Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 02/21/21
Area Forecast Discussion
National Weather Service Denver/Boulder CO
746 PM MST Sat Feb 20 2021
.UPDATE...
Issued at 737 PM MST Sat Feb 20 2021
Intense snow band from northern Park county across Denver and up
along I-76 looks on track to produce 1-2 inches of snow in 1-2
hours, but then the snow should be much lighter and probably
ending on the plains shortly behind the band. We`re seeing some
slush on the roads in the colder places around Denver, but not
everywhere. out in Fort Morgan this has been mostly rain, though
it should be getting cold enough for snow about now. Overall the
forecast looks on track, so only minor changes, mainly higher
PoPs over the next few hours.
&&
.SHORT TERM...(This evening through Sunday)
Issued at 222 PM MST Sat Feb 20 2021
A storm system will bring a variety of impacts to the mountains
and portions of the Denver metro and Palmer Divide late this
afternoon into the early overnight hours. Upper level jet streak
is currently overhead and slowly sinking south. Meanwhile, a
positively tilted shortwave continues to slide east into Utah,
with a broad area of southwesterly flow aloft. Moisture has also
increased notably over the past few hours. This has combined with
700-500mb lapse rates approaching 9C/km, and QG ascent to form
several shallow convective bands over the mountains early this
afternoon. Over the plains, fairly strong mixing allowed
temperatures to reach the 50s across much of the plains, but
temperatures should quickly cool as a cold front advances through
the area this afternoon.
Over the mountains...
Snow showers have increased in coverage this afternoon, and
widespread snow is expected over the higher terrain through late
this evening. Conditions seem ripe for a period of moderate to
heavy snow as these bands slowly shift south. Would expect some
travel concerns across the I-70 corridor from about 4 to 8PM as
the heavier snow shifts through that region. While snowfall totals
won`t be robust, the heavier snowfall rates over a short period of
time could still cause significant issues. Snowfall totals through
tonight will range from 4 to 10 inches, with the highest totals
falling in the Park range.
Over the plains...
A very difficult snow forecast for this afternoon and evening, as
guidance continues to struggle with multiple aspects of the
precipitation forecast. What we do know is that there will be
plenty of lift across the area, via upper divergence from the left
exit quadrant of the jet streak, and by frontogentical forcing.
What remains to be seen is (1) how much moisture is left in the
boundary layer and how quickly can we saturate the column, and (2)
where the best forcing sets up. Model solutions vary
significantly in regards to each of these points. The HRRR has
been notably drier and produces significantly less precipitation
over the plains, while many of the other CAMs and coarser
resolution guidance are wetter and a little further north with the
axis of heaviest precipitation. The forecast itself is very
similar to the previous forecast, with a couple inches of snow
falling in the southern half of the metro and into the southern
Foothills/Palmer Divide. However, it should be noted that there
could be locally higher totals in this area, depending where
banding sets up and how long snow lasts as the cold front sinks
south. Regardless of snowfall totals, expect some travel impacts
along I-70, as well as I-25 from the Denver metro into the Palmer
Divide.
Tomorrow will be a much quieter day. Temperatures should remain
fairly cool under brisk northwest flow, with highs in the upper
30s to near 40 across the plains. Clouds will gradually clear
through the day. A few mountain snow showers could linger around,
but any accumulations will be minor.
.LONG TERM...(Sunday night through Saturday)
Issued at 122 PM MST Sat Feb 20 2021
Sunday night through Monday night, a large upper level trough of low
pressure will cover much of the Central and Eastern U.S. with a
moderate northwesterly flow aloft over Colorado. This pattern will
produce breezy and mild conditions across North Central and
Northeastern Colorado. There may be enough moisture caught up in the
flow combined with some orographic lift to produce isolated to
scattered light snow showers over the northern mountains, mainly
over the higher peaks. Some wind prone locations along the Front
Range Mountains and higher foothills may see wind gusts to 60 mph at
times. The best chance for the stronger winds look to be on Sunday
night due to the presence of a mean state critical layer.
On Tuesday, the upper flow becomes westerly ahead of an upper level
shortwave moving across the Northern Great Basin. This should result
in lighter winds along with continued mild and dry conditions across
the CWA. However, increasing moisture ahead of the shortwave may
produce scattered snow showers across the Park Range of Zone 31
by afternoon.
A series of shortwaves and associated cold fronts will bring colder
unsettled weather to North Central and Northeastern Colorado
Wednesday through Saturday with temperatures dropping below seasonal
averages. The first two systems will impact Colorado Tuesday night
through Thursday morning with a chance of snow and colder
temperatures. The best chance of snow will be in the high country
with lesser chances across the plains. Moisture and instability with
this system looks somewhat limited, therefore snowfall should
generally be on the light side.
Drier weather is expected on Thursday as upper level high pressure
briefly builds over the Rocky Mountain Region and Northern Great
Plains States. Another system will bring more snow to the high
country Friday and Saturday with mostly dry conditions on the
plains.
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 737 PM MST Sat Feb 20 2021
The snow band over Denver is moving off of the field at KDEN this
hour, and should be past KAPA by 06z. 1-2 inch snow accumulation
is likely at KAPA. MVFR conditions should prevail, becoming VFR
05z-07z though a cloud deck at 5000-7000 ft AGL may require
instrument approaches to KDEN until 09z-12z. North winds gusting
to 20 knots will continue to diminish this evening.
For Sunday, VFR conditions with northwest winds gusting to 20
knots at KDEN/KBJC.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 5 AM MST Sunday for COZ031-033-034.
&&
$$
UPDATE...Gimmestad
SHORT TERM...Hiris
LONG TERM...jk
AVIATION...Gimmestad
Area Forecast Discussion
National Weather Service State College PA
1021 PM EST Sat Feb 20 2021
.SYNOPSIS...
High pressure will build into the region tonight, as upper
trough passes east of Pennsylvania. A fast moving system will
bring a burst of snow (perhaps rain/snow mix in the S) late
Sunday night and Monday morning. Beyond the Monday system, the
weather pattern looks less stormy through the end of February
with temperatures trending warmer, becoming near to above
average by mid week.
&&
.NEAR TERM /THROUGH SUNDAY NIGHT/...
Expect decreasing clouds areawide and diminishing snow showers
over the Alleghenies late this evening, as large scale
subsidence overspreads the region behind departing shortwave.
Some meager latent heat flux from the largely frozen Lake Erie
will result in the best chance of an additional dusting this
evening over the northwest mountains.
