Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/26/20

Area Forecast Discussion...UPDATED

National Weather Service Aberdeen SD

 803 PM CDT Tue Aug 25 2020

.UPDATE...
Issued at 802 PM CDT Tue Aug 25 2020

No major changes for the overnight period. HRRR continues to
advertise isolated late night activity with LLJ, so will keep
that going. Otherwise, temperatures/winds look fine.

&&

.SHORT TERM...(This Evening through Wednesday Night)
Issued at 304 PM CDT Tue Aug 25 2020

Forecast challenges include temperatures throughout the period,
along with thunder chances early Wednesday morning through
Wednesday night.

Currently, under a sunny sky, temperatures are warming into the
90s to near 100 degrees south of a warm frontal boundary moving up
through the forecast area. Once in the hot muggy air south of the
boundary, winds are switching from an easterly component wind to
more of a south-southeasterly component wind.

With such warm air aloft over the CWA this afternoon through late
tonight, the expectation is dry weather conditions will prevail.
There is a cold front moving out of Montana/Wyoming this afternoon.
It will overtake this warm front advancing northward overnight,
while slowly making eastward progress across the Dakotas.
Isolated/widely scattered thunderstorms late tonight across mainly
north central South Dakota are still a rather low confidence and low
probability of occurring prospect. But, there should be a fairly
decent belt of mid/upper level westerlies just off to the north/west
in the morning. And, models are hinting at the possibility of seeing
700hpa temps cool a degree or two down to around +12C to +13C across
western/northern South Dakota heading towards 12Z Wednesday.
Forcing/lift and a little bit of cooling aloft may be all that`s
needed to set off a handful of elevated showers/storms by morning.
Thermometers tonight reading close to 70F degrees puts the CWA at
appx 15 degrees above normal for low temperatures. A warm/humid late
August night for sure.

The gradual cooling trend aloft continues throughout the day
Wednesday and Wednesday night. Models do all agree on a few pockets
of convective potential, mainly associated with forcing from this
cold frontal passage that is progged to be ongoing on Wednesday,
along with the lift associated with any subtle s/w`s rotating up out
of the desert southwest in this latest rendition of monsoonal flow
up into the northern plains. But, they don`t agree on placement or
timing of those pockets of convection, so forecast confidence (and
pops) remain on the low side during the day Wednesday and Wednesday
night. At this point, models indicate there should be enough
instability/shear around Wednesday afternoon/evening to support a
few strong to possibly severe thunderstorms, should any storms
actually develop. Low level thermal progs suggest there will be a
portion of forecast zones over the eastern CWA that could warm back
up to around 90F degrees or so, prior to fropa. Locations that end
up warming up, post-frontal, on Wednesday should notice things
becoming a bit cooler/drier by the end of the day. Overall though,
high and low temperatures Wednesday and Wednesday night will
probably end up being a good 5 to 10 degrees above climo normal.

.LONG TERM...(Thursday through Tuesday)
Issued at 304 PM CDT Tue Aug 25 2020

The main focus in this period will be on convective chances followed
by a fairly noticeable cool down by the end of the term. Sfc high
pressure will be sliding northeast of our area on Thursday as sfc
low pressure organizes to our west. These features progress eastward
during the day into Thursday night. Some ongoing convection will
perhaps be moving across the region early Thursday in association
with some mid lvl s/w energy. However, better chances for convection
look to hold off until later in the day into the nighttime hours as
shear and instability become more favorable(especially southern half
of this CWA). These indices combined with a frontal boundary passage
and mid lvl s/w trough could potentially lead to a round of strong
to severe storms for portions of this forecast area Thursday night.

This activity is progged to be clear of the area Friday morning as
sfc high pressure begins to move in. This should deliver a more
comfortable airmass to the region along with slightly cooler
conditions. This respite from the active, hot weather will spill
over into the first half of the weekend as the high drifts over the
area and eastward. Southerly flow returns by Sunday as low lvl
moisture works northward ahead of the next low pressure system that
is forecast to be sliding into the western Dakotas. Storm chances
will be on the increase by Sunday, but moreso by Sunday night into
Monday. Model consensus remains up in the air with the timing and
intensity of this system. The broadbrush of PoPs will remain in the
forecast for this time, but enough agreement points to the latter
half of Sunday through the first half of Monday being the best
window for precip chances at this point. Once this system departs
early next week, models do agree the region will see a much cooler
airmass take hold.

