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 18z Friday

Southwest flow aloft continues as an upper level trough persists over the region. Light rain showers continue near KAST as a weak front pushes onshore today. This is producing predominately MVFR conditions at the coast, with periods of reduced VIS. A few low clouds are also expected to push inland, generally remaining VFR, but brief MVFR CIGs will be possible into early this afternoon. Guidance suggests increasing chances (around 50% near KONP) for LIFR conditions developing along the central Oregon coast after 02z Friday. The best chances for MVFR stratus developing inland Friday morning (12-14z) will be along the Columbia River (including KTTD and KPDX) as well as in the southern Willamette Valley (KEUG). South to southwest winds today are expected to become more westerly later this afternoon.

KPDX AND APPROACHES...Predominately VFR conditions expected through the period. A weak front pushing inland brings low chances for broken MVFR CIGs into early afternoon. There is also a 20-30% chance for MVFR stratus developing near the terminals after 12z Friday. Relatively light SSW winds are expected to veer westerly this afternoon, becoming northwest 6-8 kt by 00z Friday. /DH

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.