Some Thoughts on the Upcoming “Groundhog’s Day” Storm

Posted by pmarshwx on 31 Jan 2011 | 1 comment

A couple of things I will be watching this evening

• How the cold air interacts with the developing cyclone

The million dollar question (literally) is going to be how the cold air interacts with the developing cyclone. If the cold air plunges more south than southeast, then I would expect the ejecting surface low pressure (and associate low-to-mid-level lows) to move with a more northerly trajectory. If the cold air surges southeast, then the lows will eject with a more eastward component. This has huge implications for who will see the heaviest snows in Oklahoma and southwest Missouri.

The reason for watching how the cold air interacts with the cyclone is the result of how and where the low-level cyclones develop — which on the eastern edge of the “cold-dome”. I strongly believe the surface lows (and associated other lows) will ridge along the edge of the cold dome. Thus, if the eastern extent of the cold air has a more north-south orientation, this is how the surface low will move, placing central Oklahoma in a longer period of heavier precipitation. If the cold air orientation is more southwest to northeast, then expect the heaviest snow to shift east of central Oklahoma, as the surface development will be farther east.

• How the upper-level jet streams interact

Nearly all numerical weather prediction models are forecasting extreme precipitation amounts overnight and through the day tomorrow. It’s a bit perplexing considering the dry ambient environment. This dryness is most likely being overcome by the strong upper-level divergence associated with the ageostrophic response to a couple of a southern and northern jet streak. This strong upper-level divergence results in strong low-level convergence across portions of Oklahoma that will most likely rapidly transport moist air currently in place across eastern Texas, southern Arkansas, and Louisiana. When and where these upper-level jet streams do couple will play a major role in deciding where the heaviest precipitation bands are located.

• How does the precipitation shield evolve overnight

The last several runs of the operational GFS and NAM develop rapidly accumulating snows across eastern Oklahoma with strong low-level frontogenetic forcing. This is in spite of a +0.5C to +1.5C warm nose aloft. This would seem to favor more sleet than snow. However, if lift is strong enough, this might quickly be overcome resulting in 3-4″ per hour snow rates that are currently forecast. Farther west, the 12 and 18 UTC NAM are developing a more classic deformation zone across a large part of central Oklahoma during the late morning and early afternoon hours tomorrow. This deformation zone is more typical of substantial Oklahoma snow falls than the strong, low-level frontogenetic forcing described previously. This large deformation zone is the reason why the NAM has a large area of 6-10″ snow accumulations to the west of the 12-18″+ forecast across eastern Oklahoma.

Also, if a large squall line develops across central Texas and races east too quickly, the squall line might use up a lot of the moisture that is poised to be drawn northward into this cyclone. This would decrease snow totals across portions of Oklahoma, Kansas, and southwest Missouri.

• The evolution of the temperature vertical temperature profile

I hinted at this in a couple of the previous bullets, but how the vertical temperature profile evolves will be crucial in determining snowfall amounts. If a strong warm-conveyor belt does develop overnight, warm air might hang on longer than forecast across portions of Oklahoma. This might lead to an extended period of sleet which would cut down on snowfall totals considerably. However, 1-2″ of sleet, coupled with 2-4″ of snow would be just as bad, if not worse, than a pure 8-12″ of snow.

QOTW: Storm Prediction Center Moderate & High Risks

Posted by pmarshwx on 24 Jan 2011 | 4 comments

This week’s “Question of the Week” comes from Trevor Gramling and Ryan Vaughan.

• Climatologically, where is the most likely location to experience the first Storm Prediction Center Moderate Risk of a given year?
• What about High Risk?

Since I do not know the answer ahead of time, this may end up being a two week “Question of the Week” as I write the code to create the answers…

This ought to be fun!

