Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/24/18
AREA FORECAST DISCUSSION
National Weather Service Albany NY
935 PM EST Sun Dec 23 2018
.SYNOPSIS...
A clipper type system will bring some snow to the region overnight
into Monday. High pressure builds back in for Christmas with
fair, cold and dry weather.
&&
.NEAR TERM /THROUGH MONDAY/...
As of 930 pm, just slight tweaks to PoPs and QPF/snow
incorporating latest HRRR guidance, which is on the dry side of
the model suite. Overall forecast message remains intact.
Previous discussion...
As of 645 pm, mid and high clouds streaming toward the forecast
area ahead of southern stream wave. Leading edge of the
precipitation associated with this system is now approaching the
Mason-Dixon line and appears to be captured well by the latest
HRRR/NAM3/HREF Mean. Previous forecast reasoning holds, only
slight changes to PoPs to delay onset time of snowfall very
slightly.
Previous discussion...
As of 320 PM EST...Weak high pressure continues to be over the
region this afternoon, however some lake enhanced moisture has been
trapped beneath an inversion for clouds to dominate west of the
Hudson River Valley and down the Mohawk Valley into the Capital
Region, northern and central Taconics into the Berkshires,
Litchfield Hills and southern Greens. Locations north of the
Capital Region into the Lake George Region, and south into the mid
Hudson Valley, southern Taconics, and NW CT and east of the southern
Greens have been mostly sunny. These lower clouds should gradually
erode late this pm and early this evening, but mid and high clouds
will begin to increase from the south and west ahead of a southern
stream short-wave moving out of the TN Valley and lifting northeast
towards the OH Valley, and Mid Atlantic States. This initial
impulse will allow for clouds to thicken and lower tonight. Another
disturbance, approaching from the northern and western Great Lakes
Region associated with northern stream energy will be quickly moving
towards upstate NY and New England tomorrow in the late morning
through the afternoon.
The southern stream disturbance/short-wave shifts towards the Mid
Atlantic Coast, and southern New England between 06Z-09Z based on
the 12Z NAM/CMC/ECMWF/GFS. Weak isentropic lift/warm advection will
spread light snow across the region, especially from the Capital
Region south and west during this time frame. The column gradually
moistens and the best synoptic lift will be occurring across the
southern most zones. The moisture fetch does not look as good
further north early on. The low to midlevel southwest flow may
allow for some enhancement over the southeast Catskills, southern
Taconics, Litchfield Hills. We are expecting generally 1-2" of snow
by daybreak in the southern zones (highest totals over the higher
terrain by daybreak) with an inch or less in the mid-Hudson Valley.
Further north, the light snow will extend north and east by 7 am
with generally a dusting to a half an inch from the Capital Region
north and east. The light snow will be ongoing for the Christmas Eve
commute, so there could be some slick spots on untreated roads. The
better chance for the synoptic lift to tap into the dendritic
growth zone in the -12C to -18C range will be south and east of the
Capital Region. The best 850-700 hPa FGEN on the NAM/GFS stays south
of the region. Lows tonight will generally be in the mid to upper
20s with some mid teens to lower 20s over the southern Adirondacks,
Lake George Region, and southern VT.
Tomorrow...The southern stream disturbance quickly scoots downstream
in the morning around 12Z, as the clipper low, and its mid and upper
level northern stream short-wave trough will be approaching central
and eastern NY in the late morning. This disturbance has some
isentropic lift coupled with some cyclonic vorticity advection that
will tap some eastern Great Lakes Region moisture. Another batch of
snow will overspread the region from the eastern/northern Catskills
north and east in the late morning into the early to mid afternoon.
Limited moisture with the clipper and its warm front, but a 1 to 3
inch snowfall is possible with the clipper with the higher totals
over the western Adirondacks, western Mohawk Valley and portions of
the northern Taconics/southern Greens. Temps warm enough in the mid
Hudson Valley south and east that rain may mix with snow or change
completely to light rain for little or any additional accums. We
will have to monitor in the very late afternoon into the early
evening if some heavier snow showers or an isolated squall with the
cold front and upper trough passage impacting possibly the
northern/eastern Catskills/Schoharie Valley/western Mohawk Valley
which the 3-km NAM guidance shows the most. These may stay west of
the forecast area. The snow will taper to isolated to scattered snow
showers/flurries in the afternoon.
