Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/28/17
Area Forecast Discussion
National Weather Service Dodge City KS
543 PM CST Wed Dec 27 2017
...Updated Aviation Section...
.SHORT TERM...(This evening through Thursday)
Issued at 344 PM CST Wed Dec 27 2017
Arctic high pressure across western Kansas has been slowly receding
eastward this afternoon with lowering pressure in the lee slopes
of the Rockies. The increasing southerly flow across the western
High Plains is allowing a relatively warmer airmass from west
Texas back into far western Kansas. This along with better low
level southerly flow overnight will have some impact on low
temperature forecasts tonight. Overnight lows may be realized
early tonight especially over the southwest sections of the
forecast area and have raised overnight lows there to reflect
current temperature trends. Another wrench in the the works will
be the extent of clearing skies overnight. NAM/GFS model soundings
show the moist layer drying out overnight. The RAP shows some
drying but keeps a shallow layer of moisture in place. Visible
satellite loop shows the stratus layer thinning out in vicinity of
the Colorado border this afternoon. For now will go with mostly
clear skies in the west with clouds hanging on through the evening
over central and eastern sections of the area before scattering
out later tonight.
Thursday should see partly to mostly sunny skies. MOS guidance
suggests temperatures ranging from the 30s around Hays to the low
50s around Elkhart. A wind shift will move through the area
Thursday morning and northeasterly upslope winds may keep
temperatures a few degrees cooler than forecast.
.LONG TERM...(Thursday night through Wednesday)
Issued at 344 PM CST Wed Dec 27 2017
Friday will be another quiet day with seasonal to above normal
temperatures, before the central Plains go back into the freezer.
An upper level low pressure system over the Northwest Territories
will move southeast toward the upper Midwest and Great Lakes on Friday.
An Arctic airmass over Canada will move get pushed southward into the
northern and central CONUS on Friday with the leading edge of this
airmass moving into southwestern Kansas late Friday afternoon.
Temperatures will be back down in the single digits and teens over
most of the area through the New Years weekend. There could be
some patchy freezing drizzle around central Kansas on Saturday as
model soundings show a sufficiently cold and deep moist layer with
some weak UVV through the layer.
While details become a little more uncertain toward mid week, the
ECMWF and GFS show continued cold air intrusions into the central
Plains as a high amplitude flow pattern is progged to develop by
the models.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 537 PM CST Wed Dec 27 2017
Widespread MVFR stratus will continue through the evening, however
all indications from latest short term models are that this will
start to erode from west to east through the night as lower level
winds become more westerly. This has not happened as of very
early this evening, so will go a little bit longer than the models
show as far as scattering out to VFR. Whenever scattering out does
occur, it may set the stage for some patchy fog, putting flight
category right back to MVFR or perhaps even IFR (which is what we
are forecasting for LBL). Any early morning fog will dissipate
after 15z with VFR expected to prevail.
&&
.PRELIMINARY POINT TEMPS/POPS...
DDC 16 43 15 42 / 0 0 0 0
GCK 14 46 16 45 / 0 0 0 0
EHA 24 52 22 58 / 0 0 0 0
LBL 21 48 17 50 / 0 0 0 0
HYS 13 36 12 32 / 0 0 0 0
P28 17 41 16 40 / 0 0 0 0
&&
.DDC WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...Gerard
LONG TERM...Gerard
AVIATION...Umscheid
Previous forecast discussion is included below for reference.
31
/Issued 420 AM EST Wed Dec 27 2017/
Chaotic forecast period is in store for the extended as polar
lows continue to plague the Hudson Bay region and reinforce the
broad eastern US trough. This will keep the Southeast in a
continued cold pattern with multiple shots of arctic air and a few
opportunities for low- end winter weather events.
