Marine Weather and Tide Forecast for Frederick, MD

NEAR TERM /THROUGH TONIGHT/
Freezing Fog Advisory remains in effect until Noon today.
Impacts so far have been somewhat mute although slick spots are likely on elevated and untreated surfaces. Visibilities remain down around a 1/4 mile from DCA Airport down to Charlottesville and back toward Richmond. Expect fog to burn off between 11am- Noon with partly to mostly cloudy skies expected through this afternoon. Highs this afternoon will push back into the upper 30s and mid 40s outside the mountains. Lows tonight will fall into the teens and 20s in the wake of the Arctic frontal boundary. (See previous discussion)

Cloud cover will gradually return this evening as weak high pressure departs the region and a Arctic cold front approaches from the Great Lakes/Ohio River Valley. This front will usher in a much colder airmass for the start of the new workweek. Winds also pick up overnight behind the cold front with northerly gusts to around 15 to 25 mph. The driver of this system is a shortwave aloft which is slated to move through New England later this evening. With the forcing displaced off to the north, any upslope showers should be brief and of low impact to the Alleghenies. Total snow amounts will likely be around a coating to perhaps a half inch in spots.

SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/
Previous discussion...
The mentioned system crossing the Tennessee Valley reaches the Carolinas by midday Monday. Ample ascent ahead of this wave will have access to a cold post- frontal air mass. As such, snow should be the dominant precipitation type as the system sweeps across southern Virginia. The northern extent of this precipitation shield is uncertain. A preponderance of the models cut things off in the vicinity of I-64 while extending back into the Potomac Highlands. However, occasional high- resolution models attempt to lift this axis toward I-66. For now, will cap the northern extent of accumulations around I-64 with around a half inch to inch possible. Given cold temperatures, much of this should stick on untreated surfaces.

Relative to the previous day, Monday is likely to be much colder in the wake of the frontal passage. Forecast highs will mainly range from the upper 20s to mid 30s, with upper teens to mid 20s in the mountains. This is accompanied by north-northeasterly gusts to around 20 to 25 mph underneath mostly cloudy skies. Any light snow should exit the local area by just after dark.

A strong dome of Canadian high pressure builds in from the Great Lakes on Monday evening/night. This will set the stages for a cold night across the region. Northerly winds are forecast to diminish in strength into the night setting the stages for ample radiational cooling. The latest forecast package calls for widespread lows between 10 to 15 degrees, with upper teens to low 20s along and east of I-95. A bit of lingering wind will lower wind chills to near 0 degrees across the mountains.

Within the active northwesterly cyclonic flow regime, an additional shortwave races across the Great Lakes and Mid- Atlantic region on Tuesday. Moisture is rather scant so the only real impact is an increase in cloud cover. Underneath this mix of clouds and sun, the forecast remains chilly with highs in the 30s to low 40s (mountains in the upper 20s to mid 30s).
Despite a shift to southerly winds on Tuesday, temperatures do not rise much as 1000-500 dm thicknesses only rise by around 5 dm over a 24-hour period.

As high pressure exits offshore Tuesday evening, some warm advection precipitation begins to unfold over western Maryland on Tuesday night. This likely comes in the form of a rain/snow mix depending on temperatures. Area-wide overnight temperatures will be in the mid 20s to low 30s.

LONG TERM /WEDNESDAY THROUGH SATURDAY/
Broad upper level trough with numerous reinforcing shortwave-troughs is expected to dominate the flow across the eastern CONUS during the middle and second half of next week. The first of a series of low pressure systems will move across the eastern Great Lks Wednesday and bring the risk of rain and snow showers to the Appalachian region and northern MD, turning into snow showers in the mountains Wed afternoon and evening. The snow shower activity will continue over the mountains into Thu morning where several inches of accumulation may occur.

A second area of low pressure is expected to track from the TN River Valley and across North Carolina late Thu night into Fri and may bring some light snows to the local area and maybe rain across central Virginia. This will be another fast moving system similar to the one Friday morning. Much colder air will follow behind this system for Fri night into Sat with 850 mb temps fcst to plummet to - 15C and daytime highs struggling to reach 30F.

AVIATION /15Z SUNDAY THROUGH THURSDAY/
A Freezing Fog Advisory remains in effect until Noon today. The terminals more closely impacted are CHO and DCA. The main threat of more pronounced (IFR/ LIFR) restrictions have been to the south and east. This fog will give way to a mix of clouds and sun with light southerly winds.

An upstream cold front arrives later this evening which yields a shift to north to northwesterly winds late tonight. Gusts increase just ahead of daybreak while continuing through much of Monday. Afternoon gusts could reach 20 to 25 knots, perhaps higher at times during peak vertical mixing. VFR conditions are expected on Monday, but some sub-VFR conditions are possible at KCHO as light snow tracks near I-64.

Winds turn light on Monday night as Canadian high pressure builds to the north. As this anticyclone exits offshore, a return southerly flow ensues for Tuesday with afternoon gusts to around 15 to 20 knots. VFR conditions continue in advance of the next weather maker arriving by mid-week.

VFR conditions Wed with a risk of rain showers, mainly northern terminals. Light snow possible late Thu night into Fri, possibly rain at CHO. Shifting winds Wed night with a frontal passage.

MARINE
Winds remain on the lighter side owing to high pressure over the waters, a cold front tracks through late this evening yielding gustier winds in the wake. Expect a shift to northerly winds late tonight while turning more north-northeasterly on Monday. Gusts up to 20 to 30 knots are looking likely during this period. Small Craft Advisories will be required during this period which may even include occasional gales over the southern waters. Winds diminish into Monday night as Canadian high pressure builds to the north. Another ramp up is likely by Tuesday evening/night given southerly channeling effects. Small Craft Advisories will again be needed.

SCA conditions Wed into Thu and again Fri.

LWX WATCHES/WARNINGS/ADVISORIES
DC...Freezing Fog Advisory until noon EST today for DCZ001.
MD...Small Craft Advisory from 1 AM to 6 PM EST Monday for MDZ008.
Freezing Fog Advisory until noon EST today for MDZ013-016>018.
VA...Freezing Fog Advisory until noon EST today for VAZ036>039-050- 051-053>057-502-527.
WV...None.
MARINE...Small Craft Advisory from 1 AM to 6 PM EST Monday for ANZ530>533-538>542.
Small Craft Advisory from 3 AM to 6 PM EST Monday for ANZ534>537-543.