Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/08/20
Area Forecast Discussion
National Weather Service Denver/Boulder CO
806 PM MDT Mon Sep 7 2020
.UPDATE...
Issued at 755 PM MDT Mon Sep 7 2020
A couple different pre-front-cold-fronts came down across the CWA
late this afternoon and earlier this evening. The real front is
now across the northern CWA border, heading south. Real data
indicates that the northeasterlies, from the first front made to
the the Cameron Peak Fire. It is already showing signs of
"decrease-ment". Its smoke plume has tamed down consierably
already. The grids are in pretty good shape with the significant
weather change expected.
&&
.SHORT TERM...(This evening through Tuesday)
Issued at 348 PM MDT Mon Sep 7 2020
...SNOW AND RECORD COLD EXPECTED TUESDAY INTO WEDNESDAY...
The weather expectations remain unchanged as the north winds ahead
of the cold front are now spreading across Weld County and towards
the Denver/Boulder metro area. Strengthening north winds should
continue through the evening as cold air moves into the state.
Fire activity on the Cameron Peak fire remains vigorous to
extreme. Warnings and Advisories remain in effect for the
mountains, foothills and out onto the plains. Rain on the plains
and snow in the mountains should develop by midnight. Rain on the
plains will continue through about 6 AM, when temperatures cool
enough and the airmass becomes cold enough through the column for
precipitation to change over to snow. Mountain areas should see
accumulating snow overnight and through the day, but accumulations
on the plains will be harder to realize due to warm ground
temperatures and air temperatures in the lower 30s. Snow sill fall
through the day, but will mostly melt until later tomorrow
evening.
.LONG TERM...(Tuesday night through Monday)
Issued at 348 PM MDT Mon Sep 7 2020
The early winter storm will continue to impact the area Tuesday
night and possibly into Wednesday before finally loosening its
grip on the forecast area. We would expect mostly snow (perhaps a
mix in the far northeast corner) continue into Tuesday night with
continued upslope, but gradually weakening QG ascent. Models have
excellent agreement on the synoptic positioning of the upper level
low settling into the Utah/Arizona border/Four Corners region, but
the details on the mesoscale forcing and melting still make this
a difficult forecast, as usual for Colorado. Most of the models do
have one good batch of precipitation rotating around the upper
low and across the Front Range and northeast plains during the
evening. Apparently there is a weak embedded short wave kicking
out of the upper low, but there is little QG signature or other
mesoscale forcing like frontogenesis indicated. There has been
reasonable consistency with regard to this feature, so we do think
a period of heavier snow is possible during the evening. Snow
should continue overnight with overall weak QG lift and upslope,
although the intensity will decrease as both of these support
mechanisms weaken. Tuesday night will provide the highest chances
of meaningful accumulating snowfall across the plains, given loss
of any solar insolation and continued cooling of the near surface
soil temperatures. We`ll likely see our largest storm impacts in
this period as we accumulate heavy, wet snow on trees and elevated
surfaces. Thus, we`ll continue to message potential for broken
tree limbs and scattered power outages.
Snow will continue to taper off Wednesday as we lose our upper
level forcing and flow turns deep south/southeasterly. That said,
this flow pattern would continue to produce accumulating snow in
Park County through much of the day.
Total snow accumulations are still very tricky considering the
heat ahead of this storm and the amount of melting that will
occur, especially during the day tomorrow. The higher elevations
of the foothills and mountains should be able to hang onto most of
the falling snow as accumulation due to the very cold temps in
the teens to mid 20s, while the I-25 Urban Corridor is still a
wildcard, and will be through this entire event. We did like the
newest HRRR variable snow accumulation product, which shows 8-18
inches with locally higher amounts in the foothills, anywhere
from 2-6 inches in the I-25 Corridor (locally higher amounts
possible right near the foothills and Palmer Divide). Most of the
eastern plains would be lighter in the Trace to 4 inch range, but
if the heavier band materializes Tuesday evening then a few spots
could get more.
The upper level low will eventually fill and most likely kick
northeast across the state Thursday and Thursday night. This will
likely bring one last round of showers to the mountains with light
snow accumulations possible, and a chance of rain showers to the
lower elevations.
Record low temperatures can be expected Tuesday night, with
readings dropping below freezing over most of the plains. If
precipitation continued all night, lows could hover near 30-32F,
otherwise some upper 20s will occur. If it did drop below 30F in
Denver Wednesday morning, it would be the earliest 20s ever
recorded, and only four days after our latest 100F ever. Wednesday
looks like another cold day with highs on the plains only reaching
the 30s.
Temperatures will then gradually moderate through the end of the
week as ridging and drier westerly flow aloft develops.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 755 PM MDT Mon Sep 7 2020
Northeasterly winds currently, should gradually give way to more
due northerly winds at DIA by around 0330Z. Initially, after the
front moves through, wind gusts could reach 35-40 knots for a
couple of hours. Ceilings should come down into the BKN-
OVC020-030 range by 06Z. IFR conditions can be expected at DIA
sometime around 12Z Tuesday morning. Snow is expected as the
precipitation type from that time on into Wednesday, but it will
be unlike for any of the snow to accumulate in runways.
&&
.FIRE WEATHER...
Issued at 755 PM MDT Mon Sep 7 2020
The RFW has expired at 02Z. Hopefully, the expected incoming
moisture will have a serious impact on reducing our short/medium
range fire danger and, perhaps, putting our ongoing fires out.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
Freeze Warning from 6 PM Tuesday to noon MDT Wednesday for
COZ038>051.
