Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/15/19
Area Forecast Discussion
National Weather Service Des Moines IA
536 PM CST Sat Dec 14 2019
.DISCUSSION.../Tonight through Saturday/
Issued at 341 PM CST Sat Dec 14 2019
...Cold Temperatures Likely North Tonight...
...Light Snow Event Possible in Southern Iowa Sunday PM-Monday...
...Quiet and Warmer Weather Upcoming Week...
Cold Temperatures likely north tonight:
Key Points: High confidence that wind speeds will diminish
through the night tonight, eventually reaching less than 5 mph
after midnight. High confidence in air temperatures within a few
degrees +/- of minus 5 degrees across the northern two tiers of
Iowa counties. Ultimately, wind chill values should bottom out in
the minus 15 to minus 20 degree range around midnight. Through
noon Sunday, wind chill values will be below zero north of Highway
20, so bundle up!
Scientific Discussion: All models, including hi-res models, have
done awful today with handling cloud cover across Iowa as skies have
tried to clear from northwest to southeast throughout Saturday. In
advance of the Sunday PM-Monday system, expecting a few hours of
clearing after sunset this evening. Subsequently, temperatures will
plummet fairly rapidly (in particular across northern Iowa). Top-
down cloud increases expected through the overnight (after
midnight) will steady the rate of temperature decline. With winds
being the lightest near sunrise, lowest wind chill values will
likely occur closer to midnight tonight as winds should still be
near 10 mph or slightly under at that time. Given diminishing
winds and forecast wind chill values, Wind Chill Advisory likely
not warranted.
Sunday PM-Monday Snowfall Potential:
Key Points: Forecast has trended to push highest snowfall totals
south, into Missouri. High confidence that winds should be in the
5 mph or so range during any snow... which will mitigate
visibility reductions during periods of snow. Additionally, with
snow arriving late Sunday morning and lasting through Sunday
night... snowfall likely to be spread out over the course of 24
hours or so. With forecast totals generally in the trace to 2"
range, the snowfall rates will be very light, mitigating impacts
as well. Ultimately, feel the minimal impacts do not warrant
Winder Weather Advisory Criteria.
Scientific Discussion: As hi-res models have come into play,
southward trend in precip definitely manifested. Have leaned in
particular towards the HRRR output. Canadian a high outlier. GFS
interestingly has precip spreading across most of central Iowa,
nearing as far north as Highway 20/30. Have bought into this
slightly... interrogation of the 285K sfc does pick up on
widespread isentropic adiabatic ascent processes and some
intermittent pockets slight moisture flux convergence near the
DGZ. Large negative for accumulations is the sub-cloud dry air.
Forecast soundings have almost 1 km of "dry" air to punch through
before reaching the sfc... which is forecast to sport a dwpt
depression of +10F at times. By the time lower stratus arrives on
Sunday evening, dry air aloft from trailing high pressure already
being advected down into Iowa... nixing any semblance of
saturation through the DGZ.
If anything, current forecast snowfall may be too high. There is a
non-zero chance next forecast update will remove snowfall
accumulation >1" or so from south-central Iowa... but for now, did
not want to make too drastic of a change in case forecast track
shifted north.
Quiet, Warmer Weather Next Week:
Huge thermal ridge building behind this system as sfc high
slides into the central Midwest through early next week. By mid-
week, long- range models coming into agreement with crashing this
ridge over Iowa... potentially bringing 850mb temps near +7C to
Iowa by 12z Thu. Accompanied with sunshine, this would support
highs into the 40s across central to southern Iowa. If this
current pattern holds, may even be looking at highs in the 50s.
Tuesday and beyond has no widespread, significant precipitation
forecast.
&&
.AVIATION.../For the 00Z TAFS through 00Z Sunday evening/
Issued at 533 PM CST Sat Dec 14 2019
VFR conditions prevail for much of central Iowa over the next 24
hours. Isolated pocket of stratus remains over south central
Iowa, just south of KDSM. Satellite imagery shows this area of
stratus slowly drifting south, and may impact KOTM this evening
with MVFR level cigs. Snow spreads across the region tomorrow but
much of it should stay south of the state. -SN is possible at KOTM
and KDSM after 18z, but confidence is not high enough to include
in the current TAF.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
DISCUSSION...Kotenberg
AVIATION...Martin
becomes more zonal (see short-term forecast discussion below).
Big changes will arrive early Monday morning. A strong shortwave
trough, which is currently located about 150 miles off the Oregon
coast will dive southeast across the western CONUS and into the
Great Plains by late Sunday night. This shortwave trough will help
drive a surface cold front through our region. The cold front
should reach our northwestern counties by late Sunday evening.
Winds may become a bit northerly a little ahead of the front, as a
pre-frontal trough looks like it may become established during the
afternoon hours. The true cold front will be marked by a stronger
push of northerly winds, and colder temperatures. High
temperatures on Monday are likely to remain in the 40s northwest
of the Metroplex, in the 50s across DFW and into Central Texas,
and in the 60s in our far southeastern counties (where the cold
front will not arrive until later).
Strong ascent ahead of the cold front, supported by differential
cyclonic vorticity advection will allow for some showers and a few
thunderstorms to develop. Rain chances will increase the farther
south and east one goes. At this time, severe weather looks
unlikely, and rainfall totals should remain light.
