textproduct: Portland

..Updated aviation discussion

SYNOPSIS

Ridging aloft will maintain largely warm and dry conditions through the next week. Daytime cloud cover will introduce uncertainty into the high temperature forecast through the coming few days, but the likelihood of warmer temperatures increases next week.

DISCUSSION...Now through Wednesday

Broad upper-level ridging is favored to remain largely in place over the Pacific Northwest through the next week, driving generally persistent weather conditions across the region. The nightly encroachment of marine clouds all the way inland to the Cascades will continue to yield some uncertainty in daytime high temperatures. Differences in heating due to both spatially and temporally-varying cloud cover may produce quite different temperatures from location to location; observed highs on Wednesday differed by as much as ten degrees at sites separated by only a few miles.

There is marginally higher confidence in an earlier clearing for most inland areas as the upper ridge axis shifts overhead in the coming days, but any areas of persistent cloud cover will again yield cooler afternoon temperatures. Highs will most likely remain seasonably warm into this weekend, in the upper 50s to upper 60s along the coast and in high terrain, and in the upper 60s to low 80s within inland valleys. The warmest spots are expected to be the Hood River Valley and central Columbia Gorge where lower nocturnal cloud cover will allow for increased daytime heating. These same areas will also be the breeziest as west winds of 15-20 mph gust to 25-35 mph each afternoon. Friday should be the coolest day of the week as a shortwave trough passes over top of the ridge, but chances for any rain Friday into Friday night remain 5% or less across the area.

As upper ridging rebuilds through early next week, chances for warmer temperatures will tend to increase. The forecast for Mother's Day continues to look pleasant: high temperatures in the 70s within inland valleys and 60s elsewhere beneath partly cloudy skies. Through the middle of the workweek, uncertainty in the placement and amplitude of ridging generates uncertainty in the temperature forecast. A more western ridge axis will generally favor the warmest temperatures locally, while a more inland location represents a cooler scenario. -36

AVIATION

Satellite imagery and terminal observations as of late Thursday morning depicts high-end MVFR/low-end VFR CIGs as stratus gradually burns off across northwest Oregon and southwest Washington. By 19-21z Thu, daytime heating will have completely mixed out the atmosphere, leading to predominately VFR conditions and mostly clear skies. Tonight, onshore flow will support re- development of marine stratus with 60-80% chance for MVFR CIGs or lower along the coast at any given hour between 06-18z Fri. The highest chances will be around KONP and lower as you go toward the north Oregon coast. Marine stratus may also filter into the southern Willamette Valley, resulting in a 25-40% chance for MVFR CIGs at KEUG after 09-12z Fri. Winds generally light and north-northwesterly today, turning more south-southwesterly overnight.

KPDX AND APPROACHES...VFR conditions with high clouds through the TAF period. Northwesterly winds 4-6 kt, becoming variable under 5 kt tonight into early Friday morning. 10-20% chance for MVFR CIGs after 12z Fri. -10

MARINE

A broad onshore flow regime favors continued marine overcast which thickens and lowers overnight before lifting and backing offshore each day through the remainder of the week. Northerly flow will weaken on Thursday and turn southerly on Friday as a weak front moves over the coastal waters and decays. Southerly gusts may briefly approach 20 kt on Friday afternoon before weakening again overnight. Chances for rain on Friday remain 5% or less. Seas of 5-8 ft today will ease to 3-5 ft by Friday night.

High pressure will restrengthen offshore this weekend into next week, supporting a reintensification of northerly winds. Chances for widespread gusts of 20-30 kt gradually increase each day from Saturday through Tuesday. Seas return to 5-8 ft from Saturday morning through the middle of next week. -36

PQR WATCHES/WARNINGS/ADVISORIES

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