The Coming 7-10 Days: Two Storm Threats, Spring Arriving

As expected, the winter season appears to be winding down, and my forecast last week of the snow events being over from here on out looks accurate on long range models.  There’s a chance some snow/sleet could mix in at the onset of a storm moving in Thursday night, but with temperatures above freezing for the entire region no significant impacts are expected.  This post I’m going to run through the two main storm threats I am watching, one Thursday night into Saturday morning and another Monday night into Tuesday of next week; each one will bring some minor impacts but I am not expecting anything major.  I am watching the latter of the two for potential impacts slightly larger than the one later this week, but neither one should be cause for much concern.  Overall, the weather is relatively tranquil now as we transition from our winter-weather pattern into a more spring-like pattern of severe potential.  There’s always the chance of large, strong Nor’ Easters this time of year, but I don’t see too many of those on the horizon.  Monday night into Tuesday could try and come close to that, but I’ll discuss that more in a little.

Tomorrow should be a relatively nice day, with temperatures approaching 60 and clouds increasing throughout the day.  However, temperatures drop quickly overnight into the low 40s and upper 30s overnight as overrunning precipitation approaches the area.  Some weather models are more defined with heavier precipitation, but both agree that enough cold air will be pooled in front of the overrunning precipitation that some sleet/snow could begin inland at the onset for an hour or so before we go to all rain.  Most weather models have the heaviest rain between 4 AM and 8 AM, though again there is some variance.  Then during the day on Friday light precipitation and drizzle will continue as a very strong inversion sets up; temperatures at the surface will generally be in the 30s but aloft at 850mb (around 5,000 feet) temperatures will approach 10 degrees Celsius.  Though this warm air occlusion can be common, it occurring to this magnitude at this time of year is rare.  In fact, surface temperatures may not even reach the seasonal LOW temperature for this time of year in areas.  Either way, temperatures should remain just on the higher side of freezing, so I don’t expect we deal with any freezing issues on Friday into Friday night as light precipitation continues.  I’ll keep an eye on future surface temperatures runs, but right now I just expected stagnant air and potential air quality issues with light rain/drizzle throughout the day Friday into Friday night.  Any precipitation then winds down into the day on Saturday with total rainfall amounts anywhere from .2-.5 inches varying across the region.  A large variance, but this is a small-scale event so exactly where heavier precipitation sets up tomorrow night will determine what part of that range we reach.  Regardless, even high-end estimates are low enough that there are no flood risks or real impacts from this storm other than cold weather and nuisance rain on Friday.

Clearing comes into the weekend with high temperatures in the mid 50s and low temperatures in the mid 30s or so.  Then we start tracking the next storm system that will move through Monday into Tuesday.  Like during winter, weather models generally agree on the overall pattern but can diverge on the specifics, but the agreement here seems fairly strong, hence why I’m going to go a little more in depth with this storm system.  During Sunday night into Monday a storm system will move out of the Gulf of Mexico and progress over Ohio and then into Canada.  This has been a fairly significant trend to the west, which is good as it may help spare Southwestern Connecticut the worst of the winds with the storm system.  Generally, when strengthening low pressure centers move just west of the area, we deal with strong southerly flow that results in stronger surface winds due to relatively less friction over the Long Island Sound (especially in convection, where strong downward motion can mix down very strong winds aloft).  Some models even indicate a very weak secondary low pressure center trying to form near the area as the storm moves through, again limiting winds.  In terms of real conditions, the end result of this should be a period of heavy rain Monday night and maybe some briefly gusty winds as the precipitation shield on the southeastern flank of this low pressure center moves through.  Again, no serious impacts, but any strengthening low pressure center moving there just bears a little watching to make sure there are no more serious impacts than a period of rain, so stay tuned in case anything changes there.

The bad news for Spring and Summer lovers is that after that low pressure center moves through it will be strong enough to usher in a brief period of (relatively) very cold air.  We’re not talking teens or anything here, but areas are likely to get below freezing as temperatures aloft at the 5,000 foot level could get below 10 degrees celsius.  A very strong April sun angle will help warm things up during the day, but Wednesday night could be quite chilly as radiative cooling takes over.  Wednesday and Wednesday night maybe into Thursday will thus be unseasonable chilly, but warm air looks to flood back into the region a little more Thursday night into Friday, so we should return closer to average temperatures very late next week.

