Every 30 minutes or so, I'll post short updates with respect to the models coming in this evening and what they suggest about Tuesday's snow potential....
11:15 p.m.: As it's going to be a busy next couple of days, I'm going to end this little live blogging session with this entry. The GFS and NAM models, which suggest a light (GFS) to moderate (NAM) snow event, support our assessment from earlier today for about 1-4" - with the best chance of accumulating snow late Tuesday afternoon into Tuesday evening and the heaviest amounts northeast of D.C. We'll have a lot of coverage tomorrow...so stay tuned!
11:10 p.m. GFS liquid equivalent precip amounts (remember 1 inch of liquid is about 10 inches of snow): 0.17" for Reagan National, 0.15" for Dulles, and 0.21" for BWI. The GFS simulates nowhere near the storm for Philly to Boston that the NAM does. This is a tough forecast for the entire I-95 corridor...
10:55 p.m.: The GFS is pretty slow (a bit slower compared to earlier runs) in getting the coastal low going and slightly further east. Dry air holds back much precipitation until mid-to-late Tuesday afternoon. By Tuesday evening, the coastal low finally begins to blossom and throws back a modest amount of snow but cuts it off by midnight or so. This is not an impressive run for snow and would suggest just 1 or 2 inches.
10:25 p.m.: While we await the GFS (coming out between 10:30 and 11 p.m.), interesting to see the storm's impact in the South. There has been crippling snow and ice in Alabama and Mississippi, up to 8" of snow in parts of Arkansas, and Atlanta is now getting heavy snow (reportedly, 2" in Centennial Park). Delta Airlines is expecting 1,400 flight cancellations due to the storm in the South Monday.
10:00 p.m.: The NAM model absolutely crushes Philly to Boston Tuesday night into Wed morning. The rich get richer. (10:10 p.m.: Actually, taken literally, the NAM might change Boston over to rain due to the proximity of the low to the coast and resultant wind from the east off the ocean)
Keep reading for earlier updates...
9:50 p.m.: AccuWeather's Joe Bastardi forecast (via Twitter) "NE snow forecast(mine)DC,bwi 3-6 phl 6-12 NYC near12 local 18 pvd, bos 12-18 local 24. US model underdone ( again) hi ratio helps". I'm not sure what his basis is for stating the U.S. models are underdone "again". I don't think they've been underdone myself - at least for our area this year.
9:40 p.m.: The NAM melted liquid equivalent simulated precipitation for this event is: 0.40" at Reagan National; 0.32" at Dulles & 0.46" at BWI. Assuming 10 inches of snow to 1 inch of rain (this assumption is just approximate), the NAM would suggest 3 or 4 inches of snow, with a little more toward Baltimore. Note: the NAM has a wet bias and has been known to overdo precipitation.
9:30 p.m.: The latest NAM model is out and intensifies the coastal low more quickly compared to earlier runs. This increases the amount of snow it simulates to 2-4" or so (I'll post the exact amounts in a bit) for the metro region compared to 1-3" in the run from this afternoon. Note: this model doesn't really get the snow going until Tuesday afternoon, with most of the accumulating snow falling between 7 p.m. and midnight (Wed.).