« November 2008 | Main | January 2009 »
The Friday Frenzy looks poised to unfold for Southern New England. Last night's technical discussion can be found on this page (below) and a new, complete General Weather Summary was issued moments ago with embedded video. See the "General Weather Summary" link toward the top of this page to access it.
Be sure to check back here to utilize the radar and other observation links here during the storm, and find updates and video on our NECN Weather Team blog, too, at WeatherNewEngland.com!
-Matt
Thanks for checking back in - a late post today...as explained yesterday, pressed for time lately but wanted to pound something meaningful out before retiring for an early arrival and plenty of forecasting in the morning. The current weather pattern continues to astound me, as it's virtually the opposite signals one would normally expect for a storm. The NAO (North Atlantic Oscillation) is strongly positive, while the PNA (Pacific North America Pattern) is strongly negative. I've seen such a pattern evolve a few times in the past, though, when unfavorable planetary longwave patterns actually become so extreme, that they can bring storms, nonetheless. Consider that a positive NAO pattern features a large trough from Eastern Canada to Greenland, with strong negative height anomalies, and a large, anomalously strong ridge over the Atlantic. If the trough gets deep enough, and the ridge gets strong enough, this means fast southwest to northeast flow heading into the Eastern Seaboard, and excellent baroclinicity. Similarly, a negative PNA implies a Pacific Northwest or West Coast trough, and a warm anomaly in the Southeastern United States. Combined, these two parameters, if strongly "unfavorable" enough (like they are now), bring a pattern in which a replenishing West Coast trough launches shortwaves northeast in a fast southwest/northeast jet stream flow that moves just south of New England. Sound familiar? This is the reason that in my discussions and the "White Christmas Probability" forecasts I wasn't really excited about long term potential, but didn't give up the ship and in fact kept the chance for a White Christmas at better than 50% for even the big cities of Southern New England. I have to admit that while I saw potential in this pattern, I was ready to give up on it by this past Sunday. Without power since Thursday night, I hadn't looked at a single guidance product all weekend and heard the talk that there was no chance of snow in sight. I came into work on Monday morning ready to concede and slash probabilities...until I looked at the guidance! What a delight I saw in the longwave pattern!
A small slice of that delight was delivered to my driveway, which I just finished snowblowing, today. Three and a half inches of delight. I let the freezing drizzle work its crusty magic, then blew it all off, in hopes of getting some melting with sunshine and above freezing temps on Thursday. I also made sure to push the snow extra far off of the driveway, to leave plenty of room for the NEW snow that's on the way.
This entire setup is exciting and dynamic from a meteorological perspective. The thought of strong Pacific disturbances responsible for mudslides and record cold rain in Southern Cali making their way virtually untouched across the nation and heading toward New England is intriguing enough. To combine that with record cold in the Rockies and Plains, and bubbling warmth up the Eastern Seaboard, is the icing on the cake, and provides the baroclinicity needed to turn an otherwise fast and flat flow into something far more exciting. For the timebeing, it's important to remember the core of this pattern though - fast...flat...flow. At least for now. So as we gear up for a substantial snow on Friday, it's not going to be from a powerhouse storm that rages along the coastline. Rather, this storm should be impressive for its snowfall intensity, delivering a swift and decisive snowy blow to New England, driven by isentropic lift caused by a tightening baroclinic zone that is capitalized upon by the Pacific energy. Today's event was an excellent precursor: was there a storm today? Yes, but it was quite weak. Nonetheless, that defined storm center is what produced a cold air drainage north and northeast wind to keep icing conditions in Eastern New England. Will there be a storm center with Friday's event? Yes, again, but stronger than its predecessor. Still, it's the airmass collision that will drive the snow as an arctic front losing some of its arctic characteristics settles south across New England on Thursday, losing definition after crossing the North Country, perhaps but still representing a flow of new cold that will seep southward. As the Pacific energy approaches, warmth will be drawn northward, and the thermal gradient will be far more pronounced than this last time around, with New England on the cold side of this storm. The result should not only be heavy snow cranking out on Friday, but also very cold temperatures in the 20s during this snow, and cold enough air for snow even at the coastline, including Boston, but perhaps excepting the South Coast and Cape Cod where a change to rain is likely given the onshore flow that persists and the east-northeast trajectory. Though there are some differences in the handling of the system that do have me at least keeping my eyes wide open - namely, the NMM delayed and less intense with the precipitation - the best agreement is with the very similar solutions of the GFS, GGEM, and ECMWF. All of these models carry plowable snow way into the North Country, and this seems wise given the mid-level warm advection that is forecasted by these products, and the fact that such mid-level warmth has evidenced itself as changes to sleet and freezing rain in the last few events, and while it may not change precipitation type this time, it will manifest itself in the form of a broad snow shield. The NMM raises an eyebrow because it's essentially saying that the low level cold is so dry it will evaporate the precip before reaching the ground on the northern end, and reduce amounts elsewhere...also delaying arrival. I am wary given the model's good handling of low level cold airmasses, but prefer the superior handling of the mid-level dynamics for now.