Overall, this will be a widespread light snow
event from the two features with storm total snow amounts of 1-2" in
the valley areas, except the the western Mohawk Valley where 1-3"
may occur. The eastern Catskills, and western/souther Adirondacks
may get 2-4". The western New England higher terrain including the
Litchfield Hills, southern Greens, and Berkshires will be in the 1-
3" range. An inch or less is possible in the mid Hudson Valley.
Total liquid equivalent for the event across the region will be in
the one to two tenth of an inch range with snow to liquid ratios
blended to yield 10-15:1 values. Highs tomorrow will be in the upper
20s to mid 30s over the hills and mtns, and primarily mid and upper
30s in the lower elevations with a few lower 40F readings in the mid
Hudson Valley.
&&
.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
Any lingering snow shower activity should end Monday evening with
many areas seeing breaks in the clouds between midnight and
daybreak. The coverage of clouds will determine whether temperatures
will reach colder guidance levels or not Monday night and early
Tuesday morning. Expect lows Monday night to be in the mid teens to
upper 20s. Just intervals of clouds will become partly to mostly
sunny Tuesday. Winds will be light and temperatures will reach the
mid to upper 30s but 20s higher terrain. Mainly dry weather is
expected Tuesday night with lows in the upper teens to mid 20s.
On Wednesday a weak upper level disturbance and associated surface
trough move through the region. This system looks to be rather
moisture-starved with weak forcing, so will only mention low chance
of snow showers for areas north and west of the Hudson Valley.
Expect highs to be in the mid 20s to around 40.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
Seasonable to above normal temperatures likely ensue for the long
term period with a few threats for precipitation. Temperatures will
determine precipitation type with chances for rain, wintry mix and
snow during this final week of 2018.
We begin the extended period Wednesday night with a moisture starved
cold front pushing through northern New England. The best forcing
looks to remain well north of our region so have a dry forecast.
However, the ECMWF continues to show potential for weakening snow
showers/flurries west of the Hudson River so would not be surprised
if we reintroduced slight chance POPs for those areas in future
updates.
Surface high pressure and upper level ridge build in from the Great
Lakes in its wake for Thursday as a low pressure system intensifies
in the Central Plains. Increasing latent heat released from this low
should allow the downstream ridge and surface high to strengthen.
The general consensus among the latest global guidance is for the
high to build up to around 1040mb over the Northeast which is
impressive. This should lead to a pleasant Thursday for eastern NY
and western New England with morning sun fading behind increasing
afternoon clouds with temperatures warming to seasonable levels in
the mid - upper 30s. Clouds continue increasing Thursday night as
our upper level ridge shifts into the eastern New England and
southwesterly return flow ensues. The rate at which clouds thicken
will determine how quickly temperatures fall after dark. Given the
strength of our high, areas in western New England and the Upper
Hudson Valley may have a few hours to radiate in the evening before
the thicker clouds arrive.
Precipitation should gradually push north and eastward overnight as
isentropic lift associated with a now mature cyclone in the Midwest
increases over the Northeast. We continue to see discrepancies among
the latest global guidance on the start time of precipitation with
ECMWF showing the latest arrival time and the GFS and CMC in rather
good agreement for an earlier onset. Considering the strength of our
high and the fact that some initial precipitation may fall as virga,
we favored the ECMWF solution and held off on widespread chance POPs
until 06z-12z Friday.
Some wet-bulbing/diabatic cooling processes should take place as
precipitation overspreads the region as the low levels should be dry
to start. We should see a non-diurnal temperature trend Thursday
night with the coolest temperatures likely occurring before 06z
Friday. This set-up should allow initial precipitation to fall as
snow before transitioning to a wintry mix and then eventually rain
by Friday morning. Areas in the Upper Hudson Valley, the Berkshires
and southern VT may hold on to the wintry mix the longest into
Friday morning before the warm front finally pushes north of our
region. By Friday afternoon, all areas should see plain rain with
temperature warming nicely into the 40s and even 50s as our cyclone
travels into Ontario, Canada.
