Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/07/21
Area Forecast Discussion...UPDATED
National Weather Service Albuquerque NM
549 PM MDT Fri Aug 6 2021
.AVIATION...
00Z TAF CYCLE
Isolated showers and thunderstorms persist early this evening from
the Southwest Mountains northeastward near KABQ and KAEG and toward
KRTN. Storms have been struggling to hold together as they move into
the Rio Grande Valley, so only kept VCSH in the KABQ and KAEG TAFs,
however, will be keeping an eye on KAEG. Most storms should dissipate
around sunset. Haze will persist across much of the state tonight,
but hi-res models suggest visibility restrictions may not occur until
Saturday morning across northwest and north central NM as a denser
batch of smoke from northwest U.S. wildfires moves in. Isolated
storms Saturday afternoon will be focused across the Southwest and
South Central mountains and perhaps portions of east central NM.
34
&&
.PREV DISCUSSION...300 PM MDT Fri Aug 6 2021...
.SYNOPSIS...
Isolated thunderstorms will diminish several hours after sunset this
evening. Winds will increase Saturday as a weak cold front moves in
from the northwest. Only very slight cooling is forecast for northern
areas of the state. Thunderstorms will be confined to the southern
third of the state. Northwest winds behind the front will usher in
areas of smoke from fires in California Saturday afternoon and
Saturday night. Areas of smoke may linger into Sunday with dry
conditions forecast areawide. Monsoon moisture starts to move back
into southwest New Mexico Monday and Tuesday, continuing to push into
the remainder of the state Wednesday through Friday.
&&
.DISCUSSION...
.SHORT TERM...(TONIGHT THROUGH SATURDAY NIGHT)...
Satellite imagery this afternoon shows the center of the H5 high
over southeastern AZ while a trough tracks eastward over ID and WY.
The 12Z ABQ PWAT did trend upwards from yesterday evening to 0.90",
but most of that moisture is within the mid-levels of the
atmosphere. This mid-level moisture has allowed for isolated storms
to develop this afternoon across western NM with steering flow
moving them in a east to northeast direction. Models are also
continuing to analyze a weak shortwave across southeastern CO this
evening that may provide just enough ascent to help develop a few
showers and storms across the northeast corner of NM. However,
forecast soundings across the area indicate drier low-levels which
would be more supportive to gusty winds rather than heavy rainfall.
Isolated storm coverage will come to an end late tonight, and the
aforementioned trough will eject onto the Great Plains by mid-day
Saturday. The H5 high strengthens a decameter or two while also
expanding eastward over southern NM. PWATs and dewpoints trend down,
and the ABQ PWAT is forecast to be below 0.5" by Saturday evening.
This doesn`t bode well for precipitation chances. PWATs will hang on
to around 0.75" to 1" across the southwest which may allow for
additional isolated afternoon storms in the Gila region. PWATs also
manage to stay near an inch along the NM/TX border where models are
also highlighting this as an area to watch for isolated convection
thanks to a stalled front along the OK/TX Panhandles. What may
become the bigger story for most by Saturday is increased smoke
across NM. As the trough ejects and the high builds over the area,
northwest flow becomes dominant over the area. This will carry a lot
of smoke from the numerous western wildfires into the state. The
HRRR smoke model indicates smoke will be carried into northwest NM
by early Saturday and will rapidly spread southward as the day
continues.
LONG TERM...(SUNDAY THROUGH THURSDAY)...
The first upper-level trough in quite sometime will slide east of NM
Sunday with subsidence following in its wake. Sunday continues to
look like a true down-day with no convection forecast for the
northern two-thirds of the state. The one exception may be in far
western Catron county where storms in southeast AZ may push over the
state line near Luna. GFS and ECWMF and their ensemble members agree
that the Four Corner`s High (FCH) builds back over NM Monday. The
circulation centroid appears just far enough east (near Clines
Corners) to allow monsoon moisture from Sonora to push a bit farther
into Catron county Monday afternoon. Isolated storms are also
possible over the south- central mountain as Gulf moisture increases
on south/southeast surface winds.
Beyond Monday, global forecast models start to diverge with what
happens thereafter. ECMWF keeps a 594dm high over northern NM while
the GFS brings a warm-core upper low/inverted easterly wave traveling
up the Gulf of CA and into AZ Tuesday. ECWMF has this feature as
well but keeps it over southwest AZ Tuesday. Both models agree that
an uptick in thunderstorm activity is likely Wednesday through the
end of next week as the FCH builds back northwestward over the
northwest Great Basin and Inland Northwest.
15/33
&&
.FIRE WEATHER...
A break in the monsoon action is expected this weekend as dewpoints
trend down significantly and an area of high pressure builds over
the desert southwest. Isolated afternoon storms will still be
possible, primarily over the Gila region, but wetting precipitation
footprints will be small. Temperatures will trend up areawide with
well above normal highs expected for most. While breezy afternoon
winds will be expected, especially Saturday, wind speeds will remain
below critical thresholds. Monsoon moisture will start to filter
back into southwestern NM by Monday and will gradually spread
northward each day, although there is some uncertainty in how fast
this moisture plume redevelops. But a return to a more active
pattern with better chances for wetting precipitation does seem
likely by the latter half of next week.
15
&&
.ABQ WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Area Forecast Discussion
National Weather Service La Crosse WI
1030 PM CDT Fri Aug 6 2021
.SHORT TERM...(Tonight)
Issued at 231 PM CDT Fri Aug 6 2021
TODAY.. A weak surface front remains stretched across
central/northwest WI into southeast MN and northeast IA.
Throughout the day, convective allowing models have been slowly
phasing out activity south and east of ARX, possibly alluding to
the lack of forcing from the weak surface front draped across WI.
Solid low- level lapse rates are possible assuming afternoon
boundary destabilization and therefore convective activity cannot
be completely ruled out. Current lingering cloud decks on
satellite imagery may inhibit some of this afternoon`s convection
especially over areas east of the Mississippi River. Forecast
afternoon maximum surface-based CAPE values >3000 J/kg are
centered in south-central WI with more favorable shear lagging
west in southwestern MN and NW IA. While the upper-level shortwave
trough exits and lifts towards the Great Lakes this evening, the
weak surface boundary remains and sags slightly south and east.
TONIGHT...An upper-level shortwave ridge centered over the
Dakotas in the evening hours weakens to nearly zonal flow with
embedded impulses as it approaches MN/WI. Overnight, maximum low-
level moisture transport remains to the west, focused on an axis
from Kansas to MN containing PWATs near 1.9 inches in central MN.
This moisture transport axis spreads eastward towards the ARX
forecast area in the early morning hours. 310K isentropic analysis
has maximum ascent tomorrow morning in SE MN into western WI.
Simultaneously, early morning MUCAPE values in eastern MN push
towards 2000 J/kg while both deep and lower-tropospheric shear
values increase (0-6km >40kts; 0-3km >20kts) with influence of the
LLJ. Therefore, the start of Saturday`s precipitation appears to
point towards the early morning hours with chances for isolated
large hail.
.LONG TERM...(Saturday through Friday)
Issued at 231 PM CDT Fri Aug 6 2021
Looking over the upcoming weekend, there is only one word to
describe the pattern - messy. The weak upper level ridging heading
into the Missouri River Valley today will continue to progress
eastward and should slip past the area either late tonight or
during the day Saturday. Behind this, an upper level low will
cross the Rockies setting up a quasi-southwest flow pattern. The
pattern looks to contain numerous pieces of energy that will move
across the region over the weekend. This type of pattern makes it
very difficult to focus in on any one given short wave trough that
could be strong enough or isolated enough to generate a round of
stronger convection. The more likely outcome, looks to be several
rounds of convection with locally heavy rains the main threat.
The surface boundary floating over the region today looks to be
near the Interstate 90 corridor by Saturday morning. The
convection that fires along this overnight will have the
possibility of continuing for much of the day. With the main upper
level trough still off to the west of the area, the low level
moisture transport ahead of this will come up through the Missouri
River Valley and intersect the surface boundary. This is expected
to provide enough forcing over the boundary to interact with the
multitude of short wave troughs to keep the activity going. While
there will be ample CAPE in place south of the boundary (around
2500 J/kg ML CAPE) forecast soundings suggest this warm sector may
be weakly capped for much of the day keeping the convection tied
to and north of the boundary. Shear for much of the day looks to
be rather limited, but the RAP is suggesting the 0-3 km shear
could increase to around 30 knots for a period in the late
afternoon and early evening. This could be enough to support a
stronger storm or two with some hail, but the CAPE profile
supportive of hail looks to diminish quickly north of the front,
so would expect the hail to be a rather small threat. With warm
cloud depths around 3.5 km and precipitable water amounts in
excess of 1.75 inches, the activity looks to have the potential to
be efficient rain producers. If any of this would train over the
same locations, some localized flooding could become an issue, but
for now, believe the soils are dry enough to handle the initial
rounds of rainfall.
