November 2022

General Weather Discussions and Analysis
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jasons2k
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Re: November 2022

Post by jasons2k » Wed Nov 23, 2022 2:02 pm

Latest from Jeff Lindner:
Heavy rainfall increasingly likely Thursday/Thursday night.

Guidance has been trending wetter for the upcoming storm system that will impact the area Thursday-Friday. Of note is the increasing potential for a warm front to move inland from near Matagorda Bay to Galveston Bay early Thursday and potential progress as far inland as the US 59 corridor. This is increasing the threat for sustained heavy rainfall and training of heavy rainfall along the warm front Thursday afternoon into the evening hours. It is unclear just how far inland the warm front may move and where the axis of heavy rainfall will reside, but area along and SE of the US 59 corridor appear to have the highest risk at the moment.

Rainfall:
Rainfall amounts are being increased into the 2-4 inch range north of I-10 and 4-6 inches south of I-10 for the period from Thursday-Saturday, but the majority of this rainfall will be Thursday afternoon into Friday morning.

Hydro:
Given recent rainfall and currently wet grounds, especially south of I-10, forecasted rainfall will likely generate run-off across the county and rises on area watersheds. Street flooding will be the main threat where short duration rainfall rates exceed the local drainage capacities. At this time rises on area bayous and creeks are likely, but widespread overbank flooding looks low. Will need to keep an eye on Clear Creek and its tributaries, and the smaller watersheds in southeast Harris County depending on where the heaviest rains occur.

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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don
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Re: November 2022

Post by don » Wed Nov 23, 2022 2:18 pm

Yep, i wouldn't be surprised to see a flash flood watch issued.18Z HRRR just coming in also showing some high rainfall amounts with some isolated areas of 6+ inches.(Note: this is just showing rain from tomorrow doesn't include Friday)
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Screenshot 2022-11-23 at 13-50-49 Models HRRR — Pivotal Weather.png

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don
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Re: November 2022

Post by don » Wed Nov 23, 2022 3:55 pm

From HGX afternoon discussion just released.Alot of good info on the unfolding storm.Flood watches may be needed for Friday depending on tomorrows rainfall.Their calling for widespread rainfall amounts of 1-3 inches with isolated spots of 5-7 inches...Seems more likely now that the record will be broken at Bush for the wettest thanksgiving on record for the city,after just breaking the record last thanksgiving.LOL
imarge7.png
image6.png
By Thursday morning, an upper level trough with an embedded upper
area of low pressure will be making its way into west TX and
inducing southwesterly flow aloft. This places us in a constant flow
of PVA (source of lift), and this is just the first piece of the
puzzle. As this upper low slowly pushes in, the pressure gradient
steadily tightens leading to increased winds aloft with a 20-30 knot
LLJ and 100-120 knot upper level jet streak developing near the
Brazos Valley on Thursday morning, which adds to our 0-6km bulk
shear of 50-60 knots (more shear increases our chances of strong to
severe thunderstorms). At the surface, an area of low pressure will
attempt to develop but looks to be a surface trough (essentially an
open wave of low pressure) stretches across central Texas and
steadily moves southward. Additionally, a warm front moving inland
along the coast steadily increases dew points and introduces the
warm sector (region with increased instability) to portions of
southeast Texas. Last but not least (for the severe portion anyway),
low level winds are veering with height adding a directional shear
component in addition to the speed shear mentioned earlier.

All of these factors point towards Thursday being rather rainy with
a marginal risk of strong to severe storms for any storms that
manage to develop out ahead of the aforementioned boundary. High
resolution model guidance continues to point towards showers
beginning early in the morning in the Brazos Valley/Piney Woods area
with the LLJ helping to induce spotted coverage. For areas near the
Houston metro area, showers are possible in the morning hours, but
coverage begins to expand closer to the late morning/early afternoon
hours as temperatures rise. The main corridor for potential strong
to severe storms continues to be south of I-10 and west of I-45
(SBCAPE near 1000 J/kg; MUCAPE maxing out around 2000 J/kg [measures
of instability]), but with uncertainty still looming the marginal
risk from the Storm Prediction Center expands for most of southeast
Texas with strong winds and isolated tornadoes being the primary
threats. However, those are not the only threats for the day...

The key things to look for when forecasting heavy rain are PW values
above the 75th percentile (1.6"-1.9" is way greater than ~1.23"), a
deep warm cloud layer greater than 10,000 ft (~12,000 ft for us),
low/mid level RH`s greater than 70% (greater than 80%/90% for us),
and long/skinny CAPE generally less than 1,000 J/kg (check!). The
other factors are low cloud layer winds less than 10 knots (it`s
either near or above that for us depending on your model of choice)
and slow Corfidi up/down shear vectors less than 15 knots (we`re
well above that). Storm motion will be parallel to the boundary as
well which adds in to potential for flooding along with already
saturated soils for areas south of I-10 and a portion of the Brazos
Valley. Saturated soils means low-ish Flash Flood Guidance (FFG)
with most locations around 2-3" for 1 hour FFG and 3-4" for 3 hour
FFG, so it wouldn`t take too much rain to cause issues. As a result
of all of these factors, the Weather Prediction Center has placed
most of southeast Texas in a slight risk for excessive rainfall on
Thursday. As far as rainfall totals go, we`re expecting widespread
amounts of 1"-3", but there has been consensus on an isolated swath
of 5"-7". There is a bit of uncertainty of exactly where that swath
will be, but it appears likely that somewhere in southeast Texas
will be in that rainfall bullseye for Thursday.

As of right now, we`re not planning on any Flood Watches,
but we`ll continue to see how things progress. It`s worth noting
that the areas that receive the most rainfall on Thursday will need
to be watched on Friday for a potential Flood Watch with rainfall
continuing. While the boundary moves offshore on Thursday night,
model guidance is picking up on a coastal low developing which
keeps us in a region of inflow and moisture advection. With the
upper level low continuing to sit nearly stationary over west
Texas, we`ll continue to have the lift to produce widespread
rainfall. It`s worth mentioning that there will be a brief lull in
the moderate/heavy rain early Friday before coverage increases
again going into the afternoon. Model guidance has trended towards
areas south of I-10 and west of I-45 as the hotspot for rainfall
on Friday with an additional 1-2" of rainfall. For now, the
Weather Prediction Center has all of southeast Texas in a slight
risk of rainfall for Friday. As previously mentioned, we`ll have
to monitor any areas that receive plentiful rainfall on Thursday
as it`ll take less rain to cause issues on Friday. Be sure to stay
weather aware over the next few days, especially before heading
out on the roadways. Locally heavy rainfall in training
thunderstorms could lead to street flooding in some areas. Make
sure that you have multiple ways to receive warnings and
remember...Turn Around, Don`t Drown.

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Re: November 2022

Post by Cpv17 » Wed Nov 23, 2022 4:40 pm

The WPC is now calling for 4-7” for most of our viewing area over the next 7 days.

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don
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Re: November 2022

Post by don » Wed Nov 23, 2022 5:12 pm

Yep, here's the WPC updated rainfall totals.They also have a large slight risk area for flash flooding tomorrow and Friday.
wpc_qpf_1v68h_p.us_sc.png
WPC Thanksgiving Discussion:
Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
331 PM EST Wed Nov 23 2022

