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 and a general non-technical weather summary below, and when available (most days) a detailed technical meteorological discussion will follow. My email is contact@mattnoyes.net. This blog is for you, so I hope you enjoy it! -Matt Noyes
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Matt's Quick Weather Synopsis: Dry air brought clearing skies to most of New England Tuesday night, and Wednesday will continue mostly sunny for Southern New England. An upper level disturbance will move east from the Great Lakes Wednesday afternoon, building Northern New England clouds and spawning late afternoon and evening snow showers and heavier squalls in the mountains. Light accumulations will result, but like Tuesday's snow showers, these may be intense enough to briefly ice roadways in the mountains as they move through. Elsewhere, clouds won't increase until overnight Wednesday night, in advance of yet another energetic disturbance that will move through New England on Thursday. Thursday's system is noteably stronger, and with most of New England spending the day under mostly cloudy skies, bursts of snow will spread from Northern VT Thursday morning, to most of NH by early afternoon, to most of Eastern New England from Eastern MA through Maine by late afternoon. Localized heavy bands of snow will set up anywhere from the NH Seacoast points north and east (especially through Maine), and in these *localized* bands, a few inches of snow may fall in a short period of time. Colder air begins to move in on Friday with a few more snow showers scattered amidst sun and clouds. The forecast becomes tricky for the weekend, but right now Saturday is looking mostly dry with sunshine to start, then increasing clouds late and a chance of snow at night, giving way to a blustery and cold Sunday. -Matt
General Weather Summary: Wednesday begins with mostly sunny skies across just about all of New England as the six-state region lay between one departing energetic upper level distubance to our east, and another approaching from the west. Sunshine will prevail across most of New England with just an increase in high-altitude cirrus clouds ahead of this fast-moving disturbance late Wednesday, and a relatively light breeze from the southwest, teaming with sunshine to boost temperatures either side of 40 degrees. Much like yesterday, the mountains of Northern New England will find flurries and snow showers developing with the passage of this energy center, especially toward sundown and through the first half of the overnight. Later Wednesday night, a new energy center will draw near to New England, and most areas will find an increase in clouds during the overnight.
The overall weather pattern has been consistent this week - keeping the northern (polar) and southern (subtropical) jet streams separate - thereby keeping the significant cold and energy separate from southern moisture. These streams have been phasing to our east, across the Western Atlantic, and that's where larger storm centers have been taking shape. By Thursday, the merger of northern energy and southern moisture will occur closer to New England, at the same time a strong northern stream disturbance drops across the six-state region. The result is likely to be some enhancement to snow showers as they move across New England on Thursday, as the interaction between these two disturbances evidences itself as a weak disturbance at the surface, known as a "trough," which represents a wind shift and a line of enhanced precipitation. In fact, with very cold air moving in about 18,000 feet high in the sky - to the tune of 40 degrees below zero - a condition known as "instability" will result. This instability is the difference between the frigid air aloft and *relatively* warm air at ground level, and the presence of instability favors cloud and precipitation development - remember that warm air rises, and this type of a setup allows warm air to rise high in the sky, like a head of steam, resulting in clouds and often precipitation, as well. The combination of this instability and the nearby trough will result in a developing "Norlun Instability Trough", which is a fancy term that refers to the atmospheric setup whereby instability and a trough team together to provide enhanced snowfall in thin, localized bands, which can drop quickly accumulating snow in the extremely localized areas that are affected. It appears right now as though the heavier bursts of snow will begin as the approaching northern stream energy encounters the Green Mountains of Vermont - lighting up some of these heavier bursts across Northern Vermont Thursday morning. As the disturbance moves east, and the Norlun Trough begins to take shape, these bursts of heavier snow will expand in areal coverage while moving southeast across Central and Northern NH by early afternoon, then expanding from Eastern Southern New England all the way through Maine by late afternoon and evening. Embedded in this expanding area of snow showers will be the localized bands of heavier accumulating snow, and while we'll monitor radar imagery tomorrow to stay on top of these bands, the most likely areas for a few inches in only a few hours would be in the aforementioned areas north of the MA/NH border and especially in Maine.