Monday night will be cold with most of our CWA likely to
experience freezing temperatures (the exception being our
southeastern two tiers of counties). Tuesday night will be even
colder as clear skies and light winds should allow for excellent
radiational cooling. The entire CWA will see below freezing
temperatures on Tuesday night, with temperatures in the low to mid
20s possible in our western counties where it will be a little
drier and the elevation is slightly higher.
For the second half of the week, weak upper-level ridging will
return, bringing temperatures back up to seasonal normals (mid to
upper 50s) for Wednesday and through the end of the week. Another
upper-level shortwave trough will approach the region on Friday,
but a lack of moisture will keep rain chances low, and confined to
areas east of I-35.
Looking way ahead to Christmas, the suite of deterministic and
ensemble guidance seems to be in good agreement that a deep trough
or upper-level low will be in place over the western U.S. While
this pattern could result in some unsettled weather for the
Southern Plains and into the Southwest, this is not a pattern that
typically results in substantial cold air deliveries into our
region. It is far too early to get into any kind of details right
now, and it should be noted that this type of pattern typically
has low predictability this far out (even if the models agree on
the larger scale pattern). There`s not a whole lot to say about
the weather as we get close to Christmas other than there is great
uncertainty, and we probably won`t get a decent handle on even
the major details for another 3-5 days.
37
&&
.SHORT TERM... /Issued 1213 PM CST Sat Dec 14 2019/
/This afternoon through Sunday afternoon/
Zonal flow aloft will continue to bring in moisture from the
Pacific today, resulting in scattered high clouds. There will
still be plenty of sun across much of the region, allowing
afternoon temperatures to warm into the 60s and lower 70s. The
only exception will be along the Red River where cloud cover will
be the thickest and most persistent, keeping temperatures in the
upper 50s.
Surface high pressure will build southeast out of the Northern
Plains today bringing a quick reinforcement of dry air followed by
the return of low level moisture tonight once the surface ridge
axis moves farther east and surface low pressure deepens across
the southern High Plains. The surge of moisture over the
relatively cool ground will result in the development of advection
fog and even some drizzle. The fog could be dense at times,
especially south of I-20 and east of I-35.
Although low level warm advection will increase through the day
Sunday, some morning cloud cover and fog should slow daytime
heating a bit, especially in the southeast zones. We also expect a
cold front to arrive across the northwest zones by late Sunday
afternoon which will also noticeably lower temperatures. Afternoon
highs Sunday will range from the mid 60s in the north to near 80
across the southwest zones where daytime heating will get a boost
from southwest winds/adiabatic warming.
79
&&
.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth 48 74 42 52 32 / 0 0 5 10 0
Waco 48 78 46 57 32 / 0 0 10 20 0
Paris 42 69 45 52 29 / 0 5 40 40 0
Denton 45 73 40 49 29 / 0 0 5 5 0
McKinney 45 72 42 51 30 / 0 0 10 20 0
Dallas 48 75 43 52 32 / 0 0 5 10 0
Terrell 46 75 45 57 30 / 0 0 20 30 0
Corsicana 49 76 49 60 32 / 5 0 20 30 0
Temple 50 79 48 60 33 / 0 0 5 20 0
Mineral Wells 43 74 36 49 27 / 0 0 0 5 0
&&
.FWD WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
05/92
AREA FORECAST DISCUSSION
National Weather Service Hastings NE
934 PM CST Sat Dec 14 2019
.UPDATE...
Issued at 925 PM CST Sat Dec 14 2019
The snow has been expanding across the forecast area as expected,
but with perhaps a few heavier snow bands a bit further south
than previously thought. Therefore, we have added two rows of
counties to the advisory to bridge the gap between the previous 2
separate advisories making one continuous winter weather
advisory.
Lowered forecast snowfall amounts a bit across our northeastern
zones and increased amounts a bit south of I-80 in southern
Nebraska due to the slight shift further south with this first
wave of snow tonight. Also tweaked snowfall forecast to lower
Kansas snowfall totals from the 2nd wave of snow on Sunday as
this 2nd round may also be shifting a bit further south.
&&
.SHORT TERM...(This evening through Sunday)
Issued at 255 PM CST Sat Dec 14 2019
Although the first batch of snow arriving this evening into Sunday
morning is still more uncertain than the second round of snow coming
Sunday into Monday morning, I decided to add a row of three counties
along I-80 from Highway 281 to the west. Solid evidence of a couple
of mid-level vort maxes to possible give us a few inches of snow
tonight. The NAM and ECMWF are backing off a bit with snow amounts,
but have shifted farther south, and it looks like there may be just
enough snow to warrant a warning. The GFS trended heavier, with a
solution positioned near the NAM, ECMWF, and many CAMs. The HRRR
indicates that a few inches of snow is a distinct possibility
tonight along the I-80 corridor west of Highway 281. Still looks
like the separation of two advisories in space and time (north,
south)and (Saturday/Sunday, Sunday, Monday)is a good bet, rather
than going with a blanket advisory over the entire CWA. Also, this
still looks like an advisory situation, as snow amounts and wind
speed would not warrant anything more at this time. The HRRR
indicates a possible loss of saturation in the dendritic production
layer over parts of the western CWA toward 10Z or 11Z early Sunday
morning, but this appears to be an outlier, and I will not
introduce any other precip type but snow at this time. We could be
cold enough that if this occurred, we may get something more like
sleet. Anyway, with the HRRR being an outlier, I did not put any
other precip type but snow, but if this signal becomes more
consistent, the evening/midnight shift may have to stick something
else besides snow in there, especially for our southwest CWA from
maybe 09Z to 12Z or 13Z or so.
