Snowfall accumulation forecast maps for two upcoming rounds of precipitation

* Winter Weather Advisory for northern Maryland (including Frederick and Carroll counties) midnight tonight to 7 p.m. Saturday *

Two rounds of wintry weather will visit the region in the next 36 hours. The first, tonight, should be mostly light rain but may put down a little snow in the far northwest suburbs. The second, Saturday afternoon and evening, offers the chance of rain showers changing over to snow showers as temperatures rapidly fall, possibly creating pockets of slick travel Saturday evening.

Let’s look at a few more details...

Round 1: tonight

As low pressure develops to our south later today, some light rain is likely to develop over the region from west to east between late afternoon and mid-evening . Most locations will start off as rain, but as colder air works southeastward overnight, some spots will mix with and change to snow - starting after 12 a.m. from in our far northwest suburbs. (Loudoun, Frederick counties). Places like Dulles and Gaithersburg could see a transition from rain to wet snow somewhere in the 2-5 a.m. window. Snowflakes will have a tough time making it inside the beltway. Precipitation ends everywhere between 5 and 7 a.m.

Where it does snow, no accumulation is expected, except perhaps a coating or so from Leesburg to Frederick and to the northwest.

A NAM model printout for Reagan National Airport. The areas circled in yellow indicate precipitation amounts and temperatures Friday night and Saturday morning. They remain above freezing at Reagan National Airport - meaning rain is most likely, maybe mixing with some snow. However, the areas circled in red Saturday afternoon and evening show temperatures falling below freezing with some light precipitation - probably rain and snow, changing to snow. (Texas A & M Weather Interface)

If anything, the models have backed off a little on their precipitation amounts and have trended a little warmer suggesting the little potential for accumulations for most of the area. Temperatures don’t fall lower than 35 across the region until around 4 a.m. around Sterling, Va. and only reach 35 in D.C. at around 7 a.m. - about when the first round of precipitation ends. For that reason, most of the precipitation across the area will probably fall as rain.

Round 2: Saturday afternoon and night

During the day Saturday, an Arctic cold front will push through the region, and another round of rain and snow showers may develop later in the day as an upper level impulse zips by. As temperatures crash late Saturday afternoon and evening, any precipitation will transition to all snow across the entire region, with a dusting or so possible.

Occasionally, in these situations, where light snow showers coincide with rapidly falling temperatures, hazardous travel can quickly develop. Temperatures are forecast to dive from near freezing at sunset into the low-to-mid 20s by midnight. The snow showers may be hit or miss, but where they fall, look out for the possibility of icy roads developing in a short period of time. Also note winds will become gusty, from the northwest at 15-20 mph, with gusts to 30 mph.

Available moisture should limit accumulations to a dusting to 0.5” or so and some spots may not get flakes.

Here’s Wes’ take:

Both the GFS and NAM models are suggesting the possibility of snow showers with rapidly falling temperatures. The models tend to sometimes overdo the precipitation with these upper level impulses when they move through with cold air feeding in on northwest and west winds. However, some scattered snow shower activity is a decent bet and with the rapidly falling temperatures, if the snow falls heavily enough a dusting or so is possible in some locations. The bottom line is our best chances for seeing snow falling probably will be with the late Saturday afternoon into evening with these scattered snow showers.