Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/20/24
Area Forecast Discussion
National Weather Service Grand Junction CO
517 PM MDT Thu Sep 19 2024
.KEY MESSAGES...
- Conditions will remain dry with near to slightly above average
temperatures through Friday.
- The next system arrives on Saturday bringing scattered showers
and storms as well as a reinforcing shot of cooler air.
- The central mountains look to be favored for a majority of the
precipitation with some in the form of snow.
- The weather pattern remains cooler and unsettled early to mid
next week as additional disturbances move through, providing
at least scattered shower activity.
&&
.SHORT TERM /THROUGH FRIDAY NIGHT/...
Issued at 223 PM MDT Thu Sep 19 2024
Satellite imagery shows the models struggled to initialize the
closed low just off the West Coast on the 12Z run this morning
with 100-200 mile variation between models. The GFS seems to
best fit with the satellite observations down through the mid
level, but none of the models picked up on the low-level
features. By 18Z, the models are already tracking ahead of
observations indicating the models are a little fast bringing
this low into the region. The deterministic models are running
ahead of the ensemble means pushing the low well into Arizona by
Saturday morning as is the NAM, but the HRRR looks much better
placing the low near the Nevada-California-Arizona triple point
more in line with the ensembles. The NBM guidance seems to also
be leaning towards the HRRR solution with wrap-around moisture
pushing up into southern Utah sparking isolated to scattered
nocturnal convection overnight Friday. Models are also hinting
the southerly flow will pick up some of the Gulf of Mexico
moisture over Chihuahua and push it north through New Mexico
into the San Juan Mountains along the Divide Friday evening and
overnight, presenting a slight chance for nocturnal showers and
thunderstorms in south central Colorado mountains though
confidence in these is lower. Otherwise, look for temperatures
running near normal to a little above normal this afternoon and
overnight with a band of high clouds moving up from the south
into the central mountains. Tomorrow will be a few degrees
warmer under mostly clear skies, but the sunshine will make it
feel much warmer. Clouds will start to move in from the south
and southwest Friday evening ahead of this next system.
&&
.LONG TERM /SATURDAY THROUGH THURSDAY/...
Issued at 223 PM MDT Thu Sep 19 2024
By Saturday morning, the low that appears cut off from the main
upper level trough will lift northeast through the Four Corners from
Arizona and move through much of southeast Utah into western
Colorado. This low packs a bit of a punch and is fairly compact,
closed and vertically stacked with a 100 kt jet wrapping around
the base providing needed orographic and dynamic lift Saturday
morning into the afternoon for showers and storms. Moisture
increases more on the right and northern sides of this low as it
pulls up some moisture from the Gulf of Mexico late Saturday
afternoon and evening through Sunday morning with wraparound
precipitation. In fact, PWAT anomalies increase to 160 to 200
percent of normal late Saturday afternoon and evening across the
eastern and northern areas of this low where the wraparound
precipitation occurs. The best precipitation favors the central
mountain areas with easterly upslope flow, which favors the
mountains along the central Continental Divide on the eastern
sides, but downslopes a bit into our western sides. That being
said, storms will still develop out ahead of this low, but
precipitation amounts may not reach the amounts that the eastern
slopes would receive. This time of year, we are considering
snow levels and impacts there. At this time, it looks like snow
levels Saturday start off above 12kft and lower to around 10.5
to 11kft Saturday night, so snow is possible at the higher peaks
with maybe around 1 to 3 inches with locally higher amounts
above timberline. Not expecting much impact though at pass
level as roads remain wet given milder afternoon temperatures.
Wraparound northwest flow will keep some light snow lingering
through Sunday morning over the peaks with light rain in the
lower elevations along the Divide, before clearing out by
Sunday afternoon, with the peaks revealing some white with
perhaps colorful foliage in the foreground as the cooler
temperatures are starting to allow the leaves to change in the
higher elevations.
Drier northerly flow takes hold Sunday afternoon with fast
moving northwest flow moving in Sunday night into Monday as
another shortwave trough drops in from the northern Rockies.
