Great discussion:
Area Forecast Discussion
National Weather Service Houston/Galveston TX
340 PM CDT Mon Apr 19 2021
.DISCUSSION...
.SHORT TERM [Through Tuesday Night]...
The quiet weather pattern continues today thanks to surface high
pressure sitting over Southeast Texas. As the high slides off to
the east, winds will transition from easterly to southeasterly.
Temperatures today will be slightly below normal with highs in the
low-to-mid 70s. For tonight, temperatures will be a bit warmer
than the previous night since CAA has come to an end. Overcast
clouds moving in overnight will initially keep temperatures on the
mild side, but these will depart after midnight allowing
temperatures to drop into the low 50s. It`s worth mentioning that
some hi-res models are indicating isolated rain showers developing
after sunset due to upper-level divergence from a departing jet
streak, but with plentiful dry air in the lowest 3km above the
surface, any precipitation that falls will evaporate before it
reaches the ground. Thus, PoPs will remain less than 10%
throughout the night.
Southwesterly winds kick in and skies clear out on Tuesday morning
as surface high pressure continues its eastward trek. Resultingly,
afternoon temperatures will be slightly warmer with highs
approaching the 80 degree mark at most locations. The southwesterly
winds will gradually decrease our PW values down into the 0.6 inch
to 0.8 inch range, so our moisture profile looks relatively slim
ahead of our next cold front that will pass through the region on
Tuesday afternoon/evening. Since there will be dry air out ahead
of the front, models are in agreement that this will be a dry
FROPA. With sufficient CAA persisting through Tuesday night,
temperatures will be at least 10-15 degrees below normal with lows
ranging from the low 40s to the low 50s across Southeast Texas.
.LONG TERM [Wednesday Through Monday]...
Wednesday morning puts us in a decidedly post-frontal environment,
as a surface high sits over the Red River Valley. The cold
advection does not look particularly strong, but we also weren`t
starting from the warmest, most humid place either, so Wednesday
still looks to be unseasonably cool and dry. Of course, we are
now arriving in the time of year where your reaction to that
sentence depends wholly on how you feel about heat and humidity.
For this Wisconsin-raised forecaster, a sunny day with highs in
the upper 60s to 70s with dewpoints ranging from the upper 30s to
lower 50s sounds downright wonderful! But your mileage may vary.
Spring being a season of transition, this setup won`t stay static,
particularly since the flow aloft is relatively zonal. Wednesday
night will see winds veer to become more easterly, picking up a
connection with more humid Gulf air. Meanwhile, a surface low
should be starting to spin up over New Mexico underneath what
looks like it will be a pretty robust shortwave trough dropping
off the Rockies. This will keep the pressure gradient fairly
tight, for the back half of the week, aiding the return of deep
moisture over the area.
Depending on how quick moisture return is, we could see some low
chances for showers as early as late Thursday afternoon down by
Matagorda Bay closer to the deep moisture axis. However, by Friday
morning, the potential for showers will spread across our area.
Depending on how significant capping is, we could see some
afternoon convection on Friday, particularly if we see some pre-
frontal surface troughing as a focus mechanism, as hinted at in
at least some of the guidance. The other focus will come later
Friday night into Saturday as the front sweeps through. Though the
timing is not best, there looks to be enough instability that we
could sustain some existing, organized severe weather for some
time right on the front. SPC does have the western half or so of
our area in what is the equivalent of a slight risk area for
Friday night, and that seems a reasonable forecast. For what is a
Day 5 forecast, there`s only so much that can be divined from what
will eventually be driven by mesoscale details.
Speaking of mesoscale details, the GFS has a party with them...or
at least the best approximations of them it can resolve with the
frontal convection. There`s really zero point in trying to
speculate on details or specific timing, but it`s probably worth
being on the lookout for some kinks in the forecast as the front
rolls through.
Peering into early next week, there doesn`t appear to be much cold
advection behind the front to speak of, so this may well be a
situation where the increasingly powerful sun overwhelms any
potential cooling behind the front, and we actually end up with
warmer temperatures after the front passes. Indeed, that`s just
what I have in the forecast. My sweet, spring children, summer is
coming.