Cape Flattery to James Island WA out 10 to 60 NM Marine Forecast
|Tonight...Sw Wind 10 To 20 Kt Rising To 15 To 25 Kt After Midnight. Wind Waves 1 To 3 Ft Building To 2 To 4 Ft After Midnight. Nw Swell 10 Ft At 11 Seconds. A Chance Of Rain In The Evening. A Slight Chance Of Rain After Midnight.|
|Sun...S Wind 15 To 25 Kt. Wind Waves 2 To 4 Ft. W Swell 8 Ft At 11 Seconds.|
|Sun Night...S Wind 15 To 25 Kt. Wind Waves 2 To 4 Ft. Nw Swell 9 Ft At 11 Seconds. A Slight Chance Of Rain In The Evening Then A Chance Of Rain After Midnight.|
|Mon...S Wind 15 To 25 Kt. Wind Waves 2 To 4 Ft. Nw Swell 11 Ft At 12 Seconds.|
|Mon Night...Nw Wind 10 To 20 Kt Becoming W 5 To 15 Kt After Midnight. Wind Waves 1 To 3 Ft. Nw Swell 13 Ft At 13 Seconds.|
|Tue...Sw Wind 10 To 20 Kt. Wind Waves 1 To 3 Ft. W Swell 15 Ft At 14 Seconds.|
|Tue Night...Sw Wind 5 To 15 Kt. Wind Waves 2 Ft Or Less. W Swell 12 Ft At 13 Seconds.|
|Wed...S Wind 10 To 20 Kt Rising To 15 To 25 Kt. Wind Waves 1 To 3 Ft Building To 2 To 4 Ft. Nw Swell 11 Ft.|
|Thu...S Wind 15 To 25 Kt Rising To 20 To 30 Kt. Wind Waves 2 To 4 Ft Building To 3 To 5 Ft. W Swell 18 Ft Subsiding To 14 Ft.|
| 838 PM PST Sat Feb 27 2021 |
Northern and Central Washington Coastal and Inland Waters - PZZ100
A surface ridge shifts east of the Cascades tonight as a weak warm front and associated surface trough move in the coastal waters. A series of weak systems will affect the waters through the middle of next week.
| Area Forecast Discussion|
National Weather Service Seattle WA
739pm PST Sat Feb 27 2021
The only changes to the forecast this evening were marine related (issuing small craft advisories)-everything else is in decent shape.
In the mid and upper levels of the atmosphere this evening, a ridge of high pressure continues to nose into the PNW from the Pacific, with moisture and cloud cover spilling overtop of it and into the local area. Although the influence of the upper level ridge would argue for larger-scale subsidence, a very weak warm front (if you can really even call it that-the more organized portion of it looks to reside up along the BC Coast, closer to the robust parent low in the Gulf of Alaska) will make for increasing rain chances across the local area. In fact, local radar imagery is already picking up on precipitation- extending roughly from the far northern portion of area and S/SW through the Strait and along the Coast. Light rain (and mountain snow) will continue to spread inland overnight, gradually decreasing in coverage through Sunday morning. The Passes will likely pick up a few inches of new snow-still looking like 3 to 6 inches.
The ridge off the Pacific will be pushed across the area through the day tomorrow, but will dampen as it does so. A deepening trough will begin to take its former place across the Pacific as this occurs, with another frontal system expected to approach the area towards Monday. Still expect this trough to split early next week, with the approaching frontal system for Monday rapidly weakening as it moves closer to shore. Previous discussion follows with an updated marine and aviation section.
Periods of lowland rain and mountain snow will continue through mid- week with seasonal temperatures. A pattern change late in the week could lead to a brief period of above average temperatures and a return of persistent wet weather to Western Washington.
Short Term - Tonight Through Tuesday
Weak system continues to approach the Northwest Coast this afternoon. Mid to upper level clouds are increasing across the area and partly cloudy skies will become overcast in the next 2 to 3 hours across the entire area. Light precipitation remains on track to spread across the region this evening and into tonight, with lowland rain and mountain snow expected. The Cascade passes will generally see light amounts of 3 to 6 inches with this system through Sunday afternoon before a brief break in precipitation. While rain will give way to scattered showers on Sunday, additional rounds of light lowland rain and mountain snow will be the story through midweek, as ensemble guidance is in decent agreement in a split-flow upper air pattern setting up Monday - Tuesday, with an upper low diving south into the California Coast and quasi-zonal flow over the northwest with the northern branch of the jet. Subtle disturbances will drive POPs through the end of the period with generally light rain and snow amounts expected. Hazardous winds look to not be a factor with any of these disturbances.
Long Term - Wednesday Through Saturday
An active pattern will remain in place for the northwest through the end of the period, as ensemble guidance is in reasonable agreement in quasi-zonal flow transitioning to southwesterly flow by the Thursday - Friday timeframe. The overall upper air patten will amplify as a large ridge axis builds over the Great Basin and a large upper level low digs out of the Gulf of Alaska. There remains some variance regarding the placement of the ridge axis that keeps a fair amount of uncertainty in the forecast for the Thursday - Saturday timeframe. A more easterly oriented ridge axis will be conducive for wet and active weather across the region, while a more westerly solution will favor slightly warmer and drier conditions. This will be the main detail to monitor in the forecast as this will have ramifications on the resultant weather Thursday through the weekend.
AVIATION...With the exception of HQM, all TAF sites have hung onto VFR ceilings/conditions this evening ahead of a weak weather system. Light rain will continue to spread eastward across the area through the overnight hours. Accompanying the light rain will be MVFR (Marginal Visual Flight Rules) ceilings, so the 06z TAF update will reflect the timing of the rain at each site and the corresponding ceiling drop. Ceilings may then have a hard time recovering through the day tomorrow even as light rain subsides. May see a return to VFR towards the end of the daylight hours Sunday. Winds will be benign through the period-out of the south under 10kts.
KSEA...VFR ceilings will lower to MVFR (Marginal Visual Flight Rules) towards midnight as light rain moves into the area. Light rain will subside Sunday morning, with ceilings struggling to recover back to VFR thru much of the day. Winds out of the S generally 5-8kts.
The only change this evening was to issue a Small Craft Advisory for the Northern Inland Waters, Puget Sound, and Admiralty Inlet beginning at 15z (7AM) Sunday as south winds increase to around 21kts to extend the Small Craft Advisory for the Coastal Waters through Sunday afternoon. The previous discussion below highligheights the rest of the forecast well:
Surface ridge shifts east of the Cascades tonight as a weak warm front and associated surface trough move in the coastal waters. Low level southerly flow with this system should be enough for advisory level winds for the coastal waters and portions of the inland waters by Sunday afternoon. A series of weak systems will affect the waters through the middle of next week.
Seas of 11 or 12 feet over the coastal waters tonight will fall below 10 feet on Sunday.
Rainfall amounts will remain light through most of this week, therefore river flooding is not expected. While a flooding threat is not currently in the forecast for late week/next weekend, will need to monitor the pattern as a period of southwesterly flow is possible.
.SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...Small Craft Advisory until 4am PST Monday for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm- Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm.
Small Craft Advisory until 4am PST Sunday for Grays Harbor Bar.
Small Craft Advisory from 7am to 6pm PST Sunday for Admiralty Inlet-Northern Inland Waters Including The San Juan Islands.
Small Craft Advisory from 7am to 4pm PST Sunday for Puget Sound and Hood Canal.