textproduct: Portland

SYNOPSIS

Cool and showery conditions continue through Friday as an upper-level low sits offshore. Clear skies and calm winds may bring frost development across interior valleys Saturday morning. Mostly dry conditions return this Halloween weekend. Slight chances for precipitation return early next week.

LONG TERM

Saturday through Wednesday..The conditions mentioned above will result in clearing skies and calm winds will favor temperatures dropping into the low to mid 30s across interior valleys, which may lead to fog or frost development. Chances for Saturday morning lows dropping below 32 degrees is 55-85% across the southern Willamette Valley, northern Clark County (Battle Ground area), and the Upper Hood River Valley.

Heading into the weekend/Halloween, the majority of ensemble members are showing the offshore upper-level low moving into the Pacific Northwest. It appears that there will be limited moisture with this low coming in, so most ensembles show either dry conditions or very light precipitation amounts. However, there is still a a 10-20% chance for new precipitation amounts around 0.10 inches between 5 AM Saturday to 5 AM Sunday across northwest Oregon and southwest Washington, with the highest probability along the coast and the Central Oregon Cascades. For those going out on Halloween, the weather is not looking too impactful as we are not expecting heavy rain or strong winds.

Sunday to Wednesday, looking at WPC 500 mb clusters around 75% of the ensemble member show a ridge amplifying over the northeast Pacific and shifting over the Pacific Northwest, with around 50% of those ensemble members developing into an Omega Blocking pattern. However, 25% of ensemble members are showing an upper level trough moving into the Pacific Northwest by Monday-Tuesday. If the ridge solution manifests, a warming and drying trend is on deck for the start of next week and if the trough solution manifests then a cooler and wetter trend would be on deck for the start of next week. /42

AVIATION...Through 18Z Friday

Radar and surface weather observations from 1740Z Thursday showed scattered rain showers lingering over northwest OR and southwest WA, albeit decreasing slightly in coverage compared to earlier in the morning. A mix of VFR/MVFR ceilings were being observed, with VFR ceilings being most predominant. Expect this trend to continue the rest of today into tonight, with another uptick in shower coverage expected between 00-03Z Friday. The strongest showers will have the potential to produce brief heavy rain and small hail up to the size of peas. Chances for ceilings below 3000 ft increase to 20-30% at most TAF sites between 12-18Z Friday, with the highest chances for MVFR ceilings with passing rain showers.

KPDX AND APPROACHES...Rain showers are expected to be within the vicinity of the terminal to start out the 18Z TAF period, before showers increase in coverage again towards 00Z Friday. The strongest showers will have the potential to produce brief heavy rain and small hail up to the size of peas, with 00-03Z Friday being the most likely time period for this to occur. Ceilings today and tonight should be predominately VFR, but will occasionally drop to MVFR thresholds with passing showers. Chances for ceilings below 3000 ft increase to 20-30% between 12-18Z Friday, with the highest chances for MVFR ceilings with passing rain showers. -23

MARINE

Winds and seas will continue to subside, with gusts less than 20 kt and seas 4-6 ft through the remainder of the week and into the weekend. Peak gusts approaching 20 kt are expected on Friday. This will result in relatively benign conditions across the coastal waters, with an exception within the main channel of the Columbia River Bar where very strong ebb currents Wednesday evening and Thursday evening that will temporarily result in seas building towards 8 to 10 ft with each strong ebb.

Towards the start of next week, seas will start to re-build towards 8-10 ft as a fresh, long period west-northwest swell with a dominant period of 15-17 seconds enters into the region. Light offshore winds are expected on Monday, suggesting seas will be primarily driven by the long-period swell rather than wind waves. /42-23

PQR WATCHES/WARNINGS/ADVISORIES

OR...Freeze Watch from late Friday night through Saturday morning for ORZ105-109-114-115-123.

WA...None.

PZ...Small Craft Advisory from 5 PM this afternoon to 10 PM PDT this evening for PZZ210.