April 2023

[Cpv17]

Seen this before. Not getting hopes up.

There will be a much greater chance this time around as compared to last Saturday.

[don]

Next week is also looking pretty stormy right now starting Sunday.

[Stratton20]

Yup, GFS is very active with multiple shortwaves crossing over the state, next 10 days looks pretty active around here
12z GFS widespread 1-3 inches, isolated 6+ in some areas

[Cpv17]

The ensembles are looking a little better too.

[tireman4]

rea Forecast Discussion
National Weather Service Houston/Galveston TX
1240 PM CDT Wed Apr 19 2023

...New AVIATION...

.AVIATION...
(18Z TAF Issuance)
Issued at 1214 PM CDT Wed Apr 19 2023

VFR conditions are expected into the late evening hours. Seeing a
few sprinkles showing up on radar west of I-45 and wouldn`t be too
surprised if CLL might see a few drops this afternoon, but nothing
of consequence. Breezy SSE winds will lose their gustiness around
sunset, but probably remain in the 7-13kt range overnight. Look
for a MVFR stratus deck to begin filling in around/after midnight.
These should lift back into VFR territory (with possibly CLL being
the exception) as the morning wears on Thursday. Look for scattered
showers to begin developing north & west of the US59-I69 corridor
later in the morning. 47

&&

[Stratton20]

12z Euro has widespread 1-4 inches over the next 10 days

[don]

18Z HRRR showing a potent MCS with some discreet cells developing ahead of the line.Timeline looks to be late tomorrow night into Friday morning.

[Cpv17]

18Z HRRR showing a potent MCS with some discreet cells developing ahead of the line.Timeline looks to be late tomorrow night into Friday morning.

Screenshot 2023-04-19 at 15-10-13 Models HRRR — Pivotal Weather.pngScreenshot 2023-04-19 at 15-10-35 Models HRRR — Pivotal Weather.pngScreenshot 2023-04-19 at 15-10-46 Models HRRR — Pivotal Weather.png

Hopefully some redevelopment Friday afternoon/evening for the western parts of the area. That doesn’t look too promising for me but it’s early and I’m expecting it to change.

[don]

Very thorough discussion from HGX this afternoon regarding our severe weather potential.

LONG TERM...
(Thursday Night through next Tuesday)
Issued at 354 PM CDT Wed Apr 19 2023

Key Messages:

① Strong to severe thunderstorms possible Thursday afternoon-Friday
morning

② Main hazards will be damaging winds, large hail, and locally heavy
rainfall

③ Frontal passage on Friday afternoon trending drier

④ Breezy northerly winds behind the front going into Friday night

⑤ Pleasant and dry Saturday followed by quickly returning rain
chances on Sunday

Before we get into the nitty-gritty of the Thursday night/Friday
morning action, let`s lay out the synoptic setup (this will
backtrack a bit into the short term period). Going into late
Thursday, an upper level trough with an embedded upper level low
will be gradually progressing eastward across the Northern Plains.
At the surface, an area of low pressure will be moving
northeastward towards the Great Lakes with an associated cold
front stretching down into North Texas. Showers and thunderstorms
will begin developing out ahead of this front on Thursday
afternoon and drift into Southeast Texas. With a solid axis of
instability with CAPE values up to (and sometimes exceeding
2000-2500 J/kg), 700mb-500mb lapse rates of ~7.0-7.5°C/km, and
40-50 kts of 0-6km bulk shear, the environment will be favorable
for some of these storms to become strong to severe. The main
hazards will be damaging winds, large hail, and locally heavy
rainfall. In the afternoon/evening hours of Thursday, this severe
threat is mainly up north around the Brazos Valley area. The
threat area shifts southward going into Thursday night/Friday
morning.

The 12Z HREF members have consensus on a MCS (Mesoscale Convective
System) developing as the discrete cells from the afternoon/evening
consolidate into a linear mode as nighttime falls. The environment
is fairly favorable for MCS development (shout-out to COMET modules
for the quick refresher). We`ll have a shortwave trough embedded
in the flow aloft moving in Thursday night (wrapping around the
south side of the main upper level trough) along with a subsequent
vort max moving into the Texas panhandle, a 30-40 kt LLJ
streaming in from the Gulf providing plenty of moisture
convergence along the frontal boundary, and a weak to moderate
westerly-ish (SW to NE) oriented upper-level jet. Long story
short, the model reflectivity from the 12Z hi-res guidance is
certainly supported by the environment. The timing of this is
still in question, but in general expect a timeframe of between
Thursday evening and early Friday morning for the line of storms
to push through.

