Winter Weather

November 13, 2023 Outlook: Late season tropical system possible in the Caribbean, and we check in on — Alaska?

One-sentence summary

Today’s post talks about the potential for a late season tropical system in the Caribbean this week, as well as a detailed look at polar opposite weather that’s causing trouble in Alaska lately.

Tropical update: Caribbean mischief may present itself this week

We’ve got ourselves a late season system to possibly monitor in the southwest Caribbean later this week.

The Southwest Caribbean is highlighted with 60 percent odds of development this week by the National Hurricane Center. (Tomer Burg)

Model guidance is pretty persistent in developing low pressure off the coast of Nicaragua or Costa Rica around Wednesday or Thursday. It would quickly move northeast or north-northeast toward Jamaica, eastern Cuba, or Hispaniola from there, before accelerating out into the open Atlantic, perhaps impacting Bermuda on the way out this weekend. This will all occur quickly.

The GFS (left) and Euro (right) offer two differing outcomes but the same broad idea for the potential track of low pressure out of the Caribbean. (Tropical Tidbits)

As is often the case this time of year, the GFS model is much more aggressive with this system than the European model. The GFS has the equivalent of a strong tropical storm or low-end hurricane racing northeast of Jamaica on Saturday, whereas the Euro is a bit slower and notably weaker. The Euro has had a slightly better track record in the Caribbean, but it’s still a good idea for eastern Cuba, Jamaica, Haiti, and the Dominican Republic to monitor this potential system in the coming 2 to 3 days. From there, the Bahamas, Turks & Caicos, and Bermuda should also keep tabs on things. Whatever happens will happen fast, as this thing is going to be hauling north-northeast, tracking from the deep southwest Caribbean on Wednesday or Thursday to past Bermuda by Sunday or Monday.

U.S. Weather this week: Stormy Gulf, wet West Coast

A storm system on the Gulf Coast over the next couple days will bring some moderate to heavy precipitation between Texas and Florida, with anywhere from 2 to 5 inches likely. The highest totals are likely near Mobile, AL and Pensacola, FL. Flooding isn’t expected to be a huge concern, as the entire region is in pretty serious drought, and if anything, this will be a mostly beneficial rainfall.

This week’s rainfall will be mostly minor, except on the Gulf Coast and in coastal California and the Cascades. (Pivotal Weather)

The West will see a few surges of moisture this week thanks to a storm sitting offshore of California. This is expected to bring moderate to locally heavy rain to coastal California and some snow in the Sierra.

Rain totals have come off some versus a few days ago in California, but a wet period is expected this week. (NWS Monterey/SF Bay Area)

Overall, this should be more of a periodic ramp up/ramp down type precipitation event for California, but the rain (and snow) will add up over time. About 1 to 3 inches of rain is possible on the coast, including both San Francisco and LA, with locally higher amounts in the mountains and perhaps a little less in San Diego. Flooding isn’t a major concern at this point, particularly as the forecast has trended a little less excited about things.

Flaked Alaska: Heavy snow causes familiar problems in Anchorage

We don’t often talk about Alaska for weather unless it’s due to the pattern up there impacting the pattern for the weather across the U.S. But it’s worth talking about what’s happened in parts of Alaska to start November.

Precipitation to start the month in Alaska has been extremely heavy, with over 200% of normal for the period in southern Alaska, including the Anchorage area. (Brian Brettschneider)

Anchorage, the largest city in Alaska, with a population near 300,000 has received nearly 30 inches of snow this month so far, most of it courtesy of an atmospheric river event last week. This is the snowiest start to November on record in Anchorage. I reached out to the authority on all things Alaska weather, Brian Brettschneider, and I asked him to put into context how this sort of big time snow fits the typical climatology for Anchorage.

First, he tells me that the median snow depth for Anchorage around this time of year is about an inch or two. The snow depth there is around 2 feet, which only happens in maybe half of all winters at all there. “This snow will not fully melt out until April,” he says.

