September and October showcase some of the most variable weather here in New England. It’s for that reason, I enjoy forecasting and experiencing the weather this time of year. The warm end to summer and beginning to fall has been leading headlines as of late, but it’s looking like our first decent shot of cold temperatures will make a run at us over the weekend.
A pair of weak fronts will put an end to our recent warm stretch through mid-week, but a stronger cold front will cross the area on Friday. The air mass behind that feature is significantly colder, and will move into northern New England over the weekend. Temperatures should top out in the 50s Saturday, but a stiff wind will make it feel colder. A few showers can’t be ruled out that day either. Highs will stay in the 40s Sunday and Monday with lows dipping into the 20s for most of the area. Many mountain locations have a decent shot at seeing their first snow flakes of the season as well.
While many inland towns experienced their first frost/freeze a few weeks ago, the growing season continues for a large portion of coastal Maine. That will likely come to an end late this weekend into early next week.
Portland averages their first frost on Oct 6th, so we’re already running later than average. The latest frost/freeze on record was just last year, November 3rd 2014. The 2014 growing season was the longest on record at a whopping 196 days. Here are the top 10 latest frosts on record for the Portland Jetport.
1. November 3, 2014
2. October 25, 2013
October 25, 1949
4. October 21, 2005
October 21, 1990
October 21, 1985
7. October 19, 1970
8. October 18, 2008
9. October 17, 2007
10.October 16, 1969
October 16, 1948
A Jetport frost Sunday morning would put 2015 tied for 8th latest frost on record. A first frost Monday morning would put 2015 tied for the 7th latest frost on record.
At first glance of the 7 day forecast, you might be thinking, the party’s over. Ski season begins and winter has arrived. I don’t think that’s the case though. The cold shot should be with us for only about three days. Here are some forecast model maps (European Model and GFS Model) showing forecast temperatures around 5000 feet of elevation in degrees Celsius Monday morning.
The cold shot looks rather short lived. Here are those same forecast maps valid next Wednesday morning suggesting a nice warm-up. The images are the European model and GFS Model initialized Tuesday morning.
In addition to the chilly weekend and start to next week, that pattern would suggest some upslope snow in the mountains. Upslope snow occurs when a west or northwest encounters a north to south mountain chain. The air mass is forced upward which forces the air mass to cool and reach its dew point. The result is clouds, and often snow or rain on the western slopes and notches. This is called orographic lift.
Image from http://stormhighway.com
A slightly different enhancement can be felt Crawford, Franconia, and Pinkham Notches due to the funneling effect of the valley in addition to the upslope. While probably not an ideal set-up (I like to see more of a west wind rather than northwest wind) some accumulating snow is possible in the upslope prone areas over the weekend and early next week. Computer models don’t handle this set-up well, but a few are hinting at some accumulations. The top is the GFS and the bottom is the European valid Sunday night. Both suggest some light accumulations of snow.
For an updated look at the weekend forecast for southern and central Maine, check out wgme.com here. I anticipate some postcard looking photos next week. If the foliage can survive the wind, we may have white peaks and colorful valleys. As always, I’d love to see your pictures….