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Mar. 27-31 Severe Threats


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Day 5 issued:

WARM SECTOR WILL CONTINUE TO MOISTEN OVER THE PLAINS INTO THE MS

VALLEY BENEATH EWD EXPANDING EML WEDNESDAY /DAY 5/ DOWNSTREAM FROM

AN UPPER LOW THAT IS FORECAST TO SETTLE OVER THE SWRN STATES. GFS

REMAINS AN OUTLIER AND PLACES STRONGER EMPHASIS ON A SHORTWAVE

TROUGH THAT IT EVOLVES WITHIN THE CUTOFF LOW AND SUBSEQUENTLY MOVES

IT THROUGH THE CNTRL PLAINS...CONTRIBUTING TO A MUCH DEEPER SFC LOW.

WILL LEAN TOWARD ECMWF GIVEN DOWNSTREAM RIDGE WHICH SHOULD TEND TO

DAMPEN ANY LEAD IMPULSE...AND IT HAS ALSO BEEN MORE CONSISTENT LAST

FEW RUNS. CURRENT INDICATIONS ARE THAT THE LLJ WILL VEER AND SHIFT

EWD TOWARD THE MS AND OH VALLEY DURING THE DAY WHICH /IN ADDITION TO

A CAP/ MIGHT LIMIT DEVELOPMENT ALONG DRYLINE. HAVE INTRODUCED A 15%

AREA FOR AREA OF MOST LIKELY INITIATION ALONG THE SEWD-ADVANCING

COLD FRONT OVER THE MID MS VALLEY AS WELL AS ALONG THE COLD

FRONT/DRYLINE INTERSECTION/MERGER FROM ERN KS INTO CNTRL/ERN OK.

OTHER MORE ISOLATED SEVERE STORMS MIGHT OCCUR FARTHER SOUTH OVER TX

PORTION OF DRYLINE AS WELL AS FARTHER EAST OVER THE LOWER MS VALLEY

WITHIN WARM ADVECTION REGIME. THESE AREAS WILL CONTINUE TO BE

MONITORED FOR THE INTRODUCTION OF CATEGORICAL RISKS IN LATER

UPDATES.

SEVERE THREAT MAY CONTINUE FROM THE OH VALLEY INTO THE SERN STATES

AND ERN TX THURSDAY /DAY 6/ BUT PREDICTABILITY DECREASES AT THIS

TIME FRAME.

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The NAM/RGEM (more so the NAM) are making me increasingly interested with the region around southern IL, southern IN and western KY on Sunday. The NAM has trended around toward a slower, more focused surface low moving into the Midwest Sunday afternoon. Both the NAM/RGEM (12z, 06z) show a <1006mb low near the IL/IN border at 00z Monday with moderate instability and some backing of the low level wind fields into the Ohio Valley.

 

The NAM may be too slow, but who knows, it's been trending: Both the 4km and 12km NAM initiate storms in southeastern MO/IL during the afternoon. The 4km NAM appears to favor a broken squall line with embedded segments/semi-discrete cells.

 

This is an ever-evolving setup, but could produce some severe in the region. Damaging winds appear to be the greatest threat, but decent CAPE and mid-level lapse rates could support some large hail, while the wind fields may result in an isolated tornado threat as well.

Last four runs of the 12km NAM:
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Pretty sizeable jump north in both the slight and marginal risk areas for tomorrow in newest day 2 outlook.

 

 

 

DAY 2 CONVECTIVE OUTLOOK 
   NWS STORM PREDICTION CENTER NORMAN OK
   1230 PM CDT SAT MAR 26 2016

   VALID 271200Z - 281200Z

   ...THERE IS A SLGT RISK OF SVR TSTMS LOWER OH VALLEY TO WRN TN...

   ...THERE IS A MRGL RISK OF SVR TSTMS MIDWEST TO CNTRL GULF COAST TO
   N FL/S GA...

