Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 01/09/21

Area Forecast Discussion

National Weather Service La Crosse WI

 947 PM CST Fri Jan 8 2021

.SHORT TERM...(This evening through Tonight)
Issued at 229 PM CST Fri Jan 8 2021

Low clouds have remained locked over the area today, with no
improvement expected overnight. Given a solid stratus deck, lows
will likely be held up in the upper teens to 20s, though potential
is there to quickly drop into the low teens if any gaps form. 08.12Z
HREF suggests dense fog potential is mainly north and west of the
area tonight where visibilities are already reduced and models
suggest a little better cooling, but will have to watch along our
northwest border from portions of southeast Minnesota into north-
central Wisconsin in case this fog area ends up shifted a bit east
(the 08.18Z RAP and HRRR are most bullish with this scenario).
With temperatures near the top of the cloud layer hovering around
-10C, would not be totally surprised if a few flurries were
squeezed out as well.

.LONG TERM...(Saturday through Friday)
Issued at 229 PM CST Fri Jan 8 2021

Things are still looking fairly quiet into mid-week, with mild and
predominately dry weather.

Saturday looks very similar to today, with high pressure anchored
just west and weak flow aloft. Unfortunately, this likely means
gloomy low clouds and haze/patchy fog again, though some of the
guidance does try to break things apart a bit by afternoon and
provide some glimpses of sunshine. Not quite ready to buy into that
sunnier outlook, however. Highs top out in the 20s to near 30. A
little change occurs Sunday, as a shortwave pushes through the area.
With a dry atmosphere, this doesn`t look promising for
precipitation, but 08.12Z NAM/GFS soundings do very briefly
approach saturation, so couldn`t rule out some flurries. In
addition, with weak WAA/lift ahead of this late Saturday
night/early Sunday morning, might have to watch for patchy
freezing drizzle given moist low-levels. Confidence is low in this
occurring, however.

A couple of shortwaves push through the upper Midwest for the
beginning of the week, but the story is similar with a dry
atmosphere and not much potential for precipitation - maybe
occasional flurries or a light snow shower if forcing can briefly
overcome this dry air (a big "if"). 08.12Z GEFS plumes accumulated
QPF does not exceed 0.08" through Tuesday for any points in our area
and none of that cumulative total occurs in one go - pretty
impressive agreement for little in the way of precipitation. Cloud
forecasts are always tricky, and it remains to be seen whether any
of these shortwaves disturb the atmosphere enough to kick the low
clouds out. GEFS/EPS ensemble members show a better signal for light
precipitation toward the end of next week, as the split-flow pattern
finally breaks down a bit with larger-scale troughing across the
Midwest. However, given large differences in timing and
placement, have kept the drier NBM PoPs for now. Highs generally
range from the 20s to 30s in the extended, but could warm to the
mid and upper 30s by the middle of next week ahead of the
potential late week system.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 947 PM CST Fri Jan 8 2021

Generally expect LIFR to MVFR stratus across the region through
the TAF period. A few larger holes in the stratus were found over
northeast MN and central WI, but confidence in clearing impacting
KLSE/KRST is low. While IFR vsbys couldn`t be ruled out at KRST
early Saturday morning, current thinking is that highest chances
will be farther west. Some modest diurnal improvement in ceilings
is likely, but maintained IFR/MVFR ceilings through the day.
Light NW winds expected through the period.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&

$$

SHORT TERM...Lee
LONG TERM...Lee
AVIATION...JM



Area Forecast Discussion

National Weather Service Denver/Boulder CO

 811 PM MST Fri Jan 8 2021

.UPDATE...
Issued at 811 PM MST Fri Jan 8 2021

The upper level trough that will bring snow to the area Saturday
is dropping southeast across northern Nevada. Clouds will increase
overnight with overcast skies for Saturday. Limited forcing from
the system will keep snowfall amounts on the light side. No big
changes from the 00Z NAM and HRRR models. The NAM has trended a
little higher with snowfall amounts (up to an inch more), but the
HRRR is a little lower. With this said, will not make any changes
to the forecast at this time. Still expect the upcoming system to
bring most locations an inch or 2 of snow.

