Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 03/07/18
Area Forecast Discussion
National Weather Service State College PA
1046 PM EST Tue Mar 6 2018
A winter storm will bring accumulating snow to much of central
Pennsylvania tonight and tomorrow. The heaviest snowfall and
area of greatest impact is expected to be focused over east-
central Pennsylvania. Periods of snow are likely to continue
over the northwest Alleghenies and Laurel Highlands with
additional snow accumulation through the end of the week.
Temperatures will stay below average into the weekend.
.NEAR TERM /UNTIL 8 AM WEDNESDAY MORNING/...
New NAM is in, and the fcst is still looking good for the far
eastern areas. The biggest tweak to the fcst will be in the
morning to bump up the PoPs in the west and SC mtns where a band
of snow could move in from the west and lift across the area
during the morning. The band will be associated with/just ahead
of the connection/trough between the two lows. The residence
time of the band looks pretty short, so the going snow accums
are OK. The main worry continues to be the snow amounts over the
advy area. Latest WRF ARW skunks that area with only an inch or
two of snow. But, the HREF mean blossoms a good amount of snow
during the late morning, just nipping about 20 miles west of
Light precip over the NErn third is making a coating of
something frozen on the ground as the temps cool off. Broad
shield of precip moving up through the DC and Baltimore metro
areas. While most of the obs there are rain, the temps are 3-5F
milder than for us northerners. KHGR is snowing, now, and Camp
David is only 31/29 with the ol` unknown precip falling. What`s
wild are the thunderstorms over WV. Don`t expect those to last
too much longer, but the system is starting to weaken over
OH/wrn PA and deepen over the piedmont of NC. Pressures are now
pretty much equal between the two centers. All seems well. Did
adjust the PoPs for the next 6 hours based on latest trends and
the HRRR since it seems to have a little better handle on the
precip over the region vs 3 hours ago. Snow amounts are the
Very light mixed precip is occurring over much of the area as a
very strong jet streak noses into the Mid-Atlantic. The left-
exit region of the jet is creating a fair amount of lift and
just the barest amount of moisture included. The precip is sleet
and snow when it does make the ground. Big flakes out the
window right now. But, the ground is warm and melting taking
place initially. However, the ground should be white soon, and
then everything will stick. The air temps are dropping over the
east where the precip has begun. HRRR and RAP were a little too
far west with this batch of precip. Have extrapolated it out to
the east and bumped up the PoPs to match trends.
It still looks like this area slows down as it gets past the
Susq R, but does slide east a bit more through the middle of the
night. However, the main show (heavy snow) is going to be
moving across the MD border just before or right at sunrise.
Morning commute in the SE is not going to be easy.
Main changes with this package were to just add a buffer of
roughly one county to the west of the warnings into an advy.
While the cut off of the very heavy snow may be very sharp - and
we have seen this before - the uncertainty of where the heaviest
bands set up is still pretty high on the western edge.
Therefore, could not ignore the poss of a brief period of heavy
(1"+/hr) snow rates in the middle Susq. The elevations and
lingering snow over Sullivan and the higher elevations of far
eastern Lycoming County seemed like a good move.
Many folks asking if the wind will be a problem with this storm
(recent memory of last storm). No. SE 10mph or less gradually
backs to N then NE as the storm center runs up the east coast.
Speeds do increase to 10-15mph with gusts into the l20s over
Lanc Co - but that happens after most of our snow is gone. The
stronger winds/gusts will be for the Laurel Highlands, esp as
the storm moves away and the upslope begins for them. They may
eventually need an advy, but for now, 2-3" through Wed evening
and a little more Wed night/Thurs seems fine.
.SHORT TERM /8 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
Rapidly intensifying surface low develops over the Carolina
coast tomorrow with easterly flow developing over our CWA. Low
will move up the coastline during the day. This puts our eastern
half of the CWA into a favorable location for precipitation.
With strong lift the precipitation will fall as a moderate to
heavy snow for a time and all watches were upgraded to warnings.
