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March 6th-8th Severe Potential


andyhb

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SPC has highlighted the day 5/6 period with a 15% risk area in response to the consistent model guidance of a large upper level trough amplification along the west coast at the end of this week. As mentioned in the medium range thread, a lead, negatively tilted shortwave looks to pivot northeastward across the Plains on Monday 3/7 with a strong southerly low level jet and ample vertical shear for storms present east of the dryline.

 

Depth/quality of BL moisture return would probably be my biggest question mark for this first day, although with a pretty robust EML progged to advect over the region, it won't take a lot of low level moisture to destabilize sufficiently. I do like the prospect of the left exit region of the upper jet plowing right over top of the dryline at a relatively favorable time as it sits now.

 

As for Tuesday 3/8, the main upper level low looks to lumber eastward (and quite far south) along the US/Mexico border with a potent upper jet overspreading E TX and the Arklatex. Based on pattern recognition, these type of systems with surface lows centered near the Rio Grande Valley tend to cause a lot of problems in this area, perhaps because their flow orientation both allows EML advection (which is being shown) off the Mexican Plateau and also because it prevents convective junk from affecting the highest threat areas in the morning. With 7+ C/km mid level lapse rates projected by the Euro to overspread mid/upper 60s dewpoints, aforementioned areas will have a chance to destabilize strongly through the afternoon with strong wind fields overlapping and nearly southeasterly flow at the surface really ramping up 0-1 km shear values.

 

Would be a bit concerned about the relatively meridional flow in the mid levels and whether the orientation of forcing is more parallel to the boundary, but it is important to note that we still have quite a strong southwesterly upper jet component ejecting ahead of the boundary that should encourage ascent. From what I've seen from the Euro, its precip signal does not look very linear for Tuesday until later in the evening.

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Pretty decent sounding E of Lawton valid 00z Tuesday from the most recent GFS. Keep in mind this is generally the quietest solution (or at least has been compared to the Euro/UK over the past cycles). As I mentioned earlier, would be a bit leery of moisture depth, although the GFS has been fumbling with that for almost this entire winter (and frankly before that) so we'll see what actual quality the BL is.

 

gfs_2016030400_096_35.0--98.0.png

 

Also, can't help but laugh at this BL temperature profile at 18z Tuesday in SE TX.

 

gfs_2016030400_114_30.0--94.25.png

 

Even with clouds, it is not going to be 71 there at that time.

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The 12z NAM looses its mind for Monday.  Doesn't appear to convect, but there is great cape, marginal shear, and a cap that appears to break off the dryline based on model soundings.  It's nice to finally see some good lapse rates showing, even on the GFS.  I think this may be a good day to chase.

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SPC

 

 

 

DESPITE A PROBABLE LARGE SWATH OF CONVECTION ONGOING AT
12Z/TUE...BOTH THE ECMWF/GFS INDICATE GREATER MUCAPE WITHIN THE WARM
SECTOR ON D5 VERSUS D4 GIVEN RICHER MARITIME TROPICAL AIR SPREADING
INLAND FROM THE WRN GULF. IT IS PLAUSIBLE THAT IN THE WAKE OF
EARLY-DAY CONVECTION...ROBUST DIABATIC HEATING COULD OCCUR ACROSS S
TX. THIS MAY SUPPORT ANOTHER ROUND OF SEVERE STORMS TUE
EVENING/NIGHT. ALTHOUGH FLOW WILL BECOME INCREASINGLY
MERIDIONAL THROUGH THE PERIOD...A STRONG SLY LLJ SHOULD BE
MAINTAINED ACROSS PARTS OF ERN TX TO THE LOWER MS VALLEY. THIS MAY
SUPPORT A LONG-DURATION TORNADO RISK..
.WITH HAIL/WIND THREATS BEING
MORE PREDOMINANT UPSTREAM.
 
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Dewpoints are looking really marginal on most of recent model runs and the warm sector has really shrunk in breadth. Thinking the threat on Monday is downtrending as of now.