High pressure building in from the Ohio Valley will result in
diminishing wind and clearing skies overnight. The most
favorable radiational cooling will be over the western half of Pa,
where winds are likely to become calm by dawn. Therefore, have
undercut NBM min temp forecast in this part of the forecast
area. Expect the normally colder valleys of the Alleghenies to
drop to around zero by dawn, as the latest RAP suggests. A more
persistent breeze over eastern Pa should hold readings to the
teens in the Susq Valley, still well below average for late
February.
The center of a 1038mb high will pass just south of Pa on
Sunday, ensuring mostly sunny skies and light winds. Forecast
850mb temps moderate rapidly, as flow turns to the south.
However, snow cover and weak mixing should result in highs
several degrees below average, with afternoon readings peaking
between 30-35F over most of the region.
Thickening cloud cover is expected Sunday night, as waa aloft
overspreads the region ahead of low pressure lifting through
the Grt Lks. Models indicate an initial band fgen forcing will
lift through the area during the evening hours, perhaps
accompanied by a brief period of light snow/flurries over parts
of northwest Pa. However, the best chance of snow will come
toward dawn over western Pa, as southerly low level jet and
surge of waa arrive. A coating of snow appears likely by dawn
over most of the Allegheny Plateau, with around an inch over the
northwest corner of the forecast area.
&&
.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
The main period of snow will be during the day on Monday, done
by late afternoon. Low level temperatures will support some rain
mixing in Monday, especially across the south. I did not change
the QPF or snowfall amounts by much. Models last night and
today have lower QPF than yesterday. Also timing of the event
and warming temperatures as the clouds move in will support less
impact than recent events, given warmer low level temperatures.
Left high temperatures close to what we had in the fcst.
Some upslope and lake effect snow showers Monday night into
Tuesday. Temperatures not real cold and Lake Erie has a lot
of ice cover now. I did edge high temperatures down a little
on Tuesday.
&&
.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Medium range guidance supports fair weather Wednesday with some
of the warmest conditions we`ve seen since December, as a broad
upper ridge pushes off the east coast. An increasing southwest
flow between the retreating ridge and a low over the Grt Lks
should push readings to around 50F over much of the region. A cold
front is progged to sweep through the region Wednesday night,
perhaps accompanied by a few rain/snow showers, then followed by
fair and seasonable conditions later Thursday. All guidance
tracks a potent looking shortwave and secondary cold front
through the state Friday, which is likely to be accompanied by
scattered snow showers and a brief return to below normal
temperatures.
Latest ECENS and GEFS currently support fair and milder weather
next weekend, as an upper ridge builds along the east coast.
However, a minority of ensemble members indicate a dying cold
front could approach late in the weekend with a chance of rain
showers.
&&
.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
At 03z, MVFR cigs are hanging on over the western highlands
(BFD and JST) along with spotty light snow showers. Clouds are
expected to scatter overnight at JST, while BFD may hold onto a
deck of low /MVFR/ clouds. Elsewhere, downsloping flow will
continue to produce VFR conds.
Conds should improve to VFR area-wide on Sunday, as high
pressure passes overhead. Clouds will begin to thicken from
west to east late in the day.
Light snow will overspread central PA Sunday night, producing
widespread restrictions.
Outlook...
Sun night-Mon...Widespread restrictions developing in light
snow. Could mix with rain south on Monday.
Tues...Scattered -SHSN to bring reductions to primarily the
northern and western highlands.
Wed...VFR conds.
Wed night-Thu...Restrictions possible mainly N/W in light
rain/snow showers.
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...Lambert/Martin
NEAR TERM...Fitzgerald
SHORT TERM...Martin
LONG TERM...Fitzgerald
AVIATION...Evanego
Area Forecast Discussion
National Weather Service Dodge City KS
530 PM CST Sat Feb 20 2021
...Updated Aviation Discussion...
.SHORT TERM...(This afternoon through Sunday Night)
Issued at 1200 PM CST Sat Feb 20 2021
Temperatures warming nicely at midday, as warmer air aloft finally
mixes to the surface and the last vestiges of the arctic air mass
are removed. Many locations presently warming into the lower to
mid 50s for the first time since February 5th. The temperature at
the Dodge City Airport as of 1122 am was 54, which is the warmest
temperature since February 3rd. As balmy as this feels, it is only
a few degrees above late February normals. Southeast winds will
increase sharply this afternoon, in response to leeside
cyclogenesis on the Colorado Front Range. SE wind gusts of 30-35
mph will be common this afternoon. This will also drag in some
cooler boundary layer air to our southeast (still snowpack in NW
Oklahoma) and cap our temperatures in the lower 50s. Welcome to
life on the other side of the arctic outbreak.
As the shortwave approaches tonight, the associated surface low is
forecast by HRRR to be over the western zones at midnight. After
midnight, models are in good agreement that stratus will
overspread much of SW KS east of the surface low, with the lowest
ceilings favoring the eastern/NE zones. 12z NAM is displaying its
classic light QPF drizzle signature after midnight mainly along
and east of US 283, with best opportunity for something measurable
along the border with WFO Wichita. Current thinking is surface
temperatures will be below freezing, but not by much, in the 28-32
range as any drizzle falls. Carrying areas of freezing fog and
freezing drizzle in the grids for several hours late tonight
across the eastern zones. A light accretion of icing on elevated
surfaces is plausible east of US 283 late tonight, and a short
term winter weather advisory may be required.
Surface low will exit the southeast zones near Medicine Lodge
around sunrise Sunday, followed by increasing NW winds and dry
advection. Any light wintry mix across the eastern zones tonight
will only last about 3-4 hours, before the drier NW winds arrive
early Sunday. Clouds will decrease from west to east Sunday, with
full sunshine by late afternoon. NW winds will be strong, with
gusts of 35-40 mph common. With cool advection masked by NWly
downslope compression, Sunday will be only a few degrees cooler
than Saturday, with mid to upper 40s expected.
.LONG TERM...(Monday through Saturday)
Issued at 120 PM CST Sat Feb 20 2021
Strong warming expected Monday and Tuesday, as NWly midlevel flow
trends zonal. Afternoon temperatures will respond, near 60 Monday
and well into the 60s Tuesday. Downslope westerly breezes will
encourage the warmup Monday, with winds trending southerly Tuesday
ahead of a surface low over the SW zones...but all the winds
appear light at 10-20 mph. We have earned this fantastic weather
this February; get out and enjoy!
