APRIL 2019: Warm & Muggy WX to End The Month

[Belmer]

The latest discussion from the NWS here in Houston has done a great job detailing just how complicated this setup is. The whole discussion is worth a read if you have time, but if not... I have highlighted the important notes below:

Area Forecast Discussion
National Weather Service Houston/Galveston TX
457 AM CDT Sat Apr 6 2019

.DISCUSSION...

Severe weather and heavy rainfall are possible this weekend. While
the weekend will not be a complete washout, people need to be
diligent to monitor weather forecasts for updates, watches and
warnings.

.NEAR TERM [Through Today]...

Mesoanalysis will be essential through out the day as severe
weather and heavy rainfall begins to unfold. Starting out with the
surface, low pressure has developed over west TX in response to
the first jet streak and short wave trough to move into the
plains. This has allowed for winds to back to the ESE over much of
the area. Water vapor imagery is key to the analysis aloft today
as there are many subtle features that if go unanalyzed, could
make an impact on the forecast. Right now water vapor imagery
shows the beginnings of a jet streak coming into south Texas and
we see large scale lift increasing due to resulting shower
activity over the region. This feature may not have initialized
well in the models and could allow for a weakening of the cap more
so than the models indicate. AMDAR airplane soundings over the
area show a fairly strong cap in place with the EML around
800-700mb. Divergence from the left exit region of this southern
jet will act to enhance the LLJ today and a continuing eroding of
any capping. The focus for convection today looks to be centered
along the main jet axis with this first short wave trough pushing
into the southern Plains as a second jet streak comes into Mexico
this afternoon. This jet axis should be oriented across central
Texas towards the Arklatex. At 09Z water vapor imagery already
started to show some enhanced cloud cover over the Hill Country
into central Texas as evidence for stronger lift over the region.
The second jet streak is currently back over California and
western Arizona. There will be no lacking moisture or instability
today as AMDAR soundings also show steep lapse rates above the
EML. PWAT values this morning are 1.5 to 1.6 inches of the lower
Texas Coast. PWAT values are expected to increase through Sunday
and expand across the region.

There is a lot of analysis to digest but SPC and WPC have put
together some solid synthesis of the data. Severe weather risk of
slight to enhanced looks on track for the northern most counties.
Last few runs of the HRRR along with several WRF/HREF runs
continue to highlight an area north of College Station to Crockett
for primarily a wind/hail threat. But there is also a 5% tornado
probability. This area should have the most convergence for storms
but also where moisture/instability/shear combine for convection
capable of severe weather. Most likely the thunderstorm activity
will remain just north of this line more into the NWS Fort Worth
warning area but mesoscale processes with outflow boundaries could
shift this activity south. Our forecast leans on the higher side
of rain chances for this reason but there will be a tight gradient
in precip chances and it could shift. Storm modes look to be more
linear hence the wind/hail threat but a rotating updraft could
also be possible given the shear parameters for a low end tornado
threat. This will be especially true for the enhanced/slight risk
areas of the outlook.

WPC also has a slight risk of excessive rainfall for parts of the
northern counties from College Station to Crockett. This is due to
the possibility of storms training along the same area. Recent
runs of the HRRR and the Texas Tech WRF support this idea with
convection initiating around 15Z and going until 00Z Sunday.
These areas of training storms line up well with the lift from the
jet axis mentioned before. Due to the training, rainfall amounts
could stack up quickly and present a localized flood threat. Again
this axis of higher rainfall should be from say a Temple to
Palestine line but with mesoscale processes we will need to see if
this shifts farther south towards the Brazos valley into east
Texas. NAEFS also highlights this area for higher than normal PWAT
and moisture transport. The flood threat only complicates the
weather message when added to the severe weather threats.

.SHORT TERM [Sunday Through Monday]...

