textproduct: Portland

SYNOPSIS

Very isolated rain showers will continue to diminish in coverage as the region trends drier into the beginning of the weekend. Clear skies will see warm daytime highs and cool overnight lows, with widespread frost or freeze conditions expected tonight. Chances for additional rain returns Sunday into early next week, but long-term forecast confidence remains relatively low.

LONG TERM...Sunday through Thursday

The forecast through the long-term period hinges on the progression of an upper-level low tracking southward from the Gulf of Alaska over the Northeastern Pacific from Sunday into the middle of next week. There remains no firm consensus in long-range guidance, and resultant forecast confidence therefore also remains low. By Monday, about half of ensemble members position the low well to the southwest, off the northern California or southern Oregon coasts. Some of these solutions maintain stronger ridging overhead and therefore result in warmer and drier conditions. If the placement of the low is close enough to transport moisture from the south up toward the Cascades, these warmer temperatures could also support afternoon/evening convection Monday or Tuesday, however the chances of this remain too low to include in the forecast at this lead time. The other half of ensemble members place the low farther to the north and east, closer to the local area, yielding higher cloud cover, near to below-normal temperatures, and potential rain showers. In total, the forecast currently runs down the middle of these scenarios, but this could change substantially as guidance evolves toward a higher-confidence consensus in the coming days. Despite this period of high uncertainty, there is actually higher confidence toward the middle of the week as the low eventually tracks inland, and northwesterly onshore flow aloft tends to return temperatures to near-normal values with chances for rain on Wednesday, then warming and drying into Thursday as ridging builds anew. -36

AVIATION

Predominately VFR conditions expected through Friday as high pressure begins building over the PacNW. A few showers will continue over portions of NW OR and SW WA north of KTMK through 12z Fri. High clouds have mostly dissipated leading to scattered or broken mid level clouds, much more clear than earlier today. With the clearing skies, latest guidance indicates a 45-50% chance for fog and/or low stratus below 500 feet at KHIO beginning around 14- 15z Fri, and a 35-40% chance for cigs below 2000-3000 ft at KPDX between 12-18z Fri. Given the clearing skies and calm winds in place tonight, widespread frost is expected both inland and at the coast. One exception is at KAST and KPDX where temperatures will most likely stay above 36 degrees, thus limiting the potential for frost development. Winds remain calm through the TAF period, except for along the coast where they will become northerly and increase to around 8-10 kts after 18-20z Fri.

KPDX AND APPROACHES...Mainly VFR conditions expected over the next 24 hours. However, there is a 35-40% chance for low stratus with cigs below 2000-3000 ft between 12-18z Fri. Confidence in low stratus developing over the terminal is not high enough to reflect in the TAF. -03

MARINE

Weak northwesterly flow continues today with lingering showers decreasing this evening. Small Craft Advisory seas of 8-11 feet at 10-11 seconds persist this afternoon, mainly due to a northwesterly swell as wind speeds and wind waves are now minimal. Expect wave heights to slowly wane this evening into Saturday across both the inner and outer waters, falling below 10 ft. Note a very strong ebb current will bring steep seas of 7 to 8 ft within the main channel of the Columbia River Bar early to mid Friday morning. A Small Craft Advisory has been issued for the Columbia River Bar to cover the strong ebb current.

The ongoing northwesterly winds will become northeasterly Friday morning. Winds will then veer to the south this weekend ahead of a weak front. With the approaching front, guidance now suggests a 50-75% chance for max wind gusts over 21 kt across the outer waters Saturday evening/night. Chances decrease to 15-40% over the inner waters, with the lowest chances along the coast. Seas are expected to increase by 2-3 ft with the increase in winds, but will most likely stay under 10 ft. -23

PQR WATCHES/WARNINGS/ADVISORIES

OR...Frost Advisory until 9 AM PDT Friday for ORZ102>110-112>115.

Freeze Warning until 9 AM PDT Friday for ORZ116>119-121-123>125.

WA...Frost Advisory until 9 AM PDT Friday for WAZ203>205-207-208.

PZ...Small Craft Advisory from 3 AM to 9 AM PDT Friday for PZZ210.