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:
Heavy rain continues to fall across the Appalachian Mountain Chain, Eastern Pennsylvania and Central/Eastern New York on Tuesday, feeding off of a tap to both Tropical Atlantic and Gulf of Mexico moisture (soon to include a new tropical creature described below) and traveling north along a pathway for this rain - a frontal boundary that marks the dividing line between a drier land airmass across Canada and the Eastern Great Lakes, and the deep tropical humidity spilling northward from the warm Tropical Atlantic. The center of this warm and humid airmass is a high pressure area over the Western Atlantic, which controls a large dome of humid but fair weather within its extensive tropical envelope. As this Western Atlantic high pressure center strengthens, it will force increasing amounts of tropical air north and west, and the transition for New England has been toward these tropical and somewhat fair, humid conditions over New England.
This tropical air will continue to bring plenty of sunshine blending in with the puffy cumulus clouds Tuesday afternoon - and if you have the opportunity, check out the blue sky between clouds! This is a wonderful deep blue sky that we so rarely see in New England - since our air usually comes from the west it often is filled with pollutants from cities the air has already traveled through, but this air is coming out of the relatively pollutant-free tropics, which means the sky will be a gorgeous and clean deep blue. A bit depressing when considering how dirty our skies normally are, but certainly a wonderful sight to behold, and it makes one wonder if this is perhaps closer to the shade of blue seen by those who settled New England hundreds of years ago. With so much mugginess in the air as "dewpoint temperatures" - the measure of the amount of moisture in the air - remain quite high, a few showers and downpours are certainly able to develop in the afternoon, and while forecasting the exact location of these in such a tropical airmass is rarely possible, we all should be aware that some of the towering clouds this afternoon may drop a shower or thunderstorm with briefly heavy, tropical rainfall. You can, of course, monitor for storms through the links to radar imagery at right of this discussion. Meanwhile, the battlezone between airmasses - the dividing line mentioned above - will be draped from the Appalachian Mountains through New York and Pennsylvania, southward to the Southern Mid-Atlantic, and will help to guide a new tropical creature into North Carolina.
This tropical creature is one we've been watching for awhile now - originally a tropical wave north of the Bahamas last week, this cluster of thunderstorms made its way west to Cape Canaveral, Florida, earlier this week, now is moving north into North Carolina on Tuesday, and has been gaining a consistently more impressive structure. Both satellite imagery and surface observations indicate a center of low pressure has developed beneath this mass of thunderstorms, and its highly likely the storm is either numbered a tropical depression, or even named a weak tropical storm with tropical storm warnings required for Eastern North Carolina by the end of the day Tuesday.
While winds will kick on the east side of this storm across North Carolina and the Southern Mid-Atlantic coastline later Tuesday and Tuesday night as the system moves onshore, the big threat for the Appalachian Mountains and Mid-Atlantic will be the 6"+ of rain that falls from the system. As this system ripples north along the aforementioned frontal boundary, rains will spread through DC and Maryland, Pennsylvania and New York State Tuesday night. While the bulk of this storm remnant will stay west of New England across New York, it's likely that a swath of rain will extend into Western New England by Wednesday morning, and rain may become quite heavy through the day in Northwestern New England where flooding problems may be aggravated Wednesday across Northern and Central Vermont.
With an area of Canadian high pressure nudging southeast later in the week, the frontal boundary and focal point for tropical rains will gradually drift east and will carry lingering moisture from the tropical depression/storm, and the tropical moisture that's been steadily feeding north, thereby bringing the threat for meatier thunderstorms back into the forecast from west to east on Wednesday. The increased risk for thunder persists Thursday and Friday with the passage of a cold front. Finally, I'll also be keeping close tabs on an area of low pressure over the Atlantic, moving west toward Bermuda as of this writing, that will sweep near but likely offshore of the New England coastline late this week.
As for the upcoming weekend, indications are that new energy will drop into the Northeast, but this continues to look progressive to me, meaning the entire weekend would not be a washout. In fact, right now I'd bank on Friday's disturbance leaving behind a decent Saturday for one and all, before the chance of showers or thunder returns to the forecast on Sunday.
I'll keep you posted!
Matt
Matt's Technical Meteorological Discussion: Updated Tuesday, June 27 at 2:20 PM
Tuesday Update: Time is running short on our tropical creature south of NC but Hurricane Hunter Data from near the center is just coming in as I write this and winds have been recorded to 37 kts on the northeast side of the circulation according to the latest ob sent from the plane. Altitude was 280 meters so this is not elevated and is enough that we're looking at a compact center of circulation with a broken ring of convection evident on radar, but the official call is that of NHC - given that center is within about 50 miles of land as of this writing it's not going to much matter except for semantics and the record-keeping. Not impossible to have a last minute upgrade with warnings come out...tho again, the window has all but closed with regard to alerting the public.
