Tuesday February 27, 2024

2/27/2024

Inside runners: the story of Winter 2023-24

I spin weather-related jargon at times, which, for the new followers, maybe a bit confusing. I get messages periodically saying “What do you mean about this?” The one that I have used more often this winter has been “inside runner”. Sometimes they are referred to as a “St. Lawrence runner”. To put it in a simple context, it’s the wrong side of a NorEaster, for those wanting snow. All three major storms the region received in December and January were inside runners. While this one won’t be nearly as potent as those were, it could be problematic in spots. To put it on a spice scale, mild to medium comes to mind as I have pawed over data for the past few days. Wind is likely to be the greatest threat with this one over a fair portion of the region.

The low-level jet will be there,
but how strong will the gusts be?

This is the main question going into this event. Guidance ideas have been mixed on how much the inversion cap plays a role in the outcome. The cap here is likely caused by the cool ocean with warm tropical moisture riding over aloft. The differing temperatures are like oil to vinegar. That sets up a deflection of the low-level jet, keeping the stronger gusts aloft, but as the corkscrew hodograph in the top right indicates, there is a reasonable amount of spin going on, enough that downdraft winds could occur in areas of heavy rain or in garden variety thunderstorms.

Tuesday 10 PM (03z Wednesday) to Thursday 7 AM (12z) - A stiff breeze develops overnight into Wednesday morning and increases as the day goes along. The shorelines take the brunt of it since there is little in the way to knock the wind down, other than the inversion cap. The high-end risk for strong gusts passes through in the afternoon into the early evening. As the trailing cold front passes through Wednesday night, the wind shifts to the northwest. Given the strong pressure gradient, the threat of the strongest wind shifts to the mountains and north as the system pulls away Thursday morning.

While the worst of the wind is expected to be over Thursday morning, the stiff cold breeze is expected to continue through the day and settle down overnight into Friday.

The bottom line here is that if the inversion cap holds up, wind gusts will bust on the low end. That said, these tropically enhanced systems cannot be trusted. It would be wise to prepare for power loss and travel in the high wind watch region should be minimized with the threat of falling limbs and blowing debris. Counties in the coastal plain not under a high wind watch may end up with a wind advisory.

Expect a longer duration wind event, and prepare accordingly.

The precipitation aspect

Tuesday 10 PM (03z Wednesday) to Thursday 7 AM (12z) - Outside of a quick hit of junk for the higher hilltops, this is a rain event for all. Given the tropical infusion, the risk of thunder is there. One of the more intriguing aspects of this setup is the sharp cold filtering behind the frontal boundary. Yes, I am thinking of the chance for thundersnow as the system pulls away. Since this is passing through in the evening, the rumbles could be very loud given the rapid drop in temperature.

Precipitation ends from west to east overnight, and by Thursday morning, the wind will be what is left of this storm.

While the flood risk overall is minimal, there is potential for localized issues. Where there are areas of snow, add 1-3” of potential water content trapped in that which may be released with the warm air intrusion. With frozen ground, brooks, streams, and small rivers are a likely destination, along with sensitive basements. The ski hills may be able to absorb what rain is coming, but with dew points above 32° for upwards of 30 hours and fog potential could ripen the pack for melting.

A smattering of snow is expected on the backside of the system as the storm departs. Higher elevations may pick up a couple of inches as dynamic cooling is expected to form quicker aloft. For the valleys and areas to the south and east, perhaps a quick coating or a few flakes as a parting gift.

Temperatures are expected to crash overnight into Thursday morning. Any standing water that remains will likely turn to black ice on fairly short notice.

Stay tuned!

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Thank you to Allspeed Cyclery & Snow in Portland, Downeast Aerial Photography in Rockland, Dutch Elm Golf Club in Arundel,
and Sunrise Property Services in Bridgton, for partnering with Pine Tree Weather.

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- Mike

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