textproduct: Portland

SYNOPSIS

Scattered thunderstorms continue tonight over the central and northern Willamette Valley and Portland/Vancouver metro area. The main hazard with thunderstorms tonight will be frequent lightning. Showers and thunderstorms dissipate on Thursday with relatively cooler and drier weather. Remaining dry on Friday with temperatures trending slightly warmer, then becoming cooler again over the weekend with chances for light rain showers at the coast.

LONG TERM...Thursday Night through Wednesday

Temperatures on Friday are expected to be similar to Thursday as the upper level pattern remains largely unchanged. Heading into the weekend, a pattern change is expected with a trough dropping south from the Gulf of Alaska on Saturday. This will allow onshore flow to re- establish itself and bring a more noticeable cooling trend late this week, along with a return to more marine influence and night/morning cloud cover. This will also support a trend toward more normal temperatures in the upper 70s to low 80s inland along with overnight lows in the 50s. There is no notable precipitation signal outside of low potential for light showers along the coast on Saturday. -19

AVIATION...Through 06Z Friday

Radar and satellite observations from 05Z Thursday showed scattered thunderstorms continuing over the central and northern Willamette Valley and Portland metro. The main hazards with these thunderstorms are frequent lightning and brief heavy rain. Ceilings with these thunderstorms have remained VFR given the elevated nature of the storms. Outflow winds have been weak with most of these storms, with gusts generally staying below 20 kt.

Thunderstorms are expected to become more isolated in coverage after 06Z Thursday. However, there is a 30% chance for thunderstorms between 06-10Z Thursday at KUAO, KPDX, KTTD, and KHIO and between 06-08Z Thursday at KSLE. Although conditions will likely remain VFR even with thunderstorms, frequent lightning will remain a hazard. Thunderstorms have ended at the coast, however a stray shower or storm cannot be completely ruled out from KONP to KAST (15% chance). After 12-14Z Thursday, the thunderstorm threat shifts into southwest WA and diminishes by 18Z Thursday.

In addition to the thunderstorms, MVFR ceilings are expected to develop at all inland terminals by approximately 10-12Z Thursday before scattering out and lifting to VFR after 18-19Z Thursday. Meanwhile, LIFR to IFR ceilings are expected at the coast through Thursday morning before lifting to VFR sometime in the afternoon.

KPDX AND APPROACHES...There is a 30% chance of thunderstorms between 06-10Z Thursday, decreasing to a 15-20% chance between 10-14Z Thursday and below 10% after 14Z. The main hazard with any thunderstorm that does develop will be frequent lightning. VFR ceilings are expected to persist through approximately 10-12Z Thursday before lowering to MVFR. MVFR ceilings should scatter out and lift to VFR after 18-19Z Thursday. Northwest winds develop towards 01-02Z Friday with an incoming sea breeze, sustained between 7-10 kt. -23

MARINE

Buoy observations from late Wednesday evening showed southerly winds occurring over the coastal waters around 10-15 kt. Gusts up to around 20 kt were occurring at buoy 029. Seas were around 6 ft at 8 to 10 seconds. Expect south winds to continue through Thursday, albeit weakening significantly in the afternoon and evening to below 5-10 kt. Meanwhile, seas are expected to hold steady with minimal change.

Seas decrease to 4 to 5 ft on Friday with light southwest winds in place, resulting in benign conditions. Seas then increase to 6 to 7 ft on Saturday as southerly winds ramp up with the passage of a cold front. This front will bring wind gusts upwards of 20-25 kt and chances for rain showers. Given the increase in winds and seas, conditions are expected to become hazardous to small craft. Winds and seas then decrease on Sunday in the wake of the cold front. -23

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...None.