Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/08/17
Area Forecast Discussion
National Weather Service Burlington VT
907 PM EST Thu Dec 7 2017
Lake effect snow will continue to impact parts of the
Adirondacks and St. Lawrence Valley for tonight into tomorrow
morning with some additional accumulating snowfall. Outside of
the lake effect snow, it will remain mainly cloudy and chilly
elsewhere. Although most areas will stay dry and cold over the
weekend, a coastal storm may brush eastern areas with some
light snowfall. A more widespread snowfall is expected during
.NEAR TERM /UNTIL 10 AM FRIDAY MORNING/...
As of 901 PM EST Thursday...Lake effect snow warning and winter
weather advisory continues for St Lawrence County and southern
Franklin County. Have increased pops/qpf and snowfall across
northern VT based on radar and report from near Greensboro of
3.2 inches associated with lake effect band. Based on radar have
continued to mention likely pops thru 06z with snowfall amounts
up to 6 inches possible in the most persistent bands across
northern VT. Outside of the lake effect activity mainly cloudy
with some on and off light snow showers...with little
accumulation expected. Temps mainly in the mid 20s to lower 30s
fall back into the upper teens to mid/upper 20s by sunrise.
Previous discussion below:
The 3km HRRR and NAM both show this band to gradually shift
back southward for most of the overnight, as the flow shifts
thanks to the departing shortwave aloft. However, as the next
piece of energy quickly approaches towards sunrise, the band may
once again shift back northward in response to the changing low
to mid level flow. Some additional snow showers are possible
between sunrise and the mid morning hours on Friday across the
northern Adirondacks as the band continues to slide back
northward, with an additional light accumulation in some areas.
Meanwhile, some additional light snow showers and flurries are
ongoing across the remainder of the Adirondacks and into parts
of the central and northern Greens, especially in upslope
favored areas. This snowfall won`t amount to much, but an
additional coating cannot be ruled out. Most of this should
through the evening hours, as some drier air should be moving in
for later tonight. Otherwise, skies will remain mostly cloudy,
although some breaks are possible by later tonight, especially
for larger valley areas. Overnight lows will generally be in the
mid 20s to low 30s, although some teens will occur for the
The lake-effect band should lift towards the St. Lawrence Valley
on Friday mid to late morning, but then will be weakening and
diminishing through the day, as the flow will start to become
too southerly. Any accumulation looks rather minor for northern
St. Lawrence County through the day. Elsewhere, most areas will
be partly to mostly sunny on Friday and dry, although it will
continue to be seasonably chilly with highs in the mid 20s to
.SHORT TERM /10 AM FRIDAY MORNING THROUGH SATURDAY/...
As of 400 PM EST Thursday...Lake effect snow will finally
diminish by Friday evening, as the mixed layer flow becomes more
S-SW due to an amplifying flow pattern. There could be a few
leftover snow showers in the St. Lawrence Valley during the
evening, but should end by midnight. Tranquil conditions
expected late Friday night into Saturday morning, as a small
area of high pressure settles in across the region.
Saturday will start out dry, but there will be increasing chances
for light snow by later in the day, especially across the eastern
half of VT. The upper level flow pattern is forecast to amplify as a
trough dives southeast across the central Great Lakes and Ohio
Valley region, with downstream ridging off the southeast U.S. coast.
An area of low pressure is expected to develop along a baroclinic
zone near the eastern seaboard. Precip will spread northward through
the day, and may reach eastern VT just before sunset. Model guidance
has trended north and west with the position of the baroclinic zone
and surface cyclone, especially the ECMWF and NAM, which are favored
solutions by WPC at this time. So there could be a dusting before by
sunset Saturday, mainly from the western slopes of the Greens
eastward. Temps may reach the lower to mid 30s in valleys during the
afternoon before any snow commences.
There now appears to be a somewhat better chance for light snow,
especially across VT Saturday night. The aforementioned surface
cyclone is forecast to deepen rapidly east of New England during
this time, with snow wrapping around the low farther back to the
north and west into VT. Will need to continue to watch model
forecast trends, since the heaviest axis of QPF will not be too far
away over eastern New England. The more western track is a result of
a more amplified pattern. If even stronger downstream ridging
develops, this would result in an even more westerly track.
.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
As of 400 PM EST Thursday...It will feel like winter through
the upcoming week. A cold and potentially stormy pattern may be
setting up during this time, with the probability for
accumulating snow increasing by early to mid next week.
By Sunday, the coastal storm will be well north and east of the
region, but an upper level trough will remain over northern NY and
VT. So this will result in a continued chance of snow showers.
Temperatures are forecast to be slightly below normal, with highs
mainly in the mid 20s to lower 30s.
Another short wave trough will be approaching from the upper Great
Lakes Sunday night. Ahead of this system, low level winds will back
to a SW direction in response to the approaching trough. This will
result in the potential for some lake effect snow in parts of the
St. Lawrence Valley and NW Adirondacks. It appears light
accumulations would occur though, as the upper trough moves through
by Monday and shifts the winds to more of a westerly trajectory.
Will continue to mention chances for snow showers associated with
the trough passage on Monday.
Then, attention shifts to another potential coastal storm that may
impact the region Tuesday into Wednesday. The ECMWF is indicating a
developing cyclone just south of Cape Cod on Tuesday, then rapidly
intensifying Tuesday night as it potentially tracks into the Gulf of
Maine. A deep upper trough over the lower Great Lakes may close off
in the mid levels over SE New England by Wednesday. This could
result in a prolonged snow event depending on the evolution/track of
the system. The GFS is also depicting a developing storm, but
farther west due to a shallower upstream upper level trough with
strong isentropic lift in northern NY/VT. So despite the model
spread, there is a signal for possible widespread accumulating snow
during the time.
Colder and breezy conditions expected Wednesday night into Thursday,
behind the departing storm. Again, snow showers cannot be ruled out
in the cold/cyclonic flow regime.
