This graphic shows the probability of severe weather occurring within 25 miles of any given point (such as a house) on Saturday, mainly during the afternoon and early evening hours. The standard severe weather risk, a 15 percent chance of severe weather occuring within 25 miles of any given point, is in effect from Southwest Texas northeastward into Southern Oklahoma. This risk includes Texas cities such as San Angelo, Midland, Big Spring, Abilene, Vernon, Wichita Falls, Weatherford, Decatur, Denton, Gainesville, Sherman. In addition, Southern Oklahoma is also in the standard risk. Surrounding the standard risk, a lower risk of severe weather encompasses more of Texas.
Saturday’s setup will be one with moderate instability and low wind shear. A cold front will be moving south across the affected regions on Saturday. During the peak heating hours in the afternoon, some storms may become marginally severe as the cold front provides atmospheric lift. The primary threat on Saturday will be ‘coin-size’ hail (nickel to quarters) and a few downbursts capable of producing winds around 60 MPH. Because of very weak low level wind shear and the overall lack of any mesoscale features capable of enhancing wind shear (as what occurred on Tuesday), the tornado threat should be low.
I’m actually sitting in Philadelphia International Airport right now waiting to board my flight back to Dallas. I was originally scheduled to fly out tomorrow afternoon, but decided to push it up to avoid the flight delays on Saturday along with possibly chasing if the setup warrants.
10 PM Update on Tuesday’s Severe Weather Potential
27 February 2012David Reimer0 Comments
For complete details on tomorrow’s severe weather setup, please view our video briefing on YouTube.
Day 2 Convective Outlook
Let’s start out by detailing the latest severe weather outlook from the Storm Prediction Center. This outlook was issued just before noon today and we will have a new outlook out by midnight, which we will bring to you. As of this outlook, the standard 15% probabilities have been removed from much of North and Northeast Texas. Right now, the 15% probabilities are limited to extreme Northeast Texas, extending from Texarkana northwest to Paris, Texas. The elevated severe weather probabilities, shown in the 30% region, are placed over Eastern Oklahoma and Arkansas. That’s where the most concentrated severe weather is expected to be located. Low-end 5 percent probabilities extend from Shreveport to Mabank, northwest to Weatherford and Wichita Falls. Conditions are actually pretty favorable for severe weather across all of North Texas, but a strong cap is going to be in place which will limit thunderstorms. In fact, we may not have any thunderstorms develop at all. Mesoscale factors (differential heating boundaries, gravity waves, outflow boundaries from morning convection, etc) can’t be determined until we actually start seeing them tomorrow morning and afternoon. Weather models can’t pick up on those and they’re often only noticed hours before an event.
0Z NAM: Most Unstable Instability Values at 12 AM WednesdayIf you watched the weather video I published at 8 PM, you saw this graphic from the 18Z North American Model. This graphic shows the most unstable instability amounts at 12 Am Wednesday. The reason I'm showing values from 12 AM verses 6 PM on Tuesday is that I don't think it's likely we're going to have any storms in progress at that point. It's more likely we're going to have to wait a few hours until the cold front arrives and brings that forcing needed to break the cap. Compared to earlier model runs, the 0Z NAM has come in with higher instability amounts. It looks like much of North Texas and East Oklahoma will have instability values between 1,500 and 2,000 joules per kilogram. When looking for the possibility of severe weather during the winter/early spring months, I like to use instability amounts at or above 750 joules. Severe weather can happen with instability values below that, but I like using 750 J/Kg as a mean. Obviously we're going to have more then enough instability to support organized thunderstorms tomorrow night, but instability isn't the only ingredient you need for thunderstorms, and their associated severe weather.0Z NAM: 3 KM Helicity Values for 12 AM Wednesday
This graphic is basically a combination of multiple severe weather products. This takes into account wind shear at multiple levels of the atmosphere. Basically, this tells us how much spin is available for storms. The highest values are located over Arkansas, closer to the upper level storm system. However, enough wind shear will be present across Northeast Texas to support the possibility of organized thunderstorms.
Basically, if we had a weaker cap tomorrow, we would be dealing with a widespread severe weather outbreak in North Texas. That isn’t likely to happen because the cap is strong and the storm system will be passing to our north. We’re going to get scraped by that storm system tomorrow night, which is when we may have a few storms develop. The most likely time for thunderstorm development will be along the cold front from 9 PM to 3 AM in Northeast Texas. IF storms do develop, they’ll likely be in the form of a linear squall line or line segments. The storm mode and the southwest winds at the surface suggest the tornado threat will be limited, but there will be a threat for large hail and damaging straight-line winds.
