Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/10/21

Area Forecast Discussion...UPDATED

National Weather Service Albuquerque NM

553 PM MDT Mon Aug 9 2021

.AVIATION...
00Z TAF CYCLE
VFR conditions expected at all TAF sites through the next 24 hours.
The only exceptions would be smoke from western fires dropping the
vsby to 5SM. Also, spotty showers and thunderstorms this evening
over the Southwest and South Central Mountains and adjacent highlands
may briefly drop the vsby and/or cigs to MVFR. Most of the activity
will end around 06Z. Saturday`s crop of showers and thunderstorms
will be noticeably more with isolated to scattered storms, except
numerous showers and storms in the Southwest and South Central
Mountains.

.PREV DISCUSSION...152 PM MDT Mon Aug 9 2021...
.SYNOPSIS...
Above normal temperatures will persist through Tuesday, with chances
for showers and thunderstorms favoring locales south of Interstate
40. Moisture will increase across the area from mid week through the
weekend, bringing back a more typical Monsoonal pattern with
improved chances for showers and thunderstorms. Daytime temperatures
will trend down from mid week on due to increased cloud cover and
potential rain cooling.

.DISCUSSION...
SHORT TERM...(TONIGHT THROUGH TUESDAY NIGHT)...
Water vapor imagery this afternoon shows mid-level moisture
streaming northward, and this can also be seen on the 12Z ABQ
sounding where the PWAT trended up to 0.59". Still, lower-levels
remain quite dry with dewpoints in the 20`s and 30`s north of I-40
and in the 40`s south of I-40. With a weak disturbance over
southeast AZ, this combined with the somewhat better moisture has
allowed for isolated showers and storms mainly across the southern
half of the area. This will continue through late this evening, but
gusty outflow winds will be more common than beneficial wetting
precipitation. With southerly flow in place across the area, smoke
impacts should lessen as the evening progresses. HRRR smoke model
shows continued improving conditions as well with perhaps some smoke
or hazy skies continuing across north central and northeast NM.

The aforementioned disturbance over southeast AZ moves northward
into central NM on Tuesday as a upper-level trough tracks through
the central Rockies. This continues to draw mid-level moisture
northward with PWATs at ABQ expected to rise to around 0.90" by
Tuesday evening. Dewpoints also continue to recover across southern
NM where upper-40`s to 50`s are expected, however, dewpoints will
still remain low across the northern half of the area. This
disturbance moving into central NM will allow for greater coverage
of shower and thunderstorm activity while temperatures begin to
trend down under increased cloud cover.

LONG TERM...(WEDNESDAY THROUGH MONDAY)...
A more typical Monsoon pattern will develop from mid to late week as
the upper high becomes centered over the Great Basin, allowing the
uptrend in PWATs to continue. Expect an increase in coverage and
intensity of storms during this period, with a downtrend in daytime
temperatures to at or slightly below normal. The 12Z medium range
model solutions differ some by Friday with the strength and
orientation of the upper ridge across the Intermountain West and an
inverted trough creeping westward across our area, leading to
slightly different placement of qpf maxima. Regardless, we`re
carrying good chances for convection through the weekend and into
Monday, with locally heavy rainfall and associated flash flooding
being the primary threat. The synoptic pattern may be favorable for
the import of tropical moisture early to mid next week given the 12Z
medium range model solutions showing a potent west coast trough and
the development of what would be Hurricane Linda in the far eastern
Pacific. We`re getting into the time of year (mid Aug thru Sep) where
picking up tropical moisture from the eastern Pacific fits nicely
into our climatology.

15/11

.FIRE WEATHER...
Precipitation chances will gradually trend upwards starting Tuesday
as moisture moves into the area from the south. While storm coverage
trends up across the area Tuesday, wetting precipitation will mainly
favor southern NM. But as moisture continues to stream into the area
through the end of the week, chances for wetting precipitation will
increase each afternoon. Temperatures will also trend down and are
expected to be near normal areawide by the end of the week.

.ABQ WATCHES/WARNINGS/ADVISORIES...
None.

Area Forecast Discussion

National Weather Service Dodge City KS

1032 PM CDT Mon Aug 9 2021

...Updated Aviation...

.SHORT TERM...(This evening through Tuesday)
Issued at 152 PM CDT Mon Aug 9 2021

A moist surface layer this morning characterized by dew points
around 70 degrees F or a little higher over the lower plains and in
the 60s farther west is part of the forecast challenge this
afternoon. The HRRR model has shown some run to run consistency in
waiting until around the 19-20Z time window for a more dramatic
mixing out of the surface dew point, in effect keeping the bulk of
the area out of any excessive heat due to elevated heat indices. The
surface dew points look to mix out rapidly once the near surface
lapse rates begin steepening rapidly.

There is a synoptic cold front hanging from north central CO across
northwest Nebraska into northeast South Dakota. Ahead of the cold
front is a general area of surface toughing across southwest
Nebraska into northwest Kansas where the convective allowing models
erupt convection later today. The general trend is for slow moving
multicells to generate enough outflow over NW KS for the outflow to
reach the west central Kansas counties (areas from Lakin eastward)
no earlier than midnight. As a result of the outflow, a few new
generated clusters may happen beyond that point impacting mainly
the I-70 corridor.

A mid level wave will be moving across the northern plains during
the period, driving and 850 mb/surface cold front southward across
western Nebraska into Kansas. The boundary doesn`t move clear
through the forecast area, however will become the main areas of
focus for convective development layer in the afternoon Tuesday,
if not possibly earlier. There is a notable mid level jet in the
models immediately north of our area in all of the models which
will result in better effective shear moving norther across the
area. The north east sections of the forecast area are under a
slight risk with wind a hail risk, while locations out toward
Syracuse are probably under the least risk Tuesday afternoon.

.LONG TERM...(Tuesday night through Monday)
Issued at 248 PM CDT Mon Aug 9 2021

BY sometime Friday, another frontal boundary should be moving toward
our forecast area or at least into the KS/NE line area. This should
be a low level moisture pooling and temperature front to support
additional rounds of severe thunderstorms across the central Plains
despite an overall lack of strong deep shear. This period also
is noted with a lack of the very hot downslope temperatures off
the higher terrain like we`ve seen this last weekend. Temperatures
by next weekend may be much closer or even slightly cooler than
normal with abundant cloud cover days. The models are in very good
agreement on highs in the 80s overall during the period.

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1032 PM CDT Mon Aug 9 2021

VFR/SKC will continue tonight with S/SE winds near 10 kts. A
modest low level jet will continue through sunrise, and continued
a mention of LLWS in all TAFs. VFR will continue to prevail
Tuesday, with scattered cumulus expected by afternoon as a weak
cold front sags into SW KS. The boundary will be accompanied by a
weak NEly wind shift, and is expected to be from near/south of
HYS to near LBL by 00z Wed. Isolated convection is expected near
this boundary at peak heating, but confidence with direct airport
impacts is very low. Only mentioned VCTS/CB, and only at HYS,
for now. After 15z Tue, SW winds will gust over 20 kts at LBL,
GCK, and DDC ahead of the approaching boundary. A NEly wind shift
was included at HYS, but south winds will continue to prevail
south of the stalling boundary.

.PRELIMINARY POINT TEMPS/POPS...
DDC 74 102 71 99 / 0 20 20 10
GCK 68 100 67 99 / 0 10 10 10
EHA 70 99 67 98 / 0 20 20 10
LBL 71 101 68 99 / 0 20 20 10
HYS 70 99 70 100 / 10 10 10 10
P28 77 104 76 101 / 10 20 20 10

.DDC WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

SHORT TERM...Russell
LONG TERM...Russell
AVIATION...Turner

Area Forecast Discussion

National Weather Service Duluth MN

944 PM CDT Mon Aug 9 2021

.DISCUSSION...(This evening through Sunday)
Issued at 449 PM CDT Mon Aug 9 2021

Summary: Showers and thunderstorms are possible tonight through
Tuesday as a cold front sweeps through the region. A second round
of showers and general thunderstorms are possible along the
International Border Wednesday as well. A dry forecast is in store
for the rest of the work week and weekend.

A shortwave positioned over Saskatchewan will move east
overnight. The associated cold front is expected to bring showers
and thunderstorms across the Northland tonight through Tuesday.
Although the environment is more favorable to our west, some
severe storms are possible in north central Minnesota during the
late night and early morning hours, with strong winds and large
hail being the primary threats. The RAP model shows MUCAPE values
above 1000 J/kg should be sustained overnight due to a LLJ
transporting warm, moist air into the region. Wind shear
immediately ahead of the cold front should be weak to moderate at
25-35 kts.

Thunderstorms are expected to increase in intensity again Tuesday
as we head into the afternoon. Again, more favorable environment
will be outside of our area, but increased instability in the 2000-
4000 J/kg range could cause scattered severe thunderstorms in
northwestern Wisconsin throughout the afternoon evening. Again,
strong winds and large hail will be the main threats. Precipitable
water above 2 inches indicates some local flash flooding in low
lying areas, creeks, and streams.

After the first shortwave moves off to the east Tuesday night, a
secondary, weaker shortwave will move through on Wednesday. This
will bring another line of rain showers through the Northland,
especially near the International Border. Light accumulations are
expected from this system.

Friday, the trough in Canada will move south over the upper Midwest,
transporting some cooler air into the Northland for Friday and
Saturday. Afterward, a ridge moves into the area and temperatures
warm once more for the remainder of the weekend and into the work
week.

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 704 PM CDT Mon Aug 9 2021

VFR conditions are expected to continue through the evening hours
across the region. There is a weak front near the INL airport
terminal, so there is a small chance for a shower or thunderstorm
over the next few hours. Attention then turns to another night of
fog, especially closer to Lake Superior due to the marine layer
/low-level thermal inversion redeveloping. IFR/LIFR visibility
reductions due to fog are possible for DLH, HIB, and HYR, along
with some LIFR ceilings. Fog isn`t expected to be quite as
widespread compared to last night, but some locally dense fog is
still possible, especially near Lake Superior. A cold front is
then expected to sweep from west to east during the late morning
and early afternoon hours Tuesday. Chances of showers and
thunderstorms will increase along the front, which will help scour
out the fog and low stratus. Winds will turn more westerly behind
the front and strengthen, with gusts to around 20 knots.

