700 FXUS65 KCYS 071731 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 1131 AM MDT Wed Sep 7 2022 .SHORT TERM...(Today through Friday) Issued at 445 AM MDT Wed Sep 7 2022 Stagnant weather condition continue to prevail across a majority of the cwa at this time. Much above average surface temperatures as of 9Z remain in the 60s and 70s for areas east of I-25, and in the middle 50s to middle 60s west of I-25. The warmest temperatures reside, as of 10Z, in the northern NE Panhandle where the middle to upper 70s are present due to elevated wind gusts that have mixed the inversion temperatures down to the surface. The coolest temperatures reside in the highest mountain RAWS sites of the Snowy/Sierra Madre Ranges where the upper 30s to middle 40s are present due to this region being above the inversion aloft. A stacked dome of high pressure is presently centered over UT per RAP 500mb analysis with a nearly 600 dam height analyzed in the atmosphere! GOES-16 Water Vapor satellite imagery depicts a large region of dry air being present beneath this dominant ridging pattern over our cwa as well, which is supported by poor RH recovery in several locations where 15-30% have been observed. Overnight observations across the I-80 corridor to Rawlins and Rock Springs have returned reduced VIS and hazy conditions during the late evening and overnight hours. Have continued the AQA for the western forecast zones through 1PM MDT, and would not be surprised if we extend this headline due to hi- res guidance suggesting the haze and smoke sticking around through a majority of the day. As the day presses on, the surface temperatures will make it feel like the outdoor "oven" is stuck on high heat/broil. Near record high to record high temperatures are anticipated at most locations despite the hazy conditions being present aloft. With the continued overperformance of surface temperatures yesterday despite haze being present, have decided to not lower the anticipated highs by a degree or two. We are well above the 95th to 99th percentile of the NBM for afternoon high temperatures today. This will mark the 4th day in a row of near record to record high heat, so if folks are planning on being outdoors for prolonged periods of time, frequent water breaks are recommended. For the Wednesday night into Thursday morning period, we can expect little relief with respect to the much above average overnight lows and dry conditions. A strong LLJ ahead of a developing surface low will cause 800-850mb winds to surge across the Panhandle. GFS model guidance is trending with 35-50 knots at 850mb between 6Z-12Z Thursday. While this weather setup isn't out of the ordinary for Meteorological fall, there is a strong signal for subsidence to be coupled with the increased winds, which could easily mix the warmer temperatures aloft down to the surface. Have decided against a Heat Advisory headline for northern Sioux and Dawes County for this forecast package regarding the Wednesday night to Thursday morning timeline, but it certainly warrants another look with the next round of 12Z/18Z model data. Thursday into Thursday night will be an active weather day due to anticipated near record high to record high temperatures, fire weather concerns, and the arrival of a strong cold front. High resolution and medium range model continue to show that we will have another hot day for the cwa. Very poor RH's will be present between 7-15% with elevated winds and wind gusts. Wind gusts across a majority of SE WY will be up to 25-35mph by the afternoon hours. This strong signal has allowed for a larger lead time on issuing a Red Flag Warning for the areas that have the highest confidence. The Nebraska Panhandle may not have as high of winds, but have gone ahead with a Fire Weather Watch due to similar conditions as that of SE WY despite the slightly weaker wind gusts being advertised at this time. As the strong WAA ensues, we will see a strong cold front propagate towards the region from northwest to southeast late Thursday afternoon into the early morning hours of Friday. Unfortunately, the initial push of much cooler air may not be accompanied by much moisture. The GFS depicts slight cooling due to rain showers and possible convective initiation by 0Z Friday through SE WY, and into the NE Panhandle by 6Z Friday. This is the most aggressive scenario at this time of inspection, with a majority of the shortwave energy and rainfall being advertised as further to the north. If the cold front sweeps through the area as advertised per the GFS, we will see a sharp drop in temperatures between 0Z and 12Z for almost all of the cwa on the order of 30 to 40+ degrees, especially the NE Panhandle. On Friday, we are seeing much better model agreement regarding the previously erratic forecast high temperatures between several of the models. A secondary, and stronger push of cool air coupled with cloud cover from an upslope wind regime is