Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 11/19/17
Area Forecast Discussion
National Weather Service Gaylord MI
959 PM EST Sat Nov 18 2017
Issued at 959 PM EST Sat Nov 18 2017
Forecast for overnight into Sunday morning is not without
concerns. The basic premise remains unchanged: low pressure over
eastern Lk Erie will continue to move east. Associated synoptic
precip has exited ne lower MI. Chilly nnw winds behind the low
will contribute to increased over-lake instability. Lake effect
precip has already developed off of Lakes Superior, MI, and Huron.
This activity is light, with rain in coastal areas, mixing with
and turning to snow as you enter the higher elevations.
850mb temps over the upstream lakes are around -6C now, but will
drop into the lower minus teens by daybreak. The colder air will
increase instability over the warm lakes, resulting in more
vigorous lake effect precip overnight, and will eventually turn
coastal areas to snow. Though synoptic support does not exist for
much of the night, a shortwave diving in from the nw should result
in an uptick on Superior late in the overnight, and perhaps on
northern Lake MI toward morning. Inversion heights of 6-7k ft are
An not too terribly concerned with eastern upper MI. Prevailing
nnw flow should focus best banding into Luce Co, with the tail end
getting into western Mack. Will adjust accums to allow for circa
2 inches in western Mack (south of ERY), and will reduce amounts
in Chip Co.
Hi-res models offer differing solutions, and differing trends,
into nw lower MI. RAP runs have trended drier with time, keeping
liquid QPF less than 0.20 inches thru Sunday morning. HRRR has
been trending wetter, with the Luce Co band poking into the `Big
5` counties in northern lower. Max HRRR QPF is in excess of 0.40
inches along a narrow axis. This is concerning, but HRRR runs are
already producing vigorous banding into upper MI now, and those
vigorous bands are not evident...not yet. For this reason, will
not be increasing snow amounts in nw lower MI by too much. Will
push max snowfall in northern lower MI eastward tonight, to
between M-66 and I-75, with max accums thru morning of 2-3 inches.
When combined with expected snowfall Sunday morning, we`re getting
right to the edge of advisory-level accums. Am not going to jump
on this yet, but will be keeping an eye out. If banding on
Superior becomes more prominent on MQT/Montreal Rvr radars, and/or
obs out of ERY show the same, could well pop an advisory later
.NEAR TERM...(Tonight through Sunday)
Issued at 345 PM EST Sat Nov 18 2017
High impact weather potential: Slick spots on area roadways possibly
developing tonight. Snow covered and slippery roadways possible
...Lake effect kicking in...
Synoptic moisture peels out to the northeast through this evening as
low pressure continues to track by to our south. Progressively
colder air then advects in behind the departing system increasing
over lake instability through Sunday. This will lead to the
development of northerly flow lake effect rain and snow showers
later this afternoon which will change to snow early tonight. The
flow will back overnight into the north northwest before finally
settling into the northwest late tonight into Sunday as lake effect
snow continues. Activity may become enhanced and more widespread for
a time Sunday as a short wave drops down through the flow. Areas
roads may become slick due to falling temperatures and any rain
showers transitioning over to snow showers. Snowfall accumulations
tonight expected to range from 1 to 2 inches along and west of US
131. Accumulations Sunday of 2 to 3 inches are expected in the
normal snow belts of northwest lower and eastern upper.
.SHORT TERM...(Sunday night through Tuesday)
Issued at 400 PM EST Sat Nov 18 2017
Pattern Forecast: Active pattern continues through next week.
Background pattern remains positive PNA, with high amplitude
ridging over the western CONUS and troughing over the eastern. A
series of clippers running along the baroclinic zone, and through
the Great Lakes, will provide periodic reinforcement of the
eastern troughing with colder air helping to deepen the troughing.
The currently negative, and forecast to become more so, arctic
oscillation will certainly help the colder air push south as well.
Much of the week will see this up and down mix of brief height
rises being suppressed by a clipper before a more prolonged cold
push next weekend.
Primary Forecast Concerns/Challenges: Timing will likely be an
issue, as is often the case with these active clipper patterns.
Another rain to snow transition expected Tuesday.
Any lingering lake effect Sunday night will gradually be shut down
through the morning Monday as high pressure to our south backs the
flow to the SW and increase WAA. This will moderate temperatures a
bit, with Monday and Tuesday high temperatures near 40. Though the
Tuesday high will likely be overnight for many areas, as the next
clipper in line will arrive with colder air and precipitation by
early afternoon. Those east of I-75 may see the arrival later in the
afternoon. Precipitation will arrive mostly liquid, with a fairly
quick change over to snow through the afternoon. This should carry
into Wednesday with lake effect. Winds will begin to pickup Monday
night, remaining gusty through Tuesday night.
