861 FXUS65 KPIH 211020 AFDPIH Area Forecast Discussion National Weather Service Pocatello ID 320 AM MST Tue Jan 21 2020 .SHORT TERM...TODAY THROUGH THURSDAY NIGHT... The main weather-maker in the short term still will be an organized low pressure system moving NE over the Pacific and approaching the coast of British Columbia today. The main trough associated with this low remains just off the coast of CA/OR and will be the "main show" starting this evening. A pre-trough disturbance/ripple in the SW flow remains apparent in height analysis moving in SW Idaho. The previous forecaster mentioned that model guidance did an about-face and trended weaker/drier with this feature yesterday, and sure enough, a look at the high-res HREF ensembles and latest NAM/GFS runs is night-and-day compared to 24 hours ago when a wetter trend was noted. Thus, a few light, hit-and-miss snow showers will remain possible this morning, but accumulations should remain under 1 inch (and close to zero for most). The main trough will swing into the region tonight, with snow initiating before sunset this eve in the western Central Mntns and eastern Magic Valley (possibly mixed with rain here due to marginal temps), and then transitioning west to east across the CWA through mid-morning Wednesday. The west-facing slopes and higher peaks of the western Central Mntns (especially Sawtooths), and the Upper Snake Highlands/Tetons/Big Holes will see the greatest upslope enhancement and highest snow totals from this system, generally 2-5 inches. 1-3 inches is expected across the rest of the Central Mountains west of Challis and Arco, the Wood River Valley, southern highlands, Bear Lake region, and Caribou Highlands, with a dusting to 1 inch possible across the eastern Magic Valley, Snake Plain, and Big Lost/Little Lost River valleys. Our QPF/snowfall forecast sits comfortably near, or perhaps just slightly below, predominant clustering noted in the GFS/EC ensembles (with the GFS running a bit wetter as usual), and right on track with the NBM's 50th percentile. Even looking at the NBM's 90th percentile, amounts in the hardest- hit areas largely remain sub-advisory and the Snake Plain remains under 1 inch, so not expecting huge bust potential here and we will continue with no headlines/enhanced messaging at this time. We have also nudged winds up a bit higher overnight tonight and Wed, particularly focused over the Snake Plain and eastern Magic Valley using a composite blend of 96% NBM and 90% MAV/MET. These MOS guidance inputs demonstrate better skill than the NBM during breezier periods at lower elevations. This yields 10-20 MPH with gusts to 30 MPH in this corridor, with winds generally 10 MPH gusting to 20 MPH elsewhere across the region. That said, low temps only bottoming out in the lower 30s in this windiest corridor may help both new snow and the current snow pack to lean just slightly wetter/riper, not to mention the very light accumulations here. Thus, while we can't rule out some isolated pockets of blowing/drifting regionwide, we still do not expect this to be a major issue with this storm, a stark contrast to last week. The usual winter driving rules apply and should be our message to the public...check 511.idaho.gov before leaving, leave extra time to reach your destination, and slow down when encountering snow or slush on roadways. A ridge will build in Thursday, but a moist NW flow over the ridge may keep some light, low-impact snow showers going at times in our mountains. Accumulations should remain under an inch. - KSmith .LONG TERM...FRIDAY THROUGH NEXT TUESDAY... A fairly active and progressive weather pattern will continue in the long-term portion of the forecast, with multiple shortwaves/ disturbances moving through from Friday afternoon onward (yielding varying levels of low PoPs throughout the forecast). The GFS/ECMWF/Canadian continue to show some reasonable agreement on the wettest and most organized system impacting our region Sunday and Monday, and we continue to run with higher PoPs during this period than provided by the NBM. This system may end up having some decent QPF with it, but it remains too early to dive into further detail. Otherwise, let the NBM lead all forecast elements. Temps will continue to run above climatological norms for this time of year (matching well with the various CPC outlooks), meaning mixed rain/snow potential depending on elevation and diurnal timing of these systems. - KSmith && .AVIATION... Very weak system moving through the region this morning but sites have remained VFR and should remain so through the day. System moving through tonight is much stronger and do expect more widespread precipitation and MVFR to IFR conditions. Think IFR conditions limited to SUN and DIJ mainly after 00 to 03Z. Don't think BYI, PIH, and IDA will experience worse than MVFR conditions overnight. Will have a cold frontal passage late tonight and winds are expected to increase as well with 15 to 20 knot winds at BYI, PIH and IDA expected along the front 06Z through 12Z Wednesday morning. - GK && .PIH WATCHES/WARNINGS/ADVISORIES... None. && $$