Severe Weather Outbreak Likely Saturday

Discussion

Water vapor imagery indicates the disturbance of interest is in the southern Rockies, where elevated water vapor values are present. Thunderstorms look to be attempting to fire in portions of New Mexico and Arizona, indicating that the threat for thunderstorms in the Plains and Midwest tomorrow remains.

It should be noted that severe weather was observed upon the system's landfall last night in south California. A rule of thumb is that the stronger weather the system brings once it is onshore, the worse weather can be expected in areas that will eventually be affected. Applying that rule to our current situation means that the Plains and Midwest will be in for a bumpy Saturday evening into the overnight hours.

Model guidance fairly messy at this hour with the system. Because of limitations of the ECMWF, I will go to my own devices with the NAM and GFS. GFS prefers a more organized squall, while NAM essentially drenches the lower Great Lakes in a few mesoscale squalls over the course of 24-36 hours beginning Saturday afternoon. Upon trying to find the root cause of such model hysterics, initialization proves little- both the GFS and NAM had the system at the same spot as of 12z initialization. Initial strength did differ, but that is not of significance to me.

Bringing the WRF-ARW model into the picture for assistance to model troubles reveals a solution in between both models. The 12z WRF takes a fairly strong squall line through the Midwest and Plains, yet persists with precipitation through the Lower Great Lakes much like the NAM. In this case, the WRF seems like a good compromising point for the NAM/GFS.

Attention turns to severe threat and just what we are looking at. I believe the main threat will definitely revolve around tornadoes and damaging winds, as an enhanced jet stream and lower level winds have potential to mix down to the surface. In the midst of lacking instability (an idea thrown out by the latest NAM model), strong surface winds and enhanced shearing will get any developing cells on their feet with an initial tornado threat before the storms become more linear, favoring a squall line position.

Not concerned about timing issues within the models- storms should initiate during the day in the Plains and western Midwest before entering the interior Midwest and Lower Great Lakes overnight, likely reaching east Michigan towards daybreak.

This event looks to be the last significant one of the season, unless long range ensembles turn out to be correct in a few unusually strong systems coming through.

Andrew

Damaging Winds, Tornadoes Likely Saturday

Damaging winds and tornadoes are among the likely events that will strike Saturday into Sunday in the Midwest and Plains.

A strong disturbance will move into the Plains and fire off strong to severe thunderstorms in the afternoon and evening. The storms should start as supercells, with a tornado threat present. Iowa and Missouri could catch some of the tornadic action. However, as night falls, a more linear storm threat will take shape, and possibly extreme damaging winds will evolve as the primary threat.

Lower level winds will be strong over the expected squall line, which will start in western portions of the orange area in the evening and strike the Midwest overnight. As these lower and mid level winds strengthen with nightfall, any bow echoes that emerge from this situation have great potential to do harm across the region, with damage to structures and a risk to life present.

Tornadoes will be most probable in Iowa and Missouri, where a jet streak and favorable shearing will combine to create a feeding ground for tornadoes. However, given that instability will top out below 2000 j/kg, tornadoes that do form should be weak to moderate. Stronger cells that develop may be able to get a stronger tornado out.

I am declaring Saturday a Storm Action Day across the following states:

-Illinois
-Iowa
-Missouri
-Oklahoma
-Arkansas
-Texas

This means that people within the mentioned states should make preparations for severe weather. If the models continue to trend strong with this system, I may have to issue a Critical Storm Action Day bulletin, but that will be decided tomorrow around the 12:00-1:00PM CT timeframe. The announcement will be posted on the Facebook page, which you can find on the right sidebar.

Andrew

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LRC May Be Active This Winter

Above are ensemble forecasts for various time periods throughout the next 5 to 14 days. As you can see, there are many instances of ensemble members showing deep depressions in the US and Canada. I'm going to tell you what that means for us, and what it may do to the Lezak Recurring Cycle.

But first, WHAT IS THE LEZAK RECURRING CYCLE?
The Lezak Recurring Cycle, commonly abbreviated as the LRC, is an annual pattern that was first recognized by Gary Lezak. Lezak found that a pattern sets up in late fall (October into November) that repeats itself throughout winter. Each time this repetition happens, it is a cycle. Here's the low down.

•Each cycle lasts 40-60 days.
•Storm systems, high pressures, warm ups and cold snaps are included in these cycles.
•The pattern, while annual, is never the same as the last.

We are in the observation period of the LRC, looking for signs of the first cycle and trying to get the pieces of the puzzle to fall into place so forecasters can begin using the LRC. Above are individual ensemble member forecasts for different time frames through the next 5-14 days. As you can see, many members have deep depressions in the lines, which are forecasting the 500mb heights. These depressions are storm systems- the deeper the depression, the stronger the storm.

The fact that we are seeing such strong storm forecasts in the next couple of weeks makes me think that the Lezak Recurring Cycle may be playing a part here. Because these systems should strike when we are still in the observation stage, I find it very plausible that these systems may be found in January, when the next cycle most likely repeats.

Andrew

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Siberian Snow Cover Above Normal

Latest data from Florida State University indicates that snow cover over Siberia, Russia is currently above normal, with much of the region under some snow cover.

On the right is current snow cover in blue, superimposed with typical snow cover for this time of year, outlined in green. Right now, much of Siberia is supposed to be under snow cover. And, as you can see, blue colors exceed the climatology lines, indicating an abundance of snow cover in Siberia.

Siberian snow cover is known to be a help in predicting this winter. Multiple studies (source 1) have shown that Siberian snow cover can predict North America's winter in advance. It has been found that a lack of Siberian snow has led to below normal snowfall in the following North American winter, and this correlation is the same with above normal snowfall in Siberia.

Considering we appear to be off to the races a little bit more than normal, this bodes well with both my forecast and the hopes of many snow lovers this winter. I will be tracking Siberia through October to help me forecast the rest of winter.

Andrew

Relief From Cold Weather In Sight

There is relief from the unseasonably cold weather in sight, as the latest models are showing a warm up surfacing for much of the nation at the start of the upcoming work week.

The GFS Ensembles are showing temperature anomalies of up to 9 degrees above normal in spotty parts of the mountains out in the Rockies, with widespread 3-9 degree anomalies swarming over the general western half of the nation. This warm weather is reciprocated in the Southeast, where Gulf Coast cities like Biloxi and New Orleans may get in on temperatures up to 6 degrees above normal.

However, cities in the Northeast will not be as lucky. While coastal cities will receive a boost of a few degrees above normal, the central Great Lakes looks to stay a few degrees below normal thanks to the exiting cold shot.

Most of you should be able to put away the heavy jackets for a day or two and enjoy temperatures in the seasonable range.

Andrew