Halloween to be a bit gnarly, but not spookyPardon me as I nerd out a bit...  This 2:50 AM image shows the players on the field. The low over Kentucky has become vertically stacked, with the surface and upper-level areas of low pressure lining up on top of each other. This is also known as "occlusion", which is when a synoptic storm reaches maturity point and begins to weaken. The telltale sign is the dry air working into it, and the water vapor image reflects that. I use my term "atmospheric trash" cynically to describe slowly dissipating upper lows, which is essentially what that low is in the early hours of Thursday morning. The difference this time is that the atmospheric battery cables are out, and it will be brought back to life as it continues to track to the northeast.  Thursday 6 AM (10z) to Sunday 1 AM (06z - time change!) - This long loop of vorticity (upper-level energy) at the steering level of the atmosphere shows the upper low reinventing itself as energy enters it near Illinois. Between the energy diving in from the northwest and the ridge flexing itself to the southwest, the trough over the east punts Melissa to Newfoundland, while the core upper low gets kicked northeast over the mainland. It's kind of comical and sad at the same time. Had the upper low continued to weaken, that may have allowed Melissa to track closer, which would have allowed the trough to siphon off more moisture from it and give the region a more significant rainfall. That isn't going to happen. Drought begets drought.  Thursday 6 AM (10z) to Sunday 1 AM (06z - time change!) - The trough will pick up the outflow moisture from Melissa and drag it into the region, which will bring 50-60% more rainfall than if it didn't. The reborn upper low amplifies a surface low, which intensifies as it moves into the Gulf of St. Lawrence. The cold pool aloft brings winter to higher elevations, with high wind, bitter wind chill, and snow showers on Saturday. The wind diminishes Saturday night, bringing a frosty start to most areas Sunday morning. Rainfall timing and amounts Thursday Noon to Saturday Midnight - Light outflow showers begin over the west and south in the afternoon and spread to the north and east overnight. Rain becomes heavier heading into Friday morning, then tapers off Friday afternoon into the evening. Trick-or-treat time appears mainly dry over the south (I can't rule out a light shower), but rain gear may be needed elsewhere.  Given the progressive nature of the systems involved and the likelihood of dry air moving in quicker, forecast rainfall amounts have trended slightly less. The shoreline areas and southerly facing mountains appear to receive the most precipitation. A stiff breeze on front and backside Thursday Noon to Saturday 2 PM - The wind picks up Thursday afternoon out of the northeast and cranks up overnight into Friday morning. As the surface low tracks into the Gulf of St. Lawrence, the wind shifts more southerly Friday night and eventually northwest by Saturday morning. Wind gusts of 25-35 mph are possible on the front side and 20-30 mph on the back side, with higher speeds at higher elevations. Isolated power outages are possible. Crowe's is there when you need them Temperatures and outlook through WednesdaySunday appears mainly fair, with a snow shower possible in the far north. An upper-level trough heads southeast from Hudson Bay on Monday, and may bring showers of liquid or frozen variety overnight and into Tuesday. There are ideas out there for a potential storm around Thursday that may bring rain and snow, but confidence in that is low for now.  The PTW Weather Wall updates 24/7 Your financial support keeps the lighthouse lit |
Mike Haggett
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