Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 12/28/21
Area Forecast Discussion...CORRECTED
National Weather Service Phoenix AZ
544 PM MST Mon Dec 27 2021
.UPDATE...
Updated Aviation discussion.
&&
.SYNOPSIS...
An unsettled winter weather pattern will continue through the week
as a series of fast moving weather systems pass through the region.
Precipitation chances will occur on multiple days with the best
chances on Tuesday and Friday. The highest precipitation amounts
will be focused over the higher terrain of central Arizona.
Temperatures will remain below average through the entire week.
&&
.DISCUSSION...
GOES WV imagery and RAP H5 analysis shows a very moist jet streak
and SW flow aloft ahead of an upper level trough and PVA
anomalies dropping through coastal CA. Additional PVA anomalies
were moving through AZ ahead of the trough axis. IR METSAT imagery
depicts widespread cloudy conditions with a large high and upper-
middle cloud shield with and ahead of the low pressure system.
Radar has been showing a large area of mostly just virga
signatures south of Phoenix. The moisture profile in the latest
Phx ACARs soundings showed elevated moisture lingering in the
lower BL up through ~850 mb with an inversion cap of dry air above
that up to the moist upper-middle cloud base barely above H5,
with PW near 0.55"
Still under the heavy influence of a long-lived unsettled weather
pattern, models and ensembles agree on the next 2-3 shortwave
disturbances passing through our area from this evening through Wed
morning or possibly even Wed evening. The first of these passes
through SE CA this evening and tonight and will bring breezy to
locally windy conditions across parts of SE CA from this afternoon
through tonight. As a result a wind advisory remains in effect for
gusty winds with gusts up to 45 mph including JTNP and W Imperial
Cty and I-8.
Another fast wave(s) tomorrow into Tue night/Wed. will dramatically
increase the chance of precipitation on Tuesday to 70-80%, mainly
for Phoenix and the surrounding deserts and e-ward to the high
country. The Grand Ensembles and the NBM are in excellent
agreement on a high POP, modest QPF scenario for Phoenix on Tue-
early Wed with total rainfall for Phoenix near ~0.1-0.25".
However orographic upslope conditions will enhance the QPF totals
across the high country NE-E of Phx as a modest and fleeting IVT
plume accompanies the system. Models depict a nicely elevated
moisture levels from just under 850 mb to just above H7. As a
result high country QPF could range from 0.25-1.00" and locally
higher in moderate rain showers. For Phoenix and the lower deserts
the HREF family and the HRRR depict scattered light rain showers
for Tue-Tue evening.
The NBM and HRRR and other models have also been consistently
increasing the amount forecast snow amounts for elevations above
~4.5-5 Kft. Although an overly dry layer from -10 to -13 degrees C
and higher may inhibit dendritic production. However the NBM prob of
snowfall accumulations >4" approaches 40% ending 12Z Wed for the Hwy
60/Hilltop area of S Gila Cty. Therefore the benefit of the doubt
has been granted to the models and a winter weather advisory has
been hoisted for Tue morning through Wed morning for high
country/S Gila Cty elevations above 4,500` for snow accumulations
up to 7". As a result hazardous winter driving conditions in the
higher elevation passes are expected.
By Thursday an elongated low pressure trough digging through
offshore CA maintains strong SW flow and a jet streak across the
region. Then for Friday at least two clusters and >50% of the
members are very bullish on ejecting at least the first of a
possible pair of pronounced troughs through the region on Fri and
into the weekend. These two clusters also depict widespread and
locally heavy precip across the entire CWA, especially for Phoenix
and eastward.
Various IVT ensemble forecasts for the late week period favor the
main moisture plume surge to be centered further SE of the CWA
with only the N fringes of the plume over the CWA. However the NBM
and Grand Ensemble QPF are in very good agreement on Phx QPFs for
the New Year`s Eve Friday at an elevated range of 0.5-1.25" and
typically even much higher amounts near 1-2" across the high
elevation burn scar country.
Models are also showing some early confidence in sharply colder
temps by Sun morning with lows across the lower deserts in the mid
30s in Phx and the upper 20s in across the open deserts.
