Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/07/20
Area Forecast Discussion
National Weather Service Burlington VT
1039 PM EDT Sun Sep 6 2020
On Labor Day, a cold front approaches the region with
increasing clouds and strong gusty winds expected through the
day. A Wind Advisory is in effect beginning 8AM Monday through
8PM Monday for Grand Isle County, Vermont for wind gusts up to
50 mph possible. A few showers are possible across northwest New
York Monday night into Tuesday, but overall conditions remain
dry and seasonably warm across the forecast area until the
latter half of the work week when better chances for showers and
.NEAR TERM /THROUGH MONDAY NIGHT/...
As of 1033 PM EDT Sunday...The wind forecast remains on track
for Monday with strong southerly winds, especially within the
Champlain Valley. Slight adjustments were made to the forecast onset
time of rain showers across northern New York, now looking like
the initial round of showers will begin close to 12z (8am). In
addition, slight chance of thunder has been included in the
forecast for Monday afternoon, though instability will be
limited. Only other adjustments were to tweak the hourly
temperatures and dewpoints to match trends in observations. See
previous discussion below.
Previous Discussion...A wind advisory will be in effect
beginning 8AM Monday through 8PM Monday for Grand Isle County,
Vermont. Everything remains well on track for gusty south winds
to overspread the area Monday morning as a strong, 40-50+ knot
925-850mb low level jet moves overhead. Overnight, winds will
remain generally light and variable but as daytime mixing begins
Monday morning winds will increase fairly quickly. Most areas
should see winds gusting out of the south upwards of 20-25 mph
towards 8AM, and remain gusty throughout the day in the 25-30
mph range. Locally, in the Champlain and St Lawrence Valleys,
channeled south/southwesterly winds will produce winds in the
20-30 mph range with gusts up to 35-40 mph. Higher gusts upwards
of 50 mph are possible over the broad lake including Grand
Isle. The core of the strongest wind gusts will occur between
10AM and 2PM. After 2PM, winds will still remain breezy but will
gradually diminish as we head towards late evening. Boaters on
Lake Champlain should exercise caution if going out on the water
tomorrow afternoon as these high winds will cause waves up to 4
to 8 ft. While skies should mostly to partly sunny tomorrow,
the HRRR smoke model is showing an area of fairly decent
concentration of vertically integrated smoke advecting into the
Northeast along this front, therefore will likely see filtered
sunshine throughout the day. Still expect highs to reach onto
the mid to upper 70s across the area.
These increasing winds are in response to a deepening low pressure
system moving out of central Canada. Precipitation chances from the
attendant cold front will mainly be across St Lawrence and Franklin
Counties in New York. This front will move in after 00z, and with
any real lack of instability of surface convergence will diminish as
it moves eastward. Almost nil chances for measurable precipitation
exists from the Adirondacks eastward into Vermont. Across our
western NY zones, anywhere between 0.10-0.25" of rain is possible.
.SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/...
As of 352 PM EDT Sunday...Tuesday should be fairly quiet as we remain
under southwest flow aloft. At the surface, a frontal boundary will
waver around the international border. A weak upper disturbance will
scoot by just to our north during this afternoon, and this combined
with the weak front and daytime heating may allow a few showers to
develop, mainly over the higher terrain. These will dissipate in the
evening as the sun sets. Tuesday`s highs will be in the mid 70s to
mid 80s, coolest along the international border near the front. Lows
will be in the mid 50s to lower 60s.
.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
As of 352 PM EDT Sunday...The aforementioned frontal boundary will
remain nearly stationary near the international boundary through at
least Wednesday. Hence expect another afternoon with a few possible
showers, especially over the higher terrain. Temperatures will be
very warm as well, with mid and upper 80s expected in most spots.
The front will make its southward push sometime Thursday into Friday
as an upper trough swings across Ontario and Quebec. This will bring
the chance for showers and thunderstorms those days, along with
cooler temperatures, though both parameters hinge on the exact
timing of the frontal passage. High pressure will build over the
region Saturday, leading to a dry start to the weekend with
.AVIATION /03Z MONDAY THROUGH FRIDAY/...
Through 00Z Tuesday...VFR through the period with main aviation
concern being LLWS early this morning followed by gusty south
winds. High clouds are currently departing eastern VT leaving
clear skies across the area until 06z. After 06z, mid-level
clouds will approach from the south. There exists a slight
chance of low level status on the east side of the Greens for a
brief period between 10-12z with light southeasterly flow.
