textproduct: Portland

SYNOPSIS

Onshore flow will bring near average temperatures with varying degrees of morning clouds and afternoon sunshine for much of the next week. A series of weak fronts will bring notable chances for light rain and drizzle to portions of the north coast this afternoon and evening, Sunday and then again on Tuesday.

DISCUSSION...Now through Saturday

Visible satellite imagery reveals a small low pressure moving north-northeastward off the Washington coast. Marine clouds have pushed across much of the region except across the Cascades south of Mt Hood. Doppler radar indicates light returns (rain) spreading onto the north coast this afternoon. While rain reaching the ground has been limited so far, we are expecting at least a few locations, particularly across the higher terrain of Tillamook northward to Pacific Counties to wring out a couple hundredths of an inch of rain by later tonight. While not terribly impactful, south to southwesterly winds will be the most unusual aspect of this storm system with winds currently gusting near 30-35 mph along portions of the coast and between 15-30 mph in the Willamette Valley. Winds should subside this evening as the lower atmosphere stabilizes and the wind field aloft weakens.

A secondary stronger front is currently out near 130W off the Pacific Northwest coast. Models are in good agreement it will shift towards the region, but there remains quite a bit of uncertainty in how much it will hold together as it moves towards the region, and more importantly, whether or not it will push into our northwestern zones or stall offshore. At this point, there is a sharp gradient in rain chances between even northern Pacific County and southern Clatsop County on Sunday.

Height fields build a touch going into Monday, which will reduce rain chances and allow for high temperatures to climb more solidly into the 80s for inland valleys. Another weak front is slated to clip the Pacific Northwest Tuesday as a shortwave trough lifts northeastward into British Columbia. Rain chances will once again most likely be limited to the far north Oregon and Washington coast, but there is a 30% chance at least some light rain reaches the Kelso/Longview area. There is a just a 10% chance that rain reaches the Portland/Vancouver area on Tuesday with rain probabilities decreasing even more towards Salem and Eugene. Regardless, this passing storm system will reinforce marine clouds and cooler temperatures with high temperatures likely falling several degrees on Tuesday relative to Monday.

In general, ensembles are in general agreement that our 500 mb height field will increase midweek with the end result being a warming trend late in the work week. Around 30-40% of the global ensemble guidance suggests a shortwave trough will dampen the weak ridging in place late in the week and allow another weak front to graze our northwestern coastal zones around next Saturday. /Neuman

AVIATION...Through 18z Sunday

An area of low pressure offshore will lift to the north-northeast through the period. This will place the region under moist south-southwesterly flow with lots of marine clouds spreading across the region. This will result in predominantly a mix of IFR and MVFR conditions along the coast with a high probability that KONP drops into an extended period of LIFR/IFR conditions later this afternoon and evening. Farther inland, marine stratus appears most likely to end up just above MVFR thresholds. Nonetheless, there is a 20-30% chance at most inland terminals of ceilings lowering into high end MVFR thresholds overnight, primarily after 09z Sunday. It should be noted that gusty south-southwest winds will abruptly appear at many sites over the next 1-2 hours with gusts to around 15 kt for inland sites and to near 25 kt for coastal sites. Winds should ease around 00-03z Sunday.

KPDX AND APPROACHES...Moist onshore flow will produce plenty of ceilings, but conditions should generally remain VFR through at least 09z Sunday. Thereafter, there is a 20-30% chance for MVFR ceilings at any given hour as marine clouds lower and/or spread inland. Gusty south to southwest winds up to 15-20 kt will primarily occur between now and 00z Sunday before subsiding this evening. /Neuman

MARINE

A weak low pressure is lifting north-northeastward off the Washington coast this afternoon. This storm system has resulted in Small Craft Advisory level wind gusts of 25 kt and steep seas across portions of the water so far today. There remains about a 10% chance of wind gusts rising briefly into the 30-35 kt range within 20 NM of the coast, but this appears less and less likely based on the latest observations and trends. Expect winds to drop below advisory level thresholds upon frontal passage. This appears most likely to occur between 4-8pm Saturday. Seas will take several hours thereafter to subside, though.

Another weak front will approach the waters late Sunday into early Monday with just a 30-40% chance that the far outer waters beyond 40 NM north of Cape Falcon will see southerly wind gusts at least briefly rise into the 22-25 kt range. Another front will push towards the waters late Monday into Tuesday. While this front stands a better chance (~50-60%) of bringing southerly 22-25 kt wind gusts to all of the waters north of Cape Falcon, the probability those winds extend as far south as Cape Foulweather is just 10-20%.

Winds appear likely to return to a more typical Summertime northerly wind pattern during the latter half of next week. There is a 30-40% chance another weak front moves towards the Pacific Northwest and turns winds southerly next Saturday-ish. Once we get past the steep seas of today, seas will generally be in the 3-5 ft range for much of the next week unless some of the stronger wind scenarios mentioned above come to fruition. /Neuman

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory until 8 PM PDT this evening for PZZ210- 251>253-271>273.