Rain should transition to showers Friday night as the best warm air
advection shifts into eastern New England and our occluded cyclone
continues its track up the Saint Lawrence River Valley. The 500mb
pattern shows us turning rather zonal heading into Saturday as the
large scale ridge over the Southeast U.S remains intact. Without a
sharp trough pushing through the region, temperatures should be slow
to cool and we should stay slightly above normal for Saturday. The
cold front from our cyclone should gradually slide south and east
from Canada through the day but moisture along the boundary looks
rather lackluster. Thus, only have chance and slight chance POPs for
areas north and west of the Capital District.
As our cold front continues its slow journey through our area
Sunday, we will have to monitor a shortwave trough arriving from the
Great Lakes. This could develop into a surface low and lead to an
organized area of precipitation, potentially falling as snow as
temperatures continue cooling through the day.
&&
.AVIATION /03Z MONDAY THROUGH FRIDAY/...
VFR conditions expected to prevail through at least 06Z as mid
and high level clouds increase ahead of an upper disturbance
approaching from the Ohio Valley. Leading edge of the
precipitation associated with this system is now approaching the
Mason-Dixon line, and will spread into KPOU as light snowfall
likely between 06-08Z. Period of IFR vsby is expected there in
light snow to around 15Z. It will take longer for the light
snow to begin at KALB/KPSF, with onset time likely around
08-10Z. IFR vsby is likely, at least at times, from around
11-17Z at KALB/KPSF. Snow is not expected to begin at KGFL until
around 11-13Z, with IFR conditions more of a question mark
compared with locations further south.
Flying conditions should improve quickest at KPOU, with most of
the snowfall having ended by around 15Z, and a return to VFR
conditions by around 18Z. At KPSF, some light snow showers may
continue into the early afternoon, and possibly into the evening
at KPSF due to upslope flow. Snow showers look to be around for
much of the day at KGFL, but for now will keep conditions at
MVFR levels. All told, around 1-2 inches of snow is expected
over the terminals tonight into Monday.
Winds will be light and variable until Monday afternoon, when
they will pick up out of the west at around 5 to 10 kt, with
some gusts to around 20 kt possible at KALB/KPSF.
Outlook...
Monday Night: Low Operational Impact. Slight Chance of SHSN.
Christmas Day: No Operational Impact. NO SIG WX.
Tuesday Night: No Operational Impact. NO SIG WX.
Wednesday: No Operational Impact. NO SIG WX.
Wednesday Night: No Operational Impact. NO SIG WX.
Thursday: No Operational Impact. NO SIG WX.
Thursday Night: Moderate Operational Impact. Likely SN...SLEET.
Friday: High Operational Impact. Likely RA.
&&
.HYDROLOGY...
Some minor river flooding is still occurring along the Housatonic
River basin where the heaviest rainfall occurred. The water is
slowly receding.
The next chance of any precipitation will be tonight and Monday
when periods of mainly light snow are expected. Drier weather
into the middle of the week should allow for most area rivers
and streams to continue to gradually recede.
For details on specific area rivers and lakes, including
observed and forecast river stages and lake elevations, please
visit the Advanced Hydrologic Prediction Service /AHPS/ graphs
on our website.
&&
.ALY WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
MA...None.
VT...None.
&&
$$
SYNOPSIS...11/NAS
NEAR TERM...Thompson/Wasula
SHORT TERM...11/NAS
LONG TERM...Speciale
AVIATION...Thompson
HYDROLOGY...11/NAS
Area Forecast Discussion
National Weather Service Denver/Boulder CO
818 PM MST Sun Dec 23 2018
.UPDATE...
Issued at 818 PM MST Sun Dec 23 2018
Westerly flow aloft will transport Pacific moisture across the
Central Rockies tonight and Monday. A weak trough embedded in the
flow aloft will enhance lift and produce snow across the mountains
later tonight and Monday. Going forecast appears on track with
sub advisory amounts. Radar reflectivity upstream over Utah has
not been impressive. HRRR precipitation amounts have trended down
a little for the mountains. If anything forecasted snowfall
amounts may be a little high. However, the same impacts are
expected with snowfall producing slick roadways in places late
tonight and Monday.
