textproduct: Pendleton

DISCUSSION

Current satellite imagery shows high clouds across Kittitas/Yakima Valleys extending to the Wallowas with few to scattered high clouds over north central and central OR. This will be lifted as the upper ridge moves through the PacNW, giving us a break today from wet weather over last few days. While the break may continue for tomorrow, light rain may develop along the upper slopes of WA Cascades due to a weak frontal system and upper shortwave. The NBM raw ensembles has a 20-40% probability for QPF amounts up to 0.10 inch. But overall, the deterministic models seem to favor mostly a dry period for tomorrow. With no precip developing, most flood stages for the Yakima rivers will continue to decrease during this weekend. However, Yakima river at Kiona will peak in Major flood stage at 16 feet this morning before gradually falling to moderate this evening and then Minor tonight. Naches rivers will be below Minor flood stage as well, but remains elevated as they drop to Action stage.

Monday through Wednesday: Starting Monday, we will see another atmospheric river (AR) event (IVT above 250-650 kg m/s) sweeping across our region. In addition to the frontal system, this will bring widespread showers along with a mix of mountain rain/snow for Tuesday night into Wednesday. NBM CONUS for Probability of 6-hr Precip show a 40-60% prob for wetting amounts exceeding to 0.30 inch at the crest of WA/OR Cascades and 30-50% prob for 0.15 inch or above over the Northern Blues. With this additional rainfall, Yakima river at Kiona may decrease from Minor but will then remain in Action flood stage. The remaining Yakima rivers and Naches rivers will stay elevated through Wednesday. This AR will also bring flash flood guidance to a slight risk (at least 15%) over the crest of WA Cascades, but marginal (at least 5%) at the crest of OR Cascades for Monday. Windy conditions will prevail across the Cascade gaps and Foothills of the Northern and Southern Blue mountains Monday before spreading over the remaining forecast area Tuesday into late Wednesday afternoon. Monday, sustained winds are expecting to reach to 12-20 mph with gusts of 20-30 mph with portions of WA/OR Cascades seeing gusts at 35-45 mph. Tuesday through Wednesday afternoon, these winds will grow stronger as the system continues across our region. Gusts may exceed to 45-55 mph over the aforementioned areas including Northern Blues. NBM CONUS has a 30-50% prob for gusts reaching to 60 mph for the upper slopes of WA Cascades and crest of OR Cascades around Tuesday evening, if materializes. Winds should begin settling down late Wednesday afternoon.

A mix of mountain rain/snow over the eastern OR mountains and mountain snow at WA Cascades will develop Tuesday night onward with the persistent system with temperatures dropping 5-10 degrees below as the cold airmass return. Thanks to the frontal system along with AR, we may see moderate to heavy snow developing along the upper slopes of WA Cascades. By Wednesday, ensemble guidance remains in good agreement of the arrival of a colder airmass that could decrease snow levels to about 2.5kft to 4kft north of the forecast area and above 3.5 kft southward, allowing snow to develop across our mountain areas, including portions of central OR by Wednesday. Snow levels may continue rising just above pass levels across our other Oregon zones Thursday with a rain snow mix in these areas. Confidence is about >60% for WA Cascades seeing up to 2 ft. Feaster/97

AVIATION...12Z TAFs

High pressure will remain anchored across the region over the next 24 hours. Probability for ceilings developing in the 1000 ft or lower range (IFR) are between about 10 and 20 percent, and based on the HREF ensemble forecasts it looks like PSC and YKM are the only two that have a realistic opportunity for that to develop, at best it looks only possible in the vicinity, not at the terminal. Light and variable winds (under 10 knots). Russell/71

PRELIMINARY POINT TEMPS/POPS

PDT 57 37 55 42 / 0 0 0 0 ALW 55 40 54 44 / 0 0 10 10 PSC 54 35 53 41 / 0 0 0 0 YKM 54 36 52 40 / 0 0 10 20 HRI 54 35 53 40 / 0 0 0 0 ELN 51 34 50 38 / 0 0 10 40 RDM 61 29 57 37 / 0 0 0 0 LGD 55 37 52 39 / 0 0 0 0 GCD 59 33 56 37 / 0 0 0 0 DLS 56 40 52 43 / 0 0 20 20

PDT WATCHES/WARNINGS/ADVISORIES

OR...None. WA...None.