 

If they could hit 60-62 ahead of the dryline, that would probably be solid, but that doesn't look to be the case right now. Also, things seem to be shifting towards a more veered look with the LLJ.

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The 12z NAM looses its mind for Monday.  Doesn't appear to convect, but there is great cape, marginal shear, and a cap that appears to break off the dryline based on model soundings.  It's nice to finally see some good lapse rates showing, even on the GFS.  I think this may be a good day to chase.

 

NAM uses the BMJ convective parameterization scheme, which is pretty strongly dependent on the presence of mid level moisture. As a result, it performs well for tropical-type convection, but can often miss or be delayed with continental convection.

Especially for a day like Monday, which we know will have sparse convection anyway, take NAM precip with a grain of salt.

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The threat evolution on Tuesday through Wednesday morning is one of the more bizarre I've seen in this part of the country. The LLJ looks to be outrunning the instability axis for most of the day, but then later in the evening, another shortwave rotates around the main upper low and restrengthens it further west with SE surface winds for the entire period. Could be feasible that we're looking at the potential for supercells both in the early/mid afternoon over SE TX and SW LA and then south-central TX to SW LA again Tuesday night into Wednesday. I highly doubt the boundary layer will become decoupled SE of the triple point and there is strong destabilization throughout in the overnight period in that region. HGX's most recent AFD is pretty nonchalant about the whole thing, which I'm not sure I agree with.

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The threat evolution on Tuesday through Wednesday morning is one of the more bizarre I've seen in this part of the country. The LLJ looks to be outrunning the instability axis for most of the day, but then later in the evening, another shortwave rotates around the main upper low and restrengthens it further west with SE surface winds for the entire period. Could be feasible that we're looking at the potential for supercells both in the early/mid afternoon over SE TX and SW LA and then south-central TX to SW LA again Tuesday night into Wednesday. I highly doubt the boundary layer will become decoupled SE of the triple point and there is strong destabilization throughout in the overnight period in that region. HGX's most recent AFD is pretty nonchalant about the whole thing, which I'm not sure I agree with.

Quite an anomalous setup with a cutoff low essentially diving through Mexico and south of Texas. 

post-533-0-06253800-1457206323_thumb.jpg

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Dewpoints are looking really marginal on most of recent model runs and the warm sector has really shrunk in breadth. Thinking the threat on Monday is downtrending as of now.

 

If they could hit 60-62 ahead of the dryline, that would probably be solid, but that doesn't look to be the case right now. Also, things seem to be shifting towards a more veered look with the LLJ.

 

Well the 00z 4 km is indicating this and we have quite a ripe environment in Western OK at 00z Tuesday. A bit of an S-shape in the hodographs above 700 mb, but otherwise it's pretty darn robust for early March owing to some rather frigid temperatures aloft.

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Well the 00z 4 km is indicating this and we have quite a ripe environment in Western OK at 00z Tuesday. A bit of an S-shape in the hodographs above 700 mb, but otherwise it's pretty darn robust for early March owing to some rather frigid temperatures aloft.

The s shape has me a bit worried. Something should go up over there, but I'm thinking the tornado threat should be lessened by it.

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Wow....what location was that?

Sorry for the late response. That was for somewhere in Kansas. Broad answer, I know.

 

Dewpoints are looking really marginal on most of recent model runs and the warm sector has really shrunk in breadth. Thinking the threat on Monday is downtrending as of now.

 

If they could hit 60-62 ahead of the dryline, that would probably be solid, but that doesn't look to be the case right now. Also, things seem to be shifting towards a more veered look with the LLJ.

Yeah I thought Monday was going to be the big event... really was looking like a classic event. Not as impressive as it was, but with that said, I don't understand why OUN says the tornado threat will be "very low" when they're expecting supercells. I look at the forecast soundings on NAM and GFS, and don't get me wrong, they aren't that impressive... but it's not what I'd associate with a very low tornado threat when supercells are expected. I'd call it low to low-medium... in SPC terms I'd give it a 5%, and maybe at best, a small patch of 10%. The LCL is ~1100m which is probably seasonably high... but I think that's still low enough so that it's not a deal breaker. What am I missing?

