Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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855 FXUS65 KCYS 062159 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 359 PM MDT Thu Jun 6 2024 .KEY MESSAGES... - Warm weather will continue through late week, with widespread highs in the 80s and lower 90s on Thursday and Friday. - Saturday through Monday will see increasing chances for afternoon and evening showers and weak thunderstorms. && .SHORT TERM /THROUGH SATURDAY NIGHT/... Issued at 400 PM MDT Thu Jun 6 2024 Pleasant weather this afternoon with hardly a cloud in the sky. Temperatures are on track and currently in the 80s with a few locations across western Nebraska approaching 90 degrees. Shortwave upper level ridge axis is currently moving eastward across Wyoming and Colorado and is expected to move east of the forecast area tonight as the 700mb thermal ridge moves into the area. This will keep overnight lows on the mild side with readings in the 50s. One more very warm day forecast for Friday with highs quickly climbing into the 80s to low 90s. We may see the low to mid 80s by the late morning hours ahead of the next cold front. Models have delayed the timing of this cold front by a few more hours compared to yesterday...with FROPA along highway 18 and 20 over east central Wyoming late Friday afternoon and not across the I-80 corridor until late Friday evening. With this in mind, increased high temperatures a few more degrees due to the delay in the cooler airmass. Kept POP between 15 to 30 percent for widely scattered showers and thunderstorms later in the day and Friday night. Thunderstorms look sub-severe at this time with maybe some gusty winds possible. Northwest winds will become north and become gusty on Friday ahead/near the cold front, but high winds (gusts >58 mph) are not expected at this time. For this weekend, models show the upper level flow shifting into the northwest with east and southeast winds at this surface. Cold front will stall across the mountains and provide additional convergence across the high plains. Kept POP pretty high with numerous showers and scattered thunderstorms expected. Not seeing strong signals for strong to severe thunderstorms as thermodynamic profiles and model soundings are less than impressive with limited CAPE, poor lapse rates, and a cooler boundary layer. Moisture will definitely be in place with the NAEFS showing mean Precipitable Water in the 95th to 99th percentile for this time of the year over most of southeast Wyoming and western Nebraska Saturday afternoon. Will continue to keep an eye on this, but as of right now, the boundary layer looks a bit too stable with too much cooler air near the surface and a warm layer around 700mb, capping any surface based convection. High temperatures on Saturday will be tricky since any amount of limited sunshine this time of the year will rapidly warm the lower atmosphere. However, cloud cover and persistent upslope flow should keep max temperatures in the 70s or upper 60s for much of the day. The warmest location will likely be Carbon County and Rawlins with highs in the low 80s. Areas near the Carbon county/Albany county border, including Rawlins and Laramie, may have the best chance to see some strong to severe storms as they`ll be warmer with mostly sunny or partly sunny skies...resulting in more instability compared to areas further east. && .LONG TERM /SUNDAY THROUGH THURSDAY/... Issued at 400 PM MDT Thu Jun 6 2024 Unsettled weather will carry into the early part of next week, but conditions will turn drier and hotter by mid-week. A messy weather pattern will continue across the west on Sunday with a weakening dirty ridge over the Great Basin area and several shortwaves on its periphery. The ridge will be fairly moisture-laden with above normal precipitable water across much of the mountain west. Our area will be under a stalled stationary frontal boundary waffling back and forth close to the front range of the Rockies. A small closed low dropping out of the northern plains on Sunday will add a bit of extra lift ahead of it, with some overrunning isentropic lift promoting afternoon showers and thunderstorms. The severe weather threat looks fairly limited though, as forecast soundings show cool low level temperatures under fairly warm temperatures aloft. Thus, lapse rates look to remain rather weak. There will be some instability, so expect there to still be some thunderstorm activity. Uncertainty exists in high temperatures because of differences in how far south the upper level shortwave and associated cold front will get. GEFS members tend to be a little more aggressive with this, resulting in cool temperatures for Sunday into Monday with a strong cold front clearing most of the area. ECWMF members tend to keep this weaker and further north, leading to warmer temperatures for this time period. Monday looks similar to Sunday. The closed low from the north will be moving off to the east by this time, but another shortwave in the northwest flow will locally enhance lift again. Tuesday looks like a transition day as the ridge starts to expand eastward, pushing the stalled frontal boundary responsible for the period of unsettled weather away from our area. Lingering chances for showers and thunderstorms will exist across the area Tuesday, but a warming trend will also begin. Expect strong warm air advection into Wednesday, as ensemble median 700-mb temperatures climb up to +16C near KCYS by 00z Wednesday. A few models graze the area with a shortwave, sparing us from the brunt of the heat for Thursday, but most ensemble members keep that shortwave far enough north to bring another very hot day on Thursday, with the potential for near record highs. The NAEFS mean shows 700 and 500-mb temperatures over the 90th percentile of climatology on Wednesday and Thursday even at a 6-7 day lead time. && .AVIATION /18Z TAFS THROUGH 18Z FRIDAY/... Issued at 1137 AM MDT Thu Jun 6 2024 VFR conditions expected for the forecast period. Generally quiet day expected today with mainly clear skies and light winds aside from an occasional gust to 15 to 20 knots. Expect increasing mid to high level clouds and a return of gusty northwest winds with a cold front expected to arrive Friday morning. && .HYDROLOGY... Issued at 400 PM MDT Thu Jun 6 2024 Several days of above normal temperatures have accelerated snowmelt runoff in the North Platte and Laramie River basins. Temperatures for the next several days are forecast to remain high enough to sustain rapid snowmelt and the subsequent high flows including minor flooding through Saturday. Snowmelt from the Sierra Madre and Snowy Ranges has driven the Encampment and North Platte Rivers to bankfull stages. The Encampment River is forecast to crest above flood stage on Saturday morning. Emergency management has reported minor flooding along the Little Laramie River. This flooding is expected to continue through the weekend. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...TJT LONG TERM...MN AVIATION...MN HYDROLOGY...AJA