Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/21/18
Area Forecast Discussion
National Weather Service Denver/Boulder CO
819 PM MST Thu Dec 20 2018
.UPDATE...
Issued at 809 PM MST Thu Dec 20 2018
Downslope winds expected to develop along the east slopes of the
Front Range and as well as the foothills late tonight and Friday
ahead of a relatively weak approaching short wave trough. This
already reflected well in the grids so no update is planned at
this time.
&&
.SHORT TERM...(This evening through Friday)
Issued at 310 PM MST Thu Dec 20 2018
A dry and cool airmass is in place over the state this evening as
an upper ridge is in place over the state. Satellite imagery shows
the next batch of mid-level moisture heading our way to be out
over Nevada this afternoon. Brisk northwesterly flow aloft will
continue tonight with gusty winds over the higher mountain ridges.
Through tomorrow, short and medium range models show the upper
ridge flattening with flow aloft becoming more westerly. This will
advect warm air across the state and set up a brief chinook wind
situation through the afternoon hours. The HRRR model shows areas
of gusty winds extending out from the foothills during the
afternoon hours. Model cross sections show most of the wind
remaining over the higher foothills, but with a well mixed airmass
in the afternoon, we should see some gusty winds from the
foothills out to about the I-25 corridor for a few hours. . Gusts
of 40 to 50 MPH will be possible. Temperatures on the plains are
expected to warm into the upper 50s and lower 60s. By late in the
afternoon, the HRRR shows the winds rapidly diminishing.
No highlights for the time being.
.LONG TERM...(Friday night through Thursday)
Issued at 310 PM MST Thu Dec 20 2018
Colorado will be under the influence of a moderate northwest flow
aloft from Friday night through Monday. Plenty of moisture,
orographic lift and occasional upper level disturbances caught up
in this flow will produce periods of snow and breezy to windy
conditions across the high country through this period. The first
shortwave should produce snow in the mountains Friday evening
through Saturday with drier weather on Sunday due to weak upper
level ridging. The next system should produce another round of
snow across the mountains from late Sunday through Monday. The
plains should remain mostly dry through this period with near to
slightly above normal temperatures. However, some light snow will
be possible across the plains on Saturday due to weak upslope flow
and QG lift.
For Christmas Day and Wednesday, models show a powerful storm
system deepening across the western U.S then moving across the
Four Corners Region and Central Plains States. This system has the
potential to produce significant snowfall and blizzard conditions
across northeastern Colorado. Models have come into better
agreement over the past 24 hours, however, there is still quite a
bit of uncertainty with the track of this system which would
greatly affect snowfall amounts. The 12Z GFS has the most
favorable track for heavy snowfall and shows the 500 MB low
tracking from the Four Corners Region Tuesday evening into extreme
southeast Colorado by noon Wednesday and into north central
Kansas by Thursday morning. This solution could produce total snow
amounts between 8 and 12 inches across the Front Range Urban
Corridor and 1 to 2 feet across much of the plains on Wednesday.
However, the experimental GFSF3V (which will become the operational
GFS next month) has a much less favorable track further to the south
with much less snow amounts. The ECMWF and GEM have similar tracks
to the GFS with not quite a bit of snowfall. We will have to
continue to closely monitor possible changes in the track of this
storm system over the next few days.
&&
.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 809 PM MST Thu Dec 20 2018
VFR will prevail through the period. Winds are in the process of
following the normal diurnal trends and remain light enough that
they should have a minimal impact on airport operations tonight.
Downslope winds may spread towards BJC by late Friday morning with
some gusts in the 25-35 kt range possible after 18z.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...Cooper
SHORT TERM...Dankers
LONG TERM...jk
AVIATION...Cooper
Area Forecast Discussion...UPDATED
National Weather Service Duluth MN
555 PM CST Thu Dec 20 2018
.UPDATE...
Issued at 548 PM CST Thu Dec 20 2018
Updated for the 00z Aviation Discussion below.
