Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/29/21
Area Forecast Discussion
National Weather Service La Crosse WI
1030 PM CDT Sat Aug 28 2021
.SHORT TERM...(This evening through Sunday)
Issued at 314 PM CDT Sat Aug 28 2021
Main forecast concern is the severe weather potential heading into
tonight and ongoing flooding issues, particularly across northeast
Iowa.
Surface low pressure sits along the eastern South Dakota/Nebraska
border early this afternoon with a warm front extending northeast
toward Lake Superior. Meanwhile a mid-level shortwave is lifting
through the Upper Mississippi Valley with a decaying MCV or two
lifting into far northwest WI and the MN Arrowhead out ahead of an
approaching cold front. Clouds have blanketed much of the forecast
area today, and decaying showers and storms worked through portions
of northeast Iowa and southeast Minnesota earlier. This has once
again kept temperatures on the cooler side for much of the area (70s
to low 80s), with the exception of our far south (mid 80s to around
90) where sunshine broke through earlier. As a result of the
clouds/rain, there`s a big pool of more stable air centered over
Austin/Rochester area, but MLCAPE of 1000-2500 J/kg wraps around to
our north/east/south. Other parts of central/northern MN have also
been worked over by storms earlier.
There will continue to be some theta-e advection into our area
heading into tonight, so the question is whether that will be
sufficient to allow the atmosphere to recover. The cold front looks
to cross into our area more overnight, which also complicates the
severe potential. RAP suggests a narrow ribbon of 1000-2000 J/kg
MUCAPE immediately out ahead of the cold front this evening as it
crosses MN, with instability steadily diminishing thereafter
overnight. Does appear to be some overlapping deep layer shear
overnight as the low level jet/moisture transport gets underway.
Overall impressions of this setup is that the greatest severe threat
appears to lie north and west of our forecast area. Convection will
develop into a broken line along the front, gradually weakening as
it encounters waning instability by the time it crosses into our
north/west overnight. CAMs have been indicating this same trend with
the line fizzling out as it works into our area. If storms hold
together, pockets of enhanced wind would be the main threat, but
can`t write off isolated hail and tornadoes with the low level jet
contributing impressive low-mid level shear once again.
Some lingering rain chances in our southeast Sunday morning as the
front finally exits, perhaps a few rumbles of thunder. But otherwise
that looks to be it for wet weather for awhile. A cooler day on tap
as cold air advection gets underway with highs generally in the mid
70s to around 80.
.LONG TERM...(Sunday night through Saturday)
Issued at 314 PM CDT Sat Aug 28 2021
A much-welcomed quieter period of weather comes into play early in
the week as high pressure over Hudson Bay builds into the area with
a drier airmass. Baroclinic zone off towards Nebraska/Missouri may
support a developing MCS or two through Monday into Tuesday, but
guidance generally keeps that off to our southwest so the forecast
has been trending towards dry. The high drifts off to our east with
developing return flow late in the week, so may see rain chances
start to return towards next weekend. All in all, looks like a
pleasant, cooler, less humid week ahead with highs in the 70s to
low 80s.
&&
.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1030 PM CDT Sat Aug 28 2021
Cigs: mostly VFR bkn cigs through the night, but potential for a
few hour window of MVFR around cold front slated to move through
near 12z. Then, looking at SKC/SCT conditions for the
afternoon/night.
WX/vsby: line of storms have developed along cold front to the west,
with other storms going up north of the TAF sites on the edge of the
low level moisture transport. A few meso models suggest the line
will hold together as it reaches KRST, with weakening trend as it
nears KLSE. Will follow these trends and add more timing for a
shra/ts chances. Any thunderstorm could produce enhanced wind gusts
and heavy rain.
Winds: southerly through the night, swinging west/northwest toward
12z as the cold front moves through.
&&
.HYDROLOGY...
Issued at 314 PM CDT Sat Aug 28 2021
Additional rainfall of around 1 to 4 inches fell since early this
morning across portions of northeast Iowa and far southwest
Wisconsin. Much of northeast Iowa was already fully saturated.
Headwaters of tributaries there have already crested or are in
the process. The Turkey River is experiencing major flooding at
Spillville with moderate flooding downstream. Cedar River is also
in moderate at Charles City. Lots of standing water reported
across northeast Iowa, so have an areal flood warning in effect
into this evening. Will continue to check in with county officials
to gauge impacts in case this needs to be extended. With CAMs
indicating tonight`s line of convection should weaken/diminish as
it gets into the area, it appears the threat for additional heavy
rain impacting already flooded areas is low. However, if any
storms hold together to move over this high impact area tonight,
flooding could be exacerbated in some areas. Drier weather Sunday
and beyond will allow conditions to improve.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&
$$
SHORT TERM...Kurz
LONG TERM...Kurz
AVIATION....Rieck
HYDROLOGY...Kurz
Area Forecast Discussion
National Weather Service Bismarck ND
931 PM CDT Sat Aug 28 2021
.UPDATE...
Issued at 931 PM CDT Sat Aug 28 2021
We extended at least low chances of showers area-wide until about
05 UTC with this update, with isolated storms also still possible.
As of 02 UTC, the primary middle- and upper-level trough axis is
roughly along the Highway 83 corridor, with dynamically-forced
precipitation in advance of the wave gradually diminishing along
with pre-trough, boundary-layer-based bouyancy. However, cyclonic
flow and instability associated with the cold pool aloft behind
the trough has allowed isolated to scattered low-topped convection
to persist. CAMs are not capturing this post-trough activity well,
and while it should diminish concurrent with diurnal cooling,
radar trends supported extending its mention a few hours. Other-
wise, guidance continues to support a cool night, with lows in
the 40s F in western ND.
UPDATE Issued at 547 PM CDT Sat Aug 28 2021
Changes with this update cycle were focused on recent observed
trends, namely boosting shower chances into the likely category
over south central ND the next few hours. Time-lagged HRRR runs
capture that activity -- which is immediately ahead of a middle-
and upper-level trough axis that`s advancing eastward -- well and
served as the basis for near-term PoPs. Midlevel lapse rates are
meager in the 6 C/km range, limiting lightning activity, but the
CAPE-shear setting over the James River valley suggests the odds
of a strong or marginally severe storm are still non-zero as the
upstream forcing approaches that area the next few hours.
&&
.SHORT TERM...(This evening through Sunday)
Issued at 237 PM CDT Sat Aug 28 2021
Current surface analysis places low over western Manitoba, with
frontal boundary dropping down into western Minnesota and secondary
trough in its wake. Upper level analysis places trough sliding
over the northern plains. The combination of these systems is
resulting in some showers and a few weak thunderstorms popping up
over our area.
For the rest of this afternoon into tonight, expect showers with
some thunderstorms to continue developing over the area with the
upper trough gradually working towards the east. The only concern
for severe weather, which is actually quite marginal, would be
from far south central North Dakota into the James River Valley.
This is where the higher instability is located over our area,
though this is a bit marginal. With that said deep layer shear is
elevated, so the threat is there for a storm or two to become
severe. Shower and thunderstorms will come to an end from west to
east overnight as the trough moves east, with skies clearing in
its wake.
On Monday, modest ridge passes over the area in the wake of the
trough, resulting in a rather pleasant day with mostly sunny skies
and near to slightly below average temperatures.
.LONG TERM...(Monday through Saturday)
Issued at 237 PM CDT Sat
Aug 28 2021
An unsettled weather pattern develops for the upcoming work week
as a variety of troughs deepen and swing around an upper low
located over the far western Canadian provinces, which will
eventually meander towards the east. This will keep chances for
showers and thunderstorms in the forecast, with chances gradually
increasing as we get later in the week.
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 931 PM CDT Sat Aug 28 2021
Isolated to scattered showers and a few thunderstorms this evening
will diminish by about 06 UTC as an upper-level trough exits the
area. That will lead to dry weather into Sunday, along with
widespread VFR conditions for western and central ND.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...CJS
SHORT TERM...JJS
LONG TERM...JJS
AVIATION...CJS
Area Forecast Discussion
National Weather Service Cheyenne WY
924 PM MDT Sat Aug 28 2021
.UPDATE...
Issued at 916 PM MDT Sat Aug 28 2021
Only minor changes made to the forecast this evening. We have
removed the precipitation chances overnight, due to limited mid
level moisture and more stable lapse rates in the 700-500mb layer.
Still may seem some cloud decks around 4-5kft, but these clouds
should not stick around long as things mix out fairly quickly. A
much cooler day is expected tomorrow as cool high pressure builds
over the area.
&&
.SHORT TERM...(This evening through Monday)
Issued at 250 PM MDT Sat Aug 28 2021
Current observations across the region show a surface cold front
moving into Carbon and Albany counties this afternoon while the
eastern plains are a little cooler and more moist behind the front
after it pushed through earlier today. Thunderstorm forecast is
tricky through tonight, because there is some chance for nocturnal
convection across the southeast high plains due to cooler air
aloft moving in associated with the upper level trough, and some
elevated instability above the inversion. The frontal boundary
will be nearby and may provide enough lift to initiate a few
elevated thunderstorms this evening through tonight. As of right
now, CAMs/high res models are not showing too much, but are
hinting at some activity trying to get together along the Front
Range. Added a slight chance for thunderstorms east of Cheyenne
across the I-80 corridor. There is also the potential for fog
across the I-80 Summit, given the moist east to southeast llvl
flow. Kept it out of the forecast for now with the HRRR and
Consensus model output not showing any fog at this time.
Other than some fire weather concerns on Monday, hot temperatures
and a dry/quiet forecast is expected into early next week. All
models show the flow aloft backing into the southwest as a ridge
of high pressure builds across the 4 corners region. Highs on
Monday will likely reach the low to middle 90s for areas along and
east of the I-25 corridor. Slight cooler further west, but
afternoon temperatures should still be in the low to mid 80s
through the day.
.LONG TERM...(Tuesday through Friday)
Issued at 230 AM MDT Sat Aug 28 2021
Key Messages:
1) Elevated to near-critical fire-weather conditions Tuesday with
well above normal temperatures for the beginning of next week. Will
need to monitor for a possible Red Flag Warning but winds might be
just light enough.
2) Temperatures will cool to near normal and increased rainfall
chances are likely starting Wednesday, climbing moreso Thursday, and
continuing partly into Friday and Saturday next week. Pockets of
moderate rainfall could be possible with sub-tropical moisure
shifting into the region. Will need to monitor the Mullen Burn Scar
for any possible flash flooding impacts. See hydrology section below
for more information.
Weather Discussion: Next Tuesday will be the last hot day (for next
week anyway) across the region as a ridge over southern Colorado
starts to break down with an incoming NW Pacific trough sweeping
across ID/MT. Well above normal temperatures Tuesday with H7
temperatures of 16-18C in place leading to upper 80s to mid/upper
90s across the region. These H7 temperatures are in the 90-97.5
percentile of climatological observations for this region. Record
highs are in the low to upper 90s so unlikely we will break
records but likely be within 2-4 degrees of records. Did increase
high temperatures 1-2 degrees above NBM model guidance.
Wednesday will be the start of the cool down as more clouds shift
into the region along with high PWATs. A moisture plume of 1-1.3"
PWAT will stream in from the SW as the remnants of what is now
Tropical Storm Nora that is forecast to become a hurricane later
today in the eastern Pacific off the coast of west Mexico. These
remnants will advect poleward to the NE in the conveyer belt flow
between the Central Plains ridge and the trough across the Pacific
NW and first shift across western WY Wednesday afternoon. Isolated
to scattered showers will be likely Wednesday with more stratiform
rainfall continuing overnight Wednesday into Thursday as the
moisture plume slowly shifts east Thursday and Friday across east
Wyoming and into Nebraska with embedded vorticity impulses in a
slightly more zonal, yet unsettled pattern. Per ensemble suite and
deterministic model agreement, Thursday appears to be the wettest
day. Instability looks minimal so overall rainfall rates should
remain low but can`t rule out moderate rates that could possibly
cause impacts on the Mullen burn scar if training occurs.
Temperatures will be more seasonable through mid to late next week.
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 440 PM MDT Sat Aug 28 2021
VFR to possible MVFR conditions likely through the forecast period
of all terminals. Overall, not too many changes to the forecast,
outside of some gusty conditions tomorrow. HiRes models are
picking up on some shortwave disturbances tomorrow afternoon,
which is expected to kick up the wind speeds to around 20-25
knots. Moisture levels will remain low as Hurricane Ida
effectively cuts off the moisture flow from the Gulf, limiting
shower and thunderstorms potentials. Smoke from western wildfires
will continue to limit visibilities in our western fringes, with
RWL hovering around 6SM.
&&
.FIRE WEATHER...
Issued at 220 PM MDT Sat Aug 28 2021
Red Flag Warning remains in effect through this evening for areas
west of the Interstate 25 corridor. A surface cool front will
continue to push south and west across the region this evening
with winds shifting into the east and higher dewpoint
temperatures/humidities behind it. The front is expected to
stall near the mountains, but should eventually lift northeast
late Sunday and weaken. Although widespread critical fire weather
conditions are not anticipated on Sunday, they will likely return
on Monday with gusty southwest winds expected for most of
southeast Wyoming. Will likely need additional Watches and Red
Flag Warnings for Monday afternoon. Fire weather concerns will trend
lower by late next week as another push of monsoon moisture is
expected.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...None.
NE...None.
&&
$$
UPDATE...REC
SHORT TERM...TJT
LONG TERM...JSA
AVIATION...MD
FIRE WEATHER...TJT
AREA FORECAST DISCUSSION
National Weather Service Hastings NE
642 PM CDT Sat Aug 28 2021
.DISCUSSION...(This evening through Saturday)
Issued at 212 PM CDT Sat Aug 28 2021
Late This Afternoon Into Tonight...
The big story will be the threat for strong to severe thunderstorms
later this evening into tonight. Forecast models are in pretty good
agreement that our forecast area should remain dry through at least
6 pm. Thunderstorms are likely to develop between 5-6 pm just
northwest of our forecast area and then slide into our northwestern
zones (Ord to Gothenburg) between 6-8 pm. Storms will be slower to
reach our Tri-Cities with possible arrival time primarily between 9
pm and midnight.
There is good model agreement in the late afternoon/early evening
thunderstorm development. The questions reside more in the coverage
and intensity of these thunderstorms. The 12Z NAM NEST continues to
be the most aggressive in both coverage and intensity with the
formation of a convective line that surges south with outflow
boundaries bringing possibly severe winds. The HRRR and 12Z NAM
indicate more scattered convection that could be strong at the
onset, but then quickly decreases in coverage and intensity. The 12Z
HRW NSSL and 12Z HRW ARW both are similar to the 12Z NAM NEST
indicating that the convection should be rather widespread across
the forecast area by late evening. Our official forecast follows
more closely in-line with the wetter NAM and HRW models.
