textproduct: Portland

SYNOPSIS

The region remains underneath a pattern favoring hot, dry, and rather smoky conditions through Thursday, but relief is on the horizon. High temperatures for most inland valley locations peak in the upper 80s to mid-90s through Friday. However, temperatures will still be warm enough for widespread Moderate HeatRisk impacts. Temperatures begin to trend a 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...Tonight through Tuesday night

High pressure continues to build over the region today, but smoky skies and unhealthy air quality remain the main concerns across the area. As the upper level ridge axis begins to shift over western OR and WA later this afternoon, expect lower level winds to shift from light offshore to more westerly as an onshore push begins this evening. Models that do not take into account the smoke have been suggesting the warmest temperatures of the week occurring today, with highs reaching the mid to upper 90s. But, as of noon, temperatures are running around 1-3 degrees cooler than yesterday where the smoke is most prevalent. Temperatures in the Coast Range and Cascade foothills, though, are showing temps running around 4-8 degrees warmer than yesterday, being less impacted by wildfire smoke. Therefore, expect inland valley temperatures to be similar to what was observed yesterday, with highs reaching the upper 80s to lower 90s.

As winds turn more westerly, smoke from the Grasshopper Fire will likely remain east of the Cascades. But lingering smoke will still take some time to move out of the area on Thursday with skies more likely to see improvement by Thu night as the westerlies increase aided by a shortwave trough offshore lifting into British Columbia. Ensemble 850 mb temps of around 20-22C are expected to be similar to today as the upper level ridge remains over the region, and with the smoke gradually dispersing, more sunshine could lead to slightly warmer temperatures inland with highs in the lower to mid 90s. So will maintain the Heat Advisory through Thu evening.

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 Thursday into Friday. This will begin pushing smoke back east of the Cascades in earnest late Thursday into Friday, albeit slowly for our inland valleys initially.

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.

Friday and into the weekend, the axis of the broad upper-level ridge feature moves east of OR/WA, while more zonal flow develops over the Pacific NW, 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 on Friday, and possibly into Saturday. 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. DH/99

AVIATION...Through 06Z Fri

Satellite imagery and terminal observations as of late Wednesday evening depicts widespread smoke across northwest Oregon and southwest Washington, with the highest concentrations of smoke across the Willamette Valley. Much of the smoke has been coming from the Grasshopper Fire near Mt. Hood. This is resulting in VIS reductions to 2-4 SM with FU CIGs between 3-5 kft across the Willamette Valley. Expect this trend to continue through tonight; however, a return of winds from the west/northwest will gradually push smoke eastward tonight into Thursday. As a result, could see some improvement in VIS to 5-6SM or greater tonight, but can't rule out VIS of 3-4 SM continuing through 12-15z Thu. Areas immediately around the Grasshopper Fire may experience much lower VIS reductions from smoke. Along the coast, LIFR stratus persists at KONP while guidance favors a return of LIFR/IFR CIGs at KAST after 05-06z (>80% chance). Winds generally under 10 kt, strongest in the afternoon and evenings. Winds weaken below 5 kt tonight. By Thursday afternoon, increasing westerly winds will help clear out smoke across Western Oregon, favoring a return of VFR VIS and CIGs.

KPDX AND APPROACHES...MVFR VIS and VFR CIGs tonight due to smoke and haze. Moderate confidence for VIS/CIGs improving to VFR tonight into Thursday. High confidence for VFR conditions after 00z Fri as increasing onshore flow pushes smoke eastward. Northwesterly winds around 3-6 kt, strongest in the afternoon. -10

MARINE

Small Craft Advisories remain 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 around 6-7 feet at 8 seconds subside tonight to around 5 feet at 7-8 seconds. Seas remain mainly wind driven into next week. -19/99

FIRE WEATHER...Today through Friday

Offshore easterly flow is gradually turning onshore across the Cascades this afternoon. Elevated fire weather conditions are still anticipated for much of the region, especially the western Columbia Gorge and in the Cascades and Cascade foothills for conditions near critical thresholds, especially at ridge tops where relative humidity values are expected to fall into the upper teens to mid-20s. 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. DH/99

PQR WATCHES/WARNINGS/ADVISORIES

OR...Heat Advisory until 11 PM PDT Thursday for ORZ108>118.

WA...Heat Advisory until 11 PM PDT Thursday for WAZ204>208.

PZ...None.