A large low pressure system will approach western Wyoming today, while higher pressure remains settled over the rest of the state.  For western Wyoming, expect partly to mostly cloudy skies, breezy to gusty winds, and colder temperatures.  Highs will remain in the 30's and 40's.  There will be a chance for wet snow or a rain/snow mix near Evanston and the Utah state line.  Otherwise, expect rain showers and a few thunderstorms.  For central and eastern Wyoming, expect early sunshine with thickening clouds later in the day.  Temperatures will also remain unseasonably mild, with highs in the 50's and 60's.  Rain showers and thunderstorms will also be in the forecast.  A large low pressure system will then remain settled over the entire state of Wyoming on Friday, Saturday, and Sunday.  On Friday, expect cloudy to mostly cloudy skies, gusty to strong winds, and significantly cooler temperatures statewide.  Rain showers and thunderstorms will also be likely during the day.  Rain will then mix with and turn to wet snow throughout the state by Friday night/early morning.  There will be a chance for moderate to heavy snow in southeastern Wyoming, mainly Friday night into Saturday morning, Saturday afternoon/evening into Sunday morning, and Sunday night into Monday morning.  Elsewhere, expect light to scattered snowfall.  Travel concerns will include:  slushy to slick/very icy roadways as well as reduced visibility due to snow, blowing snow, and some areas of patchy fog.  Temperatures will also become even colder and below average this weekend.