Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/24/16
Area Forecast Discussion
National Weather Service State College PA
1024 PM EST Fri Dec 23 2016
A disturbance moving up the Ohio Valley will approach the region
early Saturday, bringing a period of mixed precipitation to
northern sections and rain showers across the south. This system
will push east of the commonwealth by Saturday afternoon. High
pressure will provide fair and dry weather for Christmas Day. Low
pressure will track north of the area early next week.
.NEAR TERM /UNTIL 9 AM SATURDAY MORNING/...
1020 PM update...
Added Schuylkill Co to the advy due to their higher terrain. Temps
down to freezing across lots of the northern tier. HRRR and RUC
do warm things up slightly as the clouds lower and thicken and
pick the winds up a bit. Most stations in the W and C have warmed
1-3F in the last hour.
730 PM update...
Light rain falling over central OH and is moving this way. Surface
dewpoints are not all that dry, but the lowest clouds are still
about 12kft up. Hardly anything should reach the ground until
after midnight. QPF looks very spotty over the NErn C0s - which is
good. Because they are more likely to see FZRA.
Extensive mid to high clouds filtering the sun across central and
western PA this afternoon...ahead of upstream wave pushing into
Main concern tonight is for temperatures upon arrival of light
precipitation associated with aforementioned wave. NCAR ensemble
and BUFKIT forecast soundings suggest brief FZRA possible, with
soundings cooling to produce mainly S- (or R- to the south where
it`s slightly warmer). Higher elevs across my far northeast will
be susceptible to minor icing in the transition late tonight into
early Saturday morning, and collaborate a Winter Weather Advisory
for Tioga, Sullivan, Northern Lycoming and Columbia Counties for
the icing threat.
.SHORT TERM /9 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
Minimal travel impacts from overnight mixed precip north as temps
there should warm above freezing by 15z and the remainder of the
late morning and afternoon will be drier...although there is still
a chance of some drizzle over the Allegheny Plateau through early
afternoon. Downsloping westerly flow yields brightening skies
across the eastern half of the state during the afternoon. Highs
Saturday will range from the mid 30s north to the mid 40s
.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
Anomalous upper level ridging progged over the northeast
CONUS Christmas Day, ensuring fair weather across Pa. All medium
range guidance still tracking a potent sfc low north of Pa early
next week. Warm advection ahead of this feature could produce a
bit of light rain/fzra across Central Pa early Monday, then a
better chance of rain showers late Monday/Monday night with
passage of trailing cold front.
High pressure will build into the region for midweek, accompanied
by mainly dry weather Tue/Wed. Air flowing over the Grt Lks may be
marginally cold enough to support scattered lake effect snow
showers across the NW Mtns Tuesday. Zonal flow and associated
Pacific air is indicated with temperatures a bit above normal for
the middle of next week.
00Z NAEFS and GEFS both track another area of low pressure west
of Pa late next week. Trailing cold front is likely to bring a
period of rain to the area Thursday. However, cold air damming
assoc with high pres over New Eng could mean an initial period of
.AVIATION /03Z SATURDAY THROUGH WEDNESDAY/...
Mid to high clouds increase this eve...with VFR conds prevailing
through late tonight.
Some rain moves into the region early tomorrow morning. Along with
the trough associated with this precipitation will be a strong LLJ
which should bring a period of LLWS between 08Z to 16Z. Expecting
mainly rain. Showers exit by mid morning Saturday.
Sat...Low CIGs poss BFD/JST. AM light shra.
Sun...AM low CIGs poss, mainly BFD/JST.
Mon...Low CIGs possible.
Tue...Low conds early, improving later in the day.
Winter Weather Advisory until 10 AM EST Saturday for PAZ037-
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
913 PM EST Fri Dec 23 2016
Broad region of isentropic ascent flanking a low amplitude wave
making steady inroads over southeast Michigan this evening. Depth
and magnitude of the dryness of the ambient air unsurprisingly
taking a toll on the early stages of the moistening process, with
more capable radar echoes just now beginning to work into the
forecast area. Both the lack of greater intensity or coverage
continues to favor simply very light rain or a rain/snow mix over
the next several hours up through at least the M-59 corridor. The
warmer RAP guidance most representative of the current temperature
landscape, which lends support for the mention of a light mix as
far north as the I-69 corridor. Temperatures hovering in that
tenuous 32 to 35 degree range, with a report of slick spots
developing on some side streets upstream. Given this Will include
a simple chance mention for freezing rain from the ridge line up
through I-69 to highlight this lower probability.
