Tornado outbreak expected today in mid-south

Some severe weather is expected in the US this afternoon – here is the warning graphic from the US Weather Prediction Center (WPC):

WPC Forecast – red areas are at risk of severe thunderstorms that may product tornadoes

An active and dangerous day of weather is set to unfold across the
Mid-South today, highlighted by a High Risk of severe weather issued by
the Storm Prediction Center. The primary weather driver of this impending
tornado outbreak is a strengthening area of low pressure out ahead of a
sharp and intense upper level trough tracking into the middle Mississippi
Valley and Ohio Valley this evening. Powerful thunderstorms are forecast
to blossom in the South this afternoon and track into the Ohio and
Tennessee Valleys tonight. These intense thunderstorms are may contain a
myriad of hazards that include violent long-track tornadoes, damaging wind
gusts, and large hail. In addition to the severe threats, hydrologic
hazards are also a serious concern from northern Alabama and Mississippi
to the Tennessee Valley and southern Appalachians. Torrential rainfall
rates in these areas that also contain overly saturated soil is a recipe
for flash flooding. As a result, a Slight Risk of excessive rainfall is in
place with a Moderate Risk located over northern Alabama, northwest
Georgia, and southeast Tennessee. Residents in these areas should have a
plan of action if severe weather threaten their respective locations. In
addition, high winds from the lower Great Lakes to the northern
Mid-Atlantic Thursday night into Friday morning. High Wind Watches are in
place for portions of these regions as strong winds may result in downed
trees and power lines.

From WPC Discussion as of 8am ET, 25 March 2021

None of this is expected to make it into the coastal GA/SC area. In Savannah GA for example, there is only a slight chance of thunderstorms Friday afternoon, and again Sunday into Sunday night.

#Severeweather risk to Coastal #Georgia, SC today …

The storm system that has already spawned tornadoes across the south continues to sweep eastward this morning …

Radar composite Thursday Morning, 18 March 2021

Inland areas of Georgia are likely to see strong thunderstorms today, with the potential for more tornadoes. It’s going to be a busy weather day. But, being self centered, what about the coast? TLDR: be prepared, hopefully you have a weather radio handy for alerts. There is a good potential for strong winds and intense thunderstorm cells, and some potential for tornadoes. For Savannah/Hilton Head, arrival times look to be at 3pm, with the main line passing through Savannah around 4pm. Here is the latest (6am) High Resolution Rapid Refresh model forecast for 3pm EST:

The wind and simulated radar at 3pm ET from the HRRR model 5am run. Click any image to embiggen

The strongest storms should stay west (inland) of I-95, and there is an area to the north of the Hampton SC area that has some potential for stronger storms and tornadoes. In the above model run you can see that area of severe storms approaching stretching up to Walterboro. But the entire region should pay attention to this event and be prepared to take shelter from any tornadoes that form. Here are some tornado preparedness tips from FEMA/DHS.

As for the details, like most things it’s complicated. As a start, while forecasts are much better, with high resolution tools running hourly to update the forecasts, this is still a dynamic situation with some uncertainty. It seems the risk along the coast is lower based on the latest data, however, here is what the National Weather Service’s office in Charleston has to say:

IMPORTANT MESSAGE: After much internal collaboration with the SPC and neighboring WFOs this morning, the earlier “moderate risk” has been replaced with an “enhanced risk” for given the continued uncertainty on how stability profiles will evolve through the day. This action SHOULD NOT be misconstrued as a lowering of the severe risk for the area as conditions still remain favorable for a potential outbreak of severe tstms some of which could produce a few strong tornadoes. It is simply an attempt to better message the uncertainty with how widespread today`s severe weather will be. Media partners are asked to help
convey this critical message today.

From NWS Forecast discussion as of 622 AM EST, Thursday 18 March 2021

It will be interesting to see how local media handles this request. Asking local weather forecasters to continue to push a message that things have the potential to be bad is likely to be successful 😛 . But … it also needs to be clear that despite the need for vigilance, these storms might well break up as they reach the coast. I’ve seen some comments that they never come here. Well, sometimes they do … so be prepared.

US Winter Storm hits in Winter!

There is a typical winter storm forming up over the US, bringing gusty winds and rain to the Southeast, and snow to the Northeast. Because, um, it’s winter 😛 …

Surface map over satellite image … click to embiggen.

Fortunately there is enough other news that everyone other than that weather channel are too preoccupied with other “breaking” news to blow this out of proportion, although adjectives like “major” are being thrown around. But it’s a strong storm, so here’s that cool swiper thingee so you can see the radar and precipitation type by grabbing the pointer with your mouse (finger on a touch screen) and slide between views.

Slide left to see precip type (white-snow, blue=rain, cyan=ice_so_be_careful), slide right to see intensity.

The usual impacts from this kind of storm, nothing catastrophic in store if people use common sense (well, I can hope!). Tomorrow will be a messy start to the week, I see that some cities like New York are taking precautions like closing schools and shifting to on-line instruction (a sad consequence of COVID is kid’s don’t get snow days so much any more). There is another storm system hitting the Pacific as well, that has washed out a chunk of the Pacific Coast Highway (caution: link goes to insufferably preachy news source, but does have drone footage).