Winter Storm Warning from midnight tonight to noon MDT Wednesday
for COZ033>037-041.
Winter Weather Advisory from midnight tonight to 6 AM MDT
Wednesday for COZ031.
Winter Weather Advisory from midnight tonight to noon MDT
Wednesday for COZ038>040-042-043-045-046.
&&
$$
UPDATE.........RJK
SHORT TERM.....Dankers
LONG TERM......Barjenbruch
AVIATION.......RJK
FIRE WEATHER...RJK
Area Forecast Discussion
National Weather Service El Paso TX/Santa Teresa NM
333 PM MDT Mon Sep 7 2020
.SYNOPSIS...
Warmer temperatures today and tomorrow, with slight chances for
storms in the higher terrain. A cold front moves in early
Wednesday morning, brining widespread rain chances and cooler
temperatures. Temperatures will drop to 15 - 20 degrees below
normal for the middle of the week. As the moisture slowly moves
out towards the end of the week, temperatures remain slow to warm
back up and storm chances transition to more convective by the
weekend.
&&
.DISCUSSION...
.SHORT TERM...Tonight and Tuesday...
Storm system starting to move into the northern plains and Rockies
today and will be moving south overnight and into Tuesday. Main
trough will become cutoff over the Great Salt Lake area by morning
and then slowly move to just north of the Four Corners region by 00Z
Wed. For the Borderland, expect increasing surface pressure gradient
as system deepens and west to southwest winds pick up overnight.
This will lead to a mild night with most lowland areas not dropping
below the mid 60s with KELP possibly remaining in the mid to upper
70s. There will be a decent moisture tap from the WSW which will
bring dew points into the 50s across the south which will lead to a
better chance for storms Tuesday afternoon.
For Tuesday, with decent moisture in place, even with some mixing
out for the afternoon, looks like good instability will result,
especially over southwest portion of area. With upper low in place,
models indicating weak disturbance moving through southwest flow
aloft into western NM during the afternoon. Operational global
models not producing much more than some storms over area mountains,
but 12Z HRRR out to 00Z Wed indicating good storm coverage by late
afternoon over much of the CWA. Went with 20-30 pops lowlands and
30-40 pops mountains for the afternoon. Shear not great with fairly
uniform westerly winds winds and little change in speed. Could still
see some strong storms though as they move quickly eastward. Also
expect cold front to be focus for some storms late in the northeast
but moreso going into the evening hours. The west to southwest
surface winds of 15-30 mph will allow temperatures to warm again
nicely. MET guidance looks out to lunch with highs for Tuesday given
the winds and warm start. Even MAV which is 5-15 degrees warmer may
not be warm enough in some locations, so went with near 100 around
Rio Grande Valley and lower to mid 90s out west and far east. Cold
front will likely have an effect at least for lower elevations of
Sacs with quickly falling temperatures around Mayhill in the late
afternoon.
&&
&&
.LONG TERM...Wednesday through Tuesday...
The story of this period is the approaching coldfront, and for
good reason. A quickly approaching upper level low spins above
southeastern UT. Global models agree on the center of the low
remaining over the eastern UT/AZ border for the first 24 hours of
the period. Moving southward with it is a surface coldfront to the
east of the upper level system. Up until today, there was good
agreement on the timing and magnitude of the front arriving.
Newest runs push back the arrival time of the front, now more
early Wednesday morning, and stall a majority of the coldest air
in eastern NM. Cooler air (850 temps in the teens) will spill into
the area Wednesday night still and reach just west of the
continental divide by day break Wednesday. These newer model runs
show the air mass to be more shallow and a bit warmer once it
spills into the area. The moisture with this modified air mass
still holds PW values around 1 - 1.25 inches (which is healthy for
a cooler air mass such as this one). As left over CAPE is pushed
southwest, a few thunderstorms could form along the boundary.
Gusty conditions will exist as the front contracts and the
pressure gradients meanders back and forth around the continental
divide area Wednesday. Temperatures are a bit hard to put an
exact number on, however we will see values drop to 15 - 20
degrees below normal. Since we still have a higher sun angle, one
break in the clouds could warm the air up significantly.
Generally, the air behind this front is cooler, and will give the
area a much needed break from the heat, especially if light rain
continues on and off throughout the day. Thunderstorms are looking
more favorable west of the continental divide with these newer
model runs. With a more shallow airmass, clouds could clear up
during the day Wed and Thursday. Models hint at the western zones
holding onto surface dew points in the low 50s. Paired with the
cooler air aloft, this could be a nice set up for some CAPE.
Models do show ~700 J/Kg around ELP for this time frame. With
organized upper level and lower level winds, we have ~30-40kts
0-6km Bulk shear to work with as well in areas of healthy CAPE.
In summary, western areas could see some storm development Wed and
Thursday afternoons.
The strongest winds look to be Wednesday night in the eastern
counties, as the coldfront has a nocturnal push westward. Wind
speeds and gusts flirt with advisory criteria, especially along
the west slopes of mountains in these areas. Temperatures remain
well below normal Thursday and Friday, but slowly warm up.
