Washington, DC 20245 Weather

This Hazardous Weather Outlook is for the Maryland portion of the Chesapeake Bay, Tidal Potomac River, and I-95 corridor through central Maryland, northern Virginia, and District of Columbia.

Day one: Today and Tonight

Patchy dense fog is possible through mid morning.

Days two through seven: Thursday through Tuesday

No hazardous weather is expected at this time.

Spotter information statement

Spotter activation is not expected at this time.

What has changed

Have made a few tweaks to the sky and fog aspects of the forecast over the next 24 to 36 hours to align with the latest trends. Overall, there are no significant changes to forecast thinking from the previous cycle, though rain chances have trended down for Sunday.

Key messages

- 1) Low clouds and fog through Thursday morning.

- 2) Well above normal temperatures Thursday and Friday afternoons, then more seasonable Saturday.

- 3) On-and-off rain showers are possible beginning Sunday into early next week.

Discussion

KEY MESSAGE 1: Low clouds and fog through Thursday morning.

Onshore flow developing around high pressure to the north and east, as well as a weak warm front slowly lifting across the Mid-Atlantic, will set the stage for increasing low-level moisture. This results in the development of low clouds and fog for much of the area, focused on the next couple of mornings.

For this morning, areas between I-95 and the Blue Ridge and Catoctin Mountains are favored as moisture banks up against the higher terrain, as well as the eastern West Virginia panhandle as moisture seeps through the Potomac River Valley. Nighttime microphysics RGB and fog difference channels from GOES-E show this well early this morning, with the development of river valley fog around an area of stratus developing over northern Virginia into north-central Maryland as of 06Z/2AM EDT. Though low clouds are favored, they may be thin at first, with areas of fog continuing to develop due to radiational cooling of a modified/moistening low-level airmass. Low clouds likely linger through midday into early afternoon closer to the eastern (upslope) areas between the Blue Ridge/Catoctin Mountains and US-15. Some drizzle is possible along the eastern slopes of the Blue Ridge/Catoctin Mountains.

Warm advection mid-level clouds may then persist much of the day as the weak warm front lifts north and moistening onshore flow continues. This is expected to keep temperatures a few degrees cooler this afternoon when compared to the previous couple of afternoons (i.e. upper 60s instead of lower 70s).

Low clouds and some fog redevelop by late evening, persisting into Thursday morning. Given a slightly more southeast (versus east) component to the low-level wind, this may allow low clouds/fog to expand further east to and across the I-95 corridor. Southern Maryland to the Northern Neck of Virginia are closer in proximity to the moisture sources of the Atlantic Ocean, Chesapeake Bay and tidal Potomac River, and may therefore have a chance at some drizzle by early Thursday.

More appreciable clearing is expected by mid/late Thursday morning as winds shift to a bit west of south, helping to scour out some of the low-level moisture.

KEY MESSAGE 2: Well above normal temperatures Thursday and Friday afternoons, then more seasonable Saturday.

Following a wind shift to the south and southwest on Thursday, well above normal temperatures are expected. Afternoon high temperatures reach into the lower to middle 70s. A dry front looks to cross the area Friday turning winds to the northwest, though I hesitate to call this a cold front with the lack of cold air advection in its wake. The airmass will be drier, and that coupled with downsloping flow is expected to push high temperatures well into the middle to upper 70s on Friday. While this is a solid 8 to 15 degrees above normal for late October, it is still several degrees shy of daily records.

Some cold advection does take hold Friday night in the wake of a secondary boundary as winds shift to the north. This should allow for low temperatures to fall into the upper 30s and 40s.

A combination of subtle cold air advection and increased clouds ahead of troughing developing over the middle of the country will result in more seasonable daytime high temperatures on Saturday - generally in the 60s (50s mountains). Anticipate lows dropping into the 40s Saturday night with a continued increase in clouds but near zero chance of precipitation.

KEY MESSAGE 3: On-and-off rain showers are possible beginning Sunday into early next week.

A broad area of low pressure will form over the Midwest, and then track east late in the weekend. There is a potential for rain showers beginning on Sunday, though it has trended drier over the past several model runs. Mentionable precipitation chances now hold off until Sunday evening in the latest forecast package. These chances linger into Monday. Temperatures remain in the upper 60s for highs Sunday and Monday (50s mountains), near to slightly above average for the start of November.

As the initial system tracks offshore by Tuesday, a second, potentially more potent upper-level low could form over the Plains and make its way to the region by the middle of next week. Uncertainty remains high regarding the track of this system, but this could bring additional rainfall to the region.

Aviation

Early morning satellite and surface observations confirm the development of an IFR stratus deck between CHO and IAD. This will expand through daybreak amid light onshore flow, likely spilling through the Potomac River Valley up to around MRB. Restrictions are less certain at DCA and BWI, and especially MTN. Any low clouds that develop may linger until late morning around IAD, and early afternoon around CHO/MRB. A period of L/IFR is likely west of the I-95 terminals around daybreak through mid morning, before lifting to MVFR and eventually VFR heading into the afternoon.

Additional low clouds or fog are expected to develop late this evening into the overnight, with higher potential reaching further east into the I-95 corridor TAF sites as light east winds shift to southeast. Clouds should lift mid to late morning Thursday as winds shift to the south and southwest in the wake of a lifting warm front, with VFR then likely through Friday as a dry cold front approaches/crosses. Winds will shift to the northwest Friday, north Friday night, then northeast to east on Saturday as another area of high pressure builds to the north.

Sunday has been trending drier as high pressure persists, although there is increasing uncertainty at this range of the forecast. Light southerly winds are expected during this time.

Marine

Light east to southeast flow is expected through tonight. A couple of rogue gusts around 15 to perhaps 20 knots can't be ruled out at times given favorable trajectories for channeling, but the background gradients are weak. Winds shift to the south and southwest Thursday at similar speeds, then become northwest to north Friday into Friday night. There may be an increase in winds due to increased vertical mixing over near-shore/narrower waterways Friday afternoon, with northerly channeling more likely to bring gusts closer to SCA thresholds Friday night.

Winds then remain below SCA thresholds through the weekend. Winds become northeast to east Saturday, then southerly Sunday.

Tides/coastal flooding

Light onshore flow through Thursday may push sensitive shoreline close to minor flood stage. Areas most at risk for reaching minor tidal flood thresholds would be places like Annapolis and Alexandria mainly during the evening tide cycles (which are astronomically higher).

Light offshore flow should lower tidal anomalies Friday into Saturday, before light southerly flow possibly causes at least a small rebound on Sunday.

Watches, warnings and advisories

DC: None. MD: None. VA: None. WV: None. MARINE: None.