A dry cold front will bring a northerly wind shift Tuesday night,
followed by temperatures returning to February reality in the 40s
Wednesday. Another weak shortwave trough will approach from the
central Rockies early Thursday. 12z ECMWF solution strongly favors
any accumulating snow with this system being relegated to the I-25
corridor in Colorado, with only light snow potential sneaking
across the CO/KS border. NBM pops were similar to this and were
accepted. Models dampen this wave significantly daylight Thursday,
and most locations will remain dry, and seasonably cool in the
40s.
Southwest flow aloft quickly reestablishes Friday, allowing
temperatures to moderate once again temporarily. This warming
appears short lived, as another progressive open trough is due to
come through early in the weekend. While NBM pops are dry, noticed
12z ECMWF has some light snow potential eastern zones Friday
night. Kept forecast dry for now. At any rate, progressive pattern
will keep any precipitation of consequence in central/eastern
Kansas early in the weekend.
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 514 PM CST Sat Feb 20 2021
Gusty southeast winds will decrease some this evening but a
southeasterly flow at around 15 knots can be expected through at
least the first half of the night as cold front approaches from
the west northwest. This southeasterly flow near the surface will
draw an area of low level moisture quickly back into southwest
Kansas, especially in the Dodge City and Hays areas. Ceilings are
expected to fall back into the MVFR category after midnight with
ceilings as low as 1000 ft AGL or less being possible for several
hours at Dodge City and Hays between 09z and 15z Sunday. There
will also be a chance for some scattered freezing drizzle in the
Hays area around daybreak. As the cold front passes between 06z
and 12z Sunday a gusty northwest wind at 15 to 20 knots will
develop across southwest Kansas. Northwest winds around 25 knots
with gusts as high as 40 knots will be possible at times during
the day on Sunday.
&&
.PRELIMINARY POINT TEMPS/POPS...
DDC 28 46 24 60 / 10 10 0 0
GCK 26 44 21 58 / 0 10 0 0
EHA 28 43 22 59 / 0 0 0 0
LBL 27 47 20 60 / 0 0 0 0
HYS 25 44 24 60 / 30 20 0 0
P28 28 47 25 60 / 20 20 0 0
&&
.DDC WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 9 PM this evening to 6 AM CST
Sunday for KSZ031-046-065-066.
&&
$$
SHORT TERM...Turner
LONG TERM...Turner
AVIATION...Burgert
Area Forecast Discussion
National Weather Service Des Moines IA
551 PM CST Sat Feb 20 2021
.SHORT TERM.../Tonight through Sunday/
Issued at 321 PM CST Sat Feb 20 2021
Forecast Highlights:
-Accumulating snow expected across most of central Iowa on Sunday.
-Winter Weather Advisory expanded southward.
-Snow amounts ranging from 1-5" expected, locally higher amounts
possible.
Tonight into Sunday...Attention today was mainly focused on the
snow potential for Sunday across much of Iowa. Warm air advection
today has helped push high temperatures above freezing in southern
Iowa and into the upper 20s in northern Iowa. Low temperatures
tonight will be more moderate, mainly in the upper teens to mid
20s, with a strong push of gulf moisture in the low levels. This
low level moisture is aided by some mid-level moisture from the
Pacific causing pwts over 0.5 through much of Sunday and QPF
values between .25 and .40 right across the central CWA. This QPF
is expected to mainly fall as snow along and north of I-80 with
total snow accumulations of 2-5 inches. Although visibilities will
be lower during snowfall, widespread blowing snow is not expected
as winds will be lighter during this storm. Further south, along
and just north of the IA/MO border, mixed precipitation is
expected with lighter snow accumulations between 1-3 inches along
with a light glaze of ice.
Snow will spread west to east tomorrow morning with the bulk of the
snow falling in central Iowa between 12-18Z. The latest HREF and
HRRR still suggest the most intense snowfall rates could be upwards
of 1" per hour with an omega bullseye in the dendritic layer around
midday Sunday. Will also not rule out the possibility for locally
higher 6" snow totals. Travel impacts are expected during much of
the day tomorrow from the snow amounts forecasted.
.LONG TERM.../Sunday night through Saturday/
Issued at 321 PM CST Sat Feb 20 2021
Near-normal temperatures and quiet weather will be the main
weather story for this upcoming work week. Ridging and increasing
west-northwest flow will encourage warming temperatures from the
western CONUS initially following Sunday`s system. We transition
to (weak) southwest flow on Tuesday which will help push high
temperatures into the 40s for much of the CWA and lead to some
melting of the current snowpack. Overnight temperatures below
freezing could cause some re-freezing impacts on any wet surfaces
from the melting snow Tuesday night into Wednesday morning but any
additional impacts from the melting snow are not anticipated at
this time. Tuesday looks to be the warmest day of the week as
another low pressure system tracks across the Rockies and into the
Central Plains by Tuesday night. Some models are hinting at a
weak mid-level disturbance on Wednesday but at this point just
left Wednesday to be a little cooler with highs in the 30s and
cloudy. Slightly colder air looks to return towards the end of the
work week into the weekend but rest assured, not to the same
extent as earlier this week.
&&
.AVIATION.../For the 00Z TAFS through 00Z Sunday evening/
Issued at 550 PM CST Sat Feb 20 2021
MVFR conditions due to fog and haze were in place across northern
IA at 00z with high cloudiness increasing north and west. MVFR and
possibly IFR conditions in fog and haze may expand later tonight
preceding snow advancing west to east starting early Sunday
morning. The snow will persist well into the afternoon in most
locations with widespread IFR conditions anticipated. Confidence
in all these trends is medium.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 6 AM to 6 PM CST Sunday for
IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-
081>085-092>096.
&&
$$
SHORT TERM...KCM/Donavon
LONG TERM...KCM/Donavon
AVIATION...Small
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
617 PM EST Sat Feb 20 2021
.AVIATION...
Clouds associated with the Lake Michigan moist plume have been
undergoing a diminishing trend this afternoon amidst large scale
subsidence across srn Mi. Latest RAP and NAM solutions suggest that
the subsidence will lower the inversion a bit tonight with just
enough remnant moisture to support some occasional low end VFR/high
end MVFR based stratus. However, observational trends suggest
conditions are a bit drier. The HRRR actually suggests clear skies
through the night. In leaning toward the drier solution, forecast
skies will be kept scattered through the night. Under southwest
flow, MBS may however be more apt to experience periodic broken
conditions this evening given that the low level flow will not veer
from southwest to south over Lake Mi until after midnight. There
will be a strengthening of the wind field atop the nocturnal stable
layer overnight, perhaps enough to limit the degree of boundary
layer cooling and thus inhibit fog development.
