textproduct: Portland

SYNOPSIS

Seasonable conditions through at least Saturday with dry conditions and highs in the 50s along the coast and 60s inland. The forecast details become unclear by Sunday with the rain potentially returning. The pattern is expected to become more unsettles by early next week as a series of systems bring impacts to the region.

DISCUSSION...Now through Thursday

Pleasant, seasonable conditions are expected over the area through at least Saturday, possibly into Sunday. Zonal flow aloft is expected to persist, supporting mostly clear skies and comfortable temperatures. Clear skies tonight will allow for efficient radiative cooling and temperatures dropping into the 30s for most locations and a some localized upper 20s in more sheltered locations. This will lead to another night with frost development which could impact sensitive outdoor vegetation. The upper level pattern amplifies slightly on Friday, supporting a jump in temperatures into the mid 60s inland. A weak surface thermal trough will maintain offshore flow on the west side of the coast range and Cascades through Friday morning. Overnight lows after tonight will be more mild, reducing the chances for frost development. Conditions remain dry on Saturday with highs close to average in the low 60s inland.

Ensemble guidance still shows a good amount of disagreement for Sunday with a roughly 10 degree spread between the 25th and 75th percentiles for high temperatures from low 50s to low 60s inland. Guidance is still struggling with precipitation timing and the overall pattern heading into next week. A trough sits over the Gulf of Alaska while a closed low sits over the eastern Pacific heading into the weekend. The trough over the Gulf of Alaska is expected to drop southeast toward the PacNW during the Sunday to Monday timeframe bringing light rain back to the area through timing is uncertain. The closed low drifts toward the West Coast but is not expected to phase together with the trough to the north. A brief break from precipitation is possible on Tuesday before another trough approaches the area from the Gulf of Alaska. Models indicate that this system could be more robust with decent probabilities for a half an inch of rain or more in 24 hours during the Wednesday/Thursday timeframe. Details remain unclear with this system given the 6 day lead time. -19

AVIATION

Dry westerly flow aloft will support predominately VFR conditions with mostly clear skies through the TAF period. Northerly pressure gradients ease and winds weaken below 10 kt tonight. Meanwhile, an offshore pressure gradient will set up across the Columbia River Gorge producing east winds gusting up to 20-25 kt after 12z Fri. Clear skies and calm winds across the Willamette Valley will support temperatures in the low to mid 30s, resulting in potential frost development between 09-16z Friday.

KPDX AND APPROACHES...VFR conditions through the TAF period. Potential for LLWS between 08-18z Fri as easterly winds increase aloft at 2kft while surface winds remain northwesterly and under 10 kt. /DH

MARINE

High pressure building over the waters is leading to northerly winds. A surface thermal trough is also developing along the coast, tightening pressure gradients and strengthening these northerly winds. Breezy northerly winds initially remain mostly south of Cape Falcon and beyond 10 NM offshore, however by Friday afternoon there is a greater than 90% chance for widespread northerly wind gusts of 21 kt or stronger across all waters south of Cape Falcon. A Small Craft Advisory has been issued for all waters south of Cape Falcon, from 5 PM this afternoon to 2 AM Saturday for waters beyond 10 NM offshore and from 2 PM Friday to 2 AM Saturday from the coast out to 10 NM. The thermal trough breaks down Saturday with high pressure continuing over the waters through the weekend. North winds will continue through the weekend, just not as gusty. Seas will generally remain between 7-9 ft at 10-11 sec through Saturday, falling to 4-6 ft by the end of the weekend. -10

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Small Craft Advisory from 2 PM Friday to 2 AM PDT Saturday for PZZ252-253.

Small Craft Advisory until 2 AM PDT Saturday for PZZ272-273.