textproduct: Portland

SYNOPSIS

An atmospheric river event keeps conditions rather wet to start the day with weather related impacts staying minor. Wednesday through the end of the work week the weather pattern appears fairly benign while trending drier, at least for the inland valleys. We'll need to watch a system undercutting the region to the south over the weekend but the weather trends dry again early next week. Conditions likely remain within our typical climatological norms through the forecast period with no significant weather impacts on the horizon.

LONG TERM...Thursday through Monday

Colder air is expected to be funneled into the PacNW behind Wednesday's shortwave. This along with clearing skies will lead to colder overnight temperatures Wednesday night with a 60-90% chance of low temperatures Thursday morning falling below freezing in the central and southern Willamette Valley and a 40-60% chance for the SW Washington lowlands. These temperatures are largely clearing depended and added cloud cover would keep lows higher than forecast. There's an off chance (~5-10%) an isolated shower wanders off the coast range or Willapa Hills into the southwest Washington lowlands during this period which would have the potential to be a rain/snow mix assuming preceding clearing headed into the sunrise hours Thursday. However, a lot of variables would have to perfectly align for this to occur. So while the forecast may introduce a mention of a slight chance (15%) for rain/snow late Wednesday night into Thursday morning, it is extremely unlikely you'll see any impacts below 1500-2000ft - in fact you'll be lucky to see anything at all.

Ensemble guidance indicates zonal flow persists Thursday through the weekend. Low precipitation chances continue across the area each day, mainly over the terrain, with limited accumulation expected. The closed low remnant from the current longwave trough is slated to move back east towards the West Coast late weekend to early next week. Most ensemble members suggest it will move inland along the CA coast, but exactly how far north or south is uncertain. This uncertainty is part of the reason for the low precipitation chances as a track further north would yield better chances for precipitatiion.

However, the jet stream along the zonal flow is expected to dip south into central OR, which would allow for colder air to impact the area once again Saturday night and Sunday night into early next week. There's a 30-60% chance overnight temperatures fall below freezing again each night for the lowlands outside of the Portland metro area. Similar to Thursday morning, a rain/snow mix may show up in the forecast for lower elevations that have a chance of precipitation, but there is less than 5% chance of accumulating snow. -99/03

AVIATION

Post frontal environment today which will lead to a mixture of CIG and VIS categories. Overall, looking at widespread MVFR conditions with pockets of IFR/LIFR CIGs in the southern Willamette Valley and some of the more prone areas like KHIO. With showers lingering in the area, may see temporary reductions to VIS with heavier rain or snow (if traveling through the Upper Hood River Valley and above freezing levels). Through the day will see little improvement. Models are scattered with cloud cover and the impacts seen from any potential clearing. There is consensus for northerly winds throughout the area though which, especially from KSLE southward, is a wind direction that traditionally promotes fog development. Right now, there is around a 30% chance of IFR CIGS/VIS reforming with fog after 13Z Wed. However, confidence is low as there will need to be adequate cooling from clearing skies.

KPDX AND APPROACHES...MVFR CIGs with reduced VIS in showers. Will struggle to see significant improvement today, however as the environment begins to mix in the afternoon, could see enough clearing that CIGs partially clear. If this does occur, there will be a trend towards fog development. Based on ensemble models, there is around a 30% chance of LIFR VIS, and a 65% chance of at least MVFR VIS after 10Z Wed. Confidence remains low at this time. -27

MARINE

Seas and winds continue to trend down today and through the middle of the week. Seas remain steep through tonight with a Hazardous Seas Warning remaining in effect until 7 PM today before transition to a Small Craft Advisory which is in effect until 10 AM Tuesday. The pattern is expected to remain benign through Thursday before a WNW swell entering the waters Friday morning pushes seas to around 10 feet with a period in the mid teens. -19

PQR WATCHES/WARNINGS/ADVISORIES

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