Sunrise 6:07 AM   Sunset 7:54 PM Moonrise 12:35 PM   Moonset 3:11 AM

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FXUS66 KPDT 172311 AFDPDT

Area Forecast Discussion National Weather Service Pendleton OR 411 PM PDT Wed Apr 17 2024

Updated Aviation Discussion

AVIATION
00z TAFs...VFR conditions expected over the next 24 hours. Sct low to mid clouds are present this afternoon over many sites, however clear skies are expected to prevail this evening onward, with light winds less than 10 kts. Winds will become terrain-driven overnight, then shift more north and east during the day Thursday. Evans/74

PREV DISCUSSION
/issued 217 PM PDT Wed Apr 17 2024/

SHORT TERM
Tonight through Friday
Forecast area will remain under a cool cyclonic flow through Thursday due to a closed low pressure centered over south central Canada. There will be some instability showers this afternoon and evening over portions of SE Washington and NE Oregon which will dissipate towards sunset. Then expect clearing skies and light winds overnight that will allow temperatures to lower to around freezing through early Thursday morning in the cold prone areas around the Lower Columbia Basin. A Freeze Warning has been issued encouraging the protection of plants that would be susceptible to damage due to cold temperatures.

Conditions Thursday will be very similar with temperatures being a couple of degrees warmer. Some shallow convective showers remain a very low chance (less than 15%) over the SE WA and NE Oregon mountains through the late afternoon and evening hours. Thursday night into Friday morning will also see temperatures lowering to around freezing in portions of the Lower Columbia Basin and further Freeze Warnings may be needed.

By Friday the low pressure over Canada moves eastward allowing a ridge of high pressure over the eastern Pacific to begin moving into the Pacific Northwest. Again, will see slightly warmer temperatures bring us back to near normal temperatures heading into the weekend.

LONG TERM
Saturday through Wednesday
The long term period will see a ridge over the area early Saturday give way as a weak system crosses along the Washington/British Columbia border Saturday afternoon through Sunday afternoon. Sunday night through Tuesday morning, another ridge will be over the area for dry and warmer weather. By Tuesday afternoon, models are in agreement about an upper low and trough affecting the area though there are substantial differences about the strength and location of the upper low and trough.

On Saturday, models are in excellent agreement in having the arriving system bring precipitation to the Cascades in the afternoon (30-40 percent increasing to 60-80 percent in the evening) and then to the eastern mountains Saturday night (30-50 percent chance). Snow levels will start out at 5000-7000 feet and drop to 3500-5000 feet overnight, so mainly rain is expected at pass levels. Rain amounts of 1 to 2 tenths of an inch are possible. A few model ensemble members put some light rain into the Blue Mountain Foothills Saturday evening, so a couple of hundredths of an inch is possible there. Temperatures will be a few degrees above normal with highs in the 60s and lower 70s. As the system arrives Saturday evening, tighter pressure gradients will bring 15 to 25 mph winds to the lower elevations which will continue into Sunday morning in the Columbia Basin.

A few light showers will linger Sunday in the higher mountains but otherwise dry conditions are expected Sunday and Monday. Cooler air brought in by the system will knock temperatures down a few degrees Sunday with highs in the upper 50s and 60s. The ridge will strengthen and build on Monday as an upper low and trough approaches out in the eastern Pacific. Temperatures will warm to the mid 60s to lower 70s with mainly lower to mid 60s in the mountains.

Models diverge on Tuesday as the ECMWF and Canadian have a deep low and front approaching the central British Columbia coast and the GFS has a weaker low and front approaching the southern Oregon and northern California coast. By Wednesday, the ECMWF and Canadian have the low at or near the central British Columbia coast. The Canadian is weaker and the low is located over northern Vancouver Island while ECMWF is stronger and the low is further northwest. The GFS has a weakening low come ashore near the Oregon/California border.
Models agree in having a chance of very light rain over the Cascades and eastern mountains with snow above 5000 feet. Amounts will be just a few hundreths of an inch. A southwest flow Tuesday will keep temperatures above normal with highs in the mid 60s to mid 70s with upper 50s to mid 60s in the mountains. Wednesday will be a degree or two cooler. Perry/83

PRELIMINARY POINT TEMPS/POPS
PDT 30 61 32 63 / 10 0 0 0 ALW 32 64 35 66 / 10 0 0 0 PSC 34 66 39 68 / 10 0 0 0 YKM 31 64 34 65 / 10 0 0 0 HRI 32 66 35 68 / 10 0 0 0 ELN 31 60 33 60 / 10 0 0 0 RDM 27 60 27 61 / 0 0 0 0 LGD 28 58 29 61 / 20 0 0 0 GCD 28 60 29 66 / 0 0 0 0 DLS 36 67 40 67 / 0 0 0 0

PDT WATCHES/WARNINGS/ADVISORIES
OR...Freeze Warning from 2 AM to 9 AM PDT Thursday for ORZ044-507.

WA...Freeze Warning from 2 AM to 9 AM PDT Thursday for WAZ026>029.

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