textproduct: Portland

SYNOPSIS

The region remains underneath a pattern favoring hot, dry, and rather smoky conditions again today but relief is on the horizon, eventually. High temperatures for most inland valley locations peak in the low to upper 90s through Thursday and Friday although wildfire smoke may dampen high temperatures several degrees - most notably today. However, temperatures will still be warm enough for widespread Moderate to locally Major HeatRisk impacts. Temperatures begin to trend touch cooler over the weekend with the return of strong onshore flow evicting any lingering wildfire smoke and haze back east of the Cascade crests by this point. More seasonable conditions are anticipated early next week.

DISCUSSION...Today through Tuesday

A smoky sky muting the sun to a burnt orange and red hue is certainly a gloomy way to start the day for most, but the combination of offshore flow and ample wildfire activity just to our east has unfortunately led to such conditions persisting. The ridge of high pressure helping to drive our offshore winds, hot temperatures, and low daytime humidity peaks over the region today into Thursday allowing temperatures to warm even more compared to the upper 80s and low 90s we saw yesterday (Tue). Current model outputs indicate high temperatures could rise into the upper 90s through tomorrow afternoon, however, the silver lining to the all the smoke giving us "Mordor" vibes is decreasing insolation and thus slightly cooler temperatures than there otherwise would be. Confidence is high maximum temperatures will once again be impacted by the smoke and while the forecast was adjusted somewhat to compensate, a 1-3 degree decrease still might not be enough. We'll continue to assess the forecast this morning once we get a better handle on the thickness of the smoke post- sunrise.

There is a growing degree of hope for the return to clearer smoke-free skies late this week. Models are in excellent agreement showing the axis of the upper level ridge slowly moving into eastern OR/WA late Wednesday into Thursday allowing the flow will begin shifting onshore from the west. Beyond the broader ~24hr period of this transition there is some uncertainty on exactly when this shift occurs at the surface along the I-5 corridor Portland southward, but it will begin pushing smoke back east of the Cascades in earnest late Thursday into Friday, albeit slowly for our inland valleys initially. If smoke clears out by the first half of Thursday, then temperatures could peak closer to the mid to upper 90s. If it doesn't clear out until later Thursday or Thursday night, smoke would continue impacting temperatures and keep them pinned in the low to mid 90s.

Regardless of the exact outcome of the temperatures the next several days, conditions will be warm enough to bring an increased risk of heat-related illnesses. As such, various Heat Advisories remain in effect for most inland valleys through today and Thursday. In areas with Air Quality Advisories in effect, it is recommended to keep windows and door shut to prevent smoke from going indoors. However, those without air conditioning who are counting on opening their windows at night to help cool down will have less options. In this scenario, something as simple as a large box fan with a damp towel draped over the front of it can be surprisingly effective given the dry airmass in place. This could also cause an impact even with slightly lower daytime temperatures as houses may retain more heat if windows can't be opened to adequately cool off.

Heading into Friday the axis of the broad upper-level ridge feature moves even east of OR/WA, helping to increase onshore flow. That said, there will likely be enough influence from the high pressure ridge aloft and slight increase in upper-level heights to keep high temperatures in the low 90s across the inland valleys. At least at this point any lingering wildfire smoke should be completely flushed from west of the Cascade crests assuming no additional new starts locally. Onshore flow is expected to strengthen further over the weekend into early next week helping temperatures to moderate back close to normal with moderate to high confidence for maximum temperatures returning to the low to mid 80s Sunday through Tuesday. If you're looking for any sort of rainfall headed through the middle of next week you're likely out of luck. There are no signs of any appreciable precipitation for the region headed into the middle of August. -99/03

AVIATION...Through 12Z Thu

Smoke and haze are the primary impacts we're monitoring today as offshore flow near the surface keeps pumping wildfire smoke from eastern Oregon and Washington overhead. Early this morning conditions are a mix of VFR to MVFR with several terminals in the Willamette Valley and Portland metro reporting 4-5SM VIS. Improvement will be hard to come by for most sites along the I-5 corridor today beyond an occasional rise to 6SM with the best chance for P6SM VIS at KHIO and along the coast. Otherwise MVFR VIS likely prevails most hours. One of the main drivers of our degraded conditions is the Grasshopper Fire by Mt. Hood, and areas in the vicinity and to the west of this fire will experience the densest smoke with the greatest VIS impacts. However, winds are expected to become more westerly in the lower levels later Wed afternoon and evening, which could help conditions improve slightly back to 6SM VFR after 00-06z Thu - low confidence regarding the exact timing. For coastal sites, expect this westerly push of air this evening to be accompanied by marine stratus and thus a growing likelihood (50-80%) for MVFR/IFR conditions after 05-08z Thursday.

KPDX AND APPROACHES...Conditions have dropped to MVFR early this morning with little improvement anticipated through the day due to the proximity to the Grasshopper Fire and easterly winds aloft this morning. Depending on fire activity, would estimate there is a 15-20% chance for sub 3SM VIS before 00-03z Thur, after which point conditions begin to gradually improve. Northwest winds around are 5-10 kt expected, strongest in the afternoon and evening. -99

MARINE

As we go through the rest of the week into the weekend high pressure will maintain northerly winds across the inner and outer waters. Small Craft Advisories are in effect for the outer waters until 5 PM today due to both winds and a choppy seas state with conditions just under criteria across the inner waters and at the Columbia River bar. Winds and seas gradually subside tonight into Thursday, with a typical summertime pattern continuing into next week. Seas through this period generally hold in the 4-7 ft range at 7-9 seconds with wind gusts between 14-20 knots, highest during the afternoon hours and across the outer waters. -99/10

FIRE WEATHER...Today through Thursday

Offshore easterly flow continues across the Cascades early this morning with observations showing gusts generally around 10-20 mph coupled with poor to moderate relative humidity values (28-40% ridgetops). The latest model guidance has decreased wind speeds today with gusts only peaking between 10-25 mph late morning, making what was already a marginal Red Flag Warning tougher to justify. Thus, the Red Flag Warning for the western Gorge was cancelled early for fire weather zone 636, although it should be emphasized elevated fire weather conditions are still anticipated for much of the region, especially the western Columbia Gorge and in the Cascade/Cascade foothills. The on Thursday we transition to onshore flow which will bring breezy westerly winds in the central Gorge and Hood River area, further increasing on Friday. Given conditions will still be dry, elevated fire to near critical weather concerns remain in place here. -99

PQR WATCHES/WARNINGS/ADVISORIES

OR...Heat Advisory until 11 PM PDT this evening for ORZ104-105. Heat Advisory until 11 PM PDT Thursday for ORZ108>118. WA...Heat Advisory until 11 PM PDT Thursday for WAZ204>208. PZ...Small Craft Advisory until 5 PM PDT this afternoon for PZZ271>273.