General Weather Discussion - April 2015

[LocoAko]

Wednesday looks pretty crazy. I wonder how far south storms will fire on the dryline. The recent NAM leaves some question on whether the cap will break. My initial chase target is Northern OK around 35 to near Wichita at the triple point. I am sure that will change. I suspect storms will probably fire off however down the dryline, just how far south? We will see... I expect a moderate risk at least by tomorrow.

Yeah, as venture noted, the NAM uses the BMJ convective scheme which can be tripped up when there is significant dry air present (which there is in the mid-levels for this event). Performs much better for deep-layer moisture events. A decent cap will be present, but I wouldn't be totally offput by the lack of QPF.

[venture]

SPC maintaining a slight risk for Wednesday with some strong verbiage should storms form...

...MID MS/LOWER OH/MID AND LOWER TN VALLEYS INTO ERN KS/OK/TX...
AN EWD-MIXING DRYLINE THROUGH A MOIST/HEATING/DESTABILIZING
AFTERNOON AIRMASS ACROSS TX/OK/KS WILL REMAIN THE PRIMARY FOCUS WITH
RESPECT TO INITIATION OF SEVERE STORMS WED.

AS THE MAIN UPPER TROUGH SHIFTS ACROSS THE INTERMOUNTAIN W THROUGH
THE DAY...A WEAK LEAD WAVE/VORT LOBE PROGGED TO BE SHIFTING NEWD OUT
OF THE SRN ROCKIES TOWARD THE PLAINS INTO THE AFTERNOON SHOULD -- IN
CONJUNCTION WITH HEATING/MIXING -- HELP TO ERODE A FAIRLY STOUT CAP
AT THE BASE OF THE EML LAYER. ALL MODEL RUNS -- BOTH PARAMATERIZED
AND CONVECTION-ALLOWING -- INDICATE THAT LOCAL BREACHES OF THE CAP
WILL RESULT IN ISOLATED STORM DEVELOPMENT...BUT WHERE AND WHEN THESE
INITIAL BREACHES WILL OCCUR VARY GREATLY IN TIME AND SPACE -- FROM
CENTRAL AND ERN KS SWD TO THE TX BIG BEND...AND FROM ROUGHLY MIDDAY
THROUGH LATE AFTERNOON...DEPENDING UPON MODEL RUN. OVERALL
HOWEVER...EACH INDIVIDUAL MODEL CONTINUES TO SUGGEST ONLY ISOLATED
TO WIDELY SCATTERED STORM COVERAGE...AND THUS WILL MAINTAIN 15% RISK
AREA ATTM.

WITH THAT SAID...THE ENVIRONMENT INTO WHICH ANY OF THESE STORMS DOES
INITIATE WILL BE QUITE FAVORABLE FOR RAPID INTENSIFICATION TO
SUPERCELL MODE. WIDESPREAD MIXED-LAYER CAPE IN THE 3000 TO 4000
J/KG RANGE EXPECTED AHEAD OF THE DRYLINE WILL FUEL RAPID UPDRAFT
GROWTH...WHILE A FLOW FIELD FEATURING VEERING/STRENGTHENING FLOW
WITH HEIGHT /H5 FLOW INCREASING TO IN EXCESS OF 50 KT DURING THE
AFTERNOON/ CONTRIBUTING TO FAVORABLE SHEAR IN BOTH LOW LEVELS AND
THE DEEPER/CLOUD-BEARING LAYER SUPPORTS RAPID EVOLUTION OF UPDRAFT
ROTATION. AS A RESULT OF THESE FACTORS...RISK FOR SIGNIFICANT
SEVERE WEATHER REMAINS EVIDENT...INCLUDING VERY LARGE HAIL AND
DAMAGING WINDS ALONG WITH TORNADOES.

[venture]

All modes of severe weather possible on Wednesday...evident by OUN adding the tornado category now.

[venture]

12Z models are rolling in...a couple quick hits...

1) Today NAM shows storms forming along the dryline from Perry North to the KS Border by 7PM. The develops more storms over Southern KS that moves through NE OK as a complex overnight into tomorrow morning.

2) Wednesday 4KM NAM shows storms initiating around 4PM along the dryline in Western OK, it races them really fast to the NE into KS by 7PM but at this point that isn't important. This is the first real indication from NAM of the cap breaking.

GFS will be out in about an hour and I'll start doing a run down of everything then.

[Bobby821]

So it sounds like this storm system is a bust for Oklahoma except the far northern counties. Still at a slight risk and the Tornado category has been knocked down from Moderate to Low so looks like we will not be having much in the way of big time severe weather in the central part of the state.

