Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/20/20

Area Forecast Discussion...UPDATED

National Weather Service Albuquerque NM

 524 PM MDT Sat Sep 19 2020

.AVIATION...
00Z TAF CYCLE
VFR prevails, winds calm overnight becoming terrain driven. Some haze
still exists over parts of far eastern NM, mixing down to the sfc
creating some hardly mentionable vis reductions.

24

&&

.PREV DISCUSSION...300 PM MDT Sat Sep 19 2020...
.SYNOPSIS...
Near to above normal temperatures and dry conditions will prevail
through the weekend. A slight chance of showers and thunderstorms
will favor the northern mountains each day through Monday, but
little to no measurable precipitation is expected. Erratic and gusty
winds will be possible with any storms that do develop. A back door
front will dive into northern New Mexico Tuesday and progress
southward into Wednesday, bringing the possibility of showers and
thunderstorms to north central New Mexico. Otherwise, hazy skies will
continue as smoke from western coast wildfires continues to filter
into the state.

&&

.DISCUSSION...
SHORT TERM...(TONIGHT THROUGH SUNDAY NIGHT)...
Upper high center has shifted to the south, with westerly winds
aloft across northern New Mexico. Breezy to windy conditions were
apparent over northeast New Mexico as well. Areas of haze from
wildfire smoke will persist, with the HRRR Smoke model indicating the
southeast third to half of the forecast area will be most affected.

Similar to Friday afternoon, cumulus clouds have developed over the
northern and some of the western high terrain this afternoon but no
cells have been detected by radar as of this writing. Any that do
develop should move to the east and will be mostly dry with gusty
winds. Forecast models have reined in the small amounts of rain
forecast over the northern high terrain on Sunday, thus Sunday
afternoon may be similar to today although any cells will move more
slowly to the east as the upper high starts to build back over New
Mexico. Temperatures will be warmer than normal for most locales.

LONG TERM...(MONDAY THROUGH SATURDAY)...
Dry conditions and warmer temperatures will kick off the work week,
with highs reaching near to several degrees above normal. Weak upper
level disturbances may help to invigorate precipitation chances on
Monday, but dry air will persist at lower levels. Little to no
measurable precipitation is anticipated from this activity, but
erratic gusty winds from virga will be possible.

Despite the forecast of Tropical Storm Beta pushing inland earlier
next week, little moisture is expected to reach the Land of
Enchantment. However, an embedded disturbance in the eastern
periphery of the ridge is expected to drop down Tuesday into north
central NM. A backdoor front will then prog south into central and
east central NM by Wednesday night. This will result in an increase
in thunderstorm potential across the northern mts and eastern plains
during the mid week. The upper level ridge will build and sustain
over the western CONUS before centering across the Four Corners
region on Thursday. Uncertainty lies after the ridge sets up, as a
trough begins to move inland off the California coast. Models differ
on the timing of these features and how exactly the trough will
affect the position of the ridge. Nonetheless, dry conditions look to
persist into the weekend, with temperatures remaining above average.

12

&&

.FIRE WEATHER...
Upper high centered over southern New Mexico this afternoon with
westerly winds aloft over northern New Mexico. The upper high builds
back over New Mexico Sunday and Monday, with potential for some mid
level moisture to work into the northwest third of the state Monday
and Tuesday.

A few dry showers and possibly a short lived thunderstorm with gusty
winds will be focused over portions of the western and northern
mountains this afternoon as well as Sunday afternoon. Best chances
for localized wetting rain will be with convection over the northern
mountains Monday and Tuesday. Most cells this afternoon and Sunday
would move to the east, although more slowly on Sunday.

There will be areas of fair to poor ventilation central and west
Sunday and Monday. Ventilation improves overall Tuesday and
Wednesday. Vent rates plummet Thursday and Friday as a strong ridge
builds overhead, bringing dry weather. Temperatures will be near to
above average. Areas of poor to fair overnight humidity recoveries
are forecast over portions of the Rio Grande Valley westward
Sunday night through Thursday night.

