Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 10/01/21
Area Forecast Discussion
National Weather Service Caribou ME
1009 PM EDT Thu Sep 30 2021
An upper level low will remain over the region through
Saturday then slowly move east on Sunday. A warm front becomes
stationary southwest of the region Monday through Tuesday,
while at the same time high pressure from Quebec builds across
northern portions of the region.
.NEAR TERM /THROUGH FRIDAY/...
1010 pm update...
Updated to increase temps slightly for the overnight as cloudy
skies are keeping temps warmer than fcst acrs nrn areas. No chgs
needed to pops for the overnight with more widespread showers
over the north and east closer to proximity of upr low with
Downeast likley in the clear after midnight.
Prev discussion blo...
The upper level and surface lows continue to spin to the NE of
the state and should lift to the N tonight. Upper air model
sounding indicate that the convergence and convective dynamics
will start to weaken tonight with the exiting low. The RAP and
Euro keep some light QPF all the way down to the coast after
midnight while HRRR, GFS, NAM and Canadian models have QPF
pulling up to just the northern half of the CWA after midnight.
Model percentiles seem to be more on track with the GFS and
HRRR, so adjusted the precip forecast to have rain pulling out
of the south after midnight. Nevertheless, rain showers will
continue for the north. Cloud cover should help keep temps from
reaching into the 30s. Expect 40s across the region.
By Friday, the upper level low will start to move more north,
which will help push the surface low more northward. This will
help keep numerous showers to the north and scattered rain
showers in the south. 925-850mb model temps show that with cold
air associated with the low and ample cloud cover, temps will
struggle to reach into the 50s in the north. Some clearing of
clouds in the south will allow some sunshine to warm temps into
the upper 50s to low 60s for the day.
.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
Low lvl moisture and s/wv trofs alf will cont to rotate arnd a
slowly exiting upper low across the Nrn Can Maritimes Fri Ngt
til about Sat eve with intermittent lgt shwrs and lgt measurable
6 hrly QPFs durg this tm span.
Conditions improve for some clrg late Sat Ngt into Sun with
intervals of msly cldy skies and still a few isold lgt shwrs or
sprinkles. Hi temps will make only a slow recovery Sat thru Sun
with cld cvr keeping temps near normal, although some clrg late
Sat ngt could allow for some pockets of below normal low temps
across Nrn vlys under lgt sfc winds.
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
A narrow sfc ridge will keep fair conditions Sun ngt, with
potential of ovrngt low temps at of below frzg and front for a
large ptn of the FA...if skies become and remain clr, which is
a little uncertain attm.
Otherwise, models are now showing anomalous Nrly component flow
high alf ovr our Rgn between the departing upper low E of the
Can Maritimes and very anomalous strong ridging/blocking ovr Nrn
Can msly keeping moisture ahead of a warm front and a Srn upper
low in the Srn Jet Stream ovr the Midwest/Srn states just SW of
our FA Mon and Tue, bringing some cldnss to all of the Rgn and
perhaps brushing far Swrn areas with sct shwrs Mon Ngt int Tue.
Ridging alf from the NW then becomes more established for Wed
and Thu with more in the way of sunshine for all of the FA. High
temps will recover a little each day, becoming quite pleasant in
the 60s by mid week. Ovrngt lows will remain chilly spcly across
the N with drier air promoting large diurnal swings upwards to
30 deg between low and high temps.
.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
NEAR TERM: MVFR expected across northern terminals through the
day tomorrow, with ocnl IFR cigs expected late tonight. Downeast
terminals will likely remain VFR with unrestricted and/or brief
SHORT TO LONG TERM: Fri Ngt - Sun...all TAF sites low VFR/high
MVFR clgs with intermittent lgt rn shwrs. Lgt winds.
Sun Ngt - Tue...all TAF sites low VFR clgs to unlmtd VFR. Lgt
NEAR TERM: Winds and seas will remain below SCA conditions
tonight and Friday. NNW winds will increase to 10-15 kts with
gusts up to 20 kts tonight, but decrease by Friday morning. Then
increase again by Friday afternoon to 10-15 kts and 20 kts
SHORT TO LONG TERM: Initially no hdlns for our waters, but wvs
in the form of very long pd of swell from Hurricane Sam over the
open Cntrl Atlc ocean will begin to arrive on Sat, reaching SCA
wv hts of 5 to 6 ft Sat Ngt thru Sun Eve, then dmnshg below 5
ft late Sun ngt and contg to subside Mon into Tue. Went with
blended model wv guidance for fcst wv hts with the main spectral
component being very long period upwards to 14 to 16 sec
radiating wv groups from Sam spcly Sat thru Sun.
