Thursday, April 18, 2013

Widespread Damage Expected With Squall Line

Severe Weather Update from SPC:
5:00pm edt - Moderate risk dropped; high-end slight risk for much of the region.
Looking at dewpoints and satellite imagery, instability is strong, but not as strong as expected. Therefore, still looking at wind damage along the line, but perhaps not as widespread as anticipated. Let's hope that trend continues.

Quick Update from SPC:
12:35pm edt - No graphical changes made. Updated discussion includes support for strong tornadoes across far west KY. Next update by around 4pm or so.

One of my favorite harbingers of storms is the warm, humid air combined with the presence of cumulus clouds in the morning hours. Typically, those cumulus clouds become favored suspects for thunderstorm development during the afternoon.

Technically, though, a decent cap should keep the precipitation chances down during the daylight hours. Nevertheless, a cold front will approach the region later this afternoon and evening accompanied by a damaging squall line.

Obviously, the cap will not hold. The loss of instability will be gradual during the nighttime hours, especially between 8pm and midnight. Expect widespread damaging winds along that line for anyone impacted before midnight. By 1:00-2:00am, scattered reports of damage can still be expected. This may include areas just east, such as Shelbyville and Frankfort.

The SPC still has Louisville on the edge of a moderate risk for severe weather. Depending on the speed of the entire squall line, Louisville may be upgraded to a moderate risk, as we will be in that 'before midnight' sector. The farther west one goes, the higher the risk for not just damaging straight-line winds but possible tornadoes.

This squall line has the potential for causing extensive damage along it. Power outages, downed trees and lines, and possible roof damage can be expected (as winds may gust to hurricane force in places).

I will update the SPC outlook within the hour. Another one should come out later this afternoon.


Wednesday, April 17, 2013

Moderate Risk for Severe Thunderstorms Thursday/Friday

First, a Severe Thunderstorm Watch is now in effect for a portion of the CWA under Louisville NWS's responsibility till 10pm edt. Counties included are Meade, Breckinridge, and Hardin.

Now, turning attention to the main event, a squall line with possible tornadoes is forecast to impact parts of the region late Thursday/early Friday.

At the moment, far west Kentucky and far west Indiana are in the moderate shading. An upper-end slight risk shading exists for those areas along and just west of I-65.

Current thinking is that robust instability will work with the strong wind fields in place and produce a damaging squall line as it races eastward. However, as the nighttime hours progress, instability is expected to wane.

While that may happen, I do expect an eastward shift of the upper-end slight risk category to include areas along and west of I-75. Damaging winds are looking quite likely for many.

Power outages and downed lines and trees could make a mess of things as preparations for Thunder Over Louisville continue. Right now, we'll just have to wait for future developments as to the timing and strength of the storms that will affect the region.


Severe Wx Looking More Likely Late Thursday/Friday

SPC is closely monitoring a significant severe weather outbreak that should climax during the late Thursday/early Friday time period. Locations to the west of I-65 stand the best shot at seeing damage.

In fact, an upgrade to moderate risk status seems plausible in light of the strong wind fields associated with the front.

A NAM analog did not seem as robust to support severe weather for our region. However, I must be quick to point out that the GFS analogs did a better job on the last storm system in predicting overall severe weather than the NAM.

Regardless, now is the time to start looking at model trends as the timing, wind fields, instability, cap strength, and so forth start becoming clearer. That's what I'll be looking at today.

I'm still quite bullish on the prospects for severe weather here in Kentucky. I'm not going to rule anyone out in this one. But, odds favor the western part of the state that would be exposed to the greatest instability.

More later.

Monday, April 15, 2013

Severe Wx Potential This Week ***0415-0419***

Last week, severe weather affected parts of the state, primarily east of I-65. At least 12 storm reports were received, mainly for damaging winds.

One of those places in Kentucky affected by the high winds was in Montgomery County near Camargo. Quite a bit of damage associated with that wind event, peak gusts were estimated at between 85 and 95 mph. Though there were no findings of tornado damage, the high winds produced damage comparable to an EF-1 tornado.

This week, I look for a more active period of severe weather compared to last week. Already, I'm looking at analogs suggesting a much broader area that will be impacted by severe weather.

As far as Kentucky is concerned, most of our action should occur later this week as a potent cold front enters the region. The top 15 GFS analogs show this strong storm system producing severe weather across much of the south by then.

At just under 5 days out, I'm already looking at a 40% chance for severe weather somewhere in Kentucky. Last week, it was a 30 percent chance about 4 days out. So, the odds are definitely showing a higher likelihood for severe weather.

