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

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FXUS64 KFWD 172332
AFDFWD

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


.AVIATION...
Concerns---Shift from S`ly to N`ly flow (all sites) and MVFR cigs
(KACT).

Visible satellite imagery shows high clouds beginning to
stream over North and Central Texas. These clouds are quite
high...at or above FL250 and should pose no operational impact.
S`ly flow persists this evening as a surface low develops over the
Great Plains. A few low clouds could develop, but moisture should
be sparse enough to preclude any MVFR cigs...but will mention
FEW018 for now. Cold front will approach the Metroplex TAF sites
around 18/1100Z. As front passes...winds will veer sharply out of
the NW at 15-20 KT and any low clouds that may be around will
clear out. High clouds should clear out by Wednesday afternoon
with winds subsiding after sunset.

As for the MVFR possibility at KACT...time-height cross-sections
as well as forecast soundings indicate that just enough boundary
layer moisture should be available for some cloud cover to develop
below FL020 by 18/0900Z. MVFR should not last long however as the
cold front should reach KACT by 18/1400Z...clearing out any low-
level moisture and bringing a return to VFR through the end of the
forecast period.

Godwin

&&


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

&&

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

$$

37/79



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