.LONG TERM...(Sunday night through Saturday)
Issued at 255 PM CST Sat Dec 14 2019
Looks like the forecast for the second round of snow Sunday into
early Monday morning is more in question on the northern side of
the main deformation snow band, as the 700 mb consolidates over
the south central Plains. Models have been generally tightened up
the gradient on the northern side of the band, although the NAM
seems to be dumping heavier qpf/snowfall within the heaviest part
of the band. The GFS has shifted snowfall farther south from
previous runs is not so bullish with QPF. The main deformation
band looks like it should remain mostly southeast of the CWA and
any precip type issues with freezing drizzle/rain looks like it
will remain south of our CWA. Still looks like an advisory
situation with snow amounts and expected wind speed, although it
would not be completely out of the question to have amounts
approaching 6 inches in a heavier band on Sunday over Mitchell
County, especially. The 12Z run of the ECMWF would indicate this.
After the system leaving Monday, the forecast is dry, but we do
have a closed mid-level system within west-northwest flow coming
through the Plains toward late work week, so I`m not completely
confident in the dry forecast.
&&
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Sunday)
Issued at 550 PM CST Sat Dec 14 2019
We continue to expect snow at our KGRI and KEAR TAF sites this
evening mainly between 8 or 9 PM through 6 to 8 AM Sunday
morning. Snow showers will become more hit and miss by later
Sunday morning and afternoon. Expecting generally 1 to 2 inches at
these airports tonight. MVFR conditions will be likely through
most of the night with perhaps periods of IFR ceilings/visibility
within the heavier snow bands.
&&
.GID WATCHES/WARNINGS/ADVISORIES...
NE...Winter Weather Advisory until 9 AM CST Sunday for NEZ039-040-046-
047-060>062-072>076-082>085.
Winter Weather Advisory from 6 AM Sunday to 9 AM CST Monday for
NEZ086-087.
KS...Winter Weather Advisory from 6 AM Sunday to 9 AM CST Monday for
KSZ005>007-017>019.
&&
$$
UPDATE...Wesely
SHORT TERM...Heinlein
LONG TERM...Heinlein
AVIATION...Wesely
Area Forecast Discussion
National Weather Service Grand Junction CO
359 PM MST Sat Dec 14 2019
.SHORT TERM...(Tonight through Sunday night)
Issued at 233 PM MST Sat Dec 14 2019
Messy forecast this afternoon as a cold front drops southward
through the CWA. Right now, the front is just south of the I-70
corridor as indicated by the heavier rain and snow showers
occurring. The jet stream aloft is supporting the front as the jet
has set up in a west to east orientation but this will also cause
the front to weaken as the day progresses. Latest radar mosaic
does appear to show a bit of weakening but some stronger echos as
well. Models also showing a definitive turning of the winds to
more northerly which follows as the front pushes through. Guidance
continues to suggest the front to drop down to just north of the San
Juans and then stall. The orientation of the jet just won`t
provide enough energy for the front to make it over the mountains.
For the next few hours then, expect some heavier rain/snowfall
with a quick inch or two possible. As far as models go, the HRRR
did really well this morning with the placement of the front and
it`s forward propagation so following it`s lead. A noticeable
decrease in precip should occur this evening with only the higher
terrain really seeing any accumulating snow but this looks to
occur from the northern mountains down to the San Juans. A few
bands are possible over Steamboat Springs and also the central
mountains so the current highlights will stay in effect. Of note,
did drop the advisory for the La Sals in Utah. Snow just didn`t
want to materialize there and latest guidance shows a quick burst
of snow as the front moves through but not enough to warrant any
highlight.
Tomorrow morning, the jet will round the base of the upstream
trough and provide enough support to get the front moving again
and provide more widespread lift. QG ascent will also start
increasing early Sunday morning which, along with the front and
upper level support, will bring a return to heavier snowfall.
By daybreak Sunday, some heavier precip will form along the front
from the Four Corners region into the San Juans. Interestingly, as
the upper trough approaches, it`ll force this area of precip
northward, possibly as far north as Vail Pass and the Grand Mesa
so again, another reason to keep the highlights in place. The
upper level trough finally pushes through Sunday evening as precip
slowly becomes more showery in nature.
.LONG TERM...(Monday through Saturday)
Issued at 233 PM MST Sat Dec 14 2019
By Monday morning, almost all snow showers will be moved east of
the San Juans as the colder airmass settles over the area
following the trough and associated cold front`s passage. As a
transient ridge sets up over the west CONUS coast, we then
experience continued northwest flow through Tuesday morning before
the ridge axis moves over us Tuesday night. Meanwhile, the trough
moves onshore and is over the Great Basin by mid-day Wednesday.