For DTW...The surface winds will shift to the southeast overnight.
Winds atop the shallow boundary layer will remain south-southwest,
with current indications less bullish with low cloud development off
Lake Erie. So a more optimistic overnight cloud forecast will be
introduced for metro.
.DTW THRESHOLD PROBABILITIES...
* Low in ceilings at or below 5000 feet tonight.
&&
.PREV DISCUSSION...
Issued at 246 PM EST Sat Feb 20 2021
DISCUSSION...
A high pressure ridge will bring one more very chilly night tonight
as light south winds and partly to mostly clear skies lead to decent
radiational cooling off of widespread snowpack. After topping out in
the mid 20s late today, expect lows to drop into the single digits
overnight. Southerly winds will then increase on Sunday within the
strengthening pressure gradient between the departing ridge of high
pressure and low pressure racing out of the central plains into the
mid Mississippi Valley. With this flow, expect temperatures to climb
into the 30 to 35 degree range by late afternoon to early evening,
ending a 15 day streak of below 30 degree weather (assuming DTW
remains in the mid to upper 20s through late this afternoon).
The southern stream shortwave that will be responsible for lee side
cyclogenesis over the plains is currently digging through parts of
California today per WV satellite imagery. As this system continues
east, expect the low pressure center to track into southern lower
Michigan by Sunday evening/overnight. Within an area of strong
isentropic lift/warm air advection in advance of this system, expect
an expanding area of snow Sunday evening. Given climbing surface
temperatures, except some rain to possibly mix with the snow into
the overnight hour as the low crosses over the forecast area. All in
all, expect a wet 1 to 2 inch (locally 3) snowfall accumulation from
Sunday evening into the overnight with any lingering snow showers
ending early Monday morning.
Relatively mild readings will then set up into mid next week as high
temperatures reach the mid 30s on Monday, around 40 on Tuesday and
upper 30s Wednesday as a short ridging translates through the region
in advance of the next northern stream shortwave and attending cold
front. This front will work through the area late Wednesday and
bring a return to cooler weather for the late week period as the
temperatures return to the 20s to lower 30s Thursday/Friday with
lows in the single digits/teens by Friday morning. This cold shot is
the first in a series of more progressive intrusions of polar/arctic
air that will sweep through the area every 3 or 4 days (each latest
a few days). This will be a more characteristic of February weather
as compared the persistent cold conditions of late.
MARINE...
The central Great Lakes will remain under the influence of a
strengthening area of high pressure moving through the Ohio Valley.
Favorable marine conditions will continue this evening into tonight
as a result. This high then moves to the eastern seaboard Sunday as
a new low develops over the central Plains. The central lakes will
reside in the interface of these two systems causing winds to shift
to south-southeast by Sunday afternoon. Winds strengthen over the
course of the day Sunday as the low approaches the region causing a
tightening the local pressure gradient. Peak winds are expected
Sunday night with a couple hour period during the first half of the
night where gusts could touch 30kts over central Lake Huron. As
mentioned in prior discussions, the thermal profile still is looking
to be relatively neutral to stable limiting mixing depths and making
stronger gusts (near gales) difficult to achieve. Moderate W-SW
winds follow behind the low and will linger through the first half
of the work week before slowly weakening midweek.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&
$$
AVIATION.....SC
DISCUSSION...DG
MARINE.......KDK
You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.
AREA FORECAST DISCUSSION
National Weather Service Sioux Falls SD
932 PM CST Sat Feb 20 2021
.UPDATE...
Issued at 915 PM CST Sat Feb 20 2021
A couple of noteworthy points in the latest initial 00z guidance
and ongoing conditions...
A subtle warm nose around 850 mbs has resulted in freezing rain
west of a Mitchell to Brookings line this evening with scattered
icy roads reported in these areas. Calls to local law enforcement
suggest that these conditions are not widespread or severe enough
currently to warrant an official headline but this will continue
to be monitored closely. Additionally, the heaviest precipitation
has now pushed north of the Hwy 14 corridor with cooling of the
column expected to result in a change over to snow for any
remaining precipitation over the coming hour or two.
The other key takeaway from evening guidance has been the focus
for two areas of potentially elevated snow totals. The first runs
roughly from Tyndall to Madison and is in response to compact
frontogenesis focused in the 800:700 mb layer. The HRRR has been
most robust with this feature and has produced as much as 0.5-0.6
QPF at times. NAM, NAM Nest, WRFs and RAP all show hints at a
similar feature but would place any banding potential closer to
the 1-2 inch range. With all of that in mind, still low confidence
in the occurrence of an enhanced band over this area but have
increased snow total in this area to highlight this potential.
Second focus area for elevated snow totals continues to key in on
portions of Northwest Iowa, mainly south and east of a Sioux City
to Spencer line. This would occur as better support from the
incoming vort max arrives around the base of the trough and
reflective surface low deepens to the south. While latest guidance
appears to have trended a touch south, HREF would suggest the
potential for snowfall rate of up to 1 inch per hour at times and
thus some potential for snowfall enhancement. Inherited forecast
for 2-4 inches across this area still seems appropriate and will
continue to message the potential for locally higher amounts.
&&
.SHORT TERM...(This Evening through Sunday Night)
Issued at 328 PM CST Sat Feb 20 2021
Early this afternoon, an area of stratus and patchy fog lingers
along and east of I-29, mainly across southwest MN and northwest IA.
Further west, cirrus builds in ahead of an approaching mid level
shortwave. Expect temperatures to fall only modestly overnight, back
into the 20s, as cirrus aloft and low level stratus collectively
blanket the region amidst continued warm air advection.
Temperatures should rise to near or above the freezing mark
Sunday, warmest further west in southeast and central SD where
more sunshine will prevail.
Main focus is on impactful winter weather expected tonight through
Sunday in the form of freezing drizzle and snow. This occurs as a
mid level shortwave, coupled with warm air advection ahead of an
inverted sfc trough, tracks through the region. Early this evening,
precipitation should initially spread into south central and
southeast SD and northeast NE. Soundings imply a saturated DGZ, but
a stout, warm mid level dry layer will take significant time to
saturate overnight, especially further south near the SD/NE border.
This would imply potential for freezing drizzle across southeast SD
and parts of northeast NE this evening. However, it will take quite
a while for the low levels to saturate deep enough to warrant any
significant icing potential, so very little if any precipitation may
occur. Have chosen to hold off on any headline given lower
confidence and will continue to monitor freezing drizzle potential
this evening.
