textproduct: Portland

SYNOPSIS

Onshore flow returns today, bringing slight relief from the hot temperatures of the past few days. However, warm and dry conditions continue through the next week.

DISCUSSION...Tuesday morning through Monday

Surface observations early Tuesday morning indicate that onshore flow has returned to NW OR and SW WA, and satellite imagery shows marine stratus slowly nearing the coast due to this. Marine stratus will return to much of the NW OR and SW WA coast this morning and will likely be a daily fixture along the coast again. Onshore flow will bring relief from the record breaking temperatures of the past few days as high temperatures across the region today will be anywhere from around 8-20 degrees cooler than yesterday. Even though onshore flow returns, high pressure still remains over the eastern Pacific, so temperatures will still remain warmer than daily normals for mid June (mid 60s along the coast and mid 70s for the interior lowlands) for the interior. As a shortwave moves through British Columbia into WA today and tomorrow and the high pressure axis pushes west, 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.

Ensemble guidance is in good agreement that the high pressure axis shifts a bit east again on Thursday, allowing high temperatures to increase into the upper 80s for the interior lowlands with a 20-45% chance of reaching or exceeding 90 degrees for locations between Corvallis and Vancouver. By Friday, ensembles indicate broad yet weak troughing developing over the far eastern Pacific with the PacNW remaining under weakening high pressure. Probabilities indicate very similar temperatures to Thursday, though the spread in potential high temperatures is larger depending on the final strength and location of the troughing. The weak troughing is slated to move inland Saturday, allowing temperatures to lower again to the upper 70s to low 80s. There is no precipitation signal with this trough except for possibly drizzle along the coast due to stronger onshore flow.

Sunday looks to be a transition day with some uncertainty in the ensemble members. Around 55% of members suggest troughing will linger over the region with the other 45% indicating the trough begins moving east with high pressure over the eastern Pacific beginning to push closer to the coast. The 10th-90th percentile temperature spread is anywhere from the low 70s to upper 80s for the interior lowlands, with the NBM deterministic forecast suggesting low to mid 80s. On Monday, 70% of ensemble members indicate some level of ridging over the PacNW with 30% suggesting troughing continues. The 10th-90th percentile temperature spread for Monday is still pretty large, but the entire distribution is warmer than Sunday: in the upper 70s to upper 90s for the interior lowlands. This is likely due to the higher number of members indicating ridging and therefore warming, though the strength of the ridging is still uncertain. However, NBM deterministic forecast increases to the upper 80s to low 90s for the interior lowlands. Probabilities for reaching or exceeding 90 degrees increase from 5-30% on Sunday to 35-65% on Monday, highest probabilities between Corvallis and Vancouver.

Overall, the forecast over the next 7 days remains on the dry and warm side with Moderate HeatRisk for portions of the interior Thursday, Friday, Sunday, and Monday. Those sensitive to the heat, especially those without adequate access to air conditioning or hydration, should take steps 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. -03

AVIATION

High pressure will maintain predominately VFR conditions for inland locations through the TAF period with FEW/SCT high clouds. There is high confidence (>90% chance) for marine stratus pushing onshore into the north Oregon and south Washington coast. This will produce MVFR CIGs at KAST by 10-12z Tue and spreading south to KTMK by 14-16z Tue. Limited mixing will maintain MVFR CIGs throughout the day along the north Oregon coast with a 35-55% chance of mixing increasing between 21z Tue to 03z Wed, allowing for a period of improvement to VFR conditions. Some uncertainty remains on whether or not marine stratus will spread to the central Oregon coast, but there is a 40-60% chance for MVFR CIGs at KONP at any given hour between 15-22z Tue. Guidance suggests mixing occurs at KONP after 21z Tue to 02z Wed, returning VFR conditions for the rest of the TAF period. Mainly light and variable winds become northwesterly and gradually increase to 8-12 kts inland and 10-14 kts along the coast after 15-18z Tue as pressure gradients tighten. Gusts up to 25 kt along the coast and up to 20 kt inland are possible. Winds gradually decrease after 06-09z Wed.

KPDX AND APPROACHES...VFR with FEW/SCT high clouds through the TAF period. Light northwesterly winds will gradually increase after 18z Tue to 8-12 kts with gusts up to 20 kt from 21z Tue-06z Wed. Winds weaken after 06z Wed. -03/10

MARINE

High pressure offshore will maintain the summertime pattern through this week. Diurnally driven northerlies are expected to peak each afternoon and evening through next week. Winds weakened last night with gusts less than 15 kts across most of the waters this morning. Winds are expected to increase across all of the coastal waters later this afternoon and evening with gusts to 25-30 kts, with this pattern persisting through late in the week. Seas around 4 to 7 ft at 8-10 seconds are expected to persist through Tuesday, driven primarily by the northerly wind chop. Seas are expected to build to around 8 to 11 ft Wednesday into Friday as a fresh northwesterly swell builds across the waters. /DH/03

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory until 8 AM PDT this morning for PZZ210.

Small Craft Advisory from 2 PM this afternoon to 5 AM PDT Thursday for PZZ251-252-271-272.

Small Craft Advisory from 11 AM this morning to 5 AM PDT Thursday for PZZ253-273.