April 14-17th Severe Weather (Day 3 Mod)

[Chicago Storm]

Obviously two different events, but the first doesn't look like it will be much to talk about...thus a combined thread.

 

Wednesday looks to have the most potential at this point. Unfortunately for chasers, this might be the last "ok" potential to chase for a while given the upcoming pattern.

[brettjrob]

It is the NAM, but... the 00z run is bordering on a "significant" event for OK/TX on Wednesday, regardless of whose terminology we use. As of now, just based on the most recent set of runs, I dare say it looks better than either day last week looked at this range. The H5 pattern is fairly solid, as is the jet structure over the warm sector/triple point. I think the ceiling of potential is fairly impressive (MDT risk territory), but the likelihood of approaching it remains highly uncertain.

[baroclinic_instability]

It is the NAM, but... the 00z run is bordering on a "significant" event for OK/TX on Wednesday, regardless of whose terminology we use. As of now, just based on the most recent set of runs, I dare say it looks better than either day last week looked at this range. The H5 pattern is fairly solid, as is the jet structure over the warm sector/triple point. I think the ceiling of potential is fairly impressive (MOD risk territory), but the likelihood of approaching it remains highly uncertain.

I would say it is much more impressive than last event ever looked, and I have been surprised by the lack of disco the last two days. My guess is folks are leery after the letdown of that event...and the similarities (especially a few days ago) with the surging cold front. Models have definitely backed off on the density/cold air with this first front.

[andyhb]

To see most of the guidance indicating 2500+ J/kg of CAPE building to east of the dryline certainly speaks of a healthy thermodynamic environment. I was noticing that the models were underestimating SBCAPE for the threat in AR on the 10th by as much as 1500 J/kg.

 

Add on a 40-50 kt LLJ and obviously there is potential here, since we do appear to be trending away from that undercutting front setup gradually (dare I say).

 

It is also of note that this trend has been noticed as the primary UL jet streak has finally nosed onto the California coast today.

[thewxmann]

The parameters are really impressive on the 0Z NAM but I wouldn't be surprised if the models goofed again with the cold front by about 100 mi. The spatial window for favorable development is really small and sensitive to model errors. Move that front to the Red River, and this setup is smoked.

 

P.S. The entire risk area is under the left exit region of the STJ, a favorable quadrant for lift. While this would normally be good (given the main forcing is lagging behind the front/dryline), in this case it might cause junk convection to form and remain entrenched in the cold sector, reinforcing the cold front and augmenting its southward progression.

[baroclinic_instability]

The parameters are really impressive on the 0Z NAM but I wouldn't be surprised if the models goofed again with the cold front by about 100 mi. The spatial window for favorable development is really small and sensitive to model errors. Move that front to the Red River, and this setup is smoked.

I agree, but there are a couple notable differences. One  the density of the cold air. This is not nearly as cold of an airmass. Second, there is a more defined and substantial southern stream upper level speed max that ejects the southern Rockies late Wed. Timing of that feature here will be crucial to this event.

[andyhb]

The parameters are really impressive on the 0Z NAM but I wouldn't be surprised if the models goofed again with the cold front by about 100 mi. The spatial window for favorable development is really small and sensitive to model errors. Move that front to the Red River, and this setup is smoked.

 

P.S. The entire risk area is under the left exit region of the STJ, a favorable quadrant for lift. While this would normally be good (given the main forcing is lagging behind the front/dryline), in this case it might cause junk convection to form and remain entrenched in the cold sector, reinforcing the cold front and augmenting its southward progression.

 

Forgive me if I'm wrong, but would this not slow the cold front somewhat in the same way that this type of convection/rain mass slows down the northward progression of a warm front? I realize the convection could better define the boundary, just questioning the translational qualities of it (since it would be on the side that the cold front is moving from, not against, like a warm front, this could be valid).

 

I'll also say that the triple point area in KS/MO (where convective initiation may be more likely) is looking better and better the more I look at it.

 

Also, yeah it's the NAM...but damn...KOUN at 00z Wednesday...

 

[andyhb]

00z GFS has a sub-996 mb sfc low in SW KS at 00z Wednesday, with convective initiation down the dryline in OK. 2500-3500 J/kg of CAPE and a 40-50+ kt LLJ, with some serious backing of the sfc winds to the east of dryline.

