textproduct: Seattle/Tacoma

SYNOPSIS

High pressure aloft with light flow in the lower levels through tonight. Ridge weakening Monday as a weak system moves by to the north. Another weak system will brush the northern portions Wednesday. Upper level trough developing offshore Wednesday night and Thursday with a more organized system arriving Thursday night or Friday.

SHORT TERM /TODAY THROUGH TUESDAY/

Satellite imagery shows low clouds and fog along the coast with low clouds and fog filling in over the interior lowlands at 3 am/10Z. Temperatures were in the mid 40s to mid 50s.

Western Washington on the backside of an upper level ridge today with light flow in the lower levels. Temperature dew point spreads are already down to two degrees or less early this morning. With the light low level flow expect fog and low clouds to form over all of the interior lowlands by sunrise. The layer will be shallow but as yesterday reminded us, the sun this time of year is losing its strength ( equivalent to late March ) so even with a shallow marine layer it going to take into the afternoon hours to dissipate. Highs today in the 60s.

Little change in the pattern tonight. Upper level ridge moving east Monday with weak low level flow continuing through the day. Low level moisture over the area once again tonight into Monday morning combined with the light low level flow for another round of low clouds and fog Monday morning. Weak system riding by to the north later in the day throwing some middle and high level clouds over the area so even after the marine layer dissipates it will still be mostly cloudy. Lows tonight in the mid 40s to lower 50s. Highs Monday once again in the 60s.

West southwesterly flow aloft Monday night into Tuesday with 500 mb heights dropping as an upper level trough develops offshore. Weak system spinning out of the trough approaching the coast late Tuesday. A little more flow in the lower levels reducing the morning fog coverage but plenty of low level moisture around for low cloud formation. Like Monday by the time the marine layer dissipates in the afternoon middle and high level clouds ahead of the next system will be spreading over the area making for another mostly cloudy day. Highs in the 60s. Lows Tuesday morning in the mid 40s to lower 50s. Felton

LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/

Models in good agreement with the weakening system reaching the coast Wednesday morning dissipating over the interior in the afternoon. Chance of showers along the north coast Tuesday night and over the entire northern portion of the area Wednesday.

Stronger upper level trough digging south out of the Gulf of Alaska Wednesday night and Thursday. Models having a little trouble on the timing of a developing system in the base of the trough then moving into the area. The timing ranges from Thursday afternoon to Thursday night/Friday morning. With the trough digging offshore there is a chance this feature could stall over Western Washington for a bit before kicking out to the east. Ensembles favor the later timing with chance pops Thursday night and chance/likely pops Friday. Upper level trough moving through Friday night keeping chance pops in the forecast. Weak split flow aloft off the coast Saturday for a good chance at a dry day.

Highs in the 60s Wednesday and Thursday and lower to mid 60s Friday and Saturday. Lows in the mid 40s to lower 50s. There is a chance that Seattle could see the first low in the 40s since June 8th ( 49 degrees ) Saturday morning. Felton

AVIATION

West-southwesterly flow prevails over the area with broad troughing over the northeast Pacific. Otherwise mostly clear skies early this morning with light winds has promoted the development of fog in the valleys across western Washington. Stratus will continue to slowly build along the immediate coastline, as well. Several area terminals, including OLM, are already experiencing LIFR conditions due to fog, and this will continue to slowly develop across the remaining area terminals through around 11- 14Z this morning. The fog should begin to lift and start to burn out from 17-20Z. Following, skies will remain mostly clear with VFR conditions through the remainder of the day today. The pattern looks to repeat with another round of fog and low stratus once again early Monday morning. Light to calm winds this morning will remain N/NW 4- 6 kt during the day today.

KSEA...VFR conditions early this morning. Fog will likely develop over the terminal with LIFR conditions as early as 13-14Z, then slowly lifting and clearing out between 18-20Z. VFR conditions prevail through the rest of the day. Another round of low clouds and fog are possible again after 12Z Monday. Light N winds 4 kt or less will increase to around 4-6 kt today. Winds remain light tonight into Monday morning.

62

MARINE

High pressure will continue to persist over the offshore waters going into early next week. A weak front will graze the area just to the north late Monday into Tuesday, which will allow for increased onshore flow Monday night. Probabilities for Small Craft Advisory winds through the Strait of Juan de Fuca increase to 60-90% Monday afternoon into early Tuesday. Another push is expected Tuesday evening, but probabilities decrease and are more confined to the Canadian side of the Strait. Additional systems may move through the waters Wednesday and towards the end of the week but widespread stronger winds are not likely at this time.

Very calm seas of around 2 to 3 ft will increase late tonight into Monday to around 7 to 9 ft as longer period northwesterly swell arrives the coastal waters. Seas look to remain around 6 to 8 ft Tuesday through the middle of the week.

62

SEW WATCHES/WARNINGS/ADVISORIES

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