NNE Fall Thread

[dryslot]

Time for a fall thread with temps becoming more frequent in the 60's and lows in the 30-40F range at night, 36.9F was the low here last night, May be a frost possibly here thurs night.

[eyewall]

Can't wait for foliage

[klw]

Looks like 29.7 was the low this morning.  There was some frost in the yard but very light.  I think this is the earliest frost in the 6 autumns we have been in the house.  Snow by the end of the month?

[OceanStWx]

Gorham, NH got down to 27 this morning. That's the coolest I've seen in our area.

 

Good news though, sounds like we can end the growing season in at least a couple zones. No more frost/freeze headlines!

[tamarack]

29 or 30 at my place, 1st morning that I had to scrape the windshield.  Unfortunately the pickup's heater, which limped thru last winter, appears to be kaput, so it was a chilly commute.  Hate having to wear a jacket in Sept, but might have to rethink that preference.

[MainePhotog]

Good to see a new fall thread. Just what I was waiting for. Adios Summer!

 

A tepid low of 43.2°F here this morning compared to other temps seen here.

[powderfreak]

I didn't see any frost on the grass because we fogged out, but all moisture on the car was frozen this morning. Luckily liberal amounts of windshield washer fluid made it so I didn't have to scrape. 34F was the low.

[dendrite]

Min 37.3F...we would've threatened 32-34F if it wasn't for the Sc deck that moved in around 3am. That was a bummer, but we'll give it another shot Thu night.

[dryslot]

Yes, I'm thinking we have a shot as well here on thurs night, Will have to wait and see how it plays out, Not uncommon for us to get our first frost around the 18th or so

[Lava Rock]

I've got to seed some new lawn this weekend. Hope it'll take.

[wxeyeNH]

Min 37.3F...we would've threatened 32-34F if it wasn't for the Sc deck that moved in around 3am. That was a bummer, but we'll give it another shot Thu night.

Wow, I beat you.  36.3F with some frost on the lawn.  Was surprised it got that low.  I got up around dawn and saw the low deck just to my south but it didn't get here.   I'm sure down the road there was a more widespread frost.

[MarkO]

I'll check the Davis when I head up this weekend, but the Davis down the road was at 31 at 7AM. Of course he's about 300' lower than me, so I probably didn't dip below freezing.

[powderfreak]

Mitch posted this in the Winter Thread, although I think it may get some more use in here as most of those posters (and for good reason) really could care less.  It seems to be more relevant to NNE from northern NH through the Greens.

 

http://www.wdtb.noaa.gov/courses/winterawoc/documents/color_PDFs/IC56.pdf

 

Some great information on orographic snows out in the western U.S. but a lot of the processes apply here too.

 

Precip efficiency... this is where the width of the Green Mountains comes in.  We were just talking about how Mansfield isn't that aesthetically pleasing in the sense of a single summit cone, but the width makes up for it in creating snowfall/precip.

 

 

Seeder-feeder we generally see a lot I think...during big storms, or smaller systems like clippers where there's precipitation falling aloft but then gets enhanced by precip processes in the low levels over the mountains.  Backsides of nor'easters can often pound the western slopes and Spine/ski areas with that deformation aloft coupled with the upslope snow occurring underneath it.

 

 

This one I don't think really matters here...the mountains aren't tall enough to really make a huge difference.  But I guess it could be the difference between just some flurries and light snow over the high elevations and just cloudy skies in the valleys.  But I can't imagine the relief is large enough to really make a big difference here like it may in the Cascades at 10,000ft or something.

 

 

This reminds me of fall-like patterns where we are getting those cellular grauple showers spark over the mountains.  I'm not sure if its exactly the same thing...but I think of the low level instability and how the mountains provide that lift to get the cells going.

 

 

 

I also found it interesting how over the Cascades and Sierras, studies have shown large droplet sizes with small droplet concentrations...while over the interior mountains like the San Juan, orographic precipitation includes small droplet radii but very dense droplet concentrations.  The later sounds more like what we see here in the Greens...when upslope rain is occurring, its often "sheet rains" that can have droplets so small it looks like mist blowing in the wind, but once you go outside in it, you realize that you are soaked solid very quickly, and looking in puddles makes it look more like its pouring. Its that very small droplet radii, but very high droplet concentration. 

 

I know J.Spin has noted that as well...its like you can immediately tell when rainfall has become orographic in nature just based on the type of rain and how it looks. 

[eyewall]

Mitch posted this in the Winter Thread, although I think it may get some more use in here as most of those posters (and for good reason) really could care less.  It seems to be more relevant to NNE from northern NH through the Greens.

 

http://www.wdtb.noaa.gov/courses/winterawoc/documents/color_PDFs/IC56.pdf

 

Some great information on orographic snows out in the western U.S. but a lot of the processes apply here too.

 

Precip efficiency... this is where the width of the Green Mountains comes in.  We were just talking about how Mansfield isn't that aesthetically pleasing in the sense of a single summit cone, but the width makes up for it in creating snowfall/precip.

