Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 01/10/23
Area Forecast Discussion
National Weather Service Denver/Boulder CO
843 PM MST Mon Jan 9 2023
.UPDATE...
Issued at 818 PM MST Mon Jan 9 2023
Only minor adjustments to the forecast this evening. Timing for
snow in zone 31 was a little slower so backed off the timing for
the onset of snow this evening by a couple of hours. It is finally
showing up in the metar observation at Rangely, so it should get
started shortly. No changes to the current Winter Weather Advisory
in effect for zone 31 starting at 9 pm. The first short wave will
across overnight through midday Tuesday, when an area of weak
mid/upper level QG ascent passes across northern CO. Strong winds
still expected to develop Tuesday morning from approximately
13-18z, with a narrow ribbon of strong gusts extending from the
foothills of southern Larimer into northern Jefferson county.
It is marginal wind event. At this time, no wind highlights
are planned but we do have gusts to 70 mph mentioned in the
grids. The magnitude of the gusts will drop off by the afternoon,
but still some gusts to 50 mph in the Front Range mountains and
foothills. Gusty west to northwest winds will persist through mid
afternoon across the adjacent plains, then decrease.
&&
.SHORT TERM...(This evening through Tuesday)
Issued at 253 PM MST Mon Jan 9 2023
Strong west-southwest flow aloft to prevail through Tuesday. This
will bring mountain snow tonight/Tuesday morning and windy
conditions east of the mountains Tuesday. Left over moisture from
the west coast atmospheric river will move across Colorado late
tonight and Tuesday morning. Not much forcing with this, but very
moist airmass moving across the mountains will result in
orographically produced snowfall with the heaviest falling over
the northern and western Colorado mountains. The mountains of
Summit and southern Grand counties will be shadowed under this
west-southwest flow aloft and just see light snowfall. Will issue
an advisory for zone 31, far west Jackson and Grand counties. Weak
subsidence and drying will shift across the region Tuesday
afternoon bringing most of the snow to an end.
Cross sections show a stable layer above ridge top Tuesday
morning with a mountain wave forming on the east slopes of the
Front Range Mountains and Foothills. HRRR shows a swath of strong
winds traveling down the mountains and foothills Tuesday morning.
Duration is very short, only about 2-4 hours. Will go with wind
gusts to 70 mph with this, just under high wind criteria. Even
once the wave breaks down, windy conditions will prevail with
gusts up to 50 mph expected near/in the foothills. These downslope
winds will produce mild temperatures will most places reaching
the mid to upper 50s across the Urban Corridor and near by plains.
.LONG TERM...(Tuesday night through Monday)
Issued at 253 PM MST Mon Jan 9 2023
An incoming system will bring another round of snow to the high
country through Wednesday evening with minor travel impacts
expected. Snow showers develop over the lower elevations Wednesday
morning with rain potentially mixing in. Confidence is low on the
location of best chances. If any, accumulations are expected to be
light.
Tuesday evening into Wednesday an upper level trough moves across
Colorado. By midnight, QG ascent increases ahead of the approaching
system. Model cross sections show increasing moisture depth in the
high country as well as improving lapse rates. This will initiate
the next round of snowfall with the best chances after midnight
through the early afternoon. For totals, most areas of the high
country will see 2-5 inches a perhaps a bit more for the upslope
favored areas such as the Park Range.
Deterministic and ens guidance still exhibits uncertainty in the
details of the system (speed and positioning) of the surface low.
General consensus tracks the low across SE CO by Wednesday
afternoon. The uncertainty in the details of the low will impact
mainly the lower elevations. There is a good chance that showers
develop over the plains Wednesday morning, but there is question as
to where and if rain will mix in for the afternoon. There is
potential for a quick "burst" of organized snowfall in the afternoon
as well with model guidance hinting at an axis of mid-level
frontogenesis on the backside of the exiting low. This may support a
brief period of moderate rates, but there is question as to where it
sets up due to uncertainty in the position of the low. Accumulations
look overall light (< 2") in most places, but can`t rule out
localized higher amounts 2-4" if a more organized band sets up. It
is also worth noting that there are drier solutions as well with
downslope slow limiting precip. chances over the plains. Overall,
this is a quick moving system with light accumulations if any.
