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

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FXUS64 KFWD 091750 AAC
AFDFWD

Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
1150 AM CST Tue Jan 9 2018

.AVIATION...
/18Z TAFs/

Concerns...Return of IFR and LIFR conditions this evening and/or
tonight.

A bank of low clouds and fog continues to slowly erode from west
to east across the DFW Metroplex. KDAL will continue to experience
LIFR conditions through about 19Z. Otherwise VFR conditions will
prevail into the evening hours at all the TAF sites.

Unfortunately there is considerable uncertainty and spread between
weather model guidance regarding the return of low clouds and fog
tonight. Timing the return of IFR/LIFR conditions will also be
affected by how far east the current cloud bank erodes this
afternoon. For this forecast issuance, have 3SM OVC004 arriving
around 03-05Z at all the TAF airports. Some guidance suggests
dense fog will be possible, potentially even occurring before the
low clouds arrive. However, a lack of substantial surface moisture
influx and surface winds around 10 kts with an increasing low
level jet imply light fog may occur, but the main impact may be
from IFR/LIFR ceilings. Again, there is a considerable amount of
uncertainty in the timing and trends, and updates within the TAF
are likely this evening once we can observe the trends. Wind
speeds will increase to 15-20 kts with gusts up to 25 kts on
Wednesday, and this will help to clear any fog and lift any cigs
to 1-2 kft by midday.

JLDunn

&&

.UPDATE... /Issued 1050 AM CST Tue Jan 9 2018/
The rest of the day will feature a demarcation between low clouds,
fog and cool temperatures in the east, but sunny and warm in the
west. Fog and low clouds prevail along and east of Interstate
35/35W this morning, but we expect a slow erosion of the low
clouds from west to east to continue through the remainder of the
day. Dense fog has been prevalent the last few hours along and
just east of the I-35 corridor, with better visibilities farther
east. The dense fog should slowly improve through midday, but fog
will likely prevail in some areas through the afternoon hours. Low
clouds will likely prevail over our northeastern counties for
most the day where temperatures will struggle to reach the lower
50s. Elsewhere along and east of I-35, temperatures will be in the
mid 50s to lower 60s. IF the clouds do not fully clear into East
Texas this afternoon or evening, there`s a good chance we will see
a return of low clouds and fog from the east this evening and
overnight, but will address this with the afternoon forecast
package.

Very different conditions will occur across the western half of
the CWA where sunny skies and southwest winds aloft are expected
to aid in temperatures warming into the upper 60s and lower 70s.

JLDunn

&&

.SHORT TERM... /Issued 351 AM CST Tue Jan 9 2018/
Satellite imagery reveals a pair of upper level low pressure
centers, one across the northern Gulf and another approaching the
Southern California coast, placing North and Central Texas
beneath an upper ridge separating the two systems. The upper level
pattern is a progressive one, and the West Coast upper low will
make a steady eastward advance into the Desert Southwest over the
next 24 hours while the Gulf system heads for Florida.

Veering low level flow ahead of the system to our west is
resulting in a westward push of shallow moisture located over East
Texas. A low cloud deck can be seen on Night Fog satellite imagery
working its way into the eastern CWA. There is some concern that
this deck of stratus will transition into areas of fog across the
eastern third to half of the region by daybreak. So, despite the
lack of any significant fog at this time, grids will continue to
indicate areas of fog across the eastern third of the region, with
patchy fog as far west as the I-35 corridor. Extrapolating the
leading edge of the low clouds brings the stratus into the Dallas
area by 7 AM or just before sunrise. We will need to keep a close
eye on visibility trends, as oftentimes fog will form near the
edge of a low cloud deck. If visibilities start to drop rapidly,
a dense fog advisory might be needed.

