Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 11/28/22

Area Forecast Discussion
National Weather Service Denver/Boulder CO
827 PM MST Sun Nov 27 2022 .UPDATE... Issued at 827 PM MST Sun Nov 27 2022 Water vapor satellite imagery showing a decent amount of mid and upper level moisture in the westerly flow aloft upstream of Colorado. Adjusted sky cover up for tonight, with waves of high clouds expected. For the mountains, expected skies to become mostly cloudy by midnight, if not sooner. Because of this adjusted low temperatures up some. Windy conditions will continue over the mountains and wind prone areas east of the Continental Divide with gusts to 70 mph possible. && .SHORT TERM...(This evening through Monday) Issued at 137 PM MST Sun Nov 27 2022 Starting to see some of the gusty winds developing in the mountains this afternoon with gusts in the 30 to 45 mph range. Expect winds to increase even more this evening as the flow backs more westerly and increases. Latest NAM cross sections showing cross barrier flow increasing 40-60kt this evening. There is some mountain top stability that develops this but strength of inversion not all that impressive. Local high wind gradient program showing a brief window of potential high winds tonight so could see a few gusts up close to 75 mph. Overall coverage of the strongest windows would be very localized and not widespread enough to warrant a wind hilite. Expect majority of the winds in the 40-60 mph range. Overall winds will decrease a bit by Monday afternoon as mountain top flow backs further around to the southwest. Meanwhile approaching broad upper trof with decent QG ascent will increase into northwest Colorado during the afternoon as moisture deepens over the mountains. Snow will rapidly develop over the northern mountains with favored southwest to west orographic flow over zone 31. Will be starting the warning at 18z over northern mountain zones which is earlier than the 00z start time issued on previous shift. Across lower elevations still one more dry and mild day before cold front comes through late Monday night. .LONG TERM...(Monday night through Sunday) Issued at 137 PM MST Sun Nov 27 2022 The timing of the synoptic scale features associated with the next storm system still look consistent for Monday night and Tuesday. The models show increase QG ascent in the mid/upper levels ahead of the trough axis, spreading it west to east across northern CO Monday night. Strong southwesterly winds in ridgetop will continue to favor zones 31 and 33 the most. The models show strong QG ascent developing over northwest CO Monday night, then it slowly weakens as it translates eastward. The combination of favorable orographics and strong QG ascent looks very good for heavy snow in the Park and Gore Ranges. This could result in storm totals up to 20 inches in those areas, with up to 16 inches in those favorable areas of zone 33 as well. As a result, with have upgraded the winter storm watch to a warning. Advisories will likely be necessary as well, but will let later shifts address this. The rest of the mountains are concerned, still decent snowfall with advisory criteria snow possible in zones 34 and 35, especially if you factor in the jet induced banding late Monday night into Tuesday morning. A cold front will push north to south across the urban corridor/northeast plains 09z-12z Tuesday morning. Northeast winds will get going a little sooner than that as a surface low sets up over east central CO around 03z Monday evening. This could usher the lower clouds and colder air into the plains sooner, but the real push will be overnight. Spatial cross-sections still show the potential for conditional symmetric instability developing coupled with post frontal upslope. Main window still appears to be 12-18z Tuesday morning which would line up with the morning commute, then a gradual decrease in coverage and intensity as the mid level trough axis starts to exit eastward into KS towards 00z. Tuesday night into Wednesday, strong mid/upper level subsidence will spread west to east, with decreasing clouds overnight. Clearing skies and strong radiational cooling following the trough will produce very cold overnight lows, especially in the high mountain valleys. This will be dependent on how fast the clearing takes place but potential for lows dropping to -20F not out of the question. Wednesday will be a little warmer, but still around 10 degrees below normal. Thursday into the weekend, a strong west/southwesterly flow aloft will remain over the region, with a short wave passing across the northern Rockies Friday into Friday night. This will result in a continued chance of snow in the mountains along the west facing slopes. Strong downslope wind potential in the Front Range mountains/foothills Thursday night into Friday. Generally dry across the plains with temperatures slightly above normal. && .AVIATION...(For the 00Z TAFS through 00Z Monday evening) Issued at 440 PM MST Sun Nov 27 2022 VFR conditions with high clouds will continue across the region tonight and Monday in advance of the next storm system. This next system is expected to bring snow to the Denver area after 06Z Tuesday. As far as winds go, light southwest to variable winds to continue the next few hours and then settle at a southerly direction through tonight and into Monday morning. Confidence in wind forecast is low after 18Z Monday. Some models show northerly winds due to a deepening surface low over southeast Colorado. The HRRR/RAP indicate strong westerly winds mix down to the surface with gusts to 30 knots possible, leaning towards the weaker north winds, because the HRRR has a bias of over mixing these stronger winds to the surface. && .BOU WATCHES/WARNINGS/ADVISORIES... Winter Storm Warning from noon Monday to 5 PM MST Tuesday for COZ031-033. && $$ UPDATE...Meier SHORT TERM...Entrekin LONG TERM...Cooper AVIATION...Meier
Area Forecast Discussion...Corrected
National Weather Service Great Falls MT
