Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/12/23

Area Forecast Discussion

National Weather Service Bismarck ND

 940 PM CST Mon Dec 11 2023

.KEY MESSAGES...

- Sub-zero wind chills are expected across much of western and
  central North Dakota late tonight into Tuesday morning.

- Milder Pacific air returns to the region Wednesday and Thursday,
  with highs forecast in the mid 30s to mid 40s.

- Little to no precipitation is in the forecast through the
  forecast period.

&&

.UPDATE...
Issued at 936 PM CST Mon Dec 11 2023

Weather remains quiet as surface high pressure slowly moves in
from the west. Temperatures in the northwest have already drop
down into the lower teens while the remainder of the state is
in the lower 20s. Clear skies and approaching surface high
pressure will drop temperatures into the single digits to lower
teens by the early morning hours. No updates are need at this
time as the forecast remains on track.


.UPDATE...
Issued at 548 PM CST Mon Dec 11 2023

Surface high pressure over eastern Montana will draw closer to
the Dakotas tonight. This will bring in cooler low temperatures
as skies remain clear promoting radiational cooling. Elevated
winds will continue to decrease tonight across eastern and
northern North Dakota as a clipper system over Manitoba pushes
eastward. No updates are needed at this time as the forecast
remains on track.

&&

.DISCUSSION...
Issued at 321 PM CST Mon Dec 11 2023

A cold front has pushed though the forecast area and gusty
northwest winds have developed across the forecast area. As of
2 PM CST winds at Minot were gusting up to 43 mph. This has been
the peak gust so far today. RAP Bufkit soundings indicate the
strongest winds in the north continuing for another 1-2 hours
before dropping off a bit. Winds across the south look to
be their strongest in an hour or so but will also be at their
strongest for 1-2 hours as well. This lines up pretty well with
the area of strongest cold advection. RAP/NAM and GFS forecast
soundings all show the mixing layer dissipating by late
afternoon. There is an area of stronger lapse rates that
continues from the north central into the northern James River
Valley. Perhaps we could see some moderate winds continuing here
into the evening, but all indications are that the gustiness
should end by 00Z Tuesday. Across the forecast area, it looks
like winds will not become light (around 5 mph or less) across
the area this evening, and probably not at all over eastern
portions of central ND. This will set us up for cold wind chills
tonight with some areas in the north central falling to around
10 below zero. Most areas could see wind chills to around zero.
These are nowhere near advisory criteria, but certainly colder
than we have seen in some time. Actual air temperatures are
forecast to be mainly in the single digits above zero. Wouldn`t
be surprised to see a few areas drop to below zero. However,
increasing high clouds and the winds not dropping off quickly
will help keep temperatures from falling off quickly tonight.
Tuesday will be colder with highs around 20 in the Turtle
Mountain region to the mid 30s far southwest.

Wednesday and Thursday will see upper level ridging over the
Northern Plains and into Canada with the airmass coming off the
Pacific. This will bring noticeably warmer temperatures to the
area with highs generally in the 30s north to 40s south. A
shortwave propagating through the mean upper ridge does look to
move through the local area lat Thursday-Friday. Especially this
far out, we`re looking at a low predictable wave. The envelope
of NBM pop solutions is to wide a this time to depict any
meaningful PoPs. The NBM 24 hour probability of a tenth of an
inch of snow ending at 6 PM Friday is less than 10 percent
across the CWA. Hardly worth mentioning, unless this is your
best chance of measurable precipitation through the entire
forecast period.

With this weak wave moving through we will cool down a bit on
Friday, but we warm right back up on Saturday, and could see the
warmest day of the entire forecast period, before another small
cooldown and a dry cold front passage late in the weekend.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 548 PM CST Mon Dec 11 2023

VFR conditions continue across the state with some elevated
winds for KJMS and KMOT tonight. Winds will decrease late tonight
has surface high pressure moves in from the east. The wind
direction will switch from northwesterly to southwesterly by
tomorrow afternoon.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

UPDATE...Johnson
DISCUSSION...TWH
AVIATION...Johnson



Area Forecast Discussion

National Weather Service Des Moines IA

 536 PM CST Mon Dec 11 2023

...Updated for the 00z Aviation Discussion...

.DISCUSSION.../Tonight through Monday/
Issued at 159 PM CST Mon Dec 11 2023

Key Messages:
- Cooler Tuesday with a return to above normal temperatures through
  this weekend.
- There is a low chance (mainly <25%) of light snow or flurries Tuesday
  night over central and southern Iowa. Accumulations are likely
  (>80%) to be below half an inch.
- Forecast favoring dry conditions into this weekend after
  Wednesday.

