Welcome to the weather blog - a regular Monday through Friday discussion of the weather! While the discussions usually will only come on days I'm working, I'll issue special updates when the weather warrants. I will always post to let you know when no discussion is expected if I'm away on vacation, etc. - if no update is here and no info is available, that likely means the server has temporarily gone on the fritz and I will update as soon as technically possible. You'll find a quick weather synopsis linked to the daily forecast at the top of the page, a general non-technical weather summary below, and when available (most days) a detailed technical meteorological discussion will follow by mid-afternoon. My email is contact@mattnoyes.net. This blog is for you, so I hope you enjoy it! -Matt Noyes
General Weather Summary:
New England continues to live life on the "mild side" as mild air has gripped a large portion of the nation. Gradually, this weather pattern will change over the coming days as a strong storm roaring through the Pacific Northwest today - hampering search efforts for the missing climbers in Oregon - redefines the flow of the jet stream winds across the nation. Those of you who read this discussion regularly or follow the weather know how important the jet stream winds are - a corridor of fast wind aloft that steers disturbances and storms, and acts as a thermostat for the atmosphere, separating cold air to the north from warm to the south. The strong storm pushing off the Pacific Ocean Friday will surge eastward, then slow in Southern Canada. A second strong storm will push into the Western U.S. coast on Saturday, into California, and will dive southward across the Southwestern US this weekend. In time, these two storms will interact to fill the Western United States with Canadian cold by the beginning of next week.
In the meantime, a fast flow of the jet stream overhead here in New England means pieces of energy riding our way, with cold air not far to the north, and mild air available from the south. The end of this past week has brought a mild win in the atmospheric struggle, though Friday afternoon's upper level disturbance is driving a cold front quickly southeastward, and this will deliver noticeably cooler air overnight Friday night into Saturday. The result will be scattered Friday afternoon and evening showers along the leading edge to the cooler air - the cold front - then drier and cooler air moves in Friday night. In the North Country, the combination of a west-northwest wind pushing up against the mountain faces, and cool air filtering in, will breed snow showers late Friday night through Saturday morning. In the higher terrain of the Green and White Mountains, a couple of inches of snow may fall early Saturday, giving a wonderful fresh coating to northern ski slopes.
Elsewhere, expect lingering Saturday morning clouds to give way to emerging sunshine and - though the air will be noticeably cooler than Thursday and Friday were - a pleasant afternoon. With a break between disturbances and the jet stream winds aloft poised to ride northward again, Sunday will bring continued mild conditions. An approaching Northern stream disturbance, however, will tug cold air southward out of Canada by later Sunday, and ahead of this cool air expect clouds to thicken from north to south later Sunday, and a few rain showers are possible by Sunday evening. This southward bleed of cold air will not come with any well defined surge, however, and therefore the cold front leading the sagging Canadian airmass will only sluggishly settle southward across New England on Monday. This is likely to bring a pronounced difference in high temperatures from north to south on Monday with plenty of clouds in milder Southern New England, where a few rain showers will be likely. Farther north, clouds and cool air are likely to outnumber breaks of sunshine, and a few snow showers are possible if enough cold air presses south. Expect a similar setup on Tuesday, though a stronger disturbance will ride overhead at the jet stream level, providing a heartier dose of rain and snow to the six-state region, with precipitation type highly dependent on the location of the frontal boundary, but more likely to be raindrops south and snowflakes north.
Meanwhile, let's not forget about the important slug of energy and cold unloading into the Western United States this weekend into next week. Though it will take some time to churn across the Rockies and move into the Ohio Valley next week, it will eventually tap Gulf of Mexico moisture. The most likely scenario is for this Gulf warmth and moisture to significantly overwhelm any Canadian cold very quickly, and this would result in a storm of mostly rain toward the end of next week. The trick comes from the chunk of cold air to the west of the storm - the same air that spills out of Canada and into parts of the Western US this weekend - as it follows the departing storm heading into next weekend. This will set up a chilly weekend leading into Christmas, but an active Pacific jet stream flow will keep bundles of energy streaming eastward across the country, and the next in line will follow in the footsteps of its predecessor, picking up Gulf of Mexico moisture. The difference this time around will be that cold air will be already present in New England. While the final outcome will depend on the storm track - a storm east leaves us cool and dry - there's well-grounded scientific reasoning to expect this storm to track within a couple of hundred miles of the East Coast. An inland track would bring a shot of snow - perhaps Christmas Eve or Christmas Day - as the incoming warmth and moisture collides with the cool airmass in place, though this inland track would also mean a change to rain. A track up the coastline or just off the coast would result in snow for most of us, and a track close enough to the coastline would mean a decent storm. This is why I insist that - for now - there remains plenty of hope for a last-minute Christmas miracle of a White Christmas. Still lots that would have to come together, but still certainly a reasonable possibility.
Enjoy your weekend!
Technical Discussion: Out shortly.
Matt
Matt's Technical Meteorological Discussion: Updated Friday, December 15 at 11:10 AM
Short term features shortwave rippling east and driving band of showers along cold front. Given vort max aloft, these showers should survive the trip in scattered form. As for temps and sky cover, inversion is developing and this will continue to make it harder to break the clouds in advance of shortwave, but increased llvl flow in warm advection ahead of wave should allow for at least a few breaks in the clouds. Still, insolation will be a small factor in temps today given the sky cover and advection does most of the work, tho I think 60 is likely out of reach for most.
