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-- Discussion containing changed information from previous version are highlighted. --
004
FXUS64 KFWD 231032
AFDFWD

Area Forecast Discussion
National Weather Service Fort Worth TX
532 AM CDT Fri Apr 23 2021

...New Short Term, Aviation...

.SHORT TERM... /NEW/
/Today and Tonight/

Low level moisture was surging northward behind a lifting warm
front early this morning. This was resulting in extensive low
clouds, patchy fog and drizzle with some visibility restrictions
between 1/2 and 1 mile across parts of Central Texas.

The atmosphere across North and Central Texas will become
favorable for thunderstorm development through the day due to
increasing large scale lift and destabilization associated with
an approaching upper trough. Mid level lapse rates were already
around 7 deg C/km and will increase even more through the day.
Nearly all guidance suggests that storms will likely not develop
until about midday across the western CWA once the upper trough
axis reaches eastern New Mexico. The first storms will likely be
elevated above a cap of warm air. However, the cap should erode
quickly during the afternoon due to increasing large scale ascent
and forcing along the dry line. Shear profiles will support long
lived updrafts capable of large hail. Mid level dry layer will
also support the formation of downbursts. The tornado potential is
a bit less uncertain since extensive cloud cover will limit low
level destabilization, however, backed surface flow near the
triple point will be more than adequate for rotating updrafts.
Therefore we will keep all modes of severe weather mentioned with
the most favorable time frame for severe storms during the
afternoon and evening hours and the most favored location along
and east of the I-35 corridor.

Storm chances will decrease from west to east this evening with
the passage of the upper trough axis, but there may be enough
lingering moisture and instability behind the departing system for
a few storms to develop along the cold front, especially near the
Red River.

Temperatures today will be warmer than Thursday even though it
will remain cloudy due to strong low level warm air advection.
Highs will range from the upper 60s in the northeast to around 80
across the west where clouds should clear behind the dryline
in the afternoon. Lows tonight will be fairly mild, ranging from
the mid 50s in the northeast to the lower 60s in the southeast.

79

&&

.LONG TERM... /Issued 231 AM CDT Fri Apr 23 2021/
/Saturday and Beyond/

A cold front will be clearing the southeastern-most zones around
daybreak Saturday as the Friday system and associated
precipitation heads for the Mississippi Valley. A 10 to 15 degree
dewpoint drop is expected behind the front with values in the 40s
and 50s by afternoon. This should make for pleasant weather over
the weekend with lows in the 50s and highs in the 70s and 80s. In
fact, with an upper ridge expected to pass overhead, some of the
western counties will see high temperatures near 90 both Sunday
and Monday.

Return flow will ramp up Sunday night into Monday due to lee side
pressure falls associated with the next upper level storm system,
which will move from California eastward through the Rockies
during the first part of next week. Breezy and warm conditions may
create some elevated fire weather concerns both Sunday and Monday
afternoons for areas along and west of Highway 281.

A northward surge of Gulf moisture will then occur on Tuesday as
the leading edge of the system to our west begins to emerge in the
Plains, with a swath of 1.5" PWATs spreading in from the south.
It looks like a dryline may set up somewhere to our west, though
the exact location will depend on how progressive the upper level
system is. The current thinking is that the dryline will be well
to our west, but close enough to keep at least a slight chance of
thunderstorms in the forecast for Tuesday late afternoon-evening,
when a lead wave is progged to lift northeast across West-Central
Texas.

The upper trough will slowly and steadily approach from the west
Tuesday night through Wednesday. Dryline storms may subside
Tuesday evening, but convection would likely get going again
overnight as the low level jet intensifies and larger scale ascent
arrives with the trough. The highest POPs with this package will
hence be Tuesday night into early Wednesday, which is right in the
middle of the model spread with regard to timing. Precipitation
would gradually end from west to east sometime Wednesday night or
early Thursday.

There is still a bit of uncertainty due to the large timing
spread among guidance, so there may be some adjustments with
regard to the onset and end time of next week`s rain/storm event
in future forecasts. Either way, there should be enough shear and
instability present (and given the time of year) for at least a
low-end severe threat to exist. Higher severe probabilities would
depend on several other unknowns, which we should gather more
information on this weekend and early next week.

A dry, northwest flow pattern will arrive in the wake of the mid-
week system, bringing what looks to be rain-free weather with
seasonable temperatures next Friday through the following weekend.

30

&&

.AVIATION... /NEW/
/12Z TAFs/

Low ceilings/visibility will be the primary aviation weather
concern this morning, thunderstorms will be the main concern this
afternoon, followed by a wind shift associated with a cold front
tonight.

MVFR to IFR ceilings covered all of North and Central Texas early this
morning. These ceilings will remain in place through the afternoon
until a dryline moves in from the west followed by a cold front
later tonight. Some visibility restrictions due to fog and drizzle
will also continue this morning, mainly across parts of Central
Texas. VFR conditions are expected early this evening and
overnight.

Model guidance continues to be in surprisingly good agreement that
storms will quickly develop early this afternoon near the I-35
corridor with the the best window of time for impacts at the
terminals between 18Z and 22Z. After 22Z, the best storm chances
will shift eastward followed by the passage of the upper trough
axis. Once the trough axis passes, a cold front will move in from
the northwest, resulting in a northwest windshift between 07 and
08Z at the Metroplex TAF sites and slightly later in Waco. Ahead
of the front, a southerly wind will continue in the 7 to 13 knot
range this morning and between 13 and 17 knots this afternoon
along with some higher gusts.

79

&&


.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth    74  56  76  52  83 / 100  50   0   0   0
Waco                76  56  77  51  84 / 100  40   0   0   0
Paris               69  57  73  49  77 / 100  90   0   0   0
Denton              72  56  75  49  82 / 100  40   0   0   0
McKinney            72  56  74  50  80 / 100  70   0   0   0
Dallas              75  57  77  53  83 / 100  70   0   0   0
Terrell             73  57  74  50  80 / 100  70   0   0   0
Corsicana           75  57  76  52  82 / 100  70   0   0   0
Temple              76  55  78  51  84 / 100  30   0   0   0
Mineral Wells       75  55  76  49  85 /  90  10   0   0   0

&&

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

$$