Very little in the overall synoptics changes through the rest of
the weekend into early next week other than some subtle
north/south shifts of where the moisture transport will be focused
and a gradual eastward movement as the main long wave
trough/upper level low works slowly east across the region. This
will likely mean the continued threat for some stronger storms at
times that could produce some hail, with the bigger threat
continuing to be heavy rain. The concern for some flooding will
likely increase through the weekend, but will have to wait to see
where the initial heavy rain falls before getting concerned about
specific locations or rivers that could be impacted.
This whole system looks to move past the area Sunday night with
just a chance for some lingering activity into Monday. The next
chance then looks to come in for Tuesday afternoon and night when
an upper level low looks to be sliding east across southern Canada
with its trough extending down across the Upper Midwest. It looks
like a weak surface boundary may come through with this system to
help focus the activity. The best chances look to be Tuesday
evening as the moisture transport ramps up ahead of the trough but
the models are showing some differences on where this looks to be
focused.
&&
.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1030 PM CDT Fri Aug 6 2021
Cigs: increasing and lowering clouds overnight. Could dip into MVFR
with shra/ts in the morning. Models aren`t clear on that though, and
no aspects of low cigs with convection out west yet. Will hold VFR
for now. VFR should continue for Sat afternoon before another round
of pcpn Sat night brings the potential for a period of MVFR back
into the picture.
WX/vsby: area of shra/ts on track to move in around/after 12z Sat
morning. Much of the morning will see some pcpn. Likely vsby
reductions to MVFR/IFR at times in heavier rain. Looking at a break
from the shra/ts for the afternoon, but meso models suggesting sfc
front could spark another round of storms by late afternoon,
potentially impacting KLSE. Next shortwave then slides in from the
west late Sat night, bringing yet more shra/ts.
Winds: sfc pressure gradient on the increase Sat...with an uptick in
winds and some higher gusts. Direction looks to swing to the
southeast.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&
$$
SHORT TERM...JAR
LONG TERM...04
AVIATION...Rieck
Area Forecast Discussion
National Weather Service Bismarck ND
1039 PM CDT Fri Aug 6 2021
.UPDATE...
Issued at 1039 PM CDT Fri Aug 6 2021
Showers and thunderstorms have increased across parts of the west
over the last hour, so ran an quick update to change to coverage
wording in the forecast for tonight.
UPDATE Issued at 940 PM CDT Fri Aug 6 2021
Regional MRMS radar loop shows a few showers (perhaps a
thunderstorm at times) moving across parts of western North
Dakota. The most organized activity has been across parts of
central and southern South Dakota, and this lines up with the best
instability / shear. Near term model Hi-Res model solutions have
also focused on areas south of the forecast area, though they
continue to advertise at least a chance of showers and
thunderstorms across western parts of the state gradually shifting
east. Have refined near term pops to limit likely pops to areas
near the South Dakota border in the southwest which lines up with
the most organized area of showers / thunderstorms coming out of
South Dakota. The remainder of the west will continue with a
chance of showers and thunderstorms tonight, with the higher
chances gradually shifting east overnight.
The more organized severe weather threat appears to have
diminished, but still can`t rule out a isolated stronger storm or
two with lingering MLCAPE of 1000-1500 J/KG in the far southwest.
Did not change much in regards to temperatures with forecast lows
in the mid 50s to mid 60s most places.
UPDATE Issued at 654 PM CDT Fri Aug 6 2021
Regional radar loop over the past hour has shown convection
developing in parts of eastern Montana and northwest South Dakota,
but it has not been able to maintain its growth very long after
initiation. The convection has been forming in an area of
sufficient instability marked by MLCAPE of 1000-1500 J/KG, but
the storms have been on the edge of the better deep layer shear
which is in South Dakota and southeast Montana. The 22Z iteration
of the HRRR still suggests we could still see some stronger
convection develop in the southwest part of the state in the next
couple of hours, but the majority of stronger storms are forecast
to be just across the border in South Dakota.
UPDATE Issued at 516 PM CDT Fri Aug 6 2021
Ran a quick update to spread slight chance pops a little further
east to start the evening. The latest regional radar loop shows a
few light showers pushing east of the Missouri River across the
south central part of the state. Have also begun to see a slight
increase in convective activity across parts of southeast Montana
which lines up with some of the HRRR runs. Instability and deep
layer shear are best in the southwest part of the state, though
the steeper low level lapse rates appear to only reach the very
far southwest. Will continue to watch trends, but think the main
window for strong to severe storms should more or less be from
about now through late evening.
&&
.SHORT TERM...(This evening through Saturday)
Issued at 212 PM CDT Fri Aug 6 2021
With the approaching upper trough, currently over the Northern
Rockies, scattered thunderstorm development is expected to begin
later this afternoon across the northern High Plains. There will
be marginal, at best, CAPE and shear to work with; however,
inverted-v forecast soundings and sufficient DCAPE will allow for
some severe-caliber wind gusts with the strongest storms. Initial
storm development is expected to our south and west, with a few
strong to severe storms potentially drifting into southwest North
Dakota before the severe threat diminishes late this evening/early
tonight.
Scattered showers with isolated thunderstorms will push east
across the CWA overnight as the upper trough advances, with
possible re-invigoration of storms across the southeast during
the day tomorrow. SPC`s Day 2 marginal risk barely nudges into the
southern James River Valley, however the greatest severe risk is
expected to be south and east of our area tomorrow.
.LONG TERM...(Saturday night through Friday)
Issued at 212 PM CDT Fri Aug 6 2021
Skies will begin to clear late Saturday into Sunday as brief
ridging builds into the region, resulting in a warm and dry day
Sunday with highs mainly in the low to mid 90s. Heading into
Sunday night, another upper trough approaches from the west,
bringing chances for showers and storms through the night and
during the day Monday. Winds may be a bit breezy during the day
Monday as well, however cloud cover and increased humidity along
with precipitation chances will be limiting factors for favorable
fire weather.
With the trough remaining overhead through mid week, there will be
continuing chances for precipitation, albeit rather low at this
time range. Temperatures will also be confined to the upper 70s to
mid 80s. The western CONUS ridge begins to pop back up towards
the end of the upcoming work week, with warming temperatures and
drier weather favored.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 940 PM CDT Fri Aug 6 2021
Regional radar loops suggest a few showers continue to move
across parts of western and central North Dakota. Forecast models
have not been very consistent in their handling of the better rain
chances, so confidence in adding any TEMPO groups for showers or
thunderstorms is low at the moment. Will have to monitor trends,
but for now mainly went with vicinity groups in the forecasts.
Overall, have gone with VFR forecasts, but will continue to
monitor the progress of showers and thunderstorms in case they
need to be added into any specific TAF locations.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...CK
SHORT TERM...Gale
LONG TERM...Gale
AVIATION...CK
Area Forecast Discussion
National Weather Service Boise ID
840 PM MDT Fri Aug 6 2021
.DISCUSSION...
Breezy northwest winds have mostly subsided this evening, and
smoke coverage is starting to improve from west to east. Weak high
pressure will return on Saturday and support warm and dry
conditions for the day. Latest HRRR runs suggest smoke will
briefly make a return late Saturday night into Sunday as
southwest flow develops aloft. Thereafter, a cold front is still
on track to move through the area Sunday afternoon and evening.
Breezy to windy conditions, cooler temperatures, and
showers/thunderstorms for west-central Idaho can be anticipated on
Sunday. Temperatures will stay below normal on Monday.
&&
.AVIATION...Generally VFR. Smoke in layers aloft is becoming thinner
and should clear out of the area later tonight, leaving mostly
clear skies over southwestern Idaho and southeastern Oregon. Some
local reduction in surface visibility is still possible in
vicinity of active wild fires. Surface winds will become light and
variable at less than 10 kts after sunset. Winds aloft at 10k
feet MSL: NW 15-25 kts.
