textproduct: Portland

SYNOPSIS

An upper level ridge will gradually build over the far northeast Pacific and western WA/OR over the next several days. This will bring a prolonged stretch of dry weather over the next seven days, along with hot conditions this weekend into early next week for inland valleys. An Extreme Heat Watch is in effect Sunday afternoon through Tuesday evening for the greater Portland/Vancouver Metro, western Columbia Gorge, central Willamette Valley, and portions of the lower Columbia for daytime highs of 95-100 degrees and overnight lows in the mid 60s or warmer, resulting in a Major HeatRisk. Remaining inland valley locations across southwest WA and northwest OR have a Moderate HeatRisk, mainly due to slightly cooler overnight lows. Temperatures will trend cooler Wednesday onward with the return of onshore flow.

SHORT TERM...Now through Friday night

Radar, satellite, and surface weather observations from early Wednesday afternoon depicted partly to mostly cloudy skies across southwest WA and northwest OR to the north and west of Oakridge with mainly dry conditions aside from a few stray sprinkles. Cloud cover will attempt breaking up late in the day as high pressure builds over the area, bringing mostly clear skies and light winds for tonight. Note a very brief period of shallow patchy fog is possible in the southern Willamette Valley shortly before sunrise on Thursday, however short nights this time of year will make fog development difficult.

Aside from some cloud cover along the coast Thursday morning, expect a mostly sunny day with noticeably warmer temperatures. Forecast highs remain in the 70s, except 60s at the coast. Friday is shaping up to be a repeat of Thursday, albeit 1-3 degrees warmer as 500 mb heights increase and 850 mb temperatures warm slightly. With an onshore flow regime in place, expect breezy westerly winds in the central Columbia River Gorge from Cascade Locks eastward on Thursday and Friday, especially during the afternoon and evening hours when winds are expected to gust as high as 30-35 mph. -23

LONG TERM...Saturday through next Wednesday

The long term forecast is highlighted by a three to four day heat event with the hottest temperatures of the year thus far expected. The hot temperatures are in response to an amplifying upper level ridge over the far northeast Pacific that will gradually move closer to western WA/OR each day. An Extreme Heat Watch is in effect Sunday afternoon through Tuesday evening for the greater Portland/Vancouver Metro, western Columbia Gorge, central Willamette Valley, and portions of the lower Columbia for daytime highs of 95-100 degrees and overnight lows in the mid 60s or warmer, resulting in a Major HeatRisk. Remaining inland valley locations across southwest WA and northwest OR have a Moderate HeatRisk, mainly due to relatively cooler overnight lows. The immediate coast has a Minor HeatRisk, while inland coastal communities such as Astoria and Tillamook have a Moderate HeatRisk.

The reason the Extreme Heat Watch has been expanded and extended in time is due to a slight uptick in forecast temperatures, especially early next week. The 06Z/June 10 iteration of the GEFS has trended temperatures slightly upward on Monday, June 15. The EURO ensemble remains relatively cooler than the GEFS, but only by a few degrees. Meanwhile, the latest iteration of the deterministic NBM has ticked up a couple degrees, and is now showing high temperatures in the upper 90s to near 100 degrees for most locations within the Extreme Heat Watch. Confidence has also increased that Tuesday will remain hot, albeit not quite as hot as Monday. Although model ensemble guidance is in good agreement the ridge will flatten out over the region on Tuesday with slightly cooler temperatures aloft Tuesday, morning low temperatures will likely be the warmest of any day during the heat event. Given plenty of sunshine in place and a warm start to the day, afternoon highs have the potential to be nearly as warm as Monday. The NBM currently shows a 25-50% chance for highs of 95 degrees or warmer on Tuesday across the Willamette Valley and Portland/Vancouver metro, and a 10-20% chance for the Cowlitz Valley, lower Columbia, Columbia River Gorge, and Upper Hood River Valley. Probabilities for a Major HeatRisk or higher on Tuesday range between 15-35% in these areas, highest in the Portland metro.

Anyone who is sensitive to heat or those who have outdoor plans should prepare for and takes steps to mitigate potential heat impacts. For those planning to seek relief by swimming in local area rivers and/or lakes to cool off, be mindful of cold water temperatures and swift currents which can become life threatening if precautions like wearing a life jacket are not taken.

In addition to the heat, there will also be increasing fire weather concerns in areas with cured grasses and finer fuels. A thermally induced surface trough will establish itself somewhere west of the Cascade crest, bringing strengthening offshore flow. This will bring breezy conditions within the western Columbia River Gorge/Cascades gaps and the Willamette Valley. As daytime highs increase, relative humidities will also decrease. Given the hot, dry, breezy conditions expected, there are increasing fire weather concerns over the weekend through the start of next week, especially Sunday afternoon through Monday afternoon. Be aware of potential ignition sources such as chains dragging on the pavement, hot vehicle components, as well as cigarette butts as 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.

Fortunately, Tuesday appears to be the last hot day. Come Wednesday, June 17, ensemble modeling systems do depict the ridge finally breaking down and shifting eastward bringing a return of relatively cooler westerly flow. As such, temperatures will trend cooler Wednesday onward when there is an 80% chance highs will cool into the 70s or lower 80s. -23/99

AVIATION

High pressure will lead to predominately VFR conditions with mostly clear skies through the TAF period for all terminals. There remains a 15-30% chance for MVFR conditions due to marine stratus along the coast between 09-18z Thu, however there is low confidence for this as light offshore winds overnight would help prevent low cloud or fog development along the coast. There is also a 10-20% chance for MVFR stratus around KTTD and KEUG between 10-15z Thu, however, there is also low confidence for this given how dry the surface is. Winds generally north- northwesterly across the region and under 10 kt, except tightening pressure gradients in the afternoon will support gusts up to 20 kt along the coast between 21z Thu-03z Fri.

KPDX AND APPROACHES...VFR with mostly clear skies through the TAF period with northwesterly winds around 5 kt or less. -10

PQR WATCHES/WARNINGS/ADVISORIES

OR...Extreme Heat Watch from Sunday morning through Tuesday evening for ORZ108>115-120.

WA...Extreme Heat Watch from Sunday morning through Tuesday evening for WAZ206-207-209.

PZ...None.