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June 26, 2011 ~ Moderate Risk

A late season potential severe weather set up has produced a moderate severe risk area being issued by the SPC for much of eastern NE, western IA and NW Missouri this afternoon and evening. 

Taking a quick look at the surface map an area of low pressure is located in south central Kansas with a stationary boundary extending to the east from the area of low pressure and set up across east central Kansas and central Missouri.  This boundary and approaching storm system should provide the trigger mechanisms for strong to severe thunderstorms later this afternoon and evening.  A dryline is also stretched across western OK and TX.  A cold front will move through during the overnight hours ending our chances of severe weather.

The latest visible satellite image shows a thin veil of clouds across northern Missouri and most of the moderate risk area.  This could limit the severe threat and depends on how quickly this cloud cover can burn off and break the area out into sunshine!  As I have typed this blog I have seen the cloud cover really being to erode in northern Missouri and I anticipate blue skies and sunshine within the next hour or so (17Z/26).

In addition, elevated to near surface based storms are forming in the warm sector across SE Kansas at this hour.   These storms are showing tops just below 50K feet.   The main hazards with these storms has been large hail and damaging downburst winds.  There has been a gradual weakening trend the last few scans. 

Nonetheless, temperatures have risen into the upper 70’s with dewpoints in the lower 70’s across northern Missouri.  Forecasted temperatures are to be in the upper 80’s with dewpoints rising into the middle 70’s by later afternoon.

Surface Theta-E:

Wind shear is very appreciable for this time of year with bulk shear values on the order of 50 to 60 kts (SFC-500mb).  A 500 mb jet streak will also be overspreading the area on the order of 50 to 60 kts. Storm Relative Helicity values will be enhanced in and near the stationary boundary draped across central Missouri and remnant outflow boundaries from any overnight/morning convection.  SRH valus are greater than 200 m2/s2 in northern Missouri.

Forecasted surface winds:

CAPE values are on the order of 2500+ J/kg across eastern Kansas as well as western and northern Missouri.  CINH values are a bit concerning or comforting depending if you are on the chaser or emergency management side of the hall.  Values are forecasted to be in the -150 range with some erosion occurring by 0Z/27.

Here is a look at the NAM sounding and hodograph for Cameron, MO in NW MO at 0Z/27.  It is very warm in the middle layers at the atmosphere with another slight inversion around the 850mb layer.  The 700mb chart also shows us on the edge of a very warm EML. 

The hodograph is a nice long and sweeping from 0-6 providing decent directional shear with height.  Initial thoughts are we will be severely capped through most of the day, however, the approaching surface low, associated height falls, may be enough to overcome the capping inversion and allow for deep convective development by 0Z/27.

Simulated reflectivity from the WRF and HRRR shows storms breaking out across the area by 0Z/27 and lasting through most of the night, including a rather impressive MCS that develops and will have the potential for damaging Derecho during the overnight hours across southern IA and northern MO. ~ CS

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FCST: May 18 ~ Severe TX/OK ~ Have my doubts!

Taking a quick look at models for Steve tonight to determine if he wants to venture out on Wednesday.  Work obligations have me tied up so no plains chasing for me this week.  This spring has not went well for me to get away and enjoy my 27 year hobby, but I have to pay the bills and put food in the tummy! 🙂

The northern jet stream is over Canada and has set up a blocking pattern the last several days over the plains.  Two areas of low pressure to note are over the western US, which will eject into the plains mid-week and into the weekend, and the other is spinning and bringing substantial rains to the northeast part of the country.  Nonetheless, severe weather will return to the plains in earnest late this week as the blocking pattern begins to break down.

Taking a look at the surface features for Wednesday, an area of deepening low pressure, on the order of 1000mb, is in the TX panhandle with a warm front draped across the Red River area, while a cold front dips back to the southwest from the low pressure center.  A dry line is setting up across west Texas by 18/12Z.  The dryline is forecasted to mix to the east and be in the eastern TX panhandle and dissecting central TX by 19/0Z.  A secondary area of low pressure is forming in SE CO and the primary area of low pressure is located just east of AMA.

Upper level dynamics will be rounding the base of the western trough by 19/0Z on the order of a 90 to 100 kt jet max out of the west / southwest.  In addition, mid level flow will be strengthening on the order of 70 to 90 kts from the same direction.  The aforementioned features will remain over the southern Rockies Wednesday evening before ejecting out into the plains on Wednesday and Thursday.

 

 

The 700mb flow turns more southwesterly when compared to the 300mb and 500mb charts.

700mb temperatures are negligible for capping issues and appear to be easily overcome with the loss of daytime heating and strengthening LLJ (850mb) on the order of 30 to 40kts.

However, 850mb temps are fairly warm at 0Z/19 and will be source of capping through the afternoon and early evening hours.

