Scientific Forecaster Discussion
fxus64 khgx 191442
Area forecast discussion
National Weather Service Houston/Galveston Texas
942 am CDT Tue Sep 19 2017
radar and satellite this morning show much less convective
activity this morning than yesterday morning around southeast
Texas. This is likely the result of subtle shortwave ridging over
the area, seen in analysis and water vapor imagery. Subsidence
from this ridging may be enough to suppress coverage of afternoon
convection, but seems unlikely to entirely defeat the emergence of
showers and storms. Though the GOES-16 tpw values are smaller than
yesterday, a large portion of the area is still around or above
2.0 inches, with the "driest" areas only dropping to 1.75 inches
or so. Rgb microphysics composites from GOES-16 also imply that
some greater vertical development may be beginning in some of the
developing cloud streets near the coast.
Long story short (too late!) - Though we may not see as much
shower and thunderstorm development as yesterday, some isolated
to scattered showers are still expected. Given the amount of
moisture present over a large portion of the area, a particularly
long-lived cell in the wrong spot could produce enough rainfall
for localized street flooding, in a manner somewhat typical for
Previous discussion... /issued 642 am CDT Tue Sep 19 2017/
radar shows a few showers off the coast that could affect klbx
and kgls but overall activity is less in coverage compared to
yesterday morning. GOES 16 10.3 to 3.9 micron difference channel
shows some patchy fog around Houston with more robust stratus
north of Houston. Obs confirm this with LIFR ceilings for most
areas north of Houston. Fog has been patchy in these areas wit
visibility ranging from 1/4 mile to 6 miles. Fog and stratus
should erode later this morning with showers possible for the
afternoon hours. Again shower coverage is not expected to be quite
like yesterday, most likely more widely scattered with an
isolated thunderstorm. Hi-res mesoscale models not showing much
thunderstorms so tafs will keep with vcsh for now, but could be
updated with vcts/tsra.
Previous discussion... /issued 348 am CDT Tue Sep 19 2017/
distinct moisture plume evident on the GOES-16 total precipitable
water image overhead of southeast Texas early this morning. Pws of
2.0 inches were across all but the far northern quarter of
counties where the pws fell to about 1.7 inches in Houston County.
The models show this moisture plume should remain overhead through
the mid afternoon period. The nambufr model forecast soundings
show the potential for thunderstorms with MUCAPE values 2000 to
2500 this afternoon. Could see gusty winds in the stronger storms
as an inverted v profile develops under 850 mb during the
afternoon. Also cold see isolated areas of locally heavy rainfall.
Even though the 2-inch pws are not significant when compared to
the historical pws for this time of the year, the k-index values
do reach 34 this afternoon. Do not think the coverage will be as
much as yesterday. The hrrr and Texas tech both show only isolated
coverage for the most part; although, the seabreeze and Bay
breeze combined with outflows should lead to scattered coverage
inland of the coastal counties.
Wednesday and possibly Thursday may see better coverage than today.
The global models depict an upper level shortwave trough will
move across the Southern Plains into southeast Texas. The models
then show the shortwave trough deepening over la into southeast
Texas on Thursday with a high pressure ridge building across the
mid MS valley into north and central Texas. The ridge should continue
to build on Friday as a deep layer upper level low pressure trough
deepens over The Rockies through Southern California. There was some
discrepancy as to how far east and south the upper ridge will be
on Thursday and Friday. By the weeknight, an upper low will form
near or over the lower MS valley area. This scenario should lead
to less shower and thunderstorm coverage over the forecast area.
The model solutions diverge next week over our area. With the
upper trough moving into the plains, do expect rain chances will
increase on Sunday and Monday.
in general, moderate southeast winds will persist through the end of
the week across the Upper Texas coast. Seas will remain around 3
feet as a result. Showers and thunderstorms will be possible along
the coast and inland with higher moisture over the region.
Preliminary point temps/pops...
College Station (cll) 93 75 93 75 91 / 20 10 20 10 40
Houston (iah) 90 76 90 75 89 / 30 10 40 20 30
Galveston (gls) 87 79 87 79 86 / 20 20 30 20 30