Fleeting window for precipitation by the early morning period
across southern sections, as supportive ascent strips to the east.
Upstream radar trends tied to the aforementioned wave itself
points to the potential for a greater window of deeper ascent as
this wave tracks from Northern Illinois through central Lower MI.
It remains along this corridor /north of I-69/, where retention of
a sufficiently cold thermal profile will maintain an accumulation
potential of 1 to 2 inches. Slow upward drift in temperatures
overnight will then leave simply some pockets of drizzle /if
anything/ as the sharp backedge of this system quickly exits 08z-
Issued at 651 PM EST Fri Dec 23 2016
Steady expansion of light precipitation on track to lift across
southeast Michigan 01z-03z this evening. While an initial
contribution of evaporative cooling as saturation commences may
allow this precipitation to briefly fall as snow, recent
observations correlate well with expectations for predominantly rain
at Detroit and a rain/snow mix at PTK. A cooler temperature profile
exists at FNT, but now marginal enough to warrant inclusion of a mix
mention. MBS positioned more favorably to hold as all snow,
reinforced by a greater likelihood to witness a period of higher
snowfall rates /04z-08z/. Subsequent deteoriation of ceiling
heights through the early morning period as deeper low level
saturation occurs within the backedge of this moisture plume. This
will yield a window for some drizzle in low MVFR/IFR through the mid
morning period. Some uncertainty yet in cloud trends for Saturday,
a mixed signal across recent model guidance in terms of moisture
depth/quality in the lowest 2000 ft. Conservative approach for now,
holding with MVFR conditions through the day.
For DTW...Advancement of light precipitation into DTW just after 01z
per latest radar trends. Air temperature currently holding at 34
degrees. While the onset of precipitation may briefly cool
temperatures enough to yield a few wet snowflakes, upstream
observations and radar evidence maintain a predominant liquid phase.
//DTW Threshold Probabilities...
* High for cigs aob 5kft.
* Low for ptype starting as rain/snow mix this evening.
Issued at 333 PM EST Fri Dec 23 2016
Despite the appearance of the regional radar mosaic, the returns now
overspreading southern Mi are not reaching the ground (virga)
courtesy of a deep low-mid level dry layer across the area. In fact,
the 19Z sfc obs indicate that the lead edge of precip reaching the
ground is still back across wrn Illinois. These returns are being
forced by a broad region of moist isentropic ascent preceding a mid
level short wave impulse. This short wave will quickly traverse
Lower Mi overnight, with the max height falls occurring over Se Mi in
the 03Z to 09Z time frame. There is a plume of deep moisture now
lifting into Illinois. This moisture will will be drawn into nrn
Indiana/srn Lower Mi during the course of the evening, concurrent
with the strongest push of isentropic lift into Se Mi. This added
moisture plume combined with the increase in ascent will prove
efficient in eroding the dry layer and allowing precip to overspread
Se Mi in the 00 to 03Z time frame (likely a few hours later across
the thumb). The departure of the mid level wave to the east late
tonight will be marked by a rapid drying in the mid levels. This
will transition precip over toward drizzle (07Z to 10Z time frame)
before low level drying occurs later Sat morning.
The approaching system is too weak and too far south to draw in
colder air. The fact that precip is falling as snow across nrn
Iowa/srn MN is a result of wet bulb cooling associated with the
extensive dry air on the lead edge and northern portions of this
system. There are some subtle differences with respect to model
thermal profiles, which unfortunately spell the difference between
snow vs rain across Se Mi. Of note, the RAP and ARW are a bit
warmer, suggesting a rain/snow mix at onset, transitioning to all
rain toward midnight as far north as the I-69 corridor. The NAM is a
bit colder and supports mainly snow from M 59 northward. While the
NAM had a decent handle on upstream moisture quality as of 12Z,
upstream RAOBS indicated a slightly deeper warm layer than
initialized. This lends enough support to warrant more of a mix of
snow/rain up to the I-69 corridor, while much of Metro Detroit and
points south are expected to see primarily rain. Model soundings
generally suggest all snow across the Saginaw Valley and thumb. With
an 8 to 10:1 ratio and total qpf of one to two tenths, a 1 to 2 inch
forecast looks good in the north. Snow amounts will be tapered
south, with little to no accums along/south of the I-94 corridor.
