Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/22/22

Area Forecast Discussion
National Weather Service La Crosse WI
959 PM CST Wed Dec 21 2022 .UPDATE... Issued at 955 PM CST Wed Dec 21 2022 With the evening update, kept winter headlines in place. Snow is ongoing-moderate at times with most visibilities in the 1 to 2 inch range. Early reports through mid to late evening have been in the 1 to 2 inch range. At 9pm surface low pressure was centered over northeast New Mexico with a weak surface low over northeast Iowa and an inverted trough into northern WI and cold front through southwest IA/northwest MO and much of Kansas. As the trough deepens over the Plains, we will continue to see waves of precipitation tonight through Thursday with the higher amounts in the 5 to 8 inch range still on track for parts of western, central, southwest WI and northeast Iowa. Northwest winds are on track to increase Thursday, especially later Thursday afternoon and Thursday night. && .DISCUSSION...(Tonight through Wednesday) Issued at 215 PM CST Wed Dec 21 2022 Key Messages: - Winter Storm impacts into holiday weekend: * snow tonight into Thu morning * strongest winds Thu night-Fri night with widespread blowing/drifting * BLIZZARD conditions expected SE MN/NE IA Thu night through Fri night * Bitter to dangerously cold wind chills into Christmas morning Strong winter storm still on track to impact the area from tonight into the weekend. Somewhat open trough as it swings across the local area Thu, winding up/strengthening as it shifts northeast across the new england states/southeast Canada. Recent model trends suggest a bit quicker, farther northeast with the cyclone. * SNOW: snow spreads west to east across the forecast area this afternoon/early evening, persisting through the night then exiting east for most during the morning/by noon. RAP soundings show a deep DGZ from time to time tonight-Sat morning, upwards of 300-400 mbs. 20:1 ratios looks like a safe bet, potentially higher. Amounts have vacillated a bit over the past few days based on track of the storm/speed, related QPF. Latest outlay would drop the higher amounts from NE IA into central WI with 6 to 8" possible. One interesting possibility is for some light snow/flurries to develop off of lake Pepin/mississippi river Thu afternoon. The NAMnest suggests this and given the fetch of winds and still some open water, it could happen. Have opted to not include localized snow chances as of now, and any amounts would be minor. * WIND: winds start to crank up Thursday afternoon as the sfc low lifts northeast across WI, potentially lingering well into Saturday before a decreasing trend Sat night as pressure gradient starts to relax with exiting of the storm/approach of sfc high. Blowing/drifting impacts could be enough to continue warning and/or and advisory for some locations through Sat afternoon. Gusts still look to push into the 40s, flirting with 50 mph (still possible). With the additional several inches of fluffy snow, widespread blowing and drifting snow is expected...with blizzard conditions (1/4 mile vsbys) mostly over the open/unsheltered areas of southeast MN/northeast IA. Have upgraded the Winter Storm Warning to reflect these conditions for Thu night into Fri night. Localized white-out conditions are possible elsewhere and do see some increased potential for more widespread blizzard conditions for some locations north of I-94 (Clark and Taylor county) and southwest WI (specially Grant Co). An upgrade in the warning could become necessary for these locations. * COLD: dangerously cold wind chills expected from late tonight through the holiday weekend. -20 to -40 F common during the late night/morning hours through Christmas, coldest Fri and Sat mornings. For now, will cover the cold impacts via the Winter Storm/Blizzard warnings...but may need to go Wind Chill Adv into Christmas morning as winter impacts focus mostly on the cold (blowing/drifting snow impacts subside). && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 550 PM CST Wed Dec 21 2022 Periods of snow are expected this evening and into the overnight hours. The more organized snow is moving into the KRST/KLSE areas this evening with MVFR conditions dropping to IFR/patchy LIFR visibilities and ceilings. Another wave will bring additional snow later tonight into Thursday morning and this should mainly affect KLSE. Light east to northeast winds shift to the northwest and increase overnight. Northwest winds 10 to 20 mph with gusts 20 to 30kts Thursday. Due to the fluffy snow and increasing winds, blowing snow is expected to develop with some visibility reductions possible. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...Winter Storm Warning until 6 AM CST Saturday for WIZ017-029- 032>034-041>044-053>055-061. MN...Winter Storm Warning until 6 PM CST Thursday for MNZ079-086>088- 094>096. Blizzard Warning from 6 PM Thursday to 6 AM CST Saturday for MNZ079-086>088-094>096. IA...Winter Storm Warning until 6 PM CST Thursday for IAZ008>011-018- 019-029-030. Blizzard Warning from 6 PM Thursday to 6 AM CST Saturday for IAZ008>011-018-019-029-030. && $$ UPDATE...Zapotocny DISCUSSION...Rieck AVIATION...Zapotocny
Area Forecast Discussion
National Weather Service Dodge City KS