&&

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

&&

$$




Area Forecast Discussion

National Weather Service Bismarck ND

 945 PM CDT Sat Sep 19 2020

.UPDATE...
Issued at 929 PM CDT Sat Sep 19 2020

Current forecast looks good. An occluded/cold front in eastern
Montana is forecast to move to central North Dakota Sunday
afternoon. At 02z/9 pm CDT regional radars show showers in
Montana that correlate well with the RAP frontogenetic forcing
along the front.

East of this area, in far western North Dakota, we believe any
radar return is mostly virga. So the better shower threat should
come late tonight and Sunday as the baroclinic zone moves east.

However, many CAM models, including the HRRR, track the forecast
showers north into Canada tonight, probably along the track of an
embedded short wave in the h500 flow. So overall the POPs on
Sunday will be low for North Dakota. This is how the current
forecast handles it so no changes needed.

UPDATE Issued at 609 PM CDT Sat Sep 19 2020

Upper level smoke/haze continues across west and central North
Dakota, but without significant visibility restrictions.

An upper trough will approach from the west tonight, and this
will bring a chance of showers, and possible thunderstorms to
western North Dakota. The main F-G forcing moves into the region
Sunday morning, so main threat of showers will be late tonight
west into the central. But without significant moisture, we will
leave the POPs low. Current forecast looks good.

&&

.SHORT TERM...(This evening through Sunday)
Issued at 246 PM CDT Sat Sep 19 2020

Slight chances for scattered showers and isolated thunderstorms
highlights the short term forecast.

This afternoon, surface height falls were ongoing as a surface
low, currently placed in southeast Montana, slowly moves
northeast. Aloft, the base of a negatively tilted trough is
located over western Montana, as seen in water vapor imagery, with
shortwave ridging ahead of the trough centered almost directly
over North Dakota. As both features and the associated surface
cold front move towards the forecast area, the chance of showers
and a few isolated thunderstorms begins late this evening in
western North Dakota, expanding east through the night.

Chance of precipitation is rather low at this point, with modeled
soundings continuing to show a mid-level dry layer that will likely
keep some precipitation from making it to the surface. Steep mid-
level lapse rates and instability values up to 500 J/kg support
the mention of thunder, but still expecting just a few isolated,
non-severe thunderstorms at most. This chance of showers and
thunderstorms pushes east along the initial frontal boundary,
ending in the James River Valley tomorrow morning.

High-res models want to then bring some wrap around showers and
possibly a few thunderstorms in the west and north central Sunday
morning and afternoon as the center of the low moves over. Still
not seeing much QPF-wise, so guessing that these will be very hit
or miss, with any chances for precip quickly decreasing through
the late afternoon and into the evening.

Expecting it to be windy on Sunday in the wake of the frontal
passage, with cold air advection and a well-mixed boundary layer.
Winds will be strongest in western North Dakota, with sustained
westerly winds around 25 to 30 mph, compared to only 20 mph in
central North Dakota, and 15 mph in the James River Valley.

Smoke aloft is thicker than it has been for the past few days,
with a few surface obs in western North Dakota reporting
visibility around 7 to 8 miles. However, the HRRR-smoke model
shows substantial clearing of smoke aloft as this system rolls
through and flow turns west-northwesterly. Because of this, opted
to not extend haze any further past tonight.

.LONG TERM...(Sunday night through Saturday)
Issued at 246 PM CDT Sat Sep 19 2020

The extended forecast is highlighted by mostly dry weather and above
average temperatures.

As precipitation chances end Sunday night, we return to quiet and
warm weather, with forecast highs on Monday in the mid 70s to
lower 80s as flow aloft becomes more zonal. Tuesday currently
looks even warmer, with highs in the low to mid 80s, but there`s
still some uncertainty in whether smoke aloft returns to the area,
which has limited high temperatures this past week.