Temps will likely drop a couple degrees with the onset of precip,
then slowly inch their way upward (mid 30s) during the night as sfc
Some phasing of the departing short wave with the northern stream
over ern Canada over the weekend and the amplification of the long
wave trough over the Rockies will force large scale subsidence
across Lower Mi Sat and Christmas, supporting the current dry
forecast. Ample dry air above the shallow mixed layer may support
partial if not full clearing on Saturday, with highs possibly
approaching 40. Very strong sfc high pressure (1046MB) will build
from nrn Ontario to Quebec on Christmas. The associated easterly sfc
flow across Se Mi will temper highs Christmas day to the 30s despite
the warming aloft.
The intense sfc low forecast across the Dakotas on Christmas day
will lift north of Lake Superior on Monday. The pre frontal warm
sector, characterized by very warm moist air for late December, will
overspread Se Mi Sun night into early Monday. This will allow rain
to expand across the area, with temps possibly eclipsing 50 over
portions of the area by Mon morning. This system will be highly
occluded, so post frontal cold air advection will generally be weak
and boundary layer stability may hinder the strongest winds from
reaching the sfc Mon night. Something that will continue to
monitored over the next few forecast cycles.
As the low pushes east away from the region, surface high pressure
begins to move in to the south by Tuesday. This will allow for
conditions to dry out for a few days before the next chance for
precipitation comes back into the picture. By later Wednesday, the
next low and associated shortwave will move across the northern
Great Lakes region. Temperatures look to remain near to
slightly above normal for the remaining days of this year.
Frontal system will move through the lakes tonight brining mainly
light rain over the water. Winds will be relatively light from the
south ahead of the front and will veer to west on Saturday. Next
major impact on the lakes will begin late Sunday as a large
strong low pressure system lifts northward through the upper Midwest.
This will produce a strong southeast flow with sustained winds up to
30kts and gusts to 40kts over most of Lake Huron. As the system
passes winds will veer to west Monday with gale force gusts
continuing into Tuesday before diminishing.
Lake Huron...Gale Watch from late Sunday night through late Monday night FOR
Gale Watch from Sunday afternoon through late Monday night FOR
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
You can obtain your latest National Weather Service forecasts online
Area Forecast Discussion
National Weather Service Austin/San Antonio TX
937 PM CST Fri Dec 23 2016
A line of showers, with an occasional lightning strike, is moving
through Val Verde County. Most recent HRRR run shows this line
dissipating over the next couple of hours. We have increased the
POPs out there until midnight. Otherwise, the forecast looks to be
in good shape and we have only adjusted the hourly grids to
account for observational trends.
.PREV DISCUSSION... /ISSUED 559 PM CST Fri Dec 23 2016/
A few breaks on cloud coverage late this afternoon have resulted
in VFR conditions for the I-35 terminals. Do not expect this
conditions to last for more than 2 hours as cigs and vbsys return
to IFR this evening. A moist southerly low level flow will
continue overnight with categories lowering to LIFR and even VLIFR
around day-break Saturday morning. We are in a moist and wet
pattern with -DZ and foggy conditions expected overnight through
at least mid-afternoon on Saturday. Low stratus will be lingering
around all day on Saturday with very limited sunshine if any.
Across KDRT, similar situation is expected such as the terminals
along the I-35 corridor but just a few hours later.
PREV DISCUSSION... /ISSUED 250 PM CST Fri Dec 23 2016/
SHORT TERM (Tonight through Saturday Night)...
A weakening upper level trough will slowly shear out as it moves
across the Plains and Texas in the short term. A warm advection
pattern with weak isentropic lift will continue with low chances
of showers as well as late evening through morning patchy drizzle.
Areas of overnight into morning fog can also be expected with
some fog possibly becoming dense. Later shifts will monitor for
possible dense fog advisory. Well above normal temperatures are
LONG TERM (Sunday through Friday)...
