Tuesday July 9, 2024

7/9/2024

Another steamy day with storm threats

I feel like a broken record while discussing the daily outlooks. We are basically on repeat through the weekend with the atmospheric dynamics. Several interior areas may make a run at 90° that will feel like 95°+. The beaches will likely be jammed. For those going, plan on leaving early as the tide will be coming in, and the threat for showers and storms increase in the afternoon.

I am still on the idea of a conditional severe threat. The upper level trough working in may fire storms to the west of the area and bring cloud cover in, which if that happens, it mutes the threat for anything too crazy. Damaging wind and torrential rainfall is the main concern. While the freezing levels dip to around 12-13,000 feet, the air will be hot enough that any hail may melt on the way to the surface, but that may depend on how tall the thunderstorm complexes rise.

"Hey Mike! Have we had more storms
than average this summer?"

A common question I have been receiving as of late. We're already ahead of last year total, but are at roughly 40% of 2022's amount. Looking at the storm numbers on the high end of the chart brings back memories of persistent driveway washouts when my family and I lived in Poland back then. My back hurts thinking about it.

Back to the future: July 9, 2021

I was looking at observations recorded by my weather station in Kennebunk and this day stuck out as 3.26" of rain fell that day. The main culprit of that was Tropical Storm Elsa traveled up the coast.

While having coffee at 3 AM this morning, I dug into the archives and found the 500mb steering level chart and compared it to the European ensemble idea below and noted the strong similarities of the strong ridges to the west and east and the trough dipping down the middle.

The difference this time is the tropical remnants of Beryl are coming in from the west, but the atmospheric river from the Gulf of Mexico is clearly shown.

Looking a bit deeper into the July 9, 2021 outcome on a similar track, a couple of locations ended up with over 5" of rainfall, but many settled in the 2-4" range by the time the rain ended. Elsa was more of a coastal event, which is where amounts were the highest. We were in the midst of drought at that point, and the area received the all rain with minimal impact, with only minor flooding reported in a few locations.

The atmospheric river is where the
flash flooding concern lies

This is a loop from the European model looking at forecast precipitable water values, which indicates how much moisture is in the air column. This is where the alarms are going off for isolated to scattered flash flood potential, in the form of scattered showers and thunderstorms. This is also similar with Elsa's track in 2021. This is a torrential rainfall signal here, not to mention excessive humidity as dew points could push well into the 70s in the red and purple areas.

With all of the flooding that happened in the summer of 2023, along with the big storms in December and January, this is concerning to me for the potential for more road and trail washouts over interior areas.

Guidance has been jumpy and nuts with suggested rainfall amounts over the past couple of days, which isn't surprising as the convective feedback from tropical systems tend to overload the physics. The consistent theme is the mountains get the higher amounts, but the question remains is the timing of the rain axis as it interacts with the trough moving in. This could push the threat further to the north if it comes in later, further south if it comes in earlier. This one idea is in the middle of the road, indicating chances for heavy rainfall for the coastal plain, as well as the foothills and mountain regions, on up into the Great North Woods.

Other impacts and outlook

I am not expecting much in the way of a breeze, outside of downdraft damaging wind potential associated with thunderstorms and tropical downpours. Fog is going to be an issue for several days as dew point values continue to run in the 60s+ through the weekend, and all of this rain will feed into the ground stratus. Off and on showers and storms are apart of the forecast through Saturday (at least) as the strong ridge to the east over the Atlantic blocks traffic, which keeps the frontal boundary stalled nearby, if not over the area until it relaxes later in the weekend.

Stay tuned.

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- Mike

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