41 votes
Accepted

What is the meaning of -999 degrees Celsius?

The value -999 is likely the "fill value" used in the dataset when data is missing or is not being properly filtered or handled when displayed. In the specific case on the website you cite, it is ...
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33 votes
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What is this "crystal ball" located at a meteorological station?

It's a Campbell-Stokes sunshine recorder, used to record the times at which the sun is shining. It acts as a lens, focusing the sunlight onto a piece of card. If the sun is shining, the focused beam ...
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  • 5,380
30 votes
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How do weather models work?

All numerical atmospheric models are built around calculations derived from primitive equations that describe atmospheric flow. Vilhelm Bjerknes discovered the relationships and thereby became the ...
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27 votes
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What do weather forecasters mean when they say "50% chance of rain"?

In the US, meteorologists forecast the probability of ANY amount of precipitation falling. The minimum amount of that we deem acceptable to meet this criteria is .01". So, we are forecasting the ...
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  • 2,598
23 votes

How do weather models work?

Weather models (or, as they are more commonly called in the field, atmospheric models) are computer programs that read in input data (initial conditions) and solve partial differential equations to ...
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  • 4,925
20 votes
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What are the major differences between weather models and climate models?

The major differences between weather and climate models are many. At their core lie the same set of primitive equations, but from here there are many differences. A weather model only (skillfully) ...
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16 votes

What are the major differences between weather models and climate models?

This answer is not complete, but it is a start. One of the most significant differences is: Weather models use measurements, whereas climate models do not Put another way: a weather model is an ...
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16 votes
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What are the applications of hydrostatic solvers vs non-hydrostatic solvers in numerical weather prediction?

The hydrostatic approximation begins with the full 3-D momentum equation (Navier-Stokes) and through scale analysis the vertical momentum equation reduces to: $$\dfrac{\partial p}{\partial z} = -\rho ...
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15 votes

If it rains harder, does it mean the rain's duration will be shorter?

The intensity of a rainstorm does not actually cause the duration of the precipitation to be shorter. There is a strong correlation, but not in the sense you may be implying here (let me get back to ...
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14 votes
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What data does a skilled meteorologist look at to predict thunderstorms?

For same day forecasting of afternoon thunderstorms, I'd start with the morning observations and the 12Z† model runs (I choose 12Z because that is the morning here in the Americas. For Europe you ...
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13 votes

What are the applications of hydrostatic solvers vs non-hydrostatic solvers in numerical weather prediction?

This is my favorite example of the difference between a hydrostatic and a non-hydrostatic code. The simulation depicts a lock exchange which you can picture as opening your window if you live in a ...
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13 votes

How do weather models work?

This is not a complete answer. One aspect of weather models consists of Data assimilation or 4D-var. I agree that they are amazing, and the question how do they work is too broad to be answered. So ...
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13 votes
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Why do forecast areas on weather.gov appear as twisted squares?

The equal-area projection used to create the continental U.S. grid for weather forecasting does not represent lines of latitude and longitude as straight lines. Instead, they are curved (note the ...
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13 votes

Is it typically colder after a storm?

The major factors in temperature change from precipitation... First, fundamentally rain is falling to the ground from higher in the sky. Precipitation typically comes from a location where it is ...
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13 votes
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Why don't weather forecast models normally take solar eclipses into account?

Total solar eclipses are rare. Globally, they only happen every 18 months. In any given spot, they are much, much rarer, with a recurrence period of many hundreds of years. Solar eclipses are ...
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12 votes

How to reconcile hourly vs. daily probability of precipitation in the forecast?

The probability of precipitation is most likely to mean the proportion of models in an ensemble or weather models in which precipitation was observed at a particular location over a particular time ...
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11 votes
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Are the storm cones introduced by Robert Fitzroy still in use?

A page in the book Come Rain or Shine, A Weather Miscellany states that the cones were discontinued on June 1, 1984, due to their being superseded by radio broadcasts and other methods.
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10 votes
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If Earth had rings would gravity exerted by Earth decrease?

Rings wouldn't decrease the gravity much, but the exact amount would depend on the exact geometry of the rings. One reason is that the gravity of one side of the ring would partially cancel the ...
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10 votes
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Are airliners sensors used to feed weather prediction models?

Indeed, airlines are equipped to measure atmospheric data and then put into weather models. The WorldMeteorological Organization's program is called AMDAR. Several articles highlight the impact that ...
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10 votes

Do wind predictions have confidence scores?

We've grown accustomed to seeing percentages for probability of precipitation. Why don't they do this for wind? No single model simulation has confidence/uncertainty associated with it. Confidence ...
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9 votes

How do weather models work?

Weather models and forecasts are governed by systems of differential equations. One starts with the current levels or values of causal variables: temperature, humidity, atmospheric pressure etc. One ...
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  • 2,194
9 votes
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Long-term Wind Speed Forecasting: reality or wishful thinking?

Warning: "long-term wind-speed forecasting for generation" has (at least) two very different meanings. One refers to forecasting a distribution of wind speeds; the other refers to hour-by-hour (or ...
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  • 4,080
9 votes
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Interpolate Gaussian grids to regular fixed grids using bilinear interpolation?

climate data operators (CDO) define grid We define a lat-lon target grid with 1°x1° grid cell size 30x30 grid cells starting at 40°N and -10°E (=10°W): ...
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9 votes

Do wind predictions have confidence scores?

Following up on Farrenthrope's answer (which I think is worthy of acceptance more than this answer) I do want to add additional detail that may not be appropriate as a comment. There is a problem with ...
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8 votes
Accepted

How do meteorologists grade their past forecasts?

Disclaimer: I am not a meteorologist. To answer this question, you need to understand how a forecast is obtained. Basically, meteorologists run computer simulations that predict how weather systems ...
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  • 294
8 votes

Is there a convenient place to get vertical wind shear info for my location?

Yes, NOAA's Storm Prediction Center's soundings page is a great source for the information you are looking for, especially the skew-T diagrams and wind hodographs. This site provides current soundings ...
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  • 4,925
8 votes

If it rains harder, does it mean the rain's duration will be shorter?

Robert Cartanio's answer makes very good points, and I'll accentuate them with some examples. Thunderstorms tend to produce "hard rain" and larger scale organized convection will have areas of hard ...
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8 votes
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How do I interpret the specs of a weather balloon?

The weight of a balloon determines most of its specifications, though I'm not sure if they are generalized or specific to a manufacturer. Looking at one supplier we can get a feel for what you need. ...
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