Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/20/23
Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
824 PM CDT Sat Aug 19 2023
.UPDATE...
Issued at 823 PM CDT Sat Aug 19 2023
Overnight forecast look good so no major changes are anticipated
this evening.
&&
.SHORT TERM...(This Evening through Sunday Night)
Issued at 252 PM CDT Sat Aug 19 2023
A line of isolated showers has developed this afternoon from Pierre
to Aberdeen. Other than the HOPWRF, no CAMS are picking up on this
activity. There`s, perhaps, a mid-level shortwave trough that is
setting them off, but all indications point to a quick dissipation
by 21z. Associated lightning has been minimal, but there have been a
few isolated strikes here and there along the line.
Temperatures have stagnated or fallen behind the cold frontal
passage this afternoon. Showers and thunderstorms become more likely
tonight on the edge of the advancing cold air advection ahead of the
Canadian high. Shortwave energy increases toward Sunday morning,
though most of it remains over North Dakota. No severe weather is
expected and most of the precipitation will be light, centered over
central SD and areas north of Hwy 12.
The HRRR Smoke also shows Canadian wildfire smoke moving in with the
sfc high this evening through tonight. The worst of the smoke is
expected to be transitory, but visibility could be reduced to 4
miles or so for a couple of hours.
With the smoke, clouds and rain, high temperatures will be
suppressed on Sunday, topping out only in the upper 60s to 70s. The
upper ridge will amplify again and build back into the region Sunday
night.
.LONG TERM...(Monday through Saturday)
Issued at 252 PM CDT Sat Aug 19 2023
Models agree rather well in the overall upper level pattern starting
off the extended period, which features a large ridge across the
central CONUS, with the northern extent over the Northern Plains. Hot
temperatures look to be the story Mon-Wed, with heat headlines
becoming rather likely as we get close to the start of next week,
although Monday may be a bit marginal. 850mb temps look to be in the
mid to upper 20s to around 30C. EC/NAEFS ENS percentiles for
700/850mb temps are showing 97th/99th or even MAX across the region
during the start of the upcoming week. M-Climate percentiles for 500-
hPa heights are generally maxed out over the region. M-Climate
return intervals for 700/850mb temps are showing an occurrence once
every 10 years or even outside of M-Climate. So, rather anomalous
heat event for this time of year, with several records possible
generally south of the CWA. Again, we are on the northern fringe of
this heat dome, but will be rather hot nonetheless with highs in the
90s to low 100s.
As for precipitation, about the only thing showing up for rain
chances is the shortwave energy that dampens the ridge on Thursday.
Highest 24-hr probs for QPF >.01 at 12Z Friday are generally across
the southern/southwest CWA where it`s showing about 50% or greater
(EC/GEFS). This is where we currently have low chance POPs.
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday Evening)
Issued at 605 PM CDT Sat Aug 19 2023
Terminals KABR,KATY,KPIR,KMBG
Mostly VFR conditions are forecast overnight. However, elevated
smoke may at times cause MVFR vsbys over the region later tonight.
&&
.ABR WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
&&
$$
UPDATE...TDK
SHORT TERM...Wise
LONG TERM...TMT
AVIATION...TDK
Area Forecast Discussion
National Weather Service La Crosse WI
951 PM CDT Sat Aug 19 2023
.DISCUSSION...(This evening through Saturday)
Issued at 222 PM CDT Sat Aug 19 2023
Key Messages:
- Some smoke aloft on Sunday.
- Hot from Tuesday through Thursday. Excessive heat
advisory/warning possible. In addition, potentially the first
100-degree temperature in our area since May 15, 2013 and the
first one in August since August 7, 2001.
Regional analysis:
RAOB analysis from 19.12Z showed a 500mb ridge centered over eastern
Oklahoma, with 596 dm heights extending across much of Kansas,
Missouri, Arkansas, and northeast Texas. From this same region into
the Central Plains, 925mb to 850mb temperatures ranged from the
upper 20s to low 30s C. As it slowly amplifies and shifts further
north, this heat dome will be the main feature of interest for us
here in the Upper Mississippi Valley as the new week unfolds.
Elsewhere across the region, surface analysis reveals a cold front
stretching from Hudson Bay into western Nebraska. Ahead of the
front, geocolor satellite imagery shows very little residual
wildfire smoke aloft impacting the local area. Behind the front is a
different story, with increasing concentrations of vertically
integrated smoke from northwest Minnesota westward through the
Dakotas. However, morning surface visibility was unrestricted in
that area, indicating an absence of near-surface haze/smoke.
Tonight:
A weak cold front will move southeast through the area. This system
has rather limited moisture aloft, so only expecting a wind shift
and some mid and high clouds from it. The RAP continues to bring
more surface smoke than the HRRR behind this cold front. Looking
at the surface observations, leaning more toward the HRRR.
Soundings continue to show a well-mixed boundary layer, so only
expecting valley fog in the Mississippi tributaries and Wisconsin
River Valley. Low temperatures tonight will range from the lower
60s to lower 70s.
Smoke forecast into Sunday:
The aforementioned cold front is progged to drop southeastward
through the ARX forecast area tonight into Sunday morning. With it
there are some model forecast concerns for some smoke aloft mixing
down near the surface. As surface heating and daytime mixing kick
into high gear this afternoon, the RAP/HRRR both show a band of
increasing near-surface smoke behind the front, stretching from
northwest Minnesota westward through North Dakota. The near-surface
smoke maximum is then shown to graze our northwestern periphery as
it rotates southwestward around the encroaching surface high
overnight.
Sunday presents more of a forecast challenge as to how the smoke
fields will evolve. Smoke aloft is likely to become quite
concentrated over the ARX forecast area, but to what extent any of
this is able to mix down to the surface during the afternoon and how
much wind dilution will be a factor is less certain. RAP/HRRR
guidance has been overzealous with mixing down near-surface smoke
lately, with no surface visibility restrictions occurring with our
most recent bout of smoke. Would like to see whether surface
visibility is impacted today by mixing across the Dakotas and
northern Minnesota before forecasting near-surface impacts locally
for Sunday, so will let later shifts evaluate.
Unfolding heat wave through Thursday:
Signals are all pointing towards a significant late August heat wave
to develop through Thursday. There is excellent consensus for the
upper ridge to become anomalously strong as it anchors itself over
Missouri Sunday through Tuesday. NAEFS and ENS ensembles both
indicate 700 and 500mb heights exceeding 3 standard deviations above
the mean, exceeding all model climatology for the period. Okay,
that`s quite impressive and all, but even *MORE* remarkable is the
fact that out of the 100 member ensemble conglomeration of GEFS,
CMC, and EPS...99 (NINETY-NINE!) percent of members have the ridge
strengthening to greater than 600 dm! That is an /incredibly rare/
signal for the region! It`s comes as no surprise, therefore, that
the ECMWF extreme forecast index has continued to increase with each
run, now with more than 90 percent of its members suggesting an
unusual heat event for the region. However, its shift of tails has
actually remained pretty consistent over the last several runs,
holding around 1 over a majority of the ARX forecast area. This
would indicate a continued decent (though not overly high) potential
for some record-breaking temperatures, though if records are broken
they probably wouldn`t be smashed.
This matches well with the conceptual model for extreme heat, given
we`ll be on the northern periphery of the anomalous ridge, not
directly underneath it where the likelihood of record breaking heat
is more of a slam dunk. Still, there are a lot of things going for
us to see a period of excessive heat Tuesday through Thursday: 1)
moderate southwest flow from 925 to 850mb, 2) temperatures climbing
above 30C at 925mb and above 26C at 850mb, 3) strong record-breaking
ridge, 4) little if any cloud cover, 5) deep afternoon dry-adiabatic
mixing, and 6) limited soil moisture (especially south of I-90).
Given the above factors, some triple-digit temperature readings are
not out of the realm of possibility. Our area hasn`t seen 100+F heat
in over a decade, and not during the month of August since 2001.
