Sunrise 5:55 AM   Sunset 8:04 PM Moonrise 8:22 PM   Moonset 5:04 AM

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FXUS66 KPDT 242341 AFDPDT

Area Forecast Discussion National Weather Service Pendleton OR 445 PM PDT Wed Apr 24 2024

Updated Aviation Discussion

SHORT TERM
Tonight through Friday night...An upper level trough will move across the Pacific Northwest tonight. Behind the front, Precip chances will increase from west to east beginning tonight. The Cascades will begin to see precipitation first generally through morning. During the morning hours, precipitation will move east of the mountains into central Oregon, the Yakima and and Kittitas Valleys and portions of the Columbia Basin and further east during the afternoon and evening hours. Precipitation should come to an end by later Friday over all areas except that mountains, where it will linger into Saturday morning.

Snow levels are fairly high 5000-6000 feet, lowering to 4000-5000 feet by Saturday morning. So, the majority of the precipitation will be in the form of rain except at the higher terrain, where snow could occur with some accumulations. Along the highest elevations of the Oregon Cascades, there could be a few inches but in most locations, less than an inch.

QPF values THursday into Friday are 0.50 inches or more along the Oregon Cascade Crest. 0.25 inches to 0.50 inches in the higher Washington Cascades and parts of the Wallowas. Generally 0.25 inches or less else where along the higher terrain and 0.10 inches or less in the lower elevations. QPF Friday into Saturday morning is lower. Generally 0.25 inches or less in the Oregon Cascade crest and .10 inches or less elsewhere and a not much if anything in central Oregon, the Columbia Basin, and Yakima Valley.
The ECMWF EFI continues to highlight and area of 0.8 to 0.9 along the Oregon Cascades.

Today's breezy winds will remain through the evening, then decrease through the morning. Thursday looks to have relatively light winds, but renewed breeziness odf 20 to 30 mph, possibly as high as 35 mph is possible again on Friday mainly across the Columbia Basin and Simcoe Highlands. NBM wind gust probabilities of >=39 mph on Friday are generally 50 to 60% across the Columbia Basin and Simcoe Highlands.

On Friday, there is also a low (20%) chance of thunderstorms mainly in the eastern Oregon mountains. the Storm Prediction Center has included portions of Wallowa, Union, Grant and Crook and Deschutes COunties in its Day 3 Outlook.

CAPE is generally 400 J/kg or less in this area Friday afternoon and rapid decreases after 00Z Saturday. LI values are between about 0 and -2 degrees C. So there there is at least some threat, albeit low at this time and we can see how this threat evolves over the next two days.

With the trough moving through temperatures will be at or below normal through the period.


LONG TERM
Saturday through Wednesday...Models are in reasonable agreement through the long term period in having a progressive and unsettled weather pattern though most precipitation will be confined to the mountains. Despite the progressive and unsettled pattern, the Extreme Forecast Index indicates no unusual weather through the period. Typical showery spring weather is expected. The main area of concern in the models are timing differences as to when various shortwaves will arrive but confidence is good in the overall weather pattern.

Saturday will see a departing trough and closed low over the Rockies while a trough and cold front in the Gulf of Alaska approaches the Pacific Northwest coast. Ahead of the front, a weak transitory ridge will be crossing the area which will give us slightly warmer temperatures with highs in the upper 50s to mid 60s and in the lower to mid 50s in the mountains. A westerly flow aloft will bring a slight chance of very light rain showers to the mountains. The greater concern will be west to southwest winds of 15 to 25 mph in the Columbia Basin in the afternoon, though at this point it doesn't look like it will reach wind advisory levels.

On Sunday, the upper low and trough will move to the central British Columbia coast and the front will move into our area though impacts will again be mainly breezy winds of 10 to 20 mph in the afternoon.
The mountains will again have a chance of very light rain showers with snow levels at 6000 feet. Temperatures will be a degree or two warmer than Saturday.

Monday through Wednesday, models are in general agreement in having the upper low and trough sink south offshore from British Columbia to the Washington coast, though model ensemble clusters have differences as to the timing and location of the closed low and trough and for the timing and strength of the shortwaves moving into the area each day. The shortwaves, aided by daytime heating, will give the mountains a 30-60 percent chance of showers each day while lower elevation rain will be confined to a 15-30 percent chance in the Blue Mountain Foothills. Showers will taper off during the overnight hours. Snow levels will be 4500-5500 feet. The mountains will get a tenth of an inch of rain or less each day while the amounts in the Blue Mountain Foothills will be barely measurable.
Temperatures on Monday will drop to the mid 50s to mid 60s with upper 40s to mid 50s in the mountains then warm a degree or two each day Tuesday and Wednesday. Breezy winds will return Monday afternoon but will be lighter on Tuesday and Wednesday. Perry/83

AVIATION
00Z TAFs...Skies are currently SCT-BKN with variable bases 8-15 kft, and clouds will thicken to BKN-OVC early Thursday morning. After 15Z, CIGS will lower to less than 10 kt as precipitation increases from the west. Guidance and forecast soundings continue to show DLS with CIGS down to 2500 feet so will keep in the forecast. WNW winds 10-15 gusting to 20-25 kt late this afternoon will decrease to less than 12 kts tonight. Winds will not be as breezy on Thursday. Wister/85



PRELIMINARY POINT TEMPS/POPS
PDT 41 60 45 61 / 0 60 70 40 ALW 46 65 48 64 / 0 60 80 60 PSC 46 65 48 68 / 0 50 30 20 YKM 41 60 41 66 / 0 50 20 10 HRI 45 64 46 67 / 0 50 40 20 ELN 40 58 41 62 / 0 50 30 20 RDM 36 55 39 55 / 0 60 50 30 LGD 39 60 43 56 / 0 50 90 70 GCD 37 61 41 56 / 0 70 80 80 DLS 47 58 48 61 / 10 80 60 30

PDT WATCHES/WARNINGS/ADVISORIES
OR...None.
WA...None.

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