Integrated Moisture Flux Convergence?

Question

What does this mean? And what would it mean if your area is shown on a map for this as a 7?

Answer 1

Its basically a summation quantity used in the water vapor conservation formula to predict total rainfall associated with a synoptic-scale cyclone. I have no idea what the numbers mean because I don't know what their units are.

Answer 2

It is showing the areas where moisture and air parcels are converging (piling up and rising) at location "C" and areas from where moisture and air parcels are diverging (replaced by sinking air) at location "D".  Units are in grams per kilograms multiplied by 10 per hour.  Thus a 20 means 2.0 grams of air and moisture per hour.  So a 7 means 0.7 grams of air and moisture per hour.  A positive value meas there there has been an increase of air and moisture (higher dewpoints) in the past hour, brought in by converging winds.  Convergence also implies lift.

Surface moisture-flux convergence is comprised of mass convergence and moisture advection.  

When the atmosphere is unstable or becoming unstable, any area with the surface moisture-flux convergence bullseyes of 20 or more should be watch for convection developing within about 2 to 3 hours. However, you should also use this chart in combination with local and recent sounding to make sure that air mass is unstable and that if a cap if in place, that cap is week enough to in break so you can get convection.  

So, in summary, positive values are telling you that the surface winds are transporting more air and water vapor into the loca, forcing the air to rise.  So when the value is increasing, one or more of the following is occuring...

a.  Wind convergence is increasing

b. moisture is increasing

c. moisture advection is increaing

A word or caution.  this chart does not describe what is happening aloft.  Therefore, it is a good idea to use this chart to support other data... and  one should not use this chart alone for forecasting convection.  This chart will not be much help in cases where you expect nocturnal convection.

There are other uses for this chart...but that is the basics.