.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
Through 00Z Saturday...Lake effect snow band impacting SLK, PBG
and BTV currently. SLK has IFR conditions, while other sites are
remaining VFR. Skies will be BKN-OVC at 3500-5000 ft with VFR
conditions and SW winds around 5-10 kts. A few higher gusts are
possible for the higher elevations. Overnight, lake-effect
should gradually meander away from SLK, although there could be
some additional snow showers there towards daybreak Friday. By
mid-morning Friday, VFR conditions are expected through the day
for all sites, with sct-bkn cigs around 4-5 kft. Southwest winds
will increase during daytime mixing to around 5-10 kts with
some higher gusts at times, especially over the higher terrain
and within the St. Lawrence Valley.
Friday: VFR. Slight chance SHSN.
Friday Night: VFR. NO SIG WX.
Saturday: VFR. NO SIG WX.
Saturday Night: VFR. Slight chance SHSN.
Sunday: Mainly VFR, with local MVFR possible. Chance SHSN.
Sunday Night: Mainly VFR, with areas MVFR possible. Chance SHSN.
Monday: Mainly VFR, with areas MVFR possible. Slight chance SHSN.
NY...Lake Effect Snow Warning until 7 AM EST Friday for NYZ029-087.
Winter Weather Advisory until 7 AM EST Friday for NYZ030.
Area Forecast Discussion
National Weather Service State College PA
1030 PM EST Thu Dec 7 2017
A wavy low pressure area may come close enough to affect
southeastern areas Saturday, otherwise the region will remain
dry. An upper trough will reinforce the cold air for Sunday
followed by a number of weak Alberta-Clipper type systems that
could keep us unsettled for much of next week.
.NEAR TERM /UNTIL MIDNIGHT TONIGHT/...
The snow showers that brought some localized light accumulations
earlier today, are now pretty much just a few leftover flurries
as of 10 PM.
A single lakeshore parallel LES snowband will remain near, or
just a few miles to the north of the I-90 corridor in far NW PA.
Latest HRRR suggests that the extreme southern edge of the band
may affect far NW Warren county for a while this evening, but
overall the bulk of the snow should remain north of the area.
Accums over Warren county will be an inch or less.
Elsewhere, central and eastern areas will see partly to mostly
cloudy skies with little more than a stray flurry.
Overnight lows in the mid teens to mid 20s will average a few
deg below normal.
.SHORT TERM /MIDNIGHT THROUGH 6 PM FRIDAY/...
The mean boundary layer flow backs to the SW again by shortly
after 05Z Friday, causing the persistent band of LES to shift
north again into SWRN New York.
As previously noted, tonight will be the best chance for snow
accums across the far NW zones. Will let it top out at 2 or 3
inches in far NW Warren Co, less than inch elsewhere in the NW
mtns. Elk county could even stay flurry-free as the fetch is
rather poor to get any bands there.
Any flurries and patchy 2-4SM light snow in the
southwest/central counties during the evening will dissipate as
weak forcing aloft moves off to the east. No additional accums
are expected there. Clouds should break up. Mins should be into
the teens west and L-M20s elsewhere, but will not drop too
drastically with some wind still going through the night.
It does seem like the gradient relaxes some on Friday
(especially across southern PA) as a ridge of high pressure at
the sfc extends from the Ohio River Valley to the Southern New
England Coast, so expect there to be a little less westerly wind.
Max temps will be 4-7F colder than Thursday`s. The old front
off to the SE may continue to push cirrus over the SErn cos, but
few other clouds will be found across the central and northern
2/3rds of the CWA.
.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
Central PA will contend with two winter weather systems this
weekend which could bring snow to different parts of the area.
Temperatures will trend progressively colder through the
weekend, with the coldest air of the season gradually taking
hold by the middle of next week.
The first system is a low pressure wave lifting north along a
stalled frontal boundary draped from the Gulf Coast into the
western Atlantic. 07/12z models have trended further northwest
with the low track in response to a sharper upstream trough and
more pronounced ridging downstream. This trend also resulted in
a northwest shift in the precip shield which introduces low
probs for snow as far west at the I-81 corridor. The 12z ECMWF
is the farthest NW with its precip shield vs. GFS/WPC/NBM. The
middle ground "edge" is probably somewhere between I-81 and
I-95 at this time. Subtle shifts in the low track will make the
difference in a potential period of light snow Saturday across
the Lower Susquehanna Valley. If models continue to trend NW,
snow risk will increase for places such as Harrisburg and
Lancaster and may extend to the west of the Susq. River into
interior parts of central PA. Continue to monitor the forecast.
The second system is a clipper tracking eastward from the Great
Lakes and eventually merging with the strengthening storm off
the Northeast coast by the second half of the weekend. Snow
showers with light accumulations are most likely over the
higher terrain of the Alleghenies but may coat the ground quickly
into parts of east-central PA. A period of lake effect and
orographic snow showers should continue into Sunday with gusty
winds and wind chills in the single digits and teens.
Lake effect trajectories back to the west-southwest into Monday
as the next shortwave digs southeast through the MS/OH Valley.
There is a decent model spread in the low track and evolution
of this system, but regardless of the details this feature
should provide a good opportunity for most of the area to see
some snow early next week. The coldest air of the season is
forecast to arrive behind this system with a shot of arctic air
and more lake effect snow lasting through midweek.
.AVIATION /04Z FRIDAY THROUGH TUESDAY/...
Bands of snow showers from the gusty westerly flow will continue
through central PA through the first half of the evening. JST is
seeing VLIFR cigs and vsbys. The snow bands are wavering though
periods of IFR and lower will continue until lifting between
00Z to 03Z.
Otherwise, widespread VFR conditions are anticipated for the
rest of the night and into tomorrow as another ridge of high
pressure will build over the PA airfields behind the cold front
tonight. This will bring a diminishing westerly wind, and
resulting VFR conditions across most, if not all, of the
forecast area. Will have to watch KBFD and KJST, where upslope
flow could potentially yield tempo MVFR to IFR cigs tonight
into Friday morning.
Fri...No sig wx expected.
