Pocatello, Idaho

• Winter Weather Advisory continues until this afternoon for portions of the central Idaho mountains.
• Moderate rainfall amounts expected into the evening hours, then tapering off overnight and Monday morning.
• Cooling trend in temperatures continues today and tonight, then warming trend in the west on Monday, nearly all areas Tuesday.

Today through Tue night...The upper level pattern has a trough to the north over western WA this morning and a closed low over northern CA, both in alignment longitudinally. By this afternoon, this pair will be at the WA-ID border in the north and over Las Vegas to the south. Weak upper level flow with abundant moisture as it gets close should develop from this, with moderate and locally heavy rainfall amounts, with snow above 7500ft elevation during the day. By midnight, this trough-low pair has exited the Gem State and a north wind develops over the forecast area. This will shut off precipitation, save for where the northerly to northwest surface wind can find an upslope condition, such as in the eastern and southeastern highlands.

Continued cloud cover will cool temperatures some more today compared to Sat, then clearer skies in the west on Mon will allow temperatures in the western areas to warm at least a little. On the eastern side, temperatures will continue to cool due to the cold air mass moving in due to the northerly wind. On Tue, depending on fog formation, nearly all areas will see a leveling off of the previous day`s warming or a warming trend. Overnight lows plunge to the teens and 20s once the clouds are gone on Tue night, except in the eastern Magic Valley where they should hover around freezing.

Moderate to strong wind possible in the wake of the trough, especially in the mountains on Mon and to a lesser extent in the Snake River plain tonight.

Wed through Sat...Even late Tue night the individual deterministic model runs differ on the timing of the next trough, with the NAM already developing precipitation at the end of the short term period above. But most have it returning to the highlands that border UT and WY on Wed. Only one cluster of 9 percent of the ensemble runs have no upper level troughing over Idaho. The upper level zonal pattern keeps the forecast highly uncertain in timeing for Thu and Fri, while Sat in all clusters appears to be dry. However, changeability in the foreast is highest here in autumn. One thing that can be said is that there are no major upper level troughs making an approach to the US northwest coast during this period.

The main trend continues to be showery precipitation turning to light to moderate rain by early Sunday as precipitation increases over eastern Idaho. CIGs and VIS will also trend toward MVFR tonight. KSUN is already 4SM in moderate rain. There is potential for intermittent IFR conditions Sunday as precipitation rates increase and terminals experience locally moderate to heavy rain. Winds will turn gusty heading into Sunday evening/night.

Humidity remains high with a low moving through during the evening hours today. Moderate to locally heavy rain is likely. Wind is fairly weak save for the southern Sawtooth NF. A shift to northerly air flow late tonight keeps temperatures cool, especially once skies fully clear for Tue/Tue night. Wed through Fri continue unsettled, with weak impulses moving through a westerly flow that could trigger light showers and bring windy conditions. By Saturday, upper level ridging develops over Idaho as a more substantial low approaches the west coast.

Winter Weather Advisory until 5 PM MDT this afternoon for IDZ073-074.