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
Thursday Podcast: Issued
General Weather Summary:
A well defined and intense energetic disturbance was diving southeast across Michigan early Thursday morning, launching a band of snow squalls east in advance of it. moving across Western New York. The progression from partly cloudy skies Thursday morning to rain and snow by late in the day will be a rapid one, but the speed at which this storm moves in will also be reflected in the speed by which it moves out.
Thursday morning began with patches of black ice where melting snowbanks alongside roadways Wednesday afternoon froze overnight, and this was a problem especially on entrance and exit ramps to highways. Temperatures will rise again on Thursday, and melting will resume in many areas. This rise in temperature will come thanks to a combination of limited and fading sunshine along with a developing southeast wind, and will ensure that at least the onset of incoming precipitation will be mixed with or even entirely rain in some spots of Central and Southern New England.
The culprit is the energy center spinning its way southeast across the Central Great Lakes. The jet stream winds aloft will continue to steer this storm southeast from its morning position, bringing it off the Northern Mid-Atlantic coast and over the waters south of New England by Thursday evening. This is extremely rapid progression that has, as of Thursday morning, already been showing signs of the anticipated "center jump." A center jump occurs when the energy aloft that's driving a storm at the surface is moving so quickly that the surface storm simply can't keep up. This results in the original surface storm weakening, while a new one develops ahead of the speedy upper level disturbance, and in this case that new surface storm will develop off the coast of New Jersey, where pressures have been falling and new snow and rain showers have been blossoming as evidence that this center jump is already underway. Nonetheless, New England will find ourselves on the northern fringe of this strong energy, and we will be dealt a glancing blow from this system, with a myriad of factors affecting our snow potential, though the overwhelming signs pointing to a relatively benign event for our six-state region. The first signs of change will come by late morning as clouds thicken ahead of the approaching disturbance. At the surface, a developing southeast wind will kick up a bit in the counter-clockwise flow of air around the dying old storm center as it dives southeast across Upstate New York, yielding to its newborn counterpart east of New Jersey. This southeast wind, coupled with what limited sun we do receive before shrouding the sky with clouds, will help to boost temperatures to around or just over 40 degrees for most of Central and Southern New England. These temperatures well above freezing will result in a mix of raindrops and snowflakes as precipitation spreads from west to east through the afternoon - early afternoon west and late afternoon to early evening east. While the air may be mild to begin with, it's also dry, and when precipitation falls into dry air, the atmosphere cools, and this "evaporational cooling" will take place Thursday evening, allowing many areas to transition from rain to snow. As we make this transition, however, the storm center south of New England will be strengthening and moving quickly east, pulling most of the action south and thereby resulting in only a brief period of moderate to perhaps locally heavy rain and snow before diminishing in intensity by midnight to 2 AM, leaving light snow for the latter half of the night. In Upstate New York, closer to the old dying storm center, some amounts close to half a foot will verify. On Cape Cod, the strengthening storm will try to keep precipitation falling heavy for a longer period of time, and the potential is there for some higher amounts on the Outer Cape than for the rest of Eastern Massachusetts, though right now I'm skeptical given the likelihood of a mix with rain keeping amounts down. Elsewhere, the storm will not be a biggie by New England standards - accumulation map posted here:
The biggest headache from this storm is likely to come early Friday morning as winds strengthen from the north and northwest behind this storm, pouring cold air southward. This new shot of chilly air won't be as intense as the one that began the week on Monday, but will move in prior to dawn, meaning the combination of rain and snow that fell Thursday evening and night will freeze on roadways prior to dawn, and some areas will have a very difficult morning ride, so you'll want to prepare accordingly. Throughout the day, sunshine will break out on Friday after lots of morning clouds, mixing in with building clouds again by afternoon and a few snow showers in the mountains, but by and large bringing a bright finish to the week, though also a very chilly end with the combination of an active wind and cold temperatures producing wind chill values in the teens south and single digits north.
