Marine Weather and Tide Forecast for Portland, OR

SHORT TERM
Now through Saturday Night...An upper level trough will swing southeast over the PacNW tonight and through Friday, brining temps 5-10 degrees below normal and a very good chance for soaking rains both Friday and Saturday. Highs will be noticeably cooler tomorrow, topping out in the low 60s inland and mid to upper 50s along the coast. A surface low is expected to move onshore early Friday morning and will send a cold front through the region. This first round of precipitation is expected to be more showery in nature, due to increasing instability within the atmosphere. The colder air in the mid /upper levels associated with the trough will lead to steepening lapse rates and surface CAPE on the scale of 100-300 j/kg throughout the Willamette Valley and Cascade foothills. This will be enough for a few rumbles of thunder and possibly some small, non-severe hail. Thunderstorm chances will be highest Friday afternoon and evening (peaking at 20- 30%). Remember to remain weather aware and when thunder roars, go indoors.
Thunderstorm chances decrease on Saturday to around 5-10% across the area as the entire atmospheric profile cools down and the cloud layer deepens.

The bulk of the precipitation is forecast from early Friday morning to early Sunday morning. 48-hour probabilities for 0.50" of rain or more from 5 AM Friday to 5 AM Sunday has increased to around 60-80% for most interior lowland valleys and 80-90% along the coast and high terrain. For 1" or more of rain in 48 hours during this same time period, probabilities are around 15-25% for most interior lowland valleys and 50-70% along the coast and high terrain. The current rain total forecast calls for 0.50-1" across the Willamette Valley and southwest Washington lowlands, 0.70-1.50" along the coast and Coast Range, and 1-1.75" across the Cascades and foothills.
Given the showery nature of precipitation this weekend, some locations may significantly overperform forecast rain amounts while other locations underperform. Either way, these rain amounts are pretty substantial for this time of year. -Batz/Alviz

LONG TERM
Sunday through Thursday...Shower chances linger early Sunday morning, but conditions will gradually dry up throughout the day as the upper level trough exits eastward. High pressure will re-build, returning sunnier and warmer conditions by Sunday afternoon with highs forecast to rebound to the low 70s.
Most ensemble members continue to suggest high pressure building heading into early next week, leading to a further warm-up. NBM guidance suggests temps rising back above normal by Monday with a 70-90% chance that temperatures exceed 80 degrees across the Willamette Valley Monday to Wednesday. -Batz/Alviz



AVIATION
Onshore flow through the forecast. Expect gusts up to 20 kt for inland locations through around 06Z Friday. Coastal locations have around a 45-60% probability of MVFR CIGS developing through 15Z Friday ahead of the next front slowly pushing in. Elsewhere, skies remain VFR until around 14-17Z Friday, then there is a 20-40% probability of MVFR CIGS. After 15Z Friday showers will move in with a 15-30% probability of thunderstorms through around 06Z Saturday. Any thunderstorms that develop could result in brief periods of lowered flight conditions as well as gusty and erratic winds.

PDX AND APPROACHES...VFR until at least 15Z Friday. There is a 20-40% chance of MVFR ceilings ahead of the next front after 15Z Friday. There is a 15-30% probability of thunderstorms through around 06Z Saturday. -42

MARINE
Weak high pressure over the coastal waters the remainder of today, producing north to northwest winds 5-15 kts with occasional gusts up to 20 kts the rest of this afternoon and evening. A modest westerly swell will build seas to 5-6 feet today. An unseasonably deep upper level low pressure system will bring multiple surface frontal systems and unsettled weather Friday into Saturday. Winds shift westerly tonight ahead of the first frontal system on Friday, then increase to likely Small Craft criteria late Friday night into Saturday (60-70% chance), and waves build to 7-9 feet by Saturday. Additionally, there is a chance of thunderstorms on Friday afternoon. -HEC/JLiu

PQR WATCHES/WARNINGS/ADVISORIES
OR...None.
WA...None.
PZ...None.