Area Forecast Discussion

SYNOPSIS

Minimal change in the forecast overall. Upper level high pressure builds over the far northeast Pacific into western WA/OR over the next several days, ushering in a prolonged stretch of dry and hot conditions. Daytime temperatures increase significantly this weekend into early next week, peaking Sunday and Monday with interior lowlands in the upper 90s to around 100 degrees. Low temperatures will not provide much relief from the heat. Heat related impacts are anticipated for much of the region with widespread Moderate to High HeatRisk. Temperatures will trend cooler for Wednesday onward with the return of onshore flow.

SHORT TERM...Now through Monday Night

High pressure continues to build over the region today which is setting the stage for a stretch of hot and dry conditions. Today has been fairly normal with highs in the mid to upper 70s inland, and near 60 along the coast. While temperatures were mild today, that will not be the case over next several days.

On Saturday, we will see highs rise into the 80s but the big consideration is actually wind. The overall flow will transition into an offshore pattern which will add a mechanical warming mechanism to the environment. As the easterly flow comes up and over the terrain, it will not only mix down warm air aloft, but it will also compress the air at the surface and thus cause increased warming. This flow pattern will also cause winds to ramp up within the Columbia River Gorge, and within the Willamette Valley. Overall, the wind speeds are not unheard of for this time of year, but rather they are impactful to some of the industries like wildfire. More details on this below.

Temperatures rise further on Sunday into Monday as the ridge axis aligns to the coastline. Daytime temperatures are expected to quickly increase into the upper 80s to low 90s on Saturday then to the mid to upper 90s for Sunday and Monday for the interior lowlands and portions of the OR Coast Range. The coast will be much warmer than normal as well, peaking in the 70s each day and near 80 degrees on Sunday. With the newest forecast, the HeatRisk for the coast has increased to Moderate and there was enough confidence in an increased heat day to issue a Heat Advisory for the coast. Probabilities for temperatures exceeding 95 degrees are around 70-90% between Salem and Vancouver and 50-70% for the rest of the interior lowlands on Sunday. There is less than a 5% chance for the Cowlitz Valley lowlands and Gorge. On Monday, those probabilities for 95 degrees F rise considerably with the NBM showing around a 85-99% chance of temperatures greater than 95 degrees F in the Valley and around 30% in the Longview area. With Monday being the hottest day in the forecast, there is around a 50% chance of temperatures of 100 degrees or more from Salem northward.

Something we continue to monitor are the overnight low temperatures. Typically we will see cooling overnight that brings much needed relief. However, in this pattern we are seeing very little as overnight lows are lingering around 65 degrees F in the interior lowlands where we see the highest daytime temperatures. Low temperatures could even remain above 70 degrees in some locations with a 30-40% chance for the greater Portland-Vancouver Metro area Sunday night into Monday morning and less than a 10% chance on Monday night into Tuesday morning.

As previously mentioned, there are some fire weather concerns in areas with cured grasses and finer fuels Saturday into Monday due to hot, dry, and breezy conditions. The thermal trough will bring breezy conditions within the western Columbia River Gorge/Cascades gaps and the Willamette Valley Saturday through Sunday night. As daytime highs increase, relative humidities will also decrease to near critical levels. Based on feedback from area partners, fuels are not quite cured enough to consider any Red Flag Warnings at this point, but there is uncertainty on how the fuels will be impacted by the continuous days of dry and hot conditions. Currently, there is around a 15-30% chance of relative humidity being below 25% and winds being greater than 15 mph on Saturday and Sunday. Be aware of potential ignition sources such as vehicle chains dragging on the pavement, hot vehicle components, sparks created by power tools, and cigarette butts as all of these could easily result in the ignition of cured grasses and dry, fine fuels. Live vegetation and larger fuels may not have enough time to dry out prior to the dry and breezy conditions, but this is a variable that is being closely monitored by our State and Federal Fire Partners. -27

LONG TERM...Tuesday through Friday

Ensemble guidance indicates high pressure continues Tuesday with heights beginning to lower along with 850 mb temperatures, which would allow for lowering temperatures on Tuesday. However, there is uncertainty in the forecast spread of both of these elements, leading to uncertainty in the high temperature for Tuesday. Additionally, it is not uncommon for models to degrade highly amplified ridges such as this one too early in the extended forecast period. There is no robust weather system in the models that is causing the lowering heights, so there is the potential that the high pressure may not break down as much as ensembles indicate on Tuesday. NBM still indicates warm daytime temperatures at least in the upper 80s for the interior lowlands. Ensembles are in good agreement that the surface thermal trough over OR will break down sometime Monday into Tuesday, so Tuesday is not expected to be quite as warm for the coast and Coast Range. With the flattening ridge, we there is the potential for a more unique wind direction pattern though. We will see a transition to northwesterly winds which will usher in cooler air to the northern portions of the forecast area while the southern zones will remain warmer. Therefore, there may be a 5 degree spread between the north and south on Tuesday. But, if the ridge remains amplified, that difference will be less significant. Either way, past heat events have shown that impacts from the heat can continue despite a cool- down, especially since morning low temperatures are expected to remain very warm Tuesday morning.

