textproduct: Portland

SYNOPSIS

Conditions remain mostly dry today but transition this evening as the upper level low shifts eastward. Increasing cloud cover is expected from south to north with increasing precipitation chances. The best signal for the coolest and most unsettled stretch remains Tuesday into Wednesday as the system moves inland. Beyond that, guidance supports a return to drier weather and a warming trend beginning Thursday and continuing into the weekend as high pressure rebuilds.

DISCUSSION...Now through Sunday

High and mid level clouds continue to stream in along southerly flow supported by the large cut-off low positioned off the coast. Overnight lows remain on the mild side as cloud cover keeps the surface insulated. Expecting lows in the mid 40s to low 50s.

Conditions start out dry for the area but will begin to transition during the latter half of the day. The upper level ridge that has controlled the region over the last few days will shift eastward as the upper level low swings inland. Cloud cover will continue to stream in through the day but could see some breaks or thinning over the northern half of the forecast area, mainly over the northern Willamette Valley and Portland/Vancouver metro. Highs are expected to top out a few degrees cooler than yesterday with highs in the upper 60s to around 70 through the central and southern Willamette Valley. Highs in the low to mid 70s around the metro with a low (10-30%) to hit 80. Coastal areas see temperatures in the upper 50s to low 60s. PoPs increase from south to north through the day as the trough begins making an eastward push. Slight chance PoPs enter the forecast area early in the afternoon and spread northward to the metro by the evening. Precipitation will be scattered and light with most locations receiving 0.10 inches or less through tonight. There is a low (~10%) chance for an isolated pop-up thunderstorm over mainly over the Cascades this evening. Not expecting anything widespread or impactful but instability could increase enough where cloud cover breaks.

Tuesday continues to look like a showery, cool day with rain showers expected to be at their greatest areal coverage and highs drop back to near normal. Highs in the low 60s inland and upper 50s can be expected. Ensembles have shifted toward a lull in precipitation Tuesday night with PoPs dropping to around 20-40% east of the Cascades. However, an area of low pressure and associated cold front are expected to bring another round of light rain on Wednesday. Rainfall totals Tuesday morning through Wednesday night have come down significantly for all areas. Areas east of the Cascades, including lowlands, Coast Range and Coast are expected to top out in the 0.15-0.35 inch range while the Cascades could see 0.50-0.80 with localized areas reaching 1.0 inches. Chances for 0.50 inches for the lowlands is around 10-25% with slightly better chances up to 40% in the Coast Range. The probability of 1 inch of rain for the Cascades during this same time frame is 20-40%.

Conditions Thursday trough Saturday trend drier and warmer with temperatures moderating back into the low to mid 60s on Thursday and low 70s on Friday and Saturday for inland locations. Shower activity could linger over the Cascades through Thursday but would remain very light. Uncertainty increases heading into the latter half of next weekend with the return of light precipitation possible. -19

AVIATION

VFR conditions prevail across the region tonight as a low pressure system offshore brings increasing BKN/OVC high clouds of 10-20 kft. Winds generally remain variable and around 5 kt or less across all terminals through 18z.

After 18-21Z Monday, a weak front associated with the low pressure system will lift northward over the area, bringing increasing southwest to west winds, lower CIGs, and increasing chances for rain showers. However, CIGs are very likely to remain VFR at all terminals through 00z Tuesday. Chances for MVFR CIGs increase first for KONP with a 30-40% chance after 00z Tuesday. Chances for inland terminals increases to 20-40% after 06z Tuesday as low clouds build westward off the Cascade foothills.

There is a low chance for an isolated thunderstorm or two around 00z Tuesday over the Cascades, foothills and/or Willamette Valley, however the probability for thunderstorms at any given TAF site is 10% or less.

KPDX AND APPROACHES...Predominately VFR conditions with CIGs between 10-20 kft. West-southwesterly winds increase Monday afternoon as the next front moves in, remaining under 10 kt. CIGs trend toward low-end VFR Tuesday evening and MVFR probabilities increase to 20-40% after 06z Tuesday. -19/10

MARINE

Benign conditions continue today and Tuesday. Winds shift to the southwest today then shift to the west on Tuesday, remaining at 10 kt or less during this timeframe. Seas 6 to 7 feet through today as a westerly swell continues to move in then gradually decreasing tonight into Tuesday to less then 5 feet.

An upper level low off the coast will support scattered light showers today with increasing chances through Tuesday. A northwest swell will also move into the waters, pushing seas back toward the 6 to 8 foot mark Tuesday night. A cold front is expected to move over the waters on Wednesday, bringing increasing seas and gusty winds. Wind gusts will approach 20 kt on Wednesday with a 30-50% chance for gusts reaching Small Craft criteria beyond 30 nm and only 10-30% within 30 nm for all waters. There is a 50-80% chance seas peak above 10 feet beyond 10 nm and a 20-30% chance for seas above 12 feet beyond 30 nm. Winds decrease by Wednesday night and seas lag, decreasing through Thursday.

Very strong ebb currents will continue across the Columbia River Bar each morning through Tuesday. Seas are expected to increase as a westerly swell moves into the waters this morning. Wave heights within the Columbia River Bar are expected to increase to around 9 feet with the very strong ebb current. Therefore, a Small Craft Advisory has been issued for the Columbia River Bar from 5 AM - Noon PDT Monday. -19/23

PQR WATCHES/WARNINGS/ADVISORIES

OR...None.

WA...None.

PZ...Small Craft Advisory from 5 AM early this morning to noon PDT today for PZZ210.