textproduct: Portland

SYNOPSIS

Overall expect little in the way of weather impacts as we progress through the next 5 to 7 days with dry conditions heavily favored today into next week. That said, we'll still have to be on the lookout for patchy morning fog at times across the inland valleys degrading visibility. Confidence is high temperatures embark on a warming trend through the weekend.

DISCUSSION...Today through Tuesday

Dry conditions are expected region-wide today as our weak frontal boundary from yesterday has passed with upper-level ridging slowly building overhead in its wake. If you enjoy dry and somewhat warmer fall conditions, you're in for a treat moving forward. Ensemble members depict high pressure over the eastern Pacific moving inland over the next few days, peaking over the PacNW on Saturday and Sunday. This will lead to a gradual warming trend for the area through the week as we gain a few degree increase each day. Due to decent clearing during the overnight/morning hours, light winds, and a more prominent temperature inversion developing each night, patchy fog development is likely, especially in our more protected valley areas with a water source. Morning fog will greatly reduce visibility wherever present. The interior lowland are expected see temperatures in the low to mid 70s today and the mid to upper 70s on Thursday and Friday. Temperatures then warm to the upper 70s to low/mid 80s for Saturday and Sunday for the interior lowlands, with upper 60s to low 70s along the coast and terrain. By Monday, the vast majority of ensemble members indicate the ridge axis shifts east of WA and OR, allowing for increased onshore flow and temperatures to begin lowering again into the 70s for the interior valleys with dry weather continuing.

Underneath this upper-level ridge pattern, ensembles indicate a near surface thermal trough develops along the coast on Friday through this weekend. This pattern is expected to cause winds to shift from the onshore (westerly) pattern the area has generally been observing over the past couple of weeks to offshore (easterly to northerly). At this time, pressure gradients don't look to be very high, peaking at a -3mb to -4mb difference between PDX and DLS, so winds aren't expected to be strong. Instead, expect to see a typical diurnal behavior of winds becoming easterly on the west side of terrain (mainly Cascades, potentially coast range peaks as well) in the overnight to morning hours and increasing to peak gusts up to 20-35 mph. Then, winds decrease over the terrain during the day and increase through the valley from the north in the afternoon hours - peak gusts up to 20 mph. The probability of wind gusts peaking above 30 mph is less than 10-25% everywhere except for through the western Columbia River Gorge and surrounding terrain at 50-65%, which is generally the windiest location during offshore flow. At least confidence is moderate to high regarding the transition back to onshore flow Sunday night into Monday which would bring an end to these drier and locally breezy conditions. -99/03

AVIATION...Through 12Z Thursday

Early this morning flight conditions are a mix across the region with generally IFR to LIFR at the coast due to fog, and generally VFR/MVFR inland although fog/low stratus is beginning to expand across the southern Willamette Valley. Expect coastal terminals to remain in this fog/low stratus layer through a decent chunk of the morning hours before CIGs lift and skies gradually clear out late morning/midday. Inland terminals trend towards MVFR CIGs this morning, persisting through 16-18z before VFR conditions return. The exception to this is likely KEUG where fog is already present - similar transition to VFR conditions by midday. Light winds increase to around 5-10 kt from the north/northwest after 18z for most terminals.

KPDX AND APPROACHES...MVFR conditions likely persist through the morning hours before clearing occurs around 18-19z. High confidence in VFR CIGs by 20-21z at the latest. Anticipate WNW winds to turn more northerly midday through the afternoon - gusts only around 8-12 knots. -99

MARINE

Expect generally calmer conditions today as post-frontal northerly winds take hold across the coastal waters. Another weak system may approach the northern waters from the west on Thursday, but it likely holds north as it moves toward the Washington coast then out of the region - winds likely gain a westerly component temporarily. Northerly winds then return Friday, likely persisting over the weekend into early next week.

As far as wave heights are concerned, mid-period west- northwesterly swell of 6 to 8 ft at 11-12 seconds continues to move through the coastal waters this morning with buoy observations showing significant wave heights around 7 to 9 ft. Seas likely hold in this range into the evening, then seas gradually subside to around 4 to 6 ft later in the week with no other prominent swells of note at this time. -99/DH

PQR WATCHES/WARNINGS/ADVISORIES

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