textproduct: Portland

SYNOPSIS

Longwave trough moves over the region today increasing onshore flow and bringing chances for light rain to the terrain. Cooler temperatures expected through the weekend. A low pressure system in the northeast Pacific shifts southward Friday night into Saturday which has higher probabilities for accumulating rainfall through Sunday. The system remains active through Tuesday.

LONG TERM...Saturday through Tuesday

The low pressure system shifts inland through Saturday with a bulk of the rain falling in the morning. Again there is quite a spread with potential accumulation with the 10th percentile (driest ensembles) showing 0.00 inch of rain and the 90th (wettest solution) is closer to 0.25-0.50 inch. Overall though, the upper end of that range has decreased each day. This is likely due to the more northerly track of the system and thus we sit on the southern edge where less of the moisture is. At that time though we are sitting in the right entrance region of the jet streak which is often associated with more energetic weather. Combine this with the divergent flow, rain, and orographic effects, cannot rule out another threat for thunderstorms in the afternoon. Of the two days (Friday and Saturday), Saturday is the most potent day with CAPE exceeding 150 J/kg in some locations.

Transitioning into Sunday we will see some post frontal showers with an inverted trough aloft. However, those conditions will be short lived as yet another low pressure system is next up to bat late Sunday into Monday. Looking at the ensemble low locations, there is quite the spread between potential outcomes and the ECMWF ensembles show the concentration of possibilities slightly further south than the GFS ensembles. There is a great level of uncertainty in exactly what this will mean specifically, but the overall general pattern will favor onshore flow, cool temperatures, and potentially more rain which will last through Tuesday. -27

AVIATION

Upper level clouds continue to increase ahead of a decaying frontal system. Marine stratus along the southern Oregon coast is starting to push northward into the central Oregon coast around KONP. CIGs below 1000 feet are expected until 14-16z when the front moves through and increases surface mixing. Sub-VFR CIGs are expected to continue moving northward toward KAST but guidance is struggling. Should see a period of lowered CIGs between now and 15z. Inland, VFR conditions are expected to persist with upper and mid level cloud cover increasing through the TAF period. CIGs expected to gradually lower to 4-6 kft between 16-20z. Winds light overnight becoming southerly around 5 kt after 12z and then shifting to the west and increasing to around 10 kt in the afternoon. Lower CIGs along the coast expected to redevelop behind the front Wednesday afternoon.

KPDX AND APPROACHES...VFR conditions expected throughout the period. Coverage of high clouds will continue to increase through CIGs lower to around 10 kft tonight then further to around 5 kft late Wednesday morning. Light winds overnight becoming south/southwesterly 5-10 kt Wednesday morning. -19

MARINE

Southwesterly flow of 5-10 kt as a decaying front traverses the waters this afternoon. With this frontal system, rain is expected though will be light overall. In the passing showers, outflow wind gusts of 20-25 kt are possible, but are not expected to be widespread. As the front exits Wednesday night into Thursday, the flow returns to the northwest. Seas of 4-6 ft at 10-12 seconds with a dominant northwest swell continue through today, before a more westerly swell builds behind the frontal passage. Seas then build to 6-8 ft at 10 seconds from late tonight into early Thursday morning.

Generally unsettled weather looks to persist over the Northeast Pacific through the remainder of the forecast period with repeated systems bringing chances for further rain showers and elevated winds, most notably from Friday night into Saturday. Despite the active pattern, winds and seas are favored to remain below hazardous thresholds aside from chances for wind gusts exceeding 20 kt when brief northerly flow redevelops Sunday afternoon and evening. -27/36

PQR WATCHES/WARNINGS/ADVISORIES

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