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:
Monitor latest river observations and forecasts from the Northeast River Forecast Center, a branch of the National Weather Service, here.
Steady and heavy rain will lead us into the weekend, resulting in flooding of streets, streams and some rivers. This heavy rain comes as New England sits just on the cool side of a battlezone between tropical warmth and Canadian cool set up just off of our coastline. Though cool air will dominate over the Northeast this weekend, warmer and drier times lay ahead for next week.
In the meantime, rain will continue lifting across New England throughout our Friday. The intensity of the rain will vary, and that variability will be the result of multiple waves of low pressure rippling along a frontal boundary sitting just offshore. This front, of course, has a history here in New England, as its passage brought the severe thunderstorms of Wednesday afternoon, and the shift of wind associated with it allowed colder air to spill southward out of Canada. That same front, draped from north to south and located east of the Atlantic Seaboard, represents the edge of each airmass, and a battlezone with an associated wind shift that will focus each burst of moisture as they march north, directing them toward New England. Along this front, waves of low pressure will develop, further enhancing rainfall. The front isn't the only important player, however, as there are disturbances on both the warm and cold side of the front that bear watching. In the tropical air, a strong disturbance that began as a tropical wave, the seed of tropical cyclones, has been traveling north from the Bahamas. This disturbance produced a large blossom of thunderstorms early Friday morning as it moved over the Gulf Stream, and appeared very close to a tropical system, but as the storm moves over colder water, it will transition to something decidedly non-tropical. But what it WILL carry with it is a copious amount of tropical moisture and warmth that will be available to feed into our nearby frontal boundary and each area of low pressure that ripples by, resulting in periods of tropical downpours. To our west, in the cold air, is a large energy center that's swirling over the Virginias, representative of lots of energy and a pool of cold air aloft. This disturbance is the same one I wrote about in yesterday's discussion, which had been moving across the Ohio Valley, and the cold air it carries aloft has helped to carve the jet stream winds southward over the Eastern Seaboard, leaving those same winds recoiling from south to north just offshore. The result will be for these southerly winds aloft to carry the gobs of tropical moisture northward and over Eastern New England, cranking out heavy rain as the tropical warmth collides with our cool airmass that's held Friday temperatures in the 40s and will keep them there through the overnight for most of us. Meanwhile, as the rain cranks out, so too will the winds, gusting from the northeast at up to 40 mph as the strongest in a series of low pressure waves ripples north along the front and toward New England. Check out the amazing satellite and radar composite, showing all of the players, here: 
The many facets of the storm bring a variety of concerns. Chief among them is the rain, which will fall on the cool side of the aforementioned front, and in this case that will be over Eastern New England. The axis of heaviest rainfall will likely produce over 4" of rain with perhaps a few spot amounts to 6", but the biggest question is exactly where this heaviest rain falls. Friday morning meteorological guidance suggests the heaviest rain may stay over the fish just east of New England and over Cape Cod, but when tropical moisture is involved and it's colliding with cool air, often our guidance is too far east and a bit underdone for rainfall amounts, so the forecast of 4"+ in Eastern Massachusetts and Rhode Island still looks decent. Amounts will drop of quickly in the drier air of Northern and Western New England, though Western MA and Western CT will get into heavier rains during the day on Saturday. The 2-4"+ rains for Eastern Southern New England will be sufficient to exceed flash flood values in some spots, meaning flooding of streets and streams is possible through the overnight. As this water runs into our rivers I'm expecting most rivers to come into moderate and minor flooding Saturday into Saturday night, meaning flood weary residents along the Merrimack River basin points south into Northern Rhode Island and the rest of Eastern Massachusetts will face renewed flooding. As linked at the top of this discussion, you can follow river levels from the National Weather Service. In general, I expect the floods of this weekend to fall short of the floods in April for most folks, because of the combination of no snowmelt, and leaves on the trees that mean trees are drinking more water than they were one month ago. These floods, therefore, will not be reminiscent of the floods from last May, nearly one year ago to the date. Expected rainfall totals are shown here: 
As for northeast winds, they will increase to 40-45 mph gusts Friday evening and night, and this will churn the seas to 15 feet overnight. At the same time, the highest astronomical tides since last April's storm and coming off the recent New Moon will occur over the next 24 hours, and this raises concerns for coastal flooding at east and northeast facing coastlines both at the high tide Friday night between 1 and 2 AM, then again around 2 PM on Saturday. This flooding also will not be as bad as April's storm, but will be minor to perhaps low-end moderate in a few spots, and beach erosion will resume on already hard-hit beachfront dunes and land. Remember that coastal flooding can occur a couple of hours either side of high tide.
