Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/27/19

Area Forecast Discussion
National Weather Service Denver/Boulder CO
342 PM MST Thu Dec 26 2019 .SHORT TERM...(This evening through Friday) Issued at 245 PM MST Thu Dec 26 2019 Stratus deck is burning off, although there`s still a few patches in eastern Boulder/Larimer Counties, and more over Washington County. While the airmass has fully mixed over the mountains and Palmer Divide with much drier air, the boundary layer remains moist and stable north of Denver and across most of the plains. That will set the stage for stratus and fog redevelopment. There should also be relative pressure falls to our south overnight as the upper low begins to inch into the Desert Southwest. This would likely result in some sort of a weak Denver cyclone or northerly surge along the Front Range, which would help stratus and fog spread south into Denver overnight. The wildcard in all of this is how thick the mid and upper level clouds get, as an earlier increase and thickening could limit the fog threat. That is not seen right now, however, so we`ll go with patchy to areas of fog overnight across most of the plains. On Friday, attention will turn toward precipitation. There is weak warm advection and generally weak QG lift through the afternoon. The flow is deep southerly just off the deck, and that type of flow would favor precipitation over the eastern plains and crest of the Palmer Divide, and also Park County/southern Summit County in local upslope. We`ll have the highest PoPs there and increase them through the day with the arrival of better lift. NAM seems overly aggressive with amount of precipitation, but a few favored spots mentioned above could see an inch or two during the afternoon hours. Temperatures look cold enough to support mostly snow, and have lowered forecast high temperatures considering the expected cloud cover. .LONG TERM...(Friday night through Thursday) Issued at 340 PM MST Thu Dec 26 2019 Model have southwesterly flow aloft decreasing Friday night with an upper trough moving eastward. On Saturday, the upper trough is progged to move eastward across Colorado. The trough axis is over the CWA from 18Z on Saturday to 08Z Sunday morning. Behind the trough axis, strong north-northwesterly flow aloft moves into the CWA. The QG Omega fields show just moderate upward vertical velocity over the CWA Friday night into Saturday evening. Downward motion moves in behind the trough axis the rest of Saturday night and Sunday. The low level pressure and wind fields show a cold front, and northerly winds behind it, to move across the CWA Friday night after midnight. The northerly winds get pretty strong through the day Saturday, especially east of the Urban Corridor. Decent northerly winds continue Saturday night with northwesterlies on Sunday. There is pretty deep moisture with the storm. Cross sections show the moisture to stick around well into Saturday night. Moisture decreases Sunday with a bit lingering in the mountains. The QPF fields show fair amounts of measurable snowfall Friday night into Saturday evening, then it decreases. There is a tad of snowfall progged to continue falling in the high mountains Sunday and Sunday night. Concerning the winter storm highlights; there is some synoptic scale energy, cold air advection, and decent moisture, however the models are not in great agreement, especially with the QPF and the QG Omega vertical motion. Will leave the watch in place and add zone 41 to it as the Palmer Ridge does pretty good in strong northerly flow. Temperatures on Saturday look to be 6-8 C colder than readings on Friday. Sunday`s high temerptures are pretty close to Saturday`s readings. For the later day`s Monday through Thursday, northwesterly flow aloft is in place Monday with more zonal flow for Tuesday into Wednesday. By Wednesday night and Thursday, the next upper trough moves across. Temperatures stay right around or slightly cooler than normal readings all four days. There will be a chance of snow in mountains most of the time and a slight chance over the plains Wednesday into Thursday. && .AVIATION...(For the 18Z TAFS through 18Z Friday afternoon) Issued at 140 PM MST Thu Dec 26 2019 There remain varying solutions concerning fog redevelopment tonight. At this time, NAM looks overly aggressive, while latest HRRR is coming around to more of the conceptual model with a weak Denver Cyclone pulling in stratus/fog. Boundary layer moisture is holding strong to the north of Denver, so without development of thicker mid/upper level cloud development until tomorrow morning the stratus/fog forecast appears on track. It`s still hard to pin down timing and extent of fog, but initial development would favor the 08Z-10Z time frame. That fog would linger through a good chunk of Friday morning before lifting. By Friday afternoon, we`ll start to focus more toward snow in the forecast. There may be an initial band of snow in the warm advection that drifts over the airports after 18-21Z. Perhaps a dusting in the grass with that band. Main threat of accumulating snow holds off until Friday night and Saturday. && .BOU WATCHES/WARNINGS/ADVISORIES... Winter Storm Watch from Friday evening through Saturday evening for COZ041-042-044>046-048>051. && $$ SHORT TERM...Barjenbruch LONG TERM...RJK AVIATION...Barjenbruch
