John1122 Posted December 31, 2013 Share Posted December 31, 2013 This is getting close, as soon as tomorrow night in the Western areas. WFO are getting more bullish for the event. The GFS has been showing something very similar to this for several runs in a row now. This was the 0z run that came out a few hours ago. MRX has made a rare, bold call from their office. FOR THURSDAY...STRONG UPPER DIVERGENCE/FRONTO-GENETIC FORCING ANDISENTROPIC LIFT WILL PRODUCE WIDESPREAD PRECIPITATION. AS FRONTALBOUNDARY PULLS EAST ACROSS THE REGION THURSDAY...COLD AIR WILL COLDARCTIC AIR WILL SPILL INTO THE SOUTHERN APPALACHIANS DURING THEAFTERNOON AND EVENING. PRECIPITATION WILL CHANGE TO SNOW FROM WESTTO EAST AND HIGH ELEVATIONS FIRST. BY LATE AFTERNOON/EVENING...A GOODPART OF THE REGION WILL EXPERIENCE SNOW.FOR THURSDAY NIGHT/FRIDAY MORNING...OROGRAPHIC NORTHWEST FLOW SNOWSWILL BE PRODUCING FAIRLY DECENT SNOWFALLS OVER THE NORTHWEST FACINGSLOPES. ALSO...STRONG COLD AIR ADVECTION ALONG WITH SOME LOW-LEVELINSTABILITY WILL PRODUCE SNOWS EVEN ACROSS THE VALLEY. WARNINGCRITERIA IS POSSIBLE OVER THE FAR EASTERN MOUNTAINS AND MOUNTAINS OFSOUTHWEST VIRGINIA...SUCH AS HIGH KNOB. ADVISORY CRITERIA SNOWS AREPOSSIBLE ACROSS THE PLATEAU...CENTRAL VALLEY...NORTHEAST TENNESSEE...VALLEYS OF SOUTHWEST VIRGINIA AND CHEROKEE/CLAY COUNTIES OF NORTHCAROLINA. WILL INCLUDE IN THE HWO. Most other AFO's are putting 50% or better chances for snow in their forecast for Wednesday night into Thursday night as a powerful coldfront crashes through the states. It appears that there is the potential for at least a ground covering event over the areas shown above on the GFS snowfall map. Temps will fall into the 10s and 20s Thursday night and likely won't recover above freezing in many areas on Friday, with some not making it out of the mid to upper 20s. The potential is higher and for higher accumulations if you live in an upslope prone area in SE KY, SW VA or East Tennessee. Let's hope this is the one that covers up some grass blades and hopefully is the start of a few days or weeks to remember for a long time to come. Link to comment Share on other sites More sharing options...
John1122 Posted December 31, 2013 Author Share Posted December 31, 2013 JKL's take on things. THE FIRST ITEM TO BE CONCERNED WITH IS A QUICK MOVING SHORTWAVEPASSING THROUGH THE REGION THURSDAY AND THURSDAY NIGHT. MODELS HAVETRENDED A LITTLE FURTHER SOUTH WITH THE WEAK SURFACE LOW. BOTH THE31/00Z RUNS OF THE GFS AND ECMWF NOW TRACK THE LOW UP THE EASTERNTENNESSEE VALLEY INTO WESTERN VIRGINIA. A LOW TRACK INTO EASTTENNESSEE TYPICALLY RESULTS IN ENOUGH WARM AIR SPREADING NORTHWARDINTO SOUTHEAST KENTUCKY THAT P-TYPE STARTS OUT AS RAIN...OR AT LEASTIS PREDOMINANTLY RAIN. HOWEVER...FURTHER NORTH P-TYPE MAY START OUTAND STAY AS SNOW...BUT EXACTLY WHERE THAT LINE SETS UP IS YET TO BEDETERMINED. ANY RAIN WILL QUICKLY CHANGE TO SNOW SHOWERS THURSDAYAFTERNOON AND THURSDAY NIGHT AS MUCH COLDER AIR FLOODS SOUTHWARDBEHIND THE LOW. MODEL QPF IS GENERALLY BETWEEN A TENTH AND QUARTER OFAN INCH FOR THE EVENT...WITH HIGHER AMOUNTS TO THE SOUTH. THIS SHOULDEQUATE TO A GENERAL 1 TO 2 INCHES OF SNOW AS IT STANDS NOW FOR MOSTLOCATIONS. FLURRIES OR ISOLATED SNOW SHOWERS WILL LINGER IN THE EASTAT THE START OF THE DAY ON FRIDAY...BUT END QUICKLY AS HIGH PRESSUREBUILDS IN AT THE SURFACE. Link to comment Share on other sites More sharing options...
