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
42
43
44
45
46
160 FXUS65 KCYS 031043 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 443 AM MDT Wed Jul 3 2024 .KEY MESSAGES... - Thunderstorms are expected this afternoon and tonight, especially across east central Wyoming and the western Nebraska Panhandle. Any developing storms will have the potential to become severe with all hazards possible. - A cool and generally pleasant Independence Day is expected in the wake of a strong cold front set to sweep across the area later tonight. A few light showers are possible, but no major impacts are expected. Daytime highs on Thursday will only be in the 70s for most areas. && .SHORT TERM /THROUGH FRIDAY/... Issued at 409 AM MDT Wed Jul 3 2024 The primary focus over the next 12 to 24 hours is the threat for strong to severe thunderstorms across portions of the CWA. Storm coverage is fairly uncertain today with a robust EML expected to spread across the majority of the CWA by early afternoon w/ 700- mb WAA contributing to 700-mb temperatures near +14 deg C by 18z over most of south central & southeast Wyoming. As such, it does appear likely that capping will be an issue for most of the area w/ the best chance for CI over our far northern & eastern zones, on the edge of the thermal ridge/EML. High-res guidance suggests initial development may occur along/southeast of a line from IBM to AIA by early afternoon as SSE boundary layer flow allows dew- points to soar into the lower to middle 60s east of the dryline, supporting rapid destabilization w/ MLCAPEs of 1500 to 2000 J/kg by 18z. It is possible that additional development will occur in the early afternoon across Converse/Niobrara counties, but would expect the better chance to occur during the evening w/ the cold frontal passage. Strengthening flow aloft & veering profiles may support effective shear of 35 to 45 knots, suggesting the threat for supercells capable of all facets of severe weather including very large/damaging hail, strong winds, and even a few tornadoes for any surface based storms in western Nebraska. Could see some elevated storms persist well into the night behind the main cold front, with a low-end risk for marginally severe hail overnight. As 700-mb temperatures plunge to between +2 and +6C by Wednesday night in the wake of the cold front, the stage will be set for a very cool Independence Day w/most areas only seeing highs in the 70s. Isolated to widely scattered instability-driven showers are expected, but overall do not expect to see much of an impact for most areas with this activity. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... Issued at 409 AM MDT Wed Jul 3 2024 Minimal changes made to the long term forecast. Still expecting a cold front over the weekend which will lead to a brief cool down, before strong ridging over western CONUS warms temperatures up again. Biggest change in the long term appears to be the timing of the cold front. Both the GFS and ECMWF show two progressive shortwaves traverse the CWA within a 36 hour period. The ECMWF shows the first shortwave as the stronger of the two, bringing colder 700 mb air into the region by Saturday morning. This is followed by quick warming of 700 mb temperatures as the first shortwave is quickly ejected eastward. The second shortwave moves in during the day Sunday, but lingers a bit longer, leading to cooler temperatures during the day. The GFS differs in that it keeps the first shortwave far enough to the northeast for the CWA to see limited effects. This leads to a warm day on Saturday. Second shortwave moves through during the day on Sunday, again, leading to cooler daytime highs. Still have fairly high confidence that temperatures on Saturday will be on the warm side, with a 5 degree increase in daytime highs compared to Friday. Sunday will likely feature below average, but pleasant high temperatures. With 700 mb temperatures as cold as +4C, highs may not make it out of the 70s for most locations. Aside from temperatures, could see some light precipitation develop with both of these shortwaves due to increased mid-level moisture and forcing. With a strengthening ridge building over western CONUS, expect warming temperatures and dry conditions through the beginning of the work week. Increasing 700 mb temperatures and rising 500 mb heights will likely lead to the return of 90 degree temperatures by the middle of next week. && .AVIATION /06Z TAFS THROUGH 06Z THURSDAY/... Issued at 1023 PM MDT Tue Jul 2 2024 West flow aloft will prevail. Mostly clear skies will occur through Wednesday afternoon, with periods of scattered clouds around 8000 feet. After 00Z, scattered to broken clouds from 8000 to 10000 feet will occur, with thunderstorms in the vicinity of the Nebraska terminals. Winds will gust to 30 knots at the Wyoming terminals from 15Z to 00Z. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...CLH LONG TERM...SF AVIATION...RUBIN