Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 02/13/21

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
926 PM CST Fri Feb 12 2021 .UPDATE... 924 PM CST The main updates this evening were to attempt and refine PoP trends and overall QPF/snow amounts tonight and into Saturday morning. 00z RAOBs out of Davenport and Lincoln sampled quite a bit of lingering dry air, with the near-surface dry layer initially noted on the DVN sounding likely having saturated quite a bit since then. Mid-level dry air was much more prevalent on the ILX sounding, and with cloud bases still at or above 10,000 ft into north-central Illinois, this is likely still the case. Given the overall modest nature of ascent overspreading the area, have trimmed PoPs quite a bit through tonight for areas south of a roughly Pontiac to DeMotte line with it unlikely that light snow will be able to chew through this dry layer. Have done the same across far northern Illinois and to the state line for similar reasons. In between these two areas, broad/disorganized f-gen will continue to develop overnight as the exit region of an anticyclonically-arcing jet streak pushes in overhead, and this appears to be where the main focus will be for steady (mainly light) snow overnight and into Saturday morning. Given the rather lazy nature to the ascent, thinking that snow-to-liquid ratios may end up a smidge lower than you`d otherwise expect given the cold thermal profiles and deep dendritic growth zone...perhaps in the 15-20:1 range. The main axis of snowfall amounts in the 2-4" range has shifted a bit north, focused more around the I-80/88 corridors with this update, with amounts lowered to for our southernmost counties to an inch or less. PoP trends for Saturday morning are a bit unclear, as we`ll begin losing the better jet support, resulting in an overall weakening to the already modest mid-level f-gen. This may allow lingering light snow near/south of I-80 to dwindle, before additional ascent from an incoming shortwave pushes across our northwestern locales. Have trimmed PoPs south and east of I-57 as a result, and left the categorical/definites going elsewhere. Lake effect is the next challenge. Near-surface convergence is tightening up near the lake, with winds turning northwesterly at the Crib, and veering more easterly across southwestern Michigan. A single lake band is evident along the western Michigan shoreline, and is starting to push west. Guidance like the 3-km NAM and RGEM, which seemingly handled yesterday`s LES event fairly well, continue to crank up quite a bit of QPF across far northern Porter county, and have been joined by the Hires WRFs. Have nudged snow amounts up in this localized area with some amounts approaching 5-6" near the lake in the latest forecast. Not entirely convinced of the double-digit output from some of the guidance given the altogether marginal LES parameters, but we`ll keep an eye on things. Either way, we`ll be continuing the Winter Weather Advisory for Porter County, and could need to sneak it into Lake County as trends become better established. Carlaw && .SHORT TERM... 234 PM CST Through Saturday night... Currently, an elongated 130-150 kt jet streak extends from eastern Minnesota to southern Ontario. In the right entrance region of the jet streak is a similarly elongated zone of radar echoes stretching from central Nebraska though northern Illinois. Recent AMDAR soundings off aircraft departing Chicago terminals depict a short but very dry layer centered at about 5000 feet, which is eating any and all snowflakes on their trip to the ground. (So, most of those aforementioned radar echoes are actually virga). The dry layer is expected to remain in place through the remainder of the afternoon and evening hours, acting to delay the onset of snow compared to previous forecasts. Using the RAP 850 mb relative humidity as a proxy to track the elimination of the dry layer, it appears light snow should start trickling down to the ground after dark and in the 9-11 pm window. Thereafter, steady, light snow will continue through Saturday morning. A deep snowflake growth layer of nearly 15,000 feet will afford fluffy snow ratios of 20:1 to 25:1, with gradual lift supporting a snow rate of 0.1 to 0.3"/hr. Upper-level lift will then wane after daybreak Saturday as the jet streak scoots eastward, though light snow showers will likely persist through much of afternoon. Generally 1 to 3" of fluffy snow looks on track with the highest amounts in the vicinity of I-80. Locally higher totals are possible along the Lake Michigan shore of Porter county, Indiana where an overnight land-breeze-forced lake effect snow band should boost snow rates after midnight. The inherited Winter Weather Advisory for Porter County thus remains appropriate. Regardless of how much snow falls across the area tonight/Saturday, untreated roadways may become slippery. Snow will end quickly Saturday evening and clouds will attempt to clear from west to east. With a fresh snowpack in place, temperatures overnight into Sunday should drop below zero areawide. Winds of 10 to 15 mph will make it feel more like 20 to 25 below zero, especially west of I-39. Not much reprieve is expected Sunday with highs in the single digits and wind chills of 5 to 15 below zero. Such cold temperatures can lead to frostbite in as few as 20 minutes, so bundling up from head to toe in multiple layers is a must if planning to head outdoors. Borchardt && .LONG TERM... 222 PM CST Sunday through Friday... Lake effect snow will likely continue Saturday night into early Sunday across Porter and possibly Lake counties of IL as 925 mb flow remains NE for a time