Surface temperatures will easily climb into the upper 80’s to mid 90’s on Wednesday afternoon.

 
Dewpoints are forecasted to be in the 50F range.  However, the surface flow is just beginning to modify over the GOM and return the moisture to the southern plains.  Anticipate 60F Dp’s as we head toward the end of the week and into the weekend.

CAPE values are forecasted to be in the 1500-2000J/kg range on Wednesday as the dryline mixes to the east.

CINH is negligible by 0Z/19 but the 850mb temps are concerning early on.

Overall shear values Wednesday are not great, but are still responsive for isolated convection across the forecast area in the 40 to 50kt range.

Crossovers are not impressive and nearly unidirectional across the forecast area.

Wednesday does not bode well for regional severe weather.  However, with the stronger dynamics rounding the base of the trough, the deepening area of low pressure, sharpening dryline and strengthening LLJ I cannot rule out isolated convection across south central OK into north central TX.  Albeit, the main risks with these storms will be isolated wind damage and hailers from more elevated convection on the nose of WAA, versus surface based convection on Wednesday evening.  In addition, Tdd’s will be horrendous. 

If I were setting up for Thursday and Friday I would stay near the WF / dryline intersection in hopes something would fire very near dark Wednesday evening.  However, I don’t hold much hope!  Now, upslope that is a different story…I am liking eastern CO and my favorite locale Limon, CO as a starting point on Wednesday but that is a lot of traveling with little sleep, IMHO, to be set up for Thursday!

Thursday and Friday appear to be somewhat better days dynamic and instability wise but we are still in need of better moisture return across the southern and central plains.  Models are forecasting a modifying flow over the Gulf of Mexico and are advertising a much better moisture return.  This is expected this time of the year but we will need to continue to monitor surface features and look for signs as we move toward mid-week.  In addition, morning convection on Friday may be the fly in the ointment as it was last Wednesday in western OK and western KS. ~ CS

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FCST: May 18 ~ Severe TX/OK ~ Have my doubts!

Taking a quick look at models for Steve tonight to determine if he wants to venture out on Wednesday.  Work obligations have me tied up so no plains chasing for me this week.  This spring has not went well for me to get away and enjoy my 27 year hobby, but I have to pay the bills and put food in the tummy! 🙂

The northern jet stream is over Canada and has set up a blocking pattern the last several days over the plains.  Two areas of low pressure to note are over the western US, which will eject into the plains mid-week and into the weekend, and the other is spinning and bringing substantial rains to the northeast part of the country.  Nonetheless, severe weather will return to the plains in earnest late this week as the blocking pattern begins to break down.

Taking a look at the surface features for Wednesday, an area of deepening low pressure, on the order of 1000mb, is in the TX panhandle with a warm front draped across the Red River area, while a cold front dips back to the southwest from the low pressure center.  A dry line is setting up across west Texas by 18/12Z.  The dryline is forecasted to mix to the east and be in the eastern TX panhandle and dissecting central TX by 19/0Z.  A secondary area of low pressure is forming in SE CO and the primary area of low pressure is located just east of AMA.

Upper level dynamics will be rounding the base of the western trough by 19/0Z on the order of a 90 to 100 kt jet max out of the west / southwest.  In addition, mid level flow will be strengthening on the order of 70 to 90 kts from the same direction.  The aforementioned features will remain over the southern Rockies Wednesday evening before ejecting out into the plains on Wednesday and Thursday.

 

 

The 700mb flow turns more southwesterly when compared to the 300mb and 500mb charts.

700mb temperatures are negligible for capping issues and appear to be easily overcome with the loss of daytime heating and strengthening LLJ (850mb) on the order of 30 to 40kts.

However, 850mb temps are fairly warm at 0Z/19 and will be source of capping through the afternoon and early evening hours.

Surface temperatures will easily climb into the upper 80’s to mid 90’s on Wednesday afternoon.

 
Dewpoints are forecasted to be in the 50F range.  However, the surface flow is just beginning to modify over the GOM and return the moisture to the southern plains.  Anticipate 60F Dp’s as we head toward the end of the week and into the weekend.

CAPE values are forecasted to be in the 1500-2000J/kg range on Wednesday as the dryline mixes to the east.

CINH is negligible by 0Z/19 but the 850mb temps are concerning early on.

Overall shear values Wednesday are not great, but are still responsive for isolated convection across the forecast area in the 40 to 50kt range.

Crossovers are not impressive and nearly unidirectional across the forecast area.

Wednesday does not bode well for regional severe weather.  However, with the stronger dynamics rounding the base of the trough, the deepening area of low pressure, sharpening dryline and strengthening LLJ I cannot rule out isolated convection across south central OK into north central TX.  Albeit, the main risks with these storms will be isolated wind damage and hailers from more elevated convection on the nose of WAA, versus surface based convection on Wednesday evening.  In addition, Tdd’s will be horrendous. 

