Sunday, January 27, 2013

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.


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.


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.