An upper level trough deepening over the California/Nevada area
in the short term lifts out into the Northern Plains on Christmas
Day/Sunday and into Ontario Canada/Upper Great Lakes on Monday.
This will force a weak cold front into the lower Pecos Valley on
Sunday before stalling across Central and South Central Texas on
Monday and Tuesday, then lifting back to the north by Wednesday.
Expect periods of light rain or showers due to the low level jet.
However, warmer surface temperatures may produce some pockets of
instability along the frontal boundary to enhance upward forcing
causing isolated thunderstorms Sunday and Monday afternoons. Well
above normal temperatures will continue early into middle of next
week. Another upper level trough moving across the Northern Plains
will force a stronger cold front across South Central Texas early
on Thursday. The rain and showers will end with the passage of the
front with near to below normal temperatures in its wake. Beyond
this forecast, a even stronger cold front with some origins in the
Yukon and Arctic has been seen on recent models for New Years Eve
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 62 74 65 75 63 / 30 30 20 30 30
Austin Bergstrom Intl Airport 63 74 64 75 64 / 30 30 20 30 30
New Braunfels Muni Airport 63 74 64 76 64 / 30 30 20 20 20
Burnet Muni Airport 60 71 63 72 59 / 40 30 20 30 30
Del Rio Intl Airport 57 69 62 73 56 / 20 20 20 20 10
Georgetown Muni Airport 61 72 64 74 62 / 40 30 20 30 40
Hondo Muni Airport 61 74 64 76 62 / 20 30 20 20 20
San Marcos Muni Airport 63 74 64 76 64 / 30 30 20 20 30
La Grange - Fayette Regional 65 76 65 79 65 / 40 30 20 30 40
San Antonio Intl Airport 62 73 65 75 64 / 20 30 20 20 20
Stinson Muni Airport 64 74 65 77 65 / 20 30 20 20 20
Public Service/Data Collection...30
Area Forecast Discussion
National Weather Service Sioux Falls SD
734 PM CST Fri Dec 23 2016
.SHORT TERM...(This evening through Saturday)
Issued at 257 PM CST Fri Dec 23 2016
Band of snow has pushed east of the forecast area with weak trough
working across the forecast area. Models are really showing a large
disparity in forecasted conditions tonight. GFS is clear and quiet,
while the NAM and Hi-Res Models have a little bit more moisture in
the boundary layer hinting at fog and low lying stratus development.
Have sided with the idea of fog developing, but not as quick as the
HRRR which currently has fog forecast across the central portions of
the state. As flow goes light tonight, expect fog to become more
widespread especially east of the James River Valley.
Southeasterly flow develops throughout the day on Saturday ahead of
the approaching trough to the west. This will result in fog and low
ceilings struggling to clear. Have undercut guidance slightly,
though southerly fetch will result in increasing warm air advection
throughout the day.
.LONG TERM...(Saturday night through Friday)
Issued at 257 PM CST Fri Dec 23 2016
Southeast wind flow will continue to increase during the night
saturday night ahead of strong storm system. As moisture pools
ahead of the storm, would expect areas of freezing drizzle to
develop but with the expected warming, the time frame where -fzra
would occur looks to be brief. Am concerned a little with SD highway
14 corridor about the freezing drizzle holding on a little
longer, but models continue to push warm air northward quickly
ahead of the storm. With the uncertainty, not going to issue any
headlines for that area, but this is definitely the area to keep
on eye on potential impacts.
Storm system begins moving through the area on Sunday with plenty of
warm air at surface and aloft to keep all the precip in the form of
rain. Thunder still not out of the question and continued to
mention. The most favored areas of thunder potential look to be in
southern section of forecast area due to expected instability per
forecast soundings. Rainfall amounts are pretty impressive for this
time of year with many areas over a half inch and some close to an
inch if not a little more. Right now, the main forecast problem and
impact for our area looks to be the strong winds. Widespread wind
gusts of 40 to 50 mph and possibly even stronger looks likely. Agree
with earlier shift about possible high wind headline, but held off
at this time to match up with neighboring offices. Looks like a
portion of the forecast area will be dry slotted as storm pulls off
to the northeast and that should quickly end the precip Christmas
evening. May have a little light snow on the back side of the storm
Sunday night and early Monday, but accumulations across the area
will be rather light as snow may have difficulty accumulating due to
the wet ground conditions expected at that time.
