April 2021

General Weather Discussions and Analysis
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don
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Re: April 2021

Post by don » Thu Apr 15, 2021 9:52 am

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These "noisy" setups with multiple small disturbances moving over the state can be sneaky sometimes... Mesoscale models are showing a thunderstorm complex developing in central Texas this afternoon and moving into the area his evening.SPC has upgraded portions of the area to a slight risk for today.Hail up to golfball size is possible today.


Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0749 AM CDT Thu Apr 15 2021

Valid 151300Z - 161200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PARTS OF
SOUTHWEST...CENTRAL AND SOUTHEAST TEXAS...

...SUMMARY...
Large hail will be the main threat with organized severe storms in
parts of southwest, central and southeast Texas, and more-isolated
potential eastward along the Gulf Coast.

...Synopsis...
In mid/upper levels, a hybrid Rex/omega blocking pattern is apparent
over western North America, with a high over BC, ridging
southwestward across the northeastern Pacific offshore from the West
Coast, and a cyclone over the Great Basin. A shortwave trough is
forecast to follow the curve around the southeast side of the BC
anticyclone while amplifying, moving from southern SK southwestward
toward the ID/NV border area by 12Z tomorrow. As that occurs, the
Great Basin low will devolve to an open-wave trough and accelerate
eastward across the CO/NM Rockies. Meanwhile, an even stronger
cyclone initially over Lake Huron will move east-southeastward over
the lower Great Lakes and northern Mid-Atlantic.

South of those cyclones, a belt of nearly zonal flow will persist,
from southern CA and northwestern MX across the Gulf Coast. One
embedded/weak perturbation -- evident in moisture-channel imagery
over the lower Mississippi Valley region -- will move eastward
across the Southeast today, likely with some convective
reinforcement/production of associated vorticity. The trough should
reach the GA Coast and northern/central FL by 00Z.

At the surface, 11Z analysis showed a cold front from eastern NC
through central GA, to a low near MSY. A marine/warm front extended
from the low east-southeastward across the northeastern Gulf, which
should move slowly northward to near the TBW and AAF areas today.
The combined frontal zone then extended west-southwestward from the
low to between PSX-CRP and west-northwestward near DRT. The front
should move slowly southward off the LA Coast, while remaining
quasistationary over south TX today. The western limb of the
boundary may move northwestward over the lower Pecos River region of
southwest TX tonight, as a dryline develops and retreats westward
between the front and the Rio Grande.

...West-central/southwest TX...
Episodes of widely scattered to scattered thunderstorms should
develop through the remainder of the morning and much of the
afternoon across this region, offering mainly large to very large
hail and isolated damaging wind. The greatest overall moisture/
instability and severe concern will be over the 15%/significant-
hail/categorical "slight risk" area. One or two dominant supercells
may emerge this afternoon from the broader area of convection and
persist into the evening over parts of central/southeast TX,
maintaining damaging-hail potential north of the surface front.

Support for the greatest hail threat over south TX will come from a
combination of frontal lift (both on the surface frontal zone and to
the north, above the surface), favorable lapse rates/deep buoyancy,
and deep shear suitable for supercells. Mostly shallow convection
has been building for several hours in northern Coahuila and
adjacent portions of southwest TX in and surrounding Val Verde
County. Persistent low-level convergence near the frontal zone will
encourage more of this activity to breach the EML-related cap over
the area, with resulting thunderstorms accessing favorable buoyancy.
MLCAPE around 2000-2500 J/kg is expected south of the front, with
MUCAPE ranging from around 2000 J/kg just north of the front to the
500-1000 J/kg range close to I-20.

Even for convection rooted north of the front, around 900-750 mb,
strong veering with height is expected from the inflow layer into
mid/upper levels. Strengthening upper-tropospheric flow will occur
as height gradient tightens southeast of the ejecting Great Basin
low/trough. These factors will contribute to effective-shear
magnitudes in the 50-70-kt range and effective SRH exceeding 200
J/kg -- more than sufficient for supercell potential. With a
substantial portion of CAPE in forecasting soundings occupying ideal
hail-growth layers, the threat exists for both high quantities of
hail and locally very large size, with the best-organized and most-
persistent cells. The main limiting factor to greater coverage will
be potential for eventual clustering of storms and resultant messy
modes. Potential for at least isolated severe hail may extend
northward across the Red River region this evening and tonight, as
elevated theta-e advection and increasing shear occur in the
mas-response zone ahead of the mid/upper perturbation.
...Gulf Coast...
An extensive area of convection is apparent over southern portions
of LA/MS/AL, in a zone of relatively maximized large-scale ascent
(DCVA and warm-advection) and frontal lift ahead of the leading
southern-stream shortwave trough. Isolated large hail and strong-
severe gusts will be possible as this activity moves eastward to
east-southeastward today. Additional development and a marginal/
conditional severe threat also may occur late in the period
(overnight) back toward southern LA and adjoining southeast TX,
north of the front.