 

ZAzj3nq.jpg

FHiXMtY.png

5k7Rob8.png

 

Tuesday snuck up on me. Looking nasty on NAM, and nasty on GFS for its standards. Looks like Tuesday's probably gonna be the big day for tornadoes... and I'm curious to see this "massive MCS" that SPC advertised this morning in their outlook.

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Sorry for the late response. That was for somewhere in Kansas. Broad answer, I know.

 

Yeah I thought Monday was going to be the big event... really was looking like a classic event. Not as impressive as it was, but with that said, I don't understand why OUN says the tornado threat will be "very low" when they're expecting supercells. I look at the forecast soundings on NAM and GFS, and don't get me wrong, they aren't that impressive... but it's not what I'd associate with a very low tornado threat when supercells are expected. I'd call it low to low-medium... in SPC terms I'd give it a 5%, and maybe at best, a small patch of 10%. The LCL is ~1100m which is probably seasonably high... but I think that's still low enough so that it's not a deal breaker. What am I missing?

 

 

 

Tuesday snuck up on me. Looking nasty on NAM, and nasty on GFS for its standards. Looks like Tuesday's probably gonna be the big day for tornadoes... and I'm curious to see this "massive MCS" that SPC advertised this morning in their outlook.

The 00z NAM sig-tor values are 2+ for sections of Texas on Tuesday.  Then again, there is a narrow strip of sig-tor values of 2+ in OK/KS on Monday.  I suppose both days could produce a regional tornado outbreak. If I were the SPC, I would call for a slight risk of all hazards on Mon and Tue, as of tonight's data.

 

Remember last year, when a number of potential tornado setups got ruined by early-day convection. Model forecasts of CAPE were wrong wherever the cool temps were. A number of times, that was in central OK. Tornado-chaser frustration for central OK was high, I imagine. I wonder if that will be the trend in 2016.

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The 00z NAM sig-tor values are 2+ for sections of Texas on Tuesday.  Then again, there is a narrow strip of sig-tor values of 2+ in OK/KS on Monday.  I suppose both days could produce a regional tornado outbreak. If I were the SPC, I would call for a slight risk of all hazards on Mon and Tue, as of tonight's data.

 

Remember last year, when a number of potential tornado setups got ruined by early-day convection. Model forecasts of CAPE were wrong wherever the cool temps were. A number of times, that was in central OK. Tornado-chaser frustration for central OK was high, I imagine. I wonder if that will be the trend in 2016.

There were also a couple surprise days, one in May I believe, and one in November, that started out the day as Slight/Enhanced days-- like this will be-- and ended up being high-end days. Although, there were many more days that ended up being duds.

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I like the 0-6KM shear vectors we have for monday, yes, they aren't perpendicular to the dryline, but they aren't too shabby. The 00Z 4K NAM is particularly impressive for monday across W OK/SW KS with its CAPE forecast and parameters, the 12K NAM is not quite as robust but is still impressive nonetheless for early march in the plains. The GFS is much less aggressive with instability on monday, really as you would expect from it, it also shows a dryline that is not nearly as sharp as on the 12/4NAM. Purely basing off of the GFS there is not too much to get excited about...

 

But attm, there would appear to be a 3 or 4 hour window along a narrow corridor where a tornado risk could arise with any discrete supercells, counting on there are some. One thing this event could have going for it tornado wise is that there likely will not be a boatload of convection creating deleterious storm interactions. A few things that are not all that impressive is the forecast CAPE in the lowest 3KM, as well as the veered H85 winds, but the 925mb winds are forecasted to be southerly, or slightly backed, and surface winds should have at least some southeast component to them for a period of time... Not a big setup by any means, but like Chinook said, it could be somewhat interesting given the right things happen. 

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The 00z NAM sig-tor values are 2+ for sections of Texas on Tuesday.  Then again, there is a narrow strip of sig-tor values of 2+ in OK/KS on Monday.  I suppose both days could produce a regional tornado outbreak. If I were the SPC, I would call for a slight risk of all hazards on Mon and Tue, as of tonight's data.

