textproduct: Portland

SYNOPSIS

High pressure over the region remains anchored over the region through at least Wednesday. Cool and dry conditions will lead a favorable environment for frost and fog development during the overnight hours through Wednesday. A pattern shift is in store starting as early as Thursday morning but higher confidence lies on Thursday evening or Friday morning. This pattern shift will bring relatively warm air along with precipitation back into the forecast through the upcoming weekend.

LONG TERM...Thursday through Monday

Uncertainty remains very high as we look into the latter part of this week and through the weekend. There are two different features we are tracking and each add a layer of complication to the forecast. Multiple model ensembles are showing a weak closed low forming off the coast of Southern California that will slowly track northward by Thursday. At the same time, a frontal system stemming from a broad and very messy low pressure system within the Gulf of Alaska is dropping down at nearly the same time, although models are continuing to have the Alaskan system follow the California system. The combination of these two features is making the overall pattern incredibly messy and as result increasing the overall uncertainty of the long term forecast. The NBM is showing rain entering the forecast early Thursday morning with PoPs in the 15-30% range. However, the GFS ensemble brings rain into the forecast early Friday morning, while the ECMWF Ensembles show rain by Thursday afternoon. It should also be noted that all ensemble solutions are showing 850 mb temperatures in the in the 3 degree C to 8 degree C range which means that rain is to be expected for lower elevations with a rain/snow mixture for higher elevations. With these series of systems, we are not looking at impactful rainfall. This overall uncertainty continues through the weekend and into the start of next week. /42/27

AVIATION

High pressure over the region will maintain predominately VFR conditions through the TAF period. Ground observations show isolated pockets of MVFR to LIFR conditions. Generally, northerly winds less than 10 kt across the forecast area for inland locations and areas along the coast south of KTMK through the TAF period. However, easterly winds through the Columbia River Gorge, will result in gusts up to 35 kt for KTTD and areas east of KPDX, in addition expect easterly winds for KAST through at least the TAF period. Given the persistent, strong easterly flow, there is the potential for LLWS for KPDX and KHIO through the TAF period as well.

Temperatures falling to the upper 20s to low 30s across the Willamette Valley will favor widespread frost development, especially over elevated, metal surfaces. Because frost is more favored, there is low confidence for fog formation. Guidance suggests a 5% chance or less for LIFR conditions between 12Z-18Z Tuesday, with the highest chances in the south Valley including KEUG.

KPDX AND APPROACHES...VFR conditions expected to persist with generally north to east winds through the day. Strong easterly winds from the Columbia River Gorge are not expected to impact the terminal directly. However, given the persistent strong, easterly flow, there is the potential for LLWS through the TAF period. /42

MARINE

High pressure remains in control of the region through the middle of the week. Winds expected to be generally easterly through Tuesday night as a thermally induce trough remains in place at the surface. Winds 10 kts or less. Seas 5 to 7 feet at 11 to 14 seconds expected through Thursday. The pattern likely becomes more active heading into the weekend as high pressure shifts inland and disturbances approach from California and Alaska. This will bring a southerly shift for winds on Friday with a 60-70% chance of wind gusts reaching up to 25 kts and around a 20-30% chance for gusts up to 35 kt. These stronger winds will also push seas into the low to mid teens by late Friday/early Saturday. /42/19