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HillsdaleMIWeather

March 13th-14th Severe Weather

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Considering a sizable chunk of the subforum is now under a Slight Risk with Enhanced being considered, good time for a thread.

 

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..LOWER OHIO VALLEY VICINITY    

A STRONG SOUTH/SOUTHWESTERLY LOW LEVEL JET WILL TRANSPORT GULF   MOISTURE FAIRLY FAR NORTHWARD FOR THIS TIME OF YEAR, WITH AT LEAST A   NARROW CORRIDOR OF LOW 60S F DEWPOINTS AS FAR NORTH AS THE LOWER   OHIO RIVER, AND LOW-TO-MID 50S F DEWPOINTS INTO SOUTHERN MICHIGAN.   WHILE THE BETTER QUALITY MOISTURE WILL REMAIN CONFINED TO THE DEEP   SOUTH, FORCING FOR ASCENT AND DEEP LAYER SHEAR ARE MUCH MORE   IMPRESSIVE FROM THE OHIO VALLEY INTO SOUTHERN MI. ADDITIONALLY,   MIDLEVEL LAPSE RATES ARE EXPECTED TO STEEPEN FROM KY/IN INTO MI AS   STRONGER HEIGHT FALLS AND COLDER TEMPERATURES ALOFT OVERSPREAD THE   REGION AHEAD OF A MIDLEVEL DRYSLOT BY MIDDAY.     ALL OF THIS COMBINED LEADS TO A NARROW WARM SECTOR CHARACTERIZED BY   500-1000 J/KG MLCAPE, 6.5-7.5 C/KM MIDLEVEL LAPSE RATES,   IMPRESSIVE/LARGE CURVED LOW LEVEL HODOGRAPHS AND 45+ KT EFFECTIVE   SHEAR. WHILE THIS PARAMETER SPACE IS MORE THAN CAPABLE OF SUPPORTING   WIDESPREAD SEVERE, INCLUDING DAMAGING WINDS AND POSSIBLE STRONG   TORNADOES, QUITE A BIT OF UNCERTAINTY STILL EXISTS. THIS IS DUE IN   PART TO SEVERAL ROUNDS OF SHOWERS AND THUNDERSTORMS EXPECTED IN THE   DAY 1/WED PERIOD, WITH ONGOING CONVECTION POSSIBLE IN WARM ADVECTION   REGIME AT THE START OF THE DAY 2/THU PERIOD. IMPACTS OF THIS   CONVECTION/RESIDUAL CLOUD COVER ON DESTABILIZATION, AND HOW   FAR/QUICKLY THE SURFACE COLD FRONT PROGRESSES BY THURSDAY MORNING   MAKES FOR A QUITE CONDITIONAL SCENARIO. AS A RESULT, HAVE OPTED TO   EXPAND THE SLIGHT RISK NORTHWARD ACROSS THE MID-SOUTH INTO SOUTHERN   MI. UNCERTAINTY AND CONDITIONAL NATURE OF THE THREAT WILL PRECLUDE   HIGHER PROBS AT THIS TIME ACROSS PARTS OF KY/IN/MI/OH, BUT POTENTIAL   CERTAINLY EXISTS FOR A HIGHER-END THREAT TO MATERIALIZE ACROSS THIS   REGION, AS IMPLIED BY VARIOUS CAMS IN THE 18-00Z TIME FRAME.   OBSERVATIONAL AND NUMERICAL GUIDANCE TRENDS WILL BE MONITORED   CLOSELY.  

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So much of tomorrow will depend on just how much instability can develop. If there is a large amount of clearing though could absolutely see some low topped strong tornadoes flying through the region tomorrow

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KIND Wed. morning thoughts on Thursday....

 

.SHORT TERM /Tonight through Friday Night/...
Issued at 354 AM EDT Wed Mar 13 2019

Forecast challenges focus on impacts from gradient winds and severe
storms Thursday as the weakening surface low tracks into the western
Great Lakes by Thursday evening. While some murkiness lingers within
the details which lowers confidence a bit...remain concerned about a
period of high impact weather for central Indiana on Thursday.

