textproduct: Portland

SYNOPSIS

High pressure will maintain dry weather throughout the week. Clear skies and cool nights increase chances for frost across interior valleys this morning and tonight. Temperatures trend warmer late this week as an upper-level ridge amplifies over the region. Chances for precipitation return towards the end of the weekend.

SHORT TERM...Today through Wednesday night

Dry weather prevails across the region as upper-level low pressure over eastern OR/WA continues to weaken and shift southward while ridging builds over western OR/WA, allowing for northerly flow. Mostly clear skies and calm winds is resulting in efficient radiational cooling, with temperatures already falling into the upper 30s to low 40s as of early Monday morning. Over the next several hours, will continue to see temperatures drop into the low to mid 30s, favoring widespread frost development. Frost Advisories remain in effect through 8 AM this morning across most interior valleys and the Coast Range lowlands, while a Freeze Warning is in effect for the Upper Hood River Valley for temperatures below freezing (28-32F). An exception would be the urban core of the Portland Metro Area, where urban heat island effects will keep temperatures a few degrees warmer than outlying areas. Anyone growing outdoor plants that are susceptible to frost damage should continue to cover plants or leave plants indoors if possible.

Dry weather prevails today through Wednesday as upper-level ridging continues to amplify offshore and extend over western OR/WA. Temperatures remain seasonable across interior valleys, with afternoon highs peaking in the mid 60s today and Tuesday, and low 70s on Wednesday. Clear skies and calm winds tonight will result in renewed potential for frost development as Tuesday morning lows drop into the mid 30s again for interior locations away from urban cores. Upper-level ridging flattens slightly Tuesday to Wednesday as a system rides the northern periphery of the ridge and heads into British Columbia. Given that this system will track further north, precipitation is not expected for the majority of our area except for a 15-20% chance for light showers along the south Washington coast Wednesday morning. Frost development looks less likely after tonight, as increased cloud cover Tuesday night and increased offshore flow Wednesday night keep overnight temperatures slightly warmer. -10

LONG TERM...Thursday through Sunday

The majority of ensemble members are in agreement that upper-level ridging will amplify further other the western U.S. on Thursday and Friday. This will result in temperatures rebounding to the low to mid 70s across interior valleys at the end of the week. Guidance also suggests that thermal troughing will also re-develop, returning offshore easterly flow across the Cascades and Columbia River Gorge late this week. Heading into the weekend, the upper ridge gets pushed further east by upper-level troughing coming down from the Gulf of Alaska. There remains uncertainty with the timing, position, and magnitude of the troughing at this point, but what we can say with higher confidence is that this pattern would return cooler temperatures and chances for precipitation for the weekend and into early next week. -10

AVIATION...Through 06Z Tuesday

VFR conditions with mostly clear skies expected across NW OR and SW WA through the TAF period due to building high pressure over the region. Light to calm winds expected overnight. Given similar conditions to last night, there is a chance that areas of fog develop in the Willamette Valley and along the coast. The best chances are in the central and southern Willamette Valley around KUAO, KSLE, and KEUG between 11-15z with a 15-30% chance of VIS below 2SM. If and fog does develop, it is expected to be short lived. Winds increase from the north/northwest late in the morning to around 5 kt.

Between 07-15z Mon, clear skies and calm winds will support temperatures falling towards 33-36 degrees F across much of the area outside of the Portland metro and as low as 28-32 degrees F in the Upper Hood River Valley. Locations that are able to cool down to these temperatures may see frost development on metal surfaces.

KPDX AND APPROACHES...VFR conditions expected through the TAF period. Light to calm winds overnight. A low 10% of patchy sub- VFR conditions early Monday morning between 11-15z. Light northwest winds around 5 kt or less through Monday. -19/03

MARINE

Benign marine conditions expected this week. A Small Craft Advisory is in effect for the main channel of the Columbia River Bar from 4-9 PM this evening for a strong ebb current bringing seas to 6-7 ft. Otherwise, high pressure will maintain light northerly winds across the waters through tonight. Tuesday to Wednesday, winds turn more southerly from a weak front, but return northerly by the end of the week. Seas remain around 4-7 ft this week with periods of 13-16 seconds through Wednesday and 10-13 seconds late this week into the weekend. A long-period west/northwesterly swell will result in a moderate threat for sneaker waves this week. 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 ORZ104-107-109- 112>119-123>125.

Freeze Warning until 8 AM PDT this morning for ORZ121.

WA...Frost Advisory until 8 AM PDT this morning for WAZ202-204>208.

PZ...Small Craft Advisory from 4 PM this afternoon to 9 PM PDT this evening for PZZ210.