Late tonight, stronger forcing from the deepening wave should prompt
mid level saturation and a transition to snow, likely after midnight
and perhaps even as late as mid morning for some sites. Further
east, confidence is a little higher in seeing patchy freezing
drizzle before the column saturates ahead of the deepening wave
given the better forcing, but ice accumulations would likely only be
a glaze. The bulk of the snow for most won`t occur until Sunday
morning. Altogether, expect very little snow for much of southeast
SD and southwest MN. Further southeast, generally 1-3 inches of snow
can be expected for northwest IA and the I-29 corridor from
Beresford to Sioux City, a little higher than previous forecasts.
The heaviest snowfall rates are expected Sunday morning southeast of
Hwy 60 across northwest IA, where mesoscale Fgen banding and weak
instability are expected to set up, locally enhancing snowfall
rates. This means a narrow band of 3-4 inches, perhaps isolated 5-6
inches, is possible for parts of northwest IA, with heightened
threat along and southeast of a Spencer to Cherokee to Onawa IA.
As the system continues to track east, deformation-related light
snow will taper off by mid day for much of southeast SD and by
Sunday night for areas east of I-29. Could see potential for fog
with a strong nocturnal inversion developing amidst low level warm
air advection from westerly flow. Otherwise expect temperatures to
dip into the teens to 20s.
.LONG TERM...(Monday through Saturday)
Issued at 328 PM CST Sat Feb 20 2021
Colder, snowy weather from the weekend will be short-lived, as
heights building aloft and westerly low level flow brings warming
for early in the week. A stronger sfc pressure gradient combined
with 850mb jet and good mixing on Monday will bring west winds
gusting into the 20s and 30s. Despite the fresh snow, there is
pretty good model agreement that high temperatures will rise into
the 40s Monday and Tuesday.
On Tuesday night, right entrance region jet forcing combined with an
upper trough digging into the Central U.S. brings a chance for
period of flurries or light snow. At this point, model guidance
favors a dry scenario with better precipitation chances remaining to
our north, but this could certainly change over the course of the
next few days.
For the second half of the work week, expect temperatures to remain
generally above normal values with no significant chances for major
winter weather impacts.
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 447 PM CST Sat Feb 20 2021
Several aviation concerns through the period with low stratus,
fog, snow and perhaps freezing drizzle all in the mix.
Currently still seeing some remnant areas of fog across portions
of SW MN and NW IA with perhaps some potential for this to build
back to the west over the next few hours. Regardless, will see
ceilings lower into the IFR/LIFR ranges by the second half of the
overnight hours with the focus being for KFSD/KSUX.
In terms of precipitation, seeing an initial area of radar returns
working through central SD as of late afternoon although a dry
layer is precluding much of this from reaching the surface with
the exception being K9V9 currently reporting UP. Not out of the
question to see a period of mix at KHON over the next few hours.
Will see a more coherent area of snow work in later tonight
through Sunday morning, again focusing across NW IA. Still some
potential for this to start as a period of FZDZ although
saturation depth in the soundings isn`t quite there for any sort
of confidence to include this in the TAFs. During periods of
heavier snow, will see fairly stout visibility reductions with
KSUX the most likely culprit.
&&
.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Winter Weather Advisory from 4 AM to 6 PM CST Sunday for SDZ071.
MN...Winter Weather Advisory from 4 AM to 6 PM CST Sunday for MNZ090.
IA...Winter Weather Advisory from 4 AM to 6 PM CST Sunday for IAZ002-
003-012>014-020>022-031-032.
NE...Winter Weather Advisory from 4 AM to 6 PM CST Sunday for NEZ013-
014.
&&
$$
UPDATE...Kalin
SHORT TERM...BP
LONG TERM...BP
AVIATION...Kalin
Area Forecast Discussion...UPDATED
National Weather Service Chicago/Romeoville, IL
920 PM CST Sat Feb 20 2021
.UPDATE...
918 PM CST
The going forecast message for the rest of tonight and into
Sunday`s snow event look good. Continue to see a slight nudging
back of onset snow time in 00Z HRRR/RAP/NAM guidance, but that
was already decently accounted for in the going forecast, so only
minor tweaks made this evening. Onset time of the main snow in
the Chicago metro looks to be after 4 pm, and possibly just after
6 pm for downtown.
A primarily clear sky across much of the CWA this mid-evening.
Southeast winds around 5 mph at the surface and around 20 mph
just a few hundred ft up (per elevated platforms and estimating
with lowest level VWP data), have prevented as rapid of a
temperature drop as last night. In general this should prevent a
fog threat such as we saw this morning with high confidence,
however some patches of shallow fog are still possible, probably a
little more in the area along/east of I-57.
Satellite imagery shows our Sunday system nicely depicted at
present from Wyoming toward the Four Corners region, with a stout
150 kt upper jet leading the way as sampled by the 00Z DNR
sounding. RAOB data between there and here sampled low-level warm
advection above the surface, with +3C as far north as OAX, which
is about 1.5C warmer than both the RAP and NAM depict. There is
plenty of room to wet-bulb cool though with a fairly dry layer.
This is where more dynamic and precipitation-induced cooling
later Sunday afternoon/early evening will be needed to have the
precipitation stay as a snow to accumulate. Still do not see that
as an issue with the evolution of the system, especially
along/north of I-80. South of there the profiles are more
marginal, including on the 00Z HRRR, which would not have much for
snow accumulation at all there. If the degree of forcing is not
strong enough south of I-80 for at least a period of time, a lean
toward a little more rain may unfold. That is already noted in the
forecast, and still a fair amount of uncertainty on how far north
that snow/rain line, or at least snow/very low quality snow line
reaches. Again too will have to watch for some slick untreated
pavement if/where any rain occurs.
Snowfall amounts look good with the ingredients shown. It remains
that north central Illinois area west of the Chicago suburbs
(Boone, DeKalb, Lee, Ogle, Winnebago Counties) where the juxtapose
of deeper forcing for ascent, stronger warm advection aloft, some
steeper lapse rates, and a little colder profiles could support
some 3+ inch totals due to a 3-5 hour period of regular heavier
rates. The steeper lapse rates were noted aloft upstream on the
OAX and TOP soundings, with the latter showing near 8C/km from
850-500 mb, although fairly dry in that layer too.