Some disagreement exists between deterministic models but this
trough axis moves across our CWA on Thursday morning. At any rate,
models keep this system fairly dry and quick moving likely
bringing the upper elevations some gusty winds. Not expecting much
in the way of precipitation across our forecast area. Beyond
that, models generally show another fairly large trough moving
toward the west CONUS coast by next weekend into the following
week. Stay tuned to future forecasts on that system and how it
could impact Christmas travel plans.
Temperatures start out cold (several degrees below normal) with the
northwest flow behind the first trough on Monday. In fact, this
looks like some of the coldest air we`ve seen so far this
season...possibly slightly colder than the October outbreak in a few
places especially on Monday night. Expect a very slow warming trend
through next week, reaching near normal temperatures by Thursday,
and continuing to gain a few degrees each day.
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 355 PM MST Sat Dec 14 2019
Several bands of rain and snow have developed across the area. The
bands will gradually shift south and east this evening with
mountain snow continue. Some sites will improve above ILS by later
this evening. Another round of snow moves in from the west later
tonight. MVFR/IFR conditions are most likely across the southern
sites especially KTEX, KGUC and KDRO. Mountains will remain
obscured through the next 24 hours in many places.
&&
.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Winter Weather Advisory until midnight MST Sunday night for
COZ014.
Winter Storm Warning until midnight MST Sunday night for COZ012-
018-019.
Winter Weather Advisory until 5 PM MST Sunday for COZ009-017.
Winter Storm Warning until 5 PM MST Sunday for COZ010.
Winter Storm Warning until 8 AM MST Sunday for COZ004-013.
Winter Weather Advisory until 8 AM MST Sunday for COZ005-008.
UT...None.
&&
$$
SHORT TERM...TGR
LONG TERM...SS
AVIATION...KJS
Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
936 PM CST Sat Dec 14 2019
.UPDATE...
Issued at 919 PM CST Sat Dec 14 2019
Only some slight changes needed to the tonight portion of the
forecast to account for southeastward clearing of stratus. However
high and mid clouds from the Plains will spread back over the area
tonight in the wake of the diminishing lower clouds. I have
slightly tweaked lows down. Tonight is tranquil.
The anticipated winter storm is still on track for Sunday into
Monday. The new deterministic 00Z NAM and latest RAP are still on
target with snow spreading west to east across the area on Sunday,
beginning in central MO from 8-10 am, far eastern MO from 10 am to
noon, and across western IL during the afternoon. These
deterministic model runs have also shifted the axis of heaviest
snow a bit further south centered along the I-70 corridor.
Impressive isentropic lift and frontogenetic forcing is expected
to support a rather wide snow band with rates at times from 0.5 to
1 inch per hour. If these solutions are in fact correct with the
intensity and location then are current snowfall amounts during
the afternoon would need to be doubled, and closer to 4-5 inches
along this axis. I hesitate making alot of changes to the forecast
at this time based on 2 deterministic models when a closer
evaluation of the full model suite and ensembles may not fully
support this decided south shift. None the less, hazardous travel
is expected on Sunday and into Sunday night. The current winter
storm watch still is reasonable and will be converted overnight to
a series of winter storm warnings and advisories.
It still appears that the first wave of snow will exit by Sunday
evening and many areas may lose ice nuclei thus light freezing
rain or drizzle would occur. Another round of snow would then
impact the region on Monday/Monday evening.
Glass
&&
.SHORT TERM... (Through Late Monday Night)
Issued at 337 PM CST Sat Dec 14 2019
Early this afternoon, a very broad-based TROF extended over much of
the CONUS with a W-SW flow aloft over our region. The strong storm
system that we have been watching carefully has come onshore and was
located over northern Arizona. At the surface, a cold front was to
the southeast of our region with colder air spilling in on NW winds.
An extensive area of clouds existed over much of the Midwest with
clearing in Iowa but additional cloud cover in Kansas already
sliding east towards our region that will likely limit any clearing
over our way. Temperatures were in the 30s for most of the area.
Quiet weather is expected tonight as we will be in-between systems.
In the meantime, colder air will settle in from a 1025mb area of
high pressure, resulting in min temps early Sunday morning mainly
in the lower to mid 20s. This will be key for what happens next.
The well-advertised next storm system continues to look set for
Sunday through Monday night. Confidence continues to increase on
the general characteristics:
(1) Two main waves of precipitation: one focused on Sunday
afternoon-evening and the other one on Monday, lingering into Monday
night. This longer duration into Monday night is a key change.
(2) The first wave on Sunday will primarily be in the form of snow
and will be driven by frontogenesis in a weak but slowly
strengthening broad WAA regime. The trend for this area seems to
have settled on a region near the Interstate 70 corridor, especially
for what could be focused bands of snow. If this materializes,
these bands of snow will be capable of heavy bursts of snow with
rates in excess of 1"/hour. The cold surfaces will allow snow to
accumulate on any untreated surfaces and result in hazardous travel.
This episode is expected to exit by late Sunday evening. Where it
lingers the longest will be capable of several inches of snow.