&&
.SHORT TERM...(This evening through Friday)
Issued at 329 PM CST Thu Dec 20 2018
A cold front draped across the Northland this afternoon will
continue its southward trek tonight while a surface ridge builds
eastward into the Upper Midwest. Low stratus is expected to linger
for most locations overnight. With skies remaining cloudy, think
most of the guidance is too cool over my northern zones. Have
raised lows to the low teens in northeast Minnesota with readings
in the low 20s in northwest Wisconsin. Northerly winds will keep a
potential for lake effect snow over portions of northern
Wisconsin, including Ashland, Iron, and Price counties. With
shallow upstream moisture and limited lake delta-Ts, don`t expect
much in the way of accumulation. Another few tenths of an inch are
possible through Friday. The high pressure ridge will slide
eastward into the Northland for the end of the work week. Think it
will be difficult to clear the stratus, so have held onto a
minimum of 50% sky cover through Friday over much of the area.
Overcast skies will be likely over northwest Wisconsin with
northerly winds keeping lake-induced clouds overhead. Highs will
top out near 20 in northeastern portions of the Arrowhead to the
upper 20s across our southern zones.
.LONG TERM...(Friday night through Thursday)
Issued at 329 PM CST Thu Dec 20 2018
A weak system crosses the Upper Great Lakes on Saturday into
Sunday and will bring light snowfall accumulations to mainly
northern Minnesota (1-2" or so). This is followed by a cool down
where light forcing may squeeze a few flurries out here and there.
The coldest air arrives overhead Christmas morning in conjunction
with a weak short wave which may offer some Christmas flurries.
This feature is a little weaker today compared to yesterday, so
have backed off on the wording a bit.
The main story continues to be the potential for a system after
Christmas. Model trends have been relatively stable with most
deterministic operational solutions in fair agreement. This gives
more confidence to some sort of winter system being in the area,
but it`s still too early to flesh out specifics. The GFS Ensembles
still vary widely among their different members which lends to a
hesitance in advertising this storm too strongly attm. Still quite
impressed with the handling of the system among the different
deterministic models this far out and their run to run consistency
is also impressive. It will be interesting to see how this
evolves.
Temperatures remain on the warm side of normals throughout the
extended period.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 555 PM CST Thu Dec 20 2018
The main focus for this evening and overnight continues to be the
MVFR/IFR ceilings that remain in place. Some of the high-
resolution guidance wants to scour out this low stratus deck later
this evening from north to south, but we`re thinking the stratus
will linger through the nighttime hours as the RAP model 950 mb
level relative humidity, which has captured the current cloud
cover very well, lingers some higher moisture through the night,
so leaned heavily on this. Gusts will gradually diminish overnight
as the low-level inversion builds, which should also help to keep
the stratus deck in place. RAP and NAM model soundings both hint
at a return to VFR conditions during the late morning and
afternoon hours Friday.
&&
.MARINE...
Issued at 329 PM CST Thu Dec 20 2018
Small craft criteria winds and waves will cover portions of the
forecast area through Friday morning while waves remain high
through Saturday morning along the South Shore.
A larger system may arrive after Christmas packing gales, but
still too early to tell where it will track and its intensity.
&&
.PRELIMINARY POINT TEMPS/POPS...
DLH 17 25 16 27 / 0 0 10 20
INL 14 21 11 26 / 0 0 20 50
BRD 19 28 19 29 / 0 0 10 20
HYR 22 28 17 30 / 0 0 0 10
ASX 24 27 19 29 / 10 10 10 10
&&
.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...Small Craft Advisory until 4 AM CST Friday for LSZ140-146-147.
Small Craft Advisory until 10 PM CST this evening for LSZ141-142.
Small Craft Advisory until 10 PM CST Friday for LSZ148.
&&
$$
UPDATE...JTS
SHORT TERM...Huyck
LONG TERM...Wolfe
AVIATION...JTS
MARINE...Wolfe
Area Forecast Discussion
National Weather Service Marquette MI
617 PM EST Thu Dec 20 2018
.SHORT TERM...(This evening through Friday)
Issued at 422 PM EST THU DEC 20 2018
Concerns tonight into Friday involve ptype issues and lake enhanced
snow amounts for west and north central counties.
WV imagery and RAP analysis indicated a mid/upper level trough from
Hudson Bay through northwest Ontario and Minnesota to eastern Texas.
At the surface, a trough/cold front has worked its way through the
nw half of Upper Mi. One area of light rain ahead of the front was
still lifting through eastern Upper Mi late this afternoon while
light mixed pcpn was occurring over the west.