&&
.AVIATION...Updated 0040Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
A series of passing weather disturbances and subtle cold fronts
over the next 24-36 hours will lead to periods of ceilings below
6kft AGL. A subset of that time will also see light showers -
mainly Tuesday afternoon which is also when MVFR conditions are
most likely. Before then, there may some spotty light showers
between 09Z-17Z. Surface winds should favor southwest directions
this evening but it would not be surprising to see southeast or
variable conditions. Above the surface, deep moderate to strong
southwesterly flow will continue.
Southeast California/Southwest Arizona including KIPL and KBLH:
A series of passing weather disturbances and subtle cold fronts
over the next 24-36 hours will lead to windy conditions this
evening and again Tuesday afternoon (favoring southwesterly
directions) with lighter southwesterly winds in between. Above
the surface, strong southwest and west winds will continue.
In addition to the winds, there will be an increase in the lower
tropospheric humidity such that scattered cumulus can be
anticipated during the day Tuesday (if not sooner) and possibly
some ceilings of BKN050 Tuesday afternoon (more likely at KIPL
than KBLH). Shower activity is not expected.
&&
.FIRE WEATHER...
Wednesday through Sunday:
Temperatures will continue in a below normal range through the week
as a moist environment results in periodic chances for
precipitation. Some eastern districts could see another round of
heavier accumulation late in the week. Snow levels in eastern
districts may fall as low as 4500ft during the middle of the week
before increasing late in the week. Minimum afternoon humidity
levels will struggle to reach 40% although some drying may arrive
over the weekend. Overnight recovery should be excellent in a 60-
100%. Wind speeds appear fairly typical for the season with
potentially some enhancement of northerly winds behind a front over
the weekend.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Winter Weather Advisory from 3 AM Tuesday to 5 AM MST Wednesday
for AZZ557-558-563.
CA...Wind Advisory until 3 AM PST Tuesday for CAZ560-562-566.
&&
$$
DISCUSSION...Sawtelle
AVIATION...AJ
FIRE WEATHER...18
Area Forecast Discussion
National Weather Service Shreveport LA
528 PM CST Mon Dec 27 2021
.AVIATION...
Skies to start this TAF period remain in VFR category, but should
begin to degrade back into MVFR by 28/06z. Skies should remain
MVFR well into tomorrow afternoon, with gradual clearing into VFR
likely by 28/18z. Gusty winds will be possible through the
afternoon tomorrow, which may effect smaller aircraft and ground
operations. Scattered rain showers will also be possible over the
next 24 hours, but confidence was not high enough to carry any
precipitation through this TAF period.
/44/
&&
.PREV DISCUSSION... /issued 311 PM CST Mon Dec 27 2021/
SHORT TERM.../Tonight through Tuesday Night/
We have just about reached our high temperature for the day as
surface observations from this afternoon show temperatures ranging
from the mid 70s to around the 80 degree mark. Satellite imagery
from this afternoon is showing some low-level cumulus clouds
across most of the region. Not expecting temperatures to climb too
much more for today, but we perhaps could squeeze out another
degree or two before all is said and done.
Mild conditions are expected to continue into the overnight hours
with overnight lows only able to fall into the lower to mid 60s
across the region. Have maintained some mention of slight
precipitation chances across portions of the area during the
overnight hours as we could see enough lift to promote a few
showers, mainly for portions of our northern zones, however, a few
models indicated that additional areas could see some showers
overnight as well.
As we move into the day Tuesday, southwest flow aloft will
continue across the region ahead of an upper-level trough the will
begin digging into the Rockies. Have kept mention of showers and
perhaps a few thunderstorms developing through the day tomorrow
across a larger portion of the forecast area. The best chances
will come across our eastern zones, where the Storm Prediction
Center currently has a General Thunderstorm Risk painted across
that eastern portion of the area. Afternoon temperatures will
still reach near record levels on Tuesday despite the increased
cloud cover and precipitation chances. Highs will be similar to
what we saw today (Monday) with readings ranging from the mid 70s
to around the 80 degree mark. Have maintained precipitation
chances into the overnight hours Tuesday night, with again the
best chances coming for our southeast zones. Lows will fall into
the mid 50s to mid 60s with the cooler temperatures across our
northern zones and warmer across our southern zones. /33/
LONG TERM.../Wednesday through Sunday Night/
Multiple rounds of high-impact weather are expected during the long-
term period, but there is also a high amount of uncertainty with
each system.
