More Severe Weather and Cooler Weather for Some

I’ve been absent from the Firsthand Weather website these last few days, but I’m hoping to start writing blogs a bit more consistently starting in May. This is usually the time of year that I begin to do a lot of my research on the upcoming hurricane season, summer/fall, and winter 2015-16. You won’t hear me saying anything about winter until later in the summer, but in the next few weeks, you will hear a lot more from me regarding the hurricane season. I’ll have an announcement on that soon.

April has been rather warm across much of the United States with a very active and wet pattern from the Southern Plains to the Gulf Coast states and extending into the Tennessee/Ohio Valley. For those of you in those mentioned regions, particularly if you’re in a place like Texas, I’m sure I just stated the obvious. This wetter pattern is going to continue for most of those regions, although a stronger trough in the eastern parts of the U.S. could begin suppressing moisture farther south next week.

In meteorology, you hear a lot about the North Atlantic Oscillation (NAO) and Arctic Oscillation (AO), with both being particular important during the winter months. When there is blocking (warming) over the Arctic and Greenland, this can displace colder/cooler air farther south into the mid-latitutides, which includes parts of the U.S. The NAO is about to go into a negative phase and the AO into a neutral/slightly negative phase, which is something that didn’t occur much of last winter. Although this will be brief, this pattern will be bringing unseasonably cooler weather for much of the eastern third of the U.S. this week and particularly into next week.

GFS departures from average for early Monday morning:

departures from average

Ridging will be pretty persistent over the southern Gulf Coast states into Florida, which should keep those areas warmer, but the models do try to dig the trough pretty far south next week, which could bring a day or two of cooler weather. Although the southern-most regions could experience some of the cooler weather, the more noteworthy cooler temps will be farther north. The mid-section of the country will consistently stay warm with more volatile temps on the West Coast.

As far as heavy rainfall and severe weather, a heightened severe weather threat could set up across the Southern Plains towards the middle of this week, which I will discuss in detail in another article. A piece of energy from the Southwestern U.S. is going to eventually get absorbed into the eastern U.S. trough towards the weekend, and surface low pressure system will likely develop/strengthen as a response to the overall pattern. I expect more moisture to get pulled up from the Gulf this weekend as this low moves east, and the conditions could be favorable across portions of the Gulf Coast states for a severe weather threat. This would not be as far north as today’s severe weather, but it is something to keep an eye on for those a little farther south.

Wetter conditions are definitely possible again for many areas this weekend:

GFS wet

As you can see, there is a lot going on. Although this upcoming pattern will favor cooler temperatures for some, it’s important to understand that this pattern will likely not persist for most of those regions. A window will likely remain open for severe weather/tornadoes through at least much of May for the typical tornado-prone zones and even across portions of the Gulf Coast states, Tennessee Valley, and eastern U.S.

Tornadoes, Some Strong, Likely To Impact U.S. Today

I posted a fairly lengthy discussion on the site the other day on this upcoming severe weather potential. Due to being busy this week, I’m not going to be able to make my own maps like I promised, so the SPC’s convective outlooks are going to have to do. SPC typically does a very good job when predicting these kinds of events!

Anyway, if you want a more detailed discussion, please refer to my older article, which is still fairly up-to-date. The environment is becoming very favorable for the development of discrete supercells later this afternoon, and I expect some of these cells to become tornadic. I won’t get as much into the thermodynamics and kinematics today like I did the other day, but I do want to show you a visible satellite image.

satellite image

As you can see, the cloud-cover is very thick over much of Texas into central Oklahoma due to storminess over the area. That doesn’t mean that tornadic storms won’t develop in that region, but if this cloud-cover can stay thick enough, it will hinder the environment from becoming as unstable. There is a pretty sizable cap over the region, so daytime heating will be needed to erode that cap.

However, the residents in the area farther north and northeast of the region mentioned above need to watch today’s severe weather situation very closely. The hotspot will be from north and northern Oklahoma, southeastern Kansas, across Missouri, and into Illinois, where tornadoes (possibly strong and long-track) could occur. As you see on satellite image, there are breaks in the cloud-cover so the atmosphere is continuing to become very unstable over that region.

Here is SPC’s tornado probability map. Especially if you’re in the black hatched region, you need to be prepared for the potential of tornadoes, some of which could be strong. Always have a plan in place, and have a way to get alerts from your local NWS office.

SPC tornado forecast

Don’t Forget To Bring The Umbrella This Week!

It is VERY late, so I’m guessing that about two people will read this article. Anyway, if you read my article that I posted earlier on the severe weather/tornado threat, you probably already know where most meteorologists and weather forecasters will be focusing all of their attention this week, unless they forecast locally. I don’t want to neglect the regions farther east since many locations across the eastern half of the U.S. will be getting several inches of rain.