 

Remember last year, when a number of potential tornado setups got ruined by early-day convection. Model forecasts of CAPE were wrong wherever the cool temps were. A number of times, that was in central OK. Tornado-chaser frustration for central OK was high, I imagine. I wonder if that will be the trend in 2016.

Yeah last spring was frustrating to watch even from Ohio. Hopefully we won't see the same thing this spring. But we've already had a number of impressive outbreaks this year, and it looks like we're in a very active pattern this March.. so maybe things will work out this spring. 

 

 

I like the 0-6KM shear vectors we have for monday, yes, they aren't perpendicular to the dryline, but they aren't too shabby. The 00Z 4K NAM is particularly impressive for monday across W OK/SW KS with its CAPE forecast and parameters, the 12K NAM is not quite as robust but is still impressive nonetheless for early march in the plains. The GFS is much less aggressive with instability on monday, really as you would expect from it, it also shows a dryline that is not nearly as sharp as on the 12/4NAM. Purely basing off of the GFS there is not too much to get excited about...

 

But attm, there would appear to be a 3 or 4 hour window along a narrow corridor where a tornado risk could arise with any discrete supercells, counting on there are some. One thing this event could have going for it tornado wise is that there likely will not be a boatload of convection creating deleterious storm interactions. A few things that are not all that impressive is the forecast CAPE in the lowest 3KM, as well as the veered H85 winds, but the 925mb winds are forecasted to be southerly, or slightly backed, and surface winds should have at least some southeast component to them for a period of time... Not a big setup by any means, but like Chinook said, it could be somewhat interesting given the right things happen. 

As I posted earlier, GFS has about 1.6 STP where NAM has 2.7. What GFS is showing is kinda impressive for its standards. I recall with one or more of the outbreaks recently, GFS held its conservative position almost all the way to the end. This far out, I assume the realistic value to be closer to NAM than GFS until HRRR and RAP get into range. I agree with you and Chinook that this should be a slight risk for all categories... maybe we'll see a strong tornado if a supercell wanders into the 2+ STP area.
 
Leaving to head back to school in less than 12 hours, but I have to stay up to see the new day 2 outlook. Priorities.
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As I posted earlier, GFS has about 1.6 STP where NAM has 2.7. What GFS is showing is kinda impressive for its standards. I recall with one or more of the outbreaks recently, GFS held its conservative position almost all the way to the end. This far out, I assume the realistic value to be closer to NAM than GFS until HRRR and RAP get into range. I agree with you and Chinook that this should be a slight risk for all categories... maybe we'll see a strong tornado if a supercell wanders into the 2+ STP area.
 
Leaving to head back to school in less than 12 hours, but I have to stay up to see the new day 2 outlook. Priorities.

 

It's not just conservative, many times it is just flat out wrong in its depiction of boundary layer thermodynamics and ageostrophic backing near the surface (latter problem is partly due to its resolution).

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For monday, SPC is not very optimistic of much of a tornado threat. Not sure I 100% agree about the "high-based" idea since once you get right off the DL, LCL's lower to around 500-750m. LL moisture is of course an issue though with DP's only progged 55-62 across W OK which seems pretty accurate with upper 40's-lower 50's DP's right now, and upper 50's-lower 60's across TX with pretty meager moisture transport. A veered, and relatively weak LLJ (~30kts over W OK) is also a mitigating factor, the fact that the main core of the LLJ (50-60kts) will also be placed over E OK does not help.

 

...SOUTHERN PLAINS...

GULF MOISTURE WILL CONTINUE A NORTHWARD MARCH ACROSS THE GREAT
PLAINS TO THE EAST OF THE DRYLINE...WITH MID 50S TO LOW 60S
DEWPOINTS ACROSS TX/OK. LOW LEVEL CLOUDINESS IS EXPECTED EAST OF THE
DRYLINE...WHICH WILL INHIBIT SURFACE BASED CONVECTION ACROSS MUCH OF
CENTRAL/NORTHERN TX INTO CENTRAL/EASTERN OK. BUT STRONG WARM
ADVECTION ON THE EASTERN PERIPHERY OF STRONGER EML SHOULD ALLOW FOR
ISOLATED TO SCATTERED THUNDERSTORM CLUSTERS THROUGH THE
AFTERNOON/EVENING. HAIL WILL BE THE MAIN CONCERN WITH THIS ACTIVITY.