.LONG TERM...(Tuesday night through Saturday)
Issued at 345 PM EST Sat Nov 18 2017
Pattern remains progressive through the extended, with clippers
moving through the flow working to suppress height rises trying to
work into the region. This will bring a very familiar period of
clipper system precip, followed by some lake effect, then a brief
clearing. Signs point to a more prolonged visit of cold air starting
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 640 PM EST Sat Nov 18 2017
Widespread mixed precip is departing ne lower MI, as low pressure
advances across Lake Erie. Lake effect showers (mixed rain/snow)
are already developing into parts of nw lower MI. These will
become more extensive, while gradually turning to all snow as
colder air enters the region. Best snowfall amounts will occur
east of TVC. Do expect occasional vsbys restrictions at TVC,
perhaps into IFR territory at times late tonight and Sunday.
Otherwise, MVFR to VFR cigs will prevail.
NNW winds will be gusty tonight and Sunday, while gradually
backing to the WNW on Sunday.
Issued at 345 PM EST Sat Nov 18 2017
Lower end gale force gusts are expected for late this afternoon and
tonight for much of Lake Michigan and Huron. This is due to a
tightening pressure gradient on the backside of developing low
pressure that crosses the srn and eastern Great Lakes. Solid
advisory winds elsewhere. NW winds taper off some heading through
Sunday afternoon and night while also backing more out of the west,
but gusty conditions still expected due to deep overlake
instability. Rain and snow showers will transition over to lake
effect snow showers tonight into Sunday evening.
LH...SMALL CRAFT ADVISORY until 7 PM EST Sunday for LHZ345-346.
GALE WARNING until 7 AM EST Sunday for LHZ349.
GALE WARNING until 11 AM EST Sunday for LHZ347-348.
LM...SMALL CRAFT ADVISORY until 7 PM EST Sunday for LMZ341.
GALE WARNING until 7 AM EST Sunday for LMZ323-342-344>346.
LS...SMALL CRAFT ADVISORY until 7 PM EST Sunday for LSZ321-322.
Area Forecast Discussion
National Weather Service Charleston SC
920 PM EST Sat Nov 18 2017
A cold front will push offshore early Sunday, then stall south
and east of the region. High pressure will build over the area
and prevail through early next week. A series of low pressure
systems could then track northeast along the stationary front,
producing unsettled conditions later Tuesday through mid to
late week. High pressure will expand over the region late week
or next weekend.
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
The only change made for the late evening update was to increase
pops to 40%. The rest of the forecast is on track.
A pronounced cold front is moving across Tennessee into Deep
South early this evening and is delineated by a sharp line of
showers/tstms. The cold front and accompanying line of
convection will move steadily east tonight, reaching far
interior areas around 3 am and coastal areas by 6 am. Do expect
at least some weakening of the line as it moves across Southeast
South Carolina and Southeast Georgia during the instability
minimum, but upper forcing associated with the right entrance
region of the upper jet will remain robust. RAP Showalter values
go slightly negative just ahead of the front suggesting the
presence of some weak elevated instability which may be just
enough to support a risk for a few tstms despite no surface
based instability. Plan to introduce a slight chance of tstms
for the early morning hours. High resolution models are similar
in showing a distinct line moving west-east across the forecast
area, so 40% pops may be a bit low, especially inland Will keep
pops capped at 40% for this update, these may need to be
increased with subsequent updates.
Lake Winds: Winds will increase on Lake Moultrie tonight ahead
of a cold front, then lull late as the front passes. At this
time it appears as though winds will mainly stay below Advisory
levels /25 kt/ in the warm advection regime given the lake water
temperatures in the 50s leading to less than favorable vertical
mixing profiles. The strongest gusts will likely occur around
the lake shores.
.SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/...
Clouds and a few showers could linger early Sunday; otherwise, the
shortwave trough and associated surface cold front will push quickly
offshore Sunday morning, followed by sunshine and drier conditions.
Downslope flow and insolation will combine to offset cold air
advection, pushing high temps into the mid/upper 60s most locations.
The cold front will eventually stall south/east of the region, and
this stationary front could play a role in our weather beginning
Dry high pressure will expand over the area Sunday night, yielding
clear skies and light winds. Strong radiational cooling will result,
allowing temps to drop into the mid 30s inland and upper 30s to
lower 40s closer to the coast. Accordingly, we introduced a mention
of frost into the late Sunday night/early Monday forecast, and we
may need to consider a Frost Advisory for Sunday night for some
portion of inland zones where the winds would be more likely to go
calm. A few of the chilliest inland locales could even bottom out
briefly around 32F early Monday, but the probabilities for freezing
temps remain too low to justify a Freeze Watch.
