Archive for the ‘Weather (other than of tropical origin)’ Category
When my television is turned on I “check out” the Weather Channel fairly often. For the most part I’ve been very impressed by explanations that are given about weather happenings. I’ve never done media weather reporting so can only imagine how frustrating it must be to provide good presentations when time is at such a premium. In the college classroom even though I had an agenda with objectives to cover I had control over the amount of time I spent on individual topics.
Recently I heard a Weather Channel reporter give a less-than-desirable explanation for the cause of lake effect snow events. I imagine that time constraints kept her from being more thorough. This is close to what she said: “The cold, dry air behind this front is moving over the warmer Great Lakes picking up moisture and then dumping snow on the land at the opposite side.”
From my point of view that was far too brief leaving out way too much. But – everything is relative. I suspect that most people would prefer her explanation to an hour lecture on the subject from me. But there would likely be one or two in a large class of meteorology students who would be dissatisfied because I left something out or left them very confused. My dad didn’t have the opportunity to teach me much but one of the things that he tried hard to get through to me was, “You can’t please ’em all.”
So – I’m not complaining about the Weather Channel presentations. I think they do a very nice job. But if I were working for them, here is the minimum that I would insist upon (which is probably one of the reasons why I’m not a suitable candidate to work for them – the brevity necessitated by time constraints would drive me up the wall and my tendency toward long-winded discussions would drive them up the wall – LOL):
Cold, dry air moving over a large, unfrozen lake surface picks up moisture in the form of water vapor made available by evaporation. More often than not unfrozen lake surface water’s temperature is higher than that of the air behind a cold front.
But in most cases clouds that provide precipitation form as a result of air rising and that is most definitely a factor in bringing about lake effect snow events. So – what makes it rise?
The moisture-laden air can rise because of an increase of elevation on the downwind side of the lake but that alone is usually not enough to create snow-producing clouds unless the increase is due to a plateau or mountains. Also, positive buoyancy can cause the air to rise and that can be created in two ways as the air is traveling over the lake water. Picking up heat energy the air can begin to lift (heated air tends to rise); a fair analogy is a hot air balloon. Also, the addition of water vapor to air can increase its buoyancy (as the specific humidity increases, the density increases so long as the temperature of the air does not drop significantly).
The factor most often omitted in a lake effect discussion of why air rises to form snow clouds is this: When air reaches the land it slows down because of the decided increase in friction. When in heavy traffic a car far ahead of you slows down – you, the cars ahead of you, and the cars behind you tend to squeeze closer together. We say the cars are converging (getting closer together). In the case of the fluid air a vertical component of motion is allowed so some of the air “piles up” and therefore moves up. Have you ever heard of cars piling up?
Therefore, even without an elevation increase of the surface over which the air flows and even without an increase in buoyancy, some air on the downwind side of a Great Lake is likely to rise because of convergence. Whether or not snow clouds form is dependent upon a combination of factors.
You’ll have to admit that my explanation is more thorough than “The cold, dry air behind this front is moving over the warmer Great Lakes picking up moisture and then dumping the snow on the land at the opposite side.” The trouble is, it took time, is very “wordy” and you really have to read carefully to pick it all up. Furthermore, as long as my explanation is, it still does not give all of the reasons behind lake effect snows. Also, it makes a blanket statement (as the specific humidity increases, the density increases so long as the temperature of the air does not drop significantly). But it does not elaborate. For most people that sounds like a real paradox – adding moisture to the air can make it less dense and therefore be a contributing factor to its rising! It’s true – and I intend to discuss that paradox on this web-log in the near future. By the way – a friend of mind from way back in high school defines paradox as “two physicians.”
YOU MIGHT HAVE TO CLICK ON THE IMAGE ABOVE TO GET IT TO ENLARGE AND LOOP.
In the radar loop above taken from a small time segment (48 minutes) earlier today (12-6-2010), you see the signature of lake effect snows in Indiana. Lake Michigan’s mean elevation is a bit over 577 ft. above mean sea level. The land between Lake Michigan and Fort Wayne is as much as 250 feet higher but I think it’s unlikely that 250 feet of elevation increase is going to create that much snow. Nor is the land heating the air to make it rise via positive buoyancy. In fact, the land surface temperature is colder than the air flowing over it. I believe that it’s convergence of the type I’ve described in this entry that is responsible for much of the snow.
What so many have been reluctant to say – probably being extra cautious because nothing is certain at this time – was finally printed in yesterday’s Wall Street Journal. In my first posting about this terrible aircraft accident I suggested that if icing was indeed the problem – the accident should never have occurred. Now – it is beginning to look as though the “reaction” to icing might have been incorrect causing the aircraft to immediately stall.