&&
.SHORT TERM...(This evening through Monday)
Issued at 134 PM MST Sun Dec 23 2018
The remainder of today will see increasing clouds as a weak short
wave trough traverses the state on Monday. WNW flow aloft will
transition to west flow as the short wave trough approaches.
Between now and midnight no precipitation is expected across our
area and generally light winds will prevail across the Plains. The
higher mountain passes will continue to have winds gusting over
50 mph into this evening before speeds come down as the pressure
gradient relaxes a bit later tonight. Overnight lows will be
seasonal area-wide and not quite at cold across the high mountain
valleys given the expected cloud cover and the start of some snow.
The aforementioned short wave trough generates rising motion
around midnight tonight, and combined with nearly saturated 700 mb
upslope flow snow should begin in the mountains and pick up as
the trough axis approaches the area. Lapse rates are likewise
favorable for accumulating snow through most of Monday. With only
modest cold advection aloft and no clear jet streak support, rates
should be light to at most briefly moderate across the highest
mountain passes, especially the Park Range. Travel could be
impacted across the highest passes like Rabbit Ears, Cameron, Gore
and Vail Passes with up to 8 inches possible throughout the day.
At lower elevations much less snow expected with 1-3 inches
expected across the mountain valley floors. The I-70 corridor from
Frisco to Bakerville could see 2-6 inches, also potentially
impacting travel from Monday morning through the evening. The
impacts may be partially mitigated by the fact that temperatures
are not terribly cold (-8 degC at 700 mb) and the bulk of the snow
will fall during daylight hours. Thus have opted not to issue an
advisory but will message the potential impacts to travel via
social media and other means. After passage of the trough axis
favorable lapse rates and continued upslope flow out of the WNW
will continue into Monday evening but snow rates should lessen
throughout the evening with stronger subsidence moving in. Expect
snow to end in the mountains shortly after midnight Tuesday
morning.
On Monday the plains will be mostly dry since downsloping will
dominate with west flow associated with the approaching short wave
trough. The trough axis will cross the Continental Divide late
morning and in its wake subsidence will spread across our area,
forcing gusty northwest winds to the surface east of the Divide.
Gusts to 20 mph are possible Monday afternoon across the eastern
plains. The bulk of the QG lift remains north of us but can`t rule
out a chance of light snow across the Cheyenne ridge into the
early afternoon until the winds go downslope there. Still talking just
slight chance PoPs and no impacts expected to travel there.
Temperature advection is neutral to slightly cooler in the low
levels so expect highs on Monday to be a few degrees cooler than
today.
.LONG TERM...(Monday night through Sunday)
Issued at 345 PM MST Sun Dec 23 2018
There will be some upper ridging for the forecast area Monday
night and Tuesday. The flow aloft will be southwesterly Tuesday
into Wednesday afternoon. An upper trough will move into western
Colorado late Tuesday night then into the CWA Wednesday afternoon
and Wednesday night. Downward synoptic scale energy is in place
Monday night. Upward motion is noted on the QG Omega fields
Tuesday through much of Wednesday night. The low level winds look
to be weak drainage Monday night. By Tuesday, weak east and
southeasterly upslope is in place over the plains and foothills.
South and southeasterlies are progged Tuesday night well into
Wednesday. A cold front and north-northeasterly upslope behind it
is progged in late Wednesday/early Wednesday evening. Moisture-
wise, Monday night is pretty dry, then moisture increases a little
on Tuesday and Tuesday night, but it increases significantly on
Wednesday and Wednesday night. The QPF fields show a tiny bit of
measurable snow in the mountains Monday evening, then again late
day Tuesday and Tuesday evening. There is a bit of measurable
snowfall over much of the the CWA Wednesday and Wednesday night.
The highest amounts are noted over the eastern plains of Colorado.
Overall, the QPF amounts are significantly less than previous
model runs indicated. The current 12Z runs show no areas of
highlight criteria snowfall. Will keep the pops in the "scattered"
to "likely" range for the mountains and eastern plains, less for
the foothills and western plains late Tuesday night into Thursday
morning. For temperatures, Tuesday`s highs are 1-3 C cooler than
Monday`s. Wednesday`s highs are 2-4 C cooler than Tuesday`s. For
the later days, Thursday through Sunday, models show a mean upper
trough developing over western North America Thursday. Colorado is
in the upper trough axis Friday and Saturday. There is upper
ridging over Colorado be next Sunday. Moisture decreases on
Thursday, then increases Thursday night and Friday. Things dry out
again Saturday night and Sunday. Temperatures stay below normals
all four days. The QPF fields show minimal snowfall Thursday
through Friday night and mainly over the mountains.
