 Advisory Center  Forecast Precipitation Type  Forecast Temperatures |
Hundreds of thousands of people or more will be without power in the upcoming days as a major ice storm digs its talons into America’s Heartland.
A frontal boundary viewable with the Fronts overlay in our Radar Center will retreat northward from the Gulf pulling warm most air into the deep south as modified arctic air east of the Rockies will form a dense shallow layer of near or below freezing air at the surface that will result in nearly idyllic temperature profiles for widespread sleet and freezing rain.
The resulting setup is the cause for a cornucopia of winter related warnings in our Advisory Center from ice storm warnings to winter storm warnings active from central Texas to the northeastern United States.
Our 12z Forecast Precipitation Type Animation shows the potential for icing to begin in Texas this afternoon then stretching through Oklahoma, Arkansas, and Missouri as tomorrow approaches. As the warmer air advances from the Gulf meeting with the modified arctic air, an elongated area of icing potential will spread across the breadth of the nation’s midsection.
The best potential for the heaviest accumulations over the next few days will extend from the Missouri / Arkansas border in a general northeast track through northern Tennessee and Kentucky where very high accumulations are likely to occur. In the surrounding areas and those highlighted in the animation above, light to significant accumulations are possible.
In addition to the ice storm, heavy snows will also occur just north of the icing line as highlighted in our Precipitation Type Animation, where on a line from the southern Illinois / Missouri border running northeast through centeral and southern Indiana, Ohio, and Pennsylvania accumulations of 4-6″ are likely, over the next few days, with the best chance for highest accumulations along the southern extent of Illinois, Indiana, and Ohio where up to 8″ or so are possible.
Please be sure to view our Advisory and Radar Centers for the latest updates and developments.
As always stay tuned to your favorite weather outlet, stay informed, and stay safe!
cheers,
–patrick
|
Update: 3pm
Governor Brad Henry of Oklahoma declared a state of emergency for all 77 counties in the state, urging motorists to “slow down or, better yet, stay off the roads if they can.” Read the full article from Channel 5 in Oklahoma City, KOMO.COM.
 Forecast Precipitation Type Animation |
 Forecast Temperature Animation |
The rains we discussed on Monday certainly have spread the wetness the southwest was so desperate for and moved its way into the intermountain west as predicted. While things have generally been quiet they are about to pick up a bit as rains and snows will continue in the southwest and west as our Forecast Precipitation Type Animation displays. Well while we are on the subject of the animation, I was asked the other day to explain it a bit, so I might as well do so again here.
Open the animation above and hit the stop button on the bottom of your screen. First, note the time stamp on the bottom. If you want to be on the same “frame” as i will be in this discussion, also please click the “first image” button.
OK, the timestamp I place on the images states:
18z F003hr Valid: Thur Jan 22 21:00:00 UTC 2009
18z means the time the “run” was made (and the first data was valid for) to create each of the images in the animation.
F003hr means the current frame in the animation is forecast 3 hours out from the time the run was initialized, or 18z plus 3 hours so it would be 21z.
The valid time is where I have a script that calculates out the valid day and hour that each frame is valid for so it is easier for the general public to understand when the frame is valid. So in other words January 22, 2100 hours (21st hour of the day) UTC (Universal Time Coordinated). At one time I converted the dates to central time, eastern time and so forth but most people who look at the maps have a general understanding of time and prefer Z / UTC since they are accustomed to it, but I of course could go back to recalculating valid eastern time if a majority chose for me to do so.
If the concept of gmt/utc/zulu is new foreign to you, wiki has this article that you may find helpful. Additionally, there is another article on the concept of time zones that may come in handy.
So, now the concept of the image. You may notice that I throw up different types of products from time to time, because I have been working in meteorology so long that I have quite a few of them. Forecasting precipitation type is one of the many pet projects I have been working on for longer than I care to mention, so I also have a suite of related products.
The animation above may be loosely translated as saying based upon data available, at three hour intervals out 84 hours, what might the radar and precipitation type look like?