Long period swell with a peak wave period of 14-16 seconds from
Hurricane Sam will reach the Downeast coast late this weekend.
The swell will likely lead to rip currents and the potential for
high surf. Astronomical tides are on the low side late this
week and into the weekend, but higher astronomical tides are
predicted for early next week.
Area Forecast Discussion...UPDATED
National Weather Service Austin/San Antonio TX
648 PM CDT Thu Sep 30 2021
.AVIATION (00Z TAFS)... /NEW/
A complicated forecast will evolve overnight as ceilings will be
tricky as thunderstorms move into the region. Overall, expect
thunderstorms to develop out west first, and slowly by surely march
east and southeastward through the late evening and into the early
morning hours on Friday. At DRT, expect thunderstorms at the airport
by 02Z and the possibility of IFR ceilings between 03Z-07Z as heavy
rain and thunderstorms look like a good bet. Beyond that, expect MVFR
ceilings through at least 18Z before a period of what should be VFR
ceilings moves over the terminal. Next, at AUS, expect storms to
arrive by 09Z and continue for a couple hours, with IFR ceilings
expected along with gusty winds up to 25 kts. Ceilings finally come
back up after 20Z Friday. Lastly, at SAT/SSF, heavy thunderstorms are
possible between 10-14Z, with winds gusting up to 35 mph or possibly
higher. IFR ceilings are expected even LIFR ceilings cannot be ruled
out. Ceilings should get back into the MVFR range by 16Z with
lingering light rain. Expecting things to attempt to dry out by the
evening hours, but trends will need to be monitored to consider
running with prevailing -SHRA through much of the 24-30 hour forecast
.PREV DISCUSSION... /ISSUED 251 PM CDT Thu Sep 30 2021/
SHORT TERM (Tonight through Friday Night)...
The slow-moving upper level low remains over AZ/UT this afternoon
with the bulk of convection associated with the low in West Texas at
the present time. Additional convection can be seen along the coast
and in our Coastal Plains counties and this activity is associated
with a weaker disturbance on the northern periphery of an upper
level ridge in the northern Gulf of Mexico. The Coastal Plains
activity will continue and push a bit farther north and east through
the late afternoon hours.
The main concern for late this afternoon into Friday morning will be
the convective evolution of the activity to the west. Latest surface
analysis shows this activity is developing along a convective
boundary. As this boundary moves southward through the afternoon and
evening, showers and thunderstorms should be on the increase with
the northwestern CWA being the first location. However, there could
be some isolated to scattered showers and storms ahead of the main
line and some of this activity could be strong. There are also some
indications in some of the high-res models that a brief linear
bowing segment could occur in Val Verde County with the initial
convection along the boundary. The biggest threat with this if it
were to occur would be the potential for strong winds.
The main focus for the threat of heavy rainfall will occur with the
potential linear activity as this boundary continues to move south.
The latest run of the HRRR shows this evolution with showers and
storms entering Val Verde County around 4z continuing south through
the night. The main area for potential locally heavy rainfall will
be in the western areas as this is where the heavier storms are
expected to move through tonight with the boundary having a better
surge southward there. Think areas in the northwestern CWA could see
2-3 inches of rainfall with isolated amounts up to 6 inches. The
soils out west are dry due to recent dry conditions and not much
falling a couple of nights ago. Therefore, do not anticipate
widespread flooding issues tonight, but some isolated flooding will
For tomorrow, the boundary is expected to make it as far south as
out southern counties before washing out with southerly flow
returning. Think the morning hours will primarily have more
scattered activity lingering from the overnight convection with a
possible break in activity. Redevelopment of scattered activity is
expected tomorrow afternoon. Some locally heavy rainfall will remain
possible. For tomorrow night, it does not appear that there will be
any appreciable boundaries but some isolated heavier showers and
thunderstorms could continue to produce local flooding concerns
dependent on soil moisture.
LONG TERM (Saturday through Thursday)...
The upper level low centered across the Desert Southwest will lift
northeastward into/through Saturday which helps to advance a cold
front into the region out of the north. Combination of the deep
column moisture with PWATS between 1.6 to 2 inches and the surface
forcing ahead of the front should result in another wet day with
scattered to numerous showers and thunderstorms. Activity looks to
generally concentrate immediately along and ahead of the surface
front. While the instability is lower on Saturday, models continue
to depict the potential for more locally heavy rain where a quick
inch or two may fall resulting in additional flooding concerns. WPC
highlights a marginal risk on the latest day 3 excessive rainfall
outlook from 12Z Saturday to 12Z Sunday over the eastern 2/3rds of
the CWA. Rain chances then push southward into the southern zones
from Saturday night into Sunday along the front. Moisture and cloud
cover keeps the afternoon highs slightly cooler while the morning
lows remain on the mild and humid side.
Drier and more comfortable conditions arrive behind the front as
winds become north-northeasterly and surface high pressure builds
across the region from later Sunday through midweek. While the
afternoon highs are to remain rather seasonable, expect for cool
nights with overnight lows that lower into the 50s and 60s across
the majority of the region.
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 71 85 72 84 69 / 40 70 50 60 30
Austin Bergstrom Intl Airport 70 85 70 84 67 / 40 70 50 60 30
New Braunfels Muni Airport 71 85 70 86 69 / 50 70 60 60 30
Burnet Muni Airport 69 82 69 83 65 / 60 70 60 70 20
Del Rio Intl Airport 71 86 71 86 70 / 80 70 80 50 30
Georgetown Muni Airport 70 84 70 83 67 / 50 70 60 70 30
Hondo Muni Airport 71 85 70 86 67 / 60 70 70 60 40
San Marcos Muni Airport 70 85 69 84 67 / 50 70 50 60 30
La Grange - Fayette Regional 73 86 72 85 71 / 40 60 30 70 30
San Antonio Intl Airport 72 84 72 85 70 / 50 70 60 60 30
Stinson Muni Airport 74 86 73 87 71 / 50 70 60 60 30
AREA FORECAST DISCUSSION
National Weather Service Hastings NE
625 PM CDT Thu Sep 30 2021
.DISCUSSION...(This evening through Thursday)
Issued at 252 PM CDT Thu Sep 30 2021
The main issues for this forecast will be chances from this
afternoon through Friday, and into Saturday.
Overall trends are for lowered POPs this afternoon and tonight as
NBM continues to overdo in this category and cold front is east of
the CWA, although slowing down and possibly stalling. Some wrap
around moisture from the surface low along the front could help
give us a slight jump in POPs later tonight, but not by much.
General consensus among hi-res models that coverage should be
spotty, and support for drizzle will be in place for this
afternoon and into tonight for a good chunk of the area. Maybe
enough instability to maintain some thunder in our far east
through this evening.
HRRR is pointing toward some fog in parts of our CWA late tonight
and early Friday, especially north half/east CWA, but I`m keeping
this out for now given the unfavorable wind direction from the
north northwest and lack of clearing expected, and also the SREF
does not hit the fog nearly as hard.
Still enough for some mention of thunder at times for
Friday/Saturday, but not enough support for severe weather.
Trends still toward drier for Friday with some shortwave ridging
in advance of a shortwave trough approaching from the southwest and
continue to go in that direction, but still non-zero POPs for
Friday/Friday night for now, and continue to decrease.
For Saturday, trends from previous runs are also farther south
for precip compared to previous 00Z runs of both operational
models and ensembles, but ensembles still indicate a decent shot
at some precip for much of the CWA, with higher chances in our
south and kept robust POPs in for Saturday for now. Operational
are definitely trending dry for the north half of the CWA with
higher QPF tending farther south.
After the trough passes, Sunday and beyond are forecast as dry and
cool as has been the general gist for the past few forecasts.
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Saturday)
Issued at 613 PM CDT Thu Sep 30 2021
Cigs continue to straddle the line between MVFR and IFR, sitting
right about 1,000 ft. This will continue to be the case for a few
more hours before cigs then come down into IFR territory for the
overnight hours through the early morning hours. Then cigs will
lift back to MVFR till the afternoon hours when the cloud deck
will begin to break up and should lift to VFR as well.
Winds will remain relatively light, less than 10 kts, and will be
generally out of the north but will shift to more northwesterly
late in the period.
Area Forecast Discussion
National Weather Service Goodland KS
934 PM MDT Thu Sep 30 2021
.SHORT TERM...(This evening through Friday night)
Issued at 219 PM MDT Thu Sep 30 2021
Satellite imagery and 500mb RAP analysis showed almost southerly
flow above the High Plains today on the eastern side of an upper
trough. This trough appeared to be digging into the Desert
Southwest, closing off into a low in the process. At 1 PM MT, cloud
cover had shifted off to the northeast and south, allowing clearing
across the central portion of the region. Northerly winds continued
at the surface, gusting around 30 mph at times, with temperatures in
For tonight, south to southwest flow persists aloft as the
aforementioned low pushes further into the southwestern CONUS. Dry
weather is anticipated with low temperatures in the 40s to low 50s.
Cloud cover may creep back into the area ahead of the disturbance as
early as the overnight hours.
On Friday, the system ejects towards southwestern Kansas, resulting
in rain showers and perhaps a few thunderstorms moving into the
region from the south. While there is a chance for precipitation
south of I-70 in the afternoon, the better opportunity for the
entire area will be Friday night as the disturbance draws nearer to
the High Plains. Severe weather is not expected with any
thunderstorms that develop. This should tend to be more of a
steady rain rather than convective, so am not anticipating flash
flooding issues at this time.
High temperatures are currently forecast in the mid 60s to low 70s.
However, with cloud cover building in through the day, this may be a
little warm. This is followed by dropping to the mid 40s to mid 50s
for Friday night.
.LONG TERM...(Saturday through Thursday)
Issued at 132 PM MDT Thu Sep 30 2021
Precipitation will be fairly widespread during the morning hours at
the start of the period with H5 low to the south of the area lifting
northeast through the day. Eastern CWA remains in favorable
WAA/Isentropic upglide with respect to low circulation through 18z,
so expect a fairly persistent area of precipitation to develop. As
system moves away from the area Div Q fields indicate strong forcing
for subsidence and with limited residual instability, expect a
pretty rapid decline in precipitation after 18z.
H5 low will continue to the east and merge with another system
forming new closed low system over the southeastern CONUS. Ridge
will amplify across the area in response to this system and one
approaching the four corners in an omega like pattern. While this
pattern will be transient and not an Omega block, net result will be
area once again under the influence of upper level ridge and
associated warmth and generally quiet conditions. Although
temperatures will be above normal, highs will generally be seasonal
in the mid 70s.
.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 920 PM MDT Thu Sep 30 2021
KGLD and KMCK expect to see VFR conditions throughout the 06Z TAF
period. KGLD starts with westerly winds around 5 kts before
becoming light and variable at 16Z. At 00Z, KGLD winds become
southerly around 5 kts then turn west-southwesterly with vicinity
showers possible at 02Z. KMCK begins with northwesterly winds at 5
kts before becoming northerly around 7 kts at 18Z. At 20Z, KMCK
winds become northeasterly around 6 kts then turn easterly by 23Z.
KMCK may also see showers possible just beyond the TAF period.
Area Forecast Discussion
National Weather Service North Platte NE
636 PM CDT Thu Sep 30 2021
.SHORT TERM...(This evening through Friday night)
Issued at 355 PM CDT Thu Sep 30 2021
The main forecast challenges through the end of the week revolve
around remnants from Wednesday night`s storm system, the next wave
of moisture slated to arrive Saturday, and temperature in the
This evening and tonight... A batch of rain showers continues to
slowly drift west across north central Nebraska with some
backbuilding or continuous development on the eastern edge. Some of
the rain has been moderate at times, with KANW recording 0.30" of
moisture since this morning. Adjusted PoP to maintain chance wording
through the overnight hours, primarily along and north of Hwy 20
from KVTN to KONL. Used a blend of recent CAMs guidance for timing
and location. Synoptically, the surface low is centered over
northeast Neb near KOFK as of 20z, while the mid/upper trough axis
cuts through the Sandhills into central Nebraska. Deep isentropic
upglide exists on the backside of the surface low and ahead of the
upper trough axis. This added lift corresponds with continued low
level moisture advection. Have not observed any thunder with this
activity today, and RAP mesoanalysis indicates marginal instability
at best with MUCAPE around 100 j/kg. Removed all thunder mention and
left as general rain showers through this period. Northerly winds
have also been relatively gusty today with 20+ kt flow at H85 being
mechanically mixed to the surface. These winds weaken tonight and
some of the thick stratus clouds will clear out of the panhandle.