Behind the exited low, synoptic subsidence works into the region
Wednesday evening which will taper rain/snow showers off.
An upper level ridge builds in Thursday continuing through much of
the weekend. This will bring a drying and warming trend to the
region with highs rebounding back into the 50s for the lower
elevations. Saturday, the upper ridge shifts east as a large trough
pushes into the west coast. There is increasing model spread in
regards to the potential for a few disturbances in the flow. With
Pacific moisture in place, this will support additional snowfall for
the high country Sun/Mon.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 546 PM MST Mon Jan 9 2023
VFR to prevail through Tuesday. Southeast winds will shift back to
a southerly direction later this evening and continue into Tuesday
morning. Gusty west winds are expected for Tuesday afternoon. The
greatest chance will be near KBJC with gusts to 40 kts possible
late Tuesday morning into the afternoon. Some question to the
magnitude of the wind at KDEN/KAPA but will continue to include gusts
to 25 kts in those terminals from 19-22z, then drop off the
stronger gusts thereafter.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until noon MST Tuesday for COZ031.
&&
$$
UPDATE...Cooper
SHORT TERM...Meier
LONG TERM...Mensch
AVIATION...Cooper
Area Forecast Discussion
National Weather Service Des Moines IA
546 PM CST Mon Jan 9 2023
...Updated for the 00z Aviation Discussion...
.DISCUSSION.../Tonight through Monday/
Issued at 304 PM CST Mon Jan 9 2023
Key Messages:
-Generally Quiet Through The Week
-Patchy Fog Possible North Tonight
-Light Rain/Snow Chances Far South Late Wednesday Night Into
Thursday Morning
A shortwave passing through to our north has resulted in efficient
warm air advection across much of the area. This warm southerly flow
has caused temperatures to overachieve today, with many locations
across southern and central Iowa nearing or exceeding 50 degrees.
This shortwave will continue to move east this evening, causing
winds to shift from southerly to more southwesterly then westerly.
An area of high pressure at the surface will tail closely behind it,
leading to a good bit of uncertainty for Tuesday`s forecast.
Overnight tonight, temperatures will fall quickly as the shortwave
departs and weak westerly flow sets up. This pattern will result in
a stout temperature inversion at the surface, trapping moisture
beneath it. As air reaches saturation beneath this inversion,
expecting fog to develop. The greatest chance for fog resides over
the far north where temperatures will be able to cool more quickly,
but would not be surprised to see this leak a bit further south into
portions of north central Iowa. However, for those that don`t see
fog develop at the surface over northern Iowa, low cloud cover is
expected to develop near the top of this inversion.
By tomorrow morning, high pressure will begin to set in over the
state, bringing with it weak northerly flow out ahead then weak
southerly flow behind. This, in conjunction with the fog and low
cloud cover has resulted in a large spread in temperatures across
the state. On one hand, weak northerly flow and cloud cover/fog
ahead of the high will help to keep temperatures cool, especially in
northern Iowa where snow pack remains in place. On the other hand,
warmer southerly flow behind the high pressure will warm
temperatures as the low pressure fills in behind the high. The
tricky part is identifying where this transition of warm vs cold
will reside, and will be dependent on how stubborn the surface
inversion is, how quickly the high pressure moves through and how
extensive the fog and cloud cover is. Generally, expecting cooler
temperatures across the north where fog and cloud cover is most
likely, as well as where the most extensive snow pack is. Then
expecting warmer temperatures southwest where warm air advection
will have a stronger role.
Tomorrow night, low pressure will continue to move into the state as
another weak shortwave passes to our north. This will mostly impact
our neighbors to the north and northwest, bringing light snow and
freezing drizzle to southern Minnesota. Short-range guidance, namely
the RAP and ARW models, have an extremely weak signal for freezing
drizzle in far northern IA. However, the moisture depth looks far
too shallow in NAM and RAP soundings and is non-existent in the GFS.
Given this, would not expect any freezing drizzle to develop this
far south at this time.