on Sunday. Sunday into early Tuesday... The anomalously lower heights in the mid-levels with the aforementioned lobe of polar air, with 500 mb values of 505 dm, will shift east/southeastward during Sunday into Monday. This influence is more so Monday afternoon into Monday night, with a more stout disturbance progged to eject northeastward from Texas/southern Plains toward the Ohio Valley. But there are still signs even late Sunday through early Monday the baroclinic zone around 700 mb tightens over the southern CWA with some saturation and possible light snow. There is some variance in guidance on specifics as far as how far north the light snow footprint may extend, still with our I-55 and southeastward corridor favored. While forecast adjustments from the blend were to still boost PoPs along and south of I-80 for mainly Monday afternoon and night, the signal for how widespread the influence of even this stronger second system is not quite as robust. Cyclogenesis is forecast over the southeastern U.S. tracking into the Appalachians region and supports the best chances for some snow to inch northward over our area. Again our highest chances remain along and southeast of I-55, but even light snow will be fluffy and could create impacts across the entire area. The potential is there for a wind chill headline going through Sunday and into Monday morning, but this may be confined to areas across north central IL and west of Chicago. Still will be solidly below zero and in some places well below to start the week on Monday morning. Lake effect snow Monday into Tuesday...Lake effect snow during this time may be ongoing through these several events, and there are hints at the development of decent convergence zone/associated surface low, in northwest Indiana Monday, and then shifting into northeast IL later Monday and Monday night. There could be some lingering snow/flurries Tuesday morning, but this period is of lower confidence than Monday night. Tuesday and beyond.... The strong arctic high will ever so slowly, but optimistically (for those of you just looking for something to hang your hat on) lose its grip on the region, and we will inch our high temperatures back into the 20s mid week. Before we finally say good riddance to the core of the arctic air, another system is currently advertised to follow a similar Texas to Tennessee valley to the Appalachians track late in the week. This could still graze our area with some light snow before the weakening ridge axis finally makes its way overhead toward week`s end and we shift the low level low back around to the southwest for the first time in quite a while. KMD && .AVIATION... For the 00Z TAFs... 539 PM...Primary forecast concern is light snow developing this evening and continuing through Saturday afternoon, along with associated cigs/vis. Light snow is expected to develop across the area by mid/late this evening and continue through at least late Saturday morning and possibly through mid afternoon. A narrow band of snow is expected to develop and then expand in coverage and there remains uncertainty regarding exactly where and when this will occur but much of the latest guidance shows light snow developing along a vys/lot/gyy line by mid evening and then expanding north through early Saturday morning. Current forecast has this trend covered well and made no significant changes. While prevailing 1-2sm vis looks on track, through midday Saturday, there may be a corridor of moderate snow that may reduce vis under 1sm but confidence for location remains low and no mention of lower vis with this forecast. Cigs are expected to lower into mvfr soon after snow begins with several hours of low mvfr expected through early Saturday afternoon. Ifr cigs will be possible if and where any moderate snow develops. As the snow tapers off Saturday afternoon, cigs will lift through mvfr with scattering/clearing expected Saturday evening. North/northwest winds around 10kt will continue through the period with speeds increasing to 12-15kts Saturday afternoon along with some gusts into the 15-20kt range possible Saturday evening. cms && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...Winter Weather Advisory...INZ002 until 6 PM Saturday. LM...None. && $$ Visit us at Follow us on Facebook, Twitter, and YouTube at:
Area Forecast Discussion
National Weather Service Lubbock TX
541 PM CST Fri Feb 12 2021 .AVIATION... MVFR ceilings will continue at KLBB and KPVW this evening before dipping back down into the IFR range late tonight. KCDS will maintain VFR ceilings this evening but will also drop back down into the MVFR range late tonight. With these low ceilings in place aircraft icing on approach/departure will remain probable through this TAF period at all terminals. There is the potential for flurries or brief snow showers to occur once again late tonight and early tomorrow morning however confidence in this activity is too low to include at this time. /WCI && .PREV DISCUSSION... /issued 308 PM CST Fri Feb 12 2021/ SHORT TERM... Our weather will continue to feel like a Midwest winter with what feels like never ending low cloud cover. Before the main winter storm on Sunday, an initial short wave currently over the Great Basin will dive fairly far to the south into northern Mexico. This short wave will eventually emerge over south Texas having little impact on the area locally. Generally, some occasional flurries can still be expected for the rest of tonight and during the day on Saturday. Closer to the South Plains, weak isentropic lift will persist through Saturday morning providing the occasional flurry chance. Temperatures at the surface and aloft are expected