By Friday morning, the upper level low lifts north east from the
AZ/UT border. This trajectory will keep most of the strongest
upper level winds to our north, keeping our surface winds calm for
the end of the week. Due to less invasive upper level westerlies,
easterly winds remain at the surface this weekend. A heat low
over the AZ desert will help pull in moisture from the east. This
added lowlevel moisture will keep temperatures near seasonal, and
continue rain chances through the end of the period for the
eastern counties.
&&
.AVIATION...18Z TAF CYCLE
P6SM FEW-SCT120-150 through period. Isolated -TSRA BKN080-100
possible between 18Z-02Z over area mountains. Winds start out S to
SW AOB 12KTS but shifting after 03Z to the W to SW at 10-20KTS.
Gusts to 25KTS after 15Z, especially around KDMN and KLRU.
&&
26
&&
.FIRE WEATHER...
One last day expected for Tuesday of very hot temperatures ahead of
an unseasonably strong cold front. Highs will again approach the
100 degree range over some lowland areas, especially southern NM and
far West TX near the Rio Grande. West to southwest winds will also
be in the 15 to 30 mph range with strongest winds over the south.
May have a few hours of near critical conditions south, but there is
an increase in low level moisture which should keep relative
humidities slightly above critical values where winds are strongest.
Cold front moves through western half of area Tuesday night which
will bring gusty E to NE winds to the area and a chance for showers
and thunderstorms areawide.
Much cooler temperatures for Wednesday, especially eastern half of
the area behind the front and with strong upper low lingering over
the Four Corners region through Thursday. As the low lifts northeast
late in the week, temperatures will be rebounding back to near
normal by the weekend with a few showers and thunderstorms still
possible.
&&
26-Grzywacz
&&
.PRELIMINARY POINT TEMPS/POPS...
El Paso 71 100 58 73 / 0 10 80 50
Sierra Blanca 64 96 54 67 / 0 20 80 50
Las Cruces 66 97 56 70 / 0 20 80 50
Alamogordo 68 99 53 70 / 0 40 80 60
Cloudcroft 51 77 35 50 / 0 40 80 70
Truth or Consequences 66 99 53 66 / 0 30 80 60
Silver City 63 91 54 67 / 0 20 70 70
Deming 68 99 56 73 / 0 20 70 60
Lordsburg 67 98 60 76 / 0 20 50 70
West El Paso Metro 73 102 60 75 / 0 10 80 40
Dell City 64 100 49 65 / 0 20 80 40
Fort Hancock 69 102 60 77 / 0 10 80 50
Loma Linda 68 94 53 65 / 0 20 80 50
Fabens 71 100 60 74 / 0 10 70 50
Santa Teresa 69 99 57 74 / 0 20 80 50
White Sands HQ 69 100 57 71 / 0 20 80 50
Jornada Range 65 99 56 70 / 0 20 80 50
Hatch 66 100 56 71 / 0 20 80 60
Columbus 71 99 60 77 / 0 20 60 50
Orogrande 67 100 55 70 / 0 20 80 50
Mayhill 58 87 38 53 / 0 40 80 70
Mescalero 56 87 37 58 / 0 40 80 70
Timberon 53 84 40 56 / 0 40 80 60
Winston 55 92 42 61 / 0 30 70 70
Hillsboro 63 99 49 68 / 0 30 70 70
Spaceport 64 99 53 69 / 0 30 80 60
Lake Roberts 52 90 48 67 / 0 20 70 70
Hurley 64 94 53 69 / 0 20 70 70
Cliff 61 97 56 74 / 0 20 60 60
Mule Creek 61 92 56 71 / 0 20 60 60
Faywood 64 94 53 68 / 0 30 70 70
Animas 66 98 59 79 / 0 20 40 60
Hachita 65 97 57 77 / 0 20 50 60
Antelope Wells 65 94 59 79 / 10 20 40 60
Cloverdale 63 89 61 75 / 10 20 40 60
&&
.EPZ WATCHES/WARNINGS/ADVISORIES...
NM...None.
TX...None.
&&
$$
26-Grzywacz/31/26
Area Forecast Discussion
National Weather Service Grand Forks ND
1008 PM CDT Mon Sep 7 2020
.UPDATE...
Issued at 1004 PM CDT Mon Sep 7 2020
The CU really has pretty much dissipated over the area. This
leaves thicker cirrus in the far south but rather thin cirrus or
mainly clear sky central and north parts of the fcst area. Not
ideal radiational cooling but degree of clearing is allowing temps
to drop into the upper 30s to low 40s area wide with pockets of
mid 30s. Will leave temp fcst as is and no changes to headlines.
Some risk of frost outside of Fargo in areas not in advisory but
unclear extent at this time as high clouds still upstream. Short
term models indicate some additional clouds dropping south toward
morning into far NE ND/NW MN but upstream shows not much in the
way of cloud cover up thru the central Interlake region north of
Winnipeg. So that remains uncertain.
UPDATE Issued at 701 PM CDT Mon Sep 7 2020
The CU is breaking up pretty good attm leaving behind some cirrus,
though that is thin in the northern fcst area. Areas of stratocu
are in Manitoba though and with high to our west will keep enough
of a north-northwest wind tonight and patches of clouds to keep
lows 30-38 across the area. Going frost/freeze headlines appear
reasonable as HRRR sfc temps indicate the two areas of psbl 32 or
lower temps, one larger area in north central ND into parts of the
DVL basin and the other in areas near Thief River/Fosston.
Will need to monitor cloud trends this evening for any temp
adjustements.