Cool high pressure will persist Monday, limiting high temps to the
upper 50s north to the mid 60s far south.
Monday night into Tuesday: East of an amplifying longwave upper
trough, forcing for ascent, moisture advection and a coastal trough
will combine to produce increasing/thickening clouds, and showers
should eventually develop. Latest guidance suggests that sufficient
dry air will persist to maintain rain-free conditions at least
through Monday night. Then, the chance for showers should increase
Tuesday. Coverage of showers remains somewhat uncertain due to a
persistent south/southeast to north/northwest moisture gradient. The
latest forecast advertises Tuesday afternoon POPs ranging from
likely far south/coastal waters to slight chance well inland.
.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
The period looks potentially unsettled though there are substantial
differences in the global models. A series of shortwaves/jet maxima
will dive into the longwave trough anchored over the eastern U.S,
pushing the trough deeper into the Gulf of Mexico. Meanwhile, a
surface stationary front will persist south/east of the forecast
area. This scenario could support serial surface cyclogenesis over
the Gulf, with individual lows tracking northeast along the
stationary front and just off the southeast coast through mid to
late week. Given ongoing uncertainty regarding the
evolution/positions of key features, maintained ongoing/
conservative POPs in the 20-30% range into late week.
.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
* Wind shift associated with cold front
* Low-end risk for LLWS
A cold front is on tap to cross the KCHS and KSAV terminals
early Sunday, roughly in the 09-11z timeframe. A broken line of
showers will accompany the front, but some weakening is
possible prior to the front reaching the terminals. Will carry
VCSH 09-12z with low-end IFR cigs for now. There is a low-risk
for tstms given the presence of some elevated instability, but
the risk is too low to justify a mention. Pre-frontal low-level
jetting will intensify this evening, but there looks to be
enough surface winds to keep conditions below low-level wind
shear thresholds. Winds will shift to the northwest behind the
front with steady clearing expected.
Extended Aviation Outlook: Periods of flight restrictions are
possible later Tuesday or Tuesday night through Wednesday.
Tonight: High pressure will be giving way to an approaching
cold front. Elevated south/southwest winds will occur ahead of
the front, although will be limited somewhat given the warm
advection pattern leading to less favorable vertical mixing
profiles. Advisories will go into effect this evening across the
Charleston County nearshore waters which will be first to see
25 kt wind gusts and 6 foot seas, then around midnight for the
rest of the waters, except Charleston Harbor which should hold
off until a bit later.
Sunday through Thursday: In the wake of cold fropa, offshore
winds will diminish, and Small Craft Advisory conditions should
end by midday Sunday across nearshore waters and around mid-
afternoon beyond 20 nm.
Between high pressure building from the northwest and an offshore
stationary front, expect an extended period of northeast winds next
week. As a series of surface low pressure systems develop and track
along the stationary front/off the Southeast coast, the pressure
gradient is expected to increase mid to late week. Small Craft
Advisory winds and/or seas could develop over portions of the waters
Wednesday night through Friday.
MARINE...Small Craft Advisory from 2 AM to 7 AM EST Sunday for AMZ330.
Small Craft Advisory until noon EST Sunday for AMZ352-354.
Small Craft Advisory until noon EST Sunday for AMZ350.
Small Craft Advisory until 4 PM EST Sunday for AMZ374.
Area Forecast Discussion
National Weather Service State College PA
1053 PM EST Sat Nov 18 2017
A storm near Erie this evening will race through the eastern
Great Lakes tonight and up into eastern Canada Sunday. A strong
cold front trailing south from this low will plow east across
the Commonwealth overnight. Colder air with strong, gusty west
to northwest winds, and some lake effect snow will then affect
the area Sunday. Conditions will gradually improve into Monday.
High pressure will bring moderating temperatures and dry
conditions Tuesday through at least Friday.
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
As of 10PM, the sub 990mb low is just about on top of Erie
heading NNE down the ST. Lawrence River Valley. Radar still
shows waves of moderate to heavy rain racing northeast across
the area, but the rain is looking more disorganized as we see the
nose of the low level warm air move into the region and the
overall warm advection begin to weaken.
The warm air has broken into Somerset county where the
temperatures have risen into the mid 50s, but the cool air
damming wedge remains well entrenched over most of the remainder
of the area. Temperatures over the ridge-valley region will
generally continue to rise overnight as the warm air creeps
north and tries to erode the dense cool air in place. The usual
scenario under these setups is for the actual warm front to
creep into southern areas as the cold front moves toward the
region, but rather than pass through most of the CWA cleanly,
it will tend to mix out briefly just ahead of the cold front,
leading to a brief spike in temperatures just before colder air
comes pouring in on a strengthening NW wind. That will tend to
happen from midnight into the wee hours of Sunday. By the time
we wake up Sunday morning, it will be turning colder and the
wind will be strong and gusty out of the NW under potent cold
The RAP and HRRR agree, the front will enter our western
counties around midnight, and should be clearing the eastern
part of the CWA by around sunrise.
