textproduct: Cheyenne
This forecast discussion was created in the public domain by the National Weather Service. It can be found in its original form here.
KEY MESSAGES
- Light to moderate snow accumulations anticipated for the Snowy and Sierra Madre mountains today into early Monday morning. Highest snowfall totals expected for elevations above 9000 feet. Winter Weather Advisories in effect through Monday morning.
- Strong winds are anticipated late Monday night into Tuesday afternoon for areas of southeast Wyoming, especially the wind prone and gap areas. Wind gusts of 60-70 mph are possible. See the latest High Wind Watches and Warnings for more details.
- Daily snow chances possible Wednesday through the weekend as an upper-level system stalls out and remains overhead.
SHORT TERM /THROUGH TUESDAY/
Issued at 244 PM MST Sun Nov 3 2024
Some light radar echoes present over the Interstate 80 corridor in Wyoming this afternoon. Hi-Res guidance does show precipitation increasing in coverage late this afternoon and into the evening hours for areas west of the Laramie Range. The bulk of this system will remain south of the CWA so impacts will be minimal. However, Winter Weather Advisories remain in effect for the Snowy and Sierra Madre Ranges, as well as the South Laramie Range. Expect accumulations up to 6 inches in the high terrain of the Snowy and Sierra Madres, and 2 to 4 inches in the South Laramie Range. Advisories run through Monday morning, with most of the snow expected to fall late this afternoon and into the first half of the overnight.
Some lingering showers will be possible tomorrow as the system to the south exits eastward. Temperatures will be on the cool side as clouds also linger throughout much of the day. Expect below average highs in the 30s west of the Laramie Range and 40s east of the range. Monday night another upper-level trough will approach from the north. This incoming trough will rapidly tighten pressure gradients along and west of the Laramie Range. CAG-CPR 700 mb height gradients will also respond to the incoming trough, with values up to 65 meters by early Tuesday morning. Winds aloft will also increase up to 65 kts with great subsidence which will increase the chances of these winds making it down to the surface. There also seems to be a slight hint at mountain wave activity within the 500 mb height gradients. In-house guidance is pinging the usual wind prone zones in southeast Wyoming with high probabilities of seeing high winds Late Monday night into Tuesday. As a result, did decided to upgrade the current High Wind Watches for the wind prones and Carbon County to High Wind Warnings. If mountain wave activity is present, other wind prone adjacent zones like Laramie and Platte Counties could also experience high winds. Due to lower confidence in these areas plus the Laramie Valley hitting high wind criteria, decided to keep these as High Wind Watches. This will be something to monitor in the coming shifts as High Wind Warnings may eventually be needed in these areas. Winds will eventually ease Tuesday evening.
The aforementioned trough will also bring a cold front across the CWA later in the afternoon Tuesday. Some precipitation could be possible along and behind the front during the day Tuesday and into Tuesday night. The high terrain will likely see snow accumulation from this next system, but lower elevation areas along Interstate 80 may also see minor snow accumulations Tuesday night.
LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/
Issued at 300 PM MST Sun Nov 3 2024
The main forecast challenge in the long term forecast period will be a slow moving storm system with lingering impacts throughout the week.
The synoptic weather pattern through the period will be dominated by the closed low left behind across the southwest CONUS. The initial trough passes through Tuesday night and the upper level low is then expected to begin closing off over the Four Corners region. The cold air behind the initial frontal passage will be quite potent for this time of year. Ensemble mean 700-mb temperatures drop to around -12C, which is below the 10th percentile of climatology. Most of southeast Wyoming will struggle to get to freezing for a high (which is fairly impressive considering we only started getting consistent lows below freezing about 7-10 days ago), while Nebraska will be stuck in the 40s. Unfortunately for our drought woes, model guidance is fairly consistent in showing the frontal boundary stalling to our south, with most of the lift over our area gone by daybreak Wednesday. Still, fairly moist low levels will keep snow showers around, particularly in the higher terrain and other areas favored by northerly flow. Additionally, the frontogenesis and overrunning warm air advection may extend into the southeast portion of the forecast area, supporting light snow in far southeast WY and the southern NE panhandle. The most likely scenario right now is around 1-3" for an area southeast of a Cheyenne to Alliance line Tuesday night into Wednesday, but we will need to watch this as the frontal boundary stalling just a little further north or south could break that forecast in either direction.