&&
.SHORT TERM...(This evening through Tuesday night)
Issued at 256 PM CDT Mon Sep 7 2020
Temperatures will be the main concerns for the period.
Some light rain over the southwestern CWA as an embedded shortwave
rounds the base of the big trough over the north central CONUS.
Clouds have continued across most of the area, with stratocu
rapidly filling in where it tried to clear out in the north. That
stratocu will dissipate this evening, so at least partial clearing
across the northern counties is expected. Still a bit of north to
northwest winds on the front side of the surface high, so
radiational cooling will not be ideal, but there will be continued
cold air advection. Given that some spots in our northwestern
counties got into the upper 30s even with cloud cover last night,
getting down into the low 30s or even upper 20s seems reasonable
in our cold spots. Will continue to keep the freeze warning going
in northeastern ND and the boggy areas of northwestern MN, with
frost advisory in the northern RRV and along the southern edges of
the warning. Still uncertain to how cold the southern counties
will get due to cloud cover, so will continue to keep them out of
any headlines for now.
Split flow aloft for tomorrow with the southern branch upper low
well to our southwest and the northern branch over our area. Cold
air aloft should help develop some decent stratocu again tomorrow,
as temps heat into the low to mid 50s. That cu will go away after
sunset, and with clearing skies and light winds as the surface
high moves into the region, temps will get very cold Tuesday
night. Will continue to keep the freeze watch going.
.LONG TERM...(Wednesday through Monday)
Issued at 256 PM CDT Mon Sep 7 2020
The Wednesday through Sunday time period brings a slight warmup and
generally quiet weather to the region. Weather impacts will be
minimal, and in association with showers and perhaps some embedded
thunderstorms Friday and Saturday.
For Wednesday, a cool start in the lower 30s will give way to
daytime warming and temperatures in the upper 50s to near 60
degrees. Lows will fall into the upper 30s to low 40s Wednesday
night into Thursday morning. At the H5 level, progressive flow will
facilitate the development of a cut off low working through the
Northern Plains and Upper Midwest Thursday through Saturday. This
will give us a chance for showers and scattered thunderstorms from
pre-dawn Friday through Saturday evening.
At this time, ensemble guidance is a bit divided regarding
temperature profiles heading into Saturday and Sunday. The general
consensus is bringing another cold front through the area Saturday
night into Sunday morning, allowing cooler air to filter into the
area as we head into next week.&&
.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1228 PM CDT Mon Sep 7 2020
VFR conditions at all TAF sites as stratus moving down from Canada
has scattered out at KTVF and KBJI. Precip will stay west and
south of the TAF sites this afternoon, with all our airports
seeing clouds of 3500 ft and above and somewhat gusty north to
northwest winds. Winds will go down a bit this evening and the
northern TAF sites should scatter out for a brief period. Could
see a repeat of stratus coming off of the Canadian lakes, so have
MVFR at KTVF and KBJI for a period again. Other locations should
remain VFR.
&&
.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1228 PM CDT Mon Sep 7 2020
VFR conditions at all TAF sites as stratus moving down from Canada
has scattered out at KTVF and KBJI. Precip will stay west and
south of the TAF sites this afternoon, with all our airports
seeing clouds of 3500 ft and above and somewhat gusty north to
northwest winds. Winds will go down a bit this evening and the
northern TAF sites should scatter out for a brief period. Could
see a repeat of stratus coming off of the Canadian lakes, so have
MVFR at KTVF and KBJI for a period again. Other locations should
remain VFR.
&&
.FGF WATCHES/WARNINGS/ADVISORIES...
ND...Freeze Watch from late Tuesday night through Wednesday morning
for NDZ006>008-014>016-024-026>030-038-039-049-052>054.
Frost Advisory from 3 AM to 9 AM CDT Tuesday for NDZ008-016-
026>030-038-054.
Freeze Warning from 3 AM to 9 AM CDT Tuesday for NDZ006-007-014-
015-024.
MN...Freeze Watch from late Tuesday night through Wednesday morning
for MNZ001>009-013>017-022>024-027>032-040.
Frost Advisory from 3 AM to 9 AM CDT Tuesday for MNZ001-002-004-
006-007-009-017-024.
Freeze Warning from 3 AM to 9 AM CDT Tuesday for MNZ005-008-
013>016-022-023.
$$
UPDATE...Riddle
SHORT TERM...JR
LONG TERM...Lynch
AVIATION...Riddle
Area Forecast Discussion
National Weather Service North Platte NE
649 PM CDT Mon Sep 7 2020
.SHORT TERM...(This evening through Tuesday night)
Issued at 322 PM CDT Mon Sep 7 2020
A strong 1040 mb hybrid Pacific-Polar high pressure system has
formed across British Columbia. The attendant cold front is
advancing south through the Nrn High Plains this afternoon. The high
pressure system will drop south through the nrn High Plains tonight
and settle across ern WY-nern Colorado by Wednesday morning.
The wind forecast uses the short term model blend plus the guidance
blend for speeds of around 25 mph tonight and Tuesday. Wind speeds
should subside Tuesday evening. The RAP model showed the strongest
wind with speeds near 30 mph. H850mb speeds have increased to 50-
55kts in that model increasing the risk of high winds but the sfc
gusts in the RAP and HRRR models increase to just 40 to 50 mph. The
wind gust forecast uses a blend of the wind regression tool plus the
RAP and HRRR models for gusts around 45 mph.