I’ll be honest with all of you right now. This is a low confidence forecast. It would only take a few things to change slightly to change this from a marginal storm setup to something more potent. If there are only a few storms tomorrow, it won’t matter how significant the overall event is, because if one hits your house you will think it was a big event. That being said, I encourage you to stay tuned tonight and tomorrow. We’re going to be around posting numerous updates on the event. If we see anything change, we’ll let you know ASAP. There is no reason to be worried or scared of storms tomorrow. This does not look like a major event! In fact, you shouldn’t be scared even if this was a major tornado outbreak. Knowledge is Power! Just stay tuned and have a way to receive weather warnings. If you go under a severe thunderstorm or tornado warning, just go ahead and take protective action. That applies to any severe weather setup, whether it be big or small.
Dinner Time Update
24 January 2012David Reimer0 Comments
Surface Dewpoints + Surface Wind at 5 PM
This graphic shows the surface dewpoint values at 5 PM. Simply put, Dewpoints are a measure of moisture. I’m expecting the highest severe weather threat to be along and south of a northward moving warm front. At 5 PM, that warm front was just north of San Antonio, where you can see the 60° dewpoint line. This warm front will continue to lift slowly northward, bringing the higher moisture amounts with it.
21Z HRRR - 1 AM Simulated Radar
This is one of our high resolution model outputs. This comes from the High Resolution Rapid Refresh. It’s indicating a squall line just west of the Interstate 35 corridor by about 1 AM. As expected, the stronger storms are down by San Antonio and Austin. However, storms that form out ahead of the squall line will have to be watched for rotation, especially south of Waco. Simply put, we could have a few severe thunderstorms overnight. This is not expected to be a major severe weather outbreak, but some large hail and straight line winds are possible, especially in the squall line. We cannot rule a a brief tornado or two because of the very favorable wind fields. Instability is lacking, otherwise this would be a major tornado outbreak. Just stay tuned tonight and have a way to get weather warnings overnight. The iMap Weather Radio is a great tool for iPhones. ABC News just aired a story this app and it works. We highly recommend it! We’ll likely go out chasing after about 9 PM and will have our live video up then. Stay tuned to our facebook and twitter pages!
11 AM Severe Weather Update
19 December 2011David Reimer1 Comment
The above three graphics show the potential of a specific hazard within 25 miles of any given location. I’ve included the chance of a tornado, large hail, and damaging winds. A standard risk of severe weather remains in effect for a large portion of Central Texas this afternoon an evening. With the new severe weather outlook just issued by the Storm Prediction Center, the standard risk line of severe weather was extended northward to include most of North Texas, including the D/FW metroplex. In comparison to this morning’s 12 AM outlook, SPC have increased the tornado probabilities across North and Central Texas. Today’s primary severe weather threat will be damaging wind, but a few tornadoes cannot be ruled out. I’m just about to go pack up the chase car and head south out of Dallas. My inital plan is to head towards Waco on I-35 and wait for storms to initate, at which point It’ll be a race to keep up with the storms.
Since today’s storms will be moving at 50-60 MPH, it’s important to take immediate action when a warning is issued for your area since the lead time may be reduced. Once we’re out chasing, we won’t be able to post constant updates on the evolving weather situation, so be sure to follow your local media outlets and National Weather Service office. Once we’re on the road, we’ll start our live video stream. We’ll publish a new post on here, along with a facebook and twitter notification when that happens. We’ll be streaming at www.texasstormchasers.com/live
Have a good Monday and stay safe!
12 AM Severe Weather Outlook
19 December 2011David Reimer0 Comments
Here’s the new severe weather outlook from the Storm Prediction Center. Severe weather probabilities have been maintained from the previous outlook. It should be noted that these values could be adjusted higher in later outlooks by the Storm Prediction Center once the details of today’s event becomes clearer. Here’s the full outlook.
...CNTRL AND EAST TX...