Weekend Outlook...A weak cold front will pass through the area on
Sunday with breezy west to northwest winds and a slight chance of
thunderstorms in the mountains...mainly north of a KBKE-KMYL-KSNT
line.
&&
.PREV DISCUSSION...
SHORT TERM...Tonight through Sunday night...Northwest flow behind
exiting upper-level low will keep breezy conditions going in the
Snake Plain through the early evening before diminishing.
Northwest flow aloft will help to push extensive smoke mostly
east of the area overnight, although pockets of smoke will likely
remain in some areas. A weak ridge passes over the area on
Saturday, with temperatures rebounding to the lower 90s in the
lowest valleys, with 70s and 80s in the mountains. On Sunday,
another upper-level low moves across the Idaho Panhandle,
generating an increase in wind. A few showers and thunderstorms
are possible in the mountains north of Baker City and McCall, but
the rest of the area should remain dry. Temperatures will cool a
few degrees again on Sunday vs. Saturday. Sunday night should be
refreshingly cool in many areas as the upper low moves east and
winds diminish overnight.
LONG TERM...Monday through Friday...Dry with a warming trend. The
upper level trough will move east of the Rockies on Monday, leaving
cooler air in its wake. Temperatures will be around 10 degrees below
normal on Monday and around 5 degrees below normal on Tuesday. An
upper level high pressure ridge will build over the Intermountain
Region starting Wednesday, raising temperatures to 5-10 degrees
above normal by Friday.
&&
.BOI WATCHES/WARNINGS/ADVISORIES...
ID...None.
OR...None.
&&
$$
www.weather.gov/Boise
www.facebook.com/NWSBoise
www.twitter.com/NWSBoise
DISCUSSION...SH
AVIATION.....JB
PREV SHORT TERM...TB
PREV LONG TERM....JT
Area Forecast Discussion
National Weather Service Burlington VT
1003 PM EDT Fri Aug 6 2021
.SYNOPSIS...
Docile weather will continue through Saturday afternoon before a
cold front descends out of Canada and brings scattered showers and
thunderstorms to the region Saturday afternoon and evening.
Additional showers and thunderstorms will be possible again on
Sunday but will largely be focused along the higher terrain. A brief
dry day will be seen on Monday before we see the potential for
afternoon showers and thunderstorms much of the upcoming week.
Temperatures will be on the rise with the potential for one or more
90 degree days during the middle of the week.
&&
.NEAR TERM /THROUGH SATURDAY NIGHT/...
As of 956 PM EDT Friday...No major changes in the forecast at
this time. Radar shows a few rain showers popping up upstream
across central New York which are tracking northeastward. We
will keep an eye on them as they head our way, but chances for
rain remain very slim for our area. See previous discussion
below:
Previous Discussion...Pesky smoke from the fires out west have
kept the skies across the North Country a nice shade of milky
white with the latest HRRR guidance suggesting the smoke resides
between 1000 and 6000 ft AGL. The good news is that deep mixing
is allowing for the smoke to dissipate slowly with all smoke
expected to mix out prior to sunset this evening. In the mean
time, just some fair weather cumulus is expected with highs in
the 80s across the region. A rather quiet night is in store for
the region as gradually increasing cloud cover after midnight
should quell the potential for the patchy dense fog seen over
the past several night.
Saturday will start off rather quiet with partly sunny skies during
the morning hours but that will change as the day progresses with
increasing cloud cover and rain chances across the North Country. A
nice slug of moisture (PWATS 1.5" to 1.75") will advect into the
region ahead of an approaching cold front which will help bring dew
points back into the mid 60s across the region. The frontal boundary
will enter the St. Lawrence Valley and northern New York between 2
and 4 PM and track southeastward across the North Country. Showers
and thunderstorms will be likely across the International Border but
will become decreasingly likely the further south you get in Vermont
and New York. Given the high PWAT values, it wouldn`t be surprising
to see some heavy rain with the thunderstorms near the International
Border. Otherwise the thunderstorms will be rather benign with
boundary layer LIs only around 2 degrees C. The shower and
thunderstorm activity will taper off overnight with just a few
scattered showers and thunderstorms expected come Sunday morning.
&&
.SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
As of 400 PM EDT Friday...Humid conditions due to lingering low level
moisture are expected Sunday morning. Daytime heating should work to
scatter the shallow cloud layer, although light winds will support
poor mixing that will make this a slow process, particularly in the
valleys. The rich boundary layer moisture will support good
thunderstorm coverage during the afternoon across the higher
terrain, with low chances of precipitation elsewhere given the lack
of large scale forcing. The low shear environment will make heavy
rainfall and lightning the primary hazards, and slow moving
thunderstorms will produce locally high hourly rainfall amounts that
will give need to monitor for flash flood potential. Deepest
moisture will likely be in southern Vermont, so this might be where
the highest chances of this flooding threat exists. Seasonable
temperatures in the upper 70s to low 80s will be accompanied by
moderately high dew points in the upper 60s to low 70s. Slightly
drier air will move in overnight as skies partially clear with
rising surface pressure. Temperatures will sink back into the upper
50s to low 60s in most locations.
&&
.LONG TERM /MONDAY THROUGH FRIDAY/...
As of 400 PM EDT Friday...Moderate warm advection is expected on
Monday with as southwesterly low level winds transport a hotter air
mass into the North Country. It looks like the core of the warmer
air will be over western New York with a bit of a west to east
gradient over our area. Despite the very warm and humid air, low
chance of thunderstorms exists with rising heights aloft ensuring
weak lapse rates with showers again tied mostly to the high terrain.
On Tuesday, the whole area should be hot with roughly 24 celsius 925
millibar temperatures and super adiabatic low-level lapse rates
should yield highs near 90 in most spots below 1000 feet elevation,
with low 90s possible in the St. Lawrence Valley, or a few degrees
above the values on Monday. Expect that the deep mixing of somewhat
dry air will help lower dew points a bit during the afternoon hours,
but have heat indices still reaching the upper 80s in many
locations. A slight chance of thunderstorms will be introduced late
in the day as some upper level cooling approaches from the west. At
this time, organized thunderstorms look to be isolated.
Increasing chances of thunderstorms, and the hottest days of the
week as a combination of temperature and humidity, may be on
Wednesday and Thursday when we may see many 90 + heat index values.
In particular, strong storms will be possible on Thursday when ample
instability will be in place along with an approaching cold front.
However, the details are fuzzy at this point owing to large model
differences with how quickly stronger upper level cooling moves into
the area. At the surface, our area should be solidly in the warm
sector ahead of the front with continued southerly flow. For now we
have the idea of thunderstorms late in the day that would allow
temperatures to recover back into the 85 to 90 range with muggy air
in place. If the front pushes through on Thursday, it still appears
to linger close enough on Friday to reintroduce thunderstorm
chances, although we trend temperatures and dew points a bit lower.
&&
.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
Through 00Z Saturday...VFR conditions and south to southwest
winds of 11 knots or less are expected through 15Z Saturday.
Thereafter, we will see channeled southerly winds bring gusts of
15 to 20 knots to portions of northern New York and the
northern Champlain Valley. A cold front will begin to descend
out of Canada around 18Z Saturday which will bring some chances
for light showers toward the end of the forecast period with the
possibility of some heavy showers or possibly a thunderstorm or
two late Saturday afternoon and Saturday evening across
northern New York and northern Vermont. TAF sites most likely to
see rain/thunderstorms and subsequent MVFR conditions would be
KMSS and KEFK.
Outlook...
Saturday Night: VFR. Chance SHRA, Slight chance TSRA.
Sunday: VFR. Chance SHRA, Chance TSRA.
Sunday Night: VFR. Slight chance SHRA, Slight chance TSRA.
Monday: VFR. Slight chance SHRA, Slight chance TSRA.
Monday Night: VFR. NO SIG WX.
Tuesday: VFR. Slight chance SHRA, Slight chance TSRA.
Tuesday Night: VFR. Chance SHRA, Slight chance TSRA.
Wednesday: Mainly VFR, with local MVFR possible. Chance SHRA,
Slight chance TSRA.
&&
.BTV WATCHES/WARNINGS/ADVISORIES...
VT...None.
NY...None.
&&
$$
SYNOPSIS...Clay
NEAR TERM...Clay/Hammond
SHORT TERM...Kutikoff
LONG TERM...Kutikoff
AVIATION...Clay/Hammond
Area Forecast Discussion
National Weather Service Billings MT
741 PM MDT Fri Aug 6 2021
.UPDATE...
