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Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
Issued by NWS Seattle/Tacoma, WA
112 FXUS66 KSEW 120347 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 847 PM PDT Sun Aug 11 2024 .SYNOPSIS...Upper level troughing over the region will promote onshore flow and cooler temperatures the next several days. Isolated thunderstorms will be possible across the North Cascades this evening and again Monday. More widespread chances of precipitation may return to western Washington by next weekend. && .SHORT TERM /TONIGHT THROUGH WEDNESDAY/...Isolated thunderstorms continue in the North Cascades in far eastern portions of Whatcom and Skagit counties this evening. This remains the main activity for the evening with stratus again returning overnight. Forecast remains on track and the previous short and long term sections follow. Upper level troughing will persist over the area through the first half of the week, generally promoting cooler and cloudier conditions across western Washington. Expect additional rounds of marine stratus to push inland during the overnight and early morning hours the next few days. Afternoon high temperatures will generally top out in the 60s and 70s. Some isolated thunderstorm chances will still be possible for portions of the North Cascades on Monday afternoon and evening, with probabilistic guidance indicating a 10-15% chance of thunderstorm development across the far northern areas near the Cascade crest and border. Chances across the Cascades really wane heading into Tuesday as the threat shifts further off to the east. .LONG TERM /THURSDAY THROUGH SUNDAY/...Upper level troughing will remain the dominant influence across the Pacific Northwest through the long term period. Another low dropping down into the region from Canada late in the week could bring more widespread shower chances back to western Washington by the weekend, however will need to see how guidance continues to trend with this over the coming days. High temperatures on Thursday look to trend closer to normal for right now (in the mid to upper 70s), with temperatures dipping to below normal (upper 60s to low 70s) again Friday into the weekend. && .AVIATION...West to southwest flow aloft with upper level troughing over western Washington. Surface winds winds will remain west- southwesterly 5 to 10 kt throughout the TAF period. Marine stratus has burned off for some interior locations especially along the I-5 corridor from BLI to OLM. Other interior locations, such as the Olympic Peninsula lowlands and the interior lowlands of Whatcom county have not seen much in the way of clearing. As a result, while VFR conditions are currently widespread locations in the San Juans, the Olympic Peninsula /save for CLM/ and along the coast are reporting MVFR conditions. Another inland push of stratus is expected to move in overnight with timings for both MVFR/IFR conditions and the gradual break-up being similar to those experienced today...making for an early to mid afternoon return to VFR conditions for most of the CWA. KSEA...VFR conditions currently in place but will erode overnight, reaching MVFR at or around 10Z early Monday morning. Timing for recovering back to VFR conditions to be similar to today...with cigs lifting starting around 18Z...but the potential for lingering MVFR/IFR conditions could last until 22Z. Winds remain southwesterly 5 to 10 kt. 18 && .MARINE...Broad high pressure over the East Pacific with low pressure inland will maintain northwesterly onshore flow over the area waters. Diurnally driven pushes down the Strait of Juan de Fuca will occur each evening. Currently winds look to remain below any thresholds through the upcoming week. Seas 6 to 8 ft at 8 seconds will ease tonight, which will allow the Small Craft Advisory to expire later this afternoon. Seas subside Monday back to 3 to 5 ft and remain like so through the week. LH && .FIRE WEATHER...Elevated fire weather conditions will persist through this evening across portions of the North Cascades as another shortwave trough brings the potential for thunderstorm development. Coverage across the western slopes looks to be less than that of the previous days, however any thunderstorms that do develop may produce frequent lightning, brief heavy downpours, hail, and gusty and erratic winds. Isolated thunderstorms will be possible across the North Cascades on Monday afternoon and evening again, however probabilities continue to wane as the greatest threat moves off to the east. Broader troughing setting up over the region this week will promote increased onshore flow and good relative humidities across the region. Apart from the isolated thunderstorm threat in the far northern Cascades on Monday, this overall trend will help to alleviate fire weather conditions through at least midweek. 14 && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...None. && $$