textproduct: Portland

SYNOPSIS

Dry weather prevails through the week. High pressure strengthens Thursday and Friday, resulting in much warmer temperatures. Over the weekend, cooler temperatures and chances for precipitation return as a trough from the Gulf of Alaska moves toward the Pacific Northwest. Chances for widespread precipitation increase further early next week.

MORNING UPDATE

The Frost Advisory has been cancelled for the coast, Coast Range, and Willapa Hills as temperatures remain above 40 degrees. Satellite imagery shows high clouds moving into the area, which is preventing further radiational cooling. Given that there are observations reporting temperatures in the mid to upper 30s across the Willamette Valley, the Frost Advisory remains in effect until 8 AM for this region. The Freeze Warning across the Upper Hood River Valley also remains in effect until 8 AM as there are reports of temperatures between 28 and 32 degrees. -10

SHORT TERM...Today through Wednesday night

Satellite imagery as of early Tuesday morning shows high level clouds moving into northwest Oregon and southwest Washington ahead of a system that's moving into British Columbia. Clear skies and calm winds earlier this evening have allowed for efficient radiational cooling; however, the increasing cloud cover may limit further cooling this morning. For now, Frost Advisories remain in effect across most areas west of the Cascades for low temperatures of 33 to 36 degrees resulting in frost development, and a Freeze Warning for the Upper Hood River Valley for sub-freezing temperatures of 28 to 32 degrees. Anyone growing outdoor plants that are susceptible to frost damage should continue to cover plants or leave plants indoors if possible. Temperatures will be monitored over the next few hours, and if high cloud cover prevents temperatures from falling into the low to mid 30s, the Frost Advisory and/or Freeze Warning may be cancelled.

Dry conditions prevail today and Wednesday as much of our area remains under an upper-level ridge. This ridge flattens out a bit today due to the system moving into British Columbia, but precipitation is generally expected to remain well-north of our area. An exception would be the south Washington coast, where there is a 15% chance for light showers tonight. The threat for frost decreases tonight as increasing cloud cover keeps Wednesday morning low temperatures slightly warmer than the last few nights. -10

LONG TERM...Thursday through Monday

Ensembles remain in agreement that upper-level ridging will amplify over the Pacific Northwest Thursday and Friday, resulting in temperatures rebounding to the mid to upper 70s across interior valleys at the end of the week. Guidance also suggests that thermal troughing will also set-up over western Oregon, returning offshore easterly flow across the Cascades and Columbia River Gorge beginning Wednesday night and lasting through Friday morning. While the Gorge remains gusty the entire time due to gap-driven winds, offshore flow over the Cascades will follow a diurnal pattern of increasing winds overnight and weakening in the afternoon. The strongest winds are expected on Thursday, where there is a 20-30% chance for peak wind gusts exceeding 40 mph through the Gorge at river-level, and a 20-40% chance for peak wind gusts up to 50-55 mph for exposed ridgetops within higher terrain surrounding the Gorge (i.e. Three Corner Rock). Offshore winds remain weaker across the Cascades, with a 20-40% chance for peak wind gusts exceeding 30 mph along the crest and exposed ridgetops of the foothills.

Over the weekend, the majority of ensemble members continue to favor an upper-level trough moving southeastward from the Gulf of Alaska and pushing the ridge eastward. While there is still uncertainty with the timing, strength, and placement of the trough, there is high confidence that we'll see cooler temperatures and increasing chances for precipitation this weekend. Chances for at least 0.25 inch of liquid precipitation from 5 AM Saturday to 5 AM Monday are around 30-45% along the along the coast, Coast Range, and Willapa Hills, and 15-30% along the I-5 corridor and Cascades. By Monday, most ensemble members suggest that the trough will enter the Pacific Northwest, bringing increased chances for more widespread precipitation. -10

AVIATION...Through 12Z Wednesday

Satellite imagery and terminal observations as of early Tuesday morning depicts high clouds moving into northwest Oregon and southwest Washington as a weak system moves into British Columbia today. Given that this system is further north, precipitation is not expected across our area and will continue to have VFR conditions with mid to high level clouds throughout the TAF period. An exception would be KAST, where there is a 20-40% chance for MVFR CIGs or lower at any given hour after 00- 03z Wed. Light northwesterly or variable winds around 5 kt or less today across all terminals.

Temperatures in the mid 30s across the southern Willamette Valley this morning may result in frost development over metal surfaces. The threat for frost decreases after 8 AM as temperatures warm up.

KPDX AND APPROACHES...VFR with mid to high level clouds through the TAF period. Northwesterly winds under 5 kt today. -10

MARINE

Benign marine conditions expected this week. Today and Wednesday, light winds turn more southerly from a weak front, then return northerly by the end of the week. Seas remain around 4-6 ft this week with periods of 13-15 seconds through Wednesday and 11-13 seconds late this week. A steeper northwesterly swell arrives this weekend, building seas to 7-9 ft by Sunday and 9-11 ft early next week. There is a 10-30% chance for seas exceeding 13 ft on Monday, with the highest chances over the waters beyond 30-40 NM. Will also note that the long periods from the swells this week will result in a moderate sneaker wave threat. Caution should be used when in or near the water. -10

PQR WATCHES/WARNINGS/ADVISORIES

OR...Frost Advisory until 8 AM PDT this morning for ORZ109-112>119- 123>125.

Freeze Warning until 8 AM PDT this morning for ORZ121.

WA...Frost Advisory until 8 AM PDT this morning for WAZ205>208.

PZ...None.