Expect some slow travel conditions for a time on Wednesday
afternoon under the heaviest snow, with rates of 1-2 inches per
hour possible. Fortunately the storm will move fast enough to
limit the heaviest snowfall to just a few hours. Further west
over the CWA the forecast is more difficult as there will be a
sharp east-west cutoff in the snow. There will be a band of snow
moving across the western half of the CWA early in the day with
an advancing shortwave that will bring a short period of
snowfall. For now it looks like the snow will not meet advisory
criteria for the western half of the area.
.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
Models are in fair agreement as the upper level low rotates
through with the Upper lows having a Fujiwara interaction as
they move through the northeast. Thursday through Friday will
see seasonably cold westerly flow which should prolong snow
showers downwind of the lakes and over the favored upslope areas
along the Allegheny Plateau. This will support additional snow
accumulation through the end of the week across the higher
elevations in the Laurel Highlands and northwest Alleghenies.
Storm potential still very much up in the air heading into early
next week with very low confidence given a large spread in the
guidance. Greater confidence exists in a continuation of below
average/seasonably cool temperatures for early to mid March.
.AVIATION /04Z WEDNESDAY THROUGH SUNDAY/...
Most of the area not seeing much going on at 10 PM...but
some snow and rain northward into the far southeast.
Another small patch near PIT.
TAFS updated for this.
Earlier discussion below.
Small bands of snow...some with large flakes...over the
area...as cold front moves eastward. Back edge near the
office...but may slow a little to the east. Interesting thing
is the huge dry slot to the west...until one gets to the upper
level low. This upper level low is not real sharp...so one
question is how fast system can grab moisture from the southeast
states and form a deep low on Wednesday. For now...left 00Z
TAFS close to the earlier package.
Thus eastern areas will likely see moderate to heavy snow
at times during the day on Wed.
Expect conditions to improve later in the day...as the coastal
storm pulls out.
Potential for this system to lift out faster...as mentioned
above...with less long duration impact...will continue to
Gusty winds expected from the northwest later on Wednesday...as
the storm pulls out.
Wed...Widespread restrictions. Periods of snow - heaviest in
the east. Becoming windy.
Thu-Fri...Mainly VFR, but restrictions in SHSN Northern and
Western Mountains. Continued breezy.
Winter Weather Advisory until 6 PM EST Wednesday for PAZ028-
Winter Storm Warning until 8 PM EST Wednesday for PAZ053-
Area Forecast Discussion
National Weather Service Indianapolis IN
1029 PM EST Tue Mar 6 2018
The AVIATION Section has been updated below.
Issued at 248 PM EST Tue Mar 6 2018
Low pressure is expected to push across Central Indiana tonight
and exit the area on Wednesday. This will bring chances for rain
showers to Central Indiana tonight.
As cooler air arrives from Canada on Wednesday and Thursday mostly
cloudy skies are expected to linger across the state along with
colder conditions and below normal temperatures.
Dry weather is then expected through at least Saturday morning as
High pressure slowly pushes across the area.
Another Low pressure system is expected to arrive in the area
on Saturday Night...bringing more chances for rain. Overall look
for temperature below seasonal normal over the next seven days.
.NEAR TERM /Tonight/...
Issued at 248 PM EST Tue Mar 6 2018
Surface analysis early this afternoon shows low pressure in place
over Northern Illinois...and cyclonic lower level flow was
building across Central Indiana. Aloft...water vapor imagery
showed an upper low with a broad trough across the region
stretching from the northern plains to Ohio and Kentucky. A tight
pressure gradient was building across Central Indiana as much of
the forecast area remained within the warm sector. Winds across
Central Indiana were gusting to over 30 mph. National Radar
Mosaics show scattered light showers wrapping around the low
across northern Illinois...WI and Michigan.