Not much going on after system pulls away. Back to below normal
temps on Monday, but highs will slowly recover through mid week.
Some hint at a system moving through Tuesday night into Wednesday,
but moisture availability is in question.
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 730 PM CST Fri Dec 23 2016
Will really have to keep an eye on the TAFs and overall conditions
for the rest of tonight and Saturday morning. Especially at KFSD
and KSUX, IFR and LIFR conditions were forecast by many of the
short term high resolution models beginning after midnight tonight
and lasting through a bulk of Saturday morning. However it is
becoming increasingly clear that much of tonight will experience
northwesterly winds just off the surface which may help to keep
the lowest portion of the atmosphere just above the surface well
mixed. If this happens, fog may have trouble forming. The winds do
go very light late tonight and in fact shift to the east and
southeast toward 12Z Saturday. So its possible fog formation may
hold off until extremely late tonight, especially if radiational
fog becomes a bit widespread. At any rate, confidence is not very
high in the 00Z TAF set.
Area Forecast Discussion
National Weather Service Memphis TN
907 PM CST Fri Dec 23 2016
Currently... At 9 PM around the region, light rain is falling
over western portions of the FA with temperatures ranging from the
mid 40s across northern areas to the mid 60s in areas south. Winds
are currently from the south behind a warm front, with warm and
moist air advecting into the region ahead of an approaching cold
front. Showers and thunderstorms will be likely tonight and
tomorrow. Have adjusted overnight lows up a degree or two as
warmer air continues to advect into the region under cloud cover.
Otherwise, the forecast is on track and no other updates are
necessary at this time.
.PREV DISCUSSION... /issued 313 PM CST Fri Dec 23 2016/
DISCUSSION...Surface analysis this afternoon places a warm front
from western Oklahoma back through northeast Texas. Meanwhile,
across the Mid-South a mid-level subtropical jet is bringing
Pacific moisture into the Lower Mississippi Valley and a low level
jet streak and southerly winds on the back side of high pressure
advecting moisture up from the Gulf of Mexico. This has resulted
in mostly cloudy to cloudy skies across the forecast area. As of 2
pm CST, temperatures across the area are predominantly in the 50s
across most locations.
A warm front and a trailing cold front is expected to move across
the Lower Mississippi Valley later tonight into Saturday morning.
This front is expected to gradually weaken and become nearly
quasi-stationary on Saturday across the area as it becomes nearly
parallel to upper level flow aloft. Several disturbances will move
along this boundary, allowing for the potential of moderate to
heavy rainfall as precipitable water values average between 1.6 to
2 inches. Overall instability appears to be mostly elevated during
this period and kept any mention minimal at this time.
This boundary is expected to begin moving north of the area
Christmas Eve night into Christmas Day. This will result in very
mild high temperatures in the upper 60s to lower/middle 70s on
Christmas Day with rain chances rather minimal. Better chances
for showers and thunderstorms will arrive across the area later
Sunday night into Monday as another cold front moves through the
region. Models show surface based instability with this second
front being slightly better than at the start of the holiday
Long term models suggest another weakening front will come through
the region for mid to late next week bringing additional rain
chances to the region. Temperatures in the long term are expected
to remain slightly above normal through much of the period.
Moist maritime air will flow into the Midsouth this evening, with
a surface warm front forming along an MEM-MKL line during the
overnight. IFR cannot be ruled out at MEM as early as 04Z, but
the best IFR probability will occur by 07Z-08Z.
TS chances nonzero at MEM after 06Z, but given limited elevated
instability on RAP and NAM Bufr soundings, have left out TS
mention for now. If TS does form, likely to be isolated. IFR
chances should be increasing by such time.
Little improvement expected at MEM and MKL on Saturday, with rich
low level moisture and the front stationary and in close proximity
through the afternoon. RUC and NAM Bufr soundings suggest LIFR
possible well into the day Saturday at MEM, while JBR may deeper
into the cool side of the boundary to see daytime MVFR. TUP
should see some daytime improvement with warm sector mixing.
Area Forecast Discussion
National Weather Service Norman OK
942 PM CST Fri Dec 23 2016
Updated temperature/dew point/wind forecast through 12Z based on
Light rain continues to shift eastward across southern Oklahoma.