Tonight and Friday, with the advance of colder air behind the front
pcpn will continue to switch over to mostly snow late this afternoon
into this evening over the west half counties. Dry slotting into
central and eastern counties could result in drizzle this evening
with a gradual change over to a mix of freezing drizzle/snow
overnight. Any light glaze of fzra/fzdz would likely be over far
eastern Marquette into Alger counties with likely less than .1 inch
of ice accumulation. Lake enhanced snow will develop tonight
especially where the upslope northerly flow is strongest over west
and north central higher terrain as 875-900 mb temps fall near -10C
over the west this evening and overnight for north central counties.
Given marginal CAA barely cold enough for adequate ice nuclei,
expect low SLR ratios closer to 10/1. This will result in one to two
inches of wet snow accumulation for most locations with perhaps 3-4
inches over the Michigamme Highlands tonight into Fri. Drying at mid-
levels from the west during the day on Friday will result in snow
quickly tapering off with minimal additional accumulation.
Expect min temps in the 20s tonight with highs Friday from the mid
20s west half to lower 30s south central and east.
.LONG TERM...(Friday night through Thursday)
Issued at 241 PM EST THU DEC 20 2018
Broad upper level troughing from central and eastern Canada across
the Great Lakes results in a colder weather pattern through the
weekend and early next week. Then, attention just beyond Christmas
turns to developing western Conus trough and the possibility for
first widespread accumulating snow in quite some time across much
of Upper Michigan late Wednesday and/or Thursday. Though it is
day 7 and the upper level system is still west of Alaska, that
system certainly bears watching as it could impact travel after
the holiday.
Friday night into Saturday: Cold northerly low-level flow in wake of
the trough moving through today may still support light lake effect
snow showers/flurries Friday night over mainly north central. Stays
blustery good part of Friday evening with north winds over 25 mph,
strongest over north central around Marquette and Munising. Given a
north wind may be breezy down toward KI Sawyer as well. Saturday
looks quiet as high pressure ridge crosses.
Saturday night through Christmas: Shortwave crossing southern
Manitoba into Ontario along with sfc low will support a batch of
light snow mostly over Keweenaw Saturday night and possibly
spreading across rest of north and eastern Upper Michigan on Sunday.
Mostly light snow but as this system passes and winds turn w-wnw
Sunday aftn into Sunday night, lake enhanced snow may increase over
Keweenaw and in snow belts east of Munising. Quick hitter but
actually does get kind of chilly with H85 temps down to -14c and
with lake temps of +4c that pushes delta t/s to around 18c. Forecast
soundings show inversions up to 8-9kft. For a change, decent amount
of DGZ is within the lake moist convective layer. Sure seems that
conditions would be favorable long enough for advisory level
snowfall to occur in the areas favored by wnw winds. Inversions fall
quickly on Monday and into Christmas Day so although light LES will
continue in wnw flow areas near Lake Superior, not looking at much
for accumulations. Temperatures this weekend into early next week
will end up at or slightly above normal with highs mostly in the mid
to upper 20s and lows in the teens to lower 20s.
Wednesday-Thursday: Wednesday will start out with light LES for wnw
flow areas near Lk Superior but then LES will shut down as winds
become more e-se ahead of approaching system. Later Wednesday night
and maybe as late as later Thursday (per 12z ECMWF) more widespread
wintry precipitation may affect much of Upper Michigan. Stronger
lead shortwave trough will support strong lee Rockies
cyclogenesis/sfc low Wed. Sfc low will deepen as it crosses the
southern Plains then maintain similar intensity as it lifts toward
western Great Lakes Wed night, through again the latest ECMWF is
much slower with this solution, not bringing the sfc low into our
area until late Thursday at a weakened state. Certainly could see a
period of at least moderate wet snow as the system lifts toward
Upper Great Lakes and maybe the snow would then change to mix of
wintry precip or only rain. Really tough to get into the specifics
this far out though considering main system will not move onshore
over northwest Conus until Monday at the earliest. Guess the main
takeaway at this point is those with travel plans in the region just
after Christmas will want to keep eye on later forecasts as we get
closer to this time frame. Probably not a good idea to get too
locked into any one specific model solution at this time as there
will likely be significant changes into next week between the
models/ensembles and even run-to-run variations of the same model.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 617 PM EST THU DEC 20 2018
A prolonged period of low cigs and/or visibilities will continue
this forecast period for all sites.
