My apologies on this post for an uncertain snow event going out so late and being so short, cramming in something that usually takes 4+ hours into 2 is hard. With that aside, I’ll do my very best to look at the forecast for tomorrow night in some detail below.
A clipper system is currently moving across Minnesota and will continue to dive SE tonight into tomorrow morning. It will end up over the Eastern Great Lakes by tomorrow afternoon. At this time, a new low will form near NYC/Long Island and move NE as it strengthens. The key to this forecast and why it is so uncertain is how fast this low intensifies. I want to stress that the difference between a widespread 3-6″ and a widespread 8-12″ event is a few hours. If the storm forms a bit earlier, there is more snow. If it is a bit late, there is less snow. Either way, a burst of heavy snow is likely tomorrow evening around or a little after the evening commute. Overall, impacts should be minor but after 7 or 8 tomorrow evening, roads are likely to become quite slick.
The Earlier Development Scenario
This is the GEM model showing the earlier development scenario. At 11PM tomorrow night, an intense band of very heavy snow is located over Western Maine centered on a Portland-Lewiston line. In this scenario, intense snow bands develop earlier and farther to the west leading to higher totals across SW areas. Based on very warm SST’s offshore and the very high amount of energy blasting SE with the clipper, I think this is the more likely scenario. The 500mb trough will also be going sharply negative.
A very negative trough with a ton of energy blasting over record warm ocean temps is a setup ripe for explosive storm development. The 12Z GEM shows this well. The other models show a similar setup and the GEM has shown itself to be very reliable when dealing with clippers and Canadian airmasses. It was the one model that caught the surprise no-show of the February 15 blizzard and I think it is on to something in terms of surprises with this storm.
This is what snow totals would look like if the low developed on the early side. Consider this my forecast.
The Late Development Scenario
It is also entirely possible things don’t pull together in time and the heavy snow bands really get going more over the eastern Midcoast than the NH-ME line. The GFS shows this well. This is the same parameter (upward motion) for the same time as the GEM map posted above. Compare them and look at how much farther NE the heavy snow bands (bright colors) are on the GFS compared to the GEM. This is the difference between 3″ and 8″ for most areas SW of Augusta. Where these snow bands set up is the entire forecast at this point. It is important to note that the GFS shows nearly the same 500mb setup. The trough on the GFS is the exact same as on the GEM with the only difference being the GFS is 30 or so miles farther NE. That is the difference between 3″ and 8″. I really want to stress how tiny the differences are in terms of the science. 30 miles is a tiny margin of error, it just so happens that this time that margin of error has tremendous impacts for a large swath of the area. Be prepared for either scenario despite the forecast being for more snow.
This is what snow totals would likely look like given the late development scenario playing out. This is not what I expect to happen but it remains a viable solution. In fact, new clues have emerged since the making of this map that indicate that totals could be slightly less than this if the low really fails to get going. Don’t be shocked if you wake up Wednesday to only a few inches SW of Augusta. Several inches look like a safe bet for the Midcoast and the NE mountains.
Coastal Mixing Concerns
Winds ahead of the clipper will be onshore and thus temps will be marginal at the coast. However, winds will turn N/NE as the coastal low develops which will act to shut off the source of warm air. Also, heavy precip acts to cool the air and precip will certainly be heavy tomorrow night. All added up, I think this will be a wet snow for most coastal areas with only the peninsulas seeing rain. Again, this part of the forecast depends on the coastal low. The faster the low develops the faster cold air rushes in.
This is a VERY uncertain forecast so I’ll try to have an in-depth update tomorrow morning with details. I’ll have another update tomorrow evening as the storm is beginning. At this point, the details will be more clear (helpful, I know!).