Thurmont, MD Weather

What Has Changed

Several Coastal Flood Advisories were extended/re-issued. Otherwise, no significant changes to the forecast thinking overnight, but did add/fine tune the mention of frost the next couple nights.

Key Messages

- 1) Frost or freezing temperatures are possible in many areas tonight and again Saturday night.

- 2) Dry and seasonable conditions are likely to continue through much of next week.

Discussion

KEY MESSAGE 1...Frost or freezing temperatures are possible in many areas tonight and again Saturday night.

With a large area of Canadian high pressure building overhead the next 24 to 48 hours, conditions will likely become favorable for radiational cooling (light to calm winds, mainly clear skies and a cool background airmass). The coldest conditions are expected through early Sunday morning, with some moderation in temperatures thereafter.

The growing season for 2026 has ended along and west of the Blue Ridge and Catoctin Mountains, but continues east of there. Any headlines for frost/freeze conditions will only be issued where the growing season remains active.

For tonight, temperatures look to fall into the mid 30s for many areas west of I-95, perhaps even into interior/rural southern MD. The typically colder spots of northern/north-central MD and the central VA piedmont could at least briefly come close to freezing. Will see what the latest guidance and trends have later this morning before making any headline decisions.

For Saturday night, more widespread cold (possible frost/freeze) conditions are apparent as high pressure settles more directly overhead. This would bring the frost/freeze threat for most areas outside the major urban centers and immediate shore of the Chesapeake Bay. If the colder temperature guidance verifies, then the growing season may end for all areas west I-95 come early Sunday morning.

Relied on a blend of MOS guidance and NBM 10th percentile for low temperatures the next couple of nights, even undercutting by a couple degrees in the typically colder locales.

Aviation

VFR conditions are expected to prevail through early next week. There are some hints that a slight uptick in low-level moisture could lead to some patchy fog or low clouds mainly during the early morning hours by later in the weekend, though confidence in timing and extent of sub-VFR is low at this time.

N winds with a few gusts to around 15 kts are expected just after daybreak until roughly 15Z, becoming NE this afternoon. Winds will be light to calm tonight. A more E flow is likely Saturday, with light to calm winds again Saturday night. Wind direction may be a bit variable, ranging from SE to NE as high pressure passes directly overhead Sunday. Light SE winds early Monday become NW by midday Monday, then N with a few gusts possible Tuesday as a backdoor cold front drops through.

It is possible that the first near-freezing temperatures of the season are observed particularly early Sunday morning for sites like CHO, IAD and BWI.