As mentioned in previous discussions, a system will begin to move
through late week bringing light rain and snow chances across the
far south. Although the signal still remains weak, there is a bit
more agreement in today`s guidance that light precipitation could be
seen further north into the state. Moisture remains the biggest
issue as this surface low pressure passes to our south. The GFS and
NAM soundings are both able to reach a saturated column early
Thursday morning, producing mainly a light snowfall. However, this
only stays in place for a few hours before dry air fills in aloft
and ice introduction is lost. Some saturation will remain near the
surface following this snowfall, which may indicate some freezing
drizzle behind, but this signal also looks weak. Regardless, it`s
hard to ignore the northward trend within recent guidance, so in
collaboration with WPC and neighboring offices have extended PoPs
further north into the state for late Wednesday night through
Thursday morning. Will continue to monitor this trend over the next
few days as the system draws nearer.
&&
.AVIATION.../For the 00Z TAFS through 00Z Tuesday evening/
Issued at 536 PM CST Mon Jan 9 2023
VFR conditions are expected for much of the overnight hours with
light winds shifting from southwesterly to northwesterly by
morning. Fog and IFR/LIFR stratus are expected to impact northern
terminals after 10z with KMCW seeing the highest impact.
Uncertainty remains in duration of IFR or lower cigs and vsbys
for KALO and KFOD so for now have indicated low cigs with SCT less
than 2kft.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
DISCUSSION...Dodson/Ansorge
AVIATION...Donavon/Jimenez
Area Forecast Discussion
National Weather Service Grand Forks ND
918 PM CST Mon Jan 9 2023
.UPDATE...
Issued at 918 PM CST Mon Jan 9 2023
Fog continues to be an issue this evening. Some locations such as
Fargo, Wahpeton, and Elbow Lake are getting dense and web cams
show that it isn`t totally patchy. On the other hand, a few sites
such as Moorhead and Fergus Falls have improved. Have been going
back and forth on an SPS vs dense fog advisory, but with RAP
settling in for some extended low visibility over the southern Red
River Valley and portions of west central MN, went ahead and put
out a dense fog advisory. Further north, the lower vis are still
very patchy, but there is some indication of fog being pushed
further north. Will hold off on anything north of the I-94
corridor for now, but will continue to monitor.
UPDATE Issued at 548 PM CST Mon Jan 9 2023
Vis at some locations is starting to drop, but other spots are
fine, and it is still very uncertain who will see stratus versus
fog and how dense fog will be. Going forecast has fog advecting
from southeastern ND northeastward and this continues to seem
reasonable. Will continue to monitor visibility and web cams as
the evening goes on.
&&
.SHORT TERM...(This evening through Tuesday night)
Issued at 318 PM CST Mon Jan 9 2023
Key Messages:
-Fog, possibly dense at times, is expected tonight into Tuesday
morning.
-Near normal low temperatures tonight warm to above normal high
temperatures on Tuesday.
-Light snow may begin to work into portions of the western CWA by
late in the day Tuesday.
Discussion...
A period of transient upper level ridging looks to build into the
region tonight into Tuesday. With large scale subsidence aloft,
precipitation chances during this time frame will be negligible
until the next shortwave arrives late Tuesday evening. As a result,
the primary forecast concern across the short term period will be
another night of fog development.
As of mid afternoon, the main area of fog depicted by surface
observations is across southeastern North Dakota into west central
Minnesota, with some patchy fog across the northern valley. A
separate area of fog is also present across portions of northeastern
South Dakota into central Minnesota. The general expectation is for
these areas of fog to advect northward and expand in coverage as
temperatures across the region cool overnight. As always, the
primary challenge is in the density and overall coverage of this
fog. Latest guidance continues to show a widespread area of fog
developing, although is likely too widespread in the area of dense
fog. Regardless, expecting at least some fog development for most
tonight. While the overall pattern is not expected to be conducive
for widepsread, strong lift, with significant low level saturation,
some flurries may again be possible. Any very light snow that does
occur should not amount to more than a dusting.
Otherwise, temperatures tonight look to cool into the single digits
across the region as high cloud cover persists. Then, moving into
the day on Tuesday, more sustained southerly winds look to advect in
warmer temperatures ahead of the next system. Resultant high
temperatures in the 20s are anticipated, with a few readings in the
low 30s possible across eastern portions of the CWA.
