Severe Weather Update!

My initial thoughts on the severe weather outbreak that will begin tomorrow have changed only slightly since last night when I first posted them.  For those who may not have seen my post from last night, here is the link to it.  At the time the Storm Prediction Center (SPC) was about to issue its first Day 2 Outlook for this event, which can be seen below.

This outlook looked very similar to the previously issued Day 3 Outlook but had some major differences when compared to the map I posted just a hour before they issued their outlook, which can be seen below.



While I did not disagree with the location of the 30% risk issued by the SPC, I questioned their reasoning for not continuing this risk into the night, downstream of their current region.  It appeared the only reason may be a concern about decreasing instability overnight but as I viewed the models again, I was confident this should not be a limiting factor.  In fact, as I will show further in this post, the best instability will actually be during the early overnight hours.

Late this morning during the next issuance of the Day 2 Outlook, the SPC issued an outlook which was much more in line with my previous thoughts from the night before, as can be seen below.  In fact, a moderate risk was even issued for some areas (seen here as the 45% hatched region).  This new outlook actually raised some areas in Mississippi from a 5% risk of severe weather within 25 miles of a point to a 45% chance of severe weather within 25 miles of a point with at least a 10% chance of significant severe weather, a very drastic change!



This will be the first significant severe weather outbreak of the year, with tens to hundreds of damaging wind reports expected and perhaps a few tornadoes as well.  Just how significant might this event be?

Well, over the past 15 years, only five Day 2 moderate risks have been issued in January by the SPC.  What happened those other four times?

January 22, 1999: 43 tornadoes, including 2 F3 tornadoes, injured 20 people and killed one across Alabama, Arkansas, Illinois, Kentucky, Louisiana, Mississippi, Tennessee, and Texas resulting in about $76 million in damages.

January 3, 2000: 11 tornadoes, including 3 F3 tornadoes, and 101 wind damage reports resulted in 21 injuries across Arkansas, Indiana, Kentucky, and Mississippi resulting in about $72 million in damages.

January 2, 2006: 18 tornadoes, including 1 EF3 tornado, and 73 wind damage reports as well as 107 reports of 3/4” hail or greater resulted in 5 injuries across Georgia, Florida, Illinois, Kentucky, and Missouri resulting in $7 million in damages.

January 13, 2006: 19 tornadoes and 45 wind damage reports injured 34 people and killed one across Alabama, Florida, Georgia, Louisiana, North Carolina, South Carolina, and Virginia resulting in $7 million in damages.

Needless to say, a multi-million dollar day in damages could be ahead of us based on these prior events.  So let’s take a look at the details using the 00Z NAM model run.  I expect that thunderstorms will be ongoing at the start of the day in the Oklahoma area and will quickly expand in coverage throughout the morning across the western portions of the threat region.  It appears initial convection will begin to form into a squall line rather quickly, though a few discrete cells out in front of the line in Arkansas, Missouri, or Illinois may not be out of the question.  By afternoon instability will be on the increase as evidenced by the image below showing CAPE values during the evening.  This will allow the squall line to intensify as it becomes more organized across Texas, Arkansas, Oklahoma, Missouri, and Illinois, as shown by the simulated reflectivity image below for the same time as the CAPE image.





As night falls, expect CAPE values to remain steady or rise slightly in front of the squall line as the trough becomes more negatively tilted.  This will allow colder air to flow in aloft resulting in steeper lapse rates and these better CAPE values.  Additionally the low-level jet will really strengthen after nightfall, aiding in shear values which could improve the chances for tornadoes as well as the chances for wind damage.  This low-level jet is shown for around the midnight hour and it can be seen that many areas will have wind speeds of 50 knots or greater just  a few thousand feet above the surface.



This could strengthen effects of the squall line even further as shown by the simulated radar image below for around midnight.  One other serious thing to note on this radar image is something the NAM model has been advertising more and more today and it will be interesting to see what the RAP and HRRR models have to say about this soon when they begin to predict out this far.  That thing is, discrete cells in front of the squall line.  According to the latest run of the NAM, these cells may start up in southern Mississippi and southern Alabama a couple hours after dark and rapidly speed toward the north northeast at 40 to 60 mph.  Current indications are that these discrete cells could affect portions of Mississippi, Alabama, and Tennessee before being overtaken by the fast-moving squall line in the early morning hours.



If these cells do indeed form, they will have incredible speed shear to work with and some directional shear.  This shear has resulted in large helicity values across the aforementioned region and EHI values could also be fairly good for this time of year.  The EHI values for around midnight are shown below.  It is important to note that while the RAP model does not show out this far in the future yet, comparing times that it does go out to with the NAM solution has indicated that the RAP believes that EHI values could be stronger than the NAM depicts.  Stronger EHI values could show a greater chance of tornadoes during the overnight hours.



Another thing that could aid in the evolution of supercells during the night is what the NAM model indicated could occur during the afternoon hours across portions of Mississippi and Alabama.  This thing is a clearing in the clouds.  If the clouds do clear for a bit or even thin during the afternoon hours, daytime temperatures could raise quickly resulting in higher values of CAPE and a much more unstable atmosphere.



After the early morning hours, discrete cells should begin to die off and merge with the squall line as instability wanes.  The squall line should also weaken some as we head into sunrise.  Given all of this information I have produced a couple more maps below indicating my threat regions for wind damage and potential for tornadoes.






Tomorrow and tomorrow night will certainly bring about many wind damage reports.  Tornadoes will certainly be a possibility, especially if those discrete cells form overnight.  Nevertheless, any sunshine that can peak through tomorrow will enhance the severe weather threat but even without the sun, a potent trough coupled with strong atmospheric winds at all levels will be enough to spark severe thunderstorms.  Keep alert and know where you can get your severe weather information tomorrow and especially tomorrow night.  Try to find a way to get notifications even when you are asleep as these will be the best hours for tornado potential.  Stay safe everyone!