textproduct: Portland

SYNOPSIS

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.

DISCUSSION...Friday through Thursday

Satellite imagery early Friday morning shows mostly clear skies over NW OR and SW WA as high pressure builds over the E Pacific. The exception is pockets of stratus are seen forming over the N OR and SW WA coastline as light NW winds push moist marine air inland. This stratus should dissipate by late morning due to surface heating. Weather conditions today will be similar to Thursday with dry weather and inland high temperatures peaking in the upper 70s to low 80s.

Attention then shifts to the significant warming trend this weekend into early next week. Ensemble guidance is in strong agreement that upper level high pressure continues building over the E Pacific with the axis shifting closer to the PacNW Saturday then shifting over the coast Sunday into Monday. At the surface, a thermal trough currently over the N CA and S OR coast will spread north into N OR west of the Cascades Saturday into Monday morning, introducing offshore flow across the area, which will have an additional warming and drying effect for many locations.

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. The offshore flow is contributing to the warmer temperatures over the Coast Range and Cascades. Probabilities for temperatures exceeding 90 degrees are around 60-90% between Salem and Vancouver on Saturday, increasing to over 90% for all of the interior lowlands and portions of the Coast Range for Sunday and Monday. Probabilities for temperatures exceeding 95 degrees are around 70-90% between Salem and Vancouver and 40-60% for the rest of the interior lowlands on Sunday, increasing to 80-95% and 60-75% respectively on Monday. Some locations between Salem and Vancouver could also reach or exceed 100 degrees, especially on Monday, with probabilities for Sunday 25-45% and Monday 45-75%.

Low temperatures are not expected to provide much relief from the daytime heat Saturday night into Sunday morning through Monday night into Tuesday morning, especially Sunday night into Monday morning. There's only a 15-35% chance of low temperatures falling below 60 degrees each night, with the warmest conditions expected for the greater Portland metro area, Coast Range, Cascade foothills, and Columbia River Gorge. Even the coast is expected to be impacted by these warmer low temperatures Sunday morning and Monday morning. Low temperatures could even remain above 70 degrees in some locations with a 5-15% chance for the greater Portland metro area and Coast Range Sunday night into Monday morning and 10-15% chance for much of the Willamette Valley and SW WA lowlands, increasing to 15-30% for the greater Portland metro area, on Monday night into Tuesday morning.

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 with a 30-50% chance of temperatures reaching or exceeding 90 degrees south of Vancouver. The NBM 90th percentile also indicates widespread low to mid 90s. 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. 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.

An Extreme Heat Warning has been issued for the greater Portland metro area and Heat Advisories for the rest of the region between the coast and Cascades for 11 AM Sunday through 11 PM Tuesday. The combination of very hot daytime temperatures and warm overnight temperatures will create Moderate to Major HeatRisk across the majority of NW OR and SW WA, excluding the Cascades. This means most of the general population will be susceptible to heat- related illness, but especially those without access to air conditioning and those spending extended time outdoors. Some fluctuations in the Major HeatRisk may be seen in the deterministic forecast as the low temperature forecasts remain right around the threshold and fluctuations of even 1-3 degrees could cause a difference between Moderate and Major HeatRisk. However, there is a 60-80% chance of Major HeatRisk across most locations between the coast and the Cascades on Sunday and Monday, what are expected to be the hottest days of this heat event. Additionally, many high and low temperatures could break records with this event. Those records can be seen in the "Climate" section below.

In addition to the heat, there will also be increasing 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. 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. 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.

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

VFR flying conditions beneath largely clear skies expected for most terminals throughout the TAF period. The only exception is MVFR cigs along the N OR and S WA coast, which will improve to VFR by 16-17z Fri as daytime heating progresses. High pressure offshore will maintain diurnal north to northwest winds, light less than 6 kts then increasing after 18-20z Fri to around 8-11 kts with gusts up to 20-22 kt along the coast. Winds decrease again after 04-06z Sat.

KPDX AND APPROACHES...VFR with clear skies through the TAF period. Northwest winds around 5 kt or less overnight, increasing near 10 kt in the afternoon as pressure gradients tighten. Winds decrease again after 04-06z Sat. -03

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 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 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 from 2 PM this afternoon to 5 AM PDT Sunday for PZZ252-272.

Small Craft Advisory until 5 AM PDT Sunday for PZZ253-273.