Brief Discussion:

Dry surface high pressure is currently moving off the East Coast, while upper-level ridging is building over the eastern half of the U.S. This ridge is going to continue to build throughout the week, but it is going to remain very flat. The overall flow (wind) aloft will be from the southwest/west, so this should pull in warm and moist air from the Pacific. Closer to the surface in the lower-levels, the pattern is going to favor moisture and warm air getting pulled up from the Gulf of Mexico.

Later in the week, the surface low pressure system that’s going to develop in response to the upper-level trough in the western United States (the feature responsible for the coming severe weather) will be moving from the Plains and will eventually shoot northeast. As this system moves across the U.S., warm and moist air will get pulled up from the Gulf of Mexico into the warm sector of the system, which is south of the warm front and ahead of the cold front.

Without getting into the nitty gritty details, get ready for rainy and stormy conditions across the Deep South, Mississippi Valley, Tennessee Valley, Ohio Valley, and all the way to the East Coast. Oh by the way, parts of California will be getting some beneficial rain/mountains snows! I shared WPC’s 5-day rainfall total forecast. You’ll have to forgive me for not making my own map.

WPC’s 5-Day Rainfall Total Map:

WPC’s 5-Day Rainfall Total Map:

Multi-Day Severe Weather/Tornado Threat This Week

This upcoming week is likely going to bring one of the biggest severe weather/tornado threats that has been seen in quite a while. Over the past two years, the tornado season has been unusually quiet, and this year hasn’t been any different so far. I mentioned on the site and on social media several weeks ago that I believed that a window would open up later in April going into May that could prove to be active and quite dangerous. We are quickly approaching that window, and this week will be the beginning of a several week period of severe weather across parts of the United States.

Before I get into the details on this week, I want to point out that some of the most memorable tornado seasons are years that were not-so-active. One recent example of that would be the 2013 EF-5 Moore tornado, which occurred during an anonymously quiet season. Regardless of the overall numbers when everything is all said and done, I can assure you that the people who are impacted by a tornado care nothing about averages, because to them, it was a bad season. With that said, the period we’re entering could bring an average to above average number of tornadoes, so I do believe we’re about to come out of this “tornado drought.”

Persistent mid and upper-level ridging over the western U.S. and Alaska (due to warmer waters in the Gulf of Alaska and along the western U.S. coast) has kept the overall pattern unfavorable for severe weather over the last couple of years. However this week, there’s going to be a change in the overall pattern, with troughing developing over the West Coast and broad ridging farther east. In fact, medium and long-range model guidance continues to hint at this being a trend the rest of this season. I believe this will be the case at least through parts of April going into May, and we’ll just have to wait and see what happens beyond that. All of this means that a more active severe weather period is probably on the way.

I want to briefly break down this week’s severe weather/tornado threat. Keep in mind that there could be an outbreak of tornadoes on Wednesday and Thursday. I use the term ‘outbreak’ loosely because different people interpret that differently than others. In this article, I’m going to use SPC’s maps, but I’ll be making my own maps and will try to have them posted by sometime Tuesday.

Tuesday:

The atmosphere is going to be very unstable across the Southern Plains on Tuesday, but it seems that a strong cap is going to be in place. A cap is a warm-layer of air on top of a cooler-layer of air at the surface. It’s almost like putting a lid on the atmosphere, which hinders storms from developing. If those air particles can’t rise, then they can’t cool (adiabatically), condense, and develop into towering clouds and produce precipitation. However, there are times when this cap can be eroded away with a certain mechanism, such as heating the surface, adding moisture to the atmosphere, or a favorable pattern forcing the air upward vertically or moving that above-the-surface warm-layer out of the area.

This is the exact situation that we have on Tuesday. IF the cap can be taken care of, then supercells capable of producing severe weather could occur and maybe even produce a few tornadoes. SPC has only placed a marginal risk for severe weather across parts of the Southern Plains, not because they don’t think these storms will be severe but because it’s uncertain whether or not they’ll actually develop due to the cap. Hopefully that makes sense, and let’s hope that the cap holds strong.

SPC’s Tuesday Outlook:

SPC's Tuesday Outlook

Wednesday and Thursday:

All of the ingredients are going to be in place to support the development of supercells across portions of the Southern Plains on Wednesday, and that threat will shift farther east on Thursday, which will include parts of the Southern Plains and extending northeastward into the central and upper Mississippi Valley and approaching parts of the Great Lakes.

Moisture is going to get pumped northward from the Gulf of Mexico, and the heating of the day will make the environment very unstable. Wind shear (the changing of wind direction and speed with height) is going to be favorable for storms to develop, maintain their strength, and rotate. The mid and upper levels will be supportive enough to lift the air up through the atmosphere, causing air particles to cool, condense, and form towering clouds and precipitation. All modes of severe weather including tornadoes will be possible. The low-level winds will also be supportive (another necessary component) for the development of possible tornadoes.