NEAR THE DRYLINE...BETTER HEATING IS EXPECTED WITH HIGH TEMPERATURES
CLIMBING INTO THE UPPER 70S TO NEAR 80 F. THIS SHOULD ALLOW FOR A
NARROW WINDOW OF OPPORTUNITY DURING THE AFTERNOON/EARLY EVENING FOR
SPARSE THUNDERSTORM DEVELOPMENT. STEEP LAPSE RATES COUPLED WITH WEAK
TO MODERATE INSTABILITY AND STRONG EFFECTIVE SHEAR WOULD SUPPORT
SUPERCELLS WITH LARGE HAIL THE PRIMARY CONCERN. STORMS MAY INITIALLY
BE ELEVATED AS THE CAP ERODES...BUT ANY STORM THAT CAN BECOME
SURFACE BASED COULD ALSO POSE A DAMAGING WIND THREAT AS WELL. WHILE
NON-ZERO...THE TORNADO THREAT APPEARS LIMITED BY LACK OF BETTER LOW
LEVEL MOISTURE AND EXPECTED HIGHER-BASED NATURE OF THE STORMS.


OVERNIGHT...CHANCES FOR THUNDERSTORM DEVELOPMENT INCREASE NEAR
EASTERN PORTIONS OF THE PERMIAN BASIN/TX SOUTH PLAINS TO THE EDWARDS
PLATEAU AS STRONGER FORCING AND GREATER HEIGHT FALLS ASSOCIATED WITH
THE APPROACHING WESTERN UPPER TROUGH OVERSPREAD THE REGION. IN
CONJUNCTION WITH INCREASING WARM ADVECTION IN THE LOW
LEVELS...ISOLATED TO SCATTERED THUNDERSTORMS ARE EXPECTED TO DEVELOP
ALONG THE RETREATING DRYLINE. STEEP LAPSE RATES AND FAVORABLE
EFFECTIVE SHEAR WILL SUPPORT SUPERCELLS. STORM DEVELOPMENT IS
EXPECTED IN THE 06-12Z TIME PERIOD...THOUGH DIFFERENCES STILL EXIST
AMONGST VARIOUS GUIDANCE IN EXACT LOCATION/COVERAGE.

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18Z NAM continues to easily destabilize post morning convection on Tuesday. Steep low level lapse rates and impressive low level veering before some mid level backing with height (which could pose some problems in storm evolution).

Impressive sounding south of Wichita Falls, TX. Plenty of helicity to work with *if* there were to be a right turner in that environment. The shear aspect of Tuesday appears to be consistent within models, however, the main placement of the instability and the orientation to the bulk shear vectors has been variable. dProg/dt seems to be more favorable for some discrete convection.

 

post-9707-0-46313300-1457298797_thumb.jp

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18Z NAM continues to easily destabilize post morning convection on Tuesday. Steep low level lapse rates and impressive low level veering before some mid level backing with height (which could pose some problems in storm evolution).

Impressive sounding south of Wichita Falls, TX. Plenty of helicity to work with *if* there were to be a right turner in that environment. The shear aspect of Tuesday appears to be consistent within models, however, the main placement of the instability and the orientation to the bulk shear vectors has been variable. dProg/dt seems to be more favorable for some discrete convection.

 

Not sure that supercells-- if there are any-- would have the easiest of times, with that VBV.

