By: Stephen McCoy

No major changes in the forecast update from Monday. Expect the remnants of now Hurricane Laura to pass to the south of the St. Louis region on its track eastward, bringing a chance for showers and/or thunderstorms around mid-day. In addition, winds are likely to increase as the outer edges of the storm approach; sustained winds are expected around 10-15 mph with gusts upwards of 25 mph. Above normal low temperatures will be present in the morning with seasonal high temperatures in the afternoon.

A cold front following immediately behind the post-tropical system will bring a slight chance for isolated showers and/or thunderstorms during the morning, with precipitation chances diminishing before noon. Winds will shift to the northwest behind the front, though at around the same speeds anticipated for Friday; similar temperatures are also expected. Partly cloudy skies are expected behind the front and will continue into Sunday.

The northwesterly winds on Saturday will cool temperatures overnight, with a low expected in the mid 60's on Sunday morning. A high pressure system passing to the northeast will shift winds to the east to southeast during the day, allowing for temperatures to warm again into the low 80's. The continuing partly cloudy conditions will persist into the afternoon when upper level cloud cover is anticipated to build in.

By: Stephen McCoy

Near-normal conditions are anticipated at Word Wide Technology Raceway this weekend, though conditions on Friday and Saturday will be influenced by the remnants of a tropical system, followed closely behind by a cold front. Chances for precipitation exist for both days, though dry conditions will move in for the remainder of the weekend after noon on Saturday.

For Friday, the remnants of Tropical Storms (potentially Hurricane) Laura is expected to move to the south of the region during the day. Outflow from the system in the upper levels will cause mostly cloudy to overcast conditions starting in the morning and increasing in the afternoon as low level clouds start to build from the approaching post-tropical cyclone. Though the system will move close by the region, sustained wind speeds at the surface are only anticipated around 5-10 mph, however wind gusts could approach 20 mph. The outer edges of Laura will bring a chance for showers and/or thunderstorms to the St. Louis area, with timing potentially delaying a portion of Friday's practice session.

For Saturday and Sunday, as Laura is passing to the south on Friday, an upper level shortwave trough is expected to initiate development of a low pressure system over Minnesota/Wisconsin. Friday night into Saturday, the low is expected to move eastward through the Great Lakes region, with a cold front extending to the southwest. The front will move through the St. Louis region Saturday morning, bringing with it a slight chance for showers and/or thunderstorms. After the front passes, surface winds will increase from the west to northwest as high pressure begins to build in behind the low. Daytime heating will allow the maximum temperature to warm near Friday's high, though temperatures will decrease into the evening and overnight with a low in the mid-60's expected for Sunday. Northwesterly winds aloft will cause clearer conditions to move in Saturday afternoon, continuing through Sunday with the majority of cloud cover in the upper levels. During the day on Sunday, the surface high pressure system will track eastward, causing winds to shift east to southeast, allowing temperatures to warm with a high expected again in the mid 80's.

By: Stephen McCoy

Predicted conditions are still fairly similar for tomorrow's race as they were earlier in the week. Low temperatures will be in the upper 60's tomorrow morning with patchy fog possible in the region as the result of highly saturated air under a low-level temperatures inversion; any fog will dissipate before noon. For the afternoon, air temperatures will be in the low 80's at the green flag, warming to a high in the mid 80's by 5 PM. Winds will likely be out of the south to southwest for the majority of the race at 5-10 mph, with some slightly stronger gusts around 15 mph.

Unfortunately, there is still a slight chance for isolated showers or t-storms in the early part of the afternoon, which could hinder the start of the race. While expected due to an approaching front earlier in the week, recent model runs have shown precipitation as the result of pop-up showers through the region. Exact location of individual storms has varied between models and model runs (and is fairly difficult to predict), however the HRRR has shown a slight increase in number of storms in the surrounding region over the latest iterations. It'll be worth watching overnight to see if the trend continues. Should any changes be necessary from this forecast, an update will be put out tomorrow before the race.

By: Stephen McCoy

Forecasted conditions remain relatively similar from the initial forecast for the Indianapolis 500 from Monday. Slightly cooler temperatures are expected compared to earlier in the week, with partly cloudy conditions for both Carb Day and race day. Precipitation chances have decreased slightly, though there is still the possibility for isolated showers and thunderstorms during Sunday afternoon.

For Friday, an upper level low pressure trough will move into the region Thursday night into Friday morning. Recent runs of forecast models suggest the trough will center itself to the west of central Indiana, contrasting the output from Monday. The trough's position implies an increase in moisture due to southerly winds aloft, resulting in more partly cloudy conditions. At the surface, an area of high pressure over New England will cause light winds from the east to northeast, though wind direction may be variable at times.