Regarding the severe weather potential, the greatest threat for
severe weather will be early on during the first several hours
after thunderstorm development primarily between 6-11 pm across
our northwestern zones. The wind threat seems to be the biggest
threat although there could be a brief window for severe hail in
that first 1-3 hours. Eventually, the belief is that these storms
should merge into a line that could produce severe winds in the
60-70 mph range until the gust front gets too far ahead of the
line and then it will just turn into a possibly heavy rain event
for some areas during the late night hours. Will have to watch out
for flooding if storms start training over the same areas, which
is a possibility.
Sunday Into Sunday Night...
This should be the best day of the bunch with cooler temperatures
behind the cold front holding highs down into the upper 70s to
around 80 over Nebraska, to lower 80s over north central Kansas.
There could be a few remaining showers/thunderstorms across our
southeastern zones in the morning, but after these exit the area,
odds are that most areas should be dry through the rest of the
day. We will then see some return flow and a low level jet that
could result in additional thunderstorms late Sunday night with
northeastern zones being most favored.
Monday Into Monday Night...
We will start the warmup with decent southerly flow and highs back
into the lower and middle 80s Nebraska zones to the upper 80s and
around 90 over north central Kansas. The big thing to watch out
for will be the chance for additional warm air advection nocturnal
thunderstorms Monday night mainly across our eastern zones,
although they may even set up east of our forecast area. We are
already in a SPC marginal risk outlook for Monday.
Tuesday and Wednesday...
We will see an upper level ridge build across the western high
plains and thus this period stands the best chance at being dry
as well as warmer. Highs should be back to at least around 90 by
Wednesday and probably well into the 90s over northern Kansas.
Thursday Through Saturday...
The upper level ridge should still be the dominate weather feature
on Thursday, but there is a slight chance that thunderstorms could
make it into our northwest zones by late day. Thursday should
still be hot with a lot of folks around 90 or better. That next
upper trough could start to influence our forecast area a little
bit more by Friday and Saturday with cooling temperatures and
increasing chances for thunderstorms.
.AVIATION...(For the 18Z KGRI/KEAR TAFS through 18Z Sunday)
Issued at 212 PM CDT Sat Aug 28 2021
The big concern as noted above will center around the chance for
strong to severe thunderstorms late this evening. The soonest that
we could see thunderstorms at our TAF sites would probably be 8 or
9 PM, but likely it will be later than that. The wind will be
gusty out of the south until the front comes through with the
thunderstorms. Strong to severe thunderstorm winds can not be
ruled out this evening and we`ll need to keep an eye out for how
the thunderstorms develop and track later this evening. Behind the
front and thunderstorms, the winds will become northerly.
&&
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Monday)
Issued at 624 PM CDT Sat Aug 28 2021
VFR conditions expected to continue for the next few hours as a
line of thunderstorms continues to develop to the northwest and
eventually propagates across both terminals. This front will
likely bring at least MVFR VSBYS with -TSRAs...and possibly some
MVFR CIGS as well, but confidence of CIGS is lower. Winds should
diminish ahead of the front before becoming northwesterly and
gusting to near 20 KTS through much of the overnight hours.
Conditions should begin to improve around daybreak Sunday...with
VFR conditions returning around 29/12-13Z.
&&
.GID WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
KS...NONE.
&&
$$
DISCUSSION...Wesely
AVIATION...Rossi
Area Forecast Discussion
National Weather Service Grand Junction CO
544 PM MDT Sat Aug 28 2021
.SHORT TERM...(Tonight through Sunday night)
Issued at 202 PM MDT Sat Aug 28 2021
Apart from the anticipated isolated storms over the far southwest
San Juan Mountains this afternoon, conditions have remained dry
and warm across the Western Slope. Near zonal flow aloft has
started the transport of smoke from the ongoing western wildfires
over the northern tier of the forecast area, as evident by the
latest GOES satellite imagery. While not overly thick thus far, it
has already moderated temperatures slightly across the north with
the Craig Airport trending 3 degrees cooler than this time Friday
(though this is also enhanced by yesterday`s trough passage). The
HRRR Smoke remains consistent in the continued advection of this
smoke through the short term period with the highest concentration
centered along and north of I-70. As a result, temperatures will
likely continue to trend slightly cooler than guidance.
The aforementioned convection over the southern mountains will
diminish after sunset, resulting in a quiet night. Westerly flow
aloft will persist across the north on Sunday while a ridge of
high pressure builds to the south. Residual moisture will once
again fuel isolated afternoon showers and thunderstorms over the
San Juans and potentially the West Elk Range. Otherwise, the
status quo will prevail with smoky skies and dry conditions.
Meanwhile, Hurricane Nora will continue to trek north through the
Gulf of California Sunday night before its progress begins to
slow down as we head into the long term period.
.LONG TERM...(Monday through Saturday)
Issued at 202 PM MDT Sat Aug 28 2021
The long term period will start off relatively quiet, with
temperatures running around 5 degrees above average and relatively
light winds. This all starts to change Tuesday night as the ridge
that builds in over eastern Utah and western Colorado during the day
begins to shift east and an upper level trough digs along the Pacifc
Coast, creating a classic monsoonal pattern. This won`t be just a
classic monsoonal push though, as moisture from Hurricane Nora will
enhance the subtropical moisture tap. With this extra boost of
moisture, PWATs are expected to increase quickly, with forecast
values climbing almost half an inch over the course of 24 hours.
PWATs are expected to peak Wednesday night into Thursday morning,
with Thursday looking like the day for widespread precipitation
as embedded shortwaves rotating around the trough combine with any
lingering forcing from Nora. The concern here, with the expected
widespread shower and thunderstorm activity, is heavy rain and
localized flash flooding, with burn scars areas of high concern.
Models are in good agreement through Thursday, that eastern Utah and
western Colorado will tap into deep subtropical moisture and that
Thursday will likely see the most widespread precipitation. With the
expected cloud cover and precipitation from mid-week onward,
temperatures will be at or below normal, with Thursday running
around 10 degrees below normal. Confidence decreases from Friday
into the weekend as discrepancies between models begin to crop
up. However, generally speaking the weekend will continue to be
unsettled with temperatures at or below average.
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 534 PM MDT Sat Aug 28 2021
A plume of smoke will continue to filter into the area this
evening and spread southward overnight. Right now, smoke is quite
vivid on satellite imagery, covering areas mainly along and north
of the I-70 corridor. Expect very little change in the next 24
hours, as near zonal remains overhead. VEL and HDN maybe see the
biggest impacts in VIS, though have included smoke in nearly every
TAF location. Otherwise, VRF conditions will prevail with light,
terrain driven winds overnight and gusty winds (up to 25 kts)
returning Sunday afternoon.
&&
.HYDROLOGY...
Issued at 202 PM MDT Sat Aug 28 2021
We are continuing to monitor the potential for heavy, widespread
precipitation from midweek onwards. Most of this will rely on the
track and strength of Nora. Regardless, subtropical moisture will
once again stream into the region as southerly flow sets up on
Wednesday in response to the high`s transition east. Passing
embedded disturbances will provide enhanced lift, most notably on
Thursday. Plenty of details need to be ironed out going forward,
as any slight deviations could greatly impact the overall coverage
and intensity of precipitation during this timeframe.