One interesting point here is that, while the vort crosses Southern New England and this supports intense upward vertical motion, especially when coupled with intense warm and moist advection, there is also some evidence of a center jump on Friday. That should be enough to scare any meteorologist at least a little, because some of the most notorious over-forecasted snow events come in center-jump scenarios, where the vorticity maximum is moving so fast the surface low can't keep up, and a new one develops farther east. This happens on Friday with one surface low left behind in Western PA, and the new one developing south of Long Island. While that's all well and good because it brings an intensifying cyclonic circulation south of New England for intensifying warm and moist conveyor belt, plus an intensifying Atlantic easterly inflow, it also means that if the center jump occurs just a touch later, somebody (or lots of somebodies) aren't getting the snow they're supposed to. Right now, this concern certainly is warranted given the speed of the vort max, but also has very little foundation given excellent agreement among the guidance on developing the new center quickly enough to do the job. In fact, 12Z guidance suite of the Canadian Ensemble continues to come on board with the leading GFS forecast, expanding the precip field and increasing amounts. Rather impressive that even the GGEM at 12Z had nearly an inch of melted QPF for Southern New Hampshire, with greater amounts through Northern and Central MA!
This is a big reason why I've had no qualms about mentioning a foot or more for some of us in New England - looks like Central and Southern New England - because the QPF is there even without the trend for increasing liquid. With such cold antecedent conditions, this is unlikely to be a straight 10:1 or 13:1 ratio, and likely will verify at least in the deformation band as a 16 or 18:1. I haven't analyzed the thermal profile yet (will tomorrow, of course) but it just makes sense to have a decent ratio given the cold in place to start, and the good warm advection that also may give us our ideal 850 mb conditions for sticky snowflakes that can grow quickly upon descent. So, right off the bat we're talking a 16-18" snowfall if the 1" QPF verifies. Now, I haven't thrown those specific numbers out there for the taking in my broadcasts yet, for the obvious reason that a center jump or southward shift like the NMM tries to paint means a big decrease in amounts. Regardless, I don't think either of those will happen, but figure saying a foot plus is bold enough from two and three days out.
As for placement of the deformation band/heavy snow band, there's likely to be two different mechanisms for banding: 1) mid-level frontogenesis, and 2) surface coastal frontogenesis. The former appears in recent runs to set up near the MA Turnpike, but given the propensity for a farther north and heavier handed distribution of precipitation, I am suspect it may verify in Northern MA to Southern NH. Nonetheless, this intense isentropic lift will mean a band of forced ascent that will create efficient snowflake production, and increased QPF. The coastal frontogenesis is unlikely to spell a rain/snow line from Boston northward, though may in Southeastern MA where more ocean fetch takes place. Still, it will define the difference in ratios, and also will help to increase surface and low level convergence. At some point, the mid-level deformation band and low level coastal front will intersect. This is likely to be your highest snow total. It's worth noting that there's good agreement on some .50-.70" amounts in only 6 hours from 18Z to 00Z Fri/Sat, and this implies snowfall rates of 1-2" per hour for an extended duration Friday afternoon and eve. Plows will not be able to keep up with this, especially at the time of evening commute, and if this still looks as menacing in tomorrow's runs, it will be essential to encourage no afternoon travel plans in my casts on Friday morning. Perhaps sooner, but that's a lot to ask of people and you want to have excellent confidence (utmost) before you suggest or request it.
Of course, this is only the first storm of the series, right? The NAO remains abnormally positive while the PNA remains abnormally negative, and this means the same strangely active pattern persists with another storm threat Sunday, then again Tuesday. One would think at least one of these storms will fail to verify - how often can you really pull the hat trick? But then again, such a strong backwards New England storm planetary pattern just might be the one scenario you could actually do it in.
See you back here before too long.
Matt
I expect to post both a technical discussion here & a general one on NECN's WeatherNewEngland.com, but I'm en route to another appearance now so it won't be until late afternoon or eve. Ironically, active weather often means I reschedule appearances to quiet days, which are days I normally would post fcsts about upcoming active weather! The catch 22 leaves me up against the wall for time, hence the delayed posts of late...not to mention the dying laptop, which failed to start yesterday but therefore should work today, based on my warped view of a 50/50 proposition...
