Dangerous Flooding Risk Will Persist Across Southeast

NAM Rainfall

A stalled frontal boundary is currently located across the southern U.S. and is going to begin pushing slowly northwest as a warm front throughout the day on Wednesday. A trough over the western U.S. and ridging located along the East Coast is going to create a southwest flow from the Gulf of Mexico, which will transport deep moisture into parts of the Southeast. A strong sub-tropical jet stream that extends from Baja California and Mexico will aid in transporting this moisture into the Southeast and creating favorable upper-level dynamics that will favor this heavy rain event setting up along the frontal boundary.

This wouldn’t be that big of a deal had some of these regions not already received copious amounts of rainfall already, driven by what has already been an exceptionally active pattern. Areas expected to be impacted by this heavy rainfall event have already gotten 200-400% + of their average rainfall for this month with most of that rain falling in the last seven days.

December flooding map

Prior to this month, the fall months were also very wet for parts of the Southeast.

3 months flooding

Even though the expected rainfall wouldn’t be too big of a deal in most cases, any additional rainfall will cause flooding issues especially over the areas that might get under some of the heavier thunderstorms. Just to give you an idea on specific locations, I posted WPC’s latest 3-day rainfall forecast below, along with the projected rainfall totals (over the next 48 hours) from the 4 km NAM model.

Rainfall Forecast

NAM Rainfall

I know this article is much shorter than most of my discussions, but I have already discussed the meteorology behind the overall pattern already. This is just another heads up on what could end up being another dangerous flooding event.

Pattern Change Along With Winter Storm Chances Increasing

European model cold

Despite the warmth that has prevailed across much of the eastern two-thirds of the United States this month, the configuration of the overall pattern has kept much of the U.S. in a very active weather pattern. The core of the warmth has been established over the eastern third of the U.S. with a tendency for troughing over the western U.S. This established a pattern that was favorable for systems moving into the Pacific Northwest, digging southeastward into the Plains, and then shooting back northeastward. This is the track that the most recent storm system will be taking, which is currently dumping copious amounts of snow over New Mexico and western Texas and was responsible for the deadly tornadoes in Dallas yesterday. This system is definitely not even close to being finished and will be bringing additional flooding, severe weather and winter weather to other regions of the U.S.

Pattern Change On The Way:

The coming pattern change that has been discussed for quite a while on Firsthand Weather is going to begin to emerge right around or just after the New Year. The persistent ridge over the eastern U.S. is going to start flattening out, and the temperatures are going to dip below average over much of the U.S. It’s important to realize that this transition is going to take some time, and there may be some volatility to the overall pattern before the anticipated colder pattern becomes established in the eastern U.S.

According to the forecast models, expansive ridging (blocking) is going to set up from the Pacific Northwest into western Canada and Alaska. This means that a general warming trend will occur in all of those regions, however it could take a decent amount of time before that warmth sets up in the northwestern U.S. into the Northern Plains. It’s important for me to point out that the forecast models have been all over the place due to this transition. While most meteorologists have gone from very warm forecasts to very cold forecasts (probably because of what the forecast models are showing), let me caution everyone that the long-range model guidance will likely not handle this transition well.

It still seems to me that the “real deal” cold won’t establish itself over the eastern half of the United States until mid-January or maybe even closer to February, but January is going to bring with it several Arctic intrusions with a number of winter storm opportunities. I think it’ll be important to have someone like the WDR Roofing Company – Cedar Park look at your roof and look at your emergency storm plans for this winter. It’s important to be prepared. As I’ve said since July, December would be warm, January would be a transition month, and February would be brutal (cold-wise). For all of you snow lovers out there, you actually don’t want such a cold pattern that the dominant storm track gets shoved too far to the south. In particular, that happened a few times last winter across the South, and I remember during the 2009-10 winter, there were places along the Gulf Coast (like Houston) getting snow before regions to the north were. In other words, you typically want to get just enough cold air for a winter storm!

Below is the projected temperature anomaly map for January 5th according to the European model. If you’re in the blue, you’re expected to get below average temperatures, and if you’re in the red, you’re expected to get above average temperatures. I’m more focused on the overall pattern than exact numbers that are shown in the legend on this map. Many of you are going to get your first real taste of winter cold as we start making this pattern transition.