Area Forecast Discussion
National Weather Service Cheyenne WY
505 PM MST Thu Dec 26 2019 .UPDATE... Issued at 500 PM MST Thu Dec 26 2019 Southeast winds here at Cheyenne this evening could create some upsloping stratus and fog conditions here. Had a report of fairly widespread fog and low visibility in eastern Cheyenne already,,,so went ahead and added areas of fog into the forecast for the Cheyenne area this evening. GFS sounding for Rawlins showing a great setup for fog out there as added areas of fog out there. Updates have been sent. && .SHORT TERM...(Late this afternoon - Friday) Issued at 210 PM MST Thu Dec 26 2019 Afternoon WV/IR imagery showed a powerful closed upper low affecting southern CA/NV and western AZ. Pacific moisture from this system was spreading northeast into the Four Corners, with a veil of high clouds over the central Rockies. A cold front extended from Lake MI across eastern MO, central OK, and northwest into southeast WY. Low clouds covered much of western NE into portions of southeast WY. Isolated light snow showers over the higher terrain will end later this afternoon. Dry and cool conditions are forecast tonight and Friday morning. Light rain and/or snow showers will develop and spread north into extreme southeast WY and the southern NE Panhandle Friday afternoon. High temperatures Friday will be near seasonal normals. .LONG TERM...(Friday Night - Thursday) Issued at 319 AM MST Thu Dec 26 2019 Winter storm concerns quickly take over as we head into Fri night/ Saturday. This is an extremely complicated forecast scenario, with very low overall confidence for this time range. Models are coming into better agreement w/ the overall evolution of the storm, but a few considerable discrepancies still exist concerning the track of the storm and resulting QPF over our CWA. On Friday, a significant northern stream short wave will dive quickly south across Montana/ western Wyoming, a continued westward trend. Meanwhile, a vigorous closed low will be drifting from southern California and along the AZ/Mexico border. This will eject into the 4 Corners & will become absorbed by the northern stream system by late Friday. Models then show significant deepening over Colorado with surface cyclogenesis likely to occur from southeast CO into western KS. The 0z ECMWF is still the most concerning being the furthest west with the track & its H7 low tracking directly over the Panhandle. The GFS & NAM are considerably further east, but other foreign models including both the GEM and UKMET are closer to the ECMWF albeit not quite as well organized as the ECMWF. Ensembles are virtually all over the place for the storm track w/ extremely high standard deviations for this being less than 48 hours out. Here is what we know. The majority of southeast WY and the western NE Panhandle will see accumulating snowfall. The heaviest snowfall will begin by late Friday night and will likely persist through at least late Saturday night. A blended approach to QPF places higher chances for 4+ inches of snow over the southern Nebraska Panhandle and areas along the Pine Ridge from Lusk-Chadron. This makes sense even with some of the more eastern storm tracks. The ECMWF remains the most aggressive with QPF, but is a favored model in the eye of our national centers. Significant discrepancies exist for the Pine Ridge, but feel confident that strong northerly low-lvl winds will lead to topographic enhancement in that area. ECMWF ensemble probs are around 40-50 percent for 6+ inches along/east of the Wyoming & Nebraska line, nudging west along the Cheyenne/Pine ridges. Values increase to 70-80 percent for 3+ inch probabilities. One important factor here will be that winds are likely to be fairly strong with excellent low-level gradients in place. Widespread gusts up to 30- 40 MPH would create problems even w/2-4 inches of snow, especially while the snow is falling. Given extensive collaboration w/ WPC and neighboring WFOs, we have agreed that a unified message is critical due to this being a very busy travel weekend following Christmas. A Winter Storm Watch will go into effect from Friday evening through early Sunday, for areas along/east of a Lusk-Torrington-Pine Bluffs line. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 500 PM MST Thu Dec 26 2019 Tricky forecast tonight as lower atmosphere still moist from recent precip and upsloping winds for a time. Followed latest HRRR guidance on the 00Z TAFs...which shows lowering conditions at KRWL and KCYS. Will continue to monitor. && .FIRE WEATHER... Issued at 210 PM MST Thu Dec 26 2019 No fire weather concerns are anticipated through early next week due to cooler than normal temperatures, widespread snowfall, and non-critical humidities. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...Winter Storm Watch from Friday afternoon through late Saturday night for WYZ102-108-119. NE...Winter Storm Watch from Friday afternoon through late Saturday night for NEZ002-003-019>021-054-055-095-096. && $$ UPDATE...GCC SHORT TERM...MAJ LONG TERM...CLH AVIATION...GCC FIRE WEATHER...MAJ
