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

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FXUS64 KFWD 121746
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
1246 PM CDT Tue Sep 12 2017


.AVIATION...
VFR through Wednesday afternoon with only scattered to broken high
clouds.

What is left of Irma will continue moving northward toward the
Ohio Valley and result in a weakening surface pressure gradient
across North Texas. Therefore, a north to northwest wind between
8 and 13 knots this afternoon will decrease after sunset and
remain light north/northwesterly overnight. The wind will become
light southerly/southeasterly Wednesday afternoon once a weak
surface trough begins to deepen across the Central High Plains.

79

&&


.SHORT TERM... /Issued 318 AM CDT Tue Sep 12 2017/
/Today through Tonight/

The latest surface analysis indicates that the center of TD Irma
is near the Georgia-Alabama border and continuing to move
northwest. Wrap-around moisture from Irma will spread mid and high
clouds westward into the eastern half of the forecast area today
as the system works its way into the Tennessee Valley. Some of the
short range hi-resolution guidance shows potential for light
precipitation east of I-35E today, and 10 POPs have been added for
the eastern-most counties where some sprinkles cannot be ruled
out. Any precipitation that manages to reach the ground will
likely not be measurable.

The added cloud-cover will keep temperatures down across the east
with highs topping out around 80 this afternoon. Mid and upper
80s are expected along I-35, with the warmest conditions across
the southwest where highs will be around 90. Persistent north
winds will keep the dry air in place, allowing for another
pleasant night tonight. Tonight`s lows will range from the upper
50s in the rural areas to mid 60s in the Metroplex and the far
southwestern locales.

30

&&

.LONG TERM... /Issued 318 AM CDT Tue Sep 12 2017/
/Wednesday Through Next Monday/

Quiet weather will continue through the latter half of the week,
as Irma`s extratropical remnants over the Lower Mississippi Valley
start to shift off to the northeast. This will be due to an upper
disturbance within the polar branch of the westerlies along the
U.S./Canadian border organizing from the Upper Midwest west toward
the Pacific Northwest. As this synoptic transition unfolds, a
transition to gradually increasing mid level heights from the west
will occur on Wednesday with a transition from modest northerly
winds at the surface more toward a westerly component, though
lighter at 5-10 mph. This will be our transition day which couldn`t
time out any more perfect considering Wednesday is usually termed
as "hump day" of any given work week for most folks. The approach
of the eastern periphery of the 850mb thermal ridge with temperatures
ranging from 22 deg C west to 17-18 deg C west will result into a
warm up of temperatures back into the lower-mid 90s for at least
areas west of the I-35/45 corridors. The east will get one more
day of reprieve with highs between 85 and 90s. Though any
downslope component is expected to be minimal due to the light
wind speeds, I did raise temperatures in the west past MOS values.

With a deep longwave trough deepening across the Western U.S.
Coast and Great Basin, it will draw in a cut off eastern Pacific
low across California and really enhance the height rises across
the Southern Plains and Texas Thursday while what`s left of Irma
moves progressively northeastward across the Ohio Valley and
Pennsylvania Piedmont region. Surface responses to the Western
U.S. trough will be dramatic with lee side pressure falls really
ramping up the south-southeast winds across the area. In addition,
the eastern periphery of the 850mb thermal ridge will shift east
across much of our area Thursday with values from 25 deg C west to
near 20 deg C east. These two days will likely be our warmest
days and have follow hotter deterministic values of the NAM/Euro
models with highs well into the 90s with an isolated reading near,
or at the century mark possible along and west of U.S. 281 each
afternoon. This is usually the time of the year when we receive
Summer`s last punch of heat in most cases. Fortunately, surface
dew point temperatures will not exceed the mid 60s per the
modified airmass over the Northwest Gulf of Mexico from the
upwelling and after effects from Harvey a week or more back. Thus
heat indices will only be a few degrees above ambient high
temperatures and not even reach 100 degrees for the most part.
Throw in occasionally gusty south-southeast winds 15-20 mph with
this round of heat not feeling near as oppressive from what we saw
earlier in the Summer.

The upper ridge should weaken somewhat this next weekend into
early next week, as energy continues to progress northeast from
the positively-tilted Western U.S. longwave upper trough and up
into the Central and Northern Plains/Upper Midwest. An upper high
will literally reform back to our southeast across the Texas and
Louisiana Coastlines and Northwest Gulf. With the low level thermal
ridge weakening and shifting slightly westward and more mid-high
level clouds in resultant southwest flow aloft, highs over the
weekend will remain warm to slightly above climatological normals
for mid September, but not overly impressive with continued south
breezes across the area. The juxtaposition of the upper high
nearby to the southeast will provide enough of a buffer and
subsidence to maintain warm, breezy, and dry conditions across the
area, as systems remain shunted mostly north and west of our neck
of the woods. A more `normal` early Fall pattern should return
next week as we approach the beginning of astronomical Autumn on
the 22nd. There are difference on the extent of troughing between
the GFS/Canadian models and the Euro model, with the former
bringing low convective chances back to our far northwest and Red
River counties. However, the Euro model wants to actually
strengthen the upper high westward across the state. With so much
uncertainty a week out, I have elected to maintain a dry and warm
forecast.

05/

&&

.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    86  64  91  70  96 /   0   0   0   0   0
Waco                89  60  94  68  97 /   0   0   0   0   0
Paris               79  58  87  60  91 /  10  10   0   0   0
Denton              85  59  90  66  95 /   0   0   0   0   0
McKinney            83  59  89  64  94 /   0   0   0   0   0
Dallas              86  64  91  71  96 /   0   0   0   0   0
Terrell             84  61  91  64  94 /   5   5   0   0   0
Corsicana           86  62  90  67  95 /   0   0   0   0   0
Temple              89  61  93  67  96 /   0   0   0   0   0
Mineral Wells       88  60  92  64  98 /   0   0   0   0   0

&&

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

$$

79/26



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