textproduct: Portland

SYNOPSIS

A cool and increasingly unsettled pattern will continue through the weekend as upper-level troughing settles over the Pacific Northwest. Periodic marine pushes and weak frontal passages will bring increasing cloud cover and low chances for precipitation, with the best opportunities along the coast and higher terrain. Temperatures may briefly rebound Sunday, although uncertainty increases into early next week.

DISCUSSION...Now through Wednesday

Conditions continue to be dominated by upper level troughing over the northeast Pacific. Marine stratus along the coast is again expected to push into the interior as onshore flow continues. A shortwave embedded within the larger upper level trough will pass overhead this morning, sending a weak cold front through the area. Chances for measurable precipitation continue to vary across the area with the best chances over the coast, coast range, and Cascade Foothills. Chances over these area are 10-30% with locally higher chances over Pacific and Wahkiakum counties in WA at 40-60%. Elsewhere, chances are 5% or less. The downward trend in highs continues with temperatures likely topping out in the upper 70s across the interior lowlands while the coast remains in the 60s.

The pattern remains very similar heading into Friday. Upper level troughing persists with northerly onshore at the surface supporting marine stratus during the morning and afternoon high temperatures in the upper 70s. Heading into Saturday, troughing persists but a reinforcing disturbance could bring a better chance for precipitation. Probabilities for measurable rainfall (0.01 inches) are 10-30% for areas north Salem.

The pattern begins to flatten out during the second half of the weekend which would allow temperatures to rebound toward the upper 70s. Ensemble clusters favor a cooler, possibly wet pattern heading into early to middle of next week. An increasing number of ensemble members do show measurable precipitation across much of the area but do still show considerable differences in timing and strength of upper level troughing that develops. -19

AVIATION...Through 12z Friday

An upper level low off the Washington Coast will continue to support onshore flow. At the coast, MVFR/IFR cigs are favored through the morning, although there is only moderate confidence, 40-70%, in IFR occurrence, highest along the central Oregon coast and decreasing to the north. At inland terminals, the highest chances for MVFR cigs are along the Lower Columbia, in the Portland area, and in the southern Willamette Valley. MVFR chances reach 50-70% in the hours through 17z. Widely scattered rain showers are possible near the upper low, with 30% chances for restricted vis within light rain at KAST from 15-20z.

Conditions trend toward VFR inland and MVFR at coastal terminals this afternoon. South to southwesterly winds around 5 kt early become more westerly 5-10 kt by the afternoon. Gusts to 20 kt are expected closer to the low at KAST.

KPDX AND APPROACHES...Increasing chances for MVFR cigs after 12z Thu, reaching 50-70% from 14-17z before low clouds begin to mix out. Southerly winds around 3-5 kt early becoming westerly then northwesterly in the afternoon and evening 6-8 kt. -19/36

MARINE

Low pressure continues to track toward Vancouver Island today, supporting southerly winds across the coastal waters, generally around 10-15 kt. A weak front will move across the waters Thursday morning briefly increasing southerlies up to 20 kt. Could see a brief period of isolated gusts up to 25 kt across the inner waters north of Cape Falcon and around the Columbia River Bar through early this afternoon.

High pressure begins to rebuild over the waters later today into Friday, returning north to northwest winds across the coastal waters into the weekend. Predominately wind driven seas are expected to remain around 3 to 6 ft through the weekend. Somewhat more active pattern may return early next week. -19/DH

PQR WATCHES/WARNINGS/ADVISORIES

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