Details: The main weather themes this week will be mainly dry
conditions outside of Tuesday night with temperatures swinging a
little below normal tomorrow before ending above normal through the
remainder of the week. Stratus clouds this morning lifted to the
northeast and attention is on a cold front that will move through
the state tonight. No precipitation will occur with this front, but
there could be some high clouds that pass over the state.
Temperatures by morning should range from the middle teens north to
middle 20s south over the state. Winds will be a tad breezy behind
the front on Tuesday, especially over northeastern Iowa, and there
is a slight push of cold air advection resulting in highs in the
30s, which will be about 5 to 10 degrees lower on Tuesday compared
to today.

Surface high pressure will slide through the region later Tuesday
and exit the region on Wednesday. This is the same time period,
mainly Tuesday night, that deterministic models including the latest
NAM, GFS, ECMWF, RAP, and HRRR are showing light QPF of a few
hundredths crossing from western through southern Iowa. There is not
a lot of moisture to work with as the Gulf of Mexico moisture
remains cut off with the surface high passing through. Forcing wise,
there is a lack of QG convergence over the state with only weak low
level thermal lift seeming to be associated with a passing shortwave
trough associated with the mean trough over Canada. Cross sections
show modest omega within this lift around the dendritic growth zone
with BUFKIT soundings show ice introduction. Looking at ensemble
data, 12z HREF has 6 hour mean QPF of a few hundredths with the
0z grand ensemble showing between 20 and 30% of members with at
least a hundreth of an inch of QPF at Creston. While low level dry
air concerns remain, there is enough support in deterministic and
ensemble guidance to include some low PoPs and QPF from west
central Iowa into south central Iowa. Snow totals will be a
dusting to a few tenths of an inch. This is supported by the HREF
6 hour probabilities of a tenth of an inch of snow averaging
between 40 and 50% from Crawford County to Davis County with
probability of snow accumulation over a half an inch under 20%.

At the same time early this week elsewhere in the country, a 500mb
trough will cut off over the southwestern US. This will begin to
move eastward late this week, but then southeastward into this
weekend keeping moisture and forcing away from Iowa. A northern
stream shortwave trough will pass through the region Friday night
into Saturday with modest QG convergence. This will bring some
clouds through the state with the new 12z global models showing QPF
over portions of the state. Looking at the 0z grand ensemble
members, there are generally 15 or less members with QPF so will
need to await more ensemble support of PoPs before deviating from
the National Blend of Models.

&&

.AVIATION.../For the 00Z TAFS through 00Z Tuesday evening/
Issued at 536 PM CST Mon Dec 11 2023

VFR conditions are expected through the TAF period. This evening a
cold front will pass across the area and winds will shift to out
of the northwest by 06-08z across all sites. Late Tuesday evening
light snow is possible, mainly at southern sites. Given low
impacts and distance range, this will be addressed in future
updates if needed.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

DISCUSSION...Ansorge
AVIATION...Hagenhoff



Area Forecast Discussion

National Weather Service Goodland KS

 210 PM MST Mon Dec 11 2023

.SHORT TERM...(This evening through Tuesday night)
Issued at 1210 PM MST Mon Dec 11 2023

Tonight...mid and especially high level cloud cover overspreads the
area ahead of a developing upper level trough, forecast to be in the
development stages well to the west of the area. Despite
favorable moisture in the 700-500mb layer stretching southeast
across locations generally north of I-70 from mid evening through
much of tonight, low and mid level lapse rates arent favorable and
forcing is rather meager to produce any precipitation. A cold
front is forecast to reach the KS/NE border area before midnight,
continuing through the rest of the area after midnight with winds
from the east and northeast at speeds of 10 to 15 mph. Low
temperatures are forecast to be in the lower to middle 20s.

Tuesday-Tuesday night...the forecast area will be under a generally
mostly cloud to cloudy sky during the day as a thick cirrus deck
remains over the area. East to southeast surface winds strengthen a
bit during the day with speeds generally to 10 to 20 mph with some
higher gusts. High temperatures are forecast to be in the upper 30s
to middle 40s. For the overnight hours, a closed 500mb low is
forecast to be near Las Vegas with increasing clouds in the 700-
500mb layer and continued thick cirrus clouds above that. Presently,
no precipitation is expected. Low temperatures are forecast to be in
the lower to middle 20s.

.LONG TERM...(Wednesday through Monday)
Issued at 159 PM MST Mon Dec 11 2023

Main points for the long term:

1. Wintry precipitation Wednesday - Friday morning.

2. Cloudy skies until Friday, clear after that.

3. Dry and warmer weekend is in store.

We will begin the period with an upper-level low pressure system
moving over the southern Rockies. It will take until Friday morning
for the axis of this feature to move over the CWA. We look to remain
under overcast conditions until Friday when a cold front will move
through the area and clear out the moisture.