Conditions Sunday afternoon and evening could remain breezy in
this pattern between systems. This low again becomes cut off
from the main flow and drops north to south across western
Colorado Monday afternoon through Tuesday afternoon, keeping
conditions unsettled with more shower activity. High pressure
builds in overhead behind this wave, leaving somewhat of a Rex
Block with the low potentially lifting back over the Four
Corners region by mid next week. Models are in somewhat decent
agreement with the overall synoptic pattern but the jury is out
as run to run consistency has not quite been there. Will have to
wait and see how this evolves with future model runs, but
something to keep an eye on. The blended solution keeps
scattered PoPs and unsettled conditions, favoring the high
terrain for now which seems reasonable. Temperatures this
weekend through mid next week remains around 5 degrees below
normal in the lower elevations with around 10 degrees below
normal over the mountains with temps modifying to near or
slightly above seasonable mid to late next week, however this
all depends on the weather pattern and what happens with this
cut off low.
&&
.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 516 PM MDT Thu Sep 19 2024
VFR conditions will prevail for the next 24 hours, with mostly
clear skies and generally light and terrain driven winds. Gusty
southerly to southwesterly winds will be possible tomorrow
afternoon.
&&
.GJT WATCHES/WARNINGS/ADVISORIES...
CO...None.
UT...None.
&&
$$
SHORT TERM...DB
LONG TERM...MDA
AVIATION...TGJT
Area Forecast Discussion
National Weather Service Grand Rapids MI
929 PM EDT Thu Sep 19 2024
.KEY MESSAGES...
- Chance for Storms Tomorrow
- Several Chances of Showers and Storms into Next Week
&&
.UPDATE...
Issued at 921 PM EDT Thu Sep 19 2024
The convection upstream in WI has been tracking slowly east this
evening. As this convection nears western MI later tonight, the
instability will be decreasing. This weakening/diminishing trend
will be seen in the convection as well. The latest HRRR shows the
tops lowering to under 30k feet as they move into the CWA. Overall
the grids/forecasts show this scenario well and we are not
planning any changes to the tonight forecast.
&&
.DISCUSSION...
Issued at 252 PM EDT Thu Sep 19 2024
- Chance for Storms Tomorrow
Clouds begin to increase late tonight as an upper low tracking from
the Northern Plains into Manitoba sends a trailing front towards
lower MI, arriving in our area Friday afternoon and evening.
Spotty showers will begin to move through the area around late
morning to mid- day, then storms will be possible during the
afternoon. Diurnal instability up to 1000 to 1400 J/kg (highest
over southern lower MI) and bulk shear to 35 to 40 knots will
support a few strong storms, with the highest chance in far
southwest lower Michigan. Damaging wind gusts will be the primary
concern with any strong storms.
- Several Chances of Showers and Storms into Next Week
The weekend starts off dry as a period of brief ridging and high
pressure advects dry air across the area. Precipitation chances then
increase later Sunday and especially Sunday Night into Monday. This
is driven by a closed low over the southwest US ejecting into the
main flow pattern and bringing ample moisture with it. Can`t even
rule out a bit. Ensemble CAPE forecasts suggest the chance of
isolated thunderstorms also exists. Grand Ensemble precipitation
probabilities show the chance for a needed soaking rain is definitely
there. Chances of over 0.5" of rain Sunday Night into Monday night
is 40-60 percent and over 1 inch is around 10 percent.
This weekend into into next week marks the start of a pattern shift
as the ridge that has brought dry weather for over a week breaks.
This change makes troughing the predominant upper-level setup.
Several additional chances of rain are possible over this time
period, however as is common with these setups, the timing of the
shortwaves and associated rain showers is still not nailed down.
Thermal troughing also causes 850mb temperatures falling to around
10C, translating to a near normal low to mid 70s for highs next week.
&&
.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 650 PM EDT Thu Sep 19 2024
VFR conditions will continue at all the terminals this evening and
overnight. Fog is not expected overnight given that some light
winds will persist near ground level with stronger winds aloft.
Clouds will gradually move in Friday and scattered showers and
isolated storms will develop at our western terminals around or
shortly after midday and then by around mid or late afternoon at
our eastern terminals. Brief reductions to MVFR and perhaps IFR
are possible in heavier showers and isolated storms.