442 PM CST Wed Dec 21 2022 ...Updated Aviation Discussion... .SHORT TERM...(This evening through Thursday night) Issued at 312 PM CST Wed Dec 21 2022 A warm front lifting north of the region resulted in low level veering winds and warm air advection across our region this morning and early afternoon. As a result, areas of dense fog have gradually improved to above a quarter mile while freezing fog deposition has piled up hoar frost on most surfaces. The HRRR gradually erodes the dense fog from west to east in the afternoon. A dense fog advisory for dense fog and freezing fog valid until 3 pm is being allowed to expire as visibility should continue to gradually improve. GOES Sat imagery continues to show an eastward track to the western edge of the very low cloud cover/fog layer, and HRRR model soundings showed and drying of the near surface layer in the T-Td spreads. Attention then turns to this evening. The cold front slams through the forecast areas between 00 and 06 UTC / or 6pm and midnight. The falling temperatures, with dendritic production zone closer to the ground will lead to efficient light snow given rapidly increasing snow ratios and saturated column. NAM models 20:1 ratios behind the front while HREF combined probabilities show the snow isn’t expected to drop visibility to more than areas of a half mile at times from Wakeeney to DDC and Pratt. Extreme cold air advection will then be the focus, combining negative temperature tendency with the very strong gradient winds, to collapse apparent temperatures to the -20 to -40 range. The leading edge of the front will arrive per the NAM12 km in the mid evening, and be through the entire area before midnight. Gradient winds on Friday will maintain the cold wind chill risk through the period of Friday morning. Though not as brutally cold, the wind chills will still be in the warning category - namely the 20 to 30 below zero area. .LONG TERM...(Friday through Wednesday) Issued at 312 PM CST Wed Dec 21 2022 By Saturday morning, the 0 to -15 below zero wind chills will seem relatively balmy as temperatures remain near zero and winds fall to around 10 mph as high pressure and less gradient plays a part. Through the weekend, the cold air retreats eastward, as as southwest boundary layer winds increase, bringing temps back above freezing. From simply a pattern recognition standpoint, Tuesday and Wednesday could be relatively warm days with mid level shortwave ridging showing up in the models, but any warmup doesn’t look sustained. In the meantime, we’ll look toward Sunday night and Monday for "some" opportunity for light precipitation, either rain or snow associated with a fast moving northwest flow shortwave, somewhere is the central plains. Officially, a dry forecast and if anything occurs, it wouldn`t be significant. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 431 PM CST Wed Dec 21 2022 Low stratus across eastern portions of the CWA continue to produce LIFR ceilings and visibility at DDC and HYS with GCK and LBL still VFR at this time. An approaching cold front will switch winds out of the north between 03-05Z north to south gusting initially up to 35kts. Winds will increase to 40-45kt gusts after 07-09Z as cold air advection helps to aid in the strongest mixing to the surface post frontal passage. Ceilings will remain MVFR to IFR but uncertainty on how low they will be. Snow will begin to fall around HYS after 06Z through about 15Z with blowing snow a factor due to the strong north winds. All other TAF sites will not see influence to much if any snowfall only carrying VCSH near GCK and DDC during this same time frame. Ceilings will begin to lift to VFR after 15Z with improving conditions as the snow and system lifts to the northeast. However, winds will remain gusting up to 35-40kts through the end of the period before diminishing at the end towards sunset Thursday evening. && .PRELIMINARY POINT TEMPS/POPS... DDC -9 5 -7 17 / 40 30 0 0 GCK -10 4 -9 16 / 40 30 0 0 EHA -6 8 -6 19 / 20 20 0 0 LBL -7 7 -7 18 / 30 20 0 0 HYS -11 2 -10 14 / 90 30 0 0 P28 -2 7 -3 17 / 40 30 0 0 && .DDC WATCHES/WARNINGS/ADVISORIES... Wind Chill Warning from 9 PM CST /8 PM MST/ this evening to noon CST /11 AM MST/ Friday for KSZ030-031-043>046-061>066-074>081- 084>090. Winter Weather Advisory from midnight tonight to 6 AM CST Thursday for KSZ030-031-043>046. && $$ SHORT TERM...Russell LONG TERM...Russell AVIATION...Lowe
Area Forecast Discussion
National Weather Service Des Moines IA
543 PM CST Wed Dec 21 2022 ...Updated for the 00z Aviation Discussion... .DISCUSSION.../Tonight through Wednesday/ Issued at 355 PM CST Wed Dec 21 2022 Key Messages: - Significant winter storm will bring blizzard conditions later Thursday into early Saturday - Blizzard conditions combined with dangerous wind chills will create life threatening conditions for anyone that ventures out during the worst of this storm Details: GOES-East upper level water vapor imagery shows the trough that will bring the high impact winter storm to the region moving over the northern Plains. A lead shortwave cutting across the Ozarks has broad isentropic ascent ahead of it and this has spurred light snow across western Iowa that has reached I-35. 