textproduct: Portland

SYNOPSIS

Low-level onshore flow will persist this weekend into next week, but will weaken early next week. Meanwhile, dry southwest flow aloft will continue. Expect near normal temperatures for this time of year this weekend, before warmer temperatures arrive early next week with highs well into the 80s for inland valleys. The temperature and precipitation forecast becomes more uncertain Wednesday through Friday, however odds are leaning towards warmer than normal temperatures continuing with mainly dry conditions.

LONG TERM...Tuesday through Friday night

There is high confidence for mostly sunny skies on Tuesday with high temperatures ranging between 85-90 degrees for inland valleys and 65-70 degrees at the coast. The only feature worth noting on Tuesday is a potential weak upper level impulse that is set to move southwest to northeast along and east of the Oregon Cascade crest. This will bring a 15-25% chance of showers and thunderstorms in far eastern Lane County near the Cascade crest Tuesday afternoon and evening, with relatively higher chances east of the crest. Given cloud layer winds will be southwesterly, any convection that does develop near the crest would move east of the crest.

The overall weather pattern becomes more uncertain Wednesday through Friday, especially in regards to the temperature and precipitation forecast. This stems from differences amongst model ensemble guidance regarding the strength, track, and evolution of a closed upper low over the far northeast Pacific. This uncertainty can be visualized well via the LREF 90th-10th percentile for 500 mb heights, which shows a large area of height differences around 15 dam, focused over the northeast Pacific and coastal waters. The largest degree of uncertainty in the upper air pattern begins Wednesday and lingers through Thursday. If this upper level low moves to our north and is focused over B.C. and/or northwest Washington, conditions will trend dry with near average to warmer than average temperatures over northwest OR and southwest WA. If this low moves directly over western OR and southwest WA, temperatures will trend slightly below average with increasing chances for rain showers.

Ensemble guidance currently favors an upper low track that is further to the north, resulting in forecast temperatures in the mid to upper 80s on Wednesday and Thursday with only a 5-15% chance of showers. However, total model spread for high temperatures on both days is over 20 degrees, with highs ranging anywhere from the mid 70s to mid 90s. Therefore, it is clear the forecast is quite uncertain mid to late in the week. Confidence increases for dry weather on Friday, however the temperature forecast remains uncertain with the NBM 10th-90th percentile for highs ranging from the lower 80s to upper 90s for inland valleys. -23

AVIATION

A weak trough continues to move northeast away from the airspace, continuing southwesterly flow aloft. While some stratus may back build along the Cascades tonight, expect VFR conditions at all inland terminals through the TAF period (less than 20% chance of MVFR CIGs between 08-15Z Sun). As for the coast, there is low confidence for ceiling conditions between 07Z and 18Z Sun, with a 40-50% chance of MVFR CIGs at all coastal terminals. While most coastal terminals are currently VFR, low scattered clouds have started to develop so MVFR CIGs may develop by 07-08Z Sun. By 15-18Z Sun, coastal terminals will return to VFR and remain so through the remainder of the TAF period. Expect winds to remain generally light and variable overnight, then increase to around 5-10 kt and shift northwesterly around 18Z Sun. Coastal terminals will see a bit stronger winds, generally 12-17 kt with gusts up to 25 kt between 18Z Sun and 04Z Mon.

KPDX AND APPROACHES...VFR with northwesterly winds, light overnight then increasing to around 10 kt by 18-21Z Sun. 10-20% chance of MVFR CIGs between 08-14Z Sun. ~12

MARINE

A weak area of low pressure sits offshore and will slowly move inland overnight. The low pressure center is enhancing the already present northwesterly swell, and winds are increasing around buoy 46029 where gusts up to 17 kt have been reported. These conditions are not necessarily going to amplify significantly tonight but we will see a response on Sunday.

The low will shift inland causing seas to slowly build to 7-9 ft at 8-9 seconds, and winds will begin to amplify. Will see Small Craft Advisory level winds in the central and southern waters as early as late Sunday morning, and then those speeds will move north incorporating the northern waters. Overall, they are going to be hovering right along the threshold of 15 to 20 kt with gusts up to 25 kt so winds may not be as widespread. However, given the incoming pattern and the high pressure developing combined with the diurnal component to our wind, there is enough confidence for at least this advisory.

Winds will ease to below thresholds on Monday but seas will remain around 7-8 ft at 8 seconds thus leaving choppier conditions. Because of this, could see the advisory extended, but at this time confidence is too low to project too far into the future given its marginal nature. -27

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory from 11 AM Sunday to 2 AM PDT Monday for PZZ251-271.

Small Craft Advisory from 11 AM Sunday to 11 AM PDT Monday for PZZ252-253-272-273.