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From DFW

 

jMExzal.jpg

 

CHANGES ARE UNDERWAY ACROSS NORTH AND CENTRAL TEXAS THIS AFTERNOON
AS LOW LEVEL MOISTURE SURGES NORTHWARD IN RESPONSE TO SURFACE LEE
TROUGHING ACROSS THE CENTRAL HIGH PLAINS. CLOUDY...BREEZY AND
HUMID CONDITIONS TONIGHT WILL KEEP OVERNIGHT LOWS GENERALLY IN THE
UPPER 50S TO LOWER 60S. A LACK OF FORCING TONIGHT SHOULD HINDER
ANY MEASURABLE PRECIPITATION. HOWEVER...SOME PATCHY DRIZZLE IS NOT
OUT OF THE QUESTION.

LARGE SCALE LIFT WILL INCREASE ON MONDAY AS A SHORTWAVE MOVES
QUICKLY FROM THE ROCKIES TO THE CENTRAL PLAINS AND A DEEP CLOSED
LOW DEVELOPS OVER SOUTHERN CALIFORNIA/NORTHERN MEXICO. ENERGY FROM
THE LIFTING SHORTWAVE WILL DESTABILIZE THE MID LEVELS OF THE
ATMOSPHERE AND INCREASE THE CHANCES FOR SHOWERS AND THUNDERSTORMS
THROUGH THE AFTERNOON. THESE STORMS SHOULD REMAIN ELEVATED DUE TO
A CAPPING INVERSION IN THE LOW LEVELS OF THE ATMOSPHERE AND
EXTENSIVE CLOUD COVER. EVEN THOUGH THE STORMS ON MONDAY WILL BE
ELEVATED THEY WILL STILL HAVE A CHANCE TO BECOME SEVERE DUE TO
DEEP LAYER SHEAR AND STEEP MID LEVEL LAPSE RATES. HAIL SHOULD BE
THE PRIMARY THREAT. HOWEVER...WE WILL HAVE TO WATCH FOR ANY AREAS
THAT GET SOME SUN ON MONDAY AS THIS COULD ELIMINATE THE CAP AND
ALLOW STORMS TO BECOME ROOTED IN THE BOUNDARY LAYER. IF THIS
OCCURS...THE SEVERE POTENTIAL WILL INCREASE.

BY LATE MONDAY AFTERNOON A DRYLINE SHOULD REACH THE WESTERN ZONES
OF NORTH TEXAS. THIS BOUNDARY WILL BE A FOCUS FOR ADDITIONAL
STORMS BUT IF STORMS MOVE OFF OF THE RETREATING DRYLINE MONDAY
EVENING THEY SHOULD LOSE THEIR TIES TO THE BOUNDARY LAYER AND
WEAKEN SOME. THEY WILL STILL HAVE THE POTENTIAL TO PRODUCE SOME
HAIL THROUGH MONDAY NIGHT.

BY TUESDAY THE CLOSED UPPER LOW WILL MOVE SLOWLY EAST ACROSS
NORTHERN MEXICO AND A 100+ KNOT JET WILL TRANSLATE FROM THE BASE
OF THE TROUGH THROUGH NORTHERN TEXAS. STORM CHANCES SHOULD INCREASE
AS THESE DYNAMICS INTERACT WITH COPIOUS AMOUNTS OF LOW LEVEL
MOISTURE. HOWEVER...IF STORMS CAN ORGANIZE INTO A COMPLEX MONDAY
NIGHT IT COULD ACTUALLY STABILIZE THE AIR ACROSS NORTH TEXAS ON
TUESDAY AFTERNOON AND LIMIT STORM COVERAGE AND STRENGTH. ON THE
FLIP SIDE...IF STORMS ARE MORE SCATTERED IN NATURE MONDAY
NIGHT/TUESDAY MORNING...THE ATMOSPHERE WILL NOT BE WORKED OVER
TUESDAY AFTERNOON AND NUMEROUS OUTFLOW BOUNDARIES MAY EXITS. IF
THIS SCENARIO PLAYS OUT...NUMEROUS STORMS WILL BE POSSIBLE WITH A
BETTER POTENTIAL FOR SEVERE WEATHER ALONG WITH LOCALLY HEAVY
RAINFALL. FOR NOW WE WILL SIDE WITH THE LATER SCENARIO WHICH IS
MORE IN LINE WITH THE HIGH RES SOLUTIONS.

 

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