pV = nRT
That's it! Let me explain, and then the attached actual weather chart from 5pm CST this evening will make all the sense in the world.
To not put you through the torture of deriving the equation, it can be simplified as simply saying:
Air Density = Air Pressure ÷ Air Temperature
All this states is that Temperature effects Pressure and Density. If the temperature changes, the pressure changes and the density (the weight of the atmosphere) changes. Likewise, if the pressure changes, so must the temperature and the density.
The first thing we all learned in science back in elementary school is that warm air rises and cold air sinks. If there is cold air at the surface (like in Wyoming and Idaho right now), then the air in the atmosphere sinks. As it sinks, more air fills in the gap. This causes more molecules to fill in, thus making the atmosphere "heavier" (i.e. more dense). The heavier (or more dense) the atmosphere, the more pressure at the earth's surface. That's why there's always a big blue "H" on the surface weather chart somewhere near the coldest place that day.
Since the earth is constantly trying to fall into equilibrium (just like when you pour hot water into cold water and they make luke-warm water), these pressure differences cause what is known as the "Pressure Gradient Force". Now this is a different physics equation, but all you really need to know is that it causes the wind to blow. ...which in return starts moving all the other pieces of weather phenomena.
Weather = Sun Heats Earth Unevenly= Pressure Changes Unevenly = Uneven Pressures Try To Equalize
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Texas, Oklahoma, Arkansas, and Southern Missouri are under the gun again for some more heavy rainfall and potential (highly likely) widespread flooding. This widespread rain event is caused by three major weather phenomena all coming together at once:
- Strong low-level moisture influx from the Gulf of Mexico
- Strong upper-level moisture influx thanks to Hurricane Sandra in the East Pacific (moving onshore to Mainland Mexico)
- Strong Cold Front pushing out of the Central Plains, but stalling in Central Texas due to strong Gulf flow
These three features characterize heavy rain, and we've seen it before just recently (October 24th-25th with Hurricane Patricia). I expect this event to begin to kick off around nightfall Thursday and persist through Sunday Morning. After the Cold Front passes during the day on Friday, portions of North Texas, as well as Oklahoma, Arkansas, and Missouri will likely see widespread ice pellets (ice storm) and winter-like weather as the temperatures will plummet into the low 30's.
The amount of rainfall expected is significant, especially through Northern Hill Country, North Texas, Oklahoma, and Arkansas may exceed 10 inches. South of the Interstate 10 in Texas, likely only 1-3 inches.
See the attached Weather Prediction Center Outlook.
Obvious Hazards: Flooding (Widespread) and Icy Roads (North Texas/Oklahoma/Arkansas/Missouri)
Stay tuned to the National Weather Service for severe weather updates and local emergency management authorities for more instructions.
Interesting weather satellite image from this evening. Most people are familiar with infrared satellite imagery which colors clouds different colors based on their temperature, even at night when human eyes can't see them. Well, This is infrared water vapor satellite imagery.
What does that mean?
Water Vapor imagery doesn't "see" clouds, it only depicts the amount of water vapor in the middle and upper troposphere and lower stratosphere. It doesn't show any clouds! Granted, we can infer that if there is a lot of water vapor somewhere, there probably are clouds there as well. But clouds are liquid water or ice crystals, not vapor (which is water in it's gaseous state). So what?
What is pointed out in the picture is the Jet Stream. Water vapor imagery is great at outlining the Jet Stream because the Jet Stream causes very dry stratospheric air to mix into the middle and upper troposphere...that's why you see dry air on water vapor imagery at these levels where my arrow point. Generally the more distinct the dry air is, the stronger the Jet Stream. The stronger the Jet Stream, the stronger the storm is that it is pushing along (over the upper Ohio River Valley in this picture).
Now, don't get confused...all dry air on this image is not the Jet Stream...other things can cause dry air to show up...but that's a semester-long course in advanced thermodynamics.
I'm sure y'all have heard of the "Polar Vortex"...a fancy name that someone created during the winter of 2013-2014 for the Jet Stream that becomes very strong and dips well into the southern states. It all starts with Water Vapor Satellite.
Below you can view a loop of model forecast Surface Relative Humidity. The blue colors are high, the yellows, greens, and reds are low. So what can you tell from this? As time progresses, you will notice that the line of blue quickly moves eastward, filled in by lower relative humidifies. This is the outline of the cold front that is passing through Texas tonight.
As you can see, most of the darkest blue indicates areas of potential rainfall...a fast-moving line impacting the majority of the state, but most notably the northern half, and east of the Interstate 35 Corridor.
Most of the severe thunderstorms expected will remain through the Panhandle, North Texas, Oklahoma, and eventually much of East Texas and Louisiana, although much of state of Texas is under-the-gun, even if just slightly. In fact, the majority of West Texas, including all of the Panhandle, as well as the Oklahoma Panhandle and western Kansas are all currently under a Tornado Watch, while East Texas, all of Louisiana, Arkansas, Mississippi, and much of Missouri, Illinois, and Western Tennessee are all poised with a flash flood watch.
Stay tuned to your local news channel and emergency management updates as this system continues to barrel down on the region.
Texas, Oklahoma, and Western Kansas are on the hook for some upcoming severe weather as a storm system barrels down on the Southern Plains. Arkansas, Louisiana, and Mississippi are shortly thereafter, followed by the remainder of the Eastern United States. A fast-moving cold front, which will bring snow to the Inter mountain West (Arizona, Utah, New Mexico, Wyoming, Colorado...) will begin to push through the Texas/Oklahoma Panhandle near sunset Monday evening, bringing severe thunderstorms followed by near-freezing temperatures. By sunrise, the cold front will have blasted through Texas Hill Country and Central Oklahoma/Kansas and will bear down on East Texas, bringing Severe Thunderstorms and potentially heavy rain to much of South-Eastern Texas (Houston Metroplex) and Coastal Louisiana. This will continue through the day on Tuesday, with rain and thunderstorms occurring through the Mississippi River Valley from New Orleans to St Louis. By sunrise Wednesday, expect the cold front ans associated weather to stretch from the Mississippi Gulf to Lake Michigan (wow!)...becoming slightly negatively titled (which is conducive for very bad weather) through the Ohio River Valley. By early morning Thursday, it will hit the Appalachians. At the same time, an additional cold push of air will enter northern Texas, bringing sub-freezing temperatures.
I've attached the Storm Prediction Center's outlook valid from 6am Monday-6am Tuesday. Thunderstorms will occur outside of the shaded areas...this is only their assessment of SEVERE THUNDERSTORM potential. Additionally, this does not account for heavy rain and flooding potential.
***Severe Thunderstorms (as issued by the National Weather Service) include quarter-sized (1-inch diameter) hail and/or wind speeds 58 mph or greater (50 knots). Tornadoes are often a possibility with severe thunderstorms, but the likelihood of a tornado is significantly less than the likelihood of a severe thunderstorm. On average, only about 20-30% of severe thunderstorms are capable of creating a funnel cloud, and even less will create an actual tornado reaching the ground. Nonetheless, the threat exists.
Dan Schreiber is a freelance meteorologist with experience