The initial axis of prefrontal convection that will expand east from
the High Plains this morning should be located in the vicinity of the
Mississippi River by early evening. While the focus for stronger
convection will remain southwest of the forecast area from mid
evening into the early overnight...expect scattered showers will
overspread the region with some embedded thunderstorms as model
soundings show elevated instability present above an expanding
shallow inversion. Surface flow will be gusty with a strong 850mb
jet nearing 70kts moving through the area late tonight...but the
presence of the strengthening inversion should keep most of the
stronger winds aloft from reaching the near surface layer through
daybreak Thursday.

The bulk of the hi-res guidance shifts most of the prefrontal
convection set to impact the region tonight east of the area
Thursday morning which when coupled with the dynamics present over
the area later in the day...raises the ceiling for potential severe
weather ahead of the occluded boundary during the afternoon. The
initial low level jet will shift east of the area Thursday morning
but a second jet will swing around the base of the upper low over
the Plains and nose back into the region by the afternoon. Further
up in the atmosphere...mid and upper level diffluence will increase
with the presence of stronger jets in both layers over the Ohio
Valley. 100+kts noted at 500mb Thursday afternoon is particular
impressive. BL shear will steadily increase across the area into the
afternoon and while strongest helicities in the 0-1km and 0-3km
layer will be focused east of central Indiana...values remain more
than sufficient to support severe convective development.

With all of the factors present above...confidence is higher in a 2-
4 hour window during the afternoon where storms can develop and may
quickly become severe as they rapidly move east. The key to whether
the severe threat is isolated or more substantial will come down to
available instability and moisture return in the dry slot between
the prefrontal convection and the occluded front. Hi-res guidance
has shifted more ominously in the direction of a potential greater
threat with MLCAPE levels rising to near 1000 j/kg with dewpoints
climbing into the mid and upper 50s within a narrow axis over the
forecast area by 18-19Z. And while lapse rates aloft are a bit lower
than would be desired to support a greater severe threat...there
does appear to be enough of a steepening within the 700-500mb layer
overlaid on the instability axis over the region.

Should this come to fruition...the hi-res solution suggestive of a
broken but potentially potent line of convection developing in the
Wabash Valley around midday and moving east through the afternoon is
becoming a real possibility. All severe threats would be on the
table...damaging winds most prevalent considering the screaming
winds aloft which any stronger cell would be able to tap into.
However...the presence of long curving hodographs courtesy of the
stronger low level helicity levels supports a tornado threat and wet
bulb zero values at 6-7kft also present a hail risk.  As mentioned
above...there is still some detail that model runs later today and
tonight will hopefully clear up...but the threat for severe storms
is higher than it looked to be Tuesday. Stay tuned.

Not to be lost in the growing severe threat is the continued concern
for strong gradient winds outside of any convection due to the
intense flow aloft. Remain reasonably concerned that there could
still be periods Thursday where stronger boundary layer mixing can
occur and support peak gusts rising into advisory criteria at a
minimum. Again...the convective development could scuttle a more
widespread and prolonged high wind threat and with some clarity
still needed...will not introduce any headlines as of yet. Will
however highlight the high wind and severe potential via an SPS.

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12z Guidance is pretty impressive, HRRR/NAM 12k/NAM 3k/CAMs all offer up  decent scenarios for fast moving tornadoes, with HRRR being the least impressive with too many discrete cells firing and creating a line with some interference it seems. Seems Ohio/East KY maybe more in the threat area, with pretty much every high res model showing these cells making their way well into Ohio in an impressive environment. 1730z Day 2 SPC outlook will be interesting. 

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2 hours ago, MattPetrulli said:

12z Guidance is pretty impressive, HRRR/NAM 12k/NAM 3k/CAMs all offer up  decent scenarios for fast moving tornadoes, with HRRR being the least impressive with too many discrete cells firing and creating a line with some interference it seems. Seems Ohio/East KY maybe more in the threat area, with pretty much every high res model showing these cells making their way well into Ohio in an impressive environment. 1730z Day 2 SPC outlook will be interesting. 

SPC, interestingly, stayed with a non-hatched SLGT risk at 1730z in spite of what seems like an obvious uptick in the risk for tomorrow in CAM-land. Continues to mention higher-end severe risk being possible.

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13 minutes ago, jojo762 said:

SPC, interestingly, stayed with a non-hatched SLGT risk at 1730z in spite of what seems like an obvious uptick in the risk for tomorrow in CAM-land. Continues to mention higher-end severe risk being possible.

