textproduct: Seattle/Tacoma

SYNOPSIS

Cool and cloudy conditions will continue through Friday as onshore flow persists. A weakening cool front will bring chances for light rains to the coastal and mountain regions Thursday with only slight chances across the lowlands. Improving conditions are expected Friday afternoon through the weekend with decreasing cloud cover and temperatures returning to near normal. Dry weather and seasonable temperatures will continue into early next week.

SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/

Previous discussion...Considerable cloud cover persists early this afternoon across much of Western WA, though clearing has begin pushing into the coastal regions. Patchy breaks in the clouds have allowed for some filtered sunshine across the lowlands with temperatures climbing into the 60s as of 1pm. Continued mostly cloudy skies with a few spotty breaks in the cloud deck are likely through the remainder of the afternoon and early evening before clouds redevelop overnight.

On Thursday, a shortwave pushing into British Columbia will drag a weakening cool front into Western WA, with light rain chances spreading into the coast and mountain terrain during the day, and just slight chances (20% or less) across the Seattle urban corridor. Otherwise, continued cloudy and cool conditions are expected.

By Friday, heights will begin to climb considerably as ridging builds into the central and western US. This will allow for an earlier afternoon clearing trend and encourage afternoon highs to climb closer to seasonal normals.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

Increasing heights over the weekend in response to strengthening ridging in the Western and Central US will allow for temperatures to return to near normal early July values. Meanwhile, morning stratus across the low-lands will tend to thin and be less persistent than observed over the past week. Dry conditions and continued seasonable temperatures will continue into early next week.

AVIATION

Northwesterly flow from an upper level trough over the western US will continue through the TAF period. VFR conditions in place over much of W WA this evening, although marine stratus resulting in MVFR conditions along the coast, including HQM. These stratus will once again push inland overnight, resulting in terminals as far east as OLM seeing MVFR conditions by early Thursday morning. Models hesitant to bring these lower clouds into the eastern terminals. Some models starting to show the prospect of this occurring, though timing and chances are limited. Opted to include this prospect as TEMPO groups until models present a more convincing argument. Cigs lift back into VFR most locations by noon Thursday. A weak passing front may allow for scattered showers, with best chances being northern and western terminals. Opted for VCSH for impacted locations, but given weak model output, this may be overdone. South to southwest winds 5 to 10 kt will continue through the period, with a few gusts of 15 to 20 knots possible this afternoon.

KSEA...VFR conditions this evening into tonight. Cigs lowering to at least low-end VFR conditions overnight. MVFR conditions possible by 12Z, but models are not terribly convincing of this outcome at this time. As such, have allowed for TEMPO groups and should output be more convincing, can upgrade these into dominant wx feature with 03Z or 06Z updates. Cigs lift by 19Z back into VFR conditions. Prospect for scattered showers Thursday, but confidence is not there for them getting as far south as the terminal at this time, hence no inclusion. South to southwesterly winds to persist at speeds ranging 5-10 kts...with the higher end of that range expected Thursday afternoon.

18

MARINE

Broad high pressure offshore and low pressure inland will continue, maintaining onshore flow. A frontal system will cross area waters on Thursday, weakening the onshore flow somewhat. Thereafter, a deepening low pressure system over the Gulf of Alaska will allow onshore flow to persist and strengthen somewhat over the Pacific Northwest. This will result in periods of diurnally driven westerly pushes through the Strait of Juan de Fuca over the next week.

A westerly push this evening through the Strait of Juan de Fuca will generate Small Craft winds through the central and east Strait. A frontal system Thursday will limit winds over area waters on Thursday. Additional westerly pushes are favored to occur Friday and Saturday evenings, and likely once again on Monday and Tuesday. A weak frontal system will also bring gusty winds to the southern coastal waters Sunday, with potential for SCA winds (60-70% chance of gusts over 30 kt).

Seas easing to 4-6 ft tonight, lowering slightly to 3 to 5 feet on Thursday before gradually building to 6 to 9 feet on Sunday and Monday. Seas slowly subside on Tuesday.

15/18

FIRE WEATHER

Little in the way of fire weather concerns in the week ahead. Upper level troughing maintaining cool and cloudy conditions with high relative humidity values and a slight chance for showers along the coast and mountains on Thursday. Drier, sunnier, and more seasonable temperatures will begin Friday continuing into early next week. Low level onshore flow will moderate daytime minimum RH values and bring in good RH recovery each night.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 2 AM PDT Thursday for Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca.