Oklahoma Severe Weather Discussion - April 2013

[venture]

Sunday Slight Risk - NW OK


DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1236 AM CDT SAT APR 06 2013

VALID 071200Z - 081200Z

...THERE IS A SLGT RISK OF SVR TSTMS FOR PARTS OF THE CNTRL/SRN
PLAINS...

...SYNOPSIS...
AN UPPER-LEVEL TROUGH WILL AMPLIFY ACROSS THE WEST WHILE A SERIES OF
SUBTLE/LOW-AMPLITUDE MID-LEVEL IMPULSES EMANATE FROM THE ROCKIES
ACROSS THE PLAINS WITHIN A QUASI-ZONAL FLOW REGIME. AT THE
SURFACE...A QUASI-STATIONARY FRONT SHOULD LIE ACROSS THE
MIDWEST...WITH WRN PORTION OF THIS BOUNDARY ATTEMPTING TO ADVANCE
NWD AS A WARM FRONT IN THE CNTRL PLAINS. DRYLINE WILL MIX INTO THE
TX BIG COUNTRY SUN AFTERNOON ARCING NWWD TO A LEE CYCLONE INVOF TX
PANHANDLE.

...CNTRL/SRN PLAINS...
LOW-LEVEL MOISTURE WILL CONTINUE TO INCREASE BENEATH A STOUT
EML...LIKELY YIELDING 50S SURFACE DEW POINTS ALONG THE
DRYLINE/QUASI-STATIONARY FRONTAL ZONE BY SUN LATE AFTERNOON.
GUIDANCE DOES INDICATE LOWER TO PERHAPS MIDDLE 60S SURFACE DEW
POINTS WILL DEVELOP AHEAD OF THE DRYLINE FROM CNTRL OK SWD TO THE
WRN GULF. ALTHOUGH THE PRESENCE OF A STRONG CAP WILL LIMIT THE DEPTH
OF THE PBL AND MIXING OF DRIER AIR ALOFT...MUCH OF THE GULF HAS
EXPERIENCED SUBSTANTIAL DRYING IN THE WAKE OF A RECENT COLD FRONT
PASSAGE. RICHER MOISTURE IS NOW CONFINED TO THE CARIBBEAN PER GOES
PW DATA...WITH ONLY A NARROW PLUME OF NEAR 60 SURFACE DEW POINTS
ALONG THE MEXICO GULF COAST. AS SUCH...SUSPECT THAT GUIDANCE IS
OVERLY AGGRESSIVE WITH THE AMPLITUDE OF LOW-LEVEL MOISTURE RETURN BY
SUN AFTERNOON.

DIURNAL TSTM DEVELOPMENT WILL LIKELY BE TIED TO A COUPLE OF SUBTLE
LOW-AMPLITUDE IMPULSES EMBEDDED WITHIN THE MODERATELY STRONG
MID-LEVEL FLOW REGIME AND INCREASING LOW-LEVEL WAA ALONG THE
QUASI-STATIONARY FRONT. MAJORITY OF GUIDANCE APPEAR TO KEY ON KS AS
THE MOST PROBABLE AREA OF CONVECTIVE DEVELOPMENT WHERE THE CAP WILL
BE WEAKER. THE NWRN PERIPHERY OF THE LOW-LEVEL MOISTURE PLUME INVOF
SWRN/CNTRL KS WOULD APPEAR MOST FAVORABLE FOR LARGE HAIL WITH A
STEEP MID-LEVEL LAPSE RATE/STRONG DEEP-LAYER SHEAR ENVIRONMENT. THIS
THREAT WILL BE INCREASINGLY CONDITIONAL WITH SRN EXTENT WITH ONLY A
NARROW SPATIAL CORRIDOR OF WEAKER MLCIN ALONG THE DRYLINE AND
PRONOUNCED CAPPING TO THE E.

[venture]

Sunday appears to be a very conditional day when it comes to severe weather. A strong cap will be in place over much of Western Oklahoma along the dryline. The dryline though will feature a bulging feature on the southern end over it (over SW OK) which can help increase convergence and storm development chances.

The 12Z NAM indicates a stronger area of convergence in this zone with the 12Z GFS showing convergence all along the dryline. The GFS is also less extensive with its cap forecast having areas in NW and West Central OK with only a weak cap by afternoon. The GFS also has precip breaking out in the late afternoon across Western OK moving into Central sections by evening.