There is a slight chance for some showers and a thunderstorm or two
late Tuesday into Wednesday morning, as a weak shortwave and surface
cold front push through the forecast area. This looks to be the only
real chance for precipitation through the end of the week, and even
then it`s rather unimpressive, with the 12 UTC suite of models
showing very little QPF, and latest GEFS plumes only have a few
members at each site showing any QPF.

In the wake of the cold front, expect Wednesday to be a bit cooler,
before broad ridging returns and we warm back up for the end of the
work week. Some uncertainty remains in how warm we will get for
Friday and Saturday, seen with the increasing spread in 1 standard
deviation for National Blend high temperatures. There are some hints
that we`ll have a relative cool down as we head into next week, both
in NBM probabilities and CIPS extended analogs.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 609 PM CDT Sat Sep 19 2020

VFR expected. A weak cold front will move from Montana to eastern
North Dakota during the forecast period. The front will bring a
wind shift from teh southeast to teh west. Otherwise, scattered
showers, and an isolated thunderstorms are possible later tonight
and Sunday. We mentioned some low level wind shear at KJMS
between 07-12z.


&&

.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...WAA
SHORT TERM...MJ
LONG TERM...MJ
AVIATION...WAA



Area Forecast Discussion

National Weather Service Des Moines IA

 635 PM CDT Sat Sep 19 2020

.DISCUSSION.../Tonight through Saturday/
Issued at 241 PM CDT Sat Sep 19 2020

General Summary...

The 7 day forecast continues to be devoid of major widespread
issues. Windy conditions will prevail today and especially Sunday,
when southerly wind gusts up to around 40 mph will be possible
across portions of northwest Iowa. Temperatures will continue to
slowly rise through the weekend and to start the week, yielding
widespread highs in the low to mid 80s by Tuesday. Precipitation
chances continue to be scant at best, only clipping northern Iowa
Sunday night and Wednesday night.

Additional Details...

The main concern within the forecast period resides at the beginning
of it, revolving around strong winds and elevated fire weather. As
the surface high continues to slowly push eastward across the
southern Great Lakes region, low pressure will continue to build in
to the northern Rockies front range and Northern Plains ahead of the
pivoting PNW upper level wave. Increasing surface pressure gradient
and deeper mixing has already yielded breezy southerly wind
conditions across portions of eastern South Dakota, eastern
Nebraska, southwest Minnesota, and northwest Iowa. Majority of winds
have fallen in line with hi-res soundings, yielding sustained winds
predominantly in the 10 to 20 mph range with gusts 20 to near 30 mph
within the state. Winds will peak over northwest Iowa Sunday
afternoon with expected 20 to 25 mph sustained and gusts 30 to 40
mph. Do not anticipate need for a wind advisory with current
available guidance and soundings, through would not surprised to see
a couple locations briefly meet advisory gust criteria.

Smoke will continue to linger aloft, obscuring sky conditions.
The large scale upper level pattern will remain fairly conducive for
at least some additional smoke to stream across the area into the
week, but fortunately should also see overall
concentrations/obscuration reduce, as depicted in the extended HRRR
Smoke runs and extrapolating based on synoptic model flow patterns.
Some minor concentrations may reach the surface, but does not appear
to be enough to raise concerns for visibility restrictions or
hazardous air quality.

The same story also continues on the temperature and precipitation
front. As the PNW upper wave continues its pivot and trek
northeastward into Canada over the next 24 to 36 hrs, amplified
ridging will continue to move across the region. That plus the
increased southerly flow will work in tandem to boost highs into the
upper 70s to lower 80s Sunday and widespread low to mid 80s for much
of the week. With the PNW wave trekking into Canada, the bulk of the
forcing will remain north of the area, with the best opportunity for
anything across far northern Iowa near a weakening boundary as the
LLJ increases Sunday night. Do not hold your breath though, showers
likley to be spotty and will lack ability to provide substantive
rainfall. Dry conditions will then prevail through mid-week within
broad upper ridging/zonal flow.