jaxjagman Posted December 31, 2013 Share Posted December 31, 2013 BNA WED NIGHT INTO THU IS WHERE IT STARTS REALLY GETTING INTERESTING. GENERALLY LEANED TOWARD PREVIOUS FORECAST REASONING WITH COLDER TEMPS EXPECTED LATE WEEK INTO THE FIRST PART OF NEXT WEEK AS THERE IS GENERALLY MORE AGREEMENT IN THE MODELS AT LEAST THRU THE FIRST PART OF THE WEEKEND COMPARED TO PREVIOUS MODEL RUNS...WITH THE EURO STILL SHOWING AN IMPRESSIVE CAA PATTERN WORKING INTO THE MID STATE LATE WEEKEND INTO EARLY NEXT WEEK. A TROUGH OVER THE CENTRAL U.S. STILL LOOKS LIKE IT WILL DEEPEN ON WED AND MOVES A WEAK LOW TO THE S OF TN VALLEY WHICH WILL BRING A GOOD CHANCE OF PCPN STARTING WED EVENING FAR W AS RAIN...WITH SPREADING EWD OVERNIGHT WITH A RAIN/SNOW MIXTURE POSSIBLE NW PORTIONS. AS THIS TROUGH AND ASSOCIATED COLD FRONT CONTINUE TO MOVE THRU THE AREA ON THU...COLD AIR BEGINS TO WORK IN ACROSS NRN PORTIONS OF MID STATE WITH SNOW LIKELY DURING THE MORNING HRS N FOR AREAS N OF I-40 DURING THE MORNING HRS...WITH A RAIN/SNOW MIXTURE JUST TO THE S...AND RAIN ACROSS THE REMAINDER OF THE MID STATE. THERE COULD BE SOME ACCUMULATING SNOWFALL POTENTIAL ACROSS THESE AREAS DURING AT LEAST THE MORNING HRS AND WILL MENTION THIS POSSIBILITY IN THE MORNING HWO ISSUANCE. LATEST MODEL RUNS POINTING TOWARD SNOW ACCUMULATION AMOUNTS AROUND ONE HALF OF AN INCH OR LESS IN THESE LOCATIONS. KEPT TEMPS IN THE MID TO UPPER 30S ACROSS THE MID STATE. SNOW SHOULD TAPER OFF DURING THE EVENING HRS ON THU...WITH DECREASING CLOUDINESS AND LOWS IN THE TEENS...AS CANADIAN HIGH PRESSURE RIDGING INFLUENCES BUILDING IN ACROSS THE MID STATE ON FRI AND CONTINUE TO INFLUENCE THE WX THRU AT LEAST THE FIRST HALF OF THE WEEKEND...RESULTING IN HIGHS ONLY IN THE UPPER 20S TO LOWER 30S ON FRI...AGAIN MID TEENS FRI NIGHT...AND THEN BACK TOWARD MORE SEASONABLE VALUES BY SAT. Link to comment Share on other sites More sharing options...
franklin NCwx Posted December 31, 2013 Share Posted December 31, 2013 A blend of the jma and ukie looks good to me! Link to comment Share on other sites More sharing options...
tnweathernut Posted December 31, 2013 Share Posted December 31, 2013 A blend of the jma and ukie looks good to me! What will be interesting to see is how much "juice" left this one has after changeover. I hate rain to snow, cold chasing moisture situations as they usually don't work out. I do remember several times in the 80s where that type of a situation brought forth surprises though, so it's not like it can't happen. Link to comment Share on other sites More sharing options...
