textproduct: Portland

SYNOPSIS

High pressure over the region through at least Wednesday will lead to frost and fog overnight with cooler temperatures. A pattern shift is in store starting as early as Thursday morning but higher confidence lies on Thursday evening or Friday morning. Precipitation persists through the weekend.

LONG TERM...Thursday through Monday

While one would assume that the passing days would lead to higher confidence in the long-term forecast, unfortunately that is not the case. 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. 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. There are some ensembles that suggest the closed low will stay further south which would bring increased rainfall to California. But if it does track northward then we would see increased rainfall. 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 late Thursday, 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. As the weekend approaches, uncertainty remains high as the pattern remains very disorganized at this time. -27/42

AVIATION

High pressure over the region is expected to maintain VFR conditions and light winds for most of the area. Winds will lighten up and become variable overnight. Expecting a similar set up for tonight, mostly clear skies leading to cold temps and frost development which will keep fog and stratus from forming. There is some model disagreements but with no major changes in the pattern expecting a similar outcome tonight and Tuesday morning. Along the coast and through the Columbia River Gorge, winds will be easterly as a thermal trough stays in place at the surface. Winds along the coast will be light 5-10 kt a bit stronger around the eastern metro and KTTD with winds 15-30 kt and gusts of 25-30 kts, weakening late Tuesday afternoon.

KPDX AND APPROACHES...High pressure supporting VFR conditions. Light northerly winds less than 5 kts. Easterly winds in the eastern metro 15-20 kt with gust to 30 kts through Tuesday morning. -19

MARINE

High pressure remains in control of the region through the middle of the week. Winds expected to 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 the west. This will shift winds to be southerly on Friday with a 40-50% chance of wind gusts reaching 20 to 25 kts. These stronger winds will also push seas into the low teens for a time on Saturday. Details beyond this time are unclear but the unsettled pattern looks to continue. -19

PQR WATCHES/WARNINGS/ADVISORIES

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