Mother nature is certainly in a mood this week. The storm system that will bring impacts is finally moving onshore in the western United States. Up until today weather models have been ‘guessing’ the initial strength of the storm system. Bad data in will usually result in a bad projection coming out. This morning’s weather models came in with significant changes with the system. These won’t generally impact the ‘warm side’ hazards of heavy rain minus the system being a bit slower. However, this slower speed and a southward shift in the storm’s track does have significant implications on the winter-weather aspect of the forecast. We’re still 36-48 hours away from the peak of the event. Hopefully, most of the storm system was sampled this evening by the upper-air weather balloon network. Assuming that’s the case we should have a better model consensus with tonight’s model runs. The winter weather aspect of this system remains a very low confidence forecast with additional alterations to the forecast probable in future updates. Anyway, since we started off with the winter weather discussion this morning we’ll reverse it and start off with the heavy rainfall aspect. Scroll down past the heavy rain discussion if you’re interested in the winter weather forecast.
Heavy Rainfall & Flood Discussion
A dreary night is expected across most of Texas. You can thank increasing moisture in all levels of the atmosphere for tonight’s cloudiness and mist. Some locally dense fog may also occur. Overall, we’re not expecting too much in the way of heavier rains tonight through tomorrow morning. Those that have temperatures below freezing overnight (the Texas Panhandle and parts of West Texas) could see freezing drizzle. Rain coverage and intensity will increase tomorrow afternoon and tomorrow night across a vast majority of Texas.
Heavy rainfall will also be probably tomorrow night in an axis from near San Antonio east/northeast all the way toward Houston and northeast toward Shreveport and Texarkana. Flash flooding is possible and flood watches are in place. Low-water crossings and typical flood troublespots will be the most likely issues. Rainfall will continue on Saturday, but we’ll see it end from west to east as our storm system begins departing. It may not be until late Saturday evening that we see precipitation end in Texas.
The Weather Prediction Center continues to show widespread 2 to 4-inch rainfall totals across South-Central Texas, Central Texas, North Texas, Northeast Texas, East Texas, and Southeast Texas. The heaviest rain axis is expected to be around the Brazos Valley and Southeast Texas. Localized rainfall amounts may approach 8 to 10 inches in that corridor – and flooding would occur if those totals materialized. Rain totals will be lower across the Rio Grande Valley and across the western half of Texas. With the southward shift in the storm’s track, we’re now also anticipating the northern Texas Panhandle will miss out on most precipitation. This graphic also includes the liquid-equivalent of any ice or snow that falls and melts. Amounts will vary over small areas, so some will receive less and some will receive more.
Dormant vegetation, cool/cold soil temperatures, and the fact most soils are saturated means most rain that falls will run-off. That run-off will move into streams, rivers, and lakes. Most watersheds across the eastern half of Texas are near or at full pool. Flood control districts do have some room. Given the antecedent soil conditions, projected rain totals and runoff, along with current watershed levels – we are anticipating that many streams and rivers will move into flood stage this weekend through next week. Many of these sites could exceed ‘moderate’ flood stage, and some may enter major. Like the October flooding across the Hill Country and Central Texas, this will be a fine-balancing effort from flood districts since many rivers and lakes will have significant inflows. Over 100 river spot locations are already forecast to get into flood stage by Sunday and Monday.Widespread and potentially significant river flooding is forecast on multiple river basins across the eastern half of Texas. It will likely take the remainder of the year to get all this new water out into the Gulf of Mexico. Click To Tweet
Winter Weather Discussion
This continues to be an exceptionally difficult forecast. Morning weather model guidance showed a more southern storm track – which would decrease accumulating winter weather potential across parts of the Texas Panhandle and northern Oklahoma. Unfourtinietly the forecast is far from that simple. Surface temperatures remain questionable and the amount of precipitation that will fall with temperatures below freezing (at the surface) is also still uncertain. It is my hope that this evening’s weather model guidance finally comes into better agreement since our storm system is now in the national weather balloon network.
A Winter Storm Watch remains in effect along and south of Interstate 40 in the Texas Panhandle. This watch extends south and includes a majority of West Texas and portions of Northwest Texas. The primary timeframe for more significant accumulations of snow looks to be from late Friday afternoon or Friday evening through Saturday afternoon. Freezing drizzle is possible as soon as late tonight and Friday morning across the Texas Panhandle and West Texas. That would result in spotty black ice on bridges, overpasses, and elevated surfaces (should it occur). Given the southward shift in the system’s track, the higher snow totals have likewise moved south.
This graphic gives a probability-based projection of the chance of four or more inches of snow accumulation with this system (Friday evening through Saturday). There is a medium chance (40%+) across the southern/eastern Texas Panhandle into the South Plains and Rolling Plains. This axis extends east into western Oklahoma and far Northwest Texas – right off the caprock. This axis could shift north or south based on what happens with model data tonight. Localized snow totals could exceed 6-7 inches across the southern Panhandle and West Texas. Chances to the overall amounts will likely occur as we finally get a good look into the upper-level storm system tonight.
We do have good news in the icing department. Given the system’s slower and more southern track the potential for a damaging ice storm is decreasing. That’s because surface temperatures will also be a few degrees warmer than anticipated in earlier forecasts. That should help with more a snow, rain/snow, or rain line versus a snow, sleet, freezing rain, and rain switchover. Some ice accumulation is certainly possible across the northern Permian Basin, Big Country, and Northwest Texas tomorrow afternoon into Saturday, but amounts look like they’ll remain below a one-quarter inch.
The forecast does not become easier as we get into Saturday in the winter department. Specifically, the chance of rain mixing with or changing over to snow in the Big Country and North Texas as the upper-level storm system begins departing to the east. At this point, it does seem possible that rain could mix with snow across western and northern sections of the D/FW Metroplex. I can’t even rule out a dusting along the Red River. However, this aspect of the forecast is one that absolutely will change. Considering we can’t get a good grasp on the system’s impacts across the Panhandle and West Texas tomorrow, I won’t even bet a dime on how this will play out on Saturday farther east. I’m a broken record, but hopefully, the upper air network’s sampling of the storm system this evening (over California) will give us a better idea or consensus on the downstream forecast.
The heavier rain aspect of this system has fairly good confidence. It is going to rain and in some places, it is going to rain a lot. Some flash flooding will be possible (low-water crossings, typical trouble spots, etc) on Friday and Saturday. More significant and widespread river and watershed flooding is expected as all the rain runs off into streams, rivers, and lakes. This threat will actually continue increasing after the system departs on Saturday into Sunday through next week. I anticipate some rivers and watersheds will be dealing with flooding for the remainder of this year.
Winter weather continues to look likely across the southern half of the Texas Panhandle, West Texas, and portions of Northwest Texas tomorrow evening through Saturday afternoon. Accumulating snow is probable with the heaviest totals along and east of Interstate 27 and south of Interstate 40. Some ice accumulation is also expected, but those totals have decreased based on the latest model data. All of this is being said with low confidence and we guarantee there will be changes to the forecast – both in terms of accumulation totals, precipitation type, the onset of winter precipitation which depends on when surface temperatures go below freezing, and just how much precipitation will fall as snow, a winter mix, or rain.
The forecast will be changing and will probably look a bit different by the time you wake up tomorrow morning. The first of this evening’s weather model data should begin arriving a bit after 8 PM, although a majority of it won’t be in until after midnight. I’ll post a short blog update around 11 PM or so with a few highlights and any obvious changes that may be needed to the forecast. I’ll likely do a Facebook Live and Periscope around 9:45 PM just to go over some of the data as it comes in. Feel free to join us!