7:45 PM Update: General Weather Summary is out on WeatherNewEngland.com. Technical discussion won't happen today - laptop is a no-go and desktop is painfully slow. Will try to crank out a techie tomorrow on this site!!
I've written a General Weather Summary on the WeatherNewEngland page that addresses and explains the few changes made to the forecast late this morning. The biggest implication is the northward shift of the sleet/snow cutoff, especially in NH. The link to my General Weather Summary page on the NECN blog can be found in the Weather link section at the top of this homepage. Enjoy a truly amazing storm...though for snow lovers, more snow in Central and Souther Louisiana and Mississippi than in Boston is a sad, sad reality!
No joke...a major winter storm is on the way. By the time you're done reading this, you'll know why I'm forecasting what I am, and we'll all sit back and see if nature can deliver. This is a rather encyclopedic post, so sit back, relax, and continue reading...
Yesterday's technical discussion is below. Today's general weather discussion on WeatherNewEngland is out and can be accessed by clicking the "Summary/Discussion" link in the Weather section above. A new technical discussion to follow up from yesterday's will be out soon. Working on it now. -Matt
In the short range, we're locked, loaded and ready to fire. In the medium range, the moving target is becoming more clear, and thankfully in a direction that makes some sense.
Let's start at the beginning - a nice burst of warm advection snow especially across Northern New England has continued to push northeast. Now, the impressive Gulf of Mexico tap and its associated thunderstorms and heavy rain are pushing east, along with the strengthening low. Not surprising to see that the NMM has slowed its frontal progression, though I think the initial instinct of the model to slide the front through very quickly is a testament to the strengthening of the anticyclone upstream that will be so important by the medium range. Though the NMM was, as it appeared to be, too hasty in sliding this anticyclone east and southeast, it does do the best job with handling low level cold airmasses thanks to its higher resolution, and this dense cold air still looks as though it will slide in quickly behind the front, which is getting a push from the shortwave that races across Quebec later Wednesday. Confluent flow follows the shortwave, and this favors sliding the high east, then holding it and strengthening it given confluence aloft. Prefrontal, most of New England will find the strongest wind late Tuesday night into Wednesday morning. Of course, there is an inversion present at about 960 mb most of Tuesday night, which rises to about 925 mb Wednesday morning, but even given this limited mixing, gusts to 45 and 50 mph remain possible through the period owing to a strong low level jet in advance of the front produced by a pronounced pressure gradient. As the front nears, the low level jet slides east with the pressure gradient, meaning that the actual frontal passage Wednesday afternoon should bring slackening though shifting wind to blow from the northwest. I've been carrying a chance for thunder in the forecast with the frontal passage, though am tempted to drop it. Total totals climb to near 50, which is impressive, but lift doesn't look sufficiently deep to reach cold enough air for multiple active ice nuclei for lightning generation, except perhaps near the immediate South Coast. Also worth noting is the time of heaviest precipitation - likely to occur either side of 18Z in most of New England as the front settles through, though early in the morning Northern New England and late in the day South Coast/Cape Cod. It's at this point that the front slows substantially as shortwave ridging in advance of the digging trough over the Southeastern U.S. combines with the longwave ridge holding steady across the Western Atlantic to stop the front dead in its tracks. Of course, this sets up the pathway for the intense and moisture-loaded system pulling northward.
This system has been the cause of great forecast uncertainty in the medium range as the guidance has struggled with how to handle the shortwave energy when it rounds the base of the longwave trough. Slowest and most pronounced in the 00Z runs from last evening was the GFS, and quickest was the GGEM (Canadian). I looked at all available guidance before the early morning shows, and had 00Z Friday low centers ranging from Louisiana to Nova Scotia! In these moments of great uncertainty, a forecaster must rely on what they know at the simplest level, and that's the upper level pattern. The Westerlies seemed too fast to allow the upper low to both close off AND drift south of the jet stream so substantially, not to mention this is climatologically quite an anomaly to forecast. Therefore, the GFS solution was discounted and weighted the ECMWF forecast slightly toward the GGEM and the bulk of its Ensemble members (ie: slightly farther east/north and slightly more progressive). This seems to be the path worth taking, at least for now, as the 12Z guidance came around nicely, though the GFS is still too laggard in its northeast acceleration of the vorticity maximum. It not only is not consistent with its own mid-level wind forecast and the confluent flow creating that increased wind, but lags behind its counterparts. Therefore, still really don't trust the GFS solution in the 12Z run. Instead, the ECMWF, GGEM, GGEM Ensemble members and to a large extent the NMM have come around nicely, and fall in decent agreement at the 500 mb level.
