textproduct: Portland

SYNOPSIS

Onshore flow continues through the weekend, bringing slight relief from the hot temperatures of the past few days. However, warm (although relatively cooler) and dry conditions persist through the weekend and into next week.

DISCUSSION...Tonight through Tuesday

Surface observations as well as satellites imagery continue to show onshore flow impacting the majority of the CWA. Persistent, onshore flow will bring relief from the record breaking temperatures of the past 72-96 hours as high temperatures across the region through tomorrow with daytime highs in the low to upper 80s inland, upper 50s to mid 60s along the coast and low 70s to low 80s for the Cascades. While onshore will persist through the remainder of the week, little to no moisture will be associated with the onshore flow. The reason for the relatively cooler temperatures and dry conditions is the overall synoptic setup. The region is sandwiched between a broad low pressure system over Alberta and Saskatchewan Provinces and high pressure over the Eastern Pacific. This set up is creating weak, but persistent northwesterly flow over the Pac NW, within the overall flow, a shortwave trough will also quickly move across the Olympic Peninsula tonight which will help to keep the region slightly cooler through Wednesday. However, as the shortwave exits the region, the eastern Pacific high pressure will return. So, expect high temperatures in the upper 70s to mid 80s across the interior lowlands and 60s along the coast with low temperatures back into the 50s. As the aforementioned Pacific high, re- establishes itself, ensemble guidance is in good agreement that daytime highs will increase into the low to upper 80s for the interior lowlands, upper 60s to mid 70s along the coast and upper 70s to mid 80s for the Cascades. Friday, is on track to be a few degrees warmer than Thursday with daytime highs in the mid 80s to low 90s for the interior lowlands, while the coast and the Cascades are expected to be a few degrees cooler with daytime highs in the mid 60s to low 70s along the coast and mid 70s to low 80s for the Cascades. Taking a look at the probabilistic information, there is a 10-45% chance of reaching or exceeding 90 degrees for locations between Corvallis, OR and Vancouver, WA. As for Friday, there is a 20-75% chance of reaching or exceeding 90 degrees for locations between Eugene, OR and Longview, WA and a 10-30% chance of reaching or exceeding 95 degrees for locations between Canby, OR and Kalama, WA.

Looking beyond Friday and into the weekend, the region looks to undergo another pattern change. SPC 500 mb clusters show very weak troughing developing around the OR/CA border (or just south of) and slowly meandering eastward Saturday and Sunday. Now, this will bring another round of relatively cooler temperatures for the weekend, with Saturday being very similar to today and Sunday being very similar to Wednesday. However, there still remains a fair amount of uncertainty for the weekend as Saturday has a roughly 10 degree spread when looking at the 10th-90th percentile and around a 5 degree spread for the 25th-75th percentile. As for Sunday the spread is a little larger with a roughly 15 degree spread when looking at the 10th-90th percentile and around a 10 degree spread for the 25th-75th percentile. The cause of the uncertainty is the strength and duration of the weekend trough. So, will maintain the current NBM 5.0 forecast.

The start of next week also looks to be rather uncertain. WPC 500 mb guidance shows a majority of the clusters bringing some type of ridging back into the forecast. This is resulting in upper 80s to mid 90s coming back into the forecast for Monday and Tuesday for inland valley locations.

Overall, the forecast through the remainder of the week and into the start of next week remains on the dry and warm side. Minor to Moderate HeatRisk remains for the interior Thursday through at least Sunday. However, Monday and Tuesday there are some stronger signals (hot daytime highs and warm overnight lows) that do point towards Major HeatRisk impacting the region. So, those who are sensitive to the heat, if you are without adequate access to air conditioning or hydration. Steps should be taken to prioritize heat safety. Also, remember that rivers and lakes remain cold despite the warm weather, increasing the risk of cold-water shock for anyone seeking relief near the water. /42

AVIATION

General high pressure over the region will lead to persistent north to northwesterly flow through the period. Marine stratus moves in overnight first along the coast after 06Z Wed. Some models suggest it mixing out and lifting, while others maintain stratus through the day. While stratus itself is likely, increasing probability that the clouds will lift to VFR after 20Z Wed. Inland, clouds will traverse the Columbia River and then back build off of the Cascades into portions of the Willamette Valley impacting KTTD, KPDX, and reaching as far south as KUAO. KSLE will see a 20-30% chance of MVFR CIGs developing. If winds stay elevated high enough within the valley, then IFR stratus will be mixed out. Winds are forecast to ease tonight before increasing once again after 18Z Wed.

High pressure intensifies through Wed into Thu which will lead to drier conditions and thus cloud cover will be more challenging to observe outside of the coastal valleys.

KPDX AND APPROACHES...VFR with northerly winds through a majority of the forecast. High resolution models show stratus back building off of the Cascade foothills and running down the Columbia River from the coast. Therefore, there is a 40% chance of MVFR CIGs as early as 12Z Wed and a 10% chance of IFR at the same time frame. Ultimately will need to see winds ease considerably to get these kinds of conditions. -27

MARINE

High pressure offshore will maintain the summertime pattern through this week. Diurnally driven northerlies are expected to peak each afternoon and evening through the weekend. Winds are expected to continue to increase across all coastal waters later this afternoon and evening with gusts to 25-30 kts, as this pattern persists through late in the week. Seas around 4 to 7 ft at 8-10 seconds today are expected to build to around 8 to 11 ft Wednesday into Friday as a fresh northwesterly swell builds across the waters. /DH

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory from 5 AM to 9 AM PDT Wednesday for PZZ210.

Small Craft Advisory until 5 AM PDT Thursday for PZZ251-252-271- 272.

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