Heading into Saturday, the energetic disturbance over the Virginias and a piece of the tropical moisture will merge, resulting in a weakening storm center backing westward directly over New England. The counter-clockwise flow of air around this swirling storm will actually yank enough dry air northward to taper showers considerably across Eastern New England, and a few breaks of sun aren't impossible, especially on Cape Cod and the Islands, Saturday afternoon. Farther west, however, the mix of moisture and energy with cooling temperatures aloft will be quite favorable for a stubborn band of persistent rain to linger over Western MA, Connecticut and Southeastern New York. It's actually during the day Saturday that these southwestern locales will see your heaviest rain of the weekend. Elsewhere, though Eastern locales will see drying, it's truly Northern Vermont and far Northern New Hampshire that will see the most drying, with a blend of sun and clouds allowing temperatures to rise into the 60s there, while the remainder of New England stays in the 40s under the rain west, and in the 50s elsewhere. At the surface, the counter-clockwise flow around the westward regressing storm center will provide what you'd expect with it - a north wind in western areas, and a southeast wind in eastern New England.
As the jet stream trough around the large upper level storm slowly
pulls east on Sunday, the energy aloft will be quite slow to drift overhead, meaning bands of clouds and showers remain in the forecast,
though I do expect improvement! Increasing amounts of dry air will at least allow for several more breaks of sun, and therefore slightly milder temperatures, than Saturday. After a break in the action on Monday,
clouds will likely return with a chance of showers Monday night thanks to warmer air
trying to move in, and that warmer air is expected to be with us for most of next
week, and may well be drier than normal for a couple of days until a chance of thunderstorms at the start of the Memorial Day weekend.
Here's to a wonderful weekend!
Matt
Matt's Technical Meteorological Discussion: Updated Friday, May 15 at 2:25 PM
Stationary front off the coast will continue to focus waves of low pressure that in turn are focusing available tropical moisture and feeding into cool dome. Did you see the satellite imagery of the tropical wave this morning? I'd swear that thing was a tropical storm with what appeared to be a closed circulation and QuikScat imagery approximating 50 knot winds. Nonetheless, the northern trek put it over cooler waters and it has been undergoing a transition to a cold core system. Chances are good that even though the system was asymmetric warm core Fri AM is still wasn't truly tropical given the band of showers and thunder extending south of it and implying some sort of weak frontal system, though convection was awfully impressive! Now that storm is a bundle of deep tropical moisture that is heading due north in the southerly midlvl flow. 500 mb analysis shows the ridge east of ME that will aid in at least hooking some of this moisture east, tho ME coastline should still get a good soaking of at least a couple of inches of rain as we saturate right thru the dry boundary layer. Farther south, I had to shift my thinking for heaviest rain axis east with 12Z guidance, tho not quite as far east at the guidance given water vapor and radar trends indicating heaviest precip still may fall over most of Ern MA, not just Cape as indicated by models. Basic difference in the 12Z runs was a weaker and therefore somewhat faster wave along the front, thereby not forcing the low level thermal gradient as far inland. Nonetheless, the 850 and 700 mb centers go far enough west to support the idea of most of Ern MA getting highest QPF, which should be somewhere around 4". Someone will see half a foot of rain, but nailing that down depends largely on the location of the heavy precip axis. Nonetheless, most rivers in Ern MA will come into flood tonight and Saturday with mostly minor but perhaps some moderate flooding. Presence of trees with leaves drinking moisture and absence of snow in mountains all spell less severe flooding than April storm, and progression of heavy rain band along with very different setup aloft means this will not be similar to the floods of about one year ago that were so devastating. Nonetheless, flash flood guidance will be attained in some of Ern MA, and so flash flooding a concern overnight with heaviest rain.