However, it was left out of the MPV TAF at this time given the
dry ambient conditions and lack of cloud cover upstream. Winds
overnight will be generally light and variable, increasing from
the south towards daybreak. LLWS will overspread the airspace
from west to east beginning at 06z through 13-14z as a 40kt
south/southwesterly low level jet moves overhead. Wind gusts
will begin picking up by 13-14z, which will limit the LLWS
threat; however, turbulence is likely through the remainder of
the day, especially within the vicinity of terrain as this low
level jet will increase to around 60kt towards 15-18z with
surface gusts up the Champlain and St Lawrence Valley up to
30-40kt. Elsewhere, gusts should remain in the 25-30kt range. In
addition, rain showers are expected across portions of northern
NY from 15z until after 00z Tuesday associated with a passing
Monday Night: VFR. Slight chance SHRA.
Tuesday: VFR. NO SIG WX.
Tuesday Night: VFR. NO SIG WX.
Wednesday: Mainly VFR, with local MVFR possible. Slight chance
SHRA, Slight chance TSRA.
Wednesday Night: VFR. Slight chance SHRA.
Thursday: Mainly VFR, with local MVFR possible. Chance SHRA,
Slight chance TSRA.
Thursday Night: Mainly MVFR, with areas VFR possible. Chance
Friday: Mainly VFR, with local MVFR possible. Slight chance SHRA,
Slight chance TSRA.
Channeled southerly winds will produce winds in the 25-35 mph
range with gusts up to 50 mph possible over the broad lake. The
core of the strongest wind gusts will occur between 10AM and
2PM. Boaters on Lake Champlain should exercise caution if going
out on the water tomorrow afternoon as these high winds will
cause waves up to 4 to 8 ft. After 2PM, winds will still remain
breezy but will gradually diminish as we head towards late
VT...Wind Advisory from 8 AM to 8 PM EDT Monday for VTZ001.
AREA FORECAST DISCUSSION
National Weather Service Eureka CA
403 PM PDT Sun Sep 6 2020
.SYNOPSIS...Hot and dry weather will continue across inland
northwest California this week, with record heat likely today and
Monday. Coastal areas will be warm and sunny through Monday, with
milder temperatures and cloudier conditions returning during the
middle of the week.
.DISCUSSION...Strong high pressure over the NE Pacific is
supporting record heat across the interior valleys of northwest
California this afternoon, with Ukiah reporting a temperature of
113 degrees and several Lake County locations hovering around 110
as of this writing. While today may prove to be the hottest day of
the week, Monday may come close as high pressure continues to
dominate the region. The Excessive Heat Warning is unchanged and
remains in effect through Tuesday. Meanwhile, most coastal
locations have generally been sunny and pleasant as weak onshore
flow keeps temperatures around 70 on the North Coast.
Moving on to the impending offshore wind event for Monday evening,
much of the 12z guidance indicated a slight westward shift in the
placement of the potent trough poised to dig into the Great Basin
Monday night/Tuesday. As a result, available Hi-Res guidance has
trended upward with winds along the ridges of interior Humboldt
and Del Norte, spurring greater fire weather concerns for those
areas in addition to the Trinity, Lake, NE Mendocino areas which
had been the focus for the past several days. Refer to the fire
weather section below for details.
Winds will subside across the area by Wednesday morning, however
hot and dry conditions will persist while slowly moderating as
high pressure weakens but remains in control over the West Coast.
.AVIATION...Widespread wildfire smoke is lingering across NW
California today. These smoke issues generated MVFR/IFR
visibility at KCEC and KUKI. Despite the smoke in the region VFR
conditions prevail at KACV. HRRR smoke guidance is suggesting
smoke will continue affecting the region with reduced
visibilities through Monday. Otherwise, mostly clear skies will
prevail for the next few days as high pressure over the region
continues to build through the NE Pacific. /ZVS
.MARINE...Northerly winds and steep seas continue across the outer
waters. These steep seas from 6 to 10 ft will continue through
Monday night for both zones. Small Craft Advisory is in effect
for southern outer waters through tonight and northern outer
waters through monday night.
Conditions across the waters will gradually improve Tuesday as
the high currently building over the NEPAC slips overhead and the
pressure gradient relaxes, possibly bringing a period of
widespread light and variable mixed with rounds of southerly
winds Wednesday into Thursday. /ZVS
.FIRE WEATHER...Opted to issue a Red Flag Warning for multiple zones as
gusty northeast winds will develop along ridgetops late Monday evening
and persist through Wednesday morning. This will combine with poor
overnight RH recoveries in the 20 to 35 percent range and afternoon
minimum RH values as low as 5 to 10 percent on area ridges to produce
critical fire weather conditions across portions of interior Humboldt,
interior Del Norte, Trinity, NE Mendocino, and Lake Counties. Winds
will subside first across interior Humboldt and Del Norte Tuesday
evening, continuing in the other areas through Wednesday morning.
