This is a set of contour plots using data from the NAM model. The output fields are consistent with other models so the models can be compared. This model gives forecast information out to 48 hours and plots are sorted 48 hour 4 panel plots where each plot has a panel for the 12, 24, 36 and 48 hour forecast and individual forecast times from initialization to 60 hours in 6 hour increments. These plots are updated once every 12 hours at roughly 11:15 EST.
Rel. Humidity/Lifted Index
Sample RH-LI Plot
The Relative Humidity/Lifted Index chart depicts two fields: integrated relative humdity from 850 to 500 mb (in color contours) and lifted index (in white line contours).
1000-500 integrated relative humidity field
The RH field is a good predictor of cloud location and thickness. Areas of RH <60% generally are clear or have partly cloud skies. Areas of 60-80% are generally overcast or mostly cloudy. Areas greater than 80% are overcast with a high likelihood of precipitation as RH approaches 100%.
Lifted index field
The LI field shows instability in the atmosphere. Where LIs are <0 (also highlighted in a gray shading), thunderstorms are possible. The lower the number, the more unstable the atmosphere is and as a result, the stronger the thunderstorms could become. Values of -4 or lower indicate areas where severe thunderstorms are possible. Values >10 indicate areas of stable weather where skies are generally clear.
NOTE: For the GFS and GFSx models, the lifted index field is not broadcast so the showalter index (a rough equivalent) is plotted instead.