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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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739 FXUS65 KBOU 071041 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 341 AM MST Sat Dec 7 2019 .SHORT TERM...(Today and tonight) Issued at 340 AM MST Sat Dec 7 2019 High level moisture rounding the upper ridge axis across the state has created thin mountain wave clouds over and just downwind of the high mountains this morning. This was portrayed quite nicely in the CIRA WRF Simulated IR. Low level moisture continued to plague southern Weld County and surrounding areas with fog. Was thinking that the increasing high cloud cover was going to lessen the severity, but it got even thicker, so am issuing another Dense Fog Advisory for this morning. The fog should become less dense and/or totally dissipate by 9 or 10 am. Viewing the CIRA WRF Simulated IR imagery through the day shows the initial thicker and lower wave cloud lasting through the morning, then a secondary but thinner wave cloud for the afternoon. This will definitely make the temperature forecast for the urban corridor have a high bust factor. We were originally thinking most of the urban corridor would see temperatures closer to 60, but if the high clouds are thick enough, they`ll help keep the inversion holding on and not allow for the significant warming we were expecting. Viewing other model data hasn`t been very conclusive either. However, looking upwind at the water vapor satellite imagery moving in from the west, will assume there will be some sort of wave cloud to influence the temperatures, especially over the northern half. Have decreased temperatures, especially in the southern Weld County area were they`ve been stuck under a strong inversion with fog to contend with as well. An upper trough off the CA coast will move inland later today to push the ridge east of the state, and switch winds aloft from the southwest and increase in speed. These winds will be reflected in the mountains, with gusts in the 35 to 50 mph range to create some patchy blowing snow. Mid level moisture will move in from the west to begin some light snow showers over the mountains mainly around and after midnight with less than an inch expected by Sunday morning. .LONG TERM...(Sunday through Friday) Issued at 340 AM MST Sat Dec 7 2019 Sunday will bring increasing moisture and snowfall to the high country. The deep upper level trough just off the California coast today will begin to shear out as another disturbance drops in from British Columbia, and then pushes southeast across the Rockies. Due to overall shearing/weakening of the upper level trough, Q-G support will be relatively weak. Nonetheless, we`ll have good orographics with flow turning more westerly by afternoon and then northwest Sunday night. That`s when the best snow should reach the northern mountains and Summit County. Overall, we`ll likely see the heavier snow totals accumulate in the northern Gore and Park Ranges, as initial westerly flow there will support better orographics for a longer period. Our preliminary forecast accumulations for the high country looks to range from 3 to 7 inches for the Front Range Mountains and Summit County, with 5 to 10 inches for the northern Gore and Park Ranges. We`ll take a look at the latest data today before hoisting any Advisories, as the main period of accumulating snow doesn`t start until late Sunday afternoon and evening for our mountains. Moisture depth may be the one thing that holds down accumulations. Winds will be strong enough to support areas of blowing and drifting snow as well. On the plains, a cold front will push southward across the High Plains and move across northeast Colorado toward midnight Sunday night. Behind that, we`ll see shallow anticyclonic upslope and thus a chance of light snow showers. If we do see snow, moisture depth and stability is quite poor so only a dusting would be expected. Mild temperatures Sunday will be replaced by below normal temperatures Monday. Temperatures should then moderate again and return to slightly above normal readings by Wednesday and Thursday. Mainly dry conditions will persist with flat upper level ridging in place both days. Models seem to be coming around to the idea that a stronger Pacific jet stream will plow across the Pacific and into the Northern and Central Rockies by Friday and Saturday. If this setup occurs, we`ll see the orographic snow machine turn on for the northern mountains. That could also bring bouts of strong, gusty winds to the plains by late in the week and next weekend. Still a long ways out on that. && .AVIATION...(For the 12Z TAFS through 12Z Sunday morning) Issued at 340 AM MST Sat Dec 7 2019 High clouds will likely be over the area terminals through most of the day. Southerly drainage winds early this morning should keep the fog over Weld County to remain north and northeast of DEN. Though some high resolution models have been wanting to let it push slightly south and west into Boulder County, so this could impact BJC, but for now am discounting it. Winds will veer to the west and northwest this afternoon before returning to a drainage overnight tonight. && .BOU WATCHES/WARNINGS/ADVISORIES... Dense Fog Advisory until 9 AM MST this morning for COZ038-042- 043. && $$ SHORT TERM...Kriederman LONG TERM...Barjenbruch AVIATION...Kriederman NWS BOU Office Area Forecast Discussion
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