Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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012 FXUS65 KCYS 010535 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 1135 PM MDT Sun Jun 30 2024 .KEY MESSAGES... - A few strong to severe thunderstorms this afternoon and evening. - Cooler week ahead before strong ridge and toasty temperatures return for next weekend. && .SHORT TERM /THROUGH TUESDAY NIGHT/... Issued at 300 PM MDT Sun Jun 30 2024 Current KCYS radar loop shows Scattered showers and widely scattered thunderstorms developing across the mountains and pushing east-northeast into the high valleys and high plains along the I-25 corridor this afternoon. Thermodynamic profiles and current mesoscale analysis are not nearly as impressive compared to what models were showing yesterday. Although 0-6km shear is currently around 40 to 45 knots, MLCAPE is still around 500 to 800 j/kg this afternoon with the best 1-6km lapse rates far north of I-80. Overall, dynamic forcing is limited and nearly nonexistent at this time with the only notable upper level shortwave lifting off to the northeast earlier today. With all this said, low level moisture is still impressive today with dewpoints in the 50s to low 60s, CIN has been slowly eroding early this afternoon, and a frontal boundary is located just west of the I-25 corridor, providing some low level lift and convergence. Therefore, didn`t change the forecast all that much with scattered showers and thunderstorms forecast through late this evening...gradually pushing east into western Nebraska. Expect a few of these storms to become strong to marginally severe. Strong gusty winds appear the most likely mode of severe weather into this evening. Expect some of the activity to linger after sunset, and possibly after midnight, as the Pacific upper level trough slides east with increasing jet energy aloft. For Monday and Tuesday, models remain in good agreement with the next Pacific cold front, and associated broad upper level trough, rapidly progressing eastward across the northern Front Range Monday and Monday night. Most of Monday should be a pretty nice day (outside of the wind) with highs in the 80s...to around 90 for areas below 5000 feet. It should start out pretty mild due to persistent cloud cover and low temperatures likely in the mid 50s to mid 60s...possibly as high as 70 degrees across the northern Nebraska Panhandle due to the persistent low level jet. Winds are forecast to shift into the west and increasing through the afternoon with gusts as high as 50 MPH possible. Not expecting gusts over 58 MPH at this time, but the last few wind events were a last minute surprise...so will continue to monitor these trends for now. These winds will also start bringing in some much drier air with a dryline-like feature develop just east of the Laramie Range and progressing rapidly eastward into western Nebraska through early to mid afternoon. This should greatly limit convection across the area, even with better forcing compared to Sunday. However, this drier air will have a hard time moving into east central Wyoming and the northern Nebraska Panhandle as a surface low develops and keeps winds relatively light or light out of the northeast for places such as Chadron, Harrison, and Lusk. This generally area (east central Wyoming and the northern Nebraska panhandle) will have the best chance to see severe thunderstorms Monday afternoon where SPC continues the Slight Risk for Severe Thunderstorms on Day 2. Coverage of thunderstorms will decrease even further Tuesday as the much drier airmass enters the forecast area with dewpoints dropping into the 20s and 30s with west to northwest winds. Isolated thunderstorms are still possible across western Nebraska and over east central Wyoming as the trough axis and upper level vort max slowly moves eastward over central Wyoming where surface dewpoints will still be in the 40s through the afternoon. It will be slightly cooler on Tuesday with highs in the mid 70s to low 80s. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... Issued at 116 PM MDT Sun Jun 30 2024 The overall weather pattern surrounding the Independence Day holiday looks generally cool-ish and dry-ish for early July. On the synoptic scale, this will be driven by the strong ridge aloft developing near or just offshore of the west coast this week. The resulting northwest flow pattern over the northern Rockies/northern Plains will suppress the monsoon moisture back to its core region in Mexico and southern AZ/NM, while frequent shortwave troughs swing through the area keeping the brunt of the summer heat at bay. On Wednesday, our area will be in between shortwave troughs. WSW flow aloft ahead of the second trough will support decent warm air advection across the area, pushing highs near to a few degrees above normal. Model guidance is still quite consistent in showing a sharp dryline developing somewhere across our area, but there its exact position ranges from the eastern border of the forecast area to just west of the WY/NE border. Expect some thunderstorm development in the afternoon along the dryline, an there will be the potential to become strong to severe. The main uncertainty remains dryline position though, as a solution on the eastern end of guidance would keep most of the storms and precipitation to our east, while the western end of guidance would result in a more active day for our area. The shortwave trough axis will push through around the Wednesday night time frame, bringing with it a fairly strong surface cold front. This is expected to lead to a cooler day on Thursday (July 4th) across our area, with some gusty northwest to northerly winds possible. Precipitation chances look more limited, but a few showers and storms are still possible mainly over and near the higher terrain, and across the northern portion of the forecast area. The trough starts to move out of the area on Friday, which should leave a pretty nice day in place across the area. Temperatures should remain a few degrees cooler than normal with lighter winds. There will still be a chance for afternoon/evening shower activity, but it looks quite limited with precipitable water below normal for this time of year. Temperatures will warm back up to near or slightly above average for Saturday. While model guidance is still somewhat split for next weekend, more members have been coming on board with continuing to delay the return of the heat. Rather, recent trends have been towards another shortwave trough coming through around the Sunday time period, which would continue to keep temperatures on the cool side. Given the lead time though, there is more uncertainty for the weekend temperatures and precipitation chicanes. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1131 PM MDT Sun Jun 30 2024 Forecast concerns with the 06Z TAFs will be low stratus in the Panhandle this morning...followed by thunderstorms Monday afternoon. Already getting IFR conditions at Sidney currently and Alliance is on the verge of going down. Showers may keep them up temporarily until they move off to the east. HRRR showing IFR/LIFR conditions at both airports and possibly KBFF if winds come around to the southeast. One more round of thunderstorms this afternoon as a boundary pushes all moisture east into central Nebraska. Will get better timing on the upcoming 12Z TAFs. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...TJT LONG TERM...MN AVIATION...GCC