(3) The interlude between the two main waves of precipitation
will begin moving in from the southwest Sunday evening and
continue into early Monday morning and will feature intermittent
freezing drizzle or light freezing rain and a resultant ice
accretion for most areas. Only where cloud ice can hang on better
in far northern MO will precipitation types of snow linger.
(4) Cloud ice will be re-introduced enough with the concluding wave
of precipitation after sunrise on Monday and looks to now
linger into Monday night with the upper level system moving slower,
but with the broad moderate WAA regime continuing. Two upper level
impulses, one lead one Monday morning will bring cloud ice back into
the equation for much of the area near and north of I-70, should
transition the freezing drizzle back over to snow, with the main
system set for Monday afternoon and evening, expanding coverage of
snow at the expense of freezing drizzle into the southern portions
of the forecast area (southeast MO and far southern IL). This
second wave of precipitation, especially where it looks to
transition back to and continue as snow looks now to intersect much
of the area that will benefit most from the first wave of snow on
Sunday.
(5) Adding it all up, there continues to be a threat for several
inches of snow for areas near and north of I-70. Much of this
area, in fact, is flirting with Warning (6") criteria and with the
trends shaping up, this threat for higher snow totals is edging
closer to the I-70 corridor. For this reason, we are continuing the
Watch, but beginning it sooner and extending it longer in time. The
southern portion of the Watch will be converted to an Advisory where
lower snow totals and icing will be an issue.
TES
.LONG TERM... (Tuesday through Next Saturday)
Issued at 337 PM CST Sat Dec 14 2019
Medium range guidance has been very consistent in keeping the mid
Mississippi Valley in cold, dry northwest flow Tuesday and into
early Wednesday behind the storm. It`s unlikely that temperatures
will rise above freezing across northeast Missouri and west central
and south central Illinois with fresh snow on the ground, however
some mid and upper 30s look likely across parts of southeast
Missouri. Wednesday morning continues to look like the coldest of
the week due to a clear sky, light wind, and the snow cover. Lows
in the low to mid teens across most of the forecast area still looks
probable. Models show the low level ridge moving east of the
Mississippi Valley Wednesday as the upper level ridge builds into
the Great Plains. The combination of increasing southerly low level
flow and rising heights will bring warmer air back to Missouri and
Illinois for the latter half of the week. Areas with snow on the
ground will still be chilly Wednesday with heights struggling up to
near freezing, but parts of southeast and central Missouri should
warm up to the low to mid 40s.
The upper level ridge axis is forecast to move east of the
Mississippi River on Thursday. Low level warm advection will
continue with southwest flow Thursday and Friday and highs are
expected to climb above normal values for Thursday and Friday. ECMWF
has trended toward the GFS which brings enough low level moisture
out of the Gulf to produce some light rain across Arkansas and
southern Missouri ahead of a short wave trough on Friday. There`s
still little if any precip indicated in our area, so have kept
Friday`s forecast dry for the time being. Saturday looks dry as
well with the trough to our east...though it`s a low confidence
temperature forecast with GFS showing slightly different surface
patterns with the GFS being the cooler of the two.
Carney
&&
.AVIATION... (For the 00z TAFs through 00z Sunday Evening)
Issued at 535 PM CST Sat Dec 14 2019
Stratus resulting in MVFR flight conditions blanketed the region
early this evening. The northern edge of the stratus stretched
across northern MO into west central IL, and this clearing line is
expected to progress southeastward this evening. Accordingly the
terminals should see flight conditions improve to VFR with the
southeastward clearing of the stratus. VFR flight conditions are
then expected to persist until around mid-morning Sunday.
Thereafter snow will develop/spread from western MO across the
region during the later part of the morning and through the
afternoon. Flight conditions will deteriorate after the onset of
snow eventually lowering to IFR.
SPECIFICS FOR KSTL:
Stratus will persist this evening resulting in MVFR flight
conditions. The stratus should clear around 05-06z resulting in
VFR flight conditions. VFR flight conditions are then expected to
persist until late morning Sunday. Snow will develop/spread into
the terminal from the west near midday, with intensity increasing
during the afternoon. Flight conditions will deteriorate after
the onset of snow eventually lowering to IFR during the afternoon.
Glass
&&
.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Winter Weather Advisory from 9 AM Sunday to midnight CST Monday
night for Crawford MO-Iron MO-Madison MO-Reynolds MO-Saint
Francois MO-Sainte Genevieve MO-Washington MO.
Winter Storm Watch from 9 AM CST Sunday through Monday evening
for Audrain MO-Boone MO-Callaway MO-Cole MO-Franklin MO-
Gasconade MO-Jefferson MO-Knox MO-Lewis MO-Lincoln MO-
Marion MO-Moniteau MO-Monroe MO-Montgomery MO-Osage MO-Pike
MO-Ralls MO-Saint Charles MO-Saint Louis City MO-Saint
Louis MO-Shelby MO-Warren MO.
IL...Winter Weather Advisory from 9 AM Sunday to midnight CST Monday
night for Randolph IL.
Winter Storm Watch from 9 AM CST Sunday through Monday evening
for Adams IL-Bond IL-Brown IL-Calhoun IL-Clinton IL-Fayette
IL-Greene IL-Jersey IL-Macoupin IL-Madison IL-Marion IL-
Monroe IL-Montgomery IL-Pike IL-Saint Clair IL-Washington
IL.