That’s a brief summary of the weather over the next 10 days or so.  Nothing too impactful expected, but two periods of unsettled weather could potentially disrupt some outdoor plans, along with a cold shot late that could throw us back to thinking it is February or March.  I’ll continue watching all future weather disruptions across the region, so make sure to keep it here for the latest!  As always, the 5-day forecast will be updated daily, and we will soon be revising the “Winter Storm Update” to make it more relevant for the spring weather we are about to see.  SWCTweather will be here throughout the Spring and Summer when bad weather threatens the region, so make sure to stay tuned!

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Colder Surface Temperatures: 30% Delayed Opening Monday

We have been tracking a strong storm system that has moved into the area and stalled over the last few days.  As it slowly tracks to the east, we are noticing models trending colder at the surface, and a result is that tonight all of Southwestern Connecticut is expected to drop below freezing after a sizable amount of rain.  This could mean some icy patches on roadways, and with light precipitation potentially continuing through the night, some sleet/freezing rain could pop up.

Precipitation may not even wind down until 8 or 9 AM tomorrow, and though it will remain quite light, it could be freezing rain and sleet lightly tonight.  I had been tracking this potential, but a combination of it being a low-end chance and a lot of school-work has prevented much constant updating.  Regardless, we are continuing to update and monitor this tonight as colder air works into the area, and we will be up at 5 AM to report on any school delays should some crop up.  Again, delays are not exactly expected, as some weather models have surface temperatures remaining above freezing or have conditions that are bearable as long as roads are properly treated, but icy patches on some roadways may be enough to delay some school districts tomorrow, especially inland.  Precipitation is in a lull now across Southwestern Connecticut, but expect it to pick up off and on again throughout the night before the storm entirely moves out.  If necessary, I’ll have another update tonight at 11 PM, so be sure to check back in then for another update as the cold air marches east.

March Misses: Chances of Scrape/Miss Skyrocket

In the post last night, I outlined three potential scenarios for Southwestern Connecticut in the upcoming storm: a direct hit, a scrape, and a miss.  I gave each one percentage chances; with new data in today it is time for a fairly drastic revision.  As I feared, the recent trend of snow storms not significantly impacting the area is going to continue.  The trend this month has been for the storms to trend away from Southwestern Connecticut, and that is the reason why I included the “miss” as an option even though there was not really any model support.  Now, it is the most likely scenario, as all weather guidance trended significantly east during the day today.  This post will be more brief as there are less impacts to outline, but I’ll run down the potential chances of each scenario and basically what I expect the final outcome will be.

If you need descriptions for the three scenarios, you can look at the previous post where I outline what each one entails.  The updated percentage chances follow:

Direct Hit: 10% (6-12+ inches of snow)

Scrape: 30% (2-6 inches of snow)

Miss: 60% (less than 2 inches of snow)

Almost all major weather guidance trended to the east with the low pressure center today, favoring instead an inverted trough scenario to our south bringing some moderate snow to the Mid Atlantic.  It still looks like some light snow could move into the region Tuesday night into early Wednesday morning, but my current forecast is for anywhere from 1-3 inches of snow.  No major impacts are expected, though scattered school delays Wednesday morning are possible depending on exact timing of the snow.  I will continue to watch that closely and report back, but as this is a smaller scale feature it will be hard to know until later tomorrow until Tuesday morning exactly what impacts can be expected.

There remains a very outside chance that this storm trends back and more significantly scrapes the region, resulting in a period of heavier snow and gustier winds.  Again, models are trending away from this scenario, and given the poor ridge axis placement that I pointed out yesterday and the general trend of the month away from snow storms in the area I really don’t think we get significant impacts from this, but sometimes weather can have a mind of its own.  This will be a very strong low pressure center, and even with this miss we will still have some gusty winds as the storm rapidly strengthens to our southeast and then east.  I will continue to cover future model runs and update the blog as necessary, but for now the going forecast is for widespread amounts of 1-3 inches of snow Tuesday night into early Wednesday morning with minimal impacts.  Keep it here for the latest storm coverage as this complex scenario continues to develop.

March Madness: Winter Pulling an Upset?

As has been outlined under the “Winter Storm Update” and on Twitter, we are following the potential for a winter storm to impact Southwestern Connecticut Tuesday into Wednesday morning.  At this time, confidence is quite high that there will be accumulating snow across Southwestern Connecticut in that time frame.  Confidence is also rising that this will be the last large snow-storm threat of the season, as we see a very clear warm-up following the storm, though as always there is no guarantee that a storm won’t come out of nowhere in April and disrupt the pattern.  I just don’t see that at all yet.  But to get to Spring, we have to deal with this one last storm threat, and it threatens to be a very strong one, potentially involving the strongest low pressure center of the entire winter season.  This post will mainly outline the 3 possibilities with this storm for Southwestern Connecticut: a hit, a scrape, and a miss.  I’ll break down which weather models support which solutions, which way I expect them to trend, and what the overall pattern appears to be dictating here.  This blog post is a day later than I planned; mainly because I am on Spring Break in another time zone and it is hard to match up exactly when I want to release blogs with when it would be feasible for people to read them and it is hard to find the time to analyze the weather models and then report them (yesterday I spent quite a bit of time looking at data but at the end of the day didn’t have time to compile it into one large blog post).  Either way, break ends tomorrow, and regular blog posts, site updates, and Twitter updates will ensue, so don’t worry; you’ll be as informed as anyone else on what the latest weather data is saying about the potential storm this coming week.  Now let’s break down what it’s currently saying.