&&

.SHORT TERM...(This evening through Saturday)
Issued at 238 PM MST Fri Jan 8 2021

The trough just onshore will drop southeast, bringing a weak
closed low across southwestern Colorado on Saturday. This will
bring a period of lift across the state, but the strongest lift
will be across the south and west, and the forcing will be quite
weak north and east of Denver. In addition, there`s not much
moisture around. The lift will gradually saturate the atmosphere
over and just east of the mountains, but developing east winds
will keep a layer of drier air near the surface out toward the
eastern border. Lower elevations west of the divide may have a
similar situation with local downsloping. In any event, winds will
be light with little orographic snow. The one exception will be in
the Front Range foothills especially from about I-70 southward and
possibly Monument Hill where there will be some weak upslope into
a shallow slightly unstable layer Saturday afternoon. These areas
could pick up 2-4 inches of snow, while elsewhere we`ll have to
rely on the weak synoptic scale processes for generally an inch or
two and even less as you go north and east.

We did speed up the timing a little bit in accordance with model
guidance which has enough low level convergence on the plains
during the day Saturday to speed things along. We expect areas of
light snow to develop during the middle of the day, though if
there`s a more significant period it should be more like late
afternoon/early evening. Current forecast and model guidance is
all good for the rest, with highs around freezing on the plains
Saturday and light winds.

.LONG TERM...(Saturday night through Friday)
Issued at 238 PM MST Fri Jan 8 2021

Not much to talk about for the extended. Departing storm Saturday
night finishes up with its snowfall by sunrise Sunday, then dry.
Slim chances for snow in the north central mountains toward the end
of the period Thursday.

Extended period picks up with the center of the 500 mb low over NW
New Mexico, with trough axis pointed northeast across eastern
Colorado into the northern plains. Trough continues to move slowly
east with sharpening ridge over the west. As upper low departs QG
ascent, what little clips the BOU forecast area, pulls away. Best
moisture limited to below 600 mb, with saturated layer present in
the -12 to -18c dendrite snow growth layer between 600-700 mb
from about 00z-04z, then moisture tapers off after 06z. Model
soundings show weak ascent continues until about the same time.
Combination of weak QG ascent with weak upslope low level flow
through 06z argue for likely to definite pops in the 00z-06z
timeframe. Best time for snow centered around 00z Saturday.

With the passage of the upper trough high pressure begins to build
on Sunday and remains in place for much of the next week.
Temperatures will see a warming trend, with highs in the 40s on the
plains and 30s higher elevation communities Monday, warming to the
50s plains and 30s & 40s in the mountains by Wednesday.

Thursday a weak trough in the upper level northwest flow dives
southeast across mainly northeast Colorado. Some good jet dynamics
with this one, with the nose of a 150 kt 300 mb jet taking aim over
the northeast. Push of northerly wind at the surface will cool
temperatures on the plains a few degrees from warm highs earlier in
the week. Little moisture to work with however, and little to no
pops. Only exception is slight chance pops in the northern mountains
highest elevations, where upslope flow will wring out any available
moisture. Possibility that the strong winds on the plains Thursday
could elevate fire weather concerns with warm temperatures and
strong winds.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 811 PM MST Fri Jan 8 2021

Clouds will increase and lower through the night as a Pacific
storm system approaches the region. Ceilings are expected to fall
below 6000 feet after 09Z Saturday. Clouds continue to lower
Saturday morning with ceilings of 500 to 2000 feet expected after
15Z Saturday. These low clouds will continue through Saturday
night. Light snow is expected, mainly after 20Z. Forecast total
snow accumulations for the Denver area for Saturday and Saturday
evening are 1 to 2 inches.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

UPDATE...Meier
SHORT TERM...Gimmestad
LONG TERM...Hanson
AVIATION...Meier



Area Forecast Discussion

National Weather Service Grand Rapids MI

 748 PM EST Fri Jan 8 2021

LATEST UPDATE...
Update

.SYNOPSIS...
Issued at 324 PM EST Fri Jan 8 2021

- Chilly night

- Fairly quiet weather for a while

- Possible trend back toward cool/snow late next week

&&

.UPDATE...
Issued at 746 PM EST Fri Jan 8 2021

The skies have cleared out around AMN where the current
temperature was already lower than the forecasted min
temperature. The clearing line was shifting steadily
south...although it has slowed down somewhat. Either way we have
updated the temperature and cloud forecast to reflect the current
trends.



&&

.DISCUSSION...(This evening through next Friday)
Issued at 324 PM EST Fri Jan 8 2021

-- Chilly night --

Satellite images show clouds gradually thinning and evaporating
over much of the lower peninsula from low-level subsidence this
afternoon. If this clearing holds through tonight, a relatively
cold night is setting up, in line with what ECMWF ensembles and
other guidance have been advertising for a few days now. There may
be quite a range in low temperatures depending on local
conditions: duration of clear skies, pockets where winds go calm,
terrain where cold air tends to drain into low areas. Overall,
seems likely for a lot of single digits and teens for low
temperatures. Leota (Clare County) last night stayed clear and
their lows fell to 0. Can`t rule out some areas of freezing fog,
particularly in northern portions of Central Michigan.