A widespread multi day heavy precipitation event developing late
day 1 and continuing into the day 2 and 3 periods ahead of the
developing closed low sinking south through the Southern Rockies
into the Southern High Plains at the beginning of the day 2 time
period. There are some timing differences after this with the
southeastward push of the closed low day 2 into the Southern High
Plains with the GFS on the more progressive side compared to the
EC, NAM and UKMET. Despite the differences, models agree that low
level flow off the western Gulf will continue to strengthen from
the south and then south southwest on day 2, spreading anomalous
PW values...2 to 2.5+ standard deviations above the mean across
the risk areas. This will support the first round of heavy rains
spreading east northeastward Thursday into Thursday night from
East Texas into the Lower MS Valley. Overall, there is good
agreement on this but with both timing differences with the
downstream push of the convection and differences with the
latitude of the heaviest totals. With respect to the latitude of
the heaviest amounts, consensus is to favor the more southern max
qpf axes solutions which would fit better with the farther south
axis of instability and position of the west to east oriented
frontal boundary expected to strengthen along the Gulf coast from
the Upper TX coast, eastward along the LA coast. This would be
closer to the farther south qpf axes of the FV3LAM, EC and UKMET.
Timing of the downstream push of convection is less certain.
Overall, however, there will be potential for training of cells in
a general west southwesterly to east northeasterly direction
across the risk area with totals in excess of 5"+ in areas of
training. The previous slight risk area was trimmed on the north
end to reflect favoring the farther south qpf solutions. The
slight risk was expanded farther to the southeast on the south end
to cover southeast LA and far southern MS as the EC, EC mean and
NAM all suggest a potential axis across these area.

Oravec
Friday Discussion:

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
332 PM EST Wed Nov 23 2022

Day 3
Valid 12Z Fri Nov 25 2022 - 12Z Sat Nov 26 2022

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
SOUTHEAST TEXAS AND SOUTHWEST LOUISIANA...

...2030Z Update...

Unlike Day 2/Thanksgiving, there has been a dramatic shift in the
total precipitation on Friday. A corridor of heavy rain is
expected to develop especially early in the day from coastal
southeast Texas northwest into central TX and even portions of the
Permian Basin before the precipitation changes over to snow in far
west Texas into NM. There is significant model disagreement on
where this axis of heavy rain will set up. However, there has been
a very notable southwestward/slower shift in the location of the
heaviest rain in nearly all of the model guidance. Normally these
large shifts in the models are limited to just one or two, but
when almost all of them latch on to this same trend, it's worth
noting and adjusting the forecast accordingly. Thus, the previous
Slight Risk has been shifted well to the west of previous.
Therefore, much of MS and LA are likely to be dry or only have
light rain on Friday, while TX gets nearly all of the heaviest
rainfall. The Slight Risk was redrawn to focus mainly on where the
greatest instability and moisture will be, so it's over much of
southeast TX, including Houston, San Antonio, Corpus Christi, and
Austin
. Areas in the marginal risk over central TX will be getting
the "leftovers" of the convection, which will include steady rain,
but is generally not expected to fall heavily enough to result in
flooding except in isolated instances.
With the continued southwestward trend in the models, additional
shifts in the Slight Risk are probable with future updates.

Wegman
Attachments
wpc_excessive_rainfall_day2.us_sc.png
wpc_excessive_rainfall_day3.us_sc.png

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don
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Re: November 2022

Post by don » Wed Nov 23, 2022 5:46 pm

Update from Jeff
Powerful storm system will bring widespread impacts Thursday-Saturday.

Heavy rainfall may lead to street flooding and rises on area creeks/bayous.

A strong storm system currently moving through the Rockies will move southward over the next 24-36 hours and cut-off from the main upper level flow aloft. This will result in widespread periods of showers and thunderstorms.

Thursday:
Surface warm front will approach the upper TX coast early Thursday morning and move inland during the morning hours. Moisture and lift both increase during this period and expect showers and thunderstorms to increase in coverage and intensity near the warm front. Warm front may approach the US 59 corridor by midday before slowing and potentially stalling Thursday afternoon. High resolution guidance has trended toward a line or several clusters of strong thunderstorms with very heavy rainfall developing near the warm front Thursday midday into the afternoon hours. Parameters will certainly be in place along and south of the warm front for isolated severe storms and excessive rainfall with good low level inflow off the Gulf, moisture levels over the 90th percentile for mid November, strong lift, and a nearly saturated warm layer. A lot of the parameters on a flash flood decision tree are checked and warm fronts are notorious in these sort of setups for producing excessive rainfall. Best case is the warm front is held closer to the coast keeping the heavier rainfall in coastal Brazoria and Galveston Counties.

