For parts of Texas the period of sunny and rainless days is about to come to a dramatic end. Let me start out by reminding you that Texas covers a lot of real estate. What one area is seeing may be completely different on the other side of the region. Keep that in mind for all Texas forecasts.

The area of high pressure that kept most of Texas under hot and dry conditions began weakening on Tuesday and is on the way out. It’s going to be replaced by a more active and stormy pattern. In the mid-levels of the atmosphere we have a relatively weak, but noticeable area of lift moving into the Plains. It’s moving at a snails pace which means we’ll have to wait until Friday evening for it to start really affecting parts of Texas. Thunderstorms across southeast Colorado this evening will move into Kansas overnight bringing locally heavy rain to those folks. The extreme northern Texas Panhandle may be impacted by that activity but a vast majority of it will remain north of Texas tonight.

Portions of the Texas Panhandle and South Plains into West-Central Texas will start lighting up with thunderstorms tomorrow afternoon. With ample moisture in place along with an unstable atmosphere we could see bouts of hail and damaging wind gusts. The severe weather threat tomorrow is mainly localized wind gusts of 60-70 MPH and perhaps some hail. Overall wind shear will be weak thus we’re not expecting a sustained or significant severe weather threat. We’ll be dealing with a few hours of localized hail/damaging winds through tomorrow evening. What will become the bigger problem is slow-moving heavy thunderstorms dropping bucket loads of rain. The dry weather since the beginning of June has allowed for some drying out. Some lakes across West Texas still need filling.

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Lets take a look at precipitable water values. Essentially the PW values indicate how much rain a thunderstorm would produce if you were to squeeze out of its water. A lot more goes into forecast rain potential but we are seeing abnormally high PWAT (precipitable water) values across the Texas Panhandle, West Texas, into Northwest Texas tomorrow night into Saturday. We now know the atmosphere will have a lot of moisture and thunderstorms will be capable of producing heavy rain. Another important factor to consider in the forecast is that mid and upper level winds are going to be weak this weekend. Those weak upper level winds are good news in the sense they will limit the potential for severe thunderstorms. Bad news is with weak winds aloft we’ll see thunderstorms moving very slow (if even at all in some cases). Stationary and training thunderstorms moving over the same areas producing heavy rainfall is a setup for localized, but significant rain accumulations. Now where will we see the best chance for very heavy rains and potential flooding?

Weather model simulated radar at 7 PM Friday

Weather model simulated radar at 7 PM Friday

By Friday afternoon as temperatures warm into the upper 80s we’ll see thunderstorms fire up in the Texas Panhandle and South Plains. This is the point where the atmosphere will be most unstable and we could see some severe thunderstorms with strong winds and hail. Not really unusual for a June day out there considering we saw the same thing today in the Oklahoma Panhandle. By early Friday evening we may already see a fairly large area of rain and thunderstorms across the eastern Texas Panhandle. This area of precipitation is not going to be in a hurry to go anywhere. With the weak upper level winds and abundant moisture being fed into the storms by southeast winds we’re talking about a heavy rain setup. The afternoon run of the North American Model (NAM) moves the initial batch of thunderstorms east into Oklahoma by early Saturday morning.

Weather model simulated radar at 4 AM Saturday

Weather model simulated radar at 4 AM Saturday

However with lift still in place it develops additional rain over the Texas Panhandle early Saturday morning. If the NAM is correct we’ll see a bit of a break in rain/storms across the Panhandle by late Saturday morning into the afternoon hours with the heaviest activity in western Oklahoma. Several factors such as cold pool generation, outflow boundaries, localized subsidence (sinking air), and more makes this is a difficult forecast so continue to check back as we make refinements. Don’t be shocked if things change a bit.

As the cluster of thunderstorms from the Texas Panhandle moves into Central Oklahoma on Saturday we’ll have to watch for additional development closer to the Red River. Unrelated to the Panhandle/Oklahoma storms we’ll also see a separate area of showers and a few pop up storms in Southeast and East Texas on Saturday. Those are related more to the tropical airmass in place and typical of June weather. Localized wind gusts of 40-60 MPH will be possible with any stronger popup storms in that area. The seabreeze may also play a role in helping storms pop up in the afternoon. This weekend won’t be a complete washout. Some times will be wet and stormy while other times it will be dry.

Weather model simulated radar at 10 PM Saturday

Weather model simulated radar at 10 PM Saturday

Weather model simulated radar at 1 PM Sunday

Weather model simulated radar at 1 PM Sunday

Weather model simulated radar at 10 PM Sunday.

Weather model simulated radar at 10 PM Sunday.

We start the process over again during the afternoon hours on Saturday with new potentially strong thunderstorms developing from the Permian Basin northward into the Texas Panhandle. Saturday night will feature an additional complex of thunderstorms in the Texas Panhandle with another area of storms possible in the Permian Basin into Southwest Texas. As I said above many factors will go into the forecast, including what happens with storms on Friday and what they leave behind. There will be forecast refinements. Thunderstorm chances will continue on Sunday across the Texas Panhandle, West Texas, Permian Basin. Storms will also be possible on Sunday in North Texas, East Texas, and Southeast Texas. We’ll talk more about Sunday as we get closer and get through the first round of storms tomorrow.

So now we’ve talked about the general timeline of storms this weekend. Lets chat about how much rain we expect for parts of Texas. Rain chances will continue for some into Monday and Tuesday as well which is included in the forecast totals below. The heaviest rains are currently forecast from the eastern Texas Panhandle into Northwest Texas and western Oklahoma. 3 to 5 inches of rain will be possible in those areas with isolated totals over 7 inches possible. Those are general totals and there will be lower spots and higher spots in localized areas. As I said previously the forecast is also dependent on where the storms end up so we’ll continue to refine the forecast. 0.50 to 2 inches of rain will be possible through Tuesday along and east of Interstate 35 from the Red River south into Central Texas. Isolated locations in Southeast Texas could pick up much heavier rain totals of 3 to 5 inches with locally higher amounts over 6 inches possible. South-Central Texas, Deep South Texas, and Southwest Texas are currently expected to miss out on most rain through Tuesday.

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Flash flooding is obviously still fresh on the minds of most Texans after the events last month. Right now it looks like Central Texas, including Wimberly and San Marcos, will miss out on most rain with this system. I’m not really worried about any flooding issues there even if we do see some minor rain accumulations. The same goes for the D/FW Metroplex and most of North Texas although we’ll have to watch for locally higher rain totals and isolated flooding. I am growing more concerned about flooding in the eastern Texas Panhandle southeast to the Caprock and Northwest Texas. With very heavy rains expected to fall tomorrow night and another round possible Sunday night I am worried we will have issues with flooding. As forecast confidence becomes higher I do expect we’ll see flood watches issued for those areas. Another trouble spot may be Southeast Texas where the afternoon popup storms associated with the seabreeze could dump very heavy rains in a short period of time. While that potential seems to be more localized we’ll watch it closely. We clearly don’t need a thunderstorm dumping 3 to 4 inches of rain in an hour over Houston again.