Effects of the mixed precipitation event will carry into the first
portion of the long term as the system begins to exit. The NAM
continues to place moisture the farthest north and tho it is an
outlier...will not completely discount until higher res models come
into play. That being said...between 00-06z do think most of the
moisture will be exiting the area.Remaining areas of precip across
southern and eastern Georgia will likely be a mix of rain and
freezing per Bufr sounding data. Accumulations during this time are
unlikely given sfc temp trends hovering right around freezing. The
system should exit the area by 12z Friday.
Friday and Saturday look dry and seasonal with highs in the
generally in the 40s north and 50s central. Next arctic blast is
progged in the Saturday/Saturday night time frame. Evolution of the
synoptic pattern by operational GFS and ECMWF really begin to
diverge in this time frame. Although subtle differences are seen in
GEFS/EPS/GEMS ensemble data...still nudging this forecast towards
the ECMWF. This would bring a strong dry arctic front through
Saturday afternoon...with cold low temps expected overnight into
Sunday with perhaps teens across the mtns. Sunday would therefore be
somewhat breezy and cooler with highs in the 30s north and mid 40s
central.
By New Year`s Eve /Sunday night/ large discrepancies exists in
regards to next winter weather threat. Almost becoming comical how
consistent each run of the EC/GFS is respectively...but the two are
complete opposites of each other. By this point...EC agrees better
with ensembles in the H5 pattern and given such a dry Canadian sfc
airmass in place...think any decent moisture will remain south along
the Gulf Coast. 00z GFS even trended deeper moisture south. Will
still really need to watch...but to account for potential...have
included slight chance of a R/S mix for a large portion of the CWA
Sunday night and Monday. Dry and cold conditions thru the rest of
the forecast.
Kovacik
&&
.AVIATION...
00Z Update...
VFR conditions across ATL/AHN/MCN will continue through the
forecast. Cigs will become VFR in CSG this evening. Low end VFR
clouds have pushed into central GA with high level clouds over
ATL/AHN. The low end VFR clouds will return to north GA Thursday.
Winds will becoming northeast late this evening and remain
easterly for the rest of the forecast.
//ATL Confidence...00Z Update...
High on all elements.
17
&&
.PRELIMINARY POINT TEMPS/POPS...
Athens 28 40 26 47 / 5 10 10 0
Atlanta 30 41 29 47 / 5 10 10 0
Blairsville 22 39 22 45 / 5 5 5 0
Cartersville 27 41 27 46 / 5 5 5 0
Columbus 36 46 34 52 / 10 20 20 0
Gainesville 27 37 27 46 / 5 5 10 0
Macon 35 43 31 51 / 10 20 20 5
Rome 24 43 27 47 / 5 5 5 0
Peachtree City 31 43 29 49 / 5 10 10 0
Vidalia 37 43 33 49 / 10 40 40 5
&&
.FFC WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...17
LONG TERM....BDL
AVIATION...17
Area Forecast Discussion
National Weather Service Lincoln IL
843 PM CST Wed Dec 27 2017
.UPDATE...
Issued at 830 PM CST Wed Dec 27 2017
High pressure centered over central Illinois this evening coupled
with a mainly clear sky has produced a wide variation in temperatures
across the forecast area. Temperatures dropped to as low as 5 below
zero in our north to the lower teens near the I-70 corridor. The
latest satellite data indicates quite a bit of cirrus and some mid
level clouds have streamed southeast into at least the western
half of the forecast area over the past couple of hours resulting
in temperatures leveling off a bit across the west. A weak shortwave
trof embedded in the fast northwest flow will race across the region
early Thursday morning bringing the threat for a brief period of light
snow, especially across the west with the latest NAM-WRF coupled with
the RAP and HRRR models suggesting an overall decrease in the snow
coverage as it crosses the Mississippi River late tonight. Based on
the 00z ILX sounding we would tend to agree with that weakening trend
as there is still a deep layer of very dry air in place across the
forecast area.
Have already made several adjustments to the grids with the overnight
lows as several areas have already reached their forecast lows. Most
of the tweaks in temperatures were across the north and eastern
counties with the ZFP already updated to take into account these early
evening trends. No additional updates to the ZFP are needed at this
time.
