Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/31/21
Area Forecast Discussion
National Weather Service La Crosse WI
1050 PM CDT Mon Aug 30 2021
.SHORT TERM...(This evening through Tuesday)
Issued at 140 PM CDT Mon Aug 30 2021
The large area of high pressure currently over the Upper Midwest is
not expected to move much through Tuesday. For the most part, this
will help to keep the weather rather quiet over the area. The one
exception to this could be a few showers over parts of the southern
sections Tuesday morning. A short wave trough coming in from the
west is expected to generate some showers and storms over the
Missouri River Valley overnight. The majority of this activity is
expected to slip by to the south of the area tonight and Tuesday
morning, but there a few hi-res meso-scale models that indicate the
northern periphery of the showers and storms could move across
portions of northeast Iowa and southwest Wisconsin and have added in
some low rain chances to account for this.
.LONG TERM...(Tuesday night through Monday)
Issued at 140 PM CDT Mon Aug 30 2021
An upper-level ridge builds in the upper plains during the overnight
hours Tuesday into Wednesday as an upstream trough digs in the
Pacific Northwest. The light wind layer (<10kts; SFC-4000ft) from
this ridge in combination with <20 degree dewpoint depressions
will likely result in a strong fog layer for Wednesday morning
across the river valleys. Blue skies return for Wednesday with
temperatures in the upper 70s as the upper-level ridge axis
continues its easterly progression through Minnesota and into the
Great Lakes by Thursday.
The previously mentioned upper-level trough associated with a closed
upper-level low in Alberta glides across the Mountain West on
Thursday. Clouds and precipitation ahead of the corresponding
surface boundaries impact our CWA from Northwest to Southeast during
the day on Thursday into the evening hours. At this time the severe
risk is low with the main driving upper-level low remaining far to
the North, the downstream jet maxima placing us in a region not
favorable for ascent, and severe parameters (CAPE/shear/moisture
advection) remaining strongest west of our CWA. It is too early to
lock down exact location of frontal set up however, and will have a
better idea of the specifics as the week progresses.
Later in the week into the weekend, upper-level flow has a
resurgence in the jet maxima along the base of the longer wave
trough over our CWA. Energy perturbations along this amplifying
trough could result in showers/storms Saturday and Sunday depending
on perturbation location and available instability in the wake of
Thursday`s anticipated precipitation.
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 1050 PM CDT Mon Aug 30 2021
Cigs: getting some high level vfr blow off clouds from convection
diving southeast across central IA. Expect these to clear toward
daybreak. Could see more high level clouds later in the day from
another round of convection dropping southeast through western IA
later Tue morning. Meanwhile, WI sct-bkn cu field could develop Tue
afternoon, but still looks to be VFR.
WX/vsby: very challenging fog forecast for KLSE. T/Td spread at 03z
only 6 F - good indicator that 1/4 SM could/would develop at KARX.
However, high clouds will hamper cooling overnight, which could keep
the T/Td spread where its at longer. Meanwhile, RAP/NAM soundings
suggesting a deep light wind field (also conducive to 1/4SM fog).
However, VWP from KARX has 15 kts of wind from the north at 925 mb
(roughly 2 kft) while the RAP sits closer to 10 kts. Only a 5 kt
difference but significant to the spread of fog into the airport.
Confidence lowering for LIFR fog as a result and will likely hold
more with a BCFG and see how the clouds/wind field evolves
overnight. If winds stay up and it does clear, a scenario with
little to no fog impact at KARX but bkn003 cigs is possible.
Winds: mostly light easterly through the period.
Issued at 140 PM CDT Mon Aug 30 2021
Mostly dry weather over the next few days will allow rivers
to work through flow already in their systems. While most forecast
points along rivers have crested and are on the decline, a couple
are forecasted to crest within the next 24 hours. Any precipitation
chances over the next few days look minimal which will assist in
forecasted decreasing of river stage height back to more normal
Area Forecast Discussion
National Weather Service Birmingham AL
726 PM CDT Mon Aug 30 2021
For 00Z Aviation.
/Updated at 0510 PM CDT Mon Aug 30 2021/
Current surface obs and KDGX RADAR depict Ida centered near Yazoo
City, MS at this time. A broad region of southerly to
southeasterly surface winds extend to its east/southeast across
much of MS, AL, and GA. The envelope of tropical moisture
surrounding Ida now covers the majority of the Deep South with PWs
as high as ~2.5" across Central and Southern MS. Higher moisture
content resides across the western portions of Central AL where
925-850 mb winds of 40-50 kts continue. This will foster periods
of light to moderate rainfall, with more robust showers and
thunderstorms capable of locally heavy downpours.
So far, western Central AL has lacked more favorable
thermodynamics for more robust showers/storms and higher rainfall
rates (SBCAPE <500 J/kg). This can be a result of low to mid-
level cloud cover limiting insolation/destabilization. Some
clearing is evident on satellite imagery closer to the coast, but
even here updrafts have struggled as of recent. (We`ll see how the
convective line currently east of I-59 in southeast MS evolves
over the next few hours). Overall, most robust convection has
remained east of I-65 for Central AL, and mainly closer to the
I-75 corridor per satellite imagery/lightning obs this afternoon.
In fact, RAP mesoanalysis depicts the best instability here
(SBCAPE <3,000 J/kg extending up through GA).
This has been good news for Central AL as most favorable
kinematics associated with the low-level jet (0-1 km SRH <300
m2/s2) has remained displaced from the best instability. So far
only one tornado is suspected to have impacted Central AL (Pike
County). It`s for these reasons a Tornado Watch has not been
issued. The balance of thermodynamics/kinematics has not been
achieved in anyone particular area and observational trends have
suggested tornadic activity is widely isolated and very brief.
Forecast confidence is just too low at this time.
Over the next few hours we`ll continue to monitor a broken line of
heavier showers/thunderstorms moving northward across portions of
eastern Central AL. These have produced wind gusts up to ~40 mph
and brief rotation despite decreased observed wind shear values.
We`ll also watch areas west of I-65 as moderate rainfall
continues. Fortunately, rainfall rates have been tempered and
flash flooding is not occurring at this time. Heavier rain rates,
2-3" per hour, have been more transient. Nonetheless, we`ll
remain diligent this evening and tonight as Ida continues to
slowly move northeast.
Previous short-term discussion:
/Updated at 1159 AM CDT Mon Aug 30 2021/
We continue to monitor Ida`s progress as the center was analyzed
just southwest of Jackson, MS at this writing.
Surface analysis also reveals potential for sustained 15 mph
winds most likely across portions of Pickens, Greene and Sumter
Counties in our forecast area. Analysis shows greatest potential
for 25 mph gusts across portions of Sumter, Greene and Marengo
Expect the wind field to continue to migrate north as the day
progresses with the strongest winds close to the
Alabama/Mississippi state line.
Torrential downpours are occurring across all of our Southwest
counties and now into portions of South-Central Alabama. Rain
rates estimated by radar are generally around a half an inch per
hour across portions of Sumter, Hale, Greene, Pickens and Marengo
Counties with areas elsewhere generally receiving around a quarter
to half of an inch an hour where rain is falling. The more intense
convection in a band from Dallas County through Western Lowndes
County that extends further south is dropping around 1 inch per
hour. We will continue to monitor trends but greatest potential
for localized flooding through early afternoon will be across our
Southwest and South-Central counties.
We expect this risk to expand further northward with time
this afternoon into the evening hours.
A collection of observational and near-term model guidance is
depicting the better sheared environment from Pickens County into
Greene and Sumter County and points south and west, while the
better low-level instability values reside to generally near and
east of the Interstate 65 corridor generally along and south of
the Interstate 85 corridor. There is not much spatial overlap in
the shear/instability parameter space and this is resulting in a
narrow corridor currently across our far southwest into our South
Central Counties, generally South of Interstate 59 corridor and
West of the Interstate 65 corridor. This risk will persist
through early afternoon.
We expect this risk to gradually migrate further north closer to
the I-59 corridor from mid to late afternoon.
/Updated at 0318 PM CDT Mon Aug 30 2021/
Drier air arrives behind Ida by Wednesday night and rain chances
will quickly diminish. As surface high pressure digs southward
into the Tennessee Valley and upper level ridging builds across
the Deep South, cooler air will arrive from the north. Made minor
changes to the temperatures and dewpoints in the extended, to
lower them each period, although on some days it was just by a
degree or two. Morning lows in the 60s and afternoon highs in the
80s will feel almost fall-like.
Previous long-term discussion:
/Updated at 0250 AM CDT Mon Aug 30 2021/
Wednesday through Sunday.
Ida will continue to pull out of the area Wednesday morning. We will
see some backside clouds and rain, but any accumulations will be
light. By Wednesday night into Thursday high pressure will build
into the regions and expand through the weekend. At the same time
the ridge aloft will build over the southern and central Plains.
Deterministic models all are now indicating a fairly dry timeframe
through the end of the week and into the weekend. Will need to
monitor the afternoons with day time heating over the weekend as
easterly flow may bring in just enough lift to trigger a
shower/storm. For now will go with a dry forecast and monitor the
trends of the middle range models.
00Z TAF Discussion.
The trend of increasing ceiling restrictions continues. The
tropical system Ida was located over south central Mississippi at
this writing. Ida will continue moving northeastward through the
period. Widespread and a slight chance or thunderstorms will be in
the forecast the next 24 hours. Due to the overall low chance of
storms, the only mention in the terminals will be rain. Surface
winds will be breezy overnight and some gust will also be present.
Winds above the surface will increase into the 40kt neighborhood
in several places, but these numbers will only put the LLWS values
right at the interface of any mention. If surface winds are
realized, not mention should be necessary. If surface winds are
slightly weaker, some mention may need to be added. Like mentioned
above, ceilings will start lowering within a few hours. IFR/MVFR
should be around by 6z, with slightly lower heights by around 12z.
These ceilings hang around much of the day on Tuesday with rain.