Risk of severe thunderstorms has ended...and have cancelled the
Severe Thunderstorm Watch for Carter County.
One shortwave is ejecting from eastern WY into the Dakotas...and
to our SE is where the risk of stronger storms has shifted. Weak
upper low over northwest WY is tracking slowly to the east. Track
of the low is less than favorable for much activity in our area,
but we should still see scattered showers and a few embedded weak
thunderstorms into the overnight hours...w/ some showers perhaps
lingering into Saturday morning in our east as the low finally
exits. Weak thunderstorms currently around our forecast area have
been producing 25-35 mph wind gusts...and activity is highly
unorganized per a lack of wind shear (except for in far southeast
MT). Potential for erratic surface winds is diminishing as we
approach sunset. Finally, HRRR has been consistently showing an
increase in near-surface smoke courtesy of NW flow behind the
shortwave...and we are seeing reduced visibility at several ASOS
stations to our northwest. Have adjusted our wx grids to show
areas of smoke tonight, which will linger tomorrow in form of
another day of very hazy skies.
JKL
&&
.DISCUSSION...
Tonight through Sunday night...
Strong upper trough over Idaho this morning was tracking eastward
across northern Wyoming this afternoon. We have had a few waves
of showers and thunderstorms already move across the region,
mainly affecting areas along the Montana/Wyoming border. Low level
moisture lapse rates over portions of our southeast are sufficient
to support risk of strong downdraft winds and marginally severe
hail late today into early this evening as the upper forcing moves
across the region. PWATs are near an inch in these areas and also
suggest risk of heavy downpours with the stronger cells.
Thunderstorms will linger in the east until around midnight, then
slide into the Dakotas. Saturday should be a bit cooler, a little
breezy as zonal flow dominates, with little if any chance of
convection.
Sunday remains a potential day for critical fire weather
conditions. As a strong upper trough develops over the Pacific NW
and tracks into Idaho, we will see pre-frontal warming boost
temperatures over our forecast area. Progged soundings suggest
deep mixing over our west and central zones by mid afternoon with
gusts over 25 mph and RH readings in the teens. Surface low
sitting over areas east of Billings may not see as much wind.
Timing of a strong frontal passage is still in question as GFS
suggest 6-9 pm Sunday evening for Billings to Sheridan. Areas
further east may not see wind shift until after midnight, which of
course means a reduced risk of fire weather concerns. EC model is
still a bit slower with the frontal passage. Fire weather
highlights may eventually be necessary for Sunday, especially in
our western sections, but the timing of the cold front remains
uncertain and will ultimately determine the extent of any fire
weather highlights. There is some post frontal precipitation that
tries to work into the area Sunday evening. We feel the NBM
guidance is a little too bullish with its PoPs given the strong
downslope winds, so adjusted them down somewhat.
Look for highs Saturday in the upper 80s to low 90s, climbing well
into the 90s for most areas Sunday. BT
Monday through Wednesday...
In the wake of Sunday`s cold front, gusty winds look to continue
over the area on Monday as an associated low slides east across
the Canadian border, keeping the pressure gradients somewhat
tight. A few showers or thunderstorms are possible with the
lingering energy in weak cyclonic flow. Another system dropping
southeast through southern Canada will keep breezy west to
northwest winds over the area on Tuesday. Ridging over the western
US will keep the region in a dry northwest flow through most of
next week. Temperatures will trend from below normal through the
middle of the week, warming to near or above normal by the end of
the week.
High temperatures in the 70s to 80s are forecast for Monday
through Wednesday, warming back towards the 90s for Thursday and
Friday. Lows in the 50s to lower 60s are forecast most nights. STP
&&
.AVIATION...
Scattered showers and a few thunderstorms will continue to impact
much of the region this evening, with erratic/gusty winds along
with brief heavy rain and MVFR conditions. Shower activity will
diminish from west to east overnight into early Saturday. VFR
will otherwise prevail. Tomorrow will be sunny w/ breezy W-NW
winds.
Wildfire smoke will continue to reduce slant range visibility
across the region. Local MVFR conditions are possible in areas of
smoke.
JKL
&&
.PRELIMINARY POINT TEMP/POPS...
Sat Sun Mon Tue Wed Thu Fri
-----------------------------------------------------------
BIL 064/091 064/098 058/080 055/087 057/087 058/091 062/091
30/H 01/U 32/T 11/U 11/U 00/U 00/U
LVM 051/089 055/092 048/078 047/084 050/087 051/091 055/091
40/N 12/T 42/T 11/U 11/U 00/U 00/U
HDN 062/092 059/099 055/081 052/088 052/087 056/092 058/092
40/H 00/U 22/T 11/U 20/U 00/U 00/U
MLS 062/092 064/097 060/079 056/085 057/085 058/088 061/092
41/H 00/U 32/W 11/U 10/U 00/U 00/U
4BQ 061/090 062/097 059/080 055/086 057/085 058/089 061/091
52/W 00/U 21/U 11/U 10/U 00/U 00/U
BHK 059/090 060/096 059/080 053/084 055/083 055/086 057/088
52/W 00/U 21/B 11/U 21/U 00/U 00/U
SHR 057/088 057/096 052/080 048/087 051/085 053/088 055/090
41/H 00/U 22/T 10/U 11/U 10/U 00/U
&&
.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...None.
WY...None.
&&
$$
weather.gov/billings
Area Forecast Discussion
National Weather Service Des Moines IA
731 PM CDT Fri Aug 6 2021
.UPDATE...
Issued at 729 PM CDT Fri Aug 6 2021
Pushed up the timing of precip chances a bit for later this evening
into tonight. Recent hi-res models have consistently developed
iso/sct convection along the nose of a strengthening LLJ later this
evening over north central Iowa. Kept PoPs in the slight/low
chance category as any thunderstorm activity will have to
overcome mechanical lift deficiencies with weak height rises
evident as a shortwave ridge axis approaches the state. However,
the atmosphere will become more conducive for elevated convective
initiation by 04- 05z as an eastward advecting EML provides more
instability rooted above 800mb. Steep lapse rates may promote some
hail growth within stronger updrafts, but meager shear profiles
should limit the overall severe threat. A complex of storms
currently out in western SD/NE may move into the state later
tonight. It remains to be seen if the storms can remain organized
enough to hold together, and if so, will the LLJ force their track
north of the forecast area.
&&
.DISCUSSION.../Tonight through Friday/
Issued at 312 PM CDT Fri Aug 6 2021
Tonight:
H5 trough axis that brought some convergence early this morning
producing light rain showers has pushed off toward east. Behind this
a weak ridge has been propagating across the central Plains, but
immediately trailing that is another H5 trough that will aid in
keeping the pattern active over the next 24-48 hours. Surface
analysis this morning continues to indicate a weak thermal boundary
along the MN-IA border, with surface winds defining the position,
northerly winds across MN and south-southwesterly across Iowa.
Convergence ahead of this boundary continues to remain weak. A few
light showers may be able to get going along this boundary, but
recent CAM cycles continue to show CIN for both surface parcels and
MU parcels through most of this evening. Further, with the stronger
mid-level flow over the central Plains, deep layer shear will remain
weak this afternoon and evening. 0-6 km bulk shear values struggle
to reach 30 kts. The organization potential for convection is
lacking. The only factor favoring any kind of convective development
will be daytime heating, which may have the ability to provide
decent lapse rates within the boundary layer. But, updrafts will
likely struggle as long as this cap remains in place. Earlier
concerns over an isolated severe wind gust with showers or
thunderstorms in northeast portions of the forecast area have now
dwindled. Overnight, the ridge axis will quickly push eastward
across Iowa as the trough directly behind it slightly digs into the
central Plains. A decent surface cyclone has already developed over
the central Plains in response to this system, and this has helped
to reinforce the surface/low-level southerly flow across Iowa. WAA
will continue overnight and through much of Saturday, leading to
shower and thunderstorm potential.
Saturday and Sunday:
Confidence in the evolution of shower and thunderstorm activity
Saturday through Sunday is medium, at best. The complicating factor
at the moment is with two periods of H5 height falls through
Saturday. Model guidance continues to lack consensus on the handling
of these two features. The threat for severe weather is conditional.
After the passing the of the ridge axis, a weak vorticity maxima
will move along the backside of the ridge. Low-level flow will
already be southerly ahead of surface cyclone centered over NE-KS
border. This will develop an airmass with enhanced theta-e content.