Precipitation amounts have ranged from a trace to couple
hundredths. Expect this area to move out later tonight. Skies have
cleared behind the wave of rain.
Otherwise, still expect fog to develop later tonight. The HRRR
continues to suggest the lowest visibilities will be just
southeast of the I-44 corridor. This area is experiencing clearing
skies and will be on the northern periphery of higher dew points
where the winds will be light and variable.
.PREV DISCUSSION... /issued 544 PM CST Fri Dec 23 2016/
Aviation discussion for the 00 UTC TAFs is below.
Worsening conditions are expected with fog development after
03 UTC with the worst conditions 12-16 UTC.
Confidence is increasing that widespread fog and dense fog with
LIFR/VLIFR conditions will form southeast of KHBR-KCSM-KSWO after
06 UTC. Conditions may go below minimums including KOKC, KOUN,
KSPS, and KLAW. Additional fog may form near KPNC, KGAG, and KWWR,
though confidence is lower. Although improving conditions are
forecast at all sites after 15 UTC, these improving conditions
may be slow to occur, especially east of KEND-KFDR where IFR or
lower conditions may linger even past 18 UTC.
PREV DISCUSSION... /issued 459 PM CST Fri Dec 23 2016/
Issued dense fog advisory for tonight through tomorrow morning.
There have been some stations starting to report fog across
southern/southeast Oklahoma (Ardmore/Durant) with even denser fog
across northeast Texas.
Latest HRRR/HRRRX/RAP/SREF have been consistent with fog rapidly
developing after 11 PM this evening across locations near and
southeast of I-44. Progged boundary layer relative humidity/dew
point depressions are consistent with this signal. In addition,
many of these locations have forecast low temperatures near or
even cooler than current dew points.
Fog should persist through at least tomorrow morning as light
southerly winds advect higher dew points northward.
PREV DISCUSSION... /issued 229 PM CST Fri Dec 23 2016/
Late this afternoon into the evening, a weak surface boundary
will move across part of northern and western Oklahoma. The main
result will be a shift in wind direction and lighter winds. Clouds
will continue to decrease this afternoon and evening, but may be
slow to clear across south central and southeast Oklahoma.
However as clouds diminish, the risk of dense fog will increase,
especially along and southeast of Interstate 44.
On Saturday, the wind and near surface moisture will increase,
especially during the afternoon. This will occur in response to a
very strong storm system approaching from the west. Low clouds and
some fog may persist much of the day in north central Oklahoma.
Saturday night, low level moisture will continue to improve, so
low clouds and some fog will certainly develop. This may also
result in light rain showers and perhaps drizzle.
On Christmas Day, a negatively tilted trough will move northeast
from the southern and central Rockies. By late Christmas evening
this storm will be located over the northern Plains. Better height
falls will occur across northwestern Oklahoma and the Oklahoma
Panhandle. This along with better jet dynamics may result in
better storm chances early in the morning in northwestern
Oklahoma. Farther south and east, only showers may form as a
capping inversion may limit convective potential. Regardless,
there should be at least scattered showers that move rather
quickly to the north and east. Any precipitation will help
transfer very strong low level winds to the surface. By Christmas
evening, better rain chances will shift east of the forecast area as
relatively dry air replaces a very humid airmass for late
Previous model runs have advertised the chance of rain, possibly
heavy, for the middle of the week (Wednesday). Unfortunately,
both of GFS and ECMwF suggest more of a west to northwest flow
around this time with better rain chances well south and east of
.PRELIMINARY POINT TEMPS/POPS...
Oklahoma City OK 37 61 55 67 / 10 10 40 50
Hobart OK 35 61 55 66 / 0 0 50 70
Wichita Falls TX 39 65 59 69 / 10 10 30 50
Gage OK 27 59 47 60 / 0 0 50 70
Ponca City OK 30 57 51 66 / 0 10 50 60
Durant OK 45 65 60 69 / 50 10 30 50
OK...Dense Fog Advisory until noon CST Saturday for OKZ019-020-
TX...Dense Fog Advisory until noon CST Saturday for TXZ086-089-090.
