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

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317
FXUS64 KFWD 081708
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
1108 AM CST Thu Dec 8 2016

.UPDATE...
Arctic air will continue to surge across the region through the
afternoon. Extensive middle clouds and continued cold air
advection will keep temperatures within a few degrees of where
they are right now. Therefore, expect highs today mainly in the
30s with wind chills mostly in the 20s. Wind speeds will slowly
decrease this evening and clouds will scatter so we still expect a
very cold night with lows in the teens and 20s.

The weak shortwave that brought some very light precipitation to
areas generally south of the Interstate 20 corridor this morning
will exit to the east later this afternoon. Dry air will filter in
behind the departing disturbance which will help the mid level
cloud deck thin and eventually scatter.

The current forecast is in good shape but we will send an update
to remove the winter mix wording for this afternoon.

79

&&

.AVIATION...
/ISSUED 603 AM CST Thu Dec 8 2016/
The much advertised arctic cold front blasted through the region
overnight. In its wake, strong and gusty north winds and much
colder temperatures have settled in. In the Metroplex, low-level
dry air continues to steadily ooze southward, although we`ll
likely hold onto an extensive deck of mid-level cloud cover
through the day. Our ascending 12Z sounding shows a lingering
moist layer right around 2 kft, and upstream observations reveal
a thin band of SCT-BKN clouds at this level. Will continue with a
brief TEMPO group through 14Z to account for these clouds
percolating through the DFW TRACON. Wind speeds will gradually
diminish through this afternoon, becoming less than 10 kts
overnight. Winds will then veer around to the southeast and then
south Friday afternoon.

At Waco, the potential for drizzle will linger for a few more
hours, but temperatures should remain safely above freezing this
morning. Gusty north winds will begin to subside this evening,
becoming light at speeds under 9 kts overnight. VFR will prevail
as dry air seeps in from the north later this morning.

Carlaw


&&


.PREV DISCUSSION... /ISSUED 603 AM CST Thu Dec 8 2016/
We only made minor tweaks to the ongoing forecast, as progress of
events with the shortwave to our west appear to be on track. As
the frontogenetical forcing aloft continue to slowly sink southeast
with time today, felt the mixture of drizzle, freezing drizzle, or
light sleet was appropriate per environmental analysis on forecast
soundings. Though a snow flurry or two can`t be ruled out, seeding
from cirrostratus aloft will be minimized due to a significant dry
layer between 800mb and 550mb. As such, do not feel the need to
add an insignificant weather element to an already complex weather
forecast. Basically, no snow accumulation is expected. As noted
the past few days, any minor impacts will be across our southwest
counties on elevated surfaces toward daybreak and through this
morning where temperatures can fall close to 30 degrees. Some
lingering forcing is expected across eastern parts of Central
Texas. However, temperatures will warm to above freezing this
afternoon, so will only advertise a slight chance for light
rain/drizzle, possibly mixed with a snow flurry or two.

The shortwave responsible for the possible, very light wintry mix
across Central Texas this morning will exit stage right this
evening. Subsidence with dry arctic air entraining into the area
will result in a gradual decrease of clouds from north to south
through the duration of the night. Despite the clouds, will continue
to advertise chilly low temperatures Friday morning from the upper
teens to the mid 20s, as clouds, and even insolation during the
daylight hours usually have little influence on very dense and
cold airmasses like the one we`ll be experiencing. That said for
Friday after a very cold start, I was hesitant to want to go more
than a 20 degree diurnal range with the highs being that models
tend to scour out arctic airmasses too quickly. For now, I`ll
only undercut guidance a few degrees and go with highs 40 to 45
degrees, though I have my reservations despite some weak return
southeast winds during the afternoon hours.

With strong zonal flow aloft for the weekend, continue to expect
strong lee cyclogenesis to occur with increasing southerly winds
and warm advection. This should put temperatures back up to near
seasonal normals for Saturday in the 50s and in the 60s for
Sunday. In addition, another shortwave moves east across the
Southern Plains late Saturday into Sunday. For the late Saturday
into Sunday morning period, it appears most of the moisture per
forecast soundings is contained below 850mb, thus per coordination
with surrounding sister offices this morning (thank you all),
we`ll only advertise low chances for a very light rain or drizzle
with very dry air above 850mb. By Sunday afternoon, the approach
of another shortwave will help to moisten the column up higher and
allow for some steepening of the mid level lapse rates that low
convective chances across our eastern counties Sunday afternoon
appear reasonable. We will NOT be worried about any wintry precip
over the weekend due to the strong warm advection expected.

Next week looks to remain primarily dry and cool to start off
with Monday into Tuesday, before what appears to be another
possible arctic air intrusion either Tuesday afternoon or Tuesday
night. The GFS is deeper with the cyclonic flow aloft versus the
Euro or Canadian models(which suggest a more shallow push of this
airmass). Either way and again with much collaboration (thank you
all again), we will use a raw blend of the model fronts and winds
and lean with an initial push into our northern counties Tuesday
afternoon, before moving through the entire area Tuesday night.
Did undercut guidance values for highs Wednesday and Thursday
considering the cold air with this airmass. I would not be
surprised if both low/high temperatures need to be lowered even
more for the latter half of next week. Luckily, it appears no
impacts at this time with a dry frontal surge expected, though the
Euro does show a potential low chance for precipitation next
Thursday. With my confidence wavering that far out in time,
prefer to lean with the dry forecast for now.

