A cold drier air mass pushing in later today. Accompanied by wind gust 15-25mph that persist through the night. That gives a standard lapse rate from the valley floor to atop Cabin Mt. Looking at the modeled 850s tomorrow morning off the ECMWF, suggest the tops above 4000′ should range -2 to +4 with colder windchills. Those standard lapse rates in play unless we get a few hour period of calmness across the high valleys that doesn’t look to occur. Therefore temps should hold +3 to +8. Last Friday a.m, the valley did go calm and rapidly fell to -12.8. The coldest Valleys should occur west of the Mts Wednesday where winds look to go calm. You may see some -5 or so readings in those cold spots.
see above prior to winds going calm at northern Canaan station to below after going calm
this isn’t off the table but looks unlikely tomorrow AM for the high valleys.
the ECMWF holds the winds up through daybreak.
the 850s tomorrow morning. Essentially the Wv high ground. Suggest -2 to +4 range above 4000′ . Standard lapse rate would suggest with wind the high valleys +3 to +8.
Then let’s set up the potential for Thursday morning-
I like the modeled ECMWF dewpoints for this vs the GFS because they over time have done a better job giving a idea of the coldest min temps when other factors fall in line. It’s why I thought last Saturday morning could exceed -20 in the coldest spots and it did. The GFS wasn’t close.
The ECMWF has modeled dewpoints for Thursday a.m as(coldest spots will run for those lowest dewpoints)
This is a not a mesoscale model so allow for error in those extremes.
The HRRR out 48hrs in which it goes to every 6 hours shows
HRRR dewpoints
Skies look to be clear with High Pressure overhead
Another factor and a very important one, wind. Does the valley decouple and radiate away all night or does the return flow come in and mix the air and wipe out the potential. It does look like light winds return on the tops. With 850s of -10c, suggest temps should slowly rise from single digits to low teens on top, while holding -10 to -20 in the valley. Unless some wind scours it out.
refer to this post to see what occurs when the wind comes in to play. A 33° Valley rise in a hour. That shouldn’t occur this time around, but any wind will mix the air mass in place and not allow for the disconnect the valley often sees.
currently modeled winds look like
Euro with some return flow
The HRRR showing a bit of return flow by morning, but at this point, we may have already hit rock bottom.
If winds do indeed remain calm across the coldest high valleys, cold pockets Thursday morning. -10 to -20 in range while the tops should run much milder. Let’s see how it plays out.
Likely won’t match this from Saturday morning when the valley fell from -20 to -31 . However we will have a better fresh snow depth in play that helps radiate better…
last Saturday A.M
Vehichle thermometer on Timberline Rd and this matches up good with years of recordings on Timberline Rd when that site would run 4 to 8 colder than the Canaan NWS COOP , as it hit-21. Then the northern site often beat the Timberline Rd site for obvious reasons.
and one more from a XC whitegrass skier Saturday morning
this site only several years old and purposely sited in attempt to capture the coldest mins. It’s important to note, this WOULD NOT be the coldest ever morning in the valley. This site is situated in a colder location than any previous recorded spots. This has 0 to do with climate change, that no day has ever been colder etc.
In the brief history of recording these cold pockets, there often is a lot of doubt by those who do not understand how it works. To be expected. Often times I’d record 20s, High ground were low 50s and the usual, your thermometer is off. However adding pics of those frosty mornings limited that. It’s a unique thing, I encourage all to learn about it if you have interest. If you have no interest further than personal beliefs, may as well move along.
Allegheny Mountains Weather 