Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 04/23/21
Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
812 PM CDT Thu Apr 22 2021
...New Short Term, Aviation...
.SHORT TERM... /NEW/
/Through Friday Night/
The primary weather concern over the next short term forecast
period revolves around chances for severe convection across North
and Central Texas. Friday will be a day that individuals should
monitor the weather closely from a trusted source as severe
weather will likely strike quickly. In addition, there will be a
risk for areas of fog/drizzle that could reduce visibility down to
below 1 mile.
Surface analysis in tandem with satellite imagery indicated a
conveyor of richer near surface moisture extended from South
Texas northwestward toward western reaches of the Hill Country.
Ceiling observations in tandem with aircraft data (AMDAR) from
Dallas Love Field and our presently ascending 00 UTC weather
balloon showed a large amount of dry air from near 5,000 feet
toward the surface across North and Central Texas. While the
radarscope has slowly continued to illuminate thanks to increased
mid-upper level ascent (implied by increasing high clouds), I
think we`ll be hard pressed to measure any rainfall over the next
6 to 12 hours thanks to the aformentioned dry air. As a result,
I`ve opted for a mention of sprinkles as opposed to rain showers
for many areas through 12 UTC Friday, though a few areas may
measure south of I-20 and west of US HWY 281 as ceilings fall
below 1,000 feet during the pre-dawn hours on Friday.
A warm front extended from near Del Rio to Victoria this evening
and thanks to observed surface pressure falls between 2-4 mbar
over the past several hours, this boundary should have no problem
lifting northward tonight. As it does, we`ll see an increased
advection fog potential between 3 am and sunrise across western
Central Texas and likely our initial shower and thunderstorm
development after sunrise Friday. While advective in nature, fog
processes may be hindered some as 925mb flow is expected to remain
quite turbulence and as a result of this, I`ll omit the mention
of "dense" fog from the worded forecast. However, we`ll monitor
this potential during the overnight hours.
One of the more significant changes made to the forecast (though
I`m still very cautious about this) was to delay the wording of
"severe" in the zones until the afternoon. Initial glances at
some of the hi- res model guidance would suggest that deep
convection could fire as early as 15 UTC. However, taking a look
at some of the synoptic guidance, it doesn`t appear that
appreciable height falls associated with the main PV anomaly
currently across western Arizona will not impinge upon our area
until closer to 17-18 UTC. Moreover, there`s still a little bit of
remnant capping evident in forecast soundings so the potential
for surface based convection in the morning looks low at this
time.
I still show high chance PoPs (50%) through 16 UTC for areas
near/southwest of a Jacksboro to Waco to Temple line, but I
believe the potential for a larger coverage of severe weather may
not occur until Friday afternoon...closer to 18-19 UTC (more in
accordance with the NSSL WRF and NCEP WRF ARW core). It`s possible
that even this timing may be a little too early. Does that mean
that we won`t have severe weather across our area in the morning?
NO! In fact, IF elevated convection gets going along the
northward lifting warm front, it`ll certainly have a large hail
potential given 0-6km bulk wind differences of 50 knots and
700-500mb lapse rates closer to 8 C/km. Because this activity
is expected to be elevated, I believe the damaging wind and
tornado threat will be low. Any surface based storm near the warm
front, however, will need to be monitored closely for a damaging
wind and/or tornado threat!
As stronger forcing for ascent emerges from the west, I do
believe that both newly formed and any ongoing convection will
strengthen very, very quickly. While widespread cloud cover will
likely dampen what would otherwise be much higher instability
values, CAPE is still progged to average out to around 2000 J/kg
across our area in a strongly sheared environment (supportive of
supercellular structures). Forecast soundings suggest that the
high shear and steep lapse rates would facilitate large to
potentially significant hail sizes (2+ in diameter), along with
damaging winds. 0-1 km shear values from hi-res guidance suggest
that these values will be maximized to the south and east of the
Metroplex, and thus I would anticipate a greater tornado risk
here. However, low level SRH may also increase farther north
across Northeast Texas (near and east of US HWY 75) depending on
where the frontal boundary stalls and any storm interacting with
the warm front (or any additional boundary) will have an enhanced
wind and tornado threat.
Storms will likely exit East Texas between 03-06 UTC, but the
dryline appears that it`ll lag back to the west. A cold front is
expected to crash southward from Oklahoma Friday night and
normally this would present another opportunity for additional
convection to fire. However, we`ll be on the subsident side of the
upper trough and this will likely suppress any deep convection.
However, they`ll likely be attempts along the boundary and if an
updrafts can realize what should still be unstable air, there
could be a brief strong to severe weather threat after midnight.
Bain
&&
.LONG TERM... /Issued 401 PM CDT Thu Apr 22 2021/
/Saturday through Thursday/
High pressure will be building into the Southern Plains on
Saturday behind tomorrow`s thunderstorm activity. Cooler and drier
air will filter into the region throughout the day, although we`ll
likely have to contend with some wrap around cloud cover through
at least midday in the northeast counties. This should clear out
by Saturday night leaving clear skies and cool conditions with
most locations in the lower 50s along with some upper 40s.
