Pennsylvania Avenue SE, DC Weather

What Has Changed

A more widespread frost tonight east of the Blue Ridge where the growing season remains active. Otherwise, little to no change in the current forecast package.

Key Messages

- 1) Frost Advisories again tonight before a warming trend kicks off the new workweek.

- 2) Dry conditions persist with increasing temperatures through the end of the week.

Discussion

KEY MESSAGE 1...Frost Advisories again tonight before a warming trend kicks off the new workweek.

High pressure will continue to drift south and west toward the central Appalachians tonight yielding less of a marine influence due to westerly low level flow. This will set us up for one more good radiational cooling night with a classic ridge-valley split. Given the westerly low level flow and sharp surface inversion expect warmer temperatures over the mountains/ridges compared to the valley floors and colder rural pockets along/west of I-95. For that reason, Frost Advisories have been issued for portions of northern/central Maryland and northern/central Virginia where the growing season is currently active. The growing season has since ended in locations west of where the Advisories have been issued (i.e along and west of the Blue Ridge).

Some subtle changes to temperatures have been noted in the near term based upon current hi-res guidance. Ended up with a blend of MOS, NBM 10th percentile, ConShort, and the regional Canadian to highlight the colder temperatures for areas points east of the mountains given the lack of a marine influence and SKC conditions as the high drifts overhead. Expect lows in the low to mid 30s in the Frost Advisory area as well as in the colder valleys west of the Blue Ridge. Mountain ridgetop locations and areas near the bay will see lows in the low to mid 40s.

Warming temperatures kick off the new workweek given downsloping low level westerly flow. Expect high temperatures to rise above normal Monday and Tuesday afternoon with highs in the upper 60s and low 70s (low to mid 60s mountains). Minimal cloud cover and light winds out of the west and northwest will persist allowing a warmer airmass to mix to the surface. Expect seasonable temperatures to continue into Wednesday with even warmer weather arriving Thursday into late week.

KEY MESSAGE 2...Dry conditions persist with increasing temperatures through the end of the week.

Upper-level ridging builds over the Mid-Atlantic through the end of the week, resulting in continued high pressure and dry, stable conditions across the region. After a slight cool down Wednesday behind the backdoor front, temperatures should gradually warm some, with afternoon highs reaching the mid-70s by Friday with overnight lows in the 50s. As the front stalls and starts lifting back north, some extra clouds may form in the warm advection pattern Wednesday into early Thursday. Mostly sunny skies will return Thursday into Friday.

Aviation

Prevailing VFR conditions are expected through at least 06z/2am. Meanwhile, the NAM and other hi-res CAM guidance continues to suggests at least a brief period of sub-VFR cigs and vsbys (fog) late tonight into early Monday morning, especially in locations west of the Blue Ridge and locations directly along the water. Confidence in fog development is medium given the modifying airmass in the low levels compared to the colder surface temperatures below. Winds will remain light out of the southeast this evening before turning westerly overnight. West to northwest winds are expected Monday at less than 10 kts.

P6SM SKC conditions are expected Monday and Tuesday as high pressure drifts around the region. A dry backdoor cold front will cross the area late Monday night into Tuesday with a dry warm front lifting into the region Tuesday night into Wednesday. Expect a few passing high clouds and a wind shift with each frontal passage. Overall winds will remain light out of the west and northwest Tuesday before switching to the south and southwest Wednesday into Thursday.