textproduct: Portland

SYNOPSIS

Temperatures warm up a few degrees this weekend as an upper level shortwave ridge moves over the area. Trending a bit cooler again next week as an upper level trough slowly drops southward from the Gulf of Alaska. Dry conditions are heavily favored through Thursday with a possible pattern shift toward cooler and wetter conditions by next Friday, September 25th.

DISCUSSION..Now through next Friday

The latest satellite imagery shows stratus still dissipating across the northern portion of the Willamette Valley and around the Portland metro. Stratus has stuck around much longer than originally expected and has kept temperatures from increasing with observations across the interior lowlands ranging from the low 60s to upper 60s where clouds have cleared. Stratus is expected to dissipate over the next hour or so and will lead to mostly clear skies through the evening and early overnight. Areas along the coast likely remain socked in with low clouds which resurge back through the coastal gaps later tonight.

The weekend looks like it will be quite pleasant with a slight warming trend through Sunday as shortwave ridging persists across the region. Each morning is expected to begin with stratus during the morning hours but this stratus layer won't be as thick moving forward and should dissipate by mid to late morning inland. Highs across the lowlands are expected to top out in the upper 70s on Saturday and low 80s on Sunday but this will depend on how quickly the stratus dissipates. There is high confidence that conditions remain dry through the weekend.

The upper level pattern begins to shift next week as a large trough over the Gulf of Alaska slowly progresses southeast through the week. The eastern periphery of the trough will shift upper level flow to the west/southwest. Temperatures will trend slightly cooler but will generally peak in the mid to upper 70s across the interior lowlands and 60s for the coast and higher terrain. The majority of ensemble members show dry conditions through the middle of the week with weak cold fronts losing steam before they reach the area. A more substantial shortwave and associated cold front is possible during the late Thursday into Friday timeframe which could finally bring some rain to the area. Roughly 40-50% of ensemble members show light rainfall by around this time. Uncertainty remains high during this time frame as models differ in strength and timing this far in advance. -19

AVIATION...Through 06Z Saturday

Late this evening marine stratus remains locked in place along the coast with generally MVFR conditions being reported at KAST and KONP. As the night goes on, these coastal terminals will see CIGs slowly lower with a 40-60% chance for IFR conditions developing between 12-17z - most likely at KONP. This stratus deck is once again expected to form inland starting around 11-13z, likely becoming fairly widespread albeit not as robust as the day prior (Friday). Additionally, there's also a 30-50% chance for the majority of inland terminals degrade to IFR (cigs) between 12-16z. Stratus is likely to hang around into the late morning and midday hours before clearing and becoming VFR after 17-20z. Compared to yesterday (Friday) models show a shallower cloud layer come Saturday morning which should add more confidence to the midday return of VFR conditions. Winds once again stay fairly light, generally less than 10 knots.

KPDX AND APPROACHES...VFR conditions remain in place through much of the overnight hours, however, starting around 12-14z Sat, low-end MVFR cigs likely return (70% chance) with a 30-40% chance of IFR cigs ~13-16z. CIGS are not expected to improve to VFR until after 18-20z. -99/03

MARINE

High pressure remains over the waters through the weekend. Light winds will strengthen out of the north Saturday afternoon and evening with gusts up to 15-20 kt, strongest over the central and southern waters. Northerly winds peak in strength Sunday afternoon and evening when there is a 50-90% chance for maximum wind gusts of 21 kt or slightly stronger across the waters, with the highest chances across the inner waters out to 10 NM offshore. Given wind gusts of this magnitude are not expected to be frequent or widespread, Small Craft Advisories are not anticipated at this time. Significant wave heights will remain around 4 to 6 ft through the weekend, mainly driven by a persistent northwesterly swell with a dominant wave period near 8 to 9 seconds.

Northerly winds are expected to linger Monday through Wednesday, with wind gusts generally staying under 20 kt. A long period west-northwesterly swell is set to arrive either Monday afternoon or evening, pushing seas up by one or two feet. However, seas will not be particularly steep as the dominant wave period with this swell will be around 11-13 seconds. -23/03

PQR WATCHES/WARNINGS/ADVISORIES

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