Hi everyone!
Ryan, Liz and I have been looking at a potential for freezing rain since late last week for tomorrow. Well…tomorrow is upon us! In a situation like this, the first thing I do is look at a forecast sounding. For those unfamiliar with what a sounding is, it’s simply a vertical temperature and wind profile of the atmosphere. It can be created from a simple weather balloon launch, but also can be created from computer forecast model data. Meteorologists can interpret lots of information from a sounding. Click on the image below to see the Wednesday 6 am forecast sounding for Omaha from the 1200 UTC Eta, courtesy Northern Illinois University:
Not trying to get into a lot of detail on this image, but the higher up on this image you go, the higher you climb in the sky. The sounding warms as you go farther right and cools as you go farther left. The white, curvy vertical lines represent the temperature (on the right of the two) and dew point (on the left of the two). If they’re close together or overlap especially in the bottom half of the image, this simply means the lower and mid-atmosphere is full of moisture sufficient for clouds and precipitation. One more thing I should point out, is the freezing line, which is 0°C on the bottom axis (marked in blue). You can see the 0°C isotherm (freezing line) going diagonally toward the upper right the higher you go.
As a forecaster, I pay close attention to where the temperature and dew point lies above or below the 0°C isotherm in the lowest third of this image…when forecasting wintry weather. In reality, if temperatures are well above freezing, let’s say 3,000 or 4,000 feet above the ground, but you have a very cold airmass at the surface well below freezing…any rain precipitating from the cloud won’t have enough time to freeze before it reaches the ground. Effectively, the hypothetical rain will hit the ground as water, but will freeze upon contact since the surface is below freezing. This, by definition, is freezing rain. It’s just the traditional rain that we get during the warm season, but in the wintertime, this causes a glaze of ice on everything. This is the setup we’re looking at for our area tonight into Wednesday.
As far as amounts, the 1200 UTC model guidance (MOS) shows QPF codes of 3+2 from the NAM and 2+2 from the GFS models between 6 pm this evening and 6 pm Wednesday for Omaha (Eppley Airfield). Translated into actual value ranges, the NAM shows a potential liquid equivalent of 0.35″-0.73″ and the GFS shows a range of 0.20″-0.48″. Therefore, the minimum liquid equivalent from this storm is 0.20″ based on the GFS for Omaha and since surface temperatures are expected to generally remain at or below freezing through the event, there’s a good chance that the 0.20″ could be ice accumulation. For your reference, please see the latest MOS for Omaha (Eppley) here: http://www.nws.noaa.gov/cgi-bin/mos/getall.pl?sta=KOMA
The Action 3 News viewing area is currently under a WINTER STORM WATCH from midnight tonight through 6 pm Wednesday. It’s very likely that the shift and lead forecasters at the Omaha/Valley National Weather Service office will consider upgrading to a Freezing Rain Advisory (if potential ice event accumulations will be less than 1/4″) or an Ice Storm Warning (if ice accumulations are expected to exceed 1/4″). Since other types of precipitation (such as snow or sleet) won’t be likely tonight and tomorrow, I have a good feeling that it will be either one of the two advisories I mentioned that are being strongly considered for our area.
I’ll simply be restating my thoughts on Action 3 News Live Midday, but you can also see what Ryan’s thoughts are on Action 3 News Live tonight at 5, 6 and 10.
In a nutshell, just plan on an ice storm affecting much of our area, including the Omaha metro beginning tonight, lasting through early Wednesday afternoon.
-C.T.