&&
.MARINE...
Issued at 252 PM EDT Thu Sep 19 2024
A weak cold front will bring a chance for scattered showers early
Friday morning. Otherwise, expect offshore winds starting Friday
with winds shifting southerly then westerly Friday afternoon
following the passage of the front. Wave heights stay generally low
through this weekend, with the highest waves to around 2 feet Sunday
evening.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.
&&
$$
UPDATE...MJS
DISCUSSION...Thielke/Thomas
AVIATION...Laurens
MARINE...Thielke
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
631 PM CDT Thu Sep 19 2024
.KEY MESSAGES...
- Slight Risk (Level 2/5) for large hail (2"), damaging winds
(60+ mph), and a few tornadoes across eastern Minnesota and
western Wisconsin this afternoon and evening.
- Rain is increasingly likely this weekend, however uncertainty
remains highest with respect to areal coverage and QPF
amounts. Latest trends favor highest rainfall amounts along
the Minnesota/Iowa border.
- Cooler air arrives early next week with highs in the 60s.
Temperatures rebound into the mid to upper 70s by late week.
&&
.DISCUSSION...
Issued at 111 PM CDT Thu Sep 19 2024
The initial round of early morning convection has all but ended
across the area. Latest KMPX radar imagery captures a few lingering
storms in western Wisconsin, which are exiting to the east. Further
west, visible satellite captures a band of stratus tied to an
eastward advancing cold front. Latest surface observations depict
the front to the east of Alexandria extending south towards Redwood
Falls. The cold front is tied to a negatively tilted closed upper-
low positioned over southeastern Saskatchewan/southwestern Manitoba.
The eastward progression of the front across a region of ascent in
the exit region of the upper-low will be the focus point for
convective development later this afternoon. Data from our special
18z balloon and ACARS data from MSP airport illustrate that
destabilization is underway, however capping will inhibit
development for a little while longer.
RAP forecast guidance and SPC mesoanalysis continue to display a
favorable environment for severe weather across eastern Minnesota
and western Wisconsin, especially by September weather standards.
Strong instability (MLCAPEs 2000-3000 J/kg), steep mid-level lapse
rates (7.0-7.5 deg/km), and sufficient bulk shear (~35 knots) all
point towards an environment capable of producing severe weather.
CAMs seem to have a decent handle on how we expect the event to
unfold, though with any event a degree of uncertainty does remain.
The general idea advertised across the CAM suite is convective
initiation to the west of I-35 by mid-afternoon, with the number of
storms becoming numerous very quickly given the strong instability
and erosion of the cap. As storms intensify and are in the more
discrete or supercellular mode, the threat for large hail (2") and
potential tornadic activity will be the highest. Our concern is that
storms will be in this phase along/near the I-35 corridor and the
large population center that is the Twin Cities Metro during rush
hour. Storms are expected to develop into clusters quickly, which
introduces more uncertainty in the evolution of the event. The
linear nature of the hodograph would suggest splitting cells with
numerous storm scale interactions. The "chaotic" nature to this type
of convective environment means storm interactions could be
constructive or destructive, so the "high-end" nature of this setup
is somewhat in question. Nonetheless, forcing from the front and low-
level jet should promote growth into more linear segments and a
transition to a damaging wind threat as storms exit eastern
Minnesota and enter western Wisconsin. Forecast wind profiles remain
supportive of a QLCS tornado threat as well. The SPC has maintained
a large Slight Risk area in the latest Day 1 convective outlook,
which includes a large hatched area for significant hail (2") across
much of the Slight Risk area.