.LONG TERM...(Wednesday through Monday)
Issued at 318 PM CST Mon Jan 9 2023
Minor winter travel impacts are possible Tuesday night into
Wednesday, otherwise the probability for impactful weather remains
low through the long range as temperatures increase (above average)
and ridging develops then transitions back to split flow in the mid
levels.
Tuesday night-Wednesday: A shortwave with it`s main closed center in
southern Canada will progress west to east through mid level flow
during these periods, with a separate vort max immediately ahead of
it is shown by some guidance to pass along the SD/ND state line. For
the guidance that shows this southern wave a transient axis of
positive frontogensis is show to move across our area with any east
to west (perpendicular to shortwave track) along/south of the I-94
corridor. This feature remains progressive and follows the wave, but
could be enough to organize a meso snow band in our south (as
reflected by HREF and also broadly reflected within about half of
GEFS members). If this type of feature doesn`t form then any areas
of snow would be driven by broad/progressive synoptic ascent and
weak WAA (much lighter/less organized snowfall). ECWMF ensemble
suite overwhelmingly favors this weaker solution with only a few
members reflecting the potential for banding in our south.
There is also uncertainty in SLR as guidance is showing lower ratios
due to variable temp profiles/saturation, however where the band
forms soundings do show potential for dendritic growth (though the
primary forcing is outside of this layer). The soundings as they
appear would seem to favor 10:1 ratios for most (possible 15:1
within the band). This could be one of those situations where most
of our CWA receives a broad dusting to 1", and where the banding
sets up 2-4" can`t be ruled out (dependent on snow ratios within the
band). This model variability is reflected in NBM4.1 with 24hr probs
of 20-40% for measurable snow (0.1"), 10-20% for 1", and less than
10% for 2" or greater. With wind forecast to be in the 15 mph range
or less, it will take higher snow rates to create advisory type
travel impacts due to moderate snow accumulations (5-10% chance I-94
corridor and south).
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 548 PM CST Mon Jan 9 2023
IFR to LIFR at the Red River airports, although KDVL and the MN
TAF sites are still VFR with high clouds. All sites should go
downhill as stratus and fog push northeastward during the night.
Already seeing 1/4SM just across the river from KFAR, so will keep
the mention of lowest vis there later tonight, with some 1/2SM or
1SM possible at other sites. Some slight improvements to IFR to
MVFR by tomorrow afternoon. Winds will begin to pick up out of the
south during the second half of the TAF period, but remains to be
seen how much fog will be dissipated versus just advected further
north.
&&
.FGF WATCHES/WARNINGS/ADVISORIES...
ND...Dense Fog Advisory until noon CST Tuesday for NDZ039-053.
MN...Dense Fog Advisory until noon CST Tuesday for MNZ003-029>031-040.
&&
$$
UPDATE...JR
SHORT TERM...Rick
LONG TERM...DJR
AVIATION...JR
Area Forecast Discussion
National Weather Service Grand Rapids MI
956 PM EST Mon Jan 9 2023
LATEST UPDATE...
Update
.UPDATE...
Issued at 954 PM EST Mon Jan 9 2023
No changes to the going forecast. Clouds continue to move over the
state. Latest HRRR continues to hint at the chance for 2-3 hrs of
light freezing rain just after sunrise Tuesday before
transitioning to some light rain. Impacts will be minimal with sfc
temperatures around freezing. Most of the precipitation will be a
mix of light rain/snow.
&&
.DISCUSSION...(This evening through next Monday)
Issued at 319 PM EST Mon Jan 9 2023
.DISCUSSION...
-- Rain/snow mix Tuesday, freezing rain less likely --
We continue to expect accumulating precipitation across most if not
all of the forecast area beginning Tuesday morning. Amounts, based
on model and WPC guidance, have also been consistent in the 0.05-
0.10 inch range. However, some of the 12Z Convection Allowing Models
(CAMs) such as the NSSL WRF, ARW WRF, and NAMNest advertise an axis
of two to three tenths of an inch across Ottawa into Kent County and
this is reflected in the HREF LPMM product. Not that this would be
particularly impactful, just an observation that locally greater
amounts remain possible.
As noted in the discussion update, we see a signal for a brief
window of freezing rain, but the predominant precipitation type
should be a snow to rain transition with few if any impacts expected.