Very confident in the need for additional heat headlines beyond this
weekend`s marginal heat advisories. Monday should offer a slight,
brief reprieve for most of the area, though the heat index may climb
to around 100 degrees in north-central Iowa. Otherwise, for Tuesday
through Thursday there is extremely high likelihood that an
excessive heat watch will be needed for much of the area. While
neighboring offices to the south and west are hoisting a watch this
afternoon, we will likely be jumping on that bandwagon tonight.
This is shaping up to be what looks like a dangerous stretch of heat
Tuesday through Thursday with heat indices currently forecast to
reach 100 to 110 degrees during peak afternoon heating (possibly a
bit higher in a few locations). It will be critical to stress the
dangers of heat illness, and also the fact that heat impacts are
cumulative/compounding. There may not be much nighttime relief for
much of the area, especially south of I-94 where forecast lows are
currently in the low to mid 70s Tue and Wed nights.
&&
.AVIATION...(For the 06Z TAFS through 06Z Sunday evening)
Issued at 950 PM CDT Sat Aug 19 2023
VFR conditions are forecast through the TAF period. Southwest winds
become northerly at the beginning of the TAF period as a cold front
moves through. Some of the smoke models were mixing smoke towards
the surface behind the cold front, but so far surface visibilities
have remained above 6 miles. There is another chance for smoke to
mix down to the surface near RST and LSE Sunday afternoon with
similar results expected. If mixing exceeds current expectations,
haze and MVFR visibility restrictions may need to be added to the
TAFs.
&&
.CLIMATE...Tuesday through Thursday
Issued at 222 PM CDT Sat Aug 19 2023
The last 100-degree or higher temperature in the La Crosse County
Warning Area occurred on May 15, 2013 when Austin MN reached 100F.
There have been a couple of 100-degree temperatures at Theilman, MN
since then, but that site has been running far too warm when
temperatures are 90F or hotter, so question these values and went
with the more likely occurrence.
The last 100-degree temperature in August was August 7, 2001 when
Sparta, WI reached 100F and Trempealeau Dam, WI reached 101F.
La Crosse, WI has not had a 100F or higher temperature since July
17, 2012 (100F).
Rochester MN has not had a 100F or higher temperature since June 7,
2011 (101F).
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Heat Advisory from 1 PM to 6 PM CDT Sunday for WIZ061.
MN...NONE.
IA...Heat Advisory from 1 PM to 6 PM CDT Sunday for IAZ030.
&&
$$
DISCUSSION...Boyne/Kurz
AVIATION...KAA
CLIMATE...Boyne
AREA FORECAST DISCUSSION
National Weather Service Bismarck ND
909 PM CDT Sat Aug 19 2023
.UPDATE...
Issued at 906 PM CDT Sat Aug 19 2023
The forecast remains on track. Rain will begin moving into western
North Dakota during the late overnight hours.
UPDATE Issued at 642 PM CDT Sat Aug 19 2023
Only minor changes were made to the forecast for this update, mainly
to incorporate the latest rapid refresh and high-resolution model
data into PoPs. The thicker smoke aloft remains present, but
thankfully it was not able to be fully mixed down to the surface as
the HRRR had been strongly suggesting.
&&
.SHORT TERM...(This Evening through Sunday)
Issued at 236 PM CDT Sat Aug 19 2023
The main concerns in the near term will be near surface smoke
initially, followed by the chances for rain.
Early afternoon satellite imagery continues to show a veil of
smoke across much of the state. The thicker smoke on satellite is
in the northern part of the state, though we are starting to see
visibilities in the east of 7sm to 9sm in haze across parts of
the east. The HRRR has maintained a consistent signal in
suggesting smoke aloft will mix down and increase the near surface
smoke, which is already well covered in the forecast. Following
the HRRR`s lead, we held the smoke into the evening before
gradually clearing it from north to south.
Attention later tonight shifts to the south and west as a H5 wave
moves through the upper ridge. Short term models are in relative
agreement that the rain chances will increase in the southwest
towards midnight, with those chances then spreading north and
east overnight. NBM probabilities for measurable precipitation
climb to near 70 percent in parts of the west later tonight into
early Sunday. Those probabilities quickly decrease farther north,
with the rain chances much less north of Highway 2. Instability
overall is very limited tonight with some small increase in MUCAPE
across southern North Dakota on Sunday.
Lows tonight should mainly be in the 50s, with highs Sunday only
in the 60s to lower 70s.
.LONG TERM...(Sunday Night through Saturday)
Issued at 1242 PM CDT Sat Aug 19 2023
The upper ridge amplifies early next week as another H5 wave
moves across the area Sunday night into Monday. The amplifying
ridge helps shift the better forcing from the wave farther north.
That gives the higher probabilities of rain to the northern
portions of the state, with the NBM suggesting at least a 40
percent chance for amounts of 0.25 inches or greater Sunday night
into early Monday.
It should dry out Monday afternoon as the ridge amplifies,
shifting the stronger forcing farther north. The building ridge
will also bring a warming trend during the first half of next
week, with temperatures in the 90s returning for parts of the
area Tuesday and Wednesday. Cooler temperatures and more rain
chances arrive late in the week as a northern stream wave moves
across the upper ridge.
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday Evening)
Issued at 906 PM CDT Sat Aug 19 2023
VFR conditions are expected through the early overnight hours.
Rain will spread across the state from west to east late tonight
into Sunday morning. The highest chances for rain are at KDIK and
KBIS, where persistent rain is likely through the morning and
scattered showers may last into the afternoon. KDIK is likely to
see a period of MVFR ceilings and visibility Sunday morning, and
IFR cannot be ruled out. KBIS may also see periods of reduced
visibility from rainfall, but confidence on duration is lower
there. Gusty north-northwest winds will subside this evening and
slowly turn to the east-southeast through Sunday afternoon.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...Hollan
SHORT TERM...King
LONG TERM...King
AVIATION...Hollan
Area Forecast Discussion
National Weather Service Denver/Boulder CO
802 PM MDT Sat Aug 19 2023
.UPDATE...
Issued at 754 PM MDT Sat Aug 19 2023
A well organized outflow boundary from the foothills convection
was enough to generate an area of storms east of the mountains
this evening. The stuff around Denver has been pesky, but it`s
getting pretty far behind the surface convergence now so we do
think it will be fading in the next hour or so. The line over Weld
county will likely push eastward for a while. Temperatures have
cooled nicely in the outflow with lots of reading around 70
degrees. We`re updating for higher PoPs downstream of the current
activity and more cloud cover.
We could be near Red Flag criteria in the Denver metro area and
other areas bordering the current warning. How low will the dew
points actually be and for how long is a hard question. The
current forecast has those areas right at warning criteria. The
HRRR is much drier but tends to be too dry on these well mixed hot
days, but other guidance may stay too moist at the surface. We`ll
hold on to what we have for now. Monday is looking similar.
&&
.SHORT TERM...(This evening through Sunday)
Issued at 240 PM MDT Sat Aug 19 2023
Upper level high centered over the Central Plains will slowly drift
north over the next 24 hours. Water vapor satellite imagery showing
somewhat dry air over eastern Colorado with drier air over New
Mexico. There will be enough moisture for showers/storms to
continue into the evening. Best coverage of storms will be north
towards the Wyoming border where the best moisture will reside.
Not much CAPE (less than 500 J/kg) for the storms today, so not
expecting any severe storms. Brief heavy rain and gusty outflow
winds to 45 mph will be possible with the stronger storms.
For Sunday, the drier air over New Mexico will move north over the
area. Looks too dry for any showers or storms. It will be another
very warm day with highs in the 90s over northeast Colorado.
Southerly winds increase Sunday afternoon across eastern Colorado
with gusts to 35 mph. This will increase the fire danger (See fire
weather discussion below).
.LONG TERM...(Sunday night through Saturday)
Issued at 240 PM MDT Sat Aug 19 2023
An upper level high will remain centered over the central US thru
Tue. This will lead to a hot and dry pattern across the area. Highs
both days could tie or break records in some areas. There could be
some minor influx of monsoon moisture, by Tue aftn, to allow for
isold to widely sct high based storms over the mtns.
By Wed, latest data shows an increase in monsoon moisture affecting
the higher terrain which will lead to a chc of aftn tstms. Across
nern CO it will remain dry and hot.
For Thu into Fri, there will be an influx of deeper monsoon moisture
across the area in SSW flow aloft. Thus, should see an increasing
tstm coverage over the higher terrain with some activity over
portions of nern CO as well. Meanwhile, a cold front is fcst to
move across nern CO Thu night into Fri. This front will finally
bring cooler temps and may enhance tstm development on Fri.
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 754 PM MDT Sat Aug 19 2023
VFR through Sunday. Scattered thunderstorms are expected to move
out of the Denver area by 03z. There`s some question about when
northerly winds will switch to southerly tonight. We expect this
will happen between 05z and 08z, but winds may stay northerly
longer or just go light for a while. Stronger southerly winds are
expected for KDEN/KAPA on Sunday with gusts to 20 knots after 18z
and gusts to 30 knots possible from 22z into the evening. Winds at
KBJC will be lighter.
&&
.FIRE WEATHER...
Issued at 240 PM MDT Sat Aug 19 2023
Southerly flow around a high over the central plains will transport
dry air residing over New Mexico into Colorado for Sunday. Relative
humidities will fall into the teens Sunday afternoon. It will also
be breezy over the plains with gusts to 35 mph. Upgraded the Fire
Weather Watch to a Red Flag Warning for Sunday afternoon for this.
Critical fire danger will be in place on Monday, across the
plains and Palmer Divide, due to dry and hot weather along with
gusty south winds. Elevated fire conditions will likely continue
for Tuesday and Wednesday as well across the Palmer Divide and
plains.
&&
.HYDROLOGY...
Issued at 240 PM MDT Sat Aug 19 2023
Scattered showers and storms will continue through mid evening
before tapering off. Brief very heavy rain will be possible with
the stronger storms. Storm movement will be quick and keep the
flash flood threat low, though a localized issue or two can`t be
ruled out. For Sunday, dry air moves into the area with no
showers or storms expected.
No thunderstorms are expected on Monday with only a slight chance of
storms on Tuesday. Monsoon moisture will gradually increase from
Wednesday through Friday with thunderstorms becoming likely. Thus
will see an increasing threat for flash flooding in the burn scars
especially Thursday and Friday.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from 2 PM to 8 PM MDT Sunday for COZ241-245>247-
249.
&&
$$
UPDATE...Gimmestad
SHORT TERM...Meier
LONG TERM...RPK
AVIATION...Gimmestad
FIRE WEATHER...Meier/RPK
HYDROLOGY...Meier/RPK
AREA FORECAST DISCUSSION
National Weather Service Eureka CA
315 PM PDT Sat Aug 19 2023
.SYNOPSIS...Interior temperatures will remain slightly above
normal through the weekend, then cool below normal early next
week. The threat of thunderstorms across mostly the interior will
persist today through Monday with some lingering activity Tuesday
afternoon over the interior mountains.
&&
.DISCUSSION...The persistent upper low off the central CA coast
continues to meander in the base of a larger scale trough that
extends S from British Columbia. However, the large upper high
over the Central Plains remains entrenched. The smoke from
wildfires will keep temperatures across Del Norte and extreme NE
Humboldt counties fairly cool. The rest of the interior has been
above normal. More cloud cover will knock temperatures down some
on Sunday, followed by greater cooling and below normal
temperatures early next week.
Scattered thunderstorms got an early start this afternoon across
inland areas, with some of the storms producing copious amounts of
rainfall and gusty winds. Storm motion has been quite slow thus
far, but it may pick up later in the afternoon with storms moving
NW-N.
The upper low will continue to tap into residual monsoonal moisture
from the S, as well as producing vorticity maxima that rotate
counter-clockwise around the broader circulation. This will
continue the threat of at least isolated afternoon and evening
thunderstorms on Sunday across mainly the interior and triggered
by daytime heat. There is a low potential for some nocturnal
storms late tonight into early Sunday morning for southern Lake
and southern Mendocino as the cut-off low edges closer to the area.
The exact coverage and timing storms will be complicated by
ongoing smoke in the area and model variability.
As we get into early next week, moisture from the remnants of
Tropical Cyclone Hilary is expected to spread N from S CA.
The bulk of the rain will be shunted east of our area. Thick
cloud cover may also inhibit the potential for storms and deep
convection in the interior. However, there will be greater
coverage of showers with embedded isolated thunderstorms, with
rainfall of one half inch to one inch possible over the SE portion
of the area. /SEC
&&
.AVIATION...Visibilities along the coast have improved into the
afternoon, while ceilings will most likely remain MVFR to IFR.
Current satellite and the HRRR smoke model indicate smoke aloft
along the coast from the fires in Del Norte, western Siskiyou, and
northern Humboldt counties which will continue to stream south along
the coast aiding in the broken to overcast skies at coastal
terminals north of Cape Mendocino. Marine stratus is expected to
take back over along the North Coast this evening and overnight
bringing visibilities and ceilings down to IFR/LIFR conditions at
coastal terminals. Isolated thunderstorms will continue to pop up in
the interior of the region, particularly eastern Humboldt, Trinity,
northeastern Mendocino, and extreme northern Lake counties. Storm
activity will diminish into the evening. VFR conditions with some
gusty southerly winds are expected at KUKI this afternoon and
evening with winds calming overnight.
&&
.MARINE...Seas will continue to diminish and by early this evening be
below hazardous sea criteria in the outer waters. Small craft wind
criteria is expected to continue in the outer waters through
tomorrow evening. Northerly winds will increase to widespread gale
force gusts, particularly in the outer waters and are forecast to
persist into early Monday afternoon. Gusts to 40 knots could occur
in the our waters with isolated gusts to 45 knots in the northern
outer waters. Seas are expected to pick back up with the gale force
winds.
&&
.FIRE WEATHER...The mid shift issued a red flag warning for
abundant lightning through 8 PM this evening for fire weather
zones 204, 211, 212, 277 and 283, and this appears to be on track.
Gusty and erratic outflow winds will fan existing fires. South-
southeasterly flow aloft will increase today compared to yesterday
and mean storm motion is expected to increase later in the day.
Winds for the remainder of the weekend will generally remain
diurnally driven under 10 mph, with stronger westerly breezes
expected over exposed ridges and in channeled terrain. Northerly
and easterly breezes with localized gusts to 25 mph over exposed
terrain are expected Sunday night.
Remnant moisture from Hurricane Hilary will spread northward late
Sunday into Monday. Expect scattered showers and isolated,
embedded thunderstorms Sunday night and Monday, with wetting
rain, mostly across the interior. /SEC
&&
.EKA WATCHES/WARNINGS/ADVISORIES...
CA...Red Flag Warning until 8 PM this evening
for CAZ204-211-212-277-283.
NORTHWEST CALIFORNIA COASTAL WATERS...
Small Craft Advisory until 9 PM this evening for PZZ450.
Gale Warning until 3 PM this afternoon for PZZ470.
Hazardous Seas Warning until 9 PM this evening for PZZ470-475.
$$
Visit us at https://www.weather.gov/eureka
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https://www.facebook.com/NWSEureka
https://www.twitter.com/NWSEureka
For forecast zone information
see the forecast zone map online:
https://www.weather.gov/images/eka/zonemap.png
Area Forecast Discussion
National Weather Service Northern Indiana
733 PM EDT Sat Aug 19 2023
.SYNOPSIS...
Issued at 212 PM EDT Sat Aug 19 2023
Warm and dry weather will turn hot later this week. Highs Wednesday
and Thursday will reach well into the 90s and with dewpoints in the
70s yield heat indicies well into the 100s.
&&
.SHORT TERM...(Tonight and Sunday)
Issued at 212 PM EDT Sat Aug 19 2023
Canadian sfc ridge that brought cool temps this morning on
the way out through the ern OH valley this morning. Vigorous warm
advection in its wake will yield much warmer min temps overnight.
This initial push of warm air will fade as backdoor cold front
washes through the area on Sunday as aftn highs temper to mainly mid
to upper 80s.
&&
.LONG TERM...(Monday through Friday)
Issued at 212 PM EDT Sat Aug 19 2023
Two backdoor cold fronts washing out across the area, both Sunday
aftn and Monday night, will put a lid on warming temps through Tue
beneath tremendous cntrl plains centered upper ridge. Thus will
continue to hold with conservative weighted blend.
Beyond that low level thermal ridge does sharpen ewd as fairly
vigorous warm advection spreads east into the wrn OH valley and
supports warmest temps (90-95) of the week Wed-Thu. While fcst
remains dry there is a non-zero risk for storms invof old frontal
zone over ne/ern zones Wed pending downstream track/persistence of
potential upper midwest/wrn lakes MCS development Tue night.
Upper ridge squashes swwd thereafter through next weekend in
response to vicarious nrn stream wave amplifying through ern Canada
and sends a decent cold front south through the cntrl/ern US.
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday Evening)
Issued at 732 PM EDT Sat Aug 19 2023
Quite a bit of low level dry air keeps at least the first portion of
the overnight VFR. NAM bufkit soundings do indicate a low level
inversion forms later tonight, but we are now a couple days removed
from flight condition-reducing fog and cross-over temperatures are
not conducive to fog. The boundary layer stays mixed enough that,
while RAP time sections indicate some low level moisture/cloudiness,
figure this is more stratus than fog. Even still, this is also not
the setup one would expect to see fog or stratus occur as low level
warm advection is occurring as opposed to cold advection. As a
result, will leave this out of the TAFs, but future shifts may want
to evaluate its potential.
Southerly winds attain a more westerly component for Sunday, but
still remain below 10 kts sustained, which would keep gusts below 20
kts.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&
$$
SYNOPSIS...T
SHORT TERM...T
LONG TERM...T
AVIATION...Roller
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Area Forecast Discussion
National Weather Service Key West FL
1020 PM EDT Sat Aug 19 2023
...New DISCUSSION, MARINE, AVIATION...
.DISCUSSION...
Issued at 1020 PM EDT Sat Aug 19 2023
Showers and storms have finally proliferated across the Florida
Keys and surrounding coastal waters during the evening, producing
a couple of recent wind gusts over 30 knots along and just north
of the Middle Keys. Surface analysis indicates that the axis of
the tropical wave has moved west of Key West this evening, with
winds all along the Keys now from the southeast. The 00Z Key West
and Miami soundings sampled an extremely moist airmass, with PWs
of 2.34 and 2.43 inches respectively. These values are well above
the 90th percentile and are very close to the daily observed
maxima for both stations. The low-level dry air layer noted in
the morning Key West sounding was no longer evident this evening.
We also see increasing ESE low-level flow in the wake of the wave
axis, with C-MAN sites reporting sustained winds near 15 knots
away from convective influences, and the sounding measuring winds
of 14-16 knots in the lowest 3000 feet. MIMIC-TPW satellite
imagery shows the axis of maximum PWs moving through our area now,
but PWs of 2 inches or greater still extend back to the central
Bahamas.
For the overnight period, current radar trends suggest that many
Keys locations will continue to see showers and storms for the
rest of this evening. We may see a short break in the activity
with a period of just leftover stratiform rain around and after
midnight, but the latest HRRR brings another round of convection
into the Keys during the predawn hours. The extremely moist
airmass will continue to allow for locally heavy downpours,
although relatively quick movement of the convective elements
should limit rainfall amounts at any one location. We will have to
watch for training cells, which could produce excessive rainfall
in a short period of time. Will continue with categorical PoPs
overnight, along with a mention of locally heavy rainfall.
Otherwise, have already updated the public forecast to remove
early evening transitional wording, and open up the overnight low
range to 75 to 80, as we have already seen temps drop to 75F at
Ocean Reef in an earlier downpour. No additional updates are
planned for this evening.
&&
.MARINE...
Issued at 1020 PM EDT Sat Aug 19 2023
Evening observations show E/SE winds increasing to near 15 knots
along the reef and at Long Key, with a few gusts over 30 knots
with passing convection. Seas at Satan Shoal are building toward 3
feet. Will post a Small Craft Exercise Caution headline for the
Straits with the late evening forecast issuance. Otherwise, will
merely remove the early evening transitional wording. Numerous
showers and scattered storms will continue to impact the Keys
waters overnight. From the synopsis, strengthening high pressure
over the eastern United States and a tropical wave moving west
through the Keys coastal waters will bring freshening easterly
breezes and another round of unsettled weather overnight and
Sunday. Moderate to fresh easterly breezes will persist through at
least Tuesday night, before diminishing Wednesday night.
&&
.AVIATION...
(00Z TAFS)
Issued at 1020 PM EDT Sat Aug 19 2023
Bouts of MVFR ceilings and MVFR to IFR visibilities are possible
overnight as convective showers become numerous in coverage with
scattered thunderstorms advancing westward from the Straits of
Florida and through the island chain. At this time initialized the
00Z TAFs for KEYW and KMTH with TEMPO for MVFR showers, but expect
additional TEMPOs overnight with inclusion of thunder and possible
IFR ceilings. A few thunderstorms could produce wind gusts near 30
knots overnight. Otherwise, surface winds will become east southeast
10 to 14 knots tonight with frequent gusts 18 to 22 knots beginning
midday Sunday.
&&
.KEY WATCHES/WARNINGS/ADVISORIES...
FL...None.
GM...None.
&&
$$
Public/Marine/Fire...Jacobson
Aviation/Nowcasts....JR
Data Acquisition.....AJP
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Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
836 PM CDT Sat Aug 19 2023
.UPDATE...
Issued at 833 PM CDT Sat Aug 19 2023
Conditions remain nice and quiet this evening, especially now that
we`ve cutoff boundary layer mixing putting an end to those gusty
winds from earlier. Quiet is the expectation for the rest of the
night, too. However, just enough ingredients are in place to
potentially stir up a couple of overnight showers or possibly even
an elevated thunderstorm or two. Through about 8PM, a few isolated
showers and even one lone thunderstorm have managed to pop over
southeastern IA. The primary culprit appears to be a subtle 30kt
850mb jet max that`s been gradually propagating along the IA/MO
border. This jet max is seated beneath a rather impressive elevated
mixed layer based at approx. 650mb featuring steep mid level lapse
rates and 2,500 to 3,000 joules of potential instability. However,
the EML has proven overall too dry to realize the majority of that
instability. The recent 00Z RAOB out of DVN sampled a ~550-400mb
layer with just enough moisture to make sense of the isolated
instances of rain we`ve seen out west, but nothing that would
support any widespread rain/storm activity. Additionally, a
pronounced hydrolapse beneath the EML has inhibited many of these
lighter showers from making it to the ground as is evident on
regional radar data, including over portions of the northwestern CWA
since the early evening.
While the EML isn`t present over most of the CWA for the time being,
it will propagate eastward through the remainder of the evening and
into the overnight advecting the bulk of that elevated instability
over northern IL. Latest RAP data suggests the already-modest 850
jet will be weakening as it continues to encroach on the CWA over
the next several hours. Our moisture profile will be very similar to
that out west where we may simply be too dry to make use of that
instability. We`ll also have that dry nose in place to shield us
from any drizzle or real light rain that wants to develop. If we can
gather enough moisture for a thunderstorm to develop, impressively
weak flow through the cloud layer should allow for updrafts to
quickly wash themselves out. The few runs of high-res guidance that
do bring precip into the area tonight do so roughly along and just
ahead of the 850mb trough axis. Otherwise, no kinematic feature
really stands out once the 850mb jet settles down. For now, opted to
add in 10% "silent" POPs for a good deal of the area overnight
into the early Sunday morning. So this was essentially a very
dragged out way of saying no significant changes in the forecast.
Doom
&&
.SHORT TERM...
Issued at 217 PM CDT Sat Aug 19 2023
Through Sunday night...
