Area Forecast Discussion
Issued by NWS Pocatello, ID
Issued by NWS Pocatello, ID
915 FXUS65 KPIH 031011 AFDPIH Area Forecast Discussion National Weather Service Pocatello ID 411 AM MDT Fri May 3 2024 .SHORT TERM...TODAY THROUGH SATURDAY NIGHT... It may be hard to believe given that it`s snowing early this AM across portions of the forecast area, but we actually have some good news in the short-term! First though...a trough is sitting over us early this AM, supporting a mix of rain and snow for many areas. In particular, a zone of light to moderate snowfall is situated across the Arco and Mud Lake Desert region, Upper Snake Plain, and Teton Valley, slowly trending south with time. Temps very near freezing will make it difficult for the snow to effectively accumulate on roadways, but motorists across this region should still be prepared to encounter reduced visibility and localized slick or slushy conditions at times, and an SPS has been issued through 7 AM to highlight this risk. Accumulations should remain less than 1 inch on the most impacted roadways, with a bit more possible on some grassy and elevated surfaces. (This band of precip may be partially convergence-induced, although sfc wind fields are a bit messy.) All high-res models show general agreement in this band sinking south across the Lower Snake Plain and adjacent terrain between 5 AM and 11 AM morning (as a mix of rain and snow with very little if any accumulation south of Blackfoot in the Snake Plain), ending by noon at which point the good news begins as breaks of sunshine develop and high temps gain just a few degrees over yesterday`s readings! Ran with the NBM today, except we massaged PoPs, Sky, and QPF this AM to introduce very light snow accumulations along the path of this precip band and slow down its progression timing just a bit. We will continue to deal with frost/freeze potential for gardens and sensitive crops up the ern Magic Valley/Snake Plain corridor through Sat AM, but then high temps surge into the 60s and low 70s by Sat afternoon. We continue to note a trend toward a later onset of precip associated with the next approaching low pressure system...likely not occurring until sunset in our far wrn zones, and potentially as late as after midnight east of I-15. NBM guidance has been a bit slow to reflect this trend but is catching up, and we massaged PoPs lower in the forecast across the ern half of the CWA Sat eve based on consensus across both high-res and coarser deterministic models. (Also note Sat will be breezy regionwide.) Thus, once we clear this morning`s rain/snow out, almost two full days of drier (and eventually warmer) conditions are on tap! Enjoy the break while it lasts, as unsettled wx returns for most, if not all, of next week. 01 .LONG TERM...SUNDAY THROUGH NEXT FRIDAY... East Idaho begins the extended period under the influence of deep low centered over the northern Great Basin. Frontal passage early in the day along with broad precipitation shield expected to return region to very cool conditions with mountain snow and mix of valley rain/snow into Monday. Thunderstorms will be possible both days across portions of the region. Ensemble/NBM means total generally 3-6" of snow accumulations Sunday and Monday for most of the mountainous regions of East Idaho but high end 90th percentile estimates are significantly higher at the 8-12" range. Needless to say, Winter Weather Advisories will likely be needed for higher terrain zones as the system approaches unless the models take an unlikely drastic turn. Despite the cooler trend, overnight lows remain above freezing initially, so minimal accumulations are expected for the Snake Plain at this time. That said, QPF amounts tell a different story. Ensemble/NBM means run 0.50-1.0", and peak values at the 90th percentile over higher terrain reach around 2.0" of water. If the higher end percentiles can be realized, East Idaho waterways could expect additional rises in river/stream levels headed into the week. Upper low shifts toward the northern Great Plains Tuesday into Wednesday, transitioning into broad northwest flow over East Idaho. Conditions remain cool and below normal. Windy conditions Monday continue into Tuesday, with guidance supportive of Wind Advisories throughout the Snake Plain. Unsettled conditions continue with showers each day, and though temperatures remain cool, daytime should be warm enough for valley rain. Ensemble clusters support a return of a ridge along the coast by the end of the week. Cluster means and NBM keep enough influence of lingering stretched trough into the Great Basin, with only 10% of the ensemble membership pushing ridge axis over East Idaho by Friday. DMH && .AVIATION... Small but well defined shortwave feature dropping southeast through East Idaho early this morning producing a mix of wet conditions across the region. MVFR DZ/-SHRA to the south will give way to more consolidated band of IFR/LIFR -SN. Band is expected to gradually shift south from KIDA/KDIJ to KPIH around sunrise, then sag south through the southeast highlands and Bear Lake through about 18Z. Behind the band of snow, expect slow clearing back to MVFR. Generally VFR conditions are expected most areas by early afternoon, though a few afternoon build ups will remain possible. High VFR clouds are expected to spill across East Idaho overnight, but conditions should remain VFR headed into the beginning of the weekend. DMH && .HYDROLOGY... Moderate flooding remains ongoing at the Portneuf River at Pocatello with the level dropping today or Saturday before rising again early next week. Minor flooding continues for the Portneuf River at Topaz where the gauge remains above flood stage and will remain so for several days. Flood warnings also remain in effect for the Blackfoot River near Shelley at Wolverine Canyon where the river has gone above flood stage and also near Blackfoot where the river has also now gone above flood stage. GK && .PIH WATCHES/WARNINGS/ADVISORIES... Frost Advisory until 9 AM MDT this morning for IDZ051-054-055. Freeze Warning until 9 AM MDT this morning for IDZ052-053. && $$