Area Forecast Discussion
National Weather Service Dodge City KS
522 PM CST Thu Dec 26 2019 ...Updated Aviation Discussion... .SHORT TERM...(This evening through Saturday) Issued at 348 PM CST Thu Dec 26 2019 A major storm system will bring prolonged precipitation to western Kansas beginning tomorrow morning. There are still a lot of question with this storm, but the focus is narrowing on pretty much a pure cold rain event for much of our southwest Kansas region. The big question initially, will be out west tomorrow morning through early afternoon as short-term higher resolution model consensus suggests surface temperatures 31 to 34F from onset of precipitation through the afternoon. The official forecast will reflect mixed precipitation, mainly in the form of freezing rain should the surface temperature be 32F or just below. All the CAMs shows the first wave of precipitation mainly along/west of U83 to the Colorado border. The storm has slowed down enough to the point that areas east of U83 and especially east of U283 will likely not see much precipitation at all until very late in the afternoon. As the main body of the warm conveyor precipitation event translates east late Friday and Friday Night, the boundary layer will continue to slowly warm, however initial wet-bulb effect could bring the surface temperature precariously close to the 32F point Friday evening. It will be close, but for now, the official forecast is a cold rain with temperature in the mid 30s, slowly warming to the upper 30s Friday Night through early Saturday. Going beyond Friday Night, the main warm conveyor precipitation event will come to an end, however given the slow movement of the whole upper trough, and with some indication of another potential vorticity anomaly rounding the base of the trough across eastern New Mexico early Saturday, there could be another round of warm conveyor precipitation developing across the Texas Panhandle and moving on north-northeast into portions of southwest and/or south central Kansas. As far as precipitation amounts go, we are still going with a widespread three-quarters inch plus, with an axis of one-inch plus, focused mainly on the U283 corridor north-northeastward up toward Ellis County. Some areas within this axis still may see up to 1.5 inches of rain given the expected training nature of heavier showers and even a lightning flash or two. Any thunder potential should be confined to areas closer to the Oklahoma border. As the main surface low and 700mb mature and develop northeast of here, the "comma head" deformation axis will likely develop well to our north across far northwest Kansas into central Nebraska. The big snow storm with this system will be confined to areas of northeast Colorado, far northwest Kansas into much of the western half of Nebraska, and continuing on into the Dakotas. We collaborated with NWS Pueblo and Amarillo about a Winter Weather Advisory in the western counties against their NWS areas, but given the remaining high uncertainty in whether the temperature will be 32 degrees long enough out there in the west, we decided to hold off. The following shifts will really need to watch these temperature trends closely, and see how actual observations are matching short- term surface temperature progs off the HRRR and other high- resolution models. .LONG TERM...(Sunday through Thursday) Issued at 348 PM CST Thu Dec 26 2019 After the weekend storm is out of here by Sunday, temperatures will slowly moderate back into the 40s by early next week, with Wednesday likely being the warmest day of the upcoming week. The global models continue to show a rather active polar jet stream entering the CONUS off the Pacific, but right now, there are no indications of another major mid-latitude cyclone affecting western Kansas. Things can change fairly quickly in this active regime, so we will continue to monitor daily changes and trends in the global numerical prediction for our next potential precipitation event. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 509 PM CST Thu Dec 26 2019 Clear skies this Thursday evening will give way to increasing MVFR ceilings along with areas of fog after midnight in the Garden City, Liberal and Dodge City areas. IFR or even a period of LIFR ceiling will be possible at Garden City and Liberal between 09z and 15z Friday. Winds overnight and Friday will be east to southeast at 10 knots or less. As an upper level trough approaches early Friday the chance for a cold rain will be possible in the Garden City and Liberal areas after 15z Friday and this area of cold rain will then begin to spread east into the Dodge City and Hays areas during the afternoon. Confidence is not high at this time but a few models models do suggest that there may be some patchy very light freezing rain/drizzle at or just west of the Garden City and Liberal areas briefly between 12z and 15z Friday. Ceilings during the day on Friday will range from 500 to 2000ft AGL. && .PRELIMINARY POINT TEMPS/POPS... DDC 26 38 33 50 / 0 90 90 30 GCK 25 36 32 45 / 0 90 90 20 EHA 29 36 31 45 / 20 90 70 20 LBL 29 36 33 47 / 10 90 90 20 HYS 25 39 32 48 / 0 80 90 60 P28 30 44 39 56 / 10 50 90 70 && .DDC WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...Umscheid LONG TERM...Umscheid AVIATION...Burgert
Area Forecast Discussion
National Weather Service North Platte NE
642 PM CST Thu Dec 26 2019 .SHORT TERM...(This evening through Friday night) Issued at 308 PM CST Thu Dec 26 2019 The models continue to advertise a vigorous warm air advection driven precipitation event Friday night. The short term model blend plus bias correction, where appropriate, was the basis for rain changing to snow and freezing rain Friday evening. Ice accumulations are about the same as the previous forecast and around 1/10 of an inch of ice is predicted along and east of highway 83 with highest ice accumulations near highway 183. Snow accumulations of up to 2 inches are in place Friday night throughout wrn and ncntl Nebraska but given the strength of the forcing, locally higher amounts could develop. The forecast Friday night could go a variety of ways as the GFS, known for deep mixing and warmer temperatures, suggests mostly rain. Meanwhile, the NAM indicates a mix of rain and freezing rain changing to snow and the 15z 39hr solution of the RAP model indicated rain changing to snow. The blended forecast appears similar to the NAM and the forecast suggests about 1/3 of an inch of liquid should fall in the form of rain, snow and freezing rain. All models indicate this area of precipitation will lift rapidly north Friday night followed by a weakening or lull in the precipitation early Saturday morning. This is the result of the forcing on the h700mb warm front lifting in South Dakota and deep convection across Kansas and eastern Nebraska blocking moisture transport into western Nebraska. .LONG TERM...(Saturday through Thursday) Issued at 308 PM CST Thu Dec 26 2019 The models are beginning to congeal on the development of a wrap around band of moderate to heavy snow Saturday across wrn Nebraska. This band of snow will either lift north through wrn and ncntl Nebraska as indicated in the ECM or translate northeast through ncntl and northeast Nebraska as suggested by the GFS, the GFS ensemble and the 12z NAM. The forecast follows a blended approach but limits snow to liquid ratios to 14 to 1 which might still be too high given the strong winds that are expected to develop Saturday afternoon and last through Sunday night. This snowfall forecast is close to the ECM and WPC with 6 to 10 inches of snow throughout wrn and ncntl Nebraska. Highest amounts are predicted along the SD border. Note that the 18z NAM does not show this band of snow developing. The upper level low in the model is still organizing Saturday evening and the model will skip over Nebraska producing the heavy snow north of the region. The wind forecast Saturday through Monday uses a blend of the consensus MOS plus bias correction. This produced speeds of 25 to 30 mph and gusts to 45 mph which is close to the 30 mph surface speeds suggested by the 500m AGL winds indicated in the models. The prospect of blizzard conditions developing appears on the low side as this storm will be operating in a very high moisture environment with temperatures mainly in the upper 20s to around 30. This tends to produce a sticky snow which generally hugs the ground. Nonetheless, it appears this storm will approach the upper limit for winter storms. Overall the models are tracking the storm through Nebraska and stalling it for a period of time across the Upper Midwest. This slower motion is allowing for stronger winds and more moisture to be ingested into the system. Storm total QPF across western and north central Nebraska has increased to 1/2 inch to 1 and 1/4 inches. The Winter Storm Watch will remain in place as the models are showing east and west storm track differences which could ultimately exclude some areas from winter storm conditions. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 533 PM CST Thu Dec 26 2019 Latest satellite imagery and surface obs show a few patches of low stratus across the Panhandle, elsewhere generally partly cloudy skies overhead with VFR ceilings. Current thinking is partly cloudy skies will persist overnight across northern NEB with increasing sky cover across southwestern NEB. Increasing concern in the potential development of low stratus late tonight-early morning earlier than presently advertised across far southwest NEB. Confidence is below average at this point but may need to update. Thinking at least low-end VFR ceilings (less than 7 kft) spreading across western NEB early morning to north central NEB by late afternoon. Ceilings will lower to MVFR-IFR late morning- afternoon across southwestern NEB and the western Sandhills. Storm system then moves into the region Friday night bringing ahead of it increased rain chances Friday afternoon with potential for a wintry mix starting late afternoon. && .LBF WATCHES/WARNINGS/ADVISORIES... Winter Storm Watch from Friday evening through late Saturday night for NEZ004>010-022>029-035>038-056>059-069>071-094. && $$ SHORT TERM...CDC LONG TERM...CDC AVIATION...ET
Area Forecast Discussion
National Weather Service Memphis TN
839 PM CST Thu Dec 26 2019 .UPDATE... Light rain or drizzle continues across portions of North Mississippi and West Tennessee this evening. Will update to add 20 POPS. The latest HRRR continues to show dense fog development along and west of the Mississippi River during the overnight hours. Will change patchy wording to areas of fog and will monitor for fog development. A Dense Fog Advisory will likely be needed at some point tonight. The combination of clouds and fog will keep lows from dropping as much as previously thought. Will also bump up lows a tad. Update will be out shortly. KRM && .DISCUSSION.../issued 218 PM CST Thu Dec 26 2019/ .SHORT TERM (Tonight through Friday Night)... Persistent low clouds, light rain and drizzle has managed to produce minor accumulations at Memphis, and the surrounding areas. Coverage seems to be diminishing over the last couple of hours. We may see some breaks in the clouds prior to sunset but low clouds and fog is expected to return overnight. Persistence is often one of the best forecast tool. With that in mind, expect clouds to linger through much of the day again tomorrow, keeping temperatures in check. 30 && .LONG TERM (Saturday through Thursday)... Numerical models are converging their solutions for a major storm system over the Central US this weekend. Northern and Southern streams of the jet combine on Saturday leading to cyclogenesis over the Plains. A mild and humid airmass is in place over the Mid- South leading us to focus on the potential for severe weather and heavy rainfall. Based on current model trends the significant brunt of showers and thunderstorms should hold off until Saturday night. Although dew points creep into the 60s and a powerful jet moves into the Plains an orientation so far west is not conducive for increasing amounts of instability. Consequently, the models struggle to muster up only a few hundred J/KG of CAPE. On Sunday another strong jet streak rotates through the base of the trough, which does prove worrisome, however the pre-frontal surface trough is already located in the eastern portion of the CWA by Sunday morning. Instability in our forecast area again proves difficult to generate. Although the evolution of this jet streak will need to be watched. The end result of all this lack of instability suggests that a marginal risk for severe weather is appropriate despite the shear. Additionally rainfall amounts as the trough progressively rotates through the region should remain generally from 1 to 2 inches, with localized 3 inch amounts, most likely in north Mississippi. This trough dominates our weather into early next week with more average temperatures before yet another shortwave ejects from the Southwest US. This next weather system shows promise for bringing us a wet 2020 New Year. Belles && .AVIATION... A mix of MVFR/VFR cigs prevail across the Mid-South this evening. Drizzle/light rain has pretty much come to an end for the time being. A weak cold front will drop into northern areas of the Mid-South early Friday morning. Expect IFR/LIFR cigs to develop along and ahead of the front with dense fog likely over parts eastern AR, the Bootheel and NW TN. Drizzle is also possible. Expect the LIFR conds to impact MEM and JBR later tonight into Friday morning with somewhat better conds at KMKL and KTUP. Winds will be light through the period. SJM && && .MEG WATCHES/WARNINGS/ADVISORIES... AR...None. MO...None. MS...None. TN...None. && $$
