Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 11/28/22
Area Forecast Discussion
National Weather Service Denver/Boulder CO
827 PM MST Sun Nov 27 2022
Issued at 827 PM MST Sun Nov 27 2022
Water vapor satellite imagery showing a decent amount of mid and
upper level moisture in the westerly flow aloft upstream of
Colorado. Adjusted sky cover up for tonight, with waves of high
clouds expected. For the mountains, expected skies to become mostly
cloudy by midnight, if not sooner. Because of this adjusted low
temperatures up some. Windy conditions will continue over the
mountains and wind prone areas east of the Continental Divide with
gusts to 70 mph possible.
.SHORT TERM...(This evening through Monday)
Issued at 137 PM MST Sun Nov 27 2022
Starting to see some of the gusty winds developing in the
mountains this afternoon with gusts in the 30 to 45 mph range.
Expect winds to increase even more this evening as the flow backs
more westerly and increases. Latest NAM cross sections showing
cross barrier flow increasing 40-60kt this evening. There is some
mountain top stability that develops this but strength of
inversion not all that impressive. Local high wind gradient
program showing a brief window of potential high winds tonight so
could see a few gusts up close to 75 mph. Overall coverage of the
strongest windows would be very localized and not widespread
enough to warrant a wind hilite. Expect majority of the winds in
the 40-60 mph range. Overall winds will decrease a bit by Monday
afternoon as mountain top flow backs further around to the
Meanwhile approaching broad upper trof with decent QG ascent will
increase into northwest Colorado during the afternoon as moisture
deepens over the mountains. Snow will rapidly develop over the
northern mountains with favored southwest to west orographic flow
over zone 31. Will be starting the warning at 18z over northern
mountain zones which is earlier than the 00z start time issued on
previous shift. Across lower elevations still one more dry and
mild day before cold front comes through late Monday night.
.LONG TERM...(Monday night through Sunday)
Issued at 137 PM MST Sun Nov 27 2022
The timing of the synoptic scale features associated with the
next storm system still look consistent for Monday night and
Tuesday. The models show increase QG ascent in the mid/upper
levels ahead of the trough axis, spreading it west to east across
northern CO Monday night. Strong southwesterly winds in ridgetop
will continue to favor zones 31 and 33 the most. The models show
strong QG ascent developing over northwest CO Monday night, then
it slowly weakens as it translates eastward. The combination of
favorable orographics and strong QG ascent looks very good for
heavy snow in the Park and Gore Ranges. This could result in storm
totals up to 20 inches in those areas, with up to 16 inches in
those favorable areas of zone 33 as well. As a result, with have
upgraded the winter storm watch to a warning. Advisories will
likely be necessary as well, but will let later shifts address
this. The rest of the mountains are concerned, still decent
snowfall with advisory criteria snow possible in zones 34 and 35,
especially if you factor in the jet induced banding late Monday
night into Tuesday morning. A cold front will push north to south
across the urban corridor/northeast plains 09z-12z Tuesday
morning. Northeast winds will get going a little sooner than that
as a surface low sets up over east central CO around 03z Monday
evening. This could usher the lower clouds and colder air into the
plains sooner, but the real push will be overnight. Spatial
cross-sections still show the potential for conditional symmetric
instability developing coupled with post frontal upslope. Main
window still appears to be 12-18z Tuesday morning which would line
up with the morning commute, then a gradual decrease in coverage
and intensity as the mid level trough axis starts to exit eastward
into KS towards 00z.
Tuesday night into Wednesday, strong mid/upper level subsidence will
spread west to east, with decreasing clouds overnight. Clearing
skies and strong radiational cooling following the trough will
produce very cold overnight lows, especially in the high mountain
valleys. This will be dependent on how fast the clearing takes
place but potential for lows dropping to -20F not out of the
question. Wednesday will be a little warmer, but still around 10
degrees below normal.
Thursday into the weekend, a strong west/southwesterly flow aloft
will remain over the region, with a short wave passing across the
northern Rockies Friday into Friday night. This will result in a
continued chance of snow in the mountains along the west facing
slopes. Strong downslope wind potential in the Front Range
mountains/foothills Thursday night into Friday. Generally dry
across the plains with temperatures slightly above normal.
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 440 PM MST Sun Nov 27 2022
VFR conditions with high clouds will continue across the region
tonight and Monday in advance of the next storm system. This next
system is expected to bring snow to the Denver area after 06Z
As far as winds go, light southwest to variable winds to continue
the next few hours and then settle at a southerly direction
through tonight and into Monday morning. Confidence in wind
forecast is low after 18Z Monday. Some models show northerly winds
due to a deepening surface low over southeast Colorado. The
HRRR/RAP indicate strong westerly winds mix down to the surface
with gusts to 30 knots possible, leaning towards the weaker north
winds, because the HRRR has a bias of over mixing these stronger
winds to the surface.
Winter Storm Warning from noon Monday to 5 PM MST Tuesday for
Area Forecast Discussion...Corrected
National Weather Service Great Falls MT
840 PM MST Sun Nov 27 2022
Areas of snow will progress further through Southwest Montana
Sunday evening. Temperatures will turn much colder through the
week ahead. A widespread light snow event is likely toward the end
of the week.
Bands of snow along with gusty winds have moved through the area and
are passing through southwest Montana, at the time of this update.
The forecast is performing well; therefore, no updates are made.
HRRR forecasts have captured reasonably effectively the observed
bands of shallow convective snow that have developed over central
Montana, expected to move through Southwest Montana this evening.
