Cascade Head to Florence OR from 10 to 60 NM Marine Forecast
|Rest Of Today...S Wind To 5 Kt. Wind Waves S 1 Ft At 4 Seconds. Nw Swell 3 Ft At 9 Seconds. Widespread Dense Fog In The Morning. Areas Of Dense Fog In The Afternoon.
|Tonight...N Wind To 5 Kt. Wind Waves N 1 Ft At 4 Seconds. Nw Swell 3 Ft At 9 Seconds. Areas Of Dense Fog In The Evening. Patchy Dense Fog After Midnight.
|Wed...Ne Wind 5 Kt, Backing To Nw To 5 Kt In The Afternoon. Wind Waves Ne 1 Ft At 4 Seconds, Shifting To The Nw At 4 Seconds In The Afternoon. Nw Swell 3 Ft At 9 Seconds. Patchy Dense Fog In The Morning.
|Wed Night...Nw Wind 5 Kt, Backing To Se After Midnight. Wind Waves Nw 1 Ft At 4 Seconds, Shifting To The Se At 4 Seconds After Midnight. Nw Swell 3 Ft At 9 Seconds.
|Thu...S Wind 5 Kt. Wind Waves S 1 Ft At 4 Seconds. Nw Swell 3 Ft At 10 Seconds.
|Thu Night...N Wind 5 To 10 Kt. Wind Waves N 2 Ft At 4 Seconds. Nw Swell 3 Ft At 10 Seconds.
|Fri...N Wind 5 To 10 Kt. Wind Waves 2 Ft. Nw Swell 4 Ft.
|Sat...Nw Wind 5 To 10 Kt. Wind Waves 2 Ft. Nw Swell 4 Ft.
| Area Forecast Discussion
...UPDATED National Weather Service Portland OR
937am PST Fri Feb 23 2024
Updated aviation discussion.
High pressure builds through Friday. A deepening low pressure system will drop down from the Gulf of Alaska Sunday night through Wednesday bringing colder air, precipitation and mountain snow Sunday night through Tuesday. Another round of precipitation possible later in the week.
.SHORT TERM /THROUGH SUNDAY/...Satellite imagery reveals a broad low pressure system spinning well off the California coast. Upper level ridging remains over the region today, bringing another pleasant day across the Pacific Northwest. Ensemble guidance suggests temperatures to be relatively the same compared to yesterday, maybe a few degrees warmer.
With winds currently light or calm at most locations and dewpoint depressions within the 1-4 deg F range, fog chances in the Willamette and lower Columbia River valleys appear higher than what the NBM suggests (15%). As a result, expect some fog in these areas early this morning.
Shortwave ridging will gradually weaken across the Pacific Northwest Saturday into Sunday as low amplitude shortwave troughs ride southeastward along the jet stream from the Gulf of Alaska into southern British Columbia. This should result in temperatures gradually cooling this weekend and rain chances increasing from north to south Saturday night into Sunday. -JH/Neuman
Long Term - Sunday Night Through Thursday
Ensembles are in relatively good agreement a shortwave trough will slide southeastward into the Pacific Northwest from the Gulf of Alaska late Sunday into Monday. A strong thermal gradient tied to the front and an area of strong mid level lift should result in a band of steadier valley rain and mountain snow with snow levels rapidly falling from above the passes Sunday afternoon to 500-1500 feet by Monday morning. Precipitation should turn more showery behind the cold front. Generally ensemble 850mb temperatures keep snow, at least accumulating snow, off the valley floor, however NBM4.2 suggests 20-30% chance of 0.1 inch of snow late Sunday night through Monday. As for the Cascade foothills and higher Coast Range passes, there is a high probability (>80% chance) that snow will fall through the aforementioned timeframe. NBM4.2 suggests a 60-70% chance that more than a foot of snow will fall in 24 hours across the Cascades above 4000 feet as well. As a result, have issued a Winter Storm Watch for elevations above 2000 ft within the Cascades and foothills from early Sunday afternoon to Monday afternoon. Given temperatures will rapidly fall, travel conditions should deteriorate rapidly and those planning to travel across the Cascades should be prepared for winter-travel conditions.
The bulk of the ensemble guidance suggests the coldest air aloft will remain north of the region and 850mb temperatures will only drop to -5C to -7C. However, there is still a small subset of ensemble guidance that suggests a colder scenario with snow levels lowering down to the valley floor Monday night. However, most ensemble guidance suggests limited Quantitative Precipitation Forecast (with already marginal temperatures) during this time so NBM probabilities for even an inch of snow decreasing to less than 10% along the beaches and the I-5 corridor appear reasonable at this time.
Uncertainty in the details of the forecast do grow as we move into next Tuesday through Thursday. However, there is still broad agreement another deepening shortwave trough will race eastward across the north Pacific late Wednesday into Thursday with the main baroclinic zone ahead of the shortwave trough hanging across the Pacific Northwest Tuesday into Wednesday. The end result is that another period of valley rain and mountain snow will occur across the area. Subtle shifts in the baroclinic zone north or south will determine how high snow levels rise and how much Quantitative Precipitation Forecast falls across the lower elevations and how much snow falls across the Cascades. Nonetheless, there is a 10-20% chance that the front end ups stronger, snow levels rise up to 5000 feet and we are getting enough rain (3-4" in 24 hours in the Coast Range) on top of snowmelt that our flashiest coastal rivers reach minor flood stage. EC EFI values of 0.6-0.8 for Quantitative Precipitation Forecast next Wednesday also suggest EPS members are beginning to enter the tail of Quantitative Precipitation Forecast values forecasted by the EPS in the past 20 years for mid-Feb to mid-Mar. Similar EFI values are also showing up for wind/wind gusts across the area, which seems reasonable given the pattern appears at least somewhat favorable for cyclogenesis along the baroclinic zone next week as well. And finally, there is also a 10% chance that the shortwave trough will bring cool enough temperatures aloft to lower snow levels down to near sea level by next Thursday. The most likely scenario is that we will instead see an extended stretch soggy cool weather in the valleys with limited impacts and the mountains pick up a lot of beneficial snow. In fact, NBM4.2 suggests a 70-80% chance that areas in the Cascades above 5000 feet see at least 3 ft of snow between 4 AM Tuesday and 4am Friday. -JH/Neuman
Quiet conditions will continue into the first half of the weekend as a cutoff low remains well offshore as it drifts southward. Light winds will remain offshore through early today before becoming northerly this evening as ridging builds over the cutoff low and into the PNW. Significant wave heigheights will be between 5-8 ft at 12-14 seconds into early Sunday.
The next system is expected to impact the PNW Sunday night into Monday. A trough dropping southeast along the British Columbia coast will amplify as it enters the PNW. Sustained W/NW winds will begin increasing Sunday afternoon an should peak Sunday night into Monday morning between 25-30 kts. Gusts will follow a similar timeline and should peak between 30-40 kts with the highest gusts farther north and lower gusts farther south. Gusts will begin to wane late Monday. Seas will build into the mid to upper teens by late Sunday night/early Monday morning and will remain in the teens through early Tuesday. /Batz
NOAA Portland OR Office: Watches - Warnings - Advisories
OR...Winter Storm Watch from Sunday afternoon through Monday afternoon for Cascade Foothills in Lane County-Cascades in Lane County-Northern Oregon Cascade Foothills-Northern Oregon Cascades-Upper Hood River Valley.
WA...Winter Storm Watch from Sunday morning through Monday afternoon for South Washington Cascades.