-- Fairly quiet weather for a while --

Two weak shortwave upper level troughs move through over the next
several days, one Saturday night into Sunday and another Monday
night into Tuesday. These don`t look like they will be able to do
much, as mid-levels will still be very dry. The boundary layer
capping inversion heights may rise slightly as these waves pass
through, but should remain below 5000 feet. Any clouds below this
inversion probably won`t get any colder than -10 C, which is
borderline for glaciation.

Mesoscale models are showing a mid-lake convergence band over
Lake Michigan on Saturday amid northeast flow from Lower Michigan
and northwest flow from Wisconsin. As northwest flow becomes more
dominant Saturday night, any lake effect clouds and snow present
within this convergence band may reach the lakeshore counties at
some point Saturday night. Even HRRR soundings in proximity to the
convergence band show the convective boundary layer capped at
5000 feet and -10 C, so some light snow showers are possible but
it`s difficult to envision any impacts from this.

-- Possible trend back toward cool/snow late next week --

Ensemble guidance is still not fully on board with the magnitude
or timing of the change in pattern late next week, but some colder
air and chances of snow may arrive in the Midwest as early as
Thursday night or Friday. Ensemble spread in temperature solutions
going into the weekend and the following week is quite high, with
the GEFS looking colder on average than the ECMWF ensembles.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 631 PM EST Fri Jan 8 2021

The latest trend in the low clouds is that they are shifting south
of several TAF sites including KGRR...KMKG and KAZO. Based on
satellite loops...the lower clouds will soon move south of KLAN
and eventually KBTL and KJXN...by 03z. After that it looks like
through the remainder of the night the conditions should remain
VFR. However...model guidance is trying to reform sub IFR
clouds/fog north of KMKG toward daybreak Saturday. If that does
happen...it is possible for those impactful conditions to track
through KMKG and possibly KGRR Saturday morning. Aviators should
monitor the latest trends through the period.


&&

.MARINE...
Issued at 324 PM EST Fri Jan 8 2021

Winds will be fairly light over the next few days, though by
early next week will turn more from the west and increase
slightly. This may build waves up to 2-4 feet at times.


&&

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

$$

UPDATE...MJS
SYNOPSIS...CAS
DISCUSSION...CAS
AVIATION...MJS
MARINE...CAS



AREA FORECAST DISCUSSION

National Weather Service Raleigh NC

 915 PM EST Fri Jan 8 2021

.SYNOPSIS...
An area of low pressure will strengthen and move northeast along the
NC coast tonight. Canadian high pressure will return to the region
over the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 900 PM this evening.

...Winter Weather Advisory will be canceled shortly.

...Special Weather Statement will be issued for some isolated or
scattered patches of black ice development late tonight in the
Piedmont.

The latest data analysis and radar trends suggest that the chance
of appreciable snowfall for our region is quickly coming to an
end. The mid/upper low was elongated and located over the SE Coastal
Plain. The most concentrated precipitation area was located just
NW-N of the aforementioned mid level circulation currently extending
from near Southern Pines to Raleigh to Rocky Mount to Elizabeth
City. Even though there has been a change to snow in the spotty
higher reflectivity on radar from Moore County NE through Wake and
Franklin Counties, the higher reflectivities are drying up
from the NW as the mid level low pulls quickly east. The
precipitation rates are lightening up from the north with a change
back to a light rain/mist as the upper lift/support shifts SE.
Therefore, the higher rates will shift into the warmer Coastal Plain
very shortly, with rain expected to be mixed with a little sleet and
snow as it ends there.

The latest RAP indicates that the main precipitation shield will
quickly rotate east of the Raleigh and Southern Pines areas before
1100 PM, then exit the Fayetteville, Goldsboro, and Rocky Mount
areas by 100 or 200 AM. Since the back-edge of the steady and
significant precipitation had already arrived for much
of western Piedmont, Triad, Southern Piedmont and portions of the NE
Piedmont - there is now a very limited chance (an hour or so) for
much more than a brief dusting of wet snow before ending. An
isolated slick spot can not be ruled out, but with temperatures
expected to remain above 32 and the roads well above freezing, as
well - the WSW will be canceled.

Some very patchy slick spots (black ice) will be possible later
tonight as the skies clear, temps and dew points fall below
freezing, and nearly calm conditions will slow the drying process.
However, the impact is expected to be limited at the current time -
and isolated. Therefore, a Special Weather Statement will follow the
WSW instead of another WSW issuance. -Badgett

Previous discussion updated at 745 PM.