&&
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 422 PM EST THU DEC 20 2018
A trough passage today followed by deepening low pres lifting nne
toward the Lower Great Lakes, will lead to a period of stronger nnw-
n winds this afternoon into Friday. Some gale force gusts over
central and eastern portions of Lk Superior will be possible late
today into Friday as colder air arrives behind the trough, but
doesn`t appear that the gales will be widespread or long lasting
enough to have a gale warning out. N-NW winds to 30 kts continue
into Friday, strongest over the east half. Winds diminish to 25 kts
or less by Saturday as sfc high pressure ridge briefly crosses.
Another trough crosses the area on Sunday, but even then winds
should remain only up to 25 kts late Sunday into Sunday night.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&
$$
SHORT TERM...Voss
LONG TERM...JLA
AVIATION...07
MARINE...Voss
Area Forecast Discussion
National Weather Service Nashville TN
819 PM CST Thu Dec 20 2018
.UPDATE...
FOR EVENING DISCUSSION.
&&
.DISCUSSION...
Surface low has moved to our east, so we`re getting plenty of
wrap-around moisture this evening and overnight and into tomorrow.
Radar imagery currently shows a break in the rain across much of
Middle Tennessee, although the HRRR keeps generally light
precipitation over the mid state the remainder of the night. Rain
will start to exit the region tomorrow morning. Current forecast
grids are in good shape so no changes are planned this shift.
&&
.AVIATION...
00Z TAF DISCUSSION.
Poor flying conditions as all mid-state terminals continue to deal
with IFR or worse. KCSV is running VLIFR and will likely remain
that low throughout the night. Categories will improve very
slowly Friday, with rain ending from west to east.
Winds will be light out the north for a couple more hours before
gusts begin to spread across all terminals about 06Z. These breezy
NW winds will persist through the remainder of the TAF cycle.
&&
.OHX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
DISCUSSION......08
AVIATION........Unger
Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
408 PM MST Thu Dec 20 2018
.DISCUSSION...(This Evening Through Thursday)
Issued at 147 PM MST Thu Dec 20 2018
Upper level analysis shows a deep trough over the eastern states,
and a ridge building over the west. Skies are mostly sunny across
the region. At the surface, winds are westerly around 10-15 mph,
and temperatures are in the 40s.
Upper ridging over the northern plains will be short-lived, as a
fast-moving wave sweeps in from the Pacific Northwest on Friday.
Some light rain/snow showers could skirt the northern third of the
CWA on Friday, with little to no snow accumulations. Winds will
become gusty behind the cold front Friday afternoon. Models are
showing 3-6 mb/3 hr pressure rises across portions of western SD,
and CAA is expected to be stronger than that of yesterday. NAM and
GFS forecast soundings show 30 to 45 kt winds mixing down,
especially around the Rapid City area, and the HRRR has 40 to 50
kt gusts possible from Meade County down through Jackson and
Bennett. May need a Wind Advisory, but since this isn`t expected
until tomorrow afternoon - and maybe only for a few short hours -
will let later shifts determine if the next model runs also
support this.
Cooler air will settle into the region for the weekend. Highs will
be in the 30s to lower 40s Saturday through Christmas Eve, with dry
conditions expected.
Still watching the potential for a post-Christmas snowstorm across
the region. The 12Z ECMWF has slowed down the track of the low, and
aligned it more with the Canadian and GFS, keeping it farther south
and east than the 00Z EC run. These solutions continue to place most
of the snowfall across Nebraska and eastern SD, but our CWA could
still see some significant snowfall. At this time, it looks like
snow will start moving into the CWA Christmas afternoon/evening,
exiting Thursday afternoon/evening. However, there is plenty of time
for the track and timing to change.
&&
.AVIATION...(For the 00Z TAFS Through 00Z Friday Evening)
Issued At 408 PM MST Thu Dec 20 2018
VFR conditions are expected through the forecast period.
Ahead of a quick moving system, winds will increase late tonight
in northeastern Wyoming along with increasing mid-to-high level
clouds. Much of the region will see winds turn northwesterly and
gust to 30-35 knots by late Friday morning into the afternoon
after cold front passes through the region.
&&
.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&
$$
DISCUSSION...Pojorlie
AVIATION...Eagan