   ...SUMMARY...
   GENERALLY ISOLATED SEVERE STORMS ARE ANTICIPATED FROM THE OHIO
   VALLEY TO CENTRAL GULF COAST TO NORTH FLORIDA/SOUTH ALABAMA.

   ...SYNOPSIS...
   A SERIES OF SHORTWAVE IMPULSES EMBEDDED WITHIN A BROAD LARGE-SCALE
   TROUGH OVER THE CNTRL STATES SHOULD PROGRESS TOWARDS THE GREAT LAKES
   AND CNTRL APPALACHIANS BY 12Z/MON. THE SRN OF THESE IMPULSES SHOULD
   AMPLIFY SUN EVENING/NIGHT OVER THE MIDWEST/LOWER GREAT LAKES
   INDUCING CYCLOGENESIS ALONG A SIMILAR TRACK. ATTENDANT COLD FRONT
   WILL ADVANCE E/SE INTO THE OH/TN VALLEYS AND DEEP SOUTH BY SUN
   NIGHT.

   ...OH VALLEY AREA TO WRN TN...
   SEVERAL LIMITING FACTORS ARE PRESENT WHICH RENDER LOW CONFIDENCE IN
   THE DEGREE OF SEVERE WEATHER COVERAGE DURING THE LATE AFTERNOON AND
   NIGHT ON SUN. OVERALL SCENARIO APPEARS TO RANGE FROM A SPORADIC
   REPORT DAY TO A TYPICAL SLIGHT RISK WITH ALL HAZARDS POSSIBLE.

   SCATTERED TO WIDESPREAD CONVECTION WILL LIKELY BE ONGOING AT 12Z/SUN
   ACROSS THE N-CNTRL GULF AND ADJACENT COASTAL STATES. AS
   SUCH...BOUNDARY-LAYER MOISTURE RETURN WILL BE LIMITED TO THE N.
   HOWEVER...THIS SHOULD BE COMPENSATED BY A PLUME OF STEEP MID-LEVEL
   LAPSE RATES NORTH OF THE MID-SOUTH THAT SHOULD SUSTAIN AT LEAST WEAK
   MLCAPE. NEVERTHELESS...GUIDANCE DIFFERS SUBSTANTIALLY IN THE DEGREE
   OF WARM SECTOR BUOYANCY.

   ISOLATED TO SCATTERED STORMS SHOULD DEVELOP LATE AFTERNOON TO
   EVENING ALONG AND JUST AHEAD OF THE COLD FRONT WITHIN A ZONE OF
   MID-LEVEL DCVA ACCOMPANYING THE PROGRESSIVE SHORTWAVE IMPULSE.
   HOWEVER...ABOVE-AVERAGE SPREAD FOR A D2 FORECAST EXISTS IN THE
   SPATIAL DETAILS OF CYCLOGENESIS AND ATTENDANT FRONTAL
   PLACEMENT...WHICH AFFECTS WHERE STORM INITIATION MOST LIKELY OCCURS.

   LOW-LEVEL SHEAR SHOULD REMAIN MODEST INITIALLY AS CONSENSUS OF
   GUIDANCE SUGGESTS CYCLOGENESIS/TROUGH AMPLIFICATION OCCURS GENERALLY
   AFTER SUNSET. THUS...STRENGTHENING KINEMATIC FIELDS SHOULD LARGELY
   BE OFFSET FROM PEAK DIABATIC HEATING. GIVEN WHAT SHOULD BE WEAK
   BUOYANCY...THE LONGEVITY OF A MORE THAN AN ISOLATED SEVERE RISK IN
   THE LATE EVENING/OVERNIGHT IS QUESTIONABLE.

 

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Also a note of less than usual confidence in a day 2 forecast. It's easy to discount the GFS, but even the ECMWF is leaning more progress than the robust NAM setup. 

 

The best analog based on a more unstable scenario, given a similar upper level and surface setup, ala NAM, is 4/7/2010. After looking at the maps, that event resulted in some pockets of 2000 J/kg SBCAPE and I'm not sure we get to that level tomorrow, but it's on the table as a possible high-end solution. Even so, no tornadoes were reported in the main "risk" area.

