Snow, ice brief update – 830 pm CST

The Arctic cold front has entered north Alabama, with winds turning to NW and temperatures falling quickly into 40s. Deeper into the cold air but not far away, it is 36 in Oxford, MS and 21 in Fayetteville, AR. That air is rushing toward Alabama partially to its own weight, at wind speeds 15-35 mph. The cold front will reach BHM, TCL, and GAD around 11 pm, and temperatures will go below freezing around 6 am.

Radar shows rain along and behind the front. There has been a lot of talk about snow and ice for tomorrow morning’s rush hour in central Alabama. It is difficult for precipitation to survive in an area of cold advection, where cold air is replacing warm air and therefore flows downhill slightly, drying up precipitation. In addition, the cold air will come in shallow,, so there will be a warm nose aloft preventing snow from reaching the ground (see figure).

Model sounding tomorrow 6 am Trussville. Note the area above freezing aloft (yellow circle)

The problem COULD BE a brief window tomorrow morning where there is still precipitation, likely rain, falling out of it, then reaching the ground and freezing, causing some icy bridges. This is most likely in north Alabama, but is even a possibility as far SE as I-59. Another possibility is that we get 1/2″ of rain overnight, and the cold air comes in so fast some of the water puddles freeze on a few bridges. The thing helping us out on this is the very warm ground temperatures, thanks to sunshine yesterday and BHM reaching 72 degrees today. I don’t see this as a big deal, but you definitely want to check weather in the morning before leaving home, and be careful on bridges and higher elevation roads.

The cold air will be downright crazy! Temperatures will hover between 30 and 35 degrees all day tomorrow in BHM, and with northwest winds 15-30 mph, wind chills will range between 5 and 20 degrees during the day! We will drop slowly through the 20s tomorrow night, ending up near 22 degrees Tuesday morning. We will be below freezing for 24 out of 28 hours from 6 am Tue through 10 am Wed, and 17 hours straight. Remember pets, plants, pipes. And most of all, the elderly or disabled who may not have access to safe, sufficient heat.

Dr. Tim Coleman

Consulting Meteorologist

Coleman and Knupp, LLC

http://www.colemanandknupp.com (check out our new website)

Major Arctic Blast Next Week

Current North American Temoeratures

Above is a map of current temperatures across North America. The large purple area covering much of central Canada, the Arctic Ocean, and Greenland, has temperatures below zero now, and some are below -20 F. We didn’t get any significant cold air flush outs in October (when it was still going above 100 F in parts of Alabama, Mississippi, and Georgia), but the sun angle has been low up in the Arctic for a while now and the days very short (0-7 hours long). So, cold air has really built up.

Over the next 2-3 days, a large upper-level ridge will build into Alaska, and the upper-level convergence on its east side will produce a large high pressure area in western Canada. Cold air is more dense and therefore heavier than warm air, and that will intensify the developing high pressure area. The shallow cold air will start to try to flow out of the dome of high pressure, but it will be blocked to its west by the Rocky Mountains, so it will be forced southeast into the U.S. starting this weekend.

Upper-levels (500 mb) and surface weather maps for Saturday morning (pivotalweather.com)

This is a very large and cold air mass. So its own weight, combined with the favorable upper-level ridge to the west keeping pressures high, and a surface low pressure area forming near the Great Lakes, will push this Arctic air deep into the central and eastern United States. By Tuesday evening, temperatures at 850 mb (about 5,000 feet) will be as much as 21 C (nearly 40 F) below normal for mid-November across most of the U.S. east of the Rocky Mtns.

850 mb temperature anomaly projected by GFS model Tue evening (pivotalweather.com)

A significant cold front will move through the Southeast US Thursday and Thursday night, with lows dropping below freezing north of I-20 (places like Little Rock, Nashville, Huntsville, and Chattanooga), and high temperatures Friday into the weekend will only be in the 40s and 50s over many areas. But this is not the main event. That moves through next Monday and Tuesday. Below is a graph of our predicted temperatures every 6 hours at Birmingham airport.

