Update earlier this AM from Jeff Lindner:
Heavy rain possible Saturday evening into early Sunday across the northern portions of SE TX.
Weak frontal boundary currently just north of Austin is sliding southward this morning with a warm and moist air mass in place across all of SE TX ahead of this feature. High resolution guidance continues the southward track of this boundary today to roughly along a line from Columbus to Tomball to Cleveland which is much further south than the global models have been suggesting. A weak disturbance is also approaching SE TX from the southwest currently similar to yesterday at this time, but the radar is mostly clear. Convection allowing models (CAMs) show some development near the frontal boundary late this afternoon and early evening from roughly Sealy to Tomball to Conroe. This may be some enhancement of the frontal boundary with an inland moving seabreeze. Anything that does develop looks to weaken and dissipate by 8-9pm.
Saturday:
Weak frontal boundary will attempt to lift northward early Saturday, but how much northward progress is questionable…effectively the boundary will be stalled/meandering somewhere between Houston and College Station during the day. CAMs show a robust disturbance moving out of MX tonight with a well defined thunderstorm complex developing over the Rio Grande plains, but this activity weakens as it moves eastward across SC TX. Can’t rule out a few showers Saturday morning with the front in the area and this disturbance approaching from the southwest.
Renewed influx of tropical air mass into the region will occur by early Saturday afternoon with PWS of 1.8-2.0 inches or near maximum levels for mid April moving into the area from the western Gulf of Mexico. Surface heating across the area when combined with the approach of a stronger upper level disturbance is setting the stage for thunderstorm development by mid to late afternoon. Short range guidance is not in great agreement on how activity will play out Saturday afternoon into the overnight period with several scenarios on the table. One scenario suggests storms begin to fire in the 3-5pm time frame from Austin County through NW Harris to Montgomery County and then slowly develop/move ENE. Another scenario is that a thunderstorm complex develops over central TX and moves into the region later in the evening. One or a combination of both of these potentials is plausible.
Heavy Rainfall:
Nearly all factors are in place for heavy rainfall late Saturday with copious moisture, a feed of tropical moisture off the Gulf, a slow moving low level boundary, and diffluent upper air winds aloft. The threat for cell training is certainly in place and this is where things could add up fast given the environment in play. Hard part of the forecast is where is the best potential for cell training and where is the southern cut-off of the heavy rainfall. There looks to be a strong rainfall gradient across the area with totals near the coast less than .50 of an inch and totals in the College Station to Livingston area of 1-3 inches. Higher isolated totals are almost certain and would not be surprised to see some locally 4-6 inches in places where storms anchor and training persists.
For the metro area think 1-2 inches north of I-10 is most likely, but will need to keep an eye on the southward extent of the potential heavy rains to the north and any trends that would suggest a slightly more southern extent to the heavy rainfall.
Hydro:
Heaviest rains on Saturday into early Sunday are expected north of HWY 105 which will impact the Trinity, east and west Forks of the San Jacinto River, Navasota, and middle Brazos basins. Currently, not expecting any significant flooding on any of these systems, but will at least need to keep an eye on the more flashy San Jacinto and Navasota basins and where any sustained corridor of heavy rainfall occurs.
Forecasted Rainfall (Today-Sunday):
Jeff Lindner
Director Hydrologic Operations Division/Meteorologist
Harris County Flood Control District
9900 Northwest Freeway | Houston, Texas 77092
346-286-4000 (main) | 346-286-4165 (direct) | 281-924-2091 (cell)
jeff.lindner@hcfcd.org | Twitter: @jefflindner1
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