textproduct: Portland

SYNOPSIS

The upcoming week is highlighted by hot and dry conditions with increasing wildfire smoke late Monday into Tuesday as offshore flow develops. High temperatures for most inland valley locations are now expected to peak between 95-100 degrees on Tuesday and Wednesday, and potentially into Thursday as well. This will result in widespread Moderate to locally Major HeatRisk. Trending relatively cooler by Friday with the return of onshore flow, which will also help push wildfire smoke east of the Cascades. Fire weather concerns remain in the forecast Monday and Tuesday as wind speeds increase and relative humidity values drop.

LONG TERM...Thursday through Saturday night

The long term forecast is highlighted by gradually cooling temperatures, decreasing wildfire smoke west of the Cascades, and decreasing fire weather concerns. It appears Thursday will be a transition day as a thermally induced surface thermal trough that will reside over western Oregon early to mid week finally shifts east of the Cascade crest, bringing a return to onshore flow. Model ensemble guidance is also in agreement the upper level ridge axis will begin shifting east of the Cascades on Thursday as well. This should bring slightly lower temperatures on Thursday with wildfire smoke beginning to slowly decrease from west to east. That being said, the onshore flow will be weak, which means at least some haze from wildfire smoke is likely to remain and temperatures will still be trending rather hot with highs somewhere in the 90s for most inland valleys.

Onshore flow is expected to strengthen more considerably Friday into next weekend, bringing more seasonable temperatures back into the 80s by Saturday. Onshore flow should be strong enough at that point to push any lingering smoke and haze east of the Cascades. Despite the increasing onshore flow, dry weather is expected to continue through at least August 9th with no signs of any precipitation. -23

AVIATION...Through 00Z Tue

Widespread VFR conditions will continue through the period for most terminals. The only exception is for some coastal terminals, where marine stratus will push into the coast around 11-12Z Mon and maintain MVFR conditions through 18Z Mon (20-50% chance of MVFR, 10-20% chance of IFR). Otherwise, expect increased north to northwesterly winds this afternoon and evening at many terminals, around 12-17 kt with gusts up to 20-25 kt.

KPDX AND APPROACHES...VFR through the TAF period. Northwesterly winds around 10-15 kt with gusts up to 20 kt in the late afternoon, weakening and shifting northerly around 06-12Z Mon. ~12

MARINE

Northerly flow begins to increase across the coastal waters this afternoon. Chances for maximum wind gusts of at least 21 knots remain greater than 85% today through the middle of the week with the highest relative probabilities across the outer waters. A Small Craft Advisory remains in effect across the inner and outer waters including the Columbia River Bar. While at this moment the Small Craft Advisory for the Columbia River Bar will come to an end at 2 AM Monday, the Small Craft Advisories for the rest of the waters will remain through at least late Tuesday afternoon. Small Craft wind concerns will shift to the outer waters on Wednesday through the end of the week. Expect wave heights through the week to hold around 4-8 ft at 7-9 seconds. ~12/99

FIRE WEATHER...Monday through Wednesday

Critical fire weather conditions are expected over the southern Willamette Valley to the south of Salem Monday afternoon and evening due to breezy north winds with gusts up to 25 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. Therefore, a Red Flag Warning has been issued for fire weather zone 685 during that time. 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. The reason for the increase in wind speeds is due to the development of a thermally induced surface trough over far southwest Oregon today into Monday, which is set to move farther inland and lift northward into the Willamette Valley Monday afternoon. This progression will cause northerly winds to increase in the Willamette Valley while increasing 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 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 on Monday to as low as 20- 25%. The slightly stronger winds in the south valley is due to a channeling/fetch component and a tighter north-south pressure gradient. These dry and breezy conditions will lead to critical fire weather concerns as they begin to overlap by mid Monday afternoon into the early evening hours.

Monday night into Tuesday, the axis of the surface thermal trough is expected to lift farther to the north towards the Columbia River Gorge, while also pushing westward towards the Oregon coast. This will bring increasing easterly winds in the Columbia River Gorge and Cascades and a lowering subsidence inversion with sharp overnight thermal belts/poor overnight humidity recoveries in the Cascades. Easterly winds 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. Therefore, a Fire Weather Watch has been issued for fire weather zone 636 Tuesday 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. Given the majority of our Cascade zones away from the Gorge should see wind speeds below red flag warning criteria, have decided not to include these zones within the Fire Weather Watch at this time. Nevertheless, elevated fire weather concerns will still exist in these zones, as well as in the Portland metro and Willamette Valley where northeast to north-northeast winds are expected to gust up to approximately 20 mph in the afternoon. Fire weather concerns gradually decrease on Wednesday as offshore winds begin to weaken. -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 to 8 PM PDT Monday 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 5 PM this afternoon to 2 AM PDT Monday for PZZ210.

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

Small Craft Advisory until 5 PM PDT Tuesday for PZZ253-273.