Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 05/12/17
the previous forecast discussion is below. STP
.SHORT TERM...valid for Fri and Sat...
Strong ridge aloft will bring hot and mainly dry weather through
Friday. Southwest flow aloft will deepen as the ridge axis shifts
gradually east, and this will allow for 700mb temps to rise to
near +10C, resulting in surface temps well into the 80s and near
90F in spots tomorrow.
Latest satellite and BLX radar show cumulus and some weak echoes
over our western mountains. Should see some convection spread
toward the Belts/Snowies by early evening along a lifting mid
level warm front. This activity will be weak and diminish quickly
with sunset. Latest HRRR shows activity spreading over our western
lower elevations but believe this to be overdone given a lack of
forcing and some mid level capping. More likely there will be
some increased cu coverage over the next few hours.
Slightly better chance of storms exists in our far west tomorrow
afternoon and evening as Pacific cold front emerges from central
MT. Stronger jet forcing and mid level baroclinicity will be to
our west, and the cold front arrives well after peak heating, so
will keep ts chances at slight. Main risks with any storms will be
gusty surface winds courtesy of steep low level lapse rates
driven by hot temps on Friday. Shower potential will spread east
and further away from the synoptic scale forcing through Friday
night. Will keep low pops to cover this, but it won`t amount to
much. Should also point out that the frontal passage itself will
usher in much cooler temps, with 850mb values near +25C Friday
afternoon falling to the single digits post-frontal. So, expect
brief W-NW wind gusts late Friday night with the fropa.
Saturday will be quite a bit cooler with highs ranging from the
mid 50s in our west to mid 70s in our east. Next shortwave in
southwest flow will bring a good chance of showers Saturday
afternoon and night. Surface temps will be much cooler, but with
some elevated instability feel that some embedded thunder is a
Will need to continue to watch river levels over the next few days
due to the hotter temps and increased mountain snow melt today
and Friday. A Flood Watch remains in effect for the Clarks Fork
from Belfry to Edgar. Other rivers will remain below flood stage
but should see the highest flows yet of the season over the
.LONG TERM...valid for Sun...Mon...Tue...Wed...Thu...
No major changes with this forecast package. Models remain in
good agreement on southwest flow dominating the Northern Rockies
through middle o next week. A strong Pacific trof will radiate impulses
of energy and moisture across the region. This will keep weather
unsettled and cool weather, with shower and thunderstorm potential
throughout the period. Temperatures will be in the 60s and 70s.
By midweek another lobe of low pressure develops and digs south
along back edge of the trof, reinforcing the established trof and
becoming the the main weather producer as a closed low within the
mean trof by Wednesday night. Models diverge on track of low
throughout life cycle to this point. Newest runs show GFS digging
closed low much further south, keeping best energy and precip
south of the area. This is a significant southward shift from
earlier model runs. ECMWF remains closer previous runs, with the
low shifting eastward across Wyoming, setting up a much wetter
period across the region beginning Thursday. Temperatures will
drop into the 50s and 60s from midweek onward, with influx of
cooler air associated with the low and increase precip and cloud
VFR conditions to prevail. Expect winds around KLVM to increase
during the afternoon up to 15 knots. Isold showers over high
terrain may result in localized brief obscurations. AAG
.PRELIMINARY POINT TEMP/POPS...
Fri Sat Sun Mon Tue Wed Thu
BIL 053/086 049/064 041/065 046/068 045/065 045/061 044/060
10/U 15/T 62/T 33/T 43/T 34/T 44/W
LVM 047/083 042/057 034/061 037/064 038/062 038/059 039/058
22/T 26/T 52/T 23/T 34/T 44/T 44/W
HDN 049/088 049/069 041/067 046/072 045/067 045/063 044/064
00/U 22/T 62/T 33/T 43/T 33/T 44/W
MLS 052/089 054/073 046/068 048/073 048/068 047/064 045/063
00/U 21/U 42/W 35/T 44/T 44/T 44/W
4BQ 048/088 050/074 044/068 045/076 047/069 045/063 043/062
00/U 21/U 41/B 44/T 43/T 34/T 44/W
BHK 046/083 052/074 044/067 044/071 046/067 044/061 040/060
00/U 20/U 41/B 34/T 44/T 44/T 44/W
SHR 044/086 047/068 039/064 041/070 042/064 041/060 039/057
00/U 22/T 52/T 33/T 44/T 43/T 45/W
Area Forecast Discussion
National Weather Service Austin/San Antonio TX
941 PM CDT Thu May 11 2017
Although new thunderstorms are developing along the pre-frontal
trough just east of the I-35 corridor near Waco, stable air left
behind by the storms that moved through Austin and our NE counties
should make development further south into our CWA difficult. A cell
that developed over Guadalupe County also quickly dissipated, so we
have removed all of the counties from the Severe Thunderstorm Watch
except for Lee County until 10 PM CDT just in case the cell there
that is currently sub-severe pulses up briefly. Aircraft soundings
from both AUS and SAT show a weak, but increasing cap at 600 mb (and
775 mb at AUS) behind the pre-frontal trough. Hi-res models continue
to trend towards lower convective coverage along and east of the
I-35 and I-37 corridors as the cold front approaches and moves
through these areas between Midnight and 4 am. Nevertheless, we will
maintain 20 POPs for these areas just in case a cell gets going,
which most likely would be south of the San Marcos and Austin Areas
due to greater CIN there leftover from our late afternoon storms. Any
cells that develop should be sub-severe, but some brief instances of
gusty winds and small hail will be possible. Winds behind the front
will become northwesterly increasing to 10-15 mph with gusts to 20-25
mph possible along the I-35 corridor tomorrow morning and afternoon
before subsiding late in the afternoon and evening hours.
