Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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312 FXUS65 KCYS 101039 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 439 AM MDT Fri May 10 2024 .KEY MESSAGES... - Daily isolated to scattered afternoon and evening thunderstorms are possible into next week. Severe weather is not expected this time. - Temperatures will remain warm through Tuesday before a cold storm system moves in on Wednesday bringing cooler temperatures. && .SHORT TERM /THROUGH SATURDAY/... Issued at 337 AM MDT Fri May 10 2024 Isolated to scattered showers and thunderstorms are possible Friday afternoon across southeast Wyoming and western Nebraska. As conditions start drying out today, areas most favored for showers and thunderstorms are the mountains and higher terrain that will have the lift needed to support development. HiRes guidance is not very robust in terms of dynamic support with cool temperatures, limited instability (50-100 J/kg of CAPE), dewpoints in the low 30s, and shear values 5 to 15 knots. Due to the main thunderstorm ingredients being limited, confidence is low in any widespread shower/thunderstorm development. Saturday, as a low in the Four Corners Region shifts eastward, some moisture wraps around back north into areas along and south of the Interstate-80 corridor, increasing precipitation chances in the afternoon. While the shear is still very weak in the 5 to 10 knot range, with the moisture increase and instability being more widespread and stronger near 200-800 J/kg across the High Plains, scattered to numerous showers and thunderstorms are possible. They will likely not be very strong thunderstorms, but the chance of them being more widespread is higher. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Issued at 337 AM MDT Fri May 10 2024 The long term forecast continues to show chances for isolated afternoon thunderstorms beginning by the weekend, with better chances for more scattered showers and thunderstorms next week. Temperatures are also expected to increase beginning this weekend into next week with temperatures likely to remain in the upper 60s to low 70s Monday and Tuesday. The biggest change noted is for a potent cold core system to move into the region on Wednesday and bring colder temperatures and more widespread precipitation chances and the possibility for high elevation snow showers. Precipitation chances on Saturday and Sunday will be driven by a slow moving and large upper level low moving across the Four Corners region. Models have been consistent over the past 24 hours in advertising a setup where this upper level low is south of a ridge building across the northern Pacific northwest with another upper level low sitting in near northern Michigan. This overall setup of upper level low and high pressure systems looks like a messy col setup across the Front Range states. The wind fields show the col pattern better as light easterly winds in close proximity of light westerly winds suggest that some type of stationary or quasi- stationary front will be located across SE Wyoming and the Nebraska Panhandle. This boundary will be the focal point for potential convective initiation Friday and again on Saturday. These storms that do develop will be in a weakly shear and low CAPE/instability environment so not expecting much in the way of deep convection, but towers that go up along the boundary or are orographically supported could be deep enough to foster the development of some small hail. This overall pattern remains in place well into Saturday evening before the closed upper low across the Four Corners begins to weaken and open into an open wave trough as it crossed through southern Colorado. Remaining stationary boundary should still be draped somewhere across the Front Range and we will also have lingering outflow boundaries in play on Saturday IF we can get a few deeper convective cores going on Friday. This system begins to speed up on Sunday but the threat for some afternoon diurnal convection will again be possible. Monday may be quiet day across the region as a weak upper level ridge axis moves but this too will quickly move east of the region throughout the day on Monday. We will see the benefits of some warmer 700mb temperatures which will allow for temperatures to jump into the 70s across much of SE Wyoming and the Nebraska Panhandle. Heading into Tuesday models have shifted a bit on the overall pattern across the region. Models are now showing a deeper trough developing across western Montanta which will have a downstream transition to to a SW flow across much of Wyoming, this deeper trough also means the ridge will hold in place longer before getting ejected to the east. The evolution of this trough becomes quite messy with models initially pushing this feature in as a positively tilted trough before pinching off a weak closed low over central Utah with strong shortwave pushing out of eastern Montanta on Wednesday. This secondary shortwave looks to push a cold front north to south across the region bringing with it colder temperatures and more widespread precipitation chances with the potential for some high elevation mountain snow showers. While the exact evolution of the main 500mb height needs to be watched, overall confidence remains that we will stay unsettled for much of next week. && .AVIATION /06Z TAFS THROUGH 06Z SATURDAY/... Issued at 337 AM MDT Fri May 10 2024 While MVFR to IFR conditions remain possible due to low CIGS and fog through mid-morning, high cirrus clouds moving in from the south will limit the fog potential across portions of far southeast Wyoming. The primary concern one the CIGS lift will be gusty winds 20 to 30 knots and a few showers and thunderstorms this afternoon across southeast Wyoming. The Nebraska panhandle terminals can expect FEW to SCT high clouds with generally light winds less than 12 knots. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...LEG LONG TERM...AW AVIATION...LEG