January Climate Outlook

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Happy New Year everyone! We made it to 2013. I haven’t posted any entries in a while, and because January looks like a mixed bag; I wanted to share some thoughts going forward the rest of the month. I am sure most will be thoroughly confused after Wednesday as temperatures will be in the 50 – 60°F range. To top it off a possibility of a round of strong storms on Thursday? I’ll take a more broad look at this month below.

Looking over the typical climate parameters: http://raleighwx.americanwx.com/models/00zlinegraphs.html  The charts show the tendencies of multiple global models the GFS, GFS Ensembles, ECMWF (Euro) and GGEM (Canadian model) and their respective ensemble (multiple models run altering specific data multiple times, then brought to an average). Remember back a few months ago I mentioned on the main fan page that I would keep a close eye on ‘climate parameters’?  It is one of a few ways we look into the future for indications of changes over time. Or short-term climate changes. This winter this method has been fairly reliable.  Here is how I am currently interpreting the latest data:

Negative NAO (North Atlantic Oscillation) still does not lock. What does that mean? Remember we discussed the North Atlantic Oscillation pattern this fall. http://tinyurl.com/avrpuea I said; for a solid cold out break typically we need to this parameter fairly negative. Well looking at the latest trend and 00z suite of models for 01/07/13:

NAO 01072013There is temporary blocking for early next week, but notice Euro (ECMWF) goes positive and the rest of the models are only somewhat negative. There is clear disagreement on how much cold air will actually drop back into the Eastern US over the later portion of the month. Certainly not the look of an arctic take over  from this perspective, or on the trend.

Another driving factor this winter has been the parameter PNA (Pacific North America pattern) and EPO (Eastern Pacific Oscillation) in fact. I think they have been bigger drivers than even the NAO. If you recall; typically it is hard for the Ohio Valley to get a respectable Winter without suppression from a very negative NAO. That really has not set up this winter. The question: How did we end up with two winter storms back to back ? Well, it was the combination of things. A) Split Flow Upper Level Jet pattern. There was a very active subtropical-jet streaming into the southwestern US, also referred to as, ‘the blowtorch’. When it is negative the blowtorch is cut off or shifted south along the Gulf Coast States, which is why they are typically so active during the winter months. When EPO is positive, it is further north, to keep it simple.

EPO 010713

B) A neutral-positive PNA. Remember this has an inverse relationship to the Eastern US. When PNA is POSITIVE it means strong ridging in the West, troughing in the East. Well, based on the latest suite models and the trend PNA is VERY negative… that would suggest the extreme cold weather again hangs out in the west, not the east over the next couple weeks, but hold on! Look what happens after the January 16th. PNA sky rockets!

PNA 010713

Something big and cold is coming east? Not quite, remember though, the NAO is not very negative suggesting it will be progressive, it will not lock. Another problem here, GFS has a known COLD bias in the extended range, read carefully, in addition the rest of the models COMPLETELY disagree, even its own ensembles…

 
To summarize: The warm up or big thaw will happen through mid-week. Well warm through the 40s today (Monday) and up to 60°F by Thursday, this is mainly because of a powerful shortwave and associated low-level jet which will pump very unseasonably warm moist air into the Midwest and Tennessee Valley, which may lead to a severe weather event especially south of the Ohio Valley. Depending on instability’s extent north we could be included. Should note I am also a bit concerned about flooding, especially across Southern Illinois and the Wabash River Valley with all of the snow melt and soon  heavy rain. I’ll cover that aspect on the fan page as we get closer to this weekend. Bottom line is we remain in an active pattern enjoy the next couple quiet/warm days. There will be problems by the end of the week, and wintry issues towards the middle-end of the month. But I am a bit skeptic on the arctic abyss setting it’s sights on the majority of the eastern US, but we’ll certainly cool compared to this week.

 

Dangerous Severe Weather Threat Friday

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I tried to remain optimistic models would trend away from a nightmare scenario, but the continue to point towards a very grim reality starting first thing on Friday morning.

Synopsis Part 1: There is a large scale upper level trough currently over the rocky mountains there will be a shortwave disturbance rotating around the base of the mean trough. As it drops into the Plains early this evening it will aid in forming a surface low in East Central Oklahoma. Cyclogenesis will be rapid. As it develops, it will send a surge of warm moist air north along a warm front which is currently stalled out from yesterday’s cold front in northern Mississippi/Alabama. This warm frontal boundary will rapidly surge north as a surface low rapidly deepens starting in NE Oklahoma and races to the NNE towards Chicago. 12z NAM and 00z GFS depicts thunderstorms erupting along and north of this warm frontal boundary by 6:00 AM Friday morning due to the rapidly evolving dynamics in the morning. These storms also have the potential to be strong to severe Friday morning. While we are dealing with potentially severe storms early, there will be stout SW low level jet regime developing and rapidly surging the boundary NNE into Central Indiana. (pictured above)