Thinking the clouds will hang around over central Neb in the
vicinity of the surface low. Forecast lows reflect this with values
ranging from near 40F far west to mid 50s far north central. The
overall change from the previous forecast is generally 2 to 3
degrees cooler where clearing is expected to little/no change in the
Friday and Fri night... The surface low and cool front finally exit
the state, but the mid/upper trough lags behind and still drapes
across eastern Neb. The bulk of the forcing and moisture convergence
should lie east of the forecast area, but cannot rule out a few
light rain showers or sprinkles east of Hwy 281. Kept schc PoP
through the day, but clouds may extend as far west as Hwy 61 as
virtually the entire CWA lies in north/northwest flow at H85. Weak
WAA occurs late in the day as low level flow begins to transition to
southerly, mainly in the panhandle. Nevertheless, used the cool end
of guidance for max temps as cloud cover should limit overall
diabatic heating potential. Forecast highs are right around 70F
areawide, which is just a hair below normal.
.LONG TERM...(Saturday through Thursday)
Issued at 355 PM CDT Thu Sep 30 2021
The main synoptic features in the extended period deal with the
upper level pattern. This weekend, a closed low moves out of the
Four Corners and cuts northeast across the central Plains before
getting absorbed into the main northern stream somewhere around
Nebraska. A separate closed low then dives south along the
Mississippi River Valley to start the workweek, then gets hung up
near the Ohio Valley. The first system will likely have the greater
effect on western Nebraska as forcing and moisture availability will
be more in proximity. Guidance is in general agreement with
precipitation brushing the southern and eastern portions of the CWA,
although discrepancies exist regarding the western extent and
timing. Temperature-wise, values will remain seasonable in the lower
to mid 70s the next several days as a weak upper ridge builds along
the Rockies and a broad high pressure settles in at the surface.
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 636 PM CDT Thu Sep 30 2021
For the KLBF terminal, expect some broken mid level clouds
overnight with ceilings around 5000 FT AGL. Expect some higher
clouds after daybreak on Friday. For the KVTN terminal: Expect
broken ceilings around 4000 FT AGL overnight with some clearing
after sunrise Friday. On Friday, expect scattered clouds ranging
from 6000 to 7000 Ft AGL. Winds for both terminals, will generally
be from the north or northwest at under 10 KTS over the next 24
Area Forecast Discussion...CORRECTED
National Weather Service Lake Charles LA
1002 PM CDT Thu Sep 30 2021
A few showers are currently present over southwestern portions of
the outer offshore areas. The shower and thunderstorm activity
from earlier in the day has dissipated with low and mid-level
clouds persisting over the region.
The current forecast is mostly on track. However, PoPs were
reduced slightly for the next several hours to account for current
radar activity and the latest run of the HRRR (00Z) showing
limited shower and thunderstorm development over the next several
hours and likely remaining offshore. Storm chances will be
expected to increase (especially for western portions of our area)
near sunrise and expand eastward as the morning progresses. The
possibly for patchy fog has been adjusted as well, with expectations
being for 07Z through 14Z primarily for inland counties and
.PREV DISCUSSION... /issued 721 PM CDT Thu Sep 30 2021/
For the 10/01/21 0000 UTC TAF package.
