Sunrise 5:39 AM   Sunset 8:32 PM Moonrise 8:09 AM   Moonset 12:06 AM

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FXUS66 KPQR 121015 AFDPQR

Area Forecast Discussion National Weather Service Portland OR 315 AM PDT Sun May 12 2024

SYNOPSIS
A shortwave trough will drop into the PNW Sunday into Monday and will bring cooler temperatures to the region.
Onshore flow will support marine stratus pushing into the Willamette Valley Monday morning. Ridging is expected to redevelop by mid-week and will support an upward trend in temperatures back into the upper 70s.

SHORT TERM
Now through Monday night...The upper level ridge axis now sits southeast of the CWA through southern Oregon and will continue to move southeast into the Great Basin through today. A shortwave trough off the PNW coast will move onshore late today into Sunday night. Flow aloft will become west/southwest surface slow remains onshore from the northwest.
Marine stratus has developed along much of the south and central Oregon coast and into the Coast Range Valleys. Stratus may try to advance farther east into the Willamette Valley around dawn but will struggle due to warmer temperatures. A few scattered clouds may pop up but shouldn't bring any impacts. Temperatures will be 8-10 degrees cooler across the Willamette Valley, peaking within a degree or two of 80. Temperatures along the coast will be 3-5 degrees cooler, peaking in the low to mid 60s after starting the day under stratus which should dissipate by noon.

The cooling pattern will continue into Monday as the shortwave trough axis passes over the Cascades Sunday night. Marine stratus is likely to develop tonight, with a better chance of reaching into the Willamette Valley as onshore flow increases.
Northwest flow aloft and onshore at the surface along with marine stratus in the morning will keep temperatures Monday afternoon much cooler. Low 70s are expected across the Willamette Valley, probabilities of highs reaching or exceeding 75 degrees range from 10-30%. Highs along the coast will struggle to make it out of the 50s though some of the valleys along the Coast Range will reach into the 60s. -Batz

LONG TERM
Tuesday through Saturday...WPC cluster analysis continues to favor ridge re- development by the middle of next week. Nearly all ensemble members display relatively strong and broad ridging by Wednesday next week, allowing temperatures to climb to the upper 70s in the latter half of the week. Agreement lessens into Friday as there is a 20-30% chance of a trough developing and pushing south into the region. This trough would bring more seasonable temperatures and light rain showers back to the area, but there is still not enough model convergence to be certain. Cluster analysis looks to be at a 50/50 in terms of a ridge vs trough developing into early next weekend, with either a broad ridge remaining overhead or a shortwave trough moving into the region. -JH/Batz

AVIATION
High pressure remains over the region, maintain mostly clear skies aloft. Thermal low pressure over the Cascades will move further eastward today, with increasing onshore flow today over much of the area. As such, IFR stratus along the coast will persist into this am, with patchy IFR stratus inland.Stratus will break apart and dissipate later this am into the afternoon, but may persist close to the beaches.

With stronger onshore flow later today into tonight, will see marine stratus reform along the coast (CIGS 1000-2000 ft) late this afternoon into this evening, with that stratus spreading inland overnight. Most of the interior will have stratus Mon am.

PDX AND APPROACHES...VFR today under most clear skies. Will see scattered clouds later today as onshore flow pick up. MVFR CIGS (around 2000 ft) will spread across Clark County late tonight, and over the PDX field between 10Z and 12Z Mon. /ROCKEY

MARINE
A summerlike pattern will persist through early next week as high pressure offshore and thermal low pressure shifting farther inland maintain moderate to strong northerly breezes for the next several days. Gradients will tighten just enough to allow winds to gust to 25 kt across the waters this afternoon, supporting low end Small Craft Advisories through late this evening. Winds will continue to follow a diurnal trend for the next few days, with additional rounds of small craft headlines possible each afternoon and evening. Seas will generally remain in the 4-6 ft range driven by northerly wind waves and a modest westerly swell. /CB/CCR

PQR WATCHES/WARNINGS/ADVISORIES

OR...None.
WA...None.
PZ...Small Craft Advisory from noon today to 11 PM PDT this evening for PZZ251>253-271>273.

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