...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Friday) Issued at 300 PM CST Thu Dec 26 2019 For tonight, the question is what will the stratus do and is there a chance for fog to develop overnight. The NAM has generally been the only model solution to hold onto the stratus this long, and the RAP has started to catch onto this as well. Forecast soundings from both models suggest the stratus will dissipate during the evening and the the boundary layer could saturated as radiational cooling occurs. Although I`m not sure what would cause the inversion and stratus to dissipate after sunset. So there is a large amount of uncertainty with the low level humidity. Have inserted some patchy fog across the north where skies are more likely to be clear for a period of time this evening. Also have held onto the stratus across eastern KS well into the evening. Lows are expected to range from the lower 20s along the NEB state line to the lower 30s over east central KS. If the clouds hold on all night, lows could easily be a few degrees warmer. Friday should start to see moisture return as the upper low over the southwest moves into the souther Rockies. Forcing for vertical motion will be on the increase through the day, but it appears to be at its strongest after Friday. So think Friday will be a mostly cloudy or overcast day with highs slowly climbing into the mid 40s to near 50. Precip chances should increase across central KS and spread east as the day progresses. .LONG TERM...(Friday night through Thursday) Issued at 300 PM CST Thu Dec 26 2019 Have categorical POPs for Friday night through Saturday. This is when models show a consensus for the best forcing and moisture to come together before a dry slot works its way into the state by Saturday evening. With good warm air advection and the forecast area remaining on the warm side of the system through Saturday, precip should be in the form of rain for all of the area. Models show some weak surface based instability developing across eastern KS Saturday afternoon. Lapse rates remain pretty marginal and near the moist adiabat, but low level and deep layer shear are progged to be good enough for possibly some organized convection. We may have to keep an eye out for a strong thunderstorm Saturday afternoon. The dry slot eventually works in Saturday evening bringing a break from precipitation. Then there may be enough wrap around moisture for some precip within the deformation band on the back side. Forecast soundings suggest a wintry mix could be the most likely precip type since saturation within the dendritic growth zone is hard to come by. However any precip looks to be very light so the forecast doesn`t anticipate a lot of impacts from this just yet. Highs Saturday over eastern KS are forecast to be near 60 thanks to persistent low level warm air advection. Further west across north central KS, highs may only make it into the lower 50s since the temp advection shouldn`t be as strong. Colder temperatures are likely Sunday as gusty northwest winds advect cold air into the region. The forecast remains dry for Sunday night through Tuesday night. Dry air is forecast to be over the area with no well organized disturbance progged by the models. There are some slight chance POPs in the forecast for Wednesday and Thursday as models show energy over the southwest trying to phase in with a northern stream trough moving through the plains. Moisture availability looks to be a limiting factor for POPs at this point. Temps are forecast to see a gradual warming trend, but remain generally seasonable with lows in the 20s and highs in the 40s. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 529 PM CST Thu Dec 26 2019 The deck of MVFR stratus continues to linger over terminals at the 00Z TAF issuance time. Forecast soundings and high res models show scattering of the cloud deck occurring around 02Z at KMHK and a few hours later at KTOP/KFOE. Confidence is not high, however, that CIGS will scatter that quickly so amendments will be possible this evening. Patchy fog is looking possible early tomorrow morning, especially if skies clear through the night. && .TOP WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...Wolters SHORT TERM...Wolters LONG TERM...Wolters AVIATION...Teefey
Area Forecast Discussion
National Weather Service Las Vegas NV
