textproduct: Seattle/Tacoma

SYNOPSIS

An upper level ridge will continue to build over Western Washington and persist through midweek, bringing drier conditions and patchy fog to the region. An active weather pattern may return as early as Thursday, bringing back lowland rain and mountain snow into the weekend.

SHORT TERM /TODAY THROUGH WEDNESDAY/

Another chilly start to the morning, with temperatures in the upper 20s to low 30s across the majority of the lowlands. Mid and high level clouds continue to pass over Western Washington, which has hindered widespread fog over the region this morning. However, patchy fog has managed to develop in some areas, particularly the southwest interior, including Olympia and Shelton. Conditions should improve late in the morning, however, for the southwest interior they may not improve until late afternoon.

Forecast remains on track as upper level ridge and its associated axis continue eastward with said axis setting up over the coast today before shifting inland Tuesday. The upper level ridge remains in place for Wednesday, even though at this point W WA finds itself on the back end of it. As the region remains under the influence of the ridge throughout the entire short term period, the risk for fog will be present during each overnight period and early morning. Given this persistence, stagnant air issues may arise though no concerns are present at this time.

Some gradual heating is expected during the short term with daytime highs today in the lower to mid 40s, while Tuesday and Wednesday see highs in the mid to upper 40s...with some spots Wednesday getting to around 50. Overnight lows show a slight increase but overall remain brisk, generally in the lower to mid 30s.

18/29

LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/

The long range also remains generally unchanged as neither deterministic nor ensemble models seem to be in much of a hurry to bring precip back into the forecast. However, there are some minor differences in opinion as to when exactly the spigot gets turned back on. ECMWF brings up moisture from an upper trough centered in CA into the area as early as Thursday morning while the GFS, focused on this same feature, delays the moisture getting here until Thursday evening. Not surprisingly, the majority of ensemble members begin to lift the mean Thursday afternoon and as such, this is the solution that the NBM has settled into...which seems reasonable. A deepening upper level trough over the Pacific will bring in the next round of precip to the area Friday afternoon. Deterministic models are hinting at some teleconnections which could allow for an atmospheric river to develop, however at this time the fire hose seems to be more pointed at northern CA...consistent with prior runs. Ensembles show a flurry of solutions...some of which do account for the possibility of an AR in our area...but overall the mean isn't biting on to that just yet. The NBM is also riding this wave of uncertainty, keeping PoPs generally around 50 pct for the interior, 60-70 pct for the coast, which, again, seems reasonable at this time.

Daytime highs remain pretty steady throughout the long term, remaining in the mid to upper 40s with the occasional 50 popping up here and there. The significant change will be in the moderation of overnight lows, while not entirely getting out of the 30s, temps are expected to range in the upper 30s to lower 40s.

18

AVIATION

Mostly VFR across the area terminals this morning with passing high clouds and IFR/LIFR in fog and low stratus across the Chehalis Basin south of the Sound. With cloud cover still filtering in over the area, it may be difficult for fog to fully scatter out for areas south of the Sound. A slight improvement in conditions is possible by the late afternoon hours, however expect improvement to be short-lived with fog and low stratus expected to redevelop tonight.

Northwesterly flow aloft will persist through the TAF period as high pressure builds aloft, with northeasterly flow persisting in the lower levels below 6000 ft. Surface winds will persist out of the north to northeast, generally between 5-10 kt.

KSEA...VFR this morning with NE winds persisting at 7-10 kt. Winds will ease around midday and persist at 3-8 kt through the remainder of the period. A few low clouds will be possible in the vicinity of the terminal Tuesday morning.

15/14

MARINE

High pressure will remain situated over the coastal waters through Wednesday. Meanwhile, a weak thermal trough will build along the coast today. This will continue to promote offshore flow through the first half of the week. Seas will build to 6 to 9 feet today as systems pass by to the north and a west-northwest swell moves into the coastal waters.

Dense fog may develop over portions of the interior waters with clearing conditions and light winds during the overnight periods the over the next few days and will likely restrict visibilities across the waters at times.

A more active pattern returns the second half of the week, with the next frontal system expected to move into the area waters on Thursday. This will allow for flow to transition back to southerly. Increasing winds and seas will likely bring the next round of headlines to the area waters.

14

HYDROLOGY

No river flooding is expected during the next 7 days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...None.