This weekend, we'll enjoy a quiet, pleasant and mostly sunny Saturday that will be perfect for outdoor winter sports. Meanwhile, a stronger storm will develop over the Central United States in response to a digging jet stream "trough" coming east from the Western U.S., and this will breed a weekend severe weather outbreak through the Plains States and into the Mississippi River Valley. Remember from past discussions that these troughs represent dips in the jet stream where cold air penetrates southward, and often can breed storms along the battlezones of protruding cold air with antecedent warmth. This will be the case over the Mississippi River Valley, and with a primary storm track to our west and counter-clockwise flow of air around the storm, warm air will surge northward along with Gulf moisture, meaning snow changing to rain is the most likely precipitation type for many of us by late Sunday, though perhaps not for all. After early sunshine, clouds will increase ahead of the approaching storm center. It will be a suspense-filled battle of incoming warmth and another dome of Canadian cold later Sunday through Monday. Here's what we know: Increasing moisture and warmth aloft will bring thickening clouds after morning sunshine on Sunday, and precipitation will develop by day's end. This precipitation may begin as rain, or a mix of rain and snow for some of far Southern New England, though will likely start as snow late Sunday for many. Sunday night and Monday, a large area of cold high pressure by Hudson Bay, Canada will nudge cold air south, while a new coastal storm developing on the fringes of the old dying storm to our west takes shape and thrusts moisture northward. This will set up a delicate boundary of mild and cold air, thereby setting up a fine and critical line of rain or snow. At this point, it appears as though Northern and Central New England finger-crossing earlier in the week will pay off enough for the Canadian high pressure cell to exert enough influence to keep cold air in and bring heavy accumulating snow. Farther south, all eyes will be on that fine line Sunday night into Monday, when the scenario for far Southern New England may feature a period of snow and rain/snow mix to all snow, to rain for some, then back to snow, while farther north into the remainder of Southern New England *may* end up with mostly snow. I'll keep watching this carefully, and as I know, you'll know through this discussion.
Have a great Thursday.
Matt
Matt's Technical Meteorological Discussion: Updated Thursday, February 22 at 1:20 PM
Precip has officially begun in NewEng with the first raindrops in Danbury, CT. Wet bulb temps are mostly above zero in far Srn NewEng with mostly below zero Tws across the remainder of the area. The lower CT river valley has warmed to above 40 while the Litchfield Hills and Berks have stayed colder, and this will play itself out thru varying ptypes at the onset of this afternoon/tonight's event. Mostly a snow event for the Berks and NW CT higher terrain where inverted trof assoc with dying primary low and connecting to new coastal low E of NJ will swing slowly E during the overnight and serve as the impetus for band of heavier snowfall amounts. The farther one goes from this inverted trof, the more difficult it will be to see anything appreciable fall from this event as the strengthening low to our south steals the show in this anticipated center jump event. Nonetheless, there will be a swath of warm advection and upper level diffluence on the north and northeast side of the vort max as it dives southeast across NY/PA/NJ and that will allow for a swath of light precip with embedded mesoscale bands of moderate to heavy precip to develop. Good consensus on half an inch of liquid equivalent assoc with the inverted trof, but much of that will be "wasted" on rainfall in lower elevations including and especially the Lower CT river valley. Farther W, however, just outside the valley, rain/snow combo will be quicker to change to snow with mostly snow higher terrain, and this is where amounts will increase, as shown in accums map in General Wx Summary above. Highest terrain certainly may exceed half a foot of snow but where most folks live will verify closer to amounts given. Other wild card is Cape Cod, closest to where low center winds up. Make no mistake that even tho I think this low is not going to deal a strong blow to NewEng, it becomes a very powerful storm, strengthening to 971 mb by Friday midday as it pulls even farther E of Cape Cod. In this strengthening process, moist influx will increase on east and then wrap around to north of storm, and that will force heavier precip onto Cape and Islands. So, how hard to we bite on heavy snow potential here? I had trouble bringing snow onto the Cape until a wind shift, and I feel better about that as I see obs that have wet bulbs above freezing as of midday and the wind is southeast. Not much chance of cooling or drying the airmass that way, even with the effects of dynamic cooling working in your favor, so I'm still not thinking of a changeover in these areas until after 06Z when the ageostrophic flow takes over and swings sfc winds to a northerly component. After that transition, somewhere between .1 and .2 inches of precip on Nantucket, and have gone with locally higher amounts there, accordingly.
Biggest concern is freezing of roads for early Fri. Presumably numerous treatments will be on the major roads, but secondary and back roads should be very icy with wintry mix melting on road surfaces then freezing with onset of new shot of cold predawn Fri. This shot of chill comes with 850 mb temps between -8 and -18 C from S to N, but 925 mb temps plummet and this keeps most of NewEng chilled - combined with gusts to 40 mph as low bombs to our east and wind chill will be a factor.