The next strong system will be moving into the western U.S. on
Sunday and lee cyclogenesis will quickly allow southerly winds to
return to the Plains. This should result in a quick warm up with
moisture beginning to spread back to the north. Highs on Sunday
should top out in the low to mid 80s across the region. As the
upper trough deepens over the 4-corners region Monday into Monday
night, strong southerly flow will begin to pull deeper moisture
rapidly northward setting the stage for a more classic spring time
severe weather event on Tuesday...or Wednesday. Unfortunately
there is quite a bit of spread in the global guidance and ensemble
cluster analysis doesn`t offer much direction in which to lean.
The tendency in the guidance has been to slow down the upper
trough to some degree...which obviously delays the moisture
transport and convective evolution. Nonetheless, it does appear
that there is a good bet for additional severe weather sometime in
the Tues-Wed timeframe. Those timing details will be worked out
over the next few days. In the meantime, a warming trend into next
week is expected.
Dunn
&&
.AVIATION... /NEW/
/00 UTC TAF Cycle/
Concerns---Ceiling trends and TSRA potential.
VFR cigs will quickly lower down into the MVFR category just
prior to 06 UTC Friday as low level moisture moves eastward. A few
spits of -SHRA are possible this evening, but this potential is
low. Dry air beneath cloud base of some of the -SHRA may support
some pockets of low level turbulence. IFR appears probable by mid-
morning with an intermittent LIFR cig potential plaguing the
Friday morning push. The chances for SHRA will increase as well
in concert with a northward lifting warm front. The latest TAF
will advertise MVFR BR associated with the approach of the warm
front, but its possible IFR BR may be needed in future TAFs during
Friday morning. Regarding the thunder potential, at present time
it appears that the greatest instability (both elevated and
surface based) won`t arrive until the afternoon hours. As such,
I`ve confined TSRA to after 18 UTC. However, if lift arrives
sooner and/or instability increases more quickly, TS may begin as
early as mid to late morning (16 UTC) and adjustments to the TAF
will be needed. Otherwise, southerly winds of 10 to 15 knots with
occasional gusts to 20 knots can be anticipated. Stronger and
more erratic winds are probable INVOF TSRA in addition to a risk
for hail with the strongest convection.
By the end of the TAF period, VFR will prevail with SHRA/TSRA
exiting to the east. Impacts will likely linger as TSRA will
likely clutter the airspace from arriving traffic along the
Bonham/Cedar Creek cornerposts as well as eastbound departure
routes. In addition, there`s a non-zero risk that additional
SHRA/TSRA may develop north of D10 airspace between 0300-0600 UTC
Saturday.
Bain
&&
.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth 58 74 56 77 54 / 10 100 50 0 0
Waco 60 76 56 78 51 / 10 100 40 0 0
Paris 56 69 57 73 49 / 10 100 90 0 0
Denton 57 72 56 75 48 / 10 100 40 0 0
McKinney 57 72 56 74 50 / 10 100 70 0 0
Dallas 59 75 57 78 55 / 10 100 70 0 0
Terrell 58 73 57 75 50 / 10 100 70 0 0
Corsicana 60 75 57 77 52 / 10 100 70 0 0
Temple 61 76 55 78 51 / 10 100 30 0 0
Mineral Wells 57 75 55 77 49 / 10 90 10 0 0
&&
.FWD WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Area Forecast Discussion
National Weather Service Phoenix AZ
507 PM MST Thu Apr 22 2021
.UPDATE...
Updated Aviation section.
&&
.SYNOPSIS...
A weak weather system will linger over the region through tonight
allowing for cooler temperatures and possibly a few isolated rain
showers this evening and tonight. A warming trend is then
expected into the weekend with high temperatures returning to
slightly above normal and more breezy to locally windy conditions.
A more substantial weather system moving in for early next week
will bring temperatures back down to below normal while also
providing fairly decent chances for rain.
&&
.DISCUSSION...
An elongated trough from UT through southern CA is evident on
water vapor this afternoon with multiple weak vorticity maximums
along the axis. Surface dew points are 30-40 degrees higher than
this time yesterday and temperatures are several degrees cooler as
well, as noted on ACARS aircraft soundings out of Phoenix. The
limited amount of moisture return since yesterday and aloft
associated with the trough has been enough for scattered cu and
weak showers to develop over northern AZ this afternoon with
100-300 J/kg SBCAPE. As the trough axis traverses the area this
evening and tonight a few showers could develop as far south as
the greater Phoenix area before moving through southern Gila
county, as a few hi-res models suggest. Have maintained a 10% PoP
for the Phoenix area late this evening. The HREF probability of
measurable rain from any shower is nearly zero, so the main
impacts will be brief gusty winds and perhaps a couple lightning
strikes.