Ahead of this activity, inland diurnal heating will be tempered by
cloud cover from the anvil canopy, though subtle heating and theta-e
advection should contribute some low-level destabilization, beneath
an area of 7-7/5 deg C/km 700-500-mb lapse rates. 35-45-kt
effective-shear magnitudes will favor sporadic storm organization,
though messy modes and lack of greater low-level shear will limit
both 1) duration of any supercells that can form, and 2) overall
coverage of severe potential.

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DoctorMu
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Re: April 2021

Post by DoctorMu » Thu Apr 15, 2021 10:32 am

Potential for showers along the front remnant near the coast today. Bigger chance tomorrow and tomorrow night along the next front. I'm going to call a bust on the disturbance approaching the Hill country as it moves past I-35. TWC is calling for late afternoon rain here in BCS. We'll see. Potential for hail, so I'd rather wait another day for rain.


FXUS64 KHGX 150911
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
411 AM CDT Thu Apr 15 2021

.SHORT TERM [Today Through Friday]...

The Southeast Texas area airmass will remain moist and occasionally
unstable today through Friday. The weak cold front now off the coast
will work its way back inland on Friday. This boundary in combination
with weak mid-level impulses in the mainly west flow aloft will bring
periods of rain with embedded showers and possible thunderstorms to
parts of the area. Brief locally heavy rainfall could occur again with
some of the stronger storms or where any training sets up in an isolated
spot or two. Some of the stronger storms will have the potential to
produce hail too. Also look for periods of mainly late night through
early morning fog that could require a Dense Fog Advisory. Cloudy to
mostly cloudy skies will help to keep today`s high temperatures on
the cooler side - mainly in the low to mid 70s. Friday`s winds coming
back around to the southeast and south will help to warm us back up
with some upper 70s to lower 80s generally along and to the west of
the I-45 corridor. 42

&&

.LONG TERM [Friday Night through Thursday]...

Our next cold front will be at our doorstep on Friday night as a
weak area of surface low pressure to the northeast continues to drag
the boundary through Central TX and into SE TX. Global models
continue to remain in fairly good agreement regarding the timing of
the fropa, with the boundary reaching the Brazos Valley just before
sunset, approaching the Houston metro prior to midnight, and
clearing the coast before daybreak on Saturday. Fueled by persistent
onshore winds on Friday, fairly robust moisture will be present in
the hours preceding the approach of the front, with the EC/GFS/NAM
all showing total PWs in the range of 1.75 to 2.0 in at most
locations by late afternoon. While shower activity should be well
underway ahead of the front`s approach, the advancing boundary
should provide sufficient lift to trigger more widespread showers
and thunderstorms overnight. Environment ahead of the the fropa
looks favorable to raise the possibility of a few stronger storms
developing, with SBCAPE values of around 1500-2000 J/kg, EBWD of 50-
60kts, and weak/minimal capping. SPC has included the northern half
of the area in a marginal risk area for severe weather during this
time. With the front slowing as it pushes offshore on Saturday,
rainfall over the bays/waters and along the coast is likely to
linger throughout the day. Additionally, the progression of the
prevailing upper jet streak will place the region within the its
favorable right front quadrant, which may allow for some additional
showers inland through the afternoon.

Moderate to strong northerlies will develop in the wake of the
departing cold front, which will help usher in a period of drier and
more seasonable weather for the area by late Saturday/early Sunday.
CAA/gradually clearing skies will allow for lows to dip into the
upper 40s to low 50s, while daytime highs should remain confined to
the upper 60s on Sunday. The approach of surface high pressure and
subsequent loss of advection will drive a gradual warming trend
through mid-week, with highs breaking into the lower 70s on Monday
and mid 70s on Tuesday. However, with reduced cloud cover and thus
more efficient nocturnal cooling, overnight lows should remain
comfortably in the 50s.

Onshore winds will return by late Wednesday as surface high pressure
drifts eastward, beginning a trend of increasing moisture which
should persist through the remainder of the week. By Wednesday and
Thursday, we will see highs return to the low 80s. Our next shot at
widespread precipitation may come towards the end of next week (late
Thursday/early Friday) with the potential approach of another
surface cold front.

Cady

Cpv17
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Re: April 2021

Post by Cpv17 » Thu Apr 15, 2021 11:00 am

I kinda think the rain chance for tomorrow is overdone. After looking at all the short range mesoscale models, I really don’t see much tomorrow for most of us.

