textproduct: Portland

SYNOPSIS

Chilly conditions with areas of frost Wednesday morning with temperatures warming nicely in the afternoon. Trending even warmer Thursday and Friday with mainly dry conditions west of the Cascade foothills. There is a 40-70% chance of showers and a 10-25% chance of thunderstorms over the central Oregon Cascades on Thursday. On Friday, there is a 70-90% chance of showers and a 15-25% chance of thunderstorms over the central and northern Oregon Cascades. A few stray showers or storms may drift into the Willamette Valley and Coast Range, especially late Friday. Becoming cooler again over the upcoming weekend with increasing chances for widespread showers.

LONG TERM...Saturday through Tuesday night

The long term forecast is highlighted by a cool and showery weather pattern that is more typical for mid April. The GEFS/ENS/GEPS ensemble mean for 500 mb heights all show a trough moving into the western CONUS Saturday into Sunday, through WPC's cluster analysis reveals there is still some uncertainty regarding the exact timing and amplitude of this trough. That said, overall uncertainty in these details is less compared to yesterday. As such, probabilities for precipitation have increased this weekend. In fact, 6 hourly PoPs now peak between 60-90% on both Saturday and Sunday, with the highest probabilities over the Cascades and foothills. Note 24-hour PoPs are even higher, peaking between 80-100% on Saturday. In other words, at least some rain is very likely to occur this upcoming weekend. Although confidence is high rain will occur, confidence is not as high regarding exact rain amounts, especially given the showery nature of precipitation. Nevertheless, the NBM v5.0 suggests there is a 50-80% chance for at least 0.25 inches of rain between 5am Saturday and 5am Sunday, except a 30-50% chance along the south WA/north OR coast. Probabilities for at least 0.25 inches between 5am Sunday and 5am Monday decrease to 25-40%, except 50-65% in the Cascades. Beyond 5am Monday, chances decrease to under 10% as most model guidance suggests showers will be dissipating by early next week.

Confidence is high temperatures will peak somewhere between the mid 50s to mid 60s on Saturday, between 50 and 60 degrees on Sunday, and between 55 and 65 degrees early next week. Regardless of the exact outcome, it will feel noticeably cooler compared to what has been observed over the past few days. -23

AVIATION

Westerly flow aloft continues with scattered high clouds, resulting in VFR flight conditions at all terminals early Wednesday morning. However, satellite imagery from 11Z Wednesday showed what appears to be fog developing 2-3 miles east of KONP. Given temperatures at KONP are in the mid 30s with calm winds in place, this is likely steam fog developing over the Yaquina River. Latest guidance suggests there is a 10-15% chance this small area of fog will expand westward into KONP between 12-14Z Wednesday. Even if this does occur, fog would likely lift by 16-17Z given how shallow the fog layer is. Aside from the potential morning fog threat at KONP, expect VFR conditions to continue today and tonight at all terminals. Note frost is also possible at KAST and KONP through 15-16Z this morning given surface temperatures are hovering between 34-37 degrees. Inland terminals have remained in the low to mid 40s as of 11Z, meaning frost is not expected at these terminals.

KPDX AND APPROACHES...VFR flight conditions will continue through 12z Thursday with scattered thin high clouds. Calm winds this morning should become northwesterly around 3-6 kt by 22-00Z this afternoon. -23

MARINE

Seas of 5-7 ft at 10 to 12 seconds, with little in the way of active weather is expected through the remainder of the workweek other than passing rain showers on the northern flank of an area of low pressure off the northern California coast by Friday. Even then, these showers will be focused over the southern waters and only have a 15-25% chance of occurring. This feature to the south may support further Small Craft Advisory conditions as there is a 30-60% chance northerly to northwesterly wind gusts exceed 25 kt on Thursday, with the highest probabilities over the central waters. -23/36

PQR WATCHES/WARNINGS/ADVISORIES

OR...Frost Advisory until 9 AM PDT this morning for ORZ104-106-108- 109-114>118-121.

WA...Frost Advisory until 9 AM PDT this morning for WAZ202>206-208.

PZ...None.