Area Forecast Discussion
Issued by NWS Houston/Galveston, TX

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FXUS64 KHGX 310434

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1134 PM CDT MON MAY 30 2016

Cirrus continues to overspread the region and feel the clouds will
limit fog potential tonight. Winds are generally light and should
remain light tonight. Things get a bit more interesting on Tuesday
as a strong short wave over northern Mexico approaches SE TX. The
disturbance should begin to generate showers over the SW areas by
mid morning and then gradually overspread all of SE TX by
afternoon. Forecast soundings support this scenario with PW values
increasing to 1.80 inches during the afternoon. Have added
VCSH/VCTS for all TAF sites during the aftn/early evening. This is
supported by both the RAP and HRRR. MVFR ceilings expected to
develop at TAF sites after 01/0600z. 43



Evening satellite imagery shows anvil cirrus from convection over
northern Mexico drifting eastward across Southeast Texas this
evening. Have increased cloud cover and bumped up overnight low
temperatures a degree or two (generally low to mid 70s) in
response. Expect a generally dry night with weak mid-level
subsidence over the area in the wake of a shortwave trough just
west of the lower Mississippi River per water vapor imagery. No
other changes made to the ongoing forecast.



VFR conditions expected to prevail through 06z. Another night of
cirrus clouds is expected as convection over N Mexico moves into
South Texas. The high clouds will once again limit the fog threat
overnight. A brief window of MVFR ceilings will be possible early
Tuesday morning before clouds begin to scatter out. PW values
reach 1.85 inches at KCLL tomorrow aftn so added a VCSH for both
KCLL and KUTS as forecast soundings show no capping and a
convective temp in the mid 80s. 43


Morning convection has left lingering cloud cover over much of SE
Texas this afternoon. This has limited day time heating and likely
keep Houston IAH from reaching 90F for a maximum temperature
again. Only one more day for Houston IAH to reach 90F in May 2016
and it`s not looking likely. The thunderstorm activity that did
move through Matagorda Bay indicates a weaker cap over the region
and perhaps less subsidence. Based on upper air analysis 500mb
heights have dropped below 588dm mainly due to a weak short wave
over the Ozarks on water vapor satellite imagery. Water vapor
imagery shows the upper level low over the Desert SW which will
begin to slowly move east through the week.

Short Term...Tuesday/Wednesday
Upper level low over the Desert SW will slowly move east across
the S Rockies through Wednesday night. This will allow for height
falls downstream of the trough over much of Texas and allow for
the upper level jet to increase. This will essentially increase
large scale lift over much of Texas which will weaken capping and
replace any subsidence. Overall think there will be more of a
severe weather threat given increase jet stream winds supporting
decent deep layer shear of 30 kts. CAPE should be around 2000-3000
J/kg over a large area. The concern will be for possibly a few
strong/severe storms over western parts of SE Texas but more so
for storms to develop over C Texas and move into the region. Low
level shear does not look strong so mainly have
pulse/multicellular convection that could organize into weak bow
segments in a squall line. There will be a frontal boundary that
slides into Texas late Wednesday into Thursday but the primary
lift will be from diffluence aloft and gentle up-slope through the
Hill Country into W Texas. Storm motions will be from the west so
expect the possibility for storms to move into the area from C
Texas. Moisture will be increasing over the area so 1.7-2.0 inches
of precipitable water can be expected well through the week.
Overall threats from storms will be hail and downburst winds with
heavy rainfall. Highest rainfall amounts will be expected
Wednesday of these two days.

Days 4-6...Thursday/Friday/Saturday
This will be the main time frame of concern for heavy rainfall and
the potential for more flash flooding and prolonged river
flooding. We know people are growing weary of hearing this and
tired of the flooding, but the reality is of a growing potential
for more rainfall. Upper level low reaches west Texas on Thursday
which support diffluence and increasing large scale ascent over
much of Texas. Widespread thunderstorm activity will be expected.
Given precipitable water values around 1.80-2.0 inches through
this time period and a slow moving upper level trough, heavy
rainfall will be the main threat with less of a threat for hail or
downburst winds. Deep layer shear weakens and storm motions also
become less than 20 knots over much of the area. This means storms
may be very efficient in producing heavy rainfall. For this time
frame there may be 2-3 inches of rainfall area wide but still hard
to pinpoint locations. Rainfall amounts will be dependent on where
any frontal boundaries move into the area and stall. Mesoscale
processes with outflow boundary collisions and cell mergers will
also support localized higher amounts above 4 inches. Depending
upon runoff and any additional rainfall Tuesday and Wednesday, a
flash flood watch may be needed for the end of the week. The upper
level low is expected to possibly stall over the area through
early next week. This will keep thunderstorm chances in the
forecast. The low should weaken but even day time heating may be
enough to produce thunderstorms with heavy rainfall Sunday into
Monday. A stronger frontal boundary may push into SE Texas Sunday
into Monday. I hesitate to call this a cold front but that is what
it is technically. Possible that drier air could filter into the
region Monday which might end rain chances. There is low
confidence in any front getting this far south but the upper level
pattern supports it with a trough over the Great Lakes.


No issues with the coastal waters forecast these next few days as
high pressure remains in charge. The generally light/moderate on-
shore winds to prevail but we should begin to see speeds increase
some Tue night into Wed. This will be in response to the slow
approach of a strong upper level storm system from the
west...which will help to tighten the gradient over the area. At
this time the worst case for the offshore waters will be
Caution/SCEC flags for Wed/Thur. An unsettled wx pattern is
progged for the remainder of the week as a weak cold front stalls
aoa SE TX and interacts with the slow moving upper low. Not too
optimistic with FROPA into the Gulf until late into next weekend
(or if at all). In the meantime will keep with a light/moderate
onshore flow in the extended. 41


College Station (CLL)      71  85  71  82  69 /  20  30  30  60  70
Houston (IAH)              71  87  71  86  70 /  20  20  10  50  50
Galveston (GLS)            77  83  77  84  76 /  10  10  10  30  50




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