Models agree that the low to our northwest will continue to push
east across Central Indiana tonight. Forecast soundings show
excellent saturation arriving this late this afternoon and
evening. Time heights concur...but show rather weak and broad
lift. HRRR shows widespread light showers arriving in the area
this evening as the upper low and associated trough axis pass
across the area late this evening. Thus with ample dynamics in
place across the area...will trend pops at or above the forecast
builder blend. However...precip amounts are still expected to
remain rather light. GFS suggests cold air advection to begin
after 03Z as winds become more NWerly. Thus even though clouds and
some light rain will be expected...will not trend overnight lows
too far from the forecast builder blend.
.SHORT TERM /Wednesday through Friday/...
Issued at 248 PM EST Tue Mar 6 2018
THe GFS and NAm suggest the surface low that will be passing
across state will be exiting Central Indiana along with the trough
axis/cold front that should be well east of Indiana by 12Z
Wednesday. Best forcing will be lost on Wednesday and Time heights
show subsidence in the wake of the departing low along with good
drying within the mid and upper parts of the column. However lower
levels remain saturated and broadly cyclonic lower level flow
continues and time heights show trapped strato-cu in place beneath
a mid level inversion. Thus will trend toward just a mostly cloudy
sky. Convective temperatures look to be near 35 on
Wednesday...which will help to fill in any holes within the
strato-cu desk and a sprinkle or flurry cannot be ruled out...but
with limited moisture pops and/or a mention are not warranted.
Given the cold air advection and cloudy skies will trend highs at
or below the forecast builder blend.
Clouds look to remain across the are on Wednesday night and
Thursday as forecast soundings and time heights continue to
suggest lower level saturation. Supporting this...broad cyclonic
flow will remain in place across the region as the mid level ridge
axis remains across the plains. Thus will trend toward mostly
cloudy skies along with temperatures at or below the forecast
builder blends given the ongoing cold air advection and cloud
Dry weather is expected to continue on Thursday night and Friday
as the cyclonic flow within the lower levels continues to weaken.
Forecast soundings show more dry air arriving and a dissipation of
the trapped strato-cu deck. Thus will again trend toward a dry
forecast with partly cloudy skies as High pressure arrives from
the west. Will not veer far form the forecast builder blends here.
.LONG TERM /Friday Night through Tuesday Night/...
Issued at 248 PM EST Tue Mar 6 2018
Models continue to trend toward rain showers on Friday afternoon
and evening as an upper wave clips the northeast portions of
central Indiana. They have since backed off on rain for Friday
night though, and only the Euro is aggressive with the rain during
the afternoon and evening on Friday. As temperatures drop during
the evening though, there will be a brief transition to snow
through Sat 06Z.
Further out, brief ridging will result in a dry day on Saturday,
but it will be short-lived as a low pressure system tracks through
the central U.S. and into the Tennessee Valley. This system will
generate much of the same (rain with snow mixed in at times) from
Saturday night through Sunday night. Again, little to no snow
accumulation. Monday and Tuesday, dry conditions will return as a
large ridge of high pressure strengthens over the central U.S.
Meanwhile, temperatures will continue to fluctuate as the pattern
slowly begins its transition from winter to spring.
.AVIATION /Discussion for the 07/0300Z IND TAF Update/...
Issued at 1012 PM EST Tue Mar 6 2018
Both VFR to MVFR ceilings have occurred at IND over the past
couple hours. Would not be surprised to see a bit of a break from
the lower clouds as the precipitation has moved southeast of the
terminal. However, light snow shower chances could return around
0800z as a band of snow showers rotates southeast out of eastern
Illinois. Confidence is lowering as precipitation echoes within
that band appears to be weakening. Thus, may pull prevailing
light snow later this evening. The previous discussion follows...
Issued at 644 PM EST Tue Mar 6 2018
Do expect conditions to continue to deteriorate as we head into
the overnight hours. Light rain, and potentially snow, showers may
affect some of the TAF sites through 1200z. Confidence not high
on timing these scattered showers into the TAF sites currently.