-- Greater precipitation amounts Thursday and Friday --
There is strong potential for more precipitation than previously
forecast. Most of this would start as rain Thursday afternoon mainly
south of a Grand Rapids to Saginaw line. Liquid accumulations could
end up well over half an inch and even more than an inch in some
spots. The changeover to snow remains a very tricky detail. But,
it`s worth noting there are indications after a transition to snow
this precipitation could be prolonged into Thursday night and early
Friday due possible TROWAL formation. So, snow accumulations on the
order of several inches also appear possible over parts of our
southeastern forecast area.
With the 12Z deterministic model cycle, we now see striking
agreement among the GFS, ECMWF, and Canadian (CMC) with respect to a
surface low track towards the Detroit area. The 09/00Z WPC cluster
analysis of ensembles previously identified the GFS ensemble (GEFS)
solution space as a northwest outlier relative to the CMC ensemble
(CMCE) and ECMWF ensemble (ECE). That is no longer the case with the
12Z ECE at least, which now shows a very similar and consistent
solution relative to the GFS/GEFS.
Side note: although the ECMWF and ECE show a similar solution flip
in this particular instance, that won`t always be the case. The
ECMWF often ends up as significant outlier relative to the ECE
solution space simply because some things that models try to
represent are highly scale-dependent and the ECMWF is a finer
resolution model than ECE members are. Model representation of
microphysics is an example of something that`s sensitive to scale.
And sometimes, microphysics plays significantly into a forecast,
especially when heavy precipitation is involved. This is just
another example of how a model might exhibit different sensitivities
to different forecast scenarios based solely on its internal
framework.
The GFS is quickest to turn us over to snow, which is not surprising
given its general aggressiveness with these situations. As noted
before, the incursion of colder air will not be particularly strong,
with 850 mb temperatures only down into the negative single digits
C. This would preclude any lake effect of note.
-- Quiet weather returns for next weekend --
We still believe there is a high likelihood of this weekend being
dry and uneventful due to high pressure dominating the area. With
high pressure comes the potential for marine modified air being
trapped under a subsidence inversion similar to the cloudy weekend
we just experienced. This is far from certain, but another dreary
weekend is something to be prepared for.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 614 PM EST Mon Jan 9 2023
The cloud deck will lower overnight as weak low pressue moves in
this direction. Light precipitation will begin shortly after
sunrise at the western terminals and move east during the day. The
duration of precipitation will only last 3-5 hrs before ending.
However, cigs will fall to MVFR by morning with the potential of
briefly touching IFR late morning/early afternoon for a couple of
hours.
At this point the precipitation looks like a mix of rain/snow.
However, there is a non zero chance of a brief period of freezing
rain from 7-10am. Forecast soundings show a narrow wedge of above
freezing air between 850-900 mb. But evaporative cooling may pull
that sounding a bit colder and mitigate the freezing rain threat
and so FZRA was not included in the terminals.
&&
.MARINE...
Issued at 319 PM EST Mon Jan 9 2023
Now that we have greater certainty about a surface low moving
northeast towards Detroit Thursday into Friday, it seems more
likely we will see strong, prolonged, long fetch northerly winds
over Lake Michigan building waves to Small Craft Advisory levels
Thursday. There is at least some chance of Gale conditions during
this time as well.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...None.
&&
$$
UPDATE...04
DISCUSSION...TJT
AVIATION...04
MARINE...TJT
Area Forecast Discussion
National Weather Service Indianapolis IN
945 PM EST Mon Jan 9 2023
.Forecast Update...
Issued at 945 PM EST Mon Jan 9 2023
Mid and high clouds continue to steadily increase across central
Indiana this evening as an elongated upper level wave approaches.
This wave may produce some echoes on regional radar mosaic, but
significant dry air aloft will prevent anything from reaching the
ground.
Diurnal cooling will gradually be inhibited by the increasing cloud
cover, and expect that current lows, which agree well with latest
HRRR runs, are in good shape. No significant changes are required to
the going forecast.
&&
.Short Term...(This evening through Tuesday)
Issued at 301 PM EST Mon Jan 9 2023
This afternoon, some high clouds were moving across central Indiana.
Surface high pressure was in control, with weak ridging aloft.