AOTW: More on January Tornadoes

Posted by pmarshwx on 21 Jan 2011 | 5 comments

The answers to this week’s “Question of the Week” might surprise some of you. But first, here are the graphs that answer these questions

Here is a chloropleth map of January tornadoes by state:

Here is a bar graph showing January tornado counts by state, ordered from most to least:

Keeping the states in descending order of most January tornadoes to fewest tornadoes, here is a bar graph depicting the number of injures by state:

And, once again, keeping the states in descending order of most January tornadoes to fewest tornadoes, here is a bar graph depicting the number of fatalities by state:

And even though this plot is a bit crowded, here is a bar chart that combines the three previous charts into one:

Could you figure out the answers? Well, if not, here they are:

1. Which state(s) had the most January tornadoes?
   • Florida (151)

2. Which state(s) had the most January tornado injuries?
   • Mississippi (580)

3. Which state(s) had the most January tornado fatalities?
   • Mississippi (42)

4. Which state(s) had the most injuries per tornado?
   • Deleware (7 per tornado)

5. Which state(s) had the most fatalities per tornado?
   • Oklahoma (0.62 per tornado)

And here are the raw numbers,


State, Tornadoes, Injuries, Fatalities, IPT*, FPT**
AL, 89, 294, 19, 3.30, 0.21
AR, 117, 218, 13, 1.86, 0.11
AZ, 6, 0, 0, 0.00, 0.00
CA, 39, 3, 0, 0.07, 0.00
DE, 1, 7, 0, 7.00, 0.00
FL, 151, 259, 5, 1.71, 0.03
GA, 91, 130, 5, 1.42, 0.05
HI, 6, 4, 0, 0.66, 0.00
IA, 13, 11, 1, 0.84, 0.07
IL, 28, 140, 1, 5.00, 0.03
IN, 17, 7, 3, 0.41, 0.17
KS, 3, 0, 0, 0.00, 0.00
KY, 24, 39, 4, 1.62, 0.16
LA, 123, 142, 10, 1.15, 0.08
MD, 3, 0, 0, 0.00, 0.00
MI, 1, 0, 0, 0.00, 0.00
MO, 77, 276, 8, 3.58, 0.10
MS, 127, 580, 42, 4.56, 0.33
NC, 24, 50, 1, 2.08, 0.04
NE, 6, 0, 0, 0.00, 0.00
NV, 1, 0, 0, 0.00, 0.00
OH, 6, 3, 0, 0.50, 0.00
OK, 16, 32, 10, 2.00, 0.62
OR, 1, 0, 0, 0.00, 0.00
PA, 6, 18, 0, 3.00, 0.00
SC, 26, 44, 0, 1.69, 0.00
TN, 48, 210, 14, 4.37, 0.29
TX, 139, 73, 2, 0.52, 0.01
UT, 1, 0, 0, 0.00, 0.00
VA, 13, 14, 1, 1.07, 0.07
WA, 3, 0, 0, 0.00, 0.00
WI, 3, 5, 0, 1.66, 0.00
WV, 2, 0, 0, 0.00, 0.00

*IPT = Injuries Per Tornado
**FPT = Fatalities Per Tornado


QOTW: More on January Tornadoes

Posted by pmarshwx on 17 Jan 2011 | 2 comments

The answer to last week’s “Question of the Week” sparked a lot of posts on Twitter and at least one question posed in the comments. These comments and questions got me thinking about more ways to dissect the tornado database. Thus, I thought for this week’s installment of QOTW, I would continue with the same theme.

Above is the image originally posted in the answer to last week’s question. It depicts the number of January tornadoes each year, broken down by F/EF-Scale rating. Although containing a lot of information, it fails to answer the question I received most often: “How many fatalities have resulted from January tornadoes?” There figure below displays the number of injuries and fatalities by year for 1950-2009. (Note: The y-axis is scaled via a square-root. The thin, smooth line is a smooth trend-line. Thanks to the fine folks on the “ggplot2” listserv for helping me debug an issue with this plot!)