Early in the week, a big upper low will slide into the Gulf of
Alaska, and ejected short wave energy is slated to affect the area
Wednesday night in the form of an open upper level wave and surface
low. This will be our best chance for precipitation, albeit not a
great one. The core of the lift and precipitation chances continues
to be anticipated north into Minnesota, leaving our best chances
along/near the surface front, yielding low end shower chances at
this point within the forecast.

&&

.AVIATION.../For the 00Z TAFS through 00Z Sunday evening/
Issued at 635 PM CDT Sat Sep 19 2020

Widespread VFR conditions to persist for entire forecast period.
Smoke layer will continue at or above 20kft. Surface winds will be
from the south to southeast and quite gusty by Sunday afternoon.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

DISCUSSION...Curtis
AVIATION...Cogil




Area Forecast Discussion

National Weather Service Grand Forks ND

 1016 PM CDT Sat Sep 19 2020

.UPDATE...
Issued at 1012 PM CDT Sat Sep 19 2020

No changes to the forecast this evening. Using the vertically
intergrated smoke from the HRRRx it is doing a good job and at 00z
the thicker smoke area was just entering Grand Forks. That was
noticed at sunset. It has the high level smoke overspreading the
area overnight into Sunday....though diminishing behind a front
from west to east late Sunday aftn/night. 00z models coming in
show very little in terms of precipitation...some CAPE exists but
smoke will be dense enough so that the high temps given by model
data of near 80 will not be achieved and therefore CAPE will be
less. Plus there will be considerable high level clouds and some
mid level clouds as well. southeast winds will keep temps much
milder than past nights with lows mostly in the 50s.


UPDATE Issued at 658 PM CDT Sat Sep 19 2020

Thicker smoke shown nicely on visible pic heading slowly
northeast and this will spread over the area by morning. HRRR
smoke forecast products indicate a hazy/smoky sky Sunday. There
will also be high clouds increasing overnight and remaining over
the area Sunday. Some mid clouds too along eastward moving front.
This will mean Sunday will be a cooler day than today. Also windy
Sunday with winds in the 15-25 kt range.

&&

.SHORT TERM...(This afternoon through Sunday night)
Issued at 328 PM CDT Sat Sep 19 2020

Minimal impacts from weather expected through the short term
periods, with main focus on complications from smoke and eventually
isolated showers/storms (weaker) on Sunday.

Regarding smoke aloft: Smoke aloft has remained within the diffluent
region behind ridge axis where flow is more from the southwest
aloft, and has been slower to overspread our CWA/impact temps. This
has resulted in highs a bit warmer than forecast closer to what
original NBM had pre smoke-adjustment. Cold front Sunday should
scour out smoke and mid level clouds will eventually have more of an
impact on temp trends than smoke later in the day. Still some
suppression of highs is still possible (difference between upper 70s
and low to mid 70s).

Tonight-Sunday night: Negatively tilted trough axis eventually
shifts across North Dakota and northwest MN west to east late
tonight through Sunday evening, with a cold front midday through the
afternoon Sunday. Strong signal in forcing aloft and steep mid level
lapse rates/elevated instability axis of 500-1000 J/KG raises
possibility of thunderstorms along/ahead of frontal zone. Convective
temps will be in the lower 80s and even if smoke/cloud cover impacts
are minimal it may be difficult to overcome the CAP. Considering
limits of low level moisture advertised and strong CAP even elevated
storms would be weaker despite the forcing/increasing deep shear
profiles. HREF/NBM/GEFS show very weak and isolated signal in our
CWA for showers or weaker thunderstorms through Sunday evening.
There is a secondary lobe of positive vorticity shown to rotate
along the International border in ND, closer to the main upper low
and cold pool aloft. This activity would likely be tied more to
diurnal heating (assuming there is post frontal clearing pre-sunset)
and CAPE would be significantly lower in the post frontal air mass.

I have low confidence in any one location observing measurable
precip late tonight-Sunday evening, but it was reasonable keeping
mention in forecast. If there are a few showers/storms they should
be isolated and weaker in nature.

