Sunrise 5:46 AM   Sunset 8:12 PM Moonrise 12:53 AM   Moonset 8:30 AM

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PZZ135 Puget Sound And Hood Canal- 859 Am Pdt Mon Apr 29 2024
Today - S wind to 10 kt. Wind waves 1 ft or less. Tonight - SW wind 5 to 15 kt. Wind waves 2 ft or less. Tue - S wind to 10 kt becoming N in the afternoon. Wind waves 1 ft or less. Tue night - NW wind to 10 kt becoming S after midnight. Wind waves 1 ft or less. Wed - S wind 5 to 15 kt. Wind waves 2 ft or less. Wed night - SW wind 5 to 15 kt becoming S to 10 kt after midnight. Wind waves 2 ft or less. Thu - S wind to 10 kt becoming w. Wind waves 1 ft or less. Fri - Light wind becoming S to 10 kt. Wind waves less than 1 ft becoming 1 ft or less.

PZZ100 859 Am Pdt Mon Apr 29 2024
Synopsis for the northern and central washington coastal and inland waters - A weak surface low will pass across the southern offshore waters this morning with rough seas and breezy conditions continuing. Another weak surface low will cross the area waters on Tuesday. High pressure will build across the region Tuesday and Wednesday before yet another weak surface low and attendant cold front move across the region Wednesday night into Thursday.

FXUS66 KPDT 291533 AFDPDT

Area Forecast Discussion National Weather Service Pendleton OR 833 AM PDT Mon Apr 29 2024

UPDATE
Latest water vapor imagery shows a well defined upper trough moving into the area at the present time. This feature will be responsible for scattered to numerous showers and mountain snow showers today. Cold temperatures aloft and 700-500 mb lapse rates of 8 C/KM will contribute to sufficient instability (200-500 J/KG)
for isolated tstms from the eastern part of the Columbia Basin to the eastern Mountains (SPC HRRR Probabilities this afternoon 15-30%). Otherwise Winter weather advisories continue for the east slopes of the Cascades until 1100 AM. Snotels and CAMS suggest that only a few inches of snow have fallen in these areas thus far. Winds will pick up this afternoon across the lower elevations with sustained west winds 20-25 mph and gusts 30-38 mph. Made a few minor adjustments to winds and sky cover for this mornings forecast update but otherwise the current forecast is on track. 78

PREV DISCUSSION
/issued 236 AM PDT Mon Apr 29 2024/

SHORT TERM
Today through Wednesday
Water vapor satellite imagery tonight shows a shortwave trough approaching the PacNW, while nighttime imagery shows areas of low to mid level clouds over the mountains, and mid to upper level cloud decks developing across the Columbia Basin. Meanwhile, while the radar shows little to nothing east of the Cascades, precipitation bands are currently impacting western WA and northwest OR. Today, the shortwave trough offshore will swing across the PacNW, increasing chances of mountain snow early this morning, with light precipitation across the lower elevations developing late in the morning through the mid afternoon hours. The main focus of this system will be the lowering snow levels facilitating moderate to locally heavy snowfall across the Cascade crest. NBM still indicates great chances of reaching 6 inches of snowfall through 11pm tonight along the Cascade crest, with a 70-80% chance above 4kft, while below this elevation chances fall to only 40-45%. The US97 corridor through central OR will see very little of this snow fall, with up to 2 inches in the Sunriver/LaPine area possible. An isolated thunderstorm or two will be possible this afternoon across the eastern mountains, supported by steep low level lapse rates and afternoon SBCAPE increasing up to 250-300 J/kg. The shortwave trough passage will also result in breezy to locally windy westerly winds developing this morning through the afternoon hours. Current guidance indicates that the surface pressure gradient between PDX- GEG will only peak around 9mb, and while this will result in breezy sustained winds 20-30mph with locally 35mph, this gradient is not conducive for widespread advisory- levels winds. Also, guidance continues to show very little jet support in the lower to mid levels, with 850mb and 700mb winds only peaking around 40mph; confidence is low (20%) that wind gusts will exceed 45mph at the surface.

Tonight through Tuesday afternoon, a weakening stacked low will make a pass across the PacNW, renewing chances of light snow in the mountains and light rain across the lower elevations. While confidence is only moderate (45-55%) for up to 1-1.5 inches of snow in the most mountain areas, the OR Cascade crest looks to be favored again, with NBM probabilities indicating a 80-95% chance of 2 to 3 inches of snowfall. With a cold core aloft and increasing surface based CAPE, a few isolated thunderstorms will be possible in the afternoon across portions of northeast OR and far southwest WA. Breezy westerly winds will continue Tuesday, with only 15-25mph sustained winds and gusts up to 35-40mph expected.