&&
.GJT WATCHES/WARNINGS/ADVISORIES...
CO...None.
UT...None.
&&
$$
SHORT TERM...MMS
LONG TERM...BGB
AVIATION...ERW
HYDROLOGY...MMS
Area Forecast Discussion
National Weather Service Lubbock TX
616 PM CDT Sat Aug 28 2021
.AVIATION...
VFR prevails for the TAF period. There exists a low chance of
convection to possibly affect the KLBB and KPVW terminals, and
areas west/northwest of the terminals, on Sunday afternoon.
Check/monitor density altitude.
Sincavage
&&
.PREV DISCUSSION... /issued 219 PM CDT Sat Aug 28 2021/
SHORT TERM...
Afternoon cumulus field showing congestus and towers developing near
the New Mexico border where the mid level capping inversion was the
weakest, and we have added late afternoon thunderstorm chances in
the extreme southwest Panhandle along the NM border. Also seeing a
few attempts toward deeper convection again along the edge of the
Caprock escarpment, but inversion so far appears holding while bulk
of short-range solutions do not indicate storms succeeding either.
We favor retaining low thunder chances this evening across the
southwest Panhandle with low shower chances later tonight spreading
slightly further south and east, similar to as indicated by the HRRR
which has been consistently indicating this throughout the day. Mild
and humid conditions otherwise will dominate tonight with light
southerly low level flow.
Sunday will see weakness in the upper level heights continuing over
the Panhandle and South Plains with a further increase in moisture
aloft, as monsoonal flow bends out of New Mexico into the western
Panhandle and South Plains. This will lead to chance mention for
thunderstorms favoring this area during the afternoon. Also the
gradual increase in moisture into the southern Rolling Plains
justifies a low thunder mention this area as well Sunday afternoon.
Temperatures Sunday should taper back another degree or two with the
increase in clouds and showers, especially cooler in the southwest
Panhandle. RMcQueen
LONG TERM...
Slight chance POPs will linger late Sunday night into the early
morning hours of Monday. Weak instability aloft and deep boundary
layer moisture supports light scattered showers with isolated
convection in our northwest zones, but will taper off before sunrise
Monday morning. It looks to be dry for the remainder of the week as
Nora tracks NNW along the Baja of California and Ida shifts north
into a zonal Polar Jet to begin the week. An upper level ridge just
to our west begins to amplify Tuesday and Wednesday, as the
jetstream begins to buckle under the weight of Ida as it moves
across the southeast CONUS into the Mid-Atlantic region. As has been
the case most of this summer, we will reside under the portion of
the ridging aloft that will spare us from extreme heat. Temperatures
will hover right around 90 degrees on the Caprock all week, and
mid/upper 90s across the Rolling Plains. Surface winds during the
afternoon will consistently be S/SE all week, keeping RH values
elevated at times, especially in the Rolling Plains. Overall, it
will be mostly sunny all week, a little humid at times, with light
winds and little to no chance for rain.
&&
.LUB WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
09
Please see the previous forecast discussion for more details on the
current warm episode and expected conditions next week. Keene
&&
.AVIATION...28/18Z TAFs...Along the coast...VFR conditions will
prevail through sunset over land areas even with persistent low
stratus just offshore from Florence through Cape Blanco. South of
Port Orford, wildfire smoke will be in play as northeasterly winds
have brought the smoke to the coast and points offshore. Vsbys due
to this smoke may drop into the MVFR category but are not expected
drop any lower than that. After sunset, IFR with local LIFR
conditions can be expected north of Cape Blanco as the marine
stratus pushes onshore but said stratus is not expected to penetrate
more than 5 miles inland.
Inland...VFR conditions are expected through Sunday morning east
of the Cascades before smoke starts arriving and reduces
visibility there Sunday afternoon. From the Cascades westward,
pockets of MVFR and localized IFR conditions due to low vsbys
associated with wildfire smoke can be expected in most areas away
from the coastline through this evening. Overnight much of this
smoke may settle in the Umpqua and Rogue Valleys to maintain
vsbys in those valleys at MVFR levels. -Sargeant/Keene
&&
.MARINE...Updated 230 PM PDT Saturday 28 August 2021...A strong
thermal trough along the coast will gradually weaken over the next
couple of days. This will cause northerly winds to gradually
diminish over the entire coastal waters such that by Monday morning,
areas north of Cape Blanco should no longer experience Small Craft
Advisory conditions. However, the thermal trof will remain strong
enough to keep northerly winds cranking and keep areas south of Cape
Blanco in Small Craft Advisory through Tuesday. Although by then,
these conditions may only be south of Gold Beach. In addition to the
high winds, areas that are in Small Craft Advisory will experience
steep wind driven seas to add to the hazardous conditions.
-Sargeant
&&
.FIRE WEATHER...Updated 245 PM PDT Saturday, 28 Aug 2021...
Northeast winds across the ridges are expected to briefly increase
this evening to gusts in the 20 to 40 mph range, strongest in the
Kalmiopsis Wilderness area, before diminishing overnight into Sunday
morning. On Sunday the thermal trough along and near the coast will
drift northeastward across the area resulting a dry, smoky, and
unstable afternoon and evening across inland areas. Decided to go
with Haines 5 conditions across the board tomorrow rather than 6, as
extensive smoke is likely to mute T/RH potential, to some degree.
Gusty westerly winds and very low humidity is expected to result in
a period of critical conditions for portions of the area east of the
Cascades Sunday afternoon and evening, specifically in FWZ624 east
of Hwy 97, and across much of the Modoc FWZ 285. Sunday night into
Monday a dry cold front will push across the area resulting in
critical wind and RH conditions for much of the area east of the
Cascades Monday afternoon and evening, specifically most of FWZ 624,
FWZ 285, and FWZ 625. Winds are expected to be 5-10 mph stronger
Monday afternoon and evening versus Sunday for the same time period.
Cooler, more seasonable conditions are then expected through the
rest of the week, though some guidance does warm up the latter
portion of the week about 5 degrees F above seasonal averages again.
~BTL
&&
.PREV DISCUSSION... /Issued 252 PM PDT Sat Aug 28 2021/
DISCUSSION...An upper level short wave ridge is over the area
currently with a surface thermal trough extending from northern
California to the SW Oregon Coast. Along the coast, this is
bringing a Chetco effect to Brookings this afternoon with
temperatures in the low-mid 90s as of 2 pm. North of Cape Blanco,
conditions are more typical with more marine influence and
temperatures in the 60s. Inland, nary a cloud can be seen, though
smoke continues to emanate from area wildfires. This is resulting
in areas of reduced visibility and air quality west of the
Cascades and in Northern California, while areas east of the
Cascades are getting a relative break from the thick smoke.
Overall, it is a warm day with most areas in the 80-90 degree
range and some locations in the west side valleys 90-95.
The thermal trough and offshore flow will weaken a bit tonight
into Sunday as an upper shortwave approaches the PacNW. This will
turn the mid-level flow to SSW across the region and smoke from
California wildfires will return from the south. The air mass
aloft will remain quite warm, so Sunday will be another warm day
inland. However, smoke from the fires could once again limit just
how warm. For this reason, we`re forecasting temperatures a bit
below the MOS guidance with highs widely in the upper 80s to the
mid 90s. Expect an increase in afternoon breezes compared to
today, highest east of the Cascades and in NorCal. It should be
cooler in Brookings due to more marine influence compared to
today.