.LONG TERM...(Monday through Saturday)
Issued at 324 PM CDT Sat Sep 19 2020

The main story for next week is the very good chance of above
normal temperatures through the majority of the week with some
days possibly bringing a summer-like warmth. Climatologically
speaking, normal temperatures range from the low 40s to mid 60s
during this time of year. Expected temperatures this week range
from the 50s to 70s, some days possibly into the 80s. Guidance
supporting this claim are the strong signal of ensemble
probabilities over 60% for anomalously warm temps aloft moving out
of the continental west underneath quasi-zonal upper flow through
mid week shifting towards upper ridging over the central CONUS by
late week. NAEFS percentiles brings H7-H8 temps into the 90th
percentile range over the Northern Plains, more notably late
Tuesday and into next weekend. This conceptually makes sense as
deterministic guidance and numerous ensemble members bring a
thermal ridge over the region ahead of one or more weak cold
fronts. The only fly in the ointment to hinder maximizing temp
potential will be the chance for smoke aloft to prevent full
diurnal heating. While mid and upper level flow does source air
mass from the western CONUS where numerous fires still exist, the
potential for smoke over the area will remain unknown outside of
the 24-48 hour window.

With the passage of the aforementioned cold fronts, there will be
some chance for scattered thunderstorms, although confidence is low
in this potential due to warm temps aloft and meager moisture return
into the Northern Plains providing decent capping inversion.
Additionally, a few breezy days are anticipated just ahead and
behind the cold fronts, particularly post frontal winds out of the
northwest and west on Monday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 658 PM CDT Sat Sep 19 2020

Haze/smoke will spread northeast tonight. There will also be an
increase in high level moisture ahead of the 500 mb trough which
will move in Sunday aftn. Overall VFR conditions, as dont expect
vsbys to be impacted blo 7 sm but overall conditions not as clear
as today. Gusty south winds 15-25 kts, gusts over 30 kts in the
RRV.


&&

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

UPDATE...Riddle
SHORT TERM...DJR
LONG TERM...CWJ
AVIATION...Riddle



Area Forecast Discussion

National Weather Service Marquette MI

 802 PM EDT Sat Sep 19 2020

.SHORT TERM...(This evening through Sunday)
Issued at 346 PM EDT SAT SEP 19 2020

Water vapor imagery and RAP analysis show a mid-level trof over the
Pacific NW into the northern Rockies, a ridge shifting out over the
Plains and a trof over eastern N America. A fairly well-defined
shortwave diving into the departing eastern trof is skirting ne Lake
Superior. This wave has supported -shra across northern and eastern
Lake Superior today. SW edge of this pcpn has brushed the tip of the
Keweenaw and Luce County with sprinkles/-shra. Otherwise, clouds
have dominated across the northern and eastern fcst area today with
skies trending to mainly sunny toward the WI/MI stateline. Temps
range from the 50s under the clouds to the low/mid 60s where skies
are mostly sunny.

Some -shra or sprinkles will continue over the far eastern fcst area
for a few more hrs in association with the aforementioned shortwave
diving se into the departing eastern N America trof. Otherwise, with
the pattern progression, healthy height rises will occur across the
Upper Lakes as the the Plains mid-level ridge shifts e, arriving
over the fcst area during Sun. This will support dry weather and
clear to partly cloudy skies. Where winds become more decoupled
tonight, interior central, temps will fall toward 40F. Temps will
range up to around 50F near Lake Superior. Under waa on Sun that
pushes 850mb temps to 10C e and 14C w, high temps will reach the 60s
across the board. Temps will top 70F at some locations over the w
under approaching thermal ridge. Winds will become breezy on Sun as
pres gradient tightens btwn 1035mb high pres to the e and sfc trof
moving across the northern Plains. Fcst soundings indicate building
mixed layer will support gusts easily to 20-30mph. Gusts to 30-35mph
are expected over the w into the n central. Wouldn`t take much
increase in mixing heights to increase gusts further. The southerly
winds up Lake MI on Sun will lead to a mdt to potentially high swim
risk for the beaches of Schoolcraft County.

