St. Louis, MO post storm analysis:
The severe weather outbreak we blogged about last night did indeed occur.  In one way, we are thankful it was a localized outbreak and not a more regional event, but on the other hand it hit a major metropolitan / populated area and significant damage is being reported.  Search and Rescue operations are on-going across the St. Louis metropolitan area.  A NWS damage survey team has assessed the damage in north St. Louis County and confirmed that the damage was caused by a tornado. 

The tornado that touched down near New Melle, MO was rated an EF-1, EF-2 damage was noted near the Lambert International Airport, EF-4 damage was discovered near Bridgeton, MO in North St. Louis County and as the tornado crossed the Mississippi River it produced EF-2 damage near Pontoon Beach.  Our thoughts and prayers continue to be with our fellow Missouri citizens in the St. Louis metro area!   

Here is a look at the surface map and a brief analysis of this potentially historic event as a tornado struck, yet again, a major metropolitan area!
An area of low pressure was located in east central Kansas at daybreak this Good Friday morning and moved to the northeast to near southeastern Iowa/northeastern Missouri by late evening.  An attendant warm front was draped across the central part of Missouri, basically from just south of the KC metro area to near St. Louis.

15Z/22

 18Z/22

 21Z/22

 00Z/23

The following images were taken from the SPC Mesoanalysis page from either 23Z/22 or 0Z/23 as the storms approached the St. Louis metro area around the 7 o’clock CDT hour.  These images eerily document the thermodynamic and kinematic environment the supercell had to work in.

A very broad warm sector developed ahead of the system with afternoon highs reaching into the mid 70’s and dewpoints in the mid to upper 60’s.  This created a thermodynamically unstable environment by late afternoon and early evening.   In addition, a highly sheared environment existed for the supercell thunderstorms to operate in.  Bulk shear values were on the order of 55 to 65 kts.
Temp / Dewpoints / PMSL:
Effective Bulk Shear values: 
 
The long track, cyclic supercell thunderstorm formed near Jefferson City, MO between 5 p.m. and 5:30 p.m.
Here is a base reflectivity image as the storm approached Hermann, MO around 5:35 p.m. CDT:

This storm continued on an easterly track into a very favorable environment with SBCAPE values on the order of 1500 j/kg and 2000 j/kg.  As the storm neared the warm front draped over the northern part of the St. Louis metro the tornadic circulation ramped up and the unfortunate chaos and significant damage ensued from possible tornadoes. 
Surface Based CAPE values:
In addition, Effective SRH values in and around the St. Louis metro at or above 400 m2/s2. 
This correlated with 0-3km SRH and 0-1km SRH values nearing 400-550 m2/s2.
Here is a Storm Relative Velocity (SRV) loop from GR2AE as the storm approaches the west side of St. Louis, MO:

Here is a still image of an intense Storm Relative Velocity (SRV) as the storm approached New Melle, MO around 6:25 p.m..  A tornado was confirmed by a NWS Survey Team and it was rated as an EF-1.

Fortunately, only minor injuries have been reported.  The active pattern continues well into next week with southern and central Missouri under the gun again Monday night with the potential for a significant severe weather outbreak.  Situational awareness is key folks, be weather aware! ~ CS

***FORECAST NOT VALID AFTER 18Z/22***

A very quick blog update this evening as this has been one heck of a week on the home front.  Here is a look at the latest IR water vapor imagery showing the storm system in the Pacific Northwest as well as the look at the current surface features:

An area of low pressure will be developing in the central plains on Friday.  The surface low pressure center of interest will be in southeastern Colorado and is forecasted to move into west central Kansas by 12Z/22. 

An attendant warm front will be draped across the southern portion of Missouri and is forecasted to retreat northward and be along a line from just north of the KC metro to just north of St. Louis, Missouri by 18Z/22.  The area of low pressure will be located in northeastern KS with a cold front extending southward into south central Kansas and northern Oklahoma.

Areas to the north of the retreating warm front will be most susceptible to elevated storms capable of producing small hail and possibly some damaging wind gusts during the morning on Friday.  This is evidenced by RUC forecasted lapse rates on the order of 6C to 7C at KCDJ (Chillicothe, MO) from 9Z/22 to 12Z/22.  These storms should be on going by 12Z/22 in areas between the I-70 and US 36 corridor, possibly a little further north, and should be out of the area by 0Z/23 as the area of low pressure lifts to the north and east of Missouri as evidenced by the NAM composite reflectivity as well as the 0Z WRF:

Farther south, a dryline will extend from southeastern Kansas dissecting central Oklahoma and Texas by 18Z/22.  However, a strong capping inversion will be in place most of the day over OK and TX.  This is
evidenced by this NAM sounding from south central OK at 18Z/22.  In addition, any appreciable forcing will diminish as the surface low pressure moves from northeastern Kansas into Iowa by 0Z/23.

Of greater concern is the advancing cold front, albeit the storm mode may very well be linear with embedded supercells.  A very unstable airmass will exist south of the warm front, generally along the I-44 corridor and south, by 0Z/23 based on 18Z model runs.  Temperatures will be in the 70’s with dewpoints in the low to mid 60’s.  A quick look at SFC-500mb crossovers on the NAM and GFS show a strongly sheared environment for supercells to work in.

As the cold front advances southward, surface based convection is expected to occur from near Joplin to the St. Louis metro area.  All modes of severe weather will be possible in these areas.  Here is a look at the simulated radar reflectivity from the 0Z WRF valid at 01Z/23:

Here is a look at the SigTor parameter per the latest run of the SREF for 21Z/22:

If we were chasing tomorrow we would set up northeast of the surface low along and just south of the warm front in hopes a discrete cell would fire early.  If this were to occur and the cell becomes supercellular and has a chance to interact with the boundary it could easily become tornadic in the strongly sheared environment. 

However, it looks like the cold front quickly overtakes the show and turns it into a linear mess and potentially impressive heavy rain event across southern Missouri and southern Illinois.  Several SKEW-T precipitable water values are well over an inch across southern MO.  The day 1-2 QPF is quite impressive for the potential for flooding rains:

One thing to note, it is quite possible, depending on the location of the retreating warm front, the best chance of severe could be pulled farther north across central Missouri.  This is something we will have to watch as the 0Z model data rolls out.  I will try to update the blog later tonight or in the morning after I have a better chance to peruse the latest model data.

Here is the Day 2 Severe Weather probability outlook from the SPC:

We will look further into the weekend and the first part of next week tomorrow night.  Needless to say, looks like the very active weather pattern we have been experiencing will continue! ~ CS

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