Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/29/20

Area Forecast Discussion...UPDATED
National Weather Service Amarillo TX
533 PM CST Mon Dec 28 2020 .AVIATION... MVFR cigs will continue to spread from south to north across the TAF sites this evening. Rain and freezing rain is expected to develop across the area mainly after midnight. Conditions will likely be down in the IFR/LIFR range overnight into early afternoon. Conditions will slowly improve from west to east during the afternoon on Tuesday. && .PREV DISCUSSION... /Issued 306 PM CST Mon Dec 28 2020/ SHORT TERM...Tonight through Tuesday Night... Isentropic lift will increase overnight as low level southerly flow increases over the top of modified shallow cool airmass in place in advance of a strong approaching trough. With very low condensation pressure deficits developing, anticipate this will lead to lowering CIGs and eventually development of widespread drizzle and/or light rain late this evening and esp after midnight. Nearly all models including most CAMs at this point, now show the southern half or so of the area remaining just above freezing tonight, but quite a bit of guidance (not all, but including the NBM) does still show temps of 29 to 32 across the northern Panhandles and a plenty deep layer of sub-freezing air to lead to frozen precip concerns. While we can`t completely rule out a mix bag of precip early (esp with some seeder-feeder potential from current high clouds), the warm nose builds substantially and quickly overnight and freezing rain and freezing drizzle should become dominant weather types in the north. Marginal temps make ice accumulation forecasts difficult, but we continue to show up to around 1/10" ice in the far north. The morning commute will be the main concern as temps should climb above freezing around mid-morning was very strong WAA erodes the cold air. We have issues a winter weather advisory from 6Z to 16Z in the northern two rows plus Hartley. Dynamics from the upper level trough and 100 kt+ jet streak on the east side will take over in the afternoon as weak SFC low and assoc trough move east across the area to maintain shra and possibly even TSTM potential along and east the the trough across the ERN Panhandles. This is where heavier precip amounts are expected, although better moisture is shunted east into OK by around 21Z per H7 theta-e. In addition to the SFC trough that helps dry out this some from west to east, the low will also user decent cold front trough the region Tue night. Models have mostly been backing off POPs for Tue night except for possibly the SE, but the 18Z HRRR has actually gone the other direction and is back to showing snow develop (or rain to changing to snow) along the H7 trough which does appear to have decent convergence along it. In fact the 18z HRRR produced 2-4" snow along this feature across a diagonal roughly Potter Co to Lipscomb/Beaver COs with the localized higher amounts near the good old Canadian River Upslope added areas near Highway 60 NE of AMA. This will have to be watched, but for now stuck close to the NBM POPs that are only 20-30 percent in this region with higher values SE. Gittinger LONG TERM... By early Wednesday morning, there should be some lingering PoPs in the east and southeast, as some snow will likely be lingering. However, any wrap around precipitation will be short lived as the main system moves east. The position of the upper low will then determine if we get anything else this week. The ECMWF keeps the upper low in Central Oklahoma, which would be just close enough for some additional wrap around precipitation in the eastern Texas Panhandle. However, the GFS is slightly further east, which means a near miss for the eastern Texas Panhandle on Friday. Given the Euro`s track record for this system in particular, have leaned on its solution for the forecast, which keeps low PoPs on Friday and early Saturday in the east. The end of the year/beginning of the year forecast is looking pretty good, although it might be a bit cold. Overnight lows Thursday into Friday will be slightly below normal, but not much. Lows will likely be in the teens to near 20. Normal lows for the 1st is 23. Afternoon highs for both Thursday and Friday will be in the lower 40s, which is about 5 degrees below normal. Once the upper low finally moves to the northeast, there should be a brief warmup, with highs getting back to near 60 degrees for the first week of 2021. Next short wave trough will then approach the area by the middle part of next week. Medium range models and their ensembles are in decent agreement in the timing and location of this next feature, but still a bit soon to determine with any confidence on what that system will bring. Fox && .AMA Watches/Warnings/Advisories... TX...Winter Weather Advisory from midnight tonight to 11 AM CST Tuesday for the following zones: Dallam...Hansford... Hartley...Lipscomb...Ochiltree...Sherman. OK...Winter Weather Advisory from midnight tonight to 11 AM CST Tuesday for the following zones: Beaver...Cimarron...Texas. && $$ 15/29
Area Forecast Discussion
National Weather Service La Crosse WI
952 PM CST Mon Dec 28 2020 .UPDATE... Issued at 945 PM CST Mon Dec 28 2020 A large area of surface high pressure extending over MN/IA and an an arctic front was still pushing through the area. Temperatures were in the teens to lower 20s, but in the single digits or colder behind the front. We are seeing a few flurries with the MVFR ceilings at Medford and earlier at KRST. These clouds have decreased over MN with some dense fog developing in southwest MN. There is a hint on the RAP/HRRR that patchy fog will develop with the dense fog remaining to the west of KRST. Some patchy dense fog may develop in northeast IA though. The forecast for the storm Tuesday afternoon into Wednesday appears on track. The forecast soundings are initially quite dry, however between 11am and 2pm really moisten up at KRST and from 1pm and 4pm. The 0 deg 850mb line from near KTOP into central MO works north toward the southern part of the forecast area by 00Z tomorrow. Some freezing rain potential and should be greater closer to the warmer air across our southern county warning area. The NAM supports a small northern shift of higher amounts and the 00Z HRRR has a small increase in amounts, but still within our current forecast range. The models continue to have the heavier snow where our current winter storm warning is. Will want to watch this warm air and just north of it for high snowfall rates of 1 to 2 inches per hour. EMC HREF 18z/00Z have a similar footprint with the heavy snow/isentropic lift/frontogenetic band from Iowa into southern WI/northern IL, so this is good to see the run to run consistency. The data is still coming in...but headlines are looking good for now. && .SHORT TERM...(This afternoon through Tuesday) Issued at 307 PM CST Mon Dec 28 2020 Clouds continue to stream southeast today per GOES satellite imagery with a sharp wind shift along an arctic front making its way through MN. At 17Z the front was located along a DLH-ABR line with colder air behind...mainly the single digits above zero. There were also some flurries along the front in the observations. Some pockets of light snow were also falling across northwest WI and have added some scattered snow showers in the forecast this afternoon north of highway 29 in WI. The arctic front moves through in the early evening with some flurries and clouds. While there are breaks across the confident these will completely clear the area tonight. Might be kind of messy. A slightly earlier timing has now focused a bit more concern on the evening commute and pushed the Winter Storm Watch over to a Warning for northeast IA and southwest WI. The strong moisture surge arrives and almost immediately begins nearly 1" per hour snow rates south of I-90. By 6 pm 2-3.5" inches will have fallen in MN/IA according to our latest forecast. .LONG TERM...