Friday-Saturday:
Models have again slowed down the movement of the upper level low to our west as is common with these digging systems…should see a break in the rainfall Friday morning, before another round of widespread at times heavy rains move back into the area Friday afternoon and evening. Will need to monitor this time period closely as grounds become increasingly saturated and run-off increases. Showers may linger into midday Saturday, before this system finally exits to the east.

Rainfall Amounts:
Rainfall amounts have increased today both due to the potential for slow moving and training thunderstorms Thursday afternoon and due to the longer duration of rainfall now expected into Friday and Saturday.

Widespread amounts of 1-3 inches can be expected on Thursday afternoon with isolated totals upwards of 5-6 inches. Some high resolution guidance continues to show a band of 5-7 inches near the warm front Thursday afternoon and this is concerning. Hourly rainfall rates of 2-3 inches may be possible Thursday afternoon and this will lead to rapid street flooding and significant rises on creeks and bayous.

Additional rainfall amounts of 1-3 inches can be expected Friday/Saturday on top of what falls on Thursday and this will only worsen ongoing run-off from the Thursday rainfall.

Hydro:
Soils are primed for run-off with recent wetting rainfall over the region. Main concern is street flooding, but do not want to disregard the potential for some significant rises on area watersheds, especially if the higher totals are realized in portions of Harris County. Greatest concern is for the southern and southeastern portions of Harris County where soils are the wettest and potential rainfall the highest, but this axis of highest rainfall could still shift around some, so not confident in pin pointing any particular watershed. Generally most of the watersheds can handle 3-4 inches…once/if we start to exceed 5 inches the concern for any flooding of bayous/creeks listed below will increase.

Overall highest concerns IF 5-7 inches are realized in Harris County would be:

Clear Creek and its tributaries
Armand Bayou
Hunting Bayou
Halls Bayou (upper around I-45)
Little Cypress Creek
Willow Creek
South Mayde Creek (lower near Greenhouse)
Keegans Bayou (lower near Beltway 8/US 59/Wilcrest area)
Willow Waterhole
Brickhouse Gully
Spring Branch Creeks (Spring Branch, Buttermilk, Briar Branch)

Jeff Lindner
Director Hydrologic Operations Division/Meteorologist

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DoctorMu
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Re: November 2022

Post by DoctorMu » Wed Nov 23, 2022 6:24 pm

jasons2k wrote:
Wed Nov 23, 2022 2:01 pm
DoctorMu wrote:
Wed Nov 23, 2022 1:19 am
Iceresistance wrote:
Mon Nov 21, 2022 6:36 pm


Not if you need it to break the drought. ;)
We're not in a drought locally now.
Ummm…yes we are. Check the drought monitor - hot off the presses, a day early. Brazos Valley and especially points west still need rain.

https://droughtmonitor.unl.edu/CurrentM ... or.aspx?TX
D1. The ground is pretty soaked here. They desperately need rain in the Hill Country. I hope they get it rather than us.

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Re: November 2022

Post by javakah » Wed Nov 23, 2022 8:54 pm

I found these clouds kind of interesting this evening as I was walking to my car from a pet store, after getting some treats to celebrate one of my dogs' birthday.

Image

Then a few moments later, once I got to my car, there was another dog involved- a sun dog!
Image

Image

Image

Cpv17
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Re: November 2022

Post by Cpv17 » Wed Nov 23, 2022 9:37 pm

My goodness the 0z 3km NAM is going bonkers with the widespread rain with this event.

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jasons2k
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Re: November 2022

Post by jasons2k » Wed Nov 23, 2022 9:55 pm

@ javakah those photos are amazing - thanks for sharing!!

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