Area Forecast Discussion
Issued by NWS Pocatello, ID
Issued by NWS Pocatello, ID
644 FXUS65 KPIH 012122 AFDPIH Area Forecast Discussion National Weather Service Pocatello ID 322 PM MDT Sat Jun 1 2024 .SHORT TERM...TODAY THROUGH SUNDAY NIGHT... A weak shortwave trough crossing the region today and tonight might be able to spark off at least isolated showers and a couple t-storms (meaning most areas will hold dry for most of the period). Forecast soundings this afternoon suggest a gusty wind environment supported by inverted-V profiles, steep low-level lapse rates, and DCAPE over 1,000 J/kg, with the best overlap of instability (400-800 J/kg SBCAPE) and HREF simulated reflectivity down across the srn highlands and UT border areas. (Best chance for a few light showers in the Snake Plain is likely during the overnight hours tonight). The NBM continues to run too dry compared to a consensus of the HREF members, so manually increased and broadbrushed 10-30% PoPs across wider swaths of the forecast area today and tonight to cover whatever does manage to develop (leaning a bit on the NamNEST for our edits). Certainly not a washout for anyone! Zonal flow with some general troughiness continues Sun with best chance for additional showers/t-storms across the ern highlands, and mostly dry elsewhere. Winds will also start to increase Sun and may be near advisory criteria across the Arco Desert region, but given the marginal setup, the fact that this area is normally the windiest in our CWA anyway, and the fact that winds will be stronger Mon in comparison, have decided not to issue a WIND ADVISORY at this time. Further south, NBM4.2 blended guidance suggests winds will be very close to LAKE WIND ADVISORY thresholds over American Falls Reservoir, but the HREF and traditional MOS-based rules-of-thumb come in lower, thus we have not issued any alerts here either. Again, looking at the forecast wholistically, Mon looks like the more favorable day where we`ll be messaging at least some advisory-level wind impacts. Rain will also start moving into the Central Mntns Sun eve, but we`ll discuss this next storm in more detail below. 01 .LONG TERM...MONDAY THROUGH NEXT SATURDAY... Main focus of the long-term is on Monday, as an atmospheric river of moisture pounds portions of our Central Mntns (especially the Sawtooths) with rain over about a 24 hour period. On the one hand, the overall duration of this event is somewhat limited, mainstem rivers are not forecast to reach flood stage, temps are not excessively warm as far as how much high-elevation snowmelt they will support, and the heaviest QPF is likely to fall just north and west of our CWA (as a westerly flow does impact at least the wrn slopes and spine of the Sawtooths and adjacent mntn ranges from west of Ketchum up to Stanley), with less certainly regarding how much heavy rain might spill over east of ID-75. On the other hand, WPC is leaning into the 90-95th percentile of the NBM with their recommended QPF which we are using for our forecast yielding 1.00 to 2.00 inches west of Clayton and Ketchum and overnight lows may hold above freezing Sun night/Mon AM even at high elevations, so this is technically a rain-on-snow event with overnight lows above freezing and QPF over 1 inch, which is always something we approach with caution. The National Water Center is modeling as much as 1-2" of SWE melt to go along with 1-2" of QPF...overall quite a bit of water might be at play here, although again not all of it within our CWA border. Following a coordination call today, an upgrade to a SLIGHT RISK of Excessive Rainfall was introduced for the Stanley to Galena Summit corridor. A FLOOD WATCH was also discussed with neighboring WFOs, and for now we have opted to hold off given some of the mixed signals noted above and relatively low confidence on how this pans out for our area. Stay tuned. The potential certainly exists for impacts from small stream/creek flooding, runoff, and backcountry road erosion from late Sun night through Mon eve. Elsewhere across the rest of the CWA, showers and t-storms are expected Mon as well with lighter QPF amounts of 0.10 to 0.50 inches, and best instability during the afternoon. Expect cooler high temps generally holding in the upper 50s to upper 60s Mon as well. We already alluded to some wind...SW winds of 25-35 MPH with gusts over 50 MPH are currently forecast across the Arco Desert, Mud Lake, and upper Snake Plain region Mon afternoon, lower but still breezy elsewhere, so a WIND ADVISORY is looking likely. Beyond Mon, drier wx and a strong warming trend resume, with lower elevation high temps potentially approaching 90 by Thu and Fri. Next chance of a shower or t-storm returning to the mix is Thu eve. 01 && .AVIATION... A weak shortwave feature moving through the region today will provide for a few isolated thunderstorms this afternoon into evening, then a higher probability of more organized showers working across the region overnight. The thunderstorm threat today works mainly across higher elevations closer to the Montana and Utah borders, staying away from the terminals. PIH and SUN and DIJ might be the closest sites to potential threat, but not enough confidence to include even VCTS at this time. Afternoon convective build-ups are likely, however. Gusty outflows 35-40kts would be possible, especially to the south. VFR -SHRA work through mainly evening and overnight, with clearing expected around or after sunrise. DMH && .FIRE WEATHER... A weak shortwave passing through the area will bring a 10 to 30 percent chance for mostly dry thunderstorms, particularly in the southern half of the Eastern Highlands. While there is a slightly better chance for a few showers overnight into Sunday (20 to 40 percent chance), any QPF looks to remain light, less than a tenth of an inch. Highs today will be in the 60s and 70s again for most, though parts of the eastern Magic Valley and lower Snake Plain will warm to near 80 degrees F. Winds will gusts around 20 to 30 mph for most this afternoon with gusts near 35 mph in the Mud Lake area. Winds will back off tonight, but pick up once again for Sunday, Monday, and Tuesday afternoons with the strongest gusts up to 45 mph in the Mud Lake/Arco Desert area and gusts 30 to 40 mph elsewhere. A few showers linger around the Wyoming border Sunday morning, but our next system moves in Sunday PM through Monday and will bring measurable rain to almost everyone in eastern Idaho. The highest rain totals will be up in the Sawtooths/Stanley area where there is a 50 to 70 percent chance of at least a half inch of QPF on Monday. After Monday, we`ll dry out and warm up through the rest of the week. AMM && .PIH WATCHES/WARNINGS/ADVISORIES... None. && $$