Otherwise, hot and dry conditions will persist into the middle of
the week with a gradual moderating trend. /CB
CA...Excessive Heat Warning until 6 PM PDT Tuesday for CAZ102-104>108-
Red Flag Warning from 10 PM Monday to 8 AM PDT Wednesday for
Red Flag Warning from 10 PM Monday to 10 PM PDT Tuesday for
NORTHWEST CALIFORNIA COASTAL WATERS...Small Craft Advisory until
midnight PDT Monday night for PZZ470.
Small Craft Advisory until 6 PM PDT this evening for PZZ475.
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Area Forecast Discussion
National Weather Service Green Bay WI
606 PM CDT Sun Sep 6 2020
Updated aviation portion for 00Z TAF issuance
.SHORT TERM...Tonight and Monday
Issued at 300 PM CDT Sun Sep 6 2020
Trends over the past couple hours are starting to lean towards a
quieter near term forecast. While there was a brief period of
sunshine this morning, ample cloud cover moved in this afternoon
and have kept temps from rising much more. As a result, not seeing
much instability build across the area, with the highest MUCAPE
readings of 600 to 800 J/kg across central WI. Additionally,
fairly impressive cap in place with CIN up to -500 J/kg. Very
isolated showers have formed across parts of central and east-
central WI (most of which is south of the GRB forecast area) with
the closest thunder near Milwaukee. Meso models have had a hard
time letting go of convection developing across mainly east-
central WI then moving south of the area, however the past couple
runs of the HRRR and the 18Z run of the RAP have cut back quiet a
bit on the overall coverage and intensity of any shower or
thunderstorms development. Have capped PoPs at the chance or
slight chance category for late this afternoon and evening, and
may lower them a bit more sometime in the next hour if trends
continue. Kept thunder mention for now, but confidence is very low
on whether that is possible. Of course, if something were to
develop, strong winds and large hail are possible given the high
shear and continued moisture advection.
Tonight...Surface cold front sweeps across the state officially
cutting off any chance of precipitation. Have PoPs ending in the
far east by midnight. Subsidence behind the front will result in
at least a partial clearing of the clouds. Lows are somewhat
difficult given the cloud forecast, although with winds remaining
gusty do not expect a large drop in temps. Lows are forecast to
range from the middle 40s in the typical Northwoods cool spots, to
the middle 50s along the lake shore.
Monday...Generally quiet weather is expected for most of the day.
Cloud cover will vary, with some clearing in the morning, then
more clouds moving in by the afternoon in advance of the next
weather system. Northwest winds will still be a little gusty in
the morning, then subside through the afternoon. Highs will feel
more fall-like, ranging from the upper 50s in north- central WI to
the middle 60s in the Fox Valley. The chance for showers enters
central WI late in the afternoon as the upper level pattern begins
to amplify and sets up a more active forecast.
.LONG TERM...Monday Night Through Sunday
Issued at 300 PM CDT Sun Sep 6 2020
A large upper level trough will bring well below normal
temperatures along with a period of rain and possibly some
thunderstorms during the middle part of the work week. An extended
period of northeasterly winds will also bring the concern for
some lakeshore flooding on the bay of Green Bay from Tuesday
through Wednesday or Wednesday night. The main change from the
previous forecast is the low located across the southwestern CONUS
becomes cut off and is no longer associated with the trough
affecting the area during the middle part of the week. This will
allow a break in the precipitation and the northeasterly winds on
Thursday and Friday as a surface high builds in across the
western Great Lakes region. The shorter duration of rainfall
should hopefully help to limit the amount of areal flooding during
the middle of the work week given the shorter than expected
duration of the moderate rainfall and a bit lower QPF amounts.
The aforementioned cut off low will then eject out of the
southwestern CONUS late in the work week, then track towards the
western Great Lakes region next weekend. The low will bring
additional chances for rain showers and isolated thunder to the
.AVIATION...for 00Z TAF Issuance
Issued at 605 PM CDT Sun Sep 6 2020
MVFR ceilings and scattered showers should give way to VFR conditions
from west to east this evening as a cold front moves across the
MVFR ceilings could return north of a RRL to IMT line late tonight
and Monday morning as cold air moving across Lake Superior produce
lake effect clouds in that area. VFR conditions are expected across
the region Monday afternoon and evening.