Please be mindful of the fact that the investigation of this accident is still in a very early stage. Here is a link to the WSJ article:
If you wish to see other posts on this weblog but are unable, please click on the “blog” tab near the top of this page.
I recommend that Florida residents who are concerned about tonight’s temperature consult your local media for the forecast in your specific area. On line you can go to http://www.weather.gov/ and at the small white rectangle near the top-left – type in your location or even easier, your 5 digit zip.
The image above shows an almost cloudless Florida earlier today. It is covered by a frigid Arctic air mass. The air is very dry and relatively clean. There is not much water vapor within it to intercept outgoing infrared; the colder the air, the less energy is available to keep water in the vapor state. During the daylight hours the incoming solar radiation exceeds the outgoing infrared but of course at night there will be no incoming solar radiation while terrestrial infrared continues to flow outward. Therefore, it will get even colder.
Some folks in my neighborhood have wells. Freezing at or near well sites is not uncommon. It happened to one of my neighbors during a recent cold spell but fortunately there was no damage. Since water expands by about 9% when it freezes, considerable damage can occur. I run an extension cord out to my well and place a shop lamp on the surface and throw some sheets over the pump and plumbing fixtures to help hold in the heat from the 60 Watt light bulb. In the several freezing episodes during the 43 months I’ve lived in this part of Florida, that method has worked for me without fail. SEE IMAGE BELOW.
A neighbor suggested to me that a slow drip at a faucet inside will also help to prevent a line closure from freezing. I have not tried that.
After tonight a slow warming trend is expected but this is probably not the last of this season’s cold episodes.
If you would like to see other posts in this weblog but are unable, please click on the blog tab near the top of this page.
This seems almost like an instant replay! We Floridians are again playing host to a couple of surges of cold air. Florida is once again cloudless and the cold air is relatively dry – therefore the state can’t count on much of a greenhouse effect to slow the loss of heat from the surface.
My neighborhood in northeast Citrus County, Florida can expect freezing temperatures on Wednesday and Thursday morning – and perhaps Friday morning. As is so often the case, the fickle microclimatology of a neighborhood can be manifested by a wider-than-expected range of low (and high) temperatures. For example, during a luncheon today a neighbor reminded me that by virtue of his property being on about the highest ground in the neighborhood, his low temperatures end up being not quite as low as those in other parts of the neighborhood. This is not always the case but it happens the majority of times because on those cold, marginal mornings when the synoptic pressure gradient is weak, the coldest (and therefore densest) air tends to spill downward into the lower vicinities.
My wife and I have given up on covering our ornamentals – deciding a while ago to allow “survival of the fittest” to kick in. But – many of my neighbors have already covered some of their plants.
This is not a mean-spirited criticism but it is a huge paradox to me that so many will go out of their way to protect a plant that isn’t meant to grow here yet some think nothing of killing a native species of harmless snake that dares to stray on to their property. I understand the fear – but not the lethal reaction.
If you are “up north” reading this, I imagine that you’d love to be enjoying our temperatures down here. Everything is relative, is it not? For example. I took my daily 3-mile walk earlier today wearing a light-weight sweater over a T-shirt and at the half-way mark the sweater came off! It has been a delightful day for early February – that’s for sure.
If you wish to see other posts on this weblog but are unable, please click on the blog tab near the top of this page.
If you will kindly read the entry in the previous post the title above will be self-explanatory. To see all posts with the most recent first (after the introduction) click on the “blog” tab near the top-left of this page.
A neighbor on the other side of our road experienced the surprise of having no water from her well this morning. Depending upon how well insulated a well head is in this part of Florida – freezing can happen in this kind of weather.
Though my well is properly insulated I take an extra precaution. I run an outdoor electric line from an exterior outlet to near the well site and then put a shop light (electric with a conventional light bulb) on the surface and drape old sheets to build a makeshift tent over the well assembly so that the heat from the bulb will help to keep the temperature up. So long as the bulb does not burn out – it provides significant protection.
When water freezes, it expands by about 9%. This exerts tremendous force if the water is confined which can do a lot of damage. Among the things that can be ruined is the pump and hose of a pressure cleaner stored where it gets very cold – e.g. a storage shed. One should be sure to blow out the water from the line leading from the pump to the spray wand. The pump can be ruined by the expansion of water inside as it freezes. There is a simple product sold in hardware stores where a lubricant/anti-freeze chemical (in a pressurized can) can easily be injected into the pump to protect it during the cold season. In my opinion, it’s well worth the peace of mind.
Ordinary garden hoses left outside can split if they are left with water inside and the nozzle at the end of the hose in the closed position. In weather like this I make sure my hoses outside are water free.
