Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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808 FXUS65 KCYS 112148 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 348 PM MDT Tue Jun 11 2024 .KEY MESSAGES... - Hot weather expected Wednesday as daytime highs climb into the 85 to 95+ degree range across the entire area. - Thunderstorm chances return to the region late this week, along with the risk for severe weather Thursday and Friday. && .SHORT TERM /THROUGH THURSDAY NIGHT/... Issued at 342 PM MDT Tue Jun 11 2024 Latest GOES WV imagery shows primarily zonal flow aloft with an upper level closed low off the southern CA coast while the polar jet sits near the Canadian border with an upper level trough moving into BC. Zooming into southeast WY, latest visible imagery shows cumulus development over east-central WY as well as eastern Laramie Co with an enhanced convergence zone based on surface observations. Precipitation chances are low, but nonzero through early this evening as an isolated storm could still develop. Will continue to monitor latest satellite trends, but any storms that develop will likely be short-lived with little to no precipitation. Zonal flow aloft will continue Wednesday with 700mb temps climbing near 15C as an upper level ridge builds just to the south over the central Rockies. This will lead to a warm day across much of the CWA with much of the NE panhandle reaching the mid-90s. With 700mb temps will climb near the climatological 90th percentile value, we are not looking to break record highs, but still could see temperatures just a few degrees below for select locations. Latest NBM probability of exceeding 100F degrees Wednesday afternoon is highest in the North Platte River valley, up to 25%. Farther west of the Laramie Range, scattered showers will develop in the afternoon with a weak shortwave passing in the flow. Forecast soundings show inverted-V profiles with dry low-levels and LCLs climbing above the freezing level. While minimal precipitation is likely from these storms, strong outflow winds will be possible in the vicinity. Hi-res guidance does continue showers east along the I-80 corridor towards Kimball before dissipating early in the evening. Better chances for showers and thunderstorms arrive later this week, starting on Thursday. SPC Day 3 Outlook currently has a Marginal Risk reaching up into Laramie Co. Post-frontal upslope flow with an upper level system passing over the central CONUS will increase moisture convergence across southeast WY and northeast CO. Despite southeasterly low-level flow, wind profiles are fairly unidirectional aloft supporting of straight hodographs and splitting storms. MLCAPE climb near 1000 J/kg with 40+ kt shear that will support strong to severe thunderstorms Thursday afternoon along the South Laramie Range and adjacent plains to the east and south of the North Platte River valley. && .LONG TERM /FRIDAY THROUGH TUESDAY/... Issued at 342 PM MDT Tue Jun 11 2024 An active start to the long term forecast is expected across southeast Wyoming and western Nebraska. On Friday, a potent, upper- level shortwave trough is progged to dig northeasterly from southern Nevada to western Colorado throughout the day. As this upper-level shortwave pushes towards the region, ample synoptic lift is expected to develop from a combination of jet dynamics and cyclonic vorticity advection at 500mb. A subtle, 700mb jet maximum is progged to be just southeast of the CWA, broadly placing western Nebraska within the left exit region of this low-level jet and further favoring lift across the region. Strong southeasterly flow at the surface will advect in significant moisture with dewpoints increasing into potentially into the 60s for portions of western Nebraska, with 50F dewpoint expected across far southeast Wyoming. NAEFS mean precipitable water for 00Z Saturday is currently progged to near the 99th- percentile for this area at this time of year. Looking more in- depth into some of the convective parameters, MUCAPE values are progged to well over 2000 J/kg with MLCAPE values approaching 2000 J/kg as well. Forecast soundings from the GFS suggest good directional shear in the lowest levels of the atmosphere, steep low- level lapse rates, and DCAPE values near 1000 J/kg. Forecast soundings across western Nebraska suggest bulk shear values approaching 50kts, with precipitable water values approaching 1.5 inches. These indicate a potentially significant hail threat across far southeast Wyoming and western Nebraska. However, hodographs are progged to be straight across this region, leading to an additional concern of slow-moving storms. Slow-moving storms accompanied by 95th-99th percentile precipitable water leads to and increase concern of torrential downpours with any storms that develop and the slow moving nature could lead to a significant flooding threat. The Weather Prediction Center has a small portion of the CWA under a Marginal risk for excessive rainfall on Friday, but this could move further west over the next few days. Overall, Friday looks to be a favored day for severe weather across western Nebraska and far southeast Wyoming. This setup will continue to be monitored as it approaches and more consistency develops within the models and hires models. The remaining long term forecast will feature quasi-zonal flow aloft across the region with 700mb temperatures increasing into the 10 to 20C range throughout the long term. Warm temperatures are expected with highs in the 70s to near 90s across western Nebraska. Could see some daily chances for isolated showers and maybe a thunderstorm or two, but coverage will be very low. Additionally, zonal flow aloft will lead to breezier conditions across the region, though winds should remain well below high wind criteria. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 1114 AM MDT Tue Jun 11 2024 VFR conditions expected through the TAF period. Some high clouds are expected to drift across the region during the day, but no major coverage is expected. Mostly calm winds today, except at KRWL and KLAR where winds could gust between 25 and 30 kts this afternoon. && .HYDROLOGY... Issued at 342 PM MDT Tue Jun 11 2024 Flows remain just below flood stage on the Medicine Bow River near Elk Mountain with a slight trend downward the past few days with early morning crests. However, with the warm weather expected the next few days including overnight lows in the mid-40s at higher elevations, decided to extend the Flood Watch for snowmelt through Thursday morning. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...MB LONG TERM...AM AVIATION...AM HYDROLOGY...MB/AJA