Right now, there are really 3 potential scenarios with the upcoming storm: a direct hit where the region sees a large snow storm to borderline blizzard (the strength of the low pressure center makes me confident that if we were directly impacted it, blizzard conditions would ensue), a scrape with southeastern New England seeing the worst and SWCT still getting some moderate snow and gusty winds, and a miss, where the low pressure skirts to the southeast and the region is left with just flurries and light snow as upper level energy swings through the area with no real low level connection.  I’m going to outline the specific impacts in each of these three scenarios, the models that support it, and then end with a conclusion focusing on what I think is most likely, what the pattern supports, and what models will likely trend towards overnight tonight and into the next few days.

DIRECT HIT (35%): Under this scenario, a rapidly strengthening low pressure center would move near or directly over the 40/70 benchmark in the Atlantic Ocean that is the typical point a classic Nor’ Easter snow storm would move over, throwing back significant moisture and tightening the pressure gradient enough to create very gusty winds.  In this scenario, we could be looking at the single largest snow event of the entire winter season, due mainly to the warmer Gulf of Mexico air and thus inflow of moisture available alongside the sheer strength of the expected low pressure center.  Weather guidance has the low pressure center dropping over 40 mb before it moves through the area, meaning if it moves close enough we could see winds gusting into the 40/50/60mph range and snowfall in excess of 6-12 inches.  This is not to hype the storm or scare anyone at this point, as stated there is only a 35% chance of this happening at this point, and actually and only one major weather model supports this outcome (the UKMET, whose accuracy has not always been great and which has little other model support); this is not the most likely.  However, there is a very real chance of it, and March is typically known for some of the most historic storms, which is why I am keeping such a close eye on this.  A slight jog west of the CMC weather model (literally 30-50 miles) would create this situation, and a few of its ensemble members show just that.  The ECMWF is fairly close to this situation as well, as a shift of just 50-100 miles west of its current solution would result in a direct hit.  So while only one weather model supports this (and it’s not one of the “big 3″ of the GFS, ECMWF, and CMC), it is a very real possibility.  In this scenario, heaviest snow would occur overnight Tuesday night and continue into Wednesday morning, with school impacts Tuesday afternoon and Wednesday likely.  This potential is why we ask you to stay tuned for the latest forecasts, because small track shifts could be the difference between this solution and the “scrape,” which is described next.

SCRAPE (50%): This is the most likely scenario, in which a very strong low pressure center (dropping below 960mb) moves far enough to our southeast that we miss the worst of the storm, with the worst centered by Cape Cod and Nantucket.  Instead, the region sees gusty winds into the 30-40 mph range and light to moderate snow accumulating in the 2-5 inch range or so.  In this scenario, snow would start Tuesday afternoon, though it would take until Tuesday evening for the snow to get heavy enough and for temperatures to drop enough for it to really stick.  Snow then would wind down early Wednesday morning when winds pick up.  School impacts would be possible Wednesday but significantly less likely than they would be in the previous scenario.  This scenario is the one supported by most weather model guidance, the CMC scrapes the region most significantly, the ECMWF also has a pretty clear “scrape” scenario with widespread amounts of around 3-4 inches of snow, and the latest GFS weather model runs also show a scrape with just a couple or few inches of snow.  Along with this, the thermal gradient in the ocean (the difference between very warm and very cold water, creating a path running from the southwest to the northeast) tracks just east of the 40/70 benchmark mentioned earlier, and often low pressure centers end up tracking along such areas of temperature difference.  In this scenario there would still be impacts from accumulating snow, but it would certainly be nothing like the “direct hit” mentioned above with severe winds and actual heavy snow.  Here, we would watch a very, very strong storm just scrape the region with the outer edge of its snow and wind, and as stated most major weather models and their ensembles support this scenario.  A small shift in track, the type that would not be able to be determined until 24-48 hours before first impact, could be the difference between this scenario, a direct hit, and a miss, which is why we are going over all these scenarios and asking you to stay tuned as additional weather data streams in.