&&
.SHORT TERM...(This evening through Thursday)
ISSUED AT 248 PM CST Wed Dec 27 2017
A shortwave trough...currently in western SD...embedded in the
fast upper level NW flow is expected to track toward central IL
late tonight and quickly exit the area shortly after daybreak
Thursday. North of the maximum upper level vorticity and in an area
of moderate mid level lift light snow will develop. Accumulating
snow less than one-half inch is expected along and west of the IL
River valley, with a dusting toward the I-55 corridor.
A longer period of mostly clear sky in eastern IL will allow
temperatures to dip below zero again from about Champaign to
Paris. The rest of the region can expect lows in the single digits
with increasing clouds.
The models are split with their depiction of available weak lift
in central IL Thursday afternoon and early evening, resulting in
light snow showers. Will side with the GFS and Canadian solution
of providing enough forcing for a dusting of light snow in central
IL. A light southerly wind will result in temperatures not as cold
for Thursday, with highs in the mid 20s in southeast IL and 15-20
in central IL.
.LONG TERM...(Thursday night through Wednesday)
ISSUED AT 248 PM CST Wed Dec 27 2017
The medium range models have come to a little better agreement for
the potential for accumulating snow Friday in most of the forecast
area...except for southeast IL. Even the timing seems to be
consistent across the board, with the snow moving in late Friday
morning/early Friday afternoon. There is some spread in the models
regarding the length of the snow, with the NAM cutting it off
quicker, and the GFS, European and Canadian keeping it going
through early Friday night. The blends end most of the
accumulating snow in central IL early Friday night, and in eastern
IL by early Saturday morning. This appears to be reasonable based
on the quickness of the system and colder air/less moisture than
this past weekend. The model QPFs, including several ensembles,
indicate up to a tenth of an inch of liquid equivalent...with snow
to liquid ratios of 18:1-20:1. This would yield 1-2 inches of
accumulation north of Havana-Lincoln-Paris line.
Another reinforcing shot of cold air is anticipated in the wake of
the snow, with highs of 5-10 central IL and teens in southeast IL,
with lows close to what we experienced this morning...below zero
in many locations. There is the potential for another weak
shortwave to bring another shot of light snow on New Year`s Eve,
but there is much less model agreement with this one. The blended
solution has chance PoPs generally south of I-72, so will stick
with that for now.
Beyond the holiday weekend, the longer range models differ in
their depiction of various troughs rotating down into the nation`s
midsection in the persistent NW flow. The key though, is that the
NW flow will continue - which means the bout of colder than normal
conditions will continue at least through the middle of next week.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 513 PM CST Wed Dec 27 2017
Arctic high pressure centered right over the area this evening
will continue to provide VFR conditions thru the night. An upper
level wave across the Dakotas this evening will race southeast
towards our area late tonight and during the morning hours of
Thursday bringing the threat for a period of light snow and lower
VFR cigs for a brief time Thursday morning. That system will shift
away from our area quickly on Thursday but we may see some additional
flurries or snow showers in the wake the system Thursday afternoon
and evening which may bring at least some tempo MVFR cigs to our
northern TAF sites. Winds will continue to be light and variable
tonight and then turn southeast towards morning at less than
10kts, and then become southerly by late in the day at 6 to 10
kts.
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...Smith
SHORT TERM...Miller
LONG TERM...Miller
AVIATION...Smith
Area Forecast Discussion...UPDATED
National Weather Service Lubbock TX
726 PM CST Wed Dec 27 2017
.UPDATE...
Low clouds have cleared across a good portion of the Caprock this
evening. However with dewpoints in the upper teens and lower 20s
the temperature won`t have far to fall before saturating. Thus,
another bout of low clouds and the potential for freezing fog
appears a good bet over much of the Caprock later tonight. Recent
runs of the HRRR, RAP and NAM support this and suggest pockets of
dense freezing fog may initially develop across the western South
Plains late this evening before spreading eastward over much of
the Caprock after midnight. Given this we started the FZFG mention
across the western zones a bit earlier, after 03Z, and expanded
the mention further east over much of the Caprock after 06Z.