Convection has largely come to an end across the area save for
some isolated light shower activity, mainly over parts of central
and south central LA. Considerable cloud cover remains, however,
chiefly in the form of a dense cirrus canopy though there are some
clouds beneath it per SFC Obs. Nevertheless, VFR is currently
prevailing at all terminals, though some low clouds may be
starting to form at the Acadiana terminals. Couple of concerns to
contend with tonight, with the initial one centered around low
stratus and/or fog formation. Guidance is a bit all over the place
in that regard, so using a blend of this guidance and persistence,
showed MVFR developing most sites later tonight, though will have
to continue monitoring trends at KLFT and KARA for the potential
of an earlier onset and/or lower category. Next item is convective
potential, with CAM guidance pointing toward some overnight and
FRI morning activity developing/moving across SE TX. PROB30 was
inserted at KBPT for this potential, with the rest of the coastal
terminals likely to see activity more scattered in nature late
morning or early afternoon.
PREV DISCUSSION... /issued 325 PM CDT Thu Sep 30 2021/
SHORT TERM [Tonight through 12Z Sunday]...
Another wet day ongoing across the CWA with scattered to
widespread convection noted on radar this afternoon. Much of this
convection has been very slow moving today, resulting in some
localized flash flooding issues across parts of south-central LA.
This looks like it will continue to be a concern through the next
few hours as some of these showers look to not be going anywhere
fast. Fortunately, short term guidance begins to fizzle these
showers out around 00-01Z, with general dry and cloudy weather
expected thereafter as we head into the overnight hours. Only
exception to this may be the coastal waters and coastal parishes
where some convection may persist overnight. Elsewhere, main issue
overnight looks to be another round of patchy fog, particularly
across the Lake Area. This fog will likely persist through
sunrise, before burning off through the morning hours.
Tomorrow, another shortwave/vort max looks to rotate around the
western CONUS trof and towards SE TX/SW LA, while at the same
time some mid-level ridging tries to build northward across the
north-central Gulf Coast. This weak ridging may help to hold POPs
down slightly across the eastern periphery of the CWA, however,
it looks like the shortwave will win out elsewhere. As a result,
expect scattered convection to begin to redevelop through the
early morning, particularly across SE TX, spreading eastward
from there. Coverage may be a bit most widely scattered across
Acadiana tomorrow, but for the most part we are expecting another
wet and muggy day. Unfortunately, it looks like Saturday will be
much of the same in a long string of wet days, with scattered to
widespread convection once again expected. However, it does look
like we may finally see a break in this pattern just beyond the
end of the short term, so hopefully we don`t have to wait too much
longer for some sunshine.
LONG TERM [Sunday through Friday]...
A shortwave trough and sfc cold front in east Texas will progress
eastward through the day on Sunday. Look for numerous showers and
thunderstorms on Sunday ahead of the front at this time... the main
issue will be from heavy rains at times... and cloud to ground
lightning. This activity will shutdown as the cold front pushes
through and this will slowly push the gulf moisture that is over the
region off to the east and south late Sunday into Monday with rain
chances tapering back and moving over the coastal waters. As the
cool front exits eastward along with the upper level trof... drier
and somewhat cooler air will gradually make it`s presents felt
Tuesday morning with low temperatures in the mid 60s and mid 80s for
afternoon high temperatures.
From Wednesday onward into the weekend the cool and dry pattern will
become established as a broad 1015 High over Texas will sit off to
the northwest establishing a northerly flow at surface. As the
pressure gradient is not expected to be become tight winds in the
coastal waters will average around 10 to 13 knots with seas around
two feet nearshore and two to three offshore.
A moderate onshore flow around 10-15 kts, with higher gusts, will
continue through the end of the week, while seas will run near
1-4 feet. Winds and seas will relax a bit as we head into the
weekend, while remaining east to southeast. Scattered to
widespread showers and thunderstorms will continue each day
through the weekend as well. Frequent cloud to water lightning
will be possible within some of these stronger storms, while winds
and seas will also be locally higher near any thunderstorms. By
early next week, a cold front is forecast to sweep through the
region. As a result, winds become offshore behind the front and
rain chances begin to lower by a fair amount.
.PRELIMINARY POINT TEMPS/POPS...
AEX 70 84 70 85 / 30 50 10 50
LCH 71 83 72 83 / 40 70 30 70
LFT 71 85 72 85 / 20 50 10 60
BPT 71 84 72 84 / 40 70 40 80
Area Forecast Discussion
National Weather Service Phoenix AZ
411 PM MST Thu Sep 30 2021
.UPDATE...Updated Aviation Discussion.
