textproduct: Portland

SYNOPSIS

Seasonably warm and dry conditions expected through much of the week with morning clouds and afternoon clearing. Winds generally out of the west to northwest, strongest in the afternoon and along the Central Columbia River Gorge and Upper Hood River Valley. Next best chances for light rainfall arrive Friday into next weekend.

DISCUSSION...Now through Saturday

Seasonably dry and warm conditions continue through the week with minimal weather impacts. The large-scale pattern remains fairly stagnant through the period, with broad and relatively flat upper-level ridging over the majority of CONUS and a weak, positively-tilted upper- level troughing over the northeast Pacific. This pattern will support continued onshore flow, maintaining near-normal daily high temperatures in the 80s within inland valleys and 60s along the coast, and overnight lows in the 50s across the region. Mornings will be characterized by clouds, especially along the coast, which will tend to clear by the afternoon. Light west to northwest winds will, peaking each afternoon. The strongest winds are likely to be along the Central Columbia River Gorge and Hood River Valley, but impacts are not anticipated.

The majority of ensemble members are in agreement that upper- level ridging over the Rockies and Great Basin will build late in the workweek, which would favor a brief warm-up on Thursday. However, ensemble guidance shows the upper-level trough over the northeast Pacific shifting onshore Friday into the weekend, resulting in slightly cooler temperatures and winds coming from the west to southwest. Chances for precipitation also increase to 10-30% across the region during this time, however, there is still high uncertainty in the timing and potential rain amounts. A weaker front at the end of the week would have a hard time counteracting the dry airmass in place and make accumulating rainfall unlikely. -10/36

AVIATION...Through 06z Tuesday

VFR flying conditions currently in place across the airspace will give way to increasing MVFR chances as low stratus develops initially along the coast and potentially within inland valleys tonight. There is high confidence (70-90% chance) in conditions deteriorating to IFR at coastal terminals as low stratus develops by 09-12z Mon, while confidence in vis restrictions is lower. There remains high uncertainty if low cloud will be able to penetrate inland; the highest confidence (50-60% chance) for MVFR cigs is along the lower Columbia River into Portland-area terminals excluding KHIO, while chances are lower (30-50%) at Willamette Valley terminals. Chances for MVFR cigs rise above 50% in the hours around sunrise, 11-13z Mon, at KPDX/KTTD, and persist through much of the morning.

By 16-18z Mon, diurnal mixing will favor clearing skies and lifting cloud bases, with prevailing VFR again very likely at inland terminals. Along the coast, low clouds will be slow to erode, with VFR conditions most likely to be limited to the mid-afternoon, if at all; there are modest (25-35%) chances that MVFR cigs may persist through the afternoon.

Light north to northwest winds tonight will build to 5-10 kt at inland terminals and to 10-15 kt with gusts near 20 kt along the coast by 17-19z Mon. Winds ease again late in the period.

KPDX AND APPROACHES...High confidence in continued VFR conditions through at least 08-10z Mon beneath sct-bkn high clouds. Only moderate confidence in the potential for MVFR cigs with chances peaking at 50-60% from 13-17z Mon. High confidence in VFR cigs as diurnal mixing erodes low cloud coverage by 18-19z Mon. Northwest winds ease below 5 kt tonight, then build to 5-10 kt by midday Monday. -36

MARINE

A largely stagnant pattern continues through much of the week with high pressure offshore supporting northerly to northwesterly winds of 8-15 kt and afternoon gusts up to 20 kt. Weak low pressure moving over the northeast Pacific Friday into next weekend will shift winds out of the west to southwest across the waters, but chances for gusts exceeding 21 kt remain low, only 5-10%. Benign seas of 3-6 ft persist through the period. -10/36

PQR WATCHES/WARNINGS/ADVISORIES

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