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 northwest flow aloft with high pressure over the region, while onshore flow in the lower levels continues today. As of 09z Tuesday, satellite imagery and surface observations reveal MVFR stratus expanding across far northwest Oregon, including KAST to KSPB, as well as over the east Portland metro. Expect these low clouds to fill in along the Columbia River with MVFR conditions likely at KPDX (30-40% chance) and KTTD (50-60% chance) by 12z this morning. Expect conditions to improve back to predominately VFR by 19-20z except along the north Oregon coast. At KAST, there is a 20-30% chance for IFR conditions between 12-22z, along with increasing chances of light rain or drizzle this afternoon as the marine layer deepens.

KPDX AND APPROACHES...VFR conditions will likely deteriorate to MVFR as low stratus pushing up the river spreads into the Portland metro area, while stratus back building off the Cascade foothills expands into KTTD. Guidance suggests there is around a 40-50% chance MVFR CIGs persist through 19-20z. Light northwest winds expected to increase again to around 7-10 kt this afternoon and evening. /DH

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 southern Oregon coast. A Small Craft Advisory is again in effect for the southern coastal waters south of Cape Foulweather later this afternoon into this evening for gusts up to 25 kt. Similar conditions are expected on Wednesday, though guidance is suggesting slightly stronger wind gusts may expand northward toward Cape Falcon. Seas around 6 to 9 feet are expected through the week as well. Chances increase on Thursday for more widespread wind gusts for all marine zones.

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

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory from 5 AM to 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 PZZ253-273.