Tropical Depression Ida will continue to impact the area through
Tuesday night. Gusty winds, heavy rains and a few tornadoes will
remain possible. Gusts up to 40 mph are possible tonight, with
sustained winds of 10 to 20 mph from the south. Winds decrease
slightly Tuesday as winds begin to turn to the southwest. Rainfall
amounts through Tuesday will average 3-5 inches across west
Alabama and 1-3 inches east of I-65. Drier weather returns
Wednesday night with cooler temperatures into the weekend. RH
Values will remain generally above 40 percent through the weekend.
.PRELIMINARY POINT TEMPS/POPS...
Gadsden 71 77 69 84 63 / 100 100 70 30 10
Anniston 72 79 70 85 64 / 90 100 70 30 10
Birmingham 71 78 70 85 64 / 100 100 50 20 10
Tuscaloosa 72 78 70 86 66 / 100 90 20 20 10
Calera 72 78 71 85 66 / 100 90 40 20 10
Auburn 72 79 71 84 66 / 90 90 70 40 10
Montgomery 73 84 72 89 68 / 90 90 50 30 10
Troy 73 82 72 87 68 / 100 90 60 40 10
Flash Flood Watch through Tuesday evening for the following
Wind Advisory until 7 PM CDT Tuesday for the following counties:
Area Forecast Discussion
National Weather Service Boise ID
833 PM MDT Mon Aug 30 2021
.DISCUSSION...Near-surface smoke worsened noticeably this
afternoon and early evening in southwest Idaho as evidenced by
satellite imagery and predicted by the HRRR smoke model. The
HRRR does show improvement from the northwest Tuesday in our
northern areas but the southern half of our CWA will stay smoky.
The improvement is related to an upper trough passing by to our
north Tuesday. The trough will also lower temperatures in the
north, while the smoke itself helps lower daytime temperatures
in the south. No rain for at least another week. Around Sept 8
the GFS has a strong trough coming in but the ECMWF has a ridge
instead, so no help there just yet. No updates to current
forecast at this time.
.AVIATION...Areas of MVFR. Wildfire smoke significantly reducing
visibility at the surface and aloft. Mountain obscurations in smoke.
Surface winds: variable 10 kt or less, becoming W-NW 5-15 kt with
gusts to around 20 kt by 31/1800Z. Winds aloft at 10kft MSL: W to SW
SHORT TERM...Tonight through Wednesday night...The area will
remain under southwest flow through Tuesday as an upper trough
tracks along the US/Canada border. Conditions will remain dry with
smoke over much of the area into the day Tuesday. A more westerly
wind aloft will work into the area late Tuesday into Wednesday
helping to clear some of the smoke. Cooling with the trough will
result in temperatures around 5 degrees below normal Tuesday and
LONG TERM...Thursday through Monday...Southwest Idaho and
southeast Oregon will remain on the interface between a cool
upper level trough over southern British Columbia and Alberta and
a strong upper level ridge containing hot temperatures and monsoon
moisture to the south and east. Afternoons will feature breezy
west-northwest winds. No precipitation expected. Temperatures
will be around 5 degrees below normal on Thursday, warming to
normal by Saturday. Upper level ridging will bring warmer
temperatures on Sunday and Monday with temperatures around 5-10
degrees above normal.
PREV SHORT TERM...DG
PREV LONG TERM....KA
AREA FORECAST DISCUSSION
National Weather Service Hastings NE
652 PM CDT Mon Aug 30 2021
.DISCUSSION...(This evening through Monday)
Issued at 244 PM CDT Mon Aug 30 2021
Two main areas of focus for storm initiation are evident for
tonight. First will be late afternoon/evening with development to
the west possible if enough CIN can erode. Decent amounts of
MLCAPE near 2000 J/kg or so along with increasing bulk shear to
near 40-45 KTS could get some severe storms going, but this is
conditional with the CIN erosion, and models are far from
agreement. I side toward the drier HRRR here, considering model
performances lately but even the more aggressive NAMnest backed
off. I did stick a bit of courtesy low POPS for mid to late
evening in our west/northwest just in case. Later on, I expect a
better potential of development as an upper level wave moves
through, with storms potentially firing in northern Nebraska,
potentially supported by the nose of a low-level jet overnight.
HiRes models generally keep the bulk of POPs north and east as
development should remain along and north of a front draped from
northwest to southeast across the CWA. The potential complex
should start diving more south toward dawn as the low-level jet
veers. This should turn into more of a wind threat with time.
Still linger some POPs in our east for the morning on Tuesday with
the exit of the MCS, but should clear by afternoon. At least low
POPs exist for late Wednesday night and beyond with a stubborn
boundary hanging around for much of the time. A cold front comes
through Thursday night into Friday and may possibly stall a bit,
especially in our south to help give us a bit higher POPs
Thursday night into Friday. Lower temps toward early next week,
with somewhat drier air, with dewpoints in the 50s possible just
beyond the extent of this seven day forecast.
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Wednesday)
Issued at 641 PM CDT Mon Aug 30 2021
Thunderstorms are expected to develop this evening to our north
and cross central and eastern Nebraska during the late night
through overnight hours. This thunderstorm activity should be
enhanced by a 40 KT LLJ...which will likely affect both terminals
through the early morning hours Tuesday. With the focus of storms
expected to be to the east of the terminals...opted to include a
mention of a VCTS at KGRI...while not mentioning any activity at
KEAR. Winds will increase out of the SSW Tuesday afternoon as the
surface pressure gradient will be fairly tight across the local
area...with gusts to near 25 KTS possible.
Area Forecast Discussion
National Weather Service Grand Junction CO
544 PM MDT Mon Aug 30 2021
.SHORT TERM...(Tonight through Tuesday night)
Issued at 244 PM MDT Mon Aug 30 2021
Westerly flow over the northern tier of the CWA has resulted in
another dry day for the majority of the region with the main concern
being continued transport of western wildfire smoke. HRRR smoke
shows this trend persisting through at least tonight before the
smoke is deflected northeast in response to the approach of our next
Pacific trough on Tuesday. Isolated storms have once again developed
over the higher terrain down south but, as this morning`s sounding
only had a PWAT of 0.46 inches (65% of normal for late August),
gusty winds will be more of a threat than rain. Additionally,
given the lack of upper level support convection is expected to
diminish overnight resulting in another quiet and mild night.
Tuesday will see the aforementioned Pacific trough dig into the
northwestern CONUS while a secondary closed low will spin off of
the southern California coast. The progression of these two
systems further inland will deflect the southwestern ridge east
towards the Southern Plains. Subtropical moisture will begin to
move north throughout the day resulting in an uptick in shower and
thunderstorm coverage. The caveat will be dry low levels which
will have to be overcome, as evident on various Bufkit soundings
from across the region. By day`s end PWATs look to increase to
0.80 to 1.00 inches over southeast Utah with 0.50 to 0.80 inches
further north and east. Unlike previous nights, nocturnal showers
will linger into Wednesday as the remnants from Nora and the
previously mentioned SoCal low begin to approach the region,
providing enough support to allow activity to persist into the
.LONG TERM...(Wednesday through Monday)
Issued at 244 PM MDT Mon Aug 30 2021
Wednesday looks to be the best day for precipitation, as the low off
the Southern California coast pushes northeast into the Great Basin
and provides ample forcing. At the same time, deep monsoonal
moisture, bolstered by the remnants of Nora, will be streaming into
eastern Utah and western Colorado, with forecast PWATs of 1.0-1.5
inches over much of the area by midday Wednesday. The best chances
for thunderstorms and moderate to heavy rain look to be Wednesday
afternoon and evening, though showers and storms will linger into
Things will begin to dry out late Thursday into Friday, although
confidence isn`t as high as it could be, as the EC and its ensembles
want to keep the monsoonal moisture streaming into Eastern Utah and
western Colorado. However, the GFS, GEFS, and other ensemble models
show the ridge of high pressure centered over Oklahoma pushing back
west into the Four Corners region, leading to dry westerly flow over
Utah and Colorado. Confidence remains low through the weekend as
these inconsistencies between solutions remain. So, chances for
afternoon convection over the higher terrain remain through the
Temperatures Wednesday and Thursday will be well below normal thanks
to cloud cover and precipitation. A warming trend is expected from
Friday onwards, with highs reaching near normal values.
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 532 PM MDT Mon Aug 30 2021
Smoke will continue to stream in from the west overnight and into
Tuesday morning, though, very little impact on visibility is
expected. Gusty winds will diminish within the next 1 to 3 hours,
then light, terrain driven winds will dictate flow overnight.
Winds will shift from the southwest late Tuesday morning which
will bring an increase in moisture from the southwest. Therefore,
expect an uptick in cloud coverage and chance for thunderstorm
activity in the afternoon. Storms will be more scattered in nature
and more likely to produce gusty outflow winds more so than rain.
So, confidence is too low to add any mention of storms in Tuesday
afternoon TAFs at the moment. Storm coverage will increase by
late evening hours, favoring southeast and east- central Utah
Issued at 244 PM MDT Mon Aug 30 2021
The potential for heavy, widespread precipitation continues to
increase at the midweek point. A weak system will move over the
Desert Southwest beginning on Tuesday. This system will tap into
moisture from the remnants of Nora and advect it into our region.
By Wednesday, that system passes overhead and causes precipitation
to become more widespread. Heavy rain and flash flooding will be
possible especially over the susceptible areas. Enough moisture
may linger on Thursday to support additional rainfall. The area of
heavy rainfall could still shift based on the track of the weak
wave. Based on the latest guidance, confidence was high enough to
issue a Flash Flood Watch for our southeast Utah zones beginning
Wednesday morning and continuing through midnight Wednesday night.
Further expansion of these highlights is expected, but confidence
was not high enough to progress into our Colorado counties at
Model trends show conditions beginning to dry out by the weekend,
but that could change.
UT...Flash Flood Watch from Wednesday morning through Wednesday
evening for UTZ022-027>029.
