Portland, OR 97293 Weather

Synopsis

Dry and cooling temperatures will occur through the work week before weak storm systems return chances for beneficial rain over the weekend and early next week.

Discussion

Now through Wednesday...A weak shortwave will move over the region today, sending a decaying cold front through the area. This will support cooler temperatures today and will signal the onset of cooler temperatures into the middle of next week. Temperatures in the 60s are expected over the lowlands and 50s at the coast from today onward. PoPs are low at 20-30% and will be restrained to the Cascades. The main concern tonight into Friday morning and again Friday night into Saturday morning will be temperatures dropping to near freezing for some locations. This would bring impacts to those with agricultural interests. For tonight, freeze watches have been issues for the southern Willamette Valley and part of the northern OR coast range. Frost advisories are in effect for many of the forecast zones adjacent to the freeze watches. Headlines for Friday night into Saturday morning have also been issued with even colder temperatures expected. Freeze watches are in effect for the central and southern Willamette Valley, Lane and Linn county Cascade Foothills, and an expanded portion of the northern OR coast range. Frost advisories are in effect for many of the adjacent forecast zones including the Portland metro and OR coastal zones.

The next shortwave trough or cutoff low is forecast to drop towards the Pacific Northwest over the weekend into early next week. There remains quite a bit of uncertainty around whether or not this storm system will cutoff, clip the region and then hang well offshore for 24-48 hours before pushing inland, hover over or close enough to the region to bring a couple bouts of rain over 48-72 hours, or if the entire storm system will remain an open shortwave trough that slides southeastward across the Rockies and keeps the area largely dry. PoPs continue to trend lower for the weekend with a 24-40% chance for most locations, slightly higher around 50% along the northern OR and southern WA coasts. Probabilities for 0.25 inches of rainfall associated with this system have dropped to around 20-30% for most locations, up to 40-50% along the coast. -19

Aviation

Through 12Z Friday...VFR conditions expected to persist for inland terminals while patchy areas of fog and stratus have started to develop along the coast. This is supporting variable conditions for both KONP and KAST as low clouds pass overhead for brief periods. Expecting this variable trend to continue through 15-17z before a weak cold front increases probabilities for MVFR or lower CIGs to around 60% between 17-22z.

Winds will be light and variable into the morning hours. Then a weak front will turn winds northwesterly and increase after 18z along the coast to 12-15 kts with gusts up to 25 kts and after 20-22z inland to 8-12 kts.

KPDX AND APPROACHES...High pressure over the region will lead to light winds and predominantly VFR conditions. Winds light and variable becoming northwest 8-10 kts after 20-22z. -19/03

Marine

North winds persist through at least Saturday. Winds will increase with the approach and passage of a cold front early this morning, increasing northerly winds to20-25 kt with gusts up to 30 kt. Small Craft Advisories remain in place for all zones until 8 PM today. However, conditions remain hazardous even after 8 PM with seas becoming very steep. Therefore, Hazardous Seas Warnings will begin at 8 PM and continue through 7 AM Friday for all waters except the Columbia River Bar where the Small Craft Advisory has been extended through the same time period.

A stronger low will approach the waters Friday. Model ensembles have been trending towards the low remaining further offshore this weekend. There is uncertainty on when and if the low will move closer to shore and a diminishing threat of gale conditions this weekend. -19/11