Texas Spring 2017

[Ntxw]

Not yet a westerly wind burst (WWB) but trades have significantly weakened. CFSv2 says we get our first 0.5C or greater Nino weekly reading later this month, lets see if that comes to fruition.

[bubba hotep]

Axis of heavy rain appears to setup just SE of Dallas maybe Ennis to Kaufman and points eastward? A shift NW into DFW could cause issues with those kinds of totals!

[vbhoutex]

This is Jeff Lindner's take on today's rainfall and flooding potential:

Heavy Rainfall Potential

Ingredients appear to be coming together to produce a heavy rainfall and potential flash flood event across mainly C TX late today into Tuesday.

Moisture levels have certainly increased over the last 24 hours as a weak cool front has progressed into the northern TX Hill Country and is in the process of stalling. Aloft a trough of low pressure is approaching from the west which will help to activate the frontal boundary with convection later this morning.

While the general model consensus has been to develop and anchor deep convection with favorable heavy rainfall parameters across C TX this afternoon and tonight, some of the latest guidance is suggesting, as stated yesterday, that a cold pool may develop and progress the convection deeper into SE TX. In fact some of the models now even move slow moving convection all the way to the coast which is a large difference from 24 hours ago. Parameters certainly appear in place by late this afternoon to support the development of deep convection from C to NE TX and this development may occur across or move into our W/NW counties from Columbus to Huntsville early this evening. Low level moist inflow feed along with a very slow moving or possible stalled frontal boundary and very high PWS air mass supports a flash flood risk tonight from C into NE TX including our W/NW counties. Rainfall amounts of 1-3 inches with isolated totals of 5-7 inches will be possible and even higher amounts may occur where sustained cell training develops.

Main question this morning is how far south this activity will move overnight. Latest high resolution guidance suggests a greater potential for organized activity to move deeper into SE TX than expected yesterday which could bring the heavy rainfall and flash flooding threat further south across the area. The development of this new trend appears to be tied to the more organized nature of the convection this evening which promotes good cold pool formation and the forcing of convection southward on outflow boundaries overnight. Effectively the outflow boundaries are being driven southward and adding a surface focus for convective development. We have seen this many times before across SE TX where developments to our NW become our problems even when models want to keep the activity to our NW.

Given the mesoscale nature of how convection may unfold, the confidence of where and how much rain may fall across the area is low. Should sustained slow moving convection enter deeper into SE TX than currently forecast rainfall totals will need to be significantly increased and flash flooding would be possible.

Air mass will become fairly unstable by mid to late afternoon with 2000 J/kg of CAPE across the region and expect that a few storms especially early this afternoon into the evening hours could become severe before the threat transitions to a heavy rainfall event overnight. The severe threat area is general in the same region as the heavy rainfall potential currently or along and NW of a line from Columbus to Huntsville.

Hydro:
Forecast QPF through Tuesday is fairly high across the middle Brazos, middle Trinity, and middle Colorado basins and the entire Navasota basin. Rainfall of this magnitude will likely result in rises to near flood stage on the mainstem rivers if it verifies and isolated higher amounts over certain basins could push levels above flood stage. The position of the heavy rainfall axis just N/NW of SE TX is cause for concern as run-off will move downstream.

[1900hurricane]

Near wherever the front settles is where a threat of locally heavy rainfall will be.

[weatherdude1108]

We're already getting streamer showers here at work.

EWX Updated Discussion:

Area Forecast Discussion...UPDATED
National Weather Service Austin/San Antonio TX
1151 AM CDT Mon Apr 10 2017

.UPDATE...
Based on the latest 12Z models and continued trend of heavy rainfall
potential into the I-35 corridor and portions of the Hill Country we
have elected to issued a Flash Flood Watch in the late morning update
for portions of the CWA. This includes much of the Hill Country and
I-35 corridor from Austin to San Antonio metro areas. Guidance has
trended slightly south and east with the heavier QPF and higher on
amounts. We have increased forecast rainfall amounts in the watch
area to 2 to 4 inches with isolated amounts up to 7 inches.

Still some uncertainties if convection that develops late this
afternoon to the north organizes into a complex and becomes cold
pool dominated or if a more slow moving front/outflow boundary
orients itself west to east from the Hill Country into portions of
the I-35 corridor. The later solution could lead to better chance of
the forecast QPF amounts being achieved. Should be pointed out that
there is an increasing signal among hi resolution models of this
happening, but they are having difficulty run to run with placement
of highest pockets of QPF.

Also, SPC has placed much of the area in a slight risk for severe
storms. The signals are there for an initial threat for large hail
this afternoon and evening, possibly transitioning into a straight-
line wind threat tonight if the former solution for an organized
complex comes to fruition.

However, the main messenging we want to stress the most for this
event is the flash flood potential given recent rainfall and the
fact this will mainly be a night time event, where it is much harder
for motorists to recognize the dangers of flash flooding.