.MARINE...
Issued at 944 PM CDT Mon Aug 9 2021

Another night of dense fog is expected for this evening through
the overnight hours across western Lake Superior. Already this
evening, visibilities at the Duluth Harbor canal, as well as
multiple locations along the South Shore, are already reporting
visibilities of 1 nautical mile or less. We have bumped up the
start time for the Dense Fog Advisory to begin as of 9 PM CDT
across the South Shore. Dense Fog Advisory from Silver Bay north
towards Grand Portage will begin later, at 1 AM CDT. This advisory
remains in effect through 10 AM CDT Tuesday morning across western
Lake Superior, including the open waters. Late tonight, a cold
front will sweep from west to east across the region, making its
way over western Lake Superior sometime in the late morning hours,
lasting into the afternoon. Chances of showers and thunderstorms
will increase along the front, some storms could be strong to
severe, capable of large hail and strong wind gusts. The front
should exit the region around mid to late afternoon Tuesday.

.PRELIMINARY POINT TEMPS/POPS...
DLH 64 85 63 81 / 20 30 10 10
INL 65 80 59 77 / 40 10 40 20
BRD 66 84 63 81 / 60 10 10 0
HYR 61 85 60 83 / 20 40 10 20
ASX 62 88 62 86 / 0 40 10 20

.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...Dense Fog Advisory until 10 AM CDT Tuesday for LSZ121-143>148-
150.

Dense Fog Advisory from 1 AM to 10 AM CDT Tuesday for LSZ140>142.

DISCUSSION...Kossen
AVIATION...JTS
MARINE...JTS

AREA FORECAST DISCUSSION

National Weather Service Eureka CA

400 PM PDT Mon Aug 9 2021

.SYNOPSIS...Warmer interior temperatures will return on Tuesday
and continue through the rest of the work week as high pressure
builds in. Later in the work week there is a slight chance of
thunderstorms over the interior, mainly in Trinity County.

.DISCUSSION...Smoke and haze from the active wildfire in Trinity
County spread out toward the north coast early this morning, and
retreating a bit during the afternoon. This thick smoke aloft is
about 3000 to 5000 feet above mean sea level. HRRR model guidance
indicates smoke will spread back to the coast early Tuesday
morning to bring another hazy day north of the highway 36.
A southerly wind reversal aided coastal stratus in forming along
the Mendocino coast this morning. The Bodega Bay profiler
indicates the marine layer depth is around 2000 feet. A shallower
marine layer and stratus are expected to develop along the Redwood
coast.

High pressure rebuilds over the area on Tuesday. This will remain
the marine layer fairly shallow through the work week as a strong
low- level inversion returns due to a rebuilding upper high
pressure ridge. The ridge will support to hotter temperatures
across the interior, and the Excessive Heat Watch continues in
place. There is a bit of uncertainty regarding the coverage and
opacity of smoke over those areas. High temperatures could
potentially be several degrees cooler in areas of thicker smoke,
and persistent smoke could allow long wave radiation to escape at
night, further reducing the heat risk. Otherwise, the stronger
warming signal looks over north of our area.

Mid and upper level monsoonal moisture is forecast to increase from
the S across the interior late in the week. Enough elevated CAPE is
expected to be present on Thursday and Friday afternoons to support a
dry thunderstorms across portions of Trinity County. /SEC&ZVS

.AVIATION...North of Cape Mendocino, the marine layer was quite shallow with
patches of stratus. Mostly Vis restrictions dropped CEC into IFR
conditions. However, a thick smoke layer advected to the Coast from
inland and resulted in Smoke (FU) layers producing low level CIGS
from 2300-5000 feet. Expect the lower FU layer to mostly scatter in
the afternoon. Along the Mendocino Coast, the marine layer was
strong and intrusive...and is surging towards the Cape. Weak
northerlies will hamper the progression north of Cape Mendocino
today. Even so, stratus will somewhat regroup along the Redwood
Coast tonight and impact ACV and CEC. Inland areas will remain
mostly cloud free, but visibilities due to smoke from wildfires will
impact interior airports/airstrips especially in Trinity, Del Norte
and mainly Eastern Humboldt. /TA

.MARINE...Conditions are forecast to remain hazardous for small
crafts in the outer waters tonight as steep waves persist in
response to robust northerly winds. A warning for Hazardous Seas has
been extended for the outer waters where NWPS has seas reaching 11
to 13 ft tonight. Conditions will begin to subside on Tuesday as a
nearshore southerly wind reversal expands north of Cape Mendocino.
Lighter winds and lower seas are expected for mid to late week as
gradients relax as an offshore upper low approaches the coast.

.FIRE WEATHER...Dry daytime RH values will continue across Trinity,
E Mendocino, and Lake counties. RH recoveries will be slightly
worse through the remainder of next week, with minimum humidities
not rising out of the 30-40% range in many interior areas. Winds
will be generally light and terrain driven, with periods of gusty
northerlies along the coast through early next week. Monsoonal
moisture will spread northward by Thursday and bring a slight
chance of thunderstorms to mainly Trinity County through Friday.
At this point, storms are forecast to be dry with very little or
no rain. /SEC&ZVS

.EKA WATCHES/WARNINGS/ADVISORIES...
CA...Excessive Heat Watch from Wednesday afternoon through Thursday
afternoon for CAZ107-108-110-111-113>115.

NORTHWEST CALIFORNIA COASTAL WATERS...Hazardous Seas Warning until 11 AM PDT Tuesday for PZZ470.

Small Craft Advisory until 6 AM PDT Tuesday for PZZ450.

Hazardous Seas Warning until 3 AM PDT Tuesday for PZZ475.

Visit us at https://www.weather.gov/eureka

For forecast zone information
see the forecast zone map online:
https://www.weather.gov/images/eka/zonemap.png

Area Forecast Discussion

National Weather Service Grand Forks ND

1018 PM CDT Mon Aug 9 2021

.UPDATE...
Issued at 1016 PM CDT Mon Aug 9 2021

T-storms moved thru NE ND and into the nrn RRV as scheduled but
have yet to see any development south into SE ND as HRRR insists
will occur. Did lower pops some in the south but kept them in the
chance range. Storm moving into Grand Forks is the same one from
earlier and has been supercellular ever since development.
Instability is starting to wane and will do so thru the overnight
into NW MN. Confidence in southern RRV and west central is rather
low attm in terms of it storms will form.

UPDATE Issued at 648 PM CDT Mon Aug 9 2021

2330z analysis shows sfc low just south of Devils Lake and is
moving east-northeast and is progged to move east-northeast toward
Grafton-Hallock area by 05z. Surface warm front from about Red
Lake MN west to Crookston to just south of Grand Forks then to
suface low between New Rockford and Devils Lake. 500 mb wave in
southeastern Saskatchewan moving northeast and main jet dynamics
and 50-60 kt effective bulk shear indicate region from DVL into NE
ND. HRRR indicates development south along front toward Jamestown
01-02z period but uncertainty in this attm. Storm has been going
on west of Lamoure for some time, but that area has less shear and
less development potential attm.

.SHORT TERM...(This evening through Tuesday night)
Issued at 327 PM CDT Mon Aug 9 2021

Weather related impacts are possible through the remainder of the
afternoon and evening, possibly into the early overnight hours. A
potent upper low is moving into an increasingly moist and unstable
environment this afternoon in eastern North Dakota, northwestern and
west-central Minnesota. Strong to severe thunderstorms are expected
to form this afternoon to the west of the area, then push through
the region through early Tuesday morning.

Scattered showers are moving out of the Devils Lake Basin at midday,
with clearing just to the west. Further south, a boundary is draped
along the Highway 200 corridor in North Dakota. This boundary has
been pushing to the south through the morning, but is currently
stalled; this boundary is expected to lift slowly northward through
the afternoon hours. It is along the zone of interaction along this
boundary, that we could see severe thunderstorms develop during the
mid to late afternoon. Forcing is rather strong thanks to an
approaching upper low. Ahead of the low, we are seeing moderate
instability with CAPE in the range of 1500 to 2500 J/Kg.

For today`s severe threat, there will be two different phases of
development. Initially, there will be a risk for supercell activity
through the Devils Lake Basin and the northern Red River Valley.
This will bring the risk of large hail, wind gusts up to 75 mph and
possibly a tornado. This phase of the event is expected to be
relatively short-lived, with more of a linear mode forming further
to the south and east. Once the line forms, the chance for wind
gusts looks to be the primary concern, along with a chance for a
brief tornado or two.

.LONG TERM...(Wednesday through Monday)
Issued at 327 PM CDT Mon Aug 9 2021

Quiet and mostly dry weather returns for the long term period.

Wednesday through the weekend...

Following the early week systems, west-southwesterly flow aloft is
expected to shift northwesterly by midweek. The northwesterly flow
aloft then looks to persist as an upper level ridge once again
builds into the Plains through the weekend. Behind the multiple cold
frontal passages from earlier in the week, breezy to windy
conditions and cooler temperatures in the 70s to low 80s are
expected across the latter half of the week. A few spotty showers
will also be possible near the international border on Wednesday
with a quick moving trough tracking eastward, north of the border.
As we move into the weekend, the ridge aloft is then expected to
amplify. This will in turn fuel a gradual warm up back up above
normal for the weekend. There are some analogs indicating that by
late weekend, the upper ridge will begin to erode and reintroduce
more zonal flow to the forecast area. A quick look at cluster
analysis does show a quite a high degree of variability between
ensembles with regards to the potential for the ridge to weaken,
however, and we will continue to monitor these trends moving
forward.

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 648 PM CDT Mon Aug 9 2021

VFR conditions outside of t-storms tonight. Low will move from DVL
into the northern RRV by 05z and a cold front will move east thru
the forecast area tonight switching winds to the west-northwest.
NW winds on Tuesday and could be some near MVFR cigs in wraparound
clouds in far NW MN in the aftn.

.FGF WATCHES/WARNINGS/ADVISORIES...
ND...None.
MN...None.
$$

UPDATE...Riddle
SHORT TERM...Lynch
LONG TERM...Rick
AVIATION...Riddle

Area Forecast Discussion...UPDATED

National Weather Service Gray ME

920 PM EDT Mon Aug 9 2021

.SYNOPSIS...
Humid tonight with fog developing along the coast. The trend
will then be toward heat and humidity during the rest of the
work week. The likelihood of widespread showers and storms
increases through the second half of the week, culminating in a
frontal passage either Friday night or Saturday. This should
bring an end to this latest bout of heat with a Canadian airmass
returning temps to near normal this weekend.