So, here we sit today near 70 degrees, we will drop to near freezing by Friday morning, have a normal, chilly weekend, then the cold blast will come Monday night. Temperatures will drop very quickly from the 50s in the early evening to the lower 30s by Tuesday morning, stay in the the 30s all day on Tuesday (with wind chills during the day in the 20s), then drop to near 20 degrees by Wednesday morning.

We have high confidence in this cold outbreak because of the ridge over Alaska and the large pool of cold air over the Arctic and Canada. Plus, all 3 major computer models (the American GFS, the Canadian GDPS, and the European ECMWF) all show this happening. A zoom-in on ECMWF model projected temperatures around the Birmingham metro ares on Wednesday morning is shown below.

ECMWF predicted temps Wed 6 am.

We didn’t have that much cold air last Winter, and if this pattern were to set up again in December or January, we could easily see temperatures near zero here in Alabama. With this cold outbreak next week, some locations in Arkansas and Tennessee may drop into the single digits, and a little snow is even possible, especially in the mountains of east Tennessee and western NC. This will be the coldest air since January 30, 2019 here in Alabama.

Interesting to note that the temperature hit 101 degrees on October 3 in Birmingham. If we drop to 21 next week, that will be an 80 degree drop in temperature in less than 45 days. This large of a temperature drop in 45 days has only occurred 5 other times since 1900.

This is the kind of cold air outbreak than can freeze pipes, kill plants, and harm animals. Go ahead and think about winterization around the home, such as covering outdoor faucets, draining water hoses, and winterizing boats. Make sure your antifreeze is good in your car and your tire pressure is sufficient (it will drop significantly next week). Once the cold air arrives, if you want any plants to live, bring them inside or cover them. Also remember that it is sometimes up to 5 degrees colder right near the ground than the official 2 meter temperature, so bring pets inside or at least make sure they have plenty of warm stuff to use inside a dog house, and dog house doors should never face north or west. Check on any elderly or disabled people you think might not have sufficient, safe heat. And check your own heating system if it hasn’t run this year.

Dr. Timothy A. Coleman

Consulting Meteorologist

Coleman and Knupp, LLC

http://www.colemanandknupp.com (check out our new website!)

Big time cold front!

The biggest cold front of the year so far will move through Alabama on Thursday. Temperatures will drop very quickly during the day, starting out near 70 at 7 am, drop to 55 by 10 am, then into the 40s during the afternoon. It will feel even colder, with northwest winds 10 to 20 mph. It will be about 25 degrees colder when you get home tomorrow evening than when you leave tomorrow morning, so dress appropriately!

Temperatures across the Southeast US show the strong cold front right now (1:45 pm CDT). It is near 70 across much of Alabama and Mississippi, but behind the cold front it is only in the 50s in central Arkansas, 40s in Fayetteville and Fort Smith, AR, then 30s in Oklahoma.

The cold front will tighten up overnight. Take a look at the computer model based temperature chart for tomorrow morning at 7 am. That is a huge temperature change over a short distance.

We may some light rain tomorrow, but it will likely move out in time for kids’ trick or treat activities. But it will be cold, so bundle them up! At 8 pm, expect 42 degrees with a wind chill in the 30s.

Early mornings this weekend we will get close to freezing, and many locations north of I-20 will get their first freeze of the year this weekend. There will probably be enough wind to prevent frost on Friday morning, but frost is possible Saturday and Sunday mornings.

Dr. Tim Coleman

Consulting Meteorologist

Coleman and Knupp, LLC

http://www.colemanandknupp.com

(See our new website!)

The heat in perspective

The above chart shows the 120-year average high temperatures in Birmingham, AL (black), along with the 1-standard deviation bands (where about 70% of all high temperatures should fall on a given date). Through most of 2019, temperatures stayed within these bands most of the time, so it was a normal year. Even the 100 degree days in August were not too far outside the normal. Note how the bands are tightly packed in the summer, meaning there is not that much variance from the normal in the Summer. The bands get much wider in the cold season. In late December, for example, high temperatures may be as low as the 20s or as high as the 70s!

