textproduct: Portland

SYNOPSIS

An unusually strong series of systems, by early September standards, takes aim at the Pacific Northwest over the next 36-48 hours. 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 Wednesday

Chances for showers and thunderstorms continue Friday and the weekend as the aforementioned, upper level low weakens but remains over the region. CAPE will be on the relatively lower side, around 100-200 J/kg each afternoon Friday through Sunday, with CIN increasing each day. Increasing CIN will lower thunderstorm chances each afternoon. Temperatures trend warmer Friday through Sunday as a short-wave ridge quickly builds over the region. Expect daytime highs to warm into the mid to upper 70s by the middle of next week 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. /42-19

AVIATION...Through 12Z Thursday

Largely VFR conditions continue across the airspace. However, an approaching frontal system will bring widespread rain and variable flight conditions through the majority of the TAF period.

Light rain expected to start along the coast around 12Z-14Z Wednesday and will bring about mostly MVFR conditions to the coast. There is the chance that intermittent IFR conditions will also occur and these conditions are likely to coincide with any increase in precipitation rate. In addition southerly winds will also increase with starting around 13Z-15Z Wednesday with gusts approaching 35 kt. Max wind gusts expected from 17Z-21Z Wednesday.

For inland locations expect the current VFR conditions to become a mixture of VFR/MVFR around 15Z-17Z Wednesday which will coincide with the start of precipitation. Persistent southerly winds are also expected with gusts approaching 25 kt. Max wind gusts expected from 18Z Wednesday through 00Z Thursday.

Also, there is a 15-25% chance for thunderstorms across the airspace from 16Z Wednesday through 03Z Thursday. Any thunderstorms that develop will have the potential to produce lightning, small hail along with gusty and erratic winds.

Conditions may begin to improve after 03Z Thursday as steady rain transitions to rain showers behind the frontal boundary. South/southwesterly winds 7-10 kts will continue through the remainder of the TAF period. Also, the airspace will likely settle into a low-end VFR/high-end MVFR mixture for the remainder of the TAF period.

KPDX AND APPROACHES...VFR conditions will slowly lower towards a VFR/MVFR mixture as an approaching frontal system will bring widespread precipitation, southerly winds with gusts up to 25 kt. Precipitation and the mixed flight categories are expected to start around 17Z Wednesday and persist through around 03Z Thursday. 15-25% chance for thunderstorms from 20Z Wednesday through 03Z Thursday. Conditions may begin to improve after 03Z Thursday as steady rain transitions to rain showers behind the frontal boundary. South/southwesterly winds 7-10 kts along with a mixture of low- end VFR/high-end MVFR conditions. /42

MARINE

An active weather pattern continues through the middle of the week as a series of systems moves into the Pac NW. A broad area of low pressure dropping from the Gulf of Alaska toward the Oregon and Washington coasts will drive a strong frontal boundary across all waters through the late afternoon, which will result in strengthening winds and building seas across the waters. South to southwest winds will reach 20-35 kt with frequent gusts of 40-45 kt early this morning through the late afternoon. 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 moves onto the coast late this morning/afternoon. As such will maintain the current suite of Gale Warnings across all waters until at least 5 PM PDT today.

Seas remain largely wind-driven, building towards to 10-14 ft. Behind the front, a fresh west/northwest swell of 7-9 ft will arrive, and help to maintain seas around 9-11 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 subside as winds and seas ease after Thursday. Fairly benign winds of 5-15 kt and seas of 4-6 ft are expected by the weekend and into early next week. /42-36

PQR WATCHES/WARNINGS/ADVISORIES

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