textproduct: Portland

SYNOPSIS

An active southwesterly flow pattern continues over the Pacific Northwest through the weekend and into early next week. However, given the fairly pedestrian nature of the weather systems moving overhead every 24 to 48 hours coupled with above normal temperatures, weather related impacts are expected to remain limited/minimal. Confidence is high (80%) beginning on Tuesday drier conditions return as a robust ridge of high pressure builds overhead, although uncertainty remains regarding the duration and persistence of this pattern shift once we get towards next weekend.

DISCUSSION...Now through Thursday

Another frontal boundary is currently hung-up across the region with light rain ongoing for a good chunk of the CWA. Models are in good agreement showing this feature lifting back northward this evening into the overnight hours as heights build aloft and conditions trend drier, albeit temporarily. We'll have to watch the degree of clearing late overnight towards the sunrise hours Saturday morning as winds lighten across the inland valleys which would enable fog formation if conditions align. The REFS gives a 40-50% chance for less than 0.5 mile visibility across the Willamette Valley from roughly Canby down through northern Lane County come 7-8am Saturday but both the REFS and HREF depict lingering mid to high cloud cover as well which would work against widespread fog. Given the overall set-up, fog will likely be patchy in nature with limited impacts focused across the aforementioned areas in addition to some of the coast range valleys.

The rest of Saturday we'll experience a relative break in precipitation through the daytime hours as we sit in-between weather disturbances. This'll change the latter half of the weekend (spoilers!). Given the broad south-southwest flow aloft and a rather warm airmass advecting overhead (+7c to +9c temperature anomaly at 850mb) afternoon highs likely rise well above normal into the upper 50s and low 60s across the lower elevations, not only inland but at the coast too. The current forecast puts us within reach of a few daily record high temperatures Saturday assuming morning fog/surface temperature inversion isn't too pervasive across the region - if morning fog is prolific, temperatures where it's present may underperform.

The break comes on an end Saturday night into Sunday with another weather disturbance ushering in precipitation although it is expected to remain light by January standards. Like the last several frontal systems, the primary moisture plume stays displaced to the north across Vancouver Island and the Olympic Peninsula. The orientation favors the highest precipitation totals to remain along the Oregon Coast, Coast Range, the southwest Washington Coast/Willapa Hills, and the southwest Washington Cascades. Inland valleys will see comparatively lower amounts, particularly across the Willamette Valley.

The weak shortwave and associated cold front crosses northeastward our of the region Sunday evening, then forecast confidence decreases as model solutions begin to diverge regarding the handling of additional shortwave energy early next week (mainly Monday). Some guidance suggests a more amplified disturbance that could bring renewed precipitation into the Willamette, while other solutions deflect this energy further north, resulting in drier weather across the interior lowlands. In either case, rainfall is favored again (60-90%) for the north Oregon coast, coast range, and southwest Washington.

Progressing into the midweek ensemble clustering has bought in on the development of a broad ridge of high pressure over the western CONUS starting Tuesday. Some uncertainty remains regarding the exact placement of the ridge axis. Should the current scenario verify (75-80%), completely dry conditions would become established across the entire region. Confidence is also growing for the development of easterly flow through the Cascade gaps and the Columbia River Gorge by the Wednesday to Thursday timeframe with most EPS members showing a -5 to -8mb pressure gradient developing from PDX to DLS. Ensemble solutions suggest the next opportunity for measurable precipitation would not arrive until late next week or the following weekend, contingent on the eventual breakdown of the ridge. -99/12

AVIATION

Current radar and surface observations show a cold front moving across the region this afternoon, resulting in primarily VFR conditions across the airspace. There are a few pockets of IFR/LIFR conditions across the airspace, but am not expecting them to persist for extended periods of time. This frontal system is currently brining rain and robust, southerly winds, with gusts up to 25 kt along the coast. Expect rain and gusty winds through around 02Z Saturday along the coast.

As this frontal system moves further eastward and over the Cascades, expect rain to persist through at least 12Z Saturday. This frontal system will also bring a low (15-20%) probability for intermittent MVFR conditions that would coincide with any precipitation. Behind the front, conditions are expected to settle into a mixture of VFR/MVFR conditions. However, within the post frontal environment, there is a low to moderate (15-30%) probability of IFR/LIFR conditions developing for multiple inland locations after 12Z Saturday.

KPDX AND APPROACHES... Predominately VFR conditions. Rain will persist through 12Z Saturday and could result in intermittent MVFR conditions. However, after 12Z Saturday the is a low (10-20%) chance of MVFR conditions developing. /42

MARINE

An active pattern across all waters continue through the start of next week. Currently, seas are in the 8 to 10 ft range and will hold around there through Saturday evening. However, a building southerly swell will result in seas building towards the 12 to 15 ft range by late Sunday afternoon, before quickly subsiding back towards 10 to 12 feet by the start of next week. Southerly winds will also persist through through the start of next week with gusts up to 30 kt. As the middle of next week approaches, high pressure aloft will result in overall conditions subsiding. While southerly winds will persist they will fall below 20 kt gusts and a westerly 6 to 8 ft swell is expected for the middle of the week. However, these relatively benign conditions will be somewhat short-lived as the next system is expected to impact the region towards the latter part of next week. /42

BEACH HAZARDS

A long period westerly swell of 13-15 ft at 14-17 seconds will result in a high threat for sneaker waves starting late tonight/early Saturday morning and will persist through the weekend and into the start of next week. Waves can run up significantly farther on a beach than normal, including over rocks and jetties. Sneaker waves can suddenly knock people off of their feet and quickly pull them into the frigid ocean which may lead to serious injury or drowning. Caution should be used when in or near the water, especially those who will be razor clamming this week. /42

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory until 4 PM PST Monday for PZZ210-251>253- 271>273.