Temperatures will start off the period above normal with highs in
the 80s to around 90 on Thursday. Slightly cooler conditions return
behind the departing system Friday into Saturday with temperatures
about normal for late August. Above normal readings return briefly
on Sunday with highs back into the 80s to around 90 degrees. The
more noticeable change arrives early next week as daytime highs look
to remain in the low-mid 70s and overnight lows fall into the 50s,
perhaps a few upper 40s by Tuesday morning.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday Evening)
Issued at 617 PM CDT Tue Aug 25 2020

Terminals KABR,KATY,KPIR,KMBG

Mainly VFR skies/vsbys are expected through tonight at all
terminals.

***Construction to improve taxiways at both KABR/KPIR terminals
may cause an occasional temporary visibility reduction due
to blowing dust (bldu), mainly during daytime hours UFN.


&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
&&

$$

UPDATE...TDK
SHORT TERM...Dorn
LONG TERM...Vipond
AVIATION...TDK



Area Forecast Discussion

National Weather Service Denver/Boulder CO

 851 PM MDT Tue Aug 25 2020

.UPDATE...
Issued at 850 PM MDT Tue Aug 25 2020

Several outflow boundary interactions over the metro areas and
plains ended up sparking scattered showers and thunderstorms this
evening, with some strong outflow gusts of 35 to 50 mph. Extended
the chance for showers and thunderstorms further east as the
outflows have lined up just right to provide extra lift into
eastern Adams, eastern Arapahoe and Washington counties. Most
convective activity is decreasing now, with diminishment expected
by midnight. Though wouldn`t be surprised to see a few weak
showers last for a couple hours after that over the northern
mountains and Cheyenne Ridge based on a slight disturbance seen
in water vapor imagery moving across Wyoming, as well as model
forecasted CAPEs.

No other forecast updates needed at this time.


&&

.SHORT TERM...(This evening through Wednesday)
Issued at 141 PM MDT Tue Aug 25 2020

The upper level ridge is near the Four Corners region this
afternoon with a weak westerly flow aloft. Weak flow coupled with
a slight increase in precipitable water values over the
mountains. One storm near Glen Haven in Larimer County produced
0.55 inch of rain in 30 minutes, so better rainfall potential with
the storms that do develop. The HRRR still shows some weaker
showers and storms developing along the urban corridor and
adjacent plains through this evening, then tapering off by
midnight. Late tonight into Wednesday morning, a shortwave trough
will pass from the central Rockies into western South Dakota.
This will nudge the ridge more to the southeast on Wednesday. This
will allow for a slightly stronger westerly flow in the mid and
upper levels. In addition, the models bring in a push of north to
northeast winds Wednesday morning that stick around in the
afternoon. Temperatures still hot on Wednesday, but there should
be a gradual increase in dewpoints over the northeast plains in
the afternoon. The models still show precipitable water values
increase across the forecast area on Wednesday, 0.75 inch in the
mountains, at or above 1.0 inch over the northeast plains. Best
shower/thunderstorm coverage will be over the mountain areas in
the afternoon, spreading across the urban corridor and northeast
plains after 21z. ML CAPE/MU CAPES 500-1000 j/kg in the afternoon
across the urban corridor/northeast plains from the NAM12 forecast
soundings. In the mountains, values similar to this afternoon
with drier air below 600 mb. Main issues will be gusty winds with
the stronger storms but there will be a better potential for
wetting rainfall.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 141 PM MDT Tue Aug 25 2020

Models still show the ridge which has dominated the area recently
weakening some on Wednesday and Thursday. Precipitable water values
are showing slight drying of the high terrain on Thursday, which
should limit convection. Highs should remain in the mid 90s in the
foothills and on the plains.

Friday, a front is expected to bring temperatures down to more
seasonable levels across the area, with highs in the low or mid 80s
in the metro area. While precipitable water and dew points don`t
increase much, the decrease in temperature should significantly
increase humidity, especially on the plains. A small, upper-level
disturbance should also contribute to showers and storms in the
afternoon and evening.