(Tuesday night through Monday) Issued at 307 PM CST Mon Dec 28 2020 Many of the winter storm signals remain unchanged for Tuesday afternoon through Wednesday morning. Among the ensembles, there remains a decent amount of spread to give a seasoned forecaster like myself more grey hair. The lower values for the storm appear to be from a more transient solution, shifting the moisture surge off to the east more rapidly. However, the deterministic runs do favor a SW-NE band of frontogenesis that remains in place after the big push northward of warm and moist advection. This is when the southern snow amounts climb higher. The 28.12Z HREF and WPC Superensemble members suggest amounts in the Warning have ~ 50% potential for 8+". The highest HREF snowfall band is 10-12" across Clayton and Grant counties. With the speed of the system, it is still a bit unnerving to go high with snow amounts...but do have 8-9" totals in the far south. With the broad isentropic lift over the region /290K surface in the RAP/ widespread accumulating snow will be found by Tuesday night. The highest impact period looks to be from onset through about 10 pm Tuesday evening south of Interstate 90. The 28.12Z SPC HREF indicates 70-80% probabilities of 1"/hr snowfall rates in that area...which was one reason the Watch was converted to a Warning. This will be a challenge for plows to keep up with. Lower snow amounts (a miss) are certainly possible with the forecast, but the WPC Superensemble of 60 members places a 90% chance for at least 2" in the north to 5" in the south. This is rooted in the strong and broad isentropic lift across the region with this system. So, confidence is high that *everyone* will see 2" of snow. There are also still chances for a wintry mix /sleet/ moving into far southwest WI, although the probabilities are low. Friday... Signals continue in the model ensemble data and deterministic runs for accumulating snow on Friday. At this time it appears WI is the main snow target with amounts of 1-3 inches as a common mean in the ensembles. This cyclone will have major Gulf of Mexico moisture as it heads due north from said Gulf. It appears most of the impact will be south and east of the area...but this storm definitely bears watching. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 559 PM CST Mon Dec 28 2020 A brief period of MVFR clouds and flurries is possible early this evening, with VFR conditions then expected later tonight into Tuesday morning. A winter storm Tuesday afternoon into the overnight is expected to bring MVFR and IFR conditions to the TAF sites. A weak cold front will bring a short period of low VFR/MVFR clouds and northwest winds early this evening, with a few flurries noted in upstream observations. Behind this, skies should clear out under brief high pressure later tonight, with winds gradually turning more southerly to southeasterly by morning. Will have to watch out for some patchy fog development with light winds and clear skies, though confidence in this occurring is low. Clouds will increase Tuesday morning ahead of a low pressure system approaching from the west, with snow and MVFR to IFR visibility and ceilings expected to work into the TAF sites by mid to late afternoon. Winds could gust to near 20 kts at times in the tight gradient ahead of the low pressure system Tuesday afternoon. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...Winter Storm Warning from noon Tuesday to noon CST Wednesday for WIZ053>055-061. Winter Weather Advisory from 6 PM Tuesday to noon CST Wednesday for WIZ017-029-034-042>044. Winter Weather Advisory from noon Tuesday to noon CST Wednesday for WIZ032-033-041. MN...Winter Weather Advisory from noon Tuesday to noon CST Wednesday for MNZ079-086>088-094>096. IA...Winter Storm Warning from noon Tuesday to noon CST Wednesday for IAZ009>011-018-019-029-030. Winter Weather Advisory from noon Tuesday to noon CST Wednesday for IAZ008. && $$ UPDATE...Zapotocny/Lee SHORT TERM...Baumgardt LONG TERM...Baumgardt AVIATION...Lee
Area Forecast Discussion
National Weather Service Binghamton NY
1046 PM EST Mon Dec 28 2020 .SYNOPSIS... Lake effect snow develops tonight and continues through Tuesday before dry weather returns later in the day. Dry weather continues Wednesday before the next shot of rain and snow Thursday and Friday. && .NEAR TERM /THROUGH TUESDAY NIGHT/... 1030 PM Update... Lake effect snow bands are developing off lake Ontario as expected and a weaker band off of lake Erie is extending across the Southern tier. The Erie band is expected to drift south, become disconnected from the Lake and dissipate across the far northern tier of PA by late evening. Meanwhile the band off Lake Ontario is now becoming better organized on an almost due westerly flow. CAMs are now in good agreement that this band will drift south through the NY Thruway corridor (Syracuse to near Utica) between now and 1AM...then its southward progress should halt...remaining nearly stationary along the NY Thruway corridor through at least daybreak. It will be in this time period that advisory level snow amounts are expected. If the band becomes well organized, snowfall rates of 1-2 inches per hour will be possible in and around the Syracuse metro for a period of time. HRRR Bufkit profiles for SYR show a very favorable setup for high snow to liquid ratios, with an omega bullseye in the snow growth layer.....and equilibrium levels just above 10 k ft agl. Will need to watch this closely, as there is potential to eclipse the 7" warning criteria quickly if the band can remain in place long enough. Then, the lake effect snow band should drift south again into the hills south of Syracuse, and across Cayuga, Cortland & Chenango counties by mid morning. The snow band breaks up into showers and flurries by afternoon. 730 PM Update... Snow showers are beginning to break out across CNY at this time as an upper level trough and associated shortwave approach from the west. Cold air advection is continuing, with 850mb temps down to around around -8C...but forecast to fall to around -14C by morning. The overall flow remains 250-260 off of Lake Ontario and Erie currently; but as this shortwave passes by to the east the flow is expected to quickly veer around to 290-300 degrees overnight. Another vort max/shortwave could temporarily shift the bands back north on a 270-280 flow for a few hours after midnight...but then it veers back between 300-320 Tuesday morning as 850mb temps fall to around -15C. West winds will be breezy at 8-15 mph, with gusts 20-25 mph overnight...increasing to 10-20 mph with gusts up to 30 mph on Tuesday. This could cause some localized blowing snow (where lake effect accumulation occurs). Otherwise, the near term forecast remains on track and only minor adjustments where made to PoPs, QPF and Snow amounts with this update. Winter weather advisory remains in effect for the lake effect snow across Onondaga, Madison and N. Oneida counties into Tuesday. 