Originally Posted At DanielSchreiber.org
Wintertime in the Central Plains can be brutal, and it was exactly that in the Texas Panhandle this morning. Just before 2AM, the cozy cattle farm town of Dalhart, Texas – straddling Dallam and Hartley Counties on the extreme northwest corner of the Texas Panhandle – plummeted from a toasty December night temperature of 55°F to a miserable 28°F as a potent cold front blasted through the Central Plains. Coupled with 40 mile-per-hour winds and wintry precipitation, wind chill temperatures plunged into the single digits almost instantaneously.
Meanwhile, at the same time 200 miles south, the bustling town of Lubbock enjoyed a breezy, but warm, early start to the weekend in the 60’s, just to be reduced to the sub-20’s by mid-day.
This strong cold front is part of a dominating winter storm that is causing hazardous winter weather to much of the Great Plains – including snow, ice pellets, and freezing rain. Further east, much of the southern portion of the Ohio River Valley, portions of the Tennessee River Valley, and the Southern Mississippi River Valley will be contending with severe thunderstorms and tornadoes, quickly swept away by the winter weather already experienced to the north and west.
– Meteorologist Dan Schreiber
Originally Posted At DanielSchreiber.org
If you’ve ever visited the National Weather Service’s Homepage (weather.gov), you’ve probably noticed a map of the United States with a bunch of colors on it. representing various weather alerts – warnings, advisories, outlooks, and so on. Occasionally, an amber alert message will show up on there, as will several non-weather related emergency messages. Here’s the map:
Ever curious what all those colors mean? And, what happens if there are several alerts in the same location?
The National Weather Service is working on creating a new system which significantly simplifies the way they do business with weather – and other emergency – alerts.
Right now, there are 122 possible messages (plus a “test” message) that the NWS could disseminate, but only one color could show on the map at a time in one location.
This creates several problems.
First: There are so many alerts, and so many colors, that it’s difficult to distinguish what alerts are in effect simply by looking at the map. For instance, there are about 25 different alerts with some shade of blue. MOST of them have something to do with cold weather, but they also include Avalanches, Rip Currents, and Severe Weather, to name a few.
Second: There are so many alike alerts that the average citizen doesn’t understand their minute differences. For example, Hard Freeze Warnings, Extreme Cold Warnings, Freeze Warnings, Frost Advisory, Freezing Fog, Freezing Spray, Heavy Freezing Spray, and Freezing Rain Advisories, and Winter Weather Warnings. The only thing that most people will understand from all of this is: Cold. The National Weather Service has considered combining several of these alerts into one, eliminating the confusion.
Third: So many alerts can lead to citizen complacency. With 122 possible alerts, there is almost always bound to be some sort of alert in effect nearby. Hazardous Weather Outlooks and Short-Term Forecasts are common, and these alerts can steal the glory from more severe weather alerts, like Severe Weather Statements, Severe Thunderstorm Watches, and Flash Flood Warnings. While there is a pecking-order of which color is displayed (for example, a Tornado Warning will display on the map over a Flood Warning), many folks don’t necessarily identify the difference between “Special Weather”, “Severe Weather”. “Hazardous Weather”, “Winter Weather”, and so-on – it’s all just “bad weather”.
Fourth: Should the Federal Government be reaching into non-severe weather alerts? This is a loaded, political question. But, it raises an interesting question. While I believe that an American citizen is entitled to the knowledge of looming life-threatening weather, how far should the federal government involve itself into local, not-imminently-life-threatening weather alerts? At what point should state governments take the lead? Food for thought.
The NWS has proposed several fixes (to all but my fourth problem, naturally). They’ve explored the possibility of only displaying four colors on the map: red, yellow, orange, and purple, indicating simply warnings (red), watches (yellow), and advisories (orange), and emergencies (purple).
Another idea proposed displaying alerts as impacts: Limited, Moderate, High, and Extreme impact. The user could then click on the map to read more.
Originally posted on DanielSchreiber.org.
As winter sets in, a weak La Niña weather pattern has started to take shape across North America. Typically, this would encourage warmer & drier winter weather through the Southern United States, and cooler and wetter winter weather through the north. On November 10th, the National Oceanic & Atmospheric Administration’s (NOAA) Climate Prediction Center (CPC) issued a La Niña Advisory, projecting weak La Niña conditions through the wintertime.
Below was their projection for December, issued on November 17th, 2016.
An unfortunate turn of events occurred later in the month of November and into early December (after the above outlook was published), which caused the CPC to change their mind a bit with the latest December Outlook below, replacing the above graphic for the same valid times.
Woops. Kind of a big change. An “upset”, some may call it. The November 17th Outlook, valid two weeks in the future called for abnormally warm and dry conditions through the west and portions of the southeast, while the November 30th Outlook, valid beginning the next day, nearly flipped the forecast around. This new forecast was issued as much of the Southeast US was inundated by severe weather.
I can’t speak for what happened at the CPC in this forecast, but I can vouch for one thing- the current weather that we’re experiencing in late November and early December through parts of the Southern United States is not very typical.
Let’s look at the satellite from today (December 3rd).
Below is a weather graphic of 500-mb Geopotential Height Anomaly for the same day as the above satellite loop. In English, this graphic shows how “normal” the weather patterns are through North America compared to long-term average, with a value of “0” being “normal”.
In this case, we note an anomalous High Pressure offshore of California pushing 3 standard-deviations higher than “normal”, and an anomalous Low Pressure over Northern Mexico, roughly 5 standard deviations lower than “normal”. And, the fact that it’s sitting this far south, while the typical storm track during La Niña years tends to stick north, is certainly not normal.
So, what are the effects?
Not surprisingly, we see a strong correlation between the 500-millibar (roughly 18,000 feet) geopotential height anomaly and the 850-millibar (roughly 5,000 feet) temperature anomaly – abnormally cool through the southwest and abnormally warm off of California. We also note some abnormal warm air over South Texas- this is due to significant cloud cover and rainfall (courtesy of the strong Low Pressure over Northern Mexico) keeping warm air trapped in the lower troposphere.
The above radar image is more-or-less in-line with the CPC’s latter December Outlook (which encompasses all of the month of December, not just one storm on one day).
December 3rd’s early-morning temperatures…with subfreezing temperatures as far south as Arizona’s Mogollon Rim and much of the State of New Mexico, also match the latest CPC Outlook, but put to shame the miserable November 17th Outlook.
Latest Climate Forecast System model output would indicate continued cooler and wetter conditions more in-line with the most recent CPC outlook. for the remainder of 2016. However, the CPC continues to pull for overall warmer and drier Southern United States conditions through the winter. While the El Niño/La Niña pattern would dictate that to be a reasonable assumption…latest Sea-Surface Temperature observations – a large contributor to global weather patterns – may indicate other plans.
We can observe a negative anomaly (blue) over the Northeast Pacific, exactly where the strong High Pressure in the satellite loop above exists. Since High Pressure and cooler surface temperatures are often related (cool air is more dense that warm air), and ocean water heats and cools slower than dry ground, it’s safe to say that a decently strong High Pressure may hang out for a bit offshore of the West Coast unless the Jet Stream strengthened enough to uproot it. Barring that scenario, the East-Pacific High Pressure becoming semi-permanent over it’s current location would continue to force Low Pressure around it’s periphery…and even into the Southwest United States and Northern Mexico, like we see today, causing cooler and more moist conditions in not-so-typical locations under the given global weather pattern.
Dan Schreiber is an operational meteorologist, with experience