An early autumn weather system begins to slowly exit the region
today providing a last chance of showers and thunderstorms through
this evening. Much of the activity will become focused over
higher terrain areas north and east of Phoenix. Building high
pressure into the weekend will allow temperatures to rebound back
to near and above normal late this weekend and next week. Another
weather system may sweep across the region during the first half
of next week resulting in another period of unsettled weather.
The RAP 500mb analysis depicts a large elongated low pressure
system over the Desert Southwest with a series of embedded vort
max`s just to the E, NE and NW of the area. WV imagery shows very
dry air pushing in with NNW flow aloft on the rear flank of the
low. Mostly clear skies with an area of rear trough PVA were
positioned to the west and northwest of the area with a large area
of nimbus cloud decks off to the east. An H5-H3 northerly jet
streak was entering the area from NNW with an area of H3
divergence over E AZ and NM. ACARS sounding showed some moisture
left in the BL and lower mid levels with PW of 0.71-0.89" and
skinny MUCAPE of 713 j/kg. Early afternoon radar showed some
modest showers and isolated storms forming along the RIM in N-Cent
AZ and additional isolated convection in SE AZ.
The HREF members are in good agreement on the timing of isolated to
scattered thunderstorms from mid-late afternoon into the early
evening, to later evening for Phoenix and the lower deserts.
Although high terrain areas northeast of the Valley floor are
favored. The latest HREF also favors a 10-20% chance of 35 mph
outflow/thunderstorm wind gusts in the late afternoon and early
evening. Because of this a few areas of patchy blowing dust can
not be ruled out either. Although there is a low chance of burn
scar flash flooding in the high country, QPF with PM storms is
anticipated to be mostly very light to modest.
From this evening and into the weekend models agree on the low
pressure system gradually ejecting as high pressure builds in over
the Desert southwest. As a result a warming and drying trend will be
in control through the weekend and into very early next week with
highs topping out in the mid 90s by late this weekend and early next
week. However, there are currently no tripple digit highs in the
forecast for the coming week with temperatures much closer to
For Sunday to Tuesday ensembles favor a cut-off low pressure system
positioned just offshore from N Baja ejecting and filling as it
moves into the CWA by Tuesday. Some ensembles show light
accumulated QPF over the deserts with more moderate amounts over
the E AZ high terrain and E-Cent AZ. GEFS Plume QPF Show an
ensemble mean of 0.15 storm total QPF for Phoenix with quite a
bit of model spread and uncertainty also remaining at this time.
.AVIATION...Updated at 2310Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Light west to southwest flow is present across the Phoenix TAF
locations. Meanwhile, shower/thunderstorm coverage north of the
terminals is increasing. Although showers will tend to weaken as
the move off of the higher terrain, some of these showers will
likely move into the Phoenix area. The most likely terminals to
see rain or lightning would be KSDL and KDVT, with a lesser chance
for KPHX and KIWA. Any remaining showers should weaken by around
4-5Z this evening. Model guidance is also showing a wind shift
between 1-2Z to the northeast as these showers move in with recent
radar scans confirming a developing outflow boundary. For most
locations we will see gusts of 15-20 kts, but an isolated gust to
25 kts is possible. SCT coverage between 080 and 120 kft will
develop as the showers and thunderstorms move through but should
clear out overnight. No weather concerns are expected for Friday.
Southeast California/Southwest Arizona including KIPL and KBLH:
No major weather impacts will exist through Friday under clear
skies. North winds will be preferred for most of the period though
some backing to westerly will occur. Speeds may occasionally reach
into the 10-15kt range this evening but these speeds will diminish
Saturday through Wednesday:
Above normal temperatures over the weekend and early next week will
cool closer to the seasonal average by midweek as dry high pressure
likely becomes replaced by a somewhat more unsettled pattern.
Minimum afternoon humidity levels will mostly fall into the teens at
lower elevations and closer to 30% over higher terrain. Slightly
more moisture could return during the middle of next week. Overnight
recovery will vary widely across the districts ranging from 25-50%
in lower deserts and above 70% across mountains. Winds will mostly
be light and follow typical diurnal tendencies, however may become
locally gusty next week with the approach of a weather disturbance.
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.