Special Morning Update - January 29 Severe Weather Event

Today is the big day. We are seeing the Storm Prediction Center maintain a Moderate Risk call for severe weather through much of Arkansas into extreme southern Missouri, extreme northern Louisiana and a very small portion of northwest Mississippi. A slight risk exists across the Plains, Midwest and Gulf Coast.

On a side note, I am maintaining my Storm Action Day call and will not upgrade to a Critical Storm Action Day unless the environment becomes more favorable for such a call.

A tornado watch has already been issued for much of Oklahoma and a few counties in northern Texas. This comes as a result of thunderstorms firing in Oklahoma, extending back through Texas. I anticipate these storms to continue strengthening along the nocturnal lower level jet stream, already feeding on the tight pressure gradient known as a dryline, which does go right up against these thunderstorms. By the looks of them, the tornado threat is highest right now, as the storms are not yet linear and are more individualized. The threat is lower in southeast Kansas and northern Texas, where there are no watches yet. Oklahoma City could be hit by some individual storm cells in coming hours as this not-yet-linear complex of cells moves east.

My main concern at the moment is extreme damaging winds. The above forecast shows wind speeds for 9 PM Central time, with wind speeds just a few thousand feet above the ground. My worry is that these winds will be provoked to move down towards the surface as the storms begin to take on a more linear shape and evolve into a squall line. When this does happen, the risk of tornadoes drops considerably and the threat for damaging winds skyrockets. Looking at the map, we would be seeing lower level winds above 72 knots in parts of the Moderate Risk area, something that could easily provoke extreme damaging winds.

I will provide updates as often as possible throughout the day, and will do another afternoon update later on in the day.

Heed all National Weather Service watches and warnings, and be prepared to seek shelter if you are in the path of these storms.

Andrew

Nasty Day Tomorrow as Significant Severe Weather Threatens

**I am declaring a Storm Action Day tomorrow, meaning that most resources will be devoted to analyzing and tracking the severe weather situation.**

The Storm Prediction Center has issued a Moderate Risk of severe weather for tomorrow, January 29th, in the face of a possibly significant severe weather threat across the outlined area.

The NAM model is shown above with the forecast for 500mb vorticity values. The term 'vorticity' defines a spinning motion in the air. This spinning motion is synoptic, or on a large scale, so it is not a producer of tornadoes. High areas of vorticity indicate low pressure is in the area, and this is how we find low pressure systems. Looking at the forecast above, which is valid for the late evening hours of January 29th, shows our storm system pressing down into Texas and Oklahoma, depicted by the deep bending of the contour lines. Something I want you to look at is how these vorticity areas are directed. For instance, if you look closely, you will see that the base of the storm system in Texas has the highest vorticity areas tilting a little towards the Southeast (if you cannot see it, I marked it in). This is a classic example of the infamous negatively-tilted storm system. The infamy of it is that, in a negatively-tilted storm system, cold air aloft is encouraged to flow over the storm system. You weather enthusiasts know that thunderstorms rise and strengthen faster in cold air aloft, so negatively-tilted storms have a tendency to produce stronger thunderstorms than their positively-tilted storm counterparts (highest vorticity values point towards the southwest).

An analysis of the upper air for roughly the same timeframe as the image above reveals a very strained jet stream. You are viewing the forecasted wind speeds for the jet stream, which can also help us identify areas of high and low pressure. If we look near the Front Range of Colorado, we see an empty space pushing down. That is our low pressure system. Again, we are seeing higher wind speeds pointing towards the southeast than winds pointing to the southwest at the base of this empty space, affirming my suspicions of a negatively-tilted storm system. The winds on this forecast are projected to max out above 150 knots in central Texas in this forecast, and winds between 130 and 150 knots in the Central Plains. These unusually high wind values are more typical of spring! Nonetheless, the strength of these upper level winds shows that any storms that do develop will have a strong backing, at least in the jet stream.