330 PM Update... Low clouds linger across the area, with temperatures having bee able to peak a little higher than expected, in the mid 40s for our valley locations. However, the cold front moving through the rest of the evening will allow temperatures to quickly fall back through the 30s. Meanwhile, another shortwave is forecast to ripple through the area. This will touch off additional chances for some snow showers across most of central NY this evening into the early part of the night. Steepening lapse rates courtesy of cooling air aloft will contribute to a chance for some of these convective snow showers to take on more squall- like activity, with periods of higher snow rates and gusty winds. As this will be well after the evening commute, we are not expecting to need to issue any additional headlines. Snow totals associated with this next round of convective snow showers should generally be less than an inch area-wide, but higher totals in excess of an inch would be more likely in northern Oneida county, where westerly flow will lead to some lake enhancement. Higher totals nearing an inch would also be possible where higher snowfall rates in any squalls can occur. However, once this passes through, the primary concern from midnight onward will be a lake effect snow as temperatures falling back to as low as -12 to -15 C under west/northwest flow. Simulated reflectivity shows a band developing across central Oneida county, then this drops southward and into the Thruway/Syracuse/Utica area by 3am. This eventually reaches the hills south of Syracuse by the late morning, but then dissipates into the afternoon as northwesterly flow starts to veer more northerly and slackens slightly. As for totals: additional snow totals up to 2 to 3 inches are now expected in northern Oneida county as the band may set up slightly to the south, but higher amounts are not out of the question where any more persistent snow showers can develop earlier in the night. Conditions will be most favorable during a period from 4 am to about 10 am where snowfall rates will be 1-2 inches per hour as the band drops more southward towards the Thruway. However, if this band checks up and/or slows down significantly, snow totals could be a bit higher. Expected totals for southern Oneida, Madison and Onondaga Counties is 2 to 5 inches, especially across a corridor from Baldwinsville to Cazenovia. Some locally higher amounts are possible Heading into the late morning, drier air working in will help to cut down on the presence of ice crystals and lessen our snowfall rates as the band moves more southward. The 850mb ridge axis will move in late Tuesday afternoon and veer the winds more to the north and also usher in some suppression and a drier air mass. This will allow the snow to come to taper off after 2 pm and come to an end completely before sunset. Temperatures will be on the cool side Tuesday with highs only into the mid and upper 20s. Gusty northwest winds will make it feel like the teens at times. Temperatures fall back into the teens Tuesday night as decreasing winds and partially clearing skies allow for better radiational cooling, but higher clouds will be working in and lowering from the west by the early hours of Tuesday. This may keep lows slightly higher across our western zones compared to the east. && .SHORT TERM /WEDNESDAY/... Next storm system is again complex and will come through in two pieces as per GFS and NAM. First an upper level low and trough is projected to track just north of the Great Lakes on Wednesday. This feature is tied to a low-level cyclone which was almost vertically stacked which reaches south of James Bay Canada by 00z Thursday. Models shows strong warm advection on a southwest low- level flow pattern during the day Wednesday across NY and PA. GFS shows decent isentropic lift between the 290 K and 300 K surfaces, but the local pressure tendency term is showing some descent canceling some of the lifting. Additionally and probably more importantly, moisture will be lacking originally. So despite strong warm air advection we don`t expect much precipitation just increasing cloud cover Wednesday. The surface layer and lower-levels start off dry so not expecting any freezing precipitation to start. So we are going to hold back or limit POPs for Wednesday before 00z Thursday. For Wednesday night, 12z NAM and 12z GFS shows a low-level frontal boundary sliding south with colder air pushing into NY and far northern PA by 12z Thursday. This colder air continues to work south and east on Thursday in a confluent flow pattern from the departing northern upper level trough across southeast Canada and the next system which is in the southern branch over Texas at 12z Thursday. Moisture from this system is feeding northeast into this confluent zone. Given the temperature gradient over NY and PA and the confluence there will be some frontogenetical forcing and moisture so we will have POPs. Looks like mainly rain as the boundary layer takes longer to cool down vs aloft. QPF amounts are pretty light so not expecting much accumulations of snow. Then for Thursday, transition from light rain showers to snow showers occurs over central NY and northeast PA as the front gets farther south of our area. Weak low-level ridging builds in later in the day before the southern branch system begins to develop and track north. So we will have POPs for rain and snow with minimal accumulations at this point. The NAM does have 1 to 3" of snow across the Twin Tiers and across northern Oneida co. The 12z Euro, 12z GFS, 12z CMC all have 1-3" over Oneida Co and less than 1" farther south. Am inclined to have 1-3" northern Oneida co and less than 1" elsewhere for starters. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Next major storm system arrives from the southern branch New Year`s Eve at night and New Year`s Day as per GFS and Euro. The CMC keeps the southern branch wave suppressed and no precipitation reaches northeast PA or central NY through 00z Saturday. The Euro/GFS have a vertically stacked / barotropic low reaching far northern Illinois at the same time. Both the 12z Euro and 12z GFS have the QPF just south of northeast PA and central NY at 12z Friday. So we will hold off/limit precipitation before 12z Friday. Then for Friday strong lifting from warm advection and from strong upper level PV advection will combine significant lifting in the presence of strong moisture transport from a 50-60 knot low- level jet. Initially dewpoints and temperatures show that the boundary layer will be cold enough for a mix of sleet and freezing rain before a change-over to rain by Friday afternoon or early evening. Timing will no doubt be hard to pin point this far in advance but we will mention so rain and freezing rain Friday. Then with strong thermal advection any mixed precipitation turns to rain which will last until overnight Friday to Saturday before tapering to rain and snow showers. Departed from NBM here since the colder CMC and other ensembles makes for unmeteorological outcomes. Using NBM you get mixed snow with sleet/freezing rain despite 850 mb temperatures way above freezing on Euro/GFS. So we used a blend of the Euro/GFS temperatures for the time period 18z Thursday to 12z Saturday. In this way we have freezing rain changing to rain everywhere given the dewpoints on the euro/gfs which exceed 35F across all of CWA by Friday evening. The colder air arrives behind this upper level low which makes it way across the Great Lakes to Quebec by 18z Saturday. Colder air will follow enough to change rain to snow showers across central NY and northeast PA by 00z Sunday. Saturday night looks like lake effect snow showers in north central NY but ridging rapidly building in at 850 mb will cut off lake effect snow showers by midday Sunday. Then both the Euro and GFS both advertise a coastal low well southeast of our area as to have no influence on our area Sunday to Monday except north winds. 