textproduct: Portland

SYNOPSIS

A relatively drier pattern with upper-level ridging atop a closed upper low over California will give way to a progressive and active pattern early next week. Repeated systems will bring cooler temperatures along with multiple chances for lowland rain and mountain snow to the region.

LONG TERM...Monday through Saturday

The beginning of next week remains active as the trough that brought Sunday's rain pinches of and develops into a cut-off low centered over the Great Basin by late Monday. Residual moisture and the proximity of the upper low is expected to support showery conditions. Expect just rain below 3000 feet while some flakes may mix in above this level in the Cascade Foothills and mainly snow on the Cascade crest.

A brief period of dry conditions under shortwave ridging will keep the latter half of Tuesday through Wednesday benign. The next potentially impactful system is expected to impact the region late Wednesday night into Thursday, though there is substantial differences among the models and their ensembles. Cluster analysis is split between solutions with around 35% showing a weak trough, 34% showing a much deeper trough with an amplified pattern, 16% close to zonal, and the last 15% with a deeper trough but well offshore. Depending on what happens with this late week system, could see impactful snow around the mountain passes through, NBM spread is quite large with some showing no snow and others showing 6 inches or more. Will need to keep an eye on this system as it approaches late next week. /19

AVIATION

Conditions have largely returned to VFR at inland sites this afternoon with ample clearing of lingering mid to high level cloud cover underway. This will likely set the stage for fog development overnight, especially in the Willamette Valley, leading to a widespread degradation of flight conditions to IFR/LIFR. However, confidence in the timing of fog formation is only moderate at this time with the onset of fog most likely around 04-08z Sun at KEUG, KSLE, and KUAO. Lower confidence comparatively for Portland Metro sites where fog/low stratus and accompanying IFR/LIFR conditions may hold off closer to 09-14z Sun - this is further complicated at KTTD by light east winds out of the Gorge working against fog and stratus formation. At the coast a mix of MVFR to IFR conditions trend towards IFR with a 40-50% chance for LIFR CIGs after 9-12z Sunday.

Another frontal systems is expected to push inland during the Sunday as well with light rain beginning at the coast 15-17z before the band of light rain advances eastward into the Willamette Valley and Portland metro by 20-22z Sun. This will aid in keeping conditions sub-VFR the latter half of the TAF period.

KPDX AND APPROACHES...Expect VFR conditions to persist into the evening and early overnight hours. Will have to be on the lookout for fog and/or low stratus formation in the 10-14z time period which would quickly push conditions to IFR or LIFR at KPDX. High resolution models project a 80% chance for IFR or lower CIGs/VIS by 14-16z Sunday. -99

MARINE...Evening Update

Current Buoy and USCG observations show seas holding around 7 to 10 ft around 10 to 12 seconds across all waters. This is resulting in minor Small Craft Advisory conditions. Therefore, have issued a Small Craft Advisory starting now with conditions expected to persist through at least the start of the upcoming week as another system will move through our waters Sunday into Monday. More info can be found in the previous discussion, which follows this update. /42

Another frontal system traverses the waters the second half of Sunday into Monday, leading to increased southwesterly winds initially quickly switching northwesterly - gusts up to 20-23 knots mainly outer waters. Behind the front, a building westerly swell will increase wave heights to 12-15 ft by Monday morning, before falling below 10 ft again on Tuesday. Given the high confidence in wave heights increasing above 10 ft during this late Sunday through Monday time-period, a Small Craft Advisory was issued for the inner and outer waters including the Columbia River Bar. The fairly active and progressive weather pattern likely ushers in a slightly stronger weather disturbance late week bringing increasing chances for hazardous winds and seas at or above 15 ft focused Thursday into Friday. -99

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory until 7 PM PST Monday for PZZ210.

Small Craft Advisory until 10 PM PST Monday for PZZ251>253- 271>273.