Showers and thunderstorms will move east of the area later this
evening and will be followed up by a dry Friday across the region. A
thermal ridge is progged to lift northeast out of the central Plains
Friday into Saturday and as a result our high temperature forecast
features the low 80s through Saturday. The weekend forecast puzzle
still has missing pieces, but the general trend is coming into
better context. A clipper-type wave is forecast to slide across the
northern Great Plains Saturday morning and will send a surface cold
front across the Upper Midwest. The passage of the front will re-
introduce scattered PoPs into the forecast Saturday afternoon and
evening. Cold advection behind the front will drop highs in the 60s
for Sunday, though that may not be the end of the active weather for
the weekend. Guidance swings a shortwave trough and associated
surface low across the Great Plains Sunday into Monday, with an
expansive shield of precipitation set to cut across portions of
Iowa/Wisconsin/Illinois etc. The northward extent of the
precipitation shield of greatest uncertainty, as there are wet and
dry members across the various ensembles. The best chance for heavy
QPF will likely be for locations in southern Minnesota, closer to
the surface low. After a cool start to the week, temperatures are
forecast to rebound into the 70s by mid to late week.
&&
.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 631 PM CDT Thu Sep 19 2024
Scattered TS across far eastern MN and WI will continue to push
east through early evening. TS is expected to clear RNH around
01Z, and EAU by 03Z.
KMSP...TS expected to remain east for the remainder of the
evening. Skies will clear by 01-02Z.
/OUTLOOK FOR KMSP/
SAT...VFR. Chc SHRA/TSRA. Wind SE 5-10kts becoming W.
SUN...VFR. Slight chc SHRA/MVFR. Wind NW 5-10 kts.
MON...VFR. Slight chc SHRA/MVFR. Wind NE 5-10 kts.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
MN...None.
WI...None.
&&
$$
DISCUSSION...Strus
AVIATION...Borghoff
Area Forecast Discussion
National Weather Service Marquette MI
648 PM EDT Thu Sep 19 2024
.KEY MESSAGES...
- Extended stretch of well above normal temperatures continues through
at least Saturday with highs mainly in the upper 70s and 80s.
- A cold front brings scattered showers and a few thunderstorms
tonight into Friday. Some stronger storms are possible in
western Upper Michigan this evening.
- Multiple rounds of precipitation possible through the first
half of next week. Thunderstorms that do form are not
expected to be severe.
- Temperatures around normal are expected to return for next week.
&&
.SHORT TERM /THROUGH TONIGHT/...
Issued at 446 PM EDT Thu Sep 19 2024
Water vapor imagery and RAP analysis show troffing over the western
U.S. with one well-defined mid-level low over southern Manitoba and
a second just off of the central CA coast. Some elevated showers and
a few storms have advanced into north central WI and western Upper
Mi this afternoon ahead of the low over Manitoba. The mid-level
ridge axis which was stationed over Upper Mi most of the week is
getting pushed slightly se this afternoon although the attendant
very dry air mass is still keeping the central and eastern U.P
shower-free this afternoon. Afternoon temps thus far have reached
into the mid 70s and lower 80s, coolest along the Lake Mi shore.
Higher dew points in the 60s have resulted in a more unstable
airmass south into north central WI where a cluster of elevated
storms have formed at the nose of a theta-e ridge.
Plenty of uncertainty regarding U.P weather for late this afternoon
into tonight as the mid-level low over Manitoba lifts north and
sends a mid-level trough and associated sfc cold front toward Upper
Mi later tonight. High resolution models suggesting stronger
convection and developing supercells now forming over southern MN in
environment of SBCAPE values 1500-2000 j/kg will pose a severe risk
into southern MN and western WI into early evening. These storms
over southern MN and western WI are then expected to transition to a
linear MCS tonight which moves east through WI. High effective shear
of 40 kts or higher and CAPE values of 1000-2000 j/kg will favor the
eastward movement of the MCS through WI tonight. Big question will
be how this MCS affects moisture for supporting convection over the
U.P tonight. A few of the CAMs suggest isolated to scattered showers
and t-storms this evening over the west could potentially become
more numerous in coverage into south central Upper Mi overnight if
northern extent of MCS moving through WI clips this portion of the
cwa. This will be something for the evening shift to keep an eye on.
Increasing effective shear to 30 kts could support some stronger
storms into the western U.P. this evening but severe threat will
likely be limited by mostly elevated CAPE of 500-1000 j/kg. Look for
min temps to stay around 60F tonight with increasing clouds and
chance for showers. Patchy fog will be possible again tonight,
especially central and east under moist southerly upslope flow.
&&
.LONG TERM /FRIDAY THROUGH THURSDAY/...
