A Chilly End to Spring

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We are facing one of the coldest patterns we have seen this spring and it comes right at the beginning of our transition to more summer-like weather that usually occurs in May! Above, the surface map shows our current rain storm we are seeing today, which is the precursor to our colder weather ahead.

As shown on the second image, an area of anomalously low heights and pressure breaks off over the Northeast over the weekend. This becomes a cutoff low that looks to stick around with us for the week and into Mother’s Day weekend. This pattern is typical of what we tend to see in the beginning of the Meteorological Spring Season (March 1st-May 31st).

Above show the typical weather types we see during the beginning of March (labelled as k = 1, 3, 4 and 6). Typically the pattern shows an area of low pressure over the Great Lakes pushes Southeast into the Eastern Seaboard. This Low can then cutoff and cause a secondary area of low pressure to form in Northern New England. These two areas of low pressure influence the weather over the region for a span of 2-5 days before finally pushing offshore into the Atlantic as High pressure from the Midwest moves into the region. (k=4 to k=3 to k=6 to k=1 is the typical pattern).

The above images show the MSLP (black lines), 500 hPa heights(yellow lines), 850 hPa winds, and temperature anomalies (blue = colder than average, red = warmer than average). This shows that for the majority of the pattern, the area can be expected to see colder than average temperatures, with the coldest occurring when the pattern is at its climax (as the two lows over Northern and Southern New England contain influence over the region). Then temperatures return to normal and slightly above normal as the pattern loses its influence over the region and high pressure from the west moves in.

So what can we expect in terms of precipitation with this pattern? Well usually the onset period of this pattern will see the most rain for the New England Region. However, all of the weather types have some precipitation over the region, which means that there could be the chance throughout the pattern for showers to occur on any of the days.

The good news is that this pattern usually lasts a max of 2 weeks on average, so we can look forward to a return to more seasonable and possibly warmer weather by the middle of the month!


Wet-Bulb Temperature and Snowfall

We hit 40° by lunchtime, but then it started snowing! Wondering why that is??? It has to deal with what’s called the wet-bulb temperature.Capture

The wet-bulb temperature is the air temperature at the surface that the air can cool to if the humidity reached 100% (meaning the air is fully saturated with water). It falls between the dew point (the green line) and the air temperature (the red line). A simple way to calculate an approximation to it is to look at the dewpoint depression (which is the difference between the temperature and the dewpoint), divide it by 3 and then subtract that number from the air temperature. 

So in our case today at noon, we saw an air temperature of around 40° and a dew point of around 18°. This gives a dew point depression of 22°, which divided by 3 is around 7°. Subtract this from the air temperature, and we would expect the air to cool to around 33° when fully saturated. This is cold enough to support wet snow to fall, but not to stick on the ground. We see after noontime, the temperature rapidly fell and the dew point rapidly rose, which is around the time the heavier precipitation bands were falling. This suggests that some of the falling snow was evaporating before these heavier bands moved in, as we only saw light snow flurries an hour before that. This cooled the air quickly towards the wet-bulb temperature and allowed for the heavier bands of precipitation to fall as snow as the atmosphere had been cooled by evaporation.

This is a typical case for the early and late winter precipitation events. Snow can happen up to 40-42°F sometimes and the best way to predict it happening is with the wet-bulb temperature.

Where Was the Snow? How the Last Storm’s Snowfall Totals Came Up Short

stormver1 There’s no doubt that the last snowstorm was a complex beast. In fact, many of our computer models had a hard time trying to pinpoint exactly where the storm would be situated, even 24 hours before the storm was set to hit the region.

As the storm started to make its pass, the National Weather Services (and some local news stations) actually INCREASED “Maximum Possible Snowfall” and “Most Likely Snowfall” estimates.


Why? Newer model data showed the storm’s “wrap-around” bands pushing further into portions of eastern and central Southern New England for a longer period of time than initially thought. Furthermore, temperatures did not seem to be as warm as initially anticipated over eastern MA locations at the beginning of the storm. This meant that both: 1. More precipitation will fall in the form of snow, rather than mix/rain.
2. Colder temperatures would cause the snowfall ratios to increase, meaning higher snowfall accumulation, even with similar forecasted QPF values.

The National Weather Service also upgraded portions of Southeastern MA (Bristol and Plymouth Counties) into the Winter Storm Warning as a result of the higher forecast totals.


By 4:30 PM Sunday, the Winter Storm Warning for coastal Plymouth County was dropped and replaced by a Winter Weather Advisory. By around 6:30 PM, the rest of Southeastern MA was also downgraded as well.

So what actually happened? Well…


As the precip shield pushed into our area through midday Sunday, banding features set up as expected through most of the area. Onshore flow eroded the cold air over southeastern/east-central MA as initially expected before the storm (but after the NWS ruled against this in their updated assessment early Sunday afternoon. Though, to be fair, they did mention the possibility…) However, the bombing surface Low formed slightly East than expected and moved out more quickly. This nudge allowed for most of the heavier bands to miss East-Central MA and even a large portion of Eastern MA (for the most part) and the precip. that DID fall in those areas was not as heavy as predicted. By midday Sunday, models trended away from the NAM’s more robust predicted totals and more towards the HRRR’s (ultimately better) values. Forecasters who placed more credence in the NAM’s solutions were proven wrong.

The result? Much lower snowfall totals than forecast. Here are some NWS estimated values 24 hours before the storm onset, compared to what verified. Note that these were the forecasted values BEFORE the NWS increased them even more early Sunday afternoon:

Saturday AM Forecasted Snowfall Totals From NWS vs. Reported:

Fitchburg/Leominster, MA -- Forecasted (as of 7:42 AM, 2/11): 13". Verified: 9.2"
 Worcester, MA -- Forecasted (as of 7:42 AM, 2/11): 11". Verified: 6.8"
 Taunton, MA -- Forecasted (as of 7:42 AM, 2/11): 4". Verified: 3"
 Boston, MA -- Forecasted (as of 7:42 AM, 2/11): 6". Verified: 4"
 Plymouth, MA -- Forecasted (as of 7:42 AM, 2/11): 5". Verified: 2"
 Amherst, MA -- Forecasted (as of 7:42 AM, 2/11): 10". Verified: 6.9"
 Provincetown, MA -- Forecasted (as of 7:42 AM, 2/11): 7". Verified: 2"
 Greenfield, MA -- Forecasted (as of 7:42 AM, 2/11): 11". Verified: 8"

To be fair, many forecast max wind gust values did verify. Every county in RI had a location with a max wind gust measuring > 50 mph. While NWS did not report any gusts over 60 mph, there were a few locations that gusted over 55 mph.

In conclusion, it’s easy to scorn over under/over-forecasting, but quite easy to forget when forecasts verify. Now we wait for the next storm…

Sloppy Storm for End of Week Will Bring “Mixed Bag” to Area

Thursday evening into Friday we will see a developing low pressure system begin to “bomb” off the New England Coast, bringing with it rain, snow, wind, and almost everything in between.

Moisture from the gulf of Mexico (seen above at 48 hours, 00z Thursday) will begin to ride a quickly deepening trough late-week. As the storm rides up the coast late Thursday, all eyes are focused on the position and strength of the rapidly intensifying low. As of the latest runs, the NAM is trending slightly east of the ECMWF as of 06z Friday. The GFS seems to be more progressive than the other two, and also seems to be underestimating the QPF we often to see with these moisture-rich systems.

Here, we see the bombing low’s placement, riding a negatively-tilted trough as of 06z Friday, according the Euro. It is always fascinating to see how quickly these storms explode off the coast: between 18z Thursday and 06z Friday, the low deepens from 1004 hPa to 976 hPa(!) according to the most recent NAM run. Even though this will not be a long-duration Nor’Easter, we will still see ample moisture, with QPF totals around 1-2″ for most of Central and Eastern MA (higher totals further east). However, the GFS, being more progressive with the storm, does not have nearly as much precip. falling over Southern New England because the storm is not fully developed at the time of impact. It is the outlier in that sense.

qpf1Now, the question on everyone’s minds: will it be rain or snow? Well… latest model trends have shown a more inside track, rather than the classic “Benchmark Blockbuster”. In fact, the GFS and the ECMWF both show temperatures around and within the I-495 corridor above freezing up to 925-hPa! This seems to be a snowstorm for interior Central New England, and Northeastern New England, the way the models are currently trending. Here’s a peek at the Euro’s snowfall projection through 1 PM ET Friday. Keep in mind… The Euro is the “snowiest” solution, as of now.


Along the coastal plain, surface winds will likely gust 30-40 mph, with up to 50 mph possible on the Cape and Islands, as well as possibly the North Shore, as intense cyclogenesis occurs.

It can’t be stressed enough: minor changes in the rain/snow line will have SIGNIFICANT impacts on our area. As is stands now, there is potential for 3-6″+ (possibly much more) outside of I-495, 2-4″ inside I-495, and even less south and east. Key word: Potential. If the storm slows down and trends further East, totals up to (and over) 12″ would not be out of the question for portions of Central and Northern MA, as well as some locations in inland NH and (particularly) interior Southern and Central Maine.

Stay Tuned to UML Weather Center for future updates because these fine details WILL change!

Bitterly Cold Air in Store for the End of the Week Will Bring Dangerous Wind Chills to Our Region

A blast of arctic air will encompass the region just in time for the end of the work week. It’s pretty uncommon to see low temperatures flirting with negative digits before the first day of Winter, but this is exactly the case as we had into the early morning hours on Friday. An unusually deep (for this time of year) trough will be entering New England Thursday into Friday, allowing arctic air to funnel down from the north.

00z NAM 500mb.pngWe see the trough axis here on Wednesday’s 00z NAM run positioned over Western NY/PA, poised to enter New England in the coming hours. The leading cold front will usher in the cA air mass. This is in excellent agreement with the 12z NAM run from Tuesday, with the exception being that the newer run was very slightly more progressive with the trough entrance into our region by 12z Thursday. To put this into perspective, these 500-hPa heights are so low for this time of year that they are almost, if not more than, 3 standard deviations below average climo!

So, what can we expect for surface temperatures Friday Morning? As of the latest SREF, by 09Z Friday morning (4 AM Eastern) temperatures dip down to -13 to -14C (between 7-8F) for Northeastern MA! Keep in mind, too, this is not the coldest air of the day; that won’t happen for another few hours later… The SREF plot below not only illustrates the mean temperatures, which stand out the most, but another key factor: decent agreement among ensemble members in the forecast, even at 66 hours out from initialization! We note the spread to only be 2-3 degrees over New England. This allows us to place higher confidence in the model’s forecast for this parameter. In fact, throughout the entire event, there is very little spread among SREF members! In terms of operation model run comparison, the newest NAM and GFS are both in good agreement for Friday morning SFC temperatures, with the NAM being slightly colder than the GFS in Eastern MA, at least at 12z Friday.


Speaking of the “entire event”, how long is this supposed to last? Well, the trough seems to be taking its time enveloping us before the flow aloft transitions to more zonal in nature, and as such, we do not expect to see a quick bounce-back to more seasonable temps. The latest GFS does not have sfc temps. above freezing from just after 18Z on Wednesday all the way through a little before 18z Saturday. GFS meteogram for KLWM (Lawrence, MA) is below.


We also see 10-meter wind speeds illustrated in the meteogram. Let’s talk about that. Overnight Thursday and into Friday morning, we will see a very well-mixed BL and a potent Low-Level Jet. If we are able to mix down some of the winds from the jet, we will see the potential for very strong, possibly damaging wind gusts at times. Below is the low-level jet position and magnitude at 06z Friday morning, according to the GFS. Note the area of 40-50kt winds over New England which, if mixed down, could cause damaging gusts at the surface at times. It would not be surprising to see some reports of downed branches, especially for Southern New England, late Thurs. into Friday. Expect Wind Advisories to be posted for MA, and maybe even High Wind Watches and Warnings possible, especially Southeast MA and CC&I.

These powerful winds, combined with the arctic air entrenched in the region, will pave the way for very dangerous wind chills Friday morning. Anybody caught outside will be at-risk for wind chills that could be well below zero at times.

Lastly, on Friday, there is the potential for some snow squall activity, thought it would probably be short-lived (though, possibly moderate to heavy at times) and likely confined mostly to southeastern New England. Greatly reduced visibility is possible, but it would be surprising to see more than a few inches of snow, based on current model QPF. The tricky part is whether or not there will be enough moisture to work with; right now the synoptic set-up is not really ideal for a classic snow squall event across the region.

The next storm system will enter the picture early this weekend and will displace the cA airmass, likely bringing a change-over to liquid precip. thanks to warmer air advecting into the region. Stay tuned for more details on that system.

Messy Forecast For the End of the Weekend

You have all probably already heard about the potential for our first Plowable Snow Storm of the season, but what you haven’t heard is what we can expect here in our Neighborhood. This system is still three days out and hasn’t fully formed yet in the Midwest, so the data is a bit sparse, but we have some pretty good ideas along with the model guidance to go off of. First off, here is one model’s suggestion as to what we will see for Sunday Night and through the day Monday.


