By: Stephen McCoy

Chances for precipitation have gone down for Sunday's ABC Supply 500 at Pocono Raceway, primarily due to rainfall overnight which used much of the available CAPE in the atmosphere. Recent model runs show CAPE values not reaching as high as initially anticipated during the day, again due to overnight storms using up the available energy. Still, mixed-layer values indicated by the GFS will still be near 1000 J/kg which is backed up by the higher-resolution HRRR model; the RAP and NAM 3km models show MLCAPE values exceeding 2000 J/kg. All this is to say a few isolated showers may not be out of the question, especially towards the end of the race as initially thought. Fog will be likely in the region during the morning due to the aforementioned overnight rainfall, with saturated air present under a temperature inversion below 1 km.

By: Stephen McCoy

Conditions have changed a bit for Saturday with partly cloudy conditions continuing to persist through the day, though with a now slight chance for scattered showers. Recent model output is very mixed on timing of precipitation, but should rainfall occur, totals are anticipated to be less than 1/10 of an inch. This is primarily due to the models predicting less energy in the atmosphere: CAPE values being predicted under 1000 J/kg, which is less indicative of convective storms. The cause of this is likely from surface winds out of the southwest instead of the southeast which would have brought more moisture to the region from the Atlantic Ocean. Ultimately, impacts to the track remain low as a result, however a light shower may be enough to stop or prematurely end any of the on-track sessions. Saturated air during the morning near sunrise may result in fog through the region.

On the other hand, Sunday's conditions have remained mostly the same from Wednesday's update, barring the maximum temperature. The models have come to a good consensus of convective precipitation around noon to the early afternoon. Mixed-layer CAPE values from the GFS, NAM, and NAM 3km are all above 1500 J/kg, indicating the increased likelihood of thunderstorms in the region. Temperatures are not predicted to be as high as initially thought due to precipitation cooling the area before the maximum temperature normally occurs. However, dew point temperatures in the low 70's will likely cause heat index values in the low 80's.

By: Stephen McCoy

The updated forecast for the ABC Supply 500 remains mostly consistent with the initial forecast, though with some warmer temperatures both days and a slight increase in precipitation chances on Saturday.

The atmospheric set-up for Saturday is similar to the previous forecast, with winds from the south to southeast now throughout the day, which will result in warmer air temperatures. Dew point temperatures are also anticipated to be warmer: mid-60's during the morning increasing to the upper 60's to low 70's in the afternoon. The low levels aren't anticipated to be as saturated as in the previous forecast, however with warmer temperatures, the chances for convective precipitation have increased. Mixed-layer CAPE values indicated by the GFS are now upwards of 1000 J/kg for Saturday. The NAM shows MLCAPE values well under what the GFS is predicting, though surface CAPE values are similar. Regardless, conditions will be similar to those seen today: hit-or-miss showers with a few thunderstorms possible. The models seem to indicate two standout times for precipitation: mid-morning and late afternoon. Impacts remain low as the uncertainty of where/when rainfall occurs is still high, however if showers do occur they will likely stop any on-track sessions. Much like in the previous forecast, fog is possible during the morning.

Sunday's set-up has changed since Monday, as the aforementioned surface low pressure system is now expected to weaken as it approaches Quebec. However a high pressure system sitting over the central Atlantic will cause winds from the south to southwest, resulting in warmer air temperatures for the day; dew point temperatures near 70F will continue from Saturday. Precipitation chances remain the same, though showers and/or storms will be initiated by convection as opposed to the cold front mentioned in the initial forecast. CAPE values are expected to be higher than those for Saturday and may lead to stronger storms. Impacts remain the same due to the models suggesting the highest chance for precipitation being in the early to mid afternoon. Should rainfall occur on Saturday, fog may be possible again on Sunday morning.

By: Stephen McCoy

Near average temperatures are expected for this weekend with a slight chance for isolated showers on Saturday followed by a higher chance for scattered showers and thunderstorms on Sunday as a cold front moves through the region. Timing of the frontal passage could bring precipitation towards the end of the main race, however when looking almost a week out, the impacts are largely subject to change.

On Saturday, a surface high pressure system sitting off the east coast of the US will cause winds from the south to southeast through most of the day; morning winds will be largely variable. Fog may be possible near sunrise as the surface air is expected to be saturated under a temperature inversion. A slight chance for isolated showers exists during the morning to early afternoon as moisture from the Atlantic saturates the air in the low levels of the atmosphere. Precipitation chances will increase if the air at the surface remains saturated through the morning; should showers occur, they will likely be non-thunderstorms. Partly cloudy conditions will be present in the low levels for the remainder of the day.

For Sunday, an upper level trough will be moving eastward through southern Canada and the Midwest US with an accompanying surface low pressure system over the Hudson Bay/Quebec region. A cold front will be extending southward from the center of the system, moving through the northeast US during Sunday afternoon. A few isolated showers may be seen in the area ahead of the front, but the bulk of the rain is expected to move through the region towards the conclusion or after the main race. The current run of the GFS shows mixed-layer CAPE values above 1000 J/kg, suggesting thunderstorms will be present along the front. The high temperature in the afternoon could vary depending on the timing of the frontal passage, though looking at model output, only by a few degrees. South to southwesterly winds at the surface and in the low levels will cause some stronger winds gusts through the day.

By Scott Martin