Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
Issued by NWS Seattle/Tacoma, WA
161 FXUS66 KSEW 232220 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 320 PM PDT Thu May 23 2024 .SYNOPSIS...Brief high pressure will pass through the region today, leading to some cloud breaks for the afternoon, and warmer temperatures. A disturbance will pass through the region Friday into Saturday, brining cooler temperatures and the return chance of showers. Sunday looks to dry out some before additional disturbance pass through next week. && .SHORT TERM /TONIGHT THROUGH SUNDAY/...Upper level analysis shows a ridge passing over Washington today. Down at the surface, a surface low/trough sits east of the Cascades, with another surface system northwest of Washington. Satellite imagery shows quite a bit of cloud cover still to be cleared out for the afternoon, with low stratus over all areas except the Olympics. Model guidance was suggesting expansive cloud breaks in Puget Sound up to the Canadian border this afternoon, but confidence is low in there being complete sunshine. Most likely will see some breaks. With temperatures also still in the mid 50s today, extended cloud coverage will likely keep highs from climbing far above 60. Areas that do clear out substantially will however have a shot of mid 60s. Winds out of the west/southwest will decrease overnight to around 5 mph. The next disturbance is quickly wrapping down into Washington from Canada. An upper level trough is expected to pass through Friday into Saturday. The main surface low will arrive on Friday, with a surface low pressure tracking southeastward over Washington. This will bring a weakening occluded front through the region, with onshore westerly flow into Washington. Moisture is limited with this round of showers, but the best chance of seeing anything over a tenth of an inch of QPF is from Snohomish to Skagit County (possible convergence zone late Friday night). If convection is able to form, amounts may exceed a quarter of an inch with the heaviest showers. A rumble of thunder is possible but not likely at this point (given increased temperatures aloft). Temperatures cool down into the 50s Friday and Saturday. Winds remain light out of the southwest 5-10 mph. Upper level ridging Sunday appears to dry out most of the region. Only caveat is a surface low will pass to the northwest of Washington well into Canada. This will keep shower chances Sunday confined to the coast, West Olympics and North Cascades. There is also a slight warm up to the 60s during the day as well. .LONG TERM /MONDAY THROUGH THURSDAY/...Agreement is good between ensemble/deterministic models for troughing to continue through much of next week. This is as upper level ridging in the Rockies/Great Plains keeps us influenced by a trough off the coast of B.C. Canada. This will stop the pattern from progressing for the first part of the week, with the blockage of the ridge eastward. Overall, shower chances will continue for much of the extended forecast with a slow moving cold front passing through Monday into Tuesday. Monday appears to be the warmest day with highs potentially topping out in the upper 60s to low 70s (depending on how much warm air advection is brought in behind the ridge before the trough). Remainder of the week brings a lot of mid 60s for high temperatures across western Washington. HPR && .AVIATION...Weak high pressure will move inland for dry conditions tonight. Ceilings remain around 3500 ft and VFR conditions will prevail overnight. Clouds will lower Friday morning with a return to MVFR conditions as the next frontal system moves in. Showers mainly along the coast 12-20z with vicinity showers in the interior. 33 KSEA...VFR conditions tonight with S wind around 5-10 kt. MVFR conditions return by 12z with showers in the vicinity through the afternoon. 33 && .MARINE...Generally light winds across the waters tonight as weak high pressure moves in. A frontal system will cross western WA on Friday with a brief westerly push down the Strait of Juan de Fuca. High pressure over the NE Pacific maintains onshore flow through Saturday with N/NW winds near Small Craft Advisory criteria over the the Outer Coastal Waters. The next frontal system will move into B.C. on Sunday with south flow increasing over the waters. 33 && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...None. && $$