Saturday, the flow aloft should turn to west-northwest with
southerly surface flow and an increase in moisture. In the
evening, MLCAPE may exceed 1500 J/kg on the eastern plains and
scattered storms can be expected. Sunday should see drying and
much less storm coverage.

Monday and Tuesday, both the GFS and ECMWF show strong troughing
across the area, with northwest flow aloft with an approaching jet
late Tuesday into early Wednesday. MOS show highs in the mid or
upper 70s in the foothills and plains. Along with an expected
increase in moisture, this situation should bring some storms. The
latest ECMWF shows a cutoff low developing all the way into the far
southwest and the GFS shows a more relaxed trough through the
plains, and the solution is expected somewhere between.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 850 PM MDT Tue Aug 25 2020

Areas of smoke/haze with poor slant visibilities will continue to
be the primary aviation impact through the next 24 hours. Surface
visibilities may drop to 6 miles at times, but VFR conditions
will prevail. Most shower/storm activity is done for the
terminals, however decaying showers just SSE of DEN is pushing
strong outflow winds into DEN and APA. These should calm down over
the next hour with surface winds shifting to drainage. Expect
north/northeast winds to push into the terminals after 15z
Wednesday and continue from that direction into the afternoon.
Should see a better chance of showers/thunderstorms Wednesday
afternoon.


&&

.FIRE WEATHER...
Issued at 141 PM MDT Tue Aug 25 2020

Slow moving showers and thunderstorms developing in the mountains
and foothills this afternoon with the potential of producing gusty
winds but also wetting rainfall. A site near Glen Haven picked up
0.55 inches in 30 minutes earlier this afternoon. More of the same
type of weather is expected to occur on Wednesday afternoon,
although the winds in the mid and upper level may be a little
stronger from the west. Overall precipitable water values should
remain high enough to produce wetting rainfall, but strong gusty
outflow winds to 40 mph as well.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

UPDATE...Kriederman
SHORT TERM...Cooper
LONG TERM...Direnzo
AVIATION...Cooper/Kriederman
FIRE WEATHER...Cooper



Area Forecast Discussion

National Weather Service Medford OR

 737 PM PDT Tue Aug 25 2020

.DISCUSSION...Isolated showers and thunderstorms east of the
Cascades earlier this evening are mostly dwindling over the past
30 minutes or so and will probably fizzle around or shortly after
8 pm. The most CG lightning occurred in Modoc County this evening
with almost 30 flashes SE of Alturas. That was in addition to the
50 or so flashes that occurred across northern Klamath/Lake
Counties earlier in the day. Have adjusted the grids to account
for the diminishing trends on satellite/radar.

Smoke/haze cover a large area from Siskiyou County northeastward,
but conditions have noticeably improved here in the Rogue Valley
this evening as north to northwest up-valley breezes helped scour
out some of the lower- level smoke. We`ll maintain the haze though
as high-level smoke continues to lift northeastward from the
fires to the south and southwest. It`s clear along the coast
currently, but we expect some stratus/fog to return to those areas
overnight into Wednesday morning. Other than that and the
isolated showers/storms this evening, tonight should be tranquil.

Wednesday will be a repeat of today with isolated storms forming
again east of the Cascades in the afternoon. That part of the
forecast looks to be in good shape. -Spilde

&&

.AVIATION...For the 26/00 TAFs...Over the coastal waters and along
the coast...Areas of IFR cigs/vsbys in low clouds and fog will
spread south into the waters around 03Z this evening, then soon
after will move onshore into the Coquille Valley. These lower
ceilings will dissipate after 16Z Wednesday morning.

Inland areas west of the Cascades in Oregon...VFR conditions will
prevail into Wednesday afternoon, but there will be areas of smoke
and haze.

Northern California and east of the Cascades...VFR conditions will
prevail into Wednesday afternoon, except for areas of MVFR vsbys in
wildfire smoke. There will be isolated thunderstorms this evening
and again Wednesday afternoon into the evening.


&&

.MARINE...Updated 730 PM PDT Tuesday 25 August 2020....A
thermal trough will persist near the coast through the week. This
will bring gusty north winds and steep to very steep seas with the
strongest winds and highest seas south of Cape Blanco. Winds and
seas will become more hazardous from Wednesday into the weekend with
gale force winds likely south of Cape Blanco and strongest south of
Ophir. All areas will remain hazardous for small craft through this
time.

