Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 10/23/23

Area Forecast Discussion

National Weather Service Glasgow MT

 739 PM MDT Sun Oct 22 2023

.DISCUSSION...

EVENING UPDATE:
Radar echos are showing precipitation moving into the area about
2 to 3 hours earlier than the HRRR was predicting. Therefore, had
to speed up when PoPs arrived in the hourlies for this evening.
GAH


AFTERNOON UPDATE:
The focus continues to be on the dynamic midweek wintry system
with significant potential impacts especially being the first
widespread snow of the season in general. Meanwhile, an initial
cold front tonight brings the first wave of cooler air and rain
showers. This looks to be generally quick-hitting for most areas
during the overnight hours moving to the southeast, it will
linger longer through the day near the I-94 corridor where a
wetting rain is much more likely.

A primary forecast concern remains the track of the low pressure
system currently in the Pacific Northwest Wednesday into Thursday
and associated baroclinic zone. The GFS ensemble in particular
favors colder/dry air intrusion with heaviest snow remaining over
southern Montana into western North Dakota. A quick transition
from any rain to snow Tuesday evening would occur based on a
secondary push of colder Canadian air dropping temperatures into
the 20s. Snow ratios are expected to be lower than usual due to
warmer temperatures and initial melting particularly on pavement.
However, below freezing highs ands lows in the teens suggest
accumulations that exceed warning criteria should be considered.
Being that this potential extends beyond Wednesday, do not have
enough confidence to put out any watch headlines yet.

-Zanker


MORNING DISCUSSION:
The upper level ridge exits our region as a trough moves in from
the west bringing cooler and wetter conditions for the rest of the
forecast period. Most of today will be dry across northeastern
Montana with rain moving into our northwestern zones by the late
afternoon and becoming widespread after midnight. Overall
accumulations are expected to be less than a tenth of an inch with
some higher probabilities (40-50%) of a quarter of an inch along
our southeastern zones including Terry, Glendive, and Sidney.

The transition from rain to snow in our area is expected to start
as early as Tuesday evening for locations along the International
Border and spreading to the rest of northeastern Montana by
Wednesday afternoon.

There are a lot of moving parts with regards to snow totals and
locations. This forecast update focused on pushing the higher
snowfall probabilities south of the Missouri River with at least a
50% chance of 2 or more inches of snow over a 48 hour period
ending Thursday evening. Higher amounts are still a bit uncertain
but the highest probabilities remain over an area spanning
southwestern Phillips, Petroleum, and Garfield counties.

Another consideration with this storm system will be snowfall
versus snow impacts. Initial snowfall will be subject to melting
and thus storm total accumulations in the model data are not
necessarily reflective of how much snow will stay on the ground to
cause adverse impacts. Snow impacts will ultimately be a function
of how long it takes to transition from rain to snow and how much
rain falls during the warm period ahead of the colder air. There
are some concerns with icy conditions developing during the
overnight hours, however, given the other moving parts it is hard
to pin down exactly how significant of a threat this will be to
the area.

Confidence will continue to increase with future updates and the
forecast will need to be monitored closely. In the meantime, the
primary messaging will center around preparing for the first
winter system of the season with the primary threats centered
around the transition from rain to snow followed by an expected
prolonged period of near to below freezing temperatures that will
continue through the rest of the week.

-thor


&&

.AVIATION...

UPDATED: 0130Z

FLIGHT CAT RANGE: VFR - IFR

DISCUSSION: Showers associated with a cold front will start to
move into the region this evening. Expect a gradual lowering of
ceilings to MVFR impacts with all sites likely affected around 12
to 15Z. IFR conditions may be possible around 18 to 20Z Monday at
KSDY and or KOLF. Rain may end across KGGW and KOLF by the late
morning but will likely return Monday evening.

WIND: North/northeast at 5 to 15 knots through Monday afternoon.
Veering to the east to southeast Monday evening.

GAH


&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...NONE.


