The forecast has recently been revised for the area due to rapidly changing weather conditions in this very complex storm. Premium subscribers have been made aware to these changes through the day. You can purchase the most recent Premium forecast, which outlines school closure percentages and other relevant data, here. Or, you can subscribe here to receive all Premium content through the storm, including updated school closure/delay forecasts for both Monday and Tuesday and additional future storm threats. Otherwise, the relevant parts of the forecast have been freely released below:
Through the night the sleet/freezing rain line will vary across the region, with it right now being just north of the Merritt Parkway. It may approach Interstate 84, but at no point do I expect it to get sizably north of there. Instead, it continues to vary from coastal areas to slightly inland areas. New data has resulted in updated accumulation ranges, putting the coast in the 2-5 inch range, while inland areas north of the Merritt Parkway see a little more precipitation and should see 3-6 inches, and further north of I-84 the precipitation will be even steadier and remain snow throughout, so the forecast of 4-8 inches there should work well too. Based on recent data, amounts in the higher ranges here (mainly at the coast) appear most supported, but the forecast remains quite variable. The accumulation forecast thus is fairly high confidence currently, but icing is still a variable that is not confident. Coastal areas could see scenarios supporting freezing rain, as you can see on the HRRR at 4 AM here. However, most freezing rain will be freezing drizzle or not accumulate much, so it may be hard for most areas to see more than a tenth of an inch of ice or so. For after that, we see everything turn over to sleet and then to snow, even at the coast. Thus, for icing I am keeping the .1-.25 inches of ice, but favoring amounts more widespread in the .1-.15 inches for ice. This is still enough to cause sizable problems, especially with travel, but I don’t see all that much model support for ice to a quarter of an inch. Then, between 7 and 11 AM I believe the entire region goes over to snow. The coast turns from that freezing drizzle/light freezing rain to sleet and then over to snow. However, the transition won’t exactly be smooth. It could jump from freezing rain to sleet to snow but then back to sleet, or something like that. Different pockets of the atmosphere will be supporting various precipitation types between 5 and 10 AM across the region, and so I expect very fluid precipitation type reporting as it could change fairly often. Whether it is sleet, freezing rain, or snow, however, surface temperatures below freezing will support those precipitation types icing up the roads. And with precipitation looking to at least continue steadily through 8 AM, I would be quite surprised to see roads improving at all tomorrow morning.
Precipitation as snow then continues as on and off snow through Tuesday afternoon before winding down Tuesday evening. Road conditions hit their worst likely sometime between 6 and 10 AM across the region, but could remain quite slippery into the afternoon as well, especially as snow falls on top of sleet and ice. Models again continue to jump around on the extent of icing, and the forecast for exact precipitation type and intensity remains volatile, but accumulations are actually becoming higher confidence, so that another update may not be necessary there. Again, tomorrow avoid travel if you can. The afternoon will definitely be more favorable than the morning, but light to moderate bursts of snow into the afternoon will certainly be possible, especially inland, so it just looks to be a widespread messy day. Please plan accordingly, and another free update will come out later tonight if there are any major changes.