842 FXUS65 KCYS 282116 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 316 PM MDT Sun Jun 28 2026 .KEY MESSAGES... - A few evening and overnight showers and thunderstorms are possible over the High Plains, mainly north of the North Platte River. - Southwest winds will increase Monday, bringing the potential for critical fire weather conditions over the High Plains and a brief period of high winds in the wind prone areas. - Elevated fire weather conditions will continue for much of the week ahead. && .SHORT TERM /THROUGH MONDAY NIGHT/... Issued at 315 PM MDT Sun Jun 28 2026 A sprawling, unseasonably strong upper level low continues to circulate over the northern Rockies this afternoon. Southwest flow continues aloft with dry air moving in from the desert areas. Temperatures are a little cooler across the area compared to yesterday, generally in the upper 70s to 80s for most. Breezy conditions are also continuing, but again, winds are less strong than yesterday. This will become a bit more interesting tonight. A surface high pressure system is moving into western Wyoming, with a boundary currently stalled roughly from Medicine Bow Peak towards the southwest corner of South Dakota. Meanwhile, lee cyclogenesis is occurring over northeast Colorado. This is expected to strengthen rapidly this evening and then begin to eject northeastward overnight. The surface cyclone is unusually strong for summer. NAEFS mean MSLP is approaching the climatological minimum this afternoon and evening. As this system strengthens, it will pull the stalled boundary to the south and east, ushering in a surge in northwest winds across the area overnight. Expect most of the area to remain breezy to windy overnight as a tight pressure gradient remains in place over the plains. Meanwhile, a secondary vort-max rotating around the primary upper level low will dig into the Great Basin, enhancing southerly flow aloft on top of the developing surface cyclone. The combination of overrunning warm air advection aloft and potent low to mid level frontogenesis will support fairly strong forcing for ascent overnight. Expect a few showers to develop late afternoon into the evening along this boundary, mostly inside/north of a Douglas to Wheatland to Chadron line. Elevated instability will increase through the evening as low level moisture recovers. Expect showers to have a bit more thunder as the evening goes on. Scattered thunderstorm potential will continue all through the night, winding down around sundown. High resolution models are not in very good agreement on the extent of this nocturnal activity, but PoPs in the 20 to 50% range are maintained in our northeastern areas (Niobrara, northern panhandle) due to the potent forcing. Models often struggle to handle nocturnal elevated convection, and the large- scale picture suggests this potential tonight even if high resolution models don't all show this. In addition, look for some shower activity moving into Carbon County overnight associated with this system. Temperatures will be cool enough that we can expect some snow mixing in about 9000 ft in elevation or so. Those camping at high elevation tonight can expect a chilly night with near freezing lows and perhaps a dusting of snow by morning. The aforementioned vort-max will swing through the area around midday Monday. Expect a brief surge in low level height gradients and 700-mb winds ahead of the boundary. Models have come into better agreement on the wind forecast. Both the GFS and NAM have 700-mb Craig to Casper height gradients peaking around 50 to 55 meters between 15z and 18z Monday, which is supportive of marginally high winds. Cross barrier MSLP gradients look good for high winds, but the window is very short as this gradient is mainly associated with a progressive frontal boundary following the vort-max aloft. So, overall, expect winds to turn back to southwest and then rapidly increase Monday morning, peak around noon, turn slightly more westerly behind the frontal boundary early afternoon, and then weaken through the remainder of the afternoon. This is pretty much a toss-up for high winds, with in-house guidance showing probabilities for high winds at 50% for Arlington and Bordeaux, and 40% for the I- 80 summit. Probabilities around 30 to 40% also extend to other areas adjacent to the typical wind prone areas in Carbon, Converse, and Platte counties. While confidence is fairly low, it is high enough at this time to at least warrant a High Wind Watch for the wind prone areas. A brief period with gusts of 60+mph may be possible in the adjacent areas, but due to the short window and lower probabilities, decided to hold off on including any of those areas in the watch. While hitting 60+mph is more uncertain, we do have high confidence in a widespread breezy to windy day. Expect fairly widespread gusts in the 40 to 50 mph range across the area. While temperatures will be cooler, a very dry airmass will continue to filter into the area, pushing RH to near critical values. South of the North Platte River, RH should be easily critical, but winds will be a little lighter here. Confidence in reaching critical RH values north of the North Platte River is lower, but due to the strong expectation for winds, the entire area was included in the Fire Weather Watch. Control issues are likely with these winds, even if RH doesn't quite reach criteria. Monday will bring little to no chance for thunderstorm activity due to the very dry airmass overspreading the area. && .LONG TERM /TUESDAY THROUGH SATURDAY/... Issued at 315 PM MDT Sun Jun 28 2026 Tuesday, The upper level low will be lifting off to the east back into the Northern Plains and Canadian providences as a strong ridge over the Midwest and Eastern Seaboard begin to build. By the late evening on Tuesday another weak shortwave will push through the Intermountain West following the parent low moving into Manitoba. There will be a few lobes of vorticity to play with as this wave moves through but it looks as though all the forcing and shower potential may lie only in the Panhandle area. As we progress past Tuesday we become stuck in Southwest flow on the front side of this ridge. The warm, dry, but smokey air from the Desert southwest and the Colorado/Utah fires will be filtering over the area for the remainder of the week. This will limit our rain chances as this dry air removes all the moisture from the surface and lower dewpoints and RH values. The models have a few shortwaves pushing into the region past Tuesday but with no moisture and very limited forcing there isn't much confidence these waves will do anything beside increase our gradient and produce the normal amount of wind through our area. Fire weather will be the biggest concern as our fuels will enter a curing state once again despite our stormy 7 days last week. Winds will be light to marginal so it may be difficult to reach Red Flag criteria for most of our area despite the low RH and curing fuels. There is a trough that is suppose to move through 4th of July weekend that the models are trying to figure out so we may get some rain but the Intermountain West would need a pretty big trough to dig through the four corners region for anything substantial to reach the ground. So we shall see how the models trend but the 4th may just be as dry as the rest of the week as well. && .AVIATION /18Z TAFS THROUGH 18Z MONDAY/... Issued at 1133 AM MDT Sun Jun 28 2026 On Satellite we may have a cumulus field starting to develop which may give KCYS a brief shower but its more for the skies to become scattered to broken this afternoon. This evening the trough that is slowly pushing through may also give KBFF a brief shower but its more likely to be like KCYS and have scattered to broken skies. The models have a weak thunderstorm dropping down from South Dakota to give KCDR thunderstorm chances in the late evening otherwise every other terminal looks dry. The winds look to pick up tonight into tomorrow as that trough moves into the Northern Plains. Gusts between 35-40 kts will be possible tomorrow afternoon. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...Fire Weather Watch from Monday morning through Monday evening for WYZ417>419-430>433. High Wind Watch from Monday morning through Monday afternoon for WYZ106-110-116. NE...Fire Weather Watch from Monday morning through Monday evening for NEZ434>437. && $$ SHORT TERM...MN LONG TERM...MM AVIATION...MM