[thewxmann]

Forgive me if I'm wrong, but would this not slow the cold front somewhat in the same way that this type of convection/rain mass slows down the northward progression of a warm front? I realize the convection could better define the boundary, just questioning the translational qualities of it (since it would be on the side that the cold front is moving from, not against, like a warm front, this could be valid).

 

I'll also say that the triple point area in KS/MO (where convective initiation may be more likely) is looking better and better the more I look at it.

 

Also, yeah it's the NAM...but damn...KOUN at 00z Wednesday...

 

[image]

 

 

Cold fronts propagate by way of colder, denser air replacing warmer, lighter air at the surface. Outflow from convection, which is typically relatively dense, reinforces the former air mass, tipping the balance further in favor of the cold air and thus cold frontal progression.

 

Warm fronts propagate by way of warmer air eroding the near-surface colder air mass, but again, the outflow reinforces the latter, making warm frontal progression more difficult.

 

So any convection in the cold sector (which is what I was referring to) will tip the balance in favor of the colder air. For some reason though, models do not properly forecast this every time -- maybe its due how convection is parameterized, I dunno.

[andyhb]

Cold fronts propagate by way of colder, denser air replacing warmer, lighter air at the surface. Outflow from convection, which is typically relatively dense, reinforces the former air mass, tipping the balance further in favor of the cold air and thus cold frontal progression.

 

Warm fronts propagate by way of warmer air eroding the near-surface colder air mass, but again, the outflow reinforces the latter, making warm frontal progression more difficult.

 

So any convection in the cold sector (which is what I was referring to) will tip the balance in favor of the colder air. For some reason though, models do not properly forecast this every time -- maybe its due how convection is parameterized, I dunno.

 

Alright, thanks. Was looking for some clarification on that, and these points make good sense.

[brettjrob]

Cold fronts propagate by way of colder, denser air replacing warmer, lighter air at the surface. Outflow from convection, which is typically relatively dense, reinforces the former air mass, tipping the balance further in favor of the cold air and thus cold frontal progression.

 

Warm fronts propagate by way of warmer air eroding the near-surface colder air mass, but again, the outflow reinforces the latter, making warm frontal progression more difficult.

 

So any convection in the cold sector (which is what I was referring to) will tip the balance in favor of the colder air. For some reason though, models do not properly forecast this every time -- maybe its due how convection is parameterized, I dunno.

 

I do share your concern regarding early elevated convection and its effect on frontal placement. However, as the 00z GFS and UKMET have rolled in, the environment looks quite impressive for much of W OK and NW TX across models. Even if the front lies near I-40 by early evening (currently a fairly conservative position), there should still be a decent window of opportunity for a localized event of significance. If the front is more like WWR-MCI (reasonable if looking strictly at dProg/dt, though I'd be quite skeptical for the same reasons you mentioned), then put simply, Wednesday suddenly becomes an ominous prospect of the type not seen since 4/14/12 in the Plains. Given available guidance tonight, I'd lean toward a 30% hatched area for the LAW/SPS/OKC region on the SWODY3.

[JoMo]

I do share your concern regarding early elevated convection and its effect on frontal placement. However, as the 00z GFS and UKMET have rolled in, the environment looks quite impressive for much of W OK and NW TX across models. Even if the front lies near I-40 by early evening (currently a fairly conservative position), there should still be a decent window of opportunity for a localized event of significance. If the front is more like WWR-MCI (reasonable if looking strictly at dProg/dt, though I'd be quite skeptical for the same reasons you mentioned), then put simply, Wednesday suddenly becomes an ominous prospect of the type not seen since 4/14/12 in the Plains. Given available guidance tonight, I'd lean toward a 30% hatched area for the LAW/SPS/OKC region on the SWODY3.

 

I'd wait on the good Dr. Euro. It was interesting to see it move the front much farther NW on the 12z from the 00z though. 

[thewxmann]

I do share your concern regarding early elevated convection and its effect on frontal placement. However, as the 00z GFS and UKMET have rolled in, the environment looks quite impressive for much of W OK and NW TX across models. Even if the front lies near I-40 by early evening (currently a fairly conservative position), there should still be a decent window of opportunity for a localized event of significance. If the front is more like WWR-MCI (reasonable if looking strictly at dProg/dt, though I'd be quite skeptical for the same reasons you mentioned), then put simply, Wednesday suddenly becomes an ominous prospect of the type not seen since 4/14/12 in the Plains. Given available guidance tonight, I'd lean toward a 30% hatched area for the LAW/SPS/OKC region on the SWODY3.

