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
41
156 FXUS65 KCYS 281011 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 411 AM MDT Tue May 28 2024 .KEY MESSAGES... - Potential for isolated dry thunderstorms capable of producing strong, erratic wind gusts across the I-80 corridor late Tuesday afternoon. - Strong to severe thunderstorms mainly along and east of I-25 into the Nebraska Panhandle Wednesday afternoon with large hail and strong winds. - Active weather pattern continues Thursday into the weekend with daily chances for showers and thunderstorms. && .SHORT TERM /THROUGH WEDNESDAY NIGHT/... Issued at 330 AM MDT Tue May 28 2024 Looking at another nice and warm day across much of southeast WY and western NE for Tuesday with afternoon highs in the 70s for most as the upper level ridge axis slides overhead. A weak shortwave passage over the central Rockies could lead to scattered showers and an isolated thunderstorm to develop over the higher terrain near the CO/WY border late this afternoon. Forecast soundings show very dry lower levels supportive of gusty outflow winds with and in the vicinity of any storms that develop. There is the possibility for these storms to spread east of the Laramie Range along the I-80 corridor early this evening with enhanced convergence along the inverted trough extending northward from eastern CO, but again expecting little to no precipitation along with gusty winds as LCLs extend well above the freezing level. Latest GOES WV imagery shows an upper level low approaching the PacNW coast that will continue to move eastward across the northwest CONUS headed into Wednesday. Strong southerly flow Wednesday morning ahead of the low will begin to advect higher dew points across much of eastern WY and the NE panhandle. This enhanced low-level moisture may even lead to a few areas of patchy fog to develop briefly before eroding with daytime heating. This will begin to prime the environment for storms in areas east of the Laramie Range Wednesday afternoon where even 10th percentile SBCAPE values are exceeding 1200 J/kg over the NE panhandle per the latest HREF with 30-35 kt of shear. SPC recently upgraded the Day 2 (Wednesday) Severe Weather Outlook to a Slight Risk for Severe Thunderstorms with large hail and strong winds possible east of I-25 into the NE panhandle. Will continue to monitor potential timing of storms, but as of right now hi-res guidance is suggesting initiation over the higher terrain around midday with storms moving east towards better moisture east of a boundary near the NE/WY border with notable CAPE values in the hail growth zone (>700 J/kg between -10C and -30C). The most likely timing for strong to severe storms will be late in the afternoon into early in the evening as an enhancing LLJ potentially supporting upscale growth into a convective line with strong outflow winds. Lingering showers and storms will be possible Wednesday night before the cold frontal passage. && .LONG TERM /THURSDAY THROUGH MONDAY/... Issued at 330 AM MDT Tue May 28 2024 A more summer-like weather pattern will dominate the week ahead with mild temperatures and near daily chances for showers and thunderstorms expected. A broad trough located over the Canadian Rockies will be the main weather maker for the end of this week. An initial shortwave ejecting underneath this feature will push a surface trough through the area by Thursday morning, leading to the dryline surging eastward and low level winds turning westerly across much of the area. Low level moisture and decent directional shear may hold on in the far eastern counties of the forecast area, but further west the isolated thunderstorms that develop will probably struggle to have rain reach the ground, ending more as wind producers in the drier low levels. Overall storm coverage should be lower on Thursday compared to Wednesday. Thursday`s highs are also expected to be a little cooler than Wednesday in the post frontal airmass. Most guidance then shows a surface high sliding down the east side of the Rockies late on Thursday, pushing the dryline back to the west and putting better moisture in place for Friday. A secondary lobe of vorticity rotating around the trough aloft on Friday should also give a slight boost to lift, although this feature doesn`t look too impressive. Look for greater storm coverage on Friday, with the possibility for strong to severe storms also potentially returning. Forecast confidence starts to break down heading into the weekend and beyond, with subtle differences in the overall synoptic pattern resulting in divergent outcomes for local surface weather. Most model guidance shows the flow aloft becoming more zonal with some weak shortwaves possibly passing through. The exact location of these shortwaves will determine each day`s temperatures and thunderstorm chances, but overall we are looking at a gradual warming trend into early next week. Saturday should maintain isolated to scattered afternoon thunderstorms, but expect things to trend drier Sunday into early next week as more ensemble guidance shows westerly low level flow and lower surface dewpoints. && .AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/... Issued at 1009 PM MDT Mon May 27 2024 Northwest flow aloft will continue overnight while a ridge aloft moves overhead by Tuesday evening. Clear skies will prevail, with ceilings near 8000 feet developing at Laramie and Cheyenne after 00Z. Winds will gust to 20 knots at Cheyenne from 15Z to 00Z, and at Laramie from 18Z to 00Z. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...MB LONG TERM...MN AVIATION...RUBIN