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

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679
FXUS64 KFWD 180446
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
1146 PM CDT Tue Apr 17 2018


.AVIATION...
06 UTC TAF Cycle

Concerns---Timing of FROPA and strong non-convective winds at all
TAF sites. MVFR ceiling potential at Waco.

Breezy south winds are expected to continue over the next 4 to 8
hours at TAF sites. Sustained speeds near 20 knots with gusts to
30 knots will be possible as a strong low level jet (at FL025) of
around 50 to 55 knots develops. At this time, non-convective LLWS
isn`t anticipated due to the strong surface winds and any
compression issues will be largely mitigated by the low volume of
air traffic. At this time, it appears that FROPA will occur
between 0900 UTC and 1000 UTC at the Metroplex with FROPA at Waco
a couple of hours later around 1200 UTC. MVFR cigs should have a
difficult time getting to the Metroplex TAF and I`ll maintain a
VFR TAF. At Waco, the potential isn`t too high for a sustained
period of MVFR stratus given the dry boundary layer and I`ve
inserted a TEMPO group for cigs at around FL022. The passage of
the cold front should scour out any remnant low level cloud cover.

Strong north winds are anticipated after FROPA with sustained
winds of 15 to 17 knots. Gusts up to 30 knots will be possible.

24

&&


.UPDATE... /Issued 948 PM CDT Tue Apr 17 2018/
The forecast is generally in good shape with just a few minor
tweaks to sky and wind grids for the overnight time period.

Satellite imagery at this hour revealed a decent plume of mid and
upper level moisture continued to stream overhead mainly for
locations near and north of I-20. A strong cold front was noted
plowing through the Oklahoma and Texas panhandles at this hour.
Based on pure extrapolation of this feature as well as the latest
3 km NAM, have bumped up the speed of FROPA across the area with
the front now forecast to near the I-20 corridor in the 9-10 UTC
Wednesday time frame and across Central Texas by around 12-13 UTC.
A majority of the colder air looks to lag behind the front
(though it`s likely that adiabatic compression behind the front is
modifying the cooler airmass) and as a result, I`ll not make any
noteworthy changes to overnight lows.

In terms of the sensible weather elements, there may be the
potential for a few sprinkles across the East and across Central
Texas. Low level moisture seems really scarce per our evening
weather balloon, but some of the clouds in the satellite imagery
do have some cumuliform elements so it (sprinkles) can`t be
completely ruled out. I`ve added in a silent 10 PoP across North,
East and Central Texas to account for this. The other element to
monitor during the overnight period into Wednesday morning will be
the possibility for patchy smoke/haze---especially along the Red
River. Experimental HRRR smoke products do suggest that the wind
shift associated with FROPA across Oklahoma will allow the plume
to become more oriented to the east and eventually southeast into
the area. The degree of mixing/dispersion at this time, however,
is unknown and precludes mention in the forecast at this time. If
HRRR guidance becomes more aggressive/consistent with greater
smoke/aerosol concentrations into North Texas, patchy smoke/haze
may be inserted into the forecast.

24

&&

.SHORT TERM... /Issued 401 PM CDT Tue Apr 17 2018/
Temperatures this afternoon have risen into the lower 80s
southeast to lower 90s northwest as strong warm air advection
takes place across the Southern Plains. This warm air advection is
occurring in response to lee cyclogenesis underway along the Front
Range of the Central Rockies. In the upper-levels, a ridge axis is
making its way through the Central CONUS, with the next trough
axis located through the Great Basin as of this morning. Height
falls as this trough axis propagates eastward should push a cold
front through North and Central Texas late tonight and Wednesday
morning.

In the near-term (rest of today), the main concern will be for
elevated fire conditions in the far western counties (west of a
Bowie to Comanche line). Relative humidity values should bottom
out in the 20-25 percent range, along with south-southwesterly
winds of 15-20 MPH, and temperatures near (or even slightly
above) the 90-degree mark. These conditions combined with ERC
values near the 50th percentile suggest that conditions are
modestly favorable for wildfire spread. Strong caution is urged if
using flames outdoors.

