Lots to talk about in this update, including your weekend forecast and some preliminary discussion on a possible storm system for next week, so let’s get right down to it.
The first thing to talk about, and what will be the primary influencer of the weekend forecast, is a system which will bring primarily rain to the area in the form of an overrunning event from the SW. Rain of varying intensities will move in this evening into the overnight in the form of scattered showers and remain as either light rain or scattered showers for Saturday before becoming heavier and steadier Saturday night. The heaviest precipitation looks to come overnight Saturday into Sunday as the coastal low from the overrunning event finally forms, which while it passes well east of us, will allow for some of it’s precipitation shield to impact the area. In general, temps will be too warm to support anything other than rain, but as the low moves out early Sunday morning, a flip to a light wintry mix could be possible in the usual colder spots, especially the NW hills. However, no significant accumulations are expected.
In terms of timing, the GFS is the quickest of the guidance, already breaking some light rain out across the western portions of the area by 7 PM tonight, and considering that systems, especially overrunning events, have been running quicker than guidance, we will lean towards this scenario. On and off rain will continue overnight and into Saturday, becoming more on than off as the day progresses. Sunday should be mostly dry and partly sunny, with perhaps a few showers in the morning, but overall not a bad day to be out and about.
Here’s the total QPF from the NAM, GGEM, UKMET, and GFS, showing relative agreement on an inch to an inch and a half or so of rain for the state(25mm = 1”), with the GFS/GGEM being on the drier side and NAM/UKMET on the wetter. We’ll just take a blend of the two and go with an inch to an inch and a half of rainfall with the higher amounts further south.
Monday will have clouds building, with a chance of precipitation moving in later in the day as we approach our next threat. Highs will be around the freezing mark.
The next threat is a coastal storm that forms as a result of a PNA spike out west(A spike in the pacific ridge), allowing a piece of energy to drop down the back side of that trough, come around the base, and amplify. Originally, models had this event moving in on Sunday night or Monday when we had a colder airmass as a result of a strong Quebec high locking in low level cold, and as a result, it would have, verbatim, resulted in a fairly significant snow event. However, over the past few model cycles, we’ve seen two trends develop which suggest that a snow event is less likely, as well as one new way that we can see snow.
The first unfavorable trend has been for the event to be pushed back on modeling to the Monday night-Tuesday timeframe as opposed to Sunday night-Monday. This means that we will no longer be under the influence of the Quebec high, instead, it will be retreating, allowing the midlevel’s of the system to flood with warm air and make us mostly rain. Secondly, the trend on modeling has been for a system closer to the coast, which pulls us into the warmer sector of the storm and as a result cuts us off from the colder flanks of it. Here are images from the UKMET’s 12z run yesterday and overnight 0z run today showing the placement closer to the coast as well as delayed timing(Both are hour 144, so the system got shifted back 12 hours essentially).You can also see the warmer thicknesses as a result of an overall warmer profile.
Model consensus is fairly strong except for the GFS, which is a complete outlier on focusing on the northern stream entirely and not digging the low at all. We will ignore it’s solution for the purpose of the forecast and take a 3:2:1 EURO/UKMET/GGEM blend for the purposes of the forecast.
In general, will forecast a chance of precipitation from Monday night through Wednesday, mainly in the form of rain, with some wintry precip possible across northern sections of the state. Highest probability for significant precipitation is on Tuesday, but timing is anywhere from Monday to Wednesday depending on the amount of wraparound precip and how far back the system gets delayed. Given the lead time, will not go into more detail, but know for right now the threat of wintry weather is diminished, but not completely eliminated. We will update as needed as models evolve.
Behind the storm, generally dry conditions and below normal temps expected for the remainder of the work week.
Have a wonderful weekend, stay dry, and thanks for reading Southern Connecticut Weather!