Area Forecast Discussion
Issued by NWS Dallas/Fort Worth, TX

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FXUS64 KFWD 171152 AAA

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
652 AM CDT Thu May 17 2018

/12Z TAFs/

VFR will prevail. Light northeast/east surface flow will gradually
veer, becoming southeasterly this afternoon.

Despite abundant sunshine and a humid air mass in place, a capping
inversion will preclude thunderstorm development today. Some
showers/thunderstorms may attempt to approach from the northwest,
but any activity should remain beyond the northwest cornerpost.
Afternoon thunderstorms along a West Texas dryline will have a
better chance to impact the TRACON early Friday morning and have
introduced VCSH to hint at this potential.



.SHORT TERM... /Issued 437 AM CDT Thu May 17 2018/
/Today and Tonight/

Northwest flow aloft will maintain the potential for two
additional convective invasions during the next 24 hours. The
first would begin this morning; the second would be late tonight
into early Friday morning.

A low-level jet has set up above the High Plains of West Texas and
the Texas Panhandle early this morning. VWP data from Amarillo
shows 50kts at 5kft AGL, but the 850mb winds are generally
30-40kts. Above a diffuse but enduring frontal boundary, gentle
moist upglide is ongoing. Although this area is currently cloud-
free, guidance remains convinced that an axis of elevated
convection will develop before daybreak from the eastern
Panhandles southward toward the Big Country. Steep mid-level lapse
rates should quickly intensify these convective elements. As the
low-level jet weakens later this morning, this activity would be
guided by the northwest flow toward the richer moisture downstream
across North Texas. However, the showers/storms would also be
entering an area that will remain adequately capped. Although the
extent of this convection (which has yet to develop) and its
resulting cold pool could help a complex to penetrate deeper into
North Texas, it appears the activity will remain confined to our
northwestern zones. While the surface layer will remain unstable
elsewhere, for the bulk of North and Central Texas, a lingering
cap and the absence of any surface focus should preclude
convective initiation during the day. Abundant sunshine will
result in unseasonably warm temperatures, and with a weak surface
wind field, an Ozone Action Day will be in effect today for the
Dallas/Fort Worth commuting area.

The morning convection will be well separated from a West Texas
dryline at peak heating today. Thunderstorms that develop along
the boundary in the western Texas Panhandle will surge down the
Plains, potentially reaching our western zones during the evening
hours. There is fairly good agreement among the convective-
allowing guidance that this will occur, but less consensus with
how widespread it will remain by the time in reaches North Texas.
If more widespread, a nocturnal MCS may remain connected to the
buoyant surface parcels downstream with an attendant wind threat.
These updrafts would be continually replenished with rich moisture
within the boundary layer, helping to overcoming increasing
inhibition farther east. But mid-level subsidence will attempt to
work against this, and the complex should weaken (though it may
still survive) as it approaches the Dallas/Fort Worth Metroplex
during the early morning hours Thursday.



.LONG TERM... /Issued 437 AM CDT Thu May 17 2018/
/Friday Through Wednesday/

In contrast to the past few days, the upper ridge over the
Southern Plains doesn`t appear it will be quite as strong as in
previous model runs. A shortwave will be transversing the crest of
the upper ridge right over North Texas to start the day Friday.
Short-range, high-resolution models and CAMS have all been
struggling not only with mesoscale features and their track in
weak flow aloft. In addition, these struggles continue with the
thermodynamic environment, strength and depth of any EML and any
dry/warm air aloft, which then is causing problems in convective
initiation and tracking of thunderstorms or storm clusters. I will
start Friday with the potential for a slight chance of showers
and storms associated with the aforementioned shortwave aloft
moving through the upper ridge. That said, any convective activity
would be be well below severe limits and of the generic variety.
Otherwise Friday afternoon and much of the following evening
appear warm, breezy, and humid before another likely weakening
cluster of storms arrives from earlier dryline activity late in
the evening and through the pre-dawn hours Saturday. The storms
should weaken as they move into a more stable and warm environment
aloft. I will carry low storm chances mainly along and west of
I-35 as it appears the EML and associated CINH would continue
increasing further east Saturday morning.

Saturday will be very warm, breezy, and humid, but rain-free into
the evening hours as the upper ridge maintains large-scale
subsidence across North and Central Texas. However, the upper
ridge will begin to dampen and shift southeast toward the Gulf of
Mexico as new mid-level energy dropping down into the Pacific
Northwest and Northern Rockies kicks out the stagnant Great Basin
mid-level low east-northeast over the Central High Plains on
Saturday before lifting northeast over the Midwest on Sunday. At
the surface, the lee side surface low will migrate east over west
central Kansas and allow the West Texas dryline to migrate closer
to our far west/northwest counties late Saturday through Sunday
night. I have adjusted the best convective chances across those
areas mainly along and west of US 281, with slight chances as far
east as I-35/35W each late day and night period. At this time, the
best severe threat will remain well northwest of our area with
weaker bulk shear across our area and just off the northwest
periphery of the weak Gulf Coast upper high. Still, with high
instability values due to high temperatures in the upper 80s to
middle 90s, some strong storms with small hail and gusty winds are
certainly possible.

For the first half of next week, we`ll be underneath weak
southwest flow aloft as another upper low/deep longwave trough
sets up from the Great Basin west over the California coast.
Similar to earlier this week, the flow aloft will be semi-
summerlike with diffluence aloft and occasional subtle shortwaves
lifting northeast over the state and triggering scattered showers
and storms near the surface dryline well west of our CWA. How
stout our capping inversion is during this period will dictate how
far east-northeast any thunderstorms can persist into our western
counties before weakening or dissipating on Monday and Monday
night. A weak surface cold front does appear (with assistance
from Central Plains convective outflow) to move somewhere into the
Panhandles and Oklahoma. I will keep low convective chances closer
to the Red River and northeast counties for any storms that can
form off the surface front to the north and potentially move into
these areas. Otherwise, North and Central Texas will be under the
influence of a broad, but not overly strong, subtropical ridge
that will extend from the Southern Rockies to the Southeast US the
remainder of the week. Although mostly dry, certainly diurnally
driven low convective chances may occur near and north of the Red
River on the periphery of the upper ridge and stronger mid-level
flow across the Central CONUS. Highs will be very warm (near 90
degrees) as seasonally humid conditions continue with southerly
low-level flow keeping rich Gulf moisture in place across the



Dallas-Ft. Worth    91  72  94  72  93 /   5  30  20  20  10
Waco                93  70  94  71  93 /   5   5   0  20   5
Paris               86  68  90  69  91 /  10  10  20  10  10
Denton              89  70  94  71  92 /   5  30  20  30  10
McKinney            89  70  92  71  92 /   5  20  20  20  10
Dallas              92  74  95  73  93 /   5  30  20  20  10
Terrell             90  70  93  71  92 /   5  20  20  10   5
Corsicana           91  71  93  71  92 /   5  10  10  10   0
Temple              93  69  93  71  92 /   5   5   0  20   0
Mineral Wells       91  68  95  69  92 /  10  20  10  30  10




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