After scattered flurries and snow showers Thursday night, the Norlun trough may linger across New England on Friday morning before being pushed southward as a surge of cold air moves in from the north. With the passage of this trough on Friday, marking the leading edge to a new installment of cold air, a few more snow showers or a heavier squall are possible betweeen intervals of sunshine and clouds. With a sliver of cold and dry air in place on Saturday, expect a mainly dry day with sunshine to start, and increasing clouds to finish.
From this point on, the forecast remains quite tricky. While Thursday and Friday's forecast is a bit tricky due to finely tuned forecasts on the regional scale, this weekend's forecast hinges upon an understanding of the large-scale weather pattern. With multiple energetic disturbances still dropping in from the north, and moisture beginning to finally ride northward to meet the energy, we will be very close to phasing the streams over or near New England. There are two ways this could go: 1) Energy slides through quickly, passing through Saturday night with a round of light to locally moderate accumulating snow and ushering in cold as a storm develops just to our east, or 2) Energy merges as it nears New England, then taps the southern moisture for a more substantial snowfall Sunday night, then allows cold air to stream in. At this point, I'm favoring the former solution, bringing thickening clouds in later Saturday, dropping accumulating snow Saturday night, then rushing a surge of arctic air in for a Sunday that would begin with lingering snow in some areas very early, then give way to windy breaks of sunshine and a few afternoon flurries, but you know I'll keep you posted on how this shakes out.
Have a wonderful Hump Day!
Matt
Matt's Technical Meteorological Discussion: Updated Wednesday, February 22 at 1:30 PM
A very tricky forecast period lay ahead from Thursday through the weekend. But let's take this one step at a time.
Multiple surface fronts evident on late morning national surface analysis with a stationary front parked north of NewEng and holding truly arctic air at bay, warm front progressing slowly ENE across NY State but losing warm frontal characteristics and ready to transition to trof that will be tricky for us, and stationary front over SE US focusing deeper southern stream moisture across Arklatex region and Lower TN River Valley.
One northern stream shortwave scooting east is producing good cloud signature across Ontario and Quebec and cumulus are building in increasingly favorable convective environment across Northern NewEng. Though later to fire up than yesterday, snow showers and heavier snow squalls will once again locally reduce visibility to 1/4 mile toward sunset, and snow showers/squalls will continue through the first half of the overnight as dynamic forcing continues with passage of vorticity maximum.
Of course, this is probably the most straight-forward part of our forecast. Shortwave located over Chicago at midday will race eastward and bring increasing clouds all areas overnight Wed Ngt. The overall pattern certainly favors shortwaves of all shapes, sizes and trajectories firing over NewEng with confluent flow into a trof axis just barely to our west over Western NY/PA. This is undoubtedly an uncomfortable synoptic position to be in, as it implies diffluence aloft is centered directly over NewEng, and this is certainly a pro to nearby storm development. For the time-being, tho, major storm development is precluded by two factors - both a lack of phasing, and, moreover, a lack of a strong enough shortwave in the short-term to close a low off and get a closed circulation developed.