After a small spike from the mid-1960s through the mid-1970s, injuries from January tornadoes decreased slightly and has held relatively steady around 20-25 per year. The exception to this was 1999, which holds the record for most number of January tornadoes, including the largest January tornado outbreak on record. Fatalities appear to follow a similar trend as injuries, albeit with much lower numbers. In total

• January Injuries: 2455 (40.9 per year)
• January Fatalities: 138 (2.3 per year)

We can break down January tornado casualties even more and examine them by F/EF-Scale ratings.

As one might expect, a general increase in casualties is found as F/EF-Scale rating increases. This leads me to this week’s questions.

Above is an image depicting the number of January tornadoes between 1950 and 2009 broken down by county. Using the above image as a guide, between 1950 and 2009:

1. Which state(s) had the most January tornadoes?
2. Which state(s) had the most January tornado injuries?
3. Which state(s) had the most January tornado fatalities?
4. Which state(s) had the most injuries per tornado?
5. Which state(s) had the most fatalities per tornado?

(Hint: A tornado that crosses a county boundary is counted in both counties. Thus, one cannot sum the number of tornadoes per county in a state to find the number of tornadoes per state.)

AOTW: January Tornadoes

Posted by pmarshwx on 15 Jan 2011 | 2 comments

I apologize that this week’s answer is a day late. I was traveling yesterday and unable to access the Internet. But without further adieu, here is this week’s answer.

1. Since 1950, how many (official) tornadoes have occurred in January?
   • There have been 1193 tornadoes during the month of January in the 60 years spanning 1950 to 2009. This equates to an average of 19.88 tornadoes per year in January. Broken down by rating:

     • F/EF-Unknown: 30
     • F/EF-0: 391
     • F/EF-1: 443
     • F/EF-2: 251
     • F/EF-3: 67
     • F/EF-4: 11
     • F/EF-5: 0

As you can see, 1999 was a very active year in terms of January tornadoes. There were several tornado outbreaks that January, including the largest January outbreak on record, which affected parts of Arkansas, Tennessee, Mississippi, and Louisiana.

Experimental 4km NSSL-WRF Precipitation Type Graphics

Posted by pmarshwx on 12 Jan 2011 | 0 comments

Back in December I started experimenting with producing precipitation type graphics from the 00 UTC initialization of a 4km WRF run daily at the National Severe Storms Laboratory (NSSL) based on suggestions from Jack Kain and Scott Dembek. The idea was to take the dominant hydrometeor from the lowest model level from the microphysics scheme (WSM6) and then assign a precipitation type. Currently I’m creating 9 different precipitation types based on the 5 different hydrometeor types from the model.

How these 9 precipitation types are calculated are given below:

1. Rain: Rain water is the dominant hydrometeor type
2. Snow: Snow is the dominant hydrometeor type
3. Graupel: Grapuel is the dominant hydrometeor type
4. Fog: Cloud water is the dominant hydrometeor type
5. Ice Fog: Cloud ice is the dominant hydrometeor type
6. Mix: Snow == Rain or Snow == Graupel or Rain == Graupel
7. Ice: Rain water is the dominant hydrometeor type, and the temperature is at or below 273.15K
8. Freezing Fog: Cloud water is the hydrometeor and the temperature is at or below 273.15K
9. Mixed Fog: Fog == Ice Fog, Fog == Freezing Fog, or Ice Fog == Freezing Fog

This EXPERIMENTAL output is updated in the morning (not when the typical model output is available) and is currently linked on the main NSSL-WRF webpage on the left hand side (second of the products). A 36 hour loop is here.

I’d ask those who tend to look at weather maps on a daily basis to consider looking at this product and provide feedback on it. We know there are issues regarding the over-forecast of “ice fog” (and possibly even other fog), but are there other problems? Again, this is highly experimental and may not always be up to date. (The model initialization time will always be plotted on the image.) Any/all feedback is greatly appreciated.

QOTW: January Tornadoes

Posted by pmarshwx on 10 Jan 2011 | 2 comments

No long post tonight; just the “Question of the Week”.

Since 1950, how many (official) tornadoes have occurred in January? Leave your answers in the comments. I’ll post the answer on Friday.