The temperature forecast leans on the short term model blend plus
bias correction for lows in the 30s to around 40 tonight, 40s
Tuesday and upper 20s to upper 30s Wednesday morning. The guidance
blend was too cold Wednesday morning. All of the models indicate
significant cloud cover will continue Tuesday night blocking any
sort of radiational cooling for widespread frost. In fact, given the
expected cloud cover, the forecast lows below freezing across
northwest Nebraska Tuesday night might be too cool and later
forecasts might raise these lows a few degrees.
There is little change in the rain and snow forecast. The RAP and
HRRR models are changing rain to snow across northwest Nebraska
between midnight and 3 am tonight. Snow levels fall to around 4000
feet tonight and to around 3000 feet Tuesday night. The best forcing
for accumulating snow will occur late tonight and the RAP model
suggested a 1 to 2 hour period of heavy snow across northwest
Nebraska. The falling snow aloft will have to overcome the strong
sensible heating effects of the warm ground. Given the warm ground
with 4 inch soil depth temperatures in the 70s according to the
Nebraska State Climate Office, the unadjusted snowfall forecast of
amounts 1 inch or less seems appropriate.
Isolated thunderstorms are possible across swrn/scntl Nebraska late
tonight associated with a southwest oriented low level jet which
will steepen lapse rates and build a few hundred J/KG of elevated
CAPE. The better thunderstorm chances will likely be south and east
across KS and ern Neb. There is also a chance for sporadic lightning
with the developing rain and snow across wrn and ncntl Nebraska
tonight. The combination of strong lift and negative theta-e lapse
rates will support convectively enhanced rain and snow bands,
possibly capable of lightning. For now, the forecast focuses on the
south for traditional thunderstorm development.
.LONG TERM...(Wednesday through Monday)
Issued at 322 PM CDT Mon Sep 7 2020
The models are in very good agreement developing a deep upper low
across the srn Rockies Tuesday. This upper low should remain
nearly stationary Wednesday and begin to lift northeast toward
Nebraska Thursday and Friday. Showers are in the forecast
Wednesday through Friday with wrn and ncntl Nebraska on the
forward or warm air advection side of the upper low. The upper
low, which is progged to open up as it lifts northeast, should be
north of the region Saturday and the forecast is dry next weekend.
Cold sfc high pressure will remain across wrn and ncntl Nebraska
Wednesday and Thursday which would be favorable for frost or freeze
conditions at night, but the models are in very good agreement
keeping skies mostly cloudy and this should block any sort of
radiation condition preventing a freeze. Clearing skies are likely
Friday.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 641 PM CDT Mon Sep 7 2020
Rain will move into the area this evening and stick around the
remainder of the forecast period. Some locations across the
northern Sandhills will see a rain/snow including KVTN terminal.
Most of the accumulating snow will be across the NW Sandhills,
west of KVTN, and will generally be less than 1 inch. MVFR and
IFR conditions will be possible at both KVTN and KLBF terminal
through the forecast period with low cigs moving in this evening
across the entire forecast area and sticking around over the next
24 hours.
&&
.LBF WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SHORT TERM...CDC
LONG TERM...CDC
AVIATION...Gomez
Area Forecast Discussion
National Weather Service Pocatello ID
123 PM MDT Mon Sep 7 2020
.SHORT TERM...Tonight through Wednesday...The cold front is just
knocking at the door along the Idaho/Montana border at this time.
Gusts exceeding 50 mph are already observed and that is well
before peak winds are expected. Little change to the forecast
package was made; the timing and strength of the frontal passage
remains on track this afternoon and evening. This means winds of
35 to 50 mph with gusts of 55 to 60+ mph. Strongest conditions
remain forecast over the Arco Desert and Upper Snake Plain and
into areas bordering Idaho/Montana where the northerly winds first
enter the state. We will leave our advisories/warnings as is at
this time. Blowing dust is possible as well or even likely in some
spots, especially in areas where precip does not occur or where
very little falls. What is an unknown however is the timing on
when conditions would improve. There seems to be indications that
these winds would remain strong overnight; which is a good 3 to 9
hours longer than previous models had it going. Not all models
agree with this thinking; instead opting to lose some energy with
end of sunlight. It feels like a good idea to let the event start
and if needed, extend the Wind advisories / warnings if necessary
tonight based on observations.
A mixture of rain and snow showers remain in the forecast tonight
for the Central Mountains, East Idaho and portions of the Snake
Plain, all associated with the passing front. Snow accumulations
would be light, at an inch or less on area mountain passes with the
exception of the Idaho Wasatch Mountains/Bear River Range/Plateau
which may very well accumulate a few inches of snow tonight. Bear
Lake area, Palisades and Caribou Highlands are most vulnerable to
higher rainfall amounts tonight, at around 1/10 to 1/4 inch of rain
or a rain/snow mixture.
Meanwhile, much colder temperatures are on the way behind the front.
Temperatures tomorrow morning at forecast in the mid to upper 30s
and while near frost/freeze concerns are possible it will be far
to windy to develop any frost on any agriculture across the Snake
Plain. The Arco Desert would be susceptible to any frost/freeze
concerns tonight temperature wise but there are also 30 mph wind
gusts forecast. That said, anyone with a garden growing in the
Stanley Basin, Soda Springs or Bear Lake area may very well see a
freeze/frost tonight as winds will not be so strong anymore
tonight. Tuesday night into Wednesday however, we will issue a
freeze warning for the entire growing area Wednesday. We are on
the cusp of a hard freeze for the Arco Desert/Upper Snake Plain
areas as temperatures will be in the mid to upper 20s; and this
may be issued tomorrow or tonight if trends continue this way.
