textproduct: Portland

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 18Z Friday

A weak southwest-northeast oriented cold front was approaching the north coast as of 17Z Thursday, bringing MVFR ceilings to KAST. Expect conditions to improve back to VFR behind the front later this afternoon. This front will eventually reach the central Oregon coast around 20-21Z Thursday, bringing a 50-60% chance for MVFR ceilings below 3000 feet at KONP for a 2-3 hour period of time before conditions likely improve back to VFR. This front will also bring gusty north to northwest winds to KAST and KONP with gusts up to 20-25 kt. Winds will decrease this evening behind the front.

Predominately VFR flight conditions are expected for inland TAF sites through this evening with scattered to broken high clouds above 15-20 kft. Northwest winds will develop this afternoon for inland TAF sites, but should generally stay under 10 kt the vast majority of the time. Heading into tonight, clearing skies and decreasing winds will support at least some patchy fog development within the Willamette Valley, particularly from KSLE to KEUG. That said, surface visibilities should stay above 6 SM at both TAF sites the majority of the TAF period, if not the entire TAF period. Probabilities for visibilities below 1 SM are less than 5-10%. Therefore, have decided not to include visibility restrictions in the TAFs, but will acknowledge there is a non-zero chance for brief visibility reductions towards 12Z Friday.

KPDX AND APPROACHES...High pressure over the region will lead to light northwest winds around 5-10 kt and VFR conditions. Winds become light and variable less than 5 kt tonight. -23

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 to 20-25 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

PQR WATCHES/WARNINGS/ADVISORIES

OR...Frost Advisory from 11 PM Friday to 9 AM PDT Saturday for ORZ101>103-105-107>109-111>113-119-123.

Freeze Warning from 11 PM this evening to 9 AM PDT Friday for ORZ104-116>118.

Freeze Watch from Friday evening through Saturday morning for ORZ104-106-114>118-124-125.

Frost Advisory from 11 PM this evening to 9 AM PDT Friday for ORZ105>107-109-114-115-124-125.

WA...Frost Advisory from 11 PM Friday to 9 AM PDT Saturday for WAZ203>208.

Frost Advisory from 11 PM this evening to 9 AM PDT Friday for WAZ203>205-208.

PZ...Small Craft Advisory until 8 AM PDT Friday for PZZ210.

Small Craft Advisory until 8 PM PDT this evening for PZZ251-271- 272.

Hazardous Seas Warning from 8 PM this evening to 8 AM PDT Friday

for PZZ251>253-271>273.

Small Craft Advisory until 8 PM PDT this evening for PZZ252-253- 273.