Expect a sharp drop in temps after the frontal passage, and a
quick increase in wind as an area of 7-9 mb/3hr sfc pressure
rises moves NE from the Ohio River Valley to the Finger Lakes
and Pocono region of NEPA between midnight and mid morning
The Wind Advisory affects the entire CWA with the exception of
the NW where a Winter Weather Advisory for Lake Effect snows
includes the mention of the strong gusty winds.
Will continue to advertise a large area of 1-1.5 inch rainfall
amounts across the region of Central PA and northern PA from
along the 22/322 corridors and points north, where models show a
stripe of enhanced QPF from the steepest ascent of the moist
and increasing unstable air over the persistent/nearly
stationary low level boundary.
.SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
A very windy and cold day is on tap for Sunday with frequent
gusts of 40 to 50 mph during the mid to late morning hours as
the area of strong 3-6 hourly pressure rises moves NE across the
SREF mean 850 mb temps of about -7C across the NW and -4 to -5C
across the SE support max temps in the l-m 30s INVOF KBFD and
KJST and mid to upper 40s INVOF KMDT and KLNS with upper 30s to
low 40s throughout the Central Mtn zones.
Scattered to numerous snow showers will bring a coating to 2
inches of wind whipped snow accum across the Laurels and
northcentral mtns, while the NW Snowbelt receives 3-5 inches of
LES. SE of the Allegheny Front, frequent flurries and a few
narrow, sinuous bands of snow showers/squalls could whiten the
ground quickly in some locations.
Some peeks of sunshine will mix in across the Lower Susq Valley
at times, with some brief, mixed rain/snow showers.
.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
The extended part of the forecast will see the season`s first
real lake effect snow event winding down early in the period,
followed by several days of cool but tranquil weather.
Model soundings show the inversion heights falling quickly
Sunday evening through Monday morning, which will begin the
process of shutting off the lake effect machine. Look for
accumulating snow to continue overnight over the normal snowbelt
areas of the NW and even down into the Laurels-with lesser
amounts. The snows will continue shrinking back closer to the
immediate vicinity of the lakes by Monday morning and by Monday
afternoon there should be little more than a few leftover
flurries as the high builds off to our south and we see the
thermal advection switch from cold to warm.
High pressure will keep conditions dry into Tuesday before a
weakening front sliding by to our north brings the small chance
of a snow shower to northern areas Tuesday night and Wednesday.
Another area of high pressure will build east and keep us mainly
dry at least through the end of the week, before a new frontal
system takes aim at the area.
.AVIATION /04Z SUNDAY THROUGH THURSDAY/...
Poor flying conditions are expected to continue through at least
the first half of tonight across much of the region with
widespread MVFR and frequent dips into the IFR CIG/VSBY range as
a warm front lifts slowly NE across PA with shallow cool air
trapped in the deep valley of Central and Northern PA until the
passage of a strong cold front around 05-06Z across TAF sites
KJST and KBFD, then 07-09Z Sunday over the Central Valleys Susq
Region. Borderline LLWS will continue until the CFROPA as a
potent 50-60 kt southwesterly wind max tops the stable colder
airmass entrenched up through a few kft AGL.
Periods of rain will continue through the first half of tonight
across the west and into the early morning hours Sunday across
Southerly winds may become gusty late this evening over the
western and southern airspace, as strong winds aloft begin
mixing to ground level. Latest NAM/HRRR suggests gusts in the
25-30kt range are possible between 00Z-06Z Sunday. Some of the
ridge tops over the Laurel could see south to SSW wind gusts
topping 40KTS early tonight as the warm front lifts north of
that region and allows better vertical mixing of the higher
wind speed air from aloft.
Sun...Windy with frequent gusts 35-40kts from 270-300 degrees.
IFR snow showers NW trending MVFR central to VFR east.
Mon...AM shsn/reduced vsbys possible NW mountains.
Tue-Wed...No sig wx expected.
Wind Advisory from 4 AM to noon EST Sunday for PAZ006-012-018-
Wind Advisory until noon EST Sunday for PAZ010-011-017.
Wind Advisory until noon EST Sunday for PAZ024-025-033-034.
Winter Weather Advisory from 4 AM Sunday to 1 PM EST Monday
NEAR TERM...La Corte
LONG TERM...La Corte
Area Forecast Discussion
National Weather Service Duluth MN
544 PM CST Sat Nov 18 2017
Issued at 539 PM CST Sat Nov 18 2017
Clouds will be slower to erode tonight and we increased cloud
cover for most areas into early morning. We also expanded on the
mention of flurries across much of the Northland.