345 PM PST Thu Dec 26 2019 .SYNOPSIS...A potent storm over southern California is pushing eastward towards southwestern Arizona and will continue to do so through Friday morning. This storm will continue produce widespread moderate to occasionally heavy rain and winter weather impacts across southeast California, southern Nevada and northwest Arizona followed by dry conditions over the weekend. Another system dropping south late Sunday into Monday will bring a quick chance of precipitation followed by gusty north winds Tuesday. && .SHORT TERM...Through Tomorrow. With the forecast more or less on track this afternoon, not many significant changes were made to the forecast through 12Z tomorrow morning. Of note, looking at the latest HRRR and 12Z HREF trends as well as satellite trends, felt fairly confident snowfall cessation for both the Spring Mountains/Mountain Springs area as well as Mountain Pass should be over between 06-12Z. Thus, trimmed back the end time of those respective WWAs to 12Z instead of 15Z. However, snowfall expectations have not changed much and thus did not see the need for further upgrades or amount updates. Farther east to Hualapai Mountain, did increase QPF a bit there (and thus snow totals) due to enhancement in the deformation zone seen on satellite as of 15Z over Mohave County. Hualapai Mountain Rd has been closed already where the majority of impacts are expected. Even with the higher totals though, expectations are on the high end of advisory level and feel fairly comfortable that this is appropriate. Still believe flash flood impacts will be isolated in nature, if any but can`t rule this possibility out due to the aforementioned enhancement seen on satellite. QPF totals have been impressive in the Twentynine Palms area (~1.25+") and with another 12ish hours of rainfall possible in the lower deserts across the Colorado River Valley and southern Mohave, did not feel comfortable canceling the watch. Latest HRRR trends quickly dissipate PoPs by 18Z tomorrow but this is on the faster end of solutions this afternoon so lingered low end chance PoPs for eastern Mohave county through 00Z tomorrow. However by this point, the bulk of the lifting associated with the low should be well east of the region and only light precip is expected, thus did not feel a extension in the watch or advisory was needed. .LONG TERM...This Weekend through New Year`s Day. Overall, weekend weather expectations have not changed much. However, looking at our next system late Sunday into Monday morning, a few intriguing details are worth noting... Looking at the deterministic GFS/ECMWF/Canadian, there suggests significant difference in the southward progression of the next low pressure system. While both are very cold lows, one is positioned along the California coast, and the other is much farther east, passing directly over southern Nevada by Monday morning. Diving into ensemble cluster analysis, there suggests evidence that about 20% of the GFS ensembles favor the 12Z ECMWF while there is much more agreement in the ECMWF ENS. Thus, the forecast overall favored this more eastward progression. What is that interesting? It would be the best possibility for snow levels to reach desert valley floors. However, this also would mean it would move through quickly, moisture would be lacking, and low temperatures Monday morning look to stay in the mid to upper 30s, so no accumulations would be expected. Also, snow levels would recover quickly by late morning, so the opportunity would be short and marginal, but not-zero. By Tuesday, it appears that the aforementioned low should be well south of the region and a drier forecast is expected. By New Year`s Day, there could be a quick opportunity for snow across Lincoln county, but details are still quite hazy. && .AVIATION...For McCarran...Vicinity light showers expected for the Las Vegas Valley through much of the overnight hours with increased chances of rain at the terminal before midnight. Winds will be fairly consistent through the majority of the TAF period with speeds 10-15 kts from the northwest until Friday mid-afternoon when they decrease to generally below 5 kts. CIGs will gradually improve through the overnight hours. CIGs aoa 4 kft should only persist through around midnight with OVC aoa 12 kft expected by daybreak. Moderate confidence on the exact timing of the lift, but ceilings expected to continue to improve throughout the day Friday as dry conditions return. For the rest of southern Nevada, northwest Arizona and southeast California...Light rain showers expected to continue through the overnight hours at KDAG, KIFP and KEED with ceilings below 5 kft at times. As daybreak approaches, CIGs will gradually improve as precipitation chances within the vicinity of the terminal decrease. CIGs will continue to improve throughout the day on Friday while dry conditions return. Gusty northerly winds down the Colorado River Valley will relax after sunset tonight with speeds around 10 kts prevailing overnight. Otherwise, area-wide improvements through the day Friday expected with breezy-to-gusty northerly winds setting back up around sunrise. && .SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report any significant winter weather or flooding impacts according to standard operating procedures. Measured snowfall accumulations are also encouraged. && $$ DISCUSSION...TB3 AVIATION...Berc For more forecast information...see us on our webpage: or follow us on Facebook and Twitter