Now we get into the forecasted simulated reflectivity, which is a forecast of what the radar could show in the future. This short range model is valid for the late morning hours of January 29th. Already, we can see some moderate rain and thunderstorms surfacing in eastern Oklahoma, and this is where I anticipate the show to start. Strong upper level winds will support eventual strengthening of these storms. However, in these late morning hours, I do not expect any big severe weather threat other than some gusty winds and hail. It's about what happens later in the day that concerns me.

We move now to the afternoon of January 29th. We now see that our storm system has blossomed, with heavy showers and elevated convection (thunderstorms that are stronger than normal, but not yet severe) ongoing in much of the eastern Plains into the Midwest. Some severe thunderstorms are ongoing in the leading edge of this squall line formation. Going by this graphic, I would expect the strongest storms to be in Arkansas and Missouri at this point, with weaker (but still heavy) storms in the Midwest.

This image, valid for the early morning hours of January 30th, shows just how big this severe weather event could be. Should this short range model's forecast verify, we could see storms stretching from border to border- Canada to Mexico (if you count the Gulf of Mexico as a border, or if you use latitudes  from northwest Mexico)! Taking a look at this image, definite strengthening has occurred in this severe weather event, with very heavy convection now plaguing the Midwest and Great Lakes. We could even see some fairly intense convection happening over Michigan. Regardless, these storms could continue through the night, if the nocturnal lower level jet stream strengthens overnight. For those unfamiliar with the term, the lower level jet stream is just like the jet stream, except weaker and located lower in the atmosphere. It is nocturnal.

I think the maps above displayed my view on the situation well, and I see no need to make a map at this moment. I do suggest, however, that all those in the Plains and southern Midwest prepare for a rough ride tomorrow, especially in the evening/overnight hours.

For you storm chasers, here's my Chase Spot: Jonesboro, AR to Jackson, TN in the evening, Memphis, TN and east after dark.

Andrew

No-Travel Notice -- January 27, 2013

**This is NOT an official statement from the National Weather Service and was issued by The Weather Centre for pure safety purposes.**

I have decided to put out a No-Travel Notice for portions of the Midwest and Great Lakes in response to the ongoing ice storm and ice yet to come. The following areas are included in this notice:

-North Illinois
-East Iowa
-Southeast Minnesota
-South Wisconsin
-Much of Michigan
-North Indiana
-Northwest Ohio

Ice continues to fall across the Midwest, especially Illinois, as a body of precipitation associated with a storm system continues to move north and east. An incoming warm front will change precipitation to all rain as the evening goes on across the Midwest, but overnight icing is likely across the central Great Lakes and portions of the Northeast. Travel is considered dangerous and potentially life-threatening in many of the highlighted areas as a result of accumulating ice. Unless you are encountering a serious emergency, travel is not advised as the ice is making roads treacherous at this time. Until the rain arrives to melt away the ice (which could take additional time), roads will continue to be very unsafe and should not be used.

Andrew

January 29-30 Potential Significant Severe Weather Event

January 29 Severe Weather Risk

January 29 Probability of Severe Weather

January 30 Severe Weather Outline

I'm continuing to observe the potential for a multi-day severe weather outbreak across much of the nation. Below is yesterday's discussion, which remains valid today.

This is the 500mb vorticity forecast for the evening of January 29th. We can see a strong storm system is present in the Southern Rockies at this timeframe, with high vorticity values being found across the mountains and Plains. The system does not appear to be tilting its highest vorticity values in any particular direction, meaning this system has a neutral tilt. This is good news for those who do not welcome severe weather, as negatively tilted systems (highest vorticity values pointing to the southeast) tend to allow enhanced severe weather chances due to cold air flowing aloft, where storms can build and strengthen faster. If you wanted to be really specific, this can be classified as a slightly positively tilted storm system, but I'm not really seeing a difference because of just how slight that positive tilt is.