Heading into tonight, model guidance is in good agreement with
the timing of the cold front. The cold front should enter our
northwestern counties by 4 AM, then reach the Dallas/Fort Worth
area by daybreak. Precipitation is not expected with this cold
front given the dry air mass that remains in place ahead of it.
While precipitation is not expected, enough low-level moisture
will be in place for some cloud cover to develop ahead of the
front, particularly in our eastern and southeastern counties where
moisture is more abundant (though still shallow). Time-height
cross-sections as well as forecast soundings indicate shallow,
but rich moisture settling in late tonight ahead of the frontal
passage. This should allow for mostly cloudy to overcast skies
generally east of a Sulphur Springs to Hillsboro to Lampasas line.
As the cold front passes, winds will veer out of the northwest at
10-15 MPH. With the exception of the northwestern counties, most
locations should hit their low temperature prior to to the arrival
of the cold front (and even then, cold air advection behind the
cold front should not be particularly robust). Because of this,
most areas will see low temperatures tonight near to slightly
above where they were Tuesday morning. Over the northwest, the
frontal passage will result in lows being about five degrees lower
than last night.

Godwin

&&

.LONG TERM... /Issued 401 PM CDT Tue Apr 17 2018/
A dry cold will sweep through the region on Wednesday. Veering
surface winds will reduce the already thin moisture across our
southeastern zones, which should have northwest winds by midday,
and no rain chances are expected. Breezy north winds will result
in a noticeably cooler day, but the sunshine should still allow
temperatures to reach the 70s Wednesday afternoon. Dew points will
plunge behind the boundary, and even with the cooler temperatures,
afternoon relative humidity values will likely fall below 25
percent in areas west of the I-35 corridor. But if the vegetation
is green enough to fight off fire initiation today, with
temperatures in the 90s, near normal daytime temperatures are even
less likely to cause fire weather concerns. A seasonally cool
night will follow, and northeast winds should prevent Thursdays`
highs from exceeding Wednesdays`.

The storm system that brought rare hail to the San Francisco Bay
area and is now dropping snow on the Rockies will transit the
Plains well to our north. Our next rainmaker is still over the
Pacific Ocean, dropping south out of the Gulf of Alaska. Though
not yet sampled by the North American RAOB network, satellite data
confirm that is moving equatorward. While it`s still near the 49th
parallel, this motion is improving confidence in the more
southerly track guidance is advertising. There is fairly good
agreement with this upper low becoming separated from the polar
flow. This would tend to slow its eastward progress significantly,
but the progressive pattern overall should prevent it from
stalling.

As this system crosses the Continental Divide, spreading lift
across eastern New Mexico and West Texas, a fetch of 850mb
moisture will feed afternoon convective development along a
sharpening dryline. It now appears that Friday`s activity may be
west of the New Mexico border, reducing the chances that any of
this will reach North Texas late Friday night. However, as the
upper low spreads large-scale forcing for ascent downstream of
the ongoing convection, a complex of storms will likely survive
overnight into Saturday morning as it invades North and Central
Texas. Additional rounds of rain may significantly disrupt outdoor
activities throughout the day Saturday, and we will prevail
extraordinarily high PoPs for a day 4 forecast. While embedded
strong storms will still appear possible during the day Saturday,
the widespread rainfall should limit the available instability.
For much of the region, the rather dry start to the spring means
that, even with multiple rounds of rainfall during the event,
significant flooding concerns are unlikely. However, the
likelihood of training echoes and the slower speed of the system
overall means that heavy rain may continue into Saturday night in
areas east of the I-35 corridor.

A cold front will invade on Saturday and result in a chilly,
breezy spring day on Sunday. Some postfrontal rain chances will
linger east of I-35 as the upper system plods eastward. Northerly
flow on the backside of the exiting low will maintain below normal
daytime temperatures into the upcoming workweek.

25

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    61  77  52  76  52 /  10  10   0   0   0
Waco                62  78  50  77  52 /   0   5   0   0   5
Paris               60  73  45  71  47 /  10  10   0   0   0
Denton              58  75  46  74  49 /  10  10   0   0   0
McKinney            60  75  46  73  49 /  10  10   0   0   0
Dallas              62  77  53  76  52 /  10  10   0   0   0
Terrell             61  76  50  74  50 /  10  10   0   0   0
Corsicana           61  76  52  75  51 /   0  10   0   0   0
Temple              61  79  52  77  52 /   0  10   5   0   5
Mineral Wells       58  77  46  77  49 /   0  10   0   0   5

&&

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

$$

24/79



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