&&

.PREV DISCUSSION... /Issued 223 PM PDT Tue Aug 25 2020/

DISCUSSION...As of 2 PM, a few showers are making their way
northeast over northern Lake County, and a line of thunderstorms
has developed over southeastern Modoc County. This activity is
likely to continue through the afternoon and into the evening as a
weak shortwave passes overhead, with additional convection likely
across northern California and the East Side of Southern Oregon.
Thunderstorms are expected to be more isolated, but several
lightning strikes and light to moderate rainfall is possible
should one of these cells move directly overhead.

The upper level trough, currently offshore, will make a run
through the region tomorrow, passing mostly to the north of us,
but it should be enough to touch off additional thunderstorms
tomorrow afternoon and evening, in the same general area as today.
This will likely be the last significant chance for thunder
and/or precipitation until a weak front makes its way into the
area this weekend into early next week. The front will most likely
pass as a dry one, but some model solutions, mainly the ECMWF, do
suggest the possibility of convection. These more amplified
solutions are in the minority, and seem more than a bit out of
place for this time of year, thus confidence is much too low to
include these in the forecast.

Otherwise, the weather for our area will be characterized by
smoke and warm but not overly hot temperatures. Once the trough
exits tomorrow, ridging will slowly begin to build in from the
west, and the thermal trough along the coast will strengthen. This
will produce a broad offshore flow, drying the region out and
potentially setting up the Chetco Effect in the Brookings area,
with high temperatures in the 80s possible there through the
weekend. The hottest day for the area (excluding the south coast)
is likely Friday, with highs reaching about 5 degrees above
normal for this time of year, but most days will hover right
around seasonal normals.

The shift in the pattern will help, but will not completely clear
smoke from area skies. The prevailing winds and the day-to-night
wind cycle will likely clear smoke from areas west of the Cascades
in Oregon, but with fires still burning strong to the south,
prevailing winds aloft, and daily mixing to the surface, smoke is
expected to continue to impact the bulk of Siskiyou, Modoc, Lake,
and Klamath Counties for the foreseeable future. -BPN

AVIATION...For the 25/18 TAFs...Over the coastal waters and along
the coast...Areas of IFR cigs/vsbys in low clouds and fog will
burn back offshore by late morning, then move back onshore
this evening. The lower ceilings will persist into Wednesday
morning.

Inland areas west of the Cascades in Oregon...VFR conditions will
prevail into Wednesday morning, but there will be areas of smoke and
haze, along with a few showers or thunderstorms Tuesday morning.

Northern California and east of the Cascades...VFR conditions will
prevail into Wednesday morning, except for areas of MVFR vsbys in
wildfire smoke. There will be isolated thunderstorms through Tuesday
evening.

MARINE...Updated 200 PM PDT Monday 24 August 2020....A thermal
trough will persist near the coast through the week. This will bring
gusty north winds and steep to very steep seas with the strongest
winds and highest seas south of Cape Blanco. Winds and seas will
become more hazardous from Wednesday into the weekend with gale
force winds likely south of Cape Blanco and strongest south of
Ophir. All areas will remain hazardous for small crafts through this
time.

FIRE WEATHER...Updated 200 PM PDT Tuesday 25 August 2020...The main
concern over the next couple of days will be thunderstorms, mainly
east of the Cascades and northern California. The one thing that
could put a cap on the amount of thunderstorms will be smoke. With
that said, recent Geocolor satellite images are showing signs of
smoke starting to thin out some in Fire Zone 285 and southeast
portions of fire zone 625. At the same time were starting to see
cumulus development in these areas. A few storms have developed in
southeast fire zone 285 and we`ll continue to keep a close watch on
further development as the afternoon progresses. The past several
runs of the HRRR (high resolution rapid refresh) model has been
rather consistent with where, when, and amount of storm development
this afternoon into this evening. It looks like the best chance for
isolated thunderstorms are expected to be between 2 and 8 pm pdt,
but would not be surprised if they begin to fizzle out an hour
earlier (7 pm pdt). At this time, were not expecting anything more
then isolated, so we`ll continue to headline in the fire weather
forecast. However, if something unforeseen happens, we will update
everyone.

Any storms will end this evening with dry conditions tonight with
mostly moderate overnight recoveries (except for the coast and Fire
zones 615 and northwest 616).

