textproduct: Portland

SYNOPSIS

Light rain continues through Monday morning. A passing ridge will support mostly dry conditions on Tuesday and Wednesday. The next impactful system takes aim at the region during the latter half of the week. There is uncertainty in the progression of this system but rain and mountain snow are possible.

LONG TERM...Tuesday Night through Sunday

A brief period of dry conditions under shortwave ridging will keep the latter half of Tuesday through Wednesday benign. The next potentially impactful system is expected to impact the region late Wednesday night into Thursday, though there is substantial differences among the models and their ensembles. Cluster analysis remains split between solutions with around 35% showing a weak trough, 34% showing a much deeper trough with an amplified pattern, 16% close to zonal, and the last 15% with a deeper trough but well offshore. Deterministic models show plenty of disagreement in the overall progression of the trough. The GFS leans towards a similar pattern with the trough base pinching off and dropping southeast, leaving northwest OR and southwest WA in a region of weaker forcing. THe EURO on the other hand, keeps the trough intact through its eastward progression, leading to better forcing, higher precipitation totals and a better chance for mountain snow. Depending on what happens with this late week system, could see impactful snow around the mountain passes though, NBM spread is quite large with some showing no snow and others showing 6 inches or more. Chances for 6 inches of snow Thursday through Friday at the Cascade passes is a mere 5%. Will need to keep an eye on this system as it approaches late next week. /19

AVIATION

A frontal system continues to progress through the region and is resulting in a widespread mixture of flight conditions across the air-space. Precipitation will remain in the forecast through the TAF period, but can't rule out some brief breaks in the precipitation through the TAF period. It should be noted that poor model performance today and the tendency for the lower cloud decks to linger this time of year, forecast confidence going forward is low in regards to the timing of any improvement in flight conditions. Southerly winds inland will slowly join the westerly winds already observed along the coast through the overnight hours. After 15Z Monday, the frontal passages should be well east of the region and as such, conditions are likely to become a mixtures of low-end VFR/high-end MVFR, with the coast likely (75-80% chance) leaning towards VFR, while inland areas are expected (70-80% chance) leaning towards MVFR conditions. Light shower activity expected to decrease through the day with generally dry conditions expected after 00Z Tuesday.

KPDX AND APPROACHES...MVFR/IFR conditions expected to persist along with light precipitation through the majority of the TAF period. After 15Z Monday, the frontal passages should be well east of the region and result in a mixture of low-end VFR/high-end MVFR, with a higher potential (70-75% chance) of MVFR conditions. /42

MARINE

A frontal boundary is progressing through the waters this afternoon with southerly winds quickly shifting northwesterly with gust up to 18-25 knots by the evening hours. This frontal feature will also support seas building to 10-14 ft at 13-14 seconds, likely lasting through most of Monday - a Small Craft Advisory remains in effect into Monday evening. After this point seas are expect to fall back into the 6-8 ft range at 11-12 seconds for Tuesday. Lighter west-northwest winds return Monday night into Tuesday as well. Looking ahead, after the continuation of fairly benign winds/wave heights by late fall standards through most of Wednesday, yet another frontal system pushes into the waters late Wednesday into Thursday. As a result, wind gusts likely increase into the 20-30 knot range with a mature swell building seas into at least mid teens. The GEFs projects a 50-70% chance for wave heights to exceed 15 ft but there is also a 10-25% chance of 20 ft seas or higher. An active weather pattern likely continues into the weekend. -99

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory until 7 PM PST Monday for PZZ210.

Small Craft Advisory until 10 PM PST Monday for PZZ251>253- 271>273.