Sat...Thickening clouds with late afternoon and nighttime snow
showers/vis reductions poss Allegheny Plateau.
Sun...AM snow showers/vis reductions poss Allegheny Plateau.
Mon...PM light snow possible, mainly northwest Pa.
Min night and Tuesday...Periods of snow and snow showers.
Widespread MVFR likely, with periods of IFR and brief LIFR cigs
NEAR TERM...La Corte
Area Forecast Discussion
National Weather Service Cheyenne WY
450 PM MST Thu Dec 7 2017
.SHORT TERM...(Tonight - Saturday)
Issued at 124 PM MST Thu Dec 7 2017
Light snow showers will linger through this afternoon, mainly over
southeast Wyoming. Overall impacts from this activity will be low,
but heavier showers could create slick roads and low visibility in
some areas. Any accumulations will be less than an inch, except in
the Snowy and Sierra Madre mountains where several inches may fall
through tonight. Mid-level energy is expected to move southeast of
the area by 00z, effectively ending precipitation chances for some
time to come.
High wind concerns for tonight and Friday. A significant upper-lvl
jet will set up over the central Dakotas, placing much of the high
plains in the RFQ of a 120+ knot H25 jet streak. The models are in
good agreement with H7-H8 flow of 55-65 kts along/E of the Laramie
Range between 06z and 12z, and an impressive W-E pressure gradient
along the spine of the Laramie Range. This, combined w/significant
subsidence may yield 50+ knot gusts over the I80 summit, and maybe
even Bordeaux as well despite northwest flow typically being an un
favorable pattern. We opted against High Wind Warning issuance for
the time being based on the pattern, and the fact that the HRRR is
only showing around 40 knot gusts through 12z. The latest forecast
soundings from the GFS also show enough of an inversion to support
the restriction of downward momentum transfer. Later shifts should
monitor this closely, however.
The GFS shows H7-H8 flow remaining in the 50-55 knot range through
mid/late Friday afternoon. This could become a concern with clouds
diminishing and improved low-level mixing after 18z. We anticipate
much of the high plains to be very close to warning-level winds on
Friday afternoon, w/ mixing and subsidence likely supporting 50-55
MPH gusts for all areas along/e of the Laramie Range. The question
mark right now is mixing depth, so confidence right now is too low
to warrant High Wind Watch/Warning issuance. We would also like to
see higher numbers on MAV/MET guidance for any highlights.
.LONG TERM...(Saturday Night - Wednesday)
Issued at 210 AM MST Thu Dec 7 2017
Weather dominated by ridge of high pressure to the west. We stay
in northwest flow. Clipper systems look to stay east of Wyoming
and western Nebraska. Dry forecast expected through Thursday.
.AVIATION...(For the 00Z TAFS through Friday afternoon)
Scattered light snow showers are possible around KLAR and KCYS this
evening, resulting in brief IFR conditions. Otherwise, conditions
will improve tonight with increasing CIGS and dry conditions. It
will remain windy through Friday though with gusts up to 40 knots
expected, mainly across the eastern plains of southeast Wyoming and
Issued at 210 AM MST Thu Dec 7 2017
Breezy to windy conditions will persist mainly east of the mtns
today through Friday with a bit less wind on Saturday. Min
humidities well above critical thresholds today then they do get
down to around 20 percent across far se Wy into the southern Neb
Panhandle both Friday and Saturday so a bit of an elevated
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1005 PM EST Thu Dec 7 2017
A moist frontal zone will linger just to our southeast through the
end of the work week allowing temperatures to drop below normal with
light wintry precipitation possible for Friday and Saturday. A cold
upper level trof will then re-amplify over the area later on Saturday
and bring a shot of snow showers to the North Carolina mountains.
Cold temperatures will persist into the first half of next week.
.NEAR TERM /THROUGH FRIDAY/...
As of 1000 PM EST Thursday: Have expanded the Advisory farther into
the NC mountains and NW NC Piedmont, and upgraded to a Winter Storm
Warning for Habersham and Rabun. To the details...event unfolding in
TX is either at or above some of the predicted levels, and HRRR is
actually doing a pretty good job of nowcasting the event, so would
like to think that the rest of the HRRR forecast is in line.
Guidance continues to bump up QPF. Atmosphere is slowly saturating
so evaporational cooling will of course have a limit, but concern
with incoming CAA will be the dynamic cooling and diabatic effects,
specifically the cooling of the surface layer from the latent heat
of melting, which will serve to continue to lower the snow layers
without a source of low-level WAA (and there really isn`t one). KFFC
00z sounding had a bit of a warm nose just above 800mb but that
should erode by the time precip gets this far north. 00z NAM bufr
soundings show a deep near-freezing isothermal layer with gradually
dropping snow levels here at GSP through the night (using the
thickness nomogram is a bit misleading with the near-freezing layer
so deep). So even with the increased QPF, think snow ratios might
not be quite as high and so have not increased snow amounts quite as
much as the QPF would suggest. In any case, since WSW criteria for
GA is 2", Rabun should easily get it, and northern Habersham as
well. Most of the SC mountains should easily get 2", but WSW
criteria for SC is 3" (4" for NC), so for now have kept SC and NC to
advisories. Would not be surprised to see the rest of the NC
mountains added to the advisory or expanded east more into the
Piedmont (right now Burke/Cleveland/Rutherford Counties are really
only included because of the Southern Mountains). Graham and Swain
actually do not currently have advisory-criteria snow amounts, but
for consistency`s sake, made sense to go ahead and include them.
Otherwise, guidance is coming into better agreement regarding the
precip potential for tonight and Friday. Deep moisture moves in this
evening with decent upper divergence from the right entrance region
of the upper jet. Short waves move over as the upper trough deepens
to the west. Low level isentropic lift develops as well, but remains
relatively weak with abundant moisture. Despite an overall cooling
trend in forecast temps and surface wet bulb values, they remain
above freezing through the night outside of the mountains, but do
fall below freezing across the mountains. Of course, precip chances
are lower where temps are colder since those locations are farther
away from the better forcing. Therefore, have snow developing in the
colder locations with mainly rain elsewhere. Forecast soundings show
the freezing level dropping low enough for snow to mix in north of I-
85 with a change over possible across the Northern Foothills. QPF is
light but could be enough for around half an inch of snow along and
near the NC/GA to NC/SC border mountain locations. Snow would be
less across the rest of the mountains.
