textproduct: Portland

SYNOPSIS

High pressure remains the dominant synoptic feature through the weekend, keeping most locations dry with daytime high temperatures mostly controlled by reoccurring marine cloud development each night. A weak shortwave Sunday will knock temperatures down a bit, but this will be short lived as the upcoming week trends warmer. However, confidence drops quickly on just how warm it gets by the middle of next week.

DISCUSSION...Now through Friday

High pressure continues to slowly build over the region today, which is keeping marine stratus from forming over the CWA. This is a stark departure from the past 48 hours. Thus, expect daytime highs in the low 60s to low 70s along the coast and higher terrain, with inland valleys generally in the low to upper 70s, with some areas possibly warming into the low 80s.

Sunday (Mother's Day) brings a subtle change as a weak shortwave slides across the Pac NW. The most noticeable effect should be an increase in cloud cover along with a slight cool-down, but the day still looks favorable for outdoor plans. Inland highs should generally hold in the low to mid 70s, while the coast and higher terrain remain in the upper 50s to mid 60s.

Looking forward through the middle of next week, ensemble guidance increasingly supports ridging rebuilding and temperatures trending upward again for the first part of the week. The primary question for Monday and Tuesday will be: Where will the ridge axis set up? If the axis develops farther west, which is currently favored by the GFS and its ensembles will result in a much warmer solution as 850 mb temperatures of 16-18 degrees C are supported. These 850 mb temperatures would translate to low 70s to mid 80s daytime highs. If the ridge axis settles more easterly, this will result in a relatively cooler solution. Currently, the ECMWF and its ensembles favor this scenario. 850 mb temperatures in this case would be in the 14-17 degrees C. which would support daytime highs in the upper 60s to upper 70s. Either solution is pointing towards Tuesday being the hottest day, but as alluded to, overall confidence is low at this time. Or as a co-worker put it so elegantly: Potential outcomes span from "pleasantly warm" to "unseasonably hot". Looking towards the latter part of the upcoming week, guidance has at least come into better agreement. The GFS, ECMWF and their ensembles are showing an upper level low making landfall somewhere between northern California and southern Oregon. Which is significantly better than the solutions shown 24 hours ago. Overall, this low will move push the upper level ridge further eastward and bring about a noticeable cooling trend to the region. Still, while the temperature spread becomes narrower by Thursday, it remains highly dependent on the progression of the synoptic pattern. /42~12

AVIATION

Westerly flow aloft continues as an upper level ridge of high pressure builds over the region, resulting in predominately VFR conditions across the airspace. Light offshore winds expected to turn northerly on Saturday with skies remaining mostly clear.

This is where the forecast gets complicated. Most guidance, along with pattern recognition, point towards VFR conditions persisting through the TAF period. However, there have been periods of intermittent, MVFR to LIFR conditions within the southern Willamette Valley as well as areas south of KTMK to K6S2, which does include KONP. Given that information there is a 10-15% chance for lowered flight conditions to develop at any hour through 17Z Saturday. Any lowered flight conditions that do linger from now through 16Z Saturday, will improve to VFR by 20Z Saturday. Afterwards, expect VFR under mostly clear skies through the remainder of the TAF period.

KPDX AND APPROACHES...Predominately VFR through the TAF period. Light and variable winds becoming northwest around less than 6 kt after 18Z Saturday. /42

MARINE

Southerly winds will become more northerly as high pressure develops over the region today. Overall, will see winds of 6 to 10 kt with gusts up to 20 kt. The highest winds are expected in zones PZZ253 and PZZ273 with a 10-20% chance of isolated gusts up 25 kt. Seas 5 to 7 ft at 10 to 12 seconds. These conditions are expected to persist through Sunday.

There is a shift on Monday as there is the potential for a low pressure system to move into the northeastern Pacific. Confidence is low at this point as there are a number of potential outcomes. However, at this time, we are expecting the northerly winds to persist and intensify on Monday with a trend towards Small Craft Advisory level speeds through Tuesday. This would be amplified by a surface ridge forming and thus seeing a typical summertime northerly wind speed paradigm. /42-27

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...None.