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
920 PM Update: Primary changes are to add drizzle along the
coast of ME given evening observations. Also..have increased
shower chances as band of shower activity arcing from FIT to
BOS has been holding together and should bring some showers to
SE NH in agreement with recent HRRR runs. Temperatures look good
through the overnight.

600 PM Update: Have made some adjustments to boost dewpoints and
lower coastal temperatures in line with late afternoon
observations. Also adjusted sky cover to refine area of coastal
stratus. Forecast in good shape for the overnight with VSBYS
likely beginning to fall rapidly along the coast after 8pm in
line with afternoon NARRE-TL and HRRR forecasts.

Previous discussion below...
Onshore flow continues this afternoon into tonight. Some breaks
in the clouds have developed late this afternoon over land, but
expect marine air to remain, leading to developing fog
overnight. Fog will likely be dense in areas, and have issued a
Dense Fog Advisory in anticipation of development. Many forecast
guidance products support the limited visibility tonight,
including many runs of the HRRR.

Precip wise, there may be just enough convergence over the
higher terrain and western mtns for some showers to develop amid
late afternoon heat, but instability is largely absent for more
than an isolated shower.

.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
Fog deteriorates Tues morning, with remaining cloud cover in
the morning tempering daytime highs. The real heat show arrives
in the extended, more on that below.

Tuesday will be dry with S flow. A weakening warm front
advances from the SW during the afternoon, which will deepen a
fairly saturated layer below a temp inversion. Overnight, not
only will this bring back the chance for patchy fog, there may
also be drizzle to mix in. Opted to go against only having
mention of showers due to dryness aloft, and weak forcing.

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Hot and Humid Conditions Expected Wednesday Through Friday...

General pattern in the extended will consist of a sprawling Bermuda
High along the Eastern Seaboard midweek through Friday. This will
lead to well above average temperatures with elevated heat index
values. Relief is expected by the weekend as a 500mb trough
approaches from Quebec on Saturday leading to cooler and less humid
conditions for the end of the weekend. Forecast confidence is above
average in regards to the general synoptic flow.

Southwest flow becomes established by Wednesday kicking out any
remaining marine layer lingering on the coast as offshore flow
becomes dominate. Dewpoints will surge across the entire CWA with a
very sticky airmass as the NBM is showing very little spread
around the 70 degree mark. Confidence continues to increase for
heat advisory levels to be reached across the coastal plain by
Wednesday. Rinse and repeat will be the forecast for Thursday
and Friday with a slight trend up in temperatures on Thursday as
the possible peak in the heat with HI values breaking the
century mark in southern NH and SW ME. The biggest impact for
this heat event will be the longevity of it and the fact that
minimum temps will remain in the 70s for both Thursday and
Friday night. Broad cyclonic flow just to our west will allow
just enough instability aloft to help aid in afternoon
convection each day, with higher props the further north and
west you go. Surface cold front looks to cross the area on
Saturday with more storms, potential for severe weather will be
a good bet based on pattern recognition. A relief is expected
towards the end of the weekend.

.AVIATION /01Z TUESDAY THROUGH SATURDAY/...
Short Term...

Summary: Weak low pressure south of New England and high pressure
over the Canadian maritimes will maintain a moist...onshore flow
across the region through Tuesday with stratus and fog. While this
low will lift north and east of the area Tuesday night...moist
conditions will continue.

Restrictions: Conditions will quickly deteriorate to LIFR along the
coast tonight...with these conditions building inland towards
MHT/CON/AUG overnight with fog developing later further inland at
HIE/LEB. Improvement comes first inland Tuesday morning working it/s
way to the coast during the afternoon with conditions returning to
at least MVFR. Another round of fog/stratus looks like Tuesday
night although it currently looks less widespread/long-lasting than
tonight.

Winds: Calm/light southerly winds overnight will remain southerly
less than 10kts for the day on Tuesday before returning to less than
5kts Tuesday night.

Lightning: No lightning is expected through Tuesday night.

LLWS: No LLWS is expected through Tuesday. Winds around 2kft
increase to 20-25kts from the southwest Tuesday night but currently
look to remain below LLWS thresholds.

Long Term...Wednesday morning IFR conditions could linger along the
coastal TAF terminals but conditions should improve by midday as all
low level stratus will be scoured out of the region with VFR
conditions expected for remainder of Wed. Thursday through Friday
the region will be dominated by high pressure will limited aviation
impacts except for the heat and passing afternoon thunderstorms.

.MARINE...
Short Term...Below SCA criteria, with dense fog tonight. Fog
will again be possible Tuesday evening and overnight.

Long Term...Seas and waves will stay below SCA conditions in the
extended as broad ridging is expected over the coastal waters from
Thursday through Friday. Periods of fog can`t be ruled out as a
moist airmass remains over the waters. Cold front is expected by
Saturday which will bring a period of thunderstorms over the waters
with a wind switch to offshore NW flow.

.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Dense Fog Advisory until 8 AM EDT Tuesday for MEZ018>028.
NH...Dense Fog Advisory until 8 AM EDT Tuesday for NHZ010-013-014.
MARINE...None.

$$
SYNOPSIS...
NEAR TERM...Arnott
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...

Area Forecast Discussion

National Weather Service Indianapolis IN

1126 PM EDT Mon Aug 9 2021

...Updated Aviation Discussion...

.Forecast Update...
Issued at 945 PM EDT Mon Aug 9 2021

Surface analysis this evening shows high pressure in place over the
southeastern states...allowing a continued flow of warm and humid
air into the Ohio Valley. Water Vapor showed a short wave over Lake
Michigan...triggering showers and thunderstorms over Northern
Illinois. A stray thunderstorm over southern Illinois was
dissipating with warming tops on GOES16. Dew point temps remained in
the lower 70s.

HRRR overnight shows the showers/storms to the north west becoming
elongated...weakening and sagging into northern Central Indiana as
the associated short wave is expected to pass across the Great
Lakes. Thus have followed that game plan for the overnight hours as
daytime heating has been lost. Will keep some small pops in the LAF
and OKK areas for a few hours after midnight. Given the lack of a
trigger for showers and storms across the southern parts of the
forecast area and the waning convection there...have removed all
pops overnight across the south. Low temps in the lower 70s seem
reasonable given the current dew point temps.

.Short Term...(This evening through Tuesday night)
Issued at 310 PM EDT Mon Aug 9 2021

DEWPOINTS OVER 75F TO PUSH HEAT INDEX VALUES TO NEAR 105F ACROSS
WESTERN CENTRAL INDIANA TUESDAY

Hot and very humid conditions will be the defining feature of the
short term period, although given this tropical-like environment,
the potential for severe weather will also be present. Lack of any
decent shear and quite high freezing levels will limit severe
threats to mainly damaging winds. With the generally mid-level
zonal flow failing to provide any organized forcing aloft, only
isolated/ scattered convective coverage is expected through the
period. However, inordinately high dewpoints amid above normal
temperatures will lead to MLCAPE values on Tuesday quickly pushing
to around 2000 J/kg by 18z...and 3000-4000 J/kg by late day,
especially over western and northwestern counties. So what does pop
should have no problem with vertical development, nor bringing
strong to perhaps severe winds down to the surface. Slight risks
through Day 2 appear reasonable given the potential theta-E. Given a
north-south gradient in precipitable water values from around 1.50
inches across northern zones to over 2.00 inches along the south
counties will promote greater flash flood threat across southern
counties...especially for the few areas that already saw greater
rains (0.50-1.50") earlier today.

While not all locations are expected to see strong thunderstorms...
the entire region will be subject to dewpoints in the mid 70s to
occasional upper 70s. Despite readings only peaking around 90F
Tuesday, heat index values will peak in the upper 90s to mid-
100s...with values near 105F for much of the afternoon and early
evening along the Wabash Valley/western counties...so felt Heat
Advisory was reasonable for these zones. Temperatures will drop
slowly to the 70-75F range tonight...rebound to 87-93 Tuesday...and
only reach the mid 70s Tuesday night.

.Long Term...(Wednesday through Monday)
Issued at 300 PM EDT Mon Aug 9 2021

A couple of vort maxes moving through a larger upper trough will
move through central Indiana Wednesday. The initial area of lift
moves through during the morning, and at that point there will be
some elevated instability available but little at the surface. 850
mb winds will only be around 15 to 20 kts out of the southwest, and
the upper jet will be off to the northwest, so looking at morning
showers with some embedded storms possible.

By Wednesday afternoon, though, the right entrance region of the
upper jet is approaching, and 850 mb flow increases as well. If
clouds from the morning showers can scatter out, instability will be
able to ramp up. Shear will be marginal, but given the potential for
a little help in the forcing department from a low level and upper
jet think there is some potential for severe on Wednesday afternoon
into the evening. With precipitable water values remaining high,
heavy rain and localized flood potential will be there as well.

Just how hot Wednesday and Thursday will wind up will be highly
dependent on if clouds can scatter out. Don`t expect the heat
potential to drop off until the cold front passes sometime on Friday.

In regards to the cold front, that and an upper wave moving through
northwest upper flow on Friday will bring additional chances for
showers and storms to the area, with the front providing additional
organization to the system. High pressure will then move in at the
surface later Friday night and move through during the weekend,
bringing dry weather back to the area and cooler (closer to normal)
temperatures.

.Aviation...(06Z TAF Issuance)
Issued at 1125 PM EDT Mon Aug 9 2021

IMPACTS:
- VFR Conditions are expected at most TAF sites.
- Isolated convection may is possible at LAF overnight
- Winds generally from the south at 8-13 kts

DISCUSSION:

An upper wave moving through the Great Lakes will depart the region
overnight...allowing ridging aloft to arrive in the area on Tuesday.
HRRR suggests convection over northern IL may brush LAF
overnight...but confidence is low in that as best forcing continues
to push across the Great Lakes. Thus have used VFR Cigs much of the
night but have included a brief window of VCTS at LAF. Any TSRA
that strikes a Taf site could cause brief MVFR/IFR Cigs.