Categorical precip chances continue generally along and south of I-
85 Friday with likely chances north of there across the foothills to
along the Blue Ridge. Good chance PoP west of there. Temps and
surface wet bulbs remain cold enough for the precip to fall as snow
across the mountains with a transition zone across the NC Foothills.
Outside of these areas, freezing levels may fall low enough for snow
to mix or possibly even briefly change over early in the morning
mainly along and north of the I-85 corridor. QPF has increased on
some of the guidance runs which increases the potential for advisory
level snow across the NE GA and Upstate mountains, along with the
Southern Mountains and possibly portions of the NC foothills. After
final national guidance is in, we may need to update to post an
advisory for those locations. While these accums would develop in
grassy and elevated areas, it is still questionable how much
accumulates on roads given the recent warmth and sunshine. Locations
where the precipitation will be mixed or only a brief change over,
no significant accums are expected with any small amounts limited to
grassy or elevated areas.
.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
As of 230 PM Thu: We will remain slightly on the cold northwest
side of a surface frontal boundary through early Saturday. Models
are now more supportive of a resurgence in precipitation over the
CWFA Friday night, as the sharp shortwave moves into the central
Gulf states, and the jet streak strengthens over the southern
Appalachians and adjacent Piedmont. GFS and EC hold the thermal
gradient relatively steady over the area thru the night; wet-bulb
temps do gradually drop across the southeast half of the CWFA,
which should permit snow to mix in with rain if not totally change
over. However, the area with wet-bulb values at or below freezing
looks likely to expand little. This minimizes the accumulating
snowfall in the greater I-85 corridor.
QPF trends overall have been upward this cycle for the Friday night
period, particularly over the Blue Ridge and adjacent mountain
ranges (namely the Balsams); compare this to earlier suggestions
that all precip may have ended there by 00z Sat. In collaboration
with our neighboring offices, we will wait another cycle to see if
this trend continues before reflecting the higher numbers in the
forecast for these mountain areas. It is possible an additional
couple of inches could result and headlines still could be needed.
Another minor yet potentially significant trend in models is for
Saturday. As before, consensus suggests strong DPVA pushing thru
the area during the day along the trough axis. The difference is
that several sources depict the moisture departing more slowly,
and hence the vort max generates some QPF. By the time this
precip develops it could have warmed up enough to fall as rain,
particularly in the east. However this is something for us to
watch closely. A small amount of SBCAPE is depicted in parts of
the eastern CWFA to boot; however it slightly lags the forcing and
colder temps. For now PoPs will be allowed to linger thru Saturday
morning over our eastern zones; temp trends suggest this will be
a rain-snow mix changing back over to rain as it ends.
Winds veer Saturday afternoon as stronger cold advection sets
in across the area. The final phase of precip in this period
thus will be northwest-flow driven snow showers along the Tenn
border, developing by late afternoon, and continuing through early
Sunday. Thermo profiles look reasonably good in terms of saturation
at snow-growth temperatures, which given the very cold air spilling
into the area will be in the upslope layer. Current expectation
is for about another inch to fall Saturday night along the spine
of the Appalachians. Brisk and gusty winds in this same timeframe
may bring wind chills below zero on the higher mtn ridges.
Settled weather is expected Sunday as dry high pressure builds
across the South. Despite abundant sunshine, the very cold nature
of the airmass will be reflected in max temps 11-13 degrees
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
As of 210 PM EST Thursday: the extended fcst picks up at 00Z on
Monday with the broad upper trof lifting NE and over New England
while steep upper ridging persists over the Western CONUS. By early
Tuesday, the long range models re-amplify the upper trof again over
the eastern half of the CONUS bringing more widespread cold air to
the region and keeping temperatures well below normal for most of
the period. By early Wed, the trof axis is expected to be moving
over the fcst area or lifting just NE of it. Beyond this point,
the trof broadens and flattens, but still remains in place over
the entire Eastern CONUS. At the sfc, another progressive low will
surge SE and across the Great Lakes on Monday and bring another cold
front to our doorstep by late Monday/early Tuesday. The front is
expected to move thru the CWFA quickly and be SE of the fcst area
by late Tues/early Wed with high pressure moving back over the area
to end the period.
.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
At KCLT and elsewhere: No changes to the KCLT TAF for the 02z
AMD. VFR conditions this evening will slowly deteriorate overnight,
with cigs dropping to MVFR and IFR (likewise for VSBY) as moisture
increases from the S. Cannot rule out brief improvement during the
day Friday to MVFR, but generally fairly solid IFR conditions
expected. Precip chances continue to increase but should remain all
liquid for all but KAVL through 00z. Have introduced PROB30 -RASN
for KCLT after 00z Saturday, and will likely have to do the same for
other TAFs with the 06z set. For KAVL, though the precip will be
light, it will most likely be mostly
-SN (with perhaps some -RA mixed in) through the period. SSW winds
this evening will trend lgt/vrb overnight before swinging NE before
sunrise and remain there through the end of the period (except KAVL
where NNW winds will prevail).
Outlook: Restrictions will be likely as well as mixed/wintry precip
through Saturday morning. Precip and associated restrictions will
decrease during the day Saturday, with dry conditions expected at
all sites into early next week. The possible exceptions would be
KAVL/KHKY with potential for northwest flow snow Saturday night.
