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 this afternoon with CIGs/VIS largely holding as a mix of IFR (Portland Metro through the central Willamette Valley) to MVFR (portions of the Oregon and the south Willamette Valley). Once the more stratiform rainfall breaks to showers around 00-03z Mon guidance gives CIGs/VIS better chances jump to MVFR with pockets of VFR possible (mainly KAST) as well through the evening hours. However it's worth noting due to 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 VIS/CIG improvement. Winds this evening into the early overnight hours likely shift from their current southerly direction to west-northwesterly as well. Going through Monday, the NBM projects a 70-80% chance for persistent MVFR conditions at inland sites with closer to 60-70% chance at the coast excluding KAST where these probabilities are notably lower - higher chances for VFR conditions north Oregon Coast. Light shower activity decreases through the day with prevail dry conditions returning for the afternoon as well.

KPDX AND APPROACHES...IFR conditions have been persistent today but the back edge of the stratiform rainfall will be moving overhead shortly. After this point we'll see better chances for MVFR conditions to finally return. However, we'll still need to watch for IFR conditions through Monday morning as the probabilities to flop back to IFR increase starting around 07-09z Mon. Passing showers may degrade conditions as well. South winds around 5-10 kt finally turn northwest between 06-09z. -99

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.