850 mb temperatures are projected to be mild on the Euro Sunday and Monday running around 3C. The GFS is a bit chillier being around -3 to -5C. So we will use NBM for the temperatures. Basically we will start with NBM for the extended but make adjustments for precip-type to keep it simple and make sure temperatures are aligned with precipitation type. As for flood potential, GFS/Euro operational models all indicate around 1" to 1.5" inches in an axis from northeast PA to the Catskills and another 1" to 1.5" inches over Oneida County. Both indicate a local minimum of QPF around the Finger Lakes into the twin tiers. with .5 to .75". The ensemble means from the Euro/GFS and CMC all are similar. Temperatures and dewpoints peak in the low to mid 40s which should keep significant melting of what is left of our snow water equivalent at bay. So we are not expecting many flood problems at this early stage. But stay tuned here as well. && .AVIATION /04Z TUESDAY THROUGH SATURDAY/... Mainly VFR to MVFR conditions are expected this evening, although brief lower restrictions are possible in scattered snow showers. A lake effect snow band then sets up east of Lake Ontario after 06Z, which will likely bring IFR-or-worse conditions to KSYR and KRME. Brief visbys of 1/2SM or less will be possible in the most persistent portion of this band. Otherwise, while mainly MVFR restrictions continue through most of Tuesday morning, gradual improvement to VFR is expected during the afternoon. Winds will be mainly westerly tonight, shifting to more northwesterly during the day on Tuesday. Winds become gusty Tuesday afternoon before diminishing by the evening. Outlook... Tuesday night...Mainly VFR. Wednesday...VFR expected. Thursday and Friday...Restrictions possible in rain showers; freezing rain possible Friday morning. Saturday...restrictions possible in rain and snow showers, mainly across KSYR and KRME. && .BGM WATCHES/WARNINGS/ADVISORIES... PA...None. NY...Winter Weather Advisory until 4 PM EST Tuesday for NYZ018-036- 037. Winter Weather Advisory until 11 AM EST Tuesday for NYZ009. && $$ SYNOPSIS...HLC NEAR TERM...HLC/MJM SHORT TERM...DJN LONG TERM...DJN AVIATION...BJG
Area Forecast Discussion
National Weather Service Dodge City KS
453 PM CST Mon Dec 28 2020 ...Updated Aviation... .SHORT TERM...(This afternoon through Tuesday night) Issued at 1200 PM CST Mon Dec 28 2020 Radar indicated a band of light snow/flurries from Ness to Rush counties at midday, moving northeast. Light snow or flurries will continue across the northern counties/I-70 corridor this afternoon and evening, with small accumulations possible. Impacts from this snow are expected to remain limited, but 12z NAM does accumulate about one inch of snow in this region into this evening. Closed 546 dm cyclone over central California at midday will weaken into an open, positively-tilted longwave trough across the Rockies by 6 am Tuesday. Ahead of this approaching trough, a strong warm air advection synoptic regime will unfold tonight and Tuesday, with low stratus and widespread precipitation expected. Made no substantial changes to the inherited winter weather advisory with the newest model guidance. Widespread rain will develop from West Texas to western Oklahoma after midnight tonight, and rapidly expand northward into SW Kansas late tonight through sunrise Tuesday. Increased pops to 100% across the central and eastern zones for several hours early Tuesday morning, with widespread warm conveyor belt precipitation production. So it comes down to the thermal profile and surface temperatures to determine phase changes. Overnight, initial bands of precipitation will take the form of light snow, but quickly transition to sleet and then freezing rain as the warm nose aloft deepens. We continue to feel confident that surface temperatures will hold in the 28-32 degree range for several hours during the first half of Tuesday morning, and this is the expected ice accumulation window. Light to moderate freezing rain is expected to yield ice accumulations of 0.1-0.2 inch, with localized amounts to 0.25 inch possible where surface temperatures can remain below 32 the longest in the face of strong warm advection (most likely NE zones). Do not feel ice storm warning criteria (1/4 inch) will be achieved, but will monitor the NE zones closely. Ice accumulations will dwindle rapidly NW of a Liberal- Jetmore line. These amounts do not sound like much, but remember it takes very little freezing rain to make sidewalks and bridges very dangerous. Allow extra time for travel Tuesday morning. Warm front will make steady NE progress through midday, with temperatures climbing above freezing, and cloud ceilings gradually improving, from west to east. Warm conveyor precipitation shield is expected to be along/east of US 283 by noon per the latest HRRR, and all precipitation is expected to be rain Tuesday afternoon. Western counties will warm well into the 40s Tuesday afternoon, with the NE zones remaining in the 30s where rain will be last to exit. SE winds of 10-20 mph tonight and Tuesday morning will trend southerly midday Tuesday as the warm sector arrives. Rain will continue well into Tuesday evening across Barber county and vicinity as the warm conveyor belt slowly migrates east. Elsewhere, cold/dry advection is expected Tuesday night as the primary trough axis arrives with an attendant cold front. An abrupt shift to NWly winds is expected Tuesday evening, and followed the stronger MAV guidance for this. Also hung on to some pops Tuesday night, with HRRR showing scattered showers progressing west to east with the trough and cold core aloft. Whatever precipitation we get Tuesday evening will change back to snow, but it should be light with an open/positive tilt trough and dry advection. Temperatures sunrise Wednesday well down into the 20s. .LONG TERM...(Wednesday through Monday) Issued at 133 PM CST Mon Dec 28 2020 The base of the positively tilted longwave trough over Arizona at 6 pm Tuesday will dig well down into Mexico Wednesday and Wednesday night, closing off another mid level cyclone south of Big Bend National Park by Thursday morning. Much more sunshine is expected Wednesday as this occurs, as a dry subsident airmass overspreads SW KS. Light north winds with temperatures not far from seasonal normals, in the upper 30s and lower 40s Wednesday afternoon. Thursday, 12z ECMWF ejects the Mexican cyclone into Texas and strengthens it further to 546 dm. New Year`s Eve will remain dry with plenty of sun, with dry air and any clouds favoring the SE zones nearest the Texas storm system. Thursday afternoon temperatures will moderate a little farther into the 40s. We will need to monitor this "Texas hooker" system closely Thursday night/early Friday (during the New Year`s holiday). NBM only introduced minimal pops for snow across the SE zones during this time, but deterministic 12z ECMWF tracks the cyclone close enough to impact areas east of US 283 with accumulating snow. 12z ECMWF places a 542 dm closed low in NE Oklahoma at 6 am Friday, with deformation shield of rain/snow impacting much of central/eastern Kansas. Further increases in pops are likely for the eastern zones during the New Year`s holiday. Quiet dry weather is expected over the upcoming weekend, with moderating afternoon temperatures. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 447 PM CST Mon Dec 28 2020 Through 01Z scattered snow showers and IFR conditions will be the case around HYS and then slightly higher ceilings and improved visibility will occur through 08Z. After 06Z cloud ceilings should start to fall for all TAF sites as a storm system enters into the Colorado and New Mexico Rockies. Expect IFR to LIFR flight categories from 11Z-21Z for all airport sites as moisture moves through western Kansas. Initial precipitation will develop after 09Z and start out as either snow or sleet. Warmer air aloft will change the precipitation to freezing rain from 11Z-18Z. Icing potential could get as high as 0.10-0.20 inch for DDC and HYS with lesser amounts for GCK and LBL. After 18Z we should see a slow transition to rain. All the precipitation should start to depart from west to east after 21Z. && .PRELIMINARY POINT TEMPS/POPS... DDC 29 41 25 39 / 70 100 30 0 GCK 27 43 21 39 / 60 70 20 0 EHA 30 48 25 41 / 40 50 20 0 LBL 26 44 23 41 / 50 80 20 0 HYS 28 38 22 37 / 80 80 30 0 P28 30 45 29 41 / 80 100 70 10 && .DDC WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 3 AM to noon CST Tuesday for KSZ064>066-076>081-085>090. Winter Weather Advisory from 3 AM to 3 PM CST Tuesday for KSZ030- 031-045-046. && $$ SHORT TERM...Turner LONG TERM...Turner AVIATION...Tatro