Busy in the South Pacific; Storm brewing over the US

We have three cyclones in the South Pacific, with two of them criss-crossing Fiji and one off of Australia headed towards New Caledonia …

Cyclone Ana is just past the main islands of Fiji, having passed over the capital and causing a lot of flooding. Right behind it is Cyclone 16, which may not reach hurricane status but will cause even further damage and misery. To the west is Cyclone Seventeen, which is headed towards the French territories of New Caledonia. It may reach major cyclone status before turning south towards the islands, is forecast to be a weakening tropical storm as it passes over the Loyalty Islands (the group of islands just to the right (east) of the “New Caledonia” label on this map).

Watching the developing Nor’easter on the US East Coast. It is windy here in Savannah this morning and rain should be moving by this afternoon, erasing the pretty blue skies. Be careful on bridges in the area this afternoon – the National Weather Service issued a special weather statement for the coastal GA/SC area, with winds expected to pick up to 35-40mph. Will try to do a post around lunchtime with the details …

US #Icestorm developing …

There is a huge frontal system slowly grinding to a halt across the US, with a low pressure system forming at the tail end over Texas. Here is the current synoptic weather map …

Synoptic weather map as of 7am ET with IR Satellite image

… and MRMS radar composite as of around 9:30am Thursday.

The low is expected to scoot up along the front, and over the next two days there is an increasing chance of a major ice storm event in an arc from Texas to the Northeast. In the this animation, the orange areas are areas where ice accumulation is possible:

GFS Simulated Radar and Precipitation Type for next couple of days (Thu/Fri/Sat). Click to embiggen.

Ice is a lot bigger problem than snow. Ice is a lot denser than snow, and tends to stick to and accumulate on things like tree branches and power lines (not to mention making roads just about impassible). The extra weight means branches and even whole trees breaking, and power lines coming down. So expect scattered outages across a wide swath of the US this New Years. The DHS/FEMA site has some advice on how to prepare for winter storms. So as you celebrate the new year, be careful!

Severe weather approaching Coastal GA, SC

The Charleston WSFO has raised severe thunderstorm warnings for most of the area, and a tornado has been detected near Hampton SC. Here’s the radar at the moment (just before 6:30pm Christmas Eve) – the tornado is the bright white dot just north (up) from the black circle of no data over the radar station …

Make sure your weather radios are on, or your mobile phones have the emergency alerts active … could be a busy hour or so.

The Coming Storm

No, not that one. Or that one. I mean the literal one, this one, the first big winter storm of the season. Here is the situation as of this morning (map forecast for 8am ET Wednesday, the storm is the “L” off the Georgia Coast):

Winter storm forming over Southeastern US … GFS model of precipitation type and moisture transport.

Like hurricanes, winter storms have to have a mix of conditions come together to cause them to grow and evolve. The key to weather on the earth is the need to balance the warm, moist air from the tropics with the cold, dry air over the poles. This happens in a number of ways, but in the summer the most dramatic are of course hurricanes. In the winter, it’s nor’easters. A classic nor’easter starts out as a low pressure system just off the coast of the Southeast. It moves northeast along the coast, carrying with it the warm moist air of the Gulf of Mexico and Bahamas, pushing that air inland where it meets cold polar air. It is along that swath where the air masses collide that the potential problems for Humans comes in. The danger this morning lies Appalachians and western North Carolina where the precipitation may be in the form of freezing rain, as well as inland in Kentucky (on the map, the red/purple area). Here is what things should look like this evening around 7pm. Notice that the low is deeper (stronger), the blue moisture transport vectors are longer (stronger), and across the New York/Pennsylvania area snow will be falling. The zone of freezing rain will by then have shifted to western Virginia.

The situation tonight …

By tomorrow morning the Low should be more elongated and off the Massachusetts coast, still pumping moist, snow-laden are into the NorthEast. The storm should be off the Canadian Marine Provinces by Friday.

Thursday Night

In terms of impacts, again the big concern is the area where freezing rain and ice will be falling. For the Northeast, snow could be fairly deep in places – some forecasts are for up to 24″ – but it’s more likely to be disruptive rather than truly dangerous, and again conditions should clear out by this weekend. For the Deep South (GA/SC), this will be a rain event, even for North Georgia. As things continue to cool off with the approaching winter season, the risk for ice storms will move further south … but the impacts of this event will be in North Carolina and the NEUS. How should you prepare for winter storm season? Take a look at the FEMA/DHS Winter Storm page for tips …

So what’s the weather going to be on Thanksgiving?