Upper level ridging will take over across the region following the
trough starting Friday and lasting through most of the weekend. A
warming trend Friday into Saturday will push daytime highs back
into the lower 90s by Saturday, likely persisting into Sunday.
This weekend will also become quite breezy with afternoon gusts
approaching 30 mph in some areas, creating another round of
elevated fire danger conditions. The increased winds will be the
result of a deep trough briefly stalling out just off the Pacific
NW coast.
Model ensembles are in very good agreement showing the deep trough
off the West Coast over the weekend before eventually tracking
eastward through the Southwestern U.S. early next week. This
trough does look to be large enough in scale and have enough
residence time over water to pick up a good amount of moisture as
PWATs of around 0.9-1.0" are forecast to reach the southern
California coast Sunday night with potentially up to 0.75" PWAT
making it into the CWA through Monday. Based on model soundings
and a long-fetch weak IVT plume, this sets up to initially be an
isentropic top down moistening scenario favoring orographic
regions. The main variance among global models at this point is
still timing and location, but latest consensus is suggesting best
rain chances will be during the latter half of Monday into Tuesday
and the trough axis pushing mostly east of the area Tuesday night.
As expected with April weather systems, potential rainfall amounts
are rather light with both the GEFS and EPS showing around
0.1-0.2" for the Phoenix area and lighter amounts over the western
deserts. Latest QPF amounts over the high terrain north of
Phoenix show up to 0.5". Any thunderstorm chances are likely to
fall on Tuesday as the timing of the trough shifts colder air
aloft over the area. We should also see much cooler temperatures
starting Monday with highs likely dipping into the mid to upper
70s.
Below normal temperatures early next week are unfortunately
likely to be short-lived as strong ridging behind the system
should push daytime highs back into the 90s by late next week
along with potentially even the first 100s for some locations.
&&
.AVIATION...Updated at 0006Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
A follow-on short wave trough is centered roughly over the Lower
Colorado River Valley extending through northern Baja Mexico and
offshore. The wave will slowly move eastward today and tonight.
Scattered light showers and isolated thunderstorms have been
occurring over the northern half of Arizona this afternoon. As the
trough moves eastward, it is anticipated that isolated showers
will brush the metro area roughly between 06Z-12Z. The most likely
area for this to occur is outside of the Loop 101 Freeway. Of the
TAF sites, DVT and SDL are more likely to have showers in their
VCNTY than PHX or IWA. There could also be a stray thunderstorm in
the mix. At this time, occurrence of -SHRA (let alone -TSRA) at
any given TAF site is too low to depict as prevailing conditions
or even TEMPO. But will continue to monitor the situation. Higher
confidence in mid level ceilings roughly 10-12kft ASL (locally 7-9
ASL) in the 06Z-12Z time frame. Clouds diminish significantly
thereafter. As for winds, southwest surface winds will weaken this
evening and trend toward southeasterly after 06Z. If showers, or
especially thunderstorms develop, more erratic patterns can be
expected. Anticipate redevelopment of southwest and west winds by
midday/early afternoon along with some gustiness (~20kts).
Southeast California/Southwest Arizona including KIPL and KBLH:
A follow-on short wave trough is centered roughly over the Lower
Colorado River Valley extending through northern Baja Mexico and
offshore. the wave will slowly move eastward today and tonight.
There is enough moisture for isolated weak showers over eastern
Riverside County with a broader area of ceilings at FL100-120.
Anticipate this to begin to dissipate with sunset. Probability of
showers at BLH too low at this time to reflect in the TAF. A stray
thunderstorm couldn`t be ruled out but probability of occurrence
at BLH is even lower than for -SHRA. Expect little if any
cloudiness at IPL. South and southwest surface winds can be
expected at BLH the rest of today and through the day Friday with
highest speeds in the afternoons (gusts ~20kts). Westerly winds
will be favored at IPL through the night with an uptrend in speeds
this evening (gusts 20-25kts) before weakening overnight. Light
westerly winds at IPL are anticipated to transition to southerly
by midday Friday.
&&
.FIRE WEATHER...
Sunday through Thursday:
Above normal temperatures are expected Sunday with highs in the
low 90s. An approaching weather system will make conditions
breezy to locally windy Sunday and Monday, with gusts up to 25-35
mph most places. Min RHs will be in the 5-10% range Sunday,
creating elevated fire danger conditions, wile RHs improve and
temperatures fall below normal Monday into Tuesday as the
aforementioned weather system moves through. Monday and Tuesday
will see decent chances for wetting rains over the high terrain
and possibly across some of the lower deserts. Following this
system, temperature quickly warm back and drier air will move back
in.
&&
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&
$$
DISCUSSION...Benedict/Kuhlman
AVIATION...AJ
FIRE WEATHER...Benedict/Kuhlman