MISS (15%): Though the least likely of scenarios, there is still a potential that the storm basically misses the region entirely.  Here, the storm gets shunted so far to the southeast, as some other storms have this winter season, that the region just sees some light flurries or snow showers Tuesday night with the associated upper level energy.  Besides a few gusts close to 20 mph and maybe an inch or so of snow, there wouldn’t be much indication that a very strong storm was forming fairly far to our southeast.  Only a few inaccurate weather models support this solution (DGEX, long range SREF members), but it remains a realistic possibility because of the trend this past month.  Many storm threats we saw form only to trend southeast inside of 84 hours as they get suppressed more than expected.  This is not expected nor forecasted for this storm due to upper level energy orientation I’ll touch upon in the conclusion, but because of this recent trend I figured it was prudent to include as a possibility, as honestly the way things have gone recently I would not be that surprised to see this storm slip fairly harmlessly out to sea.

CONCLUSION: So those are the three scenarios for Tuesday into Wednesday.  As you can see, there is still quite a range of possibilities, and every 50-100 mile shift in track will make all the difference.  The upper level energy associated with the storm moves onshore tonight, meaning that it will be better sampled by weather balloons and that hopefully weather models will begin to converge on a specific solution.  As for why I think scenario 2 (scrape) is most likely, a lot has to do with all of the upper level energy players here.  Most weather models have a ridge-axis at 500mb centered east of where I’d like it, which is right over Idaho.  Instead, we see it over western or central Montana.  Even the models and ensemble members most aggressive with the storm show that.  This of course is no deal-breaker, but it leads me to believe that the storm will be slightly east of the ideal track for the heaviest snow and worse impacts for Southwestern Connecticut.  Along with that, recent trends have not supported large snow storms across Southwestern Connecticut, and until I see surface observations and upper level observations supporting a strong model consensus for a large snow storm, it’s very hard to forecast one because of this.  Thus, at this point, a lot of this is a waiting game to see what new data comes in and what the best way to interpret is.  There are a lot of theories flying around of certain models having feedback errors or that when looking at them they “have” to trend west with this storm, but frankly I don’t entirely see it.  Yes, there is a potential for a very large storm here, and that’s why I’m watching it so closely.  But it is far from a lock that we get any significant impacts from this storm.  There are just so many factors at play here, especially with a low pressure center deepening this quickly, that each new run of the weather models and each new release of a weather balloon could be crucial to the upcoming forecast.  As always, I’ll do my best to keep you ahead of the storm and any of its potential impacts, so make sure to keep it here at swctweather.com for the latest storm information.

11 PM UPDATE: 45% Delay Inland, 40% Delay Coast

Very brief update here as sadly I haven’t had the time recently to cover this storm entirely like I would’ve wanted to.  Good news is that if there is a storm on Monday (by no means a lock but odds are rising) then I will have very strong coverage there.  But for tonight, we are seeing wind gusts finally picking up across the region, temperatures falling (down below 40 in areas already) and a squall line with moderate rain moving through the area.  With temperatures likely below freezing within the next hour, that rain from the squall line will freeze.  And winds will help speed up evaporation, there’s only about a 30-45 minute window for that to occur, and I just don’t think there will be enough time for the standing water to evaporate.  The end result in very icy roads past midnight tonight.  Treated roads will be ok, but side roads may be iffy until the sun comes up and can help melt them with a more direct March sun angle.  Only coatings of snow are likely this evening, because as I expected very little moisture is working around the back end of this system.  I always warn about expecting back-end snow, and this is another perfect example as to why you should not bank a forecast on it, as storms typically dry out slightly faster than weather model guidance shows.

As for school impacts tomorrow, I see scenarios in which there are fairly widespread delays and scenarios where there are fairly few delays; it all comes down to exactly how much water evaporates before temperatures drop below freezing.  I’m not confident enough in widespread delays to forecast them, but I do expect scattered delays both inland and at the coast due to ice, as stated by the percentage chances.  There is a scenario in which very few or no districts delay if the cold air is just too late to freeze most roads over in ice, but given the intensity of the cold I don’t buy it.  I think roads will be icy unless treated and that some districts may need to end up delaying.  This is likely not widespread, and districts that have track records of not closing or delaying easily may open on time without much trouble.  Those that have salt/sand shortages still or have track records this winter of closing/delaying easily have fairly good chances at delaying tomorrow due to ice I believe.  This will be the final update for the evening, but I’ll be back at 5 AM with reports on all the schools that have delayed, so make sure to check back in then.