Beach Hazards Statement through Monday morning for WIZ022-040-
Lakeshore Flood Advisory until 1 AM CDT Monday for WIZ022-040-
Area Forecast Discussion...UPDATED
National Weather Service Chicago/Romeoville, IL
658 PM CDT Sun Sep 6 2020
658 PM CDT
We continue to monitor for convective initiation north of I-88,
with a few apparent inhibiting factors toward eroding the current
cap. There remains a highly conditional risk of severe storms, IF
mature convection can develop. The confidence in that occurring
prior to 11 p.m. or so is on the lower side, and that`s likely the
timing needed to tap into any effective low-level air for some
Latest hand analysis along with various satellite and
observational data indicate the old outflow boundary from the
morning MCS draped from far northwest Illinois to near the
southwestern CWA border (just north of Bloomington). This extends
northwest to a 1005 mb surface low/triple point area near the
Iowa/Wisconsin/Illinois border, with a cold front extending
southwest from there to near Des Moines. The low-level air mass
has recovered fairly well behind the old outflow and ahead of the
cold front, with late day temperatures in the upper 70s to mid
80s and a pool of dew points of lower 70s immediately along/ahead
of the retreating old outflow boundary.
Visible satellite has yet to show any areas bubbling and in fact
there is a large area of more stable 6,000 ft clouds moving into
north central Illinois from the west. These look to be right below
the cap per the 19Z DVN sounding, and the early data from the 00Z
DVN sounding still shows a decent cap near 770 mb likely
inhibiting any convective growth.
The means to overcome that cap in the next few hours would be
strong cooling in that layer which has limited ability due to
the lack of a strong short wave and instead just gradual height
falls/large scale ascent. Also, lifting and saturating of the
moist low-levels would be a way, but again satellite is not
showing any imminent signs of convecting. We will continue to
watch meso sector satellite data closely to see if any tops can
start to percolate, as otherwise the kinematic environment remains
quite favorable per regional VWP data for supercellular storms if
a few can develop.
Later after 11 p.m. or so, convective chances may increase as the
cold front approaches and a stronger upper to mid-level jet
maximum rounds into Wisconsin. The convergence and forced ascent
ahead of that boundary may be enough to moisten/cool the layer of
the cap, resulting in scattered convection that would likely be
elevated. Also warm advection ascent ahead of that may allow for
spotty convection too, such as that that developed in northwest
Indiana near 6 p.m. With the very steep lapse rates of around
9C/km in the mid-levels and strong curvature in the wind fields
within the 1-6 km layer, there will be a large hail threat with
any mature storms.
Convection allowing models (CAMs) generally show some convection,
but the HRRR and the ESRL HRRR have been fairly consistent showing
the main development being along the cold front and not able to
deeply convect ahead near the old outflow/pseudo-warm front
308 PM CDT
The large footprint of a worked-over environment left in the wake
of this morning`s convection continues to leave questions about
the potential for severe weather this evening, with the low-level
and mid-level air mass recovery occurring somewhat independently
of each other. 19Z mesoanalysis, model guidance, and ILX RAOB
indicate quickly steepening lapse rates above 850 hPA, with a deep
layer of 9C/km advecting into the region. This recovery has not
been a concern over the past day. What has been, and continues to
be, the biggest question for severe storm potential this evening
is the ability to sufficiently destabilize the near-surface layer
for initiation. Most of the CWA is finally clearing out after mid-
level clouds and isolated thunderstorms continued a bit longer
into this afternoon than expected across northern Illinois. With
that said, the return of a higher surface theta-e airmass has been
steadily shifting northeastward early this afternoon, with the
theta-e gradient analyzed from just west of the Quad Cities to
just west of Springfield, IL. Extrapolation of this observed
gradient paired with model guidance indicates most of the CWA
should see a nearly full recovery of the low-levels via mainly
advection with some assistance from insolation by early this
Meanwhile, the kinematic environment is becoming more favorable
for organized convection. Low-level winds continue to increase per
recent DVN/LOT VWP data showing 45kts/40kts as low as 3 kft.
These low-level winds will edge upwards in response to an
approaching mid- level wave evident in WV imagery across southern
MN into far northwest IA. Rising mixing heights will begin to tap
into those stronger winds aloft as the afternoon progresses, with
the forecast of gusts in excess of 40 mph to locally 45 mph for a
window late this afternoon into early evening remaining on track.
Putting this altogether, a highly conditional severe thunderstorm
threat exists after 00Z/7pm through the evening hours roughly
around and north of the Kankakee river Valley westward toward
Peoria. The most significant limiting factor will be the ability
for incoming forcing to erode enough of the substantial low-level
cap currently in place. If sustained deep updrafts can develop,
the environment is favorable for semi-discrete linear segments
with embedded supercell structures capable of producing damaging
wind gusts and large hail. Additionally, a conditional QLCS
tornado/mesovortex threat exists within any convection given
impressively curved low-level hodographs producing effective SRH
values possibly to 500 m2/s2 early to mid- evening. Marginal low-
level CAPE values will be a major detriment to this potential,
with a low-level warm nose below 700 hPa limiting low-level vortex
stretching. Will still need to closely monitor the fine details
of the thermo environment this evening as a kinematic environment
like this that is highly supportive for tornadoes leaves some
The severe threat will gradually diminish through the night as
convection slowly advances SSE through the CWA, ultimately slowing
across the far southern CWA by daybreak Monday.