The expected impacts messaging from this afternoon continues to
look good at this time, with some snow-covered roads expected and
potential for locations with hazardous travel in the late day/eve.
MTF
&&
.SHORT TERM...
332 PM CST
Through Sunday night...
Somewhat of an uncertain low temperature forecast for tonight.
Earlier guidance had been hitting the re-development of low cloud
cover pretty hard, but has since backed up a bit. We`ve already
begun warm advecting aloft, and this will only increase with time
tonight, so envision we will eventually development at least patchy
lower stratus. However, if skies remain somewhat clear into the mid-
late evening, temperatures should once again be able to fall
readily -- certainly not to the degree they did last night since
dewpoints are quite a bit higher -- but based on upstream
satellite, it`s looking like we`ll have enough time to radiate
here to justify lowering temperatures a bit. After midnight or so,
would expect temperatures to remain steady or even begin slowly
rising. With the higher dewpoints and potential for several hours
of mainly clear skies, there is a threat for additional fog
development. With the flow immediately off the surface forecast to
increase with time, modified Richardson numbers don`t look overly
supportive of a dense fog threat. So while some 4-6 mile type
visibilities certainly appear possible, have left out a fog
mention at this time.
One last round of snow to cap off our unseasonably cold and snowy
pattern then awaits us on Sunday. A shortwave trough swooping
through the Rockies into the Central Plains will trigger a robust
low-level mass response that will thrust a plume of relatively
warm and moist air up into the region. Isentropic ascent will spur
the growth of precipitation over the lower Missouri River Valley
that will then track eastward into our area Sunday afternoon. The
system will initially have a bit of work to do to erode a stubborn
wedge of dry antecedent 850-600 mb air, which will delay the
onset of initial precipitation until the afternoon for most, but
expectations are that this wedge of dry air will be no more by the
mid-late afternoon hours as a substantial amount of lift and
moisture advection through the region shouldn`t have too much
trouble dynamically cooling and saturating this air. At around
this time, most of the area will find itself under the main
precipitation shield with most seeing a steady, wet (i.e. not the
fluffy snow that we`ve seen with each of our previous snow events)
snow, but some across our southern counties could begin to see
some rain mixing in with the snow by the late afternoon. The snow
and rain/snow mix will last through the evening before ending
overnight as the surface cyclone occludes to our northeast.
With 7-8 C/km lapse rates atop the dendritic growth zone (possibly
even pushing 9 C/km across our northwestern counties) and a
considerable amount of attendant forcing being driven by the
incoming shortwave, isentropic upglide, and a conveniently located
left exit region of the upper jet, the potential is there for snow
to come down at a pretty good clip, especially if any f-gen support
comes into the fray. With much lower snow ratios than we have
recently seen being progged (likely spanning a range from 7:1 down
south to up to 12:1 across our north), it doesn`t seem like we will
quite get to seeing snow rates on the order of 1" or more per
hour, but any bursts of heavier snow will still pose a problem for
anybody traveling with abrupt reductions in visibility likely
along with the usual slippery roads that accumulating snow will
cause.
The main point of forecast uncertainty at this time is how far
north the rain/snow mix will reach and how long it might last
over a given area. Guidance remains mixed on just how warm we will
get with the incoming warm advection. Most guidance suggests that
areas along and south of I-80 will climb above freezing into the
mid and even upper 30s, with some of the more aggressive guidance
shoving these warmer temperatures farther north into the Chicago
metro. Think that this guidance may be overdoing the warm
advection a bit with the deep snowpack in place and ongoing
thermodynamic cooling processes, and thus think that any rain/snow
mix will remain confined to areas south of I-80. If we get some
more sunshine during the daytime then currently expected, then
could foresee a scenario where warmer temperatures allow some
rain to mix in with snow in the heart of the Chicago metro which
would eat into final snow totals there a bit, but confidence on
this remains low.
Overall, snow totals remain on track from the previous forecast with
2-3" likely along and north of I-80, 1-2" just south of I-80, and
less than an inch expected generally south of the Kankakee River
Valley where precipitation will be more of a rain/snow mix and
perhaps even just rain at times rather than snow. There remains
potential for localized snow totals up to around 4" with the
likelihood of at least brief heavier snow rates. Have honed in on
north-central and northwest Illinois being the favored region for
this with lapse rates forecasted to be slightly higher there than
elsewhere.
We did discuss the need for an impacts-based Winter Weather
Advisory, mainly for our northwest Illinois locales near the I-39
corridor where snowfall rates and amounts may be locally maximized.
However, with snowfall amounts overall trending just a bit lower, we
elected to hold off on issuing one at this time and will defer any
headline decision to the evening and overnight shifts to take
another look at things. As we`ve already mentioned, slick roads and
visibility reductions will still occur as they do for most
accumulating snow events, and we will still message these potential
impacts via graphics and SPSs.
One last item to note is that despite air temperatures being just
above freezing where rain manages to mix in with snow, it is
possible that actual surface temperatures may not be, especially
as we cool off a bit overnight. As a result, it`s possible that
some of the rain that falls in the rain/snow mix region across our
south could freeze on some roads (especially elevated and
untreated ones) and make for some slippery travel during the early
morning hours on Monday, potentially including the morning
commute.
Carlaw/Ogorek
&&
.LONG TERM...
248 PM CST
Monday through Saturday...
Conditions will become more seasonable across the area for the
upcoming week as we finally break out of the extended period of
well- below normal temperatures.
Monday and Tuesday: The area will remain in continued WNW/NW flow
aloft in the wake of Sunday`s system, with stronger mid to upper-
level flow remaining just north of the CWA on Tuesday. While
temperatures above freezing are expected both Monday and Tuesday,
there are still questions as to how far above freezing they can
rise. Strong WAA aloft will be ongoing through this period from
downsloping flow across the northern and central Great Plains,
producing a rather strong inversion as low as 1500ft over the
area. The amount of low-level cloud trapped under this inversion
is unclear with the competition of drying from the west and
periods of enhanced lift from weak waves traversing the WNW/NW
mid-level flow. Cooling via sublimation/evaporation from gusty
west winds acting on the relatively deep snowpack throw another
wrench into the mix and may end up being the most pronounced
limiting factor for warmer conditions. Temps in the mid 30s Monday
and upper 30s Tuesday are likely, with the potential to over-
achieve up to 5 degrees higher each day if clouds are minimal.