Synopsis Part 2: This appears to be a two part event for the Tri-State one early morning with the warm front (above) and then another event from the trailing cold front in the afternoon before quickly transitioning east into SE Indiana and Central Kentucky. This is where it gets tricky and the models diverge. As the Surface and 850mb low continue to deepen (get stronger) and move NNE.  The Tri-State will be placed firmly in the warm sector by 12:00 PM in the afternoon. At this point we will be capped. That will shut off any remaining convection. Strong SW wind will kick in and skies may even clear out, which is bad… the sun will add ample support to an already very discerningly violent set up. We measure this energy with a parameter called CAPE - Convective Available Potential Energy. That simply means IF storms develop, what will they have to work with. It is very important to understand that just because there is high CAPE does NOT mean there is a guarantee for severe weather! This IMPORTANT to understand. It is however a red flag in the correct set up. That said, lets take a look at the values, as this is what will make or break the magnitude of the event. Models disagree here. NAM model has been consistently off the charts in regards to instability. To save multiple maps and pictures, and your time I will post one image that has everything we need it is called the Skew-T: 

WARNING: This is valuable information, but not non-meteorologist friendly. But a necessary tool to assess the situation.

The first thing that should jump out id all the ‘red’ on the left. These are severe weather parameters. CAPE we discussed earlier is the top value. This screenshot is taken just before storms erupt on NAM 12z model in Evansville, IN at 3:00 PM CST. NAM shows a robust and extremely unstable airmass in this image. 1800 J/kg is a scary number to see in early March. Its common in the summer if not higher. Moving moving down, EHI: Energy Helicity Index, used to measure the potential for tornadoes, is a normalized value. Anytime EHI goes above 1 we get concerned. Its at 2.99. LI - Lifted Index: this is a measure of how buoyant a parcel of air will be if there was no forcing (a front) involved. In other words if I have a section of air and I released it randomly in the atmosphere will it sink or float. The lower this value the more concerning it is. -6 is significant. One other thing  that should jump out on the image is the pink lines on the right. This is a measure of wind speed as you go UP in the atmosphere. This is extreme speed shear, winds are blowing at 60 kts or ~70 mph at ~6,000 ft off the ground… on top of that we also have winds blowing at 127kt or ~150 mph at 30,000 ft. This creates a vacuum environment. Aloft air is rapidly advected out-of-the-way, the air from the surface has to rush in to replace it, thus ENHANCING the already very unstable lift described above. This again is a recipe for disaster. You will also notice that as you get toward the bottom-right of the image you can see where the lines seem to move (and change color)? This measures the direction the wind is coming FROM. We do not like to see this change with height (as you go UP). Winds changing with height (violently) support rotating updrafts or what we call a mesocyclone (strong rotation aloft), if brought near surface can spawn large and very dangerous tornadoes. One light note, the winds are not as veered as we need to see for the more significant threat for the long track tornadoes, but keep in mind this is just a model and that is something on a mesoscale… They don’t always line up with reality.

Summary: In the interest of time. I will leave this here and summarize. I may ADD to this post later tonight after work, so look for an update. But I think the tone is clear. We are very concerned about am extreme severe weather event tomorrow. I am personally hoping and praying for a bust and this does not happen, but the data suggest we better get you the public prepared. Please if you do not already and I cannot stress this enough. GET A NOAA WEATHER RADIO! This is not a negotiation, this is not up for discussion. It will save your life. I am begging you I don’t want to see more lives lost. Be weather aware. Small updates will be on the fan page: if you have not LIKE it www.facebook.com/MoeWx Right now I will be at work during this catastrophic event I am trying to change that. For now best you can do is be prepared for the worse and and respond quickly if a Tornado WARNING is issued. It is likely we will see a PDS – Tornado WATCH  by tomorrow. Particularly Dangerous Situation. Maybe even a HIGH risk for severe weather would not shock me Not sure where yet, but its possible Probably the eastern half of the Tri-State if anywhere.

 

Possible wintry surprise for Western Kentucky

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NAM 12z likes Kentucky this morning. *This is not a forecast* (yet), but we’re watching it closely. Western KY could steal the show again this year with snow! It happened last year, its possible. Last night the forecast models ‘corrected’ themselves with the additional data that was added to them from the data dead zone in the eastern Pacific Ocean. There is a post on the fan page pertaining to the importance of the data obtained in the additional flights sent out by NOAA yesterday I encourage you to watch it.  One of the corrections took a strong coastal low and shifted approximately 300 miles NW which places a surface low in northern Alabama, Mississippi and Georgia. This places a swath of heavy wet snow across the Tennessee Valley and lower Ohio River Valley on the southern portions of the Tri-State. 