European model cold

Southern Winter Storm Chances Will Increase Through January:

The overall storm track is about to make a change, and the focus area is going to be over region 8 and lower parts of region 6 in my winter forecast. I’ll have to keep an eye on some parts of region 7, too. I posted the winter forecast map below just so you could reference it. The western edge of region 8 has already verified quite nicely.

Final 2015-16 Winter Forecast

The active sub-tropical jet stream is going to remain established from Baja California, across Mexico, and into the Southern Plains and Southeastern U.S. As numerous cold intrusions will likely dig farther and farther south as we progress through January, this is going to open the door for the Southern Plains, Southeast, and even the Mid-Atlantic to be at higher risk of getting winter storms. In January, I don’t anticipate that any trough is going to dig so far south that the moisture fetch will be suppressed too far to the south.

Right now, nothing is showing up on the models for the first half of January, but I believe that the sub-tropical jet stream is a little too far to the south in the guidance. Despite the fact that nothing is really showing up on the model guidance, I am anticipating that a winter storm will occur within the first one to two weeks of January, potentially impacting parts of the Southern Plains and Southeast and maybe even the Mid-Atlantic. Pieces of energy are going to have the tendency to enter from the Pacific and cut across the southwestern U.S. or Mexico and move eastward. IF the cold air is sufficient, we could have our first winter storm on our hands (for the areas farther east that haven’t gotten anything yet), which could also have a severe weather component with it in the warm sector of the system.

In the long-range like this, it doesn’t really matter to me if the forecast models are picking up on an individual storm. Beyond 5 to 7 days, the forecast models are going to change so much that it’s not even worth pointing anything out, especially when the overall pattern is expected to change. What I try to do is identify the regions that will be more favorable for these kinds of events occurring, and that’s what I have done here.

Also, there could be an increased chance for lake effect snow events to occur due to this changing pattern, and with any system that swings down from Canada, this could bring an increased risk for parts of the Northeast to get some wintry precipitation. Also, it’s worth noting that parts of the Northeast will be impacted by the current winter storm that all eyes are currently on.

Of course, I will continue to monitor any individual storm system that comes up and will point those out to you as they start to show up. If anything changes in any way, I will definitely let you know, so please visit Firsthand Weather as often as you can.

Tornadoes, Some Strong, Looking Likely For Tomorrow

Significant Tornado Parameter - Mid To Late Afternoon

We have a lot to discuss tonight, so I want to keep this article relatively brief and want to get into more specifics on the timeline and exact locations that will likely be impacted tomorrow (Wednesday) and tomorrow night. Last night, I wrote up a very detailed analysis on this severe weather potential that will likely take shape tomorrow, and I encourage you to go back and read that article in case you missed it. Not a lot has changed since that article.

There remains to be a pretty strong model consensus that a potential tornado outbreak could unfold tomorrow across parts of the Mississippi Valley, Tennessee Valley and also including a lot of surrounding regions. I’ll have more on specific locations in just a minute.

A Few Details I Want To Mention:

Before getting into specific locations, a broad mid to upper-level trough is continuing to move eastward as expected, which will set up the proper dynamics for this event to occur. A strong sub-tropical jet stream currently extends from the Pacific into Mexico and is feeding adequate moisture into the southeastern U.S. This moisture plume will continue to expand northward as a frontal boundary continues to push north as a warm front.

As expected, a tongue of drier air should be available at the mid-levels, further destabilizing the environment. Daytime heating tomorrow should adequately destabilize the environment further. A strong low-level jet stream will be present and eventually extend northward. The mid and upper-level winds should increasingly become favorable throughout the day due to the eastward moving trough. Winds will increase and change with height in a clockwise direction (a favorable directional and speed shear environment). Basically, conditions will be very favorable for supercells capable of producing tornadoes. In fact, some of these tornadoes could be strong.

As I’ve mentioned several times already, overnight and early-morning convection could keep the environment more stable than expected, however I wouldn’t count on that occurring. It’s really only going to take a couple hours of sunlight to quickly destabilize the atmosphere, and the model guidance indicates that any leftover convective activity will move out in time.

Locations In The Danger Zone:

Please take special note if you’re in the areas that are listed.