330 PM CDT
Monday through Sunday...
The work week continues to present challenges for forecast
confidence as well as conveying the forecast in a simple manner.
The Labor Day holiday remains looking primarily quiet during the
day with rain and some thunderstorm likelihood returning Monday
night into Tuesday morning and possibly much of Tuesday for
northern locations. The spread in forecast rain chances and
temperatures across the forecast area from northwest to southeast
grows through midweek, with higher to lower rain chances and
cooler to warmer temperatures, in general, from west to east.
The cold front will be clearing the far southern forecast area
later Monday morning or so, bringing with it most of the
thunderstorm chances. With the boundary slowing cannot completely
rule out some focus or subtle overrunning in the afternoon in the
far south, but for most areas it looks to remain dry through the
day and early evening. A strengthening high pressure ridge
centered over northern Lower Michigan will squeeze the pressure
gradient some into the afternoon resulting in a northeast wind of
around 15 mph. This should build waves some into the Chicago shore
and climatology would say that we would be at least supportive of
a marginal Beach Hazards Statement for rip currents. Have leaned
that route for the Chicago shore by mid-afternoon with a Beach
Hazards Statement, and then started the Indiana shore under one
first thing in the morning behind the cold front.
As substantial digging of the jet stream occurs over the Rockies
Monday night into Tuesday, the downstream baroclinic zone will
inch back northward over the Midwest and tighten. In addition the
anticyclonic jet will strengthen over the Great Lakes and across
southeast Canada, poising a right entrance region aloft over the
area Monday night through Tuesday. With a period of increased
low-level moisture transport in the low-level jet layer off the
deck, these ingredients should be juxtaposed to support a
blossoming area of rain and some thunderstorms Monday night,
especially after 10 p.m. or so. MUCAPE values are forecast to
climb toward 1,000 J/kg in the southern forecast area and there is
some uncertainty on how the best forcing and instability will
line up. But the dynamics are supportive of at least a marginal
severe threat for hail, and thunderstorm chances all the way to
the northern CWA with periodic heavy rainfall. The heaviest rain
amounts of 2+ inches on high resolution guidance, such as the 3 km
NAM and the HREF, and primarily west of the area but would not be
surprised to see some isolated amounts that high by midday
Tuesday along/north of I-80.
Confidence then lowers significantly and much of that is owing to
the digging trough in the west developing a dislodged, closed
upper low. The 12Z guidance has wobbled back to the west with this
and naturally slowing to eject it. With this being so far west,
more of the forecast area is impinged upon by upper ridging and
drier air from the southeast during midweek. The active
frontogenesis area and 850-700 mb moisture convergence zone
shimmies northwest of the area in the GFS and ECMWF, and the upper
support from the jet region starts to be lost too. It`s still too
early to say a heavy rain threat has diminished during that time,
but the potential for a flood threat due to a long duration heavy
rain beyond the day Tuesday looks to have diminished some.
The temperatures continue to show a large spread across the area
thanks to northeast winds, clouds, and some rain in northern areas
and potential for less clouds southeast. Forecast values for
maximum temperatures on Tuesday-Wednesday have 20-25 degree
differences from northwest to southeast for the CWA.
The GFS and ECMWF lift the closed low late this week much further
west of the forecast area than had been the case 24 hours ago.
This shows the common theme in forecasting experience that model
handling of closed lows can be very problematic, and naturally
lowers confidence. With it being further west, the chance of
convection at least lingers further into the week, but it`s also
possible we remain dry and actually more mild.
For the 00Z TAFs...
Aviation forecast concerns:
* Gusty south-southwest winds near 30 kt this evening.
* Brief period of high-end MVFR ceilings early this evening.
* Potential for strong thunderstorms late this evening.
* Wind shift to northwest with cold front after midnight and to
northeast Monday afternoon.
Convection and residual cold-pool earlier today has slowed
recovery/mixing in low level air mass through the afternoon hours.
In the near term, this has primarily worked to limit stronger wind
gusts (though still near 30 kts expected into early evening). Slow
recovery of boundary layer across northern IL has also made our
thunderstorm threat somewhat more conditional later this evening,
though the potential still exists and any storms that do develop
have the potential to be strong/severe given strong wind fields.