Nonetheless, a new shortwave over Minnesota Wed PM dives SE and moves immediately S of NewEng during the day on Thu. This puts NewEng in a weak warm advection regime in the low levels with dynamic forcing thru the entire day. At the same time the dying warm front moving into NewEng takes on the role of a trof, colder air moves in aloft with 500 mb temps of -36 to -38 C by day's end. This combination of differential advection through the atmosphere will mean increasing instability thru the day, with the trof serving as a focus for the instability by providing enhanced surface and boundary layer convergence between bubble high east of NewEng, strengthening low SE of Nantucket by several hundred miles, and southwest flow around primary low over Southern Quebec. With time, the low-level convergence is actually enhanced thanks to increasing easterly flow, and the result is a well-defined Norlun Instability Trough, slowly moving east. That being said, I'm not sure this is purely by definition a Norlun Trough, as it is still in the process of transitioning from a decaying warm front to a trough, and there is a weak wave of surface low pressure developing along it. Nonetheless, this entire combination of factors should begin by producing an area of snow showers and heavier squalls across Northern VT Thu AM ahead of this developing surface wave, then as this area of lift migrates east, it should also expand southward both in response to the shortwave south of NewEng, the assoc jet streak producing diffluence in the left front quadrant over Southern NewEng, and the southward expanding instability assoc with cooling aloft. The result is to spread the snow showers and bursts of heavier snow in a fan shape E and SE from the initial point of convection in Nrn VT, expanding to include Ern MA, NH and most of ME by afternoon. Pinpointing localized bands of heavy snow in situations like these - as regular readers know already - is a very difficult task, but it makes sense that with the trough shifting to Eastern NewEng later in the day, and a SE flow ahead of the trough, bands of heavier precip should be most easily found later in the afternoon through Eastern NewEng. As for QPF, the NAM is over a tenth of an inch, and the GFS goes over .25" in the White Mountains, so they're having no problem keying in on precip production. The problem here...and what we have to step carefully about, is the mesoscale nature and dependency of an event like this. If the models are accurate, it's possible to really nail a forecast, but if they waver again - like they did by slowing the eastward progression of the trof between the 00Z and 12Z runs - then you're ruined. The best path, in my humble opinion, is to acknowledge that accumulations of a few inches in a few hours are possible in heavier bands of snow, outline the areas that are vulnerable, and those that are *most likely* to contend with heavier bands (east side of the trof - Central/Ern NH, ME seacoast, Ern MA) then go from there. Additional factor is surface temps, which after a dry start should be able to rebound into the upper 30's in Southern NewEng and this would cut back on accums and perhaps even throw a few raindrops into the mix. Seems like best bet here is to go with a thick sloppy coating Eastern Southern NewEng, higher amounts in the colder air farther N where a few inches are possible in a short time Thu afternoon with convective development of snow squalls. Indications are that this activity will not wane much the first part of Thu ngt as it shifts E into ME, so quick accumulations of a few inches are possible thru much of ME Thu Eve/Ngt.
Merging vorticity centers diving SE over far Srn NewEng on Fri will be the impetus for pushing trough into ME Thu Ngt with warm advection ahead of them in llvls, then will whip this trof southward Fri AM as strong cold NW flow sets in. Additional flurries and squalls are possible with this southward whip of the low level convergent zone, then upper level cold core allows for convective elements of snow again later Fri afternoon.
Weekend fcst plenty difficult earlier this AM with 00Z runs split into very distinct camps of how to handle energy diving over NewEng - GFS was putting out a significant Sunday evening snowstorm as low cranked up almost overhead and had plenty of model support, while NAM had its own camp of diving flatter and faster vort S of NewEng Sat ngt. My choice this early AM was to go with the flatter and faster solution given the pattern of late, and thankfully, GFS has come in line, so my hope is that this was the right way to go. Bottom line is that with ridge expanding over and E of Greenland, but no amplified ridging upstream from NewEng, this favors positioning the mean trof position to our east - barely - and keeping shortwaves moving thru us fairly quickly. With a track S of NewEng, though, the story isn't over there at all. I still see a potential minor to moderate accumulating snow event even with this flatter solution for Sat Ngt! NAM suggests easterly flow has already established at 850 mb ahead of this closed low level circulation according to model progs, by the time it moves over the Eastern Great Lakes. I don't have to tell you, my technical readers, that an easterly flow means we have an entire ocean available for moisture. 500 mb jet streak is about 90 knots over OH Valley Sat Eve which puts NewEng in strongly diffluent left front quadrant, and just behind departing shortwave ridging to further enhance diffluent aloft. Low level warm and moist advection will be strong, and while Northern NewEng still waits to see the exact track of the vort before we get too excited, I see little reason to doubt a snow event of widespread plowable snow for Southern NewEng. Now, before we go too far off the deep end, GFS is much more open with this circulation, but this model is just now catching onto the progression of the wave, and the GGEM appears more in line with the ETA with a well defined circulation as the system moves east, so I think our chances for a Saturday night snow are looking decent right now.
To buy a faster solution means we also need to buy the faster influx of cold air, so Sunday I'd expect highs only in the teens north and lower 20's thanks largely to downsloping flow south. Cold air should be reinforced by second arctic frontal passage - perhaps with surface wave if you buy the GGEM - on Monday.
That's all for today - I think I've sufficiently peaked all of our interests in Saturday night...now we wait to see if nature cooperates.
Matt