But then, in September, we went into a very dry pattern, no cold fronts came through, and temperatures stayed very hot. Droughts and heat waves go together…the sun heats the ground which then heats the air, and if there is no water to evaporate, all of the sun’s energy goes into heating.

September 2019 was the 2nd warmest September on record with an average high of 94.5 and average temperature of 82.1. Only Sep 1925 was hotter. Sep 2019 was the 21st warmest month on record, period, beating out dozens of Julys and Augusts.

Using Coleman and Knupp, LLC’s 7-day moving average for all days going back decades, the expected distribution of high temperatures (and low temperatures) can be shown for any day of the year, in any city, with expanded precision. Below is the distribution for Oct 1, yesterday, for Birmingham. It is close to a normal distribution, with a median of 81 degrees, mode 83 degrees, standard deviation 7 degrees. We hit 99 yesterday, something that had never happened during the period Sep 29-Oct 4 before, so obviously it was a record high temperature.

But, using climate data from any site, we at Coleman and Knupp, LLC can custom design the probabilities of exceeding or going below any high or low temperature at any location, and the probability of given amounts of rain. This can be useful for planning weddings and other outdoor events beyond 2 weeks out, when we have essentially no weather predictive capability.

The good news is that a cool front may touch off come clouds and showers this weekend, cooling us off a few degrees, then a more significant cold front will sweep through early next week, making it feel a bit more like October. And, as the sun’s angle and the length of day are both decreasing rapidly now, the Northern Hemisphere has to cool off and more cold fronts will come to the eastern U.S.! Below I show the length of day at Birmingham across the year (solid), and the rate of change (dashed). Right now, our days are just under 12 hours long, and we are losing about 2 minutes of daylight every day. The Geochron-style image shows that the sun is illuminating more of the Southern Hemisphere than the Northern one now, too.

Dr. Timothy A. Coleman

Consulting Meteorologist

Coleman and Knupp, LLC

http://www.colemanandknupp.com

Cold front in July!

My forecast for temps over the next 4 days

A bona fide cold front is moving southward through the United States today, and will move all the way through most of Alabama, Mississippi, Tennessee, and Georgia tomorrow!

The term “cold front” is always used to describe the front edge of cool air masses that replace warmer ones. Of course, it is not going to get “cold” here in the Southeast U.S., but it will certainly feel much more pleasant than the sauna we have felt the past 3 weeks, with morning lows dropping near 60 degrees as far south as Birmingham and Atlanta, and daytime high temperatures only in the mid 80s.

Current temperatures (1 pm CDT)

The above map shows current temperatures from SE Kansas to NW Alabama right now. Some of the lower temperatures over parts of KY and AR are being affected by rain. But, it is 79 in Joplin, MO at 1 pm, and they have sunshine! So, this is a legitimate cool air mass. By tomorrow afternoon, winds will turn out of the north along I-20 from Jackson to Birmingham to Atlanta, and the cooler air will be moving in.

The air in places like Birmingham and Nashville will be coming from the eastern Great Lakes, as the NOAA computer model trajectories show below.

We will see some rain showers and maybe a few thunderstorms as the front moves through overnight and tomorrow morning. But, from tomorrow afternoon through Thursday, temperatures will be below normal. Some locations in the colder valleys of northeast AL, north Georgia, and east TN will easily drop well into the 50s.

Another big change that will make it feel nice will be the much lower humidity. Dewpoint is a meteorologist’s favorite measure of water vapor in the atmosphere because it is not affected by temperature, it simply indicates how much water vapor is in the air. The dewpoints over much of the Southeast U.S. the past few weeks have been between around 73, indicating a water vapor content of 17.5 grams of water vapor for every kg of air. Tuesday through Friday, dewpoints will be in the 50s, indicating water vapor contents dropping by 50%, to about 9 grams per kg. You will feel the difference!

Enjoy it, because with the strong, nearly overhead sunshine angle of July and August and warm soil, it won’t last, and we should be back into the 90s by the weekend. The humidity will come back too, with a big Gulf of Mexico nearby and water temperatures in the 80s.

