August 23, 2024

For this week, we will start with the week that was, and that will include the micro climates. Those microclimates did their thing this week over and over.

The week:

The low pressure that brought just a bit of rain last weekend and to start the week was rapidly followed by a cold area of high pressure with air right down from Hudson Bay. That’s the big story of the week. The cool temps, fall like conditions.

Temps over the last 5 days look like:

And the last 3 days:

Temps the last 3 days running 10-15° below average for later August.

Underneath the high pressure, we have seen many valleys experience 30s the last 3 mornings, with coldest pockets going below freezing. Some of those high bogs in the mid to upper 20s.

Dave Carroll of Virginia Tech recorded a high bog temp on the Sods this week of 25°, I had a 29.2° on Canaan Mt Bog, and 29.4°, and 29.6° on The Glades in Garrett County this week.

8/21 and 8/22 @ The Glades

and Canaan Mt bog 8/21 and 8/22 below

and a high Sods bog on 8/21 below

Data from The Glades and Canaan Mt Bog for 8/23 as of the time of this post have not been collected yet, but likely another morning around freezing.

At the Virginia Tech Northern Canaan Valley station,

The last 3 mornings running right around 31°. The high shallow bogs often do a bit better in the ideal summer setups vs the deeper more protected Northern Canaan Valley site, as the northern valley site tends to fog in heavier through the night, and that helps stabilize temps just a bit.

All the microclimates are sensitive to anything that disrupts the heat loss, inversion layer/decoupling. (Moisture, wind, clouds)

Just the other night watching the Northern Valley station temps online, a small pocket of low clouds moved overhead

and just that brief period, the temps that were on the plummet, respond immediately

The high shallow bogs, while just a bit less impacted by moisture as the deeper Valley station, are much more wind impacted. The inversion layer is low, shallow. As long as it’s in place, you can have at times 20°-30° spreads in a very short distance and much more extreme than the deeper valley site to the top of Cabin Mt just 2 miles as the crow flies. These high bogs, especially on the Sods can see these temp spread variations in much shorter distance and much less vertical. >100 feet vertical vs a nearly 1000′ vertical to the valley floor.

First let’s look at an inversion and radiational cooling example:

and radiational cooling

Now put that in to topography and especially high elevated open topography. I mention “open” as forest and trees inhibit outgoing longwave radiation.

There are other examples of this, but the Tucker County-Canaan /Sods area is the meca for this.

This example coming up below is a elevational profile from Canaan Mt across to Cabin Mt with the valley in between. Again, only an example and where the inversion layer sets up, if it does. That is dependent on the big factors of winds and even wind direction, cloud cover, moisture of the air mass. Once the valley decouples from the air mass above, above the inversion layer, it can continue to radiate outgoing longwave radiation. Cold air sinks. Continues to cool. Depending on how moist the airmass is, the temp, and dewpoint will equal, fog will begin to form and then the drop rate slows dramatically. As the fog later grows, it can cap off the deeper valley temp drop by limiting outgoing longwave radiation. This illustration also shows, with that inversion layer and deeper valley, how it’s more protected against winds mixing it out vs whats in the upcoming example following this with the shallow bogs. Another point not made in the illustration. There has been enough data comparison and observations in Canaan that the southern end of the valley, those coldest locations in the instances when the northern valley, which is lower, fogs in quicker and heavier, while the slightly higher, upstream southern end of the valley remains a bit more conducive for radiational heat loss vs the northern end. Overall though, it’s not frequent enough to offset the northern end being the colder end overall.

The Shallow bogs

This would not be a uncommon setup to see occur across the high bogs. Much less vertical, much shorter land distances and much greater temperature spread with the much much shallower inversion layer. These can be scoured out easier by winds, but once established they decouple from the air mass above and at night time hold their own relatively well. Surprisingly so. You can be at Bear Rocks at night and have a stiff breeze and 50° and drop in to the small bog area that’s decoupled and run 20° colder with calm conditions. Now as winds do pick up, it can wipe that out. A rough guess is 10+mph winds can do that. At night, winds tend to relax in many instances with any high pressure in place. A southwest return flow and any stronger wind with disturbances (low pressures) etc moving through would eliminate the inversion.