On top of that, this was a wet snow for Anchorage. What do we mean when we say “wet snow?” A number of factors play into what we call the “snow ratio,” or how much snow you would melt to get 1 inch of water. In general, colder and drier air masses produce higher snow ratios. It takes more snow to get that 1 inch of liquid. You see this a lot with lake effect snow. One inch of liquid may produce anywhere from 20 to 30 inches of dry, fluffy snow.

Warmer, more humid air masses tend to produce lower snow ratios, or situations where it does not take as much snow to produce an inch of liquid. A general rule of thumb, particularly on the East Coast, is that 10 inches of snow usually melts down to 1 inch of liquid. So the ratio is 10:1 (ten to one). In Anchorage, a colder and typically drier place, Brettschneider says that the average ratio is 17:1 typically. With this recent event, the snow ratio was 11:1. I wouldn’t call that “cement,” but that’s a very wet snow for Anchorage. Wet snow tends to be harder to move and clear, it can bring down trees and power lines, and it also causes significant issues on roadways as it will produce slush that can freeze into solid ice. This is one problem in Anchorage right now.

And it’s not a new problem either. Brettschneider said that it’s important to understand the current context of the situation in Anchorage. “Three rapid succession storms last December caused a month-long road-pocalypse around town. The state/city made it a priority to not let that happen again – yet here we are.”

Last December, Alaska Public Media asked “Should snow in Anchorage be this disruptive?” In a follow up article last month, APM reported that Anchorage said it was prepared should a storm like last December’s happen again. Anchorage mayor Dave Bronson said at his October news conference, “We are ready.”

The residents of Anchorage can decide if that’s the case. The second major multi-day snowstorm in Anchorage in less than a year is surely impressive. It’s also worth noting that despite the snow, it has not been cold in Anchorage, at least not compared to normal. “So far this month, the first 11 days are all warmer than normal in Anchorage – much warmer than normal,” per Brettschneider. It typically takes someone milder weather to produce this kind of snow in Alaska, as warmer air can hold more moisture.

On a serious note, the AP reports that four unhoused people died during the winter storm in Anchorage last week.

More snow is coming to Alaska today, including Anchorage.

The forecast through Tuesday afternoon in the Anchorage area calls for about another 6 inches of snow. (NWS)

As much as another half-foot or even a bit more of snow is possible in the Anchorage area today, with higher amounts in the Chugach Mountains east of the city. More snow is possible later this week.

Checking in on where our El Niño event stands as we descend toward winter

One-sentence summary

Today’s post primarily dives into where we stand with El Niño currently and what sort of impacts that could have heading into winter.

Tropics: Quiet!

We’re all quiet out there at the moment in terms of anything meaningfully developing in either the Atlantic or Eastern Pacific basins. It should be a quiet week overall.

U.S. Weather: Warmth taking hold

Overall, it should be a relatively calm week across the country. We are not expecting too much in the way of severe weather or excessive rainfall this week. One could argue that there’s at least some interesting weather happening though. A storm today and tomorrow will bring more rain and mountain snow to the Pacific Northwest. Another may follow toward the weekend. Overall, these systems look relatively minor on the atmospheric river scale this week.

The beefiest moisture this week off the Pacific will be aimed at British Columbia, with overall minor atmospheric river impacts. (UCSD C3E)

A pair of systems will bring rain and snow to the Great Lakes and southern Canada through the week. And a relatively strong system will bring showers and thunderstorms to portions of Texas later this week. There should also be a rather significant winter storm in southern Alaska later this week as well.

Temperature-wise, it looks like a very warm week nationally. Multiple record highs will be threatened from the Southern Rockies to the Carolinas this week, including close to 20 tomorrow.

Temperatures this week are expected to be above to much above normal across the Ohio Valley and Mid-South into Texas. Cool temperatures prevail primarily in Ontario, Quebec, and the Maritime Provinces. (Tropical Tidbits)

Not terribly cold in most of the country.

Updating El Niño: It’s here and still strengthening

To this point, I don’t think I would describe the behavior of the current burgeoning El Niño as “classic” in many ways. It’s basically already a “strong” El Niño event, and while its influence is there it is not complete just yet. For example, if you look at just sea-surface temperatures in what we call the El Niño box in the tropical Pacific, the current event ranks about 7th strongest since 1950 (based on the Oceanic Niño Index, or ONI).