Confidence in how thick and/or widespread the fog will become is
low, but we will watch it closely and issue an advisory if it
becomes warranted. Obviously, in addition to reducing
visibilities, any FZFG could deposit light amounts of ice which
would further complicate travel. Any fog should quickly dissipate
by mid to late morning as drying downslope breezes overspread the
South Plains. In addition to modifying the FZFG mention tonight,
we have expanded the sky cover later tonight while also tweaking
the temperature and dewpoint grids over the next few hours.
&&
.PREV DISCUSSION... /issued 552 PM CST Wed Dec 27 2017/
AVIATION...
VFR conditions in place at KLBB and KPVW with KCDS MVFR at the
start of this TAF cycle. Still quite uncertain when or if ceilings
at all three TAF sites may drop back into MVFR to IFR range but
the possibility is there as winds are expected to go light and
variable overnight. Confidence on the exact timing for transition
back to MVFR/IFR is very low and will have to watch satellite
imagery through the evening to evaluate if timing will change for
onset of low clouds at all three TAF sites. Similar to today, any
low ceilings will dissipate by Thursday afternoon with a return
to VFR conditions expected.
Jordan
PREV DISCUSSION... /issued 327 PM CST Wed Dec 27 2017/
DISCUSSION...
Low clouds have been thinning/lifting the past couple hours and
temperatures have been slowly inching up toward the freezing mark on
the Caprock, while lagging by a few degrees in the Rolling
Plains. Hopefully there will sufficient sun/warmth to clear most
of the major roads of ice before temps drop again this evening.
Some weak isentropic ascent and weak moisture advection as winds
turn southerly may result in the redevelopment of low clouds and
freezing fog across portions of the Caprock later tonight, with
low confidence in the extent of any dense fog. Lows will be mainly
in the 20s. Warmer temperatures return tomorrow with downsloping
westerly winds pushing highs into the low 60s across the western
South Plains. Farther east and off the Caprock, winds will be
weaker with less of a westerly component so high temps may be shy
of 50. The warm temperatures should spread farther east on Friday
as mid-level westerly flow strengthens in association with the
passage of a weak shortwave. However, the leading edge of a cold
front could backdoor into northeast counties late in the day which
is something we`ll have to watch.
Speaking of cold air, a bitterly cold airmass (850 mb temps around
minus 20 and 1050 mb mslp) will be spilling south through the
plains this weekend, slowly modifying on the way. The initial
surge should pass through most of our forecast area on Saturday
but could stall out near the state line, and this could lead to a
steep southwest to northeast temperature gradient with highs in
the 50s out west, but only 30s in the far southeast Panhandle/northern
Rolling Plains. The stronger surge of cold air should arrive on
Sunday, and high temperatures may struggle to reach the 30s both
Sunday and Monday, with lows in the single digits and teens.
As for precip. chances, there are indications that light drizzle
and/or freezing drizzle will develop across the Rolling Plains as
early as late Friday night. When the deeper cold air moves in on
Sunday, snow or sleet become more favorable. However, at this time
there does not appear to be any deeper-layer saturation in the
forecast soundings and this should keep precip on the light side.
Farther west on the Caprock, precipitation chances look to be lower
and we`ll keep the forecast dry at this time. One thing to look
for is very cold wind chill readings Sunday Night/New Years Eve
with northeast winds still a bit breezy, wind chill readings could
drop below zero.
The sprawling cold surface high across the southern plains by
Tuesday should be nudged east by a pair of shortwaves diving
through the plains but another front is expected Wednesday which
will temper the recovery.
&&
.LUB WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
23/14
Area Forecast Discussion
National Weather Service Melbourne FL
833 PM EST Wed Dec 27 2017
.DISCUSSION...
