Early morning analysis shows our upper level trough starting to move toward the east and some clearing occurring behind the main axis as it pivots away from Mississippi and Alabama. Some rather dense fog has been noted across especially eastern sections where it is very moist near the surface. Ice/Snow problems have taken place over the foot hills of North Carolina, but most of those problems should start to move toward the mid-Atlantic by later this morning.
Behind the system….expect temperatures to rebound quite nicely once some clearing takes place later today. Most areas in the state should touch the 60 degree mark or a little better. Northeast Alabama may be the exception where some of the cooler air will hang on just a bit longer. Much of the region should range between 70-74 degrees on Saturday with dry and mostly sunny conditions. It should be a great weekend for baseball and outdoor activities across the entire southeast.
There could be another flip in the pattern…but we will discuss that a little later. Enjoy this beautiful weekend across the south land!
Live Storms Media
Let me preface this with a concise statement: this is subject to change and southern snow storms are notoriously hard to predict. But you should be very very concerned if you live in any of the areas within the delineated areas below.
Ok. So I’m sure you are all aware of the potential snow or ice event. I wanted to let everyone see exactly why this system is giving us fits and why it will be very very hard to forecast. We are looking at a feast or famine situation, it seems. This might be a bit lengthy and for that I apologize. There’s a lot to cover.
First let’s take a look at the GFS. You can see below that there is extensive troughing stretching from Canada to Mexico. This is what we refer to as a phase or partial phase. The longer your trough axis, the slower it moves and the deeper the trough the colder the column beneath it. This scenario is shared by the NAM.
Now to the other camp, led by the Euro which is in theory the best global weather model in the world. The ECMWF (Euro) takes the southern portion of the trough and cuts it off, something the GFS had been doing until some 36 hours ago. This causes a couple of important things to happen. It forces the trough to move faster by virtue of being shorter, causes it to be less deep providing less lift, and also serves to negate some of the southerly component of the 500mb pattern that is responsible for forcing warm, moist air up and over the frontal boundary that will be situated just offshore of the northern gulf coast. All totaled, this reduces but does not eliminate the winter weather threat.
(note, these maps are 12 hours apart but still very clearly illustrate the forecast disagreement)
So who gets what … well, I’m not about to post the snow maps as they aren’t completely illustrative of the scenario. Instead, I’ll post a forecast graphic that is derived as a blend of both the GFS/NAM and the Euro.
Should the forecast thinking change, I and others at LSN will be sure to update you on the situation.
Meteorologist Logan Poole
Zach Hargrove and crew are LIVE from Grand Forks, North Dakota this morning as a major blizzard impacts the region. Please feel free to go to our Youtube channel, www.youtube.com/LiveStormsNetwork and subscribe to get the latest alerts when we have live streams and new video content available.
Good early morning!
If anyone is frequenting weather pages I’m sure you are aware that a rare arctic outbreak of cold air and a chance for snow for areas that don’t often get it is looking like a near certainty.
I won’t bore you with rehashed statements. If you are looking for a synopsis, the fine folks at the National Weather Service in Huntsville and in Birmingham are doing a great job thus far.
Instead I wanted to show you a couple things that not many are talking about, specifically a post frontal trough that I think is a bigger player than many are giving credit.
Now, as many of you probably know, flurries can get rolling where rain showers may not. It’s just easier for the atmopshere to squeeze out snowflakes that reach the surface than in the same situation (roughly) but with a thermal profile that would otherwise support rain. With a lingering post frontal trough, surface convergence would support at least a low stratus deck.
This is indicative of upper level divergence and will further aid in the development of snow showers. In addition, the upper level divergence would help lower surface pressure which matches nicely with the depicted surface troughing.
In conclusion, the NWS looks to have a good handle on this one. Just thought your curiosities might be starving for just that little bit of extra information, so I hope I satisfied it for the moment.
Have a safe (and WARM) weekend.
