Area Forecast Discussion
Issued by NWS Denver/Boulder, CO
Issued by NWS Denver/Boulder, CO
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502 FXUS65 KBOU 110148 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 748 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. && .UPDATE... Issued at 744 PM MDT Fri May 10 2024 No significant updates this evening with mostly quiet conditions across the region. A couple of lingering showers have been noted across portions of the high country. Main change to the grids this evening was to reduce... yes, reduce... cloud cover across the lower elevations. Satellite imagery this evening has shown the low/mid-level cloud cover has decreased substantially in the past few hours, with most CAMs showing mostly clear skies for the plains overnight. && .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 /00Z TAFS through 00Z Saturday/... Issued at 532 PM MDT Fri May 10 2024 Cloud cover continues to diminish this afternoon, with VFR conditions in place across the terminals. Not expecting significant changes overnight with FEW/SCT low to mid-level clouds and light drainage winds. Southerly flow is expected through the day tomorrow, with perhaps a period of stronger/gustier flow sometime near midday. Chances for showers and an isolated thunderstorm or two are just high enough to include a PROB30 for thunderstorms. Main impact during the day would be potential for ceilings to drop to about 4-5kft AGL. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Hiris SHORT TERM...Schlatter LONG TERM...Mensch AVIATION...Hiris