National Weather Service (2024)

Area Forecast Discussion
Issued by NWS Portland, OR

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-- Discussion containing changed information from previous version are highlighted. --487FXUS66 KPQR 011731 AAAAFDPQRArea Forecast DiscussionNational Weather Service Portland OR1031 AM PDT Mon Jul 1 2024.SYNOPSIS...Offshore flow slowly decays as a strengthening ridgeof high pressure develops over the Pacific. This pervasive highpressure will cause temperatures to increase significantlythrough the end of the week.&&.SHORT TERM...
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Now through Wednesday...The shortwave trough thatbrought cloudy skies and drizzle over the last few days will continueto shift inland through the day. It will generally shift east of theCascades by this late afternoon. Once that trough exits, highpressure will begin to slowly build in. We will see steady warmingand clear skies over the next week or so, so if you like warmtemperatures...this forecast is for you! The ridge will reallyamplify on Wednesday night. Overall sensible weather wise, notlooking at anything overly impactful other than the fog this morning.Will note that with these dry conditions incoming, will see asteady decline of humidity, especially east of the Coast Range.Models have struggled with the areas that sit within thesubsidence inversion around 3000 ft and above so have manuallyedited to lower the RH in those areas. -Muessle.LONG TERM...Thursday through Sunday...The longer term forecastis really where the weather is occurring...though it isn`tnecessarily active weather. The main threat in the forecast, andwhere the most time has been spent, is in regards totemperatures. The synoptic pattern shows a strengthening ridgeforming with a thermally induced trough forming right along thecoastline. This ridge will continue to amplify through theweekend. But what does this mean for us? Models are showing asteading warming trend which will lead into several days of moreintense heat. In order to capture an overall view will notnecessarily dive into each day directly.Friday and Saturday look to be the warmest days of the comingweek which coincides with our general trend of "summer startson July 5th". The thermal trough will be quite deep at thispoint which will cause winds to be northeasterly at the upperlevels, but more northerly at the lower elevations. They will beslightly elevated which will help mix down some of the warm airaloft. At 850 mb (5000 ft AGL) temperatures are forecast torange from 20-25 deg C (70-75 deg F). Even further aloft at 500mb (18,000 ft AGL), temperatures range from -7 to -3 deg C(20-25 deg F). While these temperatures may not seem asimpressive, given their elevation and what we typically see,they are trending on the warmer side. When we see this pattern,it confirms that we are looking at hotter than normaltemperatures. In fact, if we look at the "Extreme ForecastIndex", we are on the higher end of what is climatologicallynormal, with this being mainly the case from Salem southward.At this time, there is still a lack of confidence in just howwarm those temperatures will be though. In Eugene, the globalmodels are showing a fairly narrow spread in high temperaturesfor Friday and Saturday. The 25th-75th percentile (most likelyrange) shows only a 5 degree spread in the low 90s on Friday,and around a 10 degree spread on Saturday. The NBM on the otherhand too has a 5 degree spread, but in the upper 90s to up to105 degrees with little change on Saturday. So what does thatmean forecast wise? At this point, confidence is still quite lowin regards to whether we will see extreme heat. Based on theglobal models, there is a 30% chance of exceeding 100 degrees onSaturday, and the NBM is closer to 50%. There is high confidencethat conditions will be hot...hotter than what we have seen thusfar this year. But confidence is low in regards to whether ornot we will see extreme heat. Luckily we will see some reprieveovernight as lows dip near 60 degrees in the areas that will seethe highest daytime heating. -Muessle
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Marine stratus continues to linger with IFR/MVFRconditions on the coast, and these lowered conditions are expectedto slowly push offshore/scour out through 20Z Monday. Theseconditions are expected to return (50-80% probability) to thecoast around 04Z-07Z Tuesday as a marine push is expected.Inland locations currently are seeing widespread VFR, with a fewexceptions as MVFR conditions are currently impacting areas northof KSPB. Locations with lowered flight conditions are expected toimprove to VFR around 20Z Monday. VFR conditions expected todominant for inland locations through the remainder of the TAFperiod, with the exception of areas north of KSPB as a renewedmarine push, could result in MVFR conditions along portions of theColumbia River. Could also see some backbuilding clouds off theCascades, that could bring MVFR conditions (45%-65% probability)to KPDX and KTTD starting around 10Z Tuesday.Inland locations will also likely see northerly gusts up to 20 ktstarting around 02Z Tuesday through 07Z Tuesday.PDX AND APPROACHES...MVFR conditions will improve to VFR through19Z Monday. Northerly gusts up to 20 kt starting around 02ZTuesday through 07Z Tuesday. Backbuilding clouds off theCascades, that could bring MVFR conditions (45%-65% probability)to KPDX starting around 12Z Tuesday. /42
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Weak high pressure over the northeast Pacific with lowersurface pressure over California and the Great Basin will more orless continue through the week. A weak front is in the process ofpassing through, but effects look fairly minimal, with lightnorthwesterly winds through Monday morning. Afterwards, expectNNW winds across the waters as high pressure strengthens towardthe middle of next week, with the strongest winds generally offthe central coast of Oregon and lighter winds farther north. Windswill generally peak in the afternoon and evening hours each day.Small Craft Advisory remains on track for the central zones, butzones further to the north still look fairly marginal. Because asa thermal low develops along the northern California/southwestOregon coast on Tuesday and strengthening/spreading north intoWednesday and thereafter. As a result will see an increase thepressure gradient along the coast and over the waters with a >90%chance that northerly wind gusts of 20-30 kt spread northwardacross the waters by mid week. This will in return develop steepwind driven seas of 5-8 ft with a dominant period of 7-8 secondsby late Tuesday or Wednesday.
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OR...None.WA...None.PZ...Small Craft Advisory from 5 PM this afternoon to 5 AM PDT Wednesday for PZZ253-273.
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