Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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272 FXUS65 KCYS 271119 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 519 AM MDT Mon May 27 2024 .KEY MESSAGES... - A much warmer, milder week ahead expected as an upper-level ridge overtakes the region. - Chances for an active weather pattern with organized strong to potentially severe afternoon thunderstorms possible Wednesday through this weekend. && .SHORT TERM /THROUGH WEDNESDAY/... Issued at 300 AM MDT Mon May 27 2024 Light rain showers are quickly moving to the east across the NE Panhandle during the early morning hours. Northwest flow aloft from a departing shortwave should quickly assist with the rain showers pushing east by daybreak. A few sprinkles across the central and southern tier of western Nebraska are anticipated at best, with a non-severe threat to any vertically developed cumulus clouds the remainder of the night hours. A semi- stationary surface cold front is draped along the Laramie Range and Front Range of Colorado as of 8Z this morning as well. This surface cold front is anticipated to remain close to Cheyenne, with it retrograding to the east through the remainder of today. As we continue to see this frontal boundary remain semi- stationary, it will have some weak forcing and modest atmospheric lapse rates by this afternoon. We can expect mostly sunny conditions across most of the cwa, but a few cumulus clouds could bring light sprinkles or a quick shower along and east of the Laramie Range. It will be another pleasant day, with mostly sunny conditions helping temperatures rise to near- seasonal levels: Highs in the upper 60s to middle 70s for the lower elevations and high plains of western Nebraska. Tuesday will bring slightly warmer temperatures, and another round of mostly sunny conditions for a majority of the cwa. Highs in the 70s to lower 80s are expected for the lower terrain. While we will be under the influence of an amplifying upper level ridge, there will be weak ripples of shortwave energy at the H5 level on Tuesday afternoon. Model guidance is trending with the majority of any organized rain showers and thunderstorms to remain south of our cwa for the most part. However, surface CAPE is modeled to creep upwards towards 500 J/kg for the I-80 corridor. Have bumped up PoPs slightly for the higher terrain of the Snowy/Sierra Madre Mountains, and the I-80 Summit. Model soundings are showing an inverted-V signature, with calculated DCAPE readings approaching 750-1000 J/kg by 0Z Wednesday. The main impacts that could result are elevated virga rain showers, that could create some gusty microburst winds over a small area, potentially up to severe thresholds. Have not bumped up the wind forecast for Tuesday just yet, but if we see this signal on model guidance continue, there may be a need to bump up the wind forecast for Tuesday afternoon along and near the I-80 corridor of southeast WY. Wednesday will bring warm temperatures to the region, as we begin to feel the effects of an upper level ridge axis. WAA will be present, and there will be widespread middle 70s to middle 80s for daytime highs in the lower terrain. There will be an approaching longwave trough by Wednesday afternoon from the Pacific Northwest, digging southward toward the Four Corners by 0Z Thursday. It is modeled for diffluent flow to set up across the Central Rockies, as the Polar Jet stream and Subtropical jet stream phase partially. Additional weather metrics to consider will be moisture advection from the Gulf of Mexico, steep atmospheric instability/lapse rates, effective bulk wind shear, and the potential for rotating, isolated severe thunderstorms. The overnight Day 3 Storm Prediction Center severe thunderstorm outlook does indeed have portions of our cwa from the I-25 corridor toward the Nebraska Panhandle in a Marginal Risk (Category 1 out of 5). We will continue to monitor trends in the coming days as warmer weather and the potential for organized thunderstorms exists for the some areas. Until then, enjoy the pleasant holiday forecast for today. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... Issued at 300 AM MDT Mon May 27 2024 Generally, an active pattern looks to persist through the long-term period with daily chances for showers and thunderstorms as multiple shortwaves pass in the flow through the weekend. Best chances for precipitation CWA-wide will be on Wednesday and Friday evenings (30- 40%). Latest Euro keeps a lower amplitude shortwave trough farther north on Friday with minimal precipitation across the area, however ~40% of EC members depict a sharper trough with better southerly moisture return and instability (MLCAPE ~800-1200 J/kg) into areas along and east of I-25 and the NE panhandle. Enhanced flow aloft with the approaching upper level trough would support strong enough shear profiles (30-35 kt) for a few severe storms to develop, so will need to continue to monitor potential severe weather ingredients over the coming days. While 500mb height rises appear likely early next week, an active pattern may persist with multiple weak shortwaves passing overtop of the ridge along with an upper level low undercutting to the southwest. This will also support above average temperatures for the first week of June, potentially leading to the first 90F degree day over portions of the NE Panhandle ~15% chance per latest NBM guidance. && .AVIATION /12Z TAFS THROUGH 12Z TUESDAY/... Issued at 515 AM MDT Mon May 27 2024 VFR conditions expected across area terminal through the forecast period. Breezy northwest winds expected this afternoon with light showers possible in the vicinity of KCYS and KSNY late in the afternoon. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...BW LONG TERM...MB AVIATION...MB