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 12z Monday

Latest terminal observations depict widespread LIFR conditions within fog along the north and central Oregon coast while inland terminals in the southern Willamette Valley and sheltered peripheral valleys are beginning to see fog develop, yielding restricted conditions. Dense fog and LIFR vis/cigs are likely (60-80% chance) to prevail at coastal terminals until 17-18z Sun, when daytime heating and increasing winds will aid in mixing out low clouds. While VFR conditions are most likely, if cloud cover remains high enough, MVFR cigs may persist through the afternoon. Northwest winds increase to 10-15 kt with gusts to 20 kt most likely along the central Oregon coast including at KONP. Winds ease again after 03z Mon while the nightly push of marine clouds into the coast is again expected to produce restricted vis/cigs. Inland, coverage of fog or low stratus will continue to increase in the hours around sunrise. Chances for restricted vis within fog increase to the south along the Willamette Valley, as well as to the east near the Cascade foothills; southern Willamette Valley terminals (KEUG, KCVO, K77S) are the most likely (40-60% chance) to see persistent IFR/LIFR vis/cigs within fog, while central valley (KSLE, KMMV, KUAO) and other foothill terminals (KTTD) are more likely to see MVFR vis and mist with a lower likelihood (25-45% chance) of IFR/LIFR. Any low clouds or vis restrictions are expected to mix out by 17-18z Sun. Calm to light winds early this morning will build out of the north to northwest at around 5 kt today, then ease again tonight.

KPDX AND APPROACHES...VFR conditions favored throughout the period, with a 15-20% chance of IFR/LIFR cigs if fog becomes more widespread in the hours around sunrise, 13-17z Sun. Otherwise, largely clear skies are expected with diurnal northwest winds rising to around 5 kt this afternoon. -36

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. A Dense Fog Advisory therefore remains in effect through noon PDT Sunday for visibilities of 1 NM or less across the waters south Cape Falcon. Confidence for widespread dense fog is lower to the north of Cape Falcon, but the chances for restricted visibility are higher nearer to the coast, and the Advisory may be expanded if observed conditions in coastal Clatsop and Pacific Counties degrade.

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...Dense Fog Advisory until 10 AM PDT this morning for ORZ101>103.

WA...None.

PZ...Dense Fog Advisory until noon PDT today for PZZ252-253-272-273.