Why do I like this more than the other set ups, this one is actually unique, no two storms are really the same. The upper air characteristics and enhanced support has my attention. As I have said many time before I never tell you anything without looking at multiple things to back it up. While I typed this the 12z GFS model run was rolling. It looks similar, and lines up with the previous mentioned model runs but has a different opinion on the snowfall aspect, but worth watching. It has been the warmer solution of the bunch. This will be a tricky set up in that the cold air looks to be in place this weekend mainly because of the storm that is coming through today. Profiles support the idea. I took the Skew-T from Bowling Green, KY which appears to be the bullseye for now. This has the potential to be a big one. But as I always say, it has to hold! (And personally, I am ok with a slight NW shift)

 

 

The above diagram shows a moist column through 15,000 feet in addition temperatures at or below freezing through the entire column. The position of the low will support all snow as cold air advection will be taking place at this time period. Further making the set up legit. Question is, where? is this done shifting NW ? Keep it here we’ll keep you posted. I should note, if this shifts at all to the NW over the next 3 days most of Tri-State will get nailed with this. We’re watching it closely.

One other thing that has our attention with this storm  as I mentioned above is the mesoscale convective banding. The feature showed up on ECMWF model last night. and now on NAM and GFS. though it is important to note GFS is still a few miles SE of the NAM/ECMWF/CMC (Canadian) solutions. This definitely has our attention. We’ll have more details as they become available keep your fingers crossed!

Short-Term Update

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Good Evening all. I first want to apologize for the lack of updates! The weather has just been that quiet lately. If this blog is silent you can consider that a GOOD thing, if you do not enjoy active weather that is. Nevertheless, I wanted to put about a quick short-term update for the overnight into Wednesday. I’ve been discussing this vigorous upper level low pressure for a while now. It is located just west of the Mississippi River Valley and will rapidly progress east over the next few hours. Below is a radar snap shot of 10:00PM CST. It looks more deceiving than it is much of what is over Southern Illinois and Southwest Indiana is virga  (not reaching the ground).

 It will take a bit of time to moisten up the entire column I took a screen shot of the Skew-T from 02z  RUC KEVV Evansville (below), which shows a 3,000 -4,000 foot dry layer which will inhibit much in the way of precipitation initially. But shows a much more moist layer by about 5:00 AM. By then 0°C will be just off the surface, just enough to help with some snow by the morning hour. Looking for generally under an inch, but it will be enough to cause some traffic problems. I think .25 – .40″ inch of snow will be common. I think the models are just a hair behind on the temperatures, we’ll be right around freezing here at the surface, maybe slightly above. For now we wait and see what this little storm has in store for us. Enjoy :)

 

Wintry Weather to start the weekend.

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Good Morning all, I thought I’d go ahead and throw up a short-term update over the next 24 hours as location will be very important in terms of weather and precipitation type and placement. The event we are dealing with will be called overrunning, or the term isentropic lift. And to quickly define that all that really says is how the moisture is being lifted into the atmosphere. Main principles you need to understand about today will be that cold air is more dense(heavier) than warm air. Thus, if warm air is forced into an area of dense cold air it will first lift up and over as if there is a “ramp” in place. That is what we will have over Indiana going into this evening. Cold dense air is already in place. Go outside or take a look at the thermometer if you don’t believe me! Anyways, on to the forecast!

Lets take a look first at the pieces to this puzzle:
The above map shows the mean(average) upper level show, and for the most part it’s actually fairly zonal (west to east) with a very strong and fast flow going from west to east, however within this flow are waves of energy (vorticity) Red is positive and Blue is negative. We’re specifically focusing on the red approaching the Midwest. And that is because this will be associated with the life that will ultimately occur over the next 24 hours. Before spreading East, where I think things eventually turn for the worse for the Upper Ohio Valley. The map I got from Oklahoma State University: http://hoot.metr.ou.edu/upperair/vadvec/305 It was the least ‘busy’ map I could find to describe this event. It is a very good resource if you want another tool to assist in weather forecasting! Next factor will be that stationary front that will be across the upper Tennessee Valley that is the separation between the warmer moist air to the south and cold dense air to the north. It will meander a bit north over the course of today as we get the warm return (red arrows) as the disturbance (dashed line) moves in from the west. As the warm air moves in this evening it will run right into this cold air that is in place, and it will move up and over the cold air, thus the cloud cover this afternoon, and when the disturbance arrives it will become precipitation. Here is the tricky part.

Easiest way to describe this is by use of a “Skew-T” below I will highlight what you need to know.

This is a snap shot of 00z Model run last night for the GFS model. Data is from KIND in Indianapolis for about 6:00 PM EST. Today. And shows by this point the overrunning will be underway by this point. The SURFACE temperature will remain below freezing through the entire duration of this event. However, if you look on the chart you’ll notice I pointed out “Warm Air Aloft”, when you go up to about 2 -3,000 ft in the air it is ABOVE FREEZING! How is this possible. Remember, the first paragraph, I mentioned the one principle you will need to understand for this whole event. This is what it looks like on a Skew-T diagram. This set up will either produce Sleet or Freezing rain. The depth of the cold layer in this case suggests Sleet across The I-70 corridor.

Here is a horizontal map view of today’s distribution.

Keep up with Interactive Radar for the latest advisories and forecast if you’re in between the black lines going into the evening hours it will be very dangerous and slick this evening. Do not travel unless you absolutely need to.

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