Cape Shoalwater WA to Cape Lookout OR between 150 and 250 NM Offshore Forecast
|Tonight...Variable Winds Less Than 5 Kt, Becoming N To Nw. Seas 3 To 4 Ft.|
|Mon...W To Nw Winds Less Than 10 Kt, Becoming Variable. Seas 3 To 5 Ft.|
|Mon Night Through Wed...Variable Winds Less Than 5 Kt. Seas 4 To 5 Ft.|
|Wed Night...W To Nw Winds Less Than 5 Kt, Becoming Variable. Seas 3 To 4 Ft.|
|Thu...Variable Winds Less Than 5 Kt. Seas 3 To 4 Ft.|
|Thu Night...Variable Winds Less Than 10 Kt. Seas 3 To 4 Ft.|
|Fri...Variable Winds Less Than 10 Kt, Becoming W To Nw. Seas 3 To 4 Ft.|
|Fri Night...Nw Winds 5 To 10 Kt. Seas 3 To 4 Ft.|
| Area Forecast Discussion|
National Weather Service Portland OR
201pm PDT Sunday July 3 2022
A weak upper level trough over the region will maintain near to slightly below average temperatures for much of this week with morning clouds followed by afternoon sunshine each day. Chances for showers continue through at least Wednesday.
.SHORT TERM...Through Tuesday...Cool low levels beneath a cold core upper low off the coast coupled with warmth east of the Cascades is driving the weak onshore flow which was observed on the 12z Salem sounding and which was responsible for the deep, drizzly marine layer this morning. Because the marine push was so strong overnight last night, and the stratus layer is consequently so thick, it is uncertain whether much additional clearing will materialize this afternoon; in fact, HREF guidance is suggesting around a 40-50% chance that a broken deck of clouds below 6,000 feet will stick around throughout most of the Willamette Valley through the evening, with only a few peaks of clearing evident (most likely in the southern Valley and high terrain which is poking above the marine layer). Forecast soundings from the NAM and HRRR (High-Resolution Rapid Refresh) suggest that winds beneath roughly 850 mb will become virtually absent tonight, and that the boundary layer will be saturated from the surface up only to around a half kilometer. So, even though there will be negative omega in that layer, its lack of depth will lead to far less (if any) drizzle relative to what the area experienced this morning. The best chance for it will be along the north Oregon coast, where a slight chance was added to the forecast.
Otherwise, the rest of today will remain cooler than normal but dry, except in the western Coast Range and Cascade Foothills where orographic effects will continue to squeeze out a bit of the low level moisture streaming inland off the Pacific in the form of drizzle. Visible satellite imagery shows the break in cloud cover over the Cascades forecast by the HREF is manifesting at 2 PM, and if it continues some instability may materialize over the Lane and Linn Cascades where the NAM has been suggesting 700hPa lapse rates less than -7C/km and several hundred J/kg of instability. High resolution guidance suggests convection will be most widespread east of the Cascade Crest this evening, and both the NBM and SREF keep probabilities for thunder less than 15% west of the crest, so still thunder has been left out of the forecast there.
Aside from some showers (which are most likely in the south Valley and Cascades) early in the morning, Monday will be dry until the late afternoon when scattered showers are expected to move north- northeast into the area from southern Oregon ahead of another lobe of upper level low pressure rotating into the PacNW. Forecast soundings continue to advertise a stable layer around 500-600 mb, so thunderstorms Monday evening/night continue to appear unlikely for any part of the CWA. Another round of showers will be likely on Tuesday, with the overwhelming majority of members within the EPS depicting Quantitative Precipitation Forecast in our area. There are once again some hints that instability may be sufficient for thunder in the Lane and Linn Cascades Tuesday, with both NBM and SREF suggesting 20+% probabilities for thunder along and near the crest, and with forecast soundings from the NAM again suggesting more than 500 J/kg of MUCAPE. It appears that flow within the unstable layer below roughly 500mb will have a large enough westerly component that cells will be driven quickly east of the crest, but before that time a strike or two seems reasonable. Thus, a slight (i.e., 20%) chance for thunder has been added to the forecast for those areas; this means that lightning is possible with convection, though chances for not hearing thunder are 4 times greater. -Bumgardner
Wednesday through Saturday...WPC's cluster analysis page forecasts generally less than a 75 dam difference in 500 hPa height between the coolest and warmest clusters throughout the extended, indicating ensemble agreement in the medium range is high. Through at least Thursday, the upper low dominating our weather in the short term is most likely to remain just west of us over the eastern Pacific, maintaining near to slightly cooler-than-normal temperatures and transient but frequent chances for precipitation amidst south-southwesterly mid level flow.
NBM has maintained its chances for thunderstorms in the Cascades for Wednesday and Thursday, and forecast soundings display some instability supportive of this potential. Thus, no major changes have been made to the forecast for areas with slight chance mentions for thunder. Wednesday continues to look like the day with the most expansive thunder threat throughout the Cascades as it is the day with the least westerly component to the low and mid level flow (and hence storms that develop in the high terrain will not be quickly driven east of our area, but will rather ride northward along the mountains).
Uncertainty in whether the low dissipates and the PacNW is overtaken by the ridge to our east becomes apparent next weekend, when the temperature and precipitation forecasts become a little less clear. Currently the NBM's prediction for both was not touched during that time period, when chances for precipitation appear highest in the Cascades, and temperatures are forecast to climb into the mid 70s to low 80s in the Willamette Valley - near to just below climatology. -Bumgardner
Weak surface high pressure remains over the coastal waters, while upper low pressure remains off the west central Oregon coast. Pressure gradients not all that strong, keeping winds 5 to 15 kt into Tue. Seas not all that much, running 2 to 4 ft. But, will have a mix of swell fetches over next few days. Primary swell is west swell 2 to 3 ft at 10 seconds, with a secondary swell running 1 to 2 ft at 15 seconds. /Rockey
For information about upcoming marine zone changes, go online to: https://www.weather.gov/pqr/marinezone
NOAA Portland OR Office: Watches - Warnings - Advisories
OR...None. WA...None. PZ...None.