Current feeling right now is that cap will be stronger than what GFS hints, but maybe not as unbreakable as was NAM is putting for. The Dryline will be in play and both agree on positioning. Best chances for storm development will be over NW OK decreasing as your move South and East. Looking at the forecast soundings for Woodward, Enid, Norman, and Clinton show a breakable cap near Woodward becoming much tougher near the OKC area. Clinton is also still pretty stout. Wind profiles overall favor rotating storms so large hail and a tornado or two cannot be ruled out. Coverage does remain limited to one or two supercells, and also wouldn’t be shocked if storms try but fail to break though. Storm motions look reasonable moving E to ENE at around 20-25 mph.

[venture]

Monday's outlook is a bit more difficult since GFS and NAM aren't completely on the same page. They agree on dryline placement and moisture return. However, NAM has a much stronger cap whereas GFS is much weaker over the area of greater instability. NAM also keeps more precip to a minimum where GFS has storms breaking out between 5PM and 7PM that evening. This forecast outlook area is a compromise between the two. If GFS would verify the risk area would extend a bit more to the south and east to I-35.


Not really much to add compared to the previous discussions. Storms that develop will be severe and profiles are favorable for rotating storms with large hail and tornadoes. Coverage will be better than Sunday, but might be limited in areas depending on where the cap holds.

[venture]

Peak at the setup for Tuesday which will be a two parter.

Afternoon / Evening dryline pushes into Central OK but not forecast to cross I-35. Moderate to high instability and relatively weaker capping will allow for storms to develop and push off to the east. All severe modes are possible on Tuesday.



Tuesday Night into Early Wednesday will see the cold front overtake the dryline and push through. Will likely see a squall line develop along the front as it pushes through.

[venture]

Pretty good run down from NWS Norman on the next few days. The TL: DR version - strong cap will limit overall storm coverage, anything that develops will be severe.

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE NORMAN OK
301 PM CDT SAT APR 6 2013

.DISCUSSION...
SEVERE THUNDERSTORM POTENTIAL SUNDAY AFTERNOON THROUGH TUESDAY NIGHT REMAINS THE BIGGEST CONCERN.

TONIGHT INTO SUNDAY MORNING...THE AIR SHOULD REMAIN TOO CAPPED
FOR ANY THUNDERSTORMS TONIGHT...THOUGH CONFIDENCE IS NOT HIGH.
CANNOT COMPLETELY RULE OUT A STRAY STORM OR TWO NEAR THE RED RIVER
TONIGHT. ADDED MENTION FOR 20 PERCENT CHANCE OF STORMS NORTH OF
I-40 AND NEAR/EAST OF I-35 SUNDAY MORNING. IF STORMS DEVELOP...
HAIL...PERHAPS LARGE HAIL...WOULD BE THE MAIN HAZARD WITH DECENT
ELEVATED INSTABILITY. THERE IS A CHANCE FOR FOG DEVELOPMENT LATE
TONIGHT INTO SUNDAY MORNING NEAR I-44...BUT DID NOT MENTION DUE TO
LOW CONFIDENCE.

SUNDAY AFTERNOON AND EVENING...A FEW SEVERE STORMS MAY DEVELOP
NEAR A DRYLINE ACROSS WESTERN OR NORTHWEST OKLAHOMA. LARGE
HAIL...PERHAPS VERY LARGE HAIL UP TO THE SIZE OF BASEBALLS...
WOULD BE THE MAIN HAZARD. FAIRLY HIGH CLOUD BASES AND LACK OF
SIGNIFICANT LOW LEVEL WIND SHEAR MAY LIMIT THE CHANCES FOR
TORNADOES. ONLY KEPT 20 TO 30 PERCENT AS COVERAGE SHOULD REMAIN
ISOLATED AT BEST WITHOUT A GOOD TRIGGER FOR LIFT AND STRONG
CAPPING.