.SHORT TERM...(This evening through Sunday)
Issued at 230 PM CST Sat Nov 18 2017
Minimal impact snow is expected for portions of the Northland
tonight through Sunday as some lake effect snow is expected this
evening and overnight along the Gogebic Range of the Lake Superior
snow belt. Also, some lighter snow is possible from Koochiching
county southeast to the Twin Ports and into northwest Wisconsin.
For tonight, lake effect snow should develop and continue through
tonight as colder 850 mb level air moves across the region. Delta-Ts
are looking more favorable with values dropping to near 20 below
zero. Considering steadily increasing lake induced CAPE between 300
to 400 J/kg on the RAP soundings at IWD, some decent lift will also
be in place. New snow between 1" to 2" along the Gogebic Range are
expected, with some isolated higher amounts. Also, there may be some
light lake effect snow over northeast Koochiching/northern St. Louis
this evening with moisture coming off Lake of the Woods, but not
expecting much impact or accumulations from this. Due to the colder
air moving in tonight, overnight lows should range from the middle
to upper single digits over the Borderland region, to the lower
teens over the south.
For Sunday, a sfc high pressure ridge will translate across the
region during the morning hours. The southerly return flow with 850-
700 mb layer warm air and moisture advection, which will support
some chances of light snow from Koochiching and Itasca counties
southeast towards the Twin Ports and into northwest Wisconsin Sunday
morning and afternoon. NAM soundings show a decent bit of dry air in
the low-levels, which should limit snow amounts, but still think
this will be a higher PoP/low QPF kind of event, so put in some high
chance PoPs along this WAA wing. Another cold day expected for most
of the Northland, except for our extreme southwestern counties,
which should be on the warm side of the WAA wing. Highs Sunday
should range from the upper teens/lower 20s over the Arrowhead and
into the middle 30s over the Brainerd Lakes.
.LONG TERM...(Sunday night through Saturday)
Issued at 328 PM CST Sat Nov 18 2017
The main story is there does not appear to be any substantial
weather to affect travel for related to Thanksgiving until possibly
after the holiday, sometime late this week. The beginning of the
week will be relatively mild, but it will get colder for the middle
of the week.
Southerly flow will develop across the Northland Sunday night and
continue into Monday, bringing relatively warm air into the region,
in response to a Canadian Clipper moving across southern Canada.
Highs will likely hit the 40s over much of the region Monday.
The Clipper will move through Ontario Monday night and Tuesday. It`s
cold front will blow through the Northland overnight Monday into
early Tuesday, bringing a rush of Arctic air. Strong increases in
pressure and cold air advection will mean strong and efficient
mixing Monday night into Tuesday. The GFS and NAM have 30 to 40
knots within the mixing layer. The wind forecast was ramped up to
gusts of 25 to 35 mph Monday night and early Tuesday, but may need
to trend even higher with subsequent forecasts. It would not be
surprising to see some gusts over 40 mph. Those with garbage service
Tuesday morning may want to weigh down their garbage cans!
Temperatures will plummet overnight into Tuesday morning. Wind
chills will be in the single digits Tuesday morning. There will only
be a little and slow improvement through the day Tuesday, with highs
getting to upper 20s to middle teens, but with wind chills in the
single digits to lower teens.
An area of high pressure will move through the Northland late
Tuesday and early Wednesday. This will bring a period of a bit more
mild weather, with highs in the lower to middle 20s. The latest GFS
and European suggest there could be a passing wave mid-level trough
which could bring very light precipitation (probably snow) through
the Northland Wednesday and/or into Wednesday evening. Added low
precipitation chances based on these latest runs.
Northwest flow will redevelop Thanksgiving Day as high pressure
moves into the Upper Midwest. Expect partly cloudy skies and highs
ranging from the middle 20s near the Canadian border to the low 30s
from central Minnesota into northwest Wisconsin.
It is not until after the holiday where there could be any
significant weather to affect travel across the region. The GFS,
European, and Canadian are suggesting another Canadian Clipper will
likely pass through somewhere in the region, but confidence is low
on timing and track based on significant model differences. The most
concerning model is the European, which has the most intense Clipper
and takes its track right through the Northland. This European run
has the Clipper`s center of low pressure tracking across North
Dakota, central Minnesota, and into northern Wisconsin Friday night
through Saturday morning. The European`s Clipper would mean a big
impact travel conditions across the Northland Friday night and much
of Saturday, with up several inches of snow and accompanied by
gusty, cold winds. On the other hand, the Canadian Clipper is much
farther north, well into Canada, and only bring a little light snow
to the Arrowhead. The GFS`s Clipper`s track and intensity is
somewhere in between, but much less threatening than European`s
Clipper. We will need to keep a close eye on this anticipated
Clipper and for its potential to significantly impact travel
conditions for the Northland late this week.