Wednesday through Saturday: A long-wave trough shifting east from
the western CONUS will cross the region Wednesday under a
loosely- coupled pair of upper-jet streaks. A vast majority of
guidance suggests the best dynamics will remain north of the CWA
late Tuesday night into Wednesday morning, with the deterministic
GFS basically the lone outlier indicating notable forcing and
associated precip across the CWA through the day Wednesday. The
forecast was kept dry during this period, but an eventual addition
of slight chance PoPs across the north may be warranted Wednesday
morning unless more guidance falls in line with the GFS.
A brief shot of colder air is expected behind the trough Thursday
and Friday, with a potentially more-active period of weather next
weekend into the following week as consensus guidance indicates a
transition back to a rather amplified pattern across North
America.
Kluber
&&
.AVIATION...
For the 00Z TAFs...
The main concerns through the TAF period are as follows:
- Mist and pockets of fog after midnight tonight lasting a few
hours after sunrise
- Period of steady snow Monday evening through beyond the end of
the 24-30 hour TAF period, with a small/wet snowflake type
expected
- Possibility of blowing snow late Monday evening right before
the onset of snow.
- Marginal low-level wind shear between 21-03Z as a 45 kt
southwesterly low-level jet moves overhead
Outside a narrow band of clouds based near 5000 feet expected to
swing over the terminals between now and 06Z, mostly clear skies
are expected overnight. Similar to last night, mist and even
pockets of fog are expected to develop during the early morning
hours but comparatively stronger southeast winds tonight should
prevent widespread low visibility from developing. Modest
visibility restrictions will likely persist after daybreak as high
clouds move in ahead the well-advertised system approaching from
the west.
Flurries are possible as early as 16-17Z, especially at RFD,
before a "wall" of snow moves in toward the 22-00Z. At the same
time, southeasterly winds will increase, becoming sustained at
10-15 kt with gusts to 20-25 kts by late afternoon. Confidence is
lower than normal on when snow will start (questions on how fast
we`ll be able to get rid of a low- level dry layer), but
eventually a wall of snow will sweep from west to east across
northern Illinois and northwestern Indiana. We opted to maintain
the 22-23Z start time of snow at all terminals inherited from the
previous set of TAFs, though adjustments may be made with the
scheduled 03Z AMD after examining the 00Z suite of model guidance.
After snow starts, it will be steady for several hours before
becoming light as the overnight hours progress. Snow rates of 0.25
to 0.5"/hr are expected especially between the 00-05Z, with a
small and wet snowflake type likely being quite effective at
reducing visibility. At ORD/MDW where the TAF window extends to
06Z, we opted to aggressively offer a TEMPO for 1/2SM visibility
with medium confidence already that such conditions will be
observed. Surface temperatures are expected to be around 31 to 32
degrees as the snow falls. With southeast winds gusting 20-25 kts,
blowing snow will be possible especially around the onset of snow
considering the inches powdery snow siting on top of the existing
deep snowpack. For now, we decided to leave out any formal
mention of BLSN in the TAFs given otherwise unfavorable low- level
temperatures and the wet type of snow expected to fall.
Finally, a brief period of low-level wind shear is possible Monday
evening from 21-03Z as a southwesterly 45 kt (at 2000 feet) low-
level jet moves overhead. With surface winds expected to be
sustained in the 10-15 kt range and gusts even higher, no formal
mention will be made in the TAF package.
Borchardt
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory...LMZ740-LMZ741...noon Sunday to midnight
Monday.
&&
$$
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Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
608 PM CST Sat Feb 20 2021
.SHORT TERM...(This evening through Sunday night)
Issued at 256 PM CST Sat Feb 20 2021
The long-awaited warming trend has arrived and we have finally made
the 20s for the first time since Feb 4th. The sky is mostly clear
with patches of low cloud cover across southern Minnesota and even
some dense fog over southwest Minnesota. High and mid level clouds
are spreading eastward across South Dakota which will reach our area
this evening. Some fog could expand across the area tonight, but the
mid cloud cover should keep it from becoming widespread and dense.
Low level moisture is increasing over a very cold snow pack, however,
so the fog potential will need to be watched this evening.
The system for late tonight and Sunday has trended a bit weaker with
most guidance exhibiting an open wave at 500 mb. NAM remains the
strongest with a closed low across Iowa and unrealistically high QPF
across southern Minnesota. The snow will spread from west to east
late tonight and Sunday morning. Kept QPF near the ensemble means,
which still do show some spread, but the spread isn`t such that
deviating up or down from the mean will make too much difference with
resultant accumulation. Maybe one inch. Accumulations from this
forecast package call for an inch south of a line from Redwood Falls
to the Twin Cities and Ladysmith, with 2 to 3 inches along I-90 in
far southern Minnesota. Left the Winter Weather Advisory alone for
now with the potential for 3+ inches remaining if the system shifts
slightly north.
.LONG TERM...(Monday through Saturday)
Issued at 256 PM CST Sat Feb 20 2021
A strong upper level jet will send a relatively warm Pacific airmass
our way to start the week. Temperatures still look to climb into the
upper 30s and low 40s for highs, which is nearly 10 degrees above
average for late February. This will be a welcome relief to most, as
we have spent the majority of the month well below average. Westerly
winds look to be on the breezy side Monday, particularly across
western portions of the area, but will decrease into the evening
hours. Tuesday will be another warm day with highs once again
approaching 40 ahead of a surface low over the Dakotas. This system
may bring some precip across the area late Tuesday into Wednesday,
and given that temperatures are slated to be above freezing for at
least a portion of the precip onset, a rain/snow mix is possible.
Behind the aforementioned low, highs for Wednesday and Thursday will
fall slightly back to normal late February readings in the upper 20s
and low 30s. Another chance of some precip may be in the cards to end
the week as a 500mb trough moves across the upper Midwest, but will
leave low PoPs as is for now until model consensus improves.
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 608 PM CST Sat Feb 20 2021
Main change to the TAFs was to follow more of the HRRR idea where
pre-snow MVFR/IFR cigs hang out more or less where they are now,
western and central MN given the lack of low clouds across southern
MN/northern IA. For the snow, followed the idea of the GFS/RAP. 18z
NAM only produces snow at MKT and EAU, which is probably a little too
aggressive given the moist atmosphere and weak forcing we`ll have
much of the day ahead of the trough moving through Sun afternoon.
Snow accums look to be mainly under one inch, just a prolonged period
of 1 1/2sm to 3sm visibility snow. With the light southeast winds
along the trough, we could see cigs lower than currently forecast
with the snow, but for now kept things mostly in the 008 to 012
range.