The main caveat about a MCS pushing through overnight on Thursday is
how it`ll impact our chances for storms on Friday as the cold front
pushes through. Well if the 12Z hi-res guidance is right about our
MCS scenario with the line of storms pushing off the coast early
Friday morning, then there has to be a fairly decent cold pool
providing the forcing to keep this line chugging along. That would
stabilize ("work over") the environment, so if you check out the
12Z NAM or the 18Z HRRR, you`ll see that there`s no convection
depicted along the frontal boundary. That`s not to say that there
absolutely won`t be any development...I must include another
caveat that we`ll still have the instability and steep mid-level
lapse rates in place that would give us the chance of strong to
severe storms if anything manages to develop along the front
Friday afternoon like the FV3 depicts. The main hazards would be
the same as from Thursday: damaging winds, large hail, and locally
heavy rainfall. All that being said, we have growing confidence
that our severe storm threat will conclude Friday morning.

As far as forecast rainfall totals go, we`re expecting most
locations to see around 0.75"-1.50" of rain with isolated higher
amounts. Some of the 12Z HREF members are pinging totals above
2-3" where strong storms develop. There is a marginal risk of
excessive rainfall for portions of Southeast Texas on both
Thursday and Friday. We`re not expecting the line of storms to
stall, so it`ll just be a matter of monitoring rain rates in any
of the stronger storms where they develop. Widespread flooding is
NOT a concern, but some water collecting in low-lying areas and
ponding on some roadways is not out of the question. Continue to
monitor the forecast and be sure have multiple ways of receiving
alerts, especially on Thursday night.

[don]

0Z HRRR with the MCS moving through late tomorrow night.With some discreet cells developing during the evening.

[DoctorMu]

It's a definite maybe for rain tomorrow night in CLL. Models vary. 0.2 in to 2.5 inches.

The setup on the Mesos is close.

[DoctorMu]

As Don was alluding there is more shear in the UL trough tomorrow than the last system, which was more straight line winds. A chance of hail. I better mow the law tomorrow before we get some action.

[Iceresistance]

I nearly got hit with several tornadoes, they missed me to the north

[don]

SPC regarding the MCS stating a higher severe level risk may be needed tonight.

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1256 AM CDT Thu Apr 20 2023

Valid 201200Z - 211200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM CENTRAL TX
INTO THE MID MS VALLEY...

...SUMMARY...
Scattered severe thunderstorms capable of hail and severe gusts are
possible from parts of mid Mississippi Valley southwestward into the
Ark-La-Tex and central Texas this afternoon and tonight.

...Synopsis...
A longwave upper trough will deepen over the central CONUS today.
Within the larger-scale trough, one shortwave will move from the
central Plains toward the upper Great Lakes, while another will move
into the southern Plains tonight. A surface low will propagate
east-northeastward toward the upper Midwest, as a cold front sweeps
through the Plains and eventually the Ozarks.

...Southern Plains into the ArkLaTex...
Widely scattered thunderstorm development is expected this afternoon
along a southeastward-moving cold front from parts of Texas toward
the Ozark Plateau. Moderate to locally strong buoyancy will support
intense updrafts, especially along the Texas portion of the front,
though deep-layer shear may be somewhat marginal for much of the
day. Very large hail will be the initial threat, with some potential
for upscale growth this evening and a corresponding risk of
severe/damaging gusts. Low-level flow/shear across TX is expected to
remain rather modest, but may be sufficient for a threat of a
tornado or two with any sustained supercells.

Prefrontal diurnal development will be possible from east-central
into southeast TX within a weakly capped environment, with the
strongest cells in this region capable of hail, locally damaging
gusts, and possibly a tornado. Later tonight, one or more
thunderstorm clusters may move toward the upper TX Gulf Coast, with
a risk of damaging gusts, isolated hail, and possibly a brief
tornado or two.

Uncertainty remains regarding the timing of the cold front across
Texas, and the magnitude of the severe threat late tonight with any
upscale growth toward the Gulf Coast. Depending on shorter-term
observational and guidance trends, higher hail and/or wind
probabilities may eventually be needed.