Clouds will linger overnight most areas as we await actual shortwave passage, and the combo of cold advection behind cold/occluded front and upslope flow with PVA will change rain showers to snow showers in Nrn Mountains, where heavier snow squalls will likely wait until Sat AM to take hold when upslope flow establishes. Elsewhere, downsloping will help to ensure low levels dry while midlevel clouds move out with shortwave after early morning. Temps will be noticeably cooler from Thu/Fri regionwide, but also a north-south gradient as shot of Canadian cold on cool side of baroclinic zone sinks southward into Nrn NewEng but will be less pronounced south.
Shortwave rippling across Quebec induces warm advection early Sun before cold advection sags cold front southward later Sun with numerous llvl clouds given destabilization with falling temps a few thousand feet above warm ground. Actual sfc boundary to stall over NewEng on Mon and will induce plenty of clouds and at least some sct precip Mon PM near the boundary, likely mostly over Srn NewEng. Both Mon and Tue are truly somewhat tentative, however, as even small shortwave ripples could have moderate consequences along a tightly packed baroclinic zone, tho Tue looks like the more likely candidate for more widespread precip, which will contain at least some snow north of the frontal boundary, likely to lay across Nrn NewEng. The ECMWF is cranking out a monster storm on the front that would be a full-fledged nor'easter with snow on Tue, but given confluent and fast flow, this seems unlikely and thus far the Euro is the clear outlier. Most guidance indicates a wave, but a much weaker and flatter version. There is decent possibility that some of Southern New England could see snowflakes Tue given the tremendous packing of isotherms along this front - even a slight deviation south would mean a better chance of flakes.
Later in the period, I'm still looking at two periods for storms. As described in detail in the General Weather Summary above, the first comes around Thu/Fri. This is energy that's been evident as a large storm on satellite pics as it's been crossing the Pacific - moving S of Alaska yesterday and ready to move into the Wrn US coast on Sat. There, as described in the General Wx Summary above, it will interact with today's Pac NW storm. The signals on this have been steady, which makes sense given a strong upper low that will eject from the SW US and move over the OH valley then S of or over NewEng. The question with this system will be how much cold is available. An established flow of Gulf moisture assures plenty of available moisture and it's likely that the warm will win once again with no strong high forecasted to hold the cold. There will be a northern stream wave and cold front diving SE at the same time period, so solid ptype isn't out of the question, esp in Nrn NewEng where overrunning may begin and cold advection may end the event, tho at this point I'm not so excited about solid over liquid in Srn NewEng.
What I do see here, though, is this storm opening the gates to colder Canadian air late next week as it passes, and a cool Canadian high building in for the weekend leading into Christmas. Thereafter, there is disagreement on the handling of the next Pacific shortwave for the 24th/25th, but I remain rather optimistic that the chances are there for a Christmas snow. My reasoning is a trough axis that will be over the Midwest combined with a strong shortwave that will come racing across the NW US in tight, fast flow, and be ready to drop into this Midwest trof. The key to this setup is the combination of available energy from the shortwave combined with a broad area of low heights across the Ohio and TN valleys. This broad area of low heights will mean the addition of the shortwave energy will have the potential to both shift the trof position eastward to the Ohio Valley, and turn the base of the trof negatively tilted. This is key to getting a large East Coast storm brewing, and given the cold air in place over the weekend, one would expect a good chance of overrunning snow to begin a storm as long as one can make it up this way. From there, it would depend on storm track, tho I think the 850 mb warm temp anomaly in SCentral Canada the 23rd-25th is actually a plus for us to receive snow, as this is indicative of a ridge building over Ontario, and reflected in Ensemble mean MSLP plots as a bubble of high pressure. Though warmth would rebound behind this bubble high, NewEng would still be ahead of the sfc ridge axis, which would be crucial inholding cold air in place after its arrival that weekend. Therefore, I think there's more hope for a White Christmas that we've seen as hope for a White "any other day in December" so far this month. We'll see if nature decides to cooperate.
Make it a great one.
Matt
Monday's Discussion:
5:15 PM: Series of shortwaves next several days comes after ridging and assoc Canadian sfc high breaks down. Nonetheless, dense sfc cold is always sluggish to erode and that's the reasoning for keeping wintry mix in for Nrn NewEng for Wed. Earlier timing of GFS is likely to be the closest to correct, at least with regard to shower initiation thanks to warm advection and overrunning into cold llvl airmass. First upper low will be decaying when it finallly moves NE from the Ohio Valley but will have decent Gulf tap and this will help to generate precip, tho fairly progressive pattern of quickly eastward shifting ridge will help to keep things moving, and fast active flow currently over Wrn US will migrate east. This will keep a parade of shortwaves into NewEng middle to end of week, timed nearly equally between disturbances. Though each will tug at cold air in Canada, the progression of the ridge means not much cold is left to tap by mid and late week, not to mention SW flow ahead of each wave will aid in WAA. This is what leaves me with the thought that Srn NewEng will warm enuf for liquid while Nrn NewEng will be cold enuf for solid precip next several days.
Any phasing of Srn and Nrn streams looks at this point to occur safely out at sea. Well, perhaps not safely, but with no guidance currently supporting the westward phasing we saw in guidance cycles last week, no bona fide reason for deep concern at this stage.
It will get milder before it gets colder...with 850 mb temp anomalies peaking once this weekend, then again middle of next week before deep tropical tapped storm winds up in advance of strong Aleutian energy mentioned in General Wx summary. Close call on whether cold or storm come in first, but pattern shift will begin in earnest with this storm as Ern US trof redevelops and active Pacific flow continues, shifting mean track of shortwave trofs farther south and bringing likelihood for numerous moisture-laden Pacific waves with intensifying sfc waves near New Eng as each wave emerges into the diffluent region downstream from the longwave trof.
Have a good evening.
Matt