Issued at 400 PM EDT Thu Sep 19 2024
Active weather pattern to begin the long term forecast as a trio of
shortwaves will pass in the vicinity of the Upper Great Lakes Friday
through Tuesday. This will help keep more seasonal temperatures
(highs in the 60s) and periodic precipitation chances in the
forecast into the middle of next week. While there is enough spread
in the ensembles in the back half of the week to keep slight-chance
(~20%) PoPs in the forecast, ensembles have trended more dry over
the past 24 hours of runs and anomalous ridging looks to reside over
Manitoba and northern Ontario by the end of next week. Should this
ridging persist, the pattern could dry out to end September, which
aligns with the CPC 8-14 day and 3-4 week precip outlooks which put
the UP in a below normal precip pattern.
By Friday morning, the cold front associated with a 992mb occluded
low over Manitoba will be draped over central-to-eastern Upper
Michigan. This front will continue to drift eastward, though with
the parent low only slowly drifting northeast itself, the front will
take its time to push through. SBCAPE looks to be around 500-1000
J/kg along the front, so some thunderstorms are expected, but HREF
reflectivity paintball plots show that the coverage of thunderstorms
capable of 40+ dBZ will be sparse through the day Friday, so no
severe weather is expected. While not everyone will be getting a
soaking, the eastern 2/3 of the UP looks at least 50% likely to get
a tenth of an inch or more of precipitation tomorrow with the 75th
percentile of the HREF showing pockets of a half inch or more of
rain. CAMs show some afternoon redevelopment of showers in the
central UP, but otherwise, clearing skies behind the front should
allow for highs to climb up to the mid-upper 70s in the west half,
though highs will be closer to 70 in the east. Showers should exit
the UP by midnight, and overnight lows fall to the upper 40s to
upper 50s as a result.
Localized ridging will allow for a mainly dry day on Saturday with
highs back to around 80. While this is unseasonably warm, the NBM
gives less than a 5% chance of breaking a record high at the MQT WFO
that day. The break in the clouds and precip will be brief however
as a ~1005mb low will quickly jet along the Manitoba/Ontario line,
bringing showers and non-severe thunderstorms to the UP for
overnight Saturday through Sunday along the low`s cold front. Mean
daily precip rates with this system range between 0.2 to 0.4 inches,
so nothing extreme, but welcome rainfall to some areas that are
running well below normal over the past week and month.
Beyond the weekend is a surprising amount of ensemble spread. 500mb
height plots show a trough tracking from Colorado on Sunday towards
the southern Great Lakes basin by late Tuesday but weakening as it
approaches. Chances that precip arrives from this system are highest
in the east (40-50%) than in the west (20-30%), but spread in
solutions keeps the details rather muddy, though it is important to
note that these PoPs are slightly lower than the previous NBM runs.
Moving into the second half of the work week, the 12Z GEFS shows
anomalous ridging building over the Northern Plains and Canadian
Prairie with 500mb height anomaly reaching +20 dam over Manitoba by
Thursday morning. Downstream high pressure of that ridge would tend
to have the UP rather dry moving into late September, and with the
potential for higher heights to persist (LREF chance of 500mb
heights 580+ dam around 40%), the CPC outlooks of less than normal
precipitation will be on-track.
&&
.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 647 PM EDT Thu Sep 19 2024
VFR conditions should prevail thru the period at IWD and CMX and
tonight at SAW. Shra and some tsra will spread w to e across Upper
MI tonight. Models indicate the coverage of showers is still
uncertain, but expect isolated to scattered showers and t-storms
reaching IWD late evening. At SAW, upslope southerly winds and shra
should result in MVFR developing by morning and MVFR conditions
could linger a few hours after sunrise before dissipating.
&&
.MARINE...