This is the lower level wind speed forecast, again valid for the evening of January 29. These winds are forecasted for the 900mb level, not very high above the ground. We can see very strong winds at this level across the Midwest and South Plains into the Gulf Coast. Lower level winds reach as high as 74 knots in east Arkansas. This enhances my theory that Arkansas will be the center of the January 29th outbreak. For those unfamiliar with the implications of lower level winds, tornado potential is enhanced in areas of stronger lower level winds, as wind shear is increased and thunderstorms are encouraged to form.

The last image I will show you is something called surface-500mb shear, also known as Deep Layer Shear (DLS). Deep layer shear is looked at during severe weather potential timeframes to evaluate if there really is a tornado potential. The first ingredient for making a tornado (other than having a thunderstorm) is shear. If you don't have shear, you cannot have a solid tornado. However, the deep layer shear forecast calls for shearing above 100 knots in western Arkansas, a significant value for winter. If storm activity maintains an individual cellular formation and blossoms in the areas with high shearing, tornadoes could be strong and widespread.

Andrew

February 8-12 Potential Winter Storm

Image courtesy Tropical Tidbits

I am watching the potential for a winter storm between the 8th and 12th of February, with those dates very fluid and not nearly set in stone at this moment.

The above image shows Hour 312 of the 0z GFS model. We can see a modest storm system ejecting from the Rockies and producing wide precipitation shields across the Plains and down towards the Gulf Coast. Most notably is an area of heavy snow occurring in the Central Plains, where several inches of snow may be trying to accumulate. I cannot determine just how much, as the source of these graphics does not provide such a luxury. Nonetheless, accumulating snow would be falling in the Plains, with rain in the Southern Plains in a situation that may even produce some elevated convection.

Image courtesy Tropical Tidbits

Fast-forwarding to Hour 336 (12 hours later), we find ourselves with even heavier snow now occurring in the Midwest and western Great Lakes, into the Ohio Valley and Mid-Atlantic. I could see a very good accumulating snow event come out of this (that is, if this forecast even reappears in the next week), but again, I am in no position to determine exact amounts. Making a quick glance over to the rainy side I see heavy rain now ongoing across the Gulf Coast and Southeast. While the low pressure system is further north and not right on the Gulf Coast, I could still see the chance for some elevated convection if the cold front brings up the rear of the precipitation with some solid cool air.

So, you're most likely wondering why I am spending my time typing this much about a storm way out in the long long range of the GFS.

The answer: Lezak's Recurring Cycle (LRC).

The LRC involves a cycling pattern that repeats, or 'cycles' every 40-60 days. Each cycle length is different each year, and the pattern is most prevalent from winter into spring. This year, the cycle length is roughly 53 days. If we were to go back 53 days from February 10th, we would find ourselves on the date of December 21st, 2012- supposedly the day of the apocalypse.

This was the atmospheric set-up on the 21st. We had a deep low pressure system in the Central Great Lakes and Ohio Valley. W also observed high pressure in the Canadian Maritimes into New England, as well as in the Plains and Rockies. Deep low pressure was observed off the coast of the Pacific Northwest.

Now that we've got a look at December 21st, let's go to the forecast day of February 10th and see if we can spot any similarities that may validate or void this potential winter storm.

A quick comparison between the two yields many similarities. Let's list them all- First, we see a deep low pressure system once again present in the Ohio Valley, which is the main potential for the storm. We see the high pressure systems in the Plains and Canadian Maritimes into the New England region. The big thing we're missing is the deep low pressure system offshore of the Pacific Northwest, but that will likely come back into the model's field of vision as the time draws closer. Also worth nothing is the forecasted high pressure centered in eastern Greenland, resulting in an east-based negative NAO. The east-based negative NAO is favorable for cold and snow to reach the Central US over the Northeast, increasing the validity of this forecast.

We have suddenly established these two dates as very similar. The atmospheric pattern over North America (while not 100% spot-on) is similar enough that my confidence in this particular forecast is increasing. Now, we will definitely see this forecasted storm come and go in future model runs, but seeing such a close match between this forecast and December 21st tells me we should be watching for this timeframe to verify.

Andrew