Rest of this afternoon...
Quiet weather will continue with the high clouds moving through.
Tonight...
A weakening upper level low will approach central Indiana from the
northwest. While there will be some isentropic lift with this
system, there will be plenty of dry air in the lower atmosphere.
While there may be some virga, not expecting any precipitation to
reach the ground. Will go with a dry forecast.
At the surface, southerly winds will work with the mid and high
cloud cover to keep temperatures above average. Lows will be in the
lower 30s.
Tuesday...
The upper trough will move across northern Indiana. Similar to
tonight, overall moisture will be lacking, so only expect some cloud
cover with it.
At the surface, southwest winds will bring up some boundary layer
moisture. This will likely result in a lower cloud deck that will
persist through the morning, with some mixing out in the afternoon.
Wouldn`t be surprised if there was some advection fog in this setup
Tuesday morning, but right now confidence is not high enough to
include.
Warm advection will push temperatures into the 40s to around 50 for
highs Tuesday. The low cloud deck could keep readings down a bit if
it persists longer than expected though.
&&
.Long Term...(Tuesday night through Monday)
Issued at 301 PM EST Mon Jan 9 2023
The long term period will start out with mostly zonal flow aloft
before a couple of troughing systems move through. A subtle short
wave with an associated upper impulse and weak surface low may bring
light rain to the southern half of the forecast area Wednesday.
Model soundings show that the moisture will likely be fairly
shallow with a dry atmosphere aloft, which limits the confidence
of precip chances but certainly can`t rule it out. There will
however be plenty of WAA on Wednesday, allowing temperatures to
warm near to above 50 degrees. This WAA comes ahead of an
approaching upper trough with a substantial surface low that will
bring a much better chance of rain and thunderstorms from Thursday
morning and into early Friday. The low will swing northeastward
from the south- central plains and across the region. Rain could
be heavy at times through the day Thursday with the plume of
moisture advecting out of the Gulf, bringing in above normal
PWATs. As the low lifts to the NE it will slow down... so while a
bulk of the precipitation should end overnight Thursday, some may
linger into the day Friday. Temperatures will drop behind the
associated cold front Thursday night, so depending on the timing
of precipitation ending and temperatures dropping, could see snow
mix in or completely transition over before coming to an end. The
work week will end with much cooler temperatures, with highs only
expected to max out in the mid to upper 30s on Friday and
Saturday.
After a few dry days, another approaching system will quickly return
southerly flow and warming temperatures by the start of next week.
Models generally agree on the presence of the trough but there is
a bit of variance as to the timing and track of it. There seems
to be a good chance of additional rain either at the end of the
long term period or beyond it, but many details are lacking at
this time.
&&
.Aviation...(00Z TAF Issuance)
Issued at 602 PM EST Mon Jan 9 2023
Impacts:
* MVFR ceilings likely mid morning through early afternoon Tuesday.
Discussion:
As an elongated upper level wave passes through the region Tuesday
morning, MVFR ceilings are expected to develop over the sites in the
13-15Z time frame. These will persist for 4-7 hours depending upon
the site, before scattering out during the afternoon.
Otherwise, no additional significant impacts are expected. Winds
will start southerly and become more southwesterly with time,
remaining below 10KT throughout the period.
No significant obstructions to visibility are expected.
&&
.IND WATCHES/WARNINGS/ADVISORIES...None.
&&
$$
Update...Nield
Short Term...50
Long Term...KH
Aviation...Nield
Area Forecast Discussion
National Weather Service Morristown TN
1008 PM EST Mon Jan 9 2023
...New UPDATE...
.UPDATE...
Issued at 1003 PM EST Mon Jan 9 2023
Overall, not much change from the previous forecast other than
slightly higher confidence in patchy overnight fog. Went ahead and
added more fog in the grids and will send out new zones for fog
wording. Latest NAM soundings favor fog overnight for some areas.
Previous HRRR runs were also showing fog but the most recent run
has backed off. Lowered TRI overnight low by a few degrees based
off latest hourly temp/dew point trends.
&&
.SHORT TERM...
(This evening through Tuesday)
Issued at 204 PM EST Mon Jan 9 2023
Key Messages:
1. Decreasing clouds tonight will lead to cooler temperatures in
the morning. Highs tomorrow will be just above normal. Dry weather
continues.
