textproduct: Portland

SYNOPSIS

Weak low pressure over the region will maintain cool temperatures with very light scattered showers persisting through the evening. High pressure re-builds Sunday to Monday, returning dry and sunny conditions. Cool nights will bring chances for morning frost in rural valleys away from urban cores this weekend into early next week. Next chances for light rain arrive Tuesday to Wednesday. Temperatures trend warmer late in the week as an upper-level ridge amplifies over the region.

LONG TERM...Tuesday through Saturday

High pressure will maintain mostly dry conditions with seasonable temperatures through Wednesday. An exception would be southwest Washington and the north Oregon Coast Range and Cascades, where chances for light rain increase to 10-30% as a weak cold front over the coastal waters attempts pushing inland. Even if this front is able to move inland, it would be decaying, which suggests rain amounts would likely be very light if any precipitation is observed. Chances for 48 hour rain totals exceeding 0.10 inch from 5 AM Tuesday to 5 AM Thursday are 15-30% across southwest Washington and the north Oregon Coast Range and Cascades, and 5-10% across the Willamette Valley. Will also see increased cloud cover by Wednesday from this weak front, which will keep overnight temperatures warmer and reduce the threat of widespread frost by Tuesday night/Wednesday morning.

Thursday and Friday, the majority of ensemble members are in agreement that upper-level ridging will amplify again over the western CONUS. This will result in temperatures rebounding to the low to mid 70s across interior valleys at the end of the week. By next weekend, the ridge of high pressure looks to be pushed eastward by a broad area of low pressure coming from the Gulf of Alaska. However, there is some uncertainty in the clusters. Looking at the 500 mb WPC clusters, clusters 1 and 3 are leaning towards the low with a combiner probability of 59%. Clusters 2 and 4 favor the upper level ridge persisting with a combined probability of 41%. So, while a slightly cooler solution is somewhat favored, it is by no means a sure thing. /42-10

AVIATION...Through 18Z Sunday

Radar imagery continues to show light, scattered showers across the airspace as weak low pressure remains over the region. These showers are expected to linger through around 00Z Sunday, but am not expecting any impacts from these showers. Therefore, expect predominately VFR conditions across the airspace through the majority of the TAF period. High pressure will slowly re-build through daytime hours which will bring a return of drier conditions along with clearing skies. Northwesterly winds around 3-7 kt for all terminals today.

Tonight, clearing skies and calm winds will support temperatures falling towards 33-36 degrees F for more rural areas and sheltered valleys. Areas that are able to cool down to these temperatures may see frost development on metal surfaces. Could also see some IFR/LIFR conditions developing between KSLE and KEUG starting around 12Z Sunday. Any lowered flight conditions that do manifest are expected to improve towards VFR around 17Z-19Z Sunday.

KPDX AND APPROACHES...VFR with very light showers through around 00Z Sunday. Skies expected to clear through the daytime which will result in cooler overnight temperatures. Northwesterly winds 3-5 kt. /42

MARINE

Tonight through at least Monday morning, Small Craft Conditions will continue across all waters. While a renewed round of breezy north/northeasterly winds with gusts up to 20 kt are expected to develop tonight through Sunday evening, steep and choppy seas around 8-10 ft at 9-11 seconds will persist. As such, will maintain a Small Craft Advisory through at least early Monday morning. Winds weaken on Monday but will remain northerly through early Tuesday morning, before turning more southwesterly by the middle of the week ahead of an approaching weak front. Seas are also expected to also subside towards 5-7 ft by Monday with winds remaining below 15 kt. Relatively benign conditions through the majority of the week. /42

PQR WATCHES/WARNINGS/ADVISORIES

OR...Frost Advisory from midnight tonight to 9 AM PDT Sunday for ORZ104-106-113-117-121-123>125.

WA...Frost Advisory from midnight tonight to 9 AM PDT Sunday for WAZ205-208.

PZ...Small Craft Advisory until 5 AM PDT Monday for PZZ210-251>253- 271>273.