No matter the track of the late week Clipper, it looks like
temperatures will take another dive this weekend. Arctic air will
return, sending highs down from 30s on Friday to lower to middle 20s
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 544 PM CST Sat Nov 18 2017
The MVFR ceilings will be slower to diminish tonight and we
delayed the clearing at all sites. Flurries will be possible under
any of these MVFR ceilings with snow showers reducing the
visibility at KINL and along portions of the South Shore where
lake effect snow will occur. The gusty winds will gradually
subside and back tonight, becoming southwest on Sunday. An area of
warm air advection will spread in mainly low VFR ceilings and
some light snow to portions of the Northland on Sunday. We went
with VCSH for most areas but later forecasts may have to include a
2 to 4 hour period of light snow.
.PRELIMINARY POINT TEMPS/POPS...
DLH 10 26 20 40 / 10 50 0 0
INL 5 23 14 38 / 70 20 0 10
BRD 12 35 23 45 / 10 0 0 0
HYR 12 29 21 44 / 10 20 0 0
ASX 17 28 23 44 / 30 30 0 0
LS...Small Craft Advisory until 4 AM CST Sunday for LSZ121-144>148.
Area Forecast Discussion
National Weather Service Raleigh NC
1008 PM EST Sat Nov 18 2017
A cold front will sweep east across the area tonight. Chilly
high pressure will return for Sunday through Tuesday.
.NEAR TERM /THROUGH TONIGHT/...
As of 1005 PM Saturday...
No major changes made to the forecast with this update. Minor tweaks
to the timing of rainfall, though it still appears the line of
shower will move through between 04Z and 12Z from west to east
across Central NC. Continue to favor the HRRR forecast through 7 AM.
The cold front and associated pre-frontal convection, currently
stretches from the eastern Great Lakes/Western NY, southwestward
along the Appalachians into Alabama.
Previous discussion (As of 705 PM): The front is being propelled
east-se by a shortwave crossing the Great Lakes and is projected to
lift northeast into southern New England. The bulk of upper support
lifts well north of our region, as the better forcing is with the
low level front. However, this front will be encountering an
atmosphere lacking moisture and instability compared to the air mass
its currently crossing. Thus, expect the band of convection to
gradually weaken in intensity as it crosses the mountains late this
evening, and reach the Triad region after midnight (possibly closer
to 2 AM).
The increasing cloud cover and a steady breezy sly wind will cause
evening temperatures to hold steady or possibly slowly rise through
The cold front and the narrow band of showers accompanying it should
exit our coastal plain counties by sunrise. Clearing skies will
occur over the NW piedmont by 4-5 AM, possibly reaching the highway
1 corridor by sunrise.
.SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
As of 301 PM Saturday...
Skies will be clear quickly early Sunday morning. The warm start to
the day will partly offset the CAA. However, highs will still reach
the mid 50s to mid 60s NW to SE. NW winds at 10-20 mph are expected
with gusts to 25 mph.
Winds will be diminishing Sunday evening and night. Clear skies
will bring lows in the lower to mid 30s with some upper 20s in the
.LONG TERM /MONDAY THROUGH SATURDAY/...
As of 205 PM Saturday...
Mid level ridging will keep the area rain-free for Monday into early
part of Tuesday. From later Tuesday into Friday a trough will
dominate the pattern over the eastern US bringing a chance for some
rain to the local area. Best chances for rain will be Tuesday night
into early Wednesday, and again Thursday into Thursday night as waves
of low pressure move from the Gulf of Mexico across Florida to off
the southeast coast. Temperatures Thursday night will drop into the
30s but confidence is very low for frozen precipitation to mix in
with any rainfall. A rather flat west to east flow develops Friday
night and Saturday with dry and seasonable weather for central North
.AVIATION /00Z Sunday through Thursday/...
As of 725 PM Saturday...
VFR parameters across central NC early this evening will giveway to
a period of MVFR parameters as a cold front crosses the region well
after midnight. Breezy sly winds ahead of the front will gusts
between 20-27kts at most locations through 06Z, then gradually
decrease. The threat for showers will increase in vicinity of the
Triad terminals between 04Z-06Z, and in vicinity of KRDU and KFAY
between 07Z-09Z. In proximity of KRWI, the threat for a shower or
two will be greatest between 09Z-12Z. In addition to the showers,
ceilings will briefly lower into the MVFR range with bulk of
ceilings hovering around 3000ft, though a period of 1500 ft ceilings
may occur along and behind the front.
