FXUS63 KGLD 270930 AFDGLD Area Forecast Discussion National Weather Service Goodland KS 320 AM MDT Sat Jul 27 2024 .KEY MESSAGES... - A prolonged period of much above normal temperatures over 100 degrees are forecast Sunday through Thursday. Heat index values of 100 to 105 degrees are anticipated Sunday and Monday with 100 to 110 degrees Tuesday and Wednesday. - 20% to 40% chance for thunderstorms late this afternoon through about midnight. A few storms could be severe in far eastern Colorado. - 20% chance for late afternoon and early evening thunderstorms Sunday generally east of Highway 27. Low confidence that a few storms could become severe. && .SHORT TERM /THROUGH MONDAY NIGHT/... Issued at 320 AM MDT Sat Jul 27 2024 Today-tonight...latest guidance in general agreement in bringing a broken line of showers and thunderstorms into our far eastern Colorado counties around 6 PM MDT, continuing east toward Highway 25 by 12 AM MDT then out of the area or dissipating by 3 AM MDT. The HRRR is more organized with the weather system moving through while the NAM is quite dry through the 850-500mb layer with little to no signal for convection. For now, will keep pops limited to the 20% to 40% range until confidence is higher in how this plays out. Primary hazards include hail to 1" in diameter and wind gusts to 65 mph. Despite NAM/GFS 850mb temperatures rising another 2F to 5F compared to yesterday and supporting highs in the middle 90s to around 101 degrees, the better performing temperature guidance is a bit lower and advertising highs in the lower to middle 90s. Given how the better performing temperature guidance outperformed typically mixed 850mb temperatures, I followed the better performing temperatures. Low temperatures are forecast to be in the 60 to 70 degree range. Breezy to windy southerly winds are expected again today. Sunday-Sunday night...500mb flow becomes nearly zonal, in between high pressure to our southwest and troughing to our north. Presently, a weak weather system per GFS 700-500mb relative humidity moves across the area with some shower/thunderstorm potential along/east of Highway 27 or 25. NAM 700-500mb relative humidity is much drier with no precipitation forecast. Given just enough moisture and some low level wind convergence, I've included a 20% chance of afternoon thunderstorms east of Highway 27. These should weaken or exit the area to the east by early evening. There is a severe weather threat featuring hail to 1" in diameter and wind gusts to 65 mph. A blend of GFS/NAM 850mb temperatures and their bias the past 4 days plus a blend of better performing temperature guidance the past 7 days indicates high temperatures in the middle 90s to around 100 degrees in far eastern Colorado with 100-103 elsewhere. Typical mixing from 850mb would support highs in the 100 to 109 degree range, hottest across the eastern 1/2 of the forecast area. Partial mixing from 850mb is closer to the better performing temperature guidance. This is also in line with GEFS 2m temperatures. Low temperatures are forecast to be in the lower 60s to lower 70s. Monday-Monday night...we remain under westerly flow aloft, in between high pressure over Texas and low pressure to our north. With a lack of sufficient moisture from 850-500mb, we'll continue with a dry forecast. The main weather story will be the heat. The current forecast has high temperatures similar to Sunday. GFS/NAM 850mb temperatures do rise another few degrees and GEFS 2m temperatures are just a few degrees higher. Regardless, expect highs in the middle 90s to around 101 in far eastern Colorado, 102 to 105 across the rest of the area. Full mixing from 850mb would support 102 to 110 degrees. Low temperatures remain mild in the 60s to around 70. && .LONG TERM /TUESDAY THROUGH FRIDAY/... Issued at 115 AM MDT Sat Jul 27 2024 Ridging and a surface high look to be present across the region to start the extended period. Hot temperatures will continue to be the story as the region will be entrenched in this latest heat wave. Using 1000-500mb thickness a 590 dam will be present across the Tri- State area resulting in high temperatures above the triple digit mark. At this time Tuesday does appear to be the hottest day of the heat wave as the entire forecast area is forecast above the triple digit mark. The highest heat indices look to be across the east where upper 50 to low 60 dewpoints are currently present, further west across eastern Colorado much drier air will be present with heat indices less than the air temperature. Wednesday does look to be slightly cooler than Tuesday as guidance is picking up on some better 300mb and 700mb moisture which would be supportive of some cloud potential helping to keep temperatures from reaching their full potential. 1000-500mb thickness remains just under the 590 dam so this does align with my thinking of slightly cooler temperatures. Hottest temperatures looks to be east of Colby towards the eastern portion of the CWA where low to mid 100s are forecast. Some guidance does try to bring some potential for afternoon storms especially across the east where the 700-500mb moisture does increase so have added in 15% chance pops for the east. Thursday will see the upper level ridge and the surface high slowly begin to retrograde back to the west. This will continue to slowly "cool" temperatures some albeit still hot with highs in the mid 90s to low 100s across the area. As this pattern change occurs upper level flow will become more northwesterly again opening up the potential for weak waves moving along the eastern periphery of the ridge bringing the return for near daily chances for showers and storms especially across western areas. High temperatures into the latter portion of the work week and into next weekend are forecast to remain in the 90s. && .AVIATION /12Z TAFS THROUGH 12Z SUNDAY/... Issued at 320 AM MDT Sat Jul 27 2024 KGLD...VFR conditions are expected through the period. Southerly winds gusting up to 30kts are expected today, settling below 15 kts from the southeast then south-southwest tonight. There is a chance of showers and/or thunderstorms near/over the terminal in the 02z-05z timeframe with gusty winds the primary hazard. KMCK...VFR conditions are expected through the period. A southeast wind around 10kts at taf issuance will increase from the south by 14z, gusting up to 30kts through 03z. After 04z, southeast winds fall below 12kts. Showers and possible thunderstorms could impact the terminal in the 04z-06z timeframe with gusty winds the primary hazard. && .CLIMATE... Issued at 115 AM MDT Fri Jul 26 2024 July 29 High Temperature Records (F): Goodland......104 in 1947 McCook........109 in 1947 Burlington....100 in 2012 Hill City.....108 in 1917 July 30 High Temperature Records (F): Goodland......106 in 1935 McCook........105 in 2002 Burlington....101 in 2012 Hill City.....109 in 1976 July 31 High Temperature Records (F): Goodland......105 in 2002 McCook........107 in 2002 Burlington....102 in 2002 Hill City.....113 in 1934 Goodland has the potential for 5 consecutive days of highs of 100+ degrees which would tie it for the 14th longest on record. Last time this happened was July of 2012. McCook is also currently forecasted at 5 consecutive days of 100+ degree temperatures which would tie it for 20th all time. However a few days of overachieving temperatures could put them in the top 6 all time. && .GLD WATCHES/WARNINGS/ADVISORIES... KS...None. CO...None. NE...None. && $$ SHORT TERM...99 LONG TERM...Trigg AVIATION...99 CLIMATE...Trigg