May has arrived and so has the climatological peak of the severe weather season in Oklahoma, at least for tornadoes. So far this year we are running almost on average for tornadoes and May normally brings with it 20-25 every year. For 2012 however we saw a very low number of only 4, but this followed up on a very active April 2013 that had 53 (average is just around 12). There is any direct correlation between the number we have in April and what we see in May, as it go any direction. April has been largely a roller coast month and that appears it will continue. We enter May with chances of storms and also winter precip.
A few updates to the initial post this month. Updated source image for the Phased-Array Radar located in Norman. This is the radar type the NWS is hoping to use to replace the existing WSR-88Ds that are currently deployed. Also removed the CASA radar images as the testbed location has been moved to the Dallas area and is no longer SW of Oklahoma City. The satellite section is a bit cleaned up. I removed the water vapor and infrared images and then added in an additional visible image source. Tutorial section added the SPC categories and also the rough Skew-T How To guide that was in April's thread.
Current Conditions
Norman Warning Area Map
Tulsa County Warning Area Map
Tornado Warning | Tornado Watch | Severe Thunderstorm Warning | Severe Thunderstorm Watch
Red Flag Warning | Fire Warning | Severe Weather Statement | Special Weather Statement
Hazardous Weather Outlook | Fire Weather Watch Other Color Meanings: Web-Based Watch/Warning/Advisory Map Colors - NOAA's National Weather Service
Oklahoma Mesonet Current Conditions Red - Air Temp, Green - Dewpoint, Barbs - Wind Speed/Direction, Gray - Gusts, Blue - Precip since Midnight
Step 1) Go the main page: High-Resolution Rapid Refresh (HRRR)
Step 2) Click on 3km HRRR-CONUS hourly
Step 3) Under Domain select SC for South Central US
Step 4) Look at the time frames available. Usually if it isn't through Hour 06 yet, I'll just go up to Date and select the previous time.
Step 5) Depending on what you want to see you can click on the specific time or to loop all the times available you'll see a Check Mark under loop. You can click that to loop them all.
Tutorial: WHAT SPC PERCENTAGES MEANS IN RELATION TO CATEGORICAL RISK LEVEL Tutorial: HOW TO READ SKEW-T CHARTS
The main Skew-T is your 3 lines with wind barbs on both sides. So the lines first off. Solid is air temp and dashed dewpoint. The dotted line is the temp of the parcel of air as it goes up. So follow that up. If the solid line is to the right of that dotted line that is air that is warmer than that parcel and the parcel won't rise. Also known as your cap. When the air parcel gets warmer than air temp that area between the solid line and dotted line, that is your CAPE. This also shows that the parcel of air will continue to rise up until it meets the air temp again. Here is a good video to help explain it...
Okay so we are looking at that and we can things are going to be unstable with a lot of CAPE. Move of to the wind barbs on the right, that is your wind direction and speed at the various heights. This is also how we detect shear. The two main kinds are going to be speed shear and directional shear. In this exactly we are seeing surface winds out of the SE/SSE, or backed winds as you'll read often, and then they change directions to the SW and WSW as you go up in height. Good example of directional shear. Speed shear is when you have wind speed increase as you go up. We have some of that here as well. All in all this says, good shear. Sometimes you have to be careful of too much shear or speeds being too high in the upper levels because that can just rip updrafts apart.
So we got an unstable atmosphere and wind shear. Finally the squiggly line that is the hodograph. Used to find things like shear vectors and storm relative winds. These are good to help determine if you are going to be dealing with splitting storms and such. Typically in class right turning supercells we look for the hodograph to arch from the center to the right. Which we have here...for the most part. I won't get too much more into it right now, but googling should bring up a ton of resources on it.
So now we get down to the values. A lot of these are open to interpretation and how they play into storm formation, severe storms, and tornadoes. I'm just going to hit on a few of the variables instead of every one, otherwise this will be a book and probably confuse more than need be. Going left to right since these aren't perfect columns.
LI - Lifted Index. Negative is unstable, usually want lower than -4 for severe.
KI or K Index you usually want mid 20s for storm development and over 35 for strong development.
Equil P - That is where your air parcel meets the air temp again after getting warmer than it.
HAIL - Subjective to this sounding project on estimated hail size.
ConvT - Convective temperature or air temp needed to break cap without much forcing. This is more important in summer usually.
Lapse Rates also need to be looked at, in this care the value is favorable for severe weather.