For Sunday, a high pressure system located off the Atlantic coast, coupled with a low pressure system passing through southern Quebec will cause a slight increase in winds from the southwest Saturday night into Sunday, leading to warmer low temperatures Sunday morning. The increased air temperatures, in addition to relatively warm dew point temperatures could result in patchy fog in areas near sunrise, though any fog will be gone within the following few hours. An increase in moisture at the mid-to-low levels of the atmosphere could result in some isolated showers through the region during the afternoon, with an approaching cold front possibly provoking the development of thunderstorms.

By: Stephen McCoy

Fairly similar conditions are expected for the Indianapolis 500 this weekend as there were for the practice and qualifying sessions last week. Warm and sunny conditions will be present on Friday, though a cold front approaching the region will bring a chance of showers and thunderstorms on Sunday.

For Friday, an upper level trough will center itself to the east of central Indiana, resulting in upper level winds mostly from the north/northwest through the day. Drier air from Canada will move over the region, causing clear skies for much of the day. At the surface, an area of high pressure will be present over the area, keeping surface winds relatively light from the east to northeast, though at times wind direction will be variable.

For Sunday, an upper level shortwave trough will move through the northern plains on Saturday, allowing a surface low pressure system to form just to the east. The surface low is anticipated to move eastward through southern Quebec with a cold front trailing behind it to the southwest. Sunday morning, the front is expected to approach central Indiana, bringing with it a chance for showers and thunderstorms, along with slightly warmer daytime temperatures and stronger winds. Surface winds will be largely from the southwest ahead of the front, but will shift to the west if the front passes over the region. Partly cloudy skies are expected as a result of the oncoming front along with mid-level moisture moving into the region from the northwest.

By: Stephen McCoy

Not much change to the rest of the week's conditions from the previous forecasts, though the cold front originally slated to move through on Saturday now looks like it will move through the region Sunday morning, hence the slightly cooler maximum temperature. The front, moving eastward through central Indiana, will bring a chance for showers and thunderstorms until around mid-day or early afternoon at the latest. Expect increased winds from the northwest after the front has passed over with gusts exceeding at least 20 mph.

By: Stephen McCoy

Precipitation chances have diminished somewhat for the remaining practice days for the Indianapolis 500. Otherwise, conditions are staying mostly as-expected from Monday's initial forecast.

For Thursday and Friday, a surface high pressure system currently located over the Great Lakes region is expected to move towards the northeast into eastern Canada by Friday evening. The anticyclonic rotation around the high will cause surface winds mainly from the northeast each day, with a slight change to the east during the second half of Friday. A temperature inversion in the low levels of the atmosphere will inhibit convective development on Thursday and resulting in partly cloudy conditions for much of the day. Low level winds from the east/northeast on Friday will erode the inversion and allow for a slight chance for afternoon showers and/or thunderstorms around the region.

For Saturday and Sunday, an upper level low pressure trough will develop over the Missouri River Valley during Friday afternoon and into the overnight. The trough will cause a surface low pressure system to form over Tennessee/Kentucky and push northeastward through the weekend. Moisture in the lower levels will bring a chance for showers during Saturday as the low passes to the east of central Indiana. As the system continues its movement towards New England, winds in the region will shift to the north to northwest, possibly resulting in some slightly cooler temperatures, though model guidance shows uncertainty in the maximum on Sunday.

By: Stephen McCoy

There are no major surprises in the forecast for this week's practice and qualifying sessions for the Indianapolis 500: maximum temperatures are expected the mid 80's with chances for afternoon showers and/or thunderstorms.

For Wednesday through Friday, an upper level ridge over the southwestern US will influence a high pressure system at the surface, moving it northeastward through the Great Lakes region. For much of the time period, surface winds will be relatively light from the east to northeast, accompanied by partly cloudy skies. Dew point temperatures in the mid 60's could give enough convective inhibition to result in isolated to scattered showers and thunderstorms in the afternoon around the area.

For Saturday and Sunday, conditions are anticipated to be similar to those earlier in the week, however towards early Saturday afternoon, a cold front will move eastward through central Indiana, bringing with it an increased chance for precipitation, with the greatest chance occurring in the overnight hours. Winds during the day will be from the south to southwest with partly to mostly cloudy skies. After the front passes through, winds will shift towards the north to northwest for Sunday, accompanied by clearer conditions. Much like earlier in the week, a slight chance for showers and thunderstorms is present during the afternoon.