Marine Weather and Tide Forecast for Washington, DC

KEY MESSAGES
- 1) Warm and dry conditions expected today, followed by beneficial rainfall tomorrow morning, and a chance for thunderstorms tomorrow afternoon..

- 2) High pressure moves in at the end of the week, followed by weekend showers and fluctuating temperatures.

DISCUSSION
KEY MESSAGE 1...Warm and dry conditions expected today, followed by beneficial rainfall tomorrow morning, and a chance for thunderstorms tomorrow afternoon.

Broad upper troughing spans across most of North America this afternoon, with flanking ridges over the eastern Pacific and western Atlantic. At the surface, a deep and highly occluded surface low resides beneath an embedded upper low in the vicinity of James Bay, while high pressure resides offshore in the western Atlantic. A cold front extends well south and west of the surface low through the Great Lakes, Ohio Valley, Mississippi Valley, and Southern Plains. Such a surface pattern has led to southwesterly winds locally. This southwesterly flow has advected warmer air into the region. Temperatures have climbed into the low to mid 80s this afternoon beneath mostly sunny skies. Winds are gusting around 25 to 35 mph out of the south to southwest.

High clouds will be on the increase later this afternoon into this evening in advance of the upper trough and associated surface cold front. This system will make very slow southeastward progress later tonight through the day tomorrow.
Clouds will continue to thicken overnight, with light stratiform rain overspreading the area from northwest to southeast late tonight through mid-morning tomorrow. Most locations should experience a few-hour long window with light rain between late tonight and the early afternoon hours tomorrow. This stratiform rain will move out early tomorrow afternoon, potentially allowing for some limited breaks of sun tomorrow afternoon in advance of the system's cold front. Exactly how much destabilization we see in the wake of tomorrow morning's light rain remains a big forecast question.

Recent guidance has trended a bit slower with the front's progression through the area, which could potentially allow for a bit more destabilization tomorrow afternoon. As a result, the trend has also been slightly upward with CAPE values. Much of the destabilization appears to occur as a result of low-level moisture convergence in the vicinity of the surface front, which causes dewpoints to rise into the low to mid 60s. That being said, there is still a fair amount of uncertainty with respect to how much destabilization occurs, and also the areal coverage of storms that form.

Shear certainly won't be lacking tomorrow, with most soundings showing long, straight hodographs, with around 60 knots of effective bulk shear and over 100 knots of shear in the cloud bearing layer. So, if storms form, there is a conditional threat for supercells. The 12z HRRR for example, hinted at this possibility, with weak UH tracks.

The thermodynamic environment is a bit odd, and casts uncertainty with respect to what hazards storms could potentially produce, if they occur at all. Model soundings show long, straight hodographs, which would normally be supportive of hail production. However, profiles are nearly saturated and moist-adiabatic at low-levels, with a considerable amount of the CAPE below the freezing level, which is unfavorable for hail production. Winds in the mid-upper levels are very strong, but aren't overly impressive just above the surface. And model soundings show a good amount of dry air in the mid-levels (which yields DCAPE values around 700 J/kg), but very moist air at low-levels and poor low-level lapse rates, which would be unfavorable for transporting higher momentum air down from aloft. Machine learning guidance is downplaying the potential for severe thunderstorms, and SPC currently has us outlooked in general thunder. However, tomorrow is at least worth monitoring from a severe thunderstorm perspective given the CAPE/shear combination that could potentially be in place (high end scenario of around 1000 J/kg of MLCAPE, and 60 knots of effective bulk shear).

The best chance for thunderstorms tomorrow afternoon will be to the east of the Blue Ridge. Any showers and storms will progress eastward with the front tomorrow evening. Winds will turn northwesterly behind the front. While chances for thunderstorms will come to an end, showers may linger on and off behind the front tomorrow night through much of the day Thursday.

KEY MESSAGE 2...High pressure moves in at the end of the week, followed by weekend showers and fluctuating temperatures.

Surface high pressure moves into the region by Thursday night after Wednesday's frontal boundary transitions offshore, maintaining temperatures in the 50s and 60s until the end of the week.
Temperatures start to increase again going into the weekend, with highs in the 70s on Saturday and Sunday. A few rain showers associated with a shortwave upper level trough are possible on Saturday.

Looking ahead, another Great Lakes frontal boundary looks to be making its way towards the East Coast by early next week, bringing additional chances for rainfall.

AVIATION /18Z TUESDAY THROUGH SUNDAY/
VFR conditions are expected this afternoon, along with southwesterly winds gusting to around 20-30 knots. Winds will remain out of the south to southwest tonight. Current thinking is that winds will remain gusty overnight, but if we were to lose the gusts, there could be low-level wind shear overnight at some sites. Light rain moves in from northwest to southeast late tonight into early tomorrow morning. Ceilings will also drop tomorrow morning, with most sites experiencing a few hours of low-end MVFR to IFR conditions mid-morning through mid- afternoon. A brief lull in the rainfall is expected during the early afternoon hours, as ceilings slowly improve back to VFR by mid-late afternoon. Winds tomorrow will again be out of the south to southwest at around 20 to 25 knots. Showers and thunderstorms appear possible late tomorrow afternoon into early tomorrow evening as a cold front moves through. PROB30 groups highlighting thunderstorm chances were introduced for late tomorrow afternoon at DCA, BWI, and IAD. Chances for thunderstorms should come to an end tomorrow evening.

Winds will shift to out of the north to northwest behind the front tomorrow night. Sub-VFR ceilings may develop again tomorrow night, especially at CHO.

Northerly winds on Thursday shift southwest by Friday evening, with gusts up to 10-15 knots. Periodic sub-VFR conditions are still possible on Thursday as a strong cold front transitions offshore.
VFR conditions on Friday. Showers and thunderstorms are possible on Saturday with sub-VFR conditions expected during heaviest rain showers in the afternoon.

MARINE
SCA-level gusts are expected to continue within south to southwesterly flow through tomorrow afternoon. A cold front will move over the waters late tomorrow afternoon into tomorrow evening. Some thunderstorms may accompany the frontal passage, potentially leading to the issuance of SMWs late tomorrow afternoon into tomorrow evening. Winds will shift to out of the north behind the front, with sub-SCA level north to northwesterly winds expected tomorrow night through the day Thursday. Sub-SCA level westerly winds are forecast for Friday.

South winds Saturday morning gust near SCA criteria. Winds diminish to below SCA criteria Saturday evening.

FIRE WEATHER
Warm, dry, and windy conditions today lead to elevated to near critical fire weather conditions this afternoon. Gusty winds 30 to 35 mph, low humidities in the mid 20s, and fuel moisture between 8-10% are expected today, with the greatest risk for dangerous fire wx behavior west of the Blue Ridge where recent cool temperatures and freezes have slowed down green-up. Greener vegetation east of the Blue Ridge Mountains should preclude any fires from exhibiting extreme fire behavior, but gusty winds of 30-35 mph may still cause fire containment difficulty even though fuels are not as dry as they were two weeks ago. Special Weather Statements for Elevated Fire Danger have been issued across Virginia, the Eastern Panhandle of West Virginia, and Western Maryland through 7 PM this evening.

LWX WATCHES/WARNINGS/ADVISORIES
DC...None.
MD...Small Craft Advisory until 6 PM EDT Wednesday for MDZ008.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 6 PM EDT Wednesday for ANZ530>543.