Southwest Waterfront, DC Weather

What Has Changed

Patchy shallow fog has been developing early this morning, and may expand a bit before lifting quickly after daybreak.

Key Messages

- 1) Dry through the end of October.

- 2) Precipitation chances return in early November.

Discussion

KEY MESSAGE 1...Dry through the end of October.

Large scale ridging persists at the surface and aloft through the end of the week. This results in dry weather and above normal temperatures through the end of October.

Surface high pressure of Canadian origin that built over the Mid-Atlantic this past weekend will drift south and west across the central Appalachians and Tennessee Valley through tonight. This continues a gradual warming trend that began on Sunday.

A weakening cold front will approach from the north tonight, tied to low pressure over the Canadian Maritimes. But without much forcing or moisture, no precipitation is expected. The front will cross the region Tuesday morning, then stall and weaken, or perhaps lift northward as a weak warm front, through mid week. Warmer than normal temperatures will continue during this time as a result.

Another large area of high pressure will build to the north for the second half of the week. The position of the high should allow for southeast to southwest winds and continued warm temperatures by late October standards. The warmest day currently appears to be Friday when highs in the mid to upper 70s are possible.

Saturday may be a few degrees cooler as clouds begin to increase from the west ahead of a trough developing over the middle of the country. Highs will likely still be above normal into the lower 70s, however.

Aviation

It's a bit of a tricky forecast this morning due to a number of competing factors surrounding potential fog. Low-level flow is light out of the west, which typically inhibits fog, and the background airmass isn't terribly moist. However, very sharp surface temperature inversions are evident early this morning, resulting in shallow saturation. Whether this results in shallow fog or just dew is the big question, with the greatest potential for fog and IFR occurring right around daybreak when surface inversions are at their sharpest. Confidence is modest, but given IFR fog already developing in some sheltered piedmont locations and widespread T/Td spreads of less than 2 degrees as of 06Z, have inserted 1-3 hour TEMPOs around daybreak for IFR. The notion of at least brief IFR fog is supported by the RAP, HRRR, GLAMP, RRFS, and NAM/NAMNest...but not so much by the MAV/MET or WRF-ARW/HRW-FV3.

Otherwise, VFR conditions are expected to prevail through the upcoming week. Some light onshore flow Tuesday night through Thursday could result in some late night/early morning sub-VFR potential. Dry weather is anticipated with winds shifting from W today, to NE Tuesday, then SE to SW Wednesday through Friday.

The next chance of precipitation does not arrive until the second half of the upcoming weekend, but uncertainty is high at this time.