Graphical Interpretation
Top Graph (Temperatures °C)
| Temp |
The "24hr" Temperatures are the low and high values from midnight to midnight.
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AM/PM Temps are defined as follows: Min is from 7PM the preceding day until 7AM of the current day. Max is from 7AM through 7PM of the current day.
Usually, the two types of reports give the same results, but in winter, with fronts moving through, there will be differences. NWS forecasts use the AM/PM system (as do these forecasts), but the official climate data is generally midnight-to-midnight. |
| Dew Pt |
It is the temperature at which the air can now longer hold all of its water vapor.
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Dew Point is a better indicator over Humidity of how muggy or dry it feels.
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| Wet Bulb |
This temperature is the lowest temp that can be reached by the evaporation of water.
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It is the temperature you feel when your skin is wet and is exposed to moving air.
Wet Bulb Temperature is an indication of the amount of moisture in the air. |
| 850 hPa |
This temperature shows weather conditions at around 5000ft above sea level.
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There is a tendency that temperature will be higher than predicted on days the wind is light and will be lower than predicted on days the wind is strong. This is because the low-level wind effects the depth of mixing.
Does not work on cloudy days or days with afternoon precipitation.
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| Temp Adv |
Refers to change in temp caused by movement of air by the wind.
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Forecasting Temperatures using Advection involves looking at the wind direction at your station and the temperatures upstream (in the direction from which the wind is blowing). If temps are warmer, that means warmer air is being transported towards your station and the temperature should rise. |
Bottom Graph (Instability Indices)
| Positive number |
Stable |
| 0 to -4 |
Marginal instability |
| -4 to -7 |
Large instability |
| -8 or less |
Extreme instability |
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LI is used to assess low level parcel instability of the troposphere.
The more negative the LI the more unstable the troposphere and the more buoyant the acceleration will be for rising parcels of air from the PBL (Planetary Boundary Layer).
Only use LI for warm season convection. Not recommended for forecasting winter precipitation.
The LI only assesses instability in one level of the troposphere. |
| 15-25 |
Small convective potential |
| 26-39 |
Moderate convective potential |
| 40+ |
High convective potential |
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KI is used to assess convective potential.
Should not be used to determine severity of storms.
This index works best for flat areas in low to moderate elevations. It does not work for high elevations. Index value interpretation varies with season and location. |
| <44 |
Convection not likely |
| 44-50 |
Likely thunderstorms |
| 51-52 |
Isolated
severe storms |
| 53-56 |
Widely scattered
severe storms |
| >56 |
Scattered
severe storms |
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TT is used to assess storm strength.
This index works best for flat areas in low to moderate elevations. It does not work for high elevations. Index value interpretation varies with season and location.
Index will be too stable if a layer of moisture is just under the 850 hPa level. |
| Positive number |
Stable |
| 0 to -4 |
Marginal instability |
| -4 to -7 |
Large instability |
| -8 or less |
Extreme instability |
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SI is used to assess 850 mb parcel instability.
The more negative the SI the more unstable the troposphere and the more buoyant the acceleration will be for rising parcels of air from the upper PBL (Planetary Boundary Layer).
SI is great to use when there is a shallow layer of low level polar air in the PBL. In this case, lifting will occur above the polar air. Thus SI will be much more relevant to use as compared to the LI.
The SI only assesses instability in one level of the troposphere. |
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Forecast Informations
