Moisture Divergence and Wind Gusts
Return to the SURFACE IMAGES
Reference: Graphical Guidance (1994) pp. 87-90
With this map, you should be able to find the following:
- areas of strong moisture convergence/divergence or "pooling"
- wind gusts
- well developed fronts or drylines by way of convergent/divergent
"couplets"
- Content
- Moisture Divergence
- Green (Positive values are dashed)
- Every two "1/s" (8,10,12 and -8, -10, -12, etc)
- Wind Gusts
- Yellow, for Black Backgrounds
- Red, for White Backgrounds
- Plotted in knots as reported
This map is one of our favorite nowcast maps during a stormchase. You want to
find the solid lines (those are negative values, and negative
divergence IS convergence) with the highest values. More
importantly, a forecaster wants to find a bullseye of negative values.
A strong bullseye shows two things:
Strong wind
convergence
Moisture advection (or pooling)
If you couple the strong bullseye with an area where there are
strong wind gusts, you can imply that there is a fairly impressive
low pressure area (and most likely getting lower). More
importantly, it is a sign of strong convergence in a small area rather
than elongated over an entire front or near the actual synoptic surface
low pressure area.
Couple strong wind convergence at the surface in an area of high moisture
values, and the chance for precipitation and thunderstorms is highly enhanced.
An example of how to read the map is found here.
ES 198 (Meso) Outline
Surface Help Page
