textproduct: Portland

SYNOPSIS

Unseasonably warm and dry conditions continue through much of the workweek with periods of offshore flow and early morning valley and coastal fog. A trough moving into the Pacific Northwest will bring cooler temperatures and chances for rain Friday into next weekend.

LONG TERM...Wednesday through Saturday

The upper-level pattern looks to amplify again through the middle of the week, leading to a slight warming trend as inland temperatures remain around 10 degrees above normal Wednesday and Thursday. Dry weather also continues, while the resurgent ridge and warm temperatures will again allow for the development of a coastal thermal trough, nocturnal offshore winds in the Cascades and foothills, and early morning valley fog in the Coast Range and Willamette Valley.

There is increasing consensus among long-range ensemble members in the evolution of an upper-level trough arriving Friday into next weekend, bringing a return to more seasonable temperatures and potential rainfall. While there is still uncertainty in timing and amounts, rain chances peak Friday afternoon into Friday night, highest in the Cascades and along the coast from Tillamook County northward. -36

AVIATION...Through 18Z Monday

Currently LIFR/IFR stratus at coastal terminals and mostly VFR conditions inland (the exception being LIFR at KEUG). Expect conditions at terminals with deteriorated conditions to improve back to VFR by 19-20Z Sun, with the exception of KONP possibly staying IFR through the afternoon. By 03-06Z Mon, deteriorated conditions will likely return to coastal terminals, to the east near the Cascade foothills, and to the central/southern Willamette Valley. Probabilistic guidance suggests a 25-50% chance of LIFR conditions at coastal terminals, highest at KONP, and a 20-30% chance of LIFR conditions at KSLE and KEUG. As for other inland terminals, there is a 10-20% chance of LIFR conditions after 12Z Mon.

Calm to light winds early this morning will build out of the north to northwest at around 5 kt today, then ease again around 03Z Mon. Winds of 8-12 kt with gusts up to 20 kt are possible this afternoon at KONP.

KPDX AND APPROACHES...VFR conditions throughout the period, with a 15-20% chance of IFR/LIFR conditions if fog becomes more widespread around 12-17Z Sun. Diurnal northwest winds rising to around 5 kt this afternoon. ~12

MARINE

Persistent high pressure offshore will maintain northerly winds through the week, with speeds reaching diurnal peaks each afternoon. Chances for peak wind gusts of 20-25 kt generally increase daily through Wednesday, though the duration and coverage stronger gusts may not be sufficient to support Small Craft Advisories each day. Strengthening northerly flow will see largely wind-driven seas continue at 4-6 ft through much of the week, with a modest west-northwest swell at 8-9 seconds lengthening to 10-12 seconds early in the workweek.

High pressure aloft this weekend will also support areas of dense fog developing nightly as cloud bases are compressed down to the surface. The current Dense Fog Advisory which remains in effect through noon PDT Sunday for visibilities of 1 NM or less has been expanded to cover all of the waters.

More active marine conditions are likely in the latter half of the week as troughing over the Gulf of Alaska generates a building northwest swell and chances for rain return to the region Friday into next weekend. A longer period northwesterly swell may also bring a moderate sneaker wave threat. -36/10

PQR WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None. PZ...Dense Fog Advisory until noon PDT today for PZZ210-251>253- 271>273.