####018004485#### FXUS65 KCYS 102121 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 321 PM MDT Fri May 10 2024 .KEY MESSAGES... - Trending warmer through the weekend, but remaining unsettled with daily chances for showers and storms. Severe weather is not expected. - A cold frontal passage is expected on Wednesday, with much of the region returning to below-normal temperatures and increased chances for rain and high-elevation snow. && .SHORT TERM /THROUGH SUNDAY NIGHT/... Issued at 330 PM MDT Fri May 10 2024 A warming trend should persist across southeast WY & the western NE Panhandle as thermal profiles warm in response to weak upper- level ridging extending along the northern periphery of a fairly persistent, slow-moving closed low drifting across the 4 Corners region through the short term forecast period. Daytime highs may reach the upper 60s and lower 70s across much of the high plains by Sunday afternoon as 700-mb temperatures climb to +6 to +8 deg C by 00z Monday. Despite the warming trend, it should be a some- what unsettled pattern w/ daily chances for showers and thunder- storms as multiple pieces of mid-level energy continuously pivot around the north side of the aforementioned low. Rain amounts do not look to be anything substantial given the lack of organized/ stronger dynamics. Weak CAPEs under 500 J/kg & modest deep layer shear will preclude any risk for strong/severe storms. && .LONG TERM /MONDAY THROUGH THURSDAY/... Issued at 330 PM MDT Fri May 10 2024 A transient ridge will position itself across the Rockies for the early part of next week after this weekend's cutoff flow finally ejects off to the east. Multi-model ensemble mean 700-mb temperatures will climb to around +6 to +8C between Monday afternoon and Tuesday afternoon, supporting surface temperatures about 10F warmer than average for Monday afternoon. Lapse rates look fairly steep, but moisture won't be particularly abundant with dewpoints in the 30s to mid 40s and precipitable water near average for this time of year. The result will be modest instability, but enough to get some thunderstorms going during the afternoon. A trough over the Pacific northwest will be approaching early next week, and a leading shortwave ejecting out will pass through Monday night providing a boost to lift. Shear looks unimpressive, but we could see some small hail and gusty winds with inverted-v soundings in place during the afternoon. The main trough axis approaches late Tuesday or early Wednesday, setting up lift for another round of showers and thunderstorms. Expect temperatures to be cooler than Monday for much of the area, except far SE Wyoming and the southern NE panhandle which should be similar. Slightly more shear could allow for more organized convection, but the setup is quite messy with forecast soundings showing backing wind profiles and muddled lifting mechanisms. However, this period Tuesday afternoon through Wednesday morning will probably be the best chance for appreciable precipitation during the upcoming week. Expect cooler conditions across the area Wednesday as 700-mb temperatures get knocked back down to near 0C. Lingering cloud cover and scattered showers will also be present. Model consistently falls apart for the end of the week, with some (GEFS members) showing an amplified ridge over the Pacific northwest, and others (ECMWF ensemble members) showing a more zonal flow pattern. Regardless, look for drier air to work in for Thursday and Friday, leading to temperatures back to near normal and more limited precipitation chances. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 1132 AM MDT Fri May 10 2024 Improving aviation conditions today across the area, though CIGs in the 3k to 5kft range will persist through the afternoon for Wyoming terminals. Slow moving shower activity has already begun to develop, and this will expand and drift southward. Some of this activity may produce thunder, but confidence in timing is too low to add to the TAF. Expect AMDs this afternoon if and when thunderstorms develop. Skies will trend clear overnight. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...CLH LONG TERM...MN AVIATION...MN ####018006999#### FXUS65 KBOU 102124 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 324 PM MDT Fri May 10 2024 .KEY MESSAGES... - Showers and isolated thunderstorms are possible Saturday afternoon across most of the area (20-50% plains; 50-80% mountains, mountain valleys, and foothills). Snow levels should remain around 10,000 ft into the evening hours, and no significant travel impacts are expected. - Gradual warming this weekend and through Tuesday along with scattered showers and thunderstorms, most numerous this weekend and Tuesday onward. && .SHORT TERM /Through Saturday/... Issued at 119 PM MDT Fri May 10 2024 GOES-17 shows a well defined short wave trough over the CA/NV border, with a trough axis extending northeast over Utah and into NW Colorado. Weak instability near the trough axis and some QG lift should lead to weak rain showers this evening, and some light snow mainly above 9kft MSL. T-2 inches are possible through midnight, but mostly along and south of I-70. Limited to no travel impacts are expected this evening or overnight. CAMs continue to show hardly any rainfall east of I-25, with limited instability and less forcing away from the trough axis. Overnight lows