A 500 mb low pressure system looks to slowly move over the Southern
Plains Thursday through Friday evening. This low will be the driving
force for our weather, even though it will likely not pass over the
CWA. Precipitation looks to start Wednesday morning and finally
cease Friday morning. The big limiting factor for precipitation will
be the lack of forcing, with the best forcing being co-located with
the 500 mb low. This leads to increased PoPs in the southern CWA
that drop off to the north. With this run of guidance, PoPs
increased significantly over the past 24 hours. This could be
similar to last week`s system when 48-72 hours ahead of the event,
the CAMs increased PoPs and later lowered them closer to the event.
Maximum PoPs look to occur 0-12Z Thursday with ~90 PoPs in Wichita
and Greeley counties. PoPs along I-70 are generally around 60-70
with most locations north of highway 36 being under 60 PoPs.

Moisture will be provided by a high pressure system over the Midwest
forcing warm, moist Gulf air to move into the area. QPF has
continued to increase, up to around 0.65 inches in the southern
counties. Confidence for this much precipitation to occur is low,
due to the lack of forcing and the potential of the "CAM" influence
mentioned above.

P-types are very tricky with this system. As the forecast stands,
snow and a rain/snow mix will begin Wednesday around 12Z south of a
line from Hill City, KS to Joes, CO. There is a slight chance for
localized freezing rain to occur in Gove, Sheridan, and Graham
counties. This potential diminishes by 21Z Thursday as the day warms
(southern WAA) and a melting layer forms. This melting layer,
especially in the eastern CWA, is expected to persist throughout the
remainder of the event. However, this melting layer is going to be
fragile and a few minor changes could destroy it. There is
considerable uncertainty as to how far west it will extend.

It is possible that we receive weaker than expected WAA. This would
prevent a melting layer from forming. The impacts of this would be
more snow. Confidence in this occurring is around 10%.

Locations that have this melting layer (eastern portions of the CWA)
will primarily receive rain with localized rain/snow mix. Areas
without the melting layer (western/northwestern areas of the CWA)
will see more snow than rain, but a rain/snow mix is expected at
times. The current model runs are suggesting the "melting line" will
begin in Gove county Wednesday morning before retreating west during
the day. The line could be pushed back to the Colorado border before
sunset. After sunset, the WAA may not be strong enough to keep the
melting line that far west, which would allow the line to move back
east. This is a general idea of where the melting layer could be
found, but confidence is low (20%) in exact positioning.

If the currently forecast QPF and P-types do occur (low confidence
(<25%) these parameters will remain the same) an inch or two of wet,
heavy snow would fall in the southwestern CWA. I-70, and nearby
locations, in Colorado and extreme western Kansas could see up to an
inch of wet, heavy snow. Snow ratios for this event are expected to
remain in the 4-7:1 range, meaning this will be a dense, wet, heavy
snowfall. As for the small chance (<10%) freezing rain were to occur
in the southeastern CWA, only one or two hundredths would
accumulate. The rest of the CWA would receive anything from a few
tenths on an inch of snow to only cold rain with a few flurries
mixed in. There is an outside chance (<5%) an elevated melting layer
could form over the central CWA Wednesday afternoon - Thursday
morning. This would lead to freezing rain falling in these area.

There is still a chance that there may not be enough forcing for
precipitation to occur, leading to prolonged cloudy and foggy
conditions. Even if precipitation does occur, fog could still form
near the start and end of the event. GFS cross-sections show a
saturated surface layer with near 0 lapse rates and SE winds
Wednesday morning with little/no forcing above. This possibility
could be very dangerous due to the potential for freezing fog or
drizzle if/when temperatures drop below freezing. Confidence in
advection fog forming is about 15% for our southeastern counties.
Confidence in freezing fog or drizzle forming is about 5%. If fog
does not form, there will likely be very low stratus.

Winds throughout the event will be southerly and increasing Thursday
morning. By noon Thursday, sustained winds will be 15-20 kts with
gusts around 25 kts. These winds will lead to stronger WAA, but
before the warmer air moves in, blowing snow could reduce
visibilities. Confidence in impactful blowing snow is less than 5%.