.LONG TERM...(Sunday night through Saturday)
Issued at 429 PM EDT SAT SEP 19 2020

Current mid-level pattern shows a pseudo-omega geopotential height
pattern with a troffing over the Great Lakes that brought the blo-
normal temps we saw this week and another trof moving inland over
the Pacific NW with ridging between the two. By the start of the
longterm period, this ridge shifts east over the Great Lakes as the
current trof over the Great Lakes moves to the Atlantic Coast where
models and NHC have it phasing with Hurricane Teddy at the start of
next week. After Teddy moves north towards Atlantic Canada, the
ridge begins to shift east over towards New England and the central
CONUS flow becomes less amplified. Heading into the second half of
this upcoming week, models suggest a shortwave to move through the
Upper Great Lakes region Wednesday night into Thursday, which looks
like our next legitimate shot at widespread mentionable
precipitation. Overall, temperatures look to stay near or above
normal for the longterm period with troffing and negative height
anomalies over the Pacific forcing downstream ridging and positive
height anomalies over the CONUS, favoring the above normal
temperatures.

A shortwave trof moving through Canada to the north will bring a sfc
trough over Upper Michigan bringing just a slight chance of some
showers. Model soundings aren`t as promising as some raw model
output suggests, so did lower the PoPs some from the going fcst,
keeping just the slight chance PoPs across the west half Sunday
night, and over the Keweenaw Monday morning. With this trough, a
50kt LLJ will also pass over Upper Michigan, which should keep
things windy on Monday, and uncertain on the wind over night. High-
res models certainly suggest gusty conditions to linger across the
higher terrain and and downslope-favored areas as often seen with
the WAA regimes. Increased the marine winds as well during this
period, some uncertainty but increased them manually using top of BL
winds.

Breezy conditions diminish Tuesday with a ridge of high pressure
moving through. With warm return flow, above normal temperatures are
expected with dry conditions. The next shot at precipitation comes
Wednesday night into Thursday as a shortwave trough and associated
cold front pass through the UP. Have left thunder chances out of the
fcst for now, but there is some modeled CAPE. Models show pretty
good agreement in timing of this wave, but left the NBM chance PoPs
for now considering it is still on day 5.
&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 758 PM EDT SAT SEP 19 2020

With dry low-levels persisting, VFR conditions will prevail at
KIWD/KCMX/KSAW thru this fcst period. During Sun morning, winds
will become gusty to 20+kt at all terminals with a further
increase in winds during the afternoon. &&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 346 PM EDT SAT SEP 19 2020

Tightening pres gradient btwn rather strong high pres over southern
Quebec/New England and low pres moving from Saskatchewan to Hudson
Bay will lead to brisk southerly winds over much of Lake Superior
for the next couple of days. Typical for this wind direction, the
strongest winds will occur mainly over the e half of Lake Superior.
Winds tonight/Sun should mainly be under 20kt over the w and 20-25kt
over the e. Winds of 20-30kt will be common Sun night/Mon, again
strongest over the e where a few gale gusts may also occur at some
of the high obs platforms. Pres gradient will then quickly slacken,
resulting in winds settling back to under 20kt Mon night and then to
under 15kt on Tue as a high pres ridge arrives. Winds will increase
a bit on Wed, but remain under 20kt. There may be a further increase
in winds on Thu in the wake of a cold front, but trends are toward
a weaker front and thus weaker winds with its passage.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&

$$

SHORT TERM...Rolfson
LONG TERM...JAW
AVIATION...Voss
MARINE...Rolfson



...Updated Aviation Forecast Discussion...



 .DISCUSSION...
Issued at 325 PM CDT Sat Sep 19 2020

Main forecast problem is wind in the short term.