Warm front will then move northward through the morning, likely
pushing the currently present weak thermal boundary northward.
Shower development will be likely throughout the morning on
Saturday, especially as isentropic ascent strengthens. During this
time, Iowa will be entering the warm sector, but deep layer shear
will remain questionable across the forecast area into the afternoon
with 0-6km bulk values struggling to reach 30 kts. There could be
some more vigorous activity along the previous weak thermal boundary
or along the warm front itself, but the better forcing is shaping up
to be north of the forecast area into southern Minnesota and
southwest Wisconsin. Areas further north along the warm front may
see better shear as well, in the 30-40 kt range in the 0-6km layer.
Thus at this time, expectations are not overly high for severe
activity Saturday during the afternoon in our forecast area, but are
non-zero. However, if the warm front stalls a bit further south,
this could change the mesoscale environment Saturday afternoon,
especially between Hwy. 20 and the IA-MN state line. If this
afternoon scenario were to play out, the warm front may provide
extra vorticity and increase storm relative flow. An increase in
deep layer shear could then support a hail threat with discrete
cells, and if this happens low enough could support a low-end
tornado threat. With dewpoint depressions near the surface around
20F possible and steep lapse rates within the convective boundary
layer, showers and thunderstorms could produce wind gusts, downburst
like in nature. Again, the Saturday afternoon severe threat is
conditional on breaking the cap, and the location of the warm front.
There is a lot that may get in the way Saturday afternoon. Attention
then turns to the arrival of the main H5 trough, surface cyclone,
and the cold front late Saturday evening. There still remains some
discrepancies in timing of the boundary propagation, but the best
convergence continues to be favored after 04z, meaning that we are
looking at an overnight severe threat into early Sunday morning for
portions of the forecast area. CAM guidance is still spread out,
with the HRRR attempting to develop some multi-cells in the 02-04z
timeframe tomorrow night before congealing along the cold front into
a linear mode. Other solutions do not have the multi-cell clusters
developing prior to the onset of a linear system. Recent runs of the
HRRR in the middle of the afternoon though are starting to point to
a more robust QLCS along the cold front, and similar to other
solutions like the NSSL-WRF and HiResW-FV3. Convection along this
cold front will also hold severe potential. Deep layer shear will
increase along and ahead of the cold front into the evening hours as
the trough moves overhead. In addition, the LLJ will kick in ahead
of this and enhance low-level flow. If multi-cells develop first,
like it is being depicted in recent HRRR runs, greater deep layer
shear (0-6kts should be pushing over 30-40 kts at this point) will
support initial organization. With previous boundary layer
destabilization, lapse rates could become as steep as 7.5-8.0 C/km
through the middle levels. Therefore, a few storms supercellular in
nature are possible, capable of producing severe hail and severe
wind gusts. If near surface flow becomes enhanced, an elevated,
brief tornado threat cannot be ruled out. After 04z, as the cold
front enters Iowa, either multi-cells if developed will begin to
congeal, or new initiation of a QLCS will begin. If convergence is
strong enough, the QCLS may become strong. Further, the LLJ along
with this should also strengthen. Interaction between cold pool
dynamics and the shear environment, as well as the thermodynamic
environment ahead of it, will lead to a damaging wind threat. An
increase in 0-3 km bulk shear does lead to a QLCS tornado concern
overnight with the line. Currently, most model soundings are showing
30-35 kts directly along the cold front and line of convection.
However, the 0-3km shear vector is oriented parallel to the boundary
and line. While the LLJ will help to increase the flow, 30 kt line
normal shear may be difficult to achieve. There does not appear to
be any shortage of 0-3km CAPE though, so if a portion of a line
orients in a direction perpendicular to this shear vector,
mesovortex generation may become more favorable. The low-level model
hodographs curve quite a bit, and 0-1km SRH values may exceed 300
m^2/s^2. The question, is will storm motion or boundary motion favor
the storm-relative winds needed to support a tornado threat.
Regardless of QLCS tornado potential, damaging winds will become a
problem if a stronger QCLS develops overnight. Expect lingering
convection into Sunday, as the trough overhead slows down and Iowa
remain in cyclonic flow.
Extended:
Another thermal ridge develops Monday through Tuesday which will
begin an upward trend in temperatures once again, as well as
increased moisture keeping conditions humid. However this warm
pattern will not be nearly as stagnant as the one from last week, as
a stronger closed low system develops across the northern Rockies
and moves east into the northern Plains. The bulk of the vorticity
with this system is currently forecast to remain well north of Iowa,
but, mid-level flow does turn southwesterly through the middle of
this week with some enhanced CVA moving across the region. As long
as this low pressure system does not track much further northward,
this should help to deamplify the ridge and limit potentially
oppressive heat and humidity for much of the upper Midwest. In this
flow pattern, expect multiple opportunities for showers and
thunderstorms during the middle of next week. Should the closed low
system though not be as a strong as currently advertised, the heat
could once again become an issue.
&&
.AVIATION.../For the 00Z TAFS through 00Z Saturday evening/
Issued at 615 PM CDT Fri Aug 6 2021
VFR conditions prevail through the current TAF period.
TSRA possible after 06z tonight and into Saturday. Confidence in
the timing/location of any TSRA activity remains quite low at
this time, so no mention was included in the latest TAF update.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...Martin
DISCUSSION...Krull
AVIATION...Martin
Area Forecast Discussion
National Weather Service Indianapolis IN
939 PM EDT Fri Aug 6 2021
.Forecast Update...
Issued at 939 PM EDT Fri Aug 6 2021
Gulf moisture continues to stream into central Indiana this morning
in the southwest flow ahead of an upper level trough over the
northern Mississippi Valley. Current GOES16 captures this well with
some weak cyclonic rotation over IA/WI/IL. So far, the radar has
been quiet, but the best chances for any showers and thunderstorms
this afternoon will be over the northwest portions of the forecast
area where any convection/outflow boundaries closest to that upper
trough will have the best chances of drifting into central Indiana.
As far as temperatures today, cloud cover should help mitigate the
effects of the southwesterly flow. So, the current forecast of mid
80s is on track. Currently, temperatures across the area are
generally in the low to mid 70s. Updated grids have been sent.
&&
.Short Term...(This evening through Saturday night)
Issued at 256 PM EDT Fri Aug 6 2021
Weak cyclonic rotation continues over IA/WI/IL with a broad upper
trough sinking into the Mississippi Valley. This setup combined
with the surface high pressure over the southeast U.S. is conducive
to strong moisture influx from the Gulf. As a result, the hot and
muggy conditions will return to central Indiana this weekend with
daytime temperatures climbing into the upper 80s tomorrow with dew
points in the low 70s.
Despite the moisture influx, forcing will be limited and pertaining
to just the upper trough. So, the best chances for any convective
activity for the remainder of this afternoon/evening will be
confined to the northwesternmost portions of the forecast area where
forcing and moisture will be best.
Tonight, the upper trough will push farther into northern Indiana,
so shower and thunderstorm chances will become more widespread
across the northern third of central Indiana. Again though, the
best parameters will remain over northern Indiana. Nonetheless,
there will be potential for some outflow boundaries to dip into the
central portions of the forecast area. So, would not be completely
surprised if the Marginal Risk currently skimming the northwest
counties gets extended farther south.
Tomorrow, shower and thunderstorm chances will become a bit more
widespread, but still mainly concentrated over the north and eastern
portions of central Indiana as the upper trough traverses the area.
Expect a gradual decrease from west to east with the forward
propagation of that upper wave.
&&
.Long Term...(Sunday through Friday)
Issued at 256 PM EDT Fri Aug 6 2021
A warmer and more humid week is expected as the weekend comes to a
close and moves into next week, along with frequent, albeit mostly
low, chances for showers and thunderstorms as early as Sunday night
onward.
Until the approach of a surface front late in the week, much of this
activity is likely to be diurnally driven to a significant degree as
the majority of the upper level forcing remains north/northwest of
the area, but most periods will require at least low pops.
Broad southwest flow at the surface will bring more humid air back
into the region, and peak heat index values may approach or exceed
100 degrees at times, primarily Monday through Wednesday across
western portions of central Indiana. Nothing in the grids exceeds
headline criteria at this time, but will bear watching as the
forecast evolves. Cooling from any precipitation would obviously
have a major impact on this potential as well.
