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

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FXUS64 KFWD 180854

Area Forecast Discussion
National Weather Service Fort Worth TX
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.



/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.



.AVIATION... /Issued 1152 PM CDT Sat Mar 17 2018/
A secondary area of elevated showers and isolated storms has
developed on the heels of earlier convection as a weak shortwave
passes overhead. Activity is occurring across the DFW Metroplex
just north of a weak surface front, with ascent being provided by
a the disturbance aloft. A couple of hours of -SHRA with VCTS
should suffice for late this evening, after which all activity is
expected to wane.

Low level moisture should return overnight as a fairly strong
upper trough approaches from the west. MVFR cigs should
eventually return to all areas during the pre-dawn hours Sunday.
Though not certain, there is a good chance that the atmosphere
should have enough time to recover on Sunday prior to the arrival
of the upper level system. Convection allowing models are
indicating the strongest lift occurring along the Red River during
peak heating hours, which right now appears the most likely area
for convective development. Some of this convection may creep down
into the Metroplex late afternoon an early evening before moving
off to the east, so VCTS has been added accordingly.

Otherwise, a Pacific front will eventually make it through the
region Sunday night, with FROPA occurring during the extended
portion of the DFW TAF.



Dallas-Ft. Worth    85  57  77  47  65 /  30   5   0   0   0
Waco                86  51  78  47  68 /  20  10   0   0   0
Paris               73  50  73  46  62 /  60  50   0   5   0
Denton              81  52  74  45  65 /  50   5   0   0   0
McKinney            78  50  73  46  63 /  50  10   0   0   0
Dallas              82  57  76  48  66 /  30  10   0   0   0
Terrell             80  53  76  46  65 /  30  20   0   0   0
Corsicana           82  53  76  47  65 /  20  10   0   0   0
Temple              87  51  78  47  69 /  20  10   0   0   0
Mineral Wells       86  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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