Area Forecast Discussion
National Weather Service Goodland KS
532 PM MDT Mon Aug 30 2021
.SHORT TERM...(This evening through Wednesday night)
Issued at 327 PM MDT Mon Aug 30 2021
Across the Tri State area this afternoon, hot conditions have
returned to the region. Temps as of 200 PM MDT are 90s area-wide.
The region does lie east of a low/trough currently over eastern
Colorado. Gradient tight thru the day from the south with areas
seeing gusts over 30 mph at times especially spots close to the
For the remainder of today into this evening, the main wx focus will
be on the potential for strong to severe storms first off, then the
potential for isolated fires due to the strong winds in spots and
dry conditions area-wide. There has been one fire already south of
There are already showers/convection starting up along the
low/boundary in eastern Colorado. This activity is slowly working
eastward into better instability, so expect storms to pick
up in intensification over the next hour or so.
Current activity is fairly close to the latest HRRR run showing the
current line tracking east-southeast thru about 03z-04z Tuesday
before lifting out of the area. Area of focus remains along and
north of the Interstate. With models showing inverted-V soundings,
looking for wind to be the main threat, but not ruling out some
large hail and heavy rainfall as well due to potential slow movers.
Going into Tuesday and Wednesday, upper ridge in place over the
central portion of the country, with mainly surface trough to the
west and high pressure east. Hot conditions are expected during the
2-day period and with no precipitation during the afternoon hours,
fire wx concerns crop up. Please refer to the Fire wx section below.
Models do hint at amplification of the upper ridge midweek with some
eastward movement late in the day. This will allow a shortwave to
lift thru the area overnight. Based on the current track west-
northwest zones will have best chances for convection.
For temps, little change from previous guidance/forecast. Both
Tuesday and Wednesday will have highs in the mid to upper 90s.
Overnight lows for tonight into Tuesday night, mid 50s west to mid
60s east. For Wednesday night, mid 60s west to lower 70s east.
Please refer to the Climate section below for info on potential
records for Tuesday.
For heat indices, with both days expected to be fairly dry, the
lower RH will allow for indices to be at or below forecasted highs.
Highest numbers east. There could be a few isolated spots
approaching the 100F mark.
.LONG TERM...(Thursday through Monday)
Issued at 305 PM MDT Mon Aug 30 2021
At the beginning of the long-term period, model guidance shows the
CWA having a southwesterly flow as it is underneath the inflection
point of an upper air trough-ridge pattern on Thursday. Going into
Friday, the Canadian low controlling the trough is expected to move
eastward into central Canada and push the ridge to the east with an
upper air high over the south-central CONUS region. By Friday
evening, models show the CWA beginning to turn more westerly with a
split flow off to the west. Long term model scenarios for the upper
air pattern begin to show some differences beginning on Saturday.
The GFS shows the CWA having its flow controlled by the subtropical
ridge portion of the jetstream which makes it westerly due to along
with a possible shortwave trough moving across the CWA on Saturday
evening. The GFS shows a similar pattern on Sunday with a trough
forming in the southwestern CONUS. On Monday, the GFS depicts a low
developing in central Canada during the day pushing a trough down
over the Northern Plains region by Monday night. The ECMWF shows a
similar Saturday pattern to the GFS however with an upper air low
developing over southern CA. On Sunday, the low cuts off allowing a
large ridge to move over the western CONUS turning the flow over the
CWA northwesterly. Going into Monday, the CWA`s flow aloft stays
northwesterly underneath the ridge as the low stays out west off the
coast of CA. Both long-term scenarios do not appear to be favored
over the other, so this situation will be monitored in future runs
for better consistency.
At the surface, the CWA looks to see chances for precipitation on
each day during the extended period. On Thursday, a surface low
looks to move near the CO/KS/NE border bringing good chances of
isolated to scattered thunderstorms across the CWA during the
afternoon and evening hours ahead of a cold front with this low. The
cold front looks to pass through the CWA on Friday again giving the
CWA chances for showers and thunderstorms during the afternoon and
evening hours. Models show another backdoor cold front slowly moving
over southwestern NE during Saturday which will bring more chances
for precipitation during the afternoon and evening hours ahead of
the front. Models show this front making its way through the CWA on
Sunday again giving some chances for precipitation. On Monday, a
stationary front looks to set up in northeastern CO and northwestern
KS which may allow for a slight chance for showers and thunderstorms
in these areas. Exact timing of the passage on these boundaries
still varies between long term models due to the differing upper air
scenarios, so these will be monitored for better agreement in future
The Tri-State area should see high temperatures on Thursday in the
the middle 80s to middle 90s range followed by Friday through Monday
seeing daytime highs staying in the 80s. Tri-State area overnight
lows for Thursday and Friday look to stay in the upper 50s to middle
60s with lows on Saturday and Sunday being in the upper 50s to lower
60s. The remainder of the long term period expects overnight lows in
the middle 50s to lower 60s.
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 524 PM MDT Mon Aug 30 2021
KGLD expects to see VFR conditions throughout the 00Z TAF period
beginning with southerly winds around 12 kts with vicinity
thunderstorms possible. Precipitation chances look to end by 01Z
with KGLD winds become southwesterly at 10 kts at 09Z. KMCK sees
VFR conditions as well starting with southerly winds around 12 kts
before seeing southerly wind shear of 40 kts at 2 kft at 05Z. By
09Z, KMCK winds decrease to around 7 kts before turning
southeasterly at 16Z.
Issued at 328 PM MDT Mon Aug 30 2021
On Tuesday Elevated to Near Critical fire weather conditions are
expected along and west of Highway 27 in the afternoon. Humidity
values will reach criteria in the lower to mid teens, while winds
will stay below criteria.
On Wednesday Elevated to Near Critical fire weather conditions are
expected along and west of Highway 27 in the afternoon. Winds
expected to reach or exceed criteria(30-40 mph), while humidity
values will only drop into the upper teens to around 20 percent.
Issued at 328 PM MDT Mon Aug 30 2021
Here are the sites with potential to reach or break record highs for
Goodland KS 102F/1985+
Burlington CO 99F/1985
Yuma CO 101F/1948
(+) denotes multiple years for a record
Area Forecast Discussion
National Weather Service Green Bay WI
1045 PM CDT Mon Aug 30 2021
Updated aviation portion for 06Z TAF issuance
Issued at 210 PM CDT Mon Aug 30 2021
Quiet weather with seasonable temperatures and comfortable
humidities will continue through most of the work week. The next
chance for rain will hold off until Friday.
A seasonable upper pattern with a modest band of westerlies
across about the northern half of the CONUS and Canada will
persist through the Labor Day weekend. Day to day weather changes
will primarily result from modest variations in amplitude and
shortwaves propagating through the pattern.
Dry air across the area will result in fairly large diurnal
temperature ranges, with daytime highs near to a little above
normal and nighttime lows near to a little below normal. Dry
conditions are expected through Thursday with the chance for rain
returning late in the week and continuing through the Labor Day
weekend. But the weekend isn`t expected to be a wash-out.
Precipitation amounts are likely to end up below normal for the 7
.SHORT TERM...Tonight and Tuesday
Issued at 210 PM CDT Mon Aug 30 2021
The latest RAP analysis and satellite/radar imagery show high
pressure centered over the northern Mississippi Valley. A large
area of strato-cu has been pushing southeast into northern WI with
help from moisture fluxes off western Lake Superior. This area of
cloud cover is more robust than currently depicted in the models,
but is forecast to thin out through early this evening. May make
some last minute changes to slow the clearing down though if
trends continue. Besides cloud cover, forecast concerns mainly
revolve around fog potential late tonight.
Tonight...High pressure will be building into the region, which
will yield a quiet night for the most part. Still some nuisant
forecast issues to deal with, however. Mesoscale models show a
surface trough sliding south across northeast WI. No precip is
expected, but winds will shift to the north or northeast with
favorable trajectories for lake clouds to push into Door County
and parts of east-central WI. Delta T`s are around 10-12C, which
is not quite enough for precip. Second, winds are expected to drop
off across north-central WI, which will promote ground fog
formation. Temps are forecast to fall below the cross-over temp by
a few degrees, which should result in patchy to areas of fog,
which may lead to rapid reductions in visibility for the early
morning commute. Will add a mention to the HWO. Lows ranging from
the middle 40s north to near 60 south and east.
Tuesday...The fog will burn off early in the day across north-
central WI. The northeast flow will continue, which should lead to
a greater coverage of convective clouds than today, particularly
over central to east-central WI. Highs will be a few degrees
cooler and range from the mid to upper 70s.
.LONG TERM...Tuesday Night Through Monday
Issued at 210 PM CDT Mon Aug 30 2021
Quiet weather is expected for the start of the long-term portion
of the forecast. The large scale flow will be undergoing
amplification, which will keep a low-level ridge locked in across
the area. Given the dry air, relatively light winds, mostly clear
skies, many of the typical cold spots across the north will
probably drop into the 30s on Tuesday and Wednesday nights.
Lowered the NBM mins to account for this. Patchy frost is possible
as well, but will hold off adding that yet. It certainly would
not be unusual for some of these areas to start seeing frost once
we reach September.
The timing of the return of precipitation with an upper trough and
attendant cold front approaching from the Plains has slowed
considerably from yesterday, with the medium range models now in
much better agreement. Precipitation could reach the northwest
part of the area late Thursday night, but rain chances will be
better on Friday and Friday night as the front crosses the area. A
faster, more zonal flow will set up for the upcoming holiday
weekend. That may result in scattered showers at times, though
determining when they will occur is difficult given the upper
pattern and distance into the forecast. But regardless, most of
the weekend should be dry and favorable for outdoor activities.
.AVIATION...for 06Z TAF Issuance
Issued at 1044 PM CDT Mon Aug 30 2021
Good flying weather remains expected during the TAF period due to
high pressure across the region. Light winds and mostly clear
skies will likely support ground fog over central and north-
central WI overnight. The lowest visibilities are expected in the
08z-12z time period at RHI/AUW/CWA. Over northeast WI, low level
winds will veer to the northeast, which could bring in scattered
to broken lake clouds into the lakeshore and possibly the Fox
Valley early Tuesday morning. Brief broken mvfr cigs appear possible
at MTW, but left cigs scattered due to low predictability.
