textproduct: Portland

SYNOPSIS

Expect a rapid transition to hot and dry conditions with increasing wildfire smoke today into Tuesday as offshore flow takes hold across the region. High temperatures for most inland valley locations peak between 94-100 degrees by Tuesday and Wednesday, and potentially into Thursday as well. This results in widespread Moderate to locally Major HeatRisk impacts. At least conditions begin to trend cooler Friday with the return of onshore flow which will also help push any wildfire smoke back east of the Cascades. Fire weather concerns remain in the forecast Monday, Tuesday, and potentially Wednesday for select areas as winds increase and relative humidity values degrade.

LONG TERM...Thursday through Sunday

While the first half of the week is marked by a sharp warming trend, late week into the weekend is highlighted by a gradual glide-path of moderating temperatures and decreasing wildfire smoke west of the Cascades. It appears Thursday will be a transition day as the axis of the upper-level trough finally passes overhead west to east helping to kick the thermally induced surface thermal trough east of the Cascade crests. This brings a return of weak onshore flow, although it may take until the next day (Friday) to see more appreciable improvement in daytime high temperatures across the inland valleys. The pattern progression will also allow wildfire smoke to start to slowly decrease from west to east. Then onshore flow is expected to strengthen more considerably Friday into weekend, bringing more seasonable temperatures back into the 80s by Saturday. Onshore flow should be strong enough to flush any lingering smoke and haze east of the Cascades. Despite the increasing onshore flow, dry weather is expected to continue through the end of the weekend with no signs of any precipitation in the near future. -99/23

AVIATION...Through 12Z Tue

Current observations depict widespread VFR conditions across the area, likely persisting through the TAF period as skies remain mostly clear and marine stratus holds just offshore. That said, there is a 25-35% chance coastal terminals (mainly KAST) see brief MVFR CIGs between 13-17z. Winds remain out of the north to northeast today with gusts up to 15-25 knots possible along the coast and I-5 corridor this afternoon into the evening. Aloft, an easterly wind shift will also steer smoke from wildfires on the east side of the Cascades to the west side. Given the latest guidance, smoke remains in the inland TAFs from late morning/afternoon onward where concentrations will be more noticeable - only moderate confidence regarding timing however.

KPDX AND APPROACHES...VFR conditions are expected to continue locally. Northerly winds around 5-10 knots this morning increase late morning/midday with occasional gusts around 20 knots possible through the afternoon into the early evening. -99

MARINE

An upper-level ridge of high pressure building off the coast continues to drive northerly winds across the waters today with high confidence in gusts greater than 21 knots, especially this afternoon into the evening hours. A Small Craft Advisory remains in effect for the inner and outer waters into the middle of the week, including the Columbia River Bar although for a more targeted timeframe there - 1PM today through 1AM Tuesday. Come Thursday into Friday these winds begins to decrease and gain a slight westerly component, likely limiting any further marginal Small Craft conditions to the outer waters through the first half of the weekend. Expect fairly similar wave heights day to day as they hold around 4-8 ft at 7-9 seconds. -99

FIRE WEATHER...Today through Thursday

For today, confidence continues to increase for a period of critical fire weather conditions over the central/southern Willamette Valley mainly south of Salem this afternoon and evening due to breezy north winds with gusts up to 25-28 mph combined with low relative humidity values down to 20-25%. This means any new or existing fires in this area could exhibit rapid fire spread towards the south. A Red Flag Warning remains in effect for fire weather zone 685. Although wind speeds are not forecast to be quite as strong to the north of Salem, conditions will still be dry and breezy enough for elevated fire weather concerns. We have a developing thermally induced surface trough to thank for these winds as it lifts northward into the region. While winds at the surface have a large northerly component today, easterly winds will be developing aloft around 3000-6000 ft this morning. These easterly winds will bring in drier air from east of the Cascades and the downsloping action will increase compressional 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 as low as 18-25%.

Tonight into Tuesday, the surface thermal trough is expected to amplify while the axis of this feature shifts towards the Oregon coast. This will further increase easterly winds in the Columbia River Gorge and Cascades, in addition to a lowering subsidence inversion with sharp overnight thermal belts/poor overnight humidity recoveries, particularly in the Cascades. Easterly winds on Tuesday are expected to be strongest in the western Gorge with gusts up to 30-40 mph in the most wind-prone locations. Given the low relative humidity values in place at that time, critical fire weather conditions capable of rapid fire spread will be possible. A Fire Weather Watch is in effect zone 636 Tuesday early afternoon through Tuesday evening. The rest of the Cascades will have relatively weaker easterly winds with gusts generally in the 15-25 mph range. One exception would be on exposed ridgetops and west-east oriented valleys where slightly higher wind gusts are likely. Nevertheless, elevated fire weather concerns still exist in these areas, as well as in the Portland metro and Willamette Valley where NNE to NE winds are expected to gust up to approximately 15-20 mph in the afternoon. Again expect poor ridgetop relative humidity recoveries in the Cascades and Roast Range Tuesday night. Fire weather concerns decrease just a touch on Wednesday as offshore winds begin to weaken, however, we'll need to watch the western Columbia River Gorge closely as it continues to flirt with another period of critical fire weather conditions during the early to mid afternoon hours. Even on Thursday our transition to westerly flow likely shifts fire weather concerns to the central Gorge (Hood River area) due to the resident dry airmass overlapping with increasing westerly winds. Continue to monitor the forecast closely the next several days. -99/23

PQR WATCHES/WARNINGS/ADVISORIES

OR...Heat Advisory from noon Tuesday to 11 PM PDT Wednesday for ORZ104-105-108>118. Red Flag Warning from 1 PM this afternoon to 8 PM PDT this evening for ORZ685. WA...Heat Advisory from noon Tuesday to 11 PM PDT Wednesday for WAZ204>208. Fire Weather Watch from Tuesday afternoon through Tuesday evening for WAZ636. PZ...Small Craft Advisory from 1 PM this afternoon to 1 AM PDT Tuesday for PZZ210. Small Craft Advisory until 5 AM PDT Wednesday for PZZ251>253- 271>273.