Winter Weather Interpretation Tips
Nov 30, 2007

With winter weather approaching, don't forget some of your OK-FIRST winter weather tips.

First of all, don't forget that winter weather is a tough forecast and expect it to change often. Keep checking those forecast discussions!

During the event, here are some things you can do to stay informed about precipitation type and intensity:

1. Check the critical thickness plot (the default map on Choose Your Threat: Ice & Snow). On the north/cold side of all those lines, expect precip to fall as snow. On the south side, expect liquid precip to fall from the sky (which will freeze if surface temps are below freezing!). Between all the lines: a mixed bag. (example)

2. Mesonet data is critical. Find the freezing line! Remember that you can use "disappearing wind observations" to see where our wind sensors are freezing up. The sensors are 30 ft off the ground. When our wind observations start grinding down to zero, we are loading ice at 30 ft: so power lines and tree limbs are probably loading ice too.

3. Frozen precip often looks different than liquid precip on radar. Frozen precip often has a smooth or "brushed" texture and lower reflectivities. Liquid precip (rain, freezing rain) is usually more cellular or "mottled" and has pockets of higher reflectivities (example).

4. Snow and ice can stick even when soil temps are in the upper 30s. Bridges and overpasses freeze first!

5. If you came to the fall refreshers, you got a lot of info about soundings. Use the current sounding to help diagnose precip type, but remember, it's usually several hours old and a long way from your local jurisdiction. Use Mesonet data to update the surface temps!

5b. If you are comfortable interpreting soundings for precip type, here is a useful link for forecast soundings.

Remember, the freezing line is critical at the surface as well as aloft in the atmosphere. Use the OK-FIRST winter weather cheat sheet (page 1 | page 2) to help during the winter event. Also, take a look at some examples of freezing rain, sleet and snow soundings in the OK-FIRST Winter Weather Training Materials.