December 2020

[Cpv17]

Mesoscale Precipitation Discussion 0880
NWS Weather Prediction Center College Park MD
340 PM EST Wed Dec 30 2020

Areas affected...South-Central to Southeast TX

Concerning...Heavy rainfall...Flash flooding possible

Valid 302040Z - 310240Z

SUMMARY...Locally heavy showers and thunderstorms, with some brief
backbuilding of cells, may result in an isolated flash flood
threat going into the evening hours.

DISCUSSION...The latest WV imagery shows an upper trough digging
southeast across the Southwest U.S. which is expected to evolve
into a rather strong mid-level low center over northern Mexico by
this evening. Downstream of this over areas of south-central to
southeast TX, will be increasingly strong deep-layer southerly
flow which will foster strong warm-air/moisture advection in off
the western Gulf of Mexico. Along with this, will be rather strong
upper-level divergence ahead of the trough associated with
left-exit region jet dynamics approaching the region. Already some
areas of heavy showers and thunderstorms are situated across
portions of central to northeast TX as a strong cold front slowly
settles southeast across the region and coincides with the arrival
of this more conducive moisture transport and larger scale forcing
closer to the coastal plain.

The convective threat though may become a little more focused over
the next few hours and going into the evening time frame, and
especially over southeast TX as the front begins to slow down a
bit more in response to the approaching upstream height
falls/forcing. The boundary will also be interacting with a
greater uptick in PWs (reaching 1.25 to 1.5+ inches), stronger
low-level convergence/Gulf of Mexico inflow, and somewhat greater
instability with MUCAPE values of as much as 1000 to 1500 j/kg.

FFG values are quite high across the region, and generally there
is an ongoing moderate to severe drought. However, the rainfall
rates should increase somewhat this evening, and will likely get
up into the 1 to 1.5 inch/hr range occasionally. Several runs of
the HRRR have been advertising this, and with somewhat better
instability pooling across the southeast TX coastal plain, the
heavier rates will likely tend to verify. While these rates are
not overly high, there will be some potential for the cell
activity to develop and at least briefly backbuild over the same
area.

Going through early evening, some localized pockets of 2 to 3+
inch rainfall amounts will be possible. Generally any threat of
flash flooding will be highly localized and confined to the more
sensitive urban areas.

Orrison

Interesting they mention “drought”. Definitely no drought here. The ground is soaked here. There’s still even some standing water around from previous rains.

[Belmer]

Drew this up for a friend so thought I would post it here as well (black line is just I-10 & 45 for relation; blue line is where front currently is).

Screen Shot 2020-12-30 at 2.50.55 PM.png

Front looks to be where it should be, maybe running ever so slightly ahead of normal. However, it is slowing down and should continue to slow down and stall somewhere along or just west of 59. DP's are in the upper 60s to near 70 along the coast which is just uncomfortable for this time of the year... thankfully there's a breeze to help mix it.

As has been stated already and forecasted, heaviest rain will focus on where the frontal boundary stalls out. Quick spin-up of a tornado looks plausible, especially along the coast overnight into early tomorrow morning near sunrise. Should be a good soaker for most everyone in SETX... broad brush of 1" to localized areas getting 3-4"+ where training may occur.

Little more sunshine on my side of town today than I expected... only adding fuel.

Have a safe and Happy New Year everyone. Looking forward to 2021!

[tropiKal]

Interesting they mention “drought”. Definitely no drought here. The ground is soaked here. There’s still even some standing water around from previous rains.

December just was a lucky break for winter weather/rain lovers, since the La Nina was fake w/ an active Pacific storm track. But in due time, later this winter thru spring, the real La Nina will kick in, and stuff will be shunted away to the north (where it belongs). The warm, dry trend will commence afterwards.

You mean you’re always on break in your mom’s basement.

Nah, keep up man, we're in Texas - we don't got basements down here!

Seriously my dude, it’s pretty weak.

no u

[don]

The rain is more widespread than i expected this early.

[davidiowx]

The rain is more widespread than i expected this early.

Yea I’m at 1.46” already. It hasn’t been raining all day or anything but when it does it comes down quick.

[Cpv17]

The rain is more widespread than i expected this early.

Yea I’m at 1.46” already. It hasn’t been raining all day or anything but when it does it comes down quick.

It looks like Fort Bend County may get hit pretty hard. They’re right in the middle of the heaviest totals on pretty much all the models.

[Cromagnum]

Naturally. I buy a brand new truck and the very next day its hail and tornado time. The exact same thing happened to me in 2013. The day I brought my previous truck home there was inch diameter hail within a mile of my house that same evening.

[DoctorMu]

Largely a bust up here, but storms have been forming along the front and drifting north. Potent stuff west of Houston.

Sorry to hear that Cro.

Back at our old house, we had finally had the roof replaced due to a hailstorm, then another hailstorm hits weeks later and takes out my wife's minivan...fortunately, we found a dent wizard to restore the body of the vehicle.

[DoctorMu]

Just as I finished typing a cell drifting above the shallow layer of cold hits.

[Cpv17]

We’re already beginning to flood here in central Wharton County. Been pouring nonstop for an hour straight.

[DoctorMu]

A good look at current location of the front.

[jasons2k]

The front just blew through here. Looks like the axis of heavy rain will be a little SE of where they had it...1.29” so far...

[Cromagnum]

Are the storms expected to still move east through the area tonight? I'm not complaining about dodging a bullet since my yard is still saturated and I definitely don't want any hail. Looks like the SW side of Houston has been getting pounded for a few hours already.

[tropiKal]

I believe I called this earlier, and yet there were disputes. All a total non-event, just like I predicted.

[Cpv17]

Already over 4” here. Everything is flooded.

[jabcwb2]

All is quiet in Tomball

[suprdav2]

Almost 3 inches since 3:30pm here in Cypress. Getting heavy downpours in waves.

[Cpv17]

Now up to 5” here.

[DoctorMu]

Modest entraining up in CLL. Should continue through the night. 1.8 inches or rain so far. We should have 2+ more inches by tomorrow morning.

[tropiKal]

Total non-event for Houston, just like I predicted.