Discussion:
Current visible satellite imagery shows the slow erosion of low-
level clouds banked up against the mountains. The prominent
gravity waves across the Appalachians all day is evidence of
stable air, or high pressure, settling in over the area. Area 12z
soundings showed low-level moisture, but dry air aloft. Expect
this low-level moisture to eventually lift giving way to high mid
to high-level clouds overnight. Not very confident on fog
overnight as it all depends on a break in the clouds, calm
conditions, and either residual moisture or decoupling
temperatures close to the dew point. If any occurs, it should be
very patchy.
At the surface, high pressure is building overhead. This will
shift east along with the associated upper level ridge due in part
to a shortwave trough that will swing across to our north. This
has since trended dry keeping precipitation well away to the
north. So expect dry conditions into Tuesday. High pressure to
our east will allow the return of southwesterly low level
moisture and warmer temperatures. Valley locations will break
into the 50`s to upper 50`s in response.
&&
.LONG TERM...
(Tuesday night through next Monday)
Issued at 204 PM EST Mon Jan 9 2023
Key Messages:
1. Widespread showers expected on Thursday with, perhaps, some
rumbles of thunder. But severe weather chances appear low.
2. Lengthy period of northwest flow snowfall possible Thu night
through early Sat.
Discussion:
The main focus for the long term period will be the Thursday to
Saturday time frame. A strong cold front will sweep through on
Thursday bringing widespread showers to the forecast area and a
chance, albeit small I believe, for some stronger convection in the
far southern areas. This will be followed by a rapidly deepening
trough/upper low over the Appalachian chain Friday into Saturday,
which will almost certainly result in some northwest flow snow in
the higher terrain and possibly minor accumulations in the valley.
Tue night into Wed zonal flow is expected across much of the eastern
CONUS, with dry conditions expected across the forecast area.
By Wed night, a trough will be lifting northeast into the central
plains and will begin to phase with another disturbance dropping
south out of Canada. By daybreak Thu morning, an associated surface
low will be in the Ohio river valley with a surface cold front
extending southwest into western TN. This will all translate
eastward into the CWA by Thu afternoon, with widespread showers
expected by early afternoon. SPC has a 15% Day 4 area highlighted to
our south for severe weather potential. Think this still looks
reasonable for now. Models soundings from the southern valley show
very little instability present. Despite noteworthy shear in place
(effective bulk shear of around 60kt at KCHA midday Thu in GFS
soundings for example), meager instability likely means there will
be little more than occasional rumbles of thunder mainly well south
of I-40. Most model guidance struggle to bring dewpoints up into the
mid to upper 50s in the mid TN valley so this scenario of occasional
thunder and no severe weather seems more probable.
On the backside of this system, the upper trough becomes a cutoff
low over the eastern Great Lakes, with additional shortwave energy
diving southeast through the midwest and into the central and
southern Appalachians on Friday and Friday night. Temperatures fall
pretty steadily at the H85 level during the day Fri, with readings
nearing -10C by late afternoon and evening. Will probably see an
extended period of northwest flow snow showers in the higher terrain
from late Thu night through Fri night. The most interesting part of
this period likely will be the daytime hours Fri as additional
shortwave energy rotates through and model soundings show moisture
deepening up into the dendritic growth zone. At that point,
widespread snow showers all the way to the valley floor seem at
least plausible if not likely. That said, this would be mostly north
of I-40 and little to no accumulation is expected at this time as
temperatures will be in the mid 30s and it will be daylight.
Any northwest flow snowfall cuts off by midday Saturday as the
entire trough exits the east coast and ridging builds in from the
west. Another system is possible early next week but confidence is
low on timing at this time.
&&
.AVIATION...
(00Z TAFS)
Issued at 631 PM EST Mon Jan 9 2023
Earlier clouds have eroded and VFR conditions are in place at all
sites. Previous discussion mentioned no fog but recent HRRR and
NAM runs do show the potential for fog overnight. Will go ahead
and include IFR VIS at TYS and TRI from 09Z to 15Z. Will keep CHA
fog free for now. Otherwise, VFR conditions through the period.