Nonetheless, call it what you want but the big question in NewEng is how this will affect us. Water vapor loop gave a bit of concern today as did the 500 mb chart which both showed due S to N flow in the atmosphere favoring keeping this circulation just off the coast as it moves parallel to the coastline. But given the shallow nature of this tropical system, we must follow mean steering wind in the lower layers of the atmosphere, which do indeed continue the storm moving inland over the Mid-Atlantic. As it interacts with the neutral trough to its west this will usher the center of circulation quickly northward on the east side of the Appalachians. In most instances with a tropical system you'd think the NMM is on the money with keeping rain along track and wind expanding east, and while I can make a good case for wind expanding east given gradient between Western Atlantic ridge and dying circulation, this is a tropical airmass throughout and while the extratropical shift of the rain band will certainly delineate the heaviest QPF (as mentioned in yesterday's disc...should be well above guidance), I do like keeping some rain east of the track given abundant tropical moisture in place, and this means spreading rain into Western NewEng by Wed AM. Mean flow also favors taking the remnant moisture over Northern VT where - admittedly much to my surprise - today's 20-30 mph gusts are enough to down multiple trees across even Rte. 89! I knew the ground there was saturated but am surprised this light of a wind gradient is doing it. Tomorrow's additional rainfall will compound the situation with saturated ground and cause for new and additional flooding on top of the minor flooding we've already seen. Rain should come down very hard during the day Wednesday in most of VT and Nrn NH as the remnants of TD/TS move over NW NewEng. Farther E, breezes will become active on the South Coast well removed from remnant circulation - again, largely due to gradient - and I do expect at least a breezy day in most of NewEng with gusts over 20 mph, so I suppose based on today's damage that some additional tree damage is possible.
Yesterday's disc helps to lay out the plan here as we go out thru time - better chance of thunder and rain spreads E thru Wed...esp Wed Ngt thru Thu Ngt. Notice that last couple of days have featured multiple bands of heaviest tropical precip and this certainly should be the case as it all moves east, slowing again later Thu over NewEng with those multiple bands of locally heavy rain. By Fri the stronger and finally kicker shortwave comes thru - still looking like barely just in time to deflect circulation moving W over Atlantic that I'm still watching carefully and not yet entirely comfy with - with another round of thunder but enuf to dry NewEng out for a gorgeous summer Saturday. Frontal boundary on Sunday does come thru progressive thanks to progressive shortwave driving it but southern end slows in tropical air and will keep showers in most of day, but somewhat drier air for Mon and Tue July 4th, tho a few weaker Northern stream shortwaves will drive boundaries thru that may focus convection each day, tho typical progressive summer convection that will not make either day a loss. -Matt
Yesterday's Disc:
Hemispheric pattern features the polar vortex near the North Pole at 5240 geopotential meters (gpm) in height and the deepest cyclone in the Northern Hemisphere. Additional deep cyclones include 5340 cyclone west of Greenland and 5440 cyclone over Aleutian Islands. Remembering that air will flow much like water in a sink, the energy ejecting out of the polar vortex will migrate to the deeper lows, and we are seeing vorticity maximums feeding into both of the secondary upper lows. This sets up a virtually endless supply of shortwaves, and those diving into the Aleutian low directly affect NewEng as they are in turn ejected east from AK, ride over the bubbling Western US/Canada ridge, and drop into the trough that remains in place over the OH Valley. Meanwhile, the Western Atlantic ridge continues to build to 5970 gpm and this maintains steady Tropical Atlantic moisture influx to Eastern Seaboard, while SW flow ahead of trof to our west continues to tap Gulf moisture.
At the surface, frontal boundary has been the pathway for moisture and focus for convection the past few days, as it moves from a stationary position over NewEng to a warm frontal position across NY/PA and Apalachians, where it will stall again. On it's north side, it's quite evident on satellite/radar presentation that this boundary is focusing rain into Nrn NewEng, tho 700 mb flow indicates the midlevel front is racing ahead of its sfc colleague, and eventually these two will meet again in Southern Canada. The transition, however, is a wet one today in Northern and parts of far Western NewEng as moist and warm advection at 700 mb couples with moderate speed and directional convergence at 850 mb along with moist Theta-E advection to induce strong upglide and isentropic lift. This area of forcing was well progged by the guidance and the strongest lift has followed accordingly, and will continue lifting out of the Capitol District of NY and into Nrn NewEng where the Burlington NWS has active flood warnings you can access using the link under Current Conditions & Active Watches, Warnings and Advisories at left of this discussion. Total amounts of rain will be basin-wide averages of about 2" but higher amounts will fall in orographically favored areas, especially beneath greatest mid and low level forcing.
