textproduct: Portland

SYNOPSIS

Cooler temperatures will continue through Sunday in the wake of a cold front. Warm and dry Monday through Friday with breezy winds during the afternoon and evening on Monday and Tuesday. The warmest temperatures will occur on Tuesday and Wednesday with highs in the 90s for inland valleys and 70s at the coast, resulting in a Moderate HeatRisk for the interior lowlands. Wildfire smoke is expected to increase west of the Cascades on Monday and Tuesday as winds begin to turn more offshore.

LONG TERM...Tuesday through Friday Night

Models and their ensembles are in good agreement Tuesday and Wednesday will be the hottest days of the week as an upper level ridge over the coastal waters moves inland. Although the ridge axis is expected to move inland, the ridge will be deamplifying at the same time. This will prevent extreme heat with triple digit temperatures from developing. However, it will still be hot with high temperatures somewhere in the low to mid 90s for inland valleys and 70s at the coast. This will result in a Minor HeatRisk at the coast and a Moderate HeatRisk for inland valleys, bringing an increased risk for heat-related illnesses for vulnerable populations that are sensitive to heat. Probabilities for a Major HeatRisk are low, ranging between 5-20% for most inland valley locations. The good news is overnight lows in the mid 50s to lower 60s along with low humidity will offer relief for those without access to air conditioning. Tuesday will likely see hazy skies due to lingering wildfire smoke in the area that is expected to begin pushing west of the Cascades beginning on Monday as low-level offshore winds develop.

The majority of of deterministic and ensemble guidance continue to suggest depict a return to onshore winds by late Thursday and Friday, bringing slightly cooler temperatures but still a bit above average with highs in the mid to upper 80s for inland valleys. The increasing onshore flow late in the week will also help clear out any smoke and haze lingering in the area from mid-week. -23

FIRE WEATHER...Monday through Tuesday

There are elevated fire weather concerns in the Willamette Valley on Monday and Tuesday during the afternoon and evening hours due to breezy north winds and low humidity. However, confidence levels in Red Flag Warning criteria being met are lower than 50% on both days, currently ranging between 20-40%. Therefore, Fire Weather Watches have not been issued at this time, but both days bear a close watch. Details are discussed below.

The outcome will be highly dependent on the evolution of a surface thermal trough that will begin lifting northward into western Oregon Monday into Tuesday. Typically it builds overhead from southwestern Oregon (dry northerly winds when this occurs) then it modulates diurnally back-and-forth from the coast/coast range (AM) towards I-5 and/or the Cascades (PM) helping to influence the magnitude and placement of offshore flow. Currently it appears it will form along the south Oregon coast Monday morning before moving inland and further to the north in the afternoon. This progression would cause northerly winds to amplify in the Willamette Valley, and increase easterly winds aloft around 5000 ft, including in the high Cascades. These easterly winds will bring in drier air from east of the Cascades and the downsloping action will increase warming and drying in the lower elevations and in the Willamette Valley. Combine this with daytime heating and a deep layer of dry air, we will see relative humidity drop within the interior lowlands on Monday to near 25%. As the thermal trough builds into the area, could see gusts up to 20-25 mph within the Willamette Valley, Clark County lowlands, and along the coast. In the southern Willamette Valley around Eugene there is a higher probability of seeing these wind speeds than in the north. This isdue to more of a channeling/fetch component and a tighter north-south pressure gradient. These dry and breezy conditions will lead to elevated fire weather concerns as they overlap mid/late afternoon into the early evening on Monday, however winds may be just shy of meeting criteria for a Red Flag Warning in most locations. Tuesday will be even drier with humidity values well below critical thresholds, however northerly winds will be trending weaker and are not expected to meet criteria for a Red Flag Warning at this time.

AVIATION...Through 00Z Mon

VFR conditions have returned to the airspace, with lingering low VFR clouds holding on a bit as the frontal system dissipates. While VFR conditions will continue through the TAF period for inland terminals, there is a 30-50% chance of MVFR CIGs returning along the coast from 05-19Z Sun. Current west to northwesterly winds around 5-10 kt will shift entirely northwesterly this evening and continue so through the period. The one exception is winds along the coast will increase to around 10-15 kt with gusts up to 20-25 kt by 18-20Z Sun.

KPDX AND APPROACHES...VFR conditions through the TAF period, with a 10-20% chance of MVFR CIGs redeveloping between 11-15Z Sun. Northwesterly winds 5-10 kt will continue through the period. ~12

MARINE

Westerly flow today will shift northerly into Sunday as surface high pressure builds offshore. Chances for maximum wind gusts of at least 21 kt are around 85-95% from Sunday afternoon/evening through at least Tuesday night with the highest relative probabilities across the outer waters. Given this high confidence in Small Craft conditions, a Small Craft advisory was issued for the inner and outer waters, including the Columbia River Bar, starting Monday mid/late afternoon. Once we get in to the middle of the week these Small Craft concerns primarily shift to the outer waters but likely persist through the end of the week. Wave heights through the forecast period remain around 5-8 ft at 7-9 seconds. ~12/99

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory from 5 PM Sunday to 2 AM PDT Monday for PZZ210.

Small Craft Advisory from 5 PM Sunday to 5 AM PDT Tuesday for PZZ251-252-271-272.

Small Craft Advisory from 2 PM Sunday to 5 AM PDT Tuesday for PZZ253-273.