textproduct: Portland

SYNOPSIS

Very warm and dry conditions today with increasing onshore flow cooling temperatures down on Saturday. Temperatures rebound Sunday into early next week as high pressure re-builds, with the hottest days being Monday and Tuesday. This will support widespread Moderate HeatRisk across northwest Oregon and southwest Washington with localized Major HeatRisk across the Portland-Vancvouer Metro Area due to warm overnight lows. There remains uncertainty with the pattern Wednesday to Thursday and exactly how much we will cool down following this heat.

DISCUSSION...Today through Thursday

Satellite imagery and surface observations as of early Friday morning depicts some marine stratus developing along the central Oregon coast while the rest of the area remains under mostly clear skies with a few high clouds. Temperatures remain very warm today as the region remains under dry zonal flow aloft. Afternoon high temperatures forecast in the mid 80s to near 90 degrees F will result in Minor HeatRisk for most areas except for Moderate HeatRisk along the I-5 corridor from Salem, OR to Kelso/Longview, WA. This level of heat will affect those sensitive to heat, especially those without cooling and hydration.

Friday night into Saturday, an upper-level low will swing down into southern British Columbia and Alberta. Most guidance suggests that this low will remain further north of our area, however, we will still see increasing onshore flow from this system. As a result of the onshore flow, overnight lows Friday night into Saturday morning are forecast in the upper 40s to mid 50s. This should provide decent overnight relief from the daytime heat. Late Saturday morning through the evening, onshore flow will peak as pressure gradients tighten due to lower pressure east of the Cascades. The strongest winds are expected through the central Columbia River Gorge and Upper Hood River Valley, where westerly winds may gust up to 30-40 mph with a 20-30% chance for isolated wind gusts exceeding 45 mph. Temperatures on Saturday will cool down further due to onshore flow with most interior valleys forecast in the mid to upper 70s with a 40-55% chance for temperatures exceeding 80 degrees along the I-5 corridor (highest chances across the Portland- Vancouver Metro Area).

Temperatures begin to rebound into the mid to upper 80s on Sunday as ensemble guidance shows the aforementioned trough shifting eastward and upper-level ridging rebuilding offshore over the northeast Pacific. The hottest days of the week are expected on Monday and Tuesday as the majority of ensemble members show the ridge shifting over the Pacific Northwest. There is high confidence (>90% chance) for high temperatures exceeding 90 degrees F across the Willamette Valley and southwest Washington lowlands on Monday and Tuesday. There is even a 20-30% chance for temperatures exceeding 100 degrees F from Salem to Portland-Vancouver on Monday, with chances increasing to 40-50% on Tuesday. Overnight lows will also be warm, especially across the central Willamette Valley and Portland-Vancouver Metro Area where there is a 40-60% chance for Tuesday morning lows remaining above 65 degrees (highest chances across Portland-Vancouver Metro due to urban heat islands effects). Overnight lows near or above 65 degrees would provide limited overnight relief from the heat. As a result, there will be widespread Moderate HeatRisk across much of northwest Oregon and southwest Washington, with localized Major HeatRisk across the Portland-Vancvouer Metro Area from the warm overnight lows. Make sure to practice heat safety, including staying hydrated, wearing light-colored and loose-fitted clothing, wearing sun protection, and taking frequent breaks from the heat. If possible, schedule outdoor plans during the early morning or late evening when temperatures will be less intense.

Greater uncertainty remains Wednesday to Thursday as 55% of ensemble members have the upper-level ridge shifting eastward and cooling temperatures down due to increasing onshore flow. However, the remaining 45% of ensemble members maintain the ridge overhead and continuing hot temperatures. There is currently a 20 degree spread between the NBM 10th and 90th percentiles on Wednesday for the Willamette Valley, with the coolest scenario being in the low 80s while the warmest scenario is in the upper 90s to near 100 degrees F. In addition, there remains no strong signals for any significant precipitation throughout the week. -10

AVIATION

As of 18Z Fri, satellite imagery depicts marine stratus along the coast south of KAST, maintaining IFR CIGs at KTMK and IFR/MVFR conditions at KONP. While most of the stratus is south of KAST, some thinning stratus remains at KAST, which could remain and keep MVFR conditions over the terminal until 20Z Fri.

There is high confidence for marine stratus to persist at KONP through at least 18Z Sat, with a 60-80% chance of MVFR, 30-50% chance of IFR, and 10-30% chance of LIFR conditions. As for KAST, conditions will likely improve to VFR by 20Z Fri and then deteriorate back to MVFR CIGs with a 10-20% chance of IFR CIGs by 03-06Z Sat. From now until 03Z Sat, the biggest uncertainty for KAST will be vis, where some guidance suggests MVFR vis between this time range. Inland terminals will remain VFR throughout most of the TAF period. Around 12Z Sat, the a marine stratus push will bring a 30-40% chance of MVFR CIGs to all inland terminals. Expect mostly westerly to northwesterly winds 5-10 kt, strongest in the afternoon, with some terminals shifting southerly to southwesterly by 06-12Z Sat.

KPDX AND APPROACHES...VFR conditions through most of the TAF period, then a 20-30% chance of MVFR CIGs after 12Z Sat. Westerly to northwesterly winds around 5-10 kt shifting to southwesterly after 12Z Sat. ~12

MARINE

A summertime pattern continues throughout the next seven days with high pressure offshore maintaining northerly to northwesterly winds across the waters. Small Craft Advisories remain in effect across the outer waters (beyond 10 NM offshore) through 5 PM Saturday, while the Small Craft Advisory for the inner waters (from the coast to 10 NM offshore) continues through 5 AM Friday. Expect breezy northwesterly winds with gusts up to 25 kt through this evening. Tonight into early Saturday morning, northwesterly winds begin to weaken as pressure gradients ease, however seas will remain steep and choppy around 8-12 ft at 9-10 seconds. Seas subside to 5-7 ft Saturday night into Sunday. For those traveling across the Columbia River Bar, strong ebb currents are expected around 0835 Friday. -10

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory until 5 PM PDT Saturday for PZZ271>273.