12z KOAX sounding showed dry air in the 850-650mb layer and while there has likely been some saturating in this layer, we are still seeing reports of unknown precipitation. This is likely a bit of freezing drizzle with the loss of ice introduction shown in the soundings. So, for a few hours this afternoon into early this evening, parts of southern Iowa may have freezing drizzle with a glaze/accretion of around 0.01" possible. Otherwise, this event will be all snow. The isentropic lift will move east through the rest of this afternoon into early this evening with snow rates ranging between a quarter to three- quarter of an inch per hour possible. Winds through this period will generally be under 15 mph so very little blowing snow is expected. There could be a slight lull later this evening before the arctic cold front blasts its way through, which will bring another round of snow with similar rates. Attendant to this boundary will be strong, low level frontogenesis (fgen) in the 925-850mb layer, though even stout fgen is in the 850-700mb layer. Forecast soundings show that as the low and mid-levels of the atmosphere cool, more of the saturated profile will be within the dendritic growth zone (DGZ; - 12C to -18C). Cross sections show lift in this layer generally as weak to moderate; however, recent RAP runs do show stronger lift passing through briefly. Snow ratios were blended up into the upper teens given the depth of the DGZ and this is supported by Cobb output from the NAM, GFS, and RAP. The latter two even show snow ratios briefly into the 20:1s, which may be indicative of stronger omega. Behind the front, low level kinematics will ramp up with strong cold air advection beginning and modest pressure height rises following. The quickening winds with gusts of 30 to 40 mph later tonight into Thursday along with falling snow will lower visibilities under a mile and at times and in some areas below a 1/2 mile. Most of the snow with the fgen will have exited the area by midday if not by mid-morning with snow accumulations of 3 to 6 inches common across much of the area and highest in the northeastern portion of the state. Overall, snow totals this round compared to the overnight forecast were a half to perhaps an inch higher. Therefore, see no reason to adjust the winter storm warning given expected impacts. While the snow will have ended by midday Thursday, the impacts will continue Thursday into Friday waning into Saturday as strong and gusty winds persist. These winds will be due to the pressure gradient strengthening over the region as surface low pressure intensifies over the eastern Great Lakes. The strongest winds at this time with gusts over 45 mph will be Thursday night into Friday. With these winds and the recently fallen, blowable snow on the ground, severe visibility restrictions are forecast and will be worst in rural, open areas compared to any sheltered, urban areas. We worked with our neighboring offices this morning to coordinate the Blizzard Warning, which starts midday Thursday and goes until Saturday morning, along and north of I-80. To the south, land use and topography along with no existing snowpack raises questions about whether blizzard conditions would materialize. However, we will monitor in case confidence increases to expand the warning. What makes this winter storm particularly dangerous and life threatening is that wind chills for much of the period midday Thursday into midday Saturday will be 30 below zero or less (colder). Therefore, if you venture out trying to reach a destination whether for local or holiday travel and become stranded, frostbite could set in within minutes. Therefore, travel Thursday through Friday is strongly discouraged for your safety. As the mid-level trough and surface low pressure begin to pull away from the area on Saturday, winds will begin to lessen, but areas of blowing snow will still be possible with sustained winds of 15 to 25 mph and gusts of 25 to 35 mph still persisting. So, while conditions may not be blizzard, travel impacts could still remain and hamper travel on Saturday. Higher heights will move over the region this weekend and this will allow temperatures to moderate Christmas Eve into Christmas Day and early next week. However, the flow over our region will remain from the northwest on the backside of the trough and deterministic and ensemble guidance still shows a clipper system dropping through later Sunday into Monday, which could bring light snow to the state. && .AVIATION.../For the 00Z TAFS through 00Z Thursday evening/ Issued at 543 PM CST Wed Dec 21 2022 Poor aviation weather is expected for the duration of the forecast with snow and IFR to LIFR conditions overnight from low ceilings and visibilities. Strong northwest winds arrive behind an arctic front overnight and persist for the remainder of the forecast. This will produce extensive blowing snow with low visibilities persisting into Thursday and beyond. && .DMX WATCHES/WARNINGS/ADVISORIES... Winter Storm Warning until noon CST Thursday for IAZ004>007- 015>017-023>026-033>037-044>048-057>059. Blizzard Warning from noon Thursday to 6 AM CST Saturday for IAZ004>007-015>017-023>028-033>039-044>050-057>062. Winter Storm Warning until noon CST Thursday for IAZ027-028-038- 039-049-050-060>062. Winter Storm Warning until 6 AM CST Saturday for IAZ070-071-081. Winter Storm Warning until 6 AM CST Saturday for IAZ072>075- 082>086-092>097. && $$ DISCUSSION...Ansorge AVIATION...Cogil
National Weather Service Jackson KY
