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

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FXUS64 KFWD 181747

Area Forecast Discussion
National Weather Service Fort Worth TX
1247 PM CDT Sun Mar 18 2018

/18z TAFs/

Low clouds have been slow to clear this morning, but are finally
showing some signs of improvement as of 18z. The deck of IFR
clouds is beginning to lift/erode from the west as a shortwave
trough approaches while some warmer/drier air arrives from the
southwest. Will continue IFR conditions through 19-20z before
improving to VFR at all TAF sites through the late afternoon.

The next concern is the potential for convection to impact
airports later this afternoon or early this evening. Coverage of
thunderstorms remains in question, as does the most favorable
location for initial development. Stubborn cloud cover has
prevented strong destabilization from occurring thus far, and this
may inhibit the initiation of more widespread convection
throughout the afternoon. Given the presence of the strong
shortwave to our west, still think isolated thunderstorms are in
the cards especially if lift from the shortwave can be aided by
other boundaries present, such as the stationary front draped
through North Texas or the dryline positioned to the west. Will
continue a brief VCTS mention at DFW Metroplex airports centered
around 00z, but will keep rain-free TAFs at Waco for now.
Southerly winds will prevail through tonight.

Overnight, predominantly VFR conditions are expected as a Pacific
front/dryline moves through the area, although a brief period of
MVFR is possible around midnight just prior to the front`s
arrival. Have not included MVFR in the TAFs for now as the
potential looks low. Drier air behind the front will scour all
low-level moisture from the area and VFR conditions will prevail
into Monday.

A crosswind event is likely to occur through the day on Monday as
breezy west winds of 20G30KT are expected. Later in the day, winds
will turn more to the northwest as a cold front arrives, but will
remain breezy through Monday evening.



.SHORT TERM... /Issued 354 AM CDT Sun Mar 18 2018/
/Today and Tonight/

Radar imagery this morning shows a few scattered showers remaining
from last night`s convection continuing to spread east into East
Texas. In the wake of the previous convection, surface winds have
been a little disorganized but a return to east-southeast flow can
be expected through the early morning. The quasi-stationary
frontal boundary remains in place across the northern parts of
the Metroplex from near Breckenridge to North Fort Worth and then
extends east to between Paris and Sulphur Springs. Farther south,
a secondary boundary extends from near Temple to Palestine. South
of this feature, dewpoints are in the upper 60s.

Water vapor imagery over the central and western U.S. shows a
digging trough over southern California with a lead impulse
spreading across Baja California ahead of the main trough. The
latest RAP analysis has a 130 kt upper jet spreading across
northern Mexico and into West Texas associated with this
shortwave. Later this morning, as this disturbance moves eastward
into Texas, stronger height falls will overspread the region
signaling an increase in large scale forcing for ascent.
Initially, some elevated showers and perhaps a few thunderstorms
may develop across west-central Texas associated with a marked
increase in 700-500mb winds and warm advection. This activity
should spread northeast rather quickly through midday. There is
some dry air beneath 700mb associated with an elevated mixed
layer, so stronger convection could have some accelerated
downdrafts, although the boundary layer should remain relatively
stable through late morning which should mitigate any threat for
strong wind gusts.

Attention then turns to later this afternoon, as the main
shortwave trough to the west spreads into New Mexico. This will
allow stronger westerly winds to spread into West Texas
effectively forcing the dryline and Pacific front eastward.
Similar to yesterday, there will be a weak area of low pressure
tied closely to the dryline and nearly stationary frontal boundary
along the Red River. This surface low should be somewhere between
Abilene and Wichita Falls by mid afternoon. To the east of there,
the atmosphere across North and Central Texas will have had ample
time to recover from previous convection and destabilize. Thicker
mid level cloud cover will likely be shunted northeast as the lead
impulse pulls away. This should allow for some sunshine and
temperatures should respond by warming into the mid 70s along the
Red River to the mid 80s in the Metroplex and elsewhere. This
should result in strong instability with surface based CAPE in
excess of 2500 J/kg across parts of North Texas this afternoon,
especially along and south of I-20.

With the main shortwave still trailing to the west, large scale
forcing for ascent will remain present across North Texas through
this evening. Low level convergence should become maximized by mid
afternoon near the surface low with any remaining inhibition being
eroded or lifted between 2-4 pm. This is when more vigorous
convection is likely to develop, somewhere in the vicinity of
Graham to Bowie to Wichita Falls. Convection should rapidly move
east through the evening hours primarily focused in an area near
the quasi-stationary frontal boundary. Highest PoPs will generally
be along and north of I-20 to the Red River this afternoon and
evening. Additional thunderstorms will be possible farther south
into Central Texas given the large area of ascent that persists
into the evening hours, although coverage is expected to be more
isolated farther south off of the frontal boundary.