LIKE MOST POSTING ON THIS WEBLOG, WITH THE EXCEPTION OF THE TUTORIAL PORTION, THIS IS TIME-SENSITIVE. EVEN ONE DAY CAN MAKE A BIG DIFFERENCE SO IF YOU ARE NOT READING THIS CLOSE TO THE POSTING TIME, PLEASE CONSULT YOUR LOCAL MEDIA OR ON-LINE RESOURCES FOR UPDATES.
I’m posting this on the evening of January 21, 2009 from my home in Citrus County, Florida. 22 miles NE of my location is Ocala; 12 miles SSE is Inverness.
Forecasts for the low tomorrow morning in this part of Central Florida (specifically, the town of Hernando) range from 18 degrees to 24 degrees Fahrenheit (depending upon the source). Though that may seem to be a broad range it is quite possible to find those two ends of the forecasts both a reality within a very small area – arguably, less than a quarter-section (1/2 mile by 1/2 mile square). This is due to the highly variable properties of unlike surfaces (heterogeneous surfaces) when it comes to the loss of thermal energy via infrared radiation.
On a larger scale, the satellite image above, completed at 3:45 P.M. E.S.T. today shows Florida virtually cloud free. This means that all during the daylight hours, even though solar radiation was pouring in, terrestrial (earth) radiation was flowing out freely in the form of infrared – much more freely and abundantly than it would have had the air been humid and had clouds been present. Tonight, the infrared will continue escaping in its space-bound journey. The moisture content of the air is low and there will be no clouds though there could be fog (technically speaking, fog is a cloud).
Water vapor (water in the invisible gaseous state) is the most active and abundant of the so-called greenhouse gases. The presence of clouds suggests that up at that level there is plenty of water vapor (that which resides between and below the cloud droplets that has not condensed into cloud droplets). So, on a humid, cloudy day one would expect a strong greenhouse effect keeping thermal energy “trapped” at the lower levels. BUT – TONIGHT THAT IS NOT GOING TO HAPPEN because, as stated, the air is dry and cloud free. Tonight heat will be escaping rapidly and little will be sent back and none will be pouring in from the sun. So – the temperature will drop dramatically.
Typically, there is about a 30 minute period after sunrise when the thermal energy escaping earth’s surface at that location exceeds the amount of thermal energy coming in from the sun. That is why the coldest moment of a 24 hour period is most often after sunrise – about 30 minutes or so.
The satellite image shows how once the cold air coming down from a component of the north leaves the continent to flow over the Atlantic and Gulf of Mexico, moisture is picked up and clouds form. Notice how they form in short order leaving only a narrow cloud free zone over water near the land. The fact that the water surfaces are warmer than the continental surfaces at this time of year also play a role in that cloud development.
What a terrific way to start the new year in this weblog – with an image of nearly the whole earth showing cloud patterns over both the daylight half and the darkness half. The two rows of extratropical cyclones (one over the middle latitudes of each hemisphere) are striking. Since a very high percentage of the over 6.7 billion people on earth live in the middle latitudes, and since these cyclonic systems and their cold fronts commonly extend into the lower latitudes, you might very well be under the influence of one of these systems this very moment. They are marching generally from west to east in both hemispheres followed by cold (or cooler) anticyclones. For example, I live in the low latitudes at 28.972 degrees north and we get several frontal passages.
The Intertropical Convergence Zone is apparent, especially over Africa. Notice how it is further south now over that continent than during the North Atlantic hurricane season.
HERE’S WISHING YOU ALL A HAPPY NEW YEAR. That’s just the beginning because my wishes for you are many. That: You “know” love and feel both loved and lovable, you are never bored, you have a long gratitude list, happiness is not illusive, you feel as good as possible for your circumstances, life’s pros far outweigh the cons, and you experience peace and good will always.
Tonie A. Toney (Cloudman23)
= = = = = = = = = = = = = =
NOTES: Extratropical means “outside of the tropics.”
Middle latitudes are strictly defined as the regions between 30 degrees and 60 degrees latitude (both hemispheres).
Extratropical cyclones differ from tropical cyclones in the following ways. ET cyclones are “cold core” lows while T cyclones are “warm core” lows. ET cyclones generally have fronts associated with them, T cyclones do not. ET cyclones originate mostly in the middle latitudes while T cyclones originate in the low latitudes (0 degrees to 30 degrees). ET cyclones are asymetrical with decided wind direction changes and measurable temperature changes on either side of the fronts, while T cyclones are more nearly circular.
The Intertropical Convergence Zone is where the Northeast Trades and the Southeast Trades converge. Years ago it was referred to as the Doldrums and also the Equatorial Low. Those two outdated terms are still found in the literature and even on line. Generally, the ITCZ migrates northward during the northern hemisphere warm season and southward during the northern hemisphere cold season.