From the looks of it right now, the Low Pressure system that will be bringing our precipitation will pass its center over the Great Lakes Region. In meteorology, we call that an inside runner. Usually with an inside runner, we start off with some snowy precipitation as there is still cold air in place, but as the storm tracks to the west of New England, the warm front from the Low Pressure System ends up passing directly over New England allowing warm air to intrude the region and cause the snow to change over to a mix and rain. However, this storm looks like it could end up being a special case, so let’s take a look at a few things.


This image is from an analysis of Weather Types (WTs) (Weather Patterns seen during a season) in the Northeast by Roller et al (2015). Right now, we are in WT 1 as High Pressure is dominating the Southeast U.S. This storm can be seen as the Low Pressure system over the Midwest. This pattern is mostly seen during a (-PNA) phase, which is what we are seeing now. PNA is a form of teleconnection, which represents the low-frequency tropospheric height variability, as classified in the study of Barnston and Livezey (MWR, 1987). Basically it affects our weather patterns throughout the year based on the position of the jet stream and other factors. This pattern then transitions to WT 2 which sees the Low Pressure system push to the East and North. Most storm tracks tend to go into the Great Lakes Region.


A look at the current PNA and NAO Indices. A negative PNA and Neutral to Negative NAO suggest stormier weather for the Northeast U.S.

By the end of the weekend, we will see a negative PNA and neutral NAO. This usually suggests stormy weather for the Northeast, but also suggests that inside running storms are likely. That means we are most likely to see a changeover to some mix and rain at some period during the day on Monday as warmer air is pulled into the region. graphic.aspx.png

Above you will see a map of the vorticity in the upper atmosphere. When we look at vorticity, we look for the regions of bright colors, indicating a vorticity maximum. That usually suggests somewhere around the area there will be rising air and the potential for some precipitation (this is one of many factors that influence whether or not precipitation will occur). Looking at this, we see the maximum that is near the center of the Low around the Great Lakes so there is expected precipitation to the west. There is another interesting area around Virginia that suggests some precipitation off the East Coast. There is suggestion that this could be picked up by the low pressure system and form a secondary low off the coast of Massachusetts. That would cause enhanced precipitation over Southern New England leading to higher amounts by the end of the day Monday.

This storm needs to be monitored closely during the next couple of days to fully see what will happen, but either way, expect a messy start to next week!

GOES-R Successful Launch and Its Implications for the Future of Meteorology

As of 6:42 P.M.November 19th, 2016, NASA launched its revolutionary, next generation weather satellite, GOES-R, into space. After long periods of delays the satellite has finally launched and now we all wait in eager anticipation for it to begin transmitting valuable weather data back to us on Earth. All in all, it will take around 6 months to make sure everything is working properly on the satellite and then some time to check the data and make sure what the satellite is sending back is useful to us. So what does this mean for our forecasting abilities?

Our forecasting abilities will only continue to get better. The data we will be receiving from the GOES-R will be of higher resolution than what we have previously received from weather satellites and it will also update on a higher frequency than what we have seen before. This will allow us to use this higher input data not only for the forecast models, but to better predict things such as Mid-Latitude Cyclone and Hurricane tracks. This will allow for more warnings to go out in faster times to give people in danger a larger time frame to prepare for oncoming weather. Anytime that the window of warning can be extended by even a few minutes allows more lives to be saved when dealing with severe weather.

The other interesting thing about this GOES-R satellite is that it is the first satellite to have a lightening mapper with it in orbit. This will allow for the satellite to record lightning strikes and report them back as data. This can then be used to determine where severe weather is occurring without solely having to rely on weather radar and observations. This again will give more leeway to the National Weather Service and other local Meteorologists to be able to warn the public of inclement weather farther ahead of time than they currently have the ability to.

The GOES-R is still a year away from being able to provide us with this useful data, but now that it is finally in orbit, it is the start to a revolutionary change to weather forecasting. Once the data is available for use next year, forecasts will only improve greatly and many more lives will be saved from dangerous inclement weather situations.



The GOES-R satellite streaks into space aboard an Atlas V rocket in this long-exposure view of its successful launch from Cape Canaveral Air Force Station in Florida on Nov. 19, 2016.

Credit: United Launch Alliance and space.com