Monday, December 19, 2011

Mesoscale Discussion #2380- Heavy Snow (Kansas Affected)

The Storm Prediction Center has issued a mesoscale discussion concerning heavy snow for Kansas this evening. It appears that the most widespread blizzard conditions will be in Western Kansas, which is logical as sustained wind speeds are over 20 MPH at this time. Farther out east, the precipitation type will be becoming all snow as the cold air being pulled south is pulled into the system and producing snow. This means that the East Kansas area will have a very sharp cutoff for the biggest snow accumulations. As the system make its way to the northeast, these blizzard conditions should die down overnight as the precipitation continues to move northeast as well.

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Now Happening: Blizzard in South Plains

Latest Water Vapor Imagery
Water vapor imagery is easily sorting out the snow and rain apart. In Oklahoma, Arkansas and Missouri, we see abundant water vapor, indicative of rain and thunderstorms in higher water vapor values. Areas like Nebraska, Kansas and Colorado are also experiencing snowfall at this time, thus the lesser but still present water vapor values for those areas. This event is certainly going to be putting down quite a bit of snow for the South Plains region as we continue through the night. Here's forecast snow accumulations from Intellicast over the next 48 hours.

Severe Weather To Kick Off Soon in Texas, Oklahoma

A mesoscale discussion has been issued by the Storm Prediction Center for the potential for a tornado watch as a low pressure system ejects from the Southwest and moves east, or a slightly northeast direction. A cold front is in place, and with warm Gulf air being pulled north into the system, it can be expected that convective activity will be strong when the storms begin.
Water Vapor Imagery
The storms may actually be beginning fairly soon. Water vapor imagery is indicating small single-celled clusters of intense concentrations of water vapor. These concentrations appear to be updrafts, and thunderstorms should form quite soon in that area and down farther south as the updrafts mature into severe storms. However, the sounding from the KS/OK border indicates an unfavorable environment for severe thunderstorms and tornadoes, which is likely why the mesoscale discussion was kept south into Texas. When that warm Gulf air collides with the dry air (red and orange), severe thunderstorms are quick to form. It should be noted that there are updraft signatures on visible satellite imagery.

Christmas Snowstorm For The Southeast Possible

6 hour Snow Accumulations Show over 4 inches of snow
For the Southeast
The (somewhat unreliable) DGEX model is showing over 4 inches of snow in a 6 hour period for Louisiana and Mississippi. This would indeed bring travel to a standstill. While the DGEX is not a very good model, it appears to be providing a glimpse into what could happen on Dec. 26. We will provide more updates as necessary.

Christmas Snowstorm Update (Updated 12/19)

DGEX Accumulated Snowfall From Hour 84-192.
The DGEX model is showing the potential for over 12 inches of snow across a very wide swath of the Northeast. The DGEX is not a particularly good model, so take that for what it's worth. However, this is likely giving a glimpse into what might happen for a Christmas Snowstorm. If this were to verify, millions of people would be grounded and held up due to this. Travel would come to a standstill. It would be chaos across the board, but would definitely make for some good memories. More updates as the day draws closer.

Severe Weather Discussion- Dec. 19

There is a severe weather risk in Texas, including a tornado, damaging wind and hail risk. We will explain it based on the graphic above. As a pre-warning, don't let it overwhelm you.
We will explain everything that needs to be explained on this image.
Sounding from Corpus Christi, TX
Let's start on the top. There is a vertically positioned bar graph showing colors and bars. These are wind speeds with heights. Basically, the more difference there is between these bars indicates a better environment for tornadoes. We can see some difference, but nothing that really alarms me for this specific graph. Moving to the right we see a square box with what looks like a target. This is a hodograph. A hodograph, in simple terms, monitors which direction the weather balloon travels (because all this information can only be detected when sent up by a weather balloon). The direction of travel is then graphed on this target-like image to produce a squiggly line. If the line goes in a fairly circular direction, that means that there is rotation in the atmosphere and tornadoes may occur. Luckily, the only somewhat circular motion we see is very near the surface, and we need some more rotation in upper levels of the atmosphere for tornadoes.
Okay, now we get into the statistics on the bottom left. Surface CAPE (instability) is fairly low this morning, which is good, because tornadoes need high CAPE values. Forecast Surface CAPE only amounts to just over 1300 j/kg CAPE, which is still somewhat low. CINH (stability) is low, meaning that storms should be able to form somewhat easily.
PWAT values indicate the amount of water that would be present if a column of air in the atmosphere was condensed into a small space. This morning's PWAT values are at 1.5 inches, indicating a very wet atmosphere prime for wet thunderstorms.
In the small box still on the bottom left we see 'Supercell' at 6.4 units. That means that super cells have a potential to happen, especially seeing that 6.4 is a pretty substantial value. Significant Tornado (SIG TOR) values are at 0.5, which is an interesting value for December.
Something not especially noted on here is the Significant Tornado Parameter. The NAM is indicating that the Significant Tornado Parameter values may reach at 5 out of 10, which is about the same as the SIG TOR index.
The Significant Hail parameter is at 0.4, which indicates some hail could fall today.
The last thing is the box on the lower right hand corner. In small pink text below the word 'supercell', there is '9 loose matches' and then 'SARS: 67% TOR'. This means that this sounding generally matched up with 9 soundings in recent history, and out of those 9, 67% produced tornadoes. We are not entirely sure about that as information concerning this topic is somewhat scare, but this is what we have come up with.