Afternoon cumulus clouds are once again expected Tuesday
afternoon, in the VFR category.
Area Forecast Discussion
National Weather Service Elko NV
322 PM PDT Mon Aug 30 2021
.SYNOPSIS...Breezy afternoons through Wednesday, but the smoke and
haze lingers across the region. Isolated thunderstorms may develop
over eastern Nevada south of Ely.
.SHORT TERM...Tonight through Wednesday evening.
Southern fringe of the westerlies have reached northern Nevada,
with a slight amplification expected on Tuesday. Gradient flow
weakens Wednesday as the upper level trough over the northern
Intermountain region moves east. Southwest breezes in the
15-25 mph range have developed this afternoon in response to the
approaching short wave energy. The two large wildfires, Caldor
and Dixie, producing prominent smoke plumes into northern Nevada.
Smoke layer quite thick and obscuring what would be sunny clear
skies, instead lowering horizontal visibility to below 6 statute
miles. There might be slight improvement in the visibility Tuesday
afternoon as gradient winds back around to a southwest component,
but smoke and haze will continue to be present. Gradient flow
relaxes a little Wednesday afternoon, but still a little breezy.
Afternoon temperatures will be a few degrees lower in the mid to
Low to moderate grade monsoonal moisture brushes eastern Nye
County and the southeast half of White Pine County, including Ely
and Great Basin National Park. Combined with weak energy lifting
northeast from SoCal coast, a few thunderstorms can be expected.
Most storms will be east and south of Ely. Isolated storms remain
possible Wednesday afternoon, but the lifting mechanism will have
.LONG TERM...Wednesday night through next Monday.
Thursday and Friday: Southwesterly to westerly flow will persist
between an upper level trough over Western Canada and a building
ridge over the southern plains. In between these two features the
mid level moisture plume including the remnants of former eastern
Pacific hurricane Nora will at this time be departing to our NE
taking the best moisture with it. Models do agree that enough
moisture will remain in our area to give the eastern third of NV
diminishing chances of an Isolated thunderstorms. PWAT values look
to be in the 0.5 to 0.75 range that will support a mix of
wet and dry thunderstorms Thursday, and then a majority dry storm
setup for Friday as PWAT values fall further.
Saturday through Monday: Model disagreements remain for the
weekend, however the big picture is a little cleaner with recent
trends in handling one of two major features. As to the ridge of
high pressure, models agree in building this feature over the
southern plains and lower Mississippi river valley. As to the
upper level trough, recent model runs have trended in bifurcating
the upper trough into to two parts. With the northern part lifting
into the northern plains, ant the southern part forming a weak
cut-off low over the California coast. This setup will place NE NV
in an area of Southerly to Southeasterly flow aloft that would be
favorable for monsoonal moisture and the return of Isolated
thunderstorms to Central Nevada starting Monday afternoon.
Significant model differences remain as to timing and progression
of the parent trough and the cut-off low, so confidence remains in
the low to moderate range.
Smoke/haze: Smoke and haze will continue to be a nuisance for NE
Nevada through Friday given the persistent W to SW flow. If
current model trends hold, the change in wind direction to a S to
SE direction would help alleviate this issue latter in the
Temperatures: Afternoon highs will range from the low 80s into
the lower 90s with the potential of clouds and haze having day to
day impacts. Lows look to be steady ranging from the middle 40s to
the upper 50s.
Smoke and haze will lower visibility into the MVFR range at KWMC,
KBAM, KEKO, and possibly KTPH. The HRRR smoke model shows plume
from Dixie fire, and spreading across the I80 corridor. Some of
Caldor smoke may reach KTPH. KELY should maintain P6SM, but smoke
and haze could lower visibility. Local G25KTS are possible until
03Z this evening, and then again after 19Z Tuesday afternoon for
all TAF sites.
Gusty winds may reach a peak of 25 mph this afternoon and again
Tuesday afternoon across northern Nevada, but only for a brief
time. Approaching critical fire weather conditions with respect to
gusty wind, but does not exceed threshold values. Smoke and haze
will impact visibility, particularly zone 437.
Some monsoonal moisture reaches east central Nevada for isolated
dry thunderstorms, although storms near the Snake Range may
produce wetting rains. These storms will be short lived at any
given spot so will not produce much rainfall, but local storm
producing a tenth of an inch is possible.
Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
814 PM PDT Mon Aug 30 2021
There will be a noticeable cooling trend Tuesday with some
additional cooling Wednesday, before a slight warming trend for
the end of the week. The night through morning low cloud regime
will continue across the coasts, otherwise skies will be clear to
.SHORT TERM (MON-THU)...30/813 PM.
Overall, a quiet evening across the district. Thunderstorm
activity remained to the south and east this afternoon, so only
have some convective "blowoff" clouds drifting overhead. Also,
stratus/fog is becoming entrenched along the immediate coast.
Latest sounding data indicates marine inversion ranging from
around 800 feet deep across the Central Coast to around 1300 feet
deep across the LAX Basin.
Forecast-wise for the immediate short term, only issue will be the
behavior of the marine layer stratus. Overnight, models continue
to indicate some decrease in H5 heights which should allow the
inversion to deepen a little bit. With decent onshore flow, the
stratus/fog should cover the coastal plain overnight and squeeze
into the lower coastal valleys. There may even be some patchy
dense fog overnight, especially north of Point Conception. Other
than any stratus/fog, skies should remain mostly clear overnight.
Current forecast has good handle on the immediate short term. Will
issue an update around 900 PM to remove Heat headlines. Otherwise,
no significant updates are expected.
***From Previous Discussion***
Generally a cooler day across the region as onshore flow increases
ahead of a trough moving into the Pac NW. The largest 24 hour
temperature decreases are across the coastal valleys and lower
coastal mountain slopes where temperatures are down as much as 15
degrees from Sunday. Marine layer stratus is hugging the coast
this afternoon and poised to move quickly onshore and inland this
evening. Clouds expected to make it at least into the lower
coastal valleys by morning. Then an additional 3-6 degrees of
cooling there tomorrow and even more so for the far interior areas
like the Antelope Valley which were only slightly cooler today.
Keeping a close eye on the remnant moisture from Nora but so far
models have accurately drawn the dry line near or just east of the
LA County line. Expecting a similar scenario on Tuesday. On
Tuesday night the NAM and GFS are showing a weak upper level
circulation over the coastal waters south of the Mexican border
moving up towards the southern Channel Islands and then inland
somewhere between LA and San Diego County. At the same time model
soundings show precipitable waters increasing to over 1.5" with a
little bit of CAPE. While most of that moisture is at or above
13000 feet the lift from the low and cooling temperatures
overnight could allow some drops to survive the long fall from the
high cloud bases, mainly south of Pt Conception. Not quite enough
confidence to put rain in the forecast and impacts would be
minimal or none but something to watch for. The HRRR, RAP and NBM
don`t show any measurable precip and only a few of the ensembles
show even a trace but both the NAM and GFS show a few hundredths
around, mainly in the mountains.
Marine layer expected to deepen each of the next couple night,
eventually covering all the coast and coastal valleys by Wednesday
morning. Temperatures will continue their downward trend through
Wednesday with highs 5-15 degrees below normal (especially coastal
valleys). Then turning a little warmer Friday with a little less
marine layer coverage but still several degrees below normal.
.LONG TERM (FRI-MON)...30/155 PM.
Models not suggesting any big changes Friday through the weekend.
There are some differences in how the models handle a trough
moving through the Pac NW but impacts locally would be minor.
Generally cooler than normal temperatures are expected with
typical night and morning low clouds for many coastal areas,
though low confidence on that aspect of the forecast.
Both the GFS and ECMWF eventually establish a return of easterly
flow at upper levels next week. As soon as Monday according to the
ECMWF with some moisture accompanying it. Low confidence in this
as well. However, pretty high confidence that we`re not looking
at any significant heat waves in the next 10-14 days.
At 2215Z, the marine inversion at KLAX was based at 1400 feet.
The top of the inversion was 4600 feet with a temperature of
26 degrees Celsius.
Overall, moderate to high confidence in 00Z TAF package. High
confidence in return of CIG/VSBY restrictions to coastal and
coastal valleys sites, but only moderate confidence in timing and
flight category. High confidence in KPRB/KWJF/KPMD forecasts.
KLAX...Overall, moderate confidence in 00Z TAF. High confidence in
return of CIG/VSBY restrictions this evening, but moderate
confidence in timing of return (+/- 3 hours of current 02Z forecast)
and flight category changes. No significant easterly wind
component is expected.
KBUR...Overall, moderate confidence in 00Z TAF. There is a 40%
chance that conditions remain VFR overnight.
High confidence that winds and seas will remain below SCA level
through Wednesday morning. By Wednesday afternoon, there is a 30%
chance of SCA level winds at times from 10 NM west of the Central
Coast to San Nicolas Island through late in the week.
There is a 20% chance of patchy dense fog across the waters north
of Point Conception during the overnight period into Tuesday
CA...Heat Advisory in effect until 9 PM PDT this evening for zones
37-38-51-52. (See LAXNPWLOX).
Excessive Heat Warning in effect until 9 PM PDT this evening
for zone 59. (See LAXNPWLOX).
.HAZARD POTENTIAL OUTLOOK (THU-MON).
No significant hazards expected.
Area Forecast Discussion
National Weather Service Medford OR
803 PM PDT Mon Aug 30 2021
.DISCUSSION...A dry cool front has pushed through the forecast
area. After a day of smoke collecting in some valleys west of the
Cascades, smoke impacts have pushed generally south of the
Siskiyous and east of the Cascades. Wildfires have been active
today, likely in response to continued dry fuels and breezy
conditions. Critical fire weather conditions have been observed
mainly east of the Cascades, and a Red Flag Warning expires there
this evening as winds begin to diminish.