&&
$$
WFO LSX
Area Forecast Discussion
National Weather Service Marquette MI
703 PM EST Sat Dec 14 2019
.SHORT TERM...(This evening through Sunday)
Issued at 340 PM EST SAT DEC 14 2019
Water vapor imagery and RAP analysis show a shortwave trof extending
from Hudson Bay to ne MN. This feature is supporting some areas of
-sn across the fcst area this aftn. Earlier today, a sfc trof was
extending basically w to e across southern Lake Superior.
Convergence on the w end of this trof over western Lake Superior was
much stronger with sfc obs and models suggesting there may have been
a meso low on the trof there. In any event, this trof has moved s
and inland during the morning/early aftn. With its passage, there
has been mdt lake enhanced snow into far western Upper MI over the
last couple of hrs, generally vcnty of KIWD to the Porcupine Mtns.
Farther e, weaker convergence and 850mb temps a couple of C higher
than over the w has led to nothing of note in terms of shsn off Lake
Superior.
With passage of the aforementioned shortwave, colder air will spread
over the area tonight. 850mb temps are fcst to fall from -10C e and
-15C w this evening to around -17C across Lake Superior by 12z Sun.
Fcst soundings indicate inversions generally at 5-6kft with the DGZ
becoming well positioned in the lake induced convective layer under
the expected caa. As a result, will be able to fluff up a few inches
of snow tonight into Sun morning in the NNW wind snow belts.
Overall, looks like a 1-3 inch snowfall with up to around 4 for some
locations that have more persistent shsn. Given the heavier snow
that is falling this aftn far w, will maintain advy for
Ontonagon/Gogebic counties, though heaviest snow will fall during
the remainder of the aftn into the early evening with shsn then
becoming lighter tonight. Snowfall tonight will be low impact based
on increasing snow-to-water ratios in excess of 20 to 1. In exposed
areas close to Lake Superior, there will be enough wind to cause
some blsn/drsn. Lows tonight will range from the single digits above
zero interior w to the upper teens east along Lake Superior.
During Sun, low-level winds will steadily back, becoming wsw over
western Lake Superior and w over eastern Lake Superior by late aftn.
As a result, lingering LES bands and lake stratocu will shift n and
ne thru the day, leaving behind mostly sunny skies. By the end of
the aftn, the last of the shsn should be confined to Keweenaw County
and east of Grand Marais. High temps Sun will range from the lower
teens w to the lower 20s e.
.LONG TERM...(Sunday night through Saturday)
Issued at 301 PM EST SAT DEC 14 2019
General troughing across the CONUS will continue through the weekend
before ridging builds across the West Coast Sunday night into
Monday. As this ridge builds and moves inland across the West,
steeper troughing will occur downstream and cause a period of NW
flow Tuesday into Wednesday as a shortwave crosses the area bringing
another quick shot of Arctic air. As the previously mentioned ridge
continues east across the CONUS, heights will begin to rise
Wednesday afternoon, gradually cutting off LES as winds back more
southerly Wednesday evening. Models begin some disagreement going
into Thursday, as heights continue to rise and 850 temps begin to
warm. Models suggest a very subtle shortwave to pass over Lake
Superior Thursday afternoon which may bring a period of -SHSN across
the NW LES belts and eastern UP. On Friday going into the weekend,
models suggest a low pressure wave to develop across the Plains and
move east across the CONUS, staying south of the cwa.
Sunday night into Monday, 850 temps remain plenty warm for LES;
however, sounding profiles in westerly wind belts show a steep
inversion with a lack of moisture also a concern. Sounding profiles
have some differences between models, but winds begin to back more
WSW to SW for some. This backing will limit most snow showers across
only the Keweenaw for Sunday night. Shifting winds and limited
moisture will limit accumulations to under an inch.
Monday into Tuesday, winds will veer slowly to the NW as troughing
amplifies and a shortwave approaches Lake Superior. Models suggest
850mb temps will fall from -13 to -15C on Monday night, to -24 to -
26C by Tuesday night. NW LES belts are expected to produce snow
through the day Tuesday, increasing through the night. As 850 temps
fall blo -20C, DGZ saturation becomes limited again. The limited
saturation through the DGZ will limit snowfall accumulations, but
could also produce the smaller, more visibility-restricting
snowflakes often seen in arctic air.
A weak shortwave will brush the Upper Lakes on Mon, resulting in
veering winds bringing light LES back to the nw fcst area. This will
be followed by the next stronger shortwave dropping se from the n
central Canada mid-level low Tue morning. Arctic air will surge into
the area with this wave, bringing blustery conditions and increasing
nw flow LES for Tue thru Tue night. If the arctic air arrives early
in the day per GFS/CMC, temps will likely fall thru the day Tue as
850mb temps fall to at least -20C. Overall, I increased PoPs and QPF
Tuesday/Tuesday night compared to the NBM to account for this, but
didn`t go too crazy as model differences still are evident and high-
res models will become more available for this event in the next
suite of models.