National Weather Service Hastings NE
536 PM CST Mon Dec 28 2020 ...AVIATION UPDATE... .DISCUSSION...(This evening through Monday) Issued at 321 PM CST Mon Dec 28 2020 Focus for this forecast is centered around the long expected winter system pulling through the Central Plains tonight into Tuesday evening. As expected, a band of light snow/flurries has developed to the southwest with some isentropic lift/warm air advection and will eventually work its way north to give us some light snowfall by tonight. Our main problems our mounting more toward our southeast CWA. Not to say won`t see a decent amount of snow in the 3-5 inch range along and north of I-80 where we had been putting most of our focus. But, the southeast is where the heaviest QPF band seems to be setting up as models are trending toward a convergence on this solution. The 18Z run of the HRRR has backed off of the ice a bit, so that is good news. The total ice amounts may technically show close to a quarter inch in our far south, but in reality, we would possibly get ice in the morning, melt with some rain in the afternoon, and finish with a bit more light icing in the evening before ending. We are looking closer to a tenth inch of ice for max accumulation on surfaces. Models did seem to be nudging this band heavier qpf band farther northwest on 12Z runs than what we had introduced to our forecast this morning for Tuesday QPF. But 18Z runs indicate a possible nudge to the southeast again. So for now, I am thinking areas from maybe near York County, stretching down across Nuckolls, and into Osborne County in Kansas would be the extent of the highest qpf. There is clearly going to be a warm layer aloft present that appears to be warm enough to support some sleet or freezing rain. This is a very tricky forecast as this hinges heavily on a few things, including QPF, warm air aloft, temperature at the surface, and how far northwest the heavier QPF stretches. There will be a few hours during the daytime on Tuesday when our precipitation rate may be quite heavy as a nice slug of moisture works northeast into our CWA. On the northwest edge of this precip band, we may have a strip of particularly heavy snow toward 4-6 inches or snow if it comes down hard enough. Tough call on where exactly this band would set up if it does. Snow ratios may not be high enough to support this too. Down toward Mitchell County, the surface looks like we can clearly warm up enough above freezing that parts of our far southern CWA could warm up to all rain and would tamp down on ice accumulation concerns way down there, as mentioned earlier. Farther north toward the tri-cities and points northward. Forecast soundings seem a bit cool with the warm layer to allow much more to occur than sleet other than snow. I couldn`t rule out a little freezing rain, but this looks like less of an issue for points farther north. However as we start winding down, forecast soundings indicate the possibility of some freezing drizzle to put a light glaze on fallen snow. If this occurs, this may be a time period of particularly hazardous driving. It does not take much precip to create problems. Just another thing to consider with this event. Overall, this event has an earlier ending time than what had been forecast before, and I can see this being cancelled sometime during the evening if we don`t wind up getting light freezing drizzle occurring through Tuesday evening. Looking cool a few days post winter system, but nothing extreme, with a warm-up early next week. Upper low comes out of Mexico by late Thursday/Friday for parts of the central Plains, but it appears we remain too far west/north to be affected very much by this, but we do have some slight POPs in are southeast Thursday night/Friday just in case some light precip makes its way into our area. && .AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Wednesday) Issued at 532 PM CST Mon Dec 28 2020 A winter storm is on our doorstep currently and will be working its way through the area overnight tonight and through tomorrow. Cigs are expected to drop to MVFR along the leading edge and then down to IFR with the incoming snow bands. Snowfall is likely to reduce visibility at times to less than 1 mi. As temperatures warm tomorrow afternoon snow is expected to transition to a freezing rain mix until the system moves off to the east later in the evening hours. Winds could also become gusty during the morning hours tomorrow. && .GID WATCHES/WARNINGS/ADVISORIES... NE...Winter Weather Advisory from midnight tonight to midnight CST Tuesday night for NEZ040-041-047>049-062>064-075>077- 085>087. Winter Weather Advisory until midnight CST Tuesday night for NEZ039-046-060-061-072>074-082>084. KS...Winter Weather Advisory from midnight tonight to midnight CST Tuesday night for KSZ006-007-018-019. Winter Weather Advisory until midnight CST Tuesday night for KSZ005-017. && $$ DISCUSSION...Heinlein AVIATION...Shawkey
Area Forecast Discussion
National Weather Service Lincoln IL
813 PM CST Mon Dec 28 2020 .SYNOPSIS... Issued at 330 PM CST Mon Dec 28 2020 A chilly night is in store across central Illinois as low temperatures bottom out in the upper teens and lower 20s. An approaching storm system will spread wintry precipitation across locations along and west of the I-55 corridor by Tuesday afternoon. A minor accumulation of ice and snow is likely...especially northwest of the Illinois River. && .UPDATE... Issued at 805 PM CST Mon Dec 28 2020 Main changes this evening are to slow clearing of clouds and to drop temperatures several degrees NW of the Illinois River Valley. Temperatures quickly fell into the teens upon clearing in northwest portions of the CWA and lowered overnight lows into the lower teens for this area. Elsewhere, cloud cover is holding on longer than expected but does continue to slowly erode from the north and west. && .SHORT TERM...(This evening through Tuesday) ISSUED AT 330 PM CST Mon Dec 28 2020 Low clouds continue to plague central Illinois this afternoon with 21z/3pm satellite imagery showing overcast conditions across the entire KILX CWA. The clouds are beginning to dissipate/thin across the Illinois River Valley and this process will accelerate over the next couple of hours. Based on current satellite trends and HRRR forecast, will hold on to mostly cloudy skies along/east of I-57 through early evening...followed by a period of mostly clear skies across the board through early Tuesday morning. All models are showing an increase in mid/high clouds from the southwest overnight, resulting in a return to overcast conditions across the Illinois River Valley by dawn. Low temperatures will drop into the upper teens and lower 20s. A deepening upper trough over the southwest CONUS will be the main weather-maker in the short term as surface low pressure develops in the lee of the Rockies on Tuesday then tracks into the Great Lakes by Wednesday morning. An initial surge of WAA precip will develop well in advance of the low by Tuesday afternoon. The atmosphere will initially be quite dry, so top-down moistening may be slower than some CAMs suggest. Even still, enough solutions suggest precip will develop across the W/NW CWA to warrant PoPs along/northwest of a Champaign to Taylorville line during the afternoon. Will hit PoPs hardest along/northwest of the Illinois River where likely to categorical PoPs are in order. Based on NAM/GFS forecast soundings, the precip will begin as light snow. As the low approaches from the west, boundary layer flow will gradually veer to a more southerly direction...allowing temperatures to climb Tuesday night. Thermal profiles suggest mixed phase precip for a few hours during the evening, with the greatest amounts focused in the Illinois River Valley. With projected ice accumulations of up to one tenth of an inch and snowfall of 1 to 2 inches, have issued a Winter Weather Advisory for locations along and northwest of a Canton to Minonk line. Further southeast across the remainder of the area, precip will be much lighter and will temporarily come to an end during the evening. Surface temps will continue to climb overnight, allowing the precip to change to rain everywhere shortly after midnight. .LONG TERM...