 

Oh yeah, for sure. I wrote my original post before the 0Z GFS run, but dProg/dt is definitely favoring a further north front. The 0Z Euro will be the deal breaker here.

[patrick7032]

One thought...one of our general forecasters and I were discussing...was the potential for WAA convection north of the front to form into an MCS across northern Oklahoma Tuesday night...sending an outflow down into southern Oklahoma...but we plan to chase in...and possibly meet up with LoKo...in a FWD-SPS-OKC triangle. That could obviously make things more interesting for the Red River Valley area and points north. Chicagostorm...round two for a trip?

[andyhb]

00z Euro is cutting it a bit close on Wed, but still a potent looking setup over N TX and OK, 994 hPa sfc low in the TX PH and, again, a 40-50 kt LLJ to the east of dryline, the CAD/anafront definitely did retreat compared to the 00z run last night.

[JoMo]

00z Euro is cutting it a bit close on Wed, but still a potent looking setup over N TX and OK, 994 hPa sfc low in the TX PH and, again, a 40-50 kt LLJ to the east of dryline, the CAD/anafront definitely did retreat compared to the 00z run last night.

 

Yeah the front is a bit farther south (except perhaps in TX and NW OK) on the 00z Euro compared to the 12z Euro. There looks to be a ton of CAPE available even by 12z Wed morning with some areas pushing 3300. The Euro breaks out pre-frontal precip and looks to have multiple waves of precip before it lines out as the front pushes east. Looks 'interesting' for you severe weather lovers. 

[SmokeEater]

Day 3 Moderate issued, I was wondering why the outlook was almost 30 mins late.

[andyhb]

DAY 3 CONVECTIVE OUTLOOK     NWS STORM PREDICTION CENTER NORMAN OK   0224 AM CDT MON APR 15 2013      VALID 171200Z - 181200Z      ...THERE IS A MDT RISK OF SVR TSTMS ACROSS OK/SERN KS/SWRN MO...      ...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MDT RISK FROM   NWRN TX INTO CNTRL IL...      ...SIGNIFICANT SEVERE WEATHER EVENT IS POSSIBLE ACROSS PARTS OF THE   SOUTHERN PLAINS INTO THE MID MS VALLEY WEDNESDAY...      ...SRN PLAINS TO MID MS VALLEY...      LATEST MODEL GUIDANCE CONTINUES TO SUGGEST A CORRIDOR OF STRONG SWLY   FLOW ALOFT WILL SPREAD ACROSS THE PLAINS WEDNESDAY AFTERNOON.  THIS   LARGE SCALE INCREASE IN HIGH LEVEL FLOW IS CONSISTENT AMONG THE   NAM/GFS/ECMWF.  OF PARTICULAR CONCERN ARE THE DIFFERENCES REGARDING   THE SYNOPTIC POSITIONS OF THE COLD FRONT WITH THE ECMWF BEING THE   MOST AGGRESSIVE...ALBEIT SLOWER THAN EARLIER RUNS...AND THE GFS   CONSIDERABLY SLOWER WITH THE PRIMARY FRONTAL ZONE AT 18/00Z FROM   SERN NEB ACROSS NWRN KS INTO SERN CO.  LATEST THINKING IS THE NAM   MAY BE MORE ACCURATE DEPICTING AN EARLY FRONTAL SURGE THAT WILL   STALL ACROSS THE SRN PLAINS DURING THE DAY1-2 TIME FRAME BEFORE   SLOWLY RETREATING INTO SERN KS/NWRN OK BY LATE AFTERNOON.  GIVEN   THIS SCENARIO THE GREATEST BUOYANCY WILL EXIST ACROSS THE BODY OF OK   WHERE STEEPEST LAPSE RATES WILL RESIDE...WHILE SIGNIFICANT   INSTABILITY SHOULD EXTEND DOWNSTREAM INTO PORTIONS OF THE MID MS   VALLEY REGION.      EARLY IN THE PERIOD 50KT+ LLJ WILL BE FOCUSED ACROSS OK/KS.    SCATTERED ELEVATED STRONG STORMS MAY BE ONGOING ACROSS KS INTO   PORTIONS OF EXTREME NWRN MO.  THIS SHOULD SERVE TO MAINTAIN   AFOREMENTIONED BOUNDARY ACROSS SERN KS/NWRN OK WHICH WILL BECOME THE   PRIMARY FOCUS FOR RENEWED SEVERE THUNDERSTORM DEVELOPMENT LATER IN   THE DAY.  ADDITIONALLY...STRONG HEATING WILL SHARPEN A DRYLINE NEAR   THE TX PANHANDLE/OK BORDER...SSWWD INTO WEST TX.  LARGE SCALE   PATTERN APPEARS FAVORABLE FOR SCT-NUMEROUS THUNDERSTORMS FROM LATE   AFTERNOON INTO THE NIGHTTIME HOURS FROM OK NEWD INTO MO.  ANY STORMS   THAT DEVELOP SOUTH OF THE SRN MOST STALLED BOUNDARY WILL POSE THE   GREATEST RISK OF MAINTAINING SUPERCELL CHARACTERISTICS THAT WILL   FAVOR VERY LARGE HAIL/DAMAGING WINDS AND TORNADOES.  DURING THE   OVERNIGHT HOURS A SECONDARY STRONG COLD FRONTAL PUSH WILL ENCOURAGE   A FORCED LINE OF THUNDERSTORMS ALONG THE WIND SHIFT THAT WILL   PROPAGATE SEWD.  BY EARLY THURSDAY AN EXTENSIVE CORRIDOR OF   CONVECTION MAY BE NOTED FROM NRN IL...SWWD ACROSS MO INTO NWRN TX.      ..DARROW.. 04/15/2013

