Cape Shoalwater WA to Cascade Head OR out 10 NM Marine Forecast
|Rest Of Today...Sw Wind 5 Kt. Wind Waves Sw 1 Ft At 4 Seconds. Nw Swell 2 Ft At 9 Seconds. Widespread Dense Fog In The Morning. Areas Of Dense Fog In The Afternoon.|
|Tonight...Nw Wind To 5 Kt. Wind Waves Nw 1 Ft At 4 Seconds. Nw Swell 2 Ft At 9 Seconds. Areas Of Dense Fog In The Evening. Patchy Dense Fog After Midnight.|
|Wed...N Wind 5 To 10 Kt. Wind Waves N 1 Ft At 4 Seconds. Nw Swell 2 Ft At 9 Seconds.|
|Wed Night...N Wind 5 To 10 Kt. Wind Waves N 2 Ft At 4 Seconds. Nw Swell 3 Ft At 9 Seconds.|
|Thu...Ne Wind To 5 Kt, Backing To Nw 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 10 Seconds.|
|Thu Night...Nw Wind 5 Kt. Wind Waves N 1 Ft At 4 Seconds. Nw Swell 3 Ft At 10 Seconds.|
|Fri...Nw 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
843pm PDT Thu September 28 2023
Updated Aviation Discussion
Low pressure off the coast remains nearly stationary as showers continue to push inland today. Will see general troughing through Friday before high pressure builds over the weekend. Drier and slightly warmer on Saturday and Sunday. Return to showers early next week, though the overall pattern is messy.
.SHORT TERM /THROUGH MONDAY NIGHT/...Overall, a broad low aloft sits over Canada while shortwaves extend from the main "parent trough". Each of these shortwaves has a closed low sitting at the base. The current impactful low sits right around 45N/130W where it has lingered for much of the day. The low will slowly shift southeastward overnight into Friday morning which will promote showery activity. Simulated reflectivity shows the heaviest band of precipitation from Tillamook southward across the whole forecast area. While Probability of Precipitation are high, Quantitative Precipitation Forecast is not nearly as robust with the terrain seeing most of the accumulations. This is a fairly weak low (around 1000 mb), and because it is diving south, we sit on the least energetic portion.
The more exciting - for some - day of the weak is Saturday which is when the high pressure ridge begins to build into the Pacific Northwest. Ensembles remain in good agreement with the overall pattern, but there is still some uncertainty in the overall strength. The commonalities lie in the fact that conditions will be dry, and will warm up a bit. 850 mb temperatures are around 6 degrees C, but the surface has a bit of an easterly flow. Based on current alignment, there is around a 30% chance that the Willamette Valley (specifically around the Salem area) will exceed 70 degrees for a high on Sunday afternoon. The clearer skies during the day though does allow for cooler nights. Temperatures linger well above freezing, however some areas are starting to see a cooler dew point and dew point depression. This, when combined with slightly more than light winds can increase chances for frost. Right now, the chances for frost are minimal and at much higher elevations so have not included it in the forecast. Fog chances have also decreased as the winds are a bit more offshore than northerly (which tends to be our more fog prone wind direction).
The ridge begins to flatten Monday as a shortwave trough shifts southward from the Gulf of Alaska. How fast and significantly the ridge weakens will greatly depend on the track of this shortwave. There is around a 20-40% chance of rain Monday afternoon leading into Tuesday. -Muessle
.Long Term - Tuesday Through Thursday: The aforementioned low will advance southeastward from the Alaska Panhandle on Tuesday which will enhance rain through the region. The trough is taking a track over Washington State so much of the precipitation is concentrated along the northern portions of the forecast area. This is a fast moving front that will have limited impact on the area. One newer trend that is beginning to manifest with an even more amplified ridge forming. However...talk about inconsistencies! Clusters show quite a range of differences in outcomes with the GFS (Global Forecast System) being the warmest and more drastic solution, while the ECMWF (European Centre for Medium-Range Weather Forecasts) is more "troughy". The big thing to consider in this pattern is a warmup that may occur. 850 mb temperatures, with easterly flow aloft, are sitting at around 15 deg C which would lead to much warmer conditions at the surface. Around a 40% chance of 70+ degrees F during the day on Thursday. Still ample time to shift around though as the broad low continues to spin to the north. -Muessle
Seas will continue to trend down to around 5-7 ft through the weekend with weak winds overnight. Another low pressure system is slated to move through the southern Oregon waters late Thursday into Friday. There is uncertainty in the exact location and timing of this low, but generally east winds will shift north and increase with gusts up to 20 kts Friday morning. High pressure will build in west of the waters with winds then shifting north and increasing to gusts between 20 to 25 kt Friday, continuing into the weekend.
The full moon on Saturday will produce stronger tidal currents during the ebb cycles. Those moving in and out of harbors and crossing coastal bars should use caution and be aware of any bar restrictions in place.
NOAA Portland OR Office: Watches - Warnings - Advisories
OR...None. WA...None. PZ...Small Craft Advisory from 9am Friday to 5pm PDT Saturday for Coastal waters from Cape Shoalwater WA to Florence OR from 10 to 60 NM.