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National Weather Service Forecast Discussion |
National Weather Service Forecast 48 Hour Graphical Forecast Today's Weather Story |
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000 FXUS65 KBOU 081556 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 856 AM MST Mon Mar 8 2021 .UPDATE... Issued at 852 AM MST Mon Mar 8 2021 Water vapor imagery showing a weak upper level wave across Utah and Arizona with a southwest flow aloft over Colorado this morning. This wave has spread considerable mid and high level moisture over the state leading to mostly cloudy skies. Based on timing should be able to see decreasing cloudiness from mid afternoon through evening from west to east. Given the thick cloudiness may impact temperatures today so expect a few degrees cooling from Sunday`s highs. Could see a few mountain showers but low level moisture is lacking and with unfavored southwest mountain flow. There is some concern for elevated fire danger across Lincoln county this afternoon but with the cloud cover expect less mixing with a result in less winds. && .SHORT TERM...(Today and tonight) Issued at 504 AM MST Mon Mar 8 2021 Southwest flow aloft continues to keep our area warm aloft (+5 degC over NE Colorado at 700 mb), and westerly downslope flow will keep the warmth going today into Tuesday. There will however be a fair amount of cloud cover today which may limit afternoon max temperatures by 1-4 degrees compared to Sunday. Still, expect mid to upper 60s most areas of the plains including the I-25 urban corridor, and around 70 for the far eastern plains. It will remain dry. The reason for the cloud cover this afternoon is a weak short wave trough in the southern stream southwest flow. Weak QG lift combined with upslope flow could lead to a brief period of light snow above 9,000 ft this afternoon. Moisture is very much lacking especially given much of the precipitation will have already occurred across the southwest mountains of Colorado. Thus, very little if any snowfall accumulation is expected today in the higher mountains. The lift quickly departs such that any light snow should be over by the evening hours. On the backside of the weak trough, flow at 700 mb turns a little more west and increases into the 30-40 kt range. Lapse rates are not all that stable above ridgetops but weaken enough that some wave amplification is possible down the east slopes. There is no wind shear above ridgetop either so that may also help a little. All that means that gusts to 35-50 mph are possible early Tuesday from the Continental Divide down the east slopes, maybe as low as the 7,500 ft elevation. Lows tonight will remain much above average across the area for early March with 20s in the mountain valleys and 30s to near 40 across the plains. .LONG TERM...(Tuesday through Sunday) Issued at 504 AM MST Mon Mar 8 2021 The first of a series of cold fronts will drop into northeastern Colorado on Tuesday. It will still be a mild and dry day, but the wind shift will take the edge off of it. We could still be near Red Flag fire weather conditions south of I-70 before the wind shift arrives. Probably just a couple degrees drop in the afternoon, with the cooler air coming in overnight. A shortwave passing north of us will drag a moisture band across the northern mountains Tuesday night into early Wednesday. Models differ on QPF amounts, but there`s a pretty good chance of light snow in the mountains, and there could be a few showers over the plains near the northern border, probably still rain on the plains but cooling enough overnight for snow in the mountains. Another shortwave will take a similar path later Wednesday, shoving a strong temperature gradient aloft a bit further south over our area. There will be a similar likelihood of light snow over the mountains Wednesday night, with a little better chance of light showers on the plains, either snow or a rain/snow mix. Shortwave ridging ahead of the upstream system should provide a decrease or break in precipitation Thursday, probably with a little more cooling. Now things get more interesting. There`s getting to be better agreement now on a large upper low moving slowly from Southern California Thursday across the southern Rockies Saturday and to the central plains by Monday. There are still some differences in the latitude and timing, but really given such a large, slow moving system, they may not be that important. The main story is that there`s a pretty good chance of a prolonged period of at least light snow, and possibly a period of heavy snow, for most of our area. The chance of significant snow looks greatest Friday and Saturday from about Denver southward, though there are some model solutions that have the significant precipitation further north or have steady precipitation all the way from Thursday night through Monday morning. Most model QPF for the Friday through Saturday period ranges from 1 to 3 inches. There are heavier solutions. It should be cold enough for this to be mostly snow, at least at 5000 feet and probably across the area. It could be a little warmer Thursday night and Friday for some rain mixed in, but Saturday will be colder. If the system is as slow as most of the models have it, Sunday won`t be much different although there could be a transition to downslope winds near the Front Range to reduce or end the snow. There could also be some wind as the low moves east of the mountains, mainly Saturday into Saturday night and maybe into Sunday on the plains that could exacerbate issues with the snow. We`re still having difficulty pinning down the location, timing, and intensity details, but for now it`s appropriate to message the increasing probability that there will be impactful winter weather Friday through Sunday. && .AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon) Issued at 852 AM MST Mon Mar 8 2021 VFR with considerable mid and high level moisture over the terminals. Expect clearing from late afternoon/early evening with this cloud deck and departing weak upper system. Surface winds continue southwest this morning and expect a shifting to southeast this afternoon. May see a bit of west to northwest push later this afternoon, but not all that confident in that scenario given cloud deck and less mixing expected. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Entrekin SHORT TERM...Schlatter LONG TERM...Gimmestad AVIATION...Entrekin NWS BOU Office Area Forecast Discussion
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