The jury is still out on whether or not Florida will experience violent weather with this system. Cyclogenesis (birth of a cyclone) at the frontal boundary occurred sooner than I had expected – north of the Gulf instead of over the Gulf as I had previously speculated. My advice is to keep your eye on the weather today.
Target Area = the following Florida counties:
Levy, Citrus, Hernando, Pasco, Pinellas, Hillsborough
Event: Coastal Flood Statement Effective:18:38 CDT on 12-10-2008 Expires:09:00 CDT on 12-12-2008 Alert:
…INCREASING WINDS AND SEAS WILL RESULT IN HIGHER THAN NORMAL TIDES AND HIGH SURF ALONG THE FLORIDA WEST COAST THROUGH THURSDAY NIGHT…
.AN AREA OF LOW PRESSURE IS EXPECTED TO DEVELOP OVER THE NORTH CENTRAL GULF OF MEXICO AND QUICKLY STRENGTHEN AS IT MOVES NORTHEAST ACROSS THE SOUTHEASTERN STATES TONIGHT AND THURSDAY AND EVENTUALLY UP ALONG THE MID ATLANTIC COAST THURSDAY NIGHT AND FRIDAY. AS THIS SYSTEM MOVES BY TO THE NORTH IT WILL DRAG A STRONG COLD FRONT THROUGH THE GULF WATERS TONIGHT AND THURSDAY.
AHEAD OF THIS FRONT SOUTHEAST TO SOUTH WINDS ARE EXPECTED TO INCREASE TO NEAR 20 KNOTS WITH SOME HIGHER GUSTS LATER TODAY AND
TONIGHT THEN SHIFT INTO THE WEST AND NORTHWEST AT 20 TO 25 KNOTS WITH HIGHER GUSTS DURING THURSDAY AND THURSDAY NIGHT.
INCREASING SOUTHERLY WINDS AHEAD OF A COLD FRONT AND STRONG WESTERLY WINDS IN ITS WAKE WILL HELP TO BUILD SEAS OVER THE ADJACENT GULF WATERS THROUGH THURSDAY NIGHT. THE INCREASING WINDS AND SEAS WILL CAUSE TIDES TO RUN SOME 1 TO 2 FEET ABOVE NORMAL FROM TAMPA BAY NORTH TO THE SUWANNEE RIVER…WITH THE POTENTIAL FOR 2 TO 3 FEET ABOVE NORMAL TIDES FROM HOMOSASSA NORTH THROUGH CEDAR KEY TO THE SUWANNEE RIVER.
THESE ABOVE NORMAL TIDES MAY CAUSE SOME MINOR COASTAL FLOODING AND OVER-WASH AS WELL AS MINOR BEACH EROSION AT TIMES OF HIGH TIDE THROUGH THURSDAY NIGHT. IN ADDITION THE RISK OF RIP CURRENTS AND STRONG UNDERTOWS AND LARGE BREAKING WAVES ALONG AREA BEACHES WILL ALSO BE ON THE INCREASE.
RESIDENTS LIVING ALONG THE COAST SHOULD MONITOR WATER LEVELS THROUGH THURSDAY NIGHT AND BE READY TO MOVE TO HIGHER GROUND SHOULD FLOODING BE OBSERVED.
STAY TUNED TO NOAA WEATHER RADIO OR YOUR LOCAL MEDIA FOR FURTHER UPDATES ON THIS DEVELOPING WEATHER SITUATION.
I personally recommend that residents of the counties mentioned above and also adjacent inland counties pay attention to the weather tomorrow (Thursday). Cyclogenesis is predicted to occur along the front over the Gulf and that could cause it to swing around rapidly – generating a dangerous squall line ahead of it. The radar image above shows a squall currently out ahead of the front itself and I have no reason to believe that it will dissipate any time soon. So – expect squally weather tomorrow and plan accordingly.
Cloudman 23 (Tonie A. Toney)
THERE IS A TORNADO WATCH FOR MOST OF THE NORTH HALF OF FLORIDA AND PARTS OF GEORGIA NEIGHBORING FLORIDA. THE “ENDING TIME” OF THE WATCH VARIES WITH LOCATION. PLEASE CHECK YOUR LOCAL WEATHER FOR DETAILS.
THIS IS TIME-SENSITIVE,
HAVING BEEN POSTED AT APPROXIMATELY 10 A.M. EST NOVEMBER 30, 2008 – WHICH IS, INCIDENTALLY, THE LAST DAY OF THE OFFICIAL 2008 ATLANTIC HURRICANE SEASON.
For an update of the radar image above, click on the following link: