April 2nd - April 5th Severe Weather

[thewxmann]

12Z GFS is trending towards the ECMWF with a weaker main system and a more strung out low. It has also been consistent on bringing a disturbance across OK in the morning hours; the morning convection that results may have significant implications on what happens later in the day. Furthermore, strong forcing through the warm sector and unidirectional wind profiles support widespread convection in the warm sector throughout the day - this will likely be a messy cloudy type setup rather than something like Super Tuesday, despite the similar 500mb evolutions.

Lots to consider here, and this will be one of the more sensitive setups we've seen this year. Mesoscale developments will play a bigger role than usual. For instance, though the trough is more sheared out, if a secondary surface low develops further south near AR, winds may be more backed than otherwise - which would make this a much more volatile situation.

[Fred Gossage]

00Z GFS has dramatically increased the severe risk for MS/AL/TN/GA for Monday afternoon into the overnight. This run has what previous runs and previous Euro runs had.... developing the second surface low on the front.... back over Arkansas. This would increase directional shear and pressure falls down here.... and dramatically ramp up the tornado risk... closer to the richer low-level moisture and higher instability.

[Thundersnow12]

00Z GFS has dramatically increased the severe risk for MS/AL/TN/GA for Monday afternoon into the overnight. This run has what previous runs and previous Euro runs had.... developing the second surface low on the front.... back over Arkansas. This would increase directional shear and pressure falls down here.... and dramatically ramp up the tornado risk... closer to the richer low-level moisture and higher instability.

with the help of a almost due south 70kt LLJ..

[Hoosier]

It looks like the 00z GFS tries to back the surface winds a little across a good chunk of the warm sector Monday between 18z-00z.

[Thundersnow12]

It looks like the 00z GFS tries to back the surface winds a little across a good chunk of the warm sector Monday between 18z-00z.

If we get that sfc low to develop along the front like the 0z GFS is showing and as Fred said, you will get pressures to fall and winds responding to it and backing the winds nicely over a wide area. On this run its a wide area covering parts of KY/TN/AL/MS and even into extreme southwest IN with dew points in the mid 60's

[Hoosier]

If we get that sfc low to develop along the front like the 0z GFS is showing and as Fred said, you will get pressures to fall and winds responding to it and backing the winds nicely over a wide area. On this run its a wide area covering parts of KY/TN/AL/MS and even into extreme southwest IN with dew points in the mid 60's

Yes indeed.

By the way, I recently started a blog. The focus is on historical Indiana tornadoes but I'll be posting stuff about this event. Still gonna post here obviously but this gives me an outlet to babble about local stuff without boring the crap out of 95% of you.

Cheesy name but indianatornadoes was taken.

http://indianadoes.blogspot.com/

[trapperman]

Yes indeed.

By the way, I recently started a blog. The focus is on historical Indiana tornadoes but I'll be posting stuff about this event. Still gonna post here obviously but this gives me an outlet to babble about local stuff without boring the crap out of 95% of you.

Cheesy name but indianatornadoes was taken.

http://indianadoes.blogspot.com/

Birmingham with a nice disco tonight discussing this very scenario that the GFS shows...

STILL NEED TO KEEP AN EYE ON THE

THIS SECONDARY FRONTAL LOW...AS IF IT COMES TO PASS...THINGS COULD

GO DOWNHILL RATHER RAPIDLY. LOTS OF DETAIL TO WORK OUT THROUGH

NEXT MONDAY.

http://forecast.weat...on=1&glossary=1

[AppsRunner]

Nice LLJ on the GFS... this is valid 0z Tuesday.

[cyclone77]

Latest SREF tries to give a little hope for late Sunday.

[Thundersnow12]

Latest SREF tries to give a little hope for late Sunday.

The 12z NAM is trying to do the same thing and developing to sfc lows sunday afternoon, one being in KS and the other being in eastern IA. It does break the cap around DSM but thats due in part to better forcing with the cold front and not storms going up on the warm front, also the sfc winds in south central IA ahead of the cold front are veered...gosh where have I heard this before lol. In IA again??

[Thundersnow12]

WOW...talk about an increase in low-level instability up north from previous runs

[Ajdos]

12z, Woah, basicaly a bomb LOL... 970 mb.. This has the potential to be a bad severe weather event :/ with a strong squall line..

[SpartyOn]

Talk about Spring roaring in!!!!

[CUmet]

I'm becoming less impressed with the Monday/Tuesday setup, as the last few GFS runs have trended towards a solution more similar to that of the ECMWF. More of the trough energy is staying north, making it more difficult for a secondary low to form farther south and back the low-level wind field sufficiently enough. This is especially important in this case because the trough is so amplified and sharp, resulting in a backed mid-upper wind field. There's still 3 days left to go, so substantial changes could still come, but right now I'm favoring a more squall-line type event with many severe reports and some tornadoes, but a large-scale tornado outbreak appears less likely.

[Hoosier]

12z Euro remains faster with FROPA...the American models have trended that way but I seriously have to wonder if they're done trending. It's possible this may be more of a Monday morning threat instead of Monday afternoon for this area, which may lessen the impact a little but instability progs are still fairly decent even in the morning.

[AppsRunner]

12z GFS/NAM both have pretty good timing for Ohio... between 18z and 0z. ECMWF... not so much. The SPC will most likely shift the risk zone a bit north looking at how far north the NAM/GFS get the warm front. It's not a great setup here, but I've seen worse. Another Low CAPE/High Shear event- at least in Northern OH

[Jim Martin]

Here is part of the Area Forecast Discussion from the National Weather Service in Cleveland talking about Monday's severe weather potential across northern Ohio...

THE MODELS ARE STILL NOT IN AGREEMENT ON THE TIMING OF THE STRONGER STORM SYSTEM ON MONDAY. THE ECMWF IS MUCH FASTER THAN THE GFS...WITH THE COLD FRONT EAST OF THE FORECAST AREA BY EVENING. THE FORECAST WILL BE BASED ON THE SREF TIMING WHICH PUTS THE FRONT FROM NORTHWEST PENNSYLVANIA ACROSS EAST CENTRAL OHIO BY 00Z TUESDAY. TOOEARLY TO PIN DOWN ANY DETAILS BUT IT SHOULD BE A SHORT LIVED PREVIEW OF SPRING...COMPLETE WITH A GUSTY SOUTH BREEZE AND THUNDERSTORMS. WILL HAVE TO WATCH FOR THE SEVERE WEATHER THREAT AS IT WILL PROBABLY GET UNSTABLE AHEAD OF THE FRONT WITH PLENTY OF SHEAR.

[thewxmann]

I'm becoming less impressed with the Monday/Tuesday setup, as the last few GFS runs have trended towards a solution more similar to that of the ECMWF. More of the trough energy is staying north, making it more difficult for a secondary low to form farther south and back the low-level wind field sufficiently enough. This is especially important in this case because the trough is so amplified and sharp, resulting in a backed mid-upper wind field. There's still 3 days left to go, so substantial changes could still come, but right now I'm favoring a more squall-line type event with many severe reports and some tornadoes, but a large-scale tornado outbreak appears less likely.

Yep. Never bet against the ECMWF.

At this point it just looks like a normal squall line along front setup.

(EDIT: Okay, any supercell that can manage to develop ahead of the line still holds threat. But the point is - a much more docile setup.)

[Hoosier]

Paducah sounding Monday - pow

18z NAM still looks pretty slow. Something's gotta give...

[Thundersnow12]

Our new website is up and running as of today, check it out. My favorite new thing is the overlays of many products on 1km sat images, almost like AWIPS

http://weather.cod.edu/index.php

[thewxmann]

Yeah, to be honest, I'd be very surprised to see anything develop before sundown on Sunday, unless the upper air system speeds up by around 12 hr.

Just to be complete, I would like to revise now that convective temps might be reached down somewhere in TX (prob the Trans-Pecos/Edwards Plateau region?) for a few isolated high-based cells. There might also be just enough forcing for a few late storms to pop along the TP, but these would be elevated and undercut by the cold front rather quickly. Still, just for accuracy's purposes...

[hm8]

DTX talking possible severe...

