textproduct: Portland

SYNOPSIS

Calmer conditions are expected through the weekend into next week with a few largely non-impactful features worth noting. Today through Friday lingering shower chances (20-45%) remain largely confined across portions of the north Oregon Coast, Coast Range, and southwest Washington. Our focus shifts to central Oregon Saturday into Sunday as a weather system moving into northern California brushes the region - moderate confidence precipitation chances hold generally Salem southward. Completely dry weather then returns early next week, albeit only temporarily; it is late Feb/early March after all.

DISCUSSION...Now through Wednesday

Current radar and surface observations depict dry weather across the region early this morning, and unlike at this point last night, fog has been rather slow to develop likely due a some scattered mid to high level clouds drifting overhead. Still, can't rule out some patchy fog across the valley areas around sunrise. Going through today and Friday, the upper level flow remains fairly zonal keeping any light shower chances limited to SW WA, the far N OR Coast, N Coast Range/Willapa Hills, and WA Cascades. Otherwise, conditions stay dry for the rest of the area and fairly consistent day to day with high temperatures in the low to mid 50s for the lowlands, low temperatures in the low to mid 30s, the potential for foggy and/or frosty overnight conditions.

Both deterministic and ensemble guidance remain in sync with a cut-off low pressure system moving inland from the west over northern California during the late Saturday through early Monday morning time period. Even being ~3 days out there still remains a decent amount of uncertainty on how this system will impact NW OR dependent on the north/south track of the low. Based on the latest 00z guidance, if it approaches the coast closer to the CA/OR border, precipitation chances could spread as far north as the Salem to the south Portland metro area with slightly higher precipitation amounts in Lane County. However, if it approaches the coast closer to central CA, then our forecast area could remain completely dry. Looking at entire numerical ensemble space, around 50-60% indicate the low will be north enough for light precipitation around or just north of Salem with only ~20% of ensemble members keep rain just Lane County southward. The remaining 20-30% of ensemble members are somewhere in-between. In any case, not anticipating impacts from any precipitation from this system and snow level around 6000ft keep any pass snowfall concerns at bay. The temperature forecast will also be impacted by the track of this low. The farther north it tracks, more clouds will push north into N OR and SW Washington, limiting daytime warming and nighttime cooling. A southern track will allow for clear skies, warmer daytime temperatures, and colder overnight temperatures near to below freezing in the interior lowlands. Probabilities for temperatures falling below freezing continue dropping in the interior lowlands, now around 10-30% through Sunday morning, except for up to 30-60% for the SW WA lowlands and Cascade foothills.

Transient ridging likely (85-95%) returns to the PacNW for Monday and Tuesday, leading to a return of completely dry weather and increasing daytime temperatures. By Tuesday, daytime highs are expected to peak in the upper 50s to low 60s. These will be great days to squeeze in outdoor activities before rain returns on Wednesday. There is at least some timing uncertainty regarding this mid-week weather disturbance but the latest it would potential arrive is Wednesday afternoon - most ensemble guidance (70-75%) favors the dry weather coming to an end Tuesday evening or night. -99/03

AVIATION

Currently conditions are mainly VFR with a few pockets of IFR/LIFR across the region although the extent of these degraded conditions is less compared to this time yesterday. This is all thanks to a mix of mid to high level clouds which are moving across the region and limiting fog development. However, in portions of the southern Willamette Valley and along the Columbia river towards the Portland Metro observations indicate the presence of fog/low clouds which have or will soon lead to low CIGs/VIS. For locations that do see fog or low stratus development, expect fog and low clouds to scatter out by approximately 17-18z Thursday and give way to mostly clear skies. Winds remain light through the TAF period, generally less than 5-10 knots.

KPDX AND APPROACHES...Flight conditions are expected to degrade approaching sunrise this morning, and while there was hope the cloud deck at 4-4.5ft would prevent any fog/low clouds, KVUO has drop to LIFR CIGs the past few hours (10-11z) with SCT004 being reported at PDX as of 11z as well. With this in mind, confidence is moderate to high the 400ft cloud base will fill in enough by sunrise leading to a period of LIFR flight conditions at the terminal. Expect any reduced VIS/CIGs to clear near 17-18z followed by VFR conditions through the remainder of the day into Thursday evening. -99

MARINE

Overall fairly benign conditions persist across the waters today as seas hold around 4 to 7 ft. While a lingering southerly swell slowly dissipates headed into the weekend, we'll likely see the arrival of a WNW/NW swell on Friday into Saturday pushing significant wave heights up near 8 to 10 ft. This'll be accompanied by NNE wind gusts around 20-28 knots across the outer waters so Small Craft conditions likely return through Saturday night. After this point seas and winds ease back down to around 5 to 7 ft for Monday and Tuesday. -99

PQR WATCHES/WARNINGS/ADVISORIES

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