Fog and low clouds will scatter late morning and this afternoon as
southerly low level flow mixes to the surface. Return flow
combined with the presence of the upper ridge will allow
temperatures to climb into the 50s across the east, 60s in the
central and west, with a few spots across the far west possibly
seeing lower 70s. Increasing moisture will keep tonight`s
temperatures about 10 degrees above last night`s readings, with a
return of low clouds likely after midnight.

30

&&

.LONG TERM... /Issued 351 AM CST Tue Jan 9 2018/
/Wednesday through Monday/

By Wednesday morning a strong shortwave trough will be moving
through central Arizona and New Mexico with strong surface
cyclogenesis in progress across eastern Colorado and southwest
Kansas. The strong pressure falls will result in increasing
southerly winds across the region. An extensive area of low clouds
will likely be present along and east of I-35 where moisture
remains in place. Cloud cover will likely linger for much of the
day east of I-35 resulting in cooler temperatures. Farther to the
west, south-southwest winds and some scattering of clouds will
result in temperatures warming into the low to mid 70s.

The lead shortwave trough will eject northeast into the Central
Plains on Wednesday evening taking the surface cyclone eastward
while a much stronger shortwave digs into far West Texas. This
will allow a strong cold front to barrel southward through the
Plains overnight Wednesday night. The front will likely enter our
northwest counties early Thursday morning and quickly move through
the rest of the CWA by late morning. While there will be some
moisture to work with, moisture depth is rather shallow and
confined to areas east of I-35. Strong west-southwest winds above
the surface will help keep a strong capping inversion in place
across most of North Texas. As stronger forcing for ascent
spreads eastward during the late morning hours, some scattered
showers could develop along the front mainly across the eastern
counties. These should quickly move into East Texas by afternoon.
We`ll have 20-40% PoPs confined to our far eastern counties during
this time.

The airmass behind this front is cold and with the core of the
upper trough passing right over North Texas, the column will
quickly become very cold by early Thursday afternoon. We`re still
monitoring a low potential for some light snow across northwest
parts of the CWA Thursday afternoon as the core of the upper
trough passes through North Texas. All of the model guidance still
suggests an area of strong mid-level frontogenesis and forcing
for ascent will be present in a narrow axis just northwest of the
Metroplex. This lift is really maximized in an area from about
500-450 mb where there will be moisture present. While this would
normally not be overly concerning, the fact that this moisture is
present in the vicinity of very steep lapse rates suggests that
some weak instability may be available. If this does actually
exist, the localized lift could be quite strong and result in the
development of a narrow band of precipitation, which would be all
snow. The main limiting factor this time around is that the lift
is quite high up and there is a fairly substantial amount of dry
air beneath it. This would likely be sufficient to evaporate any
precipitation that developed. Nonetheless, it is still something
to watch and we`ll keep a mention of very light snow Thursday
afternoon northwest of the Metroplex with the passage of the upper
trough. No accumulations or impacts are expected at this time.

As this system passes by, we`ll enter a several day stretch of
below normal temperatures with highs in the 40s through the end of
the week. A reinforcing cold front will swing through North Texas
on Saturday knocking temps down even further. Highs may struggle
to reach 40 degrees on Saturday and Sunday in many areas with lows
in the low/mid 20s. We`ll keep an eye on moisture return late
Sunday which could result in increasing rain chances for the early
part of next week.

Dunn

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    58  44  70  49  51 /   0   0   5   5  10
Waco                63  44  70  51  55 /   0   0   5  10  10
Paris               53  43  65  51  54 /   0   0   5  10  30
Denton              57  42  69  47  49 /   0   0   0   5  10
McKinney            55  42  67  49  51 /   0   0   5   5  20
Dallas              57  44  69  50  52 /   0   0   5   5  10
Terrell             56  42  68  50  55 /   0   0   5  10  20
Corsicana           60  43  68  52  56 /   0   0   5  10  20
Temple              66  43  70  51  56 /   0   0   5  10  10
Mineral Wells       66  43  73  44  47 /   0   0   0   0  10

&&

.FWD WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

82/26



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