Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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804 FXUS65 KCYS 051739 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 1139 AM MDT Sun May 5 2024 .KEY MESSAGES... - Warmer today with strong southerly winds and the chance (~30%) for showers and thunderstorms to develop near the NE/WY border late this afternoon. - Accumulating snowfall expected starting late tonight in the Sierra Madre and Snowy Ranges, specifically at elevations over 8000 feet. - Strong winds return to southeast Wyoming and western Nebraska Monday with a prolonged period of elevated winds continuing through midweek. Wind gusts of 70-80 mph are possible for wind-prone locations. && .UPDATE... Issued at 956 AM MDT Sun May 5 2024 Had to upgrade the Dawes County High Wind Watch early as Kings Canyon RAWS reporting 63 mph currently. Looks like there may be a lull in the winds up there this afternoon...but GFS 800/850mb winds really show low level jet picking up again after 00Z. So ran the warning through 06AM Monday. && .SHORT TERM /THROUGH TUESDAY/... Issued at 330 AM MDT Sun May 5 2024 Latest GOES WV imagery shows a large scale upper level low churning across the NV/OR border and will continue to move towards the Intermountain-West today. Strong southerly flow ahead of this system will see moisture advection into the NE panhandle with CAMs showing dew points in the mid-40s. With a dryline setting up near the WY/NE border, will need to monitor this afternoon for enhanced areas of convergence along with increasing lift approaching from the west that could be supportive of shower development late this afternoon. Could even see a few thunderstorms develop with latest RAP soundings analyzing a few hundred J/kg of MLCAPE present and strong enough wind shear to support organized cells. Otherwise, expecting a warm day across southeast WY and western Ne with afternoon highs in the upper-60s to 70s. As far as headlines go, went ahead with upgrading to a High Wind Warning across much of western Carbon Co today with strong 50+ kt southerly 700mb flow moving in aloft ahead of the large scale upper level low. Steep low-level lapse rates will support vertical momentum transport during the afternoon and early evening leading to occasional gusts around 60 mph near Baggs, Rawlins, and Muddy Gap. Stronger flow will continue to move east this evening with a frontal passage bringing ample lift across areas west of the Laramie Range early Monday morning. Higher elevations above 8000 feet could see accumulating snowfall, mainly in the Sierra Madre and Snowy Ranges. Went ahead with issuing a Winter Weather Advisory for the Sierra Madres beginning late tonight as 6 to 12 inches of snowfall will be possible by Monday afternoon. Farther east across the NE panhandle Sunday night, a tight east-west mslp gradient develops ahead of the lee troughing with the approaching system. This will help setup a strong nocturnal LLJ over the NE panhandle with the strongest winds likely across the Pine Ridge, possibly downsloping into the Chadron area. Therefore, decided to add a new High Wind Watch for Dawes Co for Sunday night. Jumping ahead to Monday, strong winds still appear likely across much of southeast WY, possibly expanding in the NE panhandle during the afternoon in the wake of the strong negatively tilted upper level low with a near 980mb surface low developing in western SD. NAEFS continues to show climatological maximum 700mb winds across much of southeast WY and continues to trend upward. This is also highlighted by in-house random forest guidance with probabilities of high winds climbing to over 90% with the 18z and 00z model runs. Additionally, this ML guidance is now suggesting 70-80 mph wind gusts will be possible for wind-prone locations along Interstate 80 near Arlington and Interstate 25 near Bordeaux. Therefore, decided to issue High Wind Watches for much of southeast WY beginning Monday morning. Strongest winds look to occur midday Monday with the strongest flow aloft and steep low-level lapse rates supporting vertical momentum transport and this is also highlighted with the highest NBM probabilities of exceeding 55 mph gusts on Monday vs Tuesday. However, wind-prone locations will likely begin early Monday morning with strong flow running underneath a mountain top inversion per forecast soundings. Wind headlines very well may need to be expanded to cover portions of the NE panhandle Monday afternoon, but will continue to assess the latest model trends. In addition to winds on Monday, precipitation will be most likely across east-central WY and the northern NE panhandle, closer to the surface low, however isolated showers could move across areas farther south. Chances for precipitation return to south-central WY, mainly southern Carbon Co, Tuesday with lift associated with the secondary vort max approaching from the northwest. Additionally, strong winds look to continue for wind-prone locations, but uncertainty remains with how widespread high winds will be across adjacent foothills and plains throughout Tuesday. Upcoming forecast updates can look to refine the High Wind Watch timing for various zones across the CWA, specifically with the endtime. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... Issued at 330 AM MDT Sun May 5 2024 Tuesday night/Wednesday...Another shortwave trough aloft pivots around the primary upper trough producing scattered showers for our forecast area, with the least coverage across far southeast Wyoming and the southern Nebraska panhandle due to downslope winds. Continued windy due to low level pressure gradients and winds, with 700 mb temperatures near -2 Celsius yielding high temperatures from the upper 40s to upper 50s. Thursday...Continued cool with 700 mb temperatures near -4 Celsius yielding maximum temperatures from the upper 40s to upper 50s. Low and mid level moisture looks plentiful enough for scattered to numerous showers and isolated thunderstorms. Friday...Although dynamics look rather limited, it appears there will be enough low and mid level moisture for scattered showers and isolated thunderstorms. 700 mb temperatures rise slightly from Thursday, thus temperatures will be slightly warmer. Saturday...The upper trough continues to spin across the Great Basin states sending another shortwave trough aloft over our counties and will combine with remaining low and mid level moisture to produce isolated to widely scattered late day showers and thunderstorms. Temperatures will show a warming trend as 700 mb temperatures rise to near 4 Celsius, yielding maximum temperatures mostly in the 60s. && .AVIATION /18Z TAFS THROUGH 18Z MONDAY/... Issued at 1138 AM MDT Sun May 5 2024 Main aviation concern will be prolonged strong, gusty winds. Strong southerly winds with gusts to 50 kts at some terminals will be possible during the day today ahead of an incoming cold front. The cold front will begin to move through later this evening and tonight. Precipitation will be possible with this front, which could cause some visibility drops if snow mixes in. Low CIGs will also be possible with the front, with low stratus creating MVFR conditions. Tomorrow, winds will become more westerly behind the front, leading to continued high winds across much of southeast Wyoming and potentially in the Nebraska panhandle. Gusts over 50 kts will be possible. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...High Wind Watch from Monday morning through Tuesday evening for WYZ101-103>105-107>109-115-117>119. High Wind Warning until 9 PM MDT this evening for WYZ104-109- 111. High Wind Watch from late tonight through Wednesday morning for WYZ106-110-116. Winter Weather Advisory from 11 PM this evening to 6 PM MDT Monday for WYZ112. NE...High Wind Warning until 6 AM MDT Monday for NEZ002. && $$ UPDATE...GCC SHORT TERM...MB LONG TERM...RUBIN AVIATION...SF