Area Forecast Discussion
Issued by NWS Riverton, WY
Issued by NWS Riverton, WY
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907 FXUS65 KRIW 201816 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 1216 PM MDT Thu Jun 20 2024 .KEY MESSAGES... - Scattered rain showers and a couple isolated thunderstorms this evening along and east of the I-25 corridor. - More numerous in coverage Friday mid afternoon through the evening east of the Divide. - Warming trend and mainly dry conditions this weekend and into next week. && .DISCUSSION... Issued at 1106 AM MDT Thu Jun 20 2024 Current IR depicts southwest flow across the CWA from the base of a L/W trough along the west coast. Visible satellite shows low stratus across the I-25 corridor from Kaycee to Casper but slowly starting to burn off with daytime heating as of late this morning. This should erode by mid afternoon allowing for the atmosphere to reinvigorate itself for some development this evening and into the overnight hours. By 23-00Z this evening, expect some storm development across the southeast half of Natrona County and pushing east by sunset around 02-03Z. Much of the instability and more ample low level moisture will be pushed further east in the state and into the high plains, so, even with marginal severe clipping the county, these should just be general to weak storms and short lived. Otherwise, warmer temperatures and relatively light winds with some breezes for the I-25 corridor. Some redeveloping storm to general rain shower activity expected with more confidence towards midnight with a subtle mid level wave over a more moist lower atmosphere as a better situated advection push from the southeast. This should occur near the Wind River Basin towards Natrona and push northeastward through sunrise Friday morning. Not enough instability to substantiate to anything during nighttime cooling with lingering low level stratus lingering in the same areas through much of Friday morning before burning off with heating once again. Friday will see a redevelopment of more scattered thunderstorms and numerous rain showers with a stronger PVA signature supporting a shortwave up the L/W pattern to a ridge well eastward. Initiation will all be dependent on the aforementioned burning off of the lower clouds but ample low level moisture will be more prevalent into the mid to late afternoon for points east of the Divide. The main concerns will be gusty outflows with marginal severe weather possible during this time frame. DCAPE values over 500J/kg and steeper lapse rates further east one goes across the CWA will help support this. Any widespread severe weather, however, is not expected again with the much better ingredient to the east and northeast in the state and into the upper Great Plains. The better concern for the CWA will be for areas across Natrona and Johnson Counties for flooding concerns. PWAT values are expected to be over 3/4 of an inch up to and possibly over an inch further north and northeast, Buffalo included. This overall system is not overly progressive, and thus, allowing for some slower movement further north and northeast in the CWA. Early indications with a multitude of models in agreement on this taking place, boosting confidence in the process. Storms will drastically weaken towards sunset with radiational cooling and push east of the CWA before midnight. The weekend will see a warming trend continue with mainly dry conditions going forward in the long term forecast. The subtropical high near west Texas will continue to build with increasing convergence aloft with ridging extending through the upper Rockies as well. Temperatures east of the Divide should soar into the mid 90s for some with upper 90s to near 100 degrees not out of the question for the Bighorn Basin. This will allow for a blocking pattern that will keep a deep upper level low out of the Gulf of Alaska to skirt to the north. Even missing to the north, slightly cooler or not as hot temperatures expected by next week`s end but will minimal precipitation chances that look to be mainly for northern parts of the CWA and for the higher terrain. All in all, today and especially Friday look to be the best chances for any widespread accumulation going forward with drought and fire weather conditions expected to worsen in the coming weeks. && .AVIATION /18Z TAFS THROUGH 18Z FRIDAY/... Issued at 1215 PM MDT Thu Jun 20 2024 Low clouds have finally dissipated around KCPR and moved to the northeast so that all TAF sites are VFR to start off the afternoon. With the east-to-west moisture surge across central WY, isolated showers are possible over some areas of central WY as well as the northern mountains. KCPR has as 20-40% chance of thunderstorms from 22Z-02Z as the mid-level instability interacts with the low-level moisture. East of the divide is seeing some gusty E-NE wind while gusty southwest wind should push into Sweetwater County at KRKS in the next couple of hours. The "reversed" pressure gradient will keep higher moisture and clouds over most of the area overnight, and a disturbance over northern Colorado should help overnight showers to develop over central WY, with KRKS/KLND/KRIW/KWRL/KCPR potentially seeing showers after midnight and before sunrise. MVFR conditions are possible under and around the showers and storms, and KCPR especially could see low stratus again as moisture surges westward. Friday will see partly to mostly cloudy skies across the area with late morning showers becoming scattered showers and thunderstorms during the afternoon. Northern stream and southern stream disturbances are increasing instability, with heavier precipitation and stronger storms likely over Johnson and Natrona Counties. Strong outflow winds and heavy rain are the biggest concerns along with small hail. Showers and storms should persist into Friday evening as they move eastward. The western TAF sites will be the least impacted. MVFR conditions are certainly likely around the showers and storms. Please see the Aviation Weather Center and/or CWSUs ZDV and ZLC for the latest information on smoke, icing, and turbulence forecasts. && .RIW WATCHES/WARNINGS/ADVISORIES...None. && $$ DISCUSSION...Lowe AVIATION...McDonald