NW winds behind the sfc cold front will usher a drier, more stable
air mass into central NC. This will lead to clearing skies NW-SE,
with the clearing trend occurring in the Triad between 09-10Z,
reaching KRDU by 12Z. Skies are expected to quickly clear at KFAY
and KRWI between 12Z-14Z.
Brisk nw winds will occur after daybreak with gusts 18-23kts
anticipated. The winds will gradually subside during the afternoon.
VFR conditions Sunday through Monday. The period Tuesday through
Thanksgiving Day will feature a few opportunities for adverse
aviation conditions in the form of MVFR/IFR ceilings and areas of
light rain. This potential looks highest from Wednesday through
Area Forecast Discussion
National Weather Service Blacksburg VA
832 PM EST Sat Nov 18 2017
A strong cold front will sweep southeast through the region
tonight preceded and accompanied by gusty winds and scattered
to numerous showers. Much colder air on blustery winds will
arrive behind the front on Sunday, with clearing skies across
the Piedmont, but with abundant clouds over the mountains along
with some upsloping snow showers across the western flanks of
.NEAR TERM /THROUGH SUNDAY/...
As of 832 PM EST Saturday...
Regional WSR-88d showed showers entering the western mountains.
Adjusted POPs for the onset of showers (earlier timing) and
movement east tonight. Made some minor adjustments in
temperatures for tonight into Sunday morning. Latest surface
meso obs starting to show winds gusts above 30 mph in elevations
above 2800 feet. Wind advisories looks good, will freshen up
NPW to remove evening wording. Post frontal upslope snow showers
with light accumulation seem reasonable. Will watch evolution
with front for additional potential ISC grids adjustments.
As of 648 PM EST Saturday...
Wind advisories remain in effect until noon EST Sunday across
the higher terrain.
Made some minor adjustments in temperatures utilizing the
surface obs, trends and blended towards GLAMP. Shaped pops
towards HRRR and Hiresw-ARW-East tonight into Sunday morning.
More changes later...
As of 330 PM EST Saturday...
Strong cold front moving through the OH and TV Valley will
sweep east through the Blacksburg forecast area tonight,
preceded and accompanied by scattered to numerous showers.
Instability is very limited with this feature, such that
thunder, if any, will remain isolated and likely confined to the
extreme western or southwestern portion of the forecast area
where some mid level buoyancy will be maximized.
Strong prefrontal winds approaching 45 knots just above the
developing inversion layer, and strong post-frontal winds
behind the front of the same magnitude with 6-hour pressure
rises around 10 millibars support ongoing Wind Advisories though
Noon on Sunday for the mountains and the VA foothills. Some
localized gusts to around 50 knots possible across elevations at
or above 5K feet, but see no need at the present time to hoist
High Wind Warning for this area considering limited areal
Fast moving system should keep precipitation amounts tonight to
under one half inch, with most areas receiving a quarter inch
or less. Strong cold advection and increased upsloping should
help transition rain to snow showers later tonight across the
western flanks of the Appalachians - with a continuation through
Sunday - perhaps into the early part of the short-term period
as a second short wave trof races northeast through SE WV Sunday
afternoon into early evening.
Some spotty snowfall amounts in the 1-2" range are possible
across the highest terrain, such as at Mount Rogers, VA and
across Western Greenbrier County, WV; however, most other
upsloping areas from the mountains of NW NC north through SW VA
into SE WV should receive only an inch or less.
With the strongest cold air advection to arrive on Sunday,
expect to see temperatures flatline near freezing or even
slowly fall during the day, especially across the higher
terrain where clouds will hold fast. East of the Blue Ridge
into the Piedmont, downslope clearing and a bit later arrival
of the coldest air should allow temperatures to recover into the
lower or mid 50s.
.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
As of 215 AM EST Saturday...
While snow showers are likely to be ongoing in the mountains of
southeastern WV, a secondary shortwave trough/500 mb vort max
progged to ripple through the northwest cyclonic flow likely to lead
to a brief enhancement of snow showers in southeast WV at least.
Shortwave is expected to move across the northern half of the
forecast area through midnight, with a reinforcing shot of colder
air awaiting behind it. Froude number is initially unblocked which
supports possible flurries as far east as the Alleghany Highlands in
VA early Sunday evening, but are expected to become more neutral to
blocked by overnight. The moisture layer also begins thinning out
and PoPs taper from south to north toward dry by the pre-dawn hours.