&&

$$

weather.gov/glasgow



Area Forecast Discussion

National Weather Service Grand Rapids MI

 1024 PM EDT Sun Oct 22 2023

LATEST UPDATE...
Update

.UPDATE...
Issued at 1024 PM EDT Sun Oct 22 2023

Based on 10 pm temps already in the mid to upr 30s and clear
skies/calm winds expected for most of the night, have lowered min
temps tonight 2-5 degrees. The colder temps will allow crossover
temps to be more easily reached so some patchy ground fog or
freezing fog could form in spots overnight, possibly impacting
the Monday morning commute.

&&

.SHORT TERM...(This evening through Monday night)
Issued at 333 PM EDT Sun Oct 22 2023

The low cloud deck from this morning has dissipated, replaced by
scattered to broken diurnal cumulus across much of southwest
Michigan. This will dissipate tonight as diurnal heating is lost
resulting in notable clearing across the CWA. Temperatures then fall
to the mid 20s to lower 30s with the coldest temperatures in our
traditional cold spots in the NE CWA.

Dry conditions hold through mid day Monday even as clouds increase
Monday morning, with shower chances increasing after 15z and
particularly 18z. A shortwave then drives across the area Monday
in conjunction with the passage of an elevated warm frontal
boundary/notable warm air advection resulting in scattered showers
late Monday into early Tuesday, with the best chance across the
northern CWA where forcing and moisture is better. In
collaboration with neighboring offices, have limited max PoPs to
scattered to low end numerous for this event as ample sub 700mb
dry air will help mitigate more expansive shower coverage. Some
thunder is also possible Monday night as elevated instability
(MUCAPE values in the RAP and HREF climbing to around 1000 J/kg
across the northwest CWA by early Tuesday) moves into the CWA.
Given the decent low-level dry air, QPF amounts don`t look to be
impactful with generally under 0.10 inches expected.

.LONG TERM...(Tuesday through Sunday)
Issued at 333 PM EDT Sun Oct 22 2023

The long term forecast period will be characterized by mild but
breezy and rather unsettled conditions with several chances for
showers through most of the long range period. Strong southerly flow
waa will occur Tuesday through Thursday on the back side of the
ridge across the Eastern seaboard. This in conjunction with the
amplifying upper ridge over the eastern CONUS will allow temps to
moderate significantly into the 60s and 70s through most of the long
range fcst period.

A chance of showers is in the fcst through much of the long
range fcst period. A chance of showers late Tuesday will be
followed by numerous showers Wednesday in the south to southwest
flow waa pattern which in conjunction with the remnants of the
tropical system will cause moisture to increase significantly mid to
late week.

The relatively best chc for rain will likely come Thursday into
Friday as the main low pressure system and cold front sweep across
our region. This is also when the most robust 1000-850 mb moisture
transport is noted. Temps will tumble after fropa Friday night
and Saturday and will continue to fall late in the weekend into
early in the following week. In fact high temps by early next week
will most likely only reach the 40`s which is around 5 to 10 degrees
below normal for that time of year.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 750 PM EDT Sun Oct 22 2023

There continues to be an increase for the potential for fog early
Monday morning. The clearing skies should couple with the cold
overnight lows to allow for the patchy fog, mainly between 09Z to
13Z Monday morning. The main concern is at KGRR and KAZO.

VFR will dominate through most of Monday with a few showers
developing in the vicinity of the KMKG terminal after 21Z


&&

.MARINE...
Issued at 333 PM EDT Sun Oct 22 2023

Winds remain light through the rest of the day into the start of
Monday as high pressure moves across Lake Michigan and Lower
Michigan. Southerly return flow then increases Monday afternoon
due to an increasing gradient with winds increasing to the 15-20
knot range. Waves look to remain under Small Craft Advisory range
through Monday into early Tuesday as an offshore component to the
flow keeps the largest waves out in the open waters. Also given
ample warm air advection increasing tomorrow afternoon and
evening, and especially overnight, confidence is low in whether
the over lake stability/mixing will be enough to tap into any of
the gusty winds aloft for enough time to meet small craft
criteria. Given that this is almost 24 hours out and this is a
marginal and lower confidence event have elected to hold off on a
Small Craft Advisory at this time. As winds become more onshore
Tuesday and through much of the remainder of the week with a
decent pressure gradient, small craft advisory level waves and
winds are possible much of the rest of the week.


