Area Forecast Discussion
Issued by NWS Brownsville, TX
FXUS64 KBRO 290008 AAA
Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
708 PM CDT SAT MAY 28 2016
.DISCUSSION...Updated for latest aviation discussion below.
.AVIATION...Other than the fly in the ointment of a thunderstorm
cluster showing signs of edging close to or just across the Rio
Grande near McAllen this evening, the forecast is fairly
straightforward and a continuation of the previous forecast with
only slight changes in the overnight period.
The thunderstorm cluster moving into eastern Nuevo Leon at 7 pm
may have enough oomph to reach McAllen (KMFE) with residual
thunder/lightning and light stratiform rain as it will be in a
race to sunset as well as increasingly capped atmosphere
especially across the Lower Valley. For now, added anvil/cirrus
shield at all terminals after 02/03Z but for KMFE put in a mid
level deck and VCTS which could end up being light TSRA even with
the precipitation being more "debris" than anything else. Did not
add to KHRL or KBRO thinking that similar to Friday evening much
of the activity will be gone by the time it reaches these
Thereafter, expect the usual pre-dawn MVFR ceilings and local MVFR
visibility with southeast winds lightening a bit even compared
with this morning. Decided to be a little more pessimistic on
ceilings through late morning before scattering things out to VFR,
lower near the coast than inland, for the remainder of the
afternoon. As for wind, a similar afternoon to today though
perhaps a tad less gusty as gradient relaxes a bit.
.PREV DISCUSSION... /issued 327 PM CDT SAT MAY 28 2016/
SHORT TERM (Tonight through Sunday Night):
Upper-level ridging has begun nosing into Deep South TX today with
500-mb heights analyzed at 588 dam. This should keep a lid on
precip chances through the short-term period. IR satellite showing
only very sparse convective activity, even over the Sierra Madre, at
this time. Even if anything does develop, steering flow is more
toward the north, which would take the storms mainly west of the
area. Weak disturbances in the mid-level flow could clip the far
western/northern part of the CWA...though model guidance suggesting
such disturbances would mainly be deflected north of the area by the
ridge. At any rate, will leave in 20-25% PoP out there through
midnight tonight with "silent 10`s" elsewhere.
Heat indices have "behaved" better today with the added cloud cover
slowing heating just a bit. Still seeing readings in the 105 range.
At the surface...high pressure ridging across the central Gulf and
surface thermal trough in the Mexican interior will continue to
bring warm and moist air into the area on moderate SE winds.
Not a great deal of change for Sunday. Upper ridge strengthens
slightly overhead so temps will be a couple degrees hotter, with
heat indices forecast to be in the 105-110 range across the area.
Models hinting at a weak short-wave disturbance to perhaps clip the
western counties again Sunday evening so will keep isolated showers
and storms in for those areas again.
At the beaches, high risk of rip currents is expected to continue
through at least early Sunday, yielding hazardous conditions for
poor swimmers who enter the water and swim offshore into the surf.
Will let oncoming shift re-evaluate this for possible extension
through the remainder of Sunday. Longer-period swell which has been
driving the risk has been more difficult to find in the wave data
from Buoy 020 of late.
LONG TERM (Monday through Saturday): Two 500 mb closed lows will
be positioned over the northern and southern Rockies on Monday. As
the northern closed low moves east into the upper Midwest on
Wednesday the southern closed low will open up and will push into
the south central Plains states around midweek with this trough
eventually pushing over the lower Miss River Valley late Fri. In
the wake of this trough passage a fairly high amplitude 500 mb
ridge axis will start building back in place for Sat and Sun
maintaining a drier and more stable atms over the RGV. At the
surface the passage of this 500 mb trough will push a pretty
decent cold front into south TX which could meander south of the
RGV pm Fri and will likely stay near or just south of the RGV into
the weekend. The best moisture advection ahead of this 500 mb
trough and associated cold front sets up for the period from Wed
through Fri of next week. So expect the best pops during the
latter half of this upcoming work week as the UVV increase ahead
of the trough axis and interacts with the better moisture values
The GFS and ECMWF models are in pretty good agreement in the timing
and the magnitude of the 500 mb trough axis that approaches and
moves through the area next week. Both models are in decent
agreement on the expected temps throughout the longer range period.
However bigger disagreements show up in the pops with the ECMWF
being much more bullish on pops bringing in chc/likely pops on Tues
which is much faster than the GFS which holds off on bringing in the
better pops until Thurs. A closer look at the ECMWF shows that the
reason for the much higher pops on Tues is that this model wants to
move a pretty strong 500 mb short wave over south TX which fires off
a conv complex that moves down across the RGV. The GFS does moves
some stronger 500 mb PVA over the region on Tues but does not appear
to reflect the stronger moisture advection indicated by the ECMWF.
Will go a little closer to the drier GFS early next week and will
then go closer to the wetter ECMWF later next week. Temps will be a
roughly 50/50 blend of the GFS and ECMWF numbers. Overall confidence
in the longer range wording is above average for the temps and only
average for the pops due to the timing differences shown by the
ECMWF and GFS.
MARINE: /Tonight through Sunday night/...Winds and seas over the
marine areas have been slower to subside than expected today. Wave
models did not handle the near-term seas especially well, so issued
SCA for winds on the Laguna and winds/seas for the Gulf waters
through 7PM tonight. Hand-edited wave grids for consistency. Winds
currently on a subsiding trend over the Gulf waters may briefly bump
back up to near 20 knots between about 03-09Z tonight, but
confidence in this not especially high so will not extend SCA at
this time. SCEC conditions will prevail overnight at a minimum,
though, and likely persist through much of Sunday as moderate to
occasionally strong SE flow prevails.
Memorial Day through Thursday night...The PGF will be fairly
strong during the first half of next week as the 500 mb troughs
move across the central plains states increasing the surface
troffing over the Midwest. This may push marine conditions along
the lower TX coastline in SCEC criteria through Wed. The PGF then
weakens some after Wed as the cold front pushes southwards into TX
allowing the seas to slacken some.
TX...High Rip Current Risk through Sunday morning for TXZ251-256-257.
GM...Small Craft Advisory for winds until 7 PM CDT this evening for
Small Craft Advisory until 7 PM CDT this evening for GMZ150-155-
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