1043 PM EST Wed Dec 21 2022 .UPDATE... Issued at 1043 PM EST WED DEC 21 2022 This evening we are starting to see some returns on the WSR-88D radar, but these are likely not reaching the ground or are sprinkles at most given the 20 degree dewpoint depression that we are seeing at the surface in most locations. The column will moisten through the night and eventually this will fall in the form of rain. The questions in the deeper valleys remains from previous discussion, but seem less likely given we have seen clouds quickly modify these colder valleys. Opted to adjust the PoP grids some to align with trends and closer to the NBM hourly PoPs. Outside of those minor changes overall not much was changed for this update. The 00Z data is just now starting to trickle in for some of the CAMs. In terms of the arctic cold front, the HRRR and ARW remain much faster with the arrival of the cold air when compared to other guidance and in general it seems the guidance can bring these kinds of airmass changes in too fast. The HRRR also remains quite the outlier in terms of just how cold the 2 meter temperatures get in the wake of the surface front early Friday morning and the ARW shows similar colder air even though not as cold. Thinking these are big outliers and not to keen on putting too much stock in these solutions at this point. Will let the overnight shift further investigate the forecast and make any modifications, as none are planned on this shift. UPDATE Issued at 716 PM EST WED DEC 21 2022 The evening surface analysis reveals a weak warm front or surface trough from the Mid South into PA. An upper level shortwave is helping to increase clouds this evening at mainly the mid and high levels. This is noted with sheltered valley temperatures already dropping into the lower 30s. We will see an increasing 850mb jet through the night and this will help to moisten the column in a top down manner. This coupled with some decent lift within the lower levels will eventually lead to some rain late tonight into Thursday morning. The issue with this is how do the deeper valleys modify through the night because we will see the outside potential for this rain to fall into sub-freezing valley temperatures. Right now thinking the deeper valleys will modify by the time we moisten enough to see rain falling, but this will be monitored closely through the evening. Also, looking at road temperatures that are still well above freezing at this point. Only minor changes were needed to the current forecast grids to account for the latest obs and trends. && .SHORT TERM...(This evening through Thursday night) Issued at 512 PM EST WED DEC 21 2022 Two systems will affect the region during the short term period. The first of these will affect us tonight into Thursday, and the second and by far most significant one will hit Thursday night. Late this afternoon, a massive upper level trough was amplifying over the middle CONUS. A shortwave trough moving through the east side of this trough will pass over the Ohio Valley and southeast CONUS tonight and early Friday, supporting coastal surface low development along the southeast coast. Light precip from this will probably make it as far northwest as eastern KY. Valley temps will fall off steeply this evening before clouds thicken, but probably creep higher later in the night. There is some concern that light rain could fall into subfreezing valleys before they warm up, but the probability is low. The situation will need to be watched, though. Any meaningful rain with this system will lift out to the northeast during the day Thursday. The main event will come on Thursday night in association with an anomalously deep storm system passing to our north. The extremely intense low will send an arctic cold front through our area on Thursday night, crashing temperatures on brisk winds, and bringing a fast round of precip near the front. It will probably start as rain, but quickly transition to snow. Forecast soundings indicate elevated instability lingering after the change to snow, which raises concerns for brief intense snowfall rates and locally elevated accumulations. Accumulations will be tricky. The ground will not be frozen at the onset, and snow will tend to initially melt from the bottom up as it falls. Strong winds will also tend to favor lower ratios than would otherwise be expected. Best estimates for amounts, based on expected precip after the changeover, is generally 1 to 2 inches. The aforementioned strong winds will also cause some blowing snow, and produce very cold wind chills once temps fall off. The coldest wind chills are forecast in the long term period on Friday, but readings will be in advisory criteria before dawn, and a Wind Chill Watch was started late Thursday night to cover the onset of the hazard before the potential of warning criteria. .LONG TERM...(Friday through Wednesday) Issued at 353 PM EST WED DEC 21 2022 Key Concerns: 1. Bitterly cold temperatures in the single digits (above and below zero) in combination with strong winds will lead to wind chills of -15F to possibly as cold as -25F (-25F to -35F above 2,000 feet) late Thursday night through early Friday afternoon; then -10F to -20F (-20 to -30F above 2,000 feet) through Saturday morning. 2. Westerly winds of 15 to 25 mph will gust to between 30 and 40 mph on Friday into Friday night, potentially leading to a few downed limbs/weak trees and isolated power outages. 3. Blowing and drifting of freshly fallen snow likely Friday into Friday night, especially in open areas. 