&&
.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 818 PM MST Sun Dec 23 2018
VFR conditions will prevail through Monday in the Denver area.
High clouds will continue to stream across Colorado through Monday
with ceilings staying above 9,000 feet. Light winds are expected
to become a light south/southwest drainage direction through 18Z.
Winds are expected to turn northerly after 18Z Monday at speeds
less than 15 knots.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...Meier
SHORT TERM...Schlatter
LONG TERM...RJK
AVIATION...Meier
Area Forecast Discussion
National Weather Service State College PA
1046 PM EST Sun Dec 23 2018
.SYNOPSIS...
A weak wave will track just south of Pennsylvania tonight and
early Christmas Eve, bringing a light accumulation of snow to
the mountains of Central Pennsylvania. High pressure will track
across the region during midweek before a new area of low
pressure moves toward the forecast area by late in the week.
&&
.NEAR TERM /THROUGH MONDAY/...
Light rain and snow now covers the southern half of central Pa
and continues to lift northeastward. Southern stream low
pressure moving towards the Delmarva region with an occluded
front extending northward to the eastern GLAKS and a weak Nrn
stream low over Ontario. Primarily light snow will fall from the
Central Mountains northward overnight with light accums of a
coating to an inch or so in most areas...and perhaps 1-2 in the
the higher elevations of the Laurels/NW Mtns/and east of
Williamsport overnight. A northern stream shortwave will follow
for early Monday, bringing a chilly WNW wind behind the weak
departing low. Snow showers over the usual western and northern
higher elevations will be diminishing as the day grows older.
&&
.SHORT TERM /MONDAY NIGHT/...
High pressure builds in Christmas Eve Night as lingering light
snow showers over the NW come to an end. Lows drop into the mid
to upper 20s for most, with temps remaining milder at or just
above freezing in the SE.
&&
.LONG TERM /TUESDAY THROUGH SUNDAY/...
Christmas day will be chilly but fair. Highs in the 30s will be
slightly cooler than normal. A weak disturbance the models
cannot agree on may produce a light snow shower late in the day
or Christmas night. Otherwise high pressure will build into
central PA with an upper level ridge bringing dry weather
Wednesday into Thursday.
The high center will move off the coast Thursday ahead of the
next big weather system in the central U.S. poised to move in
for the end of the week.
Latest guidance now suggests we stay dry most of Thursday with
rain moving in overnight into Friday. Models trends have been to
slow this down some. The slower approach will increase the
chances that temperatures in the north will get down to the
freezing mark. therefore some locations may begin as a wintry
mix and then switch to a period of light freezing rain toward
Friday morning before warming back above 32 deg.
Friday looks to be rainy as the low pressure center moves north
of the area dragging a diffuse warm front through. Timing
differences then arise between the GFS and ECMWF and Canadian
models with the GFS pushing a low quickly up into eastern
Canada with a trailing cold front pushing through Saturday,
while the EC and Canadian models keep a wavy front north of the
region. Needless to say there is enough uncertainty to hedge the
POPs at the end of the forecast with us either being in a fairly
typical cold NW flow regime or south of an east-west boundary
and on the mild side.
Both the GFS and the Euro indicate a disturbance Sunday will
bring some light snow to central PA.
&&
.AVIATION /04Z MONDAY THROUGH FRIDAY/...
Low pressure will track south of Pennsylvania tonight, spreading
a period of light snow across much of state and light rain over
the southern tier. Model soundings and SREF probability charts
indicate a period of ifr cigs are likely at KBFD and KJST
overnight due to upsloping flow. The other area of concern will
be across the southeast airfields (KMDT/KLNS) where radar trends
and the latest HRRR indicate the steadiest precipitation and
reduced cigs will occur. Model soundings indicate a rain/snow
mix is likely at KMDT and probably just rain at KLNS. Elsewhere,
lack of significant precipitation or upslope flow will likely
result in only mvfr reductions overnight from KAOO northeast
through KUNV/KIPT.