05/

&&
.PREV DISCUSSION... /ISSUED 556 AM CST Thu Dec 8 2016/
.SYNOPSIS...
An arctic front was continuing to move through North-Central
Texas this morning. Despite north winds occurring all the way to
the I-10 corridor, the leading edge of the wind shift was actually
a pre-frontal trough. The frigid air was now crossing the Red
River and entering areas north of the I-20/30 corridors. The
freezing line was fast-approaching the Red River Valley as we
speak. Meanwhile aloft, an upper low was noted over Ottawa Canada,
with a detached upper trough and associated shortwave extending
southwest across the Plains and into the Southwest CONUS and
Mexico. Mid level frontogenetical forcing was noted in advance of
the shortwave along the Mexico/Southern AZ border per cooling
cloud tops (cirrus) on water vapor imagery across the Southern
High Plains. A few flurries or spotty drizzle/light rain were
occurring along/south of I-20 as we speak per clear-air mode/VCP
31 on area radars. However, there was nothing of significance with
regard to precipitation rates or amounts at this time.

.DISCUSSION...
We only made minor tweaks to the ongoing forecast, as progress of
events with the shortwave to our west appear to be on track. As
the frontogenetical forcing aloft continue to slowly sink southeast
with time today, felt the mixture of drizzle, freezing drizzle, or
light sleet was appropriate per environmental analysis on forecast
soundings. Though a snow flurry or two can`t be ruled out, seeding
from cirrostratus aloft will be minimized due to a significant dry
layer between 800mb and 550mb. As such, do not feel the need to
add an insignificant weather element to an already complex weather
forecast. Basically, no snow accumulation is expected. As noted
the past few days, any minor impacts will be across our southwest
counties on elevated surfaces toward daybreak and through this
morning where temperatures can fall close to 30 degrees. Some
lingering forcing is expected across eastern parts of Central
Texas. However, temperatures will warm to above freezing this
afternoon, so will only advertise a slight chance for light
rain/drizzle, possibly mixed with a snow flurry or two.

The shortwave responsible for the possible, very light wintry mix
across Central Texas this morning will exit stage right this
evening. Subsidence with dry arctic air entraining into the area
will result in a gradual decrease of clouds from north to south
through the duration of the night. Despite the clouds, will continue
to advertise chilly low temperatures Friday morning from the upper
teens to the mid 20s, as clouds, and even insolation during the
daylight hours usually have little influence on very dense and
cold airmasses like the one we`ll be experiencing. That said for
Friday after a very cold start, I was hesitant to want to go more
than a 20 degree diurnal range with the highs being that models
tend to scour out arctic airmasses too quickly. For now, I`ll
only undercut guidance a few degrees and go with highs 40 to 45
degrees, though I have my reservations despite some weak return
southeast winds during the afternoon hours.

With strong zonal flow aloft for the weekend, continue to expect
strong lee cyclogenesis to occur with increasing southerly winds
and warm advection. This should put temperatures back up to near
seasonal normals for Saturday in the 50s and in the 60s for
Sunday. In addition, another shortwave moves east across the
Southern Plains late Saturday into Sunday. For the late Saturday
into Sunday morning period, it appears most of the moisture per
forecast soundings is contained below 850mb, thus per coordination
with surrounding sister offices this morning (thank you all),
we`ll only advertise low chances for a very light rain or drizzle
with very dry air above 850mb. By Sunday afternoon, the approach
of another shortwave will help to moisten the column up higher and
allow for some steepening of the mid level lapse rates that low
convective chances across our eastern counties Sunday afternoon
appear reasonable. We will NOT be worried about any wintry precip
over the weekend due to the strong warm advection expected.

Next week looks to remain primarily dry and cool to start off
with Monday into Tuesday, before what appears to be another
possible arctic air intrusion either Tuesday afternoon or Tuesday
night. The GFS is deeper with the cyclonic flow aloft versus the
Euro or Canadian models(which suggest a more shallow push of this
airmass). Either way and again with much collaboration (thank you
all again), we will use a raw blend of the model fronts and winds
and lean with an initial push into our northern counties Tuesday
afternoon, before moving through the entire area Tuesday night.
Did undercut guidance values for highs Wednesday and Thursday
considering the cold air with this airmass. I would not be
surprised if both low/high temperatures need to be lowered even
more for the latter half of next week. Luckily, it appears no
impacts at this time with a dry frontal surge expected, though the
Euro does show a potential low chance for precipitation next
Thursday. With my confidence wavering that far out in time,
prefer to lean with the dry forecast for now.