[venture]

So it sounds like this storm system is a bust for Oklahoma except the far northern counties. Still at a slight risk and the Tornado category has been knocked down from Moderate to Low so looks like we will not be having much in the way of big time severe weather in the central part of the state.

Overall coverage was always a question with the cap. The NAM is just now showing the cap breaking in OK with storms by 4PM. It takes one storm to go crazy to turn it into a big day. The stance I'm taking is that the scope of tomorrow really won't be realized until we still how things start to initialize on the dryline. If we see one storms bust the cap and then start setting off additional storms, it's going to get busy fast.

SPC hasn't veered from a 15% Hatched area over Central and Northern OK.

[jn1780]

So it sounds like this storm system is a bust for Oklahoma except the far northern counties. Still at a slight risk and the Tornado category has been knocked down from Moderate to Low so looks like we will not be having much in the way of big time severe weather in the central part of the state.

If Oklahoma is being classified as anywhere from Norman to Edmond not seeing anything then yes there is a higher chance of "bust". I wouldn't say only far northern counties will only be affected though. There is a pretty good chance storms fire north of I-40.

[venture]

If Oklahoma is being classified as anywhere from Norman to Edmond not seeing anything then yes there is a higher chance of "bust". I wouldn't say only far northern counties will only be affected though. There is a pretty good chance storms fire north of I-40.

Some people just have a really narrow view.

I'll be in town starting Friday. I'd appreciate a storm while I'm there. Okay thanks, bye.

Next round Sat-Mon, so you should be in luck.

[Bobby821]

Well I was thinking it would be nice to have a little shake rattle and roll come through the south metro this evening and tomorrow. starting to get boring trying to out think the weather with this darn strong cap in place limiting storms for us.

[venture]

Tuesday Discussion...

Slightly different setup compared to yesterday and one that should be more favorable for storm development. Yesterday we had a strong cap, like we do today, but we did manage to get some CU development along the dryline. However one thing I always look out for are high level clouds over the area where storms are possible. Most of the time when you see those higher clouds move in, it'll mean the cap will hold and storms won't go. Today we are pretty void of those type of clouds. We have some over South Central OK and a few remaining over the west but they are moving pretty quick and not really as thick as yesterdays. We are also already see some CU develop in western north Texas (highlighted in yellow).



Other items to point out for the setup today. The dryline i starting to sharpen a good deal over NW OK and you can see the plume of moisture that is in place ahead of it - so moisture is not an issue today. The key today is eroding the cap. The Norman sounding is on the left below and shows an extreme cap in place this morning, but this should erode as the day progresses. I also highlighted the fact we are already pretty unstable as this balloon launch was at 7AM and we've had 4 hours of heating since then. SPC Mesoanalysis already has us with CAPE values 2500-3000 j/kg ahead of the dryline. So what do we have to look forward today?

Much like yesterday it is all about the cap. We'll have a bit more forcing today and more sun to help give updrafts a chance to bust the cap. The most likely area for this to happen is going to be over North Central into Northeast OK. 14Z HRRR has storms initiating in in SE KS by 7PM...it also has a lone storm in North Texas at the same time - moving Northeast. It has a bit of a hiccup showing storms along the dryline by 8PM, but I'm not going to focus it right now.

My expectations are we'll see a few areas make a run at busting the cap today. CIN will erode pretty well by late afternoon over Central OK. With the heating today we need to see how sharp the dryline stays and if moisture ahead of it stays pretty deep. These are the type of situations where it turns into a nowcasting situation since it is really hard for models to say for certain that an updraft will break the cap and we'll get a storm. If we should get one to bust through, it'll have a ton of energy to play with and we'll get some pretty large hail. Chances are better than yesterday, but they aren't extremely high. If you end up under one that does make it through you won't care about how low the chance was.

[venture]

Wednesday Discussion...

Severe weather appears likely tomorrow still. One big question mark that is being tossed in here is how will today's activity impact tomorrow. Any storms that form could leave and outflow boundary (or multiple) around which can really impact local environments for storms. The 4km NAM kicks out the complex over NE OK tonight and if that happens, we'll likely have a boundary stretched over NE and North Central OK going into tomorrow. This can enhance areas of lift and helicity for storms, so we just need to keep an eye on things. Wednesday STILL poses a risk for significant severe weather. Do not misread the "slight" risks to mean that it isn't possible...the extent of coverage is the big limiting factor to any outlooks right now.

