textproduct: Portland

SYNOPSIS

Warmer and drier weather conditions through tomorrow as weak offshore flow persists. Onshore flow returns late tomorrow, while dry conditions are expected to persist through the weekend. A cooler pattern may develop early next week as troughing approaches from the Gulf of Alaska.

DISCUSSION...Now through Tuesday

Warmer conditions expected through Thursday as upper level ridging over the northeast Pacific slowly shifts eastward and a closed upper level low shifts southward over northern California. A surface thermal trough will support offshore flow across the Cascades and into the Foothills and western Columbia River Gorge while north to northeast winds will be expected elsewhere. Gusts up to 20 mph will remain possible across the Willamette Valley and up to 25 mph through the Columbia River Gorge through the evening.

Dry conditions are expected for most of the area as the upper low shifts southward. The only notable chance for a stray shower is over far southeastern Lane County, closest to the upper low and where the best moisture and lift will be relatively. Satellite and radar observations indicate some broken cloud cover and light radar returns as of 130 PM but unlikely anything is making it to the ground. Chances for precipitation peak late this evening around 10- 20% along the southeastern border of Lane and Douglas county.

Thursday is still expected to be the warmest day this week with highs peaking in the low to mid 80s across the interior lowlands. Weak offshore flow is expected during the morning but will gradually shift onshore by the afternoon as the thermal trough dissipates. Probabilities for temperatures to peak at 85 or above range from 20- 60% north of Corvallis to the Portland metro with the greatest chances across the Tualatin Vally. Areas south of Corvalis are expected to top out in the low 80s. Highs in the upper 60s to mid 70s are expected along the coast and in the higher terrain of the coast range and Cascades. The upper low over northern California is expected to begin shifting northeast toward the Great Basin as ridging moves in from the west which will bring a slight increase in moisture across the Lane and Linn county Cascades. This will support a 20-40% chance for showers and a 10% chance for a stray thunderstorm.

Conditions are expected to remain dry Friday but there is a bit more spread among the ensemble models regarding high temperatures as the upper level pattern begins to shift. Friday morning likely begins with marine stratus along the coast and interior lowlands as onshore flow persists. Highs will depend on how quickly low clouds dissipate but also the position of the upper level low to the east and ridge to the west. A slower, eastward progression would keep conditions cooler in the low 70s across the interior lowlands while a more progressive pattern would lead to slightly warmer temperatures in the upper 70s. Better agreement heading into the weekend with a warming trend into the upper 70s to low 80s both Saturday and Sunday. Beyond the weekend, the pattern trends toward cooler temperatures as troughing drops southward from the Gulf of Alaska. Details are unclear at this time in the exact strength, location, and timing of this feature. -19

AVIATION...Through 00Z Friday

Predominately VFR conditions expected over the next 24 hours with offshore winds (east to northeast) aloft. At the surface, offshore winds continue increasing through the morning hours. Expect north winds along the coast and Willamette Valley terminals, northeast winds at Portland area terminals, and east winds over the Cascades and through the Columbia River Gorge. Winds will increase to 10-15 kt with gusts up to 20-25 kts, higher up to 30 kts over the Cascades and Columbia River Gorge. Winds decrease rapidly after 01-04z Thu to below 5-8 kts. Winds become light and variable by 12z Thu, remaining that way for most of the day. There's a 10-20% chance of brief cigs/vis lowering to MVFR/IFR along the coast at any given hour between 10-18z Thu, but conditions aren't expected to last long enough to include in the TAF at this moment.

KPDX AND APPROACHES...VFR conditions expected through the TAF period with mostly clear skies. Northwest winds will become north to northeast 8-12 kts with gusts up to 20 kt by 21Z Wed. Winds should weaken to below 8 kt by 01-03Z Thu, becoming light from the northwest by 12z Thu. -03

MARINE

A strengthening thermal trough inland is increasing pressure gradients across the coastal waters today, increasing north winds to 15-20 kt with gusts up to 25 kt south of Cape Falcon this afternoon, continuing overnight. Small Craft Advisories are in effect through 11 PM Wednesday, except through 2 AM Thursday for the outer waters south of Cape Foulweather.

North winds ease Thursday then become a bit more west to southwest for locations out about 40-50 NM from the coast late Thursday into Friday. A persistent northwest swell around 4 to 6 ft at 7 to 8 seconds is expected to continue through at least Friday. Northerlies strengthen again over the weekend. The waters south of Cape Falcon have around a 50-75% chance of at least occasional wind gusts exceeding 21 kt. The waters north of Cape Falcon have a 30-40% chance of wind gusts exceeding 21 kt on Saturday, increasing to 50-70% by Sunday. -03

PQR WATCHES/WARNINGS/ADVISORIES

OR...None.

WA...None.

PZ...Small Craft Advisory until 11 PM PDT this evening for PZZ252-253- 272.

Small Craft Advisory until 2 AM PDT Thursday for PZZ273.