.PREV DISCUSSION... /ISSUED 731 PM CDT Thu May 11 2017/
AVIATION.../00Z TAFS/CORRECTED FOR WINDS
Isolated thunderstorms in the vicinity of AUS are expected for the
next hour, so have included VCTS there and will amend as necessary if
further development with the cell over the terminal right now
occurs. A weak cap is beginning to develop between 600-650 mb at both
AUS and SAT that should help limit the potential for deep convection
from forming. In addition, the dryline/pre-frontal trough is also
beginning to move into the I-35 TAF sites, so that should help limit
convection as well. Winds over the next 1-2 hours will be a bit
tricky as they are veering to W-SW as the dryline/pre-frontal trough
moves through the I-35 sites, but models suggest winds will back to
S-SW by 2Z once the boundary passes. Upstream sites behind the
boundary are S-SW, so this backing of winds seems reasonable by 2Z.
Hi-res models are still suggesting that an isolated thunderstorm or
two may develop when the cold front moves through the I-35 TAF sites
around 5-6Z at AUS and 7-8Z at SAT/SSF, but for now only included
VCTS at AUS as the cap will likely be a bit stronger further south.
The timing of a front is a bit uncertain as a few hi-res models like
the HRRR speed it up an hour or two, so will amend changes to the
timing as necessary. A more delayed front would make a brief period
of MVFR ceilings and patchy fog more likely just ahead of the front
for the I-35 TAF sites, but for now have left all sites with a brief
period of SCT015 ceilings. Northwest winds behind the front will
eventually increase to 10-15 knots by mid-morning at all sites with
gusts to 20-25 knots possible at AUS and SAT through late afternoon.
PREV DISCUSSION... /ISSUED 553 PM CDT Thu May 11 2017/
Although midlevel lapse rates remain somewhat modest around 6.5-7 deg
C/km due to decent saturation between 650-800 mb, shear in excess of
40 knots has allowed a severe thunderstorm to develop over Travis
County. This cell has produced up to half dollar size hail, but is
beginning to weaken as it moves into eastern Williamson County. These
conditions will support the potential for severe thunderstorms over
the next few hours as the surface boundary/dryline eventually becomes
overtaken by a weak cold front to end the threat from west to east.
Hail to golf ball size will be the main threat with these storms, but
damaging winds to 60 mph will also be possible. Thus, the Severe
Thunderstorm Watch has been extended to include Williamson, Travis,
Hays, Bastrop, Lee, and Fayette Counties in addition to Lee County
until 10 PM CDT. After coordinating with the Fort Worth WFO, Bell
County will not be in the watch as the cell in eastern Williamson
County should move into Milam County with development not currently
expected over Bell County. Additional isolated thunderstorms may be
possible later tonight after the watch expires when the cold front
moves into the region, but hi-res model trends continue to decrease
the coverage of these storms and they should generally be sub-severe.
PREV DISCUSSION... /ISSUED 248 PM CDT Thu May 11 2017/
SHORT TERM (Tonight through Friday Night)...
Scattered showers and isolated thunderstorms are ongoing across
parts of South Central Texas east of a dryline extending from Mason
to Eagle Pass. An upper level trough will move east across the
Central/Southern Plains dragging the dryline a little further east
this evening, before a cold front overtakes it during the overnight
hours. Upward forcing ahead of these features will keep showers and
thunderstorms in the forecast this evening into the overnight hours.
The best moisture, instability and dynamics will be this afternoon
into evening resulting in the highest POPs. Still some potential for
strong to severe storms especially along and east of Highway 281
where CAPES of near 2000 J/Kg and 0-6 KM shear of 40 KTs reside. Have
issued a Severe Thunderstorm Watch for Lee County until 10 PM CDT.
However, cloud cover may serve to maintain a cap to inhibit deeper
convection. Moisture will decrease overnight as the front moves
through and go only slight chances POPs along and east of I-35. For
Friday into Friday night, ridging at the surface and aloft builds
into our area as the upper level trough moves away. A drier airmass
results in cooler nights, though minimal cold advection allows for
near normal daytime temperatures.
LONG TERM (Saturday through Thursday)...