* Oppressively hot and humid conditions still on tap for Sunday
(away from Lake Michigan).
The forecast through Sunday night on track and no significant
changes were made to the grids.
An anomalously strong upper ridge is still progged to gradually
build north while strengthening through Sunday night. As this
occurs, a surface high will continue to slowly shift eastward
allowing for the higher heat and humidity to our west to migrate
east into our area Sunday.
It still appears that shortwave trough passing well north of the
region across central Canada will allow for a weak cold front to
lay out east-west across northern Illinois Sunday morning with a
weak surface low progged to develop on the tail end of this front
over southern IA into western IL. This should allow for low-level
winds to become light and out of the east Sunday morning, which
should set the stage for a bit of a surge in the easterly winds
off the lake tomorrow afternoon as lake breeze develops.
Away from the lake cooling, moisture pooling along this weak
boundary combined with evapotranspiration should allow for
afternoon dewpoints in the mid to perhaps upper 70s. Combined with
highs mostly in the lower 90s, heat indices will shoot into the
100-107F range Sunday afternoon. The exception to this will be
near the lake.
Initially (prior to formal lake breeze), light easterly winds
should confine cooling to right along the immediate lakefront,
which should allow for areas more than a few miles from the lake
to heat up quickly Sunday morning. Despite the quick rise in temps
across western portions of Lake and Cook Co in IL, still think
heat indices across western Cook and western Lake Co will stay
below advisory criteria before lake breeze hits and results in a
bit of a temp/heat index drop off during the afternoon. All in
all, going heat advisory looks spot on and no changes planned.
- Izzi
&&
.LONG TERM...
Issued at 246 PM CDT Sat Aug 19 2023
Monday through Saturday...
* Heat wave with potential for dangerous heat indices still
appears likely Tuesday through Thursday
Overview:
Very strong mid-upper level ridge over the central Plains into
the mid-Mississippi valley will result in several days of very hot
humid conditions across a large section of the mid section of the
country. Medium range guidance does show this ridge will begin to
ever so slowly start weakening Wednesday into Thursday while also
drifting south.
Monday:
Sunday`s weak boundary should settle south of our CWA Monday with
northeasterly winds across our CWA. The temperature gradient
behind this front isn`t particularly strong, so even though the
entire CWA will be in the "post frontal" air mass, highs should
still generally climb into the mid 80s north to low 90s well
south. Moderate winds off the lake will result in cooler
conditions near lake Michigan. Dewpoints may still be in the lower
70s far southern CWA, closer to the boundary where low level
moisture will be pooling. This could allow for heat indices to
approach 100F, but still seems like they will probably remain
below advisory criteria (105F). At this point, seems we may be
able to squeak by with no heat headlines Monday, but overnight
shift can take another look and reassess.
Tuesday:
Guidance is in good agreement that the boundary will return north
as warm front Monday night into Tuesday. This should allow the
oppressively hot and humid air mass to spread back north into much
of our CWA Tuesday afternoon. Exception will likely be near the
lake where boundary`s northward progression will probably be
slowed by stubborn marine layer which will take a bit more time to
push back out over the lake (likely not until Tuesday night).
Looks like we will eventually need headlines starting Tuesday away
from the lake.
Wednesday and Thursday:
Still look to be very hot and humid, with Wednesday likely the
most oppressive day (particularly near the lake which should be
largely spared Tuesday). Forecast for temps and dewpoints, and
subsequent heat indices, is tricky. The ECMWF continues to
forecast triple digit temperatures across much of the CWA both
days.
While the ECMWF tends to perform quite well, it`s worth noting in
Chicago`s 150 years of weather records there has only been 5 days
with a high of 100+ degrees after August 16. There are a number
of potential complicating factors that could temper the magnitude
of the heat some, including: how much dewpoints will mix out, how
much of a factor evapotranspiration will play, whether sfc winds
will slacken enough for a lake breeze, or if convection with the
ring of fire to our north either slips farther south than expected
or sends temp moderating outflow south. Given that the upper
ridge will be slowly weakening and drifting south, the door is
certainly opened for something to prevent the heat from reaching
its full potential in our area.
The GFS continues to have huge issues with overly mixed boundary
layers that result in utterly absurd temps (and unreasonably low
dewpoints). The NBM bias correction does help, but still was
coming in with triple digit temperatures in our CWA for Wed and
Thu. Given the above discussed uncertainties, lowered forecast
high temps both days from the NBM values. It is possible that
dewpoints could be a bit higher than forecast, but with ECMWF now
starting to hint at dewpoints mixing out and with NBM dewpoints
higher than previous couple of days, opted to not adjust NBM
values.
Thursday night through Saturday:
Much cooler and drier conditions are expected in wake of a cold
front slated to move across the area Thursday night. Can`t rule
out a threat of showers and storms with the front, but chances
aren`t looking particularly high, so didn`t adjust from the slight
chance pops offered up by NBM.
- Izzi
&&
.AVIATION...
For the 00Z TAFs...
The primary aviation concerns are:
* Low (~10%) chance of a thunderstorm overnight at any terminal
* Timing a northeasterly wind shift as a cold front works off Lake
Michigan tomorrow morning
South to southwest winds at times gusting above 20kt continue at
press time in response to a stout low-level pressure gradient
across the Upper Mississippi River Valley. After sunset, wind
magnitudes should drop off and remain generally at or below 8 kt
through the overnight hours. Tomorrow morning, a southwesterly
wind direction (190 to 200 degrees) is preferred before a hybrid
cold front/lake breeze works inland from Lake Michigan. The
inherited timing of 1630Z at GYY and 17Z at MDW/ORD still looks
reasonable, though the latest available model guidance suggests
the wind shift may be closer to 18/19Z (particularly at ORD/MDW).
For now, opted to maintain the inherited timing at GYY/ORD/MDW in
favor of adjustments tomorrow morning as the boundary develops
and can be tracked (e.g. change the timing once rather than with
every TAF package). Behind the front, northeasterly winds will
prevail.
The other item of concern is a low (~10%) chance of a thunderstorm
overnight. Regional satellite imagery depicts an expansive area
of shallow ACCAS based around 8000 feet along the northeaster edge
of an EML plume stretching from northwestern Illinois through
much of Iowa and toward the Minnesota border. In spite of dry air
at the base of the EML, an couple of isolated thunderstorms
recently developed in eastern Iowa near the nose of a 30kt 850mb
low-level jet. Relatively anemic radar reflectivity with each
thunderstorm suggests dry air continues to prevent more meaningful
updraft development thus far. Short-term model guidance shows the
850mb jet shifting eastward into northern Illinois while
gradually weakening overnight while a 925mb cold front approaches
from the northwest. The intersection of the weakening 850mb LLJ,
925mb cold front, and edge of the EML plume (with associated
ACCAS) field may support the development of an isolated
thunderstorm near any of the TAF sites overnight, with a very
modest signal exhibited by RAP guidance near ORD/MDW/GYY between
09-12Z. Confidence in thunder developing is far too low to include
in the outgoing TAF package (again, it seems like a 10% chance or
so), but it is a scenario worth keeping an eye on overnight.
Borchardt
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Heat Advisory...ILZ003-ILZ004-ILZ005-ILZ008-ILZ010-ILZ011-ILZ012-
ILZ013-ILZ019-ILZ020-ILZ021-ILZ023-ILZ032-ILZ033-ILZ039-
ILZ105-ILZ106-ILZ107-ILZ108...1 PM Sunday to 8 PM Sunday.
IN...None.
LM...None.
&&
$$
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Area Forecast Discussion
National Weather Service Marquette MI
747 PM EDT Sat Aug 19 2023
.SHORT TERM...(This evening through Sunday)
Issued at 345 PM EDT SAT AUG 19 2023
Broad upper ridging over much of the central US is inducing
downstream suppression, with a sprawling surface high centered over
the Ohio River basin. Southerly lower-level flow into the Great
Lakes is ushering in a much warmer airmass, with temperatures well
into the 70s across most of the UP. While earlier we were
anticipating some stray showers courtesy of this thermal advection,
model and satellite-derived soundings are showing some midlevel
capping that we seem not to be overcoming. So, skies remain mostly
sunny - apart from lingering haze across much of the northern UP
with zonal upper level flow tapping into upstream wildfires.
