Saint Charles, MD Weather

What Has Changed

A Frost Advisory has been issued for portions of northern Maryland late tonight into Saturday morning. The Small Craft Advisory was cancelled, except for the middle Chesapeake and lower tidal Potomac, where it was extended until 2 AM.

Key Messages

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

- 2) Dry weather continues through next week along with generally seasonable temperatures.

Discussion

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

With a large area of Canadian high pressure building overhead through the weekend, conditions will likely become favorable for radiational cooling (light to calm winds, mainly clear skies and a cool background airmass). At the moment it is unclear which night will be the coldest, although Saturday night will have a slight advantage given the position of the high.

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 to upper 30s for many areas (slightly colder west of the Blue Ridge and slightly warmer in the urban areas and bayshore). The typically colder spots of northern MD and the central VA piedmont could at least briefly come close to freezing. For the afternoon package, a Frost Advisory was only issued from Frederick to Cecil Counties. These areas will be closer to the surface high and have lower surface dew points. Farther to the south, there will be a background easterly flow and perhaps some residual clouds, so the evening shift will watch trends to determine if the advisory needs to be expanded.

For Saturday night, more widespread cold (possible frost/freeze) conditions are possible 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 more areas west I-95 come early Sunday morning. The high will remain overhead through Monday morning, and the low level airmass doesn't change appreciably, so frost/freeze conditions will be possible again Sunday night.

Did not make appreciable changes to the previous min temperature forecasts, which are near or below the coldest guidance which performs best in radiational cooling (MOS, NBM 10 percentile and Canadian Regional).

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 during the early morning hours through the weekend, though confidence in timing and extent of sub-VFR is low at this time.

Light E to NE winds this afternoon will become light to calm tonight. A more E to SE 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.

VFR conditions are anticipated to continue across terminals through Wednesday as conditions remain dry across the Mid- Atlantic. Light westerly winds Monday shift northerly on Tuesday, then east to southeasterly on Wednesday in the wake of a backdoor cold front.