SRH this is the Storm Relative Helicity in the first kilometer of air from the service...or your low level shear. This is also modified by the direction storms will move. Usually anything over 150 would be pretty significant.
SWEAT Index helps highlight severe storm potential. Usually 300-500 is what we look for, anything higher is significant.
TTI or Total Totals is another index looked at for storm development in general. Mid 40s are usually looked at for storm development, anything higher would indicate a more volatile setup.
Storm Dir/Speed - This is your storm direction in degrees and this is where the storm is coming from. So the example here is ~ 225 degrees which translates into moving NE. Speed is in knots so take the value and multiply by 1.15 to get MPH.
CapI - Strength of cap. Usually you want 2 or lower to help keep somewhat of a lid on things early. Over 4 requires a nuke to get rid of, less would lead to grunge fest.
LCL - Lowest cooling level. This is the atmospheric pressure height (measured in millibars) where the air can condense and form clouds. So a high number here means the level is lower to the ground and better chance for surface based convection. If you see numbers lower than say 850 mb, you are talking mostly high based elevated storms. Tornadoes need high LCL values (or lower cooling levels) since they are tied with surface based storms in most cases.
Sup Potential: Value specific to this product estimating percentage chance if any storm forms that it will be severe.
Precip Water measures the amount of water in the air. Usually you don't want it more than 1.5 or 1.75 for severe storms otherwise you are looking at just heavy rain. Lower than say 0.75 and its going to be too dry for much precip.
CAPE most are familiar with. Anything over 0 is unstable. Depending on the season will determine how much you need. Usually anything over 2000 j/kg is very unstable. However as we get into late spring/summer you'll see values over 5000 but not get anything. Even though its extremely unstable, it doesn't do any good without lift or something to break a cap.
CINH: Convective inhibition. Usually when you start getting lower than -100 you have issues getting anything going.
0-1km Shear - Like earlier this is your shear in the first kilometer of air, but this isn't storm direction dependant. When you start getting over 100 to 150 in this department you need to start being vigilant.
1km EHI or Energy Helicity Index another way to measure energy/shear. Usually more than 2 or 3 is pretty high.
That's pretty much the main ones without going longer...which I already went a bit too long. We can get more specific about the individual values if more clarification is needed. I went pretty general and with a broad brush on a lot of these. This is mainly to give you an idea of what to look for. The main thing to remember is that so much goes into this, and hopefully this is another example of how much there is, that you can't focus on just a few of these and figure big time storms. Think of it as a recipe. You have to have near perfect amounts of each to get a good tasting soup...otherwise you are just left with a pot full of odd smelling/looking/tasting water.
Okay time for the look ahead to start this off. All based on the 12Z GFS and NAM so take it for what it is.
Winter's Last Hurrah?
Strong cold front poised to come in. NAM is about 6 hours ahead of GFS. NAM brings front in during the evening hours tomorrow, GFS waits until around midnight or just after. Based on history, the NAM is probably more on the nose here. Highs Thursday look like near 60 far east, 40s Central, 30s West. NAM is almost in agreement but keeps areas south of I-40 to the west a bit warmer. NAM has widespread frost/freeze over the entire body of Oklahoma Friday morning, GFS is about 5 degrees warmer but does have what would be widespread frost over Central and Western OK. Rebound in most areas Saturday, but the low could be lingering and hold temps into the 40s over parts of Central and Eastern OK. Sunday even better, maybe still cool to cold far NE. Another surge of cold air is forecast next around Monday the 13th but this should not hit Oklahoma. Upper Midwest and Great Lakes get to enjoy that one.
Snowfall is indicated on both models. NAM has snow starting to mix in early Thursday morning over NW OK. It spreads it to the east during the day on Thursday, keeping it mostly north of Highway 62 in Southern OK. Forecasts generally a quick 1-2" of snow, but melts it off with in 3-6 hours of actually falling. It keeps accumulations over far Northeast OK around a bit longer with some areas getting around 3". GFS is a bit slow and starts the snow in NW at the same time Thursday morning but lingers it through early Saturday morning. It has the most snow over NW OK, having some areas get 6" of snow and then along/north of I-44 until Osage county. Generally less than an inch to near 3" at the KS border. I personally don't buy the snowfall amounts at all, so my takeaway is that we'll see snow mix in at times with the cold rain.
Severe Weather Outlook
I'm going to focus on days with decent instability and then point out the chances of something actually falling from the sky.
Today - Most of the state will be unstable today, but very low risk of anything popping with a very strong cap.