A cold front looks to move into the region late in the week,
moderating temperatures and to a degree humidity as well as the next
weekend approaches.
&&
.Aviation...(00Z TAF Issuance)
Issued at 716 PM EDT Fri Aug 6 2021
IMPACTS:
- ISOLD shra may impact KLAF and KIND tonight.
- Mainly VFR Conditions are expected.
DISCUSSION: VFR will be the predominant flight category for the
duration of the TAF period. Nonetheless, cannot rule out quick
deterioration to MVFR in any showers/storms that do form,
particularly in the KLAF and IND tonight. For now, will only carry
VCSH overnight at KLAF and IND until confidence in timing and
location improve tonight. HRRR continues to suggest some
development overnight as the upper trough works slowly through the
region. Elsewhere, chances remain too low at this time to include
mention of showers and thunderstorms at remaining TAF sites tonight.
Again on Saturday afternoon...best instability and forcing remains
across the northern TAF sites of IND and LAF. Again...confidence too
low for a specific mention...but have included VCSH for now during
max heating diurnal periods for possible VCSH development.
Again...much of Saturday will remain VFR except the brief period
when a stray...isolated afternoon shower that could strike a TAF
site.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Update...Puma
Short Term...TDUD
Long Term...Nield
Aviation...JP
Area Forecast Discussion
National Weather Service Northern Indiana
734 PM EDT Fri Aug 6 2021
.SYNOPSIS...
Issued at 728 PM EDT Fri Aug 6 2021
Showers and thunderstorms this evening can produce locally heavy
rainfall, small hail, and damaging wind gusts. This activity is
expected to weaken after sunset. Otherwise, hot and more humid
this weekend with additional chances for wet weather.
&&
.SHORT TERM...(This Evening through Saturday)
Issued at 308 PM EDT Fri Aug 6 2021
A shortwave approaches within the large scale trough this afternoon
and evening and will serve as the focus for showers and
thunderstorms. A few showers and storms may form out ahead of the
wave this afternoon into the evening with heavy rain and gusty
winds. Then, there is still plenty of model disagreement on if
storms will actually form between 00z and 12z tonight, but if they
do they the main focus will be heavy rain that could lead to
flooding especially in urban areas. This is as a result of slower
storm movement and potential backbuilding along with boundary-
parallel flow leading to storm training. During this time, and as
the wave approaches the area, it is collocated with plenty of
SBCAPE, high moisture transport and areas of moisture flux
convergence so there is expected to be plenty of moisture and lift
to work with as it enters areas west of IN-15. Looking at forecast
soundings from the NAMNEST and RAP time-sections, the moisture
column does look moist in the low levels which is also conducive to
heavy rain. Currently have 0.5 to 1.5 inch rainfall totals west of
IN-15, but could see locally higher totals where storms are able to
slow down or train. As a result of the increased cloud cover and
slightly increased humidity, tonight`s low temps are expected to be
warmer than last night`s staying the mid 60s.
Showers and storms could linger into a portion of Saturday morning
with some left over moisture convergence and instability, but we`ll
then need to watch during the afternoon and evening time frame for
more convective development especially if clouds can break up for
instability recovery. Storms would be able to form along any remnant
outflow boundaries and would also have slow storm movement
especially later in the afternoon/early evening allowing for the
possibility of heavy rain that could lead to flooding. There is a
plume of DCAPE that appears to move in the same time as the
potential initiation period for storms looks to be, but the low
levels still look moist on forecast soundings. So if we can get some
more dryness in the low levels, gusty winds could be had within
storms that form Saturday evening. Shear is lacking between tonight
and Saturday night so the severe weather threat would be very
marginal. Saturday`s high temps won`t be much higher than today`s
especially with the remnant cloud cover in the morning, but have
them in the mid 80s as opposed to the low 80s in anticipation of
clouds scattering out during the afternoon.
&&
.LONG TERM...(Saturday Night through Friday)
Issued at 308 PM EDT Fri Aug 6 2021
Behind Saturday`s troughing, a broad ridge in between troughs moves
in. This should act to suppress thunderstorm activity during the day
and have removed PoPs during that period as a result. Now, the
southwesterly low level jet looks to edge into the west allowing for
increased heat and humidity on Sunday 850mb temps rise over 18C to
and dew points rise over 70 degrees allowing for highs in the upper
80s to near 90 degrees and low 90s for heat indices. This signifies
the first of the stretch of very hot days of 90+ degree heat indices
continuing into the middle part of the work week with Tuesday seeing
the biggest part of the area forecast to have heat indices top 100
degrees. Areas south of US-24 on Thursday still have a chance to see
90+ heat indices, but cooler temperatures could begin to edge slowly
in the from northwest as long as the the cold front starts to seep
in.
The other side of the conversation are the chances for showers. As
hinted at above, the chance for showers during this period wouldn`t
start until late Sunday night in Monday morning at the earliest as
the next trough approaches. However, normally, diurnal forcing
brings the better chance for showers than a morning chance, so if
the slower EC is right perhaps there could be a shower or storm
around during the afternoon time, but even that is moving too
quickly for scattered pop-up storms so they may just remain sub-
severe that day. Chances for pop-up storms continue Tuesday and
Wednesday as well with an outside chance at a shower or storm
Thursday as long as the front hangs back or slows up. The chance on
Tuesday could have some 6.5 to 7.5 C/km mid level lapse rates to
work with which could introduce a hail or stronger wind chance if
that comes to fruition.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday Evening)
Issued at 728 PM EDT Fri Aug 6 2021
An MCV has spawned an area of rain and thunderstorms, which are
now pushing east of KSBN. The environment toward KFWA is less
favorable for thunderstorms, so have omitted the TS mention there.
Timing of the TEMPO group is high confidence based on the current
organization and trend of the line of storms. Wind tomorrow will
generally become more westerly, but less than 10KTS.
There are non-zero chances for thunderstorms Saturday afternoon as
an upper-level vorticity maximum lingers. Coverage and timing are
questionable, so I`ll fine-tune that for the next issuance.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&
$$
SYNOPSIS...Brown
SHORT TERM...Roller
LONG TERM...Roller
AVIATION...Brown
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Area Forecast Discussion...UPDATED
National Weather Service Chicago/Romeoville, IL
805 PM CDT Fri Aug 6 2021
.UPDATE...
804 PM CDT
Thunderstorms across southeast Wisconsin gradually became more
organized late this afternoon and early this evening, establishing
a cold pool and some sustainability as they moved more south than
east. This loosely defined and small scale MCS also still has a
parent short wave trough gradually moving southeast in south
central Wisconsin. Mid-level winds and deep layer shear both
remain somewhat low with this, but ample instability and moisture
should help support some sustainability through at least 9-10 P.M.
The 00Z DVN sounding had 2,400 J/kg of mlCAPE and some portions
of the lower to mid-level profile that showed fairly steep lapse
rates. This also supports at least some sustainability, and the
potential to get isolated cells to pop toward Rockford and
Belvidere (such as has been seen in south central Wisconsin).
The initial outflow is just moving into northern Lake County and
looks like has gusts of 35 kt with it, but shortly behind it is
another surge that produced a 43 kt gust at Racine, WI. These
types of gusts will be probable especially in northern and
eastern Lake County through 9 P.M. If this can sustain itself into
Cook County, these gusts may be more confined to near the lake
front. If this were to get to the Chicago lakefront it looks like
it would be somewhere near 9:30 P.M. The potential for true severe
wind gusts still looks on the lower side, and probably would need
some stronger cores to regenerate for that.
MTF
&&
.SHORT TERM...
328 PM CDT
Through Saturday night...
Observational data has allowed convective trends to become more
apparent into this evening than earlier today, though evolution is
fairly close to the thinking from this morning. Widely scattered
thunderstorms that have developed south and southeast of an Ottawa
to downtown Chicago line will pose a threat for isolated downburst
winds and perhaps marginally severe hail from the tallest
updrafts. After a probable lull once this activity clears east in
the early evening, another round of widely scattered thunderstorms
is possible from far northeast Illinois into northwest Indiana
late this evening into the overnight, though confidence remains on
the lower side with this potential.