(Tuesday night through Monday) ISSUED AT 330 PM CST Mon Dec 28 2020 A rainy Wednesday is on tap across central Illinois. As low pressure tracks into the Great Lakes and pulls a cold front through the area, the rain will diminish from northwest to southeast during the evening. In fact, most models agree that a period of dry weather will develop across nearly the entire CWA Wednesday night into Thursday morning. After that, attention will turn to a developing surface low along the trailing end of the cold front across the lower Mississippi River Valley. 12z Dec 28 models are now in much better agreement with this process, with model consensus showing the low pivoting northward into central Illinois by Thursday night. Given a cold/dry boundary layer and E/NE flow, think freezing rain or a mix of freezing rain and snow will develop as the precip spreads back northward. The exact track of the low and the resulting wind direction/surface temps will determine how much icing will occur...however, the potential exists for icy/hazardous travel Thursday night into Friday morning before temps warm sufficiently to change the precip to rain. Once this system departs, a return to cool/dry weather is expected next weekend. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 511 PM CST Mon Dec 28 2020 MVFR conditions persist this evening but continue to slowly erode from the northwest and should clear out at the terminals overnight. NW winds this evening will become light and veer to a SE direction Monday morning, then increase through the day as low pressure approaches. Lower ceilings and wintry precip will overspread portions of the Illinois River Valley with snow initially changing over sleet and freezing rain. Best chance for precip is at PIA then BMI, but there are lesser chances at SPI/DEC/CMI so have no introduced anything more than a VCSH to those locations at this time. && .ILX WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from noon Tuesday to 4 AM CST Wednesday for ILZ027>031-036-037. && $$ UPDATE...Deubelbeiss SYNOPSIS...Barnes SHORT TERM...Barnes LONG TERM...Barnes AVIATION...Deubelbeiss
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
635 PM CST Mon Dec 28 2020 .SHORT TERM...(This evening through Tuesday night) Issued at 245 PM CST Mon Dec 28 2020 Primary concern is obviously the system moving through Tuesday and Tuesday night, which still looks to bring widespread light to moderate snow to much of the area. Until then, things will be fairly benign. An upper trough is currently moving through the region, and has a weak surface reflection evident via the subtle wind shift currently moving south through the area (along with some flurries and snow showers). A couple area of low clouds will continue to push south/east through this evening, with mostly clear skies for a good part of the night before we see mid/high clouds work in ahead of Tuesday`s system. Model guidance is actually in very good agreement with the system now, with the preponderance of solutions bringing a period of warm advection induced precipitation through the area tomorrow afternoon and evening. The heaviest activity looks like it will cover a three to four hour window from the late afternoon into mid-evening (a bit earlier west of I-35 and a bit later to the east). Consensus QPF from the guidance (including the HRRR and other CAMs which are now starting to include the system in their time window) is from around 0.2 to 0.35 inches. Forecast soundings are not particularly impressive with either the depth of the dendritic growth lower or the strength of Omega, so it looks to be more of a steady mostly light snow with visibilities of around three quarters of a mile (with mainly smaller flakes). Given these conditions, don`t expect snow to liquid ratios to differ too much from climatology, and could actually be a bit less than climatology. Considering these factors, forecast amounts are slightly less than previous values, but still sufficient (generally AOA 3") to continue an advisory across the area (and even expand it northward to cover the remainder of the forecast area). .LONG TERM...(Wednesday through Monday) Issued at 245 PM CST Mon Dec 28 2020 The tail end of the Tuesday system may bring some lingering snow into early Wednesday morning, but generally Wednesday looks dry. Cloud cover will be a bit slower to move out, lingering into the overnight hours before clearing some for Thursday. Temperatures will be cool to start the long term period with highs in the upper teens and low 20s and lows in the single digits. Looking ahead, the dry conditions stick around and temperatures slowly warm as we approach the end of the week with ridging building in. The only area that may see a slight chance of snow showers Friday is extreme southeastern Minnesota as a low skirts our area to the southeast. In any case, there do not appear to be any strong signals for measurable snow through the forecast period. However, there is agreement that temperatures will continue to warm through the weekend, with ridging and southwesterly flow intensifying for the late part of the forecast period. Highs look to approach freezing or just above by Sunday and Monday, which is nearly 10 degrees above normal for early January. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 627 PM CST Mon Dec 28 2020 Some low stratus lingers in western WI, otherwise skies will be generally clear overnight through daybreak. As a potent storm system lifts out of the Deep South tomorrow, a swath of snow will move in from the southwest midday and persist through Tuesday evening, diminishing going through the early morning hours Wednesday. Confidence is high on having snow amounts in the 3-5" range for much of central-southern MN into western WI, including at all TAF sites. MVFR conditions are likely at the onset of snowfall, with conditions dropping to IFR for about a 4-hour period shortly after the onset of snowfall. IFR conditions will most likely be due to visibility although ceilings under 1000ft may also develop. Onset of snow will be in the 18z-21z range then continuing through the end of this TAF period. Breezy southeast winds will increase to 10-15kt with gusts to around 20kt in the afternoon. While well short of blizzard conditions, the impacts to visibility will be evident. KMSP...Snowfall onset still looks to be about 21z but could vary an hour or so either way. Timing will be problematic as this is right at the start of the evening push, and peak intensity may well come during the push between 21z and 01z. Snowfall will continue through the evening hours with visibility in IFR range and ceilings below 1700ft. Not expecting frequent rates of 1 in/hr but isolated bursts of snowfall producing as such cannot be ruled out. Snowfall total for the duration of this event is expected to be 3-4". /OUTLOOK FOR KMSP/ Wed...MVFR possible early. Wind NW 10-20 kt. Thu...VFR. Wind SE 10-20 kt. Fri...VFR. Wind variable around 5 kt. && .MPX WATCHES/WARNINGS/ADVISORIES... MN...Winter Weather Advisory from 9 AM Tuesday to 6 AM CST Wednesday for Anoka-Carver-Dakota-Freeborn-Goodhue-Hennepin-Le Sueur-Ramsey- Rice-Scott-Sherburne-Steele-Waseca-Washington-Wright. Winter Weather Advisory from 9 AM Tuesday to 3 AM CST Wednesday for Benton-Blue Earth-Brown-Chippewa-Douglas-Faribault-Kandiyohi- Lac Qui Parle-Martin-McLeod-Meeker-Morrison-Nicollet-Pope- Redwood-Renville-Sibley-Stearns-Stevens-Swift-Todd-Watonwan- Yellow Medicine. Winter Weather Advisory from noon Tuesday to 6 AM CST Wednesday for Chisago-Isanti-Kanabec-Mille Lacs. WI...Winter Weather Advisory from noon Tuesday to 6 AM CST Wednesday for Barron-Chippewa-Dunn-Eau Claire-Pepin-Pierce-Polk-Rusk-St. Croix. && $$ SHORT TERM... LONG TERM...Dye AVIATION...JPC
