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FXUS66 KPDT 010514 AFDPDT

Area Forecast Discussion National Weather Service Pendleton OR 1014 PM PDT Fri May 31 2024

Updated Aviation Discussion

AVIATION
06Z TAFS...VFR conditions are favorable during TAF period with current high clouds at BKN-OVC 100-250. Gusty winds will be at 15-30 kts with sustained winds at 10-20 kts around Saturday morning for KDLS/KPDT/KRDM/KBDN until late evening. Feaster/97

PREV DISCUSSION
/issued 218 PM PDT Fri May 31 2024/

SHORT TERM
Tonight through Sunday
Satellite imagery today showing very little going on except for some thin cirrus spreading east across the forecast area. Winds have generally be light and terrain driven today, with many lower elevation locations already warming into the low to mid 70s.

These quiet and dry conditions will persist through early tomorrow morning as a transient upper ridge continue to influence the region. By tomorrow morning, the ridge will have pushed east, allowing a weak/dry shortwave trough to slide across the PacNW.
Scattered showers will develop by tomorrow morning across the WA Cascades, spreading to the OR Cascade crest and the Wallowa mountains in the afternoon. Cross Cascade pressure gradients will tighten with the shortwave passage, resulting in breezy west winds generally 15-20 mph in the lower elevations, with locally windy conditions between 20-30 mph and gusts up to 40 mph developing through the Cascade gaps and across the Simcoe Highlands, Kittitas valley, and the OR Columbia Basin. Winds and shower activity will decrease Saturday night as the shortwave exits into ID and a brief westerly flow develops aloft.

The break from precipitation will be brief Sunday morning as a parent low in the Gulf of Alaska swings an upper trough towards the PacNW. A warm front will arrive ahead of the trough late Sunday morning, with a stratiform rain spreading east across the forecast area through the evening hours. Stratiform rain will turn to showers overnight Sunday into Monday morning as a cold front follows behind the warm front exit. Ensemble and deterministic guidance are in great agreement in an Atmospheric River accompanying the cold front passage overnight Sunday into Monday.
While the lower elevations will see some impact from the AR, the mountains, especially those susceptible to upslope enhancement in westerly flows, will see moderate to heavy rainfall through Monday. By the end of Sunday night, most lower elevation locations, Ochoco-John Day Highlands, and the southern Blue Mountain foothills will see 0.05-0.1 inches of rainfall; the northern Blue mountain foothills, Grande Ronde/Wallowa valleys, and lower slopes of the Cascades will see 0.15-0.3 inches; the northern Blues and Wallowas will see 0.3 to 0.6 inches; and lastly the Cascade crest and upper slopes will see between 0.6-1.0 inches with the higher amounts near/at the crest. As for winds, the warm front passage will result in locally breezy winds from the south southwest through the evening. Lawhorn/82

LONG TERM
Monday through Friday
An upper level trough will be pushing inland on Monday. The initial wetting rains of the system moving into the forecast area will give way to increasing westerly winds becoming windy by afternoon. Precipitation will turn to showers lingering mainly over the eastern mountains with a slight chance of thunderstorms. A westerly flow remains over the region on Tuesday continuing a chance of showers along the Cascade crest and over the eastern mountains while still maintaining breezy westerly winds.

Wednesday through Friday will see the building of an upper level ridge over the western USA. There are some placement issues of the ridge position in the models that still need to be considered but overall this period will be dominated by warming temperatures. High temperatures will reach 10 to 15 degrees above normal by Friday.
Other concern will be the increasing chance of convection over the Thursday through Friday period mainly over central and eastern Oregon. For now have just placed a slight chance of showers in the Thursday through Friday forecast because of the model differences in the placement of the ridge.

PRELIMINARY POINT TEMPS/POPS
PDT 49 76 51 71 / 0 10 0 30 ALW 53 79 54 74 / 0 10 0 30 PSC 55 81 56 74 / 0 10 0 30 YKM 53 77 49 69 / 0 10 0 40 HRI 52 80 55 74 / 0 10 0 20 ELN 52 71 48 66 / 0 10 0 40 RDM 47 72 46 69 / 0 10 0 20 LGD 45 72 47 71 / 0 10 0 20 GCD 47 75 46 73 / 0 10 0 10 DLS 56 76 55 69 / 0 0 0 50

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

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