General Weather Discussion - April 2014

[bchris02]

So this is showing precipitation behind the front? Don't supercells usually form ahead of a front or dryline?

Also, should I cancel my plans for Sunday evening yet?

[SoonerDave]

So this is showing precipitation behind the front? Don't supercells usually form ahead of a front or dryline?

Also, should I cancel my plans for Sunday evening yet?

You can have what's called "wrap-around" moisture sufficient to fire off small rainshowers as the natural anticlockwise rotation around a low "pushes" moisture around its "backside." The severe threat is generally gone by then, but the rain can persist. Varies with each system, of course.

I, personally, would never suggest anyone cancel anything on the basis of what's termed (as of this morning) a "low risk" for severe weather four days in advance. You're gonna give yourself an ulcer, bchris.

[Anonymous.]

You can have storms behind cold fronts, but they usually are undercut by the front and don't have long lives and are elevated in nature.

For supercells (see tornado) you need low level moisture and warmest air you can find. Behind the cold front neither of these are there in the lower levels, thus elevated storms.


Sunday is one to watch, but right now it doesn't look like doomsday.

[venture]

12Z NAM doesn't bring any major surprises to the table. Two areas of convection Sunday. 1) Along the boundaries and 2) Ahead of everything in the warm sector.

Area 2 is already highlighted by a 30% risk are on the SPC Day 4 graphic. This is going to mainly be far SE OK and areas SE of the state.

Area 1 is going to be much of Central and Eastern Oklahoma. Looks like things should fire by mid afternoon along the front and dryline, but much will get quickly undercut as the front races through. Severe risk looks like a low end slight right now with primary risks being hail and wind. If a storm were able to get going ahead of the boundaries, or get rooted in them, then there might be a chance for some increase rotation with it - but its low right now.

Still 4 days out so things can change some.

[venture]

12 GFS is in for Sunday and it is a tad slower. Frontal passage between 4 and 7 now with the surface low digging south along the Red River. Forecast sounding for Norman at 4PM would indicate conditions would be there for severe weather, if it wasn't for the strong cap (3.3). Winds from 900 to 500 mb are nearly uniform (from the Southwest) the entire way out. Very slight backing to the winds at the surface could yield a brief window for a rotating storm, but nothing to get excited about. The big thing here is going to be cap strength that might keep a lid on things until the front passes and we get some elevated convection. At that point the severe risk would be limited to an isolated hail or wind report.

[venture]

Looking ahead a bit further looks like the next chance of storms will come in around the 17th and 18th of the month. Then quiet again. Of course things are going to change in these forecasts, but just tossing it out there.

Since 1950, we have NEVER gone without at least 2 tornado reported in the first four months of a year. The lowest year with 2 was 1998. We had 1 in March and 1 in April that year. The year ended with 83 overall with the May 24th spat of tornadoes in NW OK, June 13th in Central OK (day Frontier City was hit), and the October 4th outbreak (26 - largest in state history for October) in Central and SE OK.

Just something to think about. If a year starts off this quiet, it really doesn't mean the year will be quiet overall.

[Ginkasa]

Anecdote: the hat trick of those storm in June and October and (of course) May the following year caused me to have anxiety every time it was cloudy for two years or so.

I got over it.

[venture]

Essentially no change to the 12Z Euro from the 00Z Euro. Still has storms by 4PM along the cold front from NC Oklahoma back to Elk City and then storms along the dryline from Enid south to Lawton. Instability still forecast to be high so severe weather still possible. I would plan on a slight risk day for much of Oklahoma except far NW and the panhandle.

[Charlie40]

Mike Morgan was forcasting an upgrade to Moderate risk for Sunday and making it out to be a bigger deal than whats anticipated. Both Both 5 and 9 were just saying storms with hail rain and some wind as the main threats. I guess we will see who ends up with the correct forcast as the system gets closer.

[venture]

Payne has a moderate risk for Sunday already from roughly I-40 south to Texas.

[LocoAko]

Mike Morgan was forcasting an upgrade to Moderate risk for Sunday and making it out to be a bigger deal than whats anticipated. Both Both 5 and 9 were just saying storms with hail rain and some wind as the main threats. I guess we will see who ends up with the correct forcast as the system gets closer.

Is there a graphic available from that somewhere? I'd be curious to see it.

Sent from my HTC One using Tapatalk

[bchris02]

Payne has a moderate risk for Sunday already from roughly I-40 south to Texas.

So I am guessing this is their own moderate risk and not the NWS one?

[venture]

So I am guessing this is their own moderate risk and not the NWS one?

Indeed. SPC will probably have us in a slight when the new Day 3 comes out tonight around 2-3AM.

[PennyQuilts]

Bchris, your aviator is freaking me out. QUIT STARING!!!

[venture]

Not doing an actual forecast just yet, just some random commenting to see what others are thinking.

So the 00Z NAM puts the brakes on some more. Bringing the front in around early evening now instead of late afternoon. Instability looks good and models are kicking out precip, but then there is the issue of the forecast soundings showing a very strong cap (4 to 5). Logic would tend to say the cap would kill things, unless these are going to have some crazy elevated bases. LOL

Wind pattern looks pretty classic for a straight line winds with the strongest storms. Tornado risk doesn't look all that significant at all unless we get a right turner that creates a localized environment favorable to better directional shear.

GooFuS is just now loading in, so more comments when it finishes up.

[venture]

The 00Z GFS is similar to NAM with one notable exception, no or very little cap by afternoon. It is tough to see which one (NAM or GFS) is legit in this respect, so I want to see a couple more model runs. Here is a look at the forecast sounding mid afternoon for the metro. More thoughts tomorrow as we get the Euro in and the morning model runs.

[venture]

SPC Day 3 Slight Risk covers all but the western 2 tiers of counties and the PHs. A 30% area includes the I-35 counties and those back to the east - this includes all but the western Metro counties.

...SOUTHERN PLAINS/OZARKS TO MIDDLE/LOWER MS RIVER VALLEY...
GIVEN THE LARGE-SCALE EVOLUTION AS PREVIOUSLY DESCRIBED...IT SEEMS
LIKELY THAT A LEAD/SOUTHERN STREAM IMPULSE AND ASSOCIATED SPEED MAX
WILL SPREAD EAST-NORTHEASTWARD FROM THE SOUTHERN PLAINS TO THE
MIDDLE MS RIVER VALLEY SATURDAY/SATURDAY NIGHT. AHEAD OF THE COLD
FRONT/SURFACE LOW...PERSISTENTLY STRONG SOUTHWESTERLY LOW-LEVEL
WINDS WILL CONTINUE TO TRANSPORT MOISTURE NORTH-NORTHEASTWARD WITHIN
AN INCREASINGLY BROAD WARM/MOIST SECTOR FROM EAST-CENTRAL PARTS OF
OK/TX TO THE OZARKS/LOWER-MIDDLE MS RIVER VALLEY.

AS THE AIRMASS DESTABILIZES THROUGH AFTERNOON...AMPLE FORCING FOR
ASCENT TIED TO THE AFOREMENTIONED SHORTWAVE TROUGH AND COLD FRONT
SHOULD INFLUENCE INCREASING TSTM DEVELOPMENT PARTICULARLY SUNDAY
AFTERNOON/EVENING. GREATER CERTAINTY WILL BE FOR STRONGER DEEP
CONVECTIVE DEVELOPMENT NEAR THE COLD FRONT ACROSS PARTS OF
OK/SOUTHEAST KS AND ADJACENT MO/KS...ALTHOUGH OTHER STORMS WILL BE
POSSIBLE ACROSS ADDITIONAL PARTS OF EAST-CENTRAL TX/ARKLATEX WITHIN
THE PRE-FRONTAL WARM SECTOR.

FAVORABLE WIND PROFILES WILL SUPPORT INITIAL SUPERCELLS...ALTHOUGH
INCREASINGLY UNIDIRECTIONAL WINDS /VEER-BACK-VEERING WINDS WITH
HEIGHT/ AND THE INFLUENCE OF THE COLD FRONT SUGGEST THAT
MULTICELLS/LINE SEGMENTS SHOULD EVOLVE DURING THE EVENING...WITH
NEAR-COLD FRONTAL STORMS OTHERWISE STEADILY BEING UNDERCUT BY THE
COLD FRONT /FROM NORTHWEST TO SOUTHEAST/. LARGE HAIL IS EXPECTED TO
THE PRIMARY HAZARD...ALTHOUGH DAMAGING WINDS AND A SOME TORNADOES
MAY BE POSSIBLE AS WELL.

..GUYER.. 04/11/2014

[venture]

Thanks for nothing models. That's pretty much how I'm going into this mornings/afternoon's discussion on this. After they all started to hold hands and get timing down, they had to go get screwy again.

12Z GFS Highlights

• Cold front timing is back to what it was in yesterday's 18Z run. This rockets the front through south of a Miami to Durant line by 7PM. The 06Z run this morning had it pretty much just north of I-44 and on top of the Metro.
• Cold front initiation by 4PM along I-35 and I-44 to the north and NE of the metro. Expanding down to the Red River by 7PM.
• Warm sector initiation looks muddied with convection on going from 7AM through the evening starting in SC into SE OK.
• Wrap around looks minimal to what it was showing on earlier runs.
• Very unstable early (1PM) in North Central OK from the Metro north along I-35 with little CIN, translating to the area just east of I-35 and south of I-40 by 4PM, and then increased CIN over SE OK by 7PM with limited instability.

12Z NAM Highlights

• Cold front progression slowest in the last 4 runs. Doesn't enter the Metro until between 7 and 10PM.
• Cold front initiation by 4PM in far NW OK and KS. Storms grazing the metro north of I-40 between 7 and 10PM. Cold front never really fills out much further south than I-40.
• Warm sector initiation might be a two parter. One in NE OK by 4PM and then far SE OK by 10PM.
• No wrap around precip that is worth mentioning.
• Instability anywhere from 1500-2000 j/kg ahead of the front for most time periods, but CIN is also present for nearly the entire time as well - hence why it is hold back on precip in various areas.
• Supercell composite would be high for the Metro starting at 4PM until 10PM. Sig TOR parameters aren't anything significant though.

Forecast Sounding from the GFS at 1PM


Forecast Sounding from NAM at 4PM



So we are back to more questions than answers on what will happen with Sunday. Timing is the king here. If the NAM has the timing right, risk for severe weather goes up for Central OK. If the GFS is right, we might get a thin line of storms that will blow through early in the afternoon and that'll be that.

The new Euro will be out in about an hour or so, we'll see if that one went crazy as well.

[SomeGuy]

Mike Morgan as usual is predicting " doom and gloom" for sunday with a moderate risk for severe weather and " powerful rotating super cells"

[bchris02]

Mike Morgan as usual is predicting " doom and gloom" for sunday with a moderate risk for severe weather and " powerful rotating super cells"

Weird that he's the only one predicting that. News9 at noon said that the tornado threat is very low for this weekend and the threat is mostly damaging winds and hail.

[venture]

Keep in mind you typically need a good rotating storm for large hall. Rotating storm doesn't always mean tornadoes.

[Anonymous.]

Dewpoints already approaching 60 across most of OK and we are 2 days out. The atmosphere may be so unstable that we have linear storm formation if the cap does indeed erode early enough for pre frontal convection.

However, we saw last week where we had prime conditions but no strong intitiation factor at the correct time.

[SoonerDave]

Mike Morgan as usual is predicting " doom and gloom" for sunday with a moderate risk for severe weather and " powerful rotating super cells"

The harem-scarem crowd has always leveraged the notion of "rotating storms" to leave that tantalizing, hanging, implicit "threat" of a tornado there - just to make it sound threatening. Rotating storms just means there's lots of atmospheric movement parallel and perpendicular to the earth's surface because of the varying wind patterns aloft. Heck, that's the whole reason you get hail - moisture that freezes high in the thunderhead, falls, and then gets swept up in the storms' airflow and kicked back up into the freezing air.

I don't know how the broader crowd feels about them, but I've always liked Jed Castles and Matt Mahler on Ch 9 - neither of those guys gets very caught up in the hype. Just this morning, their own graphics were showing only a "low risk" area generally pretty consistent with what's already been put out there, and really no harem-scarem business. Castles is mostly on in the early AM news show on Ch 9..

[venture]

Day 2 Moderate Risk is out for the area East of I-35.

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0100 AM CDT SAT APR 12 2014

VALID 131200Z - 141200Z

...THERE IS A MDT RISK OF SVR TSTMS ACROSS EASTERN OK...

...THERE IS A SLGT RISK OF SVR TSTMS FROM THE SOUTHERN PLAINS/OZARKS
TO THE MIDDLE/LOWER MS RIVER VALLEY...

...SYNOPSIS...
LONGWAVE TROUGH AMPLIFICATION WITH STRENGTHENING/INCREASINGLY
PREVALENT CYCLONIC UPPER FLOW IS EXPECTED SUNDAY OVER THE CENTRAL
CONUS...WITH MULTIPLE SHORTWAVE IMPULSES OVERSPREADING THE SOUTHERN
PLAINS/MIDWEST. AT THE SURFACE...A FRONTAL BOUNDARY EXTENDING
SOUTHWEST-NORTHEASTWARD FROM KS TO THE MIDWEST WILL BEGIN TO
ACCELERATE SOUTHEASTWARD ACROSS MUCH OF THE SOUTH-CENTRAL PLAINS AND
LOWER MO VALLEY/OZARKS THROUGH SUNDAY NIGHT...WHILE A PRECEDING
DRYLINE WILL RESIDE/MOVE SLIGHTLY EASTWARD AS IT EXTENDS FROM
CENTRAL OK INTO NORTH-CENTRAL/WEST-CENTRAL TX.

...SOUTHERN PLAINS/OZARKS TO MIDDLE/LOWER MS RIVER VALLEY...
GIVEN THE LARGE-SCALE EVOLUTION AS PREVIOUSLY DESCRIBED...A
LEAD/SOUTHERN STREAM IMPULSE AND ASSOCIATED SPEED MAX
WILL SPREAD EAST-NORTHEASTWARD OVER THE SOUTHERN
PLAINS/OZARKS...REACHING THE MIDDLE MS RIVER VALLEY LATE SUNDAY
NIGHT. THE MAIN SOUTHERN PLAINS SURFACE LOW/ASSOCIATED TRIPLE POINT
WILL EXIST ACROSS WEST-CENTRAL/SOUTHERN OK SUNDAY AFTERNOON/EARLY
EVENING. EAST-SOUTHEAST OF THIS SURFACE LOW AND COLD
FRONT/DRYLINE...PERSISTENTLY STRONG SOUTHWESTERLY LOW-LEVEL
WINDS WILL TRANSPORT MOISTURE NORTH-NORTHEASTWARD WITHIN AN
INCREASINGLY BROAD WARM/MOIST SECTOR FROM EAST-CENTRAL PARTS OF
OK/TX AND OZARKS INTO THE MIDDLE/LOWER MS RIVER VALLEY.

AS THE AIR MASS DESTABILIZES THROUGH AFTERNOON...AMPLE FORCING FOR
ASCENT TIED TO THE AFOREMENTIONED SHORTWAVE TROUGH AND COLD FRONT
SHOULD INFLUENCE INCREASING NEAR-SURFACE-BASED TSTM
DEVELOPMENT...POTENTIALLY RELATIVELY EARLY IN THE AFTERNOON
ESPECIALLY NORTHEAST OF THE SURFACE TRIPLE POINT/NEAR THE COLD
FRONT...INCLUDING A CORRIDOR ACROSS SOUTHEAST KS AND
EAST-CENTRAL/NORTHEAST OK INTO ADJACENT MO. A BIT LATER IN THE
AFTERNOON...DISCRETE STRONG/SEVERE STORMS INCLUDING SUPERCELLS WILL
BE POSSIBLE ACROSS ADDITIONAL PARTS OF EASTERN OK AND
NORTH-CENTRAL/EAST TX AND ARKLATEX WITHIN THE WARM SECTOR AND/OR
NEAR THE DRYLINE EXTENDING SOUTHWARD ACROSS SOUTH-CENTRAL OK INTO
NORTH-CENTRAL/CENTRAL TX. RELATIVE EARLY AFTERNOON TIMING OF THE
PARENT MID-LEVEL SHORTWAVE TROUGH AND MODEST MASS CONVERGENCE IN
VICINITY OF THE DRYLINE ACCOUNT FOR SOME UNCERTAINTIES RELATED TO
SEVERE TSTM COVERAGE PROGRESSIVELY SOUTHWARD OF THE SURFACE TRIPLE
POINT /NAMELY ACROSS TX/.

OVERALL...FAVORABLE WIND PROFILES /45-50 KT EFFECTIVE SHEAR/ WILL
SUPPORT INITIAL SUPERCELLS...ALTHOUGH INCREASINGLY UNIDIRECTIONAL
WINDS AND THE INFLUENCE OF THE COLD FRONT SUGGEST THAT
MULTICELLS/LINE SEGMENTS SHOULD EVOLVE BY EVENING IN MOST
AREAS...WITH NEAR-COLD FRONTAL STORMS STEADILY BEING UNDERCUT BY THE
COLD FRONT /FROM NORTHWEST TO SOUTHEAST/. LARGE HAIL IS EXPECTED TO
THE DOMINANT HAZARD OVERALL...ALTHOUGH DAMAGING WINDS AND SOME
TORNADOES WILL ALSO BE POSSIBLE SUNDAY AFTERNOON/EARLY EVENING IN
AREAS NEAR/EAST OF THE SURFACE TRIPLE POINT INCLUDING EASTERN OK AND
ADJACENT PARTS OF MO/AR/NORTH TX.

[venture]

Day 2 Outlook maps...

Green = Slight, Red = Moderate




Probabilities
Brown = 5%, Yellow = 15%, Red = 30%, Purple = 45% -- White = Hatched 15% significant threat area