textproduct: Portland

SYNOPSIS

Offshore flow will bring hot, dry, and smokey conditions to northwest OR and southwest WA Tuesday through Thursday. High temperatures for most inland valley locations peak in the mid to upper 90s Tuesday to Thursday, resulting in a widespread Moderate to locally Major HeatRisk impacts. Temperatures begin to trend cooler Friday into the weekend with the return of onshore flow, which will also push any lingering wildfire smoke and haze east of the Cascades. Fire weather concerns remain in the forecast through Wednesday in the western Columbia River Gorge and portions of the Willamette Valley.

DISCUSSION...Now through Sunday night

Satellite imagery from Monday afternoon showed widespread wildfire smoke and haze spreading over southwest Washington and much of northwest Oregon to the north of a line extending from Newport to Salem to Timothy Lake in response to increasing offshore winds. Smoke has mixed down to the surface over some inland areas, lowering surface visibilities down to 5-9 miles over the greater Portland/Vancouver metro and central/northern Willamette Valley. Visibilities appear even lower over portions of the Mt. Hood National Forest, north OR Cascade foothills, and the western Columbia River Gorge due to a more concentrated smoke plume blowing westward from the Grasshopper Fire. As a result of this smoke, air quality has begun to degrade in the aforementioned areas. The Oregon Department of Environmental Quality (DEQ) and the Southwest Clean Air Agency have issued Air Quality Alerts for portions of southwest WA and northwest OR, including the Portland/Vancouver metro. For updates regarding the air quality forecast and any Air Quality Advisories that are in effect, please visit the Oregon Smoke Blog at oregonsmoke.org and the Washington Smoke Blog at wasmoke.blogspot.com.

Smoke and haze will likely continue impacting the area through at least Wednesday or Thursday before onshore flow returns and helps clear smoke out of the area from west to east late Thursday into Friday. Until then, offshore flow and upper level ridging will not only maintain smoke and haze but will also bring heat and fire weather concerns. For fire weather concerns, please refer to the fire weather discussion below. For heat, model guidance remains in good agreement for highs in the mid to upper 90s on Tuesday and Wednesday, and somewhere in the 90s on Thursday. However, the impacts of wildfire smoke on temperatures needs to be taken into account, as areas with dense wildfire smoke will see high temperatures limited by several degrees. The RRFS model, which does account for wildfire smoke, suggests highs will be most limited over the northern Willamette Valley, Columbia River Gorge, Portland/Vancouver metro and Mt. Hood National Forest on Tuesday with highs only in the low to mid 90s rather than upper 90s. Meanwhile, smoke impacts on temperatures over the rest of southwest WA and northwest OR are minimal. On Wednesday, the RRFS model suggests little to no impacts on temperatures due to a more dispersed and thinner smoke layer. Regardless of the exact outcome, it will still be hot enough to bring an increased risk of heat-related illnesses. As such, various Heat Advisories remain in effect for most inland valleys beginning Tuesday afternoon. 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.

Heading into Friday and next weekend, model ensemble guidance continues to suggest onshore flow will strengthen with temperatures trending cooler each day. This will scour out any lingering smoke and haze in the area, bring an end to heat concerns along with decreasing fire weather concerns. -23

AVIATION...Through 18Z Tue

Smoke aloft between 5000-9000 ft with easterly flow. Thermal trough forms tonight causing winds to shift to the north, especially along the coast and the Willamette Valley. Gusts upwards of 25-30 kt along the coast and south of KSLE. Cannot rule out gusts up to 25 kt around KSLE and KUAO this afternoon, but not expected to be as widespread. For the easterly flow, some observations through the Columbia River Gorge are around 25 kt but those should ease through the day.

Overnight, the smoke aloft will settle towards the surface as winds ease. This smoke will cause slight reductions to visibility down to 6SM north of Salem. However, we cannot rule out denser smoke around K4S2 and smaller runways west of the Grasshopper Fire, or any new fires that may ignite today.

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. Smoke may settle overnight reducing VIS to around 6SM. Confidence is around 35-50% for this occurring. -27/99

MARINE

An upper-level ridge of high pressure building off the coast continues to drive northerly winds across the waters today with gusts greater than 21 kt being reported on area buoys. The northern buoys have struggled to see the rises which isn't uncommon for a northerly wind, but they are still hovering right around 21 kt for gusts. A Small Craft Advisory remains in effect for all of the water into the middle of the week which, if wind waves remain elevated, could extend further. The Columbia River Bar is included in these Small Crafts due to wind. There is a slight chance (15-30%) that the bar could see a return of the wind on Tuesday evening, but right now the length of time would be for just a few hours between 1500-2000. They would also be marginal and impact the main entrance to the bar and not the interior portions of PZZ210.

Starting Thursday, flow becomes zonal and winds will shift slightly to the northwest. Therefore will see wind waves shift slightly. Overall wind speeds will decrease but seas will stay relatively similar around 6 to 8 ft at 10 seconds and being mostly wind wave driven. -27

FIRE WEATHER...Today through Thursday

Critical fire weather conditions are expected this afternoon and evening over the central/southern Willamette Valley mainly to the south of Salem this afternoon and evening due to breezy north winds with gusts up to approximately 25 mph combined with low relative humidity values down to 20-25%. A few max gusts upwards of 28 mph are possible. This means any new or existing fires in this area could exhibit rapid fire spread. As such, 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 with conditions approaching red flag warning criteria. We have a developing thermally induced surface trough causing 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. Conditions then remain dry and windy in the western Gorge as easterly winds continue Tuesday night through Wednesday evening. Winds in the Gorge will be strongest Tuesday morning through early Tuesday afternoon, and again Tuesday night through early Wednesday afternoon. Relative humidity values will be lowest Tuesday afternoon and Wednesday afternoon, down to 15-20%. Poor overnight humidity recoveries are expected Tuesday night with maximum relative humidity values ranging between 35-45%. Therefore, a Red Flag Warning has been issued for the western Gorge, fire weather zone 636, from 11 AM PDT Tuesday through 8 PM PDT Wednesday. 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 more considerably by Thursday, with one potential exception. Thursday is when we transition to onshore flow, which will bring breezy westerly winds in the central Gorge and Hood River area. Given conditions will still be dry, elevated fire weather concerns will remain in place. -23/99

PQR WATCHES/WARNINGS/ADVISORIES

OR...Heat Advisory from noon Tuesday to 11 PM PDT Wednesday for ORZ104-105-108>118.

Red Flag Warning until 8 PM PDT this evening for ORZ685.

WA...Heat Advisory from noon Tuesday to 11 PM PDT Wednesday for WAZ204>208.

Red Flag Warning from 11 AM Tuesday to 8 PM PDT Wednesday for WAZ636.

PZ...Small Craft Advisory until 1 AM PDT Tuesday for PZZ210.

Small Craft Advisory until 5 AM PDT Wednesday for PZZ251>253- 271>273.