A dry cold front will push onshore Sunday night into Monday. This
will result in a bit more of a marine push into the Umpqua Basin
by Monday morning. Most noticeable, however, will be the 5-10
degrees of cooling expected -- perhaps even a few degrees more
than that in some areas -- and some gusty afternoon west-
northwest winds. This should carry most of the thickest smoke to
the south and east and immediately downwind of the fires, likely
giving many west side areas (except NE Jackson/eastern Douglas)
another break from the smoke.
Tuesday through Thursday will be cooler. Tuesday will likely be
the coolest day of the next seven as the associated upper trough
axis moves through. Back side energy digging into WA/OR should
keep the trough in place long enough to prevent significant
warming Wed/Thu, so we`ll remain near to slightly below average
temperature-wise. Surface northerly flow could bring smoke back
into portions of the Rogue Valley at night and into the morning
hours, but upvalley NW breezes should help to clear it out in the
afternoons. Mid-level westerly flow should also keep the thickest
smoke to the east of the fires.
Models show short wave ridging moving in Friday followed by some
semblance of another upper trough next weekend. The GFS appears
stronger with the trough Friday night into Saturday, actually
suggesting some light rain is possible along the coast north of
Cape Blanco. Other guidance, including the NBM keeps the trough
weaker, so we have kept the forecast dry. -Spilde
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning from 2 PM to 8 PM PDT Sunday for ORZ624.
Fire Weather Watch from Monday afternoon through Monday evening
for ORZ624-625.
CA...Red Flag Warning from 2 PM to 8 PM PDT Sunday for CAZ285.
Fire Weather Watch from Monday afternoon through Monday evening
for CAZ285.
Pacific Coastal Waters...Small Craft Advisory until 5 PM PDT Monday for PZZ350-370.
Small Craft Advisory until 5 PM PDT Tuesday for PZZ356-376.
Gale Warning until 5 AM PDT Sunday for PZZ356-376.
$$
AREA FORECAST DISCUSSION
National Weather Service Morristown TN
959 PM EDT Sat Aug 28 2021
.UPDATE...
EVENING UPDATE.
&&
.DISCUSSION...
The isolated convection has increased again in the central
valley, and given that the latest HRRR has it holding together
for a bit as it tracks slowly north, will beef PoPs up a bit in
these areas for a few hours. Will also tweak sky to better fit
this scenario, but otherwise no additional changes.
&&
.AVIATION...
00Z TAF DISCUSSION.
Isolated convection impacting any of the terminals Sunday
afternoon looks too improbable to include in TAFS. Fog, although
possible late tonight, looks unlikely to impact vsby at any site.
Thus will go with VFR conditions for the entire period all sites
with just some high clouds around at times along with scattered
daytime CU. Winds will generally be light.
LW
&&
.PREV DISCUSSION...
/ISSUED 728 PM EDT Sat Aug 28 2021/
SHORT TERM...(Tonight and Sunday)...
Key Messages:
1)A couple of showers/thunderstorms this afternoon across the
high terrain.
2)Above normal temperatures continue tonight and on Sunday.
Discussion...
Afternoon water vapor imagery clearly shows Hurricane Ida moving
NW on the SW periphery of a h5 anticyclone anchored over the
Carolina Coasts. The surface reveals mainly high pressure across
much of the Appalachians and mid Atlantic region. 19Z obs show
temperatures warming into the upper 80`s to lower 90`s as
expected. Dewpoints in the lower 70`s is contributing to heat
index values in the mid to upper 90`s. Convection has remained
fairly isolated as of discussion time with increasing subsidence
aloft. Expect this isolated trend to continue through the rest of
the afternoon with the better chances along the northern Plateau
and higher terrain of the Southern Appalachians.
Tonight will feature tranquil conditions as high pressure and
ridging aloft continues to favor dry weather and above normal low
temperatures. Cannot rule out patchy fog in favored river valleys
tonight but not expecting this to be widespread given slightly
higher dewpoint depressions tonight. Deep layer ridging remains in
control across the Appalachians and Mid Atlantic states on Sunday
with another warm day expected as highs rise into the upper 80`s to
low 90`s. Showers and thunderstorms can be expected again with
favored areas across the Plateau and higher terrain.
Diegan
LONG TERM...(Sunday Night through Saturday)...
Key Messages:
1. The remnants of Hurricane Ida will impact the region Tuesday into
Wednesday with a less active pattern afterwards.
2. With Hurricane Ida, confidence continues to increase in potential
for strong winds and isolated tornadoes with locally heavy rainfall
still expected in western portions of the area. However, these
details are conditional on the track and evolution of the storm as
well as the mesoscale structure of rain bands.
Sunday Night through Wednesday
At the start of the period, Hurricane Ida is forecast by the
National Hurricane Center (NHC) to be making landfall in Louisiana
as a major hurricane (Category 3 or greater). During this time, a
5,900 meter 500mb high will be receding over the Carolinas. During
the day on Monday, the expectation is for Ida to move inland near or
just east of the Mississippi River. A notable weakening trend is
expected as it weakens to depression strength by Monday evening.
This will result in an increasing southerly flow pattern and
relatively scattered convection before the more notable effects take
place Tuesday into Wednesday.
The speed, evolution, and overall track of Ida`s remnants Tuesday
onward still bears uncertainty within the latest model guidance. The
NAM suggests a more notable right-turn of the storm into central
Mississippi and northern Alabama on Tuesday. However, many GEFS
members and the GFS/CMC/ECMWF deterministic solutions show a more
progressive and northward track through west and middle Tennessee.
With either solution, the bulk of local impacts will take place
Tuesday into Tuesday night before a northerly flow/more settled
pattern takes shape later in the week. If a more northerly track
occurs coincident with the consensus, vertical wind profiles support
strong (>200 m2/s2) 0-1km SRH, similarly high 0-3km SRH, LCL heights
< 1,000 meters, and S/SSE 850mb flow of 30 to 40+ kts. As such,
notable concern remains in the potential for isolated tornadoes. In
addition to the track and evolution of the system, the tornado
potential will be highly dependent on the mesoscale structure of
rain bands and destabilization. Coincident with timing and
structure, diurnal heating and breaks in clouds are both key in
efficiency of destabilization. Synoptically-driven 850mb flow with
the consensus would be sufficient for at least advisory-level winds
in the mountains. However, local mountain wave effects may prove
more than sufficient for warning criteria to be met. As such, a high
wind watch could be needed in the coming days. Regarding the heavy
rainfall threat, it still appears that the most impressive tropical
moisture will stay along our western areas and even further to the
west. Nevertheless, efficient rainfall rates and training of
convection will be the main drivers of locally heavy rainfall and
potential isolated flooding, especially along and near the
Cumberland Plateau. Initial downsloping will likely inhibit rainfall
totals further eastward. By Wednesday and Wednesday night, Ida is
expected to move either east or northeast of the region, putting the
area in a northerly flow pattern. This also comes ahead of high
pressure to the north and a frontal boundary that looks to funnel
drier air following a frontal passage.
Thursday through Saturday
For the end of the period, a more settled and seasonal pattern is
expected as high pressure stays in place to the north. The GFS
suggests an upper low forming to the south following Ida`s
progression to the northeast. Nevertheless, all global guidance
shows that an upper high is expected to expand across the Central
Plains. The result will be fairly limited daily convective coverage
and a more settled overall pattern.