A return to VFR is expected on Tuesday as the overnight wave departs
and ridging builds aloft. Forecast soundings show convective
temperatures in the lower 90s and dry air arriving within the mid
levels. Thus any CU development and/or TSRA development would be
late in the day. Again confidence for specific timing is low. Given
dry air expected within the mid levels...confidence for development
is low. Thus have just kept Tuesday VFR for now.

.IND WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from 1 PM to 8 PM EDT Tuesday for INZ021-028-029-
035-043-044-051-060-067.

Update...Puma
Short Term...AGM
Long Term...CP
Aviation...JP

Area Forecast Discussion

National Weather Service Northern Indiana

730 PM EDT Mon Aug 9 2021

.SYNOPSIS...
Issued at 320 PM EDT Mon Aug 9 2021

There is a chance for severe thunderstorms tonight, especially
toward northwest Indiana. There is an additional risk of severe
storms Tuesday night. Heat and humidity continues through Thursday
with heat indices topping 100 degrees.

.UPDATE...
Issued at 648 PM EDT Mon Aug 9 2021

We continue to monitor the line of thunderstorms moving slowly
through northern Illinois. On one hand, the severe thunderstorm
risk locally appears to be waning some. This is due to the mixed-
layer cap currently in place, paired with lackluster mid-level
lapse rates, and favored right-flank (storm relative, thus
the western edge) development of future storms. On the other hand,
0-6km shear is forecast to be 30kts or more early tonight which
will help maintain this line. Furthermore, the aformentioned cap
is forecast to mix out some, likely in response to the stout
trough aloft. However, the trough is forecast to move nearly due
east while the line of storms is to forecast to drop SE away from
the upper-level support.

Overall, I`ll be slowing down the POPs for this evening and
continuing to weight the pros and cons of this severe weather
setup. Storms could arrive in our far northwest in the window of
9 to 11 PM EDT.

.SHORT TERM...(This Evening through Tuesday)
Issued at 320 PM EDT Mon Aug 9 2021

An upper level low pressure system moves from Wisconsin into
Michigan between this afternoon and tonight. This is expected to set
off showers and thunderstorms after some recovery from morning
convection. The main focus for storms is expected to be a boundary
moving east and southeast from IL affecting areas especially west
of IN-15, but could extend farther east. There is some question
about if storms will be able to last through Lake MI as per the
NAMNest and 15z HRRR run, but will include some PoPs downstream of
the Lake in case it does. As it reaches our northwest counties
from Berrien south to White between 22z and 2z, storms will be
able to tap into 2000 to 4000 J/kg of SBCAPE as well as 30 kts of
effective shear. DCAPE ranges between 750 and 900 J/kg allowing
for a damaging wind gust potential especially since 0-3 km max
theta-e difference reaches 25C. The effective shear surpassing 30
kts, effective helicity surpassing 200 m2/s2, and LCLs below 1000m
increases the threat for a tornado with the storms coming in
especially if there are breaks in the line similar to a QLCS-type
set up. With PWATs above 1.8 inch, 850mb dewpoints above 10C, and
some large scale forcing to work with, storms will be able to
produce locally heavy rainfall, especially if training storms can
occur with boundary parallel flow. However, the storm motion is
expected to be quick enough and the antecedent conditions dry
enough to reduce the overall flood threat. Mid level lapse rates
may leave storms wanting as they only reach 5.5 to 6 C/km, but the
shear should be able to compensate allowing for at least some
sort of a severe hail chance.

Showers and storms may continue after midnight mainly east of IN-15
as SBCAPE stays over 1000 J/kg, but they will be on the downturn as
they encounter the NW OH area. The resulting cloud cover and the
continued humidity will provide a floor to the overnight lows
allowing them to fall into the low 70s to upper 60s.

Height rises follow as ridging is introduced for Tuesday morning and
into the first portion of the afternoon likely suppressing any pop-
up thunderstorm activity until the evening time frame. This will
allow more time to receive needed heat to achieve heat headlines
with heat indices rising up towards 100 in all locales and near 105
in our southwest. Have highs reaching 90 in many locations and the
low 90s in our southwest and within NW OH with low to mid 70 dew
points abounding.

The thunderstorm chances arrive between 21z and 03z in the
northwest, Tuesday, as storms fire along an outflow boundary and
form into a linear structure. Mid level lapse rates rise to between
6.5 and 7 C/km as soundings indicate dry mid levels, a set up
indicative of an EML. With marginal shear and helicity, but very
high 3 to 5 kJ/kg SBCAPE, storms will bring the threat for damaging
winds and large hail as they enter.

.LONG TERM...(Tuesday Night through Monday)
Issued at 320 PM EDT Mon Aug 9 2021

The warm advection pattern continues for Wednesday with minimal
forcing noticeable in the mid levels. As such, we`ll need to
watch for left over boundaries and MCVs. We`ll still have plenty
of instability to work with, as well as marginal shear, and
potentially some 7C/km mid level lapse rates so damaging winds and
large hail would be the main threat. A little warmer 850mb temps
than Tuesday on Wednesday in this warm advection pattern may allow
a second day of heat headlines with many area`s heat indices
rising above 100 as long as those thunderstorm chances hold off.

We have another day of high heat (90 degree Ts and 98-105 heat
indices) and storms on Thursday before the cold front pushes through
later Thursday night into Friday morning time frame. The weekend
looks dry and cooler with highs in the low to mid 80s and dew points
in the low 60s.

.AVIATION...(For the 00Z TAFS through 00Z Tuesday Evening)
Issued at 724 PM EDT Mon Aug 9 2021

Confidence is medium during this TAF period. Leftovers from the
line of thunderstorms over northern Illinois at this time are on
pace to arrive at KSBN in the 03-05z window. Current trends and
model data favor the line weakening, so this is not quite a slam-
dunk. It is unlikely that this line survives to KFWA, but some
lingering instability aloft and outflow boundaries could spark
some scattered storms tonight. MVFR ceilings may slip in later
tonight at both sites in response to moist return flow followed by
improving conditions later in the morning. Additional storm
chances reside at the tail end of this TAF period.

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Heat Advisory from noon EDT /11 AM CDT/ to 8 PM EDT /7 PM CDT/
Tuesday for INZ003>009-012>018-020-022>027-032>034.

MI...Heat Advisory from noon to 8 PM EDT Tuesday for MIZ077>081.

OH...Heat Advisory from noon to 8 PM EDT Tuesday for OHZ001-002-004-
005-015-016-024-025.

LM...NONE.
&&

UPDATE...Brown
SYNOPSIS...Skipper/Brown
SHORT TERM...Roller
LONG TERM...Roller
AVIATION...Brown

Visit us at www.weather.gov/iwx

Follow us on Facebook...Twitter...and YouTube at:
www.facebook.com/NWSNorthernIndiana
www.twitter.com/nwsiwx
www.youtube.com/NWSNorthernIndiana

Area Forecast Discussion

National Weather Service Key West FL

1016 PM EDT Mon Aug 9 2021

.DISCUSSION...
CIMSS MIMIC TPW reveals the Florida Keys are in a large swath of
drier air. The 00Z KEY RAOB highlighted this drier air by
recording a PW of 1.89 inches, in comparison to this morning`s
2.13 inches. There was still ample CAPE and little inhibition in
this environment, as also shown by this evening`s sounding. Most
of the convection this evening has remained in the offshore Gulf
Waters, with only isolated showers and thunderstorms traversing
across the Straits of Florida. The island chain has remained
mostly dry through the evening. The subtropical ridge is currently
building into the region, with the associated ridge currently
sitting over Central Florida. This is supporting primarily
moderate breezes across the Keys and coastal waters. Wind
observation platforms are currently recording winds ranging from 9
to 14 knots. Temperatures are in the lower to mid 80s, with
dewpoints in the mid 70s.

As the aforementioned subtropical ridge continues to build
overnight, our winds will increase in response. While the drier
air is currently promoting less shower activity near the island
chain and surrounding coastal waters, this wind surge may help to
keep shower activity near normal tonight. Showers have already
formed upstream in the southeastern Straits of Florida, so have
retained 30% rain chances for overnight.

The National Hurricane Center has issued the first advisory for
Potential Tropical Cyclone 6 this evening. It is too early to tell
of any potential impacts to the Florida Keys, however, there is
higher than normal uncertainty with the system at this time. We
will continue to monitor this system over the next few days.

.MARINE...
There are no watches, warnings, or advisories currently in effect
for the coastal waters of the Florida Keys. From synopsis, High
pressure extending from the western Atlantic into the
southeastern United States will maintain moderate easterly breezes
across the Keys coastal waters through Thursday. A tropical
disturbance will move west northwest through the Greater Antilles
during the week, and is forecast to move across the Keys and South
Florida Thursday night through Saturday.

.AVIATION...
VFR conditions will continue at airports this TAF period with east
to east-southeast winds 8 to 11 knots. Dry conditions are
anticipated through 10/09Z at EYW before VCSH develop per the latest
HRRR model runs, while MTH looks to remain dry.

.CLIMATE...
On this date in 1950, from the Key West Citizen, "thousands of fish
were found in the streets of Key West after a heavy rain. Most of
the fish were found along Caroline Street between William and
Grinnell. One theory was that a large waterspout had carried the
fish ashore. This theory was supported by the fact that most of
the fish were mullet, which swim on the surface and could be
picked up by a waterspout. Caroline Street regulars insisted it
had rained fish, and one man said he saw a full-grown sponge fall
from the sky."

.KEY WATCHES/WARNINGS/ADVISORIES...
FL...None.
GM...None.
&&

Public/Marine/Fire...NB
Aviation/Nowcasts....Shamburger
Data Acquisition.....DR/AP

Visit us on the web at weather.gov/key

Area Forecast Discussion...UPDATED

National Weather Service North Platte NE

1024 PM CDT Mon Aug 9 2021

.UPDATE...
Issued at 1021 PM CDT Mon Aug 9 2021

A forecast update is in place using the HRRR model which has
verified well this afternoon and this evening. The new forecast
allows for more isolated shower and thunderstorm activity across
the Sandhills tonight. Scattered shower and thunderstorm activity
is in place across swrn Nebraska where a MCS has formed.