A return to vfr conditions is expected across much of central Pa
Monday, as the storm system and associated light precipitation
exit the area around dawn. However, residual low level moisture
ascending the Appalachians is likely to result in lingering
mvfr stratocu and scattered snow showers from KBFD south through
KJST.
.Outlook...
Tue...No sig wx expected.
Wed...AM low cigs possible NW Mtns.
Thu...Evening rain/low cigs possible.
Fri...Rain/low cigs possible, especially early.
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...RXR
NEAR TERM...DeVoir/RXR
SHORT TERM...RXR
LONG TERM...Watson/La Corte
AVIATION...Fitzgerald
Area Forecast Discussion
National Weather Service Grand Junction CO
559 PM MST Sun Dec 23 2018
.UPDATE...
Issued at 555 PM MST Sun Dec 23 2018
Latest HRRR and NAMNEST guidance continues to show some
accumulating snow for the Steamboat Springs area and also the West
Elk and Sawatch mountains as the shortwave moves overhead. Both
models show precipitation picking up at midnight and continuing
overnight into tomorrow. With the holidays almost upon us, and
with many people driving this weekend, figured it best to get the
word out for some inclement weather. To that end, added the 2
areas mentioned above to the going advisories. Thinking 3 to 7
inches for Steamboat and 4 to 8 for the mountains. A bit concerned
about the Gunnison area but more so Cerro Summit which is in the
same zone but further west. Later shifts will need to monitor. Rest
of forecast looking good.
&&
.SHORT TERM...(Tonight through Monday night)
Issued at 352 PM MST Sun Dec 23 2018
After the much cooler start to the day this morning (especially
across portions of northern and central Colorado where minimum
temperatures dropped some 10 to 20 degrees to what was experienced
on Saturday), the rest of today has been a quiet transitional
day. As we head into the evening hours clouds will increase across
the area as a shortwave trough approaches from the Great Basin.
High resolution models show snow showers developing over the
northern and central mountains after 8 or 9 PM this evening before
increasing in coverage overnight. Snow will be widespread over
northern and central Colorado by daybreak Christmas Eve and
throughout the day as the nose of a 90 knot jet ushers the
shortwave to the east. The heaviest accumulations are anticipated
during the early to late morning hours on Christmas Eve as upper
level flow turns to a more favorable northwesterly. Storm total
accumulations for this shortwave will be in the 4 to 8 inch range
for the Elkhead, Park, Elk, and Gore mountain ranges as well as
Flat Tops. As a result, a Winter Weather Advisory was issued
earlier this afternoon for these areas. The West Elk and Sawatch
Mountains were getting borderline criteria but confidence just
wasn`t there to issue. Another area that might need to be
monitored closely this evening will be the Upper Yampa River
Basin. Meteograms for the Steamboat Springs area are projecting
snowfall totals of 3 to 5 inches but there some outliers
exceeding 6 or 7 inches. Additionally, daytime highs on Monday
will hover around freezing which will minimize impacts.
Showers will taper off along the Divide Monday evening but no
significant clearing is anticipated as we will already begin to
see the influence of the next storm Monday night. Upper level flow
will shift to the southwest overnight as an area of low pressure
drops south into California from the Pacific Northwest. Isolated
showers will linger through daybreak Christmas Day over the higher
terrain. Overnight lows should only cool by 3 to 6 degrees or so
Monday night.
.LONG TERM...(Tuesday through Sunday)
Issued at 352 PM MST Sun Dec 23 2018
Christmas Day will see the low progress into southern California
by midday and into southwest Arizona by the evening hours.
