textproduct: Seattle/Tacoma

SYNOPSIS

A band of showers will continue to move inland across the region this afternoon into tonight ahead of a weakening frontal system. The pattern begins to dry out going into the 4th of July weekend, with cooler temperatures and clouds transitioning to some sunshine and warmer temperatures. HeatRisk remains at the minor or yellow level as onshore flow will continue into next week. The next best chance of moisture is on Tuesday and Wednesday with a weak disturbance, with portions of the coast and mountains having the best chance of a shower or two.

SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/

Upper level and surface analysis has a shortwave trough driving a weak frontal system into western WA this afternoon. The front will continue to occlude as it comes onshore. Radar and satellite continue to remain active with this system, as bands of showers move inland from the coast across the central and north interior this afternoon. The initial showers are encountering some drier air (which combined with higher cloud bases may result in some of the moisture evaporating before it reaches the surface, a.k.a. virga). Amounts so far have been light, but a few heavier bands will move inland. There's not much of a signal of a convergence zone behind the front, but a couple showers may linger post-front in northern King County up into the northern Cascades tonight/early Friday. Otherwise amounts will generally remain very light, with a few hundredths or a tenth for inland areas, and a tenth or two of an inch for the coast.

The onshore/low level moisture behind the showers moving through tonight will produce significant low-level cloud coverage for Friday morning, which will only partially scatter out going into the afternoon for areas east of the Olympics. Another push Friday night into Saturday with a dry frontal system will again bring in extra clouds the morning of the 4th of July. However as the front collapses and the jet streak of the trough moves out, the flow will become more zonal and some high pressure trying to build in behind the front should be enough to create some clearing Saturday afternoon for the entire region.

High temperatures through this period remain cool, with 60s today increasing into the low to mid 70s for the interior. Lows remain in the 50s. HeatRisk remains minor (yellow) for those extremely sensitive to heat. Winds will generally remain out of the southwest, with brief north winds in Puget Sound Friday evening at 5 to 10 mph. A few gusts near the Strait of Juan de Fuca to 20 mph are possible next couple of afternoons with diurnal pushes. A couple gusts in Puget Sound to 20 mph are also possible with showers this afternoon, as well as along the Cascade Crest over the weekend.

LONG TERM /SUNDAY THROUGH THURSDAY/

Ensembles have the zonal flow move out Sunday in favor of a more meridional pattern between a ridge Monday/Tuesday, and a trough midweek. With higher heights building under the ridge early next week, expect temperatures across the interior to climb into the upper 70s to low 80s, with Monday being the warmest day. Given the onshore gradients remain in place, the coast will remain cooler with highs around 60. Combined with lows dropping into the 50s, the HeatRisk remains largely minor (yellow) with only a 10-20% chance of the Seattle metro seeing cases of moderate (orange) HeatRisk. A trough will bring a weak front across the region around midweek, with clouds increasing and temperatures in the interior cooling into the 70s. The best chance of showers with this front is going to be portions of the north coast, northeast Olympics, and north Cascades, with minimal precipitation expected at this time. Winds in the period overall remain light at 5 to 10 mph, but again portions of the Cascades (especially along the crest) may see gusts up to 20-25 mph.

HPR

AVIATION

A frontal system will continue to push showers across the coast, and the central/northern terminals this afternoon and evening. Convergence zone potential remains concentrated from northern King County into the Cascades, and will likely not drift towards any of the major terminals. Ceilings will gradually lower as the showers progress inland, with the coast dropping to MVFR already behind the leading line. MVFR remains likely for the interior tonight beginning at 06-09Z and lasting through 18-21Z Friday afternoon before partially clearing. IFR potential for the interior stays at around 30% for a brief period Friday morning, but becomes more certain west of Puget Sound in the Olympics and coast, where a 40-60% chance of LIFR conditions remain for Friday morning. Winds will remain out of the southwest through Friday morning at 5-10 kt (couple gusts to 20 kt possible in the interior), then transitioning to the west/northwest Friday afternoon for areas along and south of the Strait of Juan de Fuca.

KSEA...Off and on showers through tonight, with the convergence zone remaining away from the terminal to the north/east. Ceilings likely to lower to MVFR by as early as 06Z, and through 18-21Z Friday afternoon before scattering out. There remains a 30% chance of IFR from 12Z-16Z in the morning. Winds out of the southwest 5-10 kt with a couple gusts to 20 kt possible this afternoon/evening. Expect a turn to the north tomorrow afternoon around 00Z.

HPR

MARINE

A frontal system with weak low pressure will continue to move across the waters this afternoon through tonight with showers over the waters. Some low ceilings with areas of mist are likely in the coastal waters tonight/Friday morning. While another weak front will move across the waters late Friday, high pressure will in large begin to build back over the waters going into this weekend into the first part of next week. As such, onshore pushes will begin to affect the Strait of Juan de Fuca Friday night, and continuing off and on through next week. The strongest push is expected Saturday night, although the threat of gale-force gusts remains only 10%. A couple periods of strong northwest winds are also possible for the southern coastal waters this weekend and early next week, where there is a 40-60% chance of gusts over 20 kt. Another front may try to squeeze through the waters midweek next week.

Seas remain at 4-6 ft or 6-8 ft through the forecast, with the highest seas Sunday and Monday.

HPR

FIRE WEATHER

A front with some showers will continue to move across the region tonight through Friday morning. Despite the pattern becoming warmer and drier during the holiday weekend and early next week. The onshore pattern will remain intact largely during this warmup, so overnight relative humidity recoveries will provide relief for any drier air during the period as highs climb into the upper 70s and low 80s. Another front midweek may bring the chance of a few showers for portions of the mountains and the coast.

HPR

SEW WATCHES/WARNINGS/ADVISORIES

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