FXUS66 KPDT 271130 AAA AFDPDT

Area Forecast Discussion National Weather Service Pendleton OR 430 AM PDT Sat Jul 27 2024

Updated Aviation Discussion


SHORT TERM
Today through Saturday...

Bottom Line Up Front

1. Winds return today and through the weekend

2. Precipitation chances begin Monday

3. Thunderstorms along the eastern mountains Monday afternoon with precipitation across the area.

Models are in firm agreement with the west south west flow aloft over the region. Dry conditions will persist with the weak trough like pattern that will remain over the region through the weekend.
Surface pressure gradients has tightened ever so slightly with this pattern that the typical suspects will see increased winds over the weekend. 90-100% of the raw ensembles show the Gorge and Kittitas Valley will see sustained winds near 20 mph both Saturday and Sunday afternoon through evening. 60-80% of the ensembles show a smaller area through the Gaps where gusts to 30 mph will occur.

Monday models show an upper level trough begins to slide down the BC coast and make its way into the PacNW. This will cause a slight uptick chances of seeing some moisture move into the region, mostly along the Cascades. Raw ensembles show there is a 40-60% probability that the WA Cascade crests could see near 0.05 inches of precipitation. The lower elevations will have a 10-20% probability of also seeing 0.05 inches of rain. A bit of a change from the last few weeks of hot an dry.

The incoming trough will bring with in increased chances of thunderstorms for the eastern mountains. Model derived sounds over the area shows MUCAPE values to increase into and above 300 J/kg with lifted index of -2 and bulk shear nearing 35 knots, however, mid level lapse rates are relatively low in the 6.3 C/km. These storms have the signs of being mostly orthographically lifted and will be isolated across the eastern mountains. Confidence in these storms developing remains relatively low with confidence ranging from 15-30%. Bennese/90

LONG TERM
Tuesday through Saturday...Models and ensemble clusters are in good agreement on moving a shortwave trough across the region during the daytime hours on Tuesday. This will push a weak cold front across the area with a few light showers ahead of the front (20-40% POPS) mainly from the Blue Mountain Foothills eastward. The available guidance suggests there may be just enough instability for a slight chance of thunderstorms (15-24%) for the eastern mountains with the best potential over Wallowa County. The current timing of the trough has it exiting into Idaho in the afternoon, so any storms that do develop will end by mid to late afternoon.

The rest of the week will be characterized by the southern U.S.
upper ridge building northwestward back into the region bringing a significant warm up with triple digit heat in the lower elevations by Friday. The deterministic ECMWF and GFS is much warmer than the NBM and ensemble guidance from both aforementioned models. For now went with the NBM which has the warmest day on Friday with high temperatures of 100-103 in most locations below 3000 feet MSL. As the temperatures get hotter at the end of the week instability will be increasing. By Saturday afternoon an axis of 500-1000 J/kg surface based CAPE may develop up along the Cascades. Forecast soundings show significant convective inhibition however, and a lot of mid-level dry air. NBM Probabilities of TSTMS on Saturday are 10- 14%. Convective potential will have to be monitored in the coming days to see if thunderstorms need to be introduced into the forecast for Saturday.

Another concern for Friday into Saturday is fire weather. As of now the 00Z GFS is forecasting widespread Haines 5 and 6 across the forecast area. With the hot temperatures and potentially low RHs fire weather concerns could become elevated late in the week. 78
Show more