Into the evening and overnight hours, a weak frontal boundary
currently over western MN should drop through the area. Guidance
continues to remain unenthusiastic about any rain chances at all
coming out of this, with most just indicating an increase in cloud
cover. With better dynamical support staying to the north of Lake
Superior, I am rather in agreement with that solution. Will not
totally rule out a stray shower between 00Z and 06Z tonight,
otherwise expect a slight increase in clouds along the boundary
along with veering winds. Temperatures drop back into the lower to
mid 60s.
.LONG TERM...(Sunday night through Saturday)
Issued at 345 PM EDT SAT AUG 19 2023
Key Messages:
-Cooler and dry Sunday
-Band of rain expected early in the week
-Sporadic rain chances through midweek
-Ridge eventually retreats south, NW flow pattern expected to follow
With the aforementioned front having fully passed by Sunday, flow
turns northwesterly and Sunday should be a cooler day than the
previous day. The RAP and HRRR smoke guidance does show some Canada
wildfire haze passing over the region in the morning and early
afternoon hours, though the exact extent of the potential health
hazard is uncertain at this time.
Going into the week, the southern ridge continues to build
northward, but we remain on the northern periphery. This will leave
us sensitive to on and off rain chances amid mainly zonal flow. The
first chances would be later Monday with a ribbon of positive
vorticity draped atop the ridge among most of the guidance. Aided by
the temperature gradient between the cooler, northwesterly flow over
the UP and Ontario relative to the nearby record heat to the
southwest, a band of precipitation is expected mainly later in the
day Monday through early Tuesday. No extreme rainfall is expected,
though some thunderstorms are not out of the question.
Uncertainty grows greatly in the forecast midweek and beyond, with
some of the guidance continuing to show the ridge building
northward and others keeping us just on the northern fringes. With
weak ripples in the flow Wednesday through Thursday, some hit and
miss showers would not be ruled out. Otherwise, expect warming
temperatures again into the middle of next week. The upper air
patter looks to become more amplified late week. Friday into next
weekend, the ridge becomes suppressed southward again with
indications for a deeper shortwave to drop through Manitoba and
Ontario. After this passes eastward, robust ridging builds in across
most of the western CONUS with a deeper trough developing to the
east. Resulting NW flow over the Great Lakes will usher in a much
cooler, drier airmass into next weekend.
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 746 PM EDT SAT AUG 19 2023
Although a cold front passes across the area tonight, VFR conditions
will prevail at IWD/CMX/SAW thru this fcst period. Over the last few
hrs, a stratocu deck has formed ahead of the front across the w half
of Upper MI. Cloud bases with these clouds will be in the 3500-
4500ft range. SAW will be mainly affected with several hrs of bkn
cloud cover this evening. Initial nw to w winds at CMX, w to sw at
IWD and s at SAW will shift nw after fropa tonight.
&&
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 345 PM EDT SAT AUG 19 2023
Southerly winds remain breezy this afternoon, particularly across
the eastern portions of the lake, with gusts up to 15 to 25 knots
possible courtesy of a tighter pressure gradient ahead of an
approaching cold front. Winds remain gusty behind the front tonight
into Sunday as they turn northwesterly, with gusts up to 20 kts
possible over the western half of the lake overnight. Higher 20-25
kt gusts are expected over the central and eastern portions of the
lake through the second half of the night into Sunday morning. For
early next week, northeasterly winds could allow for some 20-25 kt
gusts to funnel into the far western arm of the lake before winds
fall back slightly midweek.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
Beach Hazards Statement until 9 PM EDT this evening for MIZ014.
Lake Superior...
None.
Lake Michigan...
None.
&&
$$
SHORT TERM...LC
LONG TERM...LC
AVIATION...Rolfson
MARINE...LC
...Updated Aviation Forecast Discussion...
.DISCUSSION...
Issued at 320 PM CDT Sat Aug 19 2023
Key Messages:
- Dangerous heat continues, with slightly cooler temperatures
Sunday for portions of northeast Nebraska.
- Smoke continues into Sunday, especially for northeast Nebraska.
- Relief to the oppressive heat arrives by Friday along with our
next chance for precipitation.
Tonight:
Upper level highs continue to build over the central US as a large
hot ridge settles into the nation`s mid-section. This will keep a
lid on rain across the region for the next several days. Temperatures
were a little slow to mix out this morning, but with the passage of
a weak boundary this afternoon, temperatures were able to mix out
and they continue to climb steadily along with surface dewpoints.
Dewpoints continue to push into the upper 70s in many locations
except at KBIE where surface winds out of the southwest have brought
in drier air to allow them to heat up more efficiently. In any
case, it`s hot and heat advisory criteria (105 HI) or above at
most locations is being reached as of early this afternoon.
A majority of the CAMs remain dry this evening and we will maintain
a dry forecast, but it`s not completely out of the question for a
little elevated convection along the above mentioned weak
boundary across southeast Nebraska/southwest Iowa this evening.
IF anything could develop, it is highly unlikely anything reaches
the ground so we will continue the dry forecast.
Sunday:
Smoke concentrations are forecast to increase Sunday per HRRR and
RAP output, primarily in our northern counties. Temperatures will be
a bit cooler behind the boundary for Sunday in addition to filtered
sunshine from the smoke. Heat indices of 105-110 are still
anticipated in our excessive heat warning across our southeastern
forecast area. In coordination with neighboring offices, did add
Platte and Stanton counties into a heat advisory for Sunday where
criteria looks marginal. Will need to assess if we need to upgrade
them into the warning if they appear to go the 4-day string of
above advisory criteria.
Monday through Thursday:
The oppressive heat continues through this period with near-record
to record highs possible at least into Thursday.
Both the latest deterministic models and ensemble runs show the
ridge axis amplifying across the northwestern US allowing our upper
level pattern to become more northwesterly. This would break down
the heat and allow a cold front to push into the region providing
our first possible chance at some precipitation over the area
Friday with highs dropping into the 80s.
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 611 PM CDT Sat Aug 19 2023
VFR criteria to prevail for the TAF period. Winds will shift over
the TAF period from northerly to easterly, generally remaining at
10 kts or less. Smoke will return to the area tomorrow but it is
not expected to impact visibility.
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Heat Advisory until 9 PM CDT this evening for NEZ011-012-015>018-
030>034-042-043.
Heat Advisory from noon Monday to 10 PM CDT Wednesday for NEZ011-
012-015>018-030>034.
Excessive Heat Warning until 10 PM CDT Wednesday for NEZ044-045-
050>053-065>068-078-088>093.
Heat Advisory from 1 PM Sunday to 10 PM CDT Wednesday for NEZ042-
043.
IA...Heat Advisory until 9 PM CDT this evening for IAZ043.
Heat Advisory from noon Monday to 10 PM CDT Wednesday for IAZ043.
Excessive Heat Warning until 10 PM CDT Wednesday for IAZ055-056-
069-079-080-090-091.
&&
$$
DISCUSSION...Kern
AVIATION...Fajman
Area Forecast Discussion
National Weather Service Spokane WA
336 PM PDT Sat Aug 19 2023
.SYNOPSIS...
North winds will continue to blow smoke from Canada into the
Inland Northwest this weekend. The chance for light rain will
increase across the Idaho Panhandle Sunday night into Monday. Our
best chances for significant rain will be Monday into Tuesday as
a remnants from Hurricane Hilary interact with a front. The
precipitation will be focused in Idaho and the eastern third of
Washington.
&&
.DISCUSSION...
...SMOKY WEEKEND IN STORE FOR THE INLAND NORTHWEST...