Highest risk for tornadoes tomorrow (some strong): eastern half of Arkansas, northern half of Louisiana, much of Mississippi (higher chance of strong tornadoes), western and central Tennessee (higher chance of strong tornadoes), western and northwest Alabama (higher chance of strong tornadoes in northwest Alabama)

Additional regions that could be at risk for tornadoes: the rest of Alabama, the rest of Louisiana, western half of Kentucky, southeastern Missouri, southern parts of Illinois and Indiana and early on in eastern Texas. The threat could expand eastward into parts of Georgia towards Wednesday evening. I will also be keeping a close eye on the possibility of this threat expanding into eastward parts of Tennessee, western North Carolina, and Upstate South Carolina into the overnight hours, although the greatest tornado risk will occur west of these areas.

Significant Tornado Parameter – Early Afternoon:

Significant Tornado Parameter - Early Afternoon

Significant Tornado Parameter – Mid To Late Afternoon:

Significant Tornado Parameter - Mid To Late Afternoon

Significant Tornado Parameter – Early Evening:

Significant Tornado Parameter - Early Evening

Concluding thoughts:

Again, nothing is ever certain, but this could end up being a high-impact severe weather event. I wouldn’t be surprised if SPC upgrades parts of the enhanced risk to a moderate risk for parts of Mississippi, Alabama, and western Tennessee. If you’ll be traveling during this time, please check the weather frequently and have a plan in place if you live in any of the mentioned locations.

Latest SPC Outlook (will be updated in an hour or two):

SPC Tornado Outlook

Christmas Eve Tornado and Severe Weather Threat Looking More Likely

Significant Tornado Parameter Late Evening

UPDATE: I made a big mistake, and one of my viewers pointed it out. This event is going to occur this WEDNESDAY, not on Christmas Eve. For whatever reason, I had my days mixed up. Sorry about that. Instead of going and changing every mention of Christmas Eve, just know that it’s supposed to be Wednesday, not Christmas Eve.

An interesting situation is definitely shaping up for Christmas Eve, and while there are definitely a couple of uncertainties that I’ll discuss momentarily, severe weather, including the risk for tornadoes, is looking more likely for areas of the South including parts of the Mississippi Valley and Tennessee Valley.

Detailed Analysis:

A broad mid-to-upper level trough is going to continue to build into the western United States while persistent ridging along the eastern United States is going to remain intact. A piece of energy is going to move into the United States, which is currently embedded in the westerly (west-to-east) wind flow over the northern Pacific. Once this piece of energy swings southeastward and becomes embedded in the western U.S. trough, this will trigger a surface low pressure system to most likely develop east of the Rockies, which will eventually shoot northeast towards the Great Lakes. To put it simply, all I’m really saying is that the mid and upper-level atmosphere is going to be favorable for the development of a low-pressure system at the surface.

Notice the broad trough located over the west-central U.S. on Wednesday with the ridge along the East Coast. Sorry for not actually including an explanation on the map to make this more understandable.

500 mb Map

A cold front is currently moving across the U.S., which is associated with an entirely different low-pressure system, but this front will eventually push back northward as a warm front. Anytime there is a western trough, eastern ridge setup like this, it always gets my attention for possible severe weather in between. With the very strong Pacific jet stream (winds in the upper atmosphere) that has been responsible for bringing in the parade of storm systems into the Pacific Northwest, it’s important to keep a close eye on any embedded pieces of energy that could bring some issues later down the road.

The pattern has remained overwhelmingly warmer across the eastern half of the United States this December. A strong and well-placed polar vortex remains intact over the North Pole, which supports this warmth over many regions. The Pacific and much of the Atlantic, including the Gulf of Mexico and waters off the East Coast, remain well-above average. Despite the winter season that is upon us, bodies of water do not lose heat nearly as quickly and warm the air above. Without any substantial Arctic air masses moving southward, it simply stays warm because all of that warmth gets transported eastward due to the wind flow. This particular year, the Pacific is almost unprecedentedly warm. Hopefully this makes sense and isn’t getting too confusing. Please let me know if it is!

Who Will Be Impacted?

So back to this low pressure system that I mentioned would develop! As it moves northeast, all of this warmth and moisture is going to get transported northward from the Gulf of Mexico into the warm sector of this system. With the combination of this warmth and moisture, the low and mid-to-upper level winds are going to be favorable for severe weather, including tornadoes, to develop on Christmas Eve across parts of the Mississippi Valley and Tennessee Valley. The tornado threat will be for parts of Mississippi, Alabama, Arkansas, Tennessee, Louisiana, and Texas. Georgia also needs to keep an eye on this situation in case the threat extends longer into the overnight hours on Christmas Eve. Surrounding states need to monitor all of this closely also, and I wouldn’t be surprised if additional regions have to be included in a risk zone.

