Hydrologic Outlook National Weather Service Riverton WY 1233 PM MDT Thu May 4 2017 ...Warm basin temperatures across Western and Central Wyoming through Saturday will cause steady rises in small creeks and streams Friday afternoon through Sunday afternoon... ...Rain expected across Western and Central Wyoming Tuesday through Thursday of next week will increase flood potential... Snowmelt runoff into small streams and creeks will drastically increase due to warm basin temperatures across Western and Central Wyoming through Saturday. Small streams and creeks will see steady rises Friday afternoon through Sunday afternoon with the increased snowmelt runoff. Afternoon temperatures at the 9000 foot elevation are forecasted to be into the lower 60s Friday and Saturday with overnight lows Friday night staying between 35 and 40. Temperatures are expected to cool down into the lower to middle 50s by Sunday afternoon. After the warm temperatures, the next main concern will be how much rain may fall across the area in the early to middle part of next week. A large upper level low pressure system is expected to develop over the Desert Southwest Sunday into Monday before gradually moving east to northeast into Colorado Wednesday or Thursday of next week. Some lighter amounts of rain in the form of showers and isolated thunderstorms will fall in spots late in the weekend into early next week but the most significant rain potential will likely hold off until later Tuesday night through Thursday. How much rain falls during this period is the bigger question. The computer models are differing on timing by up to a day and by quite a bit on total rainfall. The potential for a couple inches of rain do exist in the foothills of Central and Southwest Wyoming with with less in the northwest mountains. The lower elevations of the same area could see up to an inch of rain but these are just very preliminary indications. Lesser amounts of rain are possible late Sunday through Monday before the more significant rain potential begins. The bottom line is that significant rainfall could fall on the snowpack in the early to middle part of next week. Snow levels will be quite high and mostly in the 9000 feet and above level with some lowering Wednesday into Thursday. Tributary creeks and streams may reach bankfull by Sunday morning through Monday morning due to excess snowmelt runoff and rainfall runoff. Minor flooding of low lying areas is possible due to the elevated stream levels. Main stem rivers will see noticeable rises by Sunday morning with continued rises possible on Monday. Main stem rivers are expected to remain below flood levels through Monday. The forecasted rain Tuesday through Thursday will increase flood potential across Western and Central Wyoming. Stay tuned for updated outlooks, advisories, and warnings as we get closer to this developing rain on snowmelt event.