&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...None.
&&

$$

UPDATE...Meade
SHORT TERM...Thomas
LONG TERM...Laurens
AVIATION...Ceru
MARINE...Thomas



Area Forecast Discussion

National Weather Service Marquette MI

 628 PM EDT Sun Oct 22 2023

.SHORT TERM...(Through Tonight)
Issued at 321 PM EDT SUN OCT 22 2023

Key Messages:
- Lake clouds continue to diminish this evening
- Clouds work back into the west tonight followed by rain chances
into early Monday

RAP analysis shows midlevel ridging over the northern and central
Plains that is supporting surface high pressure centered over the
Great Lakes. With dry midlevel air indicated in water vapor imagery,
it is no real shock that skies have been able to clear across much
of the area. The exception remains in the eastern and far western
UP, where stubborn lake clouds hang on amid northerly flow off of
Superior. Where skies have cleared, temperatures have been able to
reach into the upper 40s and even lower 50s, but remain in the
mid/upper 40s under the lake clouds. As flow turns more anti-
cyclonic heading into the evening hours, lake clouds should continue
to erode.

High pressure drifts eastward into the night, and a tightening
pressure gradient will lead to increasing southerly return flow
aloft. At the surface, a stable boundary layer will keep winds light
for the overnight hours. Initially, clear to partly cloudy skies and
light winds should see temperatures quickly falling back mainly into
the 30s before midnight, and the 40s in the far western UP. Much of
the area (particularly the western UP) may reach overnight lows
fairly early tonight, ranging to around 30F in the eastern UP with
warmer values largely in the mid/upper 30s in the west half. Then,
temperatures largely hold steady the rest of the night with WAA
aloft and increasing clouds. Chances for showers work into the
western UP during the pre-dawn hours courtesy of some
frontogenetical forcing and an approaching shortwave trough.

.LONG TERM...(Monday through Sunday)
Issued at 416 PM EDT SUN OCT 22 2023

Key Messages:
- High temps not straying too far from normal this week, except Tue
which will be warmest day.
- Min temps above normal, at times significantly above normal.
- Colder air delayed a bit from previous fcst, arriving over the
weekend and more so early next week, bringing the first bout of LES
of the season.
- Periodic showers through the week, generally focused on Tue/Tue
night and Thu/Thu night, including thunderstorms on Tue.
- Widespread 1-2 inch rainfall totals likely by the weekend with
locally higher amounts possible.

Medium range models remain in good agreement showing a strong mid-
level positive height anomaly (~400m at 500mb) over the Bering Sea
today becoming centered over southern AK Tue night and then
remaining there thru the end of the week. Downstream flow across the
U.S. will adjust to this feature, but details of that adjustment
thru late week are complicated by undercutting of the anomaly which
will work against sharper downstream flow amplification. However,
during this week, troffing will generally set up from n central
Canada into the western U.S., resulting in general wsw to sw mid-
level flow into the Upper Great Lakes. Thereafter, guidance does
still suggest consolidation of ridging from AK southward vcnty of
the W Coast (delayed from yesterday`s guidance), which will in turn
force trof amplification downstream thru central into eastern N
America during the first half of next week. For Upper MI, this
evolution of the flow will result in high temps not straying too far
from normal this week, but tending to be at least slightly on the
warm side of normal more often than not. Min temps will be above
normal, significantly so at times. Warmest daytime likely to be on
Tue. There may be another warmer day late week, depending on track
of low pres lifting across the Upper Mississippi Valley. A definite
trend to colder weather will then occur over the weekend, but much
more so during the first half of next week under aforementioned trof
amplification. As for pcpn, expect episodes of showers this week,
focused on Tue/Tue night and Thu/Thu night. Although the first
snowflakes of the season have already been observed in Upper MI, at
Herman on Oct , majority of locations will see the first
snowflakes of the season by the end of the month, mostly from LES,
as the expected eastern trof amplification occurs. Looking farther
ahead, CFSv2 ensemble means continue to suggest an overall warmer
pattern developing for the Great Lakes region during early and mid
Nov, though not as aggressive as yesterday`s means showed.

