May 2021:

General Weather Discussions and Analysis
Iceresistance
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The CPC is showing yet ANOTHER potential of heavy rain on May 20th!

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Cpv17
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don wrote: Thu May 13, 2021 8:55 am Next week looks very wet across the state as models are showing a trough becoming negatively tilted next week.Severe weather also looks to be a issue. But models are still not in agreement on where the main storm track will be. The GFS has the main upper level low in the panhandle and ejects it into the central plains.Which keeps the main storm track also north of here across North Texas and Oklahoma.While the EURO has the trough in the same general location it ejects the trough more to the south across the southern plains instead,which pushes many disturbances from central Texas into southeast Texas next week. We'll have to watch the trends to see how everything may play out over the next few days.
We’ll see if the GFS caves to the Euro again like last time.
Cpv17
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Well the 12z Euro is definitely wet for next week but nothing crazy. 2-4” for the whole week isn’t really a big deal but it’s still a few days away so it could easily change. Definitely nowhere near as wet as it was showing.
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jasons2k
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From Jeff:

Enjoy the current dry weather…as an extended period of wet weather is likely starting this weekend into much of next week.

Surface high pressure is starting to move east and a return to onshore flow and Gulf of Mexico moisture return will begin on Friday. An upper level storm system will move into the SW US this weekend and cut off from the main upper level flow aloft resulting in a series of disturbances moving across TX and interacting with the increasing moist air mass. The end result will be periods of showers and thunderstorms with some severe weather and heavy rainfall looking likely during he period from Sunday-Wednesday.

It is difficult to determine which days or times will be most likely for rainfall, but really any point from Sunday onward could see rounds of thunderstorms. Given increasing moisture levels and the slow motion of the “parent” storm system over the SW US, an extended period of a heavy rainfall threat and flooding will be possible over portions of C, N, and E TX into next week.

It will be important to monitor forecasts over the next few days as changes are likely along with an eventual better idea when episodes of storms can be expected.

Jeff Lindner
Iceresistance
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Could have easily one of the wettest Springs at this rate! Flooding seems possible from Tomorrow all the way up to the 21st! :shock:

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don
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The pattern setting up starting this weekend and possibly lasting for the next couple of weeks as multiple troughs coming from the west coast get trapped underneath a ridge of high pressure, and slowly move into the southern plains. This pattern is very similar to May 2015. The NWS has a good discussion this morning about the upcoming pattern.


LONG TERM [Saturday Night Through Friday]...

There`s good consensus for a shortwave trough to be passing
through Saturday night into Sunday - I have the highest PoPs for
now on Sunday afternoon, but the precise timing will be very
dependent on the timing of that trough. We should see a bit of a
lull after that trough moves out, but look for another shortwave
to bring another shot of showers and storms - for now, timed to
roll through Monday afternoon. Now, why are we seeing all these
shortwaves? Well, taking a look upstream, we are seeing lobes of
vorticity being shed off a closed upper low over the Desert
Southwest.

As we get more into next week, eventually we should see that low
drift more into our region and finally replace these lead
shortwaves as the main driver of our weather. Of course, these
closed upper lows drifting across the Southwest are notoriously
difficult to forecast, so...there is a certain amount of fuzziness
to all of this.

Now, while the specifics are tough, and as a result I have some
PoPs in place from Saturday night clear through Friday (yes,
another upper trough comes into the picture for the second half of
the week), there is at least relatively high confidence in the
idea that we will see multiple rounds of showers and thunderstorms
and without a strong front to push through, continued onshore flow
will keep feeding moist, unstable air into the area to reload the
atmosphere for each new disturbance. So, while precise timing,
severity, and rainfall intensity will be difficult to pin down
at long range, the general environment will support showers and
storms each day. The NBM exceedance probability for 24 hour QPF of
at least one inch is at least 20 percent in the area every day
from Sunday to Friday.

That said, I do want to point out a couple timeframes that stand
out to me. First is Sunday - this shortwave trough is pretty stout
is most all of the guidance (particularly the GFS). The 1 inch
exceedance probability is mentioned above, but there is even a
very low signal in the 6 inch exceedance probability. Now, a 1
percent chance of getting at least 6 inches of rain is not
particularly scary on an absolute scale - but that there is a
signal for that much rain at all, especially when we are mostly in
the domain of global models, is probably worth keeping an eye on.
We do find ourselves on the southern fringe of WPC`s marginal risk
area for excessive rain, and this seems reasonable. Depending on
model trends, that area may even need to spread a little bit
further south towards the coast.

The other timeframe I want to highlight is Tuesday (potentially
into Wednesday). This is when we`ll probably see the most
influence from the upper low before it shears out and gets drawn
into the northern stream. This would likely be one of our better
shots for severe weather if the timing is right/wrong. This is
also when, for example, the NBM QPF distribution maximizes for
heavy rain at KIAH. I wouldn`t guarantee these as the highest
impact periods of the week, but given the information available at
this time, those are the two standouts to me
.
Cpv17
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Looks like the GFS might have caved towards the Euro now. It’s much wetter now. Looks like the WPC isn’t sold yet though. They’re showing a lot less QPF than what the Euro and GFS are showing, especially south of I-10 where the WPC only has about 2-3” over the next 7 days. I believe they will adjust accordingly as the event draws near. The Euro and GFS are both showing about 4-6” widespread and I even think those totals are on the conservative side. I think with this setup you could see quite a bit more than that.
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don
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I think so too, a lot of this will be driven by mesoscale features that the global models cant detect accurately this far out due to their low resolution.I think upstream and downstream river flooding is going to be a issue this coming week due to the widespread coverage of rainfall over the state. The NWS has posted early rainfall amounts.Subject to change...
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don
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May be time to start watching the tropics as the GFS is starting to become more consistent with tropical mischief late next week.If anything were to develop in the gulf based on the long range pattern the models are showing, with a western trough in place it would probably head towards either Louisiana or Texas depending on how strong the east coast ridging is at the time.But nothing to be concerned about yet,just something to keep an eye on.
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TexasBreeze
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It sure looks wet next week! Been awhile since seeing across the board 50 + percentages of rain during the week!
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