Light snow accumulations may now be confined to brief bursts of
heavier snow for the eastern Piedmont and western Sandhills as the
upper low passes overhead.

Snow already ending in the Triad region as heavier precipitation and
upper low shift south and east of Greensboro.

The latest radar data suggests that the best chance of light snow
accumulations with the ongoing changeover will be within the heavier
shower elements noted by reflectivities of 30-35+ dbz. These heavier
convective showers will bring brief bursts of snow. These "snow
islands" will be found within the larger area of widespread much
lighter returns on radar (<25-30 dbz). Note, that the heavier showers
or bursts of precipitation are becoming rather limited in coverage
as the evening wears on - even with the rain to snow transition that
is occurring more rapidly. Given the surface temperatures are likely
to remain above 32.0 until after the precipitation ends and that the
roads are wet and in the mid 30s to lower 40s - many roads will
remain just wet.

There may be some black ice potential later tonight, especially
where there is a slushy accumulation in the next few hours and where
there is lingering water runoff that will potentially freeze - as
skies clear and temperatures fall just below 32. -Badgett

As of 650 PM this evening.

Now snowing along the NC/VA border... and snow continues in the
Triad... tapering off in Winston-Salem.

We are finally getting a change over to snow from the north into
northern Granville, Vance, and Warren counties per Radar. And, the
change to snow is occurring in Orange. The main rain/snow lines
movement should accelerate in the next few hours with rapid cooling
aloft associated with the lift/cold upper low overhead, and onset of
nightfall. back edge of the accumulating snow now into Davidson and
Forsyth... sadly for snow lovers. -Badgett

Previous discussion as of 542 PM Friday...

The change-over to snow has occurred in the Triad... rain/snow line
extends from High Rock to Asheboro to Burlington to Roxboro...
moving slowly southeast.

The Correlation Coefficient (CC) off our local radars is now
depicting the main/rain snow line... slowly moving SSE through the
Piedmont. When used with the radar reflectivity it currently depicts
the main rain/snow line extending southwest to northeast... from
near High Rock Lake to near Asheboro... to near Burlington... to
Roxboro (southern Davidson through central Randolph... southeast
Guilford... central Alamance... northern Orange... and central
Person. The higher reflectivities are depicting the change-over from
rain to sleet or ice pellets. Snow was reported north and west of
the line. Reports are coming in of snow beginning to stick in
Davidson County (Lexington) and in Person (Roxboro)... and around
Greensboro. With temperatures expected to fall to around 32 or 33
with the snowfall (after change-over)... slushy accumulations will
begin on elevated surfaces first, then potentially on the
bridges/overpasses, followed by the roadways. It continues to appear
that there will be a small window of time (~2-3 hours) of high
enough snowfall rates in these bands for snowfall to accumulate,
before the snow tapers off. Note the downslope flow in Wilkes and
Surry Counties (on the back side of the system, now) already
reducing the snowfall rates (already ended at Wilkesboro and Mount
Airy). This drier air will feed into the Winston-Salem area shortly
(already seeing the reflectivity rates with the snow there reducing
quickly in NW Forsyth.

Since the main rain/snow line depicted by radar is very slow to
move... it will still be several hours before any change is likely
in the immediate Triangle. Portions of Orange and Durham will see
this change-over to snow between 6-8 PM.

We will send reports as this transition occurs. -Badgett

Previous discussion issued at 415 PM today...

The Winter Storm Warning has been replaced by a Winter Weather
Advisory.

A potent mid-upr shortwave trough over ern GA will pivot newd
to near the sern NC coast by 06Z, then offshore overnight. The
much-anticipated deformation precipitation band over wrn NC has
expanded and strengthened in advance of that trough aloft during
the past several hours, indicated by cooling cloud tops in IR
satellite imagery and an expansion and increase in radar
reflectivity. Hourly liquid equivalent amounts within that
expanding precipitation band have likewise increased from a
hundredth or two to 0.04"-0.08" in the past couple of hours.
Those precipitation rates are expected to continue at times as
the deformation band pivots ewd into the wrn Piedmont during
the next couple of hours, then ewd across the remainder of cntl
NC throughout the evening, with additional liquid equivalent
amounts of a couple of tenths likely, locally higher. With only
marginally cold boundary layer temperatures likely to limit
snow ratios generally to around 8:1, snow accumulation will
generally range from 1 to 1.5" over the nw Piedmont, where the
Warning was previously in effect, to a coating to locally around
an inch throughout the remainder of the Advisory area. While
the combination of increasing precipitation rates and loss of
insolation after sunset should allow temperatures to continue to
cool to between 32-34 degrees beneath the precipitation band and
maximum precipitation rates, temperatures may actually rise
slightly as the band departs, prior to cooler and drier air now
over VA being advected more fully swd overnight - supportive of
Sat morning lows in the upr 20s to around freezing. Given those
freezing temperatures Saturday morning, patchy black ice will
be possible late tonight-early Saturday, particularly on
bridges and overpasses.