Even though the main focus seems to be on Thursday, which I agree could be a big day, Wednesday needs to be watched just a closely. Storms that develop on Wednesday could carry over into the next day, and that will need to clear out in order for the environment to be as conducive for discrete supercells. All of the necessary ingredients will be available both days, but it only takes one small hindrance to cause a bust. At this time, I don’t expect this to be a bust for either day, so residents that are in the zone outlined on SPC’s maps below need to adequately prepare for this potential outbreak of severe weather.

Again, I’ll post my own maps on Tuesday and will also try to post another article. If I see that the severe weather threat is going to extend farther east beyond Thursday, I’ll detail that later in the week.

SPC’s Wednesday Outlook:

SPC's Wednesday Outlook:

SPC’s Thursday Outlook:

SPC's Thursday Outlook:

Tornado Potential Across Tennessee and Kentucky

A cold front is currently located from Texas through the Tennessee and Ohio Valley and northeastward. A broad surface low pressure system is currently moving from westward Kentucky into Ohio and will continue to strengthen as it moves northeast. In the mid to upper levels of the atmosphere, a couple of features are going to phase together (combine) to further enhance the tornado potential throughout the day.

Temperatures have warmed up across the Deep South into Tennessee/Kentucky as the sun has been able to break through the clouds farther north while cloud cover has been considerable less farther south, allowing even more warming. Moisture is pumping northward ahead of the cold front, and wind shear has continued to increase (an important ingredient for tornado development), particularly over parts of Tennessee and Kentucky.

Low-level wind shear is considerably weaker farther south into northern Mississippi and Alabama but farther north into central Tennessee and Kentucky, it increases substantially. Deep-layer shear is also sufficient for tornado development over parts of Tennessee into Kentucky. The threat will continue to shift eastward over the state as the day progresses.

The area that I am watching most closely for potentially tornadic storms is around Nashville, TN and extending northward into Bowling Green, KY through or just south of Louisville. The threat will initially be slightly farther west but will eventually move east into the mentioned regions. Later today into tonight, the tornado threat will likely shift even farther east, although it will die down as the night progresses. I made a map and posted it below. Although tornadoes could occur outside of this zone, this is the region I’m watching most closely.

I’m keeping a close watch farther south of my threat zone also. Although wind shear is not as sufficient, a tornado or two will still be possible even into extreme northern Alabama and Mississippi. Damaging winds and hail will be bigger threats, but I felt that was worth mentioning.

Firsthand Weather tornado threat map

Tornado Risk Later Today and Tonight

A window is going to open up later this afternoon into the evening hours for an enhanced tornado threat to develop from northeastern Oklahoma, southeastern Kansas, southwestern and southern Missouri and northwestern and northern Arkansas. The tornado threat will not be exclusive to these regions; however, this is the area in the great threat zone.

A stationary frontal boundary is currently located across the Southern Plains into the Mid-Mississippi Valley. The atmosphere has continued to become unstable as breaks in the clouds have allowed the sun to heat up the surface. The biggest question has been whether or not the heating of the day would be sufficient enough to erode away a capping inversion (cap). A cap is a layer of warmer air on top of cooler air located in the boundary layer (the layer of the atmosphere in contact with the surface). When this occurs, that air gets trapped and can’t rise. When that lowest layer sufficiently warms, then the air is able to rise, condense, and form clouds and storms.

Wind shear (changing wind speed and direction with height) is currently sufficient along with several other ingredients. I made a tornado risk zone map to give you an idea of who will have the greatest risk of seeing a tornado. Keep in mind that areas just outside the outlined region also need to keep an eye on everything.

Firsthand Weather tornado map

In addition to a tornado threat, damaging winds and hail will be a possibility with any storm that develops. Storms are already firing from the Southern Plains to the Mississippi Valley, Tennessee and Ohio Valley, and Southeast. The environment is very moist and humid over a very expansive warm-sector. Many people are either currently being or will be impacted by storms today.

I posted SPC’s convective outlook below. If anything changes, I’ll post an updated map.

spc convective outlook

Stunning Images from Space of Super Typhoon Maysak

Some of you have probably already seen these photos, but I had to share for those of you who may have missed them. Earlier today, astronauts from the International Space Station tweeted out several photos (from space, obviously) of Super Typhoon Maysak. I can honestly say that these are the most incredible photos that I have ever seen of a typhoon/hurricane from space.

Typhoon Maysak has weakened from its previous super typhoon status, but it still has sustained winds of 140 mph with gusts to 165 mph. This typhoon is currently heading towards the Philippines. The western Pacific has already had an active season so far, which is due to a number of factors such as warm sea surface temperatures, a developing El Nino, and the MJO.

Now that I added a tidbit of science to the mix, I’ll show you the photos. All of the photos below are courtesy of NASA and Astronaut Terry Virts.

Super Typhoon Maysak Image 1

Super Typhoon Maysak Image 4

Super Typhoon Maysak Image 5

Super Typhoon Maysak Image 2

Super Typhoon Maysak Image 3