.SHORT TERM...(This evening through Tuesday night)
Issued at 335 PM CDT Mon Aug 9 2021

Strong shortwave is progressing eastward across northern MT and
southern SK this afternoon. A thin plume of Pacific mid-level
moisture curves from WY into the Dakotas ahead of this feature.
Appears to be a weak wave evident per WV within that plume across
southern WY. This will track northeast across western NE this evening
and aid in the development of isolated to widely scattered
showers/thunder near a weak cold front. These will be very high
based and could pose a threat for gusty winds and possibly a few
isolated dry lightning strikes, but some rainfall is expected so
this shouldn`t be a major widespread concern. The front will sag
south into KS Tuesday with a few degrees of cooling expected across
western and north central NE. Will have to watch portions of western
NE, mainly west of HWY 83, as humidity values drop below 20% in the
Panhandle. The limiting factor for critical fire weather conditions
will be the lack of winds. Will continue to monitor.

.LONG TERM...(Wednesday through Monday)
Issued at 335 PM CDT Mon Aug 9 2021

Stronger flow aloft will remain to our north the remainder of the
week into the weekend. Upper level ridging will gradually build from
the Rockies eastward into the central and southern Plains by early
next week. Through Saturday the ridge remains anchored across the
Rockies with northwest flow aloft across our area east of the ridge.
Again, the stronger flow will remain to our north and northeast, but
a weak shortwave has been advertised in the ECMWF to move southeast
across the area on the western fringes of the northwest flow across
our area. As a result the model has been generating some chance for
rainfall Friday night into Saturday, particularly across western NE.
The GFS on the other hand is dry and much warmer, with highs well
into the 90s Friday and Saturday. Will continue a slight to low
chance pop for precipitation during this time but will not be
increasing POPS until models in better agreement. The trend lately
has been for drier and hotter conditions overall.

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 617 PM CDT Mon Aug 9 2021

Isolated showers and thunderstorms are possible tonight, but should
remain south and east of both terminals and not cause any major
impacts. Otherwise, partly to mostly cloudy skies are expected
through Tuesday with winds remaining below 10 knots.

.LBF WATCHES/WARNINGS/ADVISORIES...
None.
&&

UPDATE...CDC
SHORT TERM...Taylor
LONG TERM...Taylor
AVIATION...Kulik

Area Forecast Discussion

National Weather Service Miami FL

856 PM EDT Mon Aug 9 2021

.UPDATE...

Minimal changes with this forecast update. Isolated showers and
thunderstorms will be possible during the overnight and morning
hours, mainly across the local waters and immediate east coast
metro areas. GOES-16 water vapor imagery depicts drier midlevel
air moving westward toward South Florida, which could allow for
slightly less thunderstorm coverage along the east coast tomorrow,
with typical thunderstorm activity forecast across the interior
and Gulf Coast owing to deep easterly flow and a pinned Gulf
breeze.

.PREV DISCUSSION... (Issued 758 PM EDT Mon Aug 9 2021)

AVIATION(00Z TAFS)...

Primarily VFR conditions throughout the period. Isolated SHRA with
brief restrictions will be possible at the east coast terminals
during the morning and afternoon hours before spreading westward
and becoming TSRA over the interior. Currently leaving out
mention of TSRA for the east coast terminals owing to potentially
sparse coverage, though we will continue to monitor trends. Best
chance of MVFR to IFR conditions will be at APF during the
afternoon hours with scattered TSRA along the Gulf breeze.

PREV DISCUSSION... (Issued 326 PM EDT Mon Aug 9 2021)

DISCUSSION...

Short term (Tonight - Tuesday):

South Florida remains under the continual presence of zonally
elongated ridging aloft. Meanwhile the western periphery of a broad
1000-850 hPa western Atlantic ridge continues to encompass the
region. This is allowing for east/southeasterly flow to preside
within this layer. Sufficient differential heating between the
interior and coastal regions should allow for sea-breeze circulation
development again today, which will remain the primary foci for
convection to spawn. The easterly flow will favor development along
interior and western portions of the region, particularly during the
afternoon/evening hours. PW around 2.0 inches, 500 hPa temperatures
near -7C, and instability on the order of roughly 3000-4000 J/kg of
surface-based CAPE will continue to support deep convection.
RAP forecast soundings indicate mid-level subsidence (around 700
hPa), which may somewhat inhibit the growth of storm cells compared
to days prior. Regardless, strong wind gusts, localized flooding,
and even small hail will possible in association with robust
thunderstorms that are able to develop today. Very little deviation
in the region-wide forecast and associated impacts is anticipated
for Tuesday. The main concern will be localized and urban flooding
that could become realized across metro portions of Collier County -
should thunderstorms meander or redevelop over recently saturated
localities.

Muggy temperatures will continue across the region today, with
maximum temperatures in the upper 80s along the Atlantic coastline,
and lower 90s elsewhere. Dewpoints in the mid/upper 70s will allow
for apparent temperatures exceeding 100 in some locations. There
could be brief bouts of slightly cooler temperatures from storm
outflows and evaporative cooling processes.

Long term (Tuesday night - Sunday):

Models show weak high pressure across most of the SE CONUS, while
stronger high pressure dominates the GOMEX region. Also, ridging
across the west Atlantic ridge will extend through SoFlo, while
aloft, a TUTT over the bahamas slowly moves closer to the peninsula
through the end of the work week.

The overall synoptic setup will favor a more typical weather pattern
for this time of the year, highlighted by sea breeze interactions
becoming focal point for afternoon convection. At the low levels,
SoFlo should remains fairly humid with model soundings still showing
PWATs in the 1.5-1.8 range each day through Friday. Models also show
some drier air intrusion and increasing subsidence aloft due to the
influence of the aforementioned TUTT, But the air mass should
remain humid enough for continuing daily convection, favoring the
afternoon hours.

The described synoptic scenario will keep prevailing E/ESE flow
through much of the long term, with a typical summer-time pattern of
late morning/early afternoon showers over the east coast metro
areas, then having deeper convection over interior and west coast
areas later in the afternoon as sea breezes push inland. Highest
POPs remain on the high-end-scattered to numerous range each day.

The National Hurricane Center is following the progress of a
tropical disturbance approaching the Lesser Antilles, which is
expected to move west-northwest through the later part of the week.
At this time, it is too early to determine what specific impacts
this system could bring to our area. For now, POPs/Wx grids will
carry a littler higher POPs for Saturday in response to the
potential increased moisture that this disturbance could bring to
the area. Please refer to the latest updates from the National
Hurricane Center for the most recent information on this
disturbance.

In terms of temperatures, the hot trend will continue through the
long term with nighttime lows in the mid 70s to near 80, and
afternoon highs in the upper 80s to low 90s. The abundant low-level
humidity lingering over SoFlo will help in keeping heat index values
above 100F across much of SoFlo each day.

MARINE...

Light easterly to southeasterly flow will continue through much
of the week, as high pressure remains over the region. Sea-breezes
will allow for an onshore wind component along the coast in the
afternoons. Scattered showers and thunderstorms will be possible
today, mainly over the Gulf waters and Lake Okeechobee. Winds and
seas could be locally enhanced near thunderstorms that do develop
today.

BEACHES...

The rip current risk will gradually increase across the east coast
beaches this week as easterly winds strengthen. By this weekend,
the beach conditions could become increasingly hazardous with
gusty winds, rough surf, and increasing thunderstorm activity.

.PRELIMINARY POINT TEMPS/POPS...
Miami 80 91 79 91 / 30 40 30 50
West Kendall 79 92 77 92 / 30 40 30 50
Opa-Locka 79 91 78 92 / 30 40 30 50
Homestead 79 90 78 90 / 30 40 40 40
Fort Lauderdale 80 90 80 89 / 30 40 30 50
N Ft Lauderdale 80 90 79 90 / 30 40 20 50
Pembroke Pines 79 90 78 90 / 30 40 30 50
West Palm Beach 78 91 78 91 / 30 40 20 50
Boca Raton 79 91 79 90 / 30 40 20 50
Naples 76 92 76 92 / 30 60 30 60

.MFL WATCHES/WARNINGS/ADVISORIES...
FL...None.
AM...None.
GM...None.
&&

Update/Aviation...Weinman
Tonight/Tuesday and Marine...RAG
Tuesday Night through Monday...AR

Visit us at weather.gov/miami

Area Forecast Discussion...UPDATED

National Weather Service Twin Cities/Chanhassen MN

1049 PM CDT Mon Aug 9 2021

.UPDATE...
Issued at 847 PM CDT Mon Aug 9 2021

A clear and pleasant evening out there now, but conditions should be
changing just after midnight with an increased confidence of
convection development. An extremely unstable airmass across the mid
Missouri Valley is in place this evening with 6500 J/kg noted on the
00Z OAX sounding. The loss of mixing has allowed moisture to recover
at 850 mb in the vicinity of Sioux Falls according to SPC
mesoanalysis. Dew points exceeding +18C at that level will advance
northeastward with the development of a small LLJ. This elevated
northwest-southeast oriented warm front will be the focus for
thunderstorm development, with a secondary focus being with the cold
front advancing eastward quickly thereafter. Very steep mid level
lapse rates exceeding 8.5 C/km will generate more than enough MUCAPE
to sustain updrafts, as long as any cap above 850 mb can be overcome.
Several recent runs of the HRRR and RAP have been consistent with
development along this warm front, and as mentioned by the previous
shift, the ECMWF has been advertising this for a while as well.
Therefore, confidence is increasing in a concentrated area of
convection roughly along I-94 in Minnesota late tonight, pushing
into Wisconsin Tuesday morning. Updated PoPs to increase them to 60%
within this corridor, and once development begins they`ll probably
have to be increased further. Some storms may contain large hail or
damaging winds in the early stages following initial development,
but coverage will probably become such that updraft interference may
hinder a longer, more organized event into the pre-dawn hours.