If you focus on the 2nd and 4th charts, which date back to last December, you’ll see that the Niño 3.4 region has been slowly strengthening, while the 1+2 region (bottom) has been strong for months. (NOAA)

However, if you look at another dataset called the Multivariate ENSO (El Niño) Index, or MEI, this event is only the 9th strongest since 1979 (which is probably around the 14th or 15th highest since 1950). Why am I sharing these data points with you? Well, the ONI is looking purely at ocean temperature. The MEI is typically a better index in that it factors in other variables, which we would liken to how the atmosphere is responding. So the ONI can be a proxy for ocean response, whereas the MEI can be a proxy for atmospheric response. To this point, the atmosphere has not yet responded to the same extent as the ocean has.

But that may finally be changing. I shared the chart above showing the sea-surface temperature anomalies in the various different El Niño regions of the Pacific to highlight the differences between the 1+2 region (bottom panel, which is the eastern Pacific) and the 3.4 region (2nd panel from top, which is closer to the International Dateline.). The eastern Pacific has been revved up since spring. The central Pacific took a bit longer, but it finally appears to have hit a level where it should allow for El Niño to become the more dominant feature for global weather.

And if anything, this event is likely to intensify further in the next couple weeks. So if you’ve been wondering if this El Niño was going to show up like a typical strong El Niño, there may be reason to assume it will.

What does that mean? No relationship is perfect, but in general, El Niño has a decent correlation to a couple key elements here in North America.

El Niño relationships typically yield a cool, damp Southern U.S. and a warm North. (NOAA)

Generally, we see a cooler, wetter Southern U.S. and northern Mexico, as well as a milder Canada and northern tier of the U.S. into Alaska. Usually more storms will crash into California during El Niño winters. Sometimes, like in 2015-16 that isn’t the case. But on average, it is. Seasonal climate models are fairly confident in a warm North/cooler South but a bit split right now in terms of how they view precipitation. An American climate model, the CFS, shows a rather classic wet California and wet Texas through Southeast. The European model has the second part but shows near-normal to just slightly above average precipitation in California.

The bottom line at this point is with El Niño strengthening, one should expect the atmospheric response to also strengthen over the next couple months. And with a rather strong El Niño in place, that response would probably look similar to what is typical in El Niño as shown above. Of course, there are risks as noted, as well. I also think there are wild cards.

If you look at sea surface temperatures around the world right now, virtually all Northern Hemisphere oceans are warmer than normal.

Sea-surface temperature anomalies show almost the entirely Northern Hemispheric ocean system warmer than normal, and in some cases record warm for this time of year. (Weather Bell)

Why does this matter? We are in a bit of uncharted territory. One of the big reasons El Niño is such a big deal is not just because where it occurs is so important to global weather but also because it’s often so anomalous relative to other global sea surface temperatures. It becomes a dominant feature. Well, what happens when you trigger an El Niño on a planet with a lot of oceanic temperatures that are also extremely warm, relative to average? We’re going to find out this winter. While the smart money is probably still on El Niño leading to El Niño things, there is at least some chance the typical impact could be perhaps a bit muted because the majority of the planet is so much warmer than normal. Would I bet on that? No. Am I watching it as a forecaster? Yes.

Suffice to say, we live in interesting times.

October 12, 2023 Outlook: A windswept Central U.S., as the tropics sit mainly quiet

One-sentence summary

Strong winds will bring some risk of localized power outages across the Central U.S. and increased fire danger in the Southern Plains as a fall storm winds up today.

Tropical update: Nada

With Sean back down to tropical depression status, there’s not a whole lot else to discuss for the next few days. I would not be shocked to see the low pressure system develop that’s presently bringing rain and locally gusty winds to the coastal Southeast. A couple tornadoes were reported earlier this morning near Tampa, and there are a couple tornado warnings ongoing as of this writing. All this will race east across the Atlantic, however, and poses no further risk to land as it exits.

Rain will exit the Southeast today, but not before leading to some severe weather in Florida. (College of DuPage)

There is some potential for another lower-end Cabo Verde type system in 5 to 7 days, but at this point between that and a likely quiet Caribbean for a bit, there’s no reason to sweat anything out on land.