Elsewhere in NewEng, a truly tropical airmass is moving in from S to N and bringing breaks of tropical sun with it. Not possible to get this nice of a transition for most of Maine where a SE flow uses the cold Gulf of ME waters to keep a lid on potential temp rises. With warming boundary layer and plenty of moisture, Srn NewEng will continue to see scattered showers and downpours Mon afternoon while edge of rain shield briefly skirts extreme Western CT/MA. I expect things to quiet down tonight though as drier air moves into the midlevels, tho still plenty of moisture packed into the boundary layer and outflow boundaries that linger may allow a few showers to persist, esp across Nrn NewEng where the rain shield only slowly lift out, but in Srn NewEng as well.
Big question for Tue is whether to put any precip in the fcst. CAPE is pathetically low but that's typical in a tropical airmass and can't be used as the judge. Even tho sounding is moist and mild, 700 mb temps are not warm enough to cap the atmosphere and the only cap is dry air aloft, to the tune of a progged 10-20% at 700 mb! While logic tells me this is a cap that cannot be broken, I've been burned by tropical airmasses producing convection with little rhyme or reason in the past and for today I've opted to leave chc precip in - if I truly feel there is no trigger and a strong enough cap tomorrow, I will pull the chance.
Disagreement in the QPF fields for later Tue and Wed but relatively good agreement in the synoptics which include the system off the Florida coastline moving inland and the frontal boundary gradually pushing back eastward toward NewEng. First, regarding the system off Florida coastline, convection has increased markedly and a sfc circulation does appear evident on visible satellite imagery east of Cape Canaveral and moving north. Given the warm waters it's over, I wouldn't be at all surprised to see this system ramp up a bit on its trek northward toward the Carolina coastline - likely moving into Outer NC from the south Tue afternoon as a TD...not impossible to gain weak TS status but 850-500 mb shear appears too strong for good organization and this leads me to believe we're not going to squeeze more than a depression out of it, though it will be borderline depending on how much the east side of the circulation can increase velocity esp given northward acceleration.
Nonetheless, this is something for those of us who get excited about tropical creatures to admire, but does little to the forecast here in NewEng. The frontal boundary will still be stalled west of NewEng Tue into Wed and the focus of heaviest rainfall will be up the Appalachian Chain - were Central PA and Central NY will be under the gun and I fear QPF forecasts from the NMM/GFS of 1-2.5" are woefully underdone and will verify closer to 10" in orographically favored areas for a significant Central PA/Central NY flood event. Farther E into NewEng, however, we have to wait for height falls assoc with next shortwave digging into Great Lakes and Ohio Valley to turn trof neutral to our west and then nudge frontal boundary east, which happens largely after thrust of "TD" moves into NY, perhaps carrying the tail end of this moisture over Nrn NewEng, but still there will be plenty of moisture to work with as deep tropical atlantic flow remains established for rain/thunder to move E into Nrn/Wrn NewEng Wed AM, Central NewEng Wed PM and Eastern NewEng Wed Ngt. While QPF forecasts disagree among guidance products, synoptics back up this solution.
Later this week our forecast depends heavily on how much the northern stream shortwaves diving into the trough can beat down the NW periphery of the Atlantic ridge, as there also appears as though there will be a rogue storm development, keyed in on by the NMM for the past couple of runs. The GFS also picked up on this feature but tries to bring it north directly into a 5970 ridge which is not a likely scenario but means the GFS is picking up on the same problem it exhibited last season. Nonetheless, this low center trends closer to NewEng in each run of the NMM for later this week and must be watched carefully, as it will move W until it merges with the slowly eastward trudging front, which depends on the aforementioned northern stream short to keep it moving. That said, the closest passes to NewEng are the NMM, NOGAPS and UKMET, and at this point none are quite close enough for alarm. Still, given that we're a slowed shortwave, a slowed front, a slower decaying ridge away from this coming closer, this circulation bears watching. The guidance at this point, however, are trying to create a cold core system, which looks reasonable given its northern latitude origins, located at 60 W and 35 N, and moving due W before hooking NW, which doesn't bring it over 26 C or warmer water. Nonetheless, the atmosphere as done some strange things at this latitude in the early and late season for the tropics, and let's just keep an eye on it carefully.
As for the upcoming weekend, lots of folks are looking for some good news. One look at the Ensemble member spread makes it clear that there truly is very limited certainty with a forecast that far out. My hope here is that our next shot of northern stream energy - which does look to rotate thru the OH Valley trof leading into the weekend - will at least nudge the tropical moisture feed offshore which would mean showers but progressive...but no guarantee on that given the stubborness of the Western Atlantic Ridge, so the honest answer is we wait and see on this.
-Matt
