Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
909 FXUS65 KCYS 211733 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 1133 AM MDT Tue May 21 2024 .KEY MESSAGES... - Much cooler temperatures with more widespread showers and thunderstorms today. Accumulating snow likely above 8000 feet, with a rain and snow mix possible down to 6000 feet late Tuesday night into early Wednesday morning. - Patchy frost is expected on Wednesday morning due to temperatures hovering near or below the freezing mark. Recently planted vegetation may need to be covered to prevent any frost/freeze damage. - Daily shower and thunderstorm chances continue through the long term. Could see some elevated winds in the wind prone regions throughout the week and weekend. && .SHORT TERM /THROUGH THURSDAY/... Issued at 330 AM MDT Tue May 21 2024 Chilly temperatures, scattered rain showers, and patchy dense fog are present as of 9Z this morning across southeast WY and western NE. Observations earlier this morning around midnight had several locations reporting less than 1 mile for visibility as upslope flow and the rain showers created an abundantly moist column to contend with east of the Laramie Range. Went with a Dense Fog Advisory headline to reflect this, with model guidance showing clear signs that we should begin to erode the patchy, dense fog by daybreak for most locations. However, the rain showers and mostly cloudy conditions will be sticking around for most of the day. The rain showers present on radar as of 9Z this morning will slowly trek to the northeast as time goes on. We will have a temporary break with respect to active weather before the next shortwave disturbance arrives on the heels of the previous weather disturbance, which will push out toward the Central Plains and Great Lakes region by later today. There will be a short timeframe where partly cloudy skies are present in the Nebraska Panhandle, but the pesky cloud cover will stick around for southeast Wyoming thanks in part to continual impulses of cold air advection. There will be orographic enhanced snow shower activity in the higher terrain today. Due to some of the snow falling throughout the day, despite temperatures being near or below freezing in the higher elevations, have shaved off the total snowfall accumulations. Nonetheless, the North Laramie Range, Snowy & Sierra Madre mountains at elevations above 8000 feet will pick up light snowfall accumulations between today and late tonight. Daytime highs in the lower elevations will range from the middle 40s to upper 50s, which is well below normal. Scattered rain showers and isolated thunderstorms are anticipated from this afternoon into the early evening hours. However, severe weather isn`t anticipated compared to yesterday where we had a few stronger thunderstorms that propagated through the region. Rain/snow showers are anticipated between elevations of 6500 to 8000 feet, but accumulations are not anticipated. The shortwave disturbance will have propagated through most of the cwa by 6Z Wednesday. Surface high pressure is expected to quickly propagate toward central CO by 12Z Wednesday. As this occurs, the nighttime radiation inversion and clearing skies will cause temperatures to rapidly decrease. Have nudged temperatures down a degree or two, especially for valley areas across the cwa in southeast WY. Patchy frost is certainly plausible for several areas, and there is concern for vegetation to be covered because of overnight lows hovering near the freezing mark. Have decided against any frost/freeze headlines at this time due to the climatological average last frost/freeze dates happening around this time of spring for most of the high plains. If model guidance signals that our temperatures decrease well below freezing for areas east of the Laramie Range in the coming 24 hours, this decision may need to be revisited. Locations west of the Laramie Range typically have their last freeze in June, per our in-house climate statistics. We will have a quiet Wednesday, as seasonal temperatures make a well-deserved return to the region. Mostly sunny skies and weak upper level ridging will cause surface temperatures to rebound nicely. Daytime highs will range from the lower 60s to middle 70s, with the warmest temperatures residing in the NE Panhandle. Cooler temperatures will remain in the southeast WY mountain zones due to increasing clouds by later in the afternoon. Breezy winds will also make a return as we have an increasing surface pressure gradient. 700mb winds will ramp up to 40-50 knots between 6Z and 12Z Thursday. While we may not be looking at any high wind headlines for Thursday morning, there could be a few wind gusts of 50-55mph in the wind prone and gap regions of southeast WY. The warmer temperatures look to stick around for the majority of Thursday, especially for areas east of the Laramie Range because of weak downslope air compression effects. Daytime highs in the 60s and 70s are anticipated, with cooler temperatures further to the west as increasing clouds once again make a return ahead of our next approaching weather disturbance by Thursday evening. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... Issued at 330 AM MDT Tue May 21 2024 Fairly strong shortwave trough moving through the CWA Thursday evening. Cold front looks to move well south of the CWA with gusty north to northwest winds behind the front Thursday evening. GFS and ECMWF in good agreement with this feature along with timing. Did increase PoPs slightly over NBM guidance for areas east of the Laramie Range Thursday evening before drying out after 06Z. May see some light afternoon showers Friday as a weak shortwave moves through. ECMWF painting some light QPF over our western mountains Friday afternoon while GFS shows dry conditions. Did opt to go for some scattered showers (30-40 percent) for Friday afternoon for the I-80 Corridor from Sidney to Rawlins. Fairly flat shortwave riding for Friday night and most of Saturday before next low approaches from the west. GFS and ECMWF both showing rain developing over our western mountains Saturday morning...spreading east by the afternoon. Upper low tracks across the northern CWA Sunday with showers continuing through the day. going to be quite cool Sunday as GFS 700mb temperatures fall to -2 to -3C Sunday afternoon. Finally some drier weather for Monday as upper low tracks east into eastern Nebraska. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 1126 AM MDT Tue May 21 2024 VFR conditions currently across southeast WY terminals while low clouds remain over NE panhandle terminals late this morning with lingering MVFR conditions. These low clouds will continue to clear out through this afternoon near KSNY and KBFF, but will likely remain around KCDR and KAIA with additional showers and storms developing this afternoon and evening. Sites that do see improvements could see a brief return to lower flight conditions if any vicinity showers move directly overhead. Southeast WY terminals can expected gusty winds to continue this afternoon with latest satellite imagery showing wave clouds across the South Laramie Range and Laramie Valley that could lead to increased turbulence. Overall, cloud cover will begin to clear up overnight. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...BW LONG TERM...GCC AVIATION...MB