Current expectation is that convective initiation will occur over
the next 1-2 hours in the vicinity of far northeast IA/northwest
IL, then spread east-southeast across the forecast area through
the mid-late evening hours. 19Z RAOB from DVN depicted strong cap
was still in place at that time, though latest SPC mesoanalysis
data suggests this cap was weakening across northeast IA in
response to cooling aloft driven by large scale ascent in
association with an approaching mid-level wave and surface cold
front. Various CAM guidance continues to suggest convective
development as discussed above, potentially affecting KRFD area
01-03Z and ORD/MDW area 03-06Z. Further refinement may be needed
once thunderstorms actually develop. Of course, if cap remains too
strong for significant coverage, thunderstorm potential at any
individual terminal would be lower.
Otherwise in the near term, a high-end MVFR stratocu deck has
developed across northern IL late this afternoon and it looks like
this will impact Chicago area terminals for a couple of hours
early this evening. Duration should be short lived however, as
consolidated warm front and outflow from this mornings storms
should lift across the area toward 02Z.
Surface cold front is then expected to push east-southeast across
KRFD roughly 06-07Z and ORD/MDW 08-09Z, with thunderstorms moving
south and east of the terminals by that time. Winds shift to the
northwest 10-15 kt with frontal passage, and should remain from
that direction into Monday before shifting northeast by mid-
afternoon Monday. Daytime should be relatively quiet with dry VFR
conditions expected. Northeast winds then look to increase and
become somewhat gusty Monday evening with rain showers developing
mid-late evening. Embedded thunder not out of the question, though
low enough coverage/confidence to not include in TAF at this
308 PM CDT
A Gale Warning is in effect for all of our nearshore waters
through late this evening. Expecting wind gusts to increase
quickly this afternoon, with occasional gusts to around 40 kts
appearing possible into the evening hours. Wind speeds should
incrementally diminish overnight tonight but will remain elevated
and breezy. Long-duration Small Craft Advisory conditions are then
in the forecast through the end of the upcoming week with a
prolonged period of onshore gusty north to northeasterly winds
resulting in building and choppy wave action.
IL...Beach Hazards Statement...ILZ006 until 10 PM Sunday.
Beach Hazards Statement...ILZ103-ILZ104...3 PM Monday to 7 AM
IN...Beach Hazards Statement...INZ001-INZ002...4 AM Monday to 7 AM
LM...Gale Warning...nearshore waters until 1
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Area Forecast Discussion
National Weather Service Pocatello ID
130 PM MDT Sun Sep 6 2020
.SHORT TERM...Tonight through Tuesday night.
Quite a bit of smoke across central and east Idaho this afternoon.
Some of this smoke may clear out early this evening. However, the
HRRR shows a strong plume of smoke moving into east Idaho from fires
in the western central mountains later this evening and overnight. A
lake wind advisory for the American Falls Reservoir remains in
effect into this evening with winds expected to decrease overnight.
Big changes arrive for Monday in the form of a strong cold front.
Ahead of the front, we expect breezy west/southwesterly winds to
develop. These winds will be strong enough to reach wind advisory
levels. Then around mid afternoon the cold front will push through
central and eastern Idaho from the north. Winds will switch to a
northerly component and become very strong immediately behind the
front. 3km NAM model soundings shows +50kts in the 2000-3000ft layer
during the late afternoon and evening across the Snake Plain.
Although the sustained winds may hold in the advisory level of 30-
35kts, think there may be a short period as the front spills over
the continental divide and into the Snake Plain that we could tap
into the +50kt layer and bring those winds down to the surface in
the form of gusts. Also, unique is the wind direction, being
northerly. Strong north winds are rare across eastern Idaho. There
is some concern that trees may be more susceptible to strong
northerly winds as opposed to the typical westerly or southwesterly
winds. For those reason, we will upgrade the high wind watch to a
high wind warning for much of the Snake Plain up to Dubois. Around
the high wind warning area, indications are that the northerly winds
may be a little less robust, so will encompass the warning area with
an advisory. Expect a few light showers to accompany the front as
snow levels fall from 12000 feet around midday on Monday to 6000
feet by evening. Snow amounts across central and east Idaho look
very light, generally less than an inch so will not issue a winter
weather advisory. However, with the falling snow levels we need to
think about overnight lows. A freeze watch remains in effect for the
upper Snake Plain where Tuesday morning lows in the lower 30s remain
likely. The cold air will persist into Wednesday morning where much
of the Snake Plain and maybe even portions of the Magic Valley could
see lows in the lower 30s. Will hold off on a freeze watch for
Wednesday morning for now as we are currently gushing headlines, but
something to expect.