MONDAY AFTERNOON AND EVENING...SIMILAR TO SUNDAY...A FEW SEVERE
STORMS WITH MAINLY LARGE HAIL ARE POSSIBLE ACROSS WESTERN
OKLAHOMA. SEVERE STORM COVERAGE MAY BE A BIT BETTER DUE TO HIGHER
DEWPOINTS WHICH COMBINED WITH BETTER LOW LEVEL SHEAR...MAY ALLOW
FOR TORNADOES. HOWEVER...STRONG CAPPING SHOULD KEEP STORMS FROM
BEING WIDESPREAD.

THE MAIN SEVERE THREAT THROUGH MONDAY NIGHT SHOULD STAY WEST OF
THE OKLAHOMA CITY METRO AREA.

TUESDAY INTO TUESDAY NIGHT...PERHAPS A BETTER SHOT FOR SEVERE
STORMS WILL OCCUR ACROSS THE AREA...THOUGH CONFIDENCE IS LOW. A
FEW STORMS MAY DEVELOP ALONG A DRYLINE DURING THE AFTERNOON AND
EVENING HOURS WHICH COULD PRODUCE VERY LARGE HAIL AND TORNADOES IF
THEY CAN OVERCOME STRONG CAPPING. A LINE OF STORMS WILL LIKELY
DEVELOP ALONG AN APPROACHING COLD FRONT TUESDAY NIGHT WITH
ISOLATED SEVERE DAMAGING WIND AND HAIL REPORTS ALONG WITH PERHAPS
HEAVY RAIN AND LOCALIZED FLOODING. THE SLOWER 12Z ECMWF IS
PREFERRED...WHICH KEEPS RAIN LINGERING INTO WEDNESDAY.

WEDNESDAY THROUGH NEXT SATURDAY...RAIN WILL END ON WEDNESDAY...AND
THEN ALLOW FOR RATHER QUIET WEATHER CONDITIONS. BELOW AVERAGE
TEMPERATURES FOR THE MIDDLE OF THE WEEK WILL REBOUND TO NEAR OR
ABOVE AVERAGE BY NEXT WEEKEND.

MBS

[jn1780]

Sounds pretty typical for an Oklahoma spring. Always riding that fine line between bust and outbreak. lol


"TUESDAY INTO TUESDAY NIGHT...PERHAPS A BETTER SHOT FOR SEVERE
STORMS WILL OCCUR ACROSS THE AREA...THOUGH CONFIDENCE IS LOW"

Translation: Anything can happen at this point. Ask us again later.

[venture]

00Z NAM Update for tomorrow...

Northern half of my risk area (the white line) is the more probable. Southern half is less likely due to a stronger cap. It is near the bulge in the dryline so that can help with lift somewhat. NAM does develop some isolated storms that could move into Central OK before 10PM.



Forecast Sounding from Clinton...
Pretty strong cap (3.7) noted but overall very unstable atmosphere. EHI and Helicity values are good for rotating storms. 1km helicity doesn't look bad at all either. LCL of 815 though tells me these will be pretty high based storms so that would limit tornadic threat and put the focus on very large hail.

[OKCisOK4me]

I like the color coded geographical charts cause they're like 3rd grade and I think I can understand what they mean....

ON THE OTHER HAND...

the graphs with the lines running up and spiraling around don't do crap for me and make me wonder when I'm at work on Monday from 12-9, if I should be worried about my 2013 Hyundai being parked in the open when I have this feeling that it might be raptured by Mother Nature's fists of fury...aka...hail stones. Alas, I have no clue what the lines mean on the graph so I guess I'll just deal with the consequences...derp!

[SoonerDave]

OKC, I think the best info there is right now just says there's a good potential for severe weather, but the variable is the "cap" in the atmosphere that prevents or limits those storms' development. It's just too close to call....the ingredients are too favorable to ignore the chance for severe storms, including hail, but the mitigating factor (cap) can't be ignored, either. Dicey call to be absolute either way.

[venture]

Very little change to today's forecast. NAM shows storms firing this afternoon in NW OK and hints at them forming a small complex later this evening that would swing ESE over central OK. HRRR is mostly dry and keeps all storms north into KS. GFS hasn't ran yet, so we'll see what that says.