[JDawg512]

The setup is there for a dangerous flash flood event overnight. Definetly keeping a very close eye to the radar as we head into the evening.

[weatherdude1108]

The setup is there for a dangerous flash flood event overnight. Definetly keeping a very close eye to the radar as we head into the evening.

Yeah. We don't want too much of a good thing!

[bubba hotep]

Front still appears to be hung up just to the NW of DFW. Wonder if all of the area gets in the watch?

ETA: Denton is left out but the other counties made it in.

[jasons2k]

Look out tonight -- new Severe Thunderstorm Watch:

http://www.spc.noaa.gov/products/watch/ww0139.html

[Brent]

Already some nice downpours here so far no lightning or thunder

[Ntxw]

Front has passed DTO and KNFW, crossing DFW airport now. Areas NW of that line probably won't get much more, southeast of it will. Once it slows south of the area is where bigger totals will be

[weatherdude1108]

No need to be driving out there tonight, unless absolutely necessary.

I'm wondering how many lights will be blinking tomorrow during the morning rush, along with road closures.

000
FXUS64 KEWX 102032
AFDEWX

Area Forecast Discussion
National Weather Service Austin/San Antonio TX
332 PM CDT Mon Apr 10 2017

.SHORT TERM (Tonight through Tuesday Night)...
...Dangerous Flash Flooding Event Possible Late This Afternoon
through Tonight across South Central Texas...

Complex weather scenario taking shape late this afternoon through
tonight. The cold front was located just south of a Stephenville to
San Angelo line at 3 PM with showers and storms developing along and
just behind it in West Central Texas. Additional isolated to
scattered showers have developed through the afternoon beneath a
mid level cap across Central Texas. Aircraft sounding data from AUS
indicates the mid level cap still in place, but this is forecast to
erode late this afternoon and evening as the front approaches the
region. Initially discrete storms could pose a hail threat across the
northern Hill Country and Central Texas through the early evening.
Signals in hi resolution models then transition into an organized
complex of storms, but there are some difference in timing on how
fast this happens. Should this happen this could support a threat of
damaging straight line winds through the CWA.

However, the main concern we are messaging will be the heavy rainfall
potential that could lead to flash flooding. Precipitable water
values of 1.6-1.8 inches are pooling over the region south of the
front. This is nearly 2 standard deviations above average. Initial
slow motions of the storms and complex will yield pockets of intense
rainfall rates this evening through portions of the overnight, as
indicated by runs of the HRRR. Models the past three runs have
trended farther south and with higher QPF amounts into much of the
southern and eastern Hill Country as well as I-35 corridor. GEFS
plumes for both Austin and San Antonio have trended up, with the
lowest member at Austin around 2", highest at 4.3", and mean 2.87".
Some of the high resolution guidance suggests the highest amounts
farther south toward the San Antonio metro area.It is difficult at
this time frame to determine where the heavier pockets may occur as
there is uncertainty with the mesoscale evolution of the system.
But generally 2-4" is expected across the Flash Flood Watch area
with isolated amounts up to 7".

It is important to stress the flash flooding potential with this
system, especially since this will be occurring at night when it is
harder to recognize the dangers of flash flooding.

Tomorrow`s chances for rainfall will depend entirely on how
organized the system evolves tonight. With hi resolution guidance
trended towards and MCS, the atmosphere may become worked over and
stabilized for Tuesday.

&&

.LONG TERM (Wednesday through Monday)...
Chances for showers and thunderstorms will remain in the forecast
through the rest of the week with slightly greater chances Thursday
as a trough shifts through the region. No concentrated signals appear
to warrant hazard mention at this time during the long-term period.

Diurnal showers and thunderstorms look to be likely each afternoon
through the week as a unsettled and active southern jetstream branch
helps promote lift with the continued moist airmass in place.
Thursday and Friday appears to be a slightly better concentrated day
with the passage of stronger trough axis. Weak ridging over the
weekend may help to keep the area dry.

[bubba hotep]

Looks like the house picked up between 1.5 to 2" up in Collin County but we basically got shut out here at the office in downtown Dallas.

[Ntxw]

DFW airport picked up 0.10" of rain out of the system

[JDawg512]

Looks like the front has stalled. Nothing occuring in the immediate vicinity.

[bubba hotep]

Looks like the front has stalled. Nothing occuring in the immediate vicinity.

Looks like it is draped along I20 (may have even lifted north some back into the DFW area where there is some redevelopment) before sagging south towards Waco and then SW out into the Hill Country. Looks like some hefty totals adding up in the Waco area.

[bubba hotep]

Some hail being reported with these cells in Collin County

[bubba hotep]

Well that escalated quickly!

[bubba hotep]

It appears that an outflow boundary or maybe even the "cold front" lifting back north as a warm front NW out of Dallas County setting off the svr storms tonight

 https://twitter.com/whatisthisrds/status/851643524500115456

[bubba hotep]

Another svr warned storm firing off that boundary in DFW