.LONG TERM...Wednesday through next Sunday...A very chilly morning
is expected Wednesday with temperatures at and below the freezing
mark for the upper snake plain, Arco desert, Island Park area, east
highlands,Stanley Basin, Wood River Area and other valley locations.
This may be a very early hard freeze already, but it is just a
little to early to make to that call quite yet. Snow showers look to
have ended for all areas by Wednesday and clearing conditions are
forecast for the remainder of the week. High pressure will gradually
build in from the west with mid 70s or low 80 degree temperatures
for highs. Similar conditions are forecast over the weekend.
.AVIATION...Expect breezy conditions to diminish this evening.
Smoke across the region may lower visibilities once again tonight.
For now, continuing to forecast vfr conditions but may need to
amend. Expect strong winds to develop Monday afternoon across the
region with showers possible along a cold front.
.FIRE WEATHER...Red Flag Warnings will remain in effect until 9 pm
this evening for much of the area, including 422,410,425,427 and
413. Temperatures are much cooler today compared to yesterday but we
will are expected to see similar dry and windy conditions as
Tomorrow is an entirely different weather set-up and much attention
should be paid to it. An abnormally strong back door cold front will
pass through our forecast area tomorrow afternoon and evening.
Though RH values are marginal for some areas; the winds alone are
far too dangerous to ignore. Increasing northerly winds are forecast
starting across 411 mid-afternoon then spread quickly into the
northern portions of 410 at 35 to 45 mph with gusts around 55 mph.
These winds will track southward through 410, 425 and 413 with
similar speeds forecast throughout the afternoon and evening. As a
result, Red Flag Warnings will be in effect. Ahead of these winds,
it should also be noted that strong (But not as strong) westerly
winds are forecast around 30 mph with gusts to 40 mph. These winds
would occur until the northerly winds take over, impacting 425, 427
and portions of 413. A shower or thunderstorm may accompany the
frontal passage, but is likely to be sparse in coverage. High
elevation snow also remains in the forecast behind the frontal
passage going into Tuesday morning.
Cooler temperatures and light winds are in store for Tuesday with
high pressure gradually building in from the west.
.AIR STAGNATION...Smoke or haze is filtering through Central and
Southeast Idaho today; resulting from local and regional wildfires
to the west. This smoke/haze will persist through the remainder of
the day/evening and again settle under the inversion tonight. A few
areas are likely to be spared from seeing much impact though; which
would include areas bordering Wyoming/Idaho such as Bear Lake and
the Palisades. We would look for conditions to clear late tomorrow
after the passage of a very strong back door cold front.
Red Flag Warning until 9 PM MDT this evening for IDZ410-413-422-
Red Flag Warning from noon to 11 PM MDT Monday for IDZ410-413-
Wind Advisory from 2 PM to 11 PM MDT Monday for IDZ051-055>066-
High Wind Warning from 2 PM to 11 PM MDT Monday for IDZ052>054-
Freeze Watch from late Monday night through Tuesday morning for
Lake Wind Advisory until 9 PM MDT this evening for IDZ054.
Area Forecast Discussion
National Weather Service Pueblo CO
346 PM MDT Sun Sep 6 2020
.SHORT TERM...(This evening through Monday)
Issued at 304 PM MDT Sun Sep 6 2020
Currently...A ridge of high pressure remains in place over the
region, which has allowed temperatures to break records at Alamosa,
Colorado Springs and Pueblo, where highs so far have been 88F, 97F
and 103F as of 2:30 PM, respectively. Elsewhere, temperatures are as
hot as expected, with 2:30 PM readings in the upper 90s to lower
100s across the plains and mid 80s to around 90 in the high
valleys. Skies are generally clear except for a few clouds over the
southern mountains at this hour. Generally north to northwest winds
have moved into the plains, which has ushered in some haze from
wildfire smoke to the area.
Tonight...A back door cold front is expected to move into the region
from Kansas, bringing an increase to low level moisture and should
help to reduce some of the haze across the region. Forecast
soundings show that this low-level moisture is expected to be very
shallow, so not expecting any low clouds to move into the area. Lows
are expected to be near 40F in the San Luis Valley, which is near
average, and the upper 40s to around 60F across the remaining lower
elevations, which is slightly above average.
Tomorrow...The cold front that moves through overnight is expected
to keep temperatures a few degrees cooler across the plains and the
I-25 corridor, with highs reaching the low to mid 90s. Meanwhile,
the cold front is not expected to affect areas west of the eastern
mountains, so highs will likely be similar to today in the mid to
upper 80s for the high valleys. Alamosa could see another record
high broken tomorrow.
