textproduct: Portland

SYNOPSIS

Through the remainder of the work week the region remains on the northern periphery of an upper-level ridge of high pressure facilitating much warmer than normal conditions. However, an atmospheric river aimed at northern Washington and Vancouver Island will occasionally wobble southward from time to time giving portions of the region chances for light rain, especially in Pacific/Wahkiakum County and along the north Oregon coast. Then over the weekend we'll trend cooler as a trough swings into the Pacific Northwest although forecast confidence degrades from this point onward due to increasing model uncertainty.

LONG TERM...Saturday through Wednesday

Looking forward into the weekend the large scale pattern finally shows signs of progressing. However, exactly what that will look like is still in question. Uncertainty remains high, but the current consensus is for an upper-level trough and associated cold front will be able to further displace the southerly ridge mentioned in the short term discussion. This scenario will enable cooler 850 mb temperatures of 0 to 3 degrees C to infiltrate into the Pacific NW by Saturday and while a frontal system will normally bring precipitation with it, that might be a challenge as the strength of the system remains in question, in addition to the already entrenched dry airmass could easily scour out the majority of any moisture. As we move into the start of next week, uncertainty in the forecast remains high. The majority of models and their ensembles show a broad upper level trough developing within the Gulf of Alaska and said trough could swing southward into the Pac NW or remain somewhat stationary, yet still send slugs of cool and moist air into the region. Overall, for the start of next week through the middle of next week, conditions are most likely to cool down with some precipitation as the majority of models have a trough impacting the Pac NW by the start of next week. /42

AVIATION

Upper level ridging to the south and an atmospheric river to the north continue to influence the region. The atmospheric river is supporting mid and high level clouds across the airspace along with low level cloud cover along the coast. Predominately VFr conditions for inland locations, with a 10-25% chance for intermittent MVFR conditions through 18Z Wednesday. As for the coast, expect MVFR to LIFR conditions through the majority of the TAF period, though conditions could briefly lift to VFR between 20Z Wednesday through 03Z Thursday. Light showers expected north of KTMK through the TAF period. Expect light southerly winds less than 10 kts for inland locations. Southerly winds increase along the coast after 15Z Wednesday, 10-15 kts with occasional gusts up to 20 kts.

KPDX AND APPROACHES...Mainly VFR conditions expected with mid level clouds persisting. There is a 15-25% chance of MVFR cigs between 12Z through 18Z Wednesday. Light southerly winds less than 10 kts through the TAF period. /42

MARINE

Southerly winds across all waters expected through the middle of the week. Occasional wind gusts up to 25 kt will be possible for zones PZZ251, PZZ271 and the Columbia River Bar through Thursday. Seas of 7 to 10 feet at 10 to 13 seconds as winds increase and a southwesterly to westerly swell moves into the waters. Chances for Small Craft conditions remain low for the weak system that moves through on Thursday. Relatively benign conditions expected through the weekend and into next week. /42-19