Tag Archives: severe weather

HEAVY RAIN RETURNS AS SPRING THUNDERSTORMS FIRE FOR THE FIRST TIME

The coming week is going to be a wet one for much of North Texas, including the DFW Metroplex. A very big upper-level low will be sinking south into Mexico and then ejecting east northeast slowly. The slow movement of this system will allow abundant moisture to stream into the region ahead of it. This is already noted with overnight low temperatures well above normal for this time of year.

Showers and thunderstorms will begin to fire tomorrow along a dryline in West Texas. At the same time a jet streak will be out across the Texas and Oklahoma panhandles juxtaposing North Texas in the right entrance quadrant of a speed max which will enhance lift across the area. Some hi-res models are forecasting convective development tomorrow as far east as the I-35 corridor. All storms that form should be supercellular in nature and elevated. With 1500 to 1800 J/Kg of convective potential energy, or CAPE, available, some of these storms could be strong to severe. Large hail would be the primary threats. In addition to the severe threat, heavy rainfall will also be possible as precipitable water values, or pWATS, climb above the 99th percentile for March. This could greatly enhance rainfall rates.

Monday night into Tuesday morning models are showing an MCS (mesoscale convective system) moving across North Texas with the potential for very heavy rainfall. The outflow boundaries from this system could act as foci for additional storm development on Tuesday as widespread lift begins to encroach on the area as the upper-level low begins moving east northeast. The MCS could also serve to help stabilize the atmosphere on Tuesday which would help alleviate the severe weather threat. While it is too early to pinpoint the mesoscale environment on Tuesday, it does appear all modes of severe weather will be possible on Tuesday, including tornadoes. A dryline will sharpen west of the Metroplex and act as focus for storm development as jet streak lifts out of the lower Rio Grande Valley. In addition to the severe weather threat, heavy rainfall will also be likely given the high pWATS. It is possible that Tuesday could see the daily rain record broken.

A weak cold front will push through ending the severe weather potential, but not the rain. Overrunning showers will likely continue. The remainder of the week looks to remain wet through Friday as north and central Texas remain on the eastern flank of the upper-level low. There won’t be significant drying until the upper-low moves far enough east by the weekend to end all rain.

SEVERE WEATHER THREAT TODAY

A rather strong shortwave trough will approach the area this evening on a negative tilt providing lift for scattered convection across the area. The latest hi-res models are keeping most of the storms that fire with this disturbance east of the Metroplex, but there is a marginal threat for severe weather for any storms that can overcome the cap. For the Metroplex, the storms look to be mostly elevated limiting the severe weather threat, provided the cap can be breached. Strong to severe storms are possible with the main threats being damaging winds around 50 mph to 60 mph and moderate sized hail. As the storms push east, or further eastward development occurs, conditions are little more favorable for severe weather as the storms can become surface based. Adequate instability in the 1000 to 2000 J/Kg range and shear combined with lapse rates in the 6 to 7 C/km range leads to a slight risk area for severe weather. Storms will be able to produce damaging winds in excess of 60 mph, large hail, and pose an isolated tornado risk. This slight risk is noted in the orange color in the map below and should mostly be east of the Metroplex. As this disturbance races off to the northeast, the threat for storms will diminish after 3 am.

Severe weather threat for Tuesday evening, December 22, 2105

VERY DANGEROUS SEVERE WEATHER SETUP TODAY AND TONIGHT

The Storm Prediction Center has upgraded our forecast area to a level 4 Moderate Risk for severe weather. All modes of severe weather will be possible, including a significant tornado threat. A Tornado Watch has already been posted for much of the forecast area. An eroding cap will give way to significant lift from an approaching dryline and large storm system lifting northeast onto the Central Plains from the Desert Southwest. Storms are already forming off the dryline and moving eastward just east of Abilene. A very moist atmosphere is in place across the area. There is 3000 to 4000 J/Kg for convective available potential energy (quite high) and moderate wind shear on the order of 300 M2/S2. Of real concern is backing surface winds across the area. All these parameters point to supercellular storm mode with any storm capable of producing large and strong tornadoes and giant sized hail up to softball/grapefruit size. In addition, heavy rainfall will be possible and some of the tornadoes could become rain wrapped and difficult to see. Residents of DFW should pay close attention to the changing weather conditions, and please take seriously any Tornado Warning issued for your area by taking appropriate action. Remember the best place to go is to an interior room, without windows, on the lowest level of the building or home.

FIRST SEVERE WEATHER SETUP OF THE SEASON TODAY AND TOMORROW

Severe weather setup for Wednesday afternoon into Wednesday night. Graphic courtesy of the National Weather Service office in Fort Worth, Texas.

UPDATE: The latest data is now suggesting that the CAP will hold strong over the forecast area greatly reducing any threat of severe storms over the immediate Metroplex. This is in part because a lead short wave is now expected to move across the area earlier today, around midday, with subsidence in its wake during peak heating hours. Thus, for the CAP to break, we must await the primary shortwave expected later this evening well after peak heating when instability will be much less. Still there is a chance of thunderstorms this evening, mainly elevated, with the primary shortwave and again with the passage of moderately strong cold front. Much cooler tomorrow with overnight lows Thursday night into Friday morning falling into the upper 30s to mid 40s across the area.

The first significant severe weather event of the season is taking shape across North Texas today, but especially tomorrow.

For today, a shortwave will track across the Central Plains sending a weak cold front into North Texas this afternoon. The main dynamics with this system appear to be too far removed from North Texas to be strong enough to break a strong capping inversion aloft. However, with the weak frontal boundary in place across North Texas, mesoscale forcing and frontogenesis combined with strong compressional warming may be just enough to weaken or break the cap along and east of a line from Weatherford to Gainseville and north of the I-20 corridor. As a result, have placed 20% POPs for isolated convection that could initiate in this region. As you approach the Red River into Oklahoma, convective inhibition becomes almost negligible and a much higher chance for convection exists. Temperatures are expected to rise well into the 80s, even the upper 80s to around 90 in some places due to the compressional warming from the front. This heating could be strong enough to lift the cap. Combine this with steep lapse rates, very cold air aloft, and CAPE approaching 2000 J/Kg, any storm that is able to get going will become severe and supercellular in structure with the potential of producing very large hail and damaging winds. With the wind fields rather weak in the lower levels, I expect the tornado threat today to be rather low, but non-zero. I am not expecting a widespread severe weather outbreak today in our area, but there is an isolated risk should convection be able to initiate. In all likelihood, the CAP will hold.

For tomorrow (please see graphic above), a much different scenario will play out. Another shortwave will eject onto the Plains, much further south than today’s. As a result, a surface low will develop near Wichita Falls with a dryline extending perpendicular south/southwest to the low and a cold front off to the north/northeast forming a triple point. This will increase surface winds across North Texas tomorrow. Most of the forecast area will be strongly capped, but as the dryline approaches a line from Comanche to Mineral Wells to Gainseville, the cap will begin to lift and convection should fire along the dryline. Across this area, CAPE will again reach 2000 J/Kg with strongly sheared low level winds. Thus, convection will rapidly become severe with the threat of very large hail, damaging winds, and tornadoes. The storms will be supercellular in structure and discrete initially, but will begin to organize into a squall line as the dryline marches eastward. Across the immediate DFW Metroplex, I expect the capping inversion to hold and cause approaching surface-based convection to be become elevated over the cap as the storms approach the I-35 corridor. This will greatly reduce the tornado threat here, but large hail and damaging winds will still be a threat as 1000 to 1500 J/Kg of CAPE will still be available across our area. Should the cap lift across the Metroplex, then the severe weather threat will increase with tornadoes possible.