4. Bitterly cold, albeit moderating, temperatures persist through the remainder of the Christmas weekend. Arctic air will become entrenched over Eastern Kentucky on Friday. The 21/12z model suite analysis shows a deep closed low to our north on Friday morning. The arctic front will be well east of the area by 12z, leaving just some lingering snow showers and flurries. There are still some minor differences in the depth and track of the arctic upper low. Of the deterministic solutions, the GFS is fastest and most southerly with the ~507 dam low over Central Ohio while the Canadian is slowest and shallowest, lagging the ~512 dam low just southwest of Lake Michigan. ECWMF shows a compromise between the two, through closer to the Canadian. The low pivots back to the north over the weekend ending up near James Bay on Sunday. An unusually deep surface low reflection will start the period somewhere over the Eastern Great Lakes before lifting north and becoming vertically stacked under the upper system on Christmas. Rising heights and associated subsidence supports high pressure building over the Ohio Valley by Sunday evening/night. With these track/strength differences, there is still some uncertainty in the magnitude of the post-frontal winds and air temperatures over Eastern Kentucky on Friday. Most of the guidance shows 925mb temperatures of -15 to -24C (east to west) at 12z Friday, though there is a colder trend especially in the hi-res guidance. The recent 15z RAP13 guidance is beyond that coldest end of the spectrum with -25 to -28C 925mb temperatures. This is currently an outlier solution that would lead to extreme cold and the brutal wind chills which are being depicted by the HRRR due to its ingestion of RAP13 data. Stuck with the better model consensus which would support temperatures single digits near and above zero, at best, through the day on Friday. In addition, steep low-level lapse rates and a strong surface pressure gradient will support robust mix down of winds up to the 850 mb level. There is considerable model spread on the strength of the winds at 850 mb, ranging from as little as 20 to 30 knots in the Canadian to 40 to 50 knots in the RAP/GFS (the location of the low will prove pivotal). Given the rather large spread, favored the NBM blended sustained wind speeds, which have diminished slightly in the last 24 hours. The still results in wind chills of right around -25F for many of the ridges and colder than that for the higher mountains. Given only moderate forecaster confidence for sufficient wind speed, opted to issue a Wind Chill Watch for the entire forecast area and allow the night shift to assess upstream observations and the 00z model suite. The NBM blend favored westerly wind gusts of 30 to 40 mph on Friday into Friday night. Winds of this magnitude may be sufficient to knock down weaker trees and smaller limbs, potentially leading to isolated power outages. Any loose snow will blow and drift, especially across north-south oriented highways in exposed terrain. A Wind Advisory for gusts and Winter Weather Advisory for blowing snow may be needed for portions of the area. Lingering low-level moisture will also lead to light flurries, but expect little impact/accumulation given negligible lift and temperatures too cold for dendrites. Temperatures on Friday night are expected to hold in the single digits above (below zero above 2,000 feet) with abundant cloud cover and a well-mixed boundary layer. The winds will lighten somewhat on Saturday and more so on Sunday as high pressure builds in. BUFKIT momentum transfer supports wind gusts of 20 to 30 mph (up to 35 mph across higher ridges) on Saturday while the 925 mb temperatures moderate to between between -12 and -18C. Cloud cover should diminish as the CAA eases. Despite some sunshine, it will still be bitterly cold with highs only in the teens. The wind chills will still be frigid, keeping apparent temperatures in the single digits above and below zero at the warmest part of the afternoon. Christmas Day will still be cold, highs in the 20 to 25 degree range, but with less wind, it should feel notably "warmer". The frigid air mass will continue to retreat early next week as the pattern swings back toward more seasonable norms. It remains to be seen whether the pattern transitions quietly or with some kind of storm system. There are some hints of another much shallower trough dropping through the region on Tuesday. Various deterministic and ensemble members show a wave of low pressure developing in the lingering baroclinic zone; however, the existence, track, strength and impacts of such a system remains highly uncertain due large model spread. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) ISSUED AT 641 PM EST WED DEC 21 2022 VFR skies are the story to begin the period. We will see top down moistening tonight, as a upper level wave moves east and a low level jet increases through the night. This will lead to lowering Cigs and increased chances of rain. The Cigs will lower into the MVFR levels toward dawn Thursday and could lower further depending on how precipitation evolves. The winds will generally remain under 5 knots through the period, but will begin southeast and become more south southeast by Thursday afternoon. && .JKL WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 10 PM Thursday to 9 AM EST Friday for KYZ044-050>052-058>060-068-069-079-080-083>088-104-106>120. Wind Chill Watch from late Thursday night through Friday afternoon for KYZ044-050>052-058>060-068-069-079-080-083>088-104- 106>120. && $$ UPDATE...DJ SHORT TERM...HAL LONG TERM...GEERTSON AVIATION...DJ
Area Forecast Discussion
National Weather Service Memphis TN