Looking at the setup for tomorrow afternoon/evening the NAM forecast sounding really weakens the cap to the point where it should be able to break. The forecast sounding is pretty good in that respect where it will have very high instability and a marginal cap. Severe parameters are pretty well in line with large hail and damaging wind. Tornado threat will be there and increase into the early evening hours as the LLJ increases. The indices on the right are Sig TOR (top) and Supercell Comp (bottom) at 7PM. These indices only go up as we go into the 7 to 10PM time period. Keep in mind any boundaries interacting with each other can cause for this values to be much higher in a localized area.



So let's talk time frame. 4km NAM has storms firing off along the dryline in West Central OK and North Central OK by 4PM. Most of this activity will move off to the Northeast and into KS by 7PM - at least going by this model...so don't put a lot of weight into exact positioning and timing. GFS fires off precip in North Central OK by 4PM as well, but leaves Western OK dry. Then the NAM fires off the dryline between 7PM and 10PM between US 183 and US 81...GFS doesn't do this, but I wouldn't read much into that either. The takeaway here is that models, especially the NAM which has been dry up until this point, is showing the cap breaking with development happening. It only takes one to get going and seed additional development. And again...a lot of this is all contingent on how today evolves.

[venture]

Marginal Risk remains today for North Central into Extreme Northeast OK...also the area bordering KS in NE OK has been upgraded to a Slight Risk.

[Bobby821]

Then the NAM fires off the dryline between 7PM and 10PM between US 183 and US 81

Hey Venture, where exactly is this you are referring to in your previous discussion? Trying to place these 1 highways on the map. Will this include western and SW Oklahoma? What is your confidence level of this happening as the NAM is predicting vs nothing that the GFS is showing happening?

[venture]

https://www.google.com/maps/@35.4350498,-97.4427736,8z

183 is the North/South highway through Clinton...81 the N/S highway through El Reno.

I'm not 100% sold on either model. They don't handle mesoscale solutions that well which is why we normally have to look at the hi-res short term models to get a better idea on the most logical placement of storms.

[venture]

SPC has upgraded tomorrow to an ENHANCED RISK over North Central to Northeast OK and through KS and MO. SLIGHT RISK remains for the entire Metro area down to Lawton and east of US 183. North Central Ok into SE KS is currently in a Hatched 30% area.

[Bobby821]

SPC has upgraded tomorrow to an ENHANCED RISK over North Central to Northeast OK and through KS and MO. SLIGHT RISK remains for the entire Metro area down to Lawton and east of US 183. North Central Ok into SE KS is currently in a Hatched 30% area.

Looks like OKC metro and points south will miss out on the big time stuff for tomorrow unfortunately

[Anonymous.]

Bobby, any storm that does fire will likely be severe and more than likely a supercell. Don't get too hung up on risk categories to determine the actual severity of storms.

[venture]

Bobby, any storm that does fire will likely be severe and more than likely a supercell. Don't get too hung up on risk categories to determine the actual severity of storms.

This. If you are going to try to get so specific down to w local level this far out, you are going to be wrong and your forecast look foolish.

[Bobby821]

Yeah, it is just living where I live in Moore area you get the big supercell addiction and any ordinary thunderstorm just doesn't do it for you. Homeowners ins is paid up so I am ready for them..

[BrettM2]

Yeah, it is just living where I live in Moore area you get the big supercell addiction and any ordinary thunderstorm just doesn't do it for you. Homeowners ins is paid up so I am ready for them..

Then please start a thread about this addiction. Please stop making every other post in this thread a complaint that the weather won't be severe enough for you. Let's keep this thread for actual (relevant) weather discussions.

[LakeEffect]

Yeah, it is just living where I live in Moore area you get the big supercell addiction and any ordinary thunderstorm just doesn't do it for you. Homeowners ins is paid up so I am ready for them..

And then, if the area does get hit hard, everyone's rates will go up... ugly cycle.

[Bobby821]

And then, if the area does get hit hard, everyone's rates will go up... ugly cycle.

Rates are going up regardless.

[soonerguru]

Not a fan of mayhem and human misery.

[venture]

Enough. Back to weather...

Instability is now extreme ahead of the dryline and CIN mostly burned off. Storms are trying to form up in North Texas, this is the area that had CIN burn off before others. Southern KS still pretty suppressed for now.

[SOONER8693]

Looks like OKC metro and points south will miss out on the big time stuff for tomorrow unfortunately

You are a sick, sad human being.