AN UPPER-LEVEL LOW IN SE AZ WILL MOVE QUICKLY EAST TO NEWD ACROSS
WEST TX TODAY. TO THE EAST OF THE SYSTEM...A 45 TO 60 KT LOW-LEVEL
JET WILL STRENGTHEN...RAPIDLY TRANSPORTING MOISTURE NWD INTO CNTRL
TX THIS AFTERNOON. SFC-BASED THUNDERSTORM DEVELOPMENT IS FORECAST
THIS AFTERNOON ALONG THE WRN EDGE OF THE MOIST AXIS WHERE A LINE OF
THUNDERSTORMS IS LIKELY TO ORGANIZE AND MOVE EWD ACROSS THE I-35
CORRIDOR FROM NEAR DALLAS/FORTH WORTH SWD TO NEAR BRIAN-COLLEGE
STATION. THIS LINE SHOULD PERSIST EWD ACROSS THE SLIGHT RISK AREA
EVENTUALLY AFFECTING THE HOUSTON AREA DURING THE EVENING.
AS THE UPPER-LEVEL LOW MOVES OUT INTO THE SRN PLAINS...A 65 TO 80 KT
MID-LEVEL JET IN THE BASE OF THE TROUGH WILL CREATE STRONG DEEP
LAYER SHEAR PROFILES ACROSS THE SLIGHT RISK AREA. FORECAST SOUNDINGS
ALONG THE I-35 CORRIDOR AT 00Z SHOW 0-6 KM SHEAR VALUES IN THE 55 TO
65 KT RANGE. IN ADDITION...SFC DEWPOINTS MAY REACH THE LOWER 60S F
AS FAR NORTH AS DALLAS WITH UPPER 60S F LOCATED ALONG THE MIDDLE TX
COAST WHERE MODERATE INSTABILITY IS FORECAST. THIS ENVIRONMENT
SHOULD SUPPORT SEVERE STORMS WITH THE GREATEST POTENTIAL ACROSS THE
NRN HALF OF THE SLIGHT RISK AREA WHERE THUNDERSTORM DEVELOPMENT IS
MOST CERTAIN. AS THUNDERSTORMS INITIATE...SUPERCELL DEVELOPMENT WILL
BE POSSIBLE ACROSS THE WRN PART OF THE SLIGHT RISK AREA WHILE THE
CONVECTION REMAINS DISCRETE. AS STORMS INCREASE IN COVERAGE AND A
LINE ORGANIZES...A WIND DAMAGE THREAT MAY DEVELOP WITH THE GREATEST
POTENTIAL ACROSS THE CNTRL AND ERN PART OF THE SLIGHT RISK AREA. THE
MAGNITUDE OF THE SEVERE THREAT SHOULD DEPEND ON UPON HOW MUCH
DESTABILIZATION TAKES PLACE IN CNTRL AND EAST TX THIS AFTERNOON.
ALTHOUGH THE SRN END OF THE LINE SHOULD AFFECT THE HOUSTON AREA THIS
EVENING...LARGE-SCALE ASCENT WILL BE QUITE WEAK IN SE TX SUGGESTING
THE SEVERE THREAT COULD BE MORE ISOLATED THERE.
...NW TX/SW OK...
SCATTERED THUNDERSTORMS SHOULD BE ONGOING ACROSS WEST AND NORTHWEST
TX AT DAYBREAK. THIS ACTIVITY SHOULD BE FOCUSED ALONG THE NWRN EDGE
OF THE LOW-LEVEL JET AND ALONG THE LEADING EDGE OF LARGE-SCALE
ASCENT ASSOCIATED WITH AN APPROACHING UPPER-LEVEL LOW. FORECAST
SOUNDINGS ACROSS WEST AND NORTHWEST TX THIS MORNING SHOW SOME CAPE
IN THE 700 TO 500 MB LAYER WITH INSTABILITY INCREASING AS THE
AIRMASS WARMS THIS AFTERNOON. THIS ALONG WITH STEEP MID-LEVEL LAPSE
RATES SHOULD BE ENOUGH FOR AN ISOLATED HAIL THREAT AS CONVECTION
INITIATES JUST AHEAD OF THE UPPER-LEVEL LOW. THE HAIL THREAT APPEARS
MOST LIKELY TO AFFECT NW TX AND SW OK AS STORMS MOVE NEWD ACROSS THE
REGION LATE THIS AFTERNOON. THE POTENTIAL FOR HAIL IS EXPECTED TO
REMAIN MARGINAL WITH A 5 PERCENT HAIL PROBABILITY SUFFICIENT TO
COVER THE THREAT.