Area Forecast Discussion
National Weather Service Omaha/Valley NE
833 PM CST Mon Dec 28 2020 .UPDATE... Issued at 833 PM CST Mon Dec 28 2020 Forecast overall remains in good shape, but made some minor tweaks to the grids on timing of the arrival of the snow through 6am. Looking at 00z models just starting to come in, feel OK with the area of the winter storm warning and the potential for 6 inches of snow for southwest IA and a few counties in southeast NE, but also the potential for a mix of freezing rain/sleet. However, the 00Z Nam is now focusing a heavy band of snow perhaps one tier of counties northward, which would put this moreso toward I80. Conceptually, this is likely an area that could see heavy snowfall, just north of where the snow/freezing rain line could be setting up. This is also supported by the 00z HRRR model, but not necessarily other Hires models such as the RAP, the 3km Nam, or the Hires ARW/NMM. Very challenging forecast as an expansion of the winter storm warning may be needed into the Omaha metro area if the 00Z Nam/HRRR are correct. Will continue to look over data. && .DISCUSSION... Issued at 347 PM CST Mon Dec 28 2020 .Impact Summary: A winter storm will affect the region beginning tonight and continuing into Tuesday night. Accumulating snow and ice will result in minor to moderate travel impacts. .Tonight through Tuesday night: The forecast remains largely on track with the overall idea that the split-stream system deepens through the evening over the Northern Great Plains, making it to the area tonight. The trends in model output have decreased overall model QPF output across much of eastern Nebraska and southwestern Iowa, but regardless a slug moisture is expected to be accompanied by strong warm air advection and a strong low-level jet. Certain features of note this forecast period is a rather deep nearly-isothermal layer that for much of the area sits right around or just above freezing. 850 mb temperatures reach above freezing generally southeast of I-80 and indicates a region where increased melting to occur aloft and increased freezing rain at the surface where surface temperatures are at or below 32 degrees. Just north of the transition zone between the better snow and increasing ice is an area where heavier snowfall could occur as better dendrite maintenance and aggregation can happen. With the current model suite, the are of heavier snowfall looks like it could be from Nebraska City/Plattsmouth extending northeastward into central Iowa. This zone is still in flux, but is expected to occur just north of the snow/freezing rain transition area. Snow is expected to begin overspreading the around midnight tonight, beginning as snow and reach the Omaha area around 6 am. Surface temperatures are expected to begin warming through the morning, with freezing rain beginning to reach into southern Nebraska after 9 am. Beginning just after noon, a period of peak snowfall and general precipitation intensity is expected to occur and will be where a good chunk of snowfall and ice accumulation occur. Mid-to-late afternoon will begin the intrusion of dry mid-level air into northeastern Nebraska and will cause the back end of the snow to begin mixing in freezing drizzle, and could deposit a glaze over the fresh snow. Snow/freezing rain and drizzle are expected to exit the area during the overnight to early morning hours. The general snowfall forecast of total amounts of 2" to 4" over southeast NE and 3" to 6" elsewhere across the area continues to look on track, with a glaze of ice expected over much of the area on the backside of the snowfall. In far southeast Nebraska, high moisture output is expected to make increase ice accumulation with amounts reaching just over 0.25" just southeast of Falls City. As mentioned before, an area of higher snowfall is possible just north of the snow to ice transition and could push snow amounts slightly higher than 6". .Wednesday and Thursday: Winds out of the northwest are expected to increase and usher in cold temperatures with highs in the 20`s expected. .Friday through Monday: Mid-level troughing is expected to pass through the area and an northeastward-ejecting surface cyclone looks to clip southeastern Nebraska and southwest Iowa, bring chances for light snow back to those areas. Following the departure of that system early Saturday, dry weather and a warming trend looks to take us into next week. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 523 PM CST Mon Dec 28 2020 VFR conditions with light southeast winds at TAF issuance. Conditions deteriorate as snow moves in by 07-09z. Clouds becoming MVFR and eventually IFR by 11-15z. Snow could change to freezing rain/drizzle at KOFK by 20z, and at KLNK by 23z toward the end of the TAF period. Snow changes to freezing drizzle at KOMA just beyond the end of the TAF period. Totals snow accumulations at KOFK/KLNK 3-5" and 3-6" at KOMA. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...Winter Weather Advisory from 6 AM Tuesday to 6 AM CST Wednesday for NEZ015-034-045-052-053-090>093. Winter Storm Warning from 6 AM Tuesday to 6 AM CST Wednesday for NEZ067-068. Winter Weather Advisory from midnight tonight to 6 AM CST Wednesday for NEZ011-012-016>018-030>033-042>044-050-051- 065-066-078-088-089. IA...Winter Weather Advisory from 6 AM Tuesday to 6 AM CST Wednesday for IAZ043-055-056-069. Winter Storm Warning from 6 AM Tuesday to 6 AM CST Wednesday for IAZ079-080-090-091. && $$ UPDATE...DeWald DISCUSSION...Petersen AVIATION...DeWald
Area Forecast Discussion
National Weather Service Pueblo CO
545 PM MST Mon Dec 28 2020 .UPDATE... Issued at 539 PM MST Mon Dec 28 2020 Updated the precipitation chances across the region for this evening based on the latest radar and high-res model trends. Warm air advection lifting north across southern Colorado has led to banded snowfall over the Eastern Mountains, out into the I-25 corridor. This will continue through the next several hours. Mozley && .SHORT TERM...(This evening through Tuesday) Issued at 310 PM MST Mon Dec 28 2020 Currently... Snow continues to fall across the area, currently centered over the Sangre de Cristo and Wet Mountains and spilling east into the plains. Snowfall is also currently west of our area making its way towards the eastern San Juans. Today and Tomorrow... As the upper-level low moves onshore today, southwesterly flow aloft will be continuing to advect moisture into the area, giving us some good snowfall. Consistent with the last few days, the peaks of the San Juans and Sangres will be seeing most of the action, with 15 to almost 20 inches expected near both areas. The surrounding terrain will also be seeing a good 4 to 8 inches, as will higher portions of Lake County. Current additional concerns for the forecast begin with El Paso County this evening into tomorrow morning. Ahead of this incoming system the eastern half of our area is experiencing some good southerly flow and potent warm air advection at the mid-levels, supporting a thickening of the cloud deck and additional snowfall. An extra 3-5 inches is possible near Colorado Springs, and have issued an advisory as the snow could come down during evening rush hour. Overnight and into tomorrow morning, the mid and high levels dry out a decent bit, mostly stopping chances of additional snowfall. However, warm air and moisture will still inhabit the lower levels, and there could be enough lift present to generate a little freezing precipitation in the early morning hours. While confidence in this isn`t 100 percent, there is a possibility this could impact the morning commutes in El Paso County. The second forecast concern is for the far southeast plains, namely eastern Las Animas and most of Baca Counties. Moisture advection from the south along with cool surface temperatures suggest a strong possibility of freezing drizzle impacting that region overnight and into tomorrow morning. Most model guidance showed negligible amounts of ice accumulation, merely a short glazing, but a few runs, including the NAM, NAM Nest and some runs of the HRRR were indicating measurable ice accumulation by around 8 AM tomorrow, so went with an advisory on that as well. Precipitation over the plains is expected to wane by midday tomorrow as downslope flow increases, while snowfall is expected to persist west of I-25 through tomorrow afternoon as the trough axis dips far to the south. .LONG TERM...