15-21Z 21-03Z 03-09Z 09-12Z
KCLT High 81% High 82% Med 68% Low 56%
KGSP Med 70% Med 75% High 83% Med 64%
KAVL High 94% High 85% Med 70% High 87%
KHKY High 100% High 83% Med 66% High 100%
KGMU Med 76% High 86% High 85% Med 63%
KAND Med 76% Med 65% High 90% Med 61%
The percentage reflects the number of guidance members agreeing
with the scheduled TAF issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables and ensemble forecasts
are available at the following link:
GA...Winter Storm Warning from 5 AM Friday to 7 AM EST Saturday for
NC...Winter Weather Advisory from 5 AM Friday to 7 AM EST Saturday
SC...Winter Weather Advisory from 5 AM Friday to 7 AM EST Saturday
Area Forecast Discussion
National Weather Service Houston/Galveston TX
951 PM CST Thu Dec 7 2017
Winter Weather Advisory in effect across the north areas for snow
and icy roads.
Specifically for the Caldwell to College Station to Madisonville
area. Brief heavy snow occurred earlier this evening...no more
significant snow is expected for those areas that had the
heaviest snow. 4-6 inches observed in and around the College
Station area per social media and KBTX. Stressing that although
the precip may be over there the impacts may be getting worse.
Snow packed roads are going to get icy as well as bridges. Texas
Department of Transportation has already begun treating. Traffic
impacts may be significant overnight/early Friday. Temperatures
will struggle to get above freezing until probably 9 am with all
the snow on the ground there.
Elsewhere...the band of intense snow that was over Caldwell to
College Station to near Madisonville showing some signs of
weakening and sagging southward. Temperatures beneath the band are
running 31 to 32 thanks to wet-bulbing and is helping to account
for the accumulations. To the north of the band temperatures 35-37
and south of the band 39-42 (across the Houston area). The RAP
and HRRR have been doing a good job tonight in capturing the
focused nature of the heavier precip near CLL. GRK radar clearly
showing the drier air infiltrating and the precipitation weakening
and shifting southward. Based on current guidance looking like
two bands are likely to develop a weaker band along the southern
edge of the advisory with a second more intense band translating
up the coast and parking over the coastal counties from Jackson to
Brazoria county. AMDAR soundings (HOU/IAH) all showing the
transition over to freezing around 1700ft with freezing profile
above. As the next band develops think that rain/snow mix will
predominate across the southern areas gradually transitioning over
to mainly snow. Temperatures are forecast to remain at or above
freezing to the south of the advisory including the Houston Metro
area so the snow should melt on contact with roads. Could car
roof/grass/home rooftops accumulate a little snow yes. Areas
across Matagorda and Brazoria county might bottom out at 33 or
even 32 for an hour or two during the peak intensity but then
rebound so still just grassy areas with any accumulation.
PREV DISCUSSION... /ISSUED 619 PM CST Thu Dec 7 2017/
A band of light rain with embedded pockets of snow and sleet has
set up near CLL and UTS with light rain continuing near
IAH/SGR/HOU/LBX/GLS. Expect the wintry mix to continue near CLL
and UTS through 03Z and provide periods of IFR to MVFR ceilings
and visibilities before shifting south between 03-06Z as drier air
arrives and an upper level jet streak slides across the lower
half of region from Mexico. While VFR is expected to prevail,
heavier rain/snow bands will again result in IFR to MVFR ceiling
and visibility restrictions for the Houston/Sugar Land and coastal
terminals. Greatest potentials for terminal impacts to
Houston/Sugar Land is expected to be between 04-11Z, persisting
slightly longer along the coast before precipitation shifts south
of the coastal terminals by 14-16Z with VFR ceilings continuing to
lift and scatter by the end of the TAF period. Northerly winds in
the 8-15 knot range will continue inland tonight, with winds in
the 10-20 knot range for LBX and GLS. Stronger gusts near 30 knots
will be possible at GLS through Friday morning. Expect winds to
fall below 10 knots at inland terminals by the end of the TAF
period as surface high pressure builds into the region.
.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL) 29 50 32 60 34 / 100 0 0 0 0
Houston (IAH) 33 48 33 59 37 / 70 10 0 0 0
Galveston (GLS) 38 48 42 59 46 / 80 30 0 0 0
TX...Freeze Warning until 7 AM CST Friday for the following zones:
Winter Weather Advisory until 9 AM CST Friday for the following
GM...Small Craft Advisory until 6 AM CST Friday for the following
zones: Coastal waters from Freeport to the Matagorda Ship
Channel out 20 NM...Coastal waters from High Island to
Freeport out 20 NM...Galveston Bay...Matagorda Bay.
Gale Warning until 6 AM CST Friday for the following zones:
Waters from Freeport to the Matagorda Ship Channel from 20
to 60 NM...Waters from High Island to Freeport from 20 to
Area Forecast Discussion
National Weather Service New Orleans LA
745 PM CST Thu Dec 7 2017
Still an over-running pattern sounding but with some significant
features that are lending clues to what may unfold. Temperature
41F at the surface only cools to 38F at 1200 ft, then remains at
38F to 2700ft, which is sub-cloud dry air. Saturated inversion
layer from 850mb/4300ft, 31F at base warms to 39F at
720mb/9000ft. Then moist adiabatic lapse rate to tropopause found
at 100mb with a temperature of -70C. Winds NE 20-30kt surface to
4900ft, SW 10-108 kt above 4900ft. Peak wind 226/108kt at
Some winter micro-meteorology...a top down approach for
precipitation determination shows snow formation from 20kft
falling into a dry layer between 14kft and 11.5kft as snow virga
that melts in the warm layer from 9kft down. A 7 degree dewpoint
depression at 2600ft would yield a wet-bulb around 2C/35F, which
means a cold rain but still too warm to support sleet or snow. How
tough is the call right now? Currently 3 freezing levels noted,
the primary one at 12.9kft where the bright band melting level is
noted on radar, then a lower level shallow freezing layer between
4999ft and 4852ft - a mere 147 ft of depth for any warm raindrop
to transition into an ice pellet. As more rain aloft falls into
the column, it will slowly deepen the depth of the freeze zone to
support better sleet production later tonight. It will still take
more cold air advection in the low and sub-cloud layer to support
snow production, which may still arrive by daybreak Friday.
