textproduct: Portland

SYNOPSIS

Warm and unsettled weather is expected today as broad southerly flow keeps shower and thunderstorm chances overhead into the first half of the weekend, especially across the Cascades and adjacent foothills. At this point chances for severe thunderstorms appear low (5-10%) but activity may be impactful nonetheless. Next week we'll eventually transition into more of a westerly to northwesterly flow pattern leading to the return of cooler temperatures, Cascade snowfall, and increasing precipitation chances for late Tuesday into Wednesday.

LONG TERM...Monday through Thursday

To start the week ensemble models indicate the return to broad WNW-NW flow aloft with a weak embedded shortwave likely moving overhead on Monday maintaining shower chances (50-90%, highest Cascades). Temperatures stay near to slightly below seasonal normals as well. Shower coverage is expected to decrease Monday night into Tuesday morning thanks to a transient ridge briefly build overhead. Our attention then turns to the next Pacific frontal system expected to arrive sometime between late Tuesday and Wednesday while dropping out of the Gulf of Alaska. While timing differences persist among ensemble members, confidence continue to increase in the return of widespread precipitation during this mid-week timeframe. It's worth noting cooling temperatures along and behind the frontal boundary will likely push snow levels to or just below the Cascade passes sparking renewed snowfall concerns for these areas, primarily during the overnight hours. The NBM shows a 50-70% chance for the Cascade passes to see 6+ inches of snowfall from 5pm Tuesday to 5pm Thursday with a 10-30% for 12+ inches during that same period. This'll be something to keep an eye on as we get into next week in addition to the return of marginal frost concerns mid to late week as well. -Schuldt

AVIATION

Generally VFR conditions are in place across the region with mid to high level clouds slowly moving from south to north across the airspace. The lone exception is KEUG where patchy fog has developed on the far southern end of the Willamette Valley - IFR to LIFR conditions possible until 15-16z. Expect the airspace to remain relatively dry through around 18Z-20Z Friday. After this point showers and thunderstorms likely develop around Lane County before pushing northward along and east of the I-5 corridor the remainder of the afternoon into the early evening. Given decent model consistency, have maintained PROB30 groups mentioning thunderstorms for for KEUG, KSLE and KUAO as those sites currently have the highest chance to see activity. Confidence remains lower for terminals in the immediate Portland Metro but the period to watch will be 00-04z Sat for this area - did not include a mention of thunder with the 12z Fri TAF package. Thunderstorm chances regionally rapidly decrease Friday evening.

It should be noted locations that do see stronger showers or thunderstorms will have the potential for lightning, small hail, moderate to heavy rain, and gusty/erratic outflow wind gusts up to 35-45 knots. This activity would also result in intermittent MVFR/IFR conditions if it moves directly overhead.

KPDX AND APPROACHES...Expect predominately VFR flight conditions through the TAF period with mid to high cloud cover at times. Locally, shower (50-70%) and thunderstorm (25%) chances ramp up around 00-01z Saturday before diminishing by 05-06z. Stronger showers or thunderstorms will have the potential for lightning, small hail, moderate to heavy rain, and gusty and erratic outflow wind particularly at the onset of activity in the late afternoon hours if it occurs. -99/42

MARINE

Overall conditions remain rather benign the next several days as north to northwest winds switch southerly today into tonight before shifting more westerly by the start of next week. Confidence is high wind gusts hold below 20 kt through the Monday into Monday night. Seas around 4 to 7 ft persist through the middle of next week as well. It's worth quickly noting there is a ~10% chance of thunderstorms today through Saturday across all waters rotating in from the southeast. Any thunderstorms that do develop could produce lightning hail, gusty and erratic winds as well as a less than 2% chance for a funnel cloud or waterspout. Our attention turns to the arrival of a decently strong frontal boundary the second half of Tuesday into Wednesday likely bringing the return of Small Craft Advisory wind gusts and seas around 7-10 ft. -99/42

PQR WATCHES/WARNINGS/ADVISORIES

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