Fires: Satellite still shows active burning on the Oregon Road
Fire and the Gray fire in Spokane county this afternoon. Other
regional fires have started to pop up on shortwave IR imagery. Relative
humidities have bottomed out around 12 to 20 percent across the
region with light north/northeast winds. Leaving the red flag
warning until 7 pm in the Okanogan Valley continues to show red
flag conditions. Tomorrow looks similar in the Okanogan Valley but
with slightly higher RHs so held off on another red flag warning.
Humidities will start to rise in the evening hours above critical
conditions. Winds will start to turn easterly to southeasterly
tomorrow afternoon and getting breezier as Hurricane Hilary
changes the overall synoptic pattern. Relative humidities will
start to rise but winds will slowly pick up as well (nothing like
yesterday, gusts to 15 mph or so). Air quality will remain pitiful
for the remainder of the weekend and slowly improve Monday once
the south winds return the smoke to Canada. Temperatures are
nearly 10 degrees cooler than 24 hours ago due to the thick smoke.
Rain: Issued a flood watch in extreme SE WA and portions of the ID
Panhandle Monday and Tuesday as Hilary interacts with a frontal
boundary bringing a moisture rich airmass to the region. Warm
rain processes will dominate with PWAT anomalies 150-200% of
normal. Far SE WA/Southern Panhandle has a 60-80% chance of 0.5"
of rain Monday and Tuesday while Eastern WA has a 20% chance of
0.5" of rain Monday and Tuesday. The highest totals will be in
the watch as high as 2 inches of rain locally. Storm motions look
fast enough where flash flooding wont be a huge concern but the
total rainfall could lead to rock slides.
Beyond Wednesday: Model continue to point toward a broad trough
developing to offshore to our southwest Thursday and Friday. While
there is still some uncertainty as to how the pattern will
evolve, general conditions to expect will be daytime highs in the
80s and overnight lows in the 50s and 60s with intermittent
chances for showers regionwide.
&&
.AVIATION...
00Z TAFs: North or northeast winds with visibility reductions
will be common for all airports as Canadian smoke spills into the
region. Ceilings are the same way, confidence is low in exact
ceilings but the smoke will be the driving factor to the MVFR
conditions at regional air fields from north Idaho through eastern
Washington. The HRRR smoke model was used as guidance for how
smoke will behave.
&&
.PRELIMINARY POINT TEMPS/POPS...
Spokane 54 84 62 85 59 78 / 0 0 10 20 40 40
Coeur d`Alene 56 84 62 84 60 77 / 0 10 10 30 60 50
Pullman 54 87 59 76 53 72 / 0 10 10 50 60 60
Lewiston 65 91 69 86 66 82 / 0 10 20 60 60 70
Colville 42 84 49 86 50 77 / 0 0 10 10 50 40
Sandpoint 51 81 56 82 56 74 / 0 10 10 30 70 50
Kellogg 58 84 63 76 62 74 / 0 10 20 50 70 60
Moses Lake 55 89 60 88 59 82 / 0 0 0 10 20 10
Wenatchee 61 86 64 88 63 81 / 0 0 0 10 10 10
Omak 57 88 60 93 62 86 / 0 0 0 10 30 20
&&
.OTX WATCHES/WARNINGS/ADVISORIES...
ID...Flood Watch from late Sunday night through Tuesday afternoon for
Central Panhandle Mountains-Lewis and Southern Nez Perce
Counties-Lewiston Area.
WA...Flood Watch from late Sunday night through Tuesday afternoon for
Lower Garfield and Asotin Counties-Northeast Blue Mountains.
Red Flag Warning until 7 PM PDT this evening for Okanogan Valley
(Zone 703).
&&
$$
Area Forecast Discussion...Updated
National Weather Service Portland OR
522 PM PDT Sat Aug 19 2023
Updated Aviation...
.SYNOPSIS...Wildfires across western Canada and eastern Washington
are sending a wall of smoke south and westward into SW Washington
and NW Oregon. Smoke likely to reach the Portland/Vancouver metro
later this evening, then spread further south into the Willamette
Valley overnight. The smoke appears likely to be thick enough to
impact air quality and visibility and is expected to linger through
Sunday. The same offshore flow transporting the smoke into our
region will also bring warmer and drier air, though this may be
moderated somewhat by the smoke if it is thick enough. The remnants
of Hurricane Hilary appear likely to stay well east of the forecast
area, and its primary impact here will most likely be enhanced
onshore flow which should keep temperatures moderated well into the
upcoming week.
&&
.DISCUSSION...Tonight through Friday night...Not much change in the
short term forecast. A wall of smoke associated with several
wildfires near the WA/BC border continues to slowly approach the
forecast area. Latest air quality reports confirm that a good deal
of smoke has pushed into central Washington and northern Oregon,
including Hood River, as shown by unhealthy to very unhealthy AQI.
Higher pressure behind a decaying backdoor cold front is advecting
this smoke southwestward, and will continue to do so throughout
today per the latest runs of the HRRR and RAP smoke models.
As opposed to much of the smoke experienced so far this season which
has been aloft and of little impact to air quality outside of Lane
and Deschutes Counties, the smoke models indicate a high likelihood
that there will be significant air quality impacts at the surface
this weekend across much of SW Washington and NW Oregon. Guidance has
been fairly consistent over the past 12-24 hours that the smoke will
reach the Portland/Vancouver metro this evening, then across the
remainder of the forecast area overnight. Once the smoke arrives, it
will likely linger through Sunday evening. By that time, the region
will begin to feel changes in the pattern courtesy Hurricane Hilary,
which the National Hurricane Center still brings onshore as a
tropical storm near the US/Mexico border Sunday afternoon. The
remnants of Hilary will weaken rapidly while accelerating northward
across southern California and Nevada Sunday night, going through a
rapid extratropical transition while doing so. While Hilary will
bring copious rainfall to the desert portions of southern CA and the
Great Basin Sunday, and eventually to lower portions of the Snake
River Monday, any impacts on our forecast area would very likely be
indirect. As the remnants of Hilary pass to our east, it will
enhance onshore MSLP gradients and thus onshore flow, beginning an
improvement trend in the smoke across SW Washington/NW Oregon by
Monday.
Aside from smoke and tropical concerns, the anticipated switch to
offshore flow today would typically lead to today`s afternoon high
temps being about 5-10 deg F warmer than Friday. A trailing
shortwave looks to maintain weak offshore flow into Sunday, so temps
should remain above peak summer normals. However the smoke is a real
wild card here - if the smoke is opaque enough to prevent shadows on
the ground, it will likely be opaque enough to have a significant
impact on temperatures, potentially keeping them nearer or perhaps
even cooler than Friday. Given that the HRRR/RAP smoke models have
typically overforecasted the opacity and thickness of smoke in our
CWA, we will only shave 2-5 deg F off what the forecast would be
without the smoke. We will learn a lot today in regard to what the
impacts of the smoke will be Sunday in regard to temperature and air
quality. Currently the only existing Air Quality Advisories in our
forecast area are for much of SW Washington, as well as east Lane
County for smoke. Unless the smoke forecast models are dramatically
incorrect, would anticipate an Air Quality Advisory going up for
much of NW Oregon by Sunday morning, once we get a chance to
collaborate with Oregon DEQ on the subject Sunday morning.
One lesson learned from the September 2020 smoke episodes in our
region was that smoke tends to act like cloud in terms of
blocking/reflecting shortwave solar radiation, but smoke does NOT act
like a cloud in terms of longwave radiational cooling at night. We
took this into consideration, as there can be a cumulative cooling
effect in areas of persistent smoke.
Either way, the remnants of Hilary will increase onshore flow Monday
while passing well to our east. The 2 PM PDT NHC Advisory for Hilary
tracks the remnant low pressure center northward across Nevada and
western Oregon on Monday. This would likely spur a surge of onshore
flow later Monday into Monday night, suppressing temperatures closer
or perhaps even cooler than midsummer normals. The marine layer will
likely deepen considerably in response to this pattern shift, with
an extensive marine layer looking to be a good bet Monday and
Tuesday mornings.
The track of Hilary will also likely encourage an upper trough
drifting down the BC coast to move into the Pac NW as it joins a bit
of a Fujiwara dance with Hilary and pivots onshore. This would keep
temps near or below seasonal normals well into the upcoming week, and
could even lead to some light precipitation across the region.