Let’s think about this for a minute. Essentially what i am saying is that each frame in the animation represents a three hour window of time. Each time interval also represents the end of the time window. So above the 3 hour 21z Precipitation Type graphic means that from the three hours before and ending at 21z what type of precipitation may fall in the future and at what intensity?
Think carefully about that for a moment. My equations must take into account the entire three hour window and decide which type of precipitation to represent i.e. rain / freezing rain / sleet / snow and also interpret the intensities of that projected precipitation.
So when you advance the frames individually think in your mind as to what types of transitions may be occurring in the area you are interested in. Do you for example notice a transition of greens (liquid precipitation), pinks (mixed freezing rain/sleet.. not my color choice by the way!), or blues (snow) or somethign in that nature? If so you may be in a transition zone of temperature differentials at the surface or aloft that may move over your area of interest within each time frame, which is of course an important and interesting issue.
If weather is an interest of yours, keep the animation in mind, save it (I leave the links from the blogs on the server, that is what it is there for) and see how accurate the forecast was keeping in mind what was mentioned above.
When examining the legend for each precipitation type at the bottom, also keep in mind the intensities. The very light blues on the bottom for example, represent very light forecast snow intensities, or that there is a chance for flurries to light snows within that three hour window. The same is of course also true for rains and mixed. Very light greens for example mean the possibility for light rains to drizzle within each window, that may also be viewed from the ground as virga (precipitation falling from a cloud base that evaporates before reaching the surface).
OK, so now back to the animation and discussion of forecast precipitation type. The first frame shows the forecast rains in the southwest and blotches of snow and mixed precipitation embedded within the rain shields representing areas of elevation where orography will induce snows, however what is going on in the north?
Pacific moisture with enhanced vorticity will stream into the area aiding in the creation of snows along the northern tier over the next few days where again orographic process will aid in the higher accumulations in the central Rockies with emphasis in the mountains Idaho, Utah, Colorado, and Wyoming. While overall a wide precipitation shield will extend basically from Montana to the southwest.
As the days progress (advance frames) a little zippity do dah will spread snows and rains extending from the great plains to the midwest and south, which is especially beneficial in the drought ridden areas of the southeast where some reservoirs are still below their nominal levels. Snows with this event will not be overly excessive as the initial push exits east by Saturday evening and a new system comes barreling in from the Pacific Northwest simultaneously and reaching the plains by Sunday Morning.
Colder air is also going to invade the north again. The new Forecast Temperature Animation I have created for you goes out through 8 days instead of the 84 hours I usually put up. The reason I normally don’t put longer scale animations up is because some people still have bandwidth issues, but we will see how people respond to this setup.
A small synopsis of these since I have been asked, is that they represent what the temperatures are forecast to be at the valid time (note above) of the image. I also have what are called Tmin and Tmax images that I may start putting up as well, that represent what is the lowest or highest temperature forecast to occur within each window of time.
Now since this is an 8 day animation what you will see in the loop is that from the first hour (00z, the time of initialization) through F084 (the 84th hour from initialization) are at three hour intervals. Then from F090 through day 8 are at 6 hour intervals.
Hopefully both of the explanations above help you understand the images a bit more =)
So as we view the Forecast Temperature Animation (also handy to have two windows open at once and view the Precipitation Type Animation and Temperature Animation frames together if you are interested in weather) note as the days progress the nasty “purples” start coming into play. Something called Cold Air Advection (CAA – advection meaning horizontal movement of air as opposed to the vertical [convection]).
On initiation (000hr) note Florida has returned to more nominal temperatures than we discussed previously, and texas + the southwest are enjoying warm temperatures, but as we advance notice that as the cold purples are diving south, the red line that you know represents 32ºF is also inching its way south as well. A very normal happenstance this time of year. Fortunately it seems that the extreme may not occur in this run for Florida, but what happens as you continue to advance through next week? Is something interesting in store? Take a look and see!
Please be sure to view our Advisory and Radar Centers for the latest updates and developments.
As always stay tuned to your favorite weather outlet, stay informed, and stay safe!
cheers,
–patrick