Carvers Gap Posted December 31, 2013 Share Posted December 31, 2013 The 12z NAM shows a nice little upslope event and MRX mentioned warning criteria for the mountains and SW Virginia along with advisories for the northern valleys. I am sure the Plateau would be included. My area is awful for upslope events though I am in the northern valley. Get a bit of a rain shadow here. JC and Bristol do much better with these events. Now, when a Nor'reaster rolls we get the exact opposite effect. Link to comment Share on other sites More sharing options...
tnweathernut Posted December 31, 2013 Share Posted December 31, 2013 12z GFS continues to advertise a light snow event for I-40 north, from just west of the Clarksville and points east. Enhanced amounts in parts of NE TN. (around 2 inches). Really consistent on providing a lithe snow. NAM has been just as consistent in saying NO. I hope this is just the goofy nature of the NAM past hour 48 at play here. Would be nice to get an inch or so and then see how low temps can go with this hard hitting, but quick cold snap following the system. I bet upslope areas would hit warning level criteria with this look. Link to comment Share on other sites More sharing options...
Carvers Gap Posted December 31, 2013 Share Posted December 31, 2013 12z GFS continues to show .25-.50" for the eastern half of the valley for Thurs/Thurs night. Edit: Beat me to it tnweathernut. Good post. Thought the 12z NAM has something where 24hrs ago, had nothing. Link to comment Share on other sites More sharing options...
jaxjagman Posted December 31, 2013 Share Posted December 31, 2013 12z GFS continues to show .25-.50" for the eastern half of the valley for Thurs/Thurs night. Edit: Beat me to it tnweathernut. Good post. Thought the 12z NAM has something where 24hrs ago, had nothing. You guys always do better in the E parts Link to comment Share on other sites More sharing options...
Carvers Gap Posted December 31, 2013 Share Posted December 31, 2013 You guys always do better in the E parts What is crazy about this is that you have to be on a northwest facing slope. I am not. It is area specific within the region. The Plateau, SW VA, towards the Apps. It is a lot like lake effect snow. You have to be on the side facing the approaching moisture and have significant elevation gain. Literally, I can drive ten minutes from my house and see it, and nothing here. Pretty wild. Link to comment Share on other sites More sharing options...
John1122 Posted December 31, 2013 Author Share Posted December 31, 2013 These events are classic "know your area" events once the synoptic snow passes. But this is going to be a vigorous event with decent moisture and the upslope off the Plateau will overspread the valley area. I don't do Smokey Mountain or Eastern Mountains well, but I do well enough in Plateau events. It's also a case in Campbell County that you can get upslope with N flow too. As long as the lakes are involved. I had 8 inches of upslope in December 2010 out of an event. In 2007 I got under a band of snow that stretched directly from Lake Michigan all the way into Campbell County. It snowed 7 inches in 3 hours. Link to comment Share on other sites More sharing options...
jaxjagman Posted December 31, 2013 Share Posted December 31, 2013 These events are classic "know your area" events once the synoptic snow passes. But this is going to be a vigorous event with decent moisture and the upslope off the Plateau will overspread the valley area. I don't do Smokey Mountain or Eastern Mountains well, but I do well enough in Plateau events. It's also a case in Campbell County that you can get upslope with N flow too. As long as the lakes are involved. I had 8 inches of upslope in December 2010 out of an event. In 2007 I got under a band of snow that stretched directly from Lake Michigan all the way into Campbell County. It snowed 7 inches in 3 hours. Probably the last time we seen lake effect sn.,it's been awhile.Hopefully the lakes will freeze up and we can get some bonus tokens Link to comment Share on other sites More sharing options...
tnweathernut Posted December 31, 2013 Share Posted December 31, 2013 Euro Data for KTRI FRI 00Z 03-JAN -0.2 -6.8 1016 97 97 0.16 542 529 FRI 06Z 03-JAN -3.9 -12.6 1022 58 53 0.04 537 519 Link to comment Share on other sites More sharing options...
tnweathernut Posted December 31, 2013 Share Posted December 31, 2013 12z Euro data - The surface somehow remains above freezing in Nashville, when .19 is falling. 850's are cold enough. Might be snow north of Nashville. TYS - .17 (as snow) Link to comment Share on other sites More sharing options...