Current-Tonight...Weak cool frontal boundary will continue to sag
into the southern FL peninsula overnight with trailing band of
moisture in the low-levels. This band of moisture will bring
increasing low stratus clouds (north to south) across the area.
Local HRRR shows greatest threat for very light precip (stratiform)
over the I-4 corridor. Still feel MOS guidance remains too high for
PoPs. Winds will remain slightly elevated overnight out of the NNW
to NNE. Generally mild with overnight low temps in the M/U50s north
of the I-4 Corridor, L/M60s to the south.
Thursday...Previous Modified...A high pressure system will force
local winds to veer onshore as a fast and energetic flow pattern
continues aloft. GFS and ECMWF generally agree that most of the
surface amplification will occur to the northeast of the area,
keeping the highest rain chances confined to the coastal waters off
Volusia County. Regardless, given the weak cold air advection at the
surface and energetic flow aloft, expect a period of considerable
clouds and isolated to scattered light rain, favoring areas closer
to the coast. Daytime highs range from the M/U60s north and west of
I-4 to the M/U70s along the Treasure Coast.
&&
.AVIATION...Forecast calls for lowering CIGs overnight into Thu
morning for much of ECFL. IFR CIGs expected over a large area
tonight into Thu morning from around KVRB northward. Some patchy fog
is possible overnight, but not expected to be widespread. NNERLY
winds thru the period. Small light precip chances (stratiform)
forecast thru the period. Local HRRR not crazy on coverage and not
comfortable with widespread tempo groups in the TAFs overnight into
Thu.
&&
.MARINE...Overnight-Thu...Increasing NNERLY winds overnight as a
weak cool frontal boundary pushes into the southern peninsula. Winds
remain elevated on Thu 10-15 kts, except 15-19 kts over the open
Atlc north of the Volusia-Brevard County line. Seas 3-4 ft will
build to 4-5 ft north of Sebastian Inlet by daybreak Thu morning,
then continue in upwards of 6-7 ft Cape northward offshore by the
end of Thu afternoon, 5-6 ft Volusia coast near shore, and 3-5 ft
areas further south. Chance of rain showers over the Gulf Stream,
slighter chance nearer the coast.
Cautionary statements, at least, necessary for two northern marine
legs and offshore the Brevard coast for Thu. Future shifts will
monitor if an SCA is needed.
&&
.MLB WATCHES/WARNINGS/ADVISORIES...
FL...None.
AM...None.
&&
$$
Sedlock/Volkmer
Area Forecast Discussion
National Weather Service Raleigh NC
1017 PM EST Wed Dec 27 2017
.SYNOPSIS...
Arctic high pressure will build into the area bringing cold and dry
conditions to central NC. A few upper level disturbances of little
consequence will move through before a reinforcing shot of cold air
will keep temperatures below freezing from Sunday through the
beginning of next week.
&&
.NEAR TERM /THROUGH TONIGHT/...
As of 1010 PM Wednesday...
Very cold arctic high pressure over the Midwest will bring very cold
and dry air to central NC. Current observations show dewpoints at
this hour in the single digits across southwestern VA as the airmass
pushes southward. Some of these values could work into the NW
Piedmont by morning as temperatures bottom out in the low 20s
across the north with mid to upper 20s across southern counties.
Winds are also expected to begin picking up, especially in the
southeast where the pressure gradient between the exiting low and
the forthcoming high is strongest. Some gusts of up to 20 knots can
be expected during the early morning hours on Thursday across the
southeastern counties with 10-15 kts across the northwest Piedmont
where mixing will be less. Both the NAM and RAP solutions are
holding on to some low level moisture around 925 mb that could bring
some MVFR ceilings in from the north, but these have yet to
materialize upstream and some solutions have backed off on this.
Regardless, broken high clouds will continue to transverse the area
overnight.