Heights begin to rise again Wednesday night as winds back more from
the SW. This shift should cut off any lingering LES; however, GFS
and EC show a quick-moving shortwave that may bring light snow
showers across the Keweenaw and far eastern UP Thursday. On Friday,
the UP should remain dry. GFS and GEM suggest the development of a
low pressure system across the Plains that is progged to pass to the
south of Upper Michigan across IL. There is a chance if this
solution is correct for some snow showers across mainly the far
south, but these chances remain low. Models suggest heights continue
to rise into the weekend, with 850 temps rising above 0C. This
should lead to a drier weekend as medium-range models continue to
show some disagreements.
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 652 PM EST SAT DEC 14 2019
Expect IFR conditions at both IWD and CMX this evening in lake
effect snow, but then conditions at IWD will gradually improve to
MVFR late tonight and to VFR Sunday morning as winds gradually
back west and then sw and push lake effect clouds and showers
northward. Conditions at CMX will improve to MVFR Sunday afternoon
as lake effect -shsn push north. MVFR conditions at SAW will also
improve to VFR late Sunday morning as winds back more westerly. &&
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 340 PM EST SAT DEC 14 2019
With colder air flowing into the Upper Great Lakes tonight, expect
some freezing spray with northerly winds of 20-30kt across Lake
Superior, strongest over the e half. Winds will diminish to mostly
under 20kt on Sun as they become w to sw. Winds will then increase
back to 20-30kt Sun night, strongest over the w half, as a trof
approaches. After winds diminish a little later Mon/Mon evening, a
stronger cold front will pass across Lake Superior on Tue. Behind
it, expect nw winds to 30kt into Tue night/early Wed morning with
gales to around 35kt a good possibility, at least over the e half of
Lake Superior. With arctic air flowing across the area, heavy
freezing spray will also be possible. Winds will then quickly
diminish to under 20kt from w to e on Wed as sfc high pres ridge
arrives. After the ridge passes, expect some increase in winds
heading into Thu.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
Winter Weather Advisory until 7 AM EST /6 AM CST/ Sunday for
MIZ002-009.
Lake Superior...
None.
Lake Michigan...
None.
&&
$$
SHORT TERM...Rolfson
LONG TERM...JAW
AVIATION...Voss
MARINE...Rolfson
Area Forecast Discussion
National Weather Service Pocatello ID
838 PM MST Sat Dec 14 2019
.UPDATE...
Very minor, almost transparent, update to the forecast for cloud
cover tonight. As a whole, forecast is reasonable. Still seeing a
few residual snow showers but additional accumulations look very
light. Might see some patchy fog develop, otherwise expect low
stratus to expand across the Snake Plain and into portions of the
Magic Valley tonight.
&&
.PREV DISCUSSION... /issued 144 PM MST Sat Dec 14 2019/
SHORT TERM...Tonight through Tuesday. Early afternoon radar imagery
was showing the current storm system transitioning slowly east
through the region and gradually dissipating with time. We are
expecting at least a few more hours of light snowfall from Pocatello
into the SE mountains through early this evening but the threat of
moderate snowfall has ended. A temporary break in the action should
follow tonight before the next upstream storm system positioned
along the Oregon/British Columbia coast shears inland Sunday. The
numerical weather models show pieces of energy from this system
advancing through the region Sunday (mainly Sunday afternoon/night)
with periods of light snowfall ongoing through Monday morning until
that disturbance clears the region and a ridge of high pressure and
associated drying build east across the NW states Monday afternoon
through Tuesday. The clearing aloft anticipated with the incoming
ridge will allow temps to plummet well below normal across the
region while valley fog and low clouds develop Tuesday morning.
Huston
LONG TERM...TUESDAY NIGHT THROUGH NEXT SATURDAY. A ridge of high
pressure is forecast to remain in control Tues night into at least
the first part of Wed, with dry and cold weather but increasing
clouds. Long-range models then push another trough of low pressure
across the northern Rockies. The GFS/ECMWF/Canadian all hint at a
bit of a split-feature trough as it approaches, with one weakening
piece of energy pushing across OR/WA into Canada to our north, and a
second and stronger piece of energy pushing NE across NV, UT, and WY
Wed/Wed night, becoming a dominant closed low as it spills into the
Plains. All 3 models are interestingly dry in their deterministic
solutions with the passage of this trough (even to our south just
ahead of the axis of the dominant piece of the trough), but we see
no reason to argue with them just yet as we monitor trends. A moist
westerly flow is expected to become established in the wake of the
trough with a chance of rain/snow showers Thurs through Sat,
although confidence is low on placement and coverage, and we ran
with the fairly broad-brushed and reasonable NBM solution for now.
The best chance of additional accumulating snowfall during this
period will be in the Central Mountains west of Challis and north of
Hailey, especially again in the Sawtooths/Smokys, but at an early
glance this setup doesn`t look quite a nice or long-duration as what
we saw with our most recent storm as a ridge of high pressure tries
to potentially intrude and cut off the flow by Sat. Temps look to
creep up a few degrees each day, with highs reaching the 30s again
by Fri and Sat. - KSmith
AVIATION...It`s been a difficult day at many of the airports across
the southern half of our forecast area, with low cigs/vsbys due to
widespread snow working through the region. Snow has ended at
KBYI/KIDA/KDIJ, and should finally be ending for KPIH by about 3 PM.
