Area Forecast Discussion
Issued by NWS Pocatello, ID
Issued by NWS Pocatello, ID
479 FXUS65 KPIH 042021 AFDPIH Area Forecast Discussion National Weather Service Pocatello ID 221 PM MDT Sat May 4 2024 .SHORT TERM...Tonight through Sunday night. A powerful storm system will move in from the Pacific tonight and quickly move east with a strong cold front moving through eastern Idaho Sunday morning. Precipitation will overspread all of southeast Idaho overnight. Snow levels will start out at over 9 thousand feet and quickly drop to 5 to 6 thousand feet in the southern hills and raft river region and winter weather advisories have been issued there Sunday morning through Sunday night as some accumulations are expected with up to a foot over 8 thousand feet but snow levels dropping to 4 to 5 thousand feet overnight could cause some travel issues in interstate 84 south of Burley to Utah. The winter storm watch has been upgraded to a warning from noon Sunday through Monday night in the Bear River Range where again a foot or more may fall at the highest elevations. Winter weather advisories have been issued for the eastern mountains beginning Sunday night through Monday night. Again overnight Sunday into Monday morning could see travel problems in the eastern highlands as low elevations seeing 3 to 5 inches through Monday with much higher amounts above 6000 feet. Rain amounts over a half inch are likely in the Snake River Plain Sunday into Monday with over an inch possible in the southern and eastern mountains liquid amounts. Snow levels will be threatening to drop to valley floors late Sunday night and Monday morning so again there is a low probability of light accumulations from American Falls through Pocatello to Idaho Falls late Sunday night into Monday for now have it limited to around a half inch. So it will be a very high impact short term period with wind, rain and snow affecting everyone. It will be much colder Sunday with highs in the 40s and 50s and lows Sunday night into the 20s and 30s. Lows overnight tonight will be in the 30s and 40s. GK .LONG TERM...Monday through next Saturday. Scattered rain and snow showers will continue into Monday and Tuesday as a H5 low and negatively tilted trough shift eastward onto the Great Plains. Seasonably cold, well below normal temperatures will be the going trend for early next week with highs in the 30s/40s/50s each day with overnight lows around or below freezing. Given the placement of the low now to our east to start next week, better chances for accumulating snow will shift to being confined to ERN Idaho where snow levels support a mix of rain/snow in the valleys and predominant snow in the mountains. Light snow will also continue to be possible across the CNTRL Mountains as more moderate accumulation potential remains in ERN Idaho. While there continues to be uncertainty regarding snow levels, roadway surface temperatures will be the main focus of transportation impacts and with colder air settling in for early next week, this could present hazardous travel conditions at times. In addition to precipitation, winds will also remain elevated Monday and Tuesday aided by 30-45 kt 700 mb winds aloft and an enhanced PGF which will support gusts around 30-50 mph with locally stronger gusts across the Snake Plain and Magic Valley to around 50-65 mph. Additional WIND ADVISORIES will likely be needed to capture these strong winds as lighter winds return midweek. The passage of a shortwave trough Tuesday will keep precipitation chances going into Wednesday and also aid in keeping temperatures well below normal given its track from WRN Canada. By Wednesday with the bulk of moisture now confined east of the Continental Divide, showers will see a decrease in areal coverage as drier conditions progressively return later in the work week. This drier progression will be aided by a well defined H5 ridge building into the NE Pacific and WRN CONUS which will begin to force moisture east. As a result, 70% of ensemble clusters show a well defined ridge building into our region late next week with around 60% of clusters also favoring a Rex Block to establish which would mean a H5 low over the SW CONUS, splitting off of the main H5 low circulation on the Plains. The other 30% of ensemble clusters show this low further north across the NRN Great Basin which would mean continued isolated showers. This is split nicely amongst the ECMWF favoring the 70% solution while the GFS favors the 30% solution with latest guidance. The NBM continues to favor more closely to the ECMWF which means gradually warming temperatures through the weekend as conditions remain dry but does keep some elements of the GFS with very isolated mountain showers. The NBM 50th percentile high temperatures starting Friday through the weekend show highs returns to the 60s/70s with the potential for even some low 80s across our lowest elevations which could mean the warmest airmass we have seen so far this year. MacKay && .AVIATION...For the 18Z TAFS through 18Z Sunday. Predominant VFR and dry conditions will continue through this evening as mid/upper-level clouds increase out of the west associated with our next incoming system. Ahead of the arrival of precipitation, winds will increase out of the south as a mix of rain/snow builds in tonight through Sunday morning. MVFR CIGS/VIS will be possible as moisture builds into the region with a slight chance for IFR CIGS/VIS associated with moderate to heavy precipitation at times. The HREF model probability of thunder also shows a 10-20% chance of thunderstorms at KBYI and KSUN through 12Z Sunday morning. Those thunderstorm chances will increase and shift east for Sunday afternoon into Monday morning where a 20-50% chance will exist at KPIH, KIDA, KBYI, and KDIJ with less than a 10% chance at KSUN. Confidence remains low on Sunday regarding precipitation type at times giving varying snow levels but confidence remains high on breezy winds continuing into Sunday across the Magic Valley and Snake Plain before stronger winds move in for Monday/Tuesday. MacKay && .HYDROLOGY... Flooding has dropped to minor at the Portneuf River at Pocatello with rising levels back to moderate on Sunday and forecast to continue to be at moderate stage through next weekend. Peak is forecast to reach 10.8 inches very near major flood stage on Tuesday. Minor flooding continues for the Portneuf River at Topaz where the gauge remains above flood stage and will remain so for several days with only a slight rise expected late this weekend into early next week. Flood warnings also remain in effect for the Blackfoot River near Shelley at Wolverine Canyon with the river remaining at flood stage and also near Blackfoot where the river remains in flood stage. With the potential for significant precipitation Sunday and Monday, rivers will need to be monitored closely. GK && .PIH WATCHES/WARNINGS/ADVISORIES... Wind Advisory until 4 AM MDT Sunday for IDZ056-057. Winter Weather Advisory from 6 AM Sunday to 6 AM MDT Monday for IDZ056-057. Winter Storm Warning from noon Sunday to 6 AM MDT Tuesday for IDZ060. Winter Weather Advisory from 9 PM Sunday to 6 AM MDT Tuesday for IDZ062>066. && $$