Just like last week, it's all about timing. Right now, it is difficult to pinpoint who has the best chance at seeing storms. I will defer to Tuesday's look at analogs and a closer look at model consensus by Wed/Thur.

All I can say right now is 'heads up' for later this week.


Tuesday, April 9, 2013

Severe Wx Potential

This is for the April 10-11 time frame. This will be my final look at analogs for this upcoming system.

Severe weather potential starting to come into focus a little bit better. Again, though, remember models are still offering conflicting solutions about the frontal passage in our area.

Nevertheless, a recent NAM analog shows potential for severe weather across southern KY into central TN and northern AL. Greatest threat according to top analogs suggests the areas between Nashville TN and Huntsville AL.

The greatest threat appears to be damaging wind. However, there is a threat for tornadoes, especially across TN and AL. Scattered severe hail reports could occur anywhere along the front.

So, there is a slight chance for damaging wind here in Louisville. But, it looks like the bulk of any severe weather should be limited to the south. Yesterday, though, a GFS analog showed severe weather potential farther south than today's run of the NAM.

Again, this could be related to timing issues amongst the models.

Therefore, we'll have to fine-tune this thing still yet. So, keep up with the latest updates.


Monday, April 8, 2013

Your Weather This Week (Apr 8-12)

Just what we needed. A nice, mild weekend. Ahhh.

Prior to this, we experienced below normal temperatures for 19 days out of 20. Now, we're on a 2-day winning streak with above normal readings that should continue a few more days.

Something else I noticed over the last 15 days, we've received only 0.08" precipitation. Being cut off from the Gulf of Mexico can make that happen sometimes. Now, though, we are in the good graces of that rich moisture source.

Nevertheless, the WPC (formerly known as HPC) is showing about 0.75 - 1.00" for the upcoming week

Another item that may concern some of us is the threat for severe weather during the Wed/Thr time frame. The SPC's Day 3 Outlook has Kentucky divided in half for the slight risk of severe weather, generally along and west of I-65. I'm sure the maps will change because it sounds like the GFS and Euro models aren't in agreement about timing again.

I've been looking at analog data again. At 48-72 hours out, looks like any severe weather would be located primarily south of the region such as in parts of central or western TN. So far, this does not look like a widespread severe weather outbreak...according to the top 15 analogs.

However, the NWS Louisville continues to express concern about the possibility of severe weather this week. The frontal passage's timing should prove crucial as to who stands the best chance at seeing severe weather.

As usual, we'll stay tuned.


Tuesday, April 2, 2013

Teleconnectors 'Telling' Spring Finally

The famous teleconnectors, an alphabet soup of weather and atmospheric patterns, are showing positive signs for spring around this part of the world, finally.

Looking at the AO (Arctic Oscillation), the trend is toward positive, which means warmer conditions for us.

Similarly, the NAO (North Atlantic Oscillation) is showing a positive trend over the next 2 weeks.

Another one that I look at is the PNA (Pacific North American). It is forecast to be near neutral to negative. That generally bodes well for us here. A negative PNA leads to troughiness in the west, which produces cooler, sometimes wetter conditions. On the flip side, that troughiness can lead to a ridge over the Plains states that translates into warmer conditions here. Of course, moisture can be tapped from the Gulf with this scenario as well. Therefore, expect greater rain chances with the inflow of warmer readings.

Bring on the April showers. I just want the warmer air.


Monday, April 1, 2013

MikeS 66 Index - March 2013

My MikeS 66 Index reveals a rather cool and dry March for the country (excluding AK and HI). Thanks to persistent troughing along the east coast, weather east of the Rockies was cooler than normal. However, the west enjoyed warmer than average temperatures.

Although the official numbers from the National Climatic Data Center will be out later this week or the first part of next week, I provide a rough estimate of how temperatures and precipitation totals varied across the country.

Breaking them down into 6 regions, here are the numbers....

High Plains    33.0 (temperature average)
                     (4.3) BELOW AVERAGE
                     73.2% (of average precipitation)

Midwest        31.2
                     (5.2) BELOW AVERAGE

Northeast      37.3
                     (1.7) BELOW AVERAGE

Southeast      52.7
                    (5.3) BELOW AVERAGE

Southern       52.7
                    (2.5) BELOW AVERAGE

West            50.6
                     1.6.ABOVE AVERAGE
United States 43.0
                     (2.9) BELOW AVERAGE

Temperatures were much cooler than the 30-yr normal. However, precipitation will be among the driest March(es) on record.

Remember March 2012? Yes, it was the warmest March on record. Look at the map below. When the official data comes out later, we can compare the map below to the one from this year...


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