&&
.SHORT TERM /THURSDAY THROUGH FRIDAY/...
As of 330 PM Wednesday...
An arctic air mass will settle overhead Thu as the sfc ridge
builds/extends south from the parent high positioned over the
eastern Great Lakes. The low level air mass is quite dry, yielding
sfc dewpoints near zero or sub zero. The westerly flow aloft will
likely result in patches of high level cloudiness. Afternoon
temperatures will average about 15 degrees below normal. High
temperatures will vary 30-35 north, 35-40 degrees south.
Thursday night, an upper level disturbance crossing the lower MS
Valley will approach the SE U.S. late Thu night. This system will
induce backing of the low level flow, leading to increasing
cloudiness. The GFS and the ECMWF has trended drier with this
system, shunting the better chances for measurable precip close to
the SC/southeast NC coast. The NAM remains unsettled and has been
fairly consistent, depicting zone of low level convergence over
northeast SC/southeast NC. The low level flow is also 5-10 kts
stronger compared to the GFS. Thus the NAM is appreciably wetter
over our far se counties. initially thought about reducing PoPs to
less than 15 percent, but decided to give some credence to the NAM
due to its consistency. So will retain a slight chance PoP roughly
south of a FAY-GSB line, centered mostly over Sampson County. RH and
thermal profiles suggest that the favored dendrite growth zone never
reaches adequate saturation. Thus, appears the dominate p-type will
be patchy light freezing rain (if it occurs at all), and maybe some
sleet. If the NAM does verify, any freezing rain will be
light/spotty, resulting in no worse than a light glaze on elevated
objects. Min temps upper teens to lower 20s.
Friday, the system scoots/exits quickly east early, with decreasing
cloudiness. Deep wly flow in the wake of the exiting system will
advect a slightly "milder" air mass into central NC. Afternoon
temperatures will vary from around 40 north, and low-mid 40s south.
&&
.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
As of 238 PM Wednesday...
...Frigid, dangerously cold temperatures expected from New Year`s
Eve through the middle of next week...
The main weather story during this part of the forecast continues to
be cold temperatures, thanks to arctic high pressure and its
associated airmass that will gradually build into our area from the
west and north. Two airmass changes are progged to occur, with the
first beginning late Saturday and Saturday night behind a dry arctic
cold front. H8 temps are progged to drop nearly 10C and low level
thicknesses nearly 60m from Saturday night through early Monday as
the airmass builds in. Lows Friday night in the mid 20s will
recover to highs on Saturday in the 40s before the airmass change.
Then lows Sunday and Monday morning from the mid teens to lower 20s,
with high temps remaining around or below freezing most places both
days...except our far S/SE zones where mid 30s for highs will occur.
Then on Monday we`ll get a reinforcing shot of cold air with the
next cold front crossing our area, that will further drop H8
temps another 5+ deg C and low level thicknesses falling
another 20-30m or so. As such, lows Monday night will fall to the
lower teens across many locations, with highs on Tuesday once again
remaining at or below freezing. The airmass will finally begin to
moderate by late Tuesday and Wednesday, but not before another night
of low temps in the teens early Wednesday morning.
As for precip chances during this time...it appears to remain dry
most... if not the entire... long term period. But we`re still
keeping a close eye on things for New Years Eve into New Year Day,
as models still show southern stream jet energy lifting north and
merging with the northern stream short wave energy moving across the
Mid-Atlantic. The GFS is still more robust with the aforementioned
southern stream wave and thus better facilitates moisture advection
northward along the SE coast. The ECMWF is weaker with the southern
stream, thus allowing northern stream westerly flow to keep the
deeper moisture pinned eastward. It`s worth noting though...that
even the wetter GFS keeps the deepest moisture and best precip
chances to our east. Stay tuned!
Cntl NC residents are encouraged to make the necessary preparations
to their homes now. Ensure pets have a place to seek shelter from
the cold. Additionally, it is a good idea to check on any elderly
family members or friends that live alone.