A wind-ripped Thursday in the Central U.S. brings some fire danger and severe weather

Wind is the story today for the U.S., with a deepening low pressure system over the center of the country driving a pretty healthy wind event. Wind gusts of 40 to 50 mph or higher are likely from about South Dakota into western Nebraska, northeast Colorado, much of Kansas, northeast New Mexico, and the Texas and Oklahoma Panhandles.

Wind gusts over 50 mph are possible anywhere you see orange on the map above, from eastern South Dakota south into parts of New Mexico and the Texas and Oklahoma Panhandles. (Weather Bell)

We get a handful of these events per fall, winter, or spring so it’s not too unusual. But it may have impacts ranging from localized power outages to tree damage to wildfire risk. The “critical” area of fire danger risk today is from southwest Kansas, across the Panhandles into northeast New Mexico. The combination of drought, low humidity, and winds will combine to enhance that risk.

“Critical” fire weather danger is forecast today from northeast New Mexico into the Texas and Oklahoma Panhandles and up into Kansas. (NOAA SPC)

Wind advisories, high wind warnings, and red flag warnings are posted in many of these regions for today.

With a storm like this, you usually get some severe weather, and this may be the case today in Nebraska and Kansas in particular. There’s a modest tornado risk today but more likely, we’ll see hail or damaging winds take prime billing later today as the low pressure area works east. Tornado risks are highest in Nebraska.

A slight risk (level 2/5) for severe weather exists today across most of eastern Nebraska. (NOAA SPC)

A slight (level 2 of 5) risk of severe weather is posted today. Heavy rain will also be possible, especially across South Dakota, where as much as 3 or 4 inches of rain may fall between Pierre and Sioux Falls. Enhanced precip may also occur in the Rapid City area and Black Hills, though a chunk of that will fall as snow.

As much as a foot or so of snow could fall in the Black Hills of South Dakota from this storm, but as the NWS graphic above notes, it’s complicated! (NWS Rapid City)

Maximum snow is expected northwest of Mt. Rushmore in the Black Hills, where as much as a foot or so is possible. Snow will also occur in the mountains of Colorado and Wyoming and in parts of northwest Nebraska.

The flood risk will shift east tomorrow, when Chicago, Milwaukee, and Madison all fall into a slight risk of excessive rainfall (level 2 of 4), as 1 to 3 inches of rain are expected. More on that tomorrow.

October 10, 2023 Outlook: Tropical moisture to bring heavy rains to parts of the Gulf Coast, while the interior U.S. readies for a big storm later this week

One-sentence summary

Hurricane Lidia will make landfall near Puerto Vallarta late this evening as a moderate hurricane before weakening and merging in with a bunch of other tropical moisture that will quickly transit the Gulf toward Florida.

Tropics: Lidia makes landfall in Mexico tonight, combines with other systems to bring rain to the Gulf & South

Hurricane Lidia will approach Mexico later this evening as it intensifies, likely making landfall on the coast very near Puerto Vallarta.

A complex pattern in the Pacific and Gulf will feature Invest 93L (unlikely to develop) lifting north and then northeast, the remnants of Tropical Storm Max combining with that, and eventually Hurricane Lidia’s remnants streaking in a similar direction, close behind. (Weathernerds.org)

Lidia will bring heavy rain in Jalisco, southern Sinaloa, and Nayarit in Mexico and storm surge to areas south of where it comes ashore. Hurricane Warnings are in effect on the coast of Mexico from Playa Perula to Escuinapa. The hurricane-force winds only extend out about 25 miles, so the worst wind will be felt near the eventual landfall point not far from Puerto Vallarta. Lidia will rapidly weaken once inland in Mexico, but its remnant circulation and moisture will get drawn into a conglomerate of systems in the western Gulf of Mexico that will rocket east toward Florida.