1234snow Posted December 31, 2013 Share Posted December 31, 2013 I think the big difference between the GFS and the NAM is in how it handles the energy diving down the Rockies and the ridge to the west of that. The GFS has a slightly taller ridge which allows the energy to dig a little more to the southeast. Also the energy is stronger and more consolidated of the GFS while the NAM keeps the energy weaker and more separate. NAM Hour 30: GFS Hour 30: NAM Hour 45: GFS Hour 45: Link to comment Share on other sites More sharing options...
1234snow Posted December 31, 2013 Share Posted December 31, 2013 I think the NAM will trend toward the GFS like it did with our most recent gulf low this past Sunday. With that event the NAM was weaker with the energy and then finally caught up with the GFS. This will allow the trough to tilt more neutral/negative and pull in a little more moisture. Link to comment Share on other sites More sharing options...
1234snow Posted December 31, 2013 Share Posted December 31, 2013 18z NAM looks juicier with the back side precip. Link to comment Share on other sites More sharing options...
John1122 Posted December 31, 2013 Author Share Posted December 31, 2013 None of the models ever really handle upslope very well at all. When they do show it, they just generally show ..01 6 hour qpf panels. Link to comment Share on other sites More sharing options...
Carvers Gap Posted December 31, 2013 Share Posted December 31, 2013 18z NAM is juicier but w/ less interaction with the southern stream. Still amazing to see the variations in model output. You know HPC mentioned the other day that lack of data (over northern Pacific?) is causing problems. May be until not enough data is being invested into the computer model. Link to comment Share on other sites More sharing options...
tnweathernut Posted December 31, 2013 Share Posted December 31, 2013 18z NAM is juicier but w/ less interaction with the southern stream. Still amazing to see the variations in model output. You know HPC mentioned the other day that lack of data (over northern Pacific?) is causing problems. May be until not enough data is being invested into the computer model. Shouldn't the parcels be well within the ROAB network by now? Link to comment Share on other sites More sharing options...
1234snow Posted December 31, 2013 Share Posted December 31, 2013 None of the models ever really handle upslope very well at all. When they do show it, they just generally show ..01 6 hour qpf panels. Exactly. I guess it's just hard for the models to pick up on the fine resolution of a upslope snows. 18z NAM Total Precip Hour 63: Link to comment Share on other sites More sharing options...
Carvers Gap Posted December 31, 2013 Share Posted December 31, 2013 Shouldn't the parcels be well within the ROAB network by now? Which is why I think it is being modeled more accurately. Could be the same problem with the Jan 6 system. We have seen this the past two winters. I think that is why the Euro has struggled. Link to comment Share on other sites More sharing options...
jaxjagman Posted December 31, 2013 Share Posted December 31, 2013 That run right there just shut BNA out on the 18z,to warm Link to comment Share on other sites More sharing options...
jaxjagman Posted December 31, 2013 Share Posted December 31, 2013 AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE NASHVILLE TN 421 PM CST TUE DEC 31 2013 .DISCUSSION... A BEAUTIFUL SUNNY...BUT CHILLY END TO 2013 TODAY. WE`LL RING IN THE NEW YEAR WITH MOSTLY CLEAR SKIES AND LOW TEMPERATURES FALLING INTO THE MID 20S TONIGHT. ZONAL FLOW IS IN PLACE FOR THE NEXT 24 HOURS AND SOME SUNSHINE SHOULD ALLOW TEMPS TO CLIMB TO AROUND 50 ON WEDNESDAY. CLOUD COVER WILL BEGIN TO INCREASE IN THE AFTERNOON AS A SURFACE LOW MOVES INTO THE REGION FROM THE SOUTHWEST WEDNESDAY NIGHT. THE LOW IS EXPECTED TO MOVE JUST SOUTH OF MIDDLE TENNESSEE INTRODUCING NORTHWEST FLOW AND CONSEQUENTLY A SURGE OF COLD TEMPERATURES AND SNOW INTO THE FORECAST ON THURSDAY. PRECIP IS FORECAST TO BEGIN AS RAIN FOR MOST OF THE AREA EARLY THURSDAY MORNING...THEN TRANSITION TO SNOW FOR AREAS MAINLY NORTH OF I-40 AS THE DAY PROGRESSES. AT THIS TIME