(Tuesday night through Monday) Issued at 411 PM MST Mon Dec 28 2020 The low pressure system that is currently propagating in over the region from the southwest US will be the main factor driving the current conditions throughout the region with mostly cloudy to overcast skies, reduce visibilities at times in light to moderate snow showers, and breezy conditions for the next 36 hours. There will be gusty winds expected across the plains and on the higher mountains peaks, as well as in and along the mountain passes and canyons. Bands of snow have set up ahead of the frontal boundary and will continue to provide a feed of moisture over the Sangre De Cristo/Wet Mountains and over the plains, with a higher concentration of snowfall primarily west of the I-25 corridor. Highest accumulations of snowfall will be over the Eastern San Juan Mountains, especially the western-facing slopes with over 2 feet possible. There is a possibility of freezing drizzle for Las Animas County and Baca County early Tuesday morning. The upper- level trough will move in over the area tomorrow evening with only a few more snow showers possible. This should begin to taper off by late tomorrow evening and into early Wednesday morning with only some lingering snow showers over the eastern mountains, with clearing conditions and warmer temperatures expected by later in the day. Lows will be the coldest for Tuesday night with low upper teens in the plains, single digits for the mountains, and coldest in the mountain valleys and San Luis Valley from -5 to 5. West- southwesterly winds will also diminish by Wednesday morning to become light and variable. There will be a temporary break along with some weak ridging on Thursday and then by later in the evening on Thursday the next trough will begin to approach and allow for a slight chance for more precipitation, mainly to the north and over higher elevations along the westward facing slopes. Winds will also be a factor with the onset of this trough propagating through as the pressure gradient tightens. After the system moves through later in the week, a ridge will set back in for the weekend and continue to build into early next week, allowing for a return of clearer skies and warmer conditions over the entire region. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 310 PM MST Mon Dec 28 2020 As an area of low pressure over the southwestern US continues to propagate towards the region, expect CIGs and VIS to be impacted for all stations, primarily later this evening and into early tomorrow morning. Expect IFR criteria to be prevalent with CIGs slightly lowering later in the day, as well as on and off -SHSN. There will be a break later tomorrow morning with VFR conditions returning as early as 16Z for ALS and 15Z for both COS and PUB. Expect IFR conditions to be possible again later in the day tomorrow as the U/L low moves in over the area. && .PUB WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until 5 PM MST Tuesday for COZ058>060- 066. Winter Weather Advisory until 11 AM MST Tuesday for COZ061>063- 074-076>082. Winter Weather Advisory from 11 PM this evening to 8 AM MST Tuesday for COZ094-099. Winter Storm Warning until 5 PM MST Tuesday for COZ067-068-072- 073-075. Winter Weather Advisory until 8 AM MST Tuesday for COZ084-085. && $$ UPDATE...MOZLEY SHORT TERM...GARBEROGLIO LONG TERM...STEWARD AVIATION...STEWARD
Area Forecast Discussion
National Weather Service Topeka KS
529 PM CST Mon Dec 28 2020 ...AVIATION UPDATE... .DISCUSSION... Issued at 418 PM CST Mon Dec 28 2020 Currently, the forecast area is under a low amplitude mid level ridge that is being suppressed with a broad trough over the Great Lakes region. A deep western trough works eastward which will provide for a very active Tuesday weather wise. The forecast appears on track with some uncertainty leading to how much of any given type of precipitation will occur tomorrow morning into the early afternoon. The trend with short term and longer term model solutions appear to hinge on the strength and overall movement north of the warm nose - as well as the depth resulting in the poleward push. Cooler overnight lows with a slight northeast breeze appears to start the morning Tuesday off a bit cooler overall. This leads to a lower overall wet bulb surface temp. The end result is that the expectation will be that light snow beginning before sunrise will begin to gradually transition to a wintry mix including freezing rain. With a slower warm nose, melting precip in the warm layer will likely provide for a longer duration of freezing rainfall. This along with slightly higher wind as the system intensifies will help keep a more efficient situation in place for ice accumulation to take place. Have increased overall ice amounts with some areas being closer to the two tenths of an inch range. This also results in overall lower snowfall amounts with around 3 inches remaining along the KS/NE border. Trends overnight will be very important but there is potential that even slightly higher amounts of ice could result with a more slowly building warm nose. The GFS continues to be more aggressive with warmer air overall. But, again, a colder low level wedge of air in place longer also supports the idea of more ice potential. Thinking the transition to rain will be by mid to late afternoon but may struggle to reach the border. Higher amounts of rain appear to be likely and could act to reduce ice into later morning hours with strong isentropic ascent and negative EPV working over the area providing for some upright instability to support banding precipition. The cold air pushing into the area overnight into Wednesday morning will supporting another mixed precipitation period but overall amounts should be low, so have not extended the advisory for this period. New Year`s Eve into the day on Friday is trending toward the active side as well weather wise - this time heavy snow could be in cards. As a deepening upper low lifts into the area with the long wave trough slow to move through, a TROWAL feature develops and extends west into the area. Still no amounts to officially mention as we will take the tomorrows system one at time first. Do expect that amounts for Friday morning could be somewhat impressive. && .AVIATION...(For the 00Z TAFS through 00Z Wednesday) Issued at 529 PM CST Mon Dec 28 2020 Confidence is good in wintry precip overspreading the area Tuesday morning. Main challenge is timing when warm air advection will raise sfc temps above freezing. Have used the RAP forecast soundings along with the gridded forecast to try and time these transitions. Otherwise increasing low level moisture advection will promote lowering CIGS with LIFR conditions likely by mid day Tuesday. && .TOP WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 6 AM to 3 PM CST Tuesday for KSZ021>024-026-034-039-040. Winter Weather Advisory from 6 AM Tuesday to midnight CST Tuesday night for KSZ008>012-020. Winter Weather Advisory from 6 AM to 1 PM CST Tuesday for KSZ035>038-054>056-058-059. && $$ DISCUSSION...Drake AVIATION...Wolters