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
089 FXUS65 KCYS 032120 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 320 PM 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. && .UPDATE... Issued at 258 PM MDT Wed Jul 3 2024 Severe Thunderstorm Watch continues for western Nebraska. So will keep our updated-short term discussion brief due to active weather late this morning through this afternoon. Last night`s short term discussion is still valid through Independence Day. First round of severe thunderstorms persists across Cheyenne County with several reports of large hail up to 2 inches in diameter across Cheyenne and Morrill counties, gusty winds, and even a few tornado reports. Expect this area to push off to the south and east with relatively quiet conditions over the next few hours. Strong cold front is quickly moving south across northern Wyoming and southwest South Dakota. This will be the start of round 2 across east central Wyoming and northwest Nebraska this evening through tonight. Timing is a little uncertain with high resolution models showing some variability on coverage and the areal extent this afternoon. With the dry airmass and elevated mixing layer already pushing across Converse County and the I-25 corridor at this hour, expect the 2nd round of the severe threat to be confined to Niobrara county and the northern Nebraska Panhandle between 7 PM through midnight tonight with a few cells possibly developing across the southern Panhandle after midnight due to high elevated CAPE. Solid MUCAPE/elevated instability along with forcing along and ahead of the front will be the primary ingredients. Would like to note that the drier airmass has penetrated a little further east than previously expected...which may result in a lower thunderstorm coverage tonight. Not expecting any fog after the front moves through the area due to the much drier airmass. Otherwise, the previously advertised cooler temperatures late this week are still on track. && .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 /18Z TAFS THROUGH 18Z THURSDAY/... Issued at 1109 AM MDT Wed Jul 3 2024 VFR expected at terminals through late afternoon. VCTS will transition to -TSRA/-SHRA for KSNY this afternoon, bringing the chance of MVFR, and wind gusts up to 30-40 knots briefly. The northern Panhandle terminals are anticipated to stay in VFR until after 0Z when another round of -TSRA/+TSRA arrives for KAIA and KCDR, which will bring fluctuating IFR/MVFR conditions briefly. Wind gusts in the NE Panhandle will be gusty and erratic near and around VCTS, so wind gusts up to 30-40 knots are possible. SE WY terminals will see VFR the entire forecast period, with wind gusts up to 30-40 knots this afternoon before tapering off overnight. Please see individual TAFs for further information. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ UPDATE...TJT SHORT TERM...CLH LONG TERM...SF AVIATION...BW