100407_rpts.gif

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The 18z NAM and 4km are not backing off of 1500 cape idea around cincinnati. The nam simulated radar shows storms struggling to fire while the nam 4km has some semi-discrete and discrete cells firing. Tomorrow is looking more interesting. 

 

The main limiting factor that i see right now is sub-par shear. 

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12z Euro/EPS is getting closer to something more volatile on Thursday for the sub-forum. Has a stronger/less sheared out shortwave ejecting ENE out of that positive tilt longwave and a fairly robust EML with 700-500 mb lapse rates of 7-8 C/km (along with 60s dewpoints into the southern half of the region).

 

There's certainly plenty of deep layer shear with a large area of 50-70 kt through the warm sector. Low level shear, especially directional shear, looks a bit more iffy though, with surface winds veered slightly and fairly modest low level jet strength (that lead vort that ejects out ahead of the primary wave "steals" the low level jet response and is also likely responsible for some of the veering).

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12z Euro/EPS is getting closer to something more volatile on Thursday for the sub-forum. Has a stronger/less sheared out shortwave ejecting ENE out of that positive tilt longwave and a fairly robust EML with 700-500 mb lapse rates of 7-8 C/km (along with 60s dewpoints into the southern half of the region).

There's certainly plenty of deep layer shear with a large area of 50-70 kt through the warm sector. Low level shear, especially directional shear, looks a bit more iffy though, with surface winds veered slightly and fairly modest low level jet strength (that lead vort that ejects out ahead of the primary wave "steals" the low level jet response and is also likely responsible for some of the veering).

It continues to look better than the GFS for Wednesday as well.
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0z nam has large pockets of 1500+ cape across in/ky/oh

So does the HRRRX.

 

I'm also concerned that the 4km NAM is trending toward a more discrete/semi-discrete storm mode. Overdone or not, the NAM is showing 2000 J/kg CAPE overlapping with >7.5 C/km mid-level lapse rates and more than ample shear.

 

While this does not look like an outbreak, a few severe storms look very likely in the area between southern IL/southern IN and the western half of KY. Maybe a few significant hail events if the higher-end instability scenarios are correct? Should be an interesting day to watch and track. I like these "sleeper" events that seem to be off many people's radar.

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So does the HRRRX.

 

I'm also concerned that the 4km NAM is trending toward a more discrete/semi-discrete storm mode. Overdone or not, the NAM is showing 2000 J/kg CAPE overlapping with >7.5 C/km mid-level lapse rates and more than ample shear.

 

While this does not look like an outbreak, a few severe storms look very likely in the area between southern IL/southern IN and the western half of KY. Maybe a few significant hail events if the higher-end instability scenarios are correct? Should be an interesting day to watch and track. I like these "sleeper" events that seem to be off many people's radar.

 

4km NAM did this during last weeks event across Dixie. Trended towards a more volatile solution the night before the event but what actually wound up happening was pretty much what the expectation was about 48-72 hours before the event. With the 4km NAM's bias towards overdoing thermodynamics in these marginal situations, I'd honestly be quite surprised if it verified those higher instability values. It's overdone them all month and frankly I expect the same thing to happen again tomorrow.  

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Not overly thrilled with this setup, but considering making a run down towards southeast, or east-central IL.  Probably somewhere in the Effingham/Terre Haute/Vincennes triangle.  Forecast hodos aren't all that much to get excited over, but there is just enough shear present to make a relatively short chase seem reasonable.  I do like that punch at H5 arriving right at go time, along with a very nice vort max.  May be just enough to create a short window for tornado opportunity before things get too messy after 01-02z.  Cape looks fairly meager, but should be just enough to justify the potential.  

 

EDIT:  Even if it's a huge bust it will still be better being down where it will be in the 70s compared to the 40s and stratiform rain back here at home lol.

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Euro continues to be much more generous than the GFS in terms of CAPE on Thursday. System also slower.

OT: That cold shot on the Euro looks more like a nuisance than anything.

