Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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564 FXUS65 KCYS 012034 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 234 PM MDT Wed May 1 2024 .KEY MESSAGES... - Isolated thunderstorms will affect the Nebraska Panhandle this afternoon with a briefly gusty wind threat toward Sidney and Alliance. - A cold front will move through the region on Friday with another round of mountain snow and shower activity possible over the region. - Drier and warmer conditions will move in for the weekend. Gusty winds will move in by Sunday afternoon. && .SHORT TERM /THROUGH THURSDAY NIGHT/... Issued at 113 PM MDT Wed May 1 2024 Afternoon satellite imagery and surface obs reveal a stream of upslope flow over the Nebraska panhandle and far southeast Wyoming with surface dewpoints generally in the mid to upper 30s. Aloft, southwesterly flow carrying a band of moisture oriented southwest to northeast continues to drift east across southeast Wyoming. Mesoanalysis reveals very low-end instability on the order of 500J/kg of less has formed east of this feature with a convective nature to some of the cloud cover east of Cheyenne. CAM guidance supports the development of a few showers and thunderstorms along the advancing surface convergence boundary over the next few hours as it makes its way through southwest Nebraska. Gusty outflow winds on the order of 30-40 knots and some small hail of pea size or less will be the primary concern if any convection can become established. Farther west, expect clearing skies through the afternoon and evening as dry air moves in on westerly flow. Overnight temperatures will run around 5 to 10 degrees below average in the wake of today`s cold front. Thursday will be a transition day between two shortwave troughs as the region remains under the influence of broad longwave troughing over the western half of the CONUS. Expect a mainly dry day with mostly cloudy skies in place and temperatures continuing to run around 5-10 degrees below average. As we move into Thursday night, the vort max associated with the next storm system will dive through the northern Rockies. Support for lift will move in later on Thursday night with some mountain snow breaking out in the higher elevations of the Snowy and Sierra Madre ranges. Isolated showers are possible as well across lower elevations of Carbon, Albany, Converse and Niobrara counties as a cold front works southward. && .LONG TERM /FRIDAY THROUGH TUESDAY/... Issued at 113 PM MDT Wed May 1 2024 The long term remains active, albeit with a brief quiet period over the weekend before things ramp up again. Friday, a shortwave will drop down from the Pacific Northwest, keeping our temperatures on the cool side while bringing another round of precipitation to the area. This system is progressive, so it will only be a quick shot of moisture during the day Friday, before it moves off into central Nebraska. 700 mb temperatures will be below freezing, which will lead to below average temperatures. Mountain snow is expected, but some flakes could mix in with rain for areas west of the Laramie Range. East of the Laramie Range, rain is expected. A few rumbles of thunder or a brief thunderstorm is possible as non-zero CAPE values exist across the eastern plains. By Saturday, upper-level ridging will move into the Rockies, leading to drier and warmer conditions. 700 mb temperatures will be back above freezing with sunny skies, so afternoon highs will be able to climb back to around average for early May. An even warm day is expected Sunday as the CWA sits in a region of warm air advection ahead of the next system. Sunday will likely be the warmest day in the foreseeable future with highs above average. Headed into next work week, the forecast gets messy, both literally and figuratively. There is a a good deal of discrepancy between models regarding precipitation. The deterministic GFS shows a progressive wave passing across the CWA, followed by yet another trough that stalls out over the northern plains. The ECMWF has a closed low pass over the CWA that then stall over the northern plains. Both solutions give precipitation to the CWA but in different areas. As a result of the uncertainty, went with NBM for PoPs and QPF. There is more certainty that this system will bring cooler temperatures and much windier conditions. First, out ahead of the system, strong southerly winds will be possible as MSLP gradients across the eastern half of the CWA become tightly packed. Once FROPA occurs, expect very strong westerlies behind it. Although this system is still quite a ways out, the GFS has consistently been showing these strong winds from run to run. A prolonged period of high winds with both the southerly and westerly winds cannot be ruled out. In fact, in-house guidance is already pinging high probabilities for high wind in the usual wind prone spots, and even areas outside of it! Both the strong winds and cooler temperatures look likely at least through mid next week. && .AVIATION /18Z TAFS THROUGH 18Z THURSDAY/... Issued at 1115 AM MDT Wed May 1 2024 The timing of precipitation remains the primary forecast challenge for TAF sites this afternoon. A heavy band of snow has moved over LAR resulting in IFR conditions. This band will likely persist for the next hour or so before diminishing after 19z. Showers will develop from CYS eastward through the NE panhandle. A few thunderstorms are possible at SNY and possibly AIA. Brief reductions to MVFR are likely for both CIG and VIS as any storm moves through. Showers should end by the evening with a dry overnight expected at all terminals. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...MAC LONG TERM...SF AVIATION...MAC