The center of the remnant MCV we`ve been tracking is centered
approximately near the I-80 corridor approaching far southwest
Chicago suburbs as of this writing. It may be augmented by
slightly higher than analyzed 25 kt 500 mb winds out of the west-
southwest near the wave center and maybe a bit higher deep layer
shear. That said, still generally sub-marginal shear for
convective organization. Modest mid-level lapse rates, mid and
upper level haze from wildfire smoke topping the fairly extensive
cloud cover over the area has probably limited destabilization
more than shown on SPC mesoanalysis. We`ve still seen enough,
topping out in the 1500 J/kg of MLCAPE range, with the forcing
from the remnant MCV to allow for isolated more robust updrafts
that have thus far necessitated the issuance of a few SPS.
Can`t rule out a rogue severe thunderstorm, though all in all the
main threat is isolated downburst winds from the strongest storms
capable of downing small to medium sized tree limbs. Secondary
threat is hail that might briefly reach marginally severe limits
in the tallest updrafts, though lack of shear and warm/moist
profile portends likelihood of melting before larger hail could
reach the surface.
Turning ahead to later this evening, we`ve been watching the more
well defined wave on satellite pinwheeling over Wisconsin and not
making much southward progress in slow east-southeastward movement
of the mid-level short-wave trough. Overall activity up in
Wisconsin is on the widely scattered side as well. Therefore, as
this wave finally drops southeast later this evening while diurnal
stabilization of the boundary layer occurs, uncertain how much
coverage holds on into far northeast Illinois and then presses
southeast from there. Have noted some more robust CAM solutions
such as the NAMnest, but varies to little/no activity surviving
such as on recent HRRR runs. Given this, opted for PoPs peaking in
chance range into eastern 1/4 or so of the CWA. Would think severe
threat would be minimal at most considering unfavorable time of
night. WPC carried a level 1 marginal risk in their ERO through
tonight- thinking is that heavy downpours could cause localized
ponding on roads, but flooding threat is low unless coverage grows
more widespread than expected this afternoon-early evening and
then tonight.
Attention then turns to a possibly convectively modified short-
wave topping short-wave ridging moving over southern Minnesota
late tonight and then shifting southeast from there. If it doesn`t
maintain a decent convective footprint through the night to
enhance the wind fields and forcing, we`ll be looking at another
day of modest forcing with otherwise gradually rising heights.
A possible area to watch for a localized focus would be near an
expected lake breeze pushing slightly inland Saturday afternoon.
Upper 60s-lower 70s dew point and mid to locally upper 80s temps
point boundary layer environment point toward potential for
MLCAPE to reach or slightly exceed 2000 J/kg. So given little
capping there is likely eroding and convergence from the lake
breeze to aid in lift from the short-wave, could see widely
scattered storms from northeast Illinois into northwest Indiana,
with lower coverage back to the west and southwest. Marginal to
sub-marginal deep layer shear suggests similar threats to today,
mainly downburst winds and possibly isolated instance of
marginally severe hail. Activity should wind down quickly during
the evening as the wave exits southeast and boundary layer
stabilizes, for a warm and muggy overnight period.
Castro
&&
.LONG TERM...
344 PM CDT
Sunday through Friday...
The main story for the upcoming week, especially compared to the
week now ending, will be a return to hot, humid, and more unsettled
conditions. Persistent surface ridging across the SE CONUS will
support a prolonged period of Gulf return flow, to the point where
winds locally may not veer away from southwesterly until beyond the
end of the forecast period. Thunderstorm development in this warm
and moist low level airmass will be influenced by multiple shortwave
passages in a fairly progressive pattern aloft. Timing will of
course need to be adjusted as the days get nearer, but the best
windows for t-storm development at this time appear to be Sunday
afternoon or evening into early Monday afternoon, and then again
later Tuesday into Thursday.
The other concern with this pattern will be high heat indices,
likely exceeding 100 degrees in some locations. These will be
driven in large part by dewpoints well into the 70s, so even some
afternoon cloudiness or filtering of sunlight from smoke may not
suppress the very uncomfortable to borderline dangerous conditions.
Models are suggesting this could be relatively short lived if a cold
front manages to push through by the end of the week and bring
cooler and drier conditions for next weekend.
Lenning
&&
.AVIATION...
For the 00Z TAFs...
The primary aviation weather concerns during this upcoming TAF
period consist of:
* Low confidence forecast for showers and thunderstorms to impact
the C90 TRACON and Chicago-area terminals later this evening
* Threat for some light/patchy fog at outlying airports overnight
(mainly DPA and RFD)
* Additional low chances for showers and thunderstorms late
Saturday morning and again in the afternoon near the lake breeze
* Low chance (~30%) for the lake breeze moving through MDW and GYY
Saturday afternoon
Initial batch of showers and storms continues to push east of the
region into northern Indiana which will result in a lull in
activity across the C90 airspace for the next few hours. Main
feature of note is the complex of thunderstorms across southeast
Wisconsin which has recently shown some southeastward impetus
towards the state line. There is considerable uncertainty
regarding how far south this feature pushes, but trends suggest
convection will likely breach the northern fringes of the C90
boundary through the next 2 hours or so. Confidence in lightning
persisting all the way to the Chicago-area terminals is lower, and
at this time still too low to justify a VCTS or prevailing/TEMPO
mentions. With the 00z offering, have added a TEMPO group for a
northeast wind shift (which times out into ORD/MDW towards about
3z, perhaps a bit sooner) and a mention of VCSH to account for
precipitation entering the local area. We`ll continue to keep an
eye on trends and offer amendments for TS if trends suggest the
likelihood increases.
Otherwise, southwest winds will prevail through the forecast
period, except perhaps at GYY and MDW where there is a low chance
(~30%) that the lake breeze pushes through tomorrow afternoon.
Some patchy BR will be possible (pending convective evolution this
evening) at outlying airports.
While the remainder of the TAFs are precipitation-free, there
appear to be two windows with a non-zero potential for convection:
late morning Saturday (perhaps 16-19z) and again later in the
afternoon (21-01z). Both of these chances are too low to warrant a
formal mention in the TAFs at this time, however.
Carlaw
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&
$$
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Area Forecast Discussion
National Weather Service San Francisco Bay Area
603 PM PDT Fri Aug 6 2021
.SYNOPSIS...Smoke from fires in Siskiyou and Trinity counties
has drifted into the Bay Area today and will continue to impact
the area into tomorrow. Onshore flow during the afternoon and
evenings should help improve air quality. Otherwise, warmer and
drier today with above normal temperatures regionwide. Gradually
cooler and wetter conditions over the coming days and into early
next week, then, warmer and drier late next week.
&&
.DISCUSSION...as of 02:00 PM PDT Friday... Today is significantly
warmer, drier, and hazier than yesterday and is primarily in
response to changes in the synoptic scale flow. Dry, northerly
flow on the lee side of yesterday`s drizzlefest inducing trough is
responsible for transporting smoke from the wildfires (namely
the River Complex, McFarland, and Monument) southward into the
region last night into today. HRRR smoke model data from yesterday
and again today handled the situation admirably, nailing the fact
that most smoke would be suspended aloft at ridgetop level with
lesser concentrations at the lower elevations. Latest airport
ceilometers report overcast smoke deck at roughly 3000-4000 feet
above sea level and the various wildfire webcams confirm that the
thicker completely obscuring smoke is roughly around our higher
hills, ridges, and peaks. That said, smoke is still filtering down
to the lower elevations given fairly weak morning to lunch hour
winds and sinking air aloft. The afternoon sea breeze will
gradually strengthen before peaking by late afternoon to early
evening, and should help to partially improve conditions near the
surface (at the cost of lofting the smoke higher/into the Central
Valley). Latest air quality readings report great air quality
along the coast where the seabreeze has already begun, with lesser
good to fair conditions along the bayshore. Air quality
deteriorates with increasing elevation, so for those located at
500-3000 feet in the surrounding hills, fair to poor air quality
is occurring while poor or worse air quality exists at or above
3000 feet, mainly at ridge level. HRRR smoke model also suggested
some additional low level smoke would filter in from the north to
the North Bay through the day today, and that has begun to occur,
with poorer air quality in the North Bay than elsewhere in the
region.
So, when will the smoke situation improve? Well, we have a couple
of items in our favor that should lead to gradually improving
conditions over time, particularly by tomorrow`s seabreeze. The
first, is that the transport winds that originally brought this
smoke into the region are weaker and less capable to transport
an additional round of smoke towards us in the coming days, so we
mainly will be contending with what is already here. Second, the
onshore seabreeze should strengthen between today and tomorrow,
with the HRRR smoke model suggesting a majority of the smoke
evacuating from the region through the peak of the seabreeze early
tomorrow evening. That said, pockets of smoke are still possible
beyond this, though for most, conditions should improve by then.