Issued at 400 PM EDT Thu Sep 19 2024
Ahead of a cold front passing over Lake Superior tonight, wind gusts
out of the south and southeast are gusting to 25 knots over central
Lake Superior and will persist through the evening. Wind gusts relax
behind the front and will be near or below 20 kt for the remainder
of the forecast, with the highest chances of exceeding 20 kt coming
near a weaker cold front Saturday night and then depending on the
track of a shortwave trough, another front on Monday. Waves will be
4-6 ft over central Lake Superior tonight, subsiding below 4 ft by
Friday afternoon.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&
$$
SHORT TERM...Voss
LONG TERM...GS
AVIATION...07
MARINE...GS
Area Forecast Discussion...UPDATED
National Weather Service Morristown TN
841 PM EDT Thu Sep 19 2024
...New UPDATE...
.UPDATE...
Issued at 838 PM EDT Thu Sep 19 2024
An update will be issued to extend the chance of showers in NE TN.
HRRR shows these showers persisting until around 02Z. Will have
slight chance PoPs going a little past that time, until around
midnight, as models have been underdone with convection today. Fog
is a good bet later tonight, mainly in northern sections and near
rivers and lakes, and may be dense in some areas. We will see how
this evolves before issuing any products.
&&
.SHORT TERM...
(This evening through Friday)
Issued at 314 PM EDT Thu Sep 19 2024
Key Messages:
1. A few isolated to scattered showers, and possibly a storm,
through early evening.
2. Patchy to areas of fog overnight.
3. Dry and warmer tomorrow, with temperatures around 5 to 8 degrees
above normal.
Short term models did a poor job earlier today with the current
showers across the area. Models kept precip east of I-75 and mainly
across our higher terrain areas. Based on latest radar trends and
CU field, went ahead and put in a 15 (Slight Chance) POP for most
areas through early evening. Most locations will remain dry, but
some may cash in on a quick downpour.
Tonight, dry with patchy to areas of fog developing after midnight.
This will be especially true for any areas that receive a shower
this afternoon and evening.
Tomorrow, expect a dry day with warmer temperatures as the ridge
further builds across the area. Temperatures will be around 5 to 8
degrees above normal. Went a little lower with dewpoints tomorrow
based on today`s trends. Went with NBM10. Based on the higher temps,
we can expect min RH values down in the mid to upper 30s for some
areas. Winds remain light though which will help to alleviate most
fire weather concerns.
&&
.LONG TERM...
(Friday night through next Thursday)
Issued at 314 PM EDT Thu Sep 19 2024
Key Messages:
1. Continued well above normal temperatures (5 to 10F) through the
middle of next week.
2. Higher uncertainty for next week, but expect moderating
temperatures with gradual increase in rain chances.
Discussion:
Upper-level 500mb 590-591 dam ridge across the Southern Plains and
Lower Mississippi Valley will result in dry and warm weather into
the Tennessee Valley through the weekend. Northwest flow aloft and
subsidence will bring clear sky conditions and plenty of sunshine.
A stronger shortwave will approach the Ohio Valley by the middle of
next week with an associated surface low and cold front approaching
the Tennessee Valley on Tuesday or Wednesday. Current PoPs are
limited to 30 to 40 percent, and a look at the ensembles histogram
shows that most of these members are placing around 0.25 inch or
less across the region. Only about 15 percent of members have more
than one inch of QPF, and with the westerly zonal flow ahead of the
front, a drier solution appears more probable. If the cold front can
make it through the area, some cooler, near normal, air would be
likely late next week.
&&
.AVIATION...
(00Z TAFS)
Issued at 659 PM EDT Thu Sep 19 2024
Chance of fog appears high at TRI tonight, based on last night`s
fog plus afternoon dewpoints in the mid 60s, and a forecast low of
60. Model guidance is alo pointing to 1/4SM vis for a few hours
late tonight and Friday morning. TYS has a lower chance of fog on
the same basis, and the TAF will have MVFR vis there. Lower
dewpoints today at CHA and dry ground conditions suggest fog is
unlikely to develop.
&&
.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN 89 66 92 65 / 10 0 0 0
Knoxville McGhee Tyson Airport, TN 87 63 89 63 / 20 10 0 0
Oak Ridge, TN 89 62 89 63 / 20 10 0 0
Tri Cities Airport, TN 83 60 84 60 / 20 30 0 0
&&
.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...NONE.
VA...NONE.
&&
$$
SHORT TERM...DGS
LONG TERM....JB
AVIATION...DGS