Moisture will spill out ahead of the low into eastern Utah and
western Colorado throughout the day as precipitable water values
climb to around four tenths of an inch in the Four Corners. The
models are probably overdoing the coverage of showers during the
early part of the day on Christmas, especially across the north,
but either way we are looking at showers increasing from midday
onwards. The San Juans will be favored for activity under strong
south-southwesterly flow aloft as the low tracks east. QPF
projections were once again impressive this afternoon and did not
shift much from what was produced by the previous shift. Given the
favorable orographics, ample moisture and influence from the
upper level jet, decided to issue a Winter Storm Watch for the
San Juans this afternoon. Of course, it would be nice if issuing a
Watch guaranteed a slam dunk event but there are still a few
factors that could alter the outcome. The main consideration is
just how far south the upper level jet will dive. If the models
continue to nudge the jet and subsequently the base of the trough
further south that will shift the heavier precipitation potential
along with it. However, considering this storm falls on Christmas
Day and into the 26th when many will begin their travels back
home, felt it was important to get the word out. Preliminary
storm total snowfall projections are in the 8 to 16 inch range
with locally higher amounts possible, especially on southwest-
facing slopes. Currently the watch is set to begin at 9 AM
Christmas morning and continue through 9 PM on Wednesday the 26th.
This may need some tweaking if models slow down the arrival of
this system.
So, the San Juans are pretty much guaranteed a White Christmas
this year, but what about everywhere else? A lot of that will
depend on temperatures. South-southwesterly flow out ahead of the
storm will allow the lower valleys to jump into the upper 30s and
low 40s on Christmas. Christmas evening is looking more promising
for most areas as temperatures drop and cooler 700mb temperatures
of -4 to -8 degrees C are introduced into the region. Of course,
the eventual track of the low will ultimately decide a location`s
odds for a White Christmas. As far as the lower elevations go,
the southern valleys look to be the winner with 1 to 3 inches
expected at this time through daybreak Wednesday.
Showers will continue on Wednesday as the low eventually
transitions to an open wave and lifts to the northeast. Drier air
will filter into the region Wednesday night allowing for most
activity to come to an end. This break will be short-lived though
as yet another trough looks to drop into the northern Rockies on
Thursday. Showers will redevelop over the higher terrain of
eastern Utah and western Colorado by Thursday evening and
continuing on Friday. Extended models begin to differ on handling
the duration and track of this system Friday onwards so there is
still plenty of time for things to change. Overall though, we can
expect cooler temperatures with unsettled wintry weather
throughout much of the long term period.
&&
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 447 PM MST Sun Dec 23 2018
Increasing clouds from WNW with ceilings lowering and areas of
snow mainly mountains vcnty and north of I-70 obscuring higher
terrain. IFR ceilings and visibilities in snow expected to become
widespread in the mountains of northwest CO after 06Z tonight.
Ceilings expected to drop below ILS break points at KEGE and KASE
after 06Z tonight, at KHDN and KRIL and KTEX after 10z-12Z, and
KGUC after 15Z. Then expect improving conditions from the west
starting in eastern UT after 16Z and spreading into western CO
Sunday afternoon.
&&
.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Winter Weather Advisory from 11 PM this evening to 6 PM MST
Monday for COZ004-005-010-012-013.
Winter Storm Watch from Tuesday morning through Wednesday
evening for COZ018-019.
UT...None.
&&
$$
UPDATE...TGR
SHORT TERM...MMS
LONG TERM...MMS
AVIATION...JRP
Area Forecast Discussion
National Weather Service Charleston WV
807 PM EST Sun Dec 23 2018
.SYNOPSIS...
Cold front today with light rain changing to snow. Weak disturbance
Christmas Day. High pressure Wednesday. Milder with another rain
maker for the end of the work week.
&&
.NEAR TERM /THROUGH MONDAY/...
As of 800 PM Sunday...
Re-ran the QPF using the HRRR as a base which yielded 3-5
inches of snow across our highest elevation zones in Randolph
and Pocahontas counties. This agrees with the orientation and
trajectory of the mid level frontogenetical forcing which yields
a quick 3-6 hour thumping of wet snow this evening. As a result
I issued a Winter Weather Advisory for the aforementioned
locations.
As of 430 PM Sunday...
Made an update to the grids to better represent what is
currently happening on radar and by using spotter reports and
updated model guidance. Lowered temperatures and added to the
weather type grid to represent a strong deformation band at
700mb sweeping through the area heading northeast. The band is
dropping mostly a rain/snow mix along with some heavier snow
showers from the dynamical cooling. As the band moves out of the
area all precipitation should change over to mostly rain as we
lose that dynamic cooling this late evening then back to snow
overnight.