 

Precipitation_Efficiency.jpg

 

Seeder-feeder we generally see a lot I think...during big storms, or smaller systems like clippers where there's precipitation falling aloft but then gets enhanced by precip processes in the low levels over the mountains.  Backsides of nor'easters can often pound the western slopes and Spine/ski areas with that deformation aloft coupled with the upslope snow occurring underneath it.

 

Seeder_feeder.jpg

 

This one I don't think really matters here...the mountains aren't tall enough to really make a huge difference.  But I guess it could be the difference between just some flurries and light snow over the high elevations and just cloudy skies in the valleys.  But I can't imagine the relief is large enough to really make a big difference here like it may in the Cascades at 10,000ft or something.

 

sub cloud sublimation and evaporation.jpg

 

This reminds me of fall-like patterns where we are getting those cellular grauple showers spark over the mountains.  I'm not sure if its exactly the same thing...but I think of the low level instability and how the mountains provide that lift to get the cells going.

 

Upslope_release_potential_instability.jpg

 

 

I also found it interesting how over the Cascades and Sierras, studies have shown large droplet sizes with small droplet concentrations...while over the interior mountains like the San Juan, orographic precipitation includes small droplet radii but very dense droplet concentrations.  The later sounds more like what we see here in the Greens...when upslope rain is occurring, its often "sheet rains" that can have droplets so small it looks like mist blowing in the wind, but once you go outside in it, you realize that you are soaked solid very quickly, and looking in puddles makes it look more like its pouring. Its that very small droplet radii, but very high droplet concentration. 

 

I know J.Spin has noted that as well...its like you can immediately tell when rainfall has become orographic in nature just based on the type of rain and how it looks. 

 

This definitely makes a lot of sense. This is not necessarily terrain related (although shadowing was likely a factor), but last winter I noticed we had quite a few sugar grain events which hurt ratios. Even in the bigger snows we had snow growth become an issue at times. We rarely had parachutes or larger dendrites.

[CoastalWx]

PF, what you describe may be a function of warm process type rains. Those kinds of droplets usually develop in an environment >32F. 

[OceanStWx]

PF, what you describe may be a function of warm process type rains. Those kinds of droplets usually develop in an environment >32F. 

 

Likely culprit, especially when you consider if it's raining at the mountains and lift is being generated by the mountains, most if not all of that column must be above freezing.

[powderfreak]

PF, what you describe may be a function of warm process type rains. Those kinds of droplets usually develop in an environment >32F.

Yeah, because you can get those sheet rains in select synoptic events too...but when it's orographic in nature, we always get these small sheet rains. I figured it had to do with cloud depth.

Like right now we are getting it. Looking at the radar on phone it's very orographic in nature. The bullseye is MVL, which isn't getting anything but here on RT 108 it's small droplet rains that come down in waves/sheets. I just associate the real small droplet stuff with orographics.

[CoastalWx]

Likely culprit, especially when you consider if it's raining at the mountains and lift is being generated by the mountains, most if not all of that column must be above freezing.

 

Yeah pretty much what I thought as well. I like those events though...surprisingly efficient rain producers.

[powderfreak]

Likely culprit, especially when you consider if it's raining at the mountains and lift is being generated by the mountains, most if not all of that column must be above freezing.

Ahhh, so the large droplet stuff forms below freezing? I'm trying to figure out how this would vary in orographic precip out west too...the Sierra study showed large radii and less concentrated drops, the Rockies had small radii and dense concentration. I figured it was a moisture content deal...not temps.

[CoastalWx]

Ahhh, so the large droplet stuff forms below freezing? I'm trying to figure out how this would vary in orographic precip out west too...the Sierra study showed large radii and less concentrated drops, the Rockies had small radii and dense concentration. I figured it was a moisture content deal...not temps.

 

I can see the small droplet stuff for the front range of the Rockies. It's almost apples to oranges though as to the mechanisms of precip for the San Juan and Sierra. One is driven by a strong moisture laden jet slamming into 12,000ft peaks. The other is more from westerly flow and/or synoptic upper level lows moving across the four corners. I'm sure the lack of upward motion probably has something to do with it across CO.

[OceanStWx]

Ahhh, so the large droplet stuff forms below freezing? I'm trying to figure out how this would vary in orographic precip out west too...the Sierra study showed large radii and less concentrated drops, the Rockies had small radii and dense concentration. I figured it was a moisture content deal...not temps.

 

It's certainly easier to get large droplets that way. Because ice crystals are forming from deposition of super-cooled water droplets, then fall and melt, collecting more super-cooled droplets on the way. Otherwise in a warm cloud you are relying on collision and coalescence to grow a drop before it falls.

 

The Intermountain West is also going to feature a lot less salt nuclei than the Sierras.

[powderfreak]

Thanks Coastal and OceanSt... great discussion on a slow weather day. 