Thus, continued to cover with VCSH. Will be continually watching
to make updates on timing this evening. Expect ceilings to lower
to MVFR category by 05-0800z across many of the TAF sites. The
potential is also there to drop to IFR with ceilings around 1000
ft. Will continue to monitor ceilings as we have already seen some
bouncing down at LAF. Winds will lessen briefly overnight before
increasing again during the early morning hours from 290-310.
Winds overnight and during the morning hours should act to limit
fog formation more than last night.
Area Forecast Discussion
National Weather Service Blacksburg VA
856 PM EST Tue Mar 6 2018
A cold front will swing east across the region overnight
bringing a return to gusty northwest winds and mountain snow
showers into Wednesday. A secondary low develops along the coast
and deepens quickly as it moves northeast Wednesday and
Wednesday night. High pressure builds into the Ohio and
Tennessee Valleys behind this system on Thursday and Friday.
.NEAR TERM /THROUGH WEDNESDAY/...
As of 845 PM EST Tuesday...
Rain associated with the exiting wave to the southeast gradually
pulling out of the region and should exit in the next hour or
two. However seeing a band of shallow convection develop to the
northwest just ahead of the upstream cold front and along the
leading edge of the main southwest trough aloft. Latest
mesoanalysis showing some faint instability just west of the
region while expect this more driven by convergence/lapses on
the edge of the approaching cold pool. Thus cant rule out a
portion of this likely weakening band making it into the far
west before fading upon encountering the weak wedge over our
region. This should be followed by a transition to late night
snow showers as colder air aloft arrives behind the front after
midnight. Latest HRRR shows some of this light snowfall mostly
toward daybreak, but not enough currently to support an advisory
at this point. Otherwise updating to let pops go a bit sooner
across the east, while beefing up sooner west. Also adding more
fog in the wake of the deeper moisture as still expect plenty
of lingering low level moisture until the flow increases from
the northwest late. Lows mostly in the 30s with perhaps a few
locations dropping into the 20s over the mountains late within
the strong push of cold advection.
Previous discussion as of 1240 PM EST Tuesday...
A weak wedge remains along and east of the Blue Ridge south
into the Carolinas this afternoon. Warm moisture air advecting
over the top and modest isentropic lift will keep light to
moderate rain over the foothills and piedmont counties into this
evening. With an easterly flow, light rain is also possible
along the Blue Ridge. Rainfall amounts will range from from a
tenth along the Blue Ridge to half an inch in the piedmont.
An upper level low will track from the upper midwest to the
Ohio Valley tonight. This upper level system will help generate
a secondary low along the wedge boundary in NC this evening.
This surface low will erode the wedge and remove the rain from
the area as it tracks off the VA coast tonight. The upper level
low will weaken some overnight, but will send a cold front and a
series of short waves across the region starting early
Wednesday morning. Cold air will first arrive aloft then
eventually mix to the lower levels through Wednesday morning.
Higher elevations will have snow arriving around 4AM while the
lower levels stay warm for a cold rain. By 7am, west of the Blue
Ridge will see a wet snow with little if any accumulation below
2500 feet. Snow accumulations of 1-3 inches are possible along
higher ridges and mainly western facing slopes of SE WV. There
is a slight chance some snow will work east of the Blue Ridge to
the piedmont, mainly north of hwy 460. No accumulations are
expected east of the Blue Ridge. Precipitation chances dwindle
in the afternoon as the short wave axis lifts north of the area.
Continue northwest flow with trajectories from the Great Lakes
will keep snow along western slopes through the afternoon.
However, with the increase sun angle and mild temperatures, not
much more snow is expected to accumulate in the afternoon.
Morning low temperatures expected to drop between the upper 20s
to lower 30s. Temperatures should warm into the lower 50s east
of the Blue Ridge as clouds will break early. With clouds
expected most of the day, mountain temperatures will range from
the mid 30s to lower 40s. Breezy and gusty winds are also
expected as mixing increases through the day tomorrow. Wind
speeds of 15-25 MPH with gusts up to 45 MPH are possible along
the Blue Ridge.
