, THESE STORMS MAY BE STRONG TO SEVERE WITH A
POTENTIAL OF SOME LARGE HAIL AND THUNDERSTORM WIND GUSTS IN
EXCESS OF 50 KNOTS. PRE-FRONTAL FORCING FEATURE WILL SHIFT EAST
OF THE TERMINALS DURING THE EARLY OVERNIGHT HOURS. BETTER LOW
LEVEL MOISTURE WILL GET SHUNTED SOUTHEAST AND EAST OF TERMINALS
LATE TONIGHT, BUT THIS MOISTURE GRADIENT IS EXPECTED TO RETURN
NORTHWARD LATER FRIDAY. THE COMBINATION OF THIS RETURN MOISTURE
ADVECTION FORCING AND APPROACH OF PRIMARY UPPER LEVEL TROUGH
WILL RESULT IN RENEWED SHOWER AND STORM POTENTIAL OUTSIDE OF
THIS FORECAST VALID PERIOD LATE FRIDAY AFTERNOON/EVENING.
IWX WATCHES/WARNINGS/ADVISORIES
IN...NONE.
OH...NONE.
MI...NONE.
MARINE...NONE.
DISCUSSION...STEINWEDEL
AVIATION...MARSILI
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