BASED ON ALL THESE SCENARIOS...IT APPEARS LIKELY SOME SEMBLANCE OF THE WARM SECTOR (850 MB TEENS IN THE LOWER TEENS) WILL MAKE IT ACROSS THE BORDER SUNDAY NIGHT...WITH TEMPERATURES RISING THROUGH THE NIGHT...EVEN IF WE END UP DEALING MORE OF AN OCCLUSION DUE TO THE INFLUENCE OF THE COLD LAKES. IF THE GFS ENDS UP BEING RIGHT...TEMPERATURES WOULD BE ABLE TO MAKE IT TO 70 DEGREES ON MONDAY...WHICH COUPLED WITH SURFACE DEW PTS SURGING INTO THE LOWER 60S (SUPPORTED BY THE NAM) WOULD GIVE US SOME CONCERNS FOR SEVERE WEATHER WITH CAPES OF 500-1000+ J/KG AND EXCELLENT WIND SHEAR/HODOGRAPHS. HOWEVER...CAPE DENSITY LOOKS TO BE VERY HIGH UP...WITH LOW LEVELS REMAINING STABLE. PLANNING ON BEING A BIT MORE CONSERVATIVE ON TEMPS AND SEVERE CONCERNS (WILL LET NIGHT SHIFT INTRODUCE IN HWO IF NECESSARY)...AND WOULD PUTTING SOME WEIGHT TO THE UKMET/EUROPEAN SOLUTIONS...WHICH SHOWS THE FRONTAL BOUNDARY MOVING THROUGH AROUND 12Z MONDAY ALREADY. BASED ON THIS TIMING AND LOW LEVEL COLD ADVECTION THROUGH THE DAY...PREFER TO BE A BIT CONSERVATIVE WITH MAXES...MID 40S NORTHWEST TO MID 60S TOWARD OHIO BORDER.

[Thundersnow12]

Just to be complete, I would like to revise now that convective temps might be reached down somewhere in TX (prob the Trans-Pecos/Edwards Plateau region?) for a few isolated high-based cells. There might also be just enough forcing for a few late storms to pop along the TP, but these would be elevated and undercut by the cold front rather quickly. Still, just for accuracy's purposes...

chased down there a few times last May and saw a great supercell northwest of Pecos on 4/28/09.

[hm8]

Dr. Forbes calling for a severe weather outbreak all the way up to central MI on Mon, per his posts on his FB page

[Stebo]

Even though the risk might be lower than previously expected to the south, I think up this way with the low tracking through the area the risk potential is going up. Only issue to work out is timing.

[Hoosier]

Even though the risk might be lower than previously expected to the south, I think up this way with the low tracking through the area the risk potential is going up. Only issue to work out is timing.

Surface winds look veered even there so I'm not sure how much of a tornado threat there is. Still some time to go but today's runs are certainly backing off the apocalyptic scenario.

[Stebo]

Surface winds look veered even there so I'm not sure how much of a tornado threat there is. Still some time to go but today's runs are certainly backing off the apocalyptic scenario.

The bigger concern I have is that this is speeding up substantially.

[Fred Gossage]

Yep. Never bet against the ECMWF.

At this point it just looks like a normal squall line along front setup.

(EDIT: Okay, any supercell that can manage to develop ahead of the line still holds threat. But the point is - a much more docile setup.)

If that were true, just 36-48 hours ago, we would've been talking about bowling ball setup Monday with a surface low track through MS/AL. The ECMWF has struggled terribly in the medium range for a few months now... and at times, more so than the GFS or GFS ensembles.

[thewxmann]

If that were true, just 36-48 hours ago, we would've been talking about bowling ball setup Monday with a surface low track through MS/AL. The ECMWF has struggled terribly in the medium range for a few months now... and at times, more so than the GFS or GFS ensembles.

The ECMWF almost always does better than the GFS when evolutions off the W Coast determine ultimate trough morphology. Furthermore, when the ECMWF latches onto a scenario (let's just say about 4-5 runs of consistency) in the 72-120 hr range, take it to the bank. The ECMWF does poorly if it continues to oscillate in its progs.

It might not be perfectly right, but the fact that the GFS is trending towards it speaks volumes. Generally, I believe the ECM has the right idea, i.e. more sheared out, positive tilt.

[Fred Gossage]

The ECMWF almost always does better than the GFS when evolutions off the W Coast determine ultimate trough morphology. Furthermore, when the ECMWF latches onto a scenario (let's just say about 4-5 runs of consistency) in the 72-120 hr range, take it to the bank. The ECMWF does poorly if it continues to oscillate in its progs.

It might not be perfectly right, but the fact that the GFS is trending towards it speaks volumes. Generally, I believe the ECM has the right idea, i.e. more sheared out, positive tilt.

I didn't say otherwise... and this is what I believe is going to happen. You said to never bet against the Euro.... and if that were true just two days ago, we'd be looking at a bowling ball Monday. Period. End of discussion. Don't make me go grab the progs to prove my point. The Euro can be wrong just like anything else can... and outside of 84 hours... it has struggled like anything else since at least December.