.SHORT TERM...(This evening through Tuesday night)
Issued at 230 PM CDT Mon Aug 9 2021

The primary concern in the short term is the cold front which will
move through the area late tonight and Tuesday morning. This frontal
boundary is currently located over the eastern Dakotas and will be
kicked eastward later tonight as the upper low evident over eastern
Montana in water vapor imagery moves eastward. Some SHRA/TSRA is
ongoing with these features, and expect to see some continuation and
expansion of that through the period as things move east. The
deterministic larger scale models generally favor the best chances
farther north, closer to the main upper level forcing. However, the
ECMWF has been consistent in showing an area of heavier precipitation
along the southern edge of that area of forcing, where it
intersects with the forecast instability gradient late tonight into
Tuesday. It implies a southeastward moving MCS going from North
Dakota overnight through central and southeast Minnesota Tuesday
morning. A number of CAMs show a similar evolution of things, but
there is far from a consensus. It is not an unreasonable solution,
and we should have our answer sometime later this evening as upstream
convection evolves. Should a cluster of convection grow sufficiently
upscale and develop a large enough cold pool, one would expect it to
propagate southeastward in concert with the instability gradient and
orientation of the 0-3 km bulk shear vectors. There could be a
marginal wind and hail threat with any such activity, which is
reflected in the convective outlooks from SPC. For now, continued to
bring mostly chance PoPs eastward across the forecast area late
tonight through the day on Tuesday, lingering some into Tuesday night
across the far south/southeast as the baroclinic zone looks to hang
up down in that area as the upper trough moves east of the region.

.LONG TERM...(Wednesday through Monday)
Issued at 230 PM CDT Mon Aug 9 2021

The main concern for the extended is the persistence of dry weather
with very little precipitation forecast. There were no significant
changes from the previous update.

For Wednesday through Saturday night, an amplified longwave trough
over will be centered over Hudson Bay, with the trough axis
extending down into the western Great Lakes. Meanwhile, a strong
ridge will be centered over the northeast Pacific and the PAC NW,
which will lead to the return of northwest flow and a very dry air
mass (dew points in the 40s/50s) across the northern Midwest. The
last in a series of cold fronts is expected to sweep through
Wednesday night. Precipitation chances are near-zero with little to
no moisture available so the only notable impact will be the subtle
drop in temperatures and humidity thanks to the transition to
northwest flow aloft. Highs top out in the low to mid 80s each day
with a surface high pressure overhead.

For Sunday onward, we`ll see the upper low break down over eastern
Canada, allowing the upper ridging over the western CONUS to slide
east into the Great Lakes region. This should allow for temperatures
and humidity to increase toward the start of next week. We`ll keep
an eye on how model guidance evolves over the next few days as
current models and ensembles vary on how aggressive they want to be
with building the ridge into the eastern CONUS (aka how amplified
the pattern will be). Both outcomes result in an extended period of
dry conditions.

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1049 PM CDT Mon Aug 9 2021

Thunderstorm chances increase overnight along a warm front that will
stretch from northwest to southeast along I-94 in Minnesota.
Development would occur around 08Z and continue into the daylight
hours as the activity heads into Wisconsin. Was only confident enough
to include a tempo at STC, MSP, and RNH.

KMSP...Window of TS late tonight still appears to be 09Z-12Z.
There`s still some uncertainty with various guidance now starting to
flip flop, unlike earlier, but the environmental conditions are
favorable for development so confidence is high enough to introduce a
tempo.

/OUTLOOK FOR KMSP/
Wed...VFR. Wind SSW becoming WNW 5-10 kts.
Thu-Fri...VFR. Wind WNW 5-10 kts.

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...None.
WI...None.
&&

UPDATE...Borghoff
SHORT TERM...
LONG TERM...BPH
AVIATION...Borghoff

Area Forecast Discussion

National Weather Service Paducah KY

717 PM CDT Mon Aug 9 2021

.UPDATE...
Issued at 717 PM CDT Mon Aug 9 2021

Updated aviation discussion for the 00Z TAFs. Also, a forecast
update is forthcoming that will lower but not completely eliminate
rain chances overnight. Convection has been sparse late this
afternoon into the evening due to a lack of substantial forcing.
This trend should continue into the overnight in the absence of
any substantial upstream convective development. Relied heavily on
a combination of the 12Z NAMNest and some of the latest HRRR runs,
which appear to have the best handle on the present situation.
Following this guidance, any overnight shower and storm activity
is forecast to be isolated to widely scattered at best. The
remainder of the forecast is unchanged from the afternoon package.

.SHORT TERM...(Tonight through Thursday)
Issued at 215 PM CDT Mon Aug 9 2021

Short res modeling suggests warm conveyor convection in our late
this pm/early evening, as seen active, with new development
possible over southcentral MO/on our FA doorstep, potentially
impacting northwest portions of FA later this pm/evening. After
diurnal fuel is lost, should see diminishing returns. A marginal
risk of svr continues for much of the FA until then.

Tmrw, a slight risk envelopes much of the region, as upstream
convection gets going during the daytime, and dives this direction
in the afternoon/evening hours. It has potent upper support, so
the risk is slightly higher.

Pops wane (though not entirely) Wed-Thu, but the heat/humidity
does not. Have added the eastern half of the FA to the Heat
Advisory for tmrw afternoon, per collab with neighbors. This may
need to be extended into the mid week period if current modeling
trends hold.

.LONG TERM...(Thursday night through Monday)
Issued at 215 PM CDT Mon Aug 9 2021

In the extended period, the WFO PAH forecast area will remain along
the southern tip of the base of the faster westerlies lying in a
broad low amplitude trough covering the Mississippi/Ohio Valley.

The beginning of the forecast period, namely Friday and Friday
night, should have the greatest coverage of rain across the area.
The NBM initialization may be too low with the coverage, but kept
these PoPs in place given the uncertainty as to where the frontal
boundary will eventually stall out across the Quad State region.

Have a preference toward the European/Canadian ensemble model
solutions vs. the GFS. The deterministic guidance options of the
Canadian, suggest the a more progressive movement of the frontal
boundary south of the area. This may be a good direction to go, but
uncertainty is too high not to at least keep a small chance of rain
in the southern border counties into Sunday.

Monday remains in question with respect to rain, as the Canadian and
European model guidance have timing differences with the development
of a closed low over Missouri on Monday. For now, will split the
difference and keep a chance of rain across the area into Monday.

For the Max/Min Temperatures, kept the NBM model guidance
initialization in place for this package, but made some model blend
adjustments to the dewpoint with a blend of the NBM and Canadian
guidance to reflect a slower southward transport of high dewpoints
associated with the movement of the frontal boundary. Fortunately,
the mix of temperature/dewpoint, and winds should keep heat index
values below critical thresholds through the extended period.

.AVIATION...
Issued at 717 PM CDT Mon Aug 9 2021

VFR conditions are forecast through Tuesday. Trended the forecast
in a more optimistic direction with respect to shower/thunderstorm
potential and sky cover. That said, isolated to widely scattered
development is certainly not out of the question later tonight,
and will amend and adjust as the situation warrants. Fog shouldn`t
be much of an issue either with a steady south breeze. SSW winds
will pick up to around 10 knots on Tuesday, and some gusts could
approach 15 knots. Scattered VFR cumulus development may lead to
an isolated shower/storm by afternoon.

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...Heat Advisory until 8 PM CDT Thursday for ILZ080-084-085-088-089-
092>094.

Heat Advisory from 11 AM to 8 PM CDT Tuesday for ILZ075>078-
081>083-086-087-090-091.

MO...Heat Advisory until 8 PM CDT Thursday for MOZ076-086-087-100-
107>112-114.

IN...Heat Advisory from 11 AM to 8 PM CDT Tuesday for INZ081-082-
085>088.

KY...Heat Advisory until 8 PM CDT Thursday for KYZ001>006.

Heat Advisory from 11 AM to 8 PM CDT Tuesday for KYZ007>022.

UPDATE...RJP
AVIATION...RJP

Area Forecast Discussion

National Weather Service Phoenix AZ

511 PM MST Mon Aug 9 2021

.UPDATE...
Updated 00Z aviation discussion.

.SYNOPSIS...
A low pressure disturbance moving into Arizona from the south will
bring moisture, cooler temperatures and increasing chances of storms
and precipitation, especially Monday night and Tuesday. Persistent
humid conditions through the week should help to maintain decent
storm chances and below normal high temperatures.

.DISCUSSION...
The inverted trof that has been moving steadily northward across SE
AZ this morning did set off an area of scattered showers/TS across
parts of NW Pinal County this morning as well as spread an area of
dense overcast across the rest of S-central AZ. Some locations in
the Casa Grande area measured as much as 1.00 inch of area, which
did produce some localized flood/running washes, but most locations
saw much less, with the fact majority of the Phx metro seeing
nothing at all. The shower/TS activity has greatly diminished over
the last couple of hours, with perhaps just a sprinkle or two at the
present time. A secondary impact of all of the cloudiness is to
greatly retard sfc heating over most of south-central AZ, with KPHX
just now reaching 90 degrees at this hour.

Models remain in good agreement on the inverted trough continuing to
move steadily NNW through S-Central AZ this afternoon/evening, then
into SW AZ/SE AZ late tonight/early Tue. Current HRRR and HREF model
output continues to be very consistent in developing showers/TS over
the Rim.Gila County this afternoon, then move them slowing into the
lower elevations of S-central AZ during the mid/late evening hours
as steering flow aloft becomes more ENE-ly ahead of the inverted
trof. The HREF emsemble max wind gusts are showing 4-hr max wind
speed probs of >30 kts rising up into the 50-70% range this evening
across S-central and SW AZ, so gusty winds definitely look to be a
threat. However, locally heavy rain looks to be a greater threat, as
PWATS`s have risen into the 1.80-2.00 inch range. HREF max 3-hr QPF
probs of >1.00 inch rise up above 50% this evening across
northern/NW Maricopa County, with values remaining aoa 30% into part
of La Paz/Yuma Counties later this evening. WPC has issued a MPD
this afternoon/evening for much of S-central AZ, with the most
favored area being over Gila and extreme northern Maricopa County.
The latest HRRR model output shows a continued threat for heavy rain
late tonight/early Tue morning across SW AZ, with lesser threats
across SE CA Tue morning.

As far as Tuesday is concerned, there seem to be a strong signal
that convective activity will be significantly less than
today/tonight as the steering flow aloft becomes a less-favorable SW-
ly one and the airmass stabilizes somewhat behind the inverted trof,
as it continues to lift N-ward into NW AZ/southern NV and weakens.
However, a very moist airmass will allow any storm that form to be
very efficient rain producers with localized flash flooding possible.

The Clusters continue to hold a decent mix of signals for
recurring storms and showers, on and off, for the later half of
the week and into the weekend. They still favor anomalous high
pressure repositioning further to the N and NW of the region which
would give easterly waves and inverted troughs in N MX continued
better access to S-Cent AZ. However there is still plenty of
uncertainty on the timing and position of any storms moving into
the region during that time. For now NBM POPS favor 20-30% for the
second half of the week and 40% into the weekend with occasional
moderate amounts of WPC QPF. For SE CA POPS fall off and
temperatures warm for the later part of the week before storm
chances increase again into the low double digits this weekend.

