Synopsis
High pressure and offshore easterly winds will bring dry and unseasonably warm temperatures through Friday. Strongest east winds are expected along the Columbia River Gorge and western slopes of the Cascades. A weak cold front will bring chances for light rain late Friday night into Saturday morning, before high pressure returns dry weather Saturday night into Sunday. The next chances for rain are Monday into early Tuesday with an approaching low pressure system, although guidance continues to trend drier.
Short Term
Now through Saturday Night...Water vapor satellite imagery this afternoon shows the upper level ridge of high pressure building over the region. High pressure east of the Cascades will maintain low level offshore flow through Friday morning. Pressure gradients between Troutdale and the Dalles has peaked around -6.5 mb which is producing east wind gusts of around 25-35 mph across much of the Portland Metro area, with higher gusts up to 50-55 mph at wind prone and higher terrain areas within the Columbia River Gorge. Model guidance suggests pressure gradients remain around -4 to -6 mb through late Friday morning before easing Friday afternoon.
Sunny skies today combined with the dry, offshore flow and mid-level (850 mb) temperatures warming to around 17-18 C will allow afternoon highs to warm into the mid to upper 70s, with a few locations reaching 80 degrees, including at the coast. On Friday, the upper level ridge shifts east as an upper level trough lifts NE over the Pacific. Expect increasing high cirrus clouds across the area as the flow aloft turns more southwesterly. Marine stratus will also begin pushing onto the coast as onshore flow returns later Friday afternoon, moderating temperatures at the coast. Otherwise, expect very similar temperatures across the interior lowlands through Friday afternoon. Although high temperatures are expected to be around 10-15 degrees above normal for mid-October, most locations are not expected to break any records (which were mainly set back in 2022). These could be our last "hot" days of the year, as we typically see temperatures drop off during the second half of October.
A shortwave trough pushing into western Washington early Saturday will send a weak cold across the region. This will bring moderate to low chances of light rain to northern portions of the forecast area for Saturday morning. Mean QPF values range from a trace to 0.10 inch, generally north of Lincoln City at the coast and from the Portland metro area northward, with highest chances for rain in the southwest WA Cascades. Dry conditions by afternoon with breezy northerly winds expected behind the front, with temperatures cooling back to near seasonable normals. Will need to watch for potential frost again as overnight temperatures cool Sat night, especially in the Upper Hood River Valley. /DH
Long Term
Sunday through Wednesday Night...Dry weather expected on Sunday as low amplitude shortwave ridging moves over the region. High confidence for near seasonable temperatures warming into the mid-60s inland and 50s along the coast. Potential for early morning frost continues Sunday night into Monday morning within the Upper Hood River Valley.
Monday to Tuesday, the majority of ensemble members are in agreement that an upper-level trough from the northeast Pacific will approach the Pacific Northwest, returning chances for rain between early Monday morning and late Monday night. Will note that these chances have gone down significantly, as of 75% of ensemble members are now showing this trough staying farther offshore and progressing southward toward California rather than moving completely over the Pacific Northwest. If this scenario occurs, precipitation would be limited in our area. Chances for 24-hour rain totals exceeding 0.25 inch between 5 AM Monday to 5 AM Tuesday remain at around 15-25% along the coast and Coast Range, and 5-15% along the I-5 corridor.
By Wednesday, ensembles show the upper trough swinging into central California, while weak high pressure shifts over the Pacific Northwest, favoring predominately dry conditions. At the same time, it does appear that another upper-level trough will begin to approach British Columbia and potentially make its way down into the Pacific Northwest late next week, returning chances for precipitation. DH/10
Aviation
Through 06Z Saturday...Upper-level high pressure moves over the Pacific Northwest. Expect mostly VFR conditions through the TAF period, with the exception of deteriorated conditions along the coast overnight through the early afternoon and low chances within the interior lowlands overnight. Specifically, there is a 50-60% chance of IFR and 40-50% chance of LIFR conditions along the coast between 13-23Z Fri, earliest at KONP and latest at KAST. As for inland terminals, there is a 10-20% chance of LIFR/IFR conditions between 11-18Z Fri, with the highest chances at KEUG.
Expect mostly easterly winds until 18Z Fri, then becoming light and variable through the rest of the TAF period. The central and southern Willamette Valley will likely remain light and variable through the TAF period. Elevated winds at and east of KTTD will decrease towards 18-21Z Fri.
KPDX AND APPROACHES...VFR with clear skies through the TAF period. Breezy easterly winds continue to decrease tonight, with east winds around 4-6 kt expected through the rest of the TAF period beyond 11Z Fri. Additionally, there is a low 10-15% chance of LIFR/IFR CIGs between 12-18Z Fri.~12
Marine
Benign marine conditions continue. Light east/northeasterly winds are transitioning to north/northwesterly winds over the waters through tonight as a thermal trough slowly breaks down. A series of fronts passing through the waters will turn winds southerly Friday night into Saturday morning, and Sunday night into Monday. Seas remain around 4-7 ft at 10-12 seconds through early Saturday morning.
A steeper northwesterly swell arrives this weekend, building seas to 7-9 ft by Saturday evening and 10-13 ft early next week. Uncertainty remains on how high seas will rise early next week due to uncertainty on the track of the low pressure system associated with the swell. There is a 15-30% chance for seas exceeding 15 ft on Monday, with the highest chances beyond 30-40 NM. Will also note that the long periods from the swells will result in a moderate sneaker wave threat Friday into early next week. Caution should be used when in or near the water. -03
Pqr Watches/Warnings/Advisories
OR...None. WA...None. PZ...None.
www.weather.gov/portland
Interact with us via social media: www.facebook.com/NWSPortland x.com/NWSPortland