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Forecast Discussion for Indianapolis, IN
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602 FXUS63 KIND 081351 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 951 AM EDT Fri Aug 8 2025 .KEY MESSAGES... - Dry, warm and humid conditions continue through the weekend - Shower and thunderstorm chances return for much of next week with muggy conditions persisting && .FORECAST UPDATE... Issued at 951 AM EDT Fri Aug 8 2025 Forecast is in good shape this morning. Fog has mixed out. Some cirrus was moving through parts of the area, but skies were sunny to mostly sunny. Made some minor adjustments to hourly forecasts based on trends seen in surface observations and satellite, but no significant changes were made to the forecast. Will have to keep an eye on the upstream cirrus from convection well to the northwest to see if it holds together for potentially more sky cover this afternoon. Increasing mid-level temperatures will help prevent convection today, but still cannot rule out an isolated shower or storm. Odds continue to be too low to mention in the forecast though. && .SHORT TERM (Today and Tonight)... Issued at 244 AM EDT Fri Aug 8 2025 Skies were mainly clear early this morning as ridging aloft to the west continues to expand towards the Ohio Valley. Have already seen localized fog in a few spots and expect that to increase in coverage a bit through daybreak. 06Z temperatures were ranged from the upper 60s to the mid 70s. A sharp upper level low tracking across western Canada just north of the US border will aid in enabling the persistent upper ridge over the southern Rockies to expand east through tonight with heights aloft rising through the course of the day. This will promote a greater level of subsidence across the region which should further limit overall convective development focused during the afternoon and early evening. As mentioned above...skies will remain mostly clear through daybreak and with stagnant flow within the boundary layer anticipate a gradual expansion to ongoing patchy fog...especially across the southern and western portions of the forecast area. Any locations that received rainfall on Thursday will also be increasingly susceptible for fog through daybreak. Fog will diminish quickly after sunrise setting the table for a warm and humid day for central Indiana. There remains a non-zero threat for a stray shower or thunderstorm during peak heating...but model soundings show a strengthening mid level cap which combined with the warmer air aloft will largely place a lid on any convection. Coverage will only be 5% to 10% at best and will maintain a dry forecast for the entire area. Quiet but muggy conditions are then again expected for tonight. Temps...low level thermals support highs similar to Thursday in the upper 80s and lower 90s. The presence of subsidence in the mid levels may enable slightly drier air to be brought to the surface during the afternoon. Peak heat indices should remain in the low to mid 90s. Lows tonight will drop into the upper 60s and lower 70s. && .LONG TERM (Saturday through Thursday)... Issued at 244 AM EDT Fri Aug 8 2025 The upper low tracking across the Canadian prairies will be blocked from making it much further east than the northern Plains by strong ridging over the eastern part of the country. The ridging will move little into early next week maintaining a very warm and humid airmass across the Ohio Valley with little to no threat for convection. As the week progresses though...the upper level flow will transition to more of a quasi-zonal regime which will enable weak waves aloft to drop further south into the region and introduce a better chance for scattered convection beginning Tuesday and continuing for much of the rest of next week. Saturday through Monday Night Ridging aloft and at the surface will remain the primary features influencing the weather across the Ohio Valley through the weekend...and keeping the upper low and subsequent trough locked in place across the northern and central Plains. This will leave a typical humid midsummer airmass across central Indiana with daily highs/lows within a few degrees either side of 90 and 70 degrees respectively. The heating will breed moderate instability levels each day through Monday despite the lingering mid level cap. Similar to today...there will be a nonzero convective threat but it will be difficult to see much more than a few stray showers or storms considering the mitigating factors mentioned above. Will continue with a dry forecast Saturday and Sunday but as the cap weakens slightly by Monday...low chance pops for isolated storms will be introduced. One item to keep an eye on though will be the potential development of a convective cluster over the upper Midwest on Saturday that could drop into northern Illinois by the evening. The bulk of the convection would likely migrate south or even southwest into Saturday night following the deeper instability and riding along the nose of the low level jet. While this would not directly impact the forecast area...there could be a remnant outflow from the complex that makes it this far southeast on Sunday to give a bit of an assist to any isolated convective development for the afternoon. Tuesday through Thursday The flattening of the upper level flow will enable the perturbations aloft to make a further south track into the region and bring a daily threat for isolated to scattered convection each day. The main convective risks through the period will again be on heavy rainfall and localized flooding as a lack of substantial shear will ensure slow movement to storms that will pulse up and down in intensity. There is always the potential for a cell to strengthen enough briefly to produce localized downbursts as the cores collapse but that is likely to remain a secondary concern through late next week. The airmass will remain warm...muggy and stagnant through much of next week with highs in the mid and upper 80s and dewpoints likely creeping up a bit into the lower 70s. There are growing signals that this may continue right through next weekend and potentially even beyond with cooler and drier air being held well north of the region. && .AVIATION (12Z TAF Issuance)... Issued at 539 AM EDT Fri Aug 8 2025 Impacts: - Fog early this morning and again predawn Saturday, mainly at KBMG and KHUF Discussion: Calm winds and mainly clear skies combined with deeper moisture in the near surface layer has led to shallow ground fog with oscillating visibilities to under 1SM at both KBMG and KHUF for most of the overnight. Reduced visibilities will linger for a short time after daybreak before fog diminishes. Diurnal cu will develop this afternoon but should not be as extensive as Thursday with greater capping in the mid levels. Light S/SE winds are expected into the early evening before again becoming light and variable tonight. Patchy fog is likely to redevelop again at KBMG and KHUF during the predawn hours Saturday. && .IND WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...50 SHORT TERM...Ryan LONG TERM...Ryan AVIATION...Ryan |
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