Northwest upper flow over the region will switch to westerly and
southwesterly as ridge builds to our south. Near surface pressure
gradient will continue through Sunday, meaning strong surface
winds with gusts 30-35 kts. But not high enough for an advisory.
Smoke from fires will continue over the area and according to the
HRRR may be thicker on Sunday. The near ground smoke may also mix
down due to subsidence near front moving across the area from the
northwest. This will impact the far northwest part of the OAX
County Warning Area.

Warmer temperatures start tomorrow and continues through the work
week with highs in the 80s. The forecast is dry throughout the
entire week. The next best chance of rain is late next weekend.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 630 PM CDT Sat Sep 19 2020

VFR conditions will continue through the forecast period. Winds
will remain southerly, occasionally gusting up to 20-30 kts. LLWS
will be possible at KOFK from 03Z-15Z Sunday, and could sneak into
KLNK and KOMA between 04Z-15Z.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...None.
IA...None.
&&

$$

DISCUSSION...Smith
AVIATION...KG




Area Forecast Discussion

National Weather Service Pocatello ID

 857 PM MDT Sat Sep 19 2020

.SHORT TERM...Rest of Tonight...The latest radar imagery was
showing an area of weak convection northwest of Mud Lake working
east toward Dubois ahead of the core of a well defined upper low on
H2O satellite imagery. The latest HRRR and NAM both maintain
convection across that region into Island Park through midnight-3AM.
Thus am not going to get in to big of a hurry to reduce or remove
the precipitation potential across the NE mountains this evening. No
changes planned at this time. See the previous discussion below.
Huston

Isolated Showers and thunderstorms have already developed over the
Central Mountains this afternoon while the earlier line of showers
from this morning exits into western Wyoming. Several short term
models show a developing line of showers/thunderstorms during the
mid- afternoon hours across the Arco Desert/Upper Snake River Plain
tracking southeastward across the I-15 corridor and Idaho Falls to
Rexburg. Within the organized line would be the potential for small
hail and gusty winds while it continues it trek toward the Teton
Valley early this evening. Out ahead of this line, isolated
thunderstorms are possible this afternoon as well, including the
southern highland areas all the way to eastward to Bear Lake.
Eastern Magic Valley area and South Hills areas area least likely to
see thunderstorm develop but are expected to see gusty west or
northwest winds. Improvement to wind speeds and decreasing chances
of thunderstorms are forecast between 8 pm and 10 pm.

.Sunday through Tuesday...Zonal flow will allow for mild
temperatures and generally light winds this forecast period. A
ridge of high pressure begins to build back into the area from the
south by Monday, which will shift our winds back from the
southwest and begin to increase temperatures slightly. This time
period is expected to be precipitation free. ND

.LONG TERM...Tuesday through Saturday.  A weak system will pass east
south of Idaho but expect a chance of showers and thunderstorms in
the far eastern part of the state near the Wyoming border.  Will be
dry Wednesday and Thursday with the chance of showers returning
mainly to the central mountains and eastern highlands.  Temperatures
will be above normal through Friday with cooling expected by
Saturday as the next system works east.   Low confidence at the end
of the long term period as models greatly different with GFS slower
and wetter and European model drier and weaker with the end of the
week system.  Winds may increase by Friday into Saturday as well. GK
&&

.FIRE WEATHER...
Isolated to widely scattered thunderstorms will be possible through
sunset tonight with some breezy conditions as well.   Gusts of 20 to
30 mph will be possible especially in zones 410.  Brunt of
thunderstorm activity will be in zones 475, 476, 422, 410 and 411.
All locations will see at least isolated activity.  Humidity is way
up today and should remain so through Sunday.  Temperatures will
begin to moderate Sunday and remain above normal through next week.
Next chance for showers will be in the far east Tuesday mainly zones
413, 410 and 411.  Could be breezy as well Tuesday but not expecting
highlights as humidity stays above 15 percent. GK
&&