to be cold enough for all snow instead of freezing drizzle. Min temps in the fairly deep 3kft sub-freezing layer will be around -11 to -12C. Subsidence will quickly move in during the day on Saturday as the aforementioned short wave trough departs to the east and in advance of the larger trough to the west. LONG TERM... The main two players in the upcoming winter event are a closed upper low currently over the southwestern CONUS and a trough over the Gulf of Alaska. The low over the SW CONUS will continue to dive to the southeast towards Mexico and become an open trough. As this trough moves to our southwest, it will help to induce southwesterly flow aloft. These southwesterly winds will flow over the warm Baja California Gulf, advecting some moisture to the northeast towards the area. With the main vort max and surface boundary of the trough moving well to our south, moisture advected into the system ahead of the trough will be allowed to remain in place for the next system. The trough currently over the Gulf of Alaska will enter the northwestern CONUS early on Saturday and will begin its dive towards the area. Late Saturday, the upper trough will approach the area, bringing upper-level divergence to the area and our initial snow chances. As the main wave approaches west Texas, lift will be increased due to PVA associated with the mid-level trough and frontogenetical forcing from the associated front. With temperatures within the column being below freezing, this event will be all snow. Progged soundings indicate that decent layers of the column are in the sweet spot in regards to temperatures (DGZ) and saturation for much of the day on Sunday. This will allow for significant snow growth and periods of heavy snow. Unfortunately, with the temperatures within the column being as cold as they are, the snow will have limited liquid content. This is great if you want to have several inches of snow but not so good if you want to make snowmen or snowballs. Temperatures will continue to fall through the day on Sunday, bringing sub-zero lows and wind chills -10 to -25 F to the area for Monday morning especially from Lubbock northward. As the system moves to the east, the snow will start to taper off from west to east sometime Monday morning into early afternoon. Because of the low liquid content of the snow and the winds, blowing and drifting of snow will be a concern even after the snow starts to diminish. Temperatures will slowly creep back towards freezing by mid-week. The next system is expected to affect the area late Tuesday into Wednesday, bringing the next chance of snow to the area. Temperatures will rise above freezing on Thursday, with highs this weekend possibly reaching 50s and low 60s across the area. Kendrick && .LUB WATCHES/WARNINGS/ADVISORIES... Winter Storm Watch from late Saturday night through Monday morning for TXZ021>044. && $$ 58/01/99
Area Forecast Discussion
National Weather Service Blacksburg VA
1035 PM EST Fri Feb 12 2021 .SYNOPSIS... An Arctic boundary will extend from the DelMarVa region west into the Tennessee Valley and then southwest into deep South Texas. This cold air will continue to filter southwest into the Mid-Atlantic region from the northeastern U.S. Meanwhile, a moist southwest flow aloft and a series of disturbances will bring periods of precipitation across the region and into the cold, below freezing air, mainly in the form of freezing rain and sleet over the next few days. A significant winter storm in the form of an ice storm is likely across the Virginia Piedmont Saturday, with additional potential for winter storms well into next week as cold, Arctic air remains firmly entrenched across the region. && .NEAR TERM /THROUGH SATURDAY/... As of 1030 PM EST Friday... Have done some editing to better delineate locations where freezing fog may be an issue, and have rolled this threat into the existing Winter Weather Advisory. All else is on track with no major changes needed at this time. Previous discussion... Significant Freezing Rain Event Expected Tonight and Saturday Across the VA/NC Piedmont and Southside Areas. The upper short wave that drove the sleet and freezing rain last night and early this morning has moved to the southeast of the area, where it will stall along the baroclinic zone/frontal boundary. This afternoon, moisture overrunning the shallow wedge of cold semi- Arctic air has kept low clouds, fog, and drizzle in place. With temperatures remaining at or below freezing for all except the far southwestern and southern fringes of the CWA, freezing fog and freezing drizzle has continued across the region and this will remain in place through the evening. With regard to tonight, significant icing is expected as the baroclinic zone lifts a bit northwest in response to upper ridging off the southeast/Mid-Atlantic coast. A significant warm nose aloft in the 3000-10000 ft. layer will result in precipitation falling primarily as rain, thus freezing rain as it falls into the cold boundary layer. The wedge is going nowhere within at least the next 36 hours, perhaps even into Sunday morning. Ice accumulations are expected to be some of the most significant we have seen in a long time and in areas that are less accustomed to winter weather, namely the Piedmont. Ice accumulations of 1/4 to 1/2 inch appear likely from Reidsville and Caswell northward toward Danville, South Boston, and Lynchburg. Some sleet is possible further north, but primarily this is a freezing rain event. Soundings do not support snow at all at this point. A Winter Storm Warning has been issued for areas along and east of the Blue Ridge with a Winter Weather Advisory for areas