Any accumulations of less than an inch would be confined to western
Greenbrier southwest into parts of Mercer County before midnight,
with just a few flakes into the Alleghany Highlands. Passage of the
shortwave and pressure rises may initially maintain gusty ridgetop
winds into Sunday evening; though as inversion height shrinks the
mixed layer around midnight, a decrease in wind speeds and gusts
along the ridges can be expected. A rather cold night with many
areas likely to fall below freezing, with the coldest values in the
low 20s in southeast WV and the Mountain Empire region.
A broad area of high pressure then begins to settle into the region
Monday into Tuesday. Shot of colder air is brief, and low-level
temperatures begin to moderate as we tap into a modest west to
southwesterly component. It will be pretty chilly early on Monday
with apparent temperatures west of the Blue Ridge in the teens
through the morning commute, so bring along an extra layer as the
holiday workweek begins. Monday and Tuesday overall appear
uneventful otherwise with high pressure and ridging aloft in
control. May see a few high clouds intrude into Tuesday, but overall
lots of sunshine this period. Forecast calls for dry conditions
Monday with highs low 40s to lower 50s, lows mid 20s to near
freezing Monday night, and highs back well into the 50s come
.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 300 PM EST Friday...
GFS ensemble indicates a 500 mb pattern resembling a cold season
positive Pacific-North American (PNA) teleconnection regime centered
around the Thanksgiving holiday period. This often translates to
mean troughiness at 500 mb into the central and eastern US, as
repeated shortwave troughs round the top of a large ridge across the
Pacific Coast and dig/reinforce cyclonic flow aloft. Overall an
unsettled holiday period but nothing that would significantly hamper
travel plans attm.
The GFS and ECMWF indicate show a trough in the southern branch of
the jet across the Mississippi Valley/Deep South, and a more potent
northern stream trough over the Great Lakes/Upper Midwest Tuesday
night. Both also show a weak Gulf coast low developing on an old
frontal zone around the Wednesday timeframe. Question that will
likely govern what unfolds is if phasing can occur between the two
streams. This isn`t indicated at all in the GFS, which would serve
to keep us at least partly cloudy but dry. The ECMWF on the other
hand was indicating a little more phasing in its 00z run, which
would do two things: (1) bring an area of showers further north into
the Blue Ridge and Piedmont Tuesday night/overnight and (2) tap into
colder temperature profiles behind the departing system for the
Thanksgiving holiday Thursday. Less phasing was noted in the 12z
ECMWF, so while still some level of uncertainty to be accounted for,
sided a little closer to the more temperate GFS idea for the Tuesday
through Thursday timeframe. This keeps temperatures slightly below
normal, with only a limited chance for PoPs east of the Blue Ridge
on Tuesday night. Even if the more pessimistic ECMWF solution plays
out, it still wouldn`t likely lead to any significant/impactful
weather. Kept highs for the Thanksgiving holiday only in the 40s
with partly cloudy skies and dry conditions.
Looks to be a warming/moderating trend to temperatures Friday into
the holiday weekend and will likely trend temperatures to near/above
late-November normals. Weather pattern then turns more unsettled
after the holiday weekend with a larger degree of guidance solution
.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
As of 645 PM EST Saturday...
Winds will hinder aviation operations tonight into Sunday.
Southwest winds will continue to increase in advance of an
approaching cold front to our west. Some winds before prior to
and following the arrival of the front could gust as high as 30
knots into Sunday morning, especially in the mountains, with
localized gusts in excess of 40 knots across the highest
elevations - especially tonight into mid- morning Sunday.
VFR flight conditions will continue this evening until
prefrontal and frontal lines of showers begin to arrive from the
west. These showers expected to drive flight conditions back
down into the MVFR range at KBLF and KLWB in the 01-03Z/8-10 PM
timeframe, then reach KBCB by/around 05Z/Midnight.
Further east, look for ceilings to fall down to the 3-5K FT
level in the 05-09Z timeframe/Midnight-4AM tonight, but still in
the VFR range, as narrow lines of showers sweep east with the
Post-frontal upsloping clouds and occasional rain/snow showers
should maintain MVFR to localized IFR flight conditions across
the Southeast West Virginia terminal forecast sites for much of
Sunday, perhaps even until mid-late afternoon at KBCB.
Downsloping winds east of the Blue Ridge should maintain VFR
conditions with clearing skies elsewhere on Sunday.
Medium confidence in winds, ceilings, and visibilities
during the taf period.
Higher pressure and a weakening pressure gradient should allow
for northwesterly winds to slowly abate by late Sunday night,
along with decreasing clouds across the western flanks of the
Appalachians.Widespread VFR conditions are expected thereafter
from Sunday night into FRiday.
VA...Wind Advisory until noon EST Sunday for VAZ007-009>020-022>024-
NC...Wind Advisory until noon EST Sunday for NCZ001-002-018.
WV...Wind Advisory until noon EST Sunday for WVZ044-507-508.