Temperatures today were near to just above normal for this time of
year, and tomorrow`s high temperatures will trend a few degrees
lower. In terms of smoke coverage, the winds will slightly more
northerly, and this means smoke will drift from the Douglas County
wildfires north to south and could impact the populations of Jackson
County for most of the day with likely no reprieve like occurred
this evening. Modoc, Siskiyou, Lake, portions of Klamath County will
continue to see significant impacts from smoke. The farther west
you go from Interstate 5, the better chance of seeing clear skies.
.AVIATION...31/00Z TAFs...VFR conditions prevail across the area
this afternoon and will do so through the TAF period. The exception,
of course, will be reduced visibilities due to wildfire smoke across
the region. Visibilities have improved west of the Cascades,
including KMFR, but drainage winds will likely bring MVFR conditions
back to the Rogue Valley Tuesday morning. East of the Cascades, a
brief period of improved conditions is possible late this afternoon
and evening, including KLMT, but northwest winds will bring smoke
from the fires northwest of Crater Lake late this evening and
overnight. So expect any improvement to be short lived before
MVFR/IFR visibilities return around 04-06z. Conditions in northern
California will continue to be MVFR due to wildfire smoke.
Along the coast, any marine stratus that develops is expected to
remain mostly offshore due to northeast flow tonight into Tuesday
morning. There may be some patchy IFR cigs that develop in the
Coquille Basin and near the Brookings area, but it should be short
lived and clear Tuesday morning. /BR-y
.MARINE...Updated 230 PM PDT Monday 30 August 2021...Very steep
seas and gale force winds remain within the waters through Wednesday
evening. A thermal trough will strengthen in the afternoon and
evenings bringing gale force winds to locations roughly south of
Gold Beach and between 5 to 35 miles off shore. Outside of that
area, winds should be below gale force criteria through Wednesday
afternoon and evening. By Friday afternoon and evening, the thermal
trough will weaken and winds will quickly subside Friday into the
weekend. Seas will also be around 3 to 4 feet from Friday through
Sunday as a low moving through will disturbs the wind pattern.
FIRE WEATHER...Updated 255 PM PDT Monday, 30 Aug 2021...
Gusty westerly winds and low RHs will result in critical fire
weather conditions for portions of the area east of the Cascades
this afternoon into early this evening.
Tonight into Tuesday morning winds will diminish with better RH
recoveries in most locations, though recoveries are still expected
to be moderate to poor across some of the mountains of Northern
Cooler, temperatures are expected until late this week, but RHs will
remain generally low in the afternoons south and east of western
Douglas and Coos counties. While the GFS model warms things up as
early as Wednesday, both the ECMWF and NBM are not as quick to do
so, and this also makes sense due to smoke effects across the area.
Light to moderate easterly flow is expected each night and morning
through Friday across the ridges of the west side, with moderate to
poor recoveries developing. There`s a fair amount of model
uncertainty beginning Friday, Sep 3rd, where the GFS and ECMWF
differ by about 10 degrees on forecast highs, among other things.
.PREV DISCUSSION... /Issued 256 PM PDT Mon Aug 30 2021/
DISCUSSION...Models and ensembles show a broad upper level
trough will remain in place over the region through mid week.
Temperatures are expected to remain near seasonal normals during
this period. At the surface, a thermal trough will persist along
the coast, resulting in light to moderate northeast winds across
coastal ridges along with gusty winds at the coast and across the
coastal waters through at least Wednesday. Inland areas will see
breezy afternoon winds as well. Of concern, areas east of the
Cascades, especially in Modoc County, are expected to see periods
of breezy winds along with dry conditions in the afternoons
Tuesday and Wednesday. This may result in some elevated fire
weather concerns. Please see the fire weather discussion below for
Smoke impacts to air quality will remain a concern for some time.
The northwest to west flow yesterday and again today will allow
periods of improvement (especially during the afternoon) across
much of southwest Oregon. However, smoke will continue to bring
impacts for locations downwind of area wildfires. The HRRR model
shows improvement in the near surface smoke levels this afternoon
followed by increasing smoke this evening into tonight across
portions of eastern Douglas, eastern Jackson and Klamath Counties.
Over northern California, smoke impacts are more likely to
continue. The HRRR shows some areas in Siskiyou and Modoc Counties
may see limited periods of improvement late in the day and into
the evening today and Tuesday. An air Quality Advisory remains in
effect through at least Wedensday, and details can be seen at
Later this week, expect breezy afternoon winds and dry conditions
to continue, with temperatures gradually warming to more seasonal
values as the trough weakens and zonal flow begin to move back
into the upper levels above the forecast area.
After potentially warmer conditions due to short wave ridging
Friday, models show some semblance of a broad upper trough or
zonal flow arriving over the weekend, followed by the return of
ridging early next week. In other words, all signs are pointing
to the return of heat, with a near non-existent chance for
precipitation next week. -BPN
AVIATION...30/18Z TAFs...Some low stratus still remains within
Umpqua Basin this morning, and that stratus deck will slowly burn
off into the afternoon hours. We`ll see some MVFR ceilings under
this low stratus deck for the remainder of the evening.
Otherwise, wildfire smoke will be the only exception to VFR/clear
skies. Low visibilities will continue near airport terminals. Look
for improving visibilities west of the Cascades later this afternoon
and evening as boundary layer winds begin to increase. East of the
Cascades, visibilities will probably lower through the afternoon as
most of the smoke spills over the Cascades. In general, look for
MVFR visibilities with period of IFR visibilities in the thicker
smoke. The smoke will reduce visibilities even further near the
fires in California.
OR...Red Flag Warning until 8 PM PDT this evening for ORZ624-625.
CA...Red Flag Warning until 8 PM PDT this evening for CAZ285.
Pacific Coastal Waters...Small Craft Advisory from 2 PM Tuesday to 5 PM PDT Wednesday for
Small Craft Advisory until 5 PM PDT Wednesday for PZZ356-376.
Gale Warning from 2 PM Tuesday to 5 PM PDT Wednesday for
Hazardous Seas Warning until 2 PM PDT Tuesday for PZZ356-376.
Area Forecast Discussion
National Weather Service Pocatello ID
147 PM MDT Mon Aug 30 2021
.SHORT TERM...Tonight through Wednesday night. Multiple minor
impacts expected through the short term mid-week time frame, at
varying times: smoke, wind, and thunderstorms. For the smoke,
satellite imagery shows increased smoke coverage across the region.
HRRR near-surface smoke brings thicker concentrations into East
Idaho beginning this afternoon and lasting through most of Tuesday,
though there is a brief break early Tuesday, and then some
mitigation Tuesday night into Wednesday. Winds are still on the
increase for today, but look stronger Tuesday with increased surface
gradient and 700mb winds supportive of stronger gusts. This will
have lingering fire concerns into Tuesday - see discussion below.
Lastly, remnants of Tropical storm Nora continue to pull north
through the Great Basin Tuesday, but best chances for precipitation
stay south of the Utah border until Wednesday. That said, west-
southwest flow aloft limits northward progression, so it looks like
thunderstorm chances remain limited to the southeast corner, mainly
Bear Lake/Preston/Soda Springs, but may pull as far north as Driggs.
Confidence is varying, so expect some varying coverage as the event
draws closer. DMH
.LONG TERM...Thursday through next Monday. For Thursday and
Friday, the remnants of Eastern Pacific Tropical Disturbance Nora
finish working through the region with increased chances of
precipitation in the Eastern and Southeast Highlands. This is
unlikely to bring much in terms of meaningful precipitation, and
into Friday we are looking at an upper level pattern change. A dry
upper level trough is expected to move through Southeast Idaho on
Friday, bringing with it predominant northwest flow. This offers
an increased chance at getting some clearing conditions from the
smoke that has been in our area as a result of continued southwest
flow. Temperatures remain moderate throughout the period, with
highs generally around 80 degrees through the weekend and the
start of next week. After precipitation chances both Thursday and
Friday, west/Northwest flow remains with us to start off next week
and will be keeping things just about normal for the first full
week of September. CM
VFR conditions remain the predominant group, with smoky and hazy
conditions expected. Visibilities have generally stayed above 6SM
at all TAF sites, with conditions not expected to go far below
that. Winds this afternoon expected to be gusting at around 20kts
especially across the Snake Plain, before calming overnight.
Expect similar conditions tomorrow, with smoke and increased winds
in the afternoon. Aside from smoke, the skies remain clear. CM
.FIRE WEATHER...Winds remain the main concern into the middle of the
week with gusty winds both today, and then stronger Tuesday.
Conditions are complicated with both fuels and winds fluctuating
right at thresholds, but will keep today`s Red Flag in place. There
is better confidence for critical conditions for Tuesday afternoon,
including some higher elevations in 427 and 413. For thunderstorm
threats into midweek, we still expect some moisture to creep into
the region, with best chances Wednesday and Thursday, mainly
confined to zone 413. Storms look predominantly dry, but could see a
storm or two produce a wetting rain. But, that increased moisture
will likely keep humidities above critical thresholds moving into
mid week. DMH
Continued southwest flow into the region, is bringing with it
smoke from large-scale western wildfires. Looking towards Friday,
possible clearing is expected as an upper level trough moves
through the region. This is likely to result in associated
northwest flow, bringing some relief to smoke in the area by the
Red Flag Warning until 9 PM MDT this evening for IDZ410-422-425.
Area Forecast Discussion
National Weather Service Phoenix AZ
420 PM MST Mon Aug 30 2021
Unsettled weather conditions are expected for at least the first
half of this week with shower and thunderstorm chances increasing
through Wednesday. A Flash Flood Watch has been issued for the
entire area on Tuesday, and persisting through Wednesday across
southern Arizona as heavy rainfall and localized flooding will
become the main threats. Drying conditions are expected beginning
Thursday, but lingering chances for isolated storms will remain over
the Arizona high terrain into the weekend. Temperatures will lower
starting Tuesday with below normal readings then expected through
the end of the week.
Water vapor satellite this afternoon shows the local CWA is
sandwiched between a high near the Four Corners and a low over
the Pacific west of Baja California with deep southeasterly flow.