05/



&&
.SYNOPSIS...
An arctic front was continuing to move through North-Central
Texas this morning. Despite north winds occurring all the way to
the I-10 corridor, the leading edge of the wind shift was actually
a pre-frontal trough. The frigid air was now crossing the Red
River and entering areas north of the I-20/30 corridors. The
freezing line was fast-approaching the Red River Valley as we
speak. Meanwhile aloft, an upper low was noted over Ottawa Canada,
with a detached upper trough and associated shortwave extending
southwest across the Plains and into the Southwest CONUS and
Mexico. Mid level frontogenetical forcing was noted in advance of
the shortwave along the Mexico/Southern AZ border per cooling
cloud tops (cirrus) on water vapor imagery across the Southern
High Plains. A few flurries or spotty drizzle/light rain were
occurring along/south of I-20 as we speak per clear-air mode/VCP
31 on area radars. However, there was nothing of significance with
regard to precipitation rates or amounts at this time.

.DISCUSSION...
We only made minor tweaks to the ongoing forecast, as progress of
events with the shortwave to our west appear to be on track. As
the frontogenetical forcing aloft continue to slowly sink southeast
with time today, felt the mixture of drizzle, freezing drizzle, or
light sleet was appropriate per environmental analysis on forecast
soundings. Though a snow flurry or two can`t be ruled out, seeding
from cirrostratus aloft will be minimized due to a significant dry
layer between 800mb and 550mb. As such, do not feel the need to
add an insignificant weather element to an already complex weather
forecast. Basically, no snow accumulation is expected. As noted
the past few days, any minor impacts will be across our southwest
counties on elevated surfaces toward daybreak and through this
morning where temperatures can fall close to 30 degrees. Some
lingering forcing is expected across eastern parts of Central
Texas. However, temperatures will warm to above freezing this
afternoon, so will only advertise a slight chance for light
rain/drizzle, possibly mixed with a snow flurry or two.

The shortwave responsible for the possible, very light wintry mix
across Central Texas this morning will exit stage right this
evening. Subsidence with dry arctic air entraining into the area
will result in a gradual decrease of clouds from north to south
through the duration of the night. Despite the clouds, will continue
to advertise chilly low temperatures Friday morning from the upper
teens to the mid 20s, as clouds, and even insolation during the
daylight hours usually have little influence on very dense and
cold airmasses like the one we`ll be experiencing. That said for
Friday after a very cold start, I was hesitant to want to go more
than a 20 degree diurnal range with the highs being that models
tend to scour out arctic airmasses too quickly. For now, I`ll
only undercut guidance a few degrees and go with highs 40 to 45
degrees, though I have my reservations despite some weak return
southeast winds during the afternoon hours.

With strong zonal flow aloft for the weekend, continue to expect
strong lee cyclogenesis to occur with increasing southerly winds
and warm advection. This should put temperatures back up to near
seasonal normals for Saturday in the 50s and in the 60s for
Sunday. In addition, another shortwave moves east across the
Southern Plains late Saturday into Sunday. For the late Saturday
into Sunday morning period, it appears most of the moisture per
forecast soundings is contained below 850mb, thus per coordination
with surrounding sister offices this morning (thank you all),
we`ll only advertise low chances for a very light rain or drizzle
with very dry air above 850mb. By Sunday afternoon, the approach
of another shortwave will help to moisten the column up higher and
allow for some steepening of the mid level lapse rates that low
convective chances across our eastern counties Sunday afternoon
appear reasonable. We will NOT be worried about any wintry precip
over the weekend due to the strong warm advection expected.

Next week looks to remain primarily dry and cool to start off
with Monday into Tuesday, before what appears to be another
possible arctic air intrusion either Tuesday afternoon or Tuesday
night. The GFS is deeper with the cyclonic flow aloft versus the
Euro or Canadian models(which suggest a more shallow push of this
airmass). Either way and again with much collaboration (thank you
all again), we will use a raw blend of the model fronts and winds
and lean with an initial push into our northern counties Tuesday
afternoon, before moving through the entire area Tuesday night.
Did undercut guidance values for highs Wednesday and Thursday
considering the cold air with this airmass. I would not be
surprised if both low/high temperatures need to be lowered even
more for the latter half of next week. Luckily, it appears no
impacts at this time with a dry frontal surge expected, though the
Euro does show a potential low chance for precipitation next
Thursday. With my confidence wavering that far out in time,
prefer to lean with the dry forecast for now.

05/

&&



.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    38  25  42  32  52 /  10   0   0   0   5
Waco                39  24  45  31  51 /  20   5   0   0  10
Paris               38  20  41  29  46 /  10   0   0   0  10
Denton              38  19  40  30  50 /  10   0   0   0   5
McKinney            38  22  41  30  48 /  10   0   0   0   5
Dallas              37  25  44  32  51 /  10   0   0   0   5
Terrell             38  23  44  30  49 /  10   5   0   0  10
Corsicana           38  25  43  31  51 /  20   5   0   0  10
Temple              39  25  45  32  51 /  20   5   0   0  20
Mineral Wells       37  20  43  29  53 /  10   0   0   0   5

&&

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

$$

26/79



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