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don
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Re: April 2021

Post by don » Thu Apr 15, 2021 11:14 am

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1132 AM CDT Thu Apr 15 2021

Valid 151630Z - 161200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THROUGH TONIGHT
FOR CENTRAL TX...AS WELL AS PARTS OF NORTHWEST AND SOUTHEAST TX...

...SUMMARY...
Isolated very large hail will be possible today with elevated
supercells, mainly across central Texas.

...Southern Plains through early Friday...
A mid-upper low over northern UT this morning will evolve into more
of an open wave and move eastward to the central High Plains by
early Friday. South of the low, embedded/subtle speed maxima will
eject eastward over TX, above a shallow cool air mass near the
surface. The embedded speed maxima, and associated enhancements to
low-level warm advection, are contributing to bouts of elevated
convection, the first of which is ongoing over central TX. Per the
12z DRT sounding, MUCAPE of 2000-3000 J/kg, midlevel lapse rates
near 8 C/km, and effective bulk shear near 50 kt (with somewhat
straight hodographs above the 850 mb level) are supporting splitting
supercells rooted in the 850-700 mb layer. Given the near-storm
environment, the strongest of these supercells will be capable of
producing hail near the size of tennis balls or baseballs, and
perhaps a few strong gusts will reach the surface with the southern
storms (closer to the surface front). There will also be some
possibility for a storm or two to persist through the afternoon from
central toward parts of southeast TX.

An additional round of elevated convection is expected overnight
from northwest/north central TX into OK as warm advection increases
in response to height falls preceding the midlevel trough
approaching the High Plains. This will support some additional
northward advection of moisture atop the frontal surface, as well as
northeastward spread of steeper midlevel lapse rates. Similar to
previous days, a few of these elevated storms could be supercells
with a localized threat for large hail.



..Thompson/Kerr.. 04/15/2021
Attachments
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Cromagnum
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Re: April 2021

Post by Cromagnum » Thu Apr 15, 2021 11:47 am

Awesome. My wife and her brother are driving right into the heart of that area of concern this afternoon.

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jasons2k
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Re: April 2021

Post by jasons2k » Thu Apr 15, 2021 12:27 pm

My rain chances for tomorrow got lowered to 60%

I hope this thing isn’t a bust.

Cromagnum
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Re: April 2021

Post by Cromagnum » Thu Apr 15, 2021 12:33 pm

jasons2k wrote:
Thu Apr 15, 2021 12:27 pm
My rain chances for tomorrow got lowered to 60%

I hope this thing isn’t a bust.
Down to 50% here too

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Re: April 2021

Post by Kingwood36 » Thu Apr 15, 2021 1:43 pm

I hope it doesn't rain Saturday night I have a gig outdoors. Any idea on what the wind is looking like sat night?

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don
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Re: April 2021

Post by don » Thu Apr 15, 2021 4:14 pm

The thunderstorm complex that the models showed earlier has developed and is now moving into southeast Texas riding the 290 corridor.

SPC says a watch is possible for the area.

mcd0391.gif


Mesoscale Discussion 0391
NWS Storm Prediction Center Norman OK
0455 PM CDT Thu Apr 15 2021

Areas affected...southeast Texas

Concerning...Severe potential...Watch possible

Valid 152155Z - 160030Z

Probability of Watch Issuance...40 percent

SUMMARY...A cluster of cells producing large hail may persist for a
few hours as it moves from central into southeast Texas. Watch
chances downstream will depend on storm coverage/intensity trends.

DISCUSSION...A long-lived cell just northeast of Austin TX as of
21:55Z continues to show severe hail potential. This cell is located
within the theta-e gradient just off the surface, and is utilizing
elevated instability on the order of 1500 J/kg. Given the
southeastward motion due to moderate westerlies aloft and rightward
propagation on the southern end of the cluster, this storm is in an
environment of favorable shear and storm relative inflow. While
gusty winds may also occur, damaging hail is the most likely threat.


Very little change environmentally is forecast over the next several
hours, suggesting a status-quo scenario. Flow at 850 mb may be
slightly weaker farther east.


..Jewell/Hart.. 04/15/2021[/b]

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DoctorMu
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Re: April 2021

Post by DoctorMu » Thu Apr 15, 2021 4:28 pm

Cromagnum wrote:
Thu Apr 15, 2021 12:33 pm
jasons2k wrote:
Thu Apr 15, 2021 12:27 pm
My rain chances for tomorrow got lowered to 60%

I hope this thing isn’t a bust.
Down to 50% here too
Supercell jailbreak through the I-35 barrier and headed toward BCS. May just hold together. Better mow the backyard quickly! lol

https://radar.weather.gov/?settings=v1_ ... fQ%3D%3D#/

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