Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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922 FXUS65 KCYS 300502 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 1102 PM MDT Sat Jun 29 2024 .KEY MESSAGES... - A few strong to severe thunderstorms Sunday afternoon and evening. - Cooler week ahead before strong ridge and toasty temperatures return for the weekend. && .SHORT TERM /THROUGH MONDAY NIGHT/... Issued at 305 PM MDT Sat Jun 29 2024 Current observations across the region show pleasant weather with temperatures generally in the 70s to low 80s and light winds. A few showers have developed in the mountains, but have generally weakened as they pushed east into the I-25 corridor. Can`t rule out a few thunderstorms this afternoon and this evening as WAA and the low level jet strengthen. However, moisture will be limited, so expect coverage to remain isolated or widely scattered through tonight across southeast Wyoming and mainly the southern Nebraska Panhandle. Otherwise, expect south to southeast winds to increase overnight with gusts up to 40 MPH possible. Not seeing a clear signal for any fog tonight, so will keep out of the forecast for now. A more active day on Sunday expected as gulf moisture advects into the region with upslope south to southeast winds. A quick look at NAEFS shows PWATs in the 90th to 98th percentile across most of the area, including Carbon and Albany counties. Thermodynamic profiles look good with 0-6km shear of 40 to 50 knots and 1000 to 2000 j/kg of CAPE. The only limiting factor is the lack of any forcing with an upper level ridge axis pushing over the area and increasing 500mb to 700mb temperatures...indicating upper level subsidence. There is some weak jet energy aloft, but forcing appears pretty limited at the jet stream level. Kept POP between 20 to 35 percent for this reason, even though a few strong to severe thunderstorms are possible across eastern Wyoming and western Nebraska. Agree with SPC`s marginal risk along and east of I-25, so will not word the forecast too aggressively quite yet. For early next week, all models are in agreement and show another Pacific cold front and associated broad upper level trough digging southeast and then progressing eastward across the northern Front Range Monday and Monday night. Most of Monday should be a nice day with highs in the 80s...to around 90 for areas below 5000 feet. It should start out pretty warm in the morning 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. Would like to note that a few of our previous wind events have overperformed lately, so may need a last minute High Wind Warning for a few locations along and west of the I-25 corridor. As of right now, in-house wind models have trended lower on probabilities of wind gusts higher than 55 MPH. These winds will also bring 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. Kept POP mainly between 20 to 30 percent, with higher probs in the mountains. The most favorable area to see some strong to severe thunderstorms (likely outflow winds) will be the southern and central Nebraska panhandle. && .LONG TERM /TUESDAY THROUGH SATURDAY/... Issued at 205 PM MDT Sat Jun 29 2024 We`ll be heading into a fairly messy weather pattern for summer next week. The overall synoptic weather pattern for much of the week will be characterized by a very strong ridge located roughly near the west coast, leaving northwest-ish flow over our area. Frequent shortwave intrusions are expected over the course of the week that should help moderate the heat somewhat, at least through the end of the operational forecast period. There is reasonably good agreement amongst models that the first in this shortwave series will push through around Tuesday, but with westerlies pushing the dryline towards the eastern boundary of the forecast area. With reduced moisture, we probably won`t be looking at a lot of precipitation with this aside from the ever present high-based showers and thunderstorms. The influence of the shortwave will also lead to a cooler day with highs potentially a few degrees below average for the time of year. Look for a brief rebound in temperatures on Wednesday between shortwaves with a period of southwest flow aloft and warm air advection before the next wave arrives. Models are also in good agreement on a very sharp dryline developing somewhere across the area. Most have this fairly close to the WY/NE border. The dryline combined with a strong surface cold front may lead to stronger convective forcing Wednesday. Right now this looks like the day to watch for the week, but this setup will be sensitive to subtle changes in dryline position, frontal timing, etc., so this isn`t a sure bet yet. If we have strong thunderstorms develop, the best area looks to be in the Nebraska panhandle. After this, there is good confidence in a northwest flow pattern developing for the Independence day holiday, but ensembles are split on how strong this trough will be. Both major deterministic models have a strong trough coming through for Thursday and Friday, leading to well below normal temperatures, but there is quite a bit of spread. The 25th to 75th percentile of 700-mb temperatures at 00z Saturday ranges from 7C to 14C at KCYS. Due to this uncertainty, decided not to deviate much from the NBM forecast. Temperatures should return back to normal around Saturday. && .AVIATION /06Z TAFS THROUGH 06Z MONDAY/... Issued at 1101 PM MDT Sat Jun 29 2024 VFR conditions currently across area terminals with a few lingering showers late this evening. Expecting the southerly LLJ to increase across the NE panhandle over the next few hours with winds gusting 30-40 kt. This southerly flow will begin to increase moisture advection across the area, potentially leading to low cloud development along the I-80 corridor from KCYS to KSNY. However, HREF probability of MVFR ceilings is only around 20% at this time starting around 12z Sunday morning. Thunderstorms are expected Sunday afternoon that could lead to strong winds and reductions to visibility with heavy rainfall. Will leave any mention of potential TSRA and timing until the next TAF issuance. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...TJT LONG TERM...MN AVIATION...MB