This year people are more attuned to the weather – for good reason. Given COVID19, gatherings outdoors are far safer than inside, so the weather is a bigger factor than usual. I’m getting a lot more questions like “what’s the weather going to be like next St. Swizzen’s Day” – be it for a holiday, wedding, birthday gathering, protest march, golf game, or whatever. My usual reply is “I study disasters; if I can tell you then you probably don’t want to know” doesn’t make people happy 😛 Of course I’ve got the tools here to do pretty much any kind of forecast from “nowcasts” to climate, but how does the average person answer that question without annoying their favorite scientist/blogger? Which provider is best? As it turns out, that’s an easy question to answer. Your tax dollars have funded a really great organization, the US National Weather Service, and they have some nice on-line tools for planning your holiday. Virtually all the other providers – be it big companies, TV stations, whatever, are using NWS data and perhaps “adding value” (although in most cases I’d argue they are adding FUD, but that’s a different post). So lets walk through using the NWS web site to see what tools are available, and if you can hold that Thanksgiving gathering outside, or if everyone will have to stay home and use video …

The starting place is https://www.weather.gov. Here’s what the main page looks like. Any warnings will be color coded:

The map is clickable … click on the location you’re interested in; it doesn’t have to be perfect, you’ll get the chance to refine it. But for your home location, enter the place name you want in the box on the left. You can use a zip code or place name – for example, you can enter “Ardsley Park, Savannah, GA” and the system will give you matching names …

If you click “remember me” then whenever you go to weather.gov your local forecast will pop up on the left side. Clicking “Get detailed information” and you will jump to the point location forecast … here’s where you can really get into seeing what is going on:

The page itself is a nice overview, but if I’ve got family coming over at 4pm Thursday, with dinner at 6pm, and people will probably start to go home at 8pm. How likely is it that we can eat outside at the picnic table, or will I have to set up tables all over the house inside, or just cancel? Jackets, build a fire in the fire pit, or Savannah being Savannah will we need bug spray? If you scroll down and look under the map on the right there is a box called “additional resources” …

Click the graph and you get the hourly forecast data.

You can change the date to see up to a week in the future; in this case let’s set the start point at 12am (midnight) on Thursday. Click submit and you get:

So for Ardsley Park area in Savannah, the temperature should be 70 degrees, light wind, 31% Cloud Cover. The precip chance is 18% – but if you look at the graph, it never gets above 20%, and drops to only 8% by 7pm, so chances are this is not a sharp rain producing weather system. Now that you’ve tagged this as your “remember me” location any time you to to weather.gov on that device it will have your forecast on the main page – and you can easily get the very detailed details!

But what if you are travelling? Just click on the national map … it will take you to the forecast for that point. In this case, as noted on the first map I directly clicked on Andrews NC, then got the “additional details” to see the timing and intensity of any rain:

Looks like rain overnight Wednesday (80% chance at midnight!) and perhaps Thanksgiving morning, but will clear out and be nice overnight, with rain maybe coming back Friday night (back up to 30% chance) .

When planning an event, obviously the closer in time the better the forecast. By the time we’re within three days they are pretty good; 3 to 5 days are fair, over five days takes some interpretation. I’ll try to do some more posts on that in the future, but hopefully this will get you started …

You Got The Fire Down Below …

The fires out west are epic – you can actually see the flames from the GOES satellite in geosynchronous orbit, 22,236 miles up … here is the color view:

Click to embiggen and animate …

Here is a static view zoomed in a bit:

Yes, those red patches are actually fire!

These fires, and their impacts, are a wicked combination of short term weather patterns, human development and “management” practices, the natural order of things (fires are a normal way nature cleans out the brush; some plants and animals that depend on them actually need periodic fires to survive), and probably a bit of climate change thrown in. Either way, it’s spectacular (in a bad way if you live out there).

So what’s a derecho? (and a tropical update)

It’s fascinating to see how some terms that are used in specialist setting make their way in and out of journalistic usage. It seems that Derecho is one of those that I’ve seen more of in the last few years. The term has been around since the late 1800’s, about the same time this painting by John Curry was made …

“The Line Storm,” by John Steuart Curry, 1897-1946, a painting possibly inspired by the approach of a derecho-producing storm in Curry’s home state of Kansas. (Oil and tempera on panel, 1934; Collection of Sidney Howard, New York; Lithograph in Smithsonian American Art Museum, Washington, D.C.)

A derecho is a straight-line wind system associated with a mesoscale convective system (in other words, high winds associated with a group of stable, fast moving thunderstorms). They can cause winds over 100mph and damage over a wide area. Here’s a nice overview from the Storm Prediction Center (SPC).

Yesterday a derecho moved over the US midwest causing a lot of damage (NY Times Article). Here’s an animation of the low-level radars from the region …

Midwest RADAR composite, Monday Afternoon, 10 August 2020

This system has caused 10’s of millions in damage across the region. This was a strong and extensive MCS/Derecho, but derecho’s aren’t uncommon. A system like this happens somewhere in the midwest every 4 years or so.

In the tropics, still watching AL95. NHC has it as a 70 percent chance of spinning up, which seems more likely this morning. However, in a few days it will be moving into unfavorable conditions, so even if it does, its long term risks are still low right now. Typhono Jangmi has hit South Korea, causing mudslides and flooding, and killing at least 30. This year has been extremely wet across parts of Asia, and while there have been no severe typhoons thus far, the rain and flooding has caused extensive damage. Sadly, aside from a few brief articles noting the risk to the Three Gorges Dam, I haven’t seen lot of coverage of this in the US media.