With these high bogs, elevation in this case matters. They “can” cool more with elevation vs the deeper valley when conditions are right, and they tend to be somewhat drier. That’s 2 favorable aspects at times that favor them being colder. Limited data has been collected, enough so to draw some of these conclusions. Overall these high bogs would give you the overall coolest average temps in the state. Enough elevation to keep daytime maxes lower, but the depression at the elevation is enough to collect the cold air at night and the sum of the 2 would put it below the overall mean of the 4800′ ridges. There isn’t enough lapse rate for the daytime maxes to offset. The daytime max spread from Spruce Knob to the Northern Canaan Valley station is enough to offset the overall mean. However it’s much closer than one would think in saying 3150′ mean is not much different than the 4820′(station ele) mean.

In these inversions. Once above the inversion layer. The lapse rate is often normal. 3800′ above the inversion will be warmer than 4200′ that’s above. However throw in a 4000′ bog, that’s develops an inversion you’ll have that pocket of cold.

Many times you’ll hear or see on social media when folks ask about the temperatures at the Sods. I see many say. Look at the Davis forecast and subtract 10° or 15° etc. Davis, while isn’t a location the cold pools and continues cool.as great as some of these other sites, it’s still a open valley area and Davis at times may run 20° cooler than the ridges at the Sods at NIGHT. This is stressed at night under clear,calm conditions.

Our microclimates, believe it or not are often the first places in the east to see frost. Many times the first place to hit freezing. So far this month the coldest temp recorded on Mt.Washington is 36°. Just this morning. That’s a much different beast though, as it occured with 55mph winds.

and a well publicized location for radiational cooling with low night temps is Saranac Lake. Which has not dropped below 42 this month. They did have some moisture, clouds this week, which inhibits radiation cooling.

Local microclimates have now had frost in each month this summer and this August have been under freezing on 3 occasions while elsewhere in the east, hasn’t been really all that close.

Hopefully someday we have a live station at the Glades.

Radiational cooling is a fascinating subject. If one has kids, or perhaps looking for a school project. This is a experiment worth trying and documenting. Go to 1:30 in(or watch the whole thing) and watch from there.

Bruce Bugsbee of Apogee instruments

Another good read on the subject.

https://now.northropgrumman.com/cold-as-ice-night-sky-cooling-taps-the-temperature-in-space

Ok, on to the drought. That remains status quo

Outside of rain last weekend in to the early week, we turned dry and fall like. Rainfall amounts in general were under a inch. I had .74 at Bittinger 2NW Valley over the 7 day period of 8/13 to 8/20 which is the dates the drought monitor is updated.

many areas in that ballpark .

below normal for the brief period.

For the month

many areas in the Alleghenies in the 3-4″ range for the month which is slightly above normal. Which is mostly thanks to Debby. If you missed out on much from Debby, you’re below for the month after a much below June-July.

The recommended drought tool, that someone mentioned this week is:

A closer view

and this does appear to much better represent the status of areas east.

That did not receive much rain this week but somehow improved

Areas east improved out of the D2 drought with no rain, simply because last week’s maps were not accurate. Again, that’s areas east, not over the Alleghenies. Where stream levels are low, things are still dry. Soil moisture has improved, and the shorter days and cool temps helped that stabilize.

Looking ahead.

a quick look off the GFS downscaled MOS for Garrett County.

We do warm up. Back above normal a bit. Normal highs in the Alleghenies mainly low to mid 70s to end August. Not extreme or anything like the heat waves in June or July.

Dewpoints for a good portion, not all the time remain pretty comfortable and bearable. This off the blended model for Garrett County.

Up above 60 for dewpoints gets a bit muggy, uncomfortable, but for the most part, it’s not all that bad. With the dry air in place frequently over the period. Valley night time temps will be much cooler than modeled. Models do not model for localized topography. In general forecast do not.

Rainfall is looking pretty sparse over the next week. Slight chances early week, and late week. Which late week is plenty far out yet to see some change with that.