At first, this seems to have implications only in the "timing" of the storm. A more in-depth critique of what this really means, though, is that there's more than just timing at stake. Rather, a quicker ejection of the shortwave trough implies a quicker return to warm and moist advection across the stalled front and into Southern New England. One has to ask: Does the precipitation ever really stop? If the warm advection and isentropic lift begins sooner, this doesn't give the high time to build in like the GFS is trying to do, thereby keeping ascent near the front over Southern New England and meaning that, especially the farther south one is, precipitation doesn't really stop. It does, however, begin to morph. The cold air streaming southward from the high over the St. Lawrence Valley that strengthens to either side of 1030 mb will make inroads in the lower levels of the atmosphere. With a failure to bring in colder air aloft, however, we're going back to the seemingly unimportant point of interest discussed at the start of this discussion - the NMM's desire to charge the front through in its earlier runs, and the meaning of that with relation to dense, cold air. This dense, cold air should seep southward and hold its own interior of a coastal frontal boundary. This would appear to be a rain/snow line, but the failure of deeper cold air to establish into Southern and even South-Central New England implies it will be freezing and not frozen precipitation for these interior locales - freezing rain. Farther north, there's great agreement among the NMM and ECMWF that the 850 mb 0 C line runs from Casco Bay to Bennington, Vermont. This, however, is not the rain/snow line, because of an above freezing layer indicated in the NMM thermal profiles between 700 and 800 mb that penetrates even farther northwest, which makes sense with the lack of a good mid-level cooling signature. Having said that, I think the NMM is still slightly too far north and west with the 850 and 700 mb front as a result of pulling the 500 mb vort center just a touch too far inland, but it is in good agreement with both the ECMWF and the GGEM, and is close enough to use as a decent guide. Even a slight adjustment southeast keeps most of these Central New England areas as sleet and holds the snow line from Rutland, VT, to the Northern Lakes/Mount Washington Valley of NH, to Rumford, ME.
If I'm right on this setup, we have an almost all rain scenario for most of coastal Southern New England (surprise, surprise), a substantial freezing rain scenario for interior Southern and South-Central New England, a substantial sleet event for much of Central New England including Concord, NH, and Portland, ME, and a one to two foot snow event for some of Northern New England, from Central/North Central VT to the Mount Washington Valley to the Maine Mountains.
Remember that those of you who read this blog get my raw thoughts - I wouldn't necessarily go on the air with a map of hard and fast predictions for exact locations of ptype and amounts, because there is still lingering uncertainty with the storm track, and the efficiency of precipitation production, though I expect the latter to be high with differential temperature advection underway - warm advection aloft and cold advection below - and the cold side of the mid-level front should form the necessary deformation band on the cold side of its location to verify the heavy snow band in the North.
So, meteorologists and weather-enthusiasts alike have our work cut out for us. Watch the GFS to come in line and just a touch farther southeast than the current NMM solution, and both should be fairly close in guidance prior to the event. The biggest difference will probably come with regard to surface temp and the location for the freezing line, but the north-northeast component of the surface wind thanks to ageostrophic flow will favor colder farther south, especially given what is a good cold air damming and cold air drainage surface pattern with the strengthening then maintaining anticyclone to our northeast.
I invite your thoughts in the comments section of this post!
Matt
Am writing from the cell phone, en route to an afternoon speaking engagement, but will have a techie post out after. I'm excited to get lots of thoughts out...00z guidance was all over the place and I basically used a compromise upper lvl pttn to envision a would-be sfc pattern and the 12z runs are very close to that. That gives a feeling of good insight on storm evolution...will post more later!
Interesting find from the Washington Post:
NBC Universal made the first of potentially several rounds of staffing cuts at The Weather Channel (TWC) on Wednesday, axing the entire staff of the "Forecast Earth" environmental program during the middle of NBC's "Green Week," as well as several on-camera meteorologists. The layoffs totaled about 10 percent of the workforce, and are among the first major changes made since NBC completed its purchase of the venerable weather network in September.
Click here for more on The Weather Channel cuts from the Washington Post...
This Saturday, December 6, NECN's own meteorologist Matt Noyes and sports anchor Chris Collins will be in Lynnfield, Massachusetts, helping to bring Christmas to the children of fallen Troops. The luncheon is affordable for individuals and families alike, and not only will benefit these children, but also will feature a list of celebrities on-hand, a buffet lunch, great beverages, the Army-Navy football game, a raffle and both a silent and live auction, with Matt as an auctioneer! Continue reading this post to find out how you can be a part of the action...