.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
As of 200 PM EST Tuesday...
Little change in previous forecast reasoning, as a low pressure
system off the southern New England coast continues to deepen
Wednesday night. The mid Atlantic will be locked in gusty
northwest flow through much of the period, with a series of
subtle upper level disturbances making their way across the
central Appalachians. With shallow/very limited moisture to work
with and temperatures in the cloud layers below freezing,
expect these disturbances to trigger rounds of on-and-off snow
showers for the higher ridges of southeast West Virginia through
the Highlands of North Carolina. Believe the highest
accumulations will occur across western Greenbrier County where
3 to locally 6 inches may be on the ground by the time snow
showers end Friday night, and still consider it a possibility
that a long duration winter weather advisory would be issued if
these trends in the model data continue.
In addition to snow showers, will also be concerned with gusty
winds, though not nearly as strong as those observed last week.
Thursday afternoon gusts will range from 25 to 35 mph across the
mountains with higher gusts across the higher ridges, while 20
to 30 mph gusts will be common across the Piedmont. As such,
would not be surprised if a wind advisory is issued for portions
of the mountains. Winds will diminish only slightly on Friday,
but that could change depending on where the low pressure system
tracks heading into the weekend.
.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 200 PM EST Tuesday...
Models appear to be coming into slightly better agreement today
concerning the track and timing of a low pressure system riding
from the Tennessee Valley across the mid Atlantic on Saturday
night into Sunday, though significant difference remain in
temperature profiles and therefore precipitation types. Based on
the latest model solutions, snow is the most likely type of
precipitation in the vicinity of the Interstate 64 corridor, and
rain is more likely across the Piedmont of North Carolina. In
between, a wintry mix of sleet and snow intermixed with rain
will be possible. All of this is low confidence and will have to
be resolved in the coming days.
This system will move to the east Sunday evening, with the
possibility of upslope snow showers occurring across southeast
West Virginia through the Highlands of North Carolina for the
start of the next workweek.
.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
As of 615 PM EST Tuesday...
MVFR to IFR ceilings will prevail along and east of the Blue
Ridge this evening with periods of VFR to MVFR farther west.
Expect ongoing rain/mix to gradually taper off along the KDAN to
KLYH corridor and points east but may take until late evening,
around 04Z/11PM, for lingering spotty coverage to exit. This
will cause lingering MVFR to ocnl IFR vsbys in both rain/fog
including pockets of sleet/PL. Once the precipitation exits
appears sub-VFR may prevail at most locations as low level
moisture gets trapped beneath a subsidence inversion. This
remains uncertain espcly at KBLF/KLWB where will be gradually
shifting to a northwest flow trajectory.
Snow showers will then develop on the western slopes of the
central Appalachians late tonight. KBLF and KLWB will have a
chance for MVFR snow showers after 09Z/4AM with more widespread
coverage likely Wednesday morning with some of this light
precipitation perhaps spilling east to KBCB/KROA.
As low pressure deepens and moves northeast along the coast
winds will increase. Wind gusts up to 40 knots are possible
along the Blue Ridge from Roanoke south on Wednesday and
Wednesday night. The northwest winds will also lead to a
prolonged period of upslope snow showers at KBLF and KLWB.
Extended Aviation Discussion:
Locations east of the Blue Ridge will return to VFR as the low
tracks away from the area and high pressure builds over the Ohio
and Tennessee Valleys on Thursday and Friday.
A period of VFR looks to take shape across the region on
Saturday under weak high pressure before clouds increase again
A more potent low pressure system may bring widespread sub-VFR
in rain and wintry precipitation late Saturday night through
Sunday pending the track and strength with later model runs.
As of 300 PM EST Tuesday...
The Mount Jefferson NWR remains off the air due to a power
outage that damaged some electrical equipment. This equipment
is not expected to be fixed until Friday.