The Function Special Interest Group

Notice that we see negative OLR anomalies (blue colors) in the hovmoller diagram around January 21st near that 50E longitude line, which matches up with Phase 1 (top-left panel) in this graphic immediately above. Notice how we see our ongoing MJO wave fading near the 21st of January with the dissipation of negative OLR anomalies, as well as our second wave forming well off to the west. We see the MJO stalling out around the 160E longitude mark. Ridging then is provoked in the East US (the reason why cold weather fans in the East see La Nina’s in their nightmares). This should be a cold event lasting anywhere from 2-5 days for the USA. However, even that prospect is quickly fading, as we see a strengthening of the upper polar vortex in coming days and weeks. We see our current Madden-Julian Oscillation (MJO) wave moving eastward to the 180 degree longitude mark by around the 18th of January.

This chart shows typical alignment of outgoing longwave radiation (OLR) values by MJO phase in the west-central Equatorial Pacific. The above image once again shows forecasted outgoing longwave radiation (OLR) anomalies, but now forecasted well out into the spring. It was in use from 50’s and 60’s. Every house use to have at least a single piece of it in their house and then it disappeared after few years and now it has made its come back. The greatest threat of severe weather then appears to be damaging winds and large hail. I believe that the Midwest will get the worst of this event, but a fairly large area, including part of the Plains, is at risk for a tornado outbreak. The lack of strong helicity in the vicinity of the highest instability tells me that the tornado risk will be rather minimized. You will be warm all day, no matter what is on your agenda. An examination of the discussion issued by the SPC on this matter shows that the concerns are severe winds and tornadoes. The NAM model shows a rather small region of high instability over central Texas, extending into central Oklahoma.

One glance at the shearing chart above, and we can already define that the Midwest may be in for a rough night, with high shearing combined with strong lower level winds to give a potentially blockbuster show for the region. Try to find high quality Havarti from the deli section, or from a specialty cheese store, since all Havarti is not created equal. This stretch of high instability is slightly different from the SPC outlook in that the most able regions for thunderstorm development are just a hair east of the outlook proposed by the SPC, especially in Oklahoma. A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH AREA. Thunderstorm development is expected to commence in the late afternoon hours after the layer of stability erodes. The stability is seen in the shaded regions. However, in order for thunderstorms to start forming, the layer of stability must be eroded. In order for that to happen, we may need another warming event, ideally a true SSW.

In order to deem an event a true SSW, wind direction in the stratosphere must either significantly slow or even reverse, in addition to intense warming of temperatures. The north situations are grimmer with snow, wet and high winds amber warnings issued for Scotland where falling snow has bought down temperatures to 3C . When you have high instability with no blue shading, thunderstorms are most readily able to form. The first day of winter will not be very winter-like with high temps set to top out 5-10 above average. A look at the hovmoller diagram above will help us diagnose the atmosphere. Due to such low confidence, we’re only going to look at the long range OLR forecast as an indicator of what may come, not necessarily as something that’s “set in stone”. Very low during the summer, rising to about 40% in early October, but there there is the major ramp up to roughly 65% during the first week of November. The comparison isn’t perfect, by any means, but it’s there. Shown below is a side-by-side comparison of the last few days of January 500mb geopotential height anomalies (left), as well as typical 500mb height anomalies during a January Phase 6 MJO event, in an ENSO atmosphere reflective of this one.