Surface analysis shows 40s surface temps for much of LA and south
MS at this time. Dual Pol radar hydrometeor classification loop
does show a transition zone aloft aligned from roughly McComb to
Lafayette, LA with dendritic snow north of this zone and liquid
rain south of the zone. This is the more favored corridor for any
wintry precipitation in time, but cold air advection will have to
become more pronounced and agressive to cool the lower part of the
sounding. Did receive a report of rain mixing with sleet near
Easleyville in St Helena Parish and this does match well with the
dual pol data.
Finally, balloon burst at 15 mb some 17.4 miles up over highway 63
in George Co MS south of Lucedale. 24/RR
.PREV DISCUSSION... /issued 432 PM CST Thu Dec 7 2017/
Latest surface analysis showed an elongated 1012mb low over west
central and central Gulf. Tight pressure gradient 8mb change from
27N to the mouth of the Mississippi river. The secondary cold
front from northern Georgia to west central Mississippi to
southeast Texas. Dry air with dewpoint readings in upper 20s to
low 30s behind the front across northern Louisiana and west and
northwest Mississippi. Upper air analysis showed the trough axis
from the Great Lakes to west Texas. Regional radars showed a rain
swath from Southeast Texas to the north half of our forecast area
to central Alabama. This morning, we received several reports of
sleet mixed in with rain but no accumulation and no reports of
sleet after 12 pm.
Special 18z sounding indicates continued cooling in the low levels
of the atmosphere, but the mid-levels remain rather warm. 850mb
temperatures cooled nearly 5C from the 12z sounding, and a small
layer of air extending for less than one thousand feet has fallen
below freezing at this level. However, temperatures from 800mb up
through 650mb remain quite warm with only a 1C drop in
temperatures observed at 700mb. As a result, a significant warm
nose of around 3.5C remains in place at this level. Until this
warm nose aloft drops to 2C or less, the prospect of freezing
precipitation will remain limited. Some slight drying of the
atmosphere also occurred with precipitable water values falling
from 1.1 inches to 1.0 inch in the last 6 hours. However, the
atmosphere remains quite saturated above 850mb due to continued
strong southwest flow in the mid and upper levels of the
atmosphere. Our office will carry out an upper air flight
observation tonight 06z Friday. 32
The main trough axis will continue to press south and west to
southwest flow is expected to continue with the jet stream
positioned from Big Bend Texas to central Louisiana to Ohio
Valley Friday morning. 850-700mb relative humidity values have
the drying demarcation line northwest of the forecast area at 12z
according to SREF, NAM, GFS and EURO and EURO the most aggressive
with drying from Walthall to Morgan City at 18z. Most show the 0C
line from Southeast Mississippi to Morgan City with west flow
advect in colder and dry air by 18z. Freezing levels off of GFS
and EURO are more agreement with levels around 2000 ft around and
north of Baton Rouge at 06z tonight. Could see some rain mixed
with sleet this evening around midnight but transition will likely
occur between 06z and 12z Friday across Southwest Mississippi and
areas north of Baton Rouge.
A swath of freezing and frozen precipitation will develop near
and around Baton Rouge stretching northeast toward Pike as cold
air moves in and moisture lags to exit east. HRRR paints a swath
from Baton Rouge to Walthall, SREF paints a swath just north of
Baton Rouge to Walthall and GFS paints a swath from Terrebonne to
just west of Lake Pontchartrain to Southeast. The common area
covers Amite, Pike and Walthall counties and St Helena, northern
Tangipahoa and Washington parishes. We up the snowfall total to 2
inches for this concerned area and this area could possibly be
upgraded to a winter storm warning. In addition, we added
parishes west of Lake Pontchartrain to the Winter Weather
Upper level trough will push through slowly with the axis from
New York to Southeast Louisiana to west Gulf and moisture pushing
east Friday evening. Surface temperatures are expected to warm to
the upper 30s Friday afternoon for most area. However, cold air
will continue to filter in Friday evening and linger rain showers
could mix with snow flurries over the Mississippi Coast and south
of Lake Pontchartrain Friday evening. No accumulation is expected.
A pretty good freeze is expected across the forecast area except
south of tidal lakes. A few areas across southwest Mississippi
will flirt with a hard freeze Saturday Morning. Upper level
trough will remain over the eastern CONUS as the last disturbance
sweeps through Saturday night. The main trough will remain over
the eastern CONUS through next week and another shot of cold air
Tuesday will maintain cold temps. As a result, all areas will
experience dry weather and below normal temperatures Saturday
through next Thursday.
As a surface low moves east through the Gulf, it will interact
with strong high pressure moving south over inland areas causing
winds to remain elevated. Northerly winds will remain around 20 to
25 knots over mainly protected waters, but winds will rise to 30
to 35 knots as one moves farther offshore over the open gulf. A
gale warning remains in effect for most of the open gulf waters
through noon Friday and gusts could reach well into the 40kt
range through Friday morning in these areas. Winds will ease and
likely drop a bit below Small Craft Advisory (SCA) criteria over
tidal lakes, sounds and nearshore coastal waters Friday night or
Saturday, but remain well into SCA criteria for offshore coastal
waters well into the day Saturday.
This prolonged strong northerly wind event will also drive water
away from the coast causing very low water levels especially for
inland navigable waterways. A fairly steady cold rain will be the
norm for all marine areas through the day Friday, and these
conditions will set the stage for hypothermia conditions. Dry
conditions will return for the weekend, but it will remain on the
cold side despite winds easing by Sunday.
All terminals will be impacted by lowered cigs and reduced vsbys
at times. Biggest concern at first will be lower cigs with MVFR
conditions but these should lower further from west to east after
6z. Locations like BTR and MCB may have to deal with moderate to
heavy snow at times between 9-15z The line of rain will continue
to push east through the morning and expect all terminals to see
at least some mix of precip before 18z. /CAB/
DSS code: Blue.
Activities: Small Craft Adv
Winter Weather Advisory
Decision Support Services (DSS) Code Legend
Green = No weather impacts that require action.