Heading into Thursday, the parent trough rebounds quickly and leaves the closed low over the southwest. There is some uncertainty in how quickly the parent trough lifts out and how far south the closed low drifts, which will lead to significant disparities in forecast highs for Thursday. At the chilly end of forecasts where the closed low stays further north and the parent trough lifts out slowly, 700- mb temperatures around -8C would keep a fairly chilly day about 15F colder than average, while the warm end (low further south and parent trough faster to exit) would mean 700-mb temperatures around 0 to -2C and temperatures close to or just below average for this time of year.
Considerable uncertainty remains in the handling of the closed low exiting the region on Friday through Sunday, which leads to fairly low forecast confidence during this period. An increasing proportion of ensemble members is showing this ejection occurring close enough to our area to have impacts Friday through Saturday. Current ensemble means show about 0.25 to 0.5" of liquid precipitation over the High Plains as the closed low lifts over eastern Colorado and into Kansas/Nebraska. Still, about 10 to 20% of ensemble members are showing the high impact scenario of 1"+ liquid precipitation, and close to 50% of members have the moderate impact scenario of between 0.5 and 1.0" of liquid. The exact track of the low as it exits will be critical in determining what outcome plays out. A fairly narrow region of moderate to heavy precipitation is now likely in the TROWAL on the backside of this system, but the main question is where exactly this tracks over. Precipitation type will also be an issue with this system. On Thursday and Friday, the ridge will rebound strongly around the closed low, leaving not much of a cold air tap by the time the low is ready to exit. The colder end of possible scenarios would mean snow for most of the area except perhaps the lowest elevations of the western Nebraska panhandle, while the warmer end could push slow levels to as high as 6000'. With so much uncertainty, did not deviate far from the NBM forecast aside from decreasing snow levels to increase the mention of a rain/snow mix possible for a broader area.
AVIATION /00Z TAFS THROUGH 00Z TUESDAY/
Issued at 450 PM MST Sun Nov 3 2024
A poorly organized and weak storm system will slide southward across Utah and Colorado and into the Four Corners region tonight. Although significant impacts are not forecast for a bulk of eastern Wyoming and western Nebraska, some snow shower activity is expected along with breezy northerly winds.
HAZARDS/WEATHER TRENDS: VFR conditions will prevail across western Nebraska with CIGS remaining above 5000 feet AGL. Periods of MVFR to near IFR conditions are expected for KLAR, KRWL, and possibly KCYS between now and 12z Monday morning mainly due to snow shower activity. Confidence is limited at this time, so kept short PROB30 and TEMPO groups in the KLAR and KCYS TAF for now. Conditions will gradually improve at these locations by 15z Monday.
CYS WATCHES/WARNINGS/ADVISORIES
WY...High Wind Warning from 11 PM Monday to 11 AM MST Tuesday for WYZ104-109. High Wind Warning from 8 PM Monday to 5 PM MST Tuesday for WYZ106. High Wind Watch from late Monday night through Tuesday afternoon for WYZ107-118. High Wind Warning from 8 PM Monday to 2 PM MST Tuesday for WYZ110-116-117. Winter Weather Advisory until 11 AM MST Monday for WYZ112-114- 116. High Wind Watch from late Monday night through Tuesday afternoon for WYZ115.
NE...None.
IMPORTANT This is an independent project and has no affiliation with the National Weather Service or any other agency. Do not rely on this website for emergency or critical information: please visit weather.gov for the most accurate and up-to-date information available.
textproduct.us
is built and maintained by Joshua Thayer.