Beginning Mon, a shortwave over the Upper Mississippi Valley to
start the day will move ene across the northern Great Lakes. While
the resulting sharper isentropic ascent passes by to the s of Upper
MI as viewed on the 295 thru 305K sfcs, respectable ascent passing
across Upper MI suggests some potential of at least isold to sct
shra across the area with least coverage n and nw and greatest
coverage across the s. Expect high temps mostly in the upper 40s
to lwr 50s F.

During Mon night/Tue, minor shortwave energy will streak from the
central Rockies to northern Ontario. Responding low-level jet of 30-
40kt into the Great Lakes region will spread anomalous warmth at
850mb into the area (850mb temps rise to around 12C). Precipitable
water also increases up to around 250pct of normal. With the
anomalous warmth/moisture and steep mid-level lapse rates at around
8-8.5C/km, anomalous instability also develops for this time of year
with potential cape of 1000-2000j/kg avbl for parcels lifted from
near or above top of sfc based stable layer. NAM is most aggressive
in increasing instability with up to 2500j/kg indicated. Best chc of
shra/tsra will be during the day on Tue into Tue evening as weak sfc
low pres wave lifts into the area. Given the potential cape, there
could be a low risk of hail depending on what the effective deep
layer shear is for the elevated storms. A preliminary rough estimate
of the effective deep layer shear has +30kt shear displaced to the
nw of the greater instability. Will be something to monitor. Heavy
downpours at times are likely given the high precipitable water
values. Lows Mon night will only be in the 40s F with highs Tue
upper 50s to mid 60s F. With abnormally high precipitable water and
frontal boundary in a sw to ne orientation across central Upper MI
Tue night, conditions will be unusually warm e and s central Tue
night. Temps there may not fall blo 60F if front remains to the nw.
Min temps will range down to the mid/upper 40s F nw.

Sfc trof will drift just to the s and se of the fcst are on Wed,
largely bringing an end to shra, especially w and n. Then, wave that
drops into northern MX Mon night thru Tue night will lift ne,
reaching the Upper Great Lakes late Thu. This will force frontal
boundary that pushed s and se of the area on Wed to begin to lift
slowly back to the n late Wed night/Thu. Sfc low pres wave will also
eventually develop into the Upper Mississippi Valley. As a result,
shra will begin to spread n into southern Upper MI late Wed night
then across the rest of the area during the day Thu. Precipitable
water rising back to 200-250pct of normal will support the potential
of hvy rainfall. Some thunder possible as well. In the wake of the
low pres wave, w to nw winds may be gusty to 35-40mph across the
Keweenaw on Fri. Otherwise, colder air will begin to push se into
the area, but more so late weekend/early next week after one last
wave potentially lifts ne thru the Great Lakes. The colder trend
will set the stage for some lake effect showers over the weekend
that will increase early next week under cooling low-level w to nw
flow. Snow pytpe will also become more predominant with time early
next week as ensembles show median 850mb temps falling to around
-9C.
&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 628 PM EDT SUN OCT 22 2023

All sites will stay VFR through the period. SAW though does have
some MVFR clouds come in late Mon.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 416 PM EDT SUN OCT 22 2023

With high pres ridge continuing to drift across Lake Superior this
evening, winds will remain 15kt or less. During then night, s winds
will begin to increase on the backside of the ridge, reaching up to
20kt by sunrise Mon. A further increase to up to 25kt will occur
during Mon, mainly across the e half of Lake Superior which is
typically favored for stronger winds with a southerly direction.
Winds then diminish below 20kt after midnight Mon night as pres
gradient weakens. Although a low pres trof tracks se across the lake
during Tue and Tue night, expect winds to remain below 20kt during
this period. Winds should remain under 20kt on Wed as well since the
exiting low pres trof remains on the weak side. A low pres wave will
then lift ne across the Upper Great Lakes region Thu night/early
Fri. A period of stronger ne winds will occur ahead of the low,
particularly across the w half of Lake Superior Thu aftn/early
evening. The probability of low end gales in that area is 20-30pct.
Once the low passes, the potential of w to nw gales is 30-40pct
across mainly central and eastern Lake Superior on Fri.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&

$$

SHORT TERM...LC
LONG TERM...Rolfson
AVIATION...07
MARINE...Rolfson