Blue = Long-fused watch, warning, or advisory in effect or
high visibility event.
Yellow = Heightened impacts with short-fused watch, warning or
advisory issuances; radar support.
Orange = High Impacts; Slight to Moderate risk severe; nearby tropical
events; HazMat or other large episodes.
Red = Full engagement for Moderate risk of severe and/or
direct tropical threats; Events of National Significance.
.PRELIMINARY POINT TEMPS/POPS...
MCB 33 38 27 54 / 80 60 10 0
BTR 34 38 27 54 / 80 70 10 0
ASD 36 39 29 54 / 90 80 20 0
MSY 39 40 35 54 / 90 80 20 0
GPT 38 39 33 53 / 90 80 30 0
PQL 37 39 31 54 / 90 80 50 0
LA...Winter Weather Advisory until noon CST Friday for LAZ034>037-039-
GM...Small Craft Advisory from noon Friday to 6 AM CST Saturday for
Gale Warning until noon CST Friday for GMZ550-552-555-570-572-
Small Craft Advisory until 6 AM CST Saturday for GMZ536-538-557.
Small Craft Advisory until noon CST Friday for GMZ530-532-534.
MS...Winter Weather Advisory until noon CST Friday for MSZ068>071-077-
GM...Small Craft Advisory from noon Friday to 6 AM CST Saturday for
Gale Warning until noon CST Friday for GMZ552-555-570-572-575-
Small Craft Advisory until 6 AM CST Saturday for GMZ538-557.
Small Craft Advisory until noon CST Friday for GMZ532-534.
Area Forecast Discussion
National Weather Service Newport/Morehead City NC
941 PM EST Thu Dec 7 2017
A stationary front will remain offshore through the end of the
week as areas of low pressure develop along it. An arctic air
mass will move in over the weekend behind a stronger cold front.
Another cold front will move through by mid week.
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
As of 935 PM Thursday...Radar trends show rainfall again
starting to increase from the southwest, which is verified by
the latest HRRR and RAP models. Current forecast in good shape
with minimal changes needed. Low temperatures overnight in the
upper 30s to lower 40s in most areas with mid 40s Outer Banks.
.SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/...
As 315 PM Thurs...Waves of low pressure will continue to provide
an extensive area of stratiform rain Friday. With the front
stalled in place, and good lift available ahead of a very deep
trough over the central US, moderate to locally heavy rain will
fall for the majority of the day. Have definite PoPs for all
areas as a result. High temps will only reach the low 40s
inland, and the upper 40s along the coast.
.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
As of 330 PM Thurs...Models continue to indicate Arctic air
mass spreading in over weekend. Some model differences persist
on timing of precip ending Saturday, otherwise in good agreement
most of period. Only minor adjustments to POPs and temps with
Friday Night through Saturday...Models remain in good agreement
of wet pattern this period as slow moving upper trough from
eastern Canada to SW U.S. will tap atmospheric river from
Pacific Ocean for favorable overrunning precip development with
frontal boundary stalled offshore. Some enhanced lift expected
late Friday into early Saturday as upper trough axis approaches
and produces stronger low pressure development offshore. This
will result in periods of moderate rain into Saturday with storm
total rainfall of 1 to 2 inches, heaviest along and east of Hwy
Main core of colder air mass will remain west and north of area
until Saturday. Still looks mainly likely cold air moving in as
moisture exits but enough support to mention rain possibly
mixed with some light snow over west/northwest portions of
Duplin-Martin counties Saturday morning. No accumulation
expected due to relatively warm ground temps.
Temps mainly between 35-45 degrees most of period except some
highs near 50 along coast.
Saturday night through Monday...Arctic air mass will spread
over area producing temps 10-15 degrees below normal. Coldest
temps expected Sunday night/Monday morning with better
radiational cooling conditions with lows in lower 20s for inland
areas. Could see some frost or light freeze for Outer Banks
where growing season has not ended. Highs Sunday mainly in 40s,
moderating to around 50 Monday.
Monday night through Tuesday...Approach of next upper trough
will lead to moderating air mass Monday night and low chance POP
for showers on Tuesday afternoon, mainly as core of upper
trough moves across. Some potential for mixed precip or light
snow showers but not enough confidence to mention at this time.
Tuesday night and Wednesday...Another arctic surge will impact
area with lows 25-35 and highs near 40.
.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
Short Term /Through 00Z Saturday/...
As of 6 PM Thursday...Trends from model time sections and
numerical guidance continue to indicate that the current VFR
conditions will quickly drop to IFR between 06z and 09z as
precipitation increases in coverage and becomes steady. With
deep moisture and a NE flow below 850 mb, would expect those low
ceilings of around 1000 ft to stay locked in through the day on
Friday as well with periods of light to moderate rain.
Long Term /Fri Night through Monday/...
As of 330 PM Thursday...Sub-VFR conditions likely with
widespread overrunning precip through Saturday. Conditions
improving to VFR Saturday night and persisting rest of period
with drier and colder air mass building in.
Short Term /Tonight and Friday/...
As of 940 PM Thursday...No big changes to the marine forecast as
winds remain NW/N at 10 knots or less with seas of 2-3 feet with
some long period swell energy (12-13 seconds). Winds veer to
more Northerly overnight and increase to 10-15 knots. Winds
Friday morning will increase more to N 15-20 kts, and then 20-25
kts by Friday evening. Seas will remain steady 2-4 ft through
Friday morning, and then increase to 3-5 ft Friday afternoon.
Seas 6-8 ft are expected by Friday night. As a result of these
expected conditions, a Small Craft Advisory has been issued for
the coastal waters from Surf City to Oregon Inlet, and also for
the Pamlico Sound from Friday morning through most of the
Long Term /Friday Night through Monday/...
As of 330 PM Thurs...Behind the low pressure system Friday
night, winds will become NW and diminish slightly on Saturday
but then increase to 20-25 KT most of waters Sat night into
Sunday as arctic air mass moves in. Winds diminish again late
Sunday and Sunday night but then become SW and increase to 15-25
KT late Monday.