Weds May 1 - Instability will get moderate along the cold front as it comes down. Best instability though is back through Central TX. Prefrontal convection chances look low, so most of the rain and storms will be behind the front. Main threats maybe some high wind and probably hail with the cold air.
Weds May 8th - Low to moderate instability in Central and Western OK. Rain chances look relatively low. Moderate cap in place, best chance for storms is far SW OK. Maybe one or two marginally severe storms.
Thurs May 9th - Moderate to High instability over Western OK, especially near the TX border. Better chance of rain over Central and Western OK. Forecast sounding still shows a decent cap, but breakable. Setup looks favorable for severe weather.
Fri May 10th - Moderate to High Instability over Western and central OK. Cape values over 3000 j/kg. Looks like widespread storms appear possible here, best chances out west into North Central OK. Severe probable with the forecasted setup.
Sat May 11th - Moderate instability over much of OK, especially south of I-40. Chance of storms statewide, but best further south. Front comes through from the north will shift things out quickly through the day.
Sun May 12th - Low instability over SW OK. Decent chance of some rain and storm West.
Mon May 13th - Low instability over SW OK, again. Some more scattered storm West and South.
Tue May 14th - Low Instability over Southern 2/3rds of OK, best in SE OK. Maybe some scattered showers, nothing major.
Wed May 15th - Moderate to high instability over Central and Western OK, lower east. Looks like Isolated chances with a strong cap, but really this is 2 weeks out, the forecast isn't going to stay the same.
All in all general thoughts, one more week of March weather and then into a more typical May pattern. Wouldn't be shocked if we see this stretch well into June as well.
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1214 AM CDT WED MAY 01 2013
VALID 011200Z - 021200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM SWRN OK INTO NWRN AND
CNTRL TX...
...SYNOPSIS...
A COLD FRONT WILL SURGE SWD ACROSS THE CNTRL PLAINS AND INTO THE SRN
HIGH PLAINS DURING THE DAY BENEATH A POSITIVE TILT UPPER TROUGH WITH
AXIS ACROSS THE CNTRL ROCKIES. STRONG HEATING WILL OCCUR AHEAD OF
THE COLD FRONT FROM TX INTO OK WITH BOUNDARY LAYER DEWPOINTS NEAR 60
F. THIS FRONT WILL SERVE AS A FOCUS FOR THUNDERSTORM
INITIATION...WITH A HAIL AND WIND THREAT DEVELOPING BY AFTERNOON
FROM SWRN OK INTO TX.
ELSEWHERE...AN UPPER LOW WILL DRIFT FROM LA INTO THE NRN GULF OF
MEXICO...RESULTING IN WIDESPREAD RAIN AND NON-SEVERE STORMS FOR THE
CNTRL GULF COAST STATES.
...SWRN OK...NWRN INTO CNTRL TX...
ONGOING RAIN AND A FEW ELEVATED THUNDERSTORMS ARE LIKELY FROM NWRN
OK INTO IA...PERSISTING MUCH OF THE DAY. MOST OF THIS CONVECTION
SHOULD BE ANAFRONTAL AND WEAK. SURFACE BASED STORMS SHOULD
EVENTUALLY FORM ALONG THE FRONT FROM NW TX INTO WRN OK...WHERE
HEATING SHOULD LEAD TO ABOUT 1500 TO 2000 J/KG MUCAPE...MAXIMIZED
OVER TX. FLOW ALOFT WILL BE WEAK...BUT FORECAST SOUNDINGS INDICATE
THAT WITH SLY SURFACE FLOW...STORMS SHOULD PROPAGATE IN A SWD OR
SSEWD DIRECTION...EXPANDING INTO MUCH OF CNTRL TX. LARGE HAIL AND
DAMAGING WINDS WILL BOTH BE POSSIBLE.
Instructions: Think about how you will protect sensitive plants from the cold... Move them indoors or cover them if you can.
Message summary: ...freeze watch in effect from thursday evening through friday morning...
The national weather service in norman has issued a freeze watch...which is in effect from thursday evening through friday morning.
* temperature: generally 30 to 32 degrees...with the coldest temperatures over northwestern oklahoma where below freezing temperatures may persist 4 to 5 hours. Lows will be at or near 32 along and west of the i-35 corridor...through the oklahoma city metro and west...along and north of the i-40 corridor.
* impacts: freezing or subfreezing temperatures and areas of frost could impact sensitive and tender vegetation.