Upper level ridging drifts over our area as a long wave upper level
trough moves into the western states while the surface ridge moves
off to the east this weekend. Moisture slowly returns bringing
warmer low temperatures. Sufficient moisture and upslope flow will
generate isolated showers and thunderstorms over the Serranias del
Burro in the afternoons, however, steering flow will keep them west
of our area. The trough remains over the western states next week as
short wave troughs rotate through it with a moist lower to mid level
flow over our area. Expect periods of showers and thunderstorms near
the Rio Grande on Monday due to storms coming off the Serranias del
Burro and areawide Tuesday through Thursday from the short waves and
possible dryline intrusions. It will feel muggy with dewpoints in the
upper 60s to lower 70s much of the week.
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 64 83 61 86 62 / 40 0 0 0 0
Austin Bergstrom Intl Airport 64 84 59 86 60 / 40 0 0 0 0
New Braunfels Muni Airport 64 85 59 88 61 / 30 0 0 0 0
Burnet Muni Airport 60 80 57 84 60 / 10 0 0 0 0
Del Rio Intl Airport 63 89 62 90 66 / - 0 0 0 0
Georgetown Muni Airport 62 81 58 84 61 / 20 0 0 0 0
Hondo Muni Airport 63 87 58 89 60 / 10 0 0 0 0
San Marcos Muni Airport 64 85 59 86 60 / 40 0 0 0 0
La Grange - Fayette Regional 67 85 60 85 62 / 50 - 0 0 0
San Antonio Intl Airport 65 85 62 88 63 / 20 0 0 0 0
Stinson Muni Airport 66 87 62 90 63 / 20 0 0 0 0
Public Service/Data Collection...33
AREA FORECAST DISCUSSION
National Weather Service New Orleans LA
331 PM CDT Thu May 11 2017
An upper level low is currently moving through the southern towards
the Lower Mississippi Valley. In response to this, the upper ridge
of high pressure that has been spread across the Central Gulf Coast
for the last several days is shifting east and suppressing south. A
surface trough is developing within the base of the upper trough and
will move east into Louisiana tonight. Models are in good agreement
that convection associated with this system will begin moving into
portions of the CWA early Friday morning but differ in how far east
by sunrise. The GFS suggests all the way to St. Bernard Parish while
the ECMWF is less bullish. The HRRR is somewhat in between the 2
and likely closer to what will occur.
Lowering heights in the column from the upper trough moving in will
cool mid and upper levels. Model soundings are showing steeper mid
level lapse rates and CAPE values (ML~1000j/kg) near previous runs.
Winds in the lower levels still look weak at around 20-30 knots, but
mid and upper level winds will be strong enough to result in
sufficient overall shear to support a few severe thunderstorms.
Instability will be limited in the lower levels and could be even
lower at points further above if cloud cover ahead of convection
hinders destabilization. Overall, the probability for severe weather
is Marginal with gusty/damaging winds and hail as the main
Once that front sweeps through, looking at a nice weekend with no
rainfall and at slightly below becoming near normal temperatures
through at least early next week.
Lower level moisture will continue to move in from the south on
southerly winds this afternoon through tonight. Visible satellite
imagery showed a scattered cumulus field and a thin cirrus shield
moving from west to east over all of our taf sites. VFR conditions
will come to an end by 06z Friday as ceilings between 1500 and 2000
develop and persist at times through 18z Friday. Some restrictions
to visibility at KMCB and KHUM between 09 and 13z may occur Friday
morning. Convection will affect most taf sites after 12z Friday.
Have inserted prob30 after 12 Friday to cover this weather feature.
Surface low over central Oklahoma will continue to push east and
drag a cold front to east Texas tonight and across the forecast area
late Friday afternoon and evening. Surface winds will respond over
the coastal waters by increasing to 15 knots tonight and become more
southwesterly on Friday. Winds could occasionally increase up to 20
knots at times on Friday before the frontal passage. Caution
headlines may be used by that time frame. Once the cold front
passes, winds will shift to a northwest direction and actually ease
a bit to 10-15kt and gradually back into a rather weak regime by
Sunday. High pressure settles over the north central gulf Sunday
into the start of the new work week and gradually moves east. 18
DSS code: Blue.
Activities: River flood warnings.
Decision Support Services (DSS) Code Legend
Green = No weather impacts that require action.
Blue = Long-fused watch, warning, or advisory in effect or
high visibility event.
Yellow = Heightened impacts with short-fused watch, warning or
advisory issuances; radar support.
Orange = High Impacts; Slight to Moderate risk severe; nearby
tropical events; HazMat or other large episodes.
Red = Full engagement for Moderate risk of severe and/or direct
tropical threats; Events of National Significance.
.PRELIMINARY POINT TEMPS/POPS...
MCB 65 80 60 79 / 20 80 40 0
BTR 68 82 63 80 / 20 80 40 0
ASD 67 82 65 82 / 10 80 50 10
MSY 69 81 65 81 / 10 80 40 10
GPT 70 78 65 81 / 10 80 40 10
PQL 66 80 65 82 / 10 80 50 10