Concerning severe potential...The atmosphere will become strongly
unstable this afternoon with steep lapse rates between 850-700mb
and strong deep layer shear. This will support supercells with
mainly a large hail and damaging wind threat. There will be a
small tornado threat, mainly near the frontal boundary between
I-20 north to the Red River. This is the area where low level
winds may remain sufficiently backed to support low level
rotation. Otherwise, instability will increase markedly from the
Metroplex southward. There may be a tendency for storms to
initially develop and then turn southeastward into the stronger
instability axis, as is indicated by some of the convection
allowing models. Any storms that manage to move into the stronger
instability farther south would be capable of producing very large
hail into the evening hours.

Concerning fire weather potential...As the dryline moves east into
the area late this afternoon, areas west of I-35 and south of I-20
will see dewpoints drop into the 30s and lower 40s yielding RH
values around 20%. This combined with westerly winds 15 to 25 mph
will result in dangerous fire weather conditions through the
evening hours.

All of the afternoon and evening convection will spread east into
East Texas after dark with rain chances quickly diminishing. Drier
air will continue to filter into the region behind the Pacific
front through the overnight hours as the main shortwave pulls off
to the east.



.LONG TERM... /Issued 354 AM CDT Sun Mar 18 2018/
/Monday through Saturday/

Strong and gusty west to northwest winds will take hold across
North and Central Texas on Monday in the wake of the most recent
shortwave. While these northwest winds will result in a degree of
cold advection at the surface, the main push of cooler air will
not arrive until Monday evening and overnight with a reinforcing
cold front. As a result, temperatures should still manage to warm
well into the 70s across much of the region under passing high
clouds, with the main exceptions across the immediate Red River
counties where some post-frontal stratus may occur. While some
locations picked up a half inch or more of rain with the activity
on Saturday/Saturday evening, little additional rainfall is
expected today (Sunday). With wind speeds expected to increase to
around 20 mph with gusts to near 30 coincident with dry/cured
fuels and afternoon relative humidity values of less than 25
percent, we`ve hoisted a Fire Weather Watch for locales west of a
Graham to Mineral Wells to Gatesville line late Monday morning and
into the early evening hours. While winds will remain quite strong
to the east of the current watch area, the combination of somewhat
less receptive fine fuels (with ERC-G values running generally
below a critical threshold of 40), and questions regarding
dewpoints and subsequent relative humidity values preclude a
farther eastward extension of the watch area. However, if drier
air materializes, then additional counties may need to be added to
the east of the current watch area in subsequent forecasts.

Breezy conditions will persist into Tuesday as cooler air trickles
south of the Red River, with high temperatures forced back into
the 60s across the region. High pressure will then move overhead
Tuesday night/Wednesday morning, although Pacific moisture
streaming overhead may not allow us to fully reach our radiational
cooling potential.

A warming trend will commence Wednesday and through the end of the
week as southerly surface winds return. Breezy conditions are
expected Thursday and Friday as the next area of low pressure
develops to our north. Based on tonight`s ensemble guidance, the
most recent GFS seems a bit hasty to eject a sub-1000 mb low
pressure system across Kansas Thursday night into Friday, and have
sided with the somewhat slower ECMWF for this forecast package.

There will be a low chance for mainly showers underneath a
strengthening capping inversion over the weekend as North and
Central Texas remain within a region of persistent warm advection.



Dallas-Ft. Worth    79  57  77  47  65 /  30   5   0   0   0
Waco                81  51  78  47  68 /  20  10   0   0   0
Paris               66  50  73  46  62 /  50  50   0   5   0
Denton              77  52  74  45  65 /  40   5   0   0   0
McKinney            75  50  73  46  63 /  50  10   0   0   0
Dallas              77  57  76  48  66 /  30  10   0   0   0
Terrell             78  53  76  46  65 /  30  20   0   0   0
Corsicana           79  53  76  47  65 /  20  10   0   0   0
Temple              84  51  78  47  69 /  20  10   0   0   0
Mineral Wells       80  49  75  43  66 /  30   0   0   0   0


Fire Weather Watch from Monday morning through Monday evening
for TXZ100-115-116-129-130-141>143-156-157.



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