Either way, precautions are needed.
A closed low will sit to our south tomorrow and Wednesday, allow for
persistent northerly flow, at much lighter speeds though with cooler
temperatures. There may be a chance for precip along the border of
Idaho/Utah at times as moisture rotates around the low but right now
chances look low.
ND
.LONG TERM...Thursday through next Monday...The closed low
gradually weakens and pushes to the east and north Thursday into
Friday while high pressure continues to build over our area. Look
for clear skies and mild temperatures over our area. The weekend
and Monday also look very mild under a weak ridge of high
pressure.
ND
&&
.AVIATION...The big story will continue to be strong winds,
especially along and behind the cold front moving through this
afternoon and tonight. We are expecting sustained winds of 25-35kts
with gusts of 40-50kts possible at IDA, PIH, DIJ and BYI. While not
as confident that we will see unusually high gusts at SUN, we will
keep gusts to 40kts in the TAF for later this afternoon and evening
hours. There will be some showers around, and we have indicated -
SHRA or VCSH for all TAF sites. It`s possible we might even snow
showers at DIJ right before precipitation tapers off. While not in
the forecast, a thunderstorm or two can`t be ruled out. The
unusually strong northerly winds in the forecast will eventually die
off toward sunrise. However, breezy northeast winds will continue
Tuesday. Keyes
&&
.FIRE WEATHER....Current RED FLAG WARNINGS for all areas except the
central mountains will remain in place through this evening. In
reality, wind gusts will be strong everywhere and likely negate any
concerns with rising humidity...including the central mountains
during the day and overnight when those humidities really begin to
rise. Some gusts will easily exceed 50mph...if not 60mph especially
along and behind the front. We are also expecting some showers and
MAYBE a thunderstorm or two, but amounts and coverage aren`t
expected to be widespread. Stronger winds won`t really wind down
until well after midnight, with breezy northerly winds persisting
Tuesday. At this point, we aren`t seeing strong enough winds (or at
least widespread) where humidity drops into critical territory for
another RED FLAG WARNING on Tuesday. Colder temperatures will be
around through midweek before high pressure returns and sends
temperatures quickly upward. It should be dry for several days
behind today`s storm. Keyes
&&
.AIR STAGNATION...Hazy skies do persist this afternoon from wildfires to the
west. As a strong cold front pushes air from a northerly
direction, the HRRR Smoke model bring smoke from the Lone Star
fire in Yellowstone through our area tonight. It`s a bit of an
unknown how much of this would mix in in combination with the
possible rain and/or snow; therefore we will officially leave it
out of the forecasted grids but know that this is a possibility.
Aside from this and the unknown of any potential new smoke from
new fires in the area; conditions look to clear up tomorrow.
ND
&&
.PIH WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 11 PM MDT this evening for IDZ410-413-425-
427.
Freeze Warning from 1 AM to 9 AM MDT Wednesday for IDZ051>055.
Wind Advisory until 11 PM MDT this evening for IDZ051-055>066-
068>071-074-075.
High Wind Warning until 11 PM MDT this evening for IDZ052>054-
067.
&&
$$
Area Forecast Discussion
National Weather Service Portland OR
258 PM PDT Mon Sep 7 2020
.SYNOPSIS...A unusually potent east wind event is ramping up this
afternoon. East winds will likely peak later tonight
and early Tuesday morning. Extreme fire danger and locally damaging
winds are likely. Warm and dry weather appears likely through the
end of the week.
&&
.SHORT TERM...Tonight through Thursday...The cooler and dry air mass
well into eastern WA/OR this afternoon and is filtering into west of
the Cascades. In addition to the strong gusty winds in the Columbia
Basin, dew points are a good indicator of the air mass boundary.
There dewpoint have dropped into the low 30s. Satellite loop shows
clouds developing along the frontal boundary with the leading edge
now now approaching the Cascade crest. Rattlesnake Ridge WA is
gusting to 74 mph at noon, this is an exposed ridge south of Hanford
WA. CIRA Dust and natural color satellite imagery show dust smoke
from eastern WA fires drifting toward the west. So hazy skies will
be increasing through Tue. Hood River and Skamania, and possibly
eastern Multnomah & Clackamas counties may see reduced visibility.
With the increasing wind and cold air advection, would not be
surprised to see some dust kicked up off Mt. Saint Helens tonight and
Tue.
Overall the forecast appears on track so no changes to warnings at
this time. The KOTH-KGEG pressure gradient switched from positive
to negative 17Z and at 21Z at -9.0 mb. Models fairly close with RAP
closest to obs. NAM is a couple of millibar too high. The RAP peaks
near -23 mb, NAM -21 mb, GFS -21 mb between 3-5 am Tue.BUFR
soundings near and surrounding the Gorge - between Mt. Adams and Mt.