A weak shortwave trough embedded within strong southwesterly flow
aloft will move from the Southern Rockies and into Kansas and
Missouri by Wednesday afternoon. A surface low in the Texas/Oklahoma
Panhandles will move east, and eventually northeast, along a cold
front diving southward through the Plains. Widespread convection
should be ongoing at the start of the period across most of the
forecast area. Vertical shear profiles are sufficient to support the
development of at least a couple of severe storms between sunrise
and noon Wednesday, but a lack of instability early may prove to be
a limiting factor. Despite the earlier morning convection, strong
low-level warm air advection and compressional warming ahead of the
front may be enough to allow the atmosphere to recover after noon.
Model guidance suggests CAPE values between 1500-2000 J/kg may build
across Southern Arkansas and Northeast/North Central Louisiana
during the afternoon hours, which should allow for a greater chance
for severe storms if convection redevelops across our area Wednesday
afternoon and into the early evening. "If" is the operative word
because the best vertical ascent and upper dynamics will also be
exiting the area to the east and northeast around sunset. If severe
convection develops, damaging winds, large hail, and isolated
tornadoes will be possible.
The severe weather threat should end Wednesday evening, and the cold
front will likely stall briefly just north of the forecast area
before rapidly retreating northward during the day Thursday. Thus,
the unseasonably warm temperatures will continue through Saturday.
Showers will return to the area on Friday in a warm air advection
region ahead of the next powerful upper trough that will be digging
into the Intermountain West.
The forecast becomes increasingly complex and uncertain beyond 12z
Saturday. An arctic cold front will be diving south through the
Plains. Saturday morning, a strong surface low along the front in
Southern Kansas/Northern Oklahoma will eject northeast at the same
time as large scale ascent from the strengthening upper trough
begins to spread over the Southern Plains and Southeast CONUS. A
large area of convection should develop from Northeast Texas, into
Arkansas, and the Tennessee and Ohio River Valleys. Instability may
prove to be limiting factor once again early Saturday in regards to
any severe weather chances, but the risk for severe storms is not
zero at this point. After the initial surface low ejects towards the
Great Lakes, another surface low is expected to rapidly develop in
South Texas ahead of the upper trough. This second low will also
quickly eject northeast and across portions of the forecast area
south of Interstate 20, most likely Saturday night/early Sunday
morning. The exact track of this surface low will be vital in
determining our severe weather chances because shear profiles,
especially low-level shear profiles, should be very strong in the
warm sector in the vicinity of the surface low. All modes of severe
weather will be possible in this zones. At this time, the greatest
risk for severe storms at this time appears to be between south of a
line from Jacksonville, to Shreveport, to El Dorado. Again, there is
a high amount of uncertainty regarding the track and timing of the
synoptic features and a high degree of disagreement among the models.
If the severe weather threat wasn`t enough, a deep cold airmass will
advect into the area behind the front. With the upper trough lagging
behind the front and surface low, a broad area of wrap-around precip
will likely linger in the cold air. The GFS is notably very
aggressive with this scenario. However, it does appear very possible
for a wintry mix Sunday morning across the northwest half of the
forecast area as temperatures continue to fall through noon. Farther
east, temperatures should remain warm enough to keep the precip as
all liquid rain. Due to the uncertainty, it is far too early to
forecast any potential accumulations.
CN
&&
.PRELIMINARY POINT TEMPS/POPS...
SHV 66 79 64 77 / 30 30 30 80
MLU 64 80 65 78 / 10 30 30 80
DEQ 62 76 53 68 / 30 30 20 70
TXK 66 77 61 72 / 30 30 20 80
ELD 63 76 60 73 / 30 40 30 80
TYR 66 78 62 75 / 10 20 20 60
GGG 66 79 61 77 / 10 30 30 70
LFK 66 80 65 80 / 20 30 30 60
&&
.SHV WATCHES/WARNINGS/ADVISORIES...
AR...None.
LA...None.
OK...None.
TX...None.
&&
$$
CN/33/44