Ehh, I was surprised a bit too but at the same time I totally get it. Whether or not ongoing convection tomorrow can get out of town will play a big role in the day. I also *personally* thought the storm modes on 12z runs were just a tad messy. Totally agree the risk is on the uptick, but there also has to be a lot that goes right. 

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The 12Z SPC HREF shows a strong signal for rotating supercells across the Lower Ohio Valley late in the afternoon. Comes down to how much heating occurs ahead of the front, in my opinion.

SPC.thumb.png.e5785ee811c0a6c56418a2f8238381e6.png

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It seems like we are in rather uncharted territory with a deep 971-972 mb low out in western Kansas. Even if the low fills as it heads east  I'm thinking Thursday will depend on amount of breaks in cloud cover we get and how high the dew point gets in Indiana as key factors for svr potential.

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18z HRRR shows no lack of warmth ahead of the front.  There's a lot of SRH shown over the warm sector and mid-60s to lower-70s temperatures with dewpoints modeled in the upper 50s to lower 60s across western and central Ohio.  If storm mode can remain discrete (and sufficient cloud breaks occur as previously mentioned) it seems that the potential for tornadoes is there.  Looks promising provided that everything comes together just right.  That said, the NAM3K is a bit less aggressive with destabilization.

I know the HRRR can be a bit overdone at times, though.  It is also showing pockets of high temperatures in the lower 80s over western WV, SW PA, and SE OH, though this area is not under the moist axis (temperatures under the moist axis are generally being modeled in the 60s to near 70 at best).  The HRW models and the NAM 3k (the other CAM models available on pivotalweather.com) are at least somewhat consistent on a temperature spike into at least the mid-70s occurring over this region, though.

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12 minutes ago, BrandonC_TX said:

18z HRRR shows no lack of warmth ahead of the front.  There's a lot of SRH shown over the warm sector and mid-60s to lower-70s temperatures with dewpoints modeled in the upper 50s to lower 60s across western and central Ohio.  If storm mode can remain discrete (and sufficient cloud breaks occur as previously mentioned) it seems that the potential for tornadoes is there.  Looks promising provided that everything comes together just right.  That said, the NAM3K is a bit less aggressive with destabilization.

I know the HRRR can be a bit overdone at times, though.  It is also showing pockets of high temperatures in the lower 80s over western WV, SW PA, and SE OH, though this area is not under the moist axis (temperatures under the moist axis are generally being modeled in the 60s to near 70 at best).  The HRW models and the NAM 3k (the other CAM models available on pivotalweather.com) are at least somewhat consistent on a temperature spike into at least the mid-70s occurring over this region, though.

Considering the high res models have the dew points lower than they actually are right now, the higher numbers might happen.

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1 hour ago, Indystorm said:

It seems like we are in rather uncharted territory with a deep 971-972 mb low out in western Kansas. Even if the low fills as it heads east  I'm thinking Thursday will depend on amount of breaks in cloud cover we get and how high the dew point gets in Indiana as key factors for svr potential.

Yep, record/near record low pressure for that area

AllTimeRecordLowSLPs.thumb.gif.571a1919a94f1fdc63194c5084dda255.gif

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1 hour ago, HillsdaleMIWeather said:

Considering the high res models have the dew points lower than they actually are right now, the higher numbers might happen.

I'm not saying the higher numbers can't be realized, but with it still being mid March and a screaming low level wind field tomorrow, I am wondering how much mixing out may occur.  This is where having some clouds around could help, within reason of course.  The moisture aloft doesn't seem particularly shallow though, at least on the NAM, which is a good thing for severe prospects.

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This will be an interesting one to watch unfold. Historically these types of setups end up busting up here due to cloud cover but still may yield damaging winds along a thin low-topped convective line that may form and push east along the cold front. If we end up with more sunshine and manage to get 70°, then I’d be concerned being in close proximity to the triple-point along with moderate instability. The ingredients are definitely there for a sneak attack haha. 

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8 minutes ago, HillsdaleMIWeather said:

0Z NAM looks mediocre at first, then supercell city

Yes, the key is to get that early morning convection out of the way to allow for destabilization.  I'm a bit surprised at the amount of cells up near Chi town and nw In as well on NAM 3k 

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Well so much for tomorrow's threat with the early contamination, looking like further south in KY/TN/MS/AL might have a better shot now with the limited destabilization further north.

