Here is what the NWS out of Indianapolis is thinking:
.Long Term...(Friday through Wednesday) Issued at 303 AM EDT Thu Jun 22 2023 By Friday morning, it appears that the Rex Block pattern that has dominated this week`s weather across the eastern CONUS will have finally broken. With upper level ridging over the northern Great Lakes decaying and the cutoff low over the Tennessee and Ohio River Valleys finally propagating northwards, Friday should be the last day that these synoptic features drive the forecast for our region. The aforementioned low should eject northeastward throughout the day on Friday, but guidance depicts a lobe of cyclonic vorticity swinging around its left side in this time frame. As a result, areas along and east of I-65 will retain chance PoPs for showers on Friday afternoon. Cloud coverage will limit temperatures in this same region, and Friday`s forecast highs are marked by a steep gradient from west to east. Areas west of I-65 will see less cloud coverage and lower rain chances, and will thus rise into the 80s. Meanwhile, areas east of this corridor will only reach the mid 70s amidst thicker clouds, but a distinct pattern shift will allow conditions to improve by the weekend. On the periphery of weak upper level ridging, Saturday will be dry and warm across Central Indiana. This is not the case upstream, as a developing low pressure over the Great Plains and shortwave upper trough will trigger storms (and potentially an MCS) to develop out closer to Iowa. Locally, the development of this surface low will contribute to the breakdown of the past week`s block and will allow surface flow to veer to westerly and southerly. This, in turn, will enhance warm air advection over our forecast area, allowing temperatures to warm into the upper 80s/lower 90s on Saturday. Low level flow strengthens into Sunday, only enhancing this ongoing warm air and moisture advection and setting the stage for potential convective thunderstorm activity in Indiana. While this system is likely to give our area the best rain chances we have seen in a while, multiple questions remain up in the air regarding any severe weather potential on Sunday. The first of these questions relates to the upstream activity mentioned above; will it develop into an MCS and will this MCS make it all the way to Indiana? The presence of a seasonably potent 500mb jet streak nearby depicted in some guidance on Sunday would support this system sustaining itself. However, it will also have to overcome a loss of diurnal thermal instability, as it would approach the area overnight/early in the morning. The next question depends on the strength of any lingering activity; would it locally suppress the thermodynamic environment via latent heat processes and decrease instability for Sunday afternoon? Weaker or nonexistent Sunday morning storms would allow for greater potential for convective initiation across Indiana later in the day. Any storms that form on Sunday afternoon will exist in a favorable shear directional regime, and modeled soundings demonstrate the need to monitor severe weather approach if favorable thermodynamics are realized. More questions exist regarding the spatiotemporal placement of the driving shortwave trough; will the best forcing be displaced south or east of the area? While guidance generally agrees in the shift towards a more favorable synoptic pattern for convection (and rain!!), many of these questions will remain up in air until the system enters the range of higher-resolution modeling. Stay tuned to future forecast updates as this event approaches, as trends in the above questions will be watched in the coming days. A typical summertime weather pattern will emerge into the early part of next week. With a ridge building over the southern Plains and broad troughing over the NE states, Indiana will exist in a regime of NW flow aloft and SW flow at the surface. This combination typically results in warm, moist air over our area, increasing the potential for precipitation. Said precipitation is driven by mesoscale features beyond the scope of medium-range modeling, but expect climatologically appropriate weather for the start of the next workweek.
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