510 FXUS65 KBOU 101647 AFDBOU Area Forecast Discussion National Weather Service Denver/Boulder CO 1047 AM MDT Wed Oct 10 2018 .UPDATE... Issued at 1028 AM MDT Wed Oct 10 2018 The vort max is spinning over northern Utah pushing a baroclinic comma of energy over the western portion of state. Upslope this morning pushed enough low level moisture into the base of the foothills for some light freezing drizzle. This will generally end this hour and with clouds moving in from the SW will seed the column enough to help change it over to a rain and snow mixture through the morning. Let the freezing drizzle advisory expire as well as the freeze warning with temperatures getting above freezing over the Front Range and plains. Lowered high temperatures today slightly as conditions will not allow for much warming as well as dropped temperatures overnight. Even with the cloud cover expect snow and CAA to bring lows in the mid to upper 20s for the plains. A rain and snow mixture is expected to start over the Denver Metro around 1 pm and continue on and off into the early evening hours. Accumulations are still expected to be under and inch and mainly on grassy surfaces. UPDATE Issued at 636 AM MDT Wed Oct 10 2018 Ongoing drizzle in and near the Front range foothills has changed over to freezing drizzle with temperatures dipping just below freezing. This light frozen precipitation is expected to transition over to light rain and snow later this morning the approaching upper level storm system. Motorists are urged to slow down and allow plenty of space between vehicle to stop safely. Could see upward of a tenth of an inch of ice accumulation in this area. For that reason, a short fused Winter Weather Advisory for Freezing Drizzle has been drizzle, which will run until 9 AM MDT today. && .SHORT TERM...(Today and tonight) Issued at 250 AM MDT Wed Oct 10 2018 Sandwiched between a shortwave trough lifting over wrn Nebraska/wrn Kansas, and an energetic mid-level baroclinic comma passing over northern Utah, a heavy blanket of low clouds, areas of drizzle, light snowfall and patchy fog continue to persist east of the mtns. In the high country, showers have begun to spring up such as the cell moving off the foothills in Boulder County. This new development is in response to increasing QG ascent and mid-level destabilization in advance of the upper air disturbance over Utah. Convection was already blossoming over the Front Range, and will continue to do so during the next few hours, potentially leading to periods of light to moderate drizzle and/or rainfall, and where cold enough, light snowfall on the adjacent plains. May even see some light snow accumulation on grassy surfaces. Meanwhile, overnight temperatures didn't cool as much as earlier thought, due in large part to the lingering cloud cover and now the boundary layer mixing generated by the passing showers. Therefore, odds of seeing a hard freeze on the plains during the next few hours appears slim. Will continue to monitor temps next hour or so, and if no further cooling occurs, will drop the Freeze Warning. Attention shifts to the expanding area of cold top convection on satellite and associated shower band on radar over northeast Utah and northwest Colorado. Base on its forward progress, should see the eastern edge of this heavier precip reaching the Park/Gore mtn ranges by around 10z and the Front Range mtns about an hour later. Then a steady increase in precip both in coverage and intensity across the high country during the morning hours as per model QPF and snow accumulation fields. With that said, mtn zones 31..33 and 34 already under a Winter Weather Advisory which runs until 9 PM this evening. Latest models guidance would suggest an earlier end to precip in the high country, say around 00z/Thu (6 PM MDT today). But, dealing with so many of these clipper systems, I've learned not to cut precip off too soon. Will leave it to the day crew to re- assess the advisory if need be. As for high country snow amounts from this passing shortwave disturbance, still looks like 3 to 8 inches will dominate, although could see the colder high mtn areas ending up with 10-14 inch totals by this evening. Will need to continue to monitor the contribution of upright convection on snowfall rates today. On the plains, the broken line of light showers moving off the foothills early this morning is not expected to remain intact too far out on the plains where the ambient airmass is strongly capped. However, later this morning with mid-level destabilization and increase QG forcing for ascent, should see scattered showers moving off the Front Range and holding together long enough to generate light QPF in the form of light rain, light snow, or as a mix of the two through the afternoon. It now appears from Denver northward and across the northeast corner of the state will be in the best position to receive measurable precip during the next 12-15 hours. Could see a quick inch or so of snow in a few spots adjacent to the foothills, and hardly a dusting elsewhere on the plains. As for temperatures today, wouldn't count on much warming with the persistent overcast. Count on another day of high temps in the upper 30s. Today's weather disturbance should move east of the area by midnight tonight, with precip quick dissipating from west to east. Should still see plenty of low cloud cover around which should prevent overnight temperatures from crashing. As mentioned above, will hold off on issuing a Freeze Warning as minimum temperatures on the plains are not expected to fall much below the freezing mark. However, may end up issuing a lesser freeze advisory. .LONG TERM...(Thursday through Tuesday) Issued at 250 AM MDT Wed Oct 10 2018 On Thursday, next upper level system over the Great Basin begins to split and shear out under a moist westerly flow aloft. There is some weak upward QG ascent with this system, so looks like another day of occasional snow showers for the mountains. Orographic flow is on the weak side of 10-15kt but steep lapse rates by afternoon and moisture, spells another 2-5 inches of snow and possibly low end winter weather advisory may be needed. Potential banded snowfall may result in some localized higher amounts of snow. Across the plains on Thursday, expect some scattered showers developing in the afternoon with this wave while a fair amount of stratus will still remain. There will be some moderation of the cold airmass and expect temperatures to climb back into the 40s on the plains. Fort Thursday night, still lingering snowfall in the mountains with some accumulation given the improved orographic flow from the west and northwest. Friday looks to be the driest and warmest day of the week in post trof environment under a moderately dry northwest flow. Temperatures over the plains look to climb into the 50s, warmest since last Saturday. The break in the weather looks to be short lived as yet another system is poised to move into Colorado Saturday afternoon and night in the northwest flow. Strong cold front sweeps into northeast Colorado around midday with deepening upslope flow and moisture. 700mb temperatures drop to around -10c by Sunday morning which will support snow everywhere by later Saturday night. There is now good model consensus on this trof development and could see the first widespread snow event across northern Colorado. Best potential for accumulating snow will be over the east slopes and adjacent plains. Coldest morning temperatures also expected on Sunday and Monday mornings with readings dropping well into the 20s. Overall drying and warming trend look to be on tap for late Sunday and Monday under a moderate northwest flow regime as storm system departs into the Central plains. Given the strong north to northwest flow aloft, another push of colder air may seep into Northern Colorado on late Tuesday. && .AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon) Issued at 1028 AM MDT Wed Oct 10 2018 Variable MVFR and IFR conditions will continue through the TAF period. Light freezing drizzle will be possible from 17 to 19z with IFR ceilings down to 500 ft possible. After 19z upper clouds should help to transition to a rain and snow mixture with some light snow possible until 23z. Little to no accumulation on paved runways, but grassy surfaces could see less than an inch by this evening. Ceilings will go MVFR around 23z and continue through 14z Thursday when ILS ceilings will take over. Winds during the period will be light and from the NE to E then SE by 14z with speeds generally from 5 to 8 kts. && .BOU WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until 9 PM MDT this evening for COZ031- 033-034. && $$ UPDATE...Bowen SHORT TERM...Baker LONG TERM...Entrekin AVIATION...Bowen