With upper low gradually drifting north on Sat, sfc low gets pulled W and rain will fall on west side of low, as it did today on west side of vortex. This means cold rain Wrn MA/CT, tho dry slot that comes in late Fri ngt brings much less precip to Ern areas Sat and tho CC/Islands may get some sun, most areas will hold onto clouds even tho sfc wind becomes SE rather than NE. Excited for Nrn VT/far Nrn NH where drier air brings sun and 60s. Meanwhile, the instability resulting in convective downpours over SW PA/WV Fri will be wrapping over the mid-Atlantic with very steep 850-500 mb lapse rates over entire Mid-Atl on Sat for strong thunder with damaging winds and hail that may surprise some forecasters there, esp since this area is not even in general convection from SPC as of this writing (Ern PA to most of NJ/MD/DE). That instability wraps off the coast, then hooks north and to a lesser degree is over NewEng on Sunday, which backs up fcst for convective showers still popping up. If onshore flow verifies, we're stuck in the soup again on Sunday, and that seems increasingly likely.
Returning warmth, however, still looks on track next week.
Matt
Tuesday's Discussion:
2:15 PM: Short on time but bottom line for today is weak vort already
producing convection across Finger Lakes should be bale to carry this
convection and generate new convection thru Mohawk Valley of NY then
into Srn VT/NH and Central/Wrn/Nrn MA. No coincidence that this area
is just south of midlvl warming that occurred with morning elevated
convective precip and resultant latent heat release. Rapidly
increasing sfc based instability will allow activity to survive into
the eve as it moves into NewEng, and fast winds thru deep layer of
atmosphere will promote localized downbursts in unidirectional flow.
Tue Ngt to bring general lull and breeze enuf to preclude widespread
fog but sheltered valleys shud fill in thanks to incr sfc moisture.
Far Nrn NewEng will find renewed rain predawn Wed thanks to approaching
frontal boundary. Impressive front today on sfc obs in Srn Canada and
across Upper Midwest! This will be just as impressive over NewEng on
Wed with 50s N and near or perhaps just over 80 S. Wave of low
pressure resulting from vort max will strenghten to sub 1000 mb while
crossing NY state then start to fill while crossing NewEng. Though
filling low does not favor severe convection, intense baroclinicity and
strong veering wind profile in warm sector will promote discrete
supercell development if we can get enuf llvl instability, which will
be dependent largely upon amount of insolation prefront. Nonetheless,
believe it will be a very active severe weather day across the entire
Srn half of NewEng, with intense storms cropping up on Nrn fringe of
deep warm sector by early afternoon, then cold frontal convection with
straight-line wind/bow threat not wrapping up until eve.
Upper level cold pool Thu, and enuf cold air far Nrn ME for
accumulating snow Wed Ngt into Thu AM. As for why I keep rain
lingering many areas Wed Ngt, differing rate of cold advection shud
keep layers of instability lingering for continued shower generation
much of Wed Ngt most of NewEng, even post frontal.
Fri ngt/weekend storm not looking pretty at this point. Good trof
position for storm track to bring significant impact to NewEng, and I
think the best we can hope for is a more northern or western stall to
the storm, and that is still in the possibilities that are out there.
There does appear to be a dry slot that gets wrapped into the storm,
and therefore it actually may be most favorable Sat afternoon to be E
of the storm's longitude, but if the storm sits SE of NewEng,
astronomical high tide, copious tropical moisture and vulnerable
coastlines from last month's nor'easter all would make things
interesting. Have to admit that airmass and oceanic baroclinicity
favors the farther SE, more pessimistic scenario, but let's get some
more signals on this before going too far out with it.
Ridging returns after the weekend for most of next week with warmer and drier than normal conditions.
Matt