[tmagan]

Day 3 Moderate issued, I was wondering why the outlook was almost 30 mins late. 

When was the last Day 3 moderate?

[andyhb]

Before 4/14 last year.

[Stebo]

When was the last Day 3 moderate?

It was for 4-14-12 which verified the eventual high risk that came out.

[Chicago Storm]

Surprised they went D3 mod...bullish.

[Chicago Storm]

One thought...one of our general forecasters and I were discussing...was the potential for WAA convection north of the front to form into an MCS across northern Oklahoma Tuesday night...sending an outflow down into southern Oklahoma...but we plan to chase in...and possibly meet up with LoKo...in a FWD-SPS-OKC triangle. That could obviously make things more interesting for the Red River Valley area and points north. Chicagostorm...round two for a trip?

I'm just starting to test the waters...So I'll let you know.

[baroclinic_instability]

00z ECMWF is impressive. And wow, day 3 mod, very impressive. It is funny how quickly this went from a two post per day event to this. 

[JoMo]

Hmmm.

 

[baroclinic_instability]

Yeah the front is a bit farther south (except perhaps in TX and NW OK) on the 00z Euro compared to the 12z Euro. There looks to be a ton of CAPE available even by 12z Wed morning with some areas pushing 3300. The Euro breaks out pre-frontal precip and looks to have multiple waves of precip before it lines out as the front pushes east. Looks 'interesting' for you severe weather lovers. 

Yes, very impressive. The 00z ECMWF is indeed farther S again, but still has plenty of room along the dryline and initiates both the dryline and areas east of the triple pt where the low level hodographs are all that much more impressive. One minor worrry, and minor overall, is the ECMWF continues to come in with a slower trough ejection/300-400 hpa speed max, and now has that feature clear over Arizona nosing in New Mexico at 00z Thu. But still, this is looking impressive on paper.

[Stebo]

Surprised they went D3 mod...bullish.

 

I do agree this is a bold outlook, I was personally expecting a step lower with a 30/hatched.

[thewxmann]

Lol, the wording isn't even that bullish... and they issued a Day 3 MDT?

[andyhb]

Lol, the wording isn't even that bullish... and they issued a Day 3 MDT?

 

Tbh, I've noticed Darrow doesn't tend to outline the "strong tornadoes/etc." wording much, especially this far out, could just be forecaster wording preference.

[baroclinic_instability]

SPC clearly went ECMWF/NAM which, oddly enough, they note differences with frontal timing but they are almost identical compared to the even more bullish GFS and CMC guidance.