The bands of snow are supported by weak instability, with CAPE
values nearing 100 J/kg. Large dewpoint depressions at the surface
indicate wet bulb temperatures in the lower to mid 30s, so
evaporative cooling with the onset of precipitation is supporting
wet snow to the surface at lower elevations. The surface pressure
gradient has begun to weaken as the surface low over Southern
Alberta begins to move away to the east. Strong winds continue,
with occasional gusts to 45 mph occurring. A few locations did
earlier exceed the 58 mph high wind warning criteria, but overall
trend in forecasts and observations is below this threshold, so
high wind warnings are cancelled.
Mid-level lapse rates are steepening with colder temperatures
aloft. Thus, periods of snow are likely to continue over mountain
areas tonight. Winter Weather Advisories remain in effect for
these areas of snow and blowing snow.
Snow gradually ends tonight from north to south as surface high
pressure builds in with steadily colder temperatures. Portions of
Southwest Montana do remain under a left jet exit region, so snow
is expected to continue over this area through Monday. Generally
fair but cold weather settles in for Tuesday, with scattered light
snow flurries possible. NBM 50th percentile Max temperatures are
in the upper single digits and lower teens on Tuesday afternoon.
Weak warm advection and shortwave ridging aloft provides for a
brief rebound in temperatures on Wednesday, though still in the
teens and 20s for most areas. Wind chill below -20F may occur
Wednesday morning as wind picks up to bring the warmer air into
Another strong cold front backs into North-central Montana on
Thursday, providing a return to single digit temperatures. The
southward extent of this cold front remains uncertain, as it
depends on how far south a Pacific shortwave system tracks through
the intermountain west. Nonetheless, moisture ascending over the
cold air on the southwest flow aloft is expected to generate a
period of widespread light to moderate snow Thursday night into
Friday. The NBM is suggesting that much of the Golden Triangle
region has over a 40% chance of seeing at least 2 inches of snow,
which could be enough to cause some minor impacts if realized.
840 PM MST Sun Nov 27 2022 (28/00Z TAF period)
Blowing snow in association with gusty winds and snowfall cause
MVFR/IFR/LIFR conditions as a front passes from north northwest to
south southeast through the region. Expect mountain obscuration,
icing conditions and turbulence. Please, see the link, below for in
depth information on icing and turbulence forecasts, and more.
Refer to weather.gov/zlc for more detailed regional aviation weather
and hazard information.
.PRELIMINARY POINT TEMPS/POPS...
GTF 12 19 1 13 / 30 20 10 0
CTB 7 14 -2 10 / 70 20 10 0
HLN 12 19 1 13 / 70 20 20 0
BZN 8 20 -4 9 / 100 10 30 10
WYS 2 20 -12 12 / 90 60 40 20
DLN 6 18 -4 10 / 90 20 20 0
HVR 12 18 3 12 / 30 10 10 0
LWT 11 19 -2 9 / 50 10 10 0
WINTER WEATHER ADVISORY IN EFFECT UNTIL MIDNIGHT MST TONIGHT
FOR East Glacier Park Region...Southern Rocky Mountain
Front...Little Belt and Highwood Mountains.
WINTER WEATHER ADVISORY IN EFFECT UNTIL 9 AM MST MONDAY FOR
Gallatin Valley...Northwest Beaverhead County...Ruby Mountains
and Southern Beaverhead Mountains...Gallatin and Madison County
Mountains and Centennial Mountains.
Area Forecast Discussion
National Weather Service Tucson AZ
156 PM MST Sun Nov 27 2022
.SYNOPSIS...Dry with warmer temperatures to start the week. A
storm system will brush by to our north Monday and Tuesday,
resulting in some gusty winds across southeast Arizona along with
a few degrees of cooling. Dry and warmer conditions return for
the second half of the work week with a weak storm system
potentially impacting the region over the weekend.
.DISCUSSION...Our dry northwesterly flow will buckle into a zonal
flow over the next 24 hours as a system digs into the northern
Great Basin Monday afternoon. With our current progressive
consolidated higher latitude flow pattern, it will kick quickly
eastward before digging into our area. It should brush by close
enough for gusty winds as early as mid Monday afternoon and bring
a few degrees of cooling Tuesday. The latest HRRR shows a nice low
level moisture intrusion from the gulf late tomorrow, but it
should be pretty shallow. We might manage enough of a moisture
increase for a few light showers in the east central mountains,
but not much more.
A broad ridge is expected to develop from central Mexico through
the Gulf of Mexico and into Florida, with signs of a deeper split
near the west coast the second half of the week. Ensembles lift a
first shot of energy once again north of our area
Friday/Saturday, but a moisture increase could bring some virga or
light showers in the warm sector upslope Friday night. This could
set the table for a deeper follow-on system early next week.
Ensemble mean 5 day height anomalies are hinting at a broader and
deeper mean trough position over the west next week.
.AVIATION...Valid through 29/00Z.
Mainly clear skies thru 28/06Z then SCT-BKN clouds at or above
20k ft AGL. SFC wind 12 kts or less with normal diurnal trends
into the morning hours. Gusty southwest winds developing after
28/20Z. Aviation discussion not updated for TAF amendments.
.FIRE WEATHER...The next storm system will approach and pass
Monday into Tuesday which will increase winds by Monday afternoon
and drop temperatures on Tuesday. 20-ft winds from the southwest
at 10-20 mph are expected Monday and Tuesday. Outside of a slight
chance of showers over the White Mountains, dry weather continues
through most of the week. Afternoon RH values will drop to 10-20
percent in valley locations through Monday before moisture
increases on Tuesday.
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