textproduct: Portland

SYNOPSIS

Expect a warm and dry 4th of July weekend across northwest Oregon and southwest Washington. Temperatures warm up slightly across interior valleys on Sunday and Monday as high pressure builds, leading to localized Moderate HeatRisk. An upper-level trough moving into British Columbia Tuesday to Wednesday will cool temperatures a few degrees and bring chances for precipitation along the south Washington and north Oregon coast. Dry and warmer conditions return on Thursday. Onshore flow maintains mild conditions along the coast. Make sure to practice water safety when swimming in local rivers.

DISCUSSION...Today through Thursday

Satellite imagery and surface observations as of early Friday afternoon depicts lingering stratus along the coast and portions of the northern Willamette Valley and southwest Washington lowlands. As daytime heating progresses, mixing will continue to increase and lead to clearing skies. There has been minimal change to the overall weather pattern. We're still maintaining zonal flow aloft across the Pacific Northwest as an upper-level trough to our north swings through British Columbia and upper-level ridging holds to the south. This will help maintain onshore flow with temperatures slightly above normal for interior valleys today and into the 4th of July. Expect afternoon highs in the low 80s across interior valleys and 60s along the coast.

Sunday to Monday, ensemble guidance continues to suggest shortwave ridging moving over the Pacific Northwest, resulting in warmer temperatures across interior valleys in the mid to upper 80s. The latest NBM guidance suggests a 40-60% chance for Monday afternoon highs exceeding 90 degrees along the I-5 corridor from Salem to the Portland/Vancouver Metro Area, Columbia River Gorge, and Upper Hood River Valley. This will result in localized Moderate HeatRisk on Monday, meaning this level of heat will affect those sensitive to heat, especially those without adequate cooling or hydration. Low temperatures in the 50s across the entire area should provide decent overnight relief from the heat.

Tuesday to Wednesday, the majority of ensemble members are showing an upper-level trough from the Gulf of Alaska moving down into British Columbia. Given the more northern track of this trough, most places across the area is expected to be dry. An exception would be the south Washington and north Oregon coast where this system favors a 15-30% chance for light rain from Tuesday night to Wednesday. Despite the lack of precipitation, onshore flow will increase and support temperatures cooling a few degrees. West-northwesterly winds are generally expected to be light for most areas during this time. However, will see locally breezier along the central Columbia River Gorge and Upper Hood River Valley, where there is a 30-40% chance for at least isolated wind gusts exceeding 40 mph Tuesday and Wednesday. By Thursday, most ensemble members show the trough weakening and zonal flow returning over the Pacific Northwest, bringing warm and dry conditions.

It is important to remember that while temperatures will be warming up for the holiday weekend and next week, many local lakes and rivers remain very cold and can cause cold water shock. Also, rivers may still have swift currents in some areas, which can quickly sweep you away. Please practice water safety by wearing life jackets, visiting with a buddy, and always being aware of your surroundings. -10

AVIATION

Largely VFR flying conditions remain in place across the airspace, aside from developing marine stratus overnight. Coastal terminals will most likely (70-90% chance) fall to MVFR cigs by 09z or earlier Sat, with modest (30-50%) chances of IFR cigs from 09-12z Sat, with higher chances to the south along the central OR coast. Vis restrictions to MVFR are also favored, with a 25% or lower chance of IFR vis overnight. Skies will tend to clear Saturday morning through the early afternoon, yielding a return to VFR conditions before chances for MVFR cigs increase again late in the period, after 03z Sun. Diurnal winds will continue out of the north-northwest at 5 kt or less overnight, before building to 10-15 kt with gusts as high as 20-25 kt by 18-21z Sat. Inland, VFR conditions are favored throughout the period, however increased low cloud cover at 4-6 kft overnight is expected, with 15-35% chances cloud bases fall below MVFR levels, most likely in the central Willamette Valley (KSLE, KUAO). Skies will subsequently clear from 15-18z Sat. Diurnal north to northwest winds of less than 5 kt tonight will increase to 5-10 kt Saturday morning.

KPDX AND APPROACHES...VFR conditions are favored to continue throughout the period. Marine stratus may develop by 09-12z Sat, but chances for cloud bases below 3 kft are only 20-25%. Low clouds will quickly mix out by 15-17z Sat, with clear skies expected thereafter. Diurnal north to northwest winds will ease below 5 kt tonight, then rise to 5-10 kt Saturday morning. -36

MARINE

Overall fairly settled conditions through today but will see winds ramp up on Saturday. Winds will stay below 10 kt until Saturday afternoon as a thermal trough develops over the waters. This common summer pattern will increase wind speeds to 15 to 20 kt with gusts up to 25 kt except in the far southern waters where we could see gusts as high as 30 kt on Sunday afternoon. Seas will remain around 4-6 ft at 8 seconds before building on Sunday afternoon to 7-9 ft at 10 seconds due to an increased northerly wind wave that coincides with the strongest winds. A Small Craft Advisory is in effect for Saturday through Sunday night, but could easily see it extend into Monday. Both seas and winds ease on Tuesday but could still see isolated gusty winds up to 15 kt in the afternoon as high pressure lingers. -27

PQR WATCHES/WARNINGS/ADVISORIES

OR...None.

WA...None.

PZ...Small Craft Advisory from 11 PM Saturday to 8 PM PDT Sunday for PZZ251-271.

Small Craft Advisory from 8 PM Saturday to 8 PM PDT Sunday for PZZ252-272.

Small Craft Advisory from 2 PM Saturday to 8 PM PDT Sunday for PZZ253-273.