textproduct: Seattle/Tacoma

SYNOPSIS

High pressure under a zonal flow will keep western Washington quiet through the first part of the weekend. A trough will bring the next chance of showers Sunday into Monday, including light snow in the mountains. The zonal jet will shift eastward, inviting additional systems to pass through next week, with chances of showers.

SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/

It remains dry across western Washington this afternoon. The zonal flow pattern with the upper level jet remains in place today, with high pressure at the surface. High cirrus clouds on satellite are tracking inland from a weak front offshore to the northwest (over north Victoria B.C.). Temperatures this afternoon have reached the low to mid 50s, and Saturday is shaping up to be similar to Friday (albeit with a few more clouds that will roll in tonight and linger Saturday). A couple patches are fog can't be ruled out Saturday morning (as the cloud deck is expected to remain high in altitude and thin in coverage, but will gradually lower through the night). Temperatures tonight/Saturday night will be a few degrees warmer with the help of the cloud coverage (upper 30s-low 40s). Winds will be light and variable and calm at times through the weekend.

The next system is expected to arrive Sunday and linger into Monday, as the zonal jet and high pressure move out of the region. A weak upper level low will drop a trough behind the jet streak, which will bring the next chance of showers across the region (snow showers for elevations greater than roughly 1,500 ft). The trough will drag a cold front across the region during the day. Cooler air will sink in behind the front, with highs Sunday only reaching the upper 40s/low 50s, and lows dipping back to the upper 20s/low 30s. The moisture available with this front is limited, which will keep lowland rain accumulations to several hundredths to a few tenths of an inch, and the mountains seeing light amounts of snow (couple inches at the passes Sunday into Monday - 2-4 inches at higher elevations). The peaks of the mountains have a 50-60% chance of having snow accumulations greater than 6 inches (areas such as Paradise, Mt. Baker and Glacier Peak).

LONG TERM /MONDAY THROUGH FRIDAY/

The ensembles are in good agreement with the trough Sunday continuing to push through the region Monday. The precipitation chances decreases to near 0 late Monday into early Tuesday as any post-front convergence zone activity moves out. Breaks in the cloud coverage are likely, with temperatures slowly warming up Monday into Tuesday, with highs returning into the low to mid 50s. The air will dry out substantially Monday/Tuesday with light east/northeast winds Monday into Tuesday (some areas may see RH values dip down to as low as 40%).

The model agreement continues midweek, with nearly all of the models having a more vigorous shortwave trough passing through Wednesday. This system (if it remains on track) will produce a steady amount of precipitation from late Tuesday through Thursday. This includes mountain snow, with snow levels around 2,000 to 3,000 ft. Probabilities for more than 8 inches of snow at the passes with this system remains low at this time (15-30%). Temperatures will hold steady for the remainder of the week in the upper 40s to low 50s, with lows in the upper 30s to low 40s. A few areas Wednesday may see breezy winds up to 20-30 mph from the southwest as the midweek system passes through.

HPR

AVIATION

VFR cigs are expected to prevail throughout the valid period for all terminals. Winds are expected to remain northerly at the surface, decreasing from 8-10 kts this afternoon, to 4-6 kts after 06Z. By Saturday morning, expect winds to turn westerly for interior terminals, becoming NW in the afternoon.

KSEA...VFR cigs continuing, with high clouds streaming overhead from the NW throughout the afternoon. Winds are between 8-10 kts this afternoon, and will come down after 06Z to between 4-6 kts. Winds at the surface are northerly, becoming ENE overnight. While still VFR, there will be a SCT to FEW layer at 040 to 050 Saturday morning after 12Z, lingering into the early afternoon. Winds during this time will become WSW at 4-6 kts.

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MARINE

High pressure will be the dominant feature over the next several days as north to northwesterly winds prevail across the area. A weak front will pass by to the northwest into early Saturday and dissipate as it does so. A weak push down the Strait of Juan de Fuca will ensue Saturday evening. A disorganized low pressure system will move across the waters Sunday into early Monday, but stronger high pressure building behind it could raise winds through the coastal waters above 20-25 kt early on Monday. A stronger system looks to move into the region around mid-week, which looks to bring the next round of gustier winds and building seas to the area waters.

Seas generally remain around 5-8 ft before increasing going into mid- week.

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HYDROLOGY

No river flooding is expected in the next 7 days.

SEW WATCHES/WARNINGS/ADVISORIES

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