Yea I think the most recent outlook issue was taking the scattered morning convection into account and the low clouds in extreme W OK.
Based on the current conditions, I would even re extend the SLIGHT risk into more of SW OK tapering off into C OK. The air right now is extremely soupy with DP in the mid 60s and we will likely touch 80.
I feel for the forecasters in E KS and W MO right now, GFS and NAM fighting over where the snow band will setup and the storm track/stall out.
This is roughly what I'm thinking for a severe risk today. Outlined a small area of Central OK which is more conditional since the front will be pushing through by 6 or 7 this evening. Further southwest a better chance. HRRR keeps prefrontal precip fairly isolated over us and then has more coverage Southwest. We'll see how it plays out.
Cold front well on its way. It just passed Fairview not to long ago. Nothing along the front in Northern OK right now, but showers are popping up behind it. Air temps will drop from the 70s and 80s to 40s when the front passes. Front is moving roughly 15 mph right now to the Southeast. So rough time of arrivals...
Kingfisher - 4:00PM to 430PM
Northwest OKC/Piedmont Areas - 5:30 to 6:00PM
Norman - 7:00PM to 8:00PM
The front does then extend down along the OK/TX PH border. Could argue it is almost acting like a dryline more than a cold front there as temps really haven't crashed there yet but dewpoints have. Ahead of that part of the boundary, we are seeing cells start to pop from Arapaho south along US 183 almost all the way to the Red River. So far nothing exploding but some isolated heavy rain and a rumble of thunder out there. The air mass ahead of the front has become very unstable this afternoon so scattered storms, some severe, appear likely. As has been the case the last few weeks, they'll all get undercut by the cold front rushing in which should hold back the severe risk behind the front.
BULLETIN - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WARNING
NATIONAL WEATHER SERVICE NORMAN OK
339 PM CDT WED MAY 1 2013
THE NATIONAL WEATHER SERVICE IN NORMAN HAS ISSUED A
* SEVERE THUNDERSTORM WARNING FOR...
NORTH CENTRAL KIOWA COUNTY IN SOUTHWEST OKLAHOMA...
* UNTIL 430 PM CDT
* AT 318 PM CDT...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED A
SEVERE THUNDERSTORM LOCATED 6 MILES SOUTHEAST OF HOBART...MOVING
NORTHEAST AT 15 MPH.
HAZARDS IN THE WARNING INCLUDE...
QUARTER SIZE HAIL...
DAMAGING WINDS IN EXCESS OF 60 MPH...
* LOCATIONS IMPACTED INCLUDE...
HOBART...ROOSEVELT AND GOTEBO.
MESOSCALE DISCUSSION 0588
NWS STORM PREDICTION CENTER NORMAN OK
0343 PM CDT WED MAY 01 2013
AREAS AFFECTED...SOUTHWEST OK AND WESTERN PART OF NORTH TX/TX
ROLLING PLAINS
CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE
VALID 012043Z - 012245Z
PROBABILITY OF WATCH ISSUANCE...40 PERCENT
SUMMARY...AT LEAST AN ISOLATED SEVERE THREAT WILL DEVELOP THROUGH
LATE AFTERNOON ACROSS PORTIONS OF SOUTHWEST OK AND THE WESTERN PART
OF NORTH TX/TX ROLLING PLAINS. BOUTS OF SEVERE HAIL/WIND WILL BE
POSSIBLE WITH THE STRONGEST STORMS.
DISCUSSION...INCIPIENT TSTM DEVELOPMENT IS ONGOING ACROSS
WA****A/KIOWA COUNTIES IN SOUTHWEST OK AS OF 2030Z AMID A GRADUALLY
DEEPENING CU FIELD IN VICINITY OF A WEAK SOUTHWEST OK SURFACE
LOW/SSW-NNE ANGLING FRONTAL ZONE. ACCORDINGLY...LOW LEVEL
CONVERGENCE HAS APPEARED TO INCREASE OVER THE PAST FEW HOURS WITHIN
THIS CORRIDOR...WITH WARM SECTOR TEMPERATURES HAVING CLIMBED INTO
THE LOWER 80S F ACROSS SOUTHWEST OK/WESTERN NORTH TX WITH WEAKENING
INHIBITION. IT SEEMS PLAUSIBLE THAT STORMS WILL CONTINUE TO
DEVELOP/ZIPPER SOUTH-SOUTHWESTWARD IN VICINITY OF THE SURFACE
BOUNDARY OVER THE NEXT SEVERAL HOURS. LARGE SCALE BACKGROUND ASCENT
APPEARS TO BE RELATIVELY WEAK WITH REGIONAL DERIVED WIND DATA
INDICATING WEAK WINDS THROUGH THE LOWER-MID TROPOSPHERE ACROSS THE
REGION. HOWEVER...FRONTAL-FOCUSED ASCENT AND A STEEP LAPSE RATE
ENVIRONMENT/MODERATE BUOYANCY ENVIRONMENT WILL LIKELY YIELD SOME
SEMI-SUSTAINED MULTICELLS POTENTIALLY CAPABLE OF SEVERE HAIL/WIND
INTO EARLY EVENING.
Severe storm is barely moving and more or less back building south and the northern end of it weakens. HRRR model picked up on this earlier today, so not unexpected.
BULLETIN - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WARNING
NATIONAL WEATHER SERVICE NORMAN OK
359 PM CDT WED MAY 1 2013
THE NATIONAL WEATHER SERVICE IN NORMAN HAS ISSUED A
* SEVERE THUNDERSTORM WARNING FOR...
SOUTHEASTERN KIOWA COUNTY IN SOUTHWEST OKLAHOMA...
* UNTIL 430 PM CDT
* AT 356 PM CDT...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED A
SEVERE THUNDERSTORM LOCATED NEAR ROOSEVELT...MOVING EAST AT 10 MPH.
HAZARDS IN THE WARNING INCLUDE...
LARGE DAMAGING HAIL UP TO GOLF BALL SIZE...
DAMAGING WINDS IN EXCESS OF 60 MPH...
* LOCATIONS IMPACTED INCLUDE...
ROOSEVELT AND COOPERTON.
URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 146
NWS STORM PREDICTION CENTER NORMAN OK
455 PM CDT WED MAY 1 2013
THE NWS STORM PREDICTION CENTER HAS ISSUED A
* SEVERE THUNDERSTORM WATCH FOR PORTIONS OF
SOUTHWEST OKLAHOMA
NORTHWEST INTO CENTRAL TEXAS
* EFFECTIVE THIS WEDNESDAY AFTERNOON FROM 455 PM UNTIL MIDNIGHT
CDT.
* PRIMARY THREATS INCLUDE...
SEVERAL LARGE HAIL EVENTS WITH A FEW VERY LARGE HAIL EVENTS TO 2
INCHES IN DIAMETER POSSIBLE
SEVERAL DAMAGING WIND GUSTS TO 70 MPH POSSIBLE
THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 60
STATUTE MILES EAST AND WEST OF A LINE FROM 25 MILES NORTHEAST OF
WICHITA FALLS TEXAS TO 90 MILES SOUTHWEST OF JUNCTION TEXAS. FOR
A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH
OUTLINE UPDATE (WOUS64 KWNS WOU6).
PRECAUTIONARY/PREPAREDNESS ACTIONS...
REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE
FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
AND POSSIBLE WARNINGS. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY
DO PRODUCE TORNADOES.
&&
DISCUSSION...TSTMS ARE EXPECTED TO INCREASE IN COVERAGE AND
INTENSITY LATE THIS AFTERNOON INTO EVENING ALONG A COLD FRONT MOVING
SWWD ACROSS THE WATCH AREA. THOUGH VERTICAL SHEAR WILL REMAIN
RELATIVELY WEAK...THE PRESENCE OF STEEP LOW TO MIDLEVEL LAPSE RATES
AND RESULTING MLCAPE VALUES OF 2000-3000 J/KG WILL PROMOTE VIGOROUS
UP/DOWNDRAFTS CAPABLE OF LARGE HAIL AND DAMAGING WIND GUSTS.
AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT
TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60
KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 550. MEAN STORM
MOTION VECTOR 32020.
Seeing some rapid storm growth right over the MEtro area. Generally along and west of I-35 from Downtown to West Moore to Newcastle to Lindsey. Cold front is moving in from NW right now as well.
It looks like the high has been bumped down to 39 for tomorrow. It's hard to believe its May 2nd and we are having colder temperatures than we had through most of December. Winter is still in full swing in Oklahoma. I probably won't plant until at least May 15th.
Is there an explanation for this exceptionally late spring? This is the kind of stuff that usually happens in the high elevations of the Rockies this time of year but winter is usually long gone by now.
Oklahoma Severe Weather Discussion - May 2013
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Re: Oklahoma Severe Weather Discussion - May 2013
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