Dr. Tim Coleman

Twitter @timbhm

http://www.colemanandknupp.com

Tropical Storm Barry – Sunday Update

High-resolution visible satellite picture

Barry is still considered a tropical storm right now by NHC, even though its maximum winds are out over open waters of the Gulf of Mexico. These winds are far from the center of circulation and lowest pressure near Shreveport, Louisiana, where winds are slowed by friction and thunderstorms are not as intense. Winds over most of south Louisiana as of 2 pm had dropped to 25-35 mph.

The big story with Barry now is the rain it is producing. The regional radar composite above shows a near solid wall of rain over the state of Mississippi, extending into much of eastern Louisiana and eastern Arkansas. Along the eastern edge of the area of heaviest rain, bands of thunderstorms are forming over parts of western and southern Alabama, and these may spread into central Alabama later today. There are also a few bands of thunderstorms over northern Georgia.

Some parts of south MS, extreme south AL, and southwest LA have already received 3-8″ of rainfall from Barry, and some rivers are already flooding. As Barry’s pressure continues to rise and the circulation weakens over the next 48 hours, the mass of rain will slowly decrease in size and intensity. But, even by Tuesday, with tropical moisture in place over the Southeast US, scattered afternoon storms will be increased, and some heavy rainfall amounts will occur from Memphis to Nashville and Paducah. The NOAA total rainfall forecast for the next 7 days reflects this increase centered near Memphis, with amounts over 7″ centered there, and amounts over 4″ expected in Little Rock, Paducah, and Jackson, TN. Rainfall amounts will drop off dramatically to the east over AL, middle and eastern TN, and GA, where less than 2″ is expected. Given the alignment of the rain maximum, some flooding along the Mississippi River, especially from Cape Girardeau south, is likely.

NOAA forecast 7-day rainfall starting now

One more interesting thing being picked up by upper-air weather balloons and computer models is the warm air aloft associated with Barry. Even though it has weakened to tropical storm winds, one can still see that temperatures at 500 mb (about 18,000 feet) are 10 to 15 degrees warmer above Barry than at other locations even over the Southern United States and the Gulf of Mexico. It is this warm air aloft, produced by the latent heat release in thunderstorms, that causes the air aloft to be lighter, and therefore cause the low pressure at the surface that drives tropical systems like hurricanes.

Dr. Tim Coleman

Twitter @timbhm

http://www.colemanandknupp.com

Tropical Storm Barry

USAF C-130 planes found flight level winds sufficient for the tropical depression in the Gulf to be upgraded to Tropical Storm Barry, with sustained winds near 40 mph. The center of Barry, is located south of Pascagoula, MS, and most of the strong storms are to the south of the center. This, along with wind shear and some dry air coming in from Texas, are not conducive for rapid intensification. However, Barry is over warm water in the shallow part of the northern Gulf, and the National Hurricane Center expects Barry to become a minimal hurricane by landfall sometime on Friday or Saturday in Louisiana.

The computer models are all over the place, and the center of the storm is still disorganized and, to me, unimpressive. But, my PhD is not in hurricanes like those guys, so the chance of it becoming a hurricane is still there. It looks possible that it could turn north a little earlier and come into Gulfport, Mississippi then move slowly through Mississippi as a tropical depression this weekend, but we’ll know more about the track once it develops a little more out in the Gulf.

The weather along most of the beaches from Mobile to Panama City will be OK the next few days. There will be more scattered storms than normal, but still occasional sunshine and warm temperatures. And no threat of tropical storm winds or storm surge. However, there will be rough waves and rip currents, and the water itself is closed to the public for now. Have to look at it from the beach or balcony.

The big threat to Alabama is from heavy rain over the next few days, especially Sunday through Wednesday of next week. Assuming the track stays further west near the Mississippi River, we should only see an increase in afternoon storms around here and 1-3″ of rain over the next few days. But, if it turns north earlier and comes up through eastern Mississippi, we could see a flooding threat, with 3-5″ of rain, more in west Alabama.

Another update on Barry and possible effects on the weather here in central Alabama, coming up on Saturday.

Dr. Tim Coleman

Twitter @timbhm

http://www.colemanandknupp.com