Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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701 FXUS65 KCYS 300944 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 344 AM MDT Thu May 30 2024 .KEY MESSAGES... - Drier and cooler today with chances for showers and thunderstorms returning overnight across the Nebraska panhandle. - Daily chances for precipitation continue into the weekend before turning drier early next week with above average temperatures. && .SHORT TERM /THROUGH FRIDAY NIGHT/... Issued at 322 AM MDT Thu May 30 2024 Latest GOES WV imagery continues to show drying across much of the CWA as a cold front continues to move across the area. Based on latest observations, it appears that Cheyenne Co, NE is the only portion of the CWA still on the warm side of the front, though temperature gradients across the front are only on the order of 5- 10F degrees. Lingering widely scattered showers will continue early this morning before mostly clearing up. Looking at slightly cooler weather to wrap up the week across southeast WY and western NE, though temperatures will still be near- normal for late May in the upper-60s and 70s. With this morning`s frontal passage to the southeast, higher theta-e values will shift into eastern CO where thunderstorm activity is expected later today. Looking at dry, breezy conditions Thursday afternoon across much of south-central WY where elevated fire weather conditions are likely for much of Carbon and Albany Co. Headed into the overnight hours, a secondary cold front associated with the upper level low expected to be over the north-central CONUS will increase low-level moisture convergence. Additionally, 700mb WAA will help increase instability profiles supporting elevated convection near the I-80 corridor between Cheyenne and Sidney. While heavy rainfall and frequent lightning appear to be the main hazards, cannot rule out some hail with the strongest cores as CAPE in the -10C to -30C layer approaches 400 J/kg per the latest RAP. Latest timing based on hi-res guidance suggests convective activity picking up mostly after midnight and continuing through the early morning hours on Friday. Another round of showers and thunderstorms will be possible Friday as additional shortwave energy crosses the central Rockies under mostly zonal flow aloft. General lee troughing across the Front Range will support southeasterly moisture advection across much of the NE panhandle with MLCAPE values approaching 1000 J/kg. However, lift could be a little more in question on Friday as better PVA looks to remain farther south in CO where latest hi-res guidance keeps the greater coverage of convective activity. Both the 00z and 06z runs of the HRRR even keep the entire CWA dry Friday afternoon as a lingering mid-level warm nose may be too strong to overcome. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... Issued at 322 AM MDT Thu May 30 2024 Thunderstorm chances will continue into the weekend, but look for a warm and dry weather pattern to take over by Monday and last through much of next week. The synoptic weather pattern will transition to a more zonal flow pattern this weekend, with a few vorticity maximums and weak shortwaves expected to traverse across the area. One disturbance will draw the dryline eastward Saturday, spilling more westerly flow and dry air into the area. However, there is uncertainty on just how far east this will get. Areas east of the dryline will still have southerly flow and sufficient moisture to have a supportive environment for thunderstorms, with a chance to become strong to severe. Areas to the west will have some marginal instability and very steep lapse rates despite the lack of moisture, but this indicates more of of a virga/wind threat. A stronger shortwave will pass through the area Sunday, edging the dryline eastward once again. While much of the area SW of a Douglas to Sidney line should see very low dewpoints on Sunday, those NE of this will have chances for another round of isolated to scattered showers and thunderstorms. Steep lapse rates and added lift from the passing shortwave may allow for some shower activity in the dry area, but this will be pretty hard to get to the ground with forecast soundings showing deep inverted-v profiles up to nearly 500-mb. Expect a warming trend through the weekend also with 700-mb temperatures Saturday around +10 to +12C, and Sunday up to +12 to +14C. Sunday may bring a chance for the first 90F day of the season in the typical hotter spots of far eastern WY and the NE panhandle. Sunday`s shortwave will knock down 700-mb temperatures during the evening and overnight, but recovery will be quick as stronger ridging begins to build back into the area. Ensemble mean 700-mb temperatures recover to +15C by 00z Tuesday over KCYS. This next warmup will also feature a stronger upper level ridge than what we`ve seen so far this season. As a result, temperatures aloft will be on the increase, leading to a more stable atmosphere despite the hot low-levels. Convective development will be hard to come by in the expected environment. The next shortwave is expected around the Tuesday/Wednesday period, and will bring what will probably be the only chance for marginal precipitation of the week. The GFS and a fair number of ensembles from both major ensemble systems keeps this system too far north to deliver any precipitation, and only a brief cool down. The ECMWF and about one third of members of the grand ensemble have a much more potent shortwave dive further south, which would result in a few scattered showers (but still nothing impressive), and a much more pronounced cool down. ECMWF 700-mb temperatures drop to near 0C for our northern counties by 00z Wednesday, while the GFS keeps those areas around +10C. This results in pretty substantial forecast uncertainty for temperatures on Tuesday through Thursday. While essentially all ensembles are showing a potent upper level ridge dominating the western US beginning mid-next week, there is discrepancy on exactly where the axis will set up, ranging from near the West Coast on the western end to directly over our area on the eastern end. The latter would lead to a period of potentially near-record heat, while the former would keep the core of the heat to our west with a more northwest flow pattern over our area. The latest ensemble suite has about 25% of members in support of the ECMWF northwest flow regime, while the remaining 75% are considerably warmer. && .AVIATION /06Z TAFS THROUGH 06Z FRIDAY/... Issued at 1140 PM MDT Wed May 29 2024 While the main thunderstorm threat has moved out, some scattered shower activity along and ahead of a cold front currently crossing the area is ongoing. A few showers with the potential for gusty winds will be pushing near to KCDR, KBFF, and KAIA over the next 2-3 hours before winds turn more northwesterly behind. A few rumbles of thunder can`t be ruled out. An initial round of low clouds may graze the northern panhandle Thursday morning with MVFR CIGs favored at KCDR and KAIA, and could extend to KBFF and KSNY. This should clear by mid morning with clearing skies later in the day. A reinforcing cold front will arrive late afternoon or early evening, bringing a quick round of gusty north to northeast winds across the High Plains towards the end of the TAF period. Shower/storm activity is expected to be fairly minimal Thursday, but a round of nocturnal thunderstorms is expected to develop late Thursday evening. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...MB LONG TERM...MN AVIATION...MN