Quiet Sat. Sunday quiet most of the day - would like to bring in precip a bit earlier than models are suggesting with WAA tending to run ahead of schedule, and ECMWF does a decent job with this, but even still, we're looking at just about the entire daylight hours mostly dry. Thrust of warmth and moisture looking more and more like it will be cut off at the pass by SErn nose of high pressure over Hudson Bay that inches cold air southward, and is aided by confluent flow that will be quite sluggish to go anywhere east of NewEng. The result will be a rain/snow line that very well may stay suppressed over far Srn NewEng. Doesn't look like one big converged energy center, however - more like chunks of energy that slide S of NewEng, but this energy comes with warm and moist advection and therefore brings a slug of decent precip with a band of mesoscale snows likely in Southern NewEng.
Matt
Tuesday's Discussion:
1:55 PM: Amazing sfc temp contrast across NewEng today as boundary layer thermal gradient encourages isentropic lift to perpetuate clouds in lowest few thousand feet across Central/Nrn NewEng while sunshine has broken out for a time in warm sector across Srn NewEng. Used low level thickness fcst combined with early AM temps that were already near 40 to put fcst into the 40s for Srn NewEng. The tight baroclinic zone comes as cold dense air remains locked in place across Nrn and esp NE NewEng, preventing mixing and promoting lift. Shortwave heading for NewEng tonight is producing active CG lightning strikes over IL this afternoon and will produce convective elements over NewEng overnight Tue night. Doubt we'll be looking at any lightning, but healthy convective downpours that will quickly incorporate big, fat flakes esp as the shortwave axis swings thru and we capitalize on cold enuf air thru all levels but the boundary layer, which will cool evaporatively, dynamically and thru advection late tonight. The result will be a setup for some black ice in Srn VT/NH/Nrn MA, tho the strip affected by this will probably be rather narrow because farther north it's been cold today and farther south it'll still be above freezing Wed AM.
The remainder of Wed looks relatively quiet tho high RH progged in the lowest 100-150 mb has me on guard for widespread cold advective stratocu in esp Nrn/Central NewEng, broken up by downsloping flow and less intense CAA farther south. Our next shortwave will be compact and very impressive as it moves across or just north of the Upper Great Lakes. The problem for NewEng snowlovers is what it does thereafter. If this thing simply turned southeast and held its integrity, we could try to wring something decent out of it. Instead, it's going to become caught in very fast northwest flow over NewEng - confluent flow between the upper low north of Nova Scotia and the ridge axis over the Southern and Central Plains. This very fast motion will not only degrade the compact nature of the vort by stretching it out, but also will increase the speed of the compromised vort. The former means that vorticity advection will be channeled, and not coming tangential to the geostrophic flow, thereby creating a limited duration and areal scope of dynamic lift. The latter means an even more limited duration of CVA/PVA, thereby favoring a center jump scenario where the Srn Ontario low dies as the energy prompts new low development over Cape Cod, but in between we get a relative precip min. There are two factors to watch: 1) Confluent flow is less intense, meaning the vort maintains more consistency and a more favorable speed - this would increase the intensity and duration of squally bands and clusters, and 2) When the vort prepares to gather itself and surface cyclogenesis results, it does so a bit farther west or a bit earlier in the game, or slows a bit earlier before moving east, this would give more time for an easterly flow to develop in the lower and middle levels, thereby allowing enhanced snowfall earlier in the game. Though this doesn't appear highly likely, it is one thing to watch.
Cold air streams south on Friday with active wind and good mixing but enuf cold air aloft for instability Cu and snow showers in the mountains. Though the weekend starts quiet, Sunday brings warm and moist advection and good agreement on a spike in 850 mb temp anomalies that should mean snow changing to rain for most areas unless we can find a way to get lingering confluent flow aloft to hold in low level cold for some Northern locales. Doesn't look great right now, but there is plenty of antecedent cold, which means all we'll need is a weak bubble sfc high to hold it in for snow in the North Country - so enjoy this stretch while it's here, but don't give up all hope on pulling some snow out of Sunday/Monday system.
Have a great Tuesday.
Matt