[tireman4]

FXUS64 KHGX 201201
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
701 AM CDT Thu Apr 20 2023

...New AVIATION...

.SHORT TERM...
(Today through Friday Night)
Issued at 434 AM CDT Thu Apr 20 2023

After a mostly quiet/warm/humid start to the day, the forecast looks
to become much more active by late this afternoon into tonight/over-
night. Not much going on right now...but as the low-level jet begins
setting up, isolated WAA showers could develop over our western CWA.
Otherwise, not too many changes from the previous forecasts with the
set up of the larger scale pattern by this afternoon/tonight. Broad/
deep upper level troughing over the central CONUS will help with the
development of a strong surface low which will then help drag a cold
front down from the Southern Plains. But ahead of this boundary, pre
frontal activity may be possible given the weak capping and abundant
daytime heating. Strong to severe discrete cells could develop main-
ly across our northern counties (including the Brazos Valley). Large
hail and damaging winds should be the main threat.

Heading into the evening/overnight hours...this next round of storms
should be with the aforementioned cold front as it begin moving into
the region. Models continue to indicate the development of an MCS as
the earlier storms sort of consolidate/merge during the evening. The
environment over SE TX is progged to remain favorable for strong and
severe storms as well as locally heavy rains (even with the forecast
of a rather progressive movement of the storms) as these storms move
S/SE across the CWA. We`re still looking for large hail and damaging
winds as the main threats with these nighttime storms, but an isola-
ted tornado or two cannot be ruled out. As for rainfall...totals for
the event should average from 1-2 inches with locally higher amounts
possible from 3-5 inches. The heaviest rains should be off the coast
on/around sunrise Fri morning.

And so for the passage of the cold front on Fri...not expecting much
in terms of precipitation as the air mass will likely be quite work-
ed over. Did leave some very low POPs in the grids, mainly closer to
the coast. But with much drier/cooler air filtering down into the FA
overnight lows Fri night could range from the upper 40s to lower 50s
north...mid to upper 50s for the central/southern counties...and the
lower to mid 60s at the beaches. 41

&&

.LONG TERM...
(Saturday through Wednesday)
Issued at 434 AM CDT Thu Apr 20 2023

Saturday might end up being the only quiet weather day in the long
term forecast as a series of waves/disturbances bring periods of
showers and thunderstorms. Starting with Saturday, mostly clear to
clear skies in the morning (probably excellent to view the ISS
moving across the Houston area from south to northeast beginning
at 516 AM and lasting for four minutes) will become partly cloudy
as the day progresses with high temperatures in the upper 70s to
around 80. Rain begins to enter the area as early as Saturday evening
but more likely late Saturday night through Sunday (better chances
closer to the Matagorda Bay area and lower chances up north and northeast).
Low temperatures Saturday night will be in a mid 50s to lower 60s range,
and Sunday`s high temperatures will be in the low to mid 70s. Periods
of showers and thunderstorms will then be possible through the remainder
of this forecast period with a general/gradual warming trend (for lows,
Sunday night`s 50s/60s become 60s Monday night and 60s to around 70
Tuesday night; for highs, Monday`s 70s become 70s/80s on Tuesday and
Wednesday). 42

&&

.AVIATION...
(12Z TAF Issuance)
Issued at 701 AM CDT Thu Apr 20 2023

Patchy MVFR CIGS this morning will likely remain as such through
the early afternoon even as onshore winds strengthen. There will
chances of isolated to widely scattered storm developing by this
afternoon (~21Z) across our north/northwestern counties ahead of
the cold front. These chances for strong to severe thunderstorms
are expected to increase markedly by this evening with the arri-
val and passage of the pre-frontal trough/MCS from the NW to SE.
The timing of these storms has been a slight point of contention
with near term guidance (+/- a couple of hours), but the overall
consensus has the bulk of storms moving near CLL around 02Z-04Z,
then proceeding to IAH around 05-08Z, and then to the coast just
after/around 12Z. Will be interesting to see how the next couple
of runs resolve the timing. 41

&&

.MARINE...
Issued at 434 AM CDT Thu Apr 20 2023

A mainly moderate onshore flow and elevated seas are expected to persist
through Friday. There will be a chance of thunderstorms (some potentially
strong to severe) mainly late tonight into Friday morning as a cold
front works its way toward the area. Caution and/or advisory flags can
be expected at times. Moderate to occasionally strong north then northeast
then east winds and elevated seas will prevail over the weekend. East
winds on Monday become southeast on Monday night with this onshore flow
then expected to persist for the first half of the week. Periods of
showers and thunderstorms are back in the forecast beginning on Saturday
night or Sunday morning and continuing Tuesday evening. 42

&&

.CLIMATE...
Issued at 434 AM CDT Thu Apr 20 2023

For today`s/tonight`s event, here are some daily rainfall records
for our five major climate sites.