Area Forecast Discussion
National Weather Service Blacksburg VA
911 PM EST Fri Dec 23 2016
High pressure shifts offshore tonight as a cold front approaches
on Saturday bringing rain to the area. Weak high pressure works in
for Christmas Day although cloudiness is expected to linger.
Another front arrives Monday into Tuesday.
.NEAR TERM /THROUGH SATURDAY/...
As of 845 PM EST Friday...
Rainfall to the west continues to basically parallel the region
this evening with 00z soundings showing very dry air remaining
from the surface to 700 mb attm. This keeping precip aloft for the
moment as initial shot of low level moisture advection now
entering southern North Carolina, with mostly mid deck elsewhere
for now. Latest HRRR as well as the RAP remain rather slow to
bring rainfall into the region with best chances just before dawn
northwest zones, and perhaps spotty light showers south with the
return low level moisture after midnight. Therefore have slowed
down the onset of pops for a few hours from previous while
removing much of the early freezing rain mention northwest
valleys given warmer temps as well as lack of precip to start.
Appears could still have a spot or two of ice late where can
possibly cool the column enough to result in trapped cold air in
the deeper valleys. However this very iffy and not progged by any
recent HRRRX or 00z NAM solutions per such a warm start, so
trimmed back -fzra coverage late as well.
Otherwise beefing up winds for a few hours over the far west where
the boundary layer flow remains a bit more south/southeast. This
combined with the southerly jet aloft increasing to 40-50 knots,
may push gusts to near advisory levels BLF region before veering
flow and deeper moisture tend to curtail gusts after midnight.
Also bumped up lows despite dry dewpoints as appears any precip
will be too light to allow much wet bulb cooling as offset by
early clouds and deepening warm advection from aloft by morning.
Previous discussion as of 330 PM EST Friday...
High pressure retreats tonight with warm advection pattern
setting up ahead of a slow-moving boundary. Precipitation expected
to break out toward early morning as rain in all areas except for
possibility of a few protected northwestern valleys that are able
to radiate out after sunset trapping some cold air and with
evaporational cooling into drier air. Will have to monitor how
that develops if at all but any freezing precipitation will be
short-lived with the increasing southerly flow. An advisory for
freezing rain was considered for portions of Greenbrier and Bath
counties but LWB up to 41 degrees this afternoon so surfaces have
had a decent chance to warm up. Updated HWO to address what could
be a few hours of patchy freezing rain and will issue an SPS if
localized icy conditions seem likely to develop. A short-fused
advisory still not out of the question but clear majority of
guidance and models suggest nothing very impactful.
Used non-diurnal temperature regime with temps warming toward
early morning especially across the southwest under increasing SW flow.
The H85 jet increases to 40 to 50kts toward early morning but as
usual surface winds speeds will be considerably less, generally under
25 mph. Gusts to 40 mph not out of the question in higher
elevations above 4000 feet. Trajectory is mainly SW or S
mitigating against wind advisory for Mountain Empire counties.
Tonight, temps will drop especially with precip starting to fall
in drier air. Will see readings around 32F in the Greenbrier
Valley to portions of Bath county while most have temperatures in
the mid to upper 30s, but warming to the lower 40s late in the far
Southwest VA, southern WV mountains.
Rainfall will persist a good part of Saturday with with fairly
mild temps rising into the upper 40s to low 50s.
.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
As of 300 PM EST Friday...
A cold front will stall across the area Saturday night.
Precipitation, in the form of light rain, will likewise stall, but
become concentrated over the western potion of the region. This will
be in response to a wave moving along the front over Tennessee that
will prolong the light precipitation a bit.
A more substantial upper trough will also start to deep over the
Rockies, and shift into High Plains by Sunday afternoon. This
broader system will help induce a warm front to lift north through
the Mississippi Valley. The eastern flank of this front will skirt
the western portion of the area on Christmas day with some patchy
light rain. Southerly flow in advance of this upper system will help
low level trajectories tap the Gulf of Mexico. This moisture will
advect into the region by Sunday afternoon, and continue Sunday
night. Look for a broadening area of patchy light rain and/or
drizzle to manifest during this time period with its greatest
concentration along and near the crest of the Blue Ridge.