932 PM CST Wed Dec 21 2022 ...New UPDATE... .UPDATE... Issued at 930 PM CST Wed Dec 21 2022 The arctic front is storming across Kansas at this hour. That dangerous cold air airmass is heading for the Mid-South. The front will arrive in NE AR just after noon and reach Monroe County MS only 6-7 hours later. Cold air will build quickly. Still not expecting a whole lot of rain ahead of the cold front. Most of the precipitation will be along and behind the front. Latest data indicates that a 180 kt jet will dig into base of the upper trough over the MS Valley Thursday afternoon. This places at least the northern half of the Mid-South in a favorable area for strong lift while some deeper moisture remains over the area. This feature is a tad further south of previous model runs which should bring the accumulating snow a little further south. Latest model soundings show a 2-3 hr period where the profile is saturated and well below freezing. Northern areas have favorable profiles for about 3 hrs while further south toward Memphis...maybe 2 hours. The latest guidance has trended toward a little more snow which makes sense given the slightly further south position of the digging jet. QPF amounts are slightly higher than 24 hrs ago across the region probably due to the additional lift generated by this more favorable position. HRRR depicts 2-3 hrs of surface vsbys below one mile with areas down to 1/4 mile across the Bootheel. Given the trends in the latest data decided to bump snowfall totals up a bit with more than an inch north of a line from Jonesboro to Lexington, TN. Closer to 2 inches is likely along the KY border. Keep in mind that precipitation will start out as rain. Rain will likely cause wet roads. The cold air will rush in with temps dropping quickly and rain will quickly change to snow. Snow may melt initially due to a relatively warm ground but it will not be long before everything flash freezes. Driving could become very hazardous. It is a great idea to stay off the roads while this front and associated rain/snow moves through. The cold will be unbelievable to folks that do not wander north during the winter. This is historic cold. Wind chill values of -10 to -20 will be common Thursday night. Wind chills values this low have not happened in recent memory in the Mid-South. Winds gusts of 35 to 45 mph could cause a few power outages and areas of blowing snow. Now is the time to make plans and prepare. && .DISCUSSION... (This evening through next Tuesday) Issued at 353 PM CST Wed Dec 21 2022 Bottom line up front: winter will arrive tomorrow in the Mid-South in the form of extremely cold temperatures, flash freezes, and a light dusting to an inch of snow accumulation. One more day of benign weather with cool temperatures is on tap today due to quasi-zonal flow aloft. Tomorrow, an incredibly deep trough will dig down into the Tennessee Valley. Its associated Arctic cold front will move through late afternoon tomorrow, plunging temperatures below freezing quite rapidly post-FROPA. Though the rainfall ahead of the front is expected to be fairly light, there is a flash freezing threat due to the rapid plunge in temperatures. We could see as much as a 40 degree drop in temperatures in a matter of hours behind the front tomorrow. To account for this, while a bit unorthodox, we issued a Winter Weather Advisory for much of the Mid-South. The Winter Weather Advisory from noon tomorrow through 6AM Friday is in two segments for two separate purposes. The northern portion along the AR/MO and TN/KY state lines is for snow accumulations around 1 inch. Most of the CWA will only see a light dusting of snow, but areas farther north could see isolated pockets of 1-2 inches. The southern portion of the Winter Weather Advisory south of a Jonesboro, AR to Camden, TN line is specifically for the potential for a rare flash-freeze. This may result in hazardous travel conditions as the rapid temperature drop could cause a thin coating of ice from any residual moisture on the ground. The wind chills overnight tomorrow night remain the big story for this forecast package. The Wind Chill Warning and Advisory headlines remain unchanged; still expect wind chills in the -10 to -20F area wide by Friday morning. This is due in part to the brisk northwest winds on the back side of the Arctic front, gusting up to 40 mph overnight tomorrow night into Friday morning. Power outages could become an issue with these strong winds knocking down trees/branches onto power lines. The key message: single digit temperatures and strong northwest winds will make for brutally cold wind chills tomorrow night after the front passes. Another important note is that we`re expecting several days of sub- freezing temperatures. This is no ordinary Arctic front; once temps take a plunge late tomorrow afternoon, most areas will not climb back above freezing until early next week. With it being a holiday weekend, we`re erring on the side of caution with our headlines to make sure we get the message across that winter is coming tomorrow. After the Arctic air finally migrates off to the east by next week, temperatures begin to moderate again as midlevel ridging returns as the dominant pattern. A few deterministic models are trying to bring another weak system in on Monday, but confidence was too low to include any PoPs in the forecast. Something to watch in the coming days. CAD && .AVIATION... (00Z TAFS) Issued at 501 PM CST Wed Dec 21 2022 IFR conditions will prevail through the TAF period. Current MVFR CIGs will deteriorate late tonight and show no improvements through the period. A front will push through the region Thursday afternoon bringing the potential for gusty winds starting around 18z. Showers will push through with the front we could see a brief period of sleet before all changes over to snow. Expect snow to only last for a few hours, then to change over to light rain after the TAF period. && .MEG WATCHES/WARNINGS/ADVISORIES... AR...Winter Weather Advisory from noon Thursday to 6 AM CST Friday for ARZ009-018-026>028-035-036-048-049-058. Wind Chill Warning from 6 PM Thursday to noon CST Friday for ARZ009-018-026>028-035-036. Wind Chill Advisory from 6 PM Thursday to noon CST Friday for ARZ048-049-058. MO...Winter Weather Advisory from noon Thursday to 6 AM CST Friday for MOZ113-115. Wind Chill Warning from 6 PM Thursday to noon CST Friday for MOZ113-115. MS...Winter Weather Advisory from noon Thursday to 6 AM CST Friday for MSZ001>005-007-008-010>013. Wind Chill Warning from 6 PM Thursday to noon CST Friday for MSZ001>006-009. Wind Chill Advisory from 6 PM Thursday to noon CST Friday for MSZ007-008-010>017-020>024. TN...Winter Weather Advisory from noon Thursday to 6 AM CST Friday for TNZ001>004-019>022-048>055-088>092. Wind Chill Warning from 6 PM Thursday to noon CST Friday for TNZ001>004-019>022-048>055-088>092. && $$ PUBLIC FORECAST...SJM AVIATION...SWB