Seas 3-5 FT early Friday will build to 5-7 FT Friday night and
remain elevated into Sunday, subsiding to 3-5 Ft Sunday night
MARINE...Small Craft Advisory from 7 AM Friday to 3 PM EST Sunday for
Small Craft Advisory from 11 PM Friday to 11 AM EST Saturday
Small Craft Advisory from 1 PM Friday to 3 PM EST Sunday for
Area Forecast Discussion
National Weather Service San Francisco Bay Area
338 PM PST Thu Dec 7 2017
.SYNOPSIS...High pressure will keep clear and dry weather in place
the rest of this week and through the weekend. Look for mild days
and cool nights.
.DISCUSSION...as of 12:48 PM PST Thursday...The quiet weather
pattern continues across the San Francisco Bay Area and central
California coast this afternoon. An upper level ridge remains
parked over the West Coast, bringing plentiful sunshine and above
normal afternoon highs region-wide. Visible satellite imagery does
show areas of smoke aloft over the central coast this afternoon
as winds between 850 and 700 mb (approx 5,000 to 10,000 ft MSL)
have a southerly component. High temperatures this afternoon will
max out in the 60s and 70s across the region with some areas in
interior Monterey County approaching 80 degrees. This equates to
about 6 to 12 degrees above early December climatological normals.
Forecast models continue to advertise much of the same for the
foreseeable future as high pressure won`t be going anywhere
anytime soon. The mostly clear skies and long December nights will
allow for sufficient nocturnal cooling and chilly overnight lows
in the 30s and 40s. While overnight lows are not expected to be
as cold as the past several nights, parts of the southern Salinas
Valley and even areas of the North Bay Valleys could see some
patchy frost the next few nights.
So far this water year (beginning October 1) downtown San
Francisco has recorded 3.16 inches of rain, or about 2 inches
below the 30-year normal from October 1 to December 7. If long-
term guidance becomes reality, wouldn`t be surprised if the water
year total holds at 3.16 inches into third week of the month. Both
the Climate Prediction Center`s 6 to 10 and 8 to 14 day
precipitation outlooks (valid December 12 to 16 and December 14 to
20) gives much of the West Coast high confidence of experiencing
below normal precipitation through the period. While the upper
level ridge remains stationary over the West Coast, expect the
dry conditions to prevail.
.AVIATION...As of 03:38 PM PST Thursday...For 00z tafs. VFR
conditions with generally light and variable winds. Locally gusty
offshore winds along coastal gaps, primarily through the Golden
Gate, San Bruno gaps and in the Salinas Valley are to be expected.
Smoke from the southern California wildfires appears to have
gotten swept up in the ridge bringing high level smoke to the
area. The HRRR smoke forecast suggests this will continue tonight
and tomorrow with periods of reduced visibility possible.
Vicinity of KSFO...VFR with winds generally under 10 kt in varying
directions. High layers of smoke are expected to continue tonight
SFO Bridge Approach...Similar to KSFO.
Monterey Bay Terminals...VFR with generally light winds. High
layers of smoke are also visible due to the southern California
.MARINE...as of 02:35 PM PST Thursday...Strong high pressure will
dominate the weather pattern through the forecast period. This
will result in generally light offshore winds with locally breezy
to gusty winds at times along the coast and offshore of coastal
gaps, especially from the Marin Headlands south through about
Pescadero, and to a lesser extent west of the Monterey Bay.
Lighter, variable winds will prevail for areas protected by
coastal ridges, such as offshore of the Santa Cruz Mountains, Big
Sur, and the Sonoma coastline. Moderate period northwest seas
will also prevail.
PUBLIC FORECAST: Rowe
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Area Forecast Discussion
National Weather Service Tampa Bay Ruskin FL
815 PM EST Thu Dec 7 2017
A cold front continues to drift south over central and southwest
Florida tonight and on Friday. Radar imagery is showing rain showers
streaming in from the gulf from north of Tampa Bay over the Nature
Coast. HRRR model guidance continues to shows these showers
continuing through the night with a higher concentration of showers
and stray thunderstorm moving through the area on Friday afternoon.
Similiar to this morning, some areas of dense fog will be possible
after midnight and persisting through sunrise. This wet period will
continue across west central and southwest Florida through Saturday
as the front traverses the peninsula. Temperatures tonight and
tomorrow will be on the warm and muggy side south of Tampa bay
before a cool down on Saturday and Sunday for the entire peninsula
as the front moves over southern Florida. Made some slight increase
in POPs north of Tampa Bay based on radar coverage. Will send
updated zones shortly.
All terminals across the region will see aviation impacts over the
next 24 hours as a strong cold front moves through the region. Low
clouds are already filtering in from the north and will produce
MVFR/IFR conditions for CIG/VSBY starting between 03-06Z. Conditions
further deteriorate between 15-18Z tomorrow and will continue
through Friday evening. Some LIFR conditions will be possible as the
front passes through the region. Will keep SHRA and BR as the
predominant weather, but can`t rule out a stray thunderstorm on
A frontal boundary will stall out across the central Gulf waters
tonight through Saturday. Increasing moisture combined with this
front and weak areas of low pressure moving along the front from the
Gulf will bring increasing wind and seas and rain chances to the
waters tonight through Friday night. The front will move south of
the waters on Saturday as deepening low pressure moves northeastward
up along the mid Atlantic coast with strong and gusty winds
continuing over the Gulf waters through Saturday night. During
Sunday and Monday light winds and lower seas will return to the
waters as surface high pressure builds in over the region.
.Preliminary Point Temps/PoPs...
TPA 66 77 58 63 / 50 60 90 50
FMY 69 82 64 69 / 30 40 90 80
GIF 64 81 56 63 / 40 50 90 60
SRQ 68 78 60 65 / 40 50 90 60
BKV 59 76 52 60 / 60 60 90 40
SPG 67 76 58 64 / 50 60 90 50