BW
&&
.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN 73 92 72 89 71 / 10 20 10 40 40
Knoxville McGhee Tyson Airport, TN 72 92 71 91 71 / 20 10 10 30 30
Oak Ridge, TN 71 92 70 90 71 / 20 20 10 40 30
Tri Cities Airport, TN 67 92 68 91 68 / 10 20 10 30 20
&&
.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...NONE.
VA...NONE.
&&
$$
Area Forecast Discussion
National Weather Service Pocatello ID
125 PM MDT Sat Aug 28 2021
.SHORT TERM...Tonight through Monday night. A dry zonal flow will
prevail over the region tonight and tomorrow. By Monday morning, an
upper trough will work its way into the PAC NW, driving up some
winds in the Snake Plain. Temperatures will be a bit above normal on
Sunday and Monday as we continue under mostly dry conditions.
Moisture should remain to the south through the short-term periods,
so there`s no threat of any thunderstorms. Smoke should also remain
to our south, though HRRR suggests some will creep into our southern
zones Sunday afternoon. Increased smoke concentrations will be
possible in the Central Mountains as early as Sunday evening.
Hinsberger
.LONG TERM...Tuesday through next Saturday. The operational GFS and
ECMWF are in fairly good agreement that a low pressure system will
linger over WRN Canada Tuesday and Wednesday as the remains of Nora
work north through the Gulf of California. As a result the SSW flow
aloft is expected to advect moisture from Nora northward through
Utah and into the SE highlands as early as Wednesday morning and
continuing through Thursday night before getting shunted eastward
into Wyoming and Colorado Friday as the Canadian low and associated
trough axis finally shift east into the Panhandle. By Saturday, the
operational models fall out of phase which is also reflected in the
Cluster analysis. Thus we are happy to float along with the going
forecast and National Blend of Models which holds on to a mention of
precipitation across the eastern half of the forecast area Wednesday
through Friday. We may taking some liberties Saturday and deviate
toward drier conditions as even the progressive/wet looking GFS is
showing precipitation impacts well north of the region. Daytime
highs remain warm Tuesday and Wednesday before trending lower toward
climatology Thursday into Saturday. Huston
&&
.AVIATION...VFR conditions will prevail under a dry west flow aloft.
Huston
&&
.FIRE WEATHER...We have increasing concerns for critical fire
conditions Monday and Tuesday. Models continue to push sub 15% RH
across much of the region and wind gusts 25 to 35 mph over zones 410
and 425, perhaps even into zones 422 and 476. There is some
uncertainty on the windspeeds though, so we`ll be watching the
trends over the next couple of model runs. As troughing digs into
the PAC NW, we`ll see increasing chances of afternoon thunderstorms
Wednesday and beyond. Humidity will be increasing after mid-week
thanks to an influx of monsoon moisture. Hinsberger
&&
.PIH WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Area Forecast Discussion
National Weather Service Phoenix AZ
503 PM MST Sat Aug 28 2021
.UPDATE...Updated 00Z aviation discussion.
.SYNOPSIS...
The best storm chances will be over higher terrain areas of
Arizona this weekend, but a few isolated showers or storms and
gusty winds are likely to impact the south-central Arizona
deserts. Hot temperatures with highs just above 110 degrees are
expected this weekend across southeast California and southwest
Arizona, while highs are likely to fall just short of 110 degrees
in the Phoenix area. A much more unsettled weather pattern is
expected for a good portion of next week as tropical moisture
surges into the region by midweek. This will bring very good
chances for rainfall through the middle of next week, likely
focused across south central Arizona, while also bringing much
cooler temperatures as well.
&&
.DISCUSSION...
Latest RAP streamline analysis depicts an upper-level anticyclone
across central Arizona. This will generally result in a weak
northeasterly steering flow this afternoon and evening. Meanwhile,
in the lower levels, a well-defined gulf surge from a northern
Sonora MCS pushed through the lower Colorado River Valley this
morning. Gusts up to 30 mph were observed near Yuma, while further
west in the Imperial Valley dewpoints reached the upper 70s,
briefly yielding oppressive heat indices as high as 120 degrees.
Across the Phoenix metro area, the morning moisture has also
taken a bite out of afternoon temperatures. Current temperatures
are generally running 5 to 7 degrees cooler than they were at this
time yesterday. This is also evident in afternoon ACARS
soundings, which depict the cooler boundary layer and the area of
CIN just above that. However, further aloft temperatures are
relatively cool, right around -7 deg C at 500 mb. Consequently,
latest mesoanalysis indicates relatively steep mid-level lapse
rates and a widespread area of 1000+ J/kg MLCAPE across the lower
deserts.
Consensus from the CAMs points to scattered shower and
thunderstorm activity across the Mogollon Rim and higher terrain
approaching the foothills north and east of Phoenix. Given the
elevated DCAPE, an outflow boundary will likely push westward from
this activity into the lower deserts. However, there is
considerable uncertainty whether this boundary will be strong
enough to break through the aforementioned CIN and generate new
convection across the Valley. Latest HREF indicates roughly a 50%
chance of an outflow boundary capable of producing winds up to 35
mph along with patchy blowing dust. Across southwestern Arizona,
the chance of storms will be somewhat higher as the outflow
boundary encounters a more favorable environment where CAPEs
currently exceed 2000 J/kg. The strongest storms will also be
capable of producing localized gusts up to 60 mph, particularly
across portions of Pinal, southern Maricopa and La Paz counties.
&&
.PREVIOUS DISCUSSION...
Temperatures today will cool slightly off of the previous couple
days, but the Excessive Heat Warning with highs of 110-114 degrees
will remain across southeast California and southwest Arizona
through Sunday. The increase in boundary layer moisture across
southern Arizona should keep temperatures mostly in a 107-109
degree range in the Phoenix area, but it will still feel quite
hot. Sunday`s temperatures look to be a near mirror image of
today, but boundary layer moisture is expected to lower a bit due
to the lack of a Gulf surge tonight. Afternoon scattered storms
are again expected over the Arizona high terrain on Sunday, but
due to increasing subsidence over the region the activity is
likely to be more subdued. Slightly lower moisture levels and
reduced MUCAPEs over the lower deserts on Sunday is likely to
limit or even inhibit any storm development over the south-central
Arizona deserts.
For next week, there remains high confidence in a tropical
moisture surge first starting on Monday, but intensifying Tuesday
into Wednesday. A rather complex pattern is likely to take shape
for the first half of next week. An upper level trough just to
our southwest will become a major factor for our weather while
combining with the increasing tropical moisture well out ahead of
Hurricane Nora which is expected to gradually weaken as it tracks
into the Gulf of California.
Monday is likely to be a fairly limited storm day across most of
southern Arizona as subsidence aloft and a capping inversion is
likely to keep most storms confined to higher terrain areas.
Increasing moisture into southeast California on Monday may
present a favorable environment for some isolated to scattered
storms, possibly strong if the GFS forecast sounding for KIPL
comes to fruition. As a strengthening upper level jet associated
with the trough to our west moves northward across southern
California into the Great Basin on Tuesday, much of Arizona will
eventually become perfectly positioned within a favored vertical
ascent region. The combination of the deep tropical moisture
overtaking Arizona Tuesday into Wednesday and the favorable ascent
fields should give rise to fairly widespread shower and
thunderstorm activity sometime late Tuesday, likely lasting
through a good portion of Wednesday. Model ensembles continue to
support this main area of likely moderate to at times heavy
rainfall falling somewhere across south-central Arizona, but we
are still a few days out and it`s still possible for some shifting
in the expected heaviest rainfall. There is also a distinct
possibility of some isolated to scattered strong thunderstorms at
some point next Tuesday and Wednesday where higher instability and
shear falls, likely farther west over southeast California and/or
southwest Arizona. Forecast QPF amounts of greater than an inch
are seen over a large swath of south-central into central Arizona
for late Tuesday through Wednesday, but it is still a bit early to
know the specific details of timing and location of the greatest
heavy rainfall threat.
