Area Forecast Discussion
Issued by NWS Pocatello, ID
Issued by NWS Pocatello, ID
826 FXUS65 KPIH 170857 AFDPIH Area Forecast Discussion National Weather Service Pocatello ID 257 AM MDT Mon Jun 17 2024 .SHORT TERM...Today through Tuesday night. Satellite imagery shows shortwave feature working through Oregon early this morning. Radar imagery indicated showers have begun to creep towards the western edges of the forecast area, with some light returns and perhaps a sprinkle or two across the Island Park area where southwest flow appears to be aiding orographic lift. Upper low is projected to swing into the Idaho panhandle through the day, swinging cold front through the region, along with associated showers/storms and of course, wind. Most of the convection should be confined to the central mountains/Island Park/northern half of the eastern highlands today, but the HREF including the NAM nest and the HRRR appear to drag a band of convection across the Upper Snake area this evening as well. Given the cooler temperatures, the storms are not expected to be particularly strong. Winds are the next impact of concern today, and a Wind Advisory is in place for a significant portion of the Snake Plain. Have extended the Wind Advisory across the northern portions of the Eastern Magic Valley, namely the Shoshone zone. If stronger winds can materialize toward the higher end of the probabilities (90th percentile - 1 in 10 chance of exceedance), the Arco Desert/INL region could reach into the lower end of High Wind Warning, but right now there is little confidence in this scenario materializing, given the cloud cover and expected precipitation during peak wind hours. Winds drop off rapidly this evening. Unseasonably cool temperatures today lead to very cold temperatures tonight. A Frost Advisory is in place for tonight for the entirety of the Snake Plain, with temperatures dropping to or below 36 degrees. Caveat - the urban centers through the I-15 and I-86/I-84 corridors may remain just above those temperatures. Nevertheless, covering gardens and bringing sensitive plants indoors where possible might be prudent. Another round of showers is expected during the day Tuesday, mainly north. Temperatures remain very cool, with lower elevation daytime highs in the 60s. Another round of cold temperatures is expected Tuesday night, though slightly warmer than tonight. Another Frost Advisory is likely, mainly for the upper portions of the Snake Plain. DMH .LONG TERM...Wednesday through next Monday. We will see a significant transition from the unseasonably cool and unsettled conditions on tap for early this week to much warmer and drier conditions by late week into the weekend. EPS and GEFS ensemble means are in good agreement showing the upper low responsible for the active weather in the short term filling and shifting well northeast of the area by early Wednesday, leaving the region in a weak southwest flow aloft between a remnant weak trough axis along the West Coast and expansive ridging over the Eastern CONUS. The main impacts of this forecast period may come at the onset with another unseasonably cool morning on tap Wednesday morning, although not as cold as the previous night. Still it appears that temperatures may again dip into the mid 30s in parts of the Snake Plain primarily north and east of Pocatello, potentially yielding one more round of frost concerns. Current NBM probabilities show a 40-60% chance of temperatures falling below 36F Wednesday morning in these areas. Beyond Wednesday morning, a notable warming trend will commence under progressively rising heights amid a continued weak southwest flow aloft. High temps will climb 8-10 degrees Wednesday and another 8-10 degrees Thursday, putting values some 5-8 degrees above normals by Thursday, quite the swing from the 20 degree below normal values expected today. This warming trend will continue into the weekend as shortwave ridging amplifies ahead of a system approaching the BC coast, likely pushing lower valley highs into the lower 90s and higher elevations into the 70s and 80s. Current NBM probabilities suggest a roughly 50-70% chance of highs in the Interstate corridor from Burley to Pocatello to Idaho Falls eclipsing the 90F mark by Sunday. WPC cluster analysis shows fairly strong agreement for this pattern, although by early the following week toward the end of this forecast period we start to see some differences emerge with the strength of the upper low skirting east along the Canadian border. About 40% of the cluster membership shows a stronger system, which would support cooler temps toward the end of the period, while the other 60% advertise a weaker system and resultant warmer temps. A stronger system passing to our north would also lead to stronger winds Sunday/Monday. Precipitation chances appear minimal through the long term period, although a few light showers cannot be ruled out with weak shortwave impulses riding through the flow. Friday across the Eastern Highlands currently looks most favorable for any such light shower activity. Overall, a pronounced warming trend and primarily dry conditions will be the theme from mid-week into the weekend. KB && .AVIATION...An unseasonably strong low pressure system and attendant cold front will push across the region today, bringing strong winds and shower/thunderstorm chances to the terminals. Although a few light showers may impact any of the terminals, KDIJ will be favored for more prevailing shower activity both along the front and with wraparound showers around the low. Primarily VFR conditions are anticipated, with reductions to MVFR possible in heavier showers. West/southwest winds ramp up this morning, with KPIH and KIDA seeing the strongest winds, where gusts will increase to around 35 kts this afternoon. Winds will dissipate late this evening, becoming light after 06Z Tuesday. KB && .FIRE WEATHER...An upper-level low pressure system and attendant cold front will push across the region today, ushering in an unseasonably cold airmass. High temperatures today will run roughly 20 degrees below seasonal normals for mid June, struggling to reach 60F in many of the lower valleys except along the UT border. Today will be the coldest day of the next week, with a steady warming trend beginning Tuesday as the low pressure system weakens and shifts northeast of the area. Cold overnight lows can be expected the next couple of nights, falling into the 30s even at low elevations. Westerly winds will crank up today with the cold frontal passage, and will be strongest in the Snake Plain and Eastern Magic Valley, where gusts of 40-50 mph are expected (40-70% chance of gusts exceeding 45 mph). Precipitation chances will also accompany the storm system today and tonight, including high-elevation snow above 6500 ft. Ridgelines in the Central Mountains above 8 kft could see several inches of heavy wet snow. For lower elevations, showers and embedded thunderstorms will accompany the upper low and cold front today into tonight. Higher precipitation amounts favor northern portions of the forecast area from the Central Mountains east along the Montana Divide. Chances for greater than 0.1" of liquid precipitation exceed 70% from the Sawtooths east into the Island Park area, but drop off sharply to less than 20% south of a Hailey to Blackfoot to Afton, WY line. Some light precipitation will linger into Tuesday primarily from the Central Mountains east along the Divide into the Eastern Highlands on the backside of the upper low. Dry conditions then return for Wednesday, along with warming temperatures climbing above average by late week. Temperatures continue to climb into next weekend, reaching the low 90s in lower valleys. We may see increasing winds again by late next weekend as a low pressure system passes to the north. KB && .HYDROLOGY... The flood warning has been dropped for the Snake River as Heise as flooding is no longer expected as river levels continue to drop. Warning remains hoisted for the Teton River at Driggs. Water levels remain very close to flood stage, but are still forecast to drop. The warning can likely be dropped today if the forecast comes to fruition. McKaughan/DMH && .PIH WATCHES/WARNINGS/ADVISORIES... Frost Advisory from 2 AM to 9 AM MDT Tuesday for IDZ051>055. Wind Advisory from noon today to 8 PM MDT this evening for IDZ051>054. && $$