If I were setting up for Thursday and Friday I would stay near the WF / dryline intersection in hopes something would fire very near dark Wednesday evening.  However, I don’t hold much hope!  Now, upslope that is a different story…I am liking eastern CO and my favorite locale Limon, CO as a starting point on Wednesday but that is a lot of traveling with little sleep, IMHO, to be set up for Thursday!

Thursday and Friday appear to be somewhat better days dynamic and instability wise but we are still in need of better moisture return across the southern and central plains.  Models are forecasting a modifying flow over the Gulf of Mexico and are advertising a much better moisture return.  This is expected this time of the year but we will need to continue to monitor surface features and look for signs as we move toward mid-week.  In addition, morning convection on Friday may be the fly in the ointment as it was last Wednesday in western OK and western KS. ~ CS

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FCST: May 18 ~ Severe TX/OK ~ Have my doubts!

Taking a quick look at models for Steve tonight to determine if he wants to venture out on Wednesday.  Work obligations have me tied up so no plains chasing for me this week.  This spring has not went well for me to get away and enjoy my 27 year hobby, but I have to pay the bills and put food in the tummy! 🙂

The northern jet stream is over Canada and has set up a blocking pattern the last several days over the plains.  Two areas of low pressure to note are over the western US, which will eject into the plains mid-week and into the weekend, and the other is spinning and bringing substantial rains to the northeast part of the country.  Nonetheless, severe weather will return to the plains in earnest late this week as the blocking pattern begins to break down.

Taking a look at the surface features for Wednesday, an area of deepening low pressure, on the order of 1000mb, is in the TX panhandle with a warm front draped across the Red River area, while a cold front dips back to the southwest from the low pressure center.  A dry line is setting up across west Texas by 18/12Z.  The dryline is forecasted to mix to the east and be in the eastern TX panhandle and dissecting central TX by 19/0Z.  A secondary area of low pressure is forming in SE CO and the primary area of low pressure is located just east of AMA.

Upper level dynamics will be rounding the base of the western trough by 19/0Z on the order of a 90 to 100 kt jet max out of the west / southwest.  In addition, mid level flow will be strengthening on the order of 70 to 90 kts from the same direction.  The aforementioned features will remain over the southern Rockies Wednesday evening before ejecting out into the plains on Wednesday and Thursday.

 

 

The 700mb flow turns more southwesterly when compared to the 300mb and 500mb charts.

700mb temperatures are negligible for capping issues and appear to be easily overcome with the loss of daytime heating and strengthening LLJ (850mb) on the order of 30 to 40kts.

However, 850mb temps are fairly warm at 0Z/19 and will be source of capping through the afternoon and early evening hours.

Surface temperatures will easily climb into the upper 80’s to mid 90’s on Wednesday afternoon.

 
Dewpoints are forecasted to be in the 50F range.  However, the surface flow is just beginning to modify over the GOM and return the moisture to the southern plains.  Anticipate 60F Dp’s as we head toward the end of the week and into the weekend.

CAPE values are forecasted to be in the 1500-2000J/kg range on Wednesday as the dryline mixes to the east.

CINH is negligible by 0Z/19 but the 850mb temps are concerning early on.

Overall shear values Wednesday are not great, but are still responsive for isolated convection across the forecast area in the 40 to 50kt range.

Crossovers are not impressive and nearly unidirectional across the forecast area.

Wednesday does not bode well for regional severe weather.  However, with the stronger dynamics rounding the base of the trough, the deepening area of low pressure, sharpening dryline and strengthening LLJ I cannot rule out isolated convection across south central OK into north central TX.  Albeit, the main risks with these storms will be isolated wind damage and hailers from more elevated convection on the nose of WAA, versus surface based convection on Wednesday evening.  In addition, Tdd’s will be horrendous. 

If I were setting up for Thursday and Friday I would stay near the WF / dryline intersection in hopes something would fire very near dark Wednesday evening.  However, I don’t hold much hope!  Now, upslope that is a different story…I am liking eastern CO and my favorite locale Limon, CO as a starting point on Wednesday but that is a lot of traveling with little sleep, IMHO, to be set up for Thursday!

Thursday and Friday appear to be somewhat better days dynamic and instability wise but we are still in need of better moisture return across the southern and central plains.  Models are forecasting a modifying flow over the Gulf of Mexico and are advertising a much better moisture return.  This is expected this time of the year but we will need to continue to monitor surface features and look for signs as we move toward mid-week.  In addition, morning convection on Friday may be the fly in the ointment as it was last Wednesday in western OK and western KS. ~ CS

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FCST: April 22, 2011 Good Friday severe outbreak, potential is there!

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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steve polley storm chaser