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Area Forecast Discussion
Issued by NWS Indianapolis, IN
Issued by NWS Indianapolis, IN
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489 FXUS63 KIND 150958 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 558 AM EDT Mon Jul 15 2024 .KEY MESSAGES... - Periodic shower and thunderstorm chances through Wednesday. - Severe storms possible with the main threat damaging winds the remainder of the overnight and tonight. - Localized flash flood risk at times, particularly Tuesday and Tuesday night - Hot and humid through Tuesday - Pleasant September-like weather arrives Wednesday night...with low humidity and afternoon highs 5-10 degrees below normal && .SHORT TERM (Today and tonight)... Issued at 237 AM EDT Mon Jul 15 2024 ...SEVERE THUNDERSTORM WATCH THROUGH 5 AM EDT... ...100+ HEAT INDICES THIS AFTERNOON... Today... The work week is going to start off with potential severe weather and excessive heat and humidity. Latest MRMS radar was showing convection associated with the southwest end of an MCS moving southeast toward the upper Wabash Valley. Meanwhile, less organized scattered convection was popping up across southern Illinois and the lower Wabash Valley. Convection with the MCS will continue to track southeast and move across the upper Wabash Valley and possibly as far east as the Metro after 3 AM. Moisture convergence, a modest low level jet and still strong instability support a continued threat for damaging winds and a non-zero threat for a spin up or two through 5 AM or so. Currently, LAPS data and SPC mesoanalysis are indicating up to 3000 J/kg SB CAPE over the upper Wabash Valley. After the overnight convection dissipates and over moves out, the heat will be the next bid concern as the stagnant airmass will continue with dew points in the middle and upper 70s. If the morning cloud debris can exit early enough and only scattered diurnal cu pops up, the heat index could reach 105 degrees or so. Overall, confidence is not enough for an advisory, so will go with an SPS. This was the general thoughts of adjacent offices as well. Mostly like scenario is for temperatures to at least reach the lower 90s this afternoon based on DESI. Tonight... Another MCS is expected to sweep southeast across central Indiana late tonight. This MCS will form somewhere over the upper Midwest this afternoon, associated with the re-development of convection from the MCS currently over North Dakota or along and ahead of a nearby slow moving cold front. This activity should at least make it to near the I-70 corridor late tonight. Increasing deep shear with 0- 6km bulk shear to 40 knots coupled with CAPE to 1500 J/kg supports a risk for severe weather with damaging winds being the main threat. Best coverage with PoPs to 60% and severe weather threat will be over the upper Wabash Valley although confidence in coverage and severe risk category is not great. The muggy airmass supports overnight lows only in the middle 70s. && .LONG TERM (Tuesday through Sunday)... Issued at 237 AM EDT Mon Jul 15 2024 Tuesday and Wednesday... The forecast period`s best opportunity for organized rain will cross central Indiana from north to south within the late Tuesday to early Wednesday timeframe following a staunch cold frontal passage...which will also bring a transition from oppressive heat to mild, if not briefly cool, mid-September conditions. But first will be a final day of maximum heat indices nearing Heat Advisory criteria on Tuesday...across the region`s far southern tier where partly sunny skies ahead of the approaching front will boost readings into the low 90s, which will couple with mid-70s dewpoints to yield Heat Index Values nearing 105F. Following more active/ potentially-severe storms through the beginning of the week...a conditional/marginal threat of strong/ severe storms will accompany the cold front through PM hours Tuesday. Southwesterly winds promoting another day of 70-75F dewpoints will fuel adequate instability Tuesday. Thunderstorm updrafts should be sufficient to produce at least a few strong TRWs, yet stronger flow aloft should hold back to the north of the region. Additionally, greater cloud cover north of the I-70 corridor should squelch heating enough to focus any severe threat farther south, especially as the Tue/Tue night timeframe goes on. Stronger storms or not, expect the slow and steady frontal passage to bring additional widespread moderate rainfall, with heavier totals in excess of 1.00 inch where stronger storms or multiple rounds of showers occur. Localized flash flooding will be possible, especially for southern counties if and where heavier rains are maintained into Tuesday night. Wednesday will be a day of transition as lower chances of rain/non- severe storms slowly decrease from north to south under the departing frontal zone. Noticeably milder conditions will be the rule with northerly surface winds gusting to 10-15 mph by the afternoon and highs only around 80F for the first time (at least with lower humidity) since the beginning of July. Additional light rainfall can be expected fro most central/southern zones, with isolated 0.50-1.00 inch amounts for a few southern locations caught under a lingering storm. Wednesday Night through Sunday... Showers and t-storms will end from north to south Wednesday night as the frontal zone continues to push southward past the Ohio Valley. An uncommon mid-summer treat will then prevail through the second half of the week as Canadian high pressure brings several days of sub-normal temperatures and humidity. A rather potent mid-level trough more reminiscent of early fall will cross the Great Lakes, before a broad and amplified upstream upper ridge over western North America slows the corresponding surface high whose southern portions will slowly cross the region on Thursday and Friday. Expect 2-3 overnights with minimums ranging from 55-60F across the realm...while afternoon maximums are not expected to surpass the low 80s for most locations through at least Saturday. Thursday is currently progged to be the most refreshing day when northerly breezes gusting to around 15 mph may hold several north-central zones under 75F. The alignment of the slowly-departing air mass should prevent any southwesterly return flow through the end of the long term. Expect rain-free conditions to continue through the weekend under what should be only a modest increase in precipitable water as the high pressure slides east. The normal max/min at Indianapolis will continue at its peak tandem of 85/67 through July 22. && .AVIATION (12Z TAF Issuance)... Issued at 558 AM EDT Mon Jul 15 2024 Impacts: - Potential for convection after 05Z with a non-zero chance for 50+ knot wind gusts, especially at KLAF - Brief MVFR and worse conditions possible with thunderstorms after 05z Discussion: Thunderstorms will move in overnight, some of which could be severe and include MVFR and or worse flying conditions. Winds away from convection will be mostly SSW 10 knots and less. && .IND WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...MK LONG TERM...AGM AVIATION...MK