SPC has removed the slight risk for most of Western OK except for NW OK. Not unexpected as the cap is going to be strong and we'll likely only see a couple storms fire. If they do, they will be severe. I wouldn't be shocked if they put the slight risk back in place if it seems more probable that this would happen, but nothing to really read into yet. The story today and tomorrow as always been about the cap strength and if the dryline would provide enough lift to break it. There is also a weak warm front over Northern OK as well. Depending on how far north it goes, the intersection area of that and the dryline would hence the ability for storm development and also for a couple tornadoes.

Outlook map is pretty much what NWS Norman just put out, so at least most are on the same level of thinking with this.

[venture]

Monday's outlooks looks pretty similar. NAM and GFS show storm development north of I-40 and west of I-35 in the afternoon. Storm motions would be ENE to NE at 25-35 mph. Forecast cap is going to be the bust maker on this forecast. Convergence is expected to be decent along the dryline, but may not be enough to break through or keep storms sustained. As storms move east the cap will increase so that may kill them off as they approach I-35. I highlighted the most probable area for storms tomorrow as it looks right now, but will need to be revisited tomorrow morning based on what we actually see outside. Main concerns tomorrow would be very large hail and tornadoes in any storm that develops.

[venture]

Here is the link again for the chat room: Live Chat ? Weather Spotlight

I'll be in and out while it remains quiet. Feel free to bookmark it as this will be the permanent spot for the chat room.

[Bunty]

OKC, I think the best info there is right now just says there's a good potential for severe weather, but the variable is the "cap" in the atmosphere that prevents or limits those storms' development. It's just too close to call....the ingredients are too favorable to ignore the chance for severe storms, including hail, but the mitigating factor (cap) can't be ignored, either. Dicey call to be absolute either way.

Well, if the sky is going to be cloudy over the state, then it may be safe to assume not much of a severe nature will be able to break through the cap.

[venture]

Latest HRRR run shows storms firing in NW OK by 6PM this evening with a large supercell moving over the northern Tier of counties through the evening.

[venture]

Tuesday's Risk area... this is currently a 30% hatched slight risk on the Day 3, so SPC may upgrade to moderate if conditions continue to look impressive. Models so development along the dryline around 4PM moving into Central OK in the early evenings.

[venture]

CIN pretty well gone according to SPC Mesoanalysis, not sure I really believe it though. However, looking at the 18Z special balloon sounding from Douglas, KS (just over the border), the cap is still hanging tough. HRR still tries to develop some cells over Northern OK early this evening, but doesn't look like the lift is there yet. SW OK is beautiful and clear, but I still have the chance down there at 10% or less right now.

[venture]

This is something I've been talking about. It is where the dryline is bulging out some in SW OK. There is higher convergence in this area.



MESOSCALE DISCUSSION 0394
NWS STORM PREDICTION CENTER NORMAN OK
0626 PM CDT SUN APR 07 2013

AREAS AFFECTED...SW OK...NW TX

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY

VALID 072326Z - 080100Z

PROBABILITY OF WATCH ISSUANCE...20 PERCENT

SUMMARY...AN ISOLATED SEVERE THREAT COULD DEVELOP ACROSS PARTS OF SW
OK AND NW TX OVER THE NEXT HOUR IF A THUNDERSTORM CAN INITIATE AND
PERSIST. AN ISOLATED THREAT FOR LARGE HAIL WOULD BE THE MAIN THREAT
EARLY THIS EVENING. WW ISSUANCE DOES NOT APPEAR LIKELY DUE TO THE
ISOLATED AND CONDITIONAL NATURE OF THE THREAT.

DISCUSSION...THE LATEST VISIBLE SATELLITE IMAGERY SHOWS AGITATED
CUMULUS JUST TO THE EAST OF CHILDRESS ALONG A WELL-DEFINED DRYLINE.
IN SPITE OF THE LACK OF LARGE-SCALE ASCENT AND CAPPING...STRONG SFC
HEATING TO NEAR 90 F AT CHILDRESS MAY ALLOW FOR ISOLATED CONVECTIVE
INITIATION. SFC DEWPOINTS TO THE EAST OF THE DRYLINE ARE IN THE
LOWER 60S F WITH MLCAPE VALUES ESTIMATED IN THE 1500 TO 2500 J/KG
RANGE. THIS COMBINED WITH 50 TO 55 KT OF DEEP LAYER SHEAR WOULD
SUPPORT SUPERCELL DEVELOPMENT. IN ADDITION TO THE INSTABILITY AND
SHEAR...MID-LEVEL LAPSE RATES ARE STEEP ESTIMATED TO BE NEAR 8.0
C/KM. THIS WOULD FAVOR LARGE HAIL AS THE MAIN THREAT IF A
THUNDERSTORM CAN DEVELOP AND PERSIST.

..BROYLES/HART.. 04/07/2013

[venture]

Current Visible Sat showing agitated CU.

[venture]

This is essentially our only hope right now to the SW. LOL

[venture]

One down...3 more days of precip chances to go. Monday looks like it may have a better shot at storm development with two focal areas both having different setups. Models favor NW OK with precip late tomorrow. Instability looks good in this area overall. The cap of course becomes in the issue. LCL looks pretty high so tornado threat tomorrow looks low overall unless we see some low level moisture improvement. The one area that has my attention is further south in SW OK. There is going to be more forcing there tomorrow and CIN is actually lower in that area. Much like today where this area had the better forcing overall (by forecast), we very well could see the same tomorrow with developing CU. Now if the forcing will be good enough to bust this thermonuclear cap, we'll have to wait and see.



Tuesday and the interesting Wednesday forecast coming up.

[venture]

Tuesday is definitely the day to watch out for right now. The setup looks pretty good for a decent amount of severe weather. Wind profiles aren't ideal for tornadic development due to the winds getting a bit more linear and not as much directional shear (SE to SW instead of WSW or W as we have now). Instability will be high and maximized along the dryline which is now forecast to not push through until evening (if at all). It very well could end up staying mostly stationary until the cold front overtakes it. I'm highlighting the most likely area for significant severe weather right now, but the risk area will go well into MO, AR, and TX. So it will be two phases to the severe weather on Tuesday. Initially will be isolated/scattered supercells along the dryline and ahead of it. These will push off to the ENE or NE at about 30-35 mph. These will have the chance for large hail and perhaps a few tornadoes. The next phase is with the cold front and a quickly developing squall line that will push through.

Depending on how things go, I wouldn't be shocked to see a moderate risk go out for some portion of C and E OK.



After the front passes, we could see a wave of moderate precip come through. GFS and NAM are split on this. GFS keeps it in Western OK and NAM brings it through Central OK. The kicked? Pink isn't rain...



Some area could see a quick slushy accumulation of snow before its all said and done. I don't have much confidence that it'll happen, but might as well put it out there. It's been in the model solutions for a couple days now.

GFS Solution


NAM Solution

[bchris02]

Yeah. Winter isn't over yet. News 9 predicted snow earlier last week. I wonder if they are going to actually turn out to be right. We had a mild start to winter this year but it doesn't seem like it wants to end. This kind of reminds me of 2002 when there was highs in the 50s and lows near freezing as late as the first week of May. Coincidentally, that was an extremely quiet severe weather year.

[Anonymous.]

My gut says today, a cell or two will fire up in W/SW OK late this afternoon, but it would have to be ideal conditions.

Tuesday PM still looks like the main show. Wednesday looks like a day of winter then back to beautiful spring weather.

[venture]

Outlook for today is very conditional based on the ability for storms to break through the cap. So the map today is a little different. The shaded areas are those where convergence is forecast. On top of that you'll see the CAPE fields and also the dryline. There is a bit of a bump to the dryline this morning over SW OK, which helps to increase convergence just a bit. The dryline will flatten out a bit through the day, but this is probably what the models are picking up on. HRRR is also showing CIN vanishing over much of North Central and parts of SW OK today - hence the risk area. It keeps CIN relatively high over NW OK and SE of I-44. Should we have any chance for storms today I'm looking at these two areas as the best shot. HRRR CAPE forecasts for North Central OK are extremely high (and probably a bit over done). So should that instability be realized, that could be enough to get something up there. The other bet is for the SW part of the state. Much like yesterday, we'll probably see CU go up in this area. We had a couple weak echoes yesterday, but nothing could get established. We'll see how it works out today. Cap is really tough, and as is often the case with these setups you can have absolutely nothing or a monster storm if it can break through.

[SoonerDave]

I've come to the conclusion that the CAP is the springtime's answer to severe storm forecast uncertainty as the dryslot is to wintertime blizzard predictions