By Sunday morning the pattern becomes even more conducive for a
heavy rainfall threat but we do not want to forget about the
severe weather threat. SPC still has the area in a slight risk. By
Sunday morning the upper level trough should be over the Rio
Grande Valley with a strong area of PVA from Del Rio to Laredo.
This vorticity along with a jet streak should move over SE Texas
by 18Z Sunday with a slight negative tilt. This quickly erodes any
capping and brings more enhancement to the LLJ over the area.
PWAT increase to 1.7 to 2.0 inches depending upon the model. The
point here is that these values will be well above the 90th
percentile of climo and nearing record values for the day. NAEFS
also shows higher than 90th percentile of moisture transport
during this time so between the lift and high moisture there is a
growing concern for a heavy rainfall threat. QPF output from the
models varies quite a bit but looking at an area wide of 2 inches
possible on Sunday and likely have some bands of higher amounts.
Hi-res models are showing some signs of these enhanced bands but
again QPF output does not seem to line up well with the overall
synoptic pattern and expected moisture. The other aspect that is
relatively unknown at this point will be any interaction of the
trough with outflow boundaries for focused ascent. WRF runs seem
to be trying to key on these boundaries for higher rainfall
amounts but hard to know the exact evolution of these outflow
boundaries. This is another area where ongoing mesoanalysis will
be key to better pinpoint these details. Another question that
remains will be just how far south this second trough will drop
over Mexico and how the trough moves east or northeast across the
area. If it drops a little more south, the system could be slower
to move over the area and possible produce higher rainfall. This
all remains to be seen but alternate scenarios that deserve
attention.

We are really close to looking at possibly issuing a flash flood
watch for Sunday but this may depend upon how much rainfall falls
today. Grounds are still on the dry side but some areas have had
some rainfall. WPC slight risk of excessive rainfall looks to be a
good outline to follow for a watch area. For now we think we can
wait for the 12Z model runs to help define a watch area.

Overpeck

[jasons2k]

It’s already thundering here. Today looks like it may be on the wet side.

[Ounce]

So from the NWS morning statement, the divergent jet appears to be situated in NE Texas.

Is there much of a chance of it scooting southward towards the Huntsville Livingston area?

[DoctorMu]

Severe Thunderstorm warning for Brazos County. It look like night out there! At least I got mowing the front lawn and fertilizing in early this am.

First really muggy and nasty day on Thursday. Sign of things to come.

We'll take the rain now while we can get it - this would be a relief in the summer.

[DoctorMu]

http://radar.weather.gov/ridge/radar_li ... 0R&loop=no

https://www.weather.gov/sjt/Satellite

[mckinne63]

Gloomy and overcast here in Stafford. Had a few light sprinkles on the windshield this morning.

[Cromagnum]

And nothing in our area today. All well to the north

[Kludge]

We got a nice 0.72" and nothing severe... but a heckuva lightning show.

[DoctorMu]

0.55 in IMBY so far. Incredibly thick clouds and copious lightning strikes.

Another line of showers are on its way.

[BlueJay]

It's gloomy but no real rain yet.

[Andrew]

The threat for severe weather will shift to the southeast later tonight, but I still think the largest threat for most will be heavy rain. Already seeing some flooding across the hill country, but it will be difficult to really pin down where the heaviest rain occurs until it actually happens. One thing to note also is a lot of the models show 3-5k Jules of CAPE across a lot of the region later this afternoon. Any storms that do pop up could have a threat for hail.

Below is a sounding from the HRRR that shows steep mid level lapse rate and we are rather lucky we have just enough capping that should keep things in check. There is just enough subsidence at the surface to offset some of the upward upper-level motion associated with the active flow.

Finally, by early tomorrow the GFS shows PWATs up to 1.7inches which will be near seasonal max for this region. Looking at Western Louisiana's PWATs it is rather impressive honestly. So we have to closely monitor tonight for any MCSs.

[jasons2k]

The sun is breaking out south of I-10.

[davidiowx]

Sun has been out for the past few hours here in Richmond

[Andrew]

The sun is break out south of I-10.

83-84 here with plenty of sun. It would be very interesting to see a sounding for this region right now.

[Cpv17]

It’s 84 here and partly cloudy in Wharton. Fuel for the fire.

[Andrew]

Areas around College Station will need to be monitored over the next couple of hours for any spinups. Strongest low-level winds are exiting the region slowly but conditions currently remain favorable.

[Cromagnum]

What time tonight is the primary threat? Everything so far has been 200-300 miles NW of Houston

[stormlover]

Everything was supposed to be farther north, next system not so much

[Andrew]

What time tonight is the primary threat? Everything so far has been 200-300 miles NW of Houston

Late tonight into tomorrow morning for most of SE Texas. I think the severe threat will be limited for much of us, but we will have to monitor for any training that occurs ahead of the main line. Look out between Del Rio and Laredo tonight to see what will be heading our way. Probably will see 1-3 inches widespread but 5-6 inches in isolated areas cannot be ruled out.

[stormlover]

Andrew- when will it end for the Beaumont area tomorrow ?