Monday into Monday night, a cold front associated with what is
expected to be a closed low near the border with the northern Great
Lakes region and Canada, will be approaching the region from the
west. Anticipate a transition from southeast flow uplsope patchy
light rain and drizzle, to southwest flow overrunning precipitation
immediately in advance of the front. Again, the focus will be across
the western extent of the region through Monday night.
Temperatures during this portion of the forecast will trend milder
each day with an average temperature some 10 to 15 degree above
normal. Chance of a white Christmas, zero percent.
.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 315 PM EST Friday...
A cold front will cross the area on Tuesday. However, its best
dynamics will remain well north of the area. This will allow for a
scenario for limited coverage of precipitation east of the crest of
the Blue Ridge. By Tuesday night, any associated precipitation is
expected to have ended, or shifted south of the area.
Wednesday through Friday may be active weather days for the region.
First, we will be watching a southern stream shortwave trough that
is progged to lift northeast along the remnants of the Tuesday cold
front. Anticipate light rain to spread into the region from the
southwest Wednesday, and especially Wednesday night.
Temperatures are expected to be mild enough for plain rain.
On the heels of this southern system, will be another shortwave
trough and associated strong cold front still associated with the
Great Lakes upper low. This front is expected to cross the area on
Thursday into Thursday night. Colder air will race in behind this
front allowing for lingering precipitation to transition from rain
showers to scattered snow showers across the higher peak and ridges
of the mountains. Upslope flow behind the front will help maintain
the isolated to scattered rain/snow showers across the mountains
during the day Friday. Areas east of the crest of the Blue Ridge
can expected isolated showers, primarily early in the day.
Winds behind the front will be gusty. Early indicators suggest gusts
could approach the 40s mph range at the highest elevations late
Thursday afternoon through Friday.
Temperatures during this portion of the forecast will be warmest on
Tuesday just ahead of the first cold front. After a small decline
Wednesday, temperatures will increase a bit ahead of the second cold
front on Thursday. These three days temperatures some 10 to 15
degrees above normal are still expected. On Friday, high
temperatures will be closer to reality for this time of year.
.AVIATION /01Z SATURDAY THROUGH WEDNESDAY/...
As of 555 PM EST Friday...
Overall VFR conditions to prevail this evening with lowering mid
deck canopy mainly between 8-12k feet. This will be followed by
deteriorating conditions overnight with bases quickly lowering
into MVFR levels after midnight as low level moisture increases
from the south. Precipitation breaks out during the early morning
hours of Saturday espcly in the KLWB/KBLF corridor after 06z/1am
and perhaps around KDAN shortly thereafter. Some spotty light
freezing rain possible KLWB vicinity as well late tonight but
given isolated nature and potential to see only rain, kept out
mention. Should see widespread low cigs and vsby restrictions
develop toward early Saturday across all locations and continue
through at least midday as an axis of rain drops southeast through
the region. This will result in both IFR/MVFR cigs/vsbys until
perhaps some drying aloft occurs by mid to late afternoon when a
few sites along/east of the Blue Ridge could show some improvement
toward high end MVFR, to perhaps VFR toward the end of the day.
Winds mainly light southeast this evening becoming south then
southwest on Saturday at 5-15 kts except gusts to 20-30 kts
possible around KBLF. Low level jet will also ramp up overnight
resulting in strong winds just above the surface where winds will
be light excluding KBLF. Therefore added in LLWS for all other
locations later tonight into Saturday morning.
Extended aviation discussion...
Surface high pressure will be in place north of the area Sunday
while the front swinging to the coast weakens. With residual
moisture in the low levels, the threat of sub-VFR cigs and perhaps
some MVFR vsbys in the mountains may last Sunday into Sunday night.
Another cold front approaches Monday but appears will stay far
enough to the west to allow for mainly VFR on Monday, though some
models are keeping moisture and wedge around with sub-VFR cigs.
Front may drift across or stall near the area into Tuesday with
possible sub-VFR cigs and a few showers Monday night into Tuesday.
High pressure looks to build in from the west with a brief return
to VFR on Wednesday.
Expectation is for generally 0.25 to 0.50 inches of needed
rainfall by the time it ends Saturday evening. Much of the area
continues to experience precipitation deficits over longer time
scales. The U.S. Drought Monitor issued yesterday continues to
show moderate drought over roughly the southwest half of the CWA
and abnormally dry conditions in many other areas.