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00Z 12NAM = pretty good.

Early convection isn’t an issue in this run, resulting in ~1000J/KG CAPE, along with sustantial bulk and low-level shear... I’ll let you imagination do the rest of the thinking there...

00Z 3km NAM = meh.

Tons of morning and early afternoon crapvection across Indiana, Ohio, and Kentucky. As andyhb mentioned, still could be some potential further south, but instability looks pretty mediocre on this run until you get into AL/MS. Any storms in between Indiana and Mississippi would be absolutely torn apart by this level of shear (60-70+ kt 0-6km) with <1000J/KG CAPE. Fwiw, definitely a VBV signature being shown between the 800-600mb layer in the aforementioned southern target, providing questions over storm modes there despite a relatively better environment compared to the northern target.

 

Still waiting for more guidance but not feeling particularly sure in any one solution at this point. Either going to be a crapfest or an impressive day imo. Leaning more toward crapfest given that HRRR has been sticking toward more of a 00Z 3NAM solution for quite a while (even though the HRRR regularly over does convection).

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22 minutes ago, jojo762 said:

00Z 12NAM = pretty good.

Early convection isn’t an issue in this run, resulting in ~1000J/KG CAPE, along with sustantial bulk and low-level shear... I’ll let you imagination do the rest of the thinking there...

00Z 3km NAM = meh.

Tons of morning and early afternoon crapvection across Indiana, Ohio, and Kentucky. As andyhb mentioned, still could be some potential further south, but instability looks pretty mediocre on this run until you get into AL/MS. Any storms in between Indiana and Mississippi would be absolutely torn apart by this level of shear (60-70+ kt 0-6km) with <1000J/KG CAPE. Fwiw, definitely a VBV signature being shown between the 800-600mb layer in the aforementioned southern target, providing questions over storm modes there despite a relatively better environment compared to the northern target.

 

Still waiting for more guidance but not feeling particularly sure in any one solution at this point. Either going to be a crapfest or an impressive day imo. Leaning more toward crapfest given that HRRR has been sticking toward more of a 00Z 3NAM solution for quite a while (even though the HRRR regularly over does convection).

02 HRRR took a step back in the right direction

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The LLJ progged by the HRRR also borders on uncharted territory (reference sounding climo for BNA/ILN), solidly 60-80 knots by 18z on the nose of the forecast instability axis. It’s probably a good thing there won’t be much instability to work with...

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This almost brings back memories of the Van Wert tornado of 2002, which tracked 52.8 miles in my direction. Even so, most models show less than 500 J/kg of CAPE in Ohio.

ELM8pgQ.png

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This almost brings back memories of the Van Wert tornado of 2002, which tracked 52.8 miles in my direction. Even so, most models show less than 500 J/kg of CAPE in Ohio.
ELM8pgQ.png&key=b67420e50c8cf94e0ef6d1b45aab1df609b8367de7e7c80251bffc6a285b73b3


Which is similar to the amount of CAPE that happened on that day. Morning rain is going to be the difference maker as usual

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SPC goes enhanced for E IN/W OH with 10% tornado/30% wind. I would post the disco but still posts like crap for me when I copy and paste so someone else can do that please.

day1otlk_1200.gif

day1probotlk_1200_torn.gif

day1probotlk_1200_wind.gif

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I am a little surprised that the slight risk area extends this far west, but I guess it's not a big deal in the grand scheme as the higher probabilities are clearly farther east and south.

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With the amount of rain headed this way from southern Illinois and Indiana (which will be here by 12-2pm), our chances are slim for severe as some of the short range guidance (HRRR) has shown. Best bet is southeast of the state.

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The current RAP runs (11z) seem the most aggressive at the present moment, especially with respect to western and central OH.  Would not be surprised to see tornadoes (perhaps strong tornadoes?) if that RAP solution verifies.  Other models (like the NAM3k and HRRR) bring in less instability, so more conservatively I would not expect significant tornadoes either.

SPC's new outlook (still ENH, 10% tornado/30% wind as far east as Columbus, OH) says that if stronger instability can develop then they might have to introduce a significant tornado risk.
 

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