textproduct: Portland

SYNOPSIS

Conditions trend warmer and drier today and Friday. Temperatures generally expected to remain near to slightly above seasonable normals for late April. Chances for showers increase this weekend, particularly over the higher terrain of the Cascades and foothills. Similar conditions persist into early next week.

DISCUSSION...Now through Wednesday night

Warmer, drier conditions are expected to end the work week. Western Washington and Oregon will be positioned between upper level ridging building over the northeast Pacific and a digging trough over central and western Canada. Conditions today will be a nice improvement from the last couple days with highs back near normal. Cloud cover to start the day will gradually dissipate through the afternoon with light northwesterly winds. Lows tonight expected to drop into the upper 30s to low 40s. There is a low chance, around 10-30%, for temperatures to drop below 37 degrees in the southern Willamette Valley and slightly better chances of 20-50% in the Upper Hood River Valley that are elevation dependent. Will hold off on frost products given the low probabilities but locally cold spots could drop below 37.

The amplified pattern is expected to continue heading into Friday. The upper level ridge will build into northwestern Canada while the digging trough stalls and deepens into a closed low over south-central Canada and into the northern Plains. An area of shortwave energy is expected to drop southward between these two features toward the PacNW. Conditions are expected to remain mostly dry and seasonably warm to slightly above normal into the weekend. Highs in the mid 60s to low 70s can be expected Friday through Monday for interior lowlands with upper 50s to low 60s along the coast. Overnight lows in the upper 30s to low 40s are expected but with mostly clear skies, could see some cooler spots. There is a 10-30% chance for temperatures to drop below 37 in the Willamette Valley and Clark and Cowlitz lowlands, highest in the southern Valley. The Upper Hood River Valley has a better chance over dropping below 37 at 40-80%, elevation dependent. Beyond Friday night, there are low probabilities around 10-15% each night through Sunday night into Monday morning.

There is low potential for shower activity over the central Oregon Cascades Saturday afternoon: 15-30% PoPs with a 10% chance of thunder. Depending on the strength of the upper shortwave and amount of mid-level moisture, chances for showers may increase Sunday and Monday afternoons, with around a 10-25% chance of rain showers across the lowlands and 30-60% over the Cascades and Cascade Foothills.

Uncertainty remains in the forecast heading into next week. Ensemble clusters do show ridging pattern developing over the eastern Pacific and PacNW but strength and exact position are unclear. This is reflected in the high temperature spreads heading into Tuesday and Wednesday with low end temps in the low 60s and high end in the low 80s. There is also uncertainty in regards to precipitation with around 20-40% of ensemble members producing light rain at times during the Monday through Wednesday timeframe. -19

AVIATION

Mainly VFR conditions expected through the TAF period. BKN to OVC clouds between 3000-5000 feet are expected to persist through mid morning. Hi-res guidance does suggest a brief lowering of CIGs to around 2000-2500 feet for most terminals between 15-19z. Skies really begin to clear after 18z for most terminals with the return of mostly clear skies during the afternoon. Light southerly winds turn to the north-northwest around 5 kt or less.

KPDX AND APPROACHES...VFR CIGs around 4000 feet persist with a chance for MVFR CIGs around 2500 feet between 16-18z. Guidance is not hitting the lower CIGs hard so have kept out of TAFs for now. Light southerly winds turn northwesterly around 5 kts during the afternoon. -19

MARINE

Steep seas continue over the waters with wave heights around 10-12 feet at 11-13 seconds. Small Craft Advisories continue for all zones including the Columbia River Bar. The northwesterly swell will gradually decrease through the day with wave heights dropping below 10 feet this afternoon. Small Craft conditions are expected to end by 5 pm PDT if not slightly earlier.

Light southerly winds will turn to the northwest around 10 kt this afternoon and into the evening. An offshore pressure gradient is expected to develop Friday which will turn winds more northeasterly. Winds gusts between 20-25 kt will be possible for both inner and outer zones south of Cape Falcon during the afternoon and evening hours. Currently there is a 40-70% chance of wind gusts above 20 kt. Wave heights will continue to decrease to 6-8 feet on Friday. -19

PQR WATCHES/WARNINGS/ADVISORIES

OR...None.

WA...None.

PZ...Small Craft Advisory until 5 PM PDT this afternoon for PZZ210- 251>253-272-273.

Hazardous Seas Warning until 5 AM PDT early this morning for PZZ271.

Small Craft Advisory from 5 AM early this morning to 5 PM PDT this afternoon for PZZ271.