.AVIATION...Showers and thunderstorms have developed this
afternoon and have vicinity at all sites with SUN, BYi and DIJ
most likely to see on station but can`t rule out anywhere. Will
have 10 to 20 knot sustained winds through sunset at all sites
before dying down. Will have clear skies throughout the day Sunday
with up valley 10 to 15 knot afternoon winds at PIH and IDA. GK
&&

.AIR STAGNATION...Air Quality concerns from regional wildfire
smoke look to improve today as a low pressure trough moves through
our area and flow turns more westerly. This essentially `closes
off` flow from the CA wildfires for the time being. Keep in mind
though that smoke from local wildfires will certainly still impact
the air quality. This pattern of a general westerly flow looks to
continue through Monday before gradually opening back up again
from the southwest. ND
&&

.PIH WATCHES/WARNINGS/ADVISORIES...None.
&&

$$



Area Forecast Discussion

National Weather Service Reno NV

 410 PM PDT Sat Sep 19 2020

.SYNOPSIS...

Although smoke and decreased air quality from wildfires will
continue to impact portions of eastern California and western
Nevada, many areas will see better air quality with just some
general haze through at least Sunday. High temperatures return
to slightly above average for the bulk of next week. Dry
conditions with periods of breezy winds are expected next week.

&&

.DISCUSSION...

The key features of the forecast into next weekend:

* Smoke! I know...a big surprise.
* Potential for elevated breezes with fire weather issues and a
  return to more areas of smoke/poor air quality Monday-Tuesday,
  and late next week.
* Above average high temperatures Sunday through at least Thursday.

While denser smoke and poor air quality have decreased dramatically
in coverage across eastern California and western Nevada yesterday
and today due to a turn to more north-east flow, a general haze
persists. Most areas are currently experiencing good to moderate
air quality per `airnow.gov` with just a few pockets of poorer air
quality in Mono County. This general trend is forecast by the HRRR
to continue this weekend with light north to east flow in the
low levels.

Unfortunately for smoke coverage as well for fire concerns, winds
are expected to increase from the southwest and west Monday and
Tuesday afternoon and evening as weak low pressure moves into the
Pacific Northwest. While it is too far out to nail down details
(not in forecast yet) of smoke coverage, the wind flow brings the
solid potential for more smoke to pour into western NV and eastern
CA if the Creek and North Complex fires remain active. Isolated
pockets of critical conditions are possible Monday afternoon, with
the potential for more widespread critical conditions along the
Sierra Front northward on Tuesday.

Wednesday and Thursday, lighter winds return and temperatures
reach their peak (mid 70s-near 80 Sierra valleys, mid-upper 80s
lower valleys of western NV) as high pressure builds overhead.
However, another trough moves into the Pac NW late next week and
into the following weekend for another round of increased breezes.
Again, that will be of note for fire weather concerns as well as
for possibly increased smoke production. Temperature-wise, there
is less confidence in readings late next week. The blend of
ensembles/models at that time show a high temperature range of 10
or more degrees in some spots. The current forecast is in between
the two possible extremes...but keep in mind that highs late next
week could be several degrees warmer or cooler depending on the
timing and strength of the Pac NW trough. -Snyder

&&

.AVIATION...

A light northeasterly pressure gradient is laying over the region
with little supporting flow aloft. This will keep surface winds
easterly through the night for ridges with light to calm drainage
winds for valley locations. Heating Sunday will support a
southwesterly wind late in the afternoon, but speeds will remain
light. Southwest winds increase Monday/Tuesday afternoons with gusts
around 25kts for all terminals.

Otherwise, visibility will have some restriction for most locations,
especially MMH, due to varying degrees of smoke and/or haze. With
light flow tonight and Sunday resulting in diffuse smoke transport,
visibility will not be degraded below VFR for most area terminals.
This may change Monday depending on fire activity and how much smoke
builds in the central California valley over the weekend. Slantwise
visibility will be lower than prevailing surface VIS as well. MMH
could see an MVFR smoke layer if smoke from the Creek Fire more
efficiently spills across the Sierra crest the next couple of days.
Boyd

&&

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

$$

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