should remain up and well above freezing across all of the plains below 6500 ft MSL, with lows in the mid 30s in the cool spots to low 40s across the urban heat islands. The mountain valleys should cool into the upper 20s despite partly cloudy skies. A note about the Aurora Borealis potential: Check the NWS Space Weather Prediction center for best timing and updates, but for now that looks like midnight to 3 AM for Colorado, and skies should be partly to mostly clear during that time across the northern 1/4, maybe northern 1/3 of Colorado. However, to have a chance to see them, even under mostly clear skies, there needs to be very little light pollution to your north, since that's the only direction you will be able to see them if visible. On Saturday models show the trough moving into western Colorado, which will increase instability over out area, as well as increase QG lift. Low-level moisture will be limited with Td expected to remain in the upper 30s to low 40s across the eastern plains. There is a fair amount of mid and upper level moisture to work with, resulting in a total of about 0.50" PW across our area, on average. The trough is pretty cold for mid May, with 500 mb temps around -20 degC. So despite meager low level moisture, the cold air aloft should result in SBCAPE from 200-600 J/kg, supporting at least isolated chances of thunder, and very small hail with the strongest convection. Overall QPF amounts remain light, mostly because of the dry low-levels. The best forcing will be across central and southern Colorado, thus the northeast corner and northern tier of counties across the plains may not see any precip, while across Park County maybe as much as a half inch of liquid could fall through the evening hours. A tenth of two are possible for the Denver-Boulder metro area. Snow levels should remain around 10kft MSL through Saturday evening. With ample cloud cover much of the day, and even with some warming via southwest flow aloft just ahead of the trough axis, highs will remain near normals with highs in the upper 60s across the plains (70s northeast corner where there will be more sunshine and little to now precip during the day), and 50s in the mountain valleys. && .LONG TERM /Saturday night through Friday/... Issued at 119 PM MDT Fri May 10 2024 Sunday, the upper level low and positively tilted trough exits across eastern Colorado. The leading edge of the upper ridge moves in by the early evening, setting up thermal ridging and more northerly flow over the region. This will bring warmer temperatures with highs in the 60s for most of the lower elevations. Sufficient moisture remains in the mid-levels on Sunday. Cooler air aloft and daytime heating will provide instability (MLCAPE < 600J/kg) will work to support increased showers and storms in the afternoon. There is uncertainty in the rainfall amounts and location of highest amounts across the lower elevations. Part of this is dependent on the track of the low. Overall, both the GFS and EC ensembles show a good signal for QPF > 0.10". Ensemble means also show a signal for greater QPF (24hr 0.2-0.6") centered along I-70 through the Denver metro and eastward onto the plains. A chunk of EC members show amounts > 0.60" for the southern Denver metro. GFS is a bit drier and this is likely due to some differences in low track. Overall looking like a decent chance for a soggy Sunday. There is general agreement among ensemble guidance that a weak upper ridge moves in for Monday. Monday trends drier and more stable, resulting in lower chances/coverage of showers/storms with the higher chances confined to the higher terrain. The weak ridging will support further warming temperatures with ensembles showing a high chance at 70s across the lower elevations early next week with a shot at upper 70s across the east plains. The upper pattern then transitions to W to WNW flow aloft Tuesday and Wednesday. Uncertainty increases in the details of a shortwave trough moving by mid-week, particularly timing. Tuesday and Wednesday display the higher chances for shower/storms activity with the incoming trough providing synoptic ascent and increased moisture. Hard to say where the axis of higher instability will set up across the lower elevations and this will be dependent on how the shortwave tracks as well as the timing of the wave. && .AVIATION /18Z TAFS through 18Z Saturday/... Issued at 1145 AM MDT Fri May 10 2024 DEN should remain in VFR conditions through Saturday, though can't rule out thickening clouds around 025-035 with afternoon showers which should stay to the west. BJC and APA will have MVFR conditions into the early evening hours, especially when the chances of showers increase after 21Z. Light rain with slightly lower CIGs would be the result of any showers this afternoon. By 01 or 02Z showers should have ended and light drainage flow will be the norm through about 14Z (SSW at APA and DEN, WSW at BJC, under 10 kts). On Saturday there is a better chance of showers during the afternoon at the metro area terminals, and there is a chance of thunder but for now it's 10, maybe 15% and thus too low to include in the TAFs this far out. Winds are expected to be out of the south or southwest, and could gust over 20 kts during the afternoon. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...Schlatter LONG TERM...Mensch AVIATION...Schlatter