Hood - show winds ramping up quickly early this evening. The lower
level jet at 900 mb or roughly 2500 ft MSL winds plateauing around 2
am at 65-70 kt then subsiding after 6 am Tue.There is no big
changes in the models so still looks good for 40 to 60 mph east wind
gusts will develop with gusts 60 to 80 mph expected on exposed
ridges so High Wind Warning look good. Strong winds will affect
areas west of the Gorge to the coast as well affecting the
Portland/Vancouver metro area with gusts 40 to 55 mph, but may also
see gusts 60-65 mph across the higher terrain like the west hills
and areas near the Gorge. Similar winds extend across the north
coast range to the higher portions of the north coast zone. In
other words, the High Wind Warnings currently in good shape.
Fire: A Red Flag Warning continues into Wed across entire forecast
area due to a combination of dry fuels, very low humidities, and of
course wind. It`s a rare occurrence (likely a first) for Extremely
Critical fire category for our area from Storm Prediction Center.
Critical fire weather continue into Wed however. Since warm dry
conditions continue into Thu so may still see continuation of high
fire concerns. But fortunately winds will be considerably weaker.
Heat: A Heat Advisory for the central coast into Tue due to the
strong offshore flow and resulting downslope warming off the coast
range combined with a thermal trough right along the coast. 850 mb
temps Tue in that area are around 20-23 C. Wed into Thu the heat
shifts inland with some relief for the coast as a southerly wind
reversal occurs to bring a shallow marine layer along the coastline.
Models differ in the timing but the NAM which usually performs well
is showing this development. The south and central Willamette
Valley may reach Heat Advisory criteria Wed then expand to include
north Willamette Valley/Clark county Thu.
.LONG TERM...Thursday night through Monday...More cooling looks
likely Fri into Sat with weak onshore flow and lowering 500 mb
heights along with weak embedded shortwaves. ECMWF and GEFS ensemble
show 850 mb temps gradually lowering into the weekend for continued
warm but not hot weather. Shallow morning inversions Fri - Sun
may lead to lower somewhat stagnant air for the interior valley with
potential for lower air quality. /mh
&&
.AVIATION...The 00Z TAF period is highlighted by an impressive
east wind event beginning early this evening and continuing into
tomorrow.
Offshore flow will begin to strengthen this afternoon with
easterly to northeasterly wind gusts between 20 and 35 kt
impacting most terminals this evening. Locally stronger wind
gusts between 40 and 50 kt will be possible across the
Portland/Vancouver metro after 00Z Tuesday. In addition, expect
very strong low level wind speed shear on the order of 30 to 60
kt at around 2000 ft across portions of NW Oregon and SW
Washington.
The easterly winds will also bring upper level smoke and haze
into the Willamette Valley from nearby fires. In addition,
blowing dust from the Columbia Basin could produce hazy
conditions across the northern Valley and Columbia River Gorge
this evening. Aside from areas with smoke, skies will be clear.
Visibility reductions are not expected at the terminals at this
time.
Refer to http://weather.gov/zse for detailed regional aviation
weather and hazard information.
KPDX and APPROACHES...Upper level smoke will continue over the
next 24 hours, with increasing offshore flow this afternoon and
evening. This offshore wind event will bring very gusty east
winds to the terminal beginning late Monday afternoon, with
occasional gusts to around 50 kt expected late this evening
through tonight. Very strong low level wind shear on the order of
30-50 kt over 1000-2000 feet will likely be present over the
terminal for much of the night. -TK/DDH
&&
.MARINE...An unusually strong and impressive offshore wind event
is expected to unfold this evening and continue through Tuesday
night. Easterly wind gusts between 25 and 30 kt should be
widespread across the waters, with a few gusts approaching 35 kt.
Pockets of stronger Gale Force wind gusts will be possible
downwind of the coastal river gaps such as the mouth of the
Columbia River, Tillamook Bay, and Yaquina Bay. This will bring
another round of steep, choppy seas as wave heights rise to 7 to
9 ft with a period around 8 seconds. Therefore, a Small Craft
Advisory is in effect for all waters through this evening through
Tuesday night.
Offshore flow should weaken considerably on Wednesday as the
surface pressure gradient begins to relax over the waters. This
should result in winds falling below advisory thresholds and seas
dropping below 5 ft. By late Wednesday, low pressure is forecast
to drift off the Oregon coast and bring southerly winds across
the waters Thursday into Friday. -TK/DDH
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...Red Flag Warning until 8 PM PDT Wednesday for Central Oregon
Cascade Foothills-Central Oregon Coast-East Slopes of the
Central Oregon Coast Range-Mt. Hood National Forest West
of Cascade Crest-North Oregon Cascade Foothills-North
Oregon Coast-North Oregon Coast Range-Willamette National
Forest-Willamette Valley.
High Wind Warning until 1 PM PDT Tuesday for Coast Range of
Northwest Oregon-Greater Portland Metro Area-North Oregon
Coast-Northern Oregon Cascade Foothills-Northern Oregon
Cascades.
Heat Advisory until 11 PM PDT Tuesday for Central Coast Range
of Western Oregon-Central Oregon Coast-North Oregon Coast.
WA...Red Flag Warning until 8 PM PDT Wednesday for Clark County
Lowlands-East Willapa Hills-Eastern Gifford Pinchot
National Forest Mt Adams Ranger District-Extreme South
Washington Cascades and Foothills-South Washington Coast
and West Willapa Hills.
High Wind Warning until 1 PM PDT Tuesday for Greater Vancouver
Area-South Washington Cascade Foothills-South Washington
Cascades.