The remnants of Nora dissipated this morning, but a broad mid level
circulation is still evident. This circulation is not really
expected to be a player in our area over the next few days, but
other perturbation waves within the flow, between the previously
mentioned low and high, may invigorate the local weather.
Speaking of perturbation waves, a small wave is evident on satellite
this afternoon moving west-northwest through southwest AZ. This wave
in conjunction with peak diurnal heating is helping storms realize
the available instability. A 20Z sounding out of Yuma, AZ shows CAPE
values around 1000-1500 J/kg, which is sufficient for strong to
isolated severe storms. The sounding also shows most most of the
moisture is elevated, with a dry layer below 700 mb, but the profile
is saturated between 700-300 mb. With the dry sub-cloud layer,
strong damaging winds and dust will be a primary threat through this
afternoon, but with the deep saturated layer aloft localized flash
flooding will also be a threat and especially with storms that
anchor over the same areas. Hail contamination and evaporation below
the cloud may lead to slight radar overestimation, but with rain
rates up to 1.5-2"/hr, locally high rainfall amounts are still
possible. 12Z HREF favors our western deserts and the AZ high
terrain through the rest of this afternoon, keeping the Phoenix area
quiet. However, hi-res models are suggesting another wave moving
through tonight- tomorrow morning with another round of elevated
convection, mainly west of Phoenix, but could clip through the metro
Tuesday through Wednesday, richer moisture is expected to stream
northward out of Mexico, with 2" PWATs over a large portion of the
CWA, as deep southerly flow sets up between the high to the east and
low to the west. The low is expected to transition into an open wave
trough and push inland heading into Wednesday. Best dynamics with
this trough and southerly perturbation waves looks to line up over
the region Tuesday evening through Wednesday morning/early
afternoon. This time period currently looks the most favorable for
heavy rain and flash flooding impacts based on the 12Z HREF and
recent hi-res model runs. With the fairly uniform deep southerly
flow, banding storm structures with training over the same areas
will be a possibility and the 18Z HRRR is beginning to support this
as well. The remaining uncertainty at this time continues to be
where heaviest rain will line up and the coverage of heavy rain.
Conceptually, high terrain and upslope regions are the most favored
for highest QPF with the southerly flow. With the potential banding
structure of storms, there is still a possibility for many areas to
get no measurable rain while an area 5-10 miles away receives a few
inches within a persistent rain band. The median QPF for the Phoenix
area is 0.5-1.0" with a 10% chance of 0.01" or no rain at all. The
12Z HREF LPMM is supporting the potential for 2-4" in the upslope
regions north of Phoenix. So, while most may not see flooding
impacts from the event, the flash flood watch is certainly warranted
as the potential is definitely there for high rainfall amounts.
Much drier air aloft is now expected to spread over much of the
area Wednesday night into Thursday as the upper level trough exits
to the northeast, likely ending rain chances across the lower
deserts by Thursday morning. Another upper level trough is forecast
to approach the California coast late in the week, keeping our
region mostly under southwesterly flow aloft. Lingering boundary
layer moisture should prevail over the higher terrain of eastern
Arizona Friday into the weekend keeping at least slight chances for
afternoon storms in the forecast. Model ensembles are also starting
to agree on another round of monsoonal moisture and storm chances
moving back into the region late in the weekend into early next week.
Temperatures today will still be very warm with highs near to
slightly above normal, but that will quickly change with the
increasing moisture and more widespread rainfall starting Tuesday.
Forecast highs bottom out on Wednesday with highs a few degrees
below normal across the western deserts to around 90 degrees
across the south-central Arizona deserts. A gradual warm up should
then take place late in the week with temperatures possibly
reaching near normal readings for the upcoming weekend.
.AVIATION...Updated at 2320Z
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
There`s less than a 20% chance of thunderstorms directly impacting
any terminal this evening with better chances of abrupt outflow wind
shifts. In fact, competing multiple outflow boundaries are possible
with low confidence in timing, direction, and magnitude. A general
increase in mid/high cloud decks will occur through the evening and
overnight, and eventually elevated SHRA/TSRA should materialize
across parts of the region. Coverage into the Phoenix metro is
uncertain and have carried VCSH into the sunrise hours, and
potential exists for isold/sct TSRA.
Thick cigs 12K-15K ft AGL are likely much of the day Wednesday with
forecasts suggesting a potential deck around 6K ft. At this time,
have just carried a SCT mention with rather quiet conditions likely
through much of the day. For planning purposes, there is good
confidence an organized complex of storms will roll into the entire
Phoenix metro area Wednesday evening. Significant TSRA impacts are
Southeast California/Southwest Arizona including KIPL and KBLH:
Scattered TSRA will directly impact KBLH this evening while activity
may stay just SW of KIPL. Regardless, gusty outflow winds will be
possible at both sites. Directions will favor SW at KIPL, but will
be highly variable at KBLH depending on storm location around the
airport. While there should be a break inactivity overnight, further
elevated SHRA/TSRA will be possible again Wednesday morning. In
general, cigs should remain above 8K ft AGL through Wednesday
Wednesday through Sunday:
Elevated moisture levels from an influx of tropical moisture will
bring very good rain chances across Arizona on Wednesday, possibly
lingering across eastern Arizona into Thursday. Heavy rainfall and
flooding may impact area burn scars, particularly on Wednesday.
Drying conditions are expected from west to east on Thursday ending
rain chances for all but the eastern Arizona high terrain. After
mostly slight chances for afternoon showers and storms across the
higher terrain on Friday and Saturday, another disturbance may bring
more widespread rain chances starting Sunday. Minimum RHs will
remain quite high for much of the period across central and eastern
Arizona, while southeast CA and southwest AZ see RHs dip into the
teens to around 20% by Saturday. Winds should be relatively light,
mostly following an afternoon upslope component and overnight
drainage through the period.
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
AZ...Flash Flood Watch from Tuesday morning through late Wednesday
night for AZZ530-531-533>563.
Flash Flood Watch from Tuesday morning through late Tuesday
night for AZZ532.
CA...Flash Flood Watch from Tuesday morning through late Tuesday
night for CAZ560>570.
Area Forecast Discussion
National Weather Service Reno NV
252 PM PDT Mon Aug 30 2021
Southwest to west winds this week will bring a daily influx of
smoke and poor air quality to portions of northeast California and
western Nevada. Gusty winds again Tuesday will create dangerous
fire spread potential, with lingering concern in some areas
Wednesday. A gradual cooling trend is expected through Thursday
with early mornings remaining chilly to cool.
Not much change to the forecast thinking through Wednesday night.
The concern continues to revolve around gusty winds again Tuesday
and, for some areas near Tahoe and into far western NV, on
Wednesday as well. Afternoon winds Tuesday still look to be the
strongest for most areas with gusts 30-40 mph expected at the 20
foot level (reduced near the ground and in areas with substantial
obstacles/buildings). The breezy and dry conditions through
Wednesday are mostly a fire concern (with a secondary concern for
lake recreation, especially Tuesday) so see the fire discussion
below for more details.
Temperatures remain quite warm/hot today before gradually easing
down, especially by Wednesday, as an upper trough moving into
northern California brings cooling aloft.
As for smoke, that issue will continue through mid-week for much
of northeast CA north of Markleeville as well as western and
northern NV given the continued activity of the Dixie and Caldor
fires and gusty southwest to west winds each day. As occurred
between yesterday afternoon and this morning, the worst smoke/air
quality from the Caldor Fire is once again expected for portions
of the Tahoe Basin and near and south of Highway 50 (including
Carson Valley) in western Nevada through Tuesday (the farthest out
the HRRR smoke model currently goes). -Snyder
.LONG TERM...Thursday through early next week...
Lighter winds return late week through early next week as ridging
gradually builds over the region. High temperatures bottom out
near or slightly below average late week before the slowly
building ridge starts a modest warm up by next Sunday and Monday.
One other thing we haven`t had to think about in awhile is
convective development. Global models and hints from ensemble
clusters show a weak upper low near or inland from the central or
southern California coast over the weekend and possibly into early
next week. The weak low is simulated to be leftover from the
southern edge of the upper low moving through the Pacific
Northwest late this week. With the weak low in the proximity and
warming temperatures over the weekend, there is the potential for
cumulus buildups near the Sierra. At this point, confidence in
cumulus building into afternoon thunderstorms is very low;
however, it was worth non-zero POP due to some potential.
With the weak upper low bringing a backing of winds to more south
to southwest aloft late week, smoke may begin to more substantially
affect the Reno-Sparks and Truckee areas once again. This is a low
confidence forecast so just be mentally prepared for the return of
thicker smoke for now. -Snyder
Greatest concerns the first half of the week revolve around
increasing SW-W winds and the continued smoke and haze throughout
the region. Terminals are likely to see wind gusts reach 20-25
kts this afternoon and evening and also on Wednesday. Stronger
gusts of 30-35 kts are anticipated for Tuesday from approximately
21z-03z. Winds at FL100 to be sustained around 25-35 kts today
through Wednesday, with turbulence and a potential shear layer
across and downwind of the Sierra.
Smoke to continue to bring terrain obscuration and slantwise
visibility reductions area-wide. Based on HRRR smoke models, the
places that look to be hardest hit this afternoon and evening from
Caldor would include areas from KTVL-KMEV-KHTH. Downwind of Dixie,
areas across portions of Lassen and Plumas Counties into northern
Washoe County and east toward KWMC look to be most affected. Similar
patterns look likely for Tuesday as well.
* A period of breezy and dry conditions will exacerbate ongoing
fires and increase the threat of significant fire growth for
much of the region. Please listen to all advice from local
authorities, especially if you are in the path of the Caldor
and/or Dixie Fires. Stay safe out there.
* Red Flag Warning extended through Wednesday evening for the
Tahoe Basin, Sierra Front, and northern Mono County.
* Red Flag Warnings in effect through Tuesday evening for
northeast CA including the Dixie Fire into northwest NV for
gusty winds and low humidity.