further west, except the extreme western fringe of the CWA which remains just outside of the wedge. Significant and damaging accumulations of ice are expected in the Winter Storm Warning area, with accumulations of ice generally around 1/10 inch. Again, sleet and snow should be limited with this event. /Confidence Level in Forecast Parameters/ Temperatures - Moderate to High, Precipitation Probabilities - High, Winds - Moderate to High, Winter Weather Threat - High east, Moderate west. && .SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/... As of 300 PM EST Friday... Numerous Waves Of Wintry Precipitation Persist Into Tuesday With Next High Impact System Expected Monday Night Into Tuesday. The short term forecast starts with us wrapping up the freezing rain/sleet system that first starts impacting the forecast area Saturday. Sounding profiles continue to support freezing rain and sleet through the morning, mainly for areas north of 460 and east of 220. Sleet amounts will be greater for areas in the west like WV, over to the southern Shenadoah, while freezing rain will remain favored down around southside, north to around Lynchburg. Temperatures will gradually warm through Sunday, eventually bringing most to a cold rain: however, moisture continues to linger into Sunday night and early Monday AM at this point. This will lead to some light icing opportunities Sunday night, as well as light sleet showers. As high pressure continues to strengthen out west, a deep trough will remain dug out across the U.S., spanning overtop of the region...this means more shortwaves and thus more low pressure systems. Our next storm is set to arrive Monday into Monday night. Once again, we are looking at a mostly freezing rain event, with varying amounts between different versions of guidance. Overall, the GFS and its ensembles members from the GEFS seem too fast and mostly too warm with the beginning of work week systems. Instead, ECMWF and its ensemble versions, as well as with plumes from the CMC seem to have a better handle on the system. Overall, they are hinting at another system that could bring some areas ~0.5" of ice. As we head into Tuesday, high pressure will be moving westward, reinforcing the cold air wedge and thus increasing our icing potential through the day before moisture runs out and the front slips east. When it came to building this part of the forecast, I went for the cold side of guidance to try and help ensure a good reflection of the wedge that will remain present throughout, but with varying degrees. If you`re looking for warmer weather...this isn`t your forecast. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 315 PM EST Tuesday... Brief Break Expected Wednesday Before Another Impactful Weather System Arrives Thursday Into Friday. Guidance remains variable in exact timing and possible amounts/precipitation types with a system that will arrive Thursday into Friday. Prior to that storm, high pressure should arrive to the region, allowing the opportunity to reinforce the cold air wedge that will plague the forecast in earlier periods. With this reinforcement, a larger spread in precipitation types looks possible: it is still far too early for specifics though as different guidance versions and even runs are highly variable with the storm system`s track and speed. It does look like a trend change is possible after this last storm late in the week, but we will have to wait and see if this remains true. I continued to remain on the cold side of guidance with the obvious wedge that will be holding our temperatures down. That said, if the low`s track were to trend further west and north, it could open us more into the warm sector of the system and heat us up, but for now I`m not going for that. && .AVIATION /04Z SATURDAY THROUGH WEDNESDAY/... As of 640 PM EST Friday... LIFR ceilings and mainly LIFR/IFR visibilities were across the region. Little change is expected in this scenario over the next 24 hours. Precipitation in the form of a sleet, freezing rain, or freezing drizzle is expected overnight, with a trend to freezing rain being the dominate weather feature by sunrise Saturday. Areas of fog and freezing fog will also be across the region. Much of the area will continue to see freezing rain or freezing drizzle during the day Saturday. Southwestern and southern sections are expected to see the temperature climb slightly over the freezing mark by the afternoon to allow for some plain cold rain or drizzle. Aircraft parked outdoors overnight into Saturday will have some amount of icing on them, as much as a 1/4 to 1/2 inch between the area of KLYH-KDAN. Confidence in the above aviation scenario is high. Extended Aviation Discussion... Weather pattern is forecast to remain unsettled well into next week with increasing threat for wintry precipitation as Arctic air surges further southeast into the eastern United States. Generally MVFR or worse conditions expected through the entire period. && .EQUIPMENT... The KFCX radar will be down through about Thursday, Feb 18th for the replacement of a generator as well as other electrical components powering the facility. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...Winter Weather Advisory until noon EST Sunday for VAZ010>016- 018>020-022>024. Winter Storm Warning until noon EST Sunday for VAZ017-032>035- 043>047-058-059. NC...Winter Weather Advisory until noon EST Sunday for NCZ001>004- 018>020. Winter Storm Warning until noon EST Sunday for NCZ005-006. WV...Winter Weather Advisory until noon EST Sunday for WVZ042>044- 507-508. && $$ SYNOPSIS...RAB NEAR TERM...DS/RAB SHORT TERM...RR LONG TERM...RR AVIATION...DS/NF/WP EQUIPMENT...PM