KMSP...Heaviest snow will remain south of MSP, with snow possible as
early as 12z. Highest snow rates will occur a couple of hours on
either side of 18z. Continued to be optimistic with cig heights
Sunday, though something around 800 feet may be possible for much of
the afternoon. Some improvements in cigs are expected Sunday night,
but will wait for later TAFs to try and refine that timing.
/OUTLOOK FOR KMSP/
Mon...VFR. Wind WSW 10-15kts.
Tue...Chc MVFR/IFR and -SN late. Wind SW 5-10 kts.
Wed...Chc MVFR cigs. Wind NW 10-15 kts.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...Winter Weather Advisory from 6 AM to 6 PM CST Sunday for Blue Earth-
Faribault-Freeborn-Martin-Steele-Waseca.
WI...None.
&&
$$
SHORT TERM...Borghoff
LONG TERM...Dye
AVIATION...MPG
Area Forecast Discussion
National Weather Service Pocatello ID
130 PM MST Sat Feb 20 2021
.SHORT TERM...Tonight through Monday night. Early afternoon
satellite imagery highlighted a low amplitude trough-ridge couplet
situated from the Aleutian Islands eastward through the NE Pacific
with NW flow extending downstream across Idaho. Looking through the
forecast charts this pattern remains firm clear through 186hrs (next
Saturday). The only real change is the weak impulses that will drop
SE through the NRN rockies almost daily and two substantial waves
embedded in that flow translating through the region Monday
night/Tuesday and then again Thursday. As for the specifics here in
the short-term, it looks as if the enhanced upslope flow across the
NE highlands will come to an end shortly with gusty winds continuing
through about 6 PM before tapering off. Thus the Winter Weather
Advisory will continue across the NE highlands through about 8 PM
MDT this evening. Weak features embedded in the NW flow aloft will
translate through the Montana divide region Sunday through Monday
resulting in periods of snowfall in the favored NW upslope flow
regions of the CNTRL and NE mountains. Light sub-advisory
accumulations are favored under these conditions. As mentioned
previously, a more substantial short-wave will migrate through the
region Monday night through Tuesday. For now, snow totals run up
towards the lower end of Advisory criteria and may yet require some
sort of highlight as the event draws near. Temperatures continue to
run below normal through Monday morning and then begin to warm
Monday afternoon and Monday night ahead of the incoming trough.
Huston
.LONG TERM...Tuesday through next Saturday. A moist NW flow regime
is forecast to continue throughout all of next week into next
weekend. This patten unto itself will support continued snow shower
activity in many of our mntn regions as those air parcels are lifted
and cool/saturate against the terrain, but we`ll also see multiple
shortwaves riding the flow that will tend to "focus" our precip
chances and bring lower elevations into play as well. The first wave
is expected Tue-Wed. A 50-70kt 500mb jet remains forecast on the
leading nose of this shortwave Tue, which will likely mix down at
least 15-25kts to the sfc (if not better... NAM and GFS forecast
soundings carry steep/unstable low-level lapse rates potentially
exceeding 7 degC/km), so we continue to adjust the wind forecast
higher than NBM guidance. Snowfall amounts look relatively light
(highest values of 2-5" or so in the Sawtooths, ern Fremont County,
the Tetons, and Big Holes), but the combination of winds and even
light snowfall amounts could certainly result in highway impacts due
to blowing/drifting snow (esp in the normal trouble spots east of I-
15 where the winds will overlap with higher snow totals). Best
potential for impacts will be daybreak through sunset Tue. Winds
should be lighter Wed. The next shortwave arrives Thurs afternoon
and continues into Fri/Sat, again with the flow supporting best
accums in locales that do well with NW-induced upslope such as the
Sawtooths, Tetons, Big Holes, and Bear River Range. Both shortwave
periods this week light up nicely on the GFS/EC ensemble
meteograms...these are definitely the impact periods, but even for
mntn point locales such as Stanley and Driggs (which we often use as
proxies in these coarser/lower resolution models to feel out how the
surrounding mntns may do), snow totals over any 24-hour period are
generally less than 5 inches (with only a few outliers...highest on
the GFS). So...unsettled yes, but no death or destruction on the
horizon. High temps throughout the week will generally top out in
the mid 20s-mid 30s each day (about 5-10 degrees below climo norms
for this time of year), supporting all snow with these systems.
-KSmith
&&
.AVIATION...-SN continues to fall at KDIJ. Most high-res models have
already ended snowfall there, but radar trends are lagging 1-2 hours
behind most of the HREF reflectivity members, AND KDIJ is infamous
for not shutting down on time. Thus, have maintained -SN with MVFR-
IFR vsby reductions through 22z/3pm before backing off to VCSH and
VFR cigs/ vsbys. Otherwise, satellite trends are progressively
scattering the region out, and HRRR cigs/HREF mean cloud product
both support a SCT or better VFR regime this afternoon into tonight
which is verifying well (expect perhaps KDIJ...guidance has a hard
time resolving the Teton Valley and perhaps sometimes leans too
pessimistic, but we held on to a VFR/borderline MVFR deck there into
Sun). Thus, the main consideration for aviation at most terminals
for the rest of the day will be winds with a strong W/SW flow up the
Snake Plain through KBYI/KPIH/KIDA. Strong winds draining out of the
Central Mntn valleys MAY turn winds NW after 20z/1pm at KIDA which
is supported by the HRRR and RAP, but it will be a battle to see if
those winds can dominate that far east over the SW flow coming up
the plain (MOS guidance favors that SW flow). Have bitten off on
this for now in the TAF but confidence is low...the interface
between these two flows is currently just west of the terminal per
sfc obs. Tonight, the big question is whether fog/low stratus will
develop at KIDA and/or KDIJ. Given recent snowfall and a reasonably
saturated boundary layer, it seems like this could occur (strong
support from MOS guidance), yet the HRRR and HREF carry very little
development. Maintained an inherited drop to IFR for KIDA (backed it
up to 07z/midnight) since I don`t have confidence to remove it, but
only gently leaned in to some VCFG/MVFR cigs at KDIJ for now. Swing
shift will have 2 TAF packages to continue evaluating. IF we crash,
we`ll crash hard (lower cigs than currently forecast). If not, cigs
will likely hold MVFR or better. Moist NW flow and breezy conditions
persist on Sun, but any resultant snow showers should generally hug
the mntns with the TAF terminals staying dry. - KSmith
&&
.PIH WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory continues until 8 PM MDT this evening for
IDZ063>066.
&&
$$