Marine Weather and Tide Forecast for Fort Washington, MD

KEY MESSAGES
- 1) Very cold conditions are expected over the region through tonight.

- 2) Near-record cold this weekend, along with increasing potential for a significant winter storm.

DISCUSSION
KEY MESSAGE 1...Very cold conditions are expected over the region through tonight.

It is a very cold and in many cases blustery start across the Mid-Atlantic this morning with temperatures ranging from a few degrees below zero over the peaks of the Appalachians to the teens above zero for most of the lower elevations all the way to the Chesapeake Bay.

Temperatures struggle to escape the 20s for much of the area today (teens in the mountains) with perhaps only portions of the central VA piedmont to southern MD poking above freezing for a few hours in the afternoon. It will moderate but remain colder than normal Wednesday ahead of another approaching front.
The main thing to really note on both days outside of the cold temperatures is the very dry nature of the air mass. Some guidance is hinting at RH values in the low teens this afternoon, then in the 20s on Wednesday. With temperatures so cold, we are not necessarily anticipating a wildfire threat, so will not do an explicit Fire Weather discussion for now.
However, if this were a warmer day, it would be concerning.

Following the Wednesday front (which may bring a coating to a few inches of snow over the Alleghenies), another front slides across the region Thursday. This second front looks to come through dry even in the mountains, but it will reinforce cold temperatures across the region. A third front, which may be accompanied by a wave of low pressure gliding by to the south, swings by on Friday. Some ensemble members are a bit more amplified with this little lead wave, enough so that the 01Z NBM and 03Z SREF paint a few tenths of an inch of snow across the region. Will monitor trends and update in future cycles as needed, but for now just something to monitor ahead of a much larger threat looming for the upcoming weekend.

KEY MESSAGE 2...Near-record cold this weekend, along with increasing potential for a significant winter storm.

As mentioned above, a potent cold front pushes through the region late Thursday into Friday, followed by a reinforcing Arctic front late Friday into Saturday. This will lead to increasingly cold conditions each day from Thursday through the weekend. Well below average temperatures are forecast, especially by Sunday. In addition, some upslope snow showers are possible over the Alleghenies, with low but non-zero chances of light precipitation further east on Friday. Extremely cold temperatures are becoming likely Saturday night into next week, with lows in the single digits and wind chills at or below zero.
Near-record low temperatures are possible during this time.

The upper-level pattern becomes quite active in both the northern and southern branches of the jet stream heading into this weekend. Models continue to be in generally good agreement regarding the development of a low pressure system that tracks across the southern U.S. A broad area of baroclinic/frontogenetic forcing will develop along the interaction of an Arctic high to the north and the deepening low. Ensemble guidance continues to show an amplified southern stream influence - something we have seen very little of so far this winter (typical of La Nina).
The surface low may not escape so easily out to sea given the negative NAO block. The nearby steady source of very cold air and the amplified southern stream occurring in tandem are what raise some red flags for significant wintry precipitation potential this weekend. Ample cold air will remain aloft and at the surface with strong high pressure to the north and the strong baroclinic zone to the south. As a result, the 01Z NBM 48-hour probability for at least 6 inches of snow (ending 12Z Mon Jan 26) are at 40-70pct from NW to SE, and around 20-45pct for 1 foot of snow from NW to SE. There are some noteworthy probabilities for even higher amounts, as well, but uncertainty still remains in regards to the exact track of the system which could lead to a sharp QPF gradient on the north/northwest side of the system possibly somewhere over our area.

The latest numerical model guidance continues to show consistency in regards to the potential of this significant weekend winter storm across the area. Trends for precipitation onset time favor Saturday (most likely in the afternoon), with the heaviest precipitation over the area then occurring through Sunday afternoon. The last four runs of the ECMWF-AIFS (deterministic) have shown a southward tick to the axis of heaviest QPF, likely due in large part to a slower ejection of shortwave energy out of the Southwest CONUS causing a slightly flatter and more suppressed storm track. However, the 00Z operational ECMWF (deterministic) as well as several members of the EPS and EPS-AIFS (among a handful of members from other ensembling systems) are also slower and more amplified with a trailing northern stream wave dipping into the Rockies late in the weekend; these two slower/deeper waves then phase as they exit the Rockies and head for the Mississippi Valley. This scenario results in a broad, flat area of low pressure the gets caught underneath Arctic high pressure building over the Northeast CONUS Saturday night, and drifts over the baroclinic zone draped from the SW Atlantic into the Gulf. This low then eventually gets absorbed into the deeper phasing trough approaching from the west. This lifts the low pressure northward up the coast causing precipitation to linger into Monday. It should be noted that this is a relatively new shift, not yet reflected in 01Z NBM progs that were used as a baseline to the overnight forecast. Have not deviated from NBM and will instead wait to see if there is some consistency in this outcome, or if a more suppressed solution becomes more likely.

Depending on where the frontal zone is and where the area of low pressure tracks, there could be significant wintry precipitation this weekend over a large part of the South to Mid-Atlantic CONUS.
As noted, the potential is still there for that strong Arctic high pressure to suppress the low pressure system to our south.
However, the strengthening upstream blocking pattern could essentially put a floor on how far south the low will track.

Accumulating snow looks almost certain this weekend, with an increasing likelihood of a warning-level event for much of the region. But how exactly all of the moving pieces interact will determine the difference between a moderately impactful snowfall versus something much more significant.

It is important to monitor this threat closely this week as the different parts of the system become better sampled by surface and upper air observations. Stay tuned to weather.gov/lwx/winter for the latest updates.

AVIATION /06Z TUESDAY THROUGH SATURDAY/
Winds will remain elevated with W/NW gusts to 20-25 knots. The wind will diminish late afternoon into this evening becoming light out of the southeast by daybreak as high pressure moves overhead and then offshore. Very few clouds and no precip are expected during this time.

VFR conditions will prevail through Wednesday across the TAF sites. Winds will turn southerly ahead of the next front Wednesday with gusts between 20 to 25 kts. The front will come through dry with just a few upslope snow showers over the mountains. An additional front will cross Thursday once again leading to elevated winds across the terminals.

A lead wave of low pressure passing to the south as another front crosses could bring a little spotty precip or restrictions Friday. Sub-VFR conditions are then likely at all TAF sites this weekend due to an enhanced winter storm threat across the region. Confidence is low within the 5 day lead-time period, but significant impacts are possible.

MARINE
Waves of gusty winds will affect the tidal waters through midweek. Winds will gust 20-25 kts out of the W/NW through much of the day, then diminish this evening.

Winds turn southerly with 15-20 kt gusts possible Wednesday ahead of the next approaching front. This front should come through dry, with a secondary (dry) front Thursday. A third front, possibly accompanied by a weak wave of low pressure, will cross the region Friday. North to northeast flow then increases heading into the weekend likely prompting SCAs.

LWX WATCHES/WARNINGS/ADVISORIES
DC...None.
MD...Cold Weather Advisory until 1 PM EST this afternoon for MDZ501- 502-509-510.
VA...Cold Weather Advisory until 1 PM EST this afternoon for VAZ504- 507-508.
Extreme Cold Warning until 1 PM EST this afternoon for VAZ503.
WV...Cold Weather Advisory until 1 PM EST this afternoon for WVZ050- 055-502>504-506.
Extreme Cold Warning until 1 PM EST this afternoon for WVZ501- 505.
MARINE...Small Craft Advisory until 6 PM EST this evening for ANZ530>543.