The well-advertised trough and associated cold front that will bring
a big change to the weather begin to approach the region from the
north, which is expected to tighten pressure gradients over the
northern portions of the forecast area. As a result, gusty winds and
a drop in relative humidity values are expected over the central
mountains, La Garitas, northern portions of Sangre de Cristo and Wet
Mountains, northern half of the San Luis Valley, and the Wet
Mountain Valley. Therefore, have upgraded the Fire Weather Watch to
a Red Flag Warning for tomorrow afternoon. It should be noted that
although the southern portions of the San Luis Valley, Sangre de
Cristo and Wet Mountains, and the eastern San Juan Mountains are
included in the zones for the Red Flag Warning, these areas are not
expected to reach critical thresholds.
.LONG TERM...(Monday night through Sunday)
Issued at 304 PM MDT Sun Sep 6 2020
...Potential High Impact Winter Storm still on track for Tues/Wed
but still some uncomfortable uncertainties with the storm
Models have trended farther west and stronger with the upper low
as it drops southward through UT Monday night and closes off near
the 4 corners region Tuesday evening. EC is slower and farther
west than 12z operational GFS...though the GFS Ensemble Mean
seems to split the difference. System continues to drop southward
Tuesday night before becoming negatively tilted and lifting slowly
northeastward across CO Wed night and Thursday with the operational
GFS the farthest east in its northeast track across central
CO...while EC is farther west across western CO/eastern UT and the
Ensemble mean is somewhere in between. Confidence in the storm
track is still low but trends suggest a farther westward track
which would shift focus for snowfall west as well. Of course if
EC is correct then impacts along the I-25 corridor and southeast
plains could be less with best forcing staying a tad too far west.
Have gone with a GFS/GFS Ensemble blend for now with WPC QPF
grids looking good.
As for the sensible weather...still looking at a potent cold front
dropping south of the Palmer Divide around midnight and through
all of the southeast plains by 3 AM. North winds will gust to 50
mph or greater with 18z hrrr and 12z NamNest suggesting gusts to
60 mph will be possible across El Paso, Pueblo, Crowley
county...and Otero counties between midnight and 6 AM Tues. Will
have to watch this potential as it is certainly conceivable given
the tight pressure gradient and some acceleration southward off
the Palmer Divide that a high wind warning may be needed for
these areas. Snow fills in behind from north to south with the
heaviest hit of snow falling on Tuesday/Tuesday night as strong
isentropic upglide sets up across a large portion of our area
around the closed low. Snow and a lower elevation rain/snow mix
will spill over into the San Luis Valley and southwest mountains
during the afternoon as the upper low sinks southward.
Temperatures will fall through the day, especially across the
southeast plains where a rain/snow mix will be possible during the
late afternoon with a shift over to snow possible Tuesday night.
Residual warmth in the ground will likely play a huge roll with
snow accumulations across the lower elevations though where the
heavy snowfall rates occur, there could be a period of impactful
accumulations over the Palmer Divide and Raton Mesa region as well
as the mountains and valleys to the west. Across the southeast
plains as well as southern El Paso and Pueblo counties think the
ground warmth will mitigate this somewhat...but its conceivable
some advisories will be needed, especially to account for possible
higher accums on the western sides of Pueblo and El Paso counties.
Some impacts to be concerned about include, tree damage and power
outages in and near the mountains with heavy wet snow and strong
winds. Roads in and near the high country could become slick and
snowpacked, especially Tuesday night. And of course the cold
temperatures and snow will likely lead to a premature end to the
growing season across the plains for warm season crops. Both Tues
night and Wednesday night look to drop below freezing across the
Given the slower ejection of the upper low Wednesday and Wednesday
night it will continue unsettled with another possible round of
precipitation Wednesday evening with either wrap around in the
west or a WAA band in the east...again...highly dependent on the
storm track. Have kept at least scattered pops in during this
period and have extended the Watch through Wednesday morning.
System slowly pulls off to the northeast for Friday with the
weekend drying out and warming back up. -KT
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 304 PM MDT Sun Sep 6 2020
Mainly VFR conditions are are anticipated over the next 24 hours at
all 3 TAF sites (KALS, KCOS, KPUB). Haze from wildfire smoke is
anticipated to linger at KCOS and KPUB into tonight, with the
potential for MVFR visibilities remaining possible. Winds at KCOS
and KPUB also diminish this evening and then remain relatively light
through the rest of the forecast period.
Red Flag Warning from 11 AM to 8 PM MDT Monday for COZ220-
Winter Storm Watch from late Monday night through Wednesday
morning for COZ058>082-084-087-088-094.
For frequently asked questions about the Area Forecast Discussion