textproduct: Portland

SYNOPSIS

Dry and benign weather is expected across the region through much of the next week as high pressure builds over the Northeast Pacific, resulting in a warming trend. Weak systems aloft may bring enhanced cloud cover on some days, but rain chances are minimal. Uncertainty in the forecast increases Sunday into Monday as chances for precipitation return.

DISCUSSION...Now through Monday

Water Vapor satellite imagery this morning shows a broad upper level ridge over the NE Pacific while mid-to-upper level moisture continues to stream scattered high clouds over the area. Marine stratus is also filtering in across portions of far northwest Oregon, especially along the Columbia River this morning. Clouds should scatter out by the afternoon, except along the north Oregon coast where a deepening marine layer will bring a chance for some very light rain or drizzle near Astoria. Otherwise, expect rather comfortable weather to continue today with highs reaching into the upper 60s to lower 70s, depending on which area sees more of the sunshine today. Concerns for hazardous weather remain low through the week and into the weekend. Still expecting a slight warming trend through the week, with the warmest day most likely being on Thursday as the upper ridge axis shifts east over the Pacific NW. Temperatures on Thursday will likely warm into the upper 70s to low 80s along the I- 5 corridor. At this time, there is Minor HeatRisk forecast across the region, meaning those who are most sensitive to heat may be affected. However, there are 5-15% chances Moderate HeatRisk occurs in some urban areas along I-5 if daytime highs end up somewhat hotter. There is generally around a 10-30% chance that max temps exceed 85 degrees Thursday afternoon in the Portland Metro area.

Friday through next weekend, uncertainty in the evolution and possible break-down of the upper-level ridge introduces more uncertainty in forecast temperatures and precipitation. Forecast daytime highs currently trend downward through the holiday weekend as chances increase that ridging deamplifies or is replaced by an upper trough, but there is an increasingly wide range of possible outcomes. The 80%-confidence envelopes (the difference between the 10th and 90th percentiles) in temperature widen from 8-13 degrees on Friday and Saturday to 16-19 degrees on Sunday and Monday along the I-5 corridor. There is greater consensus that the ridge will break down late Sunday into Monday, yielding increasing chances of cooler temperatures as well as the highest chances of rainfall, 25-50%, in over a week. 36/DH

AVIATION

An upper level ridge offshore will maintain northwesterly flow across the airspace. Current satellite and surface observations (as of 16Z Tue) show generally VFR conditions with pockets of MVFR for inland locations and mostly VFR conditions with MVFR/IFR conditions for locations north of KONP. These conditions are expected to persist through the majority of the TAF period. It should be noted that guidance is showing a very weak, upper level disturbance, around 09Z-12Z Wed that could result in lowered flight conditions (IFR/LIFR) along the coast as well as some MVFR conditions backbuilding along the Cascades and pushing eastward into the Willamette Valley. This is resulting in a 45-65% chance for IFR conditions along the coast, a 25-35% chance for LIFR and a 35-55% chance for MVFR conditions for inland locations. If these conditions manifest, improvement in overall flight conditions across the airspace should start towards the very end of the TAF period.

North/northwest winds 6-10 kt persist through the TAF period with gusts up to 20 kt possible along the coast starting around 20Z-22Z Tue through around 04Z Wed.

KPDX AND APPROACHES...Predominately VFR conditions expected through the majority of the TAF period. Guidance shows backbuilding clouds along the Cascades pushing eastward starting around 09Z Wed. This is resulting in a 35-55% chance for MVFR conditions developing and impacting the terminal. If these conditions manifest, improvement towards VFR starting around 18Z Wed. North/northwest winds 6-10 kt persist through the TAF period. /42

MARINE

Northerlies are expected to persist through much of the week as the summer-like pattern settles in. Strongest winds are expected during the afternoon and evening periods as a surface thermal trough strengthens over the region. Therefore, have updated the current suite of Small Craft Advisories as gusts up to 25 kt are expected across all zones with the exception of PZZ251, this afternoon and Wednesday afternoon. Seas 6 to 9 feet are expected through the week as well. Chances increase on Thursday and Friday for widespread wind gusts for all marine zones.

Small Craft Advisories are in place for the Columbia River Bar Wednesday morning due to strong/very strong ebb currents which will produce conditions hazardous to small craft. Strong/very strong ebb currents are possible during the morning hours each day this week. /42-DH

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory until 9 AM PDT this morning for PZZ210.

Small Craft Advisory from 6 AM to 10 AM PDT Wednesday for PZZ210.

Small Craft Advisory from 5 PM this afternoon to 2 AM PDT Wednesday for PZZ252-253-271-272.

Small Craft Advisory from 4 PM to 9 PM PDT Wednesday for PZZ252- 271-272.

Small Craft Advisory from 1 PM to 9 PM PDT Wednesday for PZZ253.

Small Craft Advisory from 5 PM this afternoon to 9 PM PDT Wednesday for PZZ273.