Lots of things to keep tabs on as this next system moves up through the region tomorrow night into Saturday. Temperatures from the surface all the way up to around 750-800 mb will be cutting it close, but the strengthening low and good rates on the front end of the system will help things along.
Most spots from near the MD/PA border south and near the coast will change over to rain after the snow has fallen (and while most of you south of the Mason-Dixon are tucked away in bed). The back edge of the precipitation Saturday afternoon will likely switch back over to snow, but time of day, surface temperatures and weaker rates means it shouldn’t amount to much for most spots.
More clipper fun for the Mid-Atlantic, only surface temperatures won’t be so wonderfully cold this time around. Marginal temperatures at the surface and around 900-925 mb as far north as I-70 (maybe even further north?) along with mostly light precipitation hurting snow chances. Most or all of the snow will also fall during daylight hours. One plus is it looks like areas from around D.C. northward will get below freezing tonight before the snow moves in, so the ground should still be nice and cold. Definitely more opportunity to end up lower than my forecast as opposed to higher. The Delmarva Peninsula and southern New Jersey could see heavier banding late in the event, which is kind of alluded to on my map with the 2-4″ stripe in southern New Jersey.
I wish I could wait until the 00z models came out for better forecast confidence, but this will have to do.
Well, the model trends over the last 24 hours were not in the direction I though they were going to go, so I had to cut back the forecast along I-95 and make some smaller adjustments on the western edges of the contours. Overall, things have shifted slightly warmer across much of northern VA, DC, MD, NJ and southeastern PA in areas near and west of I-95. With such marginal temperatures of 33-36F at the surface, snowfall rates will be the big thing to watch tomorrow to see who will cash in and who will get stuck with little or nothing. Sloppy, wet snow for the major population centers along and near I-95.
The difference between 4 inches and 8 inches within that contour range will be elevation. Lower elevations can expect totals closer to 4-6 inches, with the higher elevations getting more into the 6-8 inch range. Along the Blue Ridge and Central Appalachians, a few of the higher peaks could hit 8+ inches. I didn’t include it on the map, but I wouldn’t be that surprised if there was one or two reports of 8+ inches in the highest elevations of north-central MD.
Some of the models even show some sleet mixing in, mostly from far northeastern MD into southeastern PA and NJ. That may actually be a blessing in disguise, as sleet can accumulate more easily than snow in marginal temperature situations, and a base of sleet would make it easier for any snow afterward to stick.
Forecast confidence remains on the low side, mostly with the eastern edge of the contours where the rain/snow/mix is the most problematic. A one or two degree change to the surface temperature could mean a big difference for some areas, both to the high side and the low side. There’s also still the question of where the best banding will set up, which will produce the heavier rates and increase the chance for higher accumulations for a select few. My best guess for that is just inside the eastern edge of the 4-8 inch contour up into the 8-12 inch contour.
Perhaps if we can get some big, fat dendrites cascading down along I-95, then that area could actually get a decent accumulation. However, looking at the temperature profiles, that seems pretty unlikely.
A hectic day before Thanksgiving is in store for many in the Mid-Atlantic and Northeast. Toughest challenges are 1) finding that crucial rain/snow line, and 2) honing in on QPF totals, especially when considering the deformation band that’s expected. It will be a heavy, wet snow that will at least initially struggle to accumulate on the roads. Expecting it to start as rain around the greater D.C. region, changing over to snow in the mid-to-late morning hours.
Best confidence is for places 20-30 miles north+west of I-95 and points west. Western edges could shift a decent amount still from the MD/WV Panhandles into PA, depending on the storm track. There’s high bust potential in both directions along the I-95 corridor, where heavy snow rates will battle against marginal surface temperatures of 33-35 degrees.
For years, the NWS snow forecast maps have been sometimes hard to find and inconsistent from WFO to WFO. I decided that it’s time for one web site that has links to ALL of the NWS snow forecast maps across the CONUS.
I also displayed many of the Mid-Atlantic maps directly on the page for one-stop browsing. They were chosen because I am currently D.C./Mid-Atlantic focused, and they suit my needs the most.
At the moment, I have the Northeast and Mid-Atlantic offices completed. I will hopefully have the rest done by the end of the week (at which point I will update this post).
I like to keep my seasonal forecasting short and sweet, so here it is:
- Latest model guidance and ENSO trends suggest DJF will likely be a weak El Nino.
- +PDO to support ridging in the western U.S. and troughing over the Midwest/eastern U.S.
- +AMO could help keep the Southeast milder (read: less cold).
- -QBO will allow for a greater chance for blocking in the Atlantic (-AO/-NAO) as well as stratospheric warming events. This would promote colder temperatures in the eastern half of the country.
- Drought conditions in the West will promote warmer and drier conditions there.
- The western U.S. could go warmer given favorable +PDO and long term drought.
- If -NAO/-AO becomes the main forcing mechanism for the U.S. weather pattern, it could bring colder air into the Midwest, Mid-Atlantic and Southeast while providing warm and wet risks in New England.
- If a moderate Nino develops, a stronger subtropical jet associated with it could allow for wetter conditions across the southern U.S. and Mid-Atlantic.
A note on my track record… I have been about 50/50 with long-range forecast skill since I started in 2010. There are many others out there with more long-range knowledge, reasoning and a better understanding of how the atmosphere works on a longer timescale. That said, nearly every forecast I have seen so far favors a warmer West and cooler East, so I’m not exactly breaking the mold with this forecast. It looks like we’re all in the same boat with this one. The only thing left to see is if we can sail to victory or go down with the ship in defeat.
As always, the forecast anomalies are based off the latest 30-year normals (1981-2010).
I’ve had a few opportunities to chase storms in April, and I grabbed a handful of images and uploaded them to Flickr. They’re in my 2014 East Coast Chases album, which I will keep updating with images if/when I get more.
I head out to the Plains for two weeks… IN two weeks! Same crew as last year, but with my own new-to-me personal vehicle (2010 GMC Terrain) instead of a rental. Like last year, I will be posting daily blog on the U.S. Tornadoes site, and I’ll have a post with the link and details later on.