The moderating effect that the increase in moisture and increasing
thick cloud cover will have on temperatures starts today with highs
likely remaining at/below normal for the next several days.

.AVIATION...Updated at 0010Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:

Potential convective impacts late this evening and Tuesday
morning or early afternoon will be the main aviation concerns for
the Phoenix terminals through Tuesday. Although there is still
relatively high confidence (50%) in an outflow boundary pushing in
from storms over the White Mountains and Mogollon Rim tonight,
the timing has been pushed back to 04-06Z. Both easterly and
northeasterly outflows will be possible, but the latter will most
likely be weaker and thus delayed relative to previous thinking.
Wind gusts up to 25-30 knots will be possible, with stronger gusts
possible if any convection develops along the outflows.
Confidence in that occurring has decreased due to convective
inhibition associated with cloud cover keeping temperatures in the
mid 90s for most locations. Thus, we have only included VCSH
starting as early as 0430Z for a few hours tonight and will
upgrade to VCTS if mesoscale and convective trends warrant.

Aside from convective impacts, expect southeast to southwest
winds around 10 knots to persist ahead of the outflows, with
easterly winds returning overnight. Ceilings will generally remain
above 8-10 kft without convection and 6-8 kft with convection.
Another chance of convective showers and possibly isolated
thunderstorms is possible on Tuesday morning into the early
afternoon hours as indicated by another round of VCSH in the TAFs,
but confidence in the timing and thunderstorm potential is low.

Southeast California/Southwest Arizona including KIPL and KBLH:

Convective impacts from isolated thunderstorms over eastern
Riverside and La Paz Counties will be the main aviation impact
through tonight, with additional showers expected Tuesday morning.
Although VCTS is possible at KBLH through 02Z, convective
coverage was too low to mention in the TAFs at this time. There is
higher confidence in scattered showers on Tuesday morning for the
entire region with a 20-30% of of precipitation at both KIPL and
KBLH, so VCSH has been included for both sites starting at 14Z.
Isolated thunderstorms cannot be ruled out, but are unlikely due
to the lack of daytime heating. Otherwise, winds will generally
follow a south to southeast component at 5-15 knots with gusts up
to 20-25 knots through tonight and again on Tuesday afternoon.
Ceilings will generally remain above 10 kft without convection and
8 kft with convection.

.FIRE WEATHER...
Wednesday through Sunday:
Highs over S-cent AZ will settle a few degrees below normal and
near normal in western areas. Storm chances continue through the
weekend. RH values also remain elevated with periodic influxes of
moisture and below normal temperatures in most places. Min RH will
remain above 20-30% in all areas except for the drier parts of SE
CA where they will fall into the upper teens possibly on Thu and
Fri. Apart from thunderstorms expect mostly light winds favoring
normal diurnal patterns through the period.

.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

DISCUSSION...Percha/Sawtelle
AVIATION...Hopper
FIRE WEATHER...Sawtelle

Area Forecast Discussion

National Weather Service Pueblo CO

327 PM MDT Mon Aug 9 2021

.SHORT TERM...(This evening through Tuesday)
Issued at 238 PM MDT Mon Aug 9 2021

Water vapor imagery and upper air analysis indicates modest westerly
flow aloft across the region, with an upper low and broad upper
trough currently translating across the Intermountain West. Water
vapor imagery continues to indicate dry air across the region, with
SPC analysis indicating PWATS running from 0.4 inches to around
three quarters of an inch from west to east across the region. Lee
troughing across the plains has helped to mix out the lower levels
of the atmosphere across western portions of the plains, with dew
pts in the 20s and 30s west of the trough, where as 3 pm obs
indicate current dew pts of 54F at SPD and 52F at LAA. The westerly
downslope has also helped to boost temperatures into 90s to around
the century mark across the plains, with COS, as of 3 pm, setting a
new record high of 96F, breaking the previous record for August 9th
of 95F set in 1962.

For Tonight and Tuesday...Modest westerly flow aloft continues
through the day tomorrow, as the upper level disturbance continues
across the Northern Tier of States. This passing system will send a
weak cold front across the eastern plains tonight, with breezy
northerly winds of 15 to 25 mph expected across the plains in its
wake. With a modest gain in mid level moisture, combined with late
summer solar heating and developing upslope flow behind the passing
front across the plains, latest CAMS indicate a few showers and
thunderstorms across the area tomorrow afternoon, with the best
coverage across the eastern mountains and immediate adjacent plains,
especially along the Palmer Dvd and Raton Mesa. Storms look to be
generally high based, producing lightning and gusty winds, with
little in the way of measurable rainfall expected.

As for temperatures, passing front will likely keep overnight lows
warmer than last night, with only slightly cooler high temperatures
expected areawide on Tuesday.

As for the smoke, HRRR forecasts indicate only slight improvements,
especially across SW Colorado and into the San Luis Valley, in the
smoky/hazy conditions across the region through the day tomorrow

.LONG TERM...(Tuesday night through Monday)
Issued at 238 PM MDT Mon Aug 9 2021

Upper ridge builds nw along the Pacific Coast Wed, while main
monsoon moisture is still surpressed south in srn NM/AZ. Over CO,
subtle increase in low/mid level moisture may be enough to produce
some isolated convection over the high terrain and along the NM
border, with storms perhaps aided somewhat by weak, convective
upper level circulations drifting into the area from the south.
Max temps Wed again on the hot side of seasonal averages, and some
100 degf likely again on the plains. Very similar set-up for Thu,
with perhaps a minor increase in storm coverage/strength as we
begin to recycle some convective moisture.

Weak cold front drops south through the plains late Thu/Thu night
as upper level high center drifts around the wrn U.S.
Plains/I-25/ern mts should see an increase in moisture Fri
afternoon behind the front, while mid levels continue to gradually
moisten farther west as monsoon plume slowly expands northward.
NBM has a fairly substantial increase in pops across the area Fri
afternoon and evening, which looks reasonable, and moisture looks
significant enough to begin to ramp up the flash flood risk in
the mountains by late day. Maxes Fri begin to drift downward,
mainly due to increased cloud cover and onset of afternoon
convection. Over the weekend, upper level high slips east and
weakens, while numerous convectively-induced vorticies drift
around under the ridge from Sat into Mon. In general, pattern
favors a continuation of afternoon/evening thunderstorms each day,
with highest pops over the mountains, lowest across the plains.
Picking a particular day or location for heavy rainfall becomes
difficult given the rather chaotic nature of the upper flow,
though models hint at areas along the Continental Divide seeing
the best chance for rain given deeper mid level moisture farther
west. Temperatures through the period look to run within a few
degf of seasonal averages.

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 238 PM MDT Mon Aug 9 2021

Westerly flow aloft will keep smoky/hazy conditions in place across
the Rockies through the taf period, with occasional MVFR vis
expected at the terminals through the period. A weak lee trough in
place across the plains will keep westerly winds of 10-20kts at COS
and PUB through the afternoon, with an expected cold front moving
across the plains allowing for breezy northerly winds of 15-25kts to
develop between 04z-07z at COS and PUB. A slight increase in mid
level moisture tomorrow, combined with developing low level upslope
through the afternoon across the southeast plains, will help to
develop a few high based showers and storms across the higher
terrain and immediate adjacent plains. Too low of confidence to
include in tafs attm, however best chances of storms affecting the
terminals would be at COS after 20Z.

.PUB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

SHORT TERM...MW
LONG TERM...PETERSEN
AVIATION...MW

Area Forecast Discussion

National Weather Service Reno NV

319 PM PDT Mon Aug 9 2021

.SYNOPSIS...

A dry airmass along with periods of smoke and haze will persist
through tomorrow. Daytime heat will ratchet up each day this week
with moisture and instability increasing through the latter half
of this week. This will bring back an increased risk of thunderstorms
to the region that could continue into the weekend.

.SHORT TERM...

Higher pressure building across the Desert Southwest into the
Great Basin will increase a south to southeasterly mid-level flow
across the eastern Sierra and western Nevada by mid-week. Smoke
and AQI issues will continue the next 24-36 hours while the Dixie
fire continues. Here are some highlights for the short-term
period.

* SMOKE: No end in sight to the smoke and air quality issues
during the short-term forecast period. As long as the Dixie Fire
continues to be the single major source of smoke over the
region, most mountain locations north of Lake Tahoe will see the
lowest visibility and accompanying worst AQI values. HRRR model
simulations still show a brief southward push of smoke
continuing into the evening. So for the time being widespread
haze will persist with periods of smoke. A north-south pressure
gradient strengthening this evening into Tuesday will help
spread a thicker smoke plume into the area and cause conditions
to worsen in many areas through tomorrow. Some good news is on
the horizon by Wednesday as an increasing southerly flow over
western NV should disperse heavier smoke layers north of our
area and bring somewhat better air quality to the region.

* HEAT: With upper heights rising over the next several days increased
subsidence and heating will follow over the Great Basin and
northern Sierra. Temperatures will warm through mid-week with
triple-digit heat expanding into the warmer valleys of western
NV Tue-Wed. Nothing unprecedented, but a good 5 to 10 degrees
above seasonal averages by Wednesday.

* THUNDERSTORMS: Overall, winds will become more southeast-south
by Tuesday-Wednesday, allowing an influx of monsoonal moisture
to flow northward from the subtropical eastern Pacific. An
increased threat of storms could change the smoke transport
trajectories, which could help with the current period of smoke
and AQI issues. Convective buildups will return tomorrow
afternoon with a couple of storms not out of the question
forming over the eastern Sierra areas of Mono County. Hi-Res
model guidance shows a shortwave moving west-northwest on the
southwest side of the ridge and into CA by midweek. This would
further enhance the rapid incursion of mid-level moisture and
bring a better chance of some thunderstorms Wednesday and
possibly continuing overnight as nocturnal storms into Thursday
morning. Ensemble guidance shows a 200+ percent increase of PWAT
values over the eastern Sierra by Wednesday which will continue
through the remainder of the week. Chances favoring the Sierra
and far western NV areas, these storms will tend to be high
based with narrow cores within this initial surge of mid- level
moisture. Gusty outflow winds up to 40 mph will accompany most
of these storms with brief heavy rains creating the potential
for flooding, especially in and around burn scars. -Amanda

.LONG TERM...Thursday Onward...

