Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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397 FXUS65 KCYS 022335 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 535 PM MDT Sun Jun 2 2024 .KEY MESSAGES... - Numerous showers and thunderstorms are expected across all of southeast Wyoming and the western Nebraska Panhandle today. Some storms will be strong to severe, with large hail and damaging winds. - Elevated to high winds will be possible across the Arlington wind prone and south Laramie Range foothills and I-80 Summit Tuesday and Wednesday. A High Wind watch may be needed. - Above normal temperatures likely Tuesday through Thursday as temperatures climb into the mid to upper 80s across much of the region. && .MESOSCALE... Issued at 219 PM MDT Sun Jun 2 2024 Thunderstorms are increasing in coverage & intensity across much of southeast Wyoming and the western Nebraska Panhandle with the primary focus along and southeast of a line from CYS to AIA. The air mass in this area has become moderately unstable, with steep low & mid-level lapse rates near 8.5 deg C/km and dew points 50- 60 deg F supporting MLCAPEs near 2000 J/kg. This combined w/ the strong mid-level flow upwards of 45 knots is supporting 40+ knot effective bulk shear values, favorable for supercell structures/ organized linear segments capable of producing large hail/strong wind gusts. Quasi-discrete supercells early this afternoon could have the potential for very large & destructive hail to 2 inches in diameter or larger, as evidenced by the recent supercell over Banner/Morrill/Cheyenne counties in the southern Panhandle which produced larger than golf ball size hail. Expect the main hazard to shift toward damaging winds over the next few hours with cold pool organization expected to support upscale growth into a long lived MCS downstream. Severe Thunderstorm Watch 375 is in effect until 10 PM MDT this evening. && .SHORT TERM /THROUGH MONDAY NIGHT/... Issued at 415 AM MDT Sun Jun 2 2024 Convection is finally wrapping up across the area as the lift associated with the latest vorticity maximum moves out to the east. High clouds and moisture can be seen on satellite ejecting across western Nebraska. The break will not be long-lived though. The broad but low amplitude trough axis is nearing the area and will finally push through later today and bring another round of showers and thunderstorms. This trough has supported the development of a modest surface cyclone in the lee of the Bighorns in NE WY/SE MT. The low and associated surface trough extending southward along the front range will push eastward this morning as a cool front, pushing the dryline mostly east of our area and ushering in west to northwest winds at the surface. Recent guidance has trended faster with this, which will lead to an earlier than usual max temperature today and also inhibit the heating potential somewhat. Convection will kick off early today, perhaps as early as 11AM with scattered to numerous showers and storms expected to cover much of the area by mid afternoon. While the low-levels will be fairly dry, precipitable water is above normal for this time of year thanks to good moisture between about 600 and 200 mb. Vertical wind is decent, but mostly speed shear as winds will be more or less mostly westerly through the column. These parameters and HiRes guidance indicate the potential for upscale growth into linear systems as the afternoon progresses. Storms will be capable of producing isolated to scattered strong to severe wind gusts. Isolated hail reports are certainly possible, but wind is the primary concern today. A more favorable environment for severe storms will be located just east of our forecast area, so we will be watching for more diverse storm hazards in the eastern row of counties where low-level moisture is better and there is some directional wind shear. On the bright side, this should not be a very long duration event, as the trough axis should pass through between 6 and 8PM and shut off the primary lifting mechanism behind. A few showers may linger into the evening, but the severe threat should be concluded by then. Again, the break won`t be very long as this next shortwave races out to the east and another strong but low amplitude wave drops into the Pacific northwest tonight. However, considerable warm air advection aloft overnight into tomorrow morning will result in reduced mid- level lapse rates on Monday and fairly minimal instability. While synoptic lift should still be enough to kick off shower activity along and ahead of the next front, severe convection is fairly unlikely. However, the marginal instability should be enough to have embedded thunderstorms. Monday will also be a fairly late show, since it`s more related to the synoptic cold front which will arrive in the evening. Look for activity to develop over our western zones in the late afternoon and progress eastward through about midnight. This trough will be more potent than the preceding ones, leading to a return of the gusty winds across the area. Elevated to near high winds will start as early as Monday night, but more information on this is found in the long term section below. && .LONG TERM /TUESDAY THROUGH SATURDAY/... Issued at 415 AM MDT Sun Jun 2 2024 The first half of the long term forecast period will be quiet in terms of precipitation chances, but we could see a period of elevated to high winds impacting the both the wind prone regions and locations along and east of the Laramie Range Tuesday and Wednesday. A strong shortwave trough will pass north of the region and at the base of this trough axis will be a band of 50-55kt 700mb winds that will be located across Wyoming. This flow will also be out of the west which is typically a good vector for our region to see some elevated wind gusts. Tight MSLP gradients located across the Laramie Range will be the driving force for the high winds across the Arlington wind prone and the I-80 Summit. In house model guidance still show greater than 50 percent probabilities for high wind gusts for Arlington and the south Laramie Range location Tuesday and Wednesday. If trends hold, a High Wind Watch may be needed for those areas where the confidence is highest for wind gusts greater than 58 mph will occur. Areas along and east of I-25 across SE Wyoming could see breezy conditions through this time period, but high winds are not anticipated at this time. Temperatures during this period wil also trend to above normals for much of SE Wyoming. These temperatures may also be boosted by the warm and dry downslope winds that will be ongoing. Current forecast shows temperatures int he mid 80s holding steady Tuesday through Thursday across much of SE Wyoming and the Nebraska Panhandle. With these warmer than average temperatures and gusty winds, there is some concern for some fire weather conditions to materialize during the afternoon hours. Heading toward the end of next week, ridging builds aloft which will keep the forecast predominately dry and warm but there is a chance we could see some afternoon diurnal convection over the weekend. && .AVIATION /00Z TAFS THROUGH 00Z TUESDAY/... Issued at 535 PM MDT Sun Jun 2 2024 Upper level disturbance which brought severe thunderstorms to portions of the region Sunday afternoon will continue to track east tonight. A few remnant showers and thunderstorms are expected until 03z. HAZARDS/WEATHER TRENDS: VFR conditions expected to prevail this evening through tonight. Brief MVFR VIS possible near KCYS and KLAR as a fast moving line of thunderstorms move through those locations, otherwise...conditions will improve after 03z. There is a slight chance at some fog develop near KAIA and KBFF early Monday morning, but confidence is too low (less than 10%) to add to the TAF at this time. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ MESOSCALE...CLH SHORT TERM...MN LONG TERM...AW AVIATION...TJT