* Poor overnight recoveries for mid slopes and ridges tonight and
Ongoing wind and low humidity event should last into Wednesday
based on the latest simulations. Winds still appear to be
strongest on Tuesday, where valley gusts could easily reach 30-40
mph across the region. Sierra ridge winds in the vicinity of the
Caldor Fire could exceed 50 mph at times tonight and Tuesday.
Otherwise, winds of 25-30 mph, locally 35 mph look to be the rule
for Monday and Wednesday afternoons. This combined with dry,
unstable conditions and extremely receptive fuels means critical
fire weather conditions the next 48 hours or so. Winds will
diminish a bit in most valleys tonight, with persistent winds in
thermal belts and ridgelines during the overnight hours.
Unfortunately, no real precipitation is on the horizon the next 7-10
days. However there are some simulations starting to show
potential for thunderstorms early next week as high pressure
builds over the region. Confidence is low at this time but
blended guidance favors ~10% chance over the Sierra south of
NV...Red Flag Warning until 11 PM PDT Wednesday for Lake Tahoe in
Lake Wind Advisory from 2 PM to 9 PM PDT Tuesday NVZ003-004.
Red Flag Warning until 11 PM PDT Tuesday NVZ458.
CA...Red Flag Warning until 11 PM PDT Wednesday for Lake Tahoe in
Lake Wind Advisory from 2 PM to 9 PM PDT Tuesday CAZ073.
Red Flag Warning until 11 PM PDT Tuesday CAZ270-271-278.
For more information from the National Weather Service visit...
Area Forecast Discussion
National Weather Service Blacksburg VA
1039 PM EDT Mon Aug 30 2021
Warm and humid weather will persist through Tuesday. Rain
chances increase significantly by Tuesday night and continue
through Wednesday as the remnants of Ida reach the central
Appalachians. In the wake of Ida, high pressure will build in
from the northwest for drier and less humid weather by the
.NEAR TERM /THROUGH TUESDAY/...
As of 1033 PM EDT Monday...
Weakening convection late this evening and models are keeping
most areas dry overnight with showers approaching from the west
toward morning along front stretching from Missouri to central
WV/northern VA. This front and the remnants of Ida will be our
concern heading into Tuesday afternoon into Wednesday and where
heaviest rain sets up. Currently, no changes beyond tonight to
the forecast. Still looks like the Alleghanys of VA into WV will
see the higher totals of rainfall, but narrow/spiral bands on
the southerly/southeast flow going into Tuesday night could
bring a quick 1 to 2 inches in an hour.
Enough low level convergence and CAPE across southern VA into NC
to keep several bands of convection going early this evening.
High-res models are having a hard time with this but the latest
RAP has some semblance of current radar, though its too far
north in its depiction. Will run with scattered convection this
evening, but expect the southern areas to see diminishing trend.
Otherwise, no other major changes to the forecast.
Chance of rain remains north of I-64 west of Lexington until
Main axis of showers and thunderstorms remains along and south
of a cold front that extended from Pennsylvania to central
Missouri. Greatest areal coverage will be north of a Lexington
to Lewisburg line tonight and shifts north on Tuesday morning.
As Tropical Storm Ida reaches the Tennessee Valley on Tuesday
afternoon, coverage of showers and thunderstorms will increase
from west to east across southwest Virginia, southeast West
Virginia and northwest North Carolina. Have slightly sped up
arrival time of higher probability of precipitation in the
mountains and foothills for Tuesday afternoon.
Clouds and rain have held temperatures in the lower 70s from
Bluefield into the Mountain Empire area. Surface dew points were
in the mid 60s to lower 70s. Locations that had rain today and
where clouds clear out in the evening will again have patchy fog
Highs on Tuesday will be a couple of degrees cooler than today
due to the increase of cloud cover and precipitation. Stayed
close to the NBM and short term blend for highs on Tuesday.
.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/...
As of 100 PM EST Monday...
Remnants of Tropical Storm Ida to cross the region with a
heavy rain/flooding potential, gusty winds, and tornadoes
Tuesday night is expected to begin with the remnants of Ida over
central TN, heading northeast. A strong southerly moisture feed will
already be over the western half of the region since Monday
afternoon. This moisture trajectory will continue through Tuesday
night, with the axis expanding in width, and spreading eastward
through the night. A Flash Flood Watch already will be in effect for
our mountains and foothills region. Rainfall amounts across this
region is expected to average three-quarters of an inch to one and
one-half inches through the night across the mountains (locally
higher amounts possible), with lesser amounts heading eastward
across the Piedmont. The area along and east of a Yanceyville, NC to
Buckingham, VA line may only receive up to one-tenth of an inch
through daybreak Wednesday.
Another concern for the region late Tuesday night into early
Wednesday will be the potential for tornadoes. As is common for
tropical systems, and remnants thereof, expect high values of 0-3km
storm relative helicity around 200 to 300 m2/s2 across the area late
Tuesday night, along with MUCAPE values approaching 500 J/kg. While
CAPE is not large, it does not have to be with such robust SRH
values. We will need to watch for quick spin-up tornadoes,
especially along any apparent feeder bands that may establish
themselves across the region, curving back into the center of the
remnant tropical system.
Finally, while tropical storm strength winds are not expected with
the system, do expect wind gusts to increase, especially at the
higher elevations. By daybreak Wednesday, some of the higher peaks
will experience gusts in the 25 to 35 mph range.
For Wednesday, the center of the remnants will be near the borders
of KY/TN/VA, starting to interact with an approaching cold front. As
Wednesday continues, the front and tropical remnants will start to
merge into one heavy rain producing system, especially over the area
with the Flash Flood Watch. As the day progresses, the remnants of
Ida will favor tracking along the cold front, taking the greatest
amounts of rainfall north of our area. However, the area still will
be on the wet side, especially the west. Across the eastern
sections, the tornado concern will continue, if not increase a bit
during the day if any breaks in the cloud cover can develop and
increase MUCAPE value closer to, if not slightly over, 1000 J/kg,
all the while still encountering 0-3km SRH numbers in the 200-300
Rainfall amounts will continue to be greatest across the foothills
and mountains on Wednesday, with totals averaging an additional one
to two inches, again with locally higher amounts. Across the
Piedmont region, amounts more in the range of three-quarters of an
inch to one and one-quarter inches are more probable. Locally higher
amounts are possible here too.
Wednesday night, the precipitation will exit our region from
southwest to northeast as the front/remnant low combo tracks toward
and across the Mason-Dixon line. The potential for additional storms
and isolated tornadoes will continue in the far eastern and
northeastern sections of the area through the evening hours.
Rainfall amounts will be heaviest across the east and northeast
where an additional one-quarter to three-quarters of an inch are
By Thursday, most of the deterministic models are favoring a dry
forecast for the region with the precipitation associated with the
remnants of Ida east and northeast of the region. However, the upper
trough associated with the aforementioned surface cold front will be
crossing the area. It is possible there may be enough instability
aloft from increased lapse rates the associated cold pool for some
isolated showers to develop.
By Thursday night, this upper trough will be east of the region and
surface high pressure will be building in from the west. Look for a
a dry and notably cooler night.
Temperatures during this portion of the forecast will average about
five to ten degrees cooler for the highs, and five to ten degrees
milder for the lows. The exception will be Thursday night when low
temperatures are expected to be about five degrees cooler than
Confidence in the above weather scenario is moderate to high.
.LONG TERM /FRIDAY THROUGH MONDAY/...
As of 120 PM EDT Monday...
A dry and less humid stretch of weather in the wake of Ida
for the weekend...
High pressure looks to dominate the extended with the exception
of a weak frontal passage Sunday into Monday and again midweek.
The bigger story will be the lowering humidity and cooler air
for many Friday, Saturday, and Sunday. Some locations in the
mountains could see lows in the 40s with widespread low to mid
50s elsewhere through the weekend into early next week.
Mostly sunny skies will dominate Friday and Saturday with high
pressure overhead. By Sunday and Monday will add a few more clouds
as our weak frontal boundary moves on through. Once again rain
chances will be meager at best with this front and mainly confined
to the mountains according to the latest 12z model suite.
Expect highs to top out in the mid to upper 70s over the mountains
with low to mid 80s out east by Friday afternoon. Much of the same
can be expected Saturday through Tuesday with highs increasing by a
degree or two each afternoon.
Confidence remains moderate to high in the long term period.
.AVIATION /03Z TUESDAY THROUGH SATURDAY/...
As of 723 PM EDT Monday...
Will have tempo thunder in at DAN per latest radar til 01z, then
should be VFR at all sites through 04-6z, then anticipate some
fog early at LWB/BCB then BLF/DAN and perhaps LYH overnight.
Mid and high clouds ahead of Ida should keep fog a bit less
dense, but could see LIFR at LWB for a period from 9-12z. Could
see some lower cigs as well in the mountains of IFR to MVFR
range late tonight.
Any fog and low clouds will give way to a mid deck by 14-15z. Models
hold off til late in the taf period in bringing lower cigs and
rain into the area, reaching BLF/LWB after 21z, though some
light rain from mid deck possible at BCB/ROA in the afternoon.
Average confidence on all elements this period.
Extended Aviation Discussion...
Tropical moisture and more widespread rainfall chances arrive by
Tuesday evening and continue through Wednesday. This will
result in MVFR to IFR ceilings and visibility. Wind gusts up to
25 knots are possible Tuesday afternoon and evening especially
As the tropical system moves to the northeast, winds will turn
to the northwest with 20 to 30 knot wind gusts at the highest
elevations into Wed night/early Thursday. Drier weather and
less humid conditions expected in the wake of Ida Thursday into
the weekend, with VFR, outside any valley fog.
As of 330 PM EDT Monday...
Flash Flood Watch has been expanded to the foothills of
the Blue Ridge...
Based on where there has been rainfall over the past 24 to 48
hours and the potential for more rain and heavy rainfall rates
Tuesday night and Wednesday, the Flash Flood Watch has been
expanded east into the foothills of the Blue Ridge from Virginia
into northern North Carolina.