&&
.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN 31 58 39 60 / 0 0 0 10
Knoxville McGhee Tyson Airport, TN 29 54 36 58 / 0 0 0 0
Oak Ridge, TN 29 53 35 57 / 0 0 0 0
Tri Cities Airport, TN 25 50 34 59 / 0 0 0 0
&&
.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...NONE.
VA...NONE.
&&
$$
SHORT TERM...SR
LONG TERM....CD
AVIATION...SR
Area Forecast Discussion
National Weather Service Missoula MT
213 PM MST Mon Jan 9 2023
...Mixed precipitation expected this evening...
.DISCUSSION...Water vapor satellite loops show a southwesterly
upper level jet stream bringing very moist air into the region.
Upstream temperatures are becoming quite mild, but fog and cloud
cover have kept temperatures in many of the valleys of north-
central Idaho and western Montana from warming much, which will
increase the threat of valley mixed precipitation in the form of
freezing rain, sleet, and snow. Above 4500 feet is forecast to
predominantly have snow with many inches of accumulations, and
valleys above freezing will have precipitation start as mainly
rain and transition to mixed precipitation. No matter the
precipitation type, slick conditions are expected this evening
through tonight. Both the HRRR and ECMWF models show an area of
heavier precipitation in west-central Montana, including Missoula.
This will need to be monitored for higher impacts from mixed
precipitation.
Radar projections agree that precipitation will decrease in
coverage overnight. Once showers come to an end, model forecast
soundings agree that fog will quickly return for Tuesday morning.
A negatively tilted ridge will build over the Northern Rockies by
Tuesday evening. The resulting southerly flow aloft will still
have some moisture to work with, so some chances for precipitation
will grace the forecast for north-central Idaho including Lemhi
County and southwest Montana including the southern Bitterroot
Valley on Wednesday morning. By Wednesday evening, the ridge will
shift east and flow turns southwesterly aloft. Remnant moisture
from a heavy precipitation event in California will be able to
ride the ridge into the Northern Rockies later on Thursday and
into Friday. A lack of forcing for ascent will keep snow confined
mostly to the higher terrain of Idaho and Clearwater Counties and
along the Idaho-Montana border where the topography can supply
some lift. Accumulations will be modest, so expect only a trace
along the valley roads and an inch or two up high under cloudy
skies. Enough moisture will linger into the weekend to fuel cloud
cover and mountain showers.
Ensemble solutions are leaning towards a trough to move onshore
early next week. There is still quite a bit of spread in these
ensembles to pin down any timing and intensity of impacts at this
time.
&&
.AVIATION...A moist upper level occluded front, currently over
central WA and OR as of 2100Z (1400 MST) Monday is expected to
bring snow above 4500 feet MSL and mixed precipitation in the
valleys of north-central Idaho and western Montana through early
morning Tuesday, or through 10/0900Z. The best window for steady
freezing rain is anticipated between 10/0000Z and 10/0600Z (1600
to 2200 MST) over western Montana. Dense freezing fog is expected
to develop by daybreak Tuesday and could impact the terminals. No
precipitation is expected Tuesday, but moderately strong
temperature inversions may encourage low clouds to persist.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory from 5 PM this afternoon to 6 AM MST
Tuesday for Kootenai/Cabinet Region.
Winter Weather Advisory from 5 PM this afternoon to 6 AM MST
Tuesday for West Glacier Region.
Winter Weather Advisory until 6 AM MST Tuesday for
Flathead/Mission Valleys.
Winter Weather Advisory until 6 AM MST Tuesday for Lower Clark
Fork Region.
Winter Weather Advisory until 6 AM MST Tuesday for
Missoula/Bitterroot Valleys.
Winter Weather Advisory until 6 AM MST Tuesday for
Bitterroot/Sapphire Mountains.
Winter Weather Advisory until 6 AM MST Tuesday for
Butte/Blackfoot Region.
Winter Weather Advisory until 6 AM MST Tuesday for
Potomac/Seeley Lake Region.
ID...Winter Weather Advisory until 5 AM PST Tuesday for Northern
Clearwater Mountains...Southern Clearwater Mountains.
Winter Weather Advisory until 5 AM PST Tuesday for
Orofino/Grangeville Region.
&&
$$