PZ...Small Craft Advisory until 5 AM PDT Wednesday for coastal
waters from Cape Shoalwater WA to Florence OR from 10 to
60 NM.
Small Craft Advisory until 5 AM PDT Wednesday for coastal
waters from Cape Shoalwater WA to Florence OR out 10 NM.
&&
$$
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Area Forecast Discussion
National Weather Service Reno NV
326 PM PDT Mon Sep 7 2020
.SYNOPSIS...
Gusty winds develop this afternoon and evening along with much
cooler temperatures Tuesday behind a dry cold front. Low
temperatures will fall to near or below freezing in Sierra
valleys, with 30s in colder lower valleys, Wednesday and Thursday.
It is expected to warm back to well above average for the latter
part of the week.
&&
.DISCUSSION...
Smoke and haze from fires in California continue to engulf the area
this afternoon. These conditions look to improve for the Eastern
Sierra and western Nevada tonight as a strong dry cold front moves
across the region. The HRRR and other high spatial/temporal
resolution models are showing a strong burst of wind with the FROPA,
which is expected to push into Pershing and Churchill counties by 6-
9 PM. A Blowing Dust Advisory was issued for much of western Nevada
this evening into Tuesday morning as 40-50 mph wind gusts are
expected to loft dust off the playas and dry lake beds. These winds
will bring continued fire weather concerns. For more details, see
the Fire Weather discussion below.
Behind the strong cold front, temperatures are expected to cool down
markedly. Tuesday afternoon`s high temperatures will be at least 15-
25 degrees cooler compared to Monday afternoon`s highs, with highs
in the upper-60s to mid-70s expected areawide. Breezy easterly winds
are expected Tuesday with the tightened pressure/temperature
gradient across our region. Sierra ridgetops could gust over 45-50
mph. Temperatures will remain below normal Wednesday as east-
northeast flow continues to usher in cool air.
For the latter half of the week, an area of high pressure looks to
build into our area, increasing temperatures to above average for
this time of year. Afternoon highs will increase into the 80s for
Sierra valleys and 90s for lower valleys of northeastern California
and western Nevada. With clear skies, morning lows will be chilly in
the lower valleys of the Sierra. Light slope driven winds look to
make a comeback with dry conditions continuing. -Johnston
&&
.AVIATION...
Gusty north-northwest winds are expected this afternoon before a
strong dry cold front pushes into the region, generating gusty north-
northeast winds late this evening into early Tuesday. With this
front passing quickly over the dusty playas and dry lake beds of
western Nevada, blowing dust looks to become an issue with reduced
visibility to 1/4 to 1/2 mile expected across much of western
Nevada. Turbulence will also be possible ahead and behind the front.
Easterly flow behind the front will push smoke and haze into central
and southern California for the next day or two, which should
improve slantwise and near-surface visibility. Calm and quiescent
conditions are expected for the latter half of the week as an area
of high pressure moves into the region. -Johnston
&&
.FIRE WEATHER...
* High Fire Danger continues today and Tuesday even with a
significant decrease (20-30 degrees) in temperature.
Hot and unstable conditions will dramatically disappear over the
next 24-48 hours as a cold front drives through the Great Basin.
Plan for gusty winds through Tuesday evening for many areas, as well
as extremely dry conditions even overnight.
Winds have begun to increase across NE CA and NW NV already this
afternoon and will spread across the Sierra and western Nevada
through tonight. Peak winds will likely occur during the overnight
hours as the cold front passes through Nevada with steady north
winds forecast for western NV valleys tonight. Northern Sierra ridge
gusts could reach 50+ mph late tonight and Tuesday morning,
increasing the threat for critical conditions from the Tahoe Basin
northward to Plumas and Lassen counties.
Winds should start to diminish late in the day Tuesday, though
models have trended higher for winds Tuesday afternoon. Afternoon
humidity will drop down to 5-15% and may not recover much above 25-
30% for most of western NV and mid and upper slopes of the Sierra
due to the very dry air and gusty winds. Critical fire weather
conditions may persist all day Tuesday with east winds impacting the
mid slopes and the ridges through Tuesday evening.
High pressure returns to the region again mid-late this week with
temperatures warming back up into the 80s for the Sierra and 90s for
western NV. Winds should be light. Brong/Edan
&&
.REV Watches/Warnings/Advisories...
NV...Blowing Dust Advisory until 5 AM PDT Tuesday NVZ001-003>005.
Red Flag Warning until 5 AM PDT Tuesday NVZ420-423-429-458.
Lake Wind Advisory until 11 AM PDT Tuesday for Washoe Lake in
NVZ003.
Lake Wind Advisory until 5 AM PDT Tuesday NVZ001.
Red Flag Warning until 8 PM PDT Tuesday NVZ421.
Lake Wind Advisory from 3 AM to 8 PM PDT Tuesday for Lake Tahoe
in NVZ002.
Lake Wind Advisory until 5 AM PDT Tuesday NVZ004.
CA...Red Flag Warning until 5 AM PDT Tuesday CAZ270-278.
Red Flag Warning until 8 PM PDT Tuesday CAZ274.
Lake Wind Advisory until 11 AM PDT Tuesday CAZ073.
Lake Wind Advisory from 3 AM to 8 PM PDT Tuesday for Lake Tahoe
in CAZ072.
Red Flag Warning from 5 AM to 8 PM PDT Tuesday CAZ271-272.
&&
$$
For more information from the National Weather Service visit...
http://weather.gov/reno