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Area forecast discussion
National Weather Service Fort Worth Texas
605 am CST Fri Feb 24 2017

Aviation...
/12z tafs/

VFR conditions prevail across most of the area this morning with
the exception of a narrow band of stratus along the cold front
from near Paris to just east of Dallas. With drier air quickly
moving into the region...these should erode rather quickly.

Otherwise...VFR conditions are expected to prevail through the
period with northwest winds around 15 kt becoming north overnight
around 10 kt. Winds will diminish to around 5 kt late Saturday and
become southerly Saturday night.

Dunn

&&

Previous discussion... /issued 346 am CST Fri Feb 24 2017/
after record heat across parts of the area yesterday, big changes
are underway this morning. A cold front is making southward
progress and has entered North Texas as of 3am. Gusty north-northwest winds and
sharply cooler temperatures will follow immediately behind the
front as it shoves through the forecast area. Readings in the 40s
are present across southern OK, and our northwestern zones should
see lows in the 40s and low 50s before sunrise. Much drier air
will also accompany the front which will mean mostly clear skies
for the rest of the day, aside from a few mid/high clouds with the
passing shortwave trough. Ahead of the front, modest low-level
moisture is resulting in sporadic low stratus across our
southeastern counties, but this will clear by mid morning as the
drier air arrives. The cold front is expected to clear our entire
area to the southeast by late morning or noon at the latest. Highs
will be as much as 20-30 degrees cooler than yesterday,
especially across our northwestern counties. Some borderline
elevated fire conditions will exist again this afternoon west of
I-35 where low humidity values and north winds of 10-20 mph will
be in place. The much cooler temperatures should keep fire weather
danger quite a bit lower than yesterday though. Cold/dry
advection will continue through tonight resulting in some near- or
even sub-freezing lows in rural areas across our northern and
western zones.

On Saturday, highs are expected to be below normal for the first
time in 10 days as a "cold" dome of high pressure becomes situated
across the Southern Plains. Zonal flow aloft will prevail across
most of the Continental U.S. As the trough that brought in this morning's
front departs to the northeast. Another positively-tilted trough
will be digging southeast along the West Coast during this time
which will be our next forecast concern.

As the previously-mentioned trough moves into the southwest US,
southerly flow will resume. A warm advection regime will set up
across Texas Saturday night and moisture will begin returning to the
region Sunday morning. Moisture will surge northward throughout
the day Sunday with dewpoints climbing from the low 30s into the
upper 40s and 50s due to Stout low-level southerly wind fields.
Momentum Transfer from 850mb winds of 40+ kts will make for a
breezy sunday; surface winds of 20 mph with gusts to 30 mph are
expected. By late Sunday afternoon and evening, sufficient
moisture will be in place for some elevated warm-advection
showers. Instability will be sorely lacking at this time with very
modest mid-level lapse rates. This will change later Sunday night
as mid-level cooling takes place due to the approaching trough. A
few hundred j/kg of MUCAPE will be available but the greatest
low-level moisture is expected to be strongly capped. Have went
with a mention of showers and isolated thunderstorms area-wide
overnight Sunday night as slightly stronger forcing arrives.
Coverage should be highest across the eastern zones which is where
the highest pops have been confined.

The setup for early next week remains a bit blurry due to
differences in mesoscale features among the models, although this
should be expected 4-5 days into the forecast. The larger scale
features however, are in fairly good agreement which does lend a
bit of confidence to the forecast. There are a few key features
that will need to be monitored during the Monday-Tuesday night
time frame, all of which could result in either strong/severe
storms or no storms at all in our area depending on their exact
positions.

A weak front is expected to stall along/near the Red River early
Monday morning, draped roughly east-west from a developing surface low
across the Texas Panhandle. A north-S oriented dryline will have also
taken shape across West Texas at this time. The stalled front should
surge back to the north on Monday morning as a warm front
accompanied by a swath of low/mid 60s dewpoints. While large-scale
dynamic lift won't be terribly strong during this time, lift from
warm advection should be capable of generating scattered showers
and storms within the warm sector airmass. Instability forecasts
from both the GFS and European model (ecmwf) suggest that as much as 1000 j/kg of
surface-based instability could be in place during this time with
steepening mid-level lapse rates. There will also be no shortage
of wind shear given the strong mid/upper level jets draped across
the southern portion of the US. For these reasons, we'll need to
keep a close eye on the setup Monday morning/midday for some
potential strong/severe storms within the warm sector airmass
south of the warm front and east of the approaching dryline. On
Monday afternoon, models currently suggest the dryline will be
pulled through the area by the northeastward-moving surface low,
shutting down our thunderstorm chances.

The next time frame we'll need to monitor will be Tuesday and
Tuesday night. A northwestward surge of Gulf moisture is expected
to replace the drier air associated with monday's dryline passage,
with a new dryline taking shape somewhere across the eastern half
of Texas. There are still considerable differences between the GFS
and European model (ecmwf) with the dryline's position, as should be expected.
These larger scale models will often struggle with dryline
position given their inability to diagnose shallow moisture
intrusions, not to mention their inability to handle other
important dryline mechanisms such as evapotranspiration and soil
moisture content. The European model (ecmwf) brings a surge of moisture as far
west as the I-35 corridor on Tuesday while the GFS keeps the
moisture gradient confined to East Texas and east of our forecast
area. The environment ahead of the dryline should be conducive for
some strong or severe storms given the favorable thermal profiles
and abundance of low-level moisture, not to mention the 60+ kts
of deep layer shear at the nose of a strong mid-level jet. If the
dryline sets up east of our area as the GFS suggests, then we'll
be warmer and dry. If the western solution from the European model (ecmwf) verifies,
we'll be contending with the potential for some strong or severe
storms Tuesday afternoon or evening. We'll continue to refine the
details over the weekend.

For the remainder of next week, a cold front should move through
late Tuesday night or Wednesday keeping US cool and mostly dry
through Friday.

-Stalley

&&




Preliminary point temps/pops...
Dallas-ft. Worth 64 37 55 41 68 / 5 0 0 0 20
Waco 71 38 59 40 68 / 5 0 0 0 20
Paris 62 33 54 37 63 / 5 0 0 0 40
Denton 61 33 54 38 66 / 5 0 0 0 20
McKinney 61 34 54 37 65 / 5 0 0 0 30
Dallas 64 38 55 41 67 / 5 0 0 0 30
Terrell 66 35 55 39 67 / 5 0 0 0 40
Corsicana 70 38 57 41 69 / 5 0 0 0 40
Temple 74 38 60 41 69 / 5 0 0 0 20
Mineral Wells 62 33 55 39 68 / 5 0 0 0 20

&&

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