&&

.SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
As of 350 PM Friday...

A strongly-sheared shortwave trough in wnw flow aloft over the
cntl High Plains this afternoon will dig sewd into the mid-South
by 12Z Sat, then off the SC coast by 00-06Z Sun. Associated
weak forcing for ascent may result in patches of altocumulus,
within an otherwise deeply dry and stable column in the wake of
the strong mid level cyclone now crossing the Carolinas.
In the low levels, surface high pressure building sewd from the
MS Valley will result in nwly flow and weak CAA, with highs
mostly in the mid- upr 40s and chilly lows in the mid-upr 20s.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
As of 240 PM Friday...

Dry and seasonable weather in store for Sunday. Another weather
system will move through the Southeast Monday and Tuesday with
snow possible once again across the Piedmont...

Sunday: Nearly zonal flow aloft over central NC will prevail Sunday
and Sunday night as the surface high over the Midwest ridges east
into the region. While the primary surface high remains over the
Midwest, a smaller area of high pressure is expected to develop east
of the Appalachians Sunday night. Expect dry, seasonable weather for
the end of the weekend. Highs topping out in the upper 40s to low
50s and lows dropping into the mid to upper 20s.

Monday through Tuesday night: The next weather system to impact
central NC is moving into the Pacific NW today. A shortwave will
break from the parent low and dive southeast through the Rockies and
into the southern Plains by Sunday/Sunday night. This wave will
continue to track east through the Arklatex on Monday before lifting
northeast and east into and through the mid-Atlantic Monday night
and Tuesday as the parent trough remains anchored from the Great
Lakes to TX. At the surface, high pressure over the area on Monday
will be shunted northward as a low develops over the central Gulf
Coast in response to the upper wave. As this low develops, a coastal
trough will also develop along the Southeast and Carolina coasts on
Monday. There are still some model discrepancies with the timing and
track of the low as it lifts northeast through the Southeast and
along the Carolina coast. The track and how/where the cool air
lingers over the NC Piedmont will impact the weather and potential
for non-liquid precipitation over the Piedmont Monday night/Tuesday
morning. While there is still a chance for some snow, mainly over
the Piedmont, confidence is not terribly high at this time.
Temperatures will be borderline and will likely require some wet
bulbing or heavy rates to get much snow. Will keep snow out of the
forecast grids for now, though it cannot be completely ruled out
just yet.

Wednesday through Friday: This period should once again be
predominantly dry and seasonable with surface high pressure ridging
into the area in the wake of the low. The upper trough will progress
through the eastern US midweek, but with little moisture to work
with will keep the forecast dry.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
As of 640 PM Friday...

Outside of some brief VFR ceilings at RWI, all other TAF sites to
experience IFR conditions to start the TAF period. The mid-level low
pressure system has moved further east from its position at 18Z,
located over southwest NC. Not much change from the previous
forecast, with precipitation tapering off from west to east between
02 and 06Z. Precipitation has changed over to light snow at GSO/INT.
However, the back edge of the snow has already started to move near
INT. Expecting the light snow over the Triad to taper off at or
before 02Z as drier air works in as the low pressure system pushes
eastward. VFR conditions will follow shortly thereafter. As for
RDU/FAY/RWI, latest model soundings continue to indicate some
uncertainty in regards to whether the airmass gets sufficiently
below freezing to change precipitation over to snow. Latest radar
also suggest a delay in the changeover. Have opted to keep a TEMPO
period of a rain/snow mix at RDU/FAY/RWI as a result. VFR conditions
will follow between 06 to 08Z. Winds will be light through the
period, becoming northwest on Saturday between 6 and 8 knots.

Outlook: VFR conditions take over Saturday through the first part of
Monday. Another area of low pressure moves into the region Monday
night and Tuesday, with the potential for sub-VFR conditions and
light rain.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$
SYNOPSIS...CBL/MWS
NEAR TERM...Badgett/MWS
SHORT TERM...MWS
LONG TERM...KCP
AVIATION...Kren



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