Area Forecast Discussion
National Weather Service Raleigh NC
945 PM EST Wed Dec 21 2022 .SYNOPSIS... Low pressure off the Southeast coast will move northward across the eastern Carolinas and Mid Atlantic coast Thursday and Thursday night. An unusually strong Arctic cold front will blast through the region early Friday. && .NEAR TERM /THROUGH TONIGHT/... As of 945 PM Wednesday... A weak surface low off the Florida coast will slowly deepen as it inches its way north overnight along the coastline. Radar echoes have been steadily increasing through the evening, although measurable precipitation has remained south and west of the Triangle. In most locations outside of the Triad, temperatures will stay relatively constant through the night, changing little or slightly rising. However, in the Triad there will likely be a little bit of evaporative cooling as rain moves in and saturates the lower levels of the atmosphere where the dewpoint is currently below freezing. That being said, temperature observations have trended a few degrees above the forecast temperature, and with the wetbulb zero line being north of the Triad, think that despite any cooling that does occur, there is enough of a warm nose aloft that any precipitation that falls in the Triad should manage to remain all liquid. At this point, have gone ahead and removed any mention of non-rain precipitation in Forsyth and Guilford Counties. && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... As of 244 PM Wednesday... The surface low over eastern SC is forecast in the guidance to deepen to 1009-1008 mb as it tracks roughly up along/east of the Triangle, roughly between US-1 and I-95, reaching far eastern VA by the evening and off the Mid-Atlantic by early Fri. Deep ascent with the upper-trough/jet and isentropic/WAA ascent is poised to maximize during the day, tapering off from southwest to northeast by 18-21Z. This pattern will favor likely rain in the morning, with a end to precipitation from southwest to northeast by the early afternoon in the west and early evening in the east as a dry slot pushes in with the upper trough over the Mid-Mississippi Valley. Thereafter, some light drizzle is possible with the low-level remaining saturated. The coastal warm front is forecast to be somewhere around the I-95 corridor, where some weak surface based parcels in this small warm sector could favor a marginal (level 1 out of 5) risk of damaging winds. There exists poor lapse rates in this area with only modest daytime heating, which should keep instability weak. However, low and deep-layer shear is forecast to be quite strong, which could also favor a minor tornado threat. The better tornado threat should remain offshore where greater low-level moisture is available with middle 60s dewpoints. As for highs, there will be quite the west to east gradient. The Triad and western Piedmont will be within the in-situ CAD wedge with upper 30s to lower 40s. The eastern Piedmont/Sandhills and Coastal Plain will be in the middle 50s to perhaps low/middle 60s. A narrow corridor in the Triangle will see highs in the mid to upper 40s, dependent on how far west the warm front penetrates. After a lull in precipitation Thu evening, rain showers are forecast to build back in, especially across the west into early Fri as the strong upper-trough over the Midwest becomes negatively tilted as it rotates into the Ohio Valley early Fri. The arctic front will also favor additional frontogenetical forcing. Model guidance continues to show some differences on the timing of the Arctic front. The CMC/NAM are slowest, showing the front just west of the Triad by 12Z Fri. The ECMWF and especially the GFS are faster, bringing it through the western Piedmont at this same time. Some of the high-res HRRR/NEST is also mixed, with the HRRR faster than the NEST. Some of this uncertainty may be related to how fast the cold Arctic air can move over the mountains of western NC, which usually tends to be slower than what models depict. Given this uncertainty, currently have lows reaching the middle 20s to upper 40s from NW to SE toward daybreak Fri, roughly a blend of the guidance. Temperatures ahead of the front will likely remain in the low to upper 40s/50 in the southwest flow. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... As of 350 PM Wednesday... A strong Arctic front will sweep through central NC on Friday morning with very gusty winds and dangerously cold wind chills behind it... A deep mid/upper low will move from IL/IN/OH on Friday morning NE into New England and SE Canada by Friday night. The associated ~980 mb surface cyclone initially over the lower Great Lakes will push NNE and occlude through the day, dragging a strong Arctic cold front to its south. The front will be associated with a band of light precipitation on Friday morning, with the best chance across the north where POPs are slight to low chance. Model guidance continues to trend faster with the frontal passage, but there is still some disagreement on the exact timing. The GFS is slightly faster than the ECMWF, while the NAM is on the slow end of all guidance and the HRRR/RAP are on the fast end. The official forecast is faster than NBM and reflects the middle GFS/ECMWF solution, bringing the front through the Triad just before daybreak, the Triangle around early to mid morning, and the Coastal Plain by mid to late morning. Soundings show a few snowflakes can`t be ruled out across the north right as the precipitation is ending on Friday morning, but typically these scenarios where the cold air is chasing the precipitation result in very brief snow if any, and no impacts are expected. A much bigger impact will come from the strong winds along and behind the front, and Wind Advisories will likely be needed. Model soundings show potential for 45-55 mph wind gusts to mix down to the surface as the front is passing through, with continued gusts of 35-45 mph possible through the rest of the day behind the front. This will result in very strong CAA with temperatures dropping into the 20s and 30s through the day, as well as wind chills dropping into the teens and single digits. With 1000-850 mb thicknesses dropping by as much as 100 m from early Friday to early Saturday, actual air temperatures will likely drop into the lower-to-mid-teens everywhere across central NC on Saturday morning, with statistical guidance now even showing upper single digits in the far NW. This may threaten the record low temperature of 14F on 12/24 at FAY. While winds will relax some on Friday night, they will still be strong enough for widespread wind chills from 0 to 10 below zero, so a Wind Chill Advisory will likely be needed. Very dry air will filter in through the weekend as surface high pressure builds in from the west, so skies will be mostly clear and no precipitation is expected. High temperatures on Saturday will only be in the upper-20s to mid-30s, or 20-25 degrees below normal. This will threaten the record low maximum temperatures for 12/24 at GSO (28F) and RDU (29F). Winds will be in the 10-20 mph range (gusting to 20-30 mph) and decreasing through the day, but this will still be enough to keep maximum wind chills on Saturday in the teens to lower-20s. 1000-850 mb thicknesses will then increase by around 20 m from Saturday to Sunday as the Arctic air mass begins to moderate a bit, but very cold lows in the teens are still forecast in many areas again Saturday night, as good radiational cooling will help compensate for the higher thicknesses. Highs on Sunday will still only be in the 30s, making for a very chilly Christmas Day. The good news is the winds will significantly diminish by then so the wind chills won`t be quite as low. The Arctic air mass will continue to moderate on Monday and Tuesday as the mid/upper trough lifts north into Canada. Even still, temperatures are expected to be cooler than normal with low-level thicknesses only increasing by 10-15 m each day. Models also show a weak shortwave diving south into the MS Valley on Monday, reaching the Deep South or northern Gulf of Mexico and moving off the Southeast US coast on Tuesday or Wednesday. The 00z ECMWF and a minority of its ensembles gave us precipitation from this system, but the 12z ECMWF is more like the GFS in keeping the system suppressed off the coast. For now just introduce slight chance POPs in the south and east. && .AVIATION /00Z THURSDAY THROUGH MONDAY/... As of 722 PM Wednesday... Adverse aviation conditions are likely across central NC starting later this evening. Patchy light rain and attending MVFR cigs continues to shift to the N and NW early this evening, and this rain will gradually fill in and become more steady and heavier by later this evening. This will bring cigs down to MVFR then quickly to IFR/LIFR late this evening into the overnight hours, with MVFR to IFR vsbys in steady rain. There is a small chance of patchy freezing rain over INT/GSO for a few hours near and just after midnight, however the chance of this is low, and anything that occurs would be limited to elevated surfaces with little to no accrual. Rain and IFR/LIFR conditions will remain dominant later tonight through mid afternoon Thu across the entire area, along with low level wind shear produced by 2kft winds from the SE at 40-50 kts atop surface winds from the NE at or below 10 kts. There is a small chance for an isolated thunderstorms near FAY/RWI late Thu morning into early afternoon, but the risk is too low to include in the terminal forecast at this time. Rain will end from SW to NE during mid to late Thu afternoon across central NC, bringing vsbys up a bit, although IFR/LIFR cigs are likely to persist through Thu evening. Looking beyond 00z Fri: Sub-VFR conditions are likely to remain dominant through much of Thu evening and night. While cigs/vsbys should be lifting and trending toward VFR late Thu night into early Fri morning, the strong / gusty / shifting winds will increasingly become problematic as a powerful arctic cold front approaches then sweeps east through central NC. Sustained winds from the W at 20-27 kts will frequently gust to 35-48 kts from late Thu night through Fri afternoon with clearing skies and plunging temperatures. VFR conditions with few clouds and diminishing winds but cold temps are expected Fri evening through Mon. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Kren/MWS NEAR TERM...Green SHORT TERM...Kren LONG TERM...Danco AVIATION...Hartfield