IT LOOKS LIKE THE COLD FRONT WILL SWING THROUGH THURSDAY MORNING...WHICH MEANS WE WILL LIKELY HIT THE HIGH TEMPERATURE SOMETIME BEFORE NOON ON THURSDAY AND SEE MOST OF THE AREA FALL BELOW FREEZING AS THE DAY PROGRESSES. A RAIN/SNOW MIX COULD SINK AS FAR SOUTH AS LEWIS COUNTY BEFORE THE PRECIP TAPERS OFF LATE THURSDAY NIGHT. THE NORTHWEST CORNER OF MIDDLE TENNESSEE HAS THE BEST CHANCE OF SNOW ACCUMULATION. INCREASED SNOW AMOUNTS FROM AROUND A HALF INCH TO AROUND 0.75 INCHES FOR THE NW CORNER. AREAS EAST OF I-65 AND NORTH OF I-40 COULD SEE AROUND HALF AN INCH AS WELL. ANY SNOW WILL LIKELY STICK AROUND AS TEMPERATURES DIP INTO THE TEENS FRIDAY MORNING AND ONLY WARM INTO THE UPPER 20S DURING THE DAY ON FRIDAY. Link to comment Share on other sites More sharing options...
1234snow Posted January 1, 2014 Share Posted January 1, 2014 I decided to try to make a snowfall map based on what I think might happen with this event. Don't laugh too hard as this is the 1st map I've done on here and it is not very pretty but it is a rough guess. Upslope snow is included as well. I probably got most of the orographic stuff wrong, but most of y'all know how your immediate region fares in these types of events. Link to comment Share on other sites More sharing options...
John1122 Posted January 1, 2014 Author Share Posted January 1, 2014 I think that's a fantastic job. I can't draw even close to that well! You were close in my area I think, slightly there's a bit of 3000-3500ft peaks just south and southwest of your 2-4 area here that do well here in upslope too. I decided to try to make a snowfall map based on what I think might happen with this event. Don't laugh too hard as this is the 1st map I've done on here and it is not very pretty but it is a rough guess. Upslope snow is included as well. I probably got most of the orographic stuff wrong, but most of y'all know how your immediate region fares in these types of events. Post New Years Light snow.jpg Link to comment Share on other sites More sharing options...
tnweathernut Posted January 1, 2014 Share Posted January 1, 2014 I decided to try to make a snowfall map based on what I think might happen with this event. Don't laugh too hard as this is the 1st map I've done on here and it is not very pretty but it is a rough guess. Upslope snow is included as well. I probably got most of the orographic stuff wrong, but most of y'all know how your immediate region fares in these types of events. Nice map, even if it shafts us valley guys, lol. Very reasonable. Well done. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
1234snow Posted January 1, 2014 Share Posted January 1, 2014 Nice map, even if it shafts us valley guys, lol. Very reasonable. Well done. Sent from my iPhone using Tapatalk Haha yeah it does shaft the valley but I have just have a feeling it will work out that way. John I was thinking of your area when I made the 2-4 but you know your area well and I know you always do well in upslope situations I just didn't know how far south to put it. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
1234snow Posted January 1, 2014 Share Posted January 1, 2014 0z NAM is a whole lot juicier and warmer. It dug our shortwave further to the south this time which amped up the precip. I still don't think the models are done shifting toward the south just yet. Don't know if the backside is strong enough to offset the front half of rain. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
tnweathernut Posted January 1, 2014 Share Posted January 1, 2014 0z NAM is a whole lot juicier and warmer. It dug our shortwave further to the south this time which amped up the precip. I still don't think the models are done shifting toward the south just yet. Don't know if the backside is strong enough to offset the front half of rain. Sent from my iPhone using Tapatalk I noticed that too. I am holding out hope the models will trend south and east with the late weekend system. It was nice to FINALLY see the NAM realize heavier precip amounts. It's usually the model that is OVER juiced. Link to comment Share on other sites More sharing options...
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