As the tropical storm tracks to the east, surface and low level
winds will turn to the southeast and provide at least 3 to 6
hours up enhanced upslope along the eastern side of the Blue
Ridge Tuesday night and Wednesday. Models were also showing
decent upper diffluence Tuesday night and some impressive
precipitation potential placement on Wednesday. System will be
advecting in precipitable water values approaching 2.2 inches.
Expect that rainfall rates in any of the bands around the
tropical system have the potential for very heavy rainfall
rates. While Flash Flood Guidance is not especially low, rates
of 3-4 inches per hour are not out of the question.
Looking at the impact on the main stem rivers, at this time we
are keeping an eye on the Upper James and Greenbrier Rivers for
the potential to reach action stage but, overall impact will be
minimal. This event will have much more impact on the small
rivers, creeks and streams, and in the headwaters than on the
main stems of area rivers.
VA...Flash Flood Watch from Tuesday afternoon through Wednesday
evening for VAZ007-009>020-022>024-032>035.
NC...Flash Flood Watch from Tuesday afternoon through Wednesday
evening for NCZ001>004-018>020.
WV...Flash Flood Watch from Tuesday afternoon through Wednesday
evening for WVZ042>044-507-508.
Area Forecast Discussion
National Weather Service Sacramento CA
259 PM PDT Mon Aug 30 2021
Gusty southwest winds will result in critical fire weather
conditions over the northern Sierra and southern Cascades through
mid-week. Cooler temperatures expected through the remainder of
GOES-West fire temperature product is showing increased fire
activity associated with the Caldor Fire and Dixie Fire this
afternoon. A very dry airmass is currently in place with RH
readings only in the single digits to mid teens over most of the
northern Sierra, Southern Cascades and foothill ridges. Wind gusts
up to 20-30 mph has been observed so far across the high Sierra
and southern Cascades this afternoon.
Ensemble means indicate that an upper trough will gradually
deepen into mid-week. This will result in periods of critical
fire weather conditions over the northern Sierra and southern
Cascades through mid-week. Southwest to west wind gusts of 20 to
35 mph are possible, locally higher over ridgetops. The strongest
winds are expected in the afternoon and evening hours, especially
on Tuesday. These winds combined with very low humidity and
extremely dry fuels will lead to critical fire weather conditions.
The Red Flag Warning has been extended until Wednesday evening
for the northern Sierra, given the potential for rapid spread of
new or existing wildfires. This includes the Caldor Fire and
portions of the Dixie Fire. Please practice fire safety.
Locally breezy northwest winds over the northern Coastal Range
could bring a brief period of elevated fire weather concerns early
The onshore flow will likely help with some smoke dispersal in
the Valley as the trough settles in and onshore flow persists,
pushing much of the smoke off to the east. However, the latest
HRRR smoke shows areas of smoke filtering into the northern
Sacramento Valley this evening through at least Wednesday morning
as northwest winds develop.
More significant cooling develops across the region Tuesday and
continues through at least mid-week as temperatures lower to a
little below average. Despite the cooling, humidity will remain
low outside portions of the Central Valley influenced by the Delta
Breeze. Temperatures will cool back into the mid 80s to mid 90s
during the Wednesday-Thursday timeframe.
.EXTENDED DISCUSSION (Friday THROUGH Monday)...
Troughing looks to continue over the west for the start of the
extended period. This will keep cooler temperatures in place
along with locally breezy onshore winds. The clusters show some
divergence in ensembles late weekend into early next week but
overall upper level ridging building in from the west is favored.
This will bring a warming trend into early next week. No rain or
thunderstorm chances expected.
MVFR to IFR at times for the northern Sacramento Valley terminals
next 24 hrs due to area wildfire smoke. VFR expected at other
Valley terminals. MVFR to locally IFR possible near active
wildfires, particularly over the Sierra. Gusts 15 to 30 kts
vicinity Delta and high Sierra. Elsewhere, winds generally under
Red Flag Warning until 11 PM PDT Tuesday for Burney Basin and
Northeast Plateau in Shasta County Including Northwest Lassen NF
north of Lassen NP-Eastern Portion of Shasta/Trinity NF-Northern
Motherlode From 1000 to 3000 Ft. Includes portions of Nevada-
Yuba-Placer-Amador and ElDorado Units-Northern Sierra Foothills
from 1000 to 3000 Ft. Includes portions of Shasta-Trinity and
Butte Units-Northern Sierra Including Lassen NP and Plumas and
Lassen NF/S West of the Sierra Crest (West of Evans Peak-Grizzly
Peak-Beckworth Peak)-Northern Sierra Including the Tahoe and
ElDorado NF/S West of the Sierra Crest-Southern Motherlode From
1000 to 3000 Ft. Includes portions of Calaveras-Tuolumne Unit-
Stanislaus NF West of the Sierra Crest.
Area Forecast Discussion
National Weather Service Las Vegas NV
818 PM PDT Mon Aug 30 2021
.SYNOPSIS...Excessive Heat Warnings for portions of the Mojave
Desert will expire this evening. Thunderstorm chances will be mainly
southeast of Interstate 15 this afternoon and evening, and chances
will expand farther northwest Tuesday and Wednesday. Deep moisture
associated with the remnants of Hurricane Nora will bring a risk of
heavy rain, so a Flash Flood Watch is in effect for parts of Mohave,
San Bernardino, and Clark counties Tuesday and Wednesday.
.UPDATE...The latest HRRR smoke model is showing an increase in
smoke from the Caldor fire across Inyo county overnight, and the
visibility grids have been updated to reflect this. Otherwise,
thunderstorm activity over Mohave and eastern San Bernardino
counties will continue to diminish through the evening with the
majority of the activity ending around midnight, with the exception
of southern Mohave where storms may persist a bit longer. Similar
conditions are expected Tuesday with scattered thunderstorms
developing around mid-day over Mohave county and the higher terrain
in Clark county, before moving into the Las Vegas valley during the
afternoon. No other changes were needed to the forecast for the
remainder of the period.
528 PM PDT Mon Aug 30 2021
.SHORT TERM...through Wednesday night. Midday satellite loop showed
an arc of debris clouds roughly along I-15 and moving northwest. New
convection was popping over Mountain Pass, the Clark County
mountains, the San Bernardino Mountains, and the Hualapai Mountains.
Smoke was still lingering over the southern Great Basin.
Precipitable water of one inch or greater was in place southeast of
I-15, and models show 1.5 inches of PW coming up the Colorado River
Valley tonight through Wednesday as the deep moisture arrives from
the remnants of Hurricane Nora. As has been advertised, this will
lead to a risk of flash flooding, and the Flash Flood Watch looks
good. Took a hard look at possibly expanding it into more of San
Bernardino and Clark counties, but it still seems like flash
flooding in those areas would be isolated at best Tuesday and
Tuesday night. For the rest of this afternoon, most storms should be
along and southeast of I-15, with most (but maybe not all) storms
dying off by 10 PM or so. Tuesday afternoon, most storms should be
southeast of a line from Barstow to Mount Charleston to Rachel, and
as the upper low currently spinning over the eastern Pacific moves
inland and helps lift the Nora moisture, storms will likely persist
all night. Wednesday is somewhat questionable and dependent on how
much the atmosphere gets worked over Tuesday and Tuesday night;
however, if storms are able to get going, Mohave and Lincoln
counties would be most favored. Farther west, models show drier air
working very slowly through Inyo, Esmeralda, Nye, and western San
Bernardino counties, but this drier air often makes it in more
slowly than suggested, so will keep an eye on it.
.LONG TERM...Thursday through Labor Day.
Residual moisture Thursday will keep additional chances for
showers and thunderstorms largely confined to Mohave County, but
can not rule out a few storms lingering over eastern Nevada.
Mainly dry conditions with temperatures near normal Friday into
the Labor Day Weekend. The exception is in Mohave County where
lingering moisture could still ignite a few showers and
.AVIATION...For McCarran...Southerly winds are expected to remain
through the evening with occasional gusts to around 15-20 kts. Low
confidence on any additional storms to develop to the southwest or
west this afternoon, but not out of the question for outflow winds
from the east or southeast from distant thunderstorms this evening.
Non-zero chance for some isolated showers to develop overnight/early
Tuesday morning, but confidence remains low. Higher confidence on
thunderstorms in the Las Vegas Valley and potentially moving over
the terminal Tuesday afternoon, potentially as early as 20-21Z.
Potential impacts associated with storms Tuesday include brief heavy
rainfall that could result in reduced visibility over the terminal,
gusty outflow winds, and lightning within 15 miles. Outside of
thunderstorm influences, winds should be fairly light following
typical diurnal patterns. SCT to BKN aoa 10-12 kft.
For the rest of southern Nevada, northwest Arizona and southeast
California...Isolated to scattered thunderstorms are possible again
this afternoon/early evening across southeastern portions of our
region, including in and around the Colorado River Valley and
potentially KDAG. Low confidence on storms impacting KIFP, KEED, and
KDAG directly, but vicinity thunderstorms maybe within 15 miles at
times. Main concern would be strong outflow winds impacting the
terminals, potentially bringing gusts up to 30-40 knots. There`s
some signal that outflow interactions may keep storm chances
overnight tonight across Mohave County, with a better signal for
outflow winds moving from the east and into the Colorado River
Valley tonight (05-06Z). SCT to BKN aoa 10-12 Kft will be possible
in this region, with brief reductions in visibility where storms
Further northwest, expect mostly clear skies and some occasional
breezy winds in the afternoon. That said, haze from distant wildfire
smoke will reduce slant range visibility at times, especially across
the Sierra, western Mojave Desert and parts of the southern Great
Basin. Less confident on the potential for smoke/haze to impact KBIH
overnight tonight/early tomorrow morning, with some signal of smoke
coming in from the north-northeast or not at all. If it does, the
HRRR Smoke indicates it may only drop vsbys to around 5-6 SM briefly
.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather or impacts according to standard operating
For more forecast information...see us on our webpage:
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