textproduct: Portland

SYNOPSIS

A weak cold-frontal system is slated to arrive on Sunday bringing a burst of light precipitation to the region. However, the focus remains on Monday and Tuesday when cooler air filtering into the region likely facilitates a period of lower snow levels. While a conditional rain/snow mix can't be ruled out all the way to the surface during the sunrise hours Tuesday morning, you'll almost certainly need some elevation (1000-1500ft+) to experience any noteworthy impacts. Temperatures and snow levels moderate with the arrival of a warm-frontal system midweek followed by the continuation of an active and progressive weather pattern into next weekend.

LONG TERM...Tuesday Night through Friday

Headed into the middle of next week the cold air exits as quickly as it moved in. A high pressure system off of the California Coast interacts with the low pressure in Gulf of Alaska and the compression of the flow aloft in-between these two features shoots a stronger warm-frontal system over the region. The axis of the heaviest precipitation again appears to be within Washington and British Columbia but as the the accompanying shortwave pushing through, that precipitation along a secondary frontal boundary will spread further south. While this system has some of the dynamics of an atmospheric river (decently robust swath of advected moisture), it will generally behave much like a typical March rainy system and will have minimal if any impacts. One challenge will be the timing of the precipitation of this system to any lingering cold air. If there remains cooler air trapped in the some of the coast range/Cascade valleys during the onset of this prolonged system, we cannot rule out another low-confidence snow type scenario for a few localized areas. However with the warmer air trailing quickly on Wednesday, any snow that would fall at the lower elevations would end quickly. Additional moderate to heavy snow is possible in the SW Washington Cascades Thursday into Friday, but not much else south of this near pass elevation.

In terms of other impacts, rain amounts will be steady through the remainder of the week but there are no concerns for flooding or rapid snow melt. This is a dynamically changing forecast with many components to consider so even a slight shift will completely change the outcome. -99/27

AVIATION

Westerly flow aloft increases while a weak cold front drops south across the region on Sunday. This will likely bring steadily deteriorating conditions across the area tonight into Sunday. As of 05z, Predominately IFR to low MVFR conditions are occurring along the coast, while increasing low stratus over northern portions of the area are producing MVFR to low VFR CIGs north of KUAO. VFR conditions under mostly clear skies currently persists across the southern and central Willamette Valley, but clouds are expected to begin filling in by 12z as probs for MVFR significantly rise to around 70-80%. There is also a 10-30% chance for IFR conditions to manifest between 12-18z Sunday within the southern and central parts of the Willamette Valley. As onshore flow continues, expect conditions along the coast to trend toward LIFR as probs increase to around 40% by 10z Sunday. Light rain is expected with the frontal passage beginning at the north coast by 12z Sunday morning, and slowly spreading inland and dropping south through Sunday afternoon.

KPDX AND APPROACHES...Low stratus continues to fill across the area with CIGs around 2500-3500 ft, producing predominately MVFR conditions. Conditions will likely fluctuate between MVFR and VFR through 12z Sunday, after which time probs for MVFR increase to around 60-70% through 00Z Monday. Chances for light rain increase after 16z Sunday. Light northwest winds are expected to become south to southwesterly early Sunday morning. /DH

MARINE

A persistent northwesterly swell will maintain seas at around 6 to 9 ft at 10 to 12 seconds through Sunday. A weak front will drop across the coastal waters on Sunday, with northwest winds behind the front likely producing gusts up to 20 kt, though there is a 20-40% chance that winds reach Small Craft Advisory criteria for an extended period of time. However, there is a 35-50% chance of isolated gusts up to 25 kt, with the highest probability across the northern waters of PZZ251 and PZZ271. The northwest swell is also expected to increase slightly, which will result in seas building towards 9 to 11 ft by Monday and 10 to 12 ft by Tuesday.

As the middle of the week approaches, a relatively stronger system looks to bring stronger winds and elevated seas by Wednesday and Thursday. Southerly winds will increase on Wednesday with the incoming system, with current model and ensemble guidance have a 50-70% chance of seeing gale force wind speeds during this time, but there is still some uncertainty as to where exactly the incoming system goes. In addition to the elevated winds, seas will also build Wednesday into Thursday towards 13-15 ft. Looking beyond towards the end of next week, overall conditions look to subside with seas falling below 10 ft by Friday and winds gusts around 20 kt. /42

PQR WATCHES/WARNINGS/ADVISORIES

OR...Winter Weather Advisory from 5 AM Monday to 5 PM PST Tuesday for ORZ126.

WA...Winter Weather Advisory from 5 AM Monday to 5 PM PST Tuesday for WAZ211.

PZ...None.