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Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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957 FXUS65 KCYS 182304 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 504 PM MDT Wed Sep 18 2024 .KEY MESSAGES... - Near-critical fire weather conditions today for most with gusty winds and dry conditions. Red Flag Warning is in effect for the northern Nebraska panhandle through early this evening. - Dry conditions continue through the remainder of the week before precipitation chances return over the weekend. && .SHORT TERM /THROUGH FRIDAY NIGHT/... Issued at 325 PM MDT Wed Sep 18 2024 Latest GOES WV imagery shows a mature large scale occluded cyclone over eastern MT with notable dry air and strong winds just to the south over our area. 700mb winds continue to decrease over southeast WY this afternoon limiting the high wind potential, but a few waves are still present on GOES imagery. A few sensors gusted 60-70 mph earlier this morning near Elk Mountain as well as in the immediate lee of the North Laramie Range along I-25 south of Glendo. However, winds have dropped to 35-50 mph for most sites and will continue to do so headed into this evening with hi-res and in-house guidance support. However, gusty southwest winds over the northern Nebraska panhandle have resulted in critical fire weather conditions developing this afternoon, aided by downsloping winds off the Laramie Range. Therefore, a Red Flag Warning was issued through early this evening. The remainder of the week will be dry with gradual warming temperatures as the upper level low continues to climb into the north-central CONUS while a secondary upper level low digs off the CA coast. Thursday afternoon temperatures will be around normal for mid-September while Friday will be 5-10F degrees warmer in the mid- 70s to 80s as 700mb temps reach 10-13C. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... Issued at 325 PM MDT Wed Sep 18 2024 The first portion of the long-term period will focus on a storm system moving through the central and southern Rockies and out into the high plains from Saturday through Sunday. At the same time, a broad scale trough in the northern Rockies will swing through, dragging a surface front south along the high plains up against the front range. The combination of these two events will bring a rather notable change to the weather in southeast Wyoming and western Nebraska, including a cool-down in temperatures and the possibility for some precipitation. Ensemble forecast guidance remains in excellent agreement showing a strong signal for a cool-down in temperatures on both Saturday and especially on Sunday behind the frontal system. Temperatures will likely run around 10 degrees below average on Saturday, with temperatures upwards of 15 degrees below average on Sunday as cool air from the north funnels southward along the high plains and seeps into the mountains and basins farther west. Despite strong confidence in the temperature forecast, the precipitation forecast remains much less certain. This is due to a wide dispersal in the exact location and track of a surface low pressure system expected to develop in the lee of the southern Front Range of Colorado on Saturday into Sunday. Some ensemble guidance groups favor a more southern track and develop the low farther east into the great plains. These scenarios would result in a much lower chance for precipitation north of the Colorado border into western Nebraska. Other ensemble groups still favor a track close enough to the Colorado Front Range to toss some better moisture north of the border. In these scenarios, afternoon showers and thunderstorms would be possible in the higher terrain of southeast Wyoming, with general light rain spreading eastward through the evening hours behind any stronger convection. With cooler mid-level temperatures in place on the north side of this system/behind the cold front, the highest elevations of the Snowy Range including Medicine Bow Peak could be in line for a light snow accumulation. However, this would only take place if this system takes the more northern track. The latest guidance trends certainly support the drier, more southern track resulting in much lower precipitation chances for southeast Wyoming and western Nebraska. We will continue to monitor this system for any changes in guidance. Dramatic differences in ensemble guidance emerge even by Sunday and last through the middle of next week, casting a large amount of uncertainty on the long-term period. ECMWF ensemble guidance favors a slower departure of our weekend storm system, with clouds and some shower chances lasting through the day on Sunday, compared with the drier GEFS. We will favor the drier trend for now given the pattern shown in recent model cycles but can not fully eliminate the chance for precipitation and especially clouds on Sunday. A very weak trough will likely pass through sometime on Monday, with a reinforcing cold front that will keep temperatures on Monday and Tuesday below average. Most guidance supports a dry passage of this system without a Pacific moisture connection. A ridge of high pressure then looks to develop by midweek over the southwestern CONUS however some ensemble guidance keeps this feature suppressed allowing for repeated trough passages over the central and northern Rockies, whereas other guidance favors a more sprawling ridge. Temperatures do look to warm a bit by Wednesday onward, possibly returning to average or even slightly above average for the last full week of September. && .AVIATION /00Z TAFS THROUGH 00Z THURSDAY/... Issued at 501 PM MDT Wed Sep 18 2024 Gusty conditions across southeast Wyoming and western Nebraska with clear to mostly clear skies. VFR conditions are expected to continue through the 00Z TAF period. Winds begin to decrease over the next 1-3 hours, with overnight winds fairly calm. Winds will begin to increase across western Nebraska and KRWL late tomorrow morning and remain elevated through the afternoon. No precipitation expected at this time. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...Red Flag Warning until 7 PM MDT this evening for NEZ434. && $$ SHORT TERM...MB LONG TERM...MAC AVIATION...AM