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.
We 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.