Increased chances for thunderstorms will continue through the
latter half of the week. PWAT values will show an accompanying
increase through the week with 0.7-0.8 by Thursdays, increasing to
nearly an inch across the Sierra and far western Nevada by
Friday. Steering layer flow will be relatively light, which means
there is a higher potential for slow-moving, wetter storms over
the eastern Sierra over the more complex terrain areas initially
that afford better instability, low-level convergence, and decent
moisture. Later in the afternoon, west winds will kick storms off
the crest into basin areas of western Nevada. There will be a
similar setup for Friday afternoon through the evening as well.
Thunderstorm outflow boundaries may kick off new storms late into
the evening, with the potential for a few overnight showers as
well.

By this weekend the upper winds will shift and increase from the
southwest as an upper wave advances closer to the west coast. This
upper waves infringement from the west will bring drier air
and increased stability across the region. Even though PWs
necessary for an increased potential for thunderstorms and showers
will push eastward, PWATs should still hover around 0.6 inches.
Therefore some potential for a few isolated storms may remain over
higher elevation areas of northeast CA and far northern Washoe
County Saturday afternoon. This will complement the potential that
remains over the Mono-Mineral County convergence zone. Model
soundings for the weekend time frame show faster storms, with a
higher risk for strong downdrafts and outflow winds.

Bottom line: If you have outdoors plans Thursday into the weekend,
be sure to have a backup plan if thunderstorms develop. -Edan/Amanda

.AVIATION...

Smoke and haze slowly thickens into far western Nevada this
afternoon and evening as a light north to northeast flow filters
into the region. Any improvements in smoke and haze density
earlier this morning have gradually been reversed this afternoon
over terminals outside the Sierra will see airfield conditions
lower going into the overnight hours. Slantwise visibility
concerns will continue into the evening as well.

KRNO-KCXP-KMEV will be predominately MVFR overnight into Tuesday
morning. Brief periods of IFR conditions are a real possibility
later this evening into the early morning hours Tuesday as some
thicker smoke layers settle into the area due to increased
stability within the surface-based layer. Some improvement is
expected through Tuesday evening as winds increase from the south
and southeast, dispersing denser smoke layers northward. KTRK-KTVL
could see a brief period of MVFR conditions in lower VIS/CIG
later this evening and early morning Tuesday as some smoke layers
wrapping back into the Tahoe Basin and areas just west.

Increased thunderstorm chances return to the Sierra and western
Nevada on Wednesday. Thunderstorm outflow winds may result in
better mixing and clearing out of the smoke and haze. -Amanda

..FIRE WEATHER...

Thunderstorms return to the region this week as midlevel flow begins
to shift out of the southeast. Thunderstorms could return as early
as Tuesday afternoon, mainly in the Eastern Sierra of Mono County.
Thunderstorm chances increase Wednesday and Thursday, especially for
those areas south of US-50 as additional moisture and instability
increases.

Storms on Wednesday will be a hybrid mix of wet/dry storms as storm
motions remain nearly stationary with localized heavy rainfall
possible under the main storm cores. There is slight chance of dry
lightning outside the cores as well, although with the slow storm
motions, we don`t expect to see a major dry lightning event. The
main threats from these storms will be occasional lightning, gusty
outflow winds up to 40 mph, and localized heavy rainfall.

Convective activity may continue into the evening and possibly
Wednesday night as well as a weak shortwave moves up from southern
Nevada. It doesn`t look like a very strong signal, just something to
keep an eye on. Thunderstorm chances will continue Thursday and into
the weekend as moisture and instability remain over the Eastern
Sierra, western Nevada and pushing into northeast California. -Hoon

.REV Watches/Warnings/Advisories...
NV...None.
CA...None.
&&

For more information from the National Weather Service visit...
http://weather.gov/reno

Area Forecast Discussion

National Weather Service Topeka KS

552 PM CDT Mon Aug 9 2021

...AVIATION UPDATE...

.DISCUSSION...
Issued at 357 PM CDT Mon Aug 9 2021

Weak ridging with zonal flow holds across the Central/Southern
Plains while an upper shortwave trough continues to progress through
Montana. A surface low sits over the Dakotas ahead of that shortwave
with southerly low-level flow keeping the hot and humid air mass
over our area. This moisture combined with the thermal axis and
plenty of insolation has resulted in a toasty afternoon with
widespread heat indices in the 105 to 110 degree range. Little
relief is expected tonight as lows only fall back to the mid to
upper 70s. This evening we continue to monitor for storms to develop
in western KS/NE as a lee sfc trough deepens and is aided by another
weak shortwave embedded in the upper flow. CAMs continue to show a
weakening trend as these storms move east, but have kept small PoPs
in north central KS for a few hours overnight with chances
decreasing again around sunrise.

As far as the heat is concerned, the forecast remains on track and
have made no changes to headlines at this point. The thermal axis
remains overhead at least through Wednesday, with better chances for
relief coming by the end of the week as a frontal boundary pushes
south and we transition back to northwest flow. Some questions
remain regarding Thursday as the weak front approaches and dew
points appear slightly better than the early part of the week, but
at this time heat indices look to improve enough to remain below
advisory criteria.

Regarding storm chances, the entire area has a possibility of seeing
storms Tuesday, particularly in the afternoon and evening with
plenty of instability. Shear still doesn`t look overly impressive
(up to 35 kts) and with weak forcing aside from daytime heating,
it`s tough to pinpoint any certain location that has the best chance
of seeing storms, especially any that would be strong to severe.
Given the amount of instability, any pulsing updrafts could produce
strong wind gusts and large hail. Periodic thunderstorm chances
remain the rest of the week with weak waves in the upper flow and
ample instability, with some uncertainty remaining on where synoptic
or outflow boundaries may set up. Predominantly dry and relatively
cooler conditions return by Saturday for the rest of the weekend.

.AVIATION...(For the 00Z TAFS through 00Z Wednesday)
Issued at 552 PM CDT Mon Aug 9 2021

VFR conditions are likely to persist through Tuesday. Main concern
is potential for elevated SHRA and TS to move into the region
earlier in the day Tuesday than the forecast has. NAM and the HRRR
are suggesting the convection currently developing across
southwest NEB could eventually move into the area after 12Z. If
this occurs, MHK would have a higher chance of being impacted. At
this time limited coverage from the NAM and HRRR along with some
CAMS keeping dry weather into the morning will preclude a mention
of precip in the forecast at this time. Something else to watch
will be LLWS. Models show a 30KT to 35KT low level jet developing
overnight. Think the pressure gradient should be strong enough to
keep surface winds from decoupling. So LLWS chances look marginal
and will monitor trends through the evening.

.TOP WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 8 PM CDT Wednesday for KSZ011-012-023-024-
026-038>040-054>056-058-059.

Heat Advisory until 8 PM CDT Tuesday for KSZ008>010-020>022-
034>037.

DISCUSSION...Picha
AVIATION...Wolters

Area Forecast Discussion

National Weather Service Tucson AZ

848 PM MST Mon Aug 9 2021

.SYNOPSIS...Increasing shower and thunderstorm chances will bring
temperatures a few degrees below average much of this week. Some
storms will generate strong winds and heavy rain.

.UPDATE...
Activity this afternoon and evening has struggled to get going.
Any decent convection moving in from south of the border
weakened as it transitioned into Arizona. Instability was
severely lacking after the storm activity early today followed by
widespread cloud cover. Stronger activity has been along and north
of our border with Phoenix and Flagstaff`s area where a more
conducive environment for storm develop has been situated today. A
few light showers continue to fire across our part of the state
but activity should dwindle in the coming hours. Adjusted the PoP
grids downward to reflect this trend for the next few hours.
Taking a look at some of the latest hi-res model output and HREF
members, there is a scenario that some are jumping on that has
convection beginning early on Tuesday, moving in from the south as
early as 5 AM followed by a second later afternoon round of
storms. Alternatively and the more likely scenario is storms
beginning in the afternoon as things destabilize with slow
movement from south to north. Overnight convection looks possible
Tuesday night into Wednesday as a weak impulse rotates northward
across the area which latest runs of the HRRR are beginning to
pick up on.

.PREV DISCUSSION... /issued 228 PM MST Mon Aug 9 2021/

.DISCUSSION...A couple of features were affecting the weather today
across SE AZ in terms of the cloudiness and the lull in showers and
thunderstorms so far this afternoon. The first was a weak
circulation over the area from remnants of a thunderstorm complex
that developed in northern Sonora, Mexico last night and has been
responsible for the debris cloudiness this morning. The other
feature was a larger scale disturbance lifting northward through the
state. Subsidence in the wake of this disturbance was helping hinder
the development of additional showers and thunderstorms this
afternoon. High resolution models continued to show limited
thunderstorm activity through this evening, but cannot rule out a
few storms with locally heavy rainfall and strong winds yet today.
Otherwise, deeper moisture will continue to spread into the region
this week into early next week. Several weather features will play a
role in an increase in shower and thunderstorm activity through the
week. The timing of these features will impact the daily coverage of
this activity, but in general the concern for more widespread heavy
rainfall will remain in the forecast.

.AVIATION...Valid through 11/00Z.
Mostly SCT-BKN clouds 10-14k ft MSL through the forecast period.
Isolated SHRA/TSRA expected, perhaps diminishing in later tonight.
Local MVFR conditions and gusty winds with SHRA/TSRA. Outside of
SHRA/TSRA, SFC winds will be less than 10 kts following a normal
diurnal flow of sly/sely during the night/early morning and mainly
wly/nwly late morning through afternoon. Scattered SHRA/TSRA
developing Tuesday afternoon and evening with similar cloud cover.
Aviation discussion not updated for TAF amendments.

.FIRE WEATHER...Ample moisture this week along with periodic
mid level disturbances will result in at least a mid grade monsoon
pattern. Given the higher levels of moisture and cloud coverage,
temperatures will be cooler this week. Strong, erratic winds and
locally heavy rainfall will be possible with any stronger storms
that develop. 20-foot winds will generally be less than 15 mph when
not influenced by thunderstorms.

.TWC WATCHES/WARNINGS/ADVISORIES...
None.
&&

UPDATE...Guillet

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