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

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FXUS64 KFWD 220520

Area Forecast Discussion
National Weather Service Fort Worth TX
1120 PM CST Mon Jan 21 2019

/06z TAFs/

Widespread MVFR cigs are overspreading the region as ample
moisture surges northward within a 40-50 kt low level jet. TAF
sites will experience predominantly MVFR conditions from midnight
through 00z Tuesday evening with breezy southerly winds of 20 kts
and gusts as high as 30 kts. At this time, cigs are generally just
above 2 kft, but should lower below 2 kft in a few hours as
moisture continues to deepen overnight. While more aggressive
guidance suggests periods of IFR, elected to keep cigs above 1 kft
with considerations from mechanical mixing due to strong winds
through the depth of the boundary layer. Some light rain may
occasionally affect airports throughout Tuesday in the form of
warm advection driven streamer showers, although the greater
potential will remain east of the TAF sites.

A strong cold front will arrive at the DFW Metroplex around 23-00z
Tuesday evening, causing winds to turn rather abruptly to the
northwest around 20 kts. In addition, a thin band of rain showers
is expected to accompany the front, which has been handled with
VCSH in the TAFs. Thunder appears unlikely owing to limited
instability. The frontal passage should occur an hour or two later
at Waco. Behind the front, the arrival of drier low level air
will scour any remaining MVFR cigs from the airports with VFR cigs
prevailing into Tuesday evening along with gusty northwest winds.
There is some concern that a band of post-frontal precipitation
may affect parts of Central Texas through the overnight hours into
Wednesday morning, some of which could fall as sleet or snow.
This most likely would not occur until after the valid Waco TAF
period, but will need to be monitored for future forecasts. This
area of precipitation (should it develop) would most likely
remain southeast of DFW area TAF sites.



.UPDATE... /Issued 809 PM CST Mon Jan 21 2019/
The forecast is largely in good shape this evening, and have only
made some minor adjustments to account for latest observational
trends. Low-level moisture is beginning to result in low clouds
across our southeast which will continue to overspread the area
throughout the overnight hours. While winds have decreased
slightly since this afternoon, they will remain breezy overnight
since the boundary layer won`t fully decouple. Some light rain or
drizzle may be possible after midnight, mostly east of I-35 within
the deepest moisture.

Otherwise, we`ll continue to assess new 00z guidance with regards
to the potential for a brief bout with wintry precipitation across
portions of Central Texas late Tuesday night and Wednesday
morning. The forecast setup strongly suggests there will be a
frontogenetical precipitation band behind the cold front Tuesday
night, although its exact placement is highly uncertain. Ingredients
could come together for banded or conceivably even convective
precipitation rooted within the 600-500mb layer across parts of
Central Texas. Presumably this would culminate in a mixed bag of
precipitation, with rain changing to predominately sleet with
possibly some snow as well. Confidence in this scenario remains
quite low at this time, despite only being 24-36 hours into the



.SHORT TERM... /Issued 343 PM CST Mon Jan 21 2019/
/Tonight through Tuesday Night/

An active pattern continues across North America with a deep
trough over the eastern U.S., ridging through the central U.S.,
and another deep trough over the western U.S. After a couple of
cold days, strong southerly winds have returned under mostly sunny
skies, allowing temperatures to climb into the upper 50s and lower
60s. The strong winds are due mainly to falling pressures in the
Plains ahead of the digging upper trough over the western U.S. and
these should continue through the overnight hours. Visible
satellite imagery shows a broken cumulus deck across southeast
Texas this afternoon indicative of increasing low level moisture.
This is confirmed as well by the GOES precipitable water product
showing an expanding area of steadily increasing PW values over
the southeastern half of the state. As we get into tonight, the
low level jet will strengthen to around 50 kt allowing this
moisture to stream northward beneath a stout capping inversion.
Widespread low cloud cover is expected to overspread the region
a few hours after sunset and remain in place most of the day