Latest indication is that things may continue to worsen for some
until 3-4PM today when the afternoon seabreeze begins to reach its
full strength, and then improving conditions through the rest of
day and into the evening. This lesser smoke intrusion should be a
reminder for all in the area to prepare for what is likely to be
another active fire season and to prepare accordingly. As winds
shift from predominately onshore during the summer to more often
offshore by the fall, it is more likely to see smoke transported
towards our area.
Otherwise, today is significantly warmer than yesterday and one of
the rare summer 2021 days where most locations are warmer than
normal (+3-10 degrees). This is partly due to the aforementioned
drier air entrained into the region yesterday as drier air is
easier to warm and also because the cooling marine layer was less
resilient today. The other contributing factor is that high
pressure to our south expanded closer towards us today, advecting
warmer air towards the region, while also further suppressing the
marine layer.
Looking ahead, smoke aside, each of the next several days into
early next week should feature progressively cooler and less dry
conditions. This is due to the high pressure ridge to the south
retreating in favor of a passing trough to the north. Seasonable
to warmer conditions are then possible through most of next week
in response to building high pressure along our periphery.
&&
.AVIATION...as of 6:03 PM PDT Friday...For the 00z TAFs. The
marine layer is compressed to 800 to 1,000 feet with further
compression possible under additional warming tonight near the
925 mb level. Wildfire smoke will reduce slant range visibilities
through the period. Surface visibilities are reduced /MVFR-IFR/
in wildfire smoke over the interior valleys/mtns of the North Bay,
East Bay and South Bay while afternoon seabreezes closer to the
coastline and the San Francisco Bay within the marine layer are
helping to keep visibilities VFR. Areas of marine layer stratus
and fog are filling back in along the coast late this afternoon.
It`s dry aloft, however fairly water vapor rich air continues
within the marine layer with surface dewpoint temps mainly in the
50s/60. Onshore winds favor the inland transport of stratus and
fog, and as fog mixes with inland surface smoke overnight may tend
to form dense fog with visibilities reducing to 1/4 mile or less.
Dry air aloft, radiational cooling, stable weather conditions
tonight also favor spontaneous formation of fog farther inland on or
mix with nongaseous particles such as smoke and haze, similar to
evaporated sea salt spray which doesn`t necessarily need 100%
humidity or air mass saturation for fog to form. May also see patchy
light coastal drizzle tonight and Saturday morning. Just a heads up,
could be a challenging night and morning ahead, have decided to add
VLIFR-IFR to some of the TAFs for tonight and Saturday morning.
Depending how fog/smoke/haze coverage develops tonight and Saturday
morning clearing Saturday could be a slow process.
Vicinity of KSFO...VFR with a west wind near 15 knots possibly
gusting to 20 to 25 knots until 04z this evening. Generally good
visibility along the immediate coastline this evening then smoke,
haze, and maybe fog reducing the visibility and ceiling to IFR by
11z Saturday. West wind through the period which should help bring
back VFR to SFO by late morning Saturday.
KSFO Bridge Approach...Similar to KSFO.
Monterey Bay...It`s VFR except patchy IFR ceilings are developing
around the Monterey Bay. Increasing coverage of IFR through the
evening, ceilings and vsbys lowering to VLIFR-IFR in fog. Light
patchy drizzle also possible late tonight and Saturday morning.
Conditions improving to MVFR-VFR late Saturday morning and
afternoon. IFR cigs/vsbys due to stratus and fog likely returning
Saturday evening and night.
&&
.MARINE...as of 01:08 PM PDT Friday...Continued breezy to locally
gusty northwest winds across the coastal waters through this
evening. Expect coastal jets to develop this afternoon north of
Point Reyes, between Pigeon Point and Point Pinos, and south of
Point Sur. Additionally, gusty westerly winds are anticipated
once again through the Golden Gate gap and into the Delta. The
sea state remains dominated by steep short period northwest waves
at 5 to 8 seconds along with a moderate period southerly swell.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
.Tngt...SCA...SF Bay until 9 PM
SCA...Mry Bay until 9 PM
SCA...Pigeon Pt to Pt Pinos 0-10 nm until 9 PM
SCA...Pt Arena to Pigeon Pt 10-60 nm
SCA...Pt Reyes to Pigeon Pt 0-10 nm until 3 AM
SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm until 3 AM
SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm until 3 AM
SCA...Pt Arena to Pt Reyes 0-10 nm
&&
$$
PUBLIC FORECAST: DRP
AVIATION: Canepa
MARINE: Lorber
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Area Forecast Discussion
National Weather Service Las Vegas NV
750 PM PDT Fri Aug 6 2021
.SYNOPSIS...Dry and breezy conditions to prevail today due to an
upper level shortwave passing to the north. This will also serve
to provide some temperature relief through early next week. Moving
through next week, monsoonal moisture may be returning with shower
and thunderstorm chances on the rise.
&&
.UPDATE...Smoke from the western wildfires has begun to move into
the Las Vegas Valley. Desert Rock has been reporting a visibility
of 3 miles for the past few hours, and the last visible satellite
images of the evening show the leading edge making of it into the
Centennial Hills area. The 00Z HRRR run shows it continuing to
spread into the valley overnight before thinning out some on
Saturday, and the short term grids have been updated to indicate
this. The remaining periods of the forecast look to be on-track and
no other updates were needed at this time.
&&
.PREV DISCUSSION...
146PM PDT Fri Aug 6 2021
.SHORT TERM...Tonight through Monday.
Breezy winds across northern Mohave this afternoon will diminish
this evening and overnight. Expecting lighter winds for the weekend
as the shortwave that generated the increased winds moves away from
the region. In general, expecting near normal temperatures and clear
skies through the weekend into Monday as zonal flow sets up aloft.
Will need to monitor the smoke situation as smokey skies may persist
at times through at least tonight before northwest winds become more
westerly, which might be a less favorable trajectory for smoke to
overspread the region.
.LONG TERM...Tuesday through Friday.
The forecast is starting to become a bit clearer for next week,
though a lot of uncertainty still remains. In general, it seems
models continue a more active weather pattern starting Tuesday. The
flow becomes more southerly late Monday, which should help push at
least modest moisture into the region by Tuesday. There still
remains some uncertainty to how much moisture will work its way up
the Colorado River Valley into southern Nevada and Mohave County as
models continue to show a differing picture of PWAT values and how
far north moisture will push. It can be said at least at this point,
moisture will not be as high as a few weeks ago with our last round
of monsoon moisture. The most active period next week should be
Tuesday and Wednesday. Thursday and Friday may see a slight decrease
in thunderstorm coverage as models show the main high shifting west
and causing the southerly flow to become squirrely for a period.
Dont think there will be no thunderstorms on Thursday or Friday,
but they may just be less numerous than Tuesday and Wednesday.
Looking ahead...next weekend may be active. The flow looks to become
more southerly again and could link up to deep moisture off the
Mexican coast. Models show PWATs that are higher than what we will
see most of next week, so this might be the most active period with
highest threat for monsoon impacts through the next 14 days. Will
continue to watch this potential for deep monsoonal moisture as
everything will need to line up right in order to tap into that
better moisture pool. Stay tuned!
&&
.AVIATION...For McCarran...Winds should subside by sunset and return
to more typical diurnal overnight trends. Tomorrow morning smoke
from California wildfires are likely to make it into the terminal
area and reduce visibilities. Worst case scenario would create IFR
conditions if smoke is thick enough. The More likely conditions
would see some reduced visibility down to MVFR.
Visibilities will improve as the atmosphere mixes in the later
morning. Otherwise no other aviation concerns of note.
For the rest of southern Nevada, northwest Arizona and southeast
California...The primary issue is smoke from wildfires in
California. This smoke layer has been working south through the day
and is now reducing visibilities north of a line from KDAG to KSGU.
For the most part conditions are MVFR or above. That smoke will push
further south overnight affecting more terminals. Conditions in
areas where the smoke is thicker could create IFR conditions for
short periods of time in the early morning. Visibilities will
improve as the atmosphere mixes in the later morning. Otherwise no
other aviation concerns of note.
&&
.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather or impacts according to standard operating
procedures.
&&
$$
UPDATE...Planz
DISCUSSION...Nickerson
AVIATION...Lericos
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