FXUS65 KPIH 082048 AFDPIH Area Forecast Discussion National Weather Service Pocatello ID 248 PM MDT Wed May 8 2024 .SHORT TERM...Tonight through Thursday night. Remnants of the deep upper low refuse to give up impacting East Idaho with trough draped east-west across the state this afternoon. Mainly isolated showers remain possible through early evening as moisture works around the low and drops into East Idaho from Montana. Gusty northerly downslope winds are draining out of the Central Mountains and off the Divide, supporting slightly warmer but breezy conditions continuing tonight. Elsewhere through the Snake Plain, the downslope conditions are not quite as strong, so temperatures around/less than 36F are expected, supporting another night of Frost Advisory. Models support the trough dropping into Utah and briefly closing off over the Great Basin Tuesday, allowing the wrap around moisture to shift across mainly the southern highlands during the day. Thus showers and isolated thunderstorms will be possible mainly across the southern and southeast highlands in the afternoon. The gusty northeast gradient will continue, with the strongest winds centered across the Arco Desert region. Wind speeds may be marginal for Wind Advisory but hoisted the headline anyway as the northeasterly direction may catch drivers off guard along US-20 and US-26, especially those that commute those routes routinely. Northeasterly gradient continues into Thursday night, but slackens considerably. Strong possibility that one more Frost Advisory will be needed, particularly along zones containing the I-15 growing corridor. Could see a few pockets of fog in protected valley regions, and have retained the previous forecast. DMH .LONG TERM...FRIDAY THROUGH NEXT WEDNESDAY... This portion of the forecast continues to resemble a lunchmeat sandwich as an elongated W-E zone of low pressure...the leftovers of the active wx we've been munching on for days...sinks southward across the Four Corners region to central Plains, and a "tongue" of high pressure noses in on top of it eastward across the nrn Rockies from the Pacific. This overall synoptic configuration should whet our appetites for spring w/ drier conditions and a strong warming trend Fri-Sat-Sun with highs by Sun ranging from about 70 to 80 degF for most lower elevation population centers, but the proximity of low pressure to our south is close enough that we can't completely rule out some limited coverage of at least isolated afternoon shower/t-storm activity down across some of our SE highlands into Bear Lake, as reflected by light PoPs carried in our forecast courtesy of the NBM. Confidence in coverage of any precip is low, whereas confidence in dry conditions for MOST of the CWA is higher. Compared to this time yesterday, both long-range deterministic model solutions and resultant 500mb height cluster analysis are now a bit more progressive with trying to kick this low pressure zone out to the east by Sun-Mon, with perhaps some trend toward opening up the NW flow storm track and allowing fresh disturbances to take aim at our region during the Mon-Tue-Wed period next week. The strength of Pacific ridging will in part govern whether this storm track will be held further to our N/NE (keeping us dry) or will take better aim at SE Idaho , with the NBM for now brushing our ern highlands and Upper Snake Highlands with light PoPs from time to time and no significant reduction in overall temps. Height clusters are split on this as well. A tightening pressure gradient between the Pacific ridge and this storm track may tend to increase winds over these days, most notable diurnally during the afternoons. For now, no major airmass changes or significant precip events are expected, and we'll need to watch the impact warmer temps will have on mid-high elevation snowmelt and resultant river responses. - KSmith && .AVIATION... The world of aviation is SLOWLY trending less impactful as low pressure just to our east sinks southward and increasingly surrenders synoptic control to a tongue of high pressure nosing in eastward across the nrn Rockies off the Pacific. Showers at KDIJ and VCSH elsewhere continue, but will trend down this eve and end for the night by 02-05z/8-11pm depending on the terminal. Clouds are still widespread but are now VFR everywhere except KDIJ and will slowly rise/thin out as we head into tonight, reaching at least SCT coverage if not FEW. Winds remain breezy but generally not as strong as yesterday, and will relax slightly for the overnight. Biggest challenge through this eve is really to capture the timing as winds evolve from WSW to NNE everywhere but KSUN (which will be a runway crosswind at many airports)...current TAF thinking for this timing is based on a blend of MOS guidance and the latest hourly HRRR, with moderate confidence. Otherwise, main impacts will be occasionally MVFR cigs/vsbys continuing at KDIJ through about 00-01z/6-7pm when most rain/snow showers finally end, and the potential for criteria- borderline LLWS developing at KPIH after about 05z/11pm as sfc winds relax and decouple. This will be almost entirely speed shear as winds should be roughly out of the NE throughout the column. LLWS criteria are not currently expected to be met elsewhere across the forecast area, but this will be monitored. Heading into Thu, still can't rule out a few afternoon showers or even VCTS as departing low pressure is still too close for comfort, but with winds continuing to slowly relax day by day and a continued overall trend toward drier, calmer VFR wx as we round out the week and head into the weekend. - KSmith && .HYDROLOGY... Recent precipitation and warming temperatures are expected to influence East Idaho waterways in the coming days. Whatever snowfall was realized recently at mid-slope is likely to melt off, and temperature profiles support some snow melt at higher elevations. Flood Warnings remain in place for the Blackfoot and Portneuf rivers. High, fast, and cold flows are expected to continue and/or increase on other waterways. As the conditions turn warmer and drier, people recreating on/near East Idaho rivers and streams are urged to remain cautious, and keep children and pets away from the water. DMH && .PIH WATCHES/WARNINGS/ADVISORIES... Frost Advisory from 3 AM to 9 AM MDT Thursday for IDZ051-053-055. Wind Advisory from 10 AM to 7 PM MDT Thursday for IDZ052. && $$