textproduct: Portland

SYNOPSIS

A gradual cooling trend is underway across the Pacific Northwest as an upper-level trough develops offshore. Interior lowland highs will remain in the low 80s today before dropping into the 70s to end the week. Increasing onshore flow will bring a stronger push of marine air into the interior today. Cooler and more unsettled conditions are favored into the weekend, with periodic frontal passages bringing low precipitation chances.

DISCUSSION...Now through Tuesday

Upper level troughing across the northeast Pacific will slowly shift eastward toward western Canada and the PacNW today, supporting lowering heights and cooler temperatures. Increasing onshore flow is expected to bring marine status to the interior lowlands early this morning will aid in keeping afternoon highs near the seasonal average in the low 80s inland and 60s along the coast. Low cloud cover across the interior is expected to break up late in the morning with stratus over the coast lingering into the afternoon hours.

Another marine stratus push into the interior is expected tonight into Thursday morning as onshore flow continues. A shortwave embedded within the larger upper level trough will pass overhead early Thursday, sending a weak cold front through the area. Chances for measurable precipitation 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 County 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 15-30% for areas north of Salem. However, models still show a good amount of uncertainty.

The pattern begins to flatten out during the second half of the weekend which would allow temperatures to rebound toward the 80s. Ensemble clusters favor a cooler, possibly wet pattern heading into early to middle of next week. Members do not show a clear "slam dunk" scenario with wide variability in timing and strength of upper level troughing that develops. -19

AVIATION...Through 12z Thursday

MVFR stratus along the coast is expected to persist while spreading inland. Stratus is beginning to show up on satellite across the lower Columbia and western Portland metro. Probabilities are expected to peak by 15-16Z this morning. At terminals along the I-5 corridor, chances for MVFR cigs reach 50-70% in the Lower Columbia Valley, Portland area, and southern Willamette Valley. Confidence is lower (30-50% chance of MVFR cigs) in the central Willamette Valley (KSLE, KUAO, KMMV) where cloud coverage may be lower. Low clouds will mix out by 18-19z Wed inland, yielding a return to VFR conditions, while more persistent low clouds at 2-3 kft may see MVFR conditions linger later on the coast. Winds 5-10 kt out of the southwest and veer more westerly through much of the day, before easing Wednesday evening. Strengthened onshore flow should keep smoke from fires in the Cascades and attendant vis restrictions to the east of area terminals.

KPDX AND APPROACHES...VFR conditions expected to prevail through 12-14z today, when low clouds reaching inland along the Columbia River will increase the chances for MVFR cigs, which reach 50-70% from 14-18z before cloud cover decreases as low clouds mix out by the afternoon. South winds around 5 kt and veer out of the southwest to west later today. -19/36

MARINE

Southerly winds expected today with speeds 10-15 kt and gusts less than 20kt, weakening tonight. Another weak front approaches the inner waters Thursday morning, briefly increasing southerlies, but in general, winds are expected to remain below 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 between 8 AM and 2 PM. Will hold off on any Small Craft Advisories at this time given the short window and isolated nature.

High pressure begins to rebuild over the waters later Thursday 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.