Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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033 FXUS65 KCYS 092153 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 353 PM MDT Sun Jun 9 2024 .KEY MESSAGES... - There is a risk for a couple of strong thunderstorms in the vicinity of the Laramie Range this afternoon and evening. - A more widespread threat for showers and thunderstorms will occur with a cold frontal passage on Monday afternoon and evening. A few storms may be severe. - Mainly dry and rather warm conditions will prevail for Tuesday through Thursday, with increasing chances for showers and thunderstorms for Friday and Saturday, along with slightly cooler temperatures. && .SHORT TERM /THROUGH TUESDAY NIGHT/... Issued at 400 PM MDT Sun Jun 9 2024 It`s a much quieter afternoon than yesterday, but not quite a blue sky day. Moist southeasterly flow over the High Plains was able to maintain a stratus deck into the early afternoon hours, which is finally almost fully broken up at this time. Even though sunshine is breaking through now, much of the areas east of I-25 is pretty strongly capped. This is leading to lower overall storm coverage compared to yesterday. However, an axis of uncapped and fairly potent instability is still present along the Laramie range, primarily in Albany and Converse counties. Low level southeast winds have been able to pull deeper moisture up into the Laramie Valley, holding the dryline in the western part of Albany county. This is the primary zone of concern for strong thunderstorms today, and we are indeed already seeing the best updrafts here. Storm motion vectors are expected to be pretty slow, so some locally heavy rainfall will be possible through the afternoon and early evening hours today. Storms could also briefly produce large hail and/or gusty winds. Any storms will probably struggle once they get east of the Laramie range/I-25 as they run into the more capped environment. A few additional showers and storms will remain possible through the night, mainly north of US20. Continued moist southerly flow will lead to some areas of patchy fog once again, but this time more limited to the I-80 summit and I-80 corridor across Laramie county. A more active weather day is expected for Monday as an upper level shortwave approaches from the west. A rapid but brief period of warm air advection will occur across the area tonight into Monday morning ahead of this wave. Expect highs warmer than today especially east of the Laramie range with a decent chance at 90F between Wheatland and Scottsbluff. Expect storms to initially fire off the dryline in Laramie/Goshen/Platte counties, but then get carried eastward more rapidly once a potent surface cold front arrives later in the afternoon. Forecast soundings show steeper lapse rates possibly exceeding 8C/km and CAPE in the 1000-2000 J/kg range. The flow aloft doesn`t look overly strong, but veering profiles atop southerly surface flow will provide sufficient shear to get a few strong to severe storms. HiRes models show fairly rapid upscale growth into a more linear system by the time the convection reaches the eastern side of the forecast area. Storms will be more progressive, but will still include locally heavy rainfall. While the main line of storms is expected to reach the eastern edge of the area around 5-7PM, we will need to watch for some post-frontal convection developing later in the evening hours as the front will actually increase low-level moisture. Lastly, a trailing vort-max may keep the chance for thunderstorms around through the night in zones north of roughly US20. Drier air works into the middle atmosphere on Tuesday, leading to reduced precipitation chances. Storms should be confined to the higher terrain and adjacent areas, and will be much more isolated than preceding days. Expect temperatures some 5-10F above normal as the ridge re-strengthens over the southwest CONUS. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... Issued at 400 PM MDT Sun Jun 9 2024 Models in reasonable late this week and into next weekend. Hot temperatures expected on Wednesday with all models showing a flat upper level ridge over the Front Range and 700mb temperatures of 15c to 18c across southeast Wyoming and western Nebraska under westerly flow. With mostly sunny/partly cloudy skies, expect high temperatures to peak in the mid 80s west of I-25, and range from 90 to 95 degrees along and east of I-25 including the western Nebraska Panhandle. May see a few late afternoon showers or thunderstorms, but hardly any of this rain is forecast to reach the ground, so kept POP below 15 percent for most areas. For later in the week, models show a backdoor shallow cool front moving into the high plains for Thursday as the upper level ridge axis amplifies northward west of the continental divide. Not as warm on Thursday, but highs in the 80s to low 90s are still expected. Very little moisture to work with on Thursday, even as the shallow cool front moves south across the area, so kept POP between 10 to 15 percent with a slight chance of showers and thunderstorms in and near the mountains. Our next forecast concern will be Friday and Friday night as models are in good agreement on the movement and placement of a central Pacific upper level low tracking northeast across southern California and into Arizona and Utah. Will have to watch this system since NAEFS is already showing 90th to 95th percentile precipitable water values and low level east to southeast winds. Deterministic models and ensembles showing a good chance for some widspread moderate to heavy rainfall due to scattered to numerous thunderstorms, mainly east of the Laramie Range. It`s unclear what the severe potential is 6 days from now, but the overall pattern is favorable for strong to severe thunderstorms. Temperatures will trend cooler as we head into Friday and Saturday, but still remain near seasonal averages. && .AVIATION /12Z TAFS THROUGH 12Z MONDAY/... Issued at 1140 AM MDT Sun Jun 9 2024 Low clouds and patchy fog will slowly lift and dissipate early this afternoon for the western Nebraska terminals and KCYS through 20z. A quick moving upper level ridge axis will be overhead today, and combined with the low stratus, may greatly limit shower and thunderstorm potential today and this evening. HAZARDS/WEATHER TRENDS: Expect KCYS to hold onto IFR CIGS for the next hour (19z) before low clouds lift and dissipate. VFR expected after 20z for the rest of the afternoon and into the evening hours. Some patchy fog or low clouds may reform tonight, but should primary impact KCYS and KSNY with brief IFR possible towards sunrise Monday. && .HYDROLOGY... Issued at 400 PM MDT Sun Jun 9 2024 Warm temperatures are continuing to produce rapid snowmelt in the high mountains of SE Wyoming. Warm to hot temperatures are expected to continue through much of the week ahead, which will lead to continued high flows along snowmelt fed rivers across the area. The latest forecasts for the Encampment and upper North Platte Rivers no longer show flood stage being reached in Encampment or Saratoga in the coming days. These rivers should peak Monday morning below flood stage. The Flood Watches/Warnings for those rivers have been cancelled. Plentiful runoff continues to come off of the Snowy range. Emergency managers reported little change in flood impacts along the Little Laramie River in Albany county. Therefore, decided to extend the Flood Warning for another 24 hours. While the stage has receded today, the typical diurnal cycle is expected to result in another peak Monday morning. The Medicine Bow River near Elk Mountain also remains at action stage. The latest crest this morning was just below flood stage. Thus, extended the Flood Watch another 24 hours as well. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...MN LONG TERM...TJT AVIATION...TJT HYDROLOGY...MN