Hurricane Lidia will make landfall near Puerto Vallarta before rapidly weakening once inland. (NOAA NHC)

This mashup includes Invest 93L in the Bay of Campeche and the remnants of Tropical Storm Max which made landfall yesterday. As this family of outcasts speeds east across the Gulf Wednesday, it will bring a burst of rainfall from South Texas, into the open Gulf, and across extreme southeast Louisiana and Florida.

Rainfall from the tropical trio through Friday morning will be highest offshore, but 1-3″ will be likely in North Florida, South Georgia, southeast Louisiana, and perhaps on the coast of Alabama or Mississippi (Pivotal Weather)

This rain looks fairly manageable overall, with about 1 to 3 inches in the Rio Grande Valley and Corpus Christi areas, New Orleans, much of the Florida Panhandle, and the southern half of Georgia. Isolated areas will see more. There will also likely be a pretty sharp gradient on the northern fringe of this precipitation that perhaps limits amounts a bit in San Antonio, Houston, Baton Rouge, Montgomery, and Atlanta.

Rain totals in Texas will be highest south of Corpus Christi. (Pivotal Weather)

Aside from this sloppiness, the Atlantic tropics are quiet in terms of land impacts. Invest 92L continues to look like a late season Cabo Verde system, likely to develop over the next few days. But it will not impact land. There’s a little bit of model percolation in the Caribbean in about 10 to 12 days, but I am not ready to jump aboard that train just yet.

Central & Eastern U.S. storm to bring heavy rain and a whole lotta wind late this week

I presume most of the country’s attention with respect to weather late this week will be on the significant storm that is going to develop tomorrow night into Thursday over the Central Plains. This storm will bring a variety of weather to much of the northern half of the country.

Rainfall/flooding

In terms of rain, we’re looking at a slight chance of flash flooding on Thursday from northern Nebraska and southeast South Dakota into northwest Iowa and southwest Minnesota. On Friday, that expands east to include Chicago, Madison, and Milwaukee east to western Michigan.

Thursday and Friday will see a slight chance (level 2 of 4) for excessive rainfall in the Plains and Midwest, which will expand into Pennsylvania and New Jersey on Saturday. (NOAA WPC)

By Saturday, that will move toward the Mid-Atlantic and southern New England, including, again, New York City.

7-day national rain totals show 1 to 4 inches from the tropical moisture in the Gulf and another 1 to 4 inches from Nebraska and South Dakota to Michigan, as well as centered on New Jersey. (Pivotal Weather)

Expect about 1 to 4 inches from western Michigan west through Nebraska and South Dakota. Another 1 to 3 inches is possible in portions of eastern Pennsylvania and the New York City metro. Much of this region only needs an inch or two of rain over 6 to 12 hours to get flash flooding started. So I would expect to see flood watches get posted at some point in many areas.

Severe weather

With a powerful area of low pressure developing on the Plains, you almost always get some kind of severe weather. For Thursday that will probably be in Kansas and southeast Nebraska. On Friday that potential may moderate some as the storm comes east, but I still wouldn’t be shocked to see some reports of severe weather.

Thursday’s severe weather forecast calls for a slight (level 2 of 5) risk from about Kansas City north and west, with hail and strong winds being the main concerns. (NOAA SPC)

Strong winds and large hail are probably the main concerns, along with a non-zero tornado risk. There will be only a moderate amount of warm, moist Gulf air available so that may cap this event a little bit. Either way, expect to see (and hear) rumblings about that this week.

Strong winds

Expect to see a wide swath of 30 to 50 mph wind gusts across Wyoming, the Central Plains, and the Midwest as this storm marches east. The strongest winds will probably be in the Texas Panhandle, western Kansas and Nebraska, and portions of South Dakota.

Forecast wind gusts may exceed 40 or 50 mph with this storm over a wide swath of the Great Plains into the Upper Midwest. (Weather Bell)

Strong winds will march east as well, but they will probably ease up a bit once to the Ohio Valley and East.

Snow

Lest we ignore the powder! Snow will likely fall in Colorado and Wyoming (and perhaps Utah) as this system unfolds. Some snow may even fall in the Black Hills as well. Winter Storm Watches are already posted for a number of higher elevation spots from Wyoming into western South Dakota.

It’s getting to be that time of year! We’ll have more on this for you through the rest of the week.