Significant Tornado Parameter Map For Late Afternoon:

Note: This is a multi-component index that takes several factors into account. Brighter colors indicate a higher risk for a given area to have storms capable of producing tornadoes.

Significant Tornado Map

Significant Tornado Parameter Map For Early Evening:

Significant Tornado Parameter Late Evening

A tongue of drier air is going to likely work its way into the mid levels of the atmosphere across parts of Louisiana, Mississippi and Alabama on Wednesday and eventually extend northward. Believe it or not, this actually makes the atmosphere more unstable than it otherwise would be. I won’t get into the reasoning behind all of that, but it can promote the development of deep convection (thunderstorms).

Here’s my biggest uncertainty at this point. Leftover thunderstorms from Tuesday could be over the region of concern going into Wednesday. This could keep the atmosphere more stable than expected, but that is very difficult to predict. Generally, I warn my audience not to count on that occurring, and try to prepare as many people as possible. With this kind of setup, it’s only going to take a couple of hours of sunlight to destabilize atmosphere enough to allow for this event to unfold.

With all of that said, a tornado outbreak is not out of the question at this point, and the areas that I just mentioned need to be on high alert and make adequate preparations now. This will be an event that could continue as it becomes dark. If you’ll be traveling, please check the weather frequently.

Storm Prediction Center’s Latest Outlook For Christmas Eve:

Storm Prediction Center's Outlook

Flooding Threat:

Deep tropical moisture will be pushing northward as the warm front moves northward. A sub-tropical jet stream that will be cutting across Mexico and extending northeastward into the Southeastern U.S. will be responsible for transporting deep moisture well to the north into parts of the eastern United States. I posted WPC’s latest predicted 3-Day rainfall totals to give a general idea of which areas could get the highest rainfall totals.

Latest Projected 3-Day Rainfall Totals From WPC:

Projected 3 Day Rainfall Totals

Do Warm Decembers Mean Winter Will Never Show?

Feb 1958 Temperature Anomaly Map

Around this time every year (mainly the years that I’m predicting a colder winter for certain regions), I start seeing this same argument from certain people: “It’s been so warm, so the forecast is a bust. Winter isn’t coming this year.” What always makes it a bit more humorous (or sad) is that those claims are often made even before the meteorological winter starts. Also, let’s not forget that this very warm December was predicted months ago, and I’d say that the majority of meteorologists were predicting a warmer December. Where my forecast really starts to diverge with others is later in January going into February.

But anyway, I want to dispel the myth that you can’t get brutal cold later in the winter if it’s very warm in December. It’ll only take me a minute.

The maps below show departure from average temperatures for a given month. The legend below each image shows by how many degrees the temperatures were above or below average for a given area.

December 1957:

Dec 1957 Temperature Anomaly Map

February 1958:

Feb 1958 Temperature Anomaly Map

If you’ve read my forecasts since July, you know that the 1957-58 winter has been a winter that I believe could be similar to this upcoming winter, although there will be some differences.

December 1984:

Dec 1984 Temperature Anomaly Map

January 1985:

January 1958 Temperature Anomaly Map

This was the winter that the historic Arctic outbreak occurred in January. But guess what? The prior December was exceptionally warm in the East! Even though this winter isn’t in my analog package for this upcoming winter, it proves my point.

December 2014:

Dec 2014 Temperature Anomaly Map

February 2015:

Feb 2014 Temperature Anomaly Map

But you know what’s crazy? You ONLY have to go back one year to prove that this argument is nonsense. Last December was very warm, but February 2015 was the first or second coldest February for many locations in the eastern third of the U.S.

There are MANY other reasons that you should be skeptical about my forecasts, but a warm December shouldn’t be one of them. I tell my followers to always question EVERYTHING, but keep in mind that I might just have a response to those questions. But this particular argument is one that I can always prove to be a myth. The ideas that I have presented to you are going to definitely be challenged by this upcoming winter. Everything is going right along with the forecast, but that doesn’t mean it will down the road. That’s what’s great about meteorology. Your ideas and research get challenged, questions get answered (sometimes only partially), and you become a better meteorologist as a result. That’s what science is.