&&
.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
As of 620 PM Wednesday...
Widespread VFR parameters expected through 00Z Thu, with the
exception of potential MVFR ceilings at RDU/FAY/RWI thanks to a
stubborn stratus deck expected for only a short amount of time
between 06z - 12z overnight. Lower confidence on specific location,
but higher confidence on the shorter duration of the cloud shield,
which should quickly exit as mixing increases tomorrow around
daybreak. Winds should stay light to moderate, with a few gusts
possible through the TAF period.
VFR parameters should persist across central NC through the weekend.
A series of upper level disturbances will cause variably cloudy
skies at times, though precipitation should be limited. Patchy light
wintry mix may occur late Thu night-early Fri morning to the south
and east of KFAY and KGSB, though ice accrual, if any, is expected
to be very light and spotty.
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...Ellis
NEAR TERM...Ellis
SHORT TERM...WSS
LONG TERM...np
AVIATION...JJM/WSS
Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
420 PM MST Wed Dec 27 2017
.DISCUSSION...(This Evening Through Wednesday)
Issued at 252 PM MST Wed Dec 27 2017
Large upper trough persist across the eastern two-thirds of the
CONUS today. Surface high pressure has moved into the upper
Mississippi Valley with return flow over the area. Temperatures are
widely varying with highs in the single digits to teens across the
western South Dakota plains. Temps across northeast Wyoming and the
Black Hills have reached the 20s and 30s, as warmer air continues to
push into the area. Southeasterly surface winds across the plains
have kept temps much colder, not warming to previously expected
temperatures. Temps tonight will be steady or drop into the single
digits area wide. Colder air will push into the area late tonight,
as the next Canadian surface high slides into the northern Plains. A
weak upper wave crossing the region will bring chances of slight
snow mainly to parts of northeast Wyoming into the northern Black
Hills area. Snow amounts will be light, with most areas seeing
accumulations of an inch or less. Deep northwest flow will continue
across the region through the end of the week into the weekend.
Generally dry weather is expected Thursday, then a series of upper
waves will cross the baroclinic zone bringing a band of snow from
eastern Montana through the CWA. This band will begin Thursday night
and continue into Friday with an inch or two of accumulation. Snow
will let up somewhat late Friday, then the next upper wave will push
through later Friday night and continue through Saturday. A stronger
wave is then progged to cross the region later Saturday into
Saturday night bringing the best chances for accumulating snow. By
Sunday, there could be snow ranging from 2 inches to 6 or more
inches. There is still a wide range of discrepancy between models
and within the GFS ensemble runs. The lower end is the ECMWF at 2
inches and the GFS looks to be on the higher extreme at 6 to 8
inches or so. Snow accumulation is expected to be very gradual
through a two to three day period. A very strong arctic surface
high will push into the region especially toward Sunday with 850mb
temps dropping to around -25C. It looks like it will be a very
cold day with highs not reaching above zero across much of the
western SD plains. Lows could drop below -20F, with wind chills
below -35F. Much warmer and drier air will push into the area
early next week with highs reaching into the 20s.
&&
.AVIATION...(For the 00Z TAFS Through 00Z Thursday Evening)
Issued At 420 PM MST Wed Dec 27 2017
MVFR CIGS will overspread northeast WY through 06z as snow begins
to saturate the low levels. Will likely see some IFR VSBYS and
ceilings 06-10z at GCC. Will refine timing/intensity of these
conditions or introduce tempo groups as we approach 06z.
VFR conditions will generally prevail elsewhere across the area
overnight. MVFR CIGS may develop across western SD late Thursday
morning into the afternoon, but a continued downslope wind component
east of the Black Hills could maintain VFR conditions at RAP
through the TAF period. For now, will keep any low clouds at RAP SCT.
&&
.UNR WATCHES/WARNINGS/ADVISORIES...
SD...None.
WY...None.
&&
$$
DISCUSSION...13
AVIATION...Sherburn