textproduct: Portland

SYNOPSIS

Largely dry weather is expected into the weekend as a ridge of high pressure builds in over the region. This pattern will favor overnight fog and frost development. A pattern shift early next week will favor conditions turning wetter.

LONG TERM...Sunday through Thursday

An upper level trough looks to move inland around Vancouver Island on Sunday and slowly drag an associated cold front across the Pac NW. At the same time a broad area of low pressure over the Great Basin, will aid in the funneling of some warm, tropical moisture associated with a weak atmospheric river. Current GEFS and ECWMF runs are showing IVT values around 250 kg/(ms). This would slowly funnel a stream of moisture into the WA and northern OR coast with a 30-60% chance of rain hovering in this region through the day Saturday. As Sunday approaches, a relatively stronger, upper level low will finally push this moisture inland, bringing a round of widespread rain through Sunday afternoon, before becoming more showery through Monday. Rain totals from Saturday night through Monday evening range from amounts will once again be on a low side with 0.30-0.90 inches along the coast and terrain and 0.15-0.40 inches for the inland valleys.

Colder air will return to the region behind this frontal system Sunday night into Monday night, especially as a shortwave ridge builds over the eastern Pacific and along the coast into Tuesday. This will bring about another round of frosty overnight conditions with 50-80% chance of morning low temperatures falling below 36 degrees. Currently, the coldest night at this time looks to be Monday night into Tuesday morning. Daytime temperatures on Tuesday also look to be on the chilly side with the majority of the CWA struggling to reach 50 degrees.

In terms of precipitation, guidance becomes more uncertain as we move into the middle of next week and beyond. Some ensembles indicate a weak weather system could undercut the ridging sometime on Tuesday or Wednesday, leading to increasing precipitation chances. With colder air expected to be in place, there is a low probability that near freezing temperatures along with a 15-30% chance of precipitation could result in a mixture of rain/snow to be observed. However, probabilities for any accumulating snow (greater than 0.01 inch) are near zero, so if any snow does fall, it would be flurries or slushy rain. Once we move into Wednesday and beyond, warmer temperatures are expected to return along with another round of warm precipitation for the Pac NW. It should be noted that exact timing and precipitation amounts for the latter part of next week are still unknown. So, those who are planning on any travel for the upcoming holiday should pay attention to the forecast and remain as flexible as possible in their plans. -42

AVIATION

High pressure over the area will lead to a mixture of VFR and IFR conditions today. This morning dense fog lingers in the central and southern Willamette Valley with LIFR stratus of a 200 ft AGL. Conditions will remain stagnant until later in the morning/early afternoon when the sun eats away at the stratus. A limiting factor is that there is a high stratus shield which may insulate enough to keep it socked in around KSLE and KEUG. Elsewhere VFR conditions persist - especially along the coast where winds are easterly. Through the day skies will clear with VFR conditions but will be short lived as the high pressure will lead to yet another round of fog late tonight into early Saturday. There is high confidence in widespread dense fog with VIS less than 1/4 SM throughout the Willamette Valley and coastal gaps. There is around a 30% chance in the lowlands north of KUAO but with this pattern, models sometimes struggle to realize this small scale feature. Fog will likely remain through the morning on Saturday.

KPDX AND APPROACHES...IFR in low stratus but generally focused right at the terminal and not on the approaches - especially from the east. This low stratus will burn off but it may take several hours due to a lack of wind. VFR conditions return but will once again fall overnight. There is a 30-50% chance of IFR conditions returning again tonight after 08Z Sat. Temperatures will lower tonight once again but freezing is not expected. -27

MARINE

A ridge of high pressure continues to builds over the region, which is resulting in winds generally less than 10 kt through the remainder of the week. On Sunday, a fast moving frontal system on Sunday will result in increasing southerly winds on Sunday before turning northwesterly by Sunday evening/night as a frontal system crosses the waters. A strong west/northwest swell will keep seas 9-14 feet at 12-16 seconds through at least early Monday morning. As a result, will maintain the current suite of Small Craft Advisories up through at least early Monday morning. An active weather pattern continues through much of next week. -42

BEACH HAZARDS

An energetic westerly swell is expected along the northwestern Oregon and southwestern Washington coasts for a long duration through Monday. Seas 9-14 ft at 12-16 seconds through the the weekend. These energetic waves can run significantly farther up a beach than normal, including over rocks and jetties, creating potentially life-threatening conditions in the surf zone when beachgoers can be unexpectedly knocked off their feet and pulled out into cold ocean waters.

A Beach Hazards Statement has therefore been issued through 5 AM Monday. Caution should be used when in or near the water, and beachgoers with children should be especially watchful. Never turn your back on the ocean, and be sure to keep an eye on the waves. Those participating in razor clam digs should additionally exercise caution. -42

PQR WATCHES/WARNINGS/ADVISORIES

OR...Dense Fog Advisory until 1 PM PST this afternoon for ORZ114>118. WA...None. PZ...Small Craft Advisory until 4 AM PST Monday for PZZ210-251>253- 271>273.