Friday will see a cold front sweep through the area and clear out
most of the lingering moisture and precipitation. Even with a cold
front moving through, the clear skies will allow Friday to warm up
into the 50s, about 10 degrees warmer than the previous two days.
With the cleared skies, Friday night will cool off efficiently,
likely into the lower 20s. That would be about 10 degrees cooler
than Wednesday night. Thursday night looks to cool into the 20s to
low 30s. Saturday through Monday look to warm into the 50s under
clear skies with overnight lows cooling into the mid to lower 20s. A
weak warm front looks to move through Saturday followed by a weak
cold front on Sunday. The cold front Sunday could bring in northerly
winds at 20-25 kts.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 210 PM MST Mon Dec 11 2023

KGLD...VFR conditions are currently expected through the period.
Light and variable winds at taf issuance will establish an east-
northeast component at speeds up to 10kts through 15z. From
16z-22z, east-southeast winds increase slightly around 15kts with
higher gusts. After 23z, east-southeast winds subside a bit to
around 11kts. The latest NAM and HRRR models are suggesting sub
VFR cigs somewhere in the 12z-16z timeframe. For now, have
introduced a scattered deck around 500`.

KMCK...VFR conditions are expected through the period. Light and
variable winds around 5kts at taf issuance will continue through
04z before establishing a northeasterly direction at speeds up to
10kts through 13z. After 14z, winds will be generally from the
east up to 11kts or so. A few gusts to 20kts are possible.

&&

.GLD WATCHES/WARNINGS/ADVISORIES...
KS...NONE.
CO...NONE.
NE...NONE.
&&

$$

SHORT TERM...99
LONG TERM...CA
AVIATION...99



Area Forecast Discussion

National Weather Service Pocatello ID

 142 PM MST Mon Dec 11 2023

.SHORT TERM...Tonight and Tuesday
As the day has progressed, snow activity is becoming more
"showery" in nature and this will likely continue into the evening
and overnight before activity becomes very isolated towards
Tuesday morning. Hi-res models have not had a very good handle on
this system and confidence over the next 12 hours is quite low,
honestly. The 18Z HRRR dries us out in the next 1-2 hours while
the 3km NAM keeps the activity going and into the overnight with
some modest accumulations across the southernmost portions of the
area. Current forecast is basically a blend of both solutions
keeping scattered snow showers in the forecast with additional
accumulations of less than an inch. At this point, it`s basically
wait and see as to what happens as I have very little confidence
at this point based on how the models have done as a whole with
this event. Do think there will be some fog potential overnight
but given the uncertainty in the precip forecast, not sure how the
fog will setup with lingering cloud cover, likely, and additional
precip, possible. Tuesday should be less impactful across the
region as only a few very isolated snow showers are possible
across the southern third of the forecast area during the first
half of the day. Most areas will be dry although clouds will
likely linger across the region with temperatures in the mid to
upper 30s across much of the area. McKaughan

.LONG TERM...Wed through next Mon night
An upper level ridge dominates the pattern for the entire time.
Perhaps Mon in this period will result in a wave entering the
coast and starting the breakdown of this ridge. However, it hasn`t
yet, so this entire period should be dry with eventual sunshine
each afternoon. The main forecast problem will be fog and stratus,
and this in the valleys and basins of central and eastern Idaho.
This far out, hard to know exactly where the "fog monster" will
strike, but best guess is the Snake River plain/eastern Magic
Valley, Bear Lake basin, and the many southern canyons/valleys
that drain into the Snake River, including Teton Basin, Swan
Valley, etc. Overnight lows may be mild if the stratus hangs in,
with mostly 20s in the lower elevations, but if it is clear, more
like 10 to 20 deg F. Afternoon highs, if sufficient clearing, will
likely be in the lower to middle 40s. The central Idaho mountains
should bask in sunshine or a clear night most of the time, so
temperatures will be more extreme, with typical basins getting
into the single digits at night, but still 40s during the day. The
"heat" may even set some records in Stanley basin. As always
under high pressure, wind will be of little consequence, save for
pushing late night and morning fog around. Messick


&&

.AVIATION...
Rain-snow line is hovering right around the SRP airport
elevations, creating a headache for VSBY forecast with a phase
change to rain expected for the afternoon and thus an increase in
VSBY to end the IFR risk. Precipitation should taper off anyway,
even if it stays cold enough to snow. Then the overnight cooling
will bring fog and stratus to bear on all the airdromes, wreaking
havoc with morning schedules. Expect some IFR at a minimum, but
believe only KBYI as risk of closure (and this actually more due
to CIG). There is some late night snow in isolated areas that
could also add to the VSBY challenge and even bring some CIG
challenges. However, CIGs expected outside of KBYI to be marginal
VFR with little impact. Improvements expected after 12/18Z with
abundant sunshine under high pressure. Wind of little consequence,
except for KSUN where a southerly wind could bring in some
afternoon impactful CIG if the stratus develops in the lower Wood
River Valley, below KSUN. Messick

&&

.PIH WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$