textproduct: Portland

SYNOPSIS

Warmer than normal temperatures and dry weather with onshore flow persist through the weekend. Signal is increasing for hotter temperatures returning early next week with widespread Moderate to locally Major HeatRisk as high pressure builds over the western US, but uncertainty in strength and location of the high pressure brings uncertainty in exact temperature forecast.

DISCUSSION...Wednesday morning through Tuesday

NW OR and SW WA remain situated between upper level high pressure over the eastern Pacific and longwave troughing over the Midwest and eastern US. Under this pattern, onshore flow continues today with north to northwesterly winds across the region. Northwesterly winds along the south WA and north OR coast are allowing for another push of marine stratus along the coast early this morning. As this marine influence has continued for the past 24 hours or so, models are indicating marine stratus could form inland this morning with stratus spreading east/south along the Columbia River as well as along the western Cascades and back building into the Willamette Valley. Best chances are north of Aurora. Stratus should dissipate by midday, leading to mostly clear skies and high temperatures in the upper 70s to low 80s across the interior lowlands and 60s along the coast.

Thursday into Friday, the majority of 500mb ensemble members indicate weak yet broad troughing developing in the eastern Pacific as high pressure lingers over the PacNW into the Desert SW. High temperatures will warm back up into the mid to upper 80s for the interior lowlands on Thursday and upper 80s to low 90s for Friday. Chances for reaching or exceeding 90 degrees remain around 20-45% for locations between Corvallis and Vancouver on Thursday but have increased to 45-75% on Friday.

The weak troughing is slated to move inland Saturday, lowering temperatures again to the upper 70s to low 80s for the interior lowlands. There is no precipitation signal with this trough except for possibly drizzle along the coast due to stronger onshore flow. Ensemble members are in better agreement that troughing weakens as it moves east and high pressure begins building over the western US. This would allow for temperatures to raise a few degrees again back into the mid to upper 80s for inland valleys.

The majority of ensemble members (75-85%) indicate high pressure continuing to build over the western US Monday into Tuesday, potentially bringing another period of widespread inland temperatures over 90 degrees. NBM indicates a 60-85% chance of temperatures reaching or exceeding 90 degrees both days for the interior lowlands. NBM has moderate probabilities for reaching or exceeding 95 degrees as well with a 50-70% chance between Vancouver and Salem and a 25-45% chance for the rest of the interior lowlands. However, the NBM 10th-90th percentile temperature spread is still around 15 degrees ranging from the the mid to upper 80s to low 100s. This is due to a combination of uncertainty in the strength of the high pressure as well as exactly where the axis will set up. Some guidance suggests the axis will be closer to the PacNW, which will lead to hotter solutions, where other guidance has the axis a bit more east, leading to the slightly cooler solutions. Also, note that this overall temperature spread has warmed from the previous two forecasts, leading to increasing confidence in hotter temperature solutions.

Overall, the forecast over the next 7 days remains on the dry and warm side with Moderate HeatRisk for portions of the interior Thursday and Friday, becoming widespread with specks of Major HeatRisk on 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 and keep an eye on the rising forecast for early next week. 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 over the region will lead to persistent northwesterly flow aloft through the period. Marine stratus with MVFR CIGs remains along the north OR and south WA coast. Inland, MVFR stratus persists through the lower Columbia River valley and into the western Cascade foothills, including portions of the northern Willamette Valley. Expect MVFR cigs at Portland area terminals to persist through 18z. Conditions across all terminals are expected to improve to VFR after 18-21z Wed as lower clouds scatter out. High pressure strengthens later tonight into Thu which will lead to drier conditions and thus cloud cover will be more challenging to observe outside of the coastal locations.

Winds along the coast are expected to increase to 12-15 kts with gusts to around 25 kts this afternoon. Inland, winds increase after 20z to 8-12 kts with gusts up to 20 kts. Winds expected to decrease after 06-08z Thu.

KPDX AND APPROACHES...Broken stratus with MVFR CIGs around FL025 is expected to scatter out this afternoon as conditions improve to VFR by 18-19z. Northwest winds increase this afternoon to 8-11 kt with gusts up to 18-20 kt, easing again by 07z Thu. /DH

MARINE

High pressure offshore will maintain a summertime pattern through this week. Diurnally driven northerlies are expected to peak each afternoon and evening through the weekend. Winds expected to peak each afternoon and evening with gusts to 25-30 kts, decreasing a bit in the late overnight to morning hours. Seas around 7 to 8 ft at 8-10 seconds are expected to build to around 8 to 9 ft tonight then build to 8-11 ft Friday into Saturday as a fresh northwesterly swell builds across the waters. /DH/03

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory until 5 AM PDT Friday for PZZ251>253- 271>273.