textproduct: Portland

SYNOPSIS

An unusually strong series of systems, by early September standards, takes aim at the Pacific Northwest for the middle of the week. These systems look to bring widespread rainfall, locally breezy/gusty winds, and a 15-30% chance for pop-up thunderstorms, with higher chances on Thursday. Conditions trend slightly drier by late Thursday/Friday and continue into the weekend. However, cooler than normal temperatures and shower chances persist.

LONG TERM...Friday through Tuesday

Chances for showers and thunderstorms continue into Friday and the weekend as the upper level low weakens but remains overhead. CAPE will be on the lower side, around 100 j/kg during each afternoon Friday through Sunday. Temperatures do trend upward Friday through Sunday back into the mid 70s during the weekend across the interior as cloud cover becomes more broken and less overcast. Drier, more benign conditions are expected to return early next week as shortwave ridging develops across the PacNW. -19

AVIATION...Through 06z Thursday

Largely VFR conditions continue across the airspace with cigs of 4-6 kft ahead of an approaching frontal system expected to bring widespread rain and cig/vis restrictions Wednesday. While light rain showers may begin in the vicinity of coastal terminals when chances for MVFR cigs exceed 50% after 06-09z Wed, more widespread steady rain will hold off until 12-14z Wed at the coast and then reach inland terminals by 15-17z Wed as rain begins spreading from south to north. MVFR/IFR cigs are likely to persist with MVFR vis while rain continues along the coast, while inland terminals will initially maintain VFR vis/cigs until chances for MVFR vis/cigs reach 60-75% after 17-20z Wed. Conditions may begin to improve after 00-03z Thu as steady rain transitions to rain showers behind the frontal boundary.

South winds will steadily increase overnight as the frontal boundary approaches. Along the coast, 10-15 kt winds with gusts to 20 kt will build to 15-20 kt with gusts of 25-30 kt by 12z Wed, before easing slightly and becoming southwest behind the boundary after 18-20z Wed. Inland, 5-10 kt winds this will rise to 10-15 kt with gusts near 20 kt after 16-18z Wed. Winds ease quickly behind the frontal boundary, 22z Wed - 00z Thu along the coast and 00-03z inland.

KPDX AND APPROACHES...VFR conditions favored to prevail through the night. Steady rain arrives from the southwest after 15-17z, with chances for MVFR vis/cigs increasing to 60-70% as rain continues late in the period, after 17-20z Wed. Cigs likely to return to VFR after 00-03z Thu as steady rain passes and transitions to scattered showers. Winds continue out of the south to southwest, but increase overnight to 10-15 kt with gusts near 20 kt by 16-18z Wed. Winds ease below 8-10 kts after 00-02z Thu. -36/03

MARINE

An active weather pattern continued through the middle of this week. A broad area of low pressure dropping from the Gulf of Alaska toward the Oregon and Washington coasts will drive a strong frontal boundary eastward over the waters on Wednesday, which will see strengthening winds and building seas across the waters. South to southwest winds will reach 30-35 kt with frequent gusts of 40-45 kt from early Wednesday morning (3-5 AM PDT) until the early afternoon beyond 10 NM of the coast and until the mid- afternoon within 10 NM of the coast including the Columbia River Bar. The strongest gusts will most likely occur between 8 AM and Noon PDT beyond 30 NM from the coast, and between 10 AM and 3 PM within 30 NM. While not expected to be persistent or widespread, there are 20-40% chances of isolated storm-force gusts within 20 NM as the front impinges on the coast Wednesday afternoon. Gale Warnings therefore remain in effect from 11 PM PDT this evening until 5 PM PDT Wednesday across the waters.

Seas will remain largely wind-driven ahead of the frontal passage, rising to 10-13 ft during the daylight hours on Wednesday. Behind the boundary, a west-northwest swell of 7-9 ft will arrive, yielding seas around 10 ft through much of Thursday. These steep seas may require Small Craft or Hazardous Seas alerts if confidence in their timing, occurrence, and persistence increases. There will also be 15-30% chances for isolated to scattered thunderstorms on Thursday, which will be capable of producing gusty and erratic winds, small hail, and lightning.

While relatively active weather with lingering rain showers will continue into the weekend, marine conditions will tend to improve as winds and seas ease in the latter half of the workweek. Fairly benign winds of 5-15 kt and seas of 4-6 ft are expected by the weekend and into early next week. -36

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Gale Warning until 5 PM PDT Wednesday for PZZ210-251>253- 271>273.