Wednesday, the remnants of the upper low will move east of the region, with a weak northerly flow over the intermountain PacNW.
While most of the forecast area will remain dry, wrap-around moisture from a low over the far northern Great Plains will result in continued light snow chances across the northern Blues and the Wallowas, with light rain across the lower portions of Union and Wallowa counties. Light to locally breezy winds will develop by the afternoon in the lower elevations, though a decent cross Cascade surface pressure gradient will result in breezy northwest winds through the Kittitas valley. Lawhorn/82

LONG TERM
Thursday through Monday
Forecasting the long term period continues to be a frustrating endeavor as ensemble guidance remains out of sync, especially next weekend onward. As a result, forecast confidence after Friday is low (30-40%), but at least the remainder of the work week looks a bit more solid across guidance, with higher confidence in the 60-70% range.

The PacNW will find itself under NW flow as a broad area of low pressure develops over the northern Plains states. There is disagreement amongst guidance on whether or not a shortwave embeds itself into this NW flow, which would yield greater chances for precip outside of the mountains, but QPF ensembles do suggest at least a slight chance of precip occurring across the Basin on Thursday, with PoPs in the 20-30% range. Such a NW flow pattern would favor better precip chances over the central Washington Cascades and the eastern mountains, while PoPs fall off heading south towards central Oregon and the Oregon Cascades.

Guidance then depicts transitory ridging building in sometime around Friday, however the upper-level pattern is progressive enough such that pinning down timing is difficult. This is because, across deterministic guidance over the weekend, the ECMWF depicts a low coming in from the northwest, while the GFS suggests a system will arrive from the southwest. Ensemble guidance suggests that a low of some kind will impact the forecast area next weekend, but the origin of this system and where it ultimately centers itself remains uncertain. A more northwesterly system would mean colder air and potentially mountain snow, while a southwesterly system would advect in warmer, more moist air and potentially spawn thunderstorms in the forecast area. So based on guidance, we can say confidence is moderate to high (50-60%) that a low and thus precip of some kind will impact us next weekend, but details are elusive until guidance gets a grip on where exactly this low comes from.

Despite the continuous model discrepancies over the past several days, ensemble clusters are strangely in agreement around the tail- end of the period, suggesting yet another, broader low will usher in SW flow aloft into the forecast area. Can't speak with too much confidence this far out, but the first week of May does look to be semi-active as we head into the beginnings of the warm season.
Evans/74

AVIATION
12z TAFs
VFR conditions expected, with gusty winds becoming a concern yet again for the period. A frontal system will move through the forecast area today, bringing with it gusty winds and light showers. Precip is expected to be light, and MVFR conditions are not anticipated as a result, however cigs may approach MVFR levels at times under shower activity. Snow may mix in with rain at BDN/RDM, however no accumulations are expected. Winds will primarily be out of the west, with gusts approaching 30 kts at times, possibly higher at sites like PDT and DLS. The precip threat is expected to end by the mid afternoon, however breezy conditions may persist well into the evening hours tonight. Evans/74

PRELIMINARY POINT TEMPS/POPS
PDT 54 34 54 34 / 60 10 30 20 ALW 56 37 57 37 / 70 30 40 20 PSC 61 42 61 40 / 40 10 20 10 YKM 58 35 56 34 / 50 10 20 0 HRI 60 39 59 37 / 40 10 20 10 ELN 54 34 54 35 / 50 20 20 0 RDM 49 27 48 27 / 50 10 30 10 LGD 49 30 49 32 / 80 20 50 40 GCD 49 27 50 30 / 80 10 40 30 DLS 57 38 57 39 / 80 20 30 10

PDT WATCHES/WARNINGS/ADVISORIES
OR...Winter Weather Advisory until 11 AM PDT this morning for ORZ509.

WA...Winter Weather Advisory until 11 AM PDT this morning for WAZ522.

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Des Moines
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Mon -- 01:58 AM PDT     Moonrise
Mon -- 03:45 AM PDT     7.95 feet Low Tide
Mon -- 05:54 AM PDT     Sunrise
Mon -- 07:45 AM PDT     9.77 feet High Tide
Mon -- 09:34 AM PDT     Moonset
Mon -- 03:36 PM PDT     -1.07 feet Low Tide
Mon -- 08:18 PM PDT     Sunset
Mon -- 11:31 PM PDT     11.58 feet High Tide
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Des Moines, Washington, Tide feet

Duwamish Waterway
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Mon -- 01:59 AM PDT     Moonrise
Mon -- 03:48 AM PDT     7.48 feet Low Tide
Mon -- 05:54 AM PDT     Sunrise
Mon -- 07:41 AM PDT     9.20 feet High Tide
Mon -- 09:34 AM PDT     Moonset
Mon -- 03:39 PM PDT     -1.00 feet Low Tide
Mon -- 08:19 PM PDT     Sunset
Mon -- 11:27 PM PDT     10.90 feet High Tide
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Duwamish Waterway, Washington, Tide feet

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