FXUS66 KPQR 151118 AFDPQR Area Forecast Discussion National Weather Service Portland OR 418 AM PDT Wed Apr 15 2026 .SYNOPSIS...The back edge of a cold frontal boundary which has spread ample precipitatiion and mountain snowfall across the Pacific Northwest quickly progresses through the region this morning followed by a showery airmass and a 15-30% chance for thunderstorms this afternoon. A Winter Storm Warning remains in effect for the Cascades through tonight. Concerns shift to cooler overnight temperatures and possible frost/freeze conditions to round out the week. After a brief stint of dry and warmer weather Saturday, precipitation chances return by early next week although forecast confidence Sunday onward is low. && .SHORT TERM...Now through Thursday Night...Early this morning satellite and radar observations show our latest weather disturbance in the form of a cold-frontal boundary and the wide band of stratiform precipitation dropping NW to SE across western Oregon. Snow-levels are expected to quickly bottom out around 1500-2000ft in the cold airmass behind the frontal boundary by late morning with snowfall continuing to be the primary impact with this disturbance focused over the Cascades. We're still watching for a potential for 1-3 hr period of dynamic cooling artificially lowering snow levels closer to ~1000ft around sunrise this morning, particularly in coast range and southwest Washington southward through portions of Clackamas County. However, as far as travel is concerned, it'll be challenging to get accumulation on roadways at this elevation should a period of wet snow or a rain/snow mix occur. The chances for a light slush-up gets higher once you reach 1500ft, particularly in the Cascade foothills/valleys, but due to the warm antecedent conditions most impacts remain 2000-2500ft+. The heavier precipitation early to mid morning helping to drive these lower snow levels will also help to boost snowfall rates at pass level, likely reaching 1-1.5+ in/hr until the frost passes. If you plan to traverse across the mountain passes today, please prepare for winter-like travel conditions. Once we get into the midday and afternoon hours we'll have transition to a more convective and showery post frontal environment thanks to the core of a upper level low moving overhead. Most models still show Convective Available Potential Energy (CAPE) values peaking around 200 to 500 j/kg this afternoon leading to a 15-30% chance for thunderstorm development across the CWA. The main time period of focus is 11AM to 7PM today when heating between shower bands is maximized. Convective Allowing Model (CAM) soundings are showing a skinny CAPE profile and along with cooler temperatures aloft, this does support tiny hail/graupel development with any thunderstorms that develop and given that when spring time thunderstorms develop within our CWA, they have a tendency to produce a lot of tiny pea size hail. Also be on the lookout for infrequent lightning, gusty winds, and heavy rain associated with any activity. With the loss of daytime heating thunderstorm chances decrease Wednesday night although showers likely persist. At this point the axis of the upper-level low pulls to our east with increasing heights on northerly flow aloft by sunrise Thursday morning helping to decrease shower activity. The lingering cooler temperatures aloft and partial clearing by sunrise should allow overnight lows to drop below normal bottoming out in the mid 30s across the lowlands. Below freezing temperatures are even forecast for the higher coast range/Cascade valleys, including the Hood River Valley, and potentially in the Cascade foothills mainly around and south of OR-22. Give the moderate to high confidence in these low temperatures panning out, have issued frost advisories for much of the region including a Freeze Watch for the Upper Hood River Valley and a couple of the aforementioned Oregon Cascade foothill zones. A few showers likely lingering through Thursday, increasing in the afternoon due to daytime heating, however, the bulk of the activity will be pinned to terrain features in the Cascades and coast range. Similar frost/freeze conditions may develop again Thursday night into Friday morning and additional highlights may be needed for this period. Even though temperatures warm slightly aloft Thursday night compared to Wednesday night/Thursday morning, weak pressure gradients combined with a building ridge of high pressure aloft and better clearing may prove to be a better set-up for frost development. -99/42 .LONG TERM...Friday through Tuesday...Looking towards the weekend confidence is high among both deterministic and ensemble guidance in a ridge of high pressure continuing to build aloft allowing temperatures to gradually warm and reduce frost concerns. However the pattern remains rather progressive as models show the ridge quickly followed by another low pressure system on Sunday originating from the Gulf of Alaska. WPC Cluster Guidance does favor this low dropping almost straight southward across the eastern Pacific favoring this low holding just off the OR/WA coast. How far this low holds off the coast will heavily modulate conditions locally. Should it stay more to our west, warmer conditions and broad southerly flow would be favored, That said, any moisture riding south to north within this flow pattern could spell the return of convection. Thus forecast confidence Sunday onward into the middle of next week is low. -99/42 && .AVIATION...As we move through the morning hours steadier rain will transition to showers behind the frontal boundary moving overhead - KAST has already seen an improvement back to VFR as a result. Expect a south to northwest wind switch when the front passes this morning as well. However, as bands of showers move overhead, especially during the afternoon and evening hours, brief drop to MVFR or IFR can be expected. On the whole there is a 20-40% chance for MVFR conditions at the coast this afternoon with a 15-25% inland. It's also worth highlighting there is also a 20-30% chance for thunderstorms for all terminals after roughly 18-21z today with lightning and gusty/erratic winds the primary impacts. Chances for these storms quickly drop off around 4-6z Thur. KPDX AND APPROACHES...MVFR conditions and breezy southerly winds likely persist until 14-16z this morning while the primary precipitation band sits overhead. After his point winds gain a westerly component while rainfall turns more showery, but at least it trends more towards VFR the remainder of the TAF period. Keep in mind there will be a 20-25% chance for thunderstorms locally after ~20z through -4z this evening. Any robust showers or storms may briefly drop conditions to MVFR/IFR. -99 && .MARINE...A cold frontal boundary is quickly progressing across the coastal waters early this morning with winds switching northwesterly in its wake. Expect gusts between 20-30 knots the remainder of the day as an area of low pressure drops along the Canadian coast toward the region. This feature will also bring a 15-25% chance of thunderstorms over the waters into the evening hours. Seas are expected to persist at around around 9 to 10 ft, building slightly to around 10 to 12 ft tonight as a fresh northwest swell moves through the waters. The Small Craft Advisory remains in place through Thursday morning for both the inner and outer waters, including the Columbia River Bar. High pressure then builds over the waters Thursday into the weekend as northerly winds return and seas gradually subside to around 3 to 6 ft Friday into Saturday. It appears there's a 40-60% chance for north winds to gust above 21 knots into Small Craft Criteria on Saturday. Looking ahead there is potential for another weather system to impact the waters later this weekend, possibly increasing winds and seas. -99/DH && .PQR WATCHES/WARNINGS/ADVISORIES... OR...Frost Advisory from 1 AM to 9 AM PDT Thursday for ORZ104>107- 109-114>118-123. Freeze Watch from late tonight through Thursday morning for ORZ121-124-125. Winter Weather Advisory until 11 AM PDT this morning for ORZ123. Winter Storm Warning until 5 AM PDT Thursday for ORZ126>128. WA...Frost Advisory from 1 AM to 9 AM PDT Thursday for WAZ204-205- 208. Winter Storm Warning until 5 AM PDT Thursday for WAZ211. PZ...Small Craft Advisory until 5 AM PDT Thursday for PZZ210. Small Craft Advisory until 11 AM PDT Thursday for PZZ251>253- 271>273. && $$ www.weather.gov/portland Interact with us via social media: www.facebook.com/NWSPortland x.com/NWSPortland