By late Wednesday, the upper level support should be waining as
the jet max lifts well to our north, but some model guidance shows
at least some jet dynamics supporting our region into late next
week. What happens with the remnant circulation of Nora is
impossible to know at this point, but it seems unlikely an intact
circulation will make it as far north as Arizona. Even without a
direct impact of Nora, the increased moisture is likely to stick
around over much of our region through the end of next week
resulting in at least a chance for showers and storms.
Forecast temperatures for next week take a big dive into the
middle part of the week as highs are likely to dip into the 90s
across a good portion of the lower deserts as early as Tuesday,
but definitely by Wednesday. For now it seems likely the areas
that see fairly continuous rainfall, or at least thick cloud cover
on Wednesday will struggle to reach 90 degrees. The below normal
temperatures are then likely persist through the rest of next
week, especially if the deeper moisture sticks around the region.
&&
.AVIATION...Updated at 0003Z
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Primary aviation concern through the TAF period will be the
potential for convective impacts, mainly outflows from decaying
thunderstorms. While the chances for VCTS at any terminals now looks
to be quite low (10-20%), strong winds with dust from surroundings
storms are more probable. Current thinking is that a relatively weak
boundary may move thru first from the east or east-northeast. Wind
speeds will likely be on the low side (gusts into the 20-25kt range
at most). Then another outflow from more of a southeasterly
direction will attempt to move into the region, bringing slightly
strong winds and (perhaps) a bit of blowing dust int the Phoenix
area during the 03-05Z timeframe. This 2nd outflow is expected to
keep elevated southeasterly winds going thru sometime after
midnight, with more typical lighter southeasterly winds thereafter.
Cloud bases should remain elevated around 12 kft and above,
outside of storms. There are indications high-based ACCAS showers
may develop Sunday morning, but outside some brief gusty winds and
shifts, they should be minimal impact. Another round (similar to
today) of showers/TS is expected to develop along the Rim/White
Mountains Sunday afternoon/evening, bring the likelihood of outflows
back into the Phoenix area during the evening, with VCTS chances
once again remaining quite low (10-20%).
Winds to remain mainly out of a southeasterly direction at KIPL and
a southerly direction at KBLH through the TAF period. Thunderstorms
are still not anticipated at either terminal, but outflow winds from
storms southwest of KIPL and east of KBLH cannot be completely ruled
out. Elevated convection may also move into the region Sunday
morning from the east, but confidence is too low to add any mention
to the TAFs. Cloud bases should remain aoa 12 kft.
&&
.FIRE WEATHER...
Monday through Friday:
Increasing moisture and rain chances will be seen early next week
with temperatures eventually cooling to below normal by Tuesday.
Shower and thunderstorm chances are likely to peak Tuesday into
Wednesday with widespread wetting rains likely as tropical
moisture surges into the region. Rain chances are likely to
persist to some degree late in the period, but is likely to be
more of the scattered variety. Minimum RH values will increase
from around 25% on Monday to 40-50% by Wednesday before gradually
lowering late in the period. Winds should be relatively light with
an afternoon upslope component and overnight drainage expected for
a good portion of next week, but southerly winds are also likely
to be seen a bit more than typical.
&&
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning until 8 PM MST Sunday for AZZ530>533-535-
536.
CA...Excessive Heat Warning until 8 PM PDT Sunday for CAZ560>570.
&&
$$
DISCUSSION...Hirsch
PREVIOUS DISCUSSION...Kuhlman
AVIATION...Percha/Benedict
FIRE WEATHER...Kuhlman
Area Forecast Discussion
National Weather Service Sacramento CA
227 PM PDT Sat Aug 28 2021
.SYNOPSIS...
Hot and very dry through the weekend. Gusty southwest to west winds
early next week could bring critical fire weather concerns to the
northern Sierra and southern Cascades. Cooler weather returns
next week.
&&
.DISCUSSION...
GOES-West satellite imagery reveals smoky skies blanketing
portions of interior NorCal this afternoon as wildfires continue
to burn. Winds have subsided as surface pressure gradients are
weaker than yesterday. Hot and dry conditions persist across the
region this afternoon under flat ridging. Afternoon temperatures
are generally running 2 to 6 degrees warmer across most of the
area compared to 24 hours ago. Thick wildfire smoke may inhibit
additional warming at some locations this afternoon. Forecast
highs on Sunday will range from the upper 90s to around 103
resulting in moderate heat risk.
Ensembles and cluster analysis indicate that an upper trough will
start to take shape off the West Coast Sunday afternoon and
gradually deepen into mid-week. This will promote increased
onshore flow/southwest winds and cooler temperatures. However,
these gusty winds will bring increasing fire weather concerns
to the northern Sierra and southern Cascades Sunday into
Wednesday. At this point, the strongest winds are expected Monday
and Tuesday with gusts ranging from 20-35 mph. The strongest winds
area expected in the afternoon and evening hours. A Fire Weather
Watch has been issued for the higher elevations of the northern
Sierra and southern Cascades from 11 AM Monday through 11 PM
Tuesday given the potential for rapid spread of new or existing
wildfires.
The onshore flow will likely help with some smoke dispersal in
the Valley. The HRRR smoke model shows improvement near the Delta
influenced areas Sunday afternoon. A stronger onshore
flow/southwest winds will get going Monday, which should push the
smoke eastward out of the Valley and much of the foothills.
A gradual cooling trend is expected during the Monday-Wednesday
timeframe with mid 80s to low 90s returning by mid-week.
&&
.EXTENDED DISCUSSION (Wednesday THROUGH Saturday)...
Ensemble guidance is in good agreement large scale troughing will
likely persist over the West Coast through the extended forecast
period. This pattern will support a Delta breeze and slightly
below average temperatures. Gusty southwest to west winds over the
higher elevations of the mountains are possible in the afternoon
into evening hours.
&&
.AVIATION...
Areas of MVFR to IFR due to area wildfire smoke. Gusts 15 to 20
kts vicinity Delta. Elsewhere, winds generally under 12 kts.
Breezy conditions develop after around 21 UTC Sunday.
&&
.STO WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from Monday morning through Tuesday evening
for Burney Basin and Northeast Plateau in Shasta County
Including Northwest Lassen NF north of Lassen NP-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-Stanislaus NF West of the Sierra Crest.
&&
$$
Area Forecast Discussion
National Weather Service Tucson AZ
854 PM MST Sat Aug 28 2021
.SYNOPSIS...Scattered afternoon showers and storms are expected each
afternoon and evening this weekend. Early next week an increase in
storm activity is forecast as tropical moisture moves into the area
and lingers through mid to late in the week. Concerns for heavy
rainfall leading to flash flooding will also rise as a result.
&&
.DISCUSSION...Rather boisterous convection around southeast Arizona
with strong convection still occurring over far western Pima county.