Ensemble guidance indicates the high pressure axis shifts west back over the E Pacific Wednesday and Thursday as a strong upper trough digs into the Midwest. However, uncertainty in the strength of the trough leads to uncertainty in the high pressure over the Western US/E Pacific. There is high confidence that temperatures will be quite cooler than Sunday and Monday, but 50-60% of ensemble members still keep just enough high pressure over the region for high temperatures to remain in the low to mid 80s for the interior lowlands. -HEC

AVIATION

High pressure will maintain VFR conditions with clear skies through the TAF period across all terminals. Tonight, variable winds around 5 kt or less inland with light offshore winds along the coast. After 15-18z Sat, offshore pressure gradients will tighten and support northerly to northeasterly winds across the region, with gusts up to 20-25 kt at any given terminal. After 03-04z Sun, winds should gradually weaken as pressure gradients ease.

In addition, temperatures between 90 to 100 degrees F are forecast across the Willamette Valley Saturday through early next week. Be aware of high density altitude which may reduce aircraft performance.

KPDX AND APPROACHES...VFR with clear skies through the TAF period. Light northwesterly winds around 5 kt or less overnight, turning more northeasterly after 16-18z Sat with gusts up to 20 kt through the afternoon. Winds weaken in the evening after 03z Sun. -10

MARINE

Expect a typical summertime pattern persist into next week as high pressure builds offshore. Diurnal northerly winds will strengthen, peaking each afternoon and evening. Expect winds of 15-20 kt with gusts up to 25 kt south of Cape Falcon on Friday, increasing to 15-25 kts with gusts up to 30 kts on Saturday. Overnight, wind gusts may fall below Small Craft Criteria for the inner water zones, but still expecting gusts up to 25 kt for the outer waters. Will maintain the current suite of Small Craft Advisories, but they could get extended through Sunday as there is minimal changes in overall conditions. Seas 4-7 ft at 9-11 seconds with a persistent westerly swell.

Long-range guidance brings a more active weather pattern towards the end of next week. Which could result in seas near 10 ft as well as gusts up to 30 kt, but overall confidence in this pattern change is low at this time.

CLIMATE

Record high temperatures and warm low temperatures for Sunday, June 14

High Temperatures: Warm Low Temperatures: Portland Int'l 89F (1988) 62F (1985) Vancouver, WA 93F (1986) 61F (1931) Hillsboro 96F (1961) 60F (1963) McMinnville 93F (1986) 59F (1936) Salem 92F (1961) 59F (1936) Eugene 92F (1914) 57F (1993) Astoria 86F (1914) 58F (1972)

Record high temperatures and warm low temperatures for Monday, June 15

High Temperatures: Warm Low Temperatures: Portland Int'l 95F (1966) 60F (1969) Vancouver, WA 95F (1930, 1966) 62F (1961) Hillsboro 99F (1961) 60F (1963) McMinnville 96F (1961) 59F (1936) Salem100F (1966) 59F (1931) Eugene 96F (1966) 60F (1961) Astoria 91F (1966) 58F (1997)

Record high temperatures and warm low temperatures for Tuesday, June 16

High Temperatures: Warm Low Temperatures: Portland Int'l 95F (1958) 60F (2012) Vancouver, WA 92F (1961) 67F (1966) Hillsboro100F (1961) 65F (1961) McMinnville 98F (1961) 59F (1966) Salem 97F (1961) 61F (1961) Eugene 95F (1961) 62F (1961) Astoria 87F (1958) 59F (1997)

PQR WATCHES / WARNINGS / ADVISORIES

OR...Heat Advisory from 11 AM to 11 PM PDT Sunday for ORZ101>103.

Heat Advisory from 11 AM Sunday to 11 PM PDT Tuesday for ORZ104>108-113>119-121>125.

Extreme Heat Warning from 11 AM Sunday to 11 PM PDT Tuesday for ORZ109>112-120.

WA...Heat Advisory from 11 AM to 11 PM PDT Sunday for WAZ201.

Heat Advisory from 11 AM Sunday to 11 PM PDT Tuesday for WAZ202>205-208-210.

Extreme Heat Warning from 11 AM Sunday to 11 PM PDT Tuesday for WAZ206-207-209.

PZ...Small Craft Advisory until 5 AM PDT Sunday for PZZ252-253-272- 273.