 

I just always sort of assumed it had to do with how high up in the atmosphere it was formed...like stuff way up there (thunderstorms with tall tops, etc) would be large droplet...while the low level stuff such as orographic precipitation, ocean effect rain showers, surface convergence, etc was the small droplet stuff that produces the mist/drizzle/sheet rains.  I guess that is probably the case but I was assuming it for the wrong reasons.  I guess I didn't put together the temperature correlation, just figured way up high in the atmosphere there's more time for the droplets to grow large like in a thunderstorm, vs. low level processes create the small drops. 

[powderfreak]

It's certainly easier to get large droplets that way. Because ice crystals are forming from deposition of super-cooled water droplets, then fall and melt, collecting more super-cooled droplets on the way. Otherwise in a warm cloud you are relying on collision and coalescence to grow a drop before it falls.

 

The Intermountain West is also going to feature a lot less salt nuclei than the Sierras.

 

A very good point.

[dendrite]

Euro came in a little south and colder with that high on Thu/Fri. -2C 850s over my head in the AM...-4C near the Canadian border and 0C near the NH/MA line. MET/MAV is 29/35 for CON right now with low 20s up in Coos.

[OceanStWx]

Euro came in a little south and colder with that high on Thu/Fri. -2C 850s over my head in the AM...-4C near the Canadian border and 0C near the NH/MA line. MET/MAV is 29/35 for CON right now with low 20s up in Coos.

 

We're going 58 for PWM, which would tie the record cold high temp. CON is a ways off, the record being 54.

[dendrite]

We're going 58 for PWM, which would tie the record cold high temp. CON is a ways off, the record being 54.

I'm racking up the 50s highs this past week. 59F today, 58F Sun, and 56F Sat.

[powderfreak]

BTV going 27F here on Thursday night.

 

 

CONDITIONS ARE IDEAL FOR A WIDESPREAD FROST/FREEZE EVENT THURSDAY
NIGHT...AS STRONG HIGH PRESSURE SETTLES SOUTHEASTWARD ACROSS THE
REGION FROM ONTARIO AND SWRN QUEBEC. 1000-500MB RH VALUES DROP
BELOW 30 PERCENT...AND ANTICIPATE GENERALLY CLEAR SKIES WITH LIGHT
WINDS. WILL LIKELY NEED FREEZE WARNINGS FOR MOST SECTIONS...EXCEPT
FROST ADVISORY FOR THE CHAMPLAIN VALLEY WHERE THE MODERATING
INFLUENCE OF THE WARMER LAKE WATERS SHOULD LOCALLY PRECLUDE A
FREEZE. TEMPS WILL RANGE FROM 33-36F IN THE CHAMPLAIN VALLEY...AND
GENERALLY MID 20S TO LOWER 30S ELSEWHERE. HAVE MAINTAINED WORDING IN
THE HAZARDOUS WEATHER OUTLOOK CONCERNING THIS POTENTIAL...AND THE
FREEZE WILL BE CLIMATOLOGICALLY EARLY BY 1-2 WEEKS IN MANY AREAS OF
CENTRAL/ERN VT AND THE ST. LAWRENCE VALLEY OF NY.

[Ginx snewx]

BTV going 27F here on Thursday night.

CONDITIONS ARE IDEAL FOR A WIDESPREAD FROST/FREEZE EVENT THURSDAY

NIGHT...AS STRONG HIGH PRESSURE SETTLES SOUTHEASTWARD ACROSS THE

REGION FROM ONTARIO AND SWRN QUEBEC. 1000-500MB RH VALUES DROP

BELOW 30 PERCENT...AND ANTICIPATE GENERALLY CLEAR SKIES WITH LIGHT

WINDS. WILL LIKELY NEED FREEZE WARNINGS FOR MOST SECTIONS...EXCEPT

FROST ADVISORY FOR THE CHAMPLAIN VALLEY WHERE THE MODERATING

INFLUENCE OF THE WARMER LAKE WATERS SHOULD LOCALLY PRECLUDE A

FREEZE. TEMPS WILL RANGE FROM 33-36F IN THE CHAMPLAIN VALLEY...AND

GENERALLY MID 20S TO LOWER 30S ELSEWHERE. HAVE MAINTAINED WORDING IN

THE HAZARDOUS WEATHER OUTLOOK CONCERNING THIS POTENTIAL...AND THE

FREEZE WILL BE CLIMATOLOGICALLY EARLY BY 1-2 WEEKS IN MANY AREAS OF

CENTRAL/ERN VT AND THE ST. LAWRENCE VALLEY OF NY.

congrats, enjoy the first flakes this weekend

[powderfreak]

Euro came in a little south and colder with that high on Thu/Fri. -2C 850s over my head in the AM...-4C near the Canadian border and 0C near the NH/MA line. MET/MAV is 29/35 for CON right now with low 20s up in Coos.

 

For MVL the MET/MAV is 23/30F... pretty big difference lol.  23F is like no contest everything is frozen solid, 30F is still freeze but not quite to the same level.

[powderfreak]

congrats, enjoy the first flakes this weekend

 

Doesn't look like any real chance this weekend...moisture moves out before the cold arrives.

 

Early next week may have some summit flurry potential though.