Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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028 FXUS65 KCYS 151744 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 1144 AM MDT Wed May 15 2024 .KEY MESSAGES... - Cooler today w/ scattered to numerous showers and a few thunderstorms. Severe weather is not expected. - A warming trend will occur through the remainder of the week, with lower to middle 80s possible by Friday especially for areas along and east of I-25. - Elevated wind gusts are expected in the southeast Wyoming wind corridors on Friday and Friday night. && .SHORT TERM /THROUGH FRIDAY/... Issued at 407 AM MDT Wed May 15 2024 Scattered to numerous showers & a few thunderstorms are expected across a large portion of southeast Wyoming and western Nebraska today. The greatest coverage of this activity is likely to occur in the morning (12z-18z) given more favorable dynamic support w/ lingering mid-level vort energy associated with the strong short wave responsible for the strong/severe storms on Tuesday. Should see this support gradually wane during the afternoon and evening as the bulk of the energy pinches off and drifts south/southwest into the Four Corners region. As such, overall storm coverage is likely to decrease with time. Despite this, the 700-500-hpa cold pool associated w/ the mid upper-level low should promote decent mid-level instability over much of the CWA and thus an increased chance for scattered storms. Modest shear precludes any concerns for organized clusters or stronger storms. Much cooler for today with 700-mb temperatures close to 0C, likely restricting daytime highs to the mid/upper 50s to near 60 deg F. Overall, conditions should rapidly improve for Thursday & Friday, courtesy of rising mid-level heights as the primary disturbances remain well to the north and south of the CWA. A warming trend will commence w/ 700 mb temperatures climbing to +10 to +12 C across much of the area by Friday, supporting the potential for widespread daytime highs in the 80s especially along and east of I-25. An episode of high winds will be possible across the southeast WY wind corridors on Friday, given significantly increased low-level height gradients as a sharp mid-level short wave tracks across the inter-mountain west and northern high plains. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... Issued at 407 AM MDT Wed May 15 2024 Models have continued to come into better agreement on the passage of a cold front and upper-level trough Friday into Saturday. The upper-level trough will slowly progress easterly Friday night into Saturday with westerly winds developing at 700mb and the surface. Some disagreement remains between the GFS and the ECMWF for how strong the westerly 700mb winds will be, but the GFS suggests it could be around 50kts, while the ECMWF keeps it much lower around 30kts. The GFS solution is significantly more favorable for a potential short lived, high wind event for the wind prone regions of southeast Wyoming. The ECMWF solution suggests the potential for elevated winds Saturday, but likely not near the high wind criteria line. Craig to Casper height gradients increase to around 50-55m, which suggests the potential for some gusts near 50mph at the Arlington wind prone. In house guidance is not overly onboard with the potential high winds and only suggests a 30-40% chance for elevated winds Saturday. This system will need to be monitored to determine if ingredients come together for another strong wind event across the region. As the upper-level trough continues to move out of the region, a split flow regime takes shape with a dominant subtropical jet and a weaker polar jet across the western CONUS. This setup will turn upper-level winds southwesterly, with 700mb and surface winds following suit. Precipitation will be favored Sunday into Monday at the region will be under two separate forcings for synoptic lift. The right entrance region of the northern jet will be overhead and supported by the left exit region of the southern jet. Therefore, favorable conditions for widespread synoptic lift is favored. However, the ECMWF keeps the northern jet more zonal and further north, with significantly decreases the lift across the region and makes PoPs continue to be a headache early into the week. Did decrease PoPs for most days for the upcoming week, with 30-40% PoPs in place across the region Monday into Tuesday. Decided to keep PoPs relatively low due to the uncertainty in the upper-level evolution. Additionally, the GFS suggests a secondary cold front moving through the region Monday, while the ECMWF does not have this front. Decided to decrease temperatures slightly for Monday and Tuesday, as slightly cooler temperatures are favored, despite the poor model agreement. Further model disagreement persists into the mid-week timeframe. The ECMWF and GFS both suggest and incoming upper-level trough by mid- week, but the GFS is about a day behind the ECMWF with displacement to the west, compared to the ECMWF. Decreased PoPs for Tuesday onward to the 20-30% range, due to the uncertainty between the long range models at this time. Despite model disagreement in precipitation, warm temperatures are expected throughout the long term, with highs consistently in the 60s, 70s, and 80s across the region. && .AVIATION /18Z TAFS THROUGH 18Z THURSDAY/... Issued at 1114 AM MDT Wed May 15 2024 Showers and isolated weak thunderstorms will move through the region throughout the day today affecting many terminals. The most likely areas for brief showers are at LAR, CYS, BFF and CDR. CIG heights at all terminals will hover in the MVFR range today. IFR looks to be just a bit lower than guidance so kept things above that threshold. Expect showers to diminish quickly after 0z with partly cloudy skies overnight. Overnight fog is a low but nonzero threat at LAR especially if skies are slow to clear this afternoon keeping surface moisture nearby. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...CLH LONG TERM...AM AVIATION...MAC