It most definitely is better looking than the GFS.

Timing is one of the bigger issues at this point, with the GFS being much faster than the ECMWF. The GFS is pretty much a one and done deal, with Wednesday being the only real interesting day, and it's not the best looking. The ECMWF continues to show Wednesday the main day west of the sub-forum, with potential on Thursday as well in the sun-forum.

Will be interesting to see how things pan out regarding to timing.

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Even here, the 4km NAM is pretty bullish with the potential for strong convection and heavy rain (2-3"+) later today and tonight..

 

Latest NAM builds MLCAPE up to 500 J/KG by 03z Monday.

 

At least locally, it's the most bullish run instability-wise.

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It most definitely is better looking than the GFS.

Timing is one of the bigger issues at this point, with the GFS being much faster than the ECMWF. The GFS is pretty much a one and done deal, with Wednesday being the only real interesting day, and it's not the best looking. The ECMWF continues to show Wednesday the main day west of the sub-forum, with potential on Thursday as well in the sun-forum.

Will be interesting to see how things pan out regarding to timing.

 

 

GFS has been too quick on more than one system lately...doesn't mean it will happen this time but it wouldn't be all that unreasonable to expect a slower outcome imo.

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I'm kind of liking what the HRRR is selling for later this afternoon as it depicts a prefrontal semi-discrete line of storms forming ahead of the main line in an area from IND up to FWA and toward TOL.  It also shows a pocket of 2000 j/kg CAPE right over Indystorm's head. WRF's are kind of hinting at it also. It will interesting to see what SPC does with the slight risk on their next update.

 

Might get to do the first Skywarn activation of the year.

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Not overly thrilled with this setup, but considering making a run down towards southeast, or east-central IL.  Probably somewhere in the Effingham/Terre Haute/Vincennes triangle.  Forecast hodos aren't all that much to get excited over, but there is just enough shear present to make a relatively short chase seem reasonable.  I do like that punch at H5 arriving right at go time, along with a very nice vort max.  May be just enough to create a short window for tornado opportunity before things get too messy after 01-02z.  Cape looks fairly meager, but should be just enough to justify the potential.  

 

EDIT:  Even if it's a huge bust it will still be better being down where it will be in the 70s compared to the 40s and stratiform rain back here at home lol.

 

Looks like the storms will fire more into Indiana now.  Not going to drive that far for a somewhat questionable setup.  

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I'm kind of liking what the HRRR is selling for later this afternoon as it depicts a prefrontal semi-discrete line of storms forming ahead of the main line in an area from IND up to FWA and toward TOL.  It also shows a pocket of 2000 j/kg CAPE right over Indystorm's head. WRF's are kind of hinting at it also. It will interesting to see what SPC does with the slight risk on their next update.

 

Might get to do the first Skywarn activation of the year.

 

At the very least, my guess is the marginal risk area will be extended back NW into portions of Michigan (maybe along/SE of the I-69 corridor).

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I'm kind of liking what the HRRR is selling for later this afternoon as it depicts a prefrontal semi-discrete line of storms forming ahead of the main line in an area from IND up to FWA and toward TOL.  It also shows a pocket of 2000 j/kg CAPE right over Indystorm's head. WRF's are kind of hinting at it also. It will interesting to see what SPC does with the slight risk on their next update.

 

Might get to do the first Skywarn activation of the year.

I'll eat my hat if CAPE gets that high.  Clear skies and 64 presently.  Have to wonder about moisture, although I see that Cincinnati is 55 dewpoint and PAH is 59.  But I will be watching.

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Even the GGEM has the slower timing as well. 12z GFS did slow down some from the previous run.

Yeah it is noticeably slower than previous runs, that would really allow for moisture to stream northward and improve the chances of a higher end event. As it stands it would be in between but slow down closer to the Euro and we'd be looking good. Regardless there looks to be a pretty good potential of a synoptic wind event with this especially if the low ends up as strong as the GFS shows. The GGEM's timing actually looks really good locally.
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