textproduct: Portland

SYNOPSIS

Warm conditions persist today, though shower and thunderstorm chances increase later this afternoon and evening over the central Oregon Cascades and foothills as southerly to southeasterly flow develops aloft. Weak ridging will support inland highs in the low to mid 70s, with 60s along the coast. Activity becomes more widespread Friday into Saturday, with the greatest coverage over the Cascades. Cooler, unsettled conditions follow Sunday into early next week.

LONG TERM...Sunday through Wednesday night

A cool, showery pattern becomes established Sunday as the closed low settles over northern California and far southern Oregon. Wrap-around moisture on the northern periphery of the circulation will maintain scattered showers, especially during the afternoon. Precipitation probabilities range from 60-90%, highest over the Oregon Cascades and foothills. Thunder chances diminish to below 10% as instability weakens. Sunday is expected to be much cooler compared to Saturday, with lowland highs in the upper 50s to low 60s.

On Monday, ensemble cluster analysis indicates the low shifting southeastward, with northwesterly flow developing aloft. A weak embedded shortwave may move through during the day, maintaining a 60-85% chance of light showers across the Cascades and a 30-60% westward. Temperatures remain near to slightly below seasonal normals. Shower coverage decreases Monday night into Tuesday as transient ridging and westerly flow briefly build overhead. Attention then turns to the next Pacific frontal system expected sometime between late Tuesday and Wednesday. While timing differences persist among ensemble members (9+ hour arrival time difference), confidence is increasing that widespread rain will return during that window. Current NBM probabilities suggest a 40-60% chance of 0.25+ inches of rainfall over 24 hours between Tuesday evening and Wednesday evening across the lowlands, increasing to 50-75% in the Coast Range and Cascades. Probabilities of 0.5+ inches range from 20-35% in the lowlands and 35-60% in the mountains. Chances of 1+ inches remain around 5-10% across the interior valleys and 20-35% in the higher terrain. ~12

AVIATION

Current observations show VFR conditions mid to high level clouds slowly moving from south to north as southerly upper level flow persists across the airspace. Showers persist along the coast through around 09Z Friday. Otherwise, the airspace will remain relatively dry through around 18Z-22Z Friday. Afterwards, showers return and will take a south to north track over the airspace. Thunderstorms also return to the majority of the airspace with a 15-30% chance of thunderstorms also spreading south to north from 18Z Friday through 06Z Saturday. Have included PROB30 groups for KEUG, KSLE and KUAO as those sites currently have the highest probability. Other inland locations do have the chance for thunderstorms, but at this time, those chances are less than 30%. There is moderate confidence in that the probabilities of thunderstorms will increase with the 12Z TAF package.

It should be noted that locations that do see stronger showers or thunderstorms will have the potential for brief moderate to heavy rain, small hail, and gusty and erratic outflow wind gusts up to 35 kt. These showers could also result in periods of MVFR/IFR conditions, which will likely coincide with showers and thunderstorms.

KPDX AND APPROACHES...Expect predominately VFR flight conditions through the TAF period. Showers expected around 22Z Friday, with a 15-20% chance for thunderstorms starting around 00Z Saturday. Stronger showers or thunderstorms will have the potential for brief moderate to heavy rain, small hail, and gusty and erratic outflow wind gusts up to 35 kt. Showers/thunderstorms could also result in periods of MVFR/IFR conditions. /42

MARINE

Tranquil conditions are expected to persist over the coastal waters through early next week. North to west winds will continue over the coastal waters, before becoming southerly on Friday then becoming northerly again by Saturday, then more westerly by the start of the week. Winds expected to be below 20 kt through the weekend and into the middle of next week. Seas around 5 to 7 ft through the middle of next week as well.

There is a 5-10% chance of thunderstorms Thursday through Saturday afternoons across all waters. Any thunderstorms that do develop could produce hail, gusty and erratic winds as well as a less than 2% chance for a funnel cloud or waterspout.

It is unlikely Small Craft Advisory conditions will occur over waters at any point in time through Monday, aside from one potential minor exception. Between 4-9 PM PDT Thursday, marginal small craft advisory level wind gusts as high as 22 kt may occur over portions of the northern and central outer waters. Although probabilities for max wind gusts to peak around this range are fairly high at 30-50% over PZZ272 and it appears wind gusts of this magnitude would only occur for a 1-3 hour period at any given location. Given seas are only expected to range between 5 and 6 ft at that time, have decided not to issue a Small Craft Advisory as conditions appear too marginal and short-lived to justify a headline. /42-23

PQR WATCHES/WARNINGS/ADVISORIES

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