As the clouds associated with the snow push out on satellite, they
are revealing some low stratus in the eastern Magic Valley, Snake
Plain, and adjacent valleys. While some of this has perhaps been
reflected in the ASOS observations (contaminated due to the snow),
this has otherwise been hard to fully diagnose so far due to those
lower clouds being blocked on satellite by the retreating higher
clouds, but we expect some of this stratus will linger for the rest
of the day, and then lower and intensify tonight for at least
KPIH/KIDA/KDIJ. Have started working this thinking into the TAFs,
and have also added some BR and VCFG to a few terminals with a very
moist low-level airmass, recent snowpack, and light winds, all
largely based on MOS guidance and the HRRR cig/vsby products. We
will try to continue to refine the timing and impact of this
activity with the 00z TAF package. - KSmith
&&
.PIH WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Area Forecast Discussion
National Weather Service Riverton WY
401 PM MST Sat Dec 14 2019
.SHORT TERM...This evening through Sunday night
Issued at 1248 PM MST Sat Dec 14 2019
Isolated snow showers linger across the area, as the upper level
system exits to the east. Activity is beginning to pick up in eastern
Fremont and southern Natrona counties much the way the HRRR has been
indicating. Southern Natrona looks like it will have the best chance
of getting measurable snow with an inch or two possible. These
showers should begin to weaken around 00Z, with all areas largely
dry around 03Z or so. With some warm advection aloft, inversions
will likely set up in the basins. Many areas will see single digit
temperatures overnight with the Green River Basin looking to
bottom out in the negatives.
Sunday still looks like a quieter day. A weak wave will bring some
snow showers to western Wyoming, but with limited moisture to
work with any amounts look small. Any chance for showers east of
the Divide will likely be confined to the mountains. Basin
inversions will keep temperatures cold Sunday afternoon, with
many areas struggling to get out of the teens. Decreasing cloud
cover will allow for more widespread negative temperatures across
the area Sunday night.
.LONG TERM...Monday through Saturday
Issued at 1248 PM MST Sat Dec 14 2019
Unseasonably cold Monday, as a strong 1040mb surface high builds
into the Intermountain West. Highs are expected to be 10 to 20
degrees below average. Cannot rule out a few snow showers over the
far west. On Tuesday, an upper level ridge will build into the
area with 700mb temperatures warming by around 10 Celsius. Trapped
basins and valleys will remain well below average, while the
mountains and some adjacent foothills will see a decent warm up
Tuesday. The best potential for valley/basin fog in the extended
will be Tuesday night, as a very strong surface inversion sets up
with a very dry air mass just above the surface.
Models indicate a trough pushing over California Tuesday night,
but diverge on the track Wednesday into Thursday. The GFS has been
fairly consistent in swinging this trough northeast across the
region late Wednesday into Wednesday night, while the ECMWF has
been farther south and a bit slower. However, both models have
been dry ahead and along the trough axis as models have a very dry
atmosphere ahead of the trough. In wake of the trough, models are
showing a moist westerly flow impacting the area with chances of
snow over the far west Thursday into Friday. The GFS has been more
bullish on this solution than the ECMWF. Have trended PoPs upward
over the far west/northwest.
&&
.AVIATION...For the 00Z TAFS through 00Z Monday
West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals
Decreasing cloudiness will continue this evening into the overnight
hours in most locations, except for the far western valleys
including KJAC where a ceiling between 3-6kft agl is expected to
persist. There could be patchy morning fog Sunday, but limited areal
coverage and overall low confidence of it forming, precludes any
mention at any terminal for now. A few snow showers will be possible
over the northwest Sunday afternoon, and will have VCSH at the KJAC
terminal. Otherwise, VFR conditions and light winds Sunday.
East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals
Areas of light snow across central areas with MVFR ceilings and
MVFR/IFR visibility will end from west to east this evening. After
04Z, the snow should have exited the area with clouds lifting to
VFR or scattering out.
Although there will be a small chance of fog Sunday morning, the
limited areal coverage and overall low confidence of it forming,
precludes any mention at any terminal for now. Sunday looks to be
VFR with light winds with some mid-high level cloudiness
overspreading the area Sunday afternoon.
Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on icing and turbulence forecasts.
&&
.FIRE WEATHER...
Issued AT 1248 PM MST Sat Dec 14 2019
The current weather system will exit to the east this evening with
isolated snow showers lingering in western Sweetwater and Fremont
counties though 6 pm and southern Natrona County until 9 pm.
Humidity will remain well above critical levels. Gusty winds will
decrease this evening in southern Wyoming and remain light
overnight. Winds will be moderately gusty in the mountains Sunday
afternoon and across the Wind Corridor from Sweetwater to Natrona
counties. Mixing and smoke dispersal will be generally poor
through Sunday. Inversions are likely to set up in the basins
tonight and into Sunday.
&&
.RIW WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 5 PM MST this afternoon for
WYZ023>025-027>030.
&&
$$
SHORT TERM...Hulme
LONG TERM...Murrell
AVIATION...Murrell
FIRE WEATHER...Hulme