College Station: Today (4/20) is 2.40" (1915)
Tomorrow (4/21) is 3.43" (1921)

City of Houston: Today (4/20) is 2.70" (1985)
Tomorrow (4/21) is 3.76" (1890)

Houston Hobby: Today (4/20) is 3.62" (1977)
Tomorrow (4/21) is 1.54" (2018)

Galveston: Today (4/20) is 5.09" (1977)
Tomorrow (4/21) is 2.02" (1890)

Palacios: Today (4/20) is 2.55" (1985)
Tomorrow (4/21) is 2.20" (2006)

42

&&

.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL) 80 65 77 52 / 60 70 30 0
Houston (IAH) 82 68 82 57 / 40 70 40 0
Galveston (GLS) 79 70 80 65 / 20 80 60 10

&&

.HGX WATCHES/WARNINGS/ADVISORIES...
TX...High Rip Current Risk through this evening for TXZ436>439.

GM...Small Craft Should Exercise Caution through this evening for
GMZ330-335-350-355-370-375.

&&

$$

SHORT TERM...Batiste
LONG TERM....Batiste
AVIATION...41
MARINE...Batiste

[tireman4]

Severe Weather Outlook

[don]

The latest HRRR model run on tonight's MCS.

[Cromagnum]

Why do I get the feeling NW area is gonna get soaked, and the southern half is gonna get a quick broken line like usual?

[don]

Watch may be issued soon for semi discreet cells that look to form this afternoon.Before the MCS forms tonight.

Mesoscale Discussion 0573
NWS Storm Prediction Center Norman OK
1208 PM CDT Thu Apr 20 2023

Areas affected...Portions of eastern Texas and northwestern
Louisiana

Concerning...Severe potential...Watch possible

Valid 201708Z - 201915Z

Probability of Watch Issuance...60 percent

SUMMARY...Scattered gusty winds and severe hail possible through
early afternoon. This area will be monitored for a potential watch.

DISCUSSION...An area of pre-frontal clustered cell development is
expected across portions of eastern Texas and northwestern
Louisiana. Breaks in mid-level cloud cover have allowed daytime
heating, with around 2000-3000 J/kg MLCAPE noted in surface
objective analysis. Shear profiles are marginal, around 20-30 kts
from VAD profiles at SHV and FWS. Morning 16Z RAOBs from FWD reveals
deepening moisture and eroding inhibition at the base of an elevated
mixed layer, with steep mid-level lapse rates around 8 C/km. Given
the marginal shear for organization and steep lapse rates, severe
hail and gusty winds will be possible with storms that develop ahead
of the approaching cold front. This area is being monitored for a
potential watch.

[tireman4]

.AVIATION...
(18Z TAF Issuance)
Issued at 1232 PM CDT Thu Apr 20 2023

Southerly winds with gusts up to 20 knots at times will prevail
into the evening hours along with MVFR to VFR ceilings.
Showers/storms will begin popping up around our northwestern sites
this afternoon, and have already begun to do so around UTS/CXO.
The main impacts will be in the overnight hours when a line of
strong thunderstorms pushes through the region. Currently, timing
is set to around 01Z-04Z for northern sites, 05Z-08Z around the
Houston metro area sites, and 07Z-10Z for the coastal sites. Some
model guidance is trending faster and some are trending slower
with this line of storms, so be on the lookout for updates in
later TAF packages. Ceilings will decrease overnight with IFR
conditions expected through early Friday morning. There is also
potential for slightly reduced visibilities due to patchy fog
after the line of storms moves through as winds become light and
variable ahead of an approaching cold front. Conditions improve
after 16Z with ceilings lifting to MVFR, and the cold front itself
moves through in the afternoon hours. Expect gradually clearing
skies and northerly winds to follow in the wake of the front on
Friday afternoon.

Batiste