Meteorologist Logan Poole
The Storm Prediction Center (SPC) has officially gotten on board, and the probability of a significant regional severe weather event is increasing. They have issued a Day 2 moderate risk for severe weather in a narrow corridor through eastern Arkansas, northeast Louisiana, and much of western Mississippi.
Glancing over the 12z data this morning, it seems like this is a reasonable outline of both the moderate and slight risks. I wouldn’t be surprised if the moderate is shifted a bit further east as we get closer to the event, however.
UPDATE: The SPC apparently agrees with me looking at the new midday Day 2 update, also expanding the moderate south and west:
Let’s talk about the highlights of the morning data. The NAM has continued its move towards the GFS solution, which is promising to see. On the surface both models almost look the same, however there are some critical differences in some of the smaller scale details which will be very important to how this potential outbreak could unfold. Both solutions show a potentially serious situation, and at this point, I feel confident in saying we will have some sort of severe weather outbreak. The NAM, however seems to be showing more of a standard cool season squall line/QLCS event, while the GFS may be onto something more substantial.
Both models show a subtle pre-frontal trough, something that has been talked about for days. However, the GFS is much better defined with this feature. This feature is circled in the images below (GFS and NAM respectively) and can be noted with the slight kinks in the isobars:
Further, in these two images, it should be noted that the Theta-E ridge is significantly more impressive on the GFS. If the GFS is correct with this feature, then the threat for significant discrete convection out ahead of the cold front increases dramatically. It is our belief that these higher Theta-E values are reinforcing the prefrontal trough. My initial thoughts were that the NAM was most likely to resolve this trough considering it is run at a higher resolution, but after talking things over with Logan Poole, I’m not so sure. The upper level system is still is not completely on shore and it is likely that the global models are ingesting more correct observational data than the regional NAM. Also, the NAM very well could be underestimating the amount of moisture in the boundary layer (which would also explain lower CAPE values). In our discussion, Logan noted that about 100 miles south of Louisiana, dewpoints are already approaching 68 degrees Fahrenheit. 27 hours out (from 12z today) we are looking at parcels entering the threat area from the deep tropics, at the very least as far south as Cuba. Using a rough calculation of moisture transport of 35 miles per hour at the 925 mb level (assuming near frictionless flow over the ocean in the boundary layer), Logan found that parcels should only take approximately 19 hours to reach the gulf coast. Therefore, we are both fairly confident the NAM is underestimating moisture in the boundary layer.
Before wrapping up, let’s look at a couple other interesting maps. The 06z 4 km NAM CONUS Nest does show some possible discrete/semi-discrete convection popping out ahead of the line:
Also, it is worth looking at the SREF eye candy. It should be noted that the SREF significant tornado ingredients product has been altered over the past year and it is not as difficult to produce significant values. However, the output that is spitting out is definitely concerning for this time of year. The SREF would suggest that we would continue with the threat over night and even a bit into southern Alabama and Georgia on Sunday. Below are the SREF significant tornado ingredients from 21z Saturday through 06z on Sunday. Also included is 21z Sunday to illustrate the potential threat on day 3:
I would like to be able to go deeper into the discussion, but holiday travel awaits. I wish everyone luck chasing and I am hopeful that the general public is taking this threat seriously. If the GFS verifies (and it does seem to be the most realistic option at this stage) then we could have a very serious December event on our hands. All modes of severe weather are possible with a handful of strong tornadoes as well as very strong and widespread wind damage. The Arkansas, Louisiana, and Mississippi junction looks primed for the worst of the weather and I would personally setup somewhere in that area or maybe just a bit further east. Make sure to have a plan to cross the river if you are west of it and make sure you are vigilant in your nowcasting. These storms will be screaming and they will be rain makers. Some of the wind profiles show a subtle veer back veer pattern in the midlevels which could make a messy wet day even messier with HP supercells and bowing segments most likely the norm. Even if this ends up being a predominately QLCS event, it could still be very significant with the shear values in place. As always, follow LiveStormsNow.com throughout the day as we will have many chasers in the field covering this event for you. If you have loved ones in the the threat areas, please share this!