280 FXUS65 KRIW 150850 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 250 AM MDT Mon Oct 15 2018 .SHORT TERM...(Today through Wednesday night) With the fold over ridge moving down from the north, a classic radiation fog pattern is currently in place along with clear skies, light winds, and fresh snow cover for the Wind River and Big Horn Basins as well as for the area along the North Platte River in Natrona County this morning as most of the snow fell yesterday east of the divide. In addition, warm bodies of water in the area lakes will clash with this cold air where original dew points will be well above these colder ambient air temperatures, also helping to produce the fog. Temp/Dew point spreads are finally closing in. This morning will feature the coldest temperatures of the season thus far with many areas east and west of the divide expected to dip to 5 to 10 degrees above zero, with isolated readings around zero this morning. Some Mountain locations are already reporting temps between one below zero and 5 above, but these temps should begin to rise for the rest of this morning. But temps in the valleys and basins should continue to drop until a little after sunrise this morning. One other fly in the ointment this morning is a weak weather feature diving southeast across the Northern Plains which could produce a few isolated snow showers across the Northern Absaroka/Northern Big Horn Mtns this morning although the better isentropic lift appears to be relegated farther north in Montana from this feature. Southwest winds between South Pass and Casper will increase this morning in response to the relatively brief tightening of the gradient due to this weather feature, but will diminish this afternoon. These southwest winds will help warm highs today in the 40s. Tuesday will be even warmer with highs in the 50s expected and well up into the 50s Wednesday with continued dry weather with the high still overhead. The trough that delivered the snowfall to the area Saturday has exited off to the east, however. Although a piece of this energy will break off this positively tilted trough and form a closed low that will spin over the Desert Southwest and actually move northeast toward Wyoming and threaten far Southwest Sweetwater County with some isolated rain or snow showers Wednesday night. .LONG TERM...(Thursday through Monday) A seasonably mild and dry pattern will prevail Thursday through Monday. Most of west and central Wyoming will be in between two weather systems on Thursday and Friday. The first will be a cutoff southwest low that should be over Utah that is expected to at least partially shear out northeast over southern and eastern Wyoming Thursday morning. We continue to keep chances of precipitation out of the area with this system, mainly spreading some mid and high clouds across the southeast half of Wyoming. The second system will be a clipper diving southeast out of central Canada into the northern Plains on Friday. A weak, dry cold front is expected to clip northern and eastern Wyoming with this system, bringing slightly cooler highs roughly along and north of a Cody to Casper line. Upper level high pressure is then expected to build into the area over the weekend with temperatures expected to warm to near 5F- 10F above normal on Sunday and Monday. && .AVIATION...(For the 12Z TAFS through 12Z Tuesday morning) VFR conditions will occur through the period. Patchy fog is possible in the Big Horn and Wind River Basins, as well as parts of Natrona County until 16Z. Local MVFR/IFR conditions are expected. Will keep VCFG in some of the terminal sites. One side note...some isolated snow showers could occur in the northern Absaroka and Big Horn Mountains this morning. && .FIRE WEATHER... Issued AT 212 AM MDT Mon Oct 15 2018 A combination of a clear sky and fresh snow will bring a cold start to the day this morning. Expect patchy fog in the basins and valleys east of the divide this morning. Otherwise, today looks to be a dry day with temperatures not as cold as on Sunday. A weak weather system moving across Montana will bring breezy conditions from South Pass through Casper at times today. No rain or snow is expected though, except some isolated snow showers are expected in the northern zones this morning from a weak weather feature. Relative humidity will remain above critical levels. Mixing and smoke dispersal will be generally fair to poor. && .RIW WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...Lipson LONG TERM...Meunier AVIATION...Ross FIRE WEATHER...Lipson |