becoming more likely. The cooler, dense air mass is forecast to get hung up on the Laramie and Front Range, so surface temperatures due east of these areas could see the daytime maximum high temperatures occur near the midnight hour of early Friday morning. Areas that see extended cloud cover for a majority of Friday will struggle to get out of the 50s for the afternoon maximum. This will be a sharp contrast with respect to Thursday, as daytime highs may be 35-50 degrees cooler east of the Laramie Range for Friday afternoon. As previously mentioned, the cold air will get hung up along the Laramie Range, but warmer afternoon highs will still be expected west of the Laramie Range. High temperatures may still eclipse the 70 degree mark over western Albany County and Carbon County. .LONG TERM...(Friday night through Tuesday) Issued at 445 AM MDT Wed Sep 7 2022 The season's first taste of Autumn will be upon us this weekend with cool temperatures and precipitation chances. The cool, fall air initially arrives Friday behind Thursday night's cold front. However, a colder push of air is progged to arrive Saturday morning as the main upper-level trough digs further south. 700 mb temperatures drop as low as -2C for our far northern zones! The 0C isotherm could make it as far south as Cheyenne, per the ECMWF. Both the ECMWF and the GFS keep the coldest air on the east side of the Laramie Range as high pressure builds off to the west. Most deterministic models portray solutions colder than the NBM, with high temperatures in the 40s and 50s on Saturday for Cheyenne. The GFS is one of the warmer solutions with highs in the 60s on Saturday. Ensembles also tell a similar story with most members of the ECMWF Ensemble showing highs in the upper 40s for Saturday and approximately half of the GEFS members showing highs in the upper 50s and 60s. One possible answer to this temperature discrepancy is that the ECMWF shows more cloud cover and more precipitation on Saturday than the GFS. Decided to trend temperatures towards the ECMWF as most other models want a colder solution on Saturday and the ECMWF has been fairly consistent form run to run. Precipitation also looks more likely with this secondary push of cold air. ECMWF still looks to be the most aggressive with precipitation with decent 6 hour QPF amounts during the day on Saturday. Areas east of the Laramie Range look to have the best chance at seeing precipitation, especially our northern zones and the Nebraska panhandle. These areas could see light to moderate rain at times. There is still a good deal of uncertainty with regards to both precipitation and temperature on Saturday. Would like to see better model agreement, but nonetheless, its probably safe to say that Saturday will be a cool, fall day with below average temperatures. Some people may wake up to a frosty morning on Sunday! Low temperatures Sunday morning may fall into the 30s for areas west of the Laramie Range, which could lead to patchy frost. Sensitive vegetation could be impacted by the sharp temperature change. A quick warm-up is expected Sunday into Monday as an upper-level ridge builds over western CONUS. Highs on Sunday will be in the 70s, with 80s likely on Monday. Dry conditions should persist while under the ridge. A disturbance looks to move through the area on Tuesday which could bring slightly cooler temperatures and another chance of precipitation. && .AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon) Issued at 1128 AM MDT Wed Sep 7 2022 Mainly VFR conditions expected for the forecast period. Smoke from distant wildfires is occasionally reducing visibility below 10 SM, but should remain above 5SM. A low level jet is expected to develop tonight over Nebraska panhandle terminals. This will likely produce some LLWS with 40 to 45-kt winds just above the surface. Gusts may occasionally mix down to the surface through the night. Turning breezy with more westerly flow by late morning Thursday. && .FIRE WEATHER... Issued at 445 AM MDT Wed Sep 7 2022 Near record to record high temperatures will continue today and Thursday. Minimum RH values of 7-15% will occur, but wind gusts will remain between 10-20mph today. Poor overnight RH recovery is anticipated late tonight into Thursday morning, with maximum RH of 20-30% for SE WY FWZs as wind gusts increase. Red Flag conditions are expected Thursday as west to northwest winds sustained 15-20mph, with gusts up to 35mph for SE WY. Near critical fire weather conditions are expected for the NE Panhandle on Thursday, with gusts up to 25-30mph possible. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...Fire Weather Watch from Thursday morning through Thursday evening for WYZ417-431-433. Red Flag Warning from 10 AM to 7 PM MDT Thursday for WYZ418>425- 427>430-432. NE...Fire Weather Watch from Thursday morning through Thursday evening for NEZ434>437. && $$ SHORT TERM...BW LONG TERM...SF AVIATION...MN FIRE WEATHER...BW