Strong height falls will spread into the Southern Plains late
tonight into Tuesday morning. This will be when low level warm
advection is maximized and we may see some scattered streamer
showers try to develop beneath the strong capping. PoPs will
generally remain around 20% through the mid morning hours. As the
upper trough progresses eastward through the day, a strong cold
front will head southward and should be approaching our northwest
counties by early Tuesday afternoon. The stronger capping will be
lifting during this time, and a better coverage of showers is
likely to develop, especially east of I-35 as the core of the low
level jet continues to shift eastward. The front will be
approaching the Metroplex by late afternoon and will swing through
the rest of the forecast area during the evening hours. Scattered
showers will continue along the front as it progresses into
southeast Texas. We`ll hang on to some PoPs into Tuesday night as
a strong band of 925-850 mb frontogenesis, associated with
deepening colder air, moves southward with the base of the upper
trough swinging through North Texas. Gusty northwest winds will
follow the front along with colder air filtering into North Texas.

At this time, we left the prevailing precipitation type as all
showers given that instability is lacking, however, given the
strong forcing associated with the upper trough, a rumble of
thunder may be possible here and there. PoPs will also be high
generally east of I-35, but total rainfall is expected to
generally be less than 1/2" given the fast nature of the system.



.LONG TERM... /Issued 343 PM CST Mon Jan 21 2019/
/Wednesday Through Next Week/

Precipitation may linger after daybreak Wednesday morning in our
southeastern counties. Profiles could briefly become cold enough
to support snow or a rain/snow mix before the precipitation exits
the area; however, surface temperatures are expected to remain
above freezing, and this light precipitation is not anticipated to
result in significant impacts to travel. Skies will rapidly clear
Wednesday, but brisk north winds will cap temperatures in the 40s.

After the upper trough axis responsible for our precipitation
event passes to the east, northwest flow will begin an extended
stay. During the latter part of the week and into the upcoming
weekend, synoptic-scale troughing will dominate the eastern half
of the country with ridging anchored along the West Coast. The
ridge`s attempts to move inland will be repeatedly thwarted by
frequent cold air intrusions into the Great Lakes and Northeast.
The northwest flow over Texas will bring rapid-fire cold frontal
passages every 24-48 hours through early next week. Although
North and Central Texas will be on the fringe of the cold air, the
reinforcing shots will assure temperatures are unable to climb
above normal during the southerly flow interludes.

While not particularly strong, dry westerly winds may help buoy
afternoon temperatures in our western zones Thursday afternoon
before the second front of the week arrives late in the day and
into the evening hours. Temperatures will plunge into the 20s
Friday morning, and although the winds will diminish after
daybreak, the northerly breeze will still yield wind chill values
in the teens across much of the region for the morning commute.
The postfrontal high will quickly transit the area on Friday, but
the abundant sunshine will only allow the dry air to warm so
much, and many areas will peak in the 40s Friday afternoon.

Despite low-level warm advection Friday night, temperatures will
still fall into the low to mid 30s Saturday morning in advance of
the next front. While the atmosphere may be too dry for any
precipitation, this is one of those scenarios in which the column
will be quite cold. Extended guidance varies considerably with
the strength of a postfrontal impulse on Saturday, but a decent
consensus in position swings the best (albeit dry) lift through
West and South Texas. However, the most favorable moisture
profiles may be in East Texas where we will carry some low-end
rain chances. We will continue to assess the potential for winter
weather as the event approaches.

There will be little opportunity for a warm-up on Sunday before
the next cold front arrives on Monday next week, maintaining the
persistent below normal temperatures.



Dallas-Ft. Worth    53  64  33  47  32 /  10  30   0   5   0
Waco                55  65  35  48  31 /   5  50  20  10   0
Paris               46  60  30  42  29 /  20  80  30   5   0
Denton              52  63  32  47  31 /  10  20   0   0   0
McKinney            51  63  32  45  31 /  20  40   5   5   0
Dallas              53  64  33  47  32 /  10  30   5   5   0
Terrell             51  64  32  45  30 /  20  70  20  10   0
Corsicana           53  65  33  44  30 /  10  80  30  10   0
Temple              54  65  35  49  32 /   5  50  20  10   0
Mineral Wells       52  64  31  48  31 /  10   5   0   0   0




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