840 PM MST Sun Nov 27 2022 .SYNOPSIS... Areas of snow will progress further through Southwest Montana Sunday evening. Temperatures will turn much colder through the week ahead. A widespread light snow event is likely toward the end of the week. && .UPDATE... Bands of snow along with gusty winds have moved through the area and are passing through southwest Montana, at the time of this update. The forecast is performing well; therefore, no updates are made. - Fogleman && .DISCUSSION... HRRR forecasts have captured reasonably effectively the observed bands of shallow convective snow that have developed over central Montana, expected to move through Southwest Montana this evening. The bands of snow are supported by weak instability, with CAPE values nearing 100 J/kg. Large dewpoint depressions at the surface indicate wet bulb temperatures in the lower to mid 30s, so evaporative cooling with the onset of precipitation is supporting wet snow to the surface at lower elevations. The surface pressure gradient has begun to weaken as the surface low over Southern Alberta begins to move away to the east. Strong winds continue, with occasional gusts to 45 mph occurring. A few locations did earlier exceed the 58 mph high wind warning criteria, but overall trend in forecasts and observations is below this threshold, so high wind warnings are cancelled. Mid-level lapse rates are steepening with colder temperatures aloft. Thus, periods of snow are likely to continue over mountain areas tonight. Winter Weather Advisories remain in effect for these areas of snow and blowing snow. Snow gradually ends tonight from north to south as surface high pressure builds in with steadily colder temperatures. Portions of Southwest Montana do remain under a left jet exit region, so snow is expected to continue over this area through Monday. Generally fair but cold weather settles in for Tuesday, with scattered light snow flurries possible. NBM 50th percentile Max temperatures are in the upper single digits and lower teens on Tuesday afternoon. Weak warm advection and shortwave ridging aloft provides for a brief rebound in temperatures on Wednesday, though still in the teens and 20s for most areas. Wind chill below -20F may occur Wednesday morning as wind picks up to bring the warmer air into the region. Another strong cold front backs into North-central Montana on Thursday, providing a return to single digit temperatures. The southward extent of this cold front remains uncertain, as it depends on how far south a Pacific shortwave system tracks through the intermountain west. Nonetheless, moisture ascending over the cold air on the southwest flow aloft is expected to generate a period of widespread light to moderate snow Thursday night into Friday. The NBM is suggesting that much of the Golden Triangle region has over a 40% chance of seeing at least 2 inches of snow, which could be enough to cause some minor impacts if realized. && .AVIATION... 840 PM MST Sun Nov 27 2022 (28/00Z TAF period) Blowing snow in association with gusty winds and snowfall cause MVFR/IFR/LIFR conditions as a front passes from north northwest to south southeast through the region. Expect mountain obscuration, icing conditions and turbulence. Please, see the link, below for in depth information on icing and turbulence forecasts, and more. - Fogleman Refer to for more detailed regional aviation weather and hazard information. && .PRELIMINARY POINT TEMPS/POPS... GTF 12 19 1 13 / 30 20 10 0 CTB 7 14 -2 10 / 70 20 10 0 HLN 12 19 1 13 / 70 20 20 0 BZN 8 20 -4 9 / 100 10 30 10 WYS 2 20 -12 12 / 90 60 40 20 DLN 6 18 -4 10 / 90 20 20 0 HVR 12 18 3 12 / 30 10 10 0 LWT 11 19 -2 9 / 50 10 10 0 && .TFX WATCHES/WARNINGS/ADVISORIES... WINTER WEATHER ADVISORY IN EFFECT UNTIL MIDNIGHT MST TONIGHT FOR East Glacier Park Region...Southern Rocky Mountain Front...Little Belt and Highwood Mountains. WINTER WEATHER ADVISORY IN EFFECT UNTIL 9 AM MST MONDAY FOR Gallatin Valley...Northwest Beaverhead County...Ruby Mountains and Southern Beaverhead Mountains...Gallatin and Madison County Mountains and Centennial Mountains. && $$
Area Forecast Discussion
National Weather Service Tucson AZ
156 PM MST Sun Nov 27 2022 .SYNOPSIS...Dry with warmer temperatures to start the week. A storm system will brush by to our north Monday and Tuesday, resulting in some gusty winds across southeast Arizona along with a few degrees of cooling. Dry and warmer conditions return for the second half of the work week with a weak storm system potentially impacting the region over the weekend. && .DISCUSSION...Our dry northwesterly flow will buckle into a zonal flow over the next 24 hours as a system digs into the northern Great Basin Monday afternoon. With our current progressive consolidated higher latitude flow pattern, it will kick quickly eastward before digging into our area. It should brush by close enough for gusty winds as early as mid Monday afternoon and bring a few degrees of cooling Tuesday. The latest HRRR shows a nice low level moisture intrusion from the gulf late tomorrow, but it should be pretty shallow. We might manage enough of a moisture increase for a few light showers in the east central mountains, but not much more. A broad ridge is expected to develop from central Mexico through the Gulf of Mexico and into Florida, with signs of a deeper split near the west coast the second half of the week. Ensembles lift a first shot of energy once again north of our area Friday/Saturday, but a moisture increase could bring some virga or light showers in the warm sector upslope Friday night. This could set the table for a deeper follow-on system early next week. Ensemble mean 5 day height anomalies are hinting at a broader and deeper mean trough position over the west next week. && .AVIATION...Valid through 29/00Z. Mainly clear skies thru 28/06Z then SCT-BKN clouds at or above 20k ft AGL. SFC wind 12 kts or less with normal diurnal trends into the morning hours. Gusty southwest winds developing after 28/20Z. Aviation discussion not updated for TAF amendments. && .FIRE WEATHER...The next storm system will approach and pass Monday into Tuesday which will increase winds by Monday afternoon and drop temperatures on Tuesday. 20-ft winds from the southwest at 10-20 mph are expected Monday and Tuesday. Outside of a slight chance of showers over the White Mountains, dry weather continues through most of the week. Afternoon RH values will drop to 10-20 percent in valley locations through Monday before moisture increases on Tuesday. && .TWC WATCHES/WARNINGS/ADVISORIES... None. && $$ Meyer Visit us on Facebook...Twitter...YouTube...and at