As of 1 PM Sunday...
A fairly potent short wave will cross the region this evening
through tonight. Temperatures across most of the area will be
warm enough for mostly rain to fall this afternoon and evening,
however, CAA quickly takes hold this evening and tonight. A
changeover to snow, even in the Lowlands may be possible for a
brief period, but very little to no accumulation is expected.
Across the mountains, precip may start off as rain, but
expecting a quick transition to snow as those colder T850 rush
in this evening. Does appear likely that accumulations will
amount to much, but higher elevations could see a 2 to 3 inch
snow by Monday morning, with about an inch elsewhere in our
mountain zones.
Considered the possibility of a Winter Weather Advisory, as
amounts will be well below criteria, but with temperatures
dropping into the 20s, road conditions may become quite slick by
tomorrow morning if left untreated. However, decided to hold off
for now as... 1. Confidence in how quickly temperatures drop is
still low and 2. Areas most likely affected are the highest
elevations and impacts there will be limited, especially with
snowfall occurring during the overnight hours.
Snow showers will come to an end in the mountains Monday morning
and conditions will improve throughout the day with high
pressure building into the area.
&&
.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/...
As of 130 PM Sunday...
A weak disturbance will move across the area on Christmas day.
With lots of dry air in the low levels, will mostly just produce
some clouds. However, some light rain or snow could make it to
the ground in central Ohio and northern West Virginia.
A high pressure system will then provide dry weather for
Wednesday.
&&
.LONG TERM /THURSDAY THROUGH SUNDAY/...
As of 130 PM Sunday...
A strong system over the central US will then push a warm
front/cold front combo through the area on Thursday and Friday.
Although there will be a good dose of rain, with the main low
lifting into the Great Lakes region, should be much less than
the last 2 big events.
Models show another system Saturday night into Sunday. However,
models vary considerably with this system, leading to low
confidence on the details.
&&
.AVIATION /01Z MONDAY THROUGH FRIDAY/...
As of 700 PM Sunday...
A fast moving, but potent system will be crossing the region
this evening. Expect deteriorating conditions with widespread
rain, mixing with snow across the lowlands and all snow in the
mountains. Cigs will lower into IFR with some LIFR as well.
Variable vsby warranted some IFR/LIFR tempo groups, with a
period of predominate IFR vsby across the mountains. Conditions
will start to improve from the west during the predawn hours,
though taking until mid or late morning for cigs to lift at
CKB/EKN.
Winds becoming more westerly tonight as the surface low
pressure passes. Some gusts of 30-40kts are likely across the
mountains.
FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 00Z TUESDAY...
FORECAST CONFIDENCE: Medium.
ALTERNATE SCENARIOS: Timing of restrictions this evening will
likely vary depending on the intensity/type of precipitation.
EXPERIMENTAL TABLE OF FLIGHT CATEGORY OBJECTIVELY SHOWS CONSISTENCY
OF WFO FORECAST TO AVAILABLE MODEL INFORMATION:
H = HIGH: TAF CONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL.
M = MEDIUM: TAF HAS VARYING LEVEL OF CONSISTENCY WITH MODELS.
L = LOW: TAF INCONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL.
DATE MON
UTC 1HRLY 00 01 02 03 04 05 06 07 08 09 10 11
EST 1HRLY 19 20 21 22 23 00 01 02 03 04 05 06
CRW CONSISTENCY H H H H H M H H H M H H
HTS CONSISTENCY H H H H H L H M H H H H
BKW CONSISTENCY H H H M M H L H H M H H
EKN CONSISTENCY H H M H M H H H M L H H
PKB CONSISTENCY H M H M H H L M M H H H
CKB CONSISTENCY M H L M H H H M H H H L
AFTER 00Z TUESDAY...
No widespread IFR expected.
&&
.RLX WATCHES/WARNINGS/ADVISORIES...
WV...Winter Weather Advisory until 7 AM EST Monday for WVZ523-526.
OH...None.
KY...None.
VA...None.
&&
$$
SYNOPSIS...RPY/MPK
NEAR TERM...JZ
SHORT TERM...RPY
LONG TERM...RPY
AVIATION...30