Here are the complete details from the National Weather Service:
Short Term...(Today through Friday) Issued at 307 AM EDT Thu Oct 14 2021 Broad warm advection regime ongoing this morning across the Ohio Valley and advecting deep moisture into the region. This has brought plenty of cloud cover and in some spots lower stratus. A few showers were across the Wabash Valley and continued to weaken as they moved away from the primary areas of lift closer to the cold front back across western Illinois. Humid conditions currently by October standards as 0630Z temperatures were in the upper 60s and lower 70s with dewpoints in the upper 60s as well. Active and unsettled weather will dominate the short term with increasing threats for heavier rainfall and embedded convection by late today throughout the day Friday. Aforementioned cold front extending from an occluding low pressure over the northern Plains... then looping through the western Great Lakes back into the mid Mississippi Valley and southern Plains. The boundary is in a quasi- stationary state this morning due to a couple factors: 1) the front has become nearly parallel with broad southwest flow aloft...2) the front is being left behind by a deep upper low and the northern Plains surface low which will track north into Manitoba through the day...and 3) its forward progress is effectively blocked by a large surface ridge extending from eastern Canada into the southeast States. The boundary will drift east slowly today and eventually settle into the region tonight and Friday which will put central Indiana in the bullseye for rounds of convection and locally heavy rainfall beginning late today and persisting through Friday night. The development of a secondary surface wave on the boundary over the southern Plains late today will ultimately be partly responsible for kicking the front east of the region by the beginning of the weekend. This wave will lift north into the Ohio Valley on Friday and strengthen as a upper level trough approaching from the west amplifies late Friday. Convection is firing along the boundary early this morning in western Illinois aided by stronger 850mb flow. While some of this activity may sneak into the northern Wabash Valley later this morning...expect the bulk of this convection to track N/NE and remain to the northwest of central Indiana. Additionally...a few showers and perhaps a rumble or two of thunder will be possible through early to mid afternoon across the northwest half of the forecast area...but expect the bulk of the rain will remain in proximity to the boundary to the west. The impacts from this multifaceted storm system will come in two parts with the first one set to commence by late day as the front approaches our northwest counties and continue tonight and through Friday morning with the boundary likely to be bisecting the forecast area from southwest to northeast by predawn Friday. Tropical moisture from the remnants of Pamela currently over northern Mexico will continue to advect northeast along the boundary and into the region over the next 36-48 hours. This will bring unseasonably high PWATs into the Ohio Valley peaking near the climatological max and at roughly 250% of normal for mid October. The deep moisture plume will interact with increasing isentropic lift and a developing nocturnal low level jet to bring increasing convective coverage in the zone along and immediately ahead of the cold front tonight across the northwest half of the forecast area...with some training of cells as well focused along an axis near or perhaps just north of a Terre Haute-Indy-Muncie line. Will focus highest pops in this area overnight with activity likely to be more scattered across southeast counties. Weak instability aloft will be sufficient for scattered thunderstorms as well and certainly appears some locations may see upwards of an inch through Friday morning. Enhanced low level flow from the southwest will maintain numerous showers and storms into early Friday afternoon...but the increasing influence from the approaching upper trough will change the game a bit for Friday afternoon into Friday evening...as additional parameters come into play to maintain precip coverage and likely present an uptick in convective intensity as well. The secondary surface wave will be in the process of intensifying as it tracks across the region Friday afternoon...and model soundings/RH progs both hint at a narrow window for scattering of cloud coverage which would increase heating and consequently instability. The confidence level is higher in this occurring south of the region across the lower Ohio Valley into Tennessee...but increasing BL shear and low level SRH ahead of the front even up into central Indiana at least raises the potential for a short 1-3 hour period for severe storms during the late afternoon and early evening focused mainly across the southeast half of the forecast area. Damaging winds would be the main concern but the higher SRH values and presence of directional shear in the near surface layer at least offers the possibility for a few rotating cells as well. Lot of moving parts here and would like to see all of the parameters better phased...but this will be something to monitor. To sum it all up...primary concerns remain focused on heavy rain and the potential for localized flooding with growing confidence at 1-3 inches of rain across much of the forecast area by Saturday morning. The thermodynamic setup is supportive for embedded thunderstorms throughout the next 2 days with a slightly higher ceiling for a short period late Friday afternoon and evening for severe storms. Rain will continue into Friday night before tapering off early Saturday as the system moves east. More on the tail end of the storm system and its impacts in the long term section below. Temps...Even with a fair amount of cloud cover and limited sunshine today...should not have much trouble warming into the upper 70s and lower 80s across much of the forecast area considering our very warm start this morning. Temperatures on Friday are more challenging with the boundary draped across the forecast area. Low level thermals largely support a range from the lower 70s over the northern Wabash Valley to the upper 70s in the southeast counties. Lows tonight will range from the upper 50s north to the mid 60s south of Interstate 70. && .Long Term...(Friday Night through Wednesday) Issued at 307 AM EDT Thu Oct 14 2021 The period will begin as central Indiana is transitioning regimes from warm/rather humid to cool/quite dry...amid soaking rains and thunderstorms as a strong cold front crosses the CWA. By Friday evening, the day`s moderate to locally heavy rainfall will be tapering off from west to east. Strong, to perhaps briefly severe, thunderstorms will be possible east of the I-69 corridor as 150-250 m2/s2 of 0-3 km storm relative helicity, and up to 70 kts of 0-6 km bulk shear attempt to catch what very limited instability may linger ahead of the front after 00z. Appears the ample dynamics may just miss this opportunity, although any small variations in the quick frontal passage`s timing would certainly change the scenario. Nevertheless after 00z high confidence in rain ending west to east, moderate confidence in a few lingering heavy downpours east of Indy, and low confidence in any severe storms. Saturday will, despite ample sunshine, feature the coolest afternoon highs since the second week of May...as the region dries out courtesy of west-northwesterly surface wind gusts as high as 20-25 mph as the exiting system`s upper level trough axis crosses Indiana. Several dry days of seasonably chilly mornings and pleasant autumnal afternoons weather will follow, with Gulf moisture cut-off from the Mid-West by high pressure prevailing over the eastern US. Conditions will slowly moderate amid modest southwesterly winds out of the surface ridge axis to our south, and mid level heights slowly rising as a ridge approaches from the Plains while flattening. Mostly clear skies under H850 temps trending from about 5C on Sunday to near 12C by Wednesday...support slightly below to slightly above normal temperatures. The normal max/min for the long term period is 65/45. Lower confidence surrounds the end of the long range, on where any wave would develop over the central US as Canadian air descends into the US, however decent certainty that any slight chance POPs would hold off until at least after Wednesday.
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