textproduct: Portland

SYNOPSIS

Onshore flow persists through much of the next week, while high pressure building offshore will see temperatures trend warmer through Friday. A frontal system Saturday will bring the next chances for light rain and usher in a broad pattern change favoring warmer weather into next week.

LONG TERM...Saturday through Wednesday

A more substantial pattern shift will be underway by Saturday morning as an upper trough moves from the Gulf of Alaska inland over the Pacific Northwest. This system will bring a cold front into the coast on Saturday. Chances for rain peak during the day on Saturday, most notably along the coast and within coastal terrain, as well as inland to the north of Portland. There are 50% or greater chances of accumulating (0.01 inches or more) rain from Newport northward on the coast, and 80-90% chances from Tillamook north through the Long Beach Peninsula. Inland, the probability of accumulating rain rises from only 5% in Portland to 55-65% in the Lewis and Cowlitz Valleys. Rainfall amounts are very likely to be 0.05-0.10 inches or less, with only a 10% chance of seeing 0.20 inches in coastal Clatsop and Pacific Counties. During and behind the frontal passage, below normal high temperatures in the low to mid 60s along the coast and mid to upper 70s inland are expected through the weekend.

As the progressive upper trough exits eastward, there is higher uncertainty in the evolution of the pattern by early next week. Long-range ensembles depict a high probability of strong upper ridging developing over the Four Corners, but whether that will translate to hot weather locally is lower confidence. While temperatures are very likely to be warmer compared to the weekend, the spread of potential solutions remains somewhat wide. At this point, there is an 80% chance of highs in the 80s within inland valleys on Monday and a 75% chance of reaching the 90s on Tuesday, before the potential envelope of outcomes widens substantially on Wednesday, when highs anywhere in the 80s or 90s remain possible. In the warmer solutions, inland ridging and resultant coastal thermal troughing may be sufficient to drive periods of offshore flow, resulting in potential gusty north winds along the coast and within the Willamette Valley. -36

AVIATION...Through 12z Friday

Largely VFR flying conditions continue early this morning with scattered low clouds across the airspace per latest satellite imagery. Terminal observations have shown intermittent MVFR cigs along the coast, and have maintained TEMPO groups given low stratus coverage expected to persist through much of the morning (16-18z Thu) and short-range guidance continuing to favor 60-80% probabilities of at least bkn cloud cover below 3 kft. At inland terminals, confidence in cloud bases below 3 kft is lower (30-40%), except within the southern Willamette Valley including KEUG where chances for MVFR cigs are just over 50% through much of the morning. Where cloud breaks are more widespread, there are low (<10%) chances for fog development yielding IFR/LIFR cigs, and have only included vis restrictions at KSLE where LIFR vis has already been observed. Low clouds will tend to mix out by 16-18z, returning conditions to VFR across the region. Light winds this morning will build to 5-10 kt out of the north to northwest by this afternoon, then ease below 5 kt after 04-08z Fri.

KPDX AND APPROACHES...VFR conditions likely throughout the period. Low to moderate (30%) chances of MVFR cigs this morning if stratus coverage increases, with skies clearing by this afternoon. Diurnal northwest winds expected to rise to around 5 kt by 18z Thu, then ease after 06-08z Fri. -36

MARINE

Buoy observations continue show seas of 4-5 ft early Thursday morning, which are expected to persist through much of the week with a dominant west to northwest swell at 7-9 seconds and a secondary long-period south-southwesterly swell. Backing winds are expected today ahead of a frontal system approaching the waters Friday into Saturday, mainly for the waters north of Cape Falcon and the waters beyond 30-40 NM south of Cape Falcon. Chances for light rain peak Saturday morning during the frontal passage, with 10% or less chances of rain beginning before dawn.

Behind the boundary, initial westerly flow will veer out of the north through the weekend as surface high pressure builds offshore. Chances for maximum wind gusts of at least 20-25 kt are greater than 90% across the waters from Sunday through at least Tuesday. Chances that peak afternoon gusts reach gale-force are the highest on Monday afternoon and increase to the south, from less than 5% north of Cape Falcon to 35-50% south of Cape Foulweather. -36

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...None.