Uncertainty in the forecast increases dramatically beyond midweek as
models differ in how long the upper trough will linger. As such, we
leaned heavily on NBM for the extended forecast. Weagle/DH
&&
.FIRE WEATHER...Model guidance is in good agreement that a thermal
trough of low pressure will shift westward over the Cascades towards
the foothills and far eastern portions of the Willamette Valley this
afternoon. This will result in increasing instability, and when
coupled with the expected critical relative humidities around 20-
25%, may result in plume-driven fire growth on existing fires.
Concerns then linger Saturday evening through Sunday morning as
easterly winds develop over the Cascades and increase to around 5-15
mph (thankfully not overly strong, but just enough to warrant at
least some concern), strongest along the mid and upper slopes. In
addition, poor overnight humidity recoveries are likely over the
Cascades Saturday night due to a lowering subsidence inversion. Many
locations in the Cascades will likely see max RHs between 30-45%. It
appears east winds will weaken Sunday afternoon before winds
transition back to westerly by Sunday evening, which will bring some
improvement. However, still concerned for dry and unstable
conditions on Sunday before onshore flow returns late in the day.
Given all of these factors combined, have decided to maintain a Red
Flag Warning for the Cascades Saturday afternoon through Sunday
evening. Fire weather concerns are minimal early next week as stable
onshore flow returns to the area and relative humidities improve.
One wild card to all of this is what the impact of smoke might be on
temperatures and thus RH. At this time, our forecast only has the
smoke impacting temperatures minimally with little effect on the
anticipated critical fire weather conditions. Weagle/TK/DH
&&
.AVIATION...00Z TAFs...VFR conditions being observed across the
majority of NW Oregon and SW Washington as of 23Z Saturday, until
03Z Monday. The main concern Saturday will be increasing smoke
and haze from the north and east, as wildfire smoke is pulled into
the region from fires in central Washington and Canada. This
smoke could cause periods of MVFR cigs and vis across all areas in
addition to impacting slant-range visibilities through at least
the end of the period. Additionally, smoke from wildfires in Lane
County is impacting much of Linn County and eastern Lane County.
North to northwest winds with gusts up to 20 to 25 kts along the
coast throughout the period and inland areas having winds increase
to 10-15 kts with local gusts up to 20 kts around 23Z Sunday.
KPDX AND APPROACHES...VFR conditions expected for majority of the
period, with expected smoke and haze brought by northerly winds.
This will likely bring MVFR cigs and vis at times as well as
impacting slant-range visibilities through at least 21Z Sunday.
-JH
&&
.MARINE...High pressure remains offshore with low pressure over
eastern Oregon and eastern Washington through the weekend,
causing tightening surface pressure gradients. Expect diurnally
driven northerly winds with periodically steep, wind-driven seas.
Gusts generally up to 25 kts possible through Monday morning for
inland waters and up to 30 kts in outer waters, locally up to 35
kts Sunday afternoon. Seas 8 to 11 ft through Monday morning. Seas
will decrease to 4 to 6 ft by Monday evening, remaining steady
through the next few days.
Increasing smoke and haze from the east will likely reach the
waters late Saturday evening and could impact visibilities at
times. This smoke and haze is expected to linger through Sunday
afternoon, pushing east Sunday evening.
Hurricane Hilary is situated off of the coast of Baja California.
Although remnants of this system are forecast to move north along
the western US and into eastern Oregon late Sunday into Tuesday,
no impacts are expected to the waters off of NW Oregon and SW
Washington. -HEC/42
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning until 9 PM PDT Sunday for Mt. Hood National
Forest West of Cascade Crest-Willamette National Forest.
WA...Red Flag Warning until 9 PM PDT Sunday for Eastern Gifford
Pinchot National Forest Mt Adams Ranger District-Extreme
South Washington Cascades and Foothills.
PZ...Small Craft Advisory until 2 PM PDT Monday for Coastal waters
from Cape Shoalwater WA to Florence OR out 60 NM.
&&
$$
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Area Forecast Discussion
National Weather Service Sacramento CA
244 PM PDT Sat Aug 19 2023
.SYNOPSIS...
Near to slightly above normal temperatures with isolated mountain
thunderstorms today. Moisture moving north with remnants of
weakening Hurricane Hilary will bring widespread showers mostly
light, late Sunday into Monday. Drier with a warming trend during mid-
week. Breezy north winds Sunday, then breezy south winds Monday.
&&
.DISCUSSION....
Afternoon satellite and radar imagery depicts convective
development along the southern Cascades, Coastal Range, and the
northern Sierra this afternoon. HREF still indicates the best
potential for additional thunderstorm development will be over
the Coastal Range, and eastern Shasta County (including Lassen
Park) through this evening. Main storm hazards will be brief heavy
rain, gusty outflow winds, small hail, and lightning. Afternoon
Valley highs ranging from 95 to 100 degrees will bring areas of
moderate heat risk. Increased cloud cover and moisture will cool
Valley temperatures back into the low to mid 90`s Sunday and 80`s
Monday. Increased cloud cover and moisture will cool Valley high
temperatures back into the low to mid 90s Sunday and 80s Monday.
An upper low off the Central CA Coast will remain stationary or
drift slowly east into Monday. This will pull tropical moisture
from Hurricane Hilary northward, with the remnants eventually
tracking through eastern and central Nevada late Sunday into
Monday per latest National Hurricane Center guidance. Hi-Res
models show a surge of moisture that could bring light showers to
the Sierra, southern Cascades, and portions of the Valley tonight
into Sunday morning.
Breezy north to northeast winds will develop Sunday and Sunday
night along the west side of the Sacramento Valley and adjacent
terrain, with gusts up to 20-30 mph. The northerly winds may push
some wildfire smoke into portions of the northern and central
Sacramento Valley Sunday afternoon into the overnight hours per
latest HRRR guidance. Then, gusty south to southeast winds look
to develop Monday as pressure gradient tightens, with gusts up to
20-30 mph. This will bring in more low-level moisture and the
best widespread shower chances.
The Extreme Forecast Index indicates anomalous QPF amounts
for this time of year as tropical moisture surges northward. The
National Blend of Models (NBM) projects a 30-65% probability of
0.25" of rain for the Valley through Tuesday morning, with 50-90%
over the Sierra and southern Cascades. Latest WPC guidance for the
Sunday night into early Tuesday period indicates generally light
precipitation amounts with less than 0.15-0.25 inches over the
Valley and 0.50-1.00 inches over the mountains. The heaviest
amounts will be over the Sierra south I-80, with some local
amounts approaching 1.50 inches over Tuolumne county. Locally
heavier amounts will also be possible where thunderstorms develop.
Drier weather returns by Tuesday afternoon as upper low lifts out
over the area into a trough pushing much of the moisture east of
the area, although there will still be a few lingering showers
over the mountains.
&&
.EXTENDED DISCUSSION (Wednesday THROUGH Saturday)...
Ensemble members and cluster analysis project another upper level
trough developing over the Eastern Pacific Wednesday and
remaining into the weekend, as upper level high pressure over the
southern Plains gradually builds westward towards the four
corners. This will keep NorCal in a southwest flow pattern with
gradually rising heights. Above normal temperatures will continue
through the end of the week. Lingering moisture could bring a
10-20% chance for isolated mountain showers/thunderstorms through
the end of the week. Additionally, onshore flow will lead to
locally breezy conditions with higher gusts around the Delta and
at higher elevations.
&&
.AVIATION...
General VFR conditions anticipated across interior northern
California over the next 24 hours except for possible isolated
MVFR conditions due to thunderstorms over the mountains. Valley
winds will be mostly under 15 kts. Winds surrounding the Delta
will be southwesterly, sustained at 15-20 kts. Northerly winds
developing after 15Z gusting 15-20 kts after 20Z Sunday may pull
wildfire smoke into the northern Sacramento Valley resulting in
local MVFR conditions.
&&
.STO WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$