A few of the storm complexes caused damage and others were efficient
rain producers resulting in some local flash flooding. Even had a
decent surge down the CDO Wash thanks to heavy rainfall over the
Catalina Mountains.
For the remainder of the night most of the action will be across
western Pima County where instability remains high and inhibition
low allowing storm development with outflows. Elsewhere the HRRR
continues to bubble up residual showers well into the night before
it all ends before dawn. I went ahead and adjusted the forecast
through the remainder of the night to account for current and
expected trends.
&&
.AVIATION...Valid through 30/00Z.
FEW-SCT clouds at 8k-12k ft MSL (locally BKN into the early morning
hours, mainly west of KTUS) thru the forecast period. ISOLD-SCT
SHRA/TSRA thru 29/09Z and then again aft 30/19Z. MVFR conditions and
mountain-top obscurations near TSRA, along with wind gusts up to 45
kts. Otherwise, SFC wind favoring an ELY/SELY direction and generally
less than 12 kts. Aviation discussion not updated for TAF
amendments.
&&
.FIRE WEATHER...Isolated to scattered showers and thunderstorms are
expected for much of the forecast area through Monday. Deeper
moisture will then overspread the area Tuesday through Thursday of
next week as moisture associated with the remnants of Nora shifts
northward. This will result in increasing precipitation chances mid
to late next week across southeast Arizona, with potentially heavy
rainfall at times. 20-foot winds will generally be less than 15 mph
when not influenced by thunderstorms gusts.
&&
.PREV DISCUSSION... /issued 330 PM MST Sat Aug 28 2021/
Scattered thunderstorms developing as expected this afternoon.
Precipitable water values range from 1.2 inches east to 1.5 inches
west. Easterly to southeasterly steering flow for storms with a
decent shear environment for our corner of the state. Watch for
isolated strong to near severe thunderstorms in and amongst the
garden variety pulse storms, with some organized outflow pushing
toward the lower deserts. We`ll see how things hold together for
Tucson Metro over the next few hours and if we end up kicking up some
dusty outflows. A chance of thunderstorms will continue through the
weekend.
Next we watch for deeper surge activity pushed up the gulf ahead
of hurricane Nora. A convective complex that pushed from Sonora
into the northern Gulf already assisted with a relatively deep
moisture push through Yuma with southerly flow stacked 6k feet
deep and the Yuma depot jumping 20 degrees over the past 24 hours.
This will likely weaken before we see something stronger early in
the new week.
Current Nora projections bring her up very near the western coast
of Mexico over the next 72 hours. She may be able to hang on to
hurricane status as this happens, but not much more than that this
close to the coast. A trajectory like this often ends up with the
tropical system decoupling over southern Sonora with just mid
level remnants making it across the AZ border, but we`ll have to
see. A bit more to the east and we could see it shearing apart
earlier than expected. A bit more to the west and it should hang
on through the central Gulf.
It is, however, becoming increasingly likely that we will see a
deep and sustained surge through the Gulf of California as well as
inland ahead of the storm. NAEFS and ECMWF ensemble means suggest
an integrated water vapor transport maximum Monday night into
Tuesday, with maximum precipitable water values Wednesday in
excess of 1.75 inches. For SE AZ, our best precip chances (with
possible heavy rain threat) could end up being multiple periods
from Monday afternoon through most of the week. Tricky though. We
get too much moisture and we could see a few days of light to
moderate rainfall with storm totals in the 1 to 2 inch range, but
not with rainfall rates that would suggest flash flooding. Or we
could have multiple periods where we see twice as much storm total
rainfall accompanied by flash flood threats. Or anything in
between. Tropical systems (especially weaker ones like Nora) are a
tough call.
&&
.TWC WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Public...Cerniglia/Meyer
Aviation...Zell
Fire Weather....Zell
Visit us on Facebook...Twitter...YouTube...and at weather.gov/Tucson
Area Forecast Discussion
National Weather Service Las Vegas NV
843 PM PDT Sat Aug 28 2021
.SYNOPSIS...Hot temperatures and isolated thunderstorms are
expected through Monday with Excessive Heat Warnings in effect for
much of the region. Moisture will be increasing through the middle
of next week aided by the remnants of Nora. This moisture will lead
to better chances for shower and thunderstorm activity to Mohave
County Sunday, expanding west and north into southern Nevada through
mid-week.
&&
.UPDATE...Isolated thunderstorms that developed late in the
afternoon over southern Mohave County dissipated early this evening.
One thunderstorm also developed in eastern San Bernardino near
Essex. The gulf surge that occurred this morning will be a primer to
the expected influx of moisture that will spread up the next few
days as Hurricane Nora slowly works its way up the Gulf of
California. We have at least until Tuesday before we should see a
significant moisture increase and the latest model ensembles support
the forecast trends from the previous discussion. No immediate
changes needed.
&&
.PREV DISCUSSION...
200 PM PDT Sat Aug 28 2021
.DISCUSSION...Through next Saturday
What caught our eyes this morning was the ongoing gulf surge that
was induced by the inverted trough presently crossing the northern
Gulf of California. Moisture quickly spread northward up the
Colorado River Valley and southern Mohave County with surface
dewpoints climbing into the low 60s at Lake Havasu City and near 50
at Kingman. Radar indicates thunderstorms developing along the
northeast slopes of the Hualapai mountains east of Kingman. Moisture
may be too shallow but can not rule out a stray shower or
thunderstorm over the mountains near Primm or southeast San
Bernardino County later this afternoon or evening. With the moisture
now in place expect better coverage in storms Sunday into Monday and
relied on the camPoPs for the short term forecast.
This moisture surge may dampen the temperatures a bit but overall
readings will remain above normal Sunday and Monday.
Through mid-week, moisture will continue to stream northward into
the Desert Southwest well ahead of a weakening Nora. Combination of
weak disturbance moving in from the west and strengthening jet
streak interacting with that moisture will lead to widespread
showers and thunderstorms on Wednesday. Still some uncertainty if
there will be a heavy rain threat for Las Vegas and eastern San
Bernardino County. But confidence is increasing that threat will
exist probably from the Colorado River Valley east across Mohave
County. Collaborated earlier with NHC, WPC and surrounding offices
and we agreed no headline will be issued at this time. Will continue
to brief primary partners. Its a given that temperatures will be
cooler with the additional moisture and cloud cover.
As dynamics wane and moisture slowly decreases late week, chances
for showers and thunderstorms lower from west to east heading into
the holiday weekend.
&&
.AVIATION...For McCarran...Light winds favoring an easterly
direction will remain before giving way to southwesterly winds this
afternoon around 22Z. Expect winds around 10-12 knots with some
occasional gusts around 15-20 knots lasting through 03-04Z. Winds
will decrease overnight, eventually becoming light and variable.
Skies will be mostly clear, with some FEW aoa 12 Kft this afternoon.
For the rest of southern Nevada, northwest Arizona and southeast
California...Typical wind patterns are expected across the region
today with some afternoon southerly breezes possible. Gusts should
generally remain below 20 knots with winds returning to typical
drainage patterns tonight. Skies will be mostly clear with some FEW
aoa 12 Kft across some of the higher terrain in the Mojave Desert.
Although, 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.
At KBIH, wildfire smoke is not expected to be quiet as dense
tonight, and may not even drop below 7 SM based on the latest HRRR
Smoke Runs.
&&
.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather or impacts according to standard operating
procedures.
&&
$$
UPDATE...Adair
DISCUSSION...Pierce
AVIATION...Peters
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