Wednesday, the upper trough axis remains west of out area which will
still put us in a favorable position for isolated thunderstorms from
the Siskiyous south and Cascades east Wednesday afternoon and
evening. Like today, smoke will be the main wild card and could
limit surface heating and thus cap the amount of thunderstorms.

After Wednesday, the threat for thunderstorms are almost or at zero
through at least next Tuesday. However, our focus will go from
thunderstorms to winds and low relative humidity starting as early
as Thursday morning. Details follow below.

A thermal trough will develop along the coast Thursday and could
very well last into the early next week. This will bring gusty winds
near and at the ridges in fire zones 618, 619, 620, and 280 with
moderate to locally poor overnight recoveries. Meanwhile, an upper
trough will slide northeast of our area Sunday and we could see
gusty winds and low relative humidity for fire weather zones 624,
625 and 285 Sunday afternoon into Sunday evening as the pressure
gradient tightens up.

Afternoon temperatures are not expected to vary much from one day to
the next through Thursday. They are expected to increase for most
inland locations Friday and Saturday, followed by slight cooling
Sunday. At the coast, mainly south of Cape Blanco, they are expected
to increase (due to increasing offshore flow and Chetco effect)
Thursday through the weekend. -Petrucelli

&&

.MFR WATCHES/WARNINGS/ADVISORIES...
OR...
CA...None.

Pacific Coastal Waters...Small Craft Advisory until 11 PM PDT Thursday
     for PZZ356-370-376.
     Gale Warning from 11 AM Wednesday to 11 PM PDT Thursday for
     PZZ356-376.
     Small Craft Advisory from 11 AM Wednesday to 11 PM PDT Thursday
     for PZZ350.

$$

MAS/DW



...Updated Aviation Forecast Discussion...



 .DISCUSSION...
Issued at 248 PM CDT Tue Aug 25 2020

Today and Tomorrow:
A visual check of the sky and satellite imagery reveal there is a
bit of a haze above the area today. The experimental HRRR
vertically integrated smoke parameter shows values around 150
mg/m^2 (a high value) over the northern Plains. The source of the
smoke is the wildfires over the western CONUS. The HRRR does show
that this value should decrease over Nebraska and Iowa over the
next couple of days due to a change in the upper level wind
pattern. The smoke shouldn`t have a great effect in the area. The
haze may linger for a couple of days and temperatures may be a
degree or two lower due to the increased aerosols in the air.

Temperatures this afternoon could reach 100 degrees in some spots.
Winds this afternoon have been observed in the 15 to 20 mph range
gusting up to 25 mph. They`ll begin to taper off this evening.
Temperatures tomorrow will be similar to today, but a degree or
two cooler. More of the forecast area should see increased wind
speeds as a surface low moves in from the west. Expect winds
tomorrow from the south at 15 to 20 mph gusting up to 30 mph.
There is a slight chance for rain along the NE/SD border Wednesday
after 7 pm. It is a small chance for rain and even if rain does
materialize, the total amount would be less than a tenth of an
inch.

Thursday through Monday:
By Thursday the ridge will have begun to flatten. The hottest
temperatures should be confined to southeast Nebraska. The best
chance for rain in the area is going to be late Thursday night
into Friday morning. An upper level disturbance is expected to
develop off the Rocky Mountains in Wyoming and move across South
Dakota. The main mechanisms for lift will be the upper level
disturbance and a cold front that is expected to stall out
Thursday across South Dakota. Significant rain in Nebraska isn`t
looking likely, but it is more than 48 hours yet. The SPC has
issued a slight risk for severe weather for that period. With
strong shear behind the front, the primary severe weather threats
are strong gusty winds and hail.

The weekend will be much cooler as the upper level disturbance
will break down the ridge and bring in cooler temperatures. High
temperatures Saturday and Sunday should be in the 80 to 85 degree
range. Another upper level disturbance is expected to move south
from the Canadian Plains on Monday and further reduce
temperatures which should lead to a cool start to the week.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 624 PM CDT Tue Aug 25 2020

VFR conditions will prevail through the period. Threat for LLWS at
all terminals though early Wednesday morning.

&&

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

$$

DISCUSSION...Fajman
AVIATION...DEE