Area Forecast Discussion
Issued by NWS Northern Indiana
Issued by NWS Northern Indiana
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015 FXUS63 KIWX 022236 AFDIWX Area Forecast Discussion National Weather Service Northern Indiana 636 PM EDT Tue Jul 2 2024 .KEY MESSAGES... - A Marginal Risk of severe storms for Wednesday afternoon and early evening mainly east of Interstate 69 across northeast Indiana and northwest Ohio. Isolated damaging wind is the potential main threat. - Warmer and more humid for Wednesday with peak afternoon heat indices in low to mid 90s south of US Route 24. - Isolated severe weather is also possible on Friday, but low confidence at this time. && .DISCUSSION... Issued at 335 PM EDT Tue Jul 2 2024 Broad positive mid-level theta-e advection across the western Great Lakes has shifted across southern Lower Michigan this afternoon. This elevated moisture return combined with small scale vort max tracking across southern Great Lakes has allowed for rain showers, primarily north into central Lower Michigan. Passage of this vort max and axis of better mid level moisture will cut-off additional rain chances for the remainder of the day. Focus for the rest of the day into this evening will be upstream as renewed convection develops across the Corn Belt in a zone of stronger frontal/moisture convergence. The upstream short wave helping to initiate this convection will shear out as it ejects northeast into the UP of Michigan, and low level convergence will weaken as this axis shifts into the southern Great Lakes Wednesday morning. Still some uncertainty as to the coverage of rain showers/embedded storms into west/northwest portions of the area early Wednesday morning, but overall trend should be weakening through the late morning hours. Convective potential for Wednesday remains a challenge as residual cloud cover will likely be accompanying primary low-mid level theta-e ridge as it sags into the southeast half of the forecast area Wednesday afternoon. Weak sfc cool front will also likely be lagging back across the western Great Lakes early Wednesday afternoon, and strength of low level convergence in guidance progs looks to be relatively weak. At this forecast distance, it remains difficult to differentiate whether actual cold front, or pre-frontal confluence zone across the Ohio River Valley will be more favorable for convective initiation. This pre-frontal area southeast of the local area may also be characterized by some pockets of differential heating Wednesday afternoon. Have not made many changes to previous forecast with NW to SE PoP gradient Wednesday afternoon. Westerly deep layer shear on the order of 30-35 knot and potential of some SBCAPES on the order of 2000 J/kg could yield a small window of isolated severe risk in the 18Z-00Z timeframe, mainly along and south of US Route 24. Weak mid level lapse rates and marginal westerly shear would point to main threat as isolated strong wind gusts with precip loaded cores. Lull in the greater rain chances still looks to set up Wednesday night into early Thursday as this low level theta-e gradient stalls out south of US 24. It is possible there may not be much impetus for return advection and northward retreat of this boundary until later Thursday night as next convectively enhanced vort max lingers back across the Mid MS Valley during the day Thursday. On Friday, guidance still points to a stronger synoptic upper level trough affecting the area with flow backing to the southwest allowing for better northward moisture transport. Some Dprog/DT trends have indicated a slight tendency to a more open wave, with perhaps a slightly faster progression of SLP minimum and sfc cold front. Shear will be a bit more robust by Friday downstream of this more vigorous wave which leaves the main ingredient of uncertainty as instability. There could be a good deal of cloud cover from advective forcing to begin the day Friday which could limit destabilization. If some moderate instability can be realized, some strong/severe potential is possible given expected background shear. Passage of this trough will lead to cooler and less humid conditions for Saturday. Maintained some slight chance PoPs across the northeast Saturday as departing upper level trough across the Great Lakes allows for slightly cooler upper level temps and weak pocket of lingering MUCAPE. Predictability in the finer details diminishes post-Saturday as medium range guidance depicts additional waves in western CONUS northwest flow aloft dropping into the region with additional fropa potential. At this forecast distance, have just maintained broadbrush low PoPs late Sunday into Tuesday along with seasonable temps. && .AVIATION /00Z TAFS THROUGH 00Z THURSDAY/... Issued at 636 PM EDT Tue Jul 2 2024 VFR/dry with sse winds near 10 knots and little in the way of cloud cover through the early overnight. A developing intense QLCS over eastern Iowa will weaken with eastward progression later tonight as it outruns more favorable flow and buoyancy into a stable environment over the southern Great Lakes and Ohio Valley. This still could push a thinning line of showers and embedded thunder into KSBN later tonight, possibly lingering into Wednesday morning. Much lesser chances of any rain surviving into KFWA, with post outflow saturation and fold over of a low level theta-e ridge axis supporting a trend toward high MVFR to low VFR cigs on Wednesday. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...None. OH...None. MI...None. MARINE...None. && $$ DISCUSSION...Marsili AVIATION...Steinwedel