Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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383 FXUS65 KCYS 162337 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 537 PM MDT Fri Aug 16 2024 .KEY MESSAGES... - A few severe thunderstorms possible this afternoon across eastern zones where moisture will be better for storm development. - Seasonable temperatures will continue through the period. Showers and thunderstorms will be most likely on Monday, Wednesday and Thursday, with less coverage for Tuesday. && .SHORT TERM /THROUGH SUNDAY/... Issued at 210 PM MDT Fri Aug 16 2024 Current Visible Satellite loop shows mostly sunny skies across southeast Wyoming and western Nebraska early this afternoon with surface observations indicating temperatures in the 80s to near 90 across the area. One lone thunder shower is currently northwest of Cheyenne, but is struggling to intensify as it moves into the I-25 corridor. This is mainly due to drier air aloft, especially above 8000 feet as indicated by recent observations with dewpoints falling in the higher valleys and midslopes. Further east, dewpoints have remained in the 50s to near 60 and have even increase a few degrees since this morning indicating some weak moisture advection across the eastern plains. Models all show a dryline boundary forming along the I-25 corridor shortly and progressing eastward through this afternoon and into this evening. With a dewpoint of 34 at Vedauwoo, and 53 at Cheyenne...believe this boundary is developing as we speak. Along and to the east of this boundary is where isolated showers and thunderstorms will form. Expect the coverage to be limited today due to the drier airmass aloft, which will take it`s time mixing down to the surface. CAMs and high res guidance shows only a few thunderstorm cells developing this afternoon and mainly impacting western Nebraska and far eastern Wyoming. Can`t rule out one or two strong to marginally severe cells, but not terribly confident either due to limited coverage and forcing. Kept POP between 15 to 25 percent into early this evening, with showers and thunderstorms dissipating around sunset. For Saturday, drier airmass will remain over the whole forecast area with the potential for thunderstorms less than 5 percent through Saturday afternoon. 700mb temperatures will continue to increase between 16c to 19c, resulting in highs in the upper 80s to upper 90s...hottest below 5000 feet. Models show a fast moving upper level disturbance lifting north across western Colorado and southern Wyoming later Saturday. This feature may trigger widely scattered late evening thunderstorms across south central Wyoming as some cooler air aloft moves into Carbon and Albany counties. Confidence is limited at this time, so kept POP around 20 to 30 percent for now. This will be the start of the next monsoon push as PWATs increase above 0.75 to around 1.00 inch across the forecast area on Sunday and early next week. Similar weather on Sunday with highs in the mid 80s to mid 90s across the area. Upper level disturbance is forecast to shift eastward during the day with a more favorable environment for showers and thunderstorms. Expect most of this activity to be in the late afternoon and evening hours as moisture will be slow to increase through the day. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Issued at 116 PM MDT Fri Aug 16 2024 A persistent ridge of high pressure over the southwestern CONUS will remain in place for the entirety of the long-term period from Sunday night through Friday of next week. With this ridge in place, expect afternoon high temperatures to remain above average by around 5 to 10 degrees. Temperatures would probably be higher through the long- term period if not for the prominent monsoon pattern expected to continue underneath the ridge through the week ahead. PWAT normalized anomalies from both the GEFS and ECMWF ensemble guidance suggest running around 1-2 sigma through the period, with peak deterministic PWAT values themselves reaching in to the 1.25" category across southeast Wyoming and western Nebraska by Thursday and Friday. As one would expect, daily monsoon showers and thunderstorms will be possible each day, first originating in orographically favored areas in the high terrain and then moving downvalley by the later afternoon and evening hours each day. Tuesday appears to be the driest day of the week given a slight push of dry air from the north, with recovering chances of thunderstorm activity each day through Friday. On Wednesday and Thursday, a piece of the subtropical jet is progged to drift northward around the ridge, increasing flow in the mid and upper levels. This increased wind shear will help support a better chance of organized convection as some guidance supports the idea of one or two thunderstorm clusters/outflows pushing well east of the mountains and into the WY/NE high plains in the evening hours each day. Overall, total precipitation through the long-term has at least a 60% chance of running above average given the favorable monsoon pattern. There is high confidence (above 60%) of seeing above-normal temperatures as well through the period. && .AVIATION /00Z TAFS THROUGH 00Z SUNDAY/... Issued at 535 PM MDT Fri Aug 16 2024 Isolated showers with occasional lightning continue between KCYS, KBFF, and KSNY, but have been short-lived and expected to dissipate over the next hour or two. VFR conditions expected across area terminals through the forecast period. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...Red Flag Warning until 8 PM MDT this evening for WYZ420>423- 425-427-428. NE...None. && $$ SHORT TERM...TJT LONG TERM...RUBIN AVIATION...MB