Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/27/19
Area Forecast Discussion
National Weather Service Denver/Boulder CO
342 PM MST Thu Dec 26 2019
.SHORT TERM...(This evening through Friday)
Issued at 245 PM MST Thu Dec 26 2019
Stratus deck is burning off, although there`s still a few patches
in eastern Boulder/Larimer Counties, and more over Washington
County. While the airmass has fully mixed over the mountains and
Palmer Divide with much drier air, the boundary layer remains
moist and stable north of Denver and across most of the plains.
That will set the stage for stratus and fog redevelopment. There
should also be relative pressure falls to our south overnight as
the upper low begins to inch into the Desert Southwest. This would
likely result in some sort of a weak Denver cyclone or northerly
surge along the Front Range, which would help stratus and fog
spread south into Denver overnight. The wildcard in all of this is
how thick the mid and upper level clouds get, as an earlier
increase and thickening could limit the fog threat. That is not
seen right now, however, so we`ll go with patchy to areas of fog
overnight across most of the plains.
On Friday, attention will turn toward precipitation. There is weak
warm advection and generally weak QG lift through the afternoon.
The flow is deep southerly just off the deck, and that type of
flow would favor precipitation over the eastern plains and crest
of the Palmer Divide, and also Park County/southern Summit County
in local upslope. We`ll have the highest PoPs there and increase
them through the day with the arrival of better lift. NAM seems
overly aggressive with amount of precipitation, but a few favored
spots mentioned above could see an inch or two during the
afternoon hours. Temperatures look cold enough to support mostly
snow, and have lowered forecast high temperatures considering the
expected cloud cover.
.LONG TERM...(Friday night through Thursday)
Issued at 340 PM MST Thu Dec 26 2019
Model have southwesterly flow aloft decreasing Friday night with
an upper trough moving eastward. On Saturday, the upper trough is
progged to move eastward across Colorado. The trough axis is over
the CWA from 18Z on Saturday to 08Z Sunday morning. Behind the
trough axis, strong north-northwesterly flow aloft moves into the
CWA. The QG Omega fields show just moderate upward vertical
velocity over the CWA Friday night into Saturday evening. Downward
motion moves in behind the trough axis the rest of Saturday night
and Sunday. The low level pressure and wind fields show a cold
front, and northerly winds behind it, to move across the CWA
Friday night after midnight. The northerly winds get pretty strong
through the day Saturday, especially east of the Urban Corridor.
Decent northerly winds continue Saturday night with northwesterlies
on Sunday. There is pretty deep moisture with the storm. Cross
sections show the moisture to stick around well into Saturday
night. Moisture decreases Sunday with a bit lingering in the
mountains. The QPF fields show fair amounts of measurable snowfall
Friday night into Saturday evening, then it decreases. There is a
tad of snowfall progged to continue falling in the high mountains
Sunday and Sunday night. Concerning the winter storm highlights;
there is some synoptic scale energy, cold air advection, and
decent moisture, however the models are not in great agreement,
especially with the QPF and the QG Omega vertical motion. Will
leave the watch in place and add zone 41 to it as the Palmer Ridge
does pretty good in strong northerly flow. Temperatures on
Saturday look to be 6-8 C colder than readings on Friday. Sunday`s
high temerptures are pretty close to Saturday`s readings. For the
later day`s Monday through Thursday, northwesterly flow aloft is
in place Monday with more zonal flow for Tuesday into Wednesday.
By Wednesday night and Thursday, the next upper trough moves
across. Temperatures stay right around or slightly cooler than
normal readings all four days. There will be a chance of snow in
mountains most of the time and a slight chance over the plains
Wednesday into Thursday.
&&
.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 140 PM MST Thu Dec 26 2019
There remain varying solutions concerning fog redevelopment
tonight. At this time, NAM looks overly aggressive, while latest
HRRR is coming around to more of the conceptual model with a weak
Denver Cyclone pulling in stratus/fog. Boundary layer moisture is
holding strong to the north of Denver, so without development of
thicker mid/upper level cloud development until tomorrow morning
the stratus/fog forecast appears on track. It`s still hard to pin
down timing and extent of fog, but initial development would favor
the 08Z-10Z time frame. That fog would linger through a good
chunk of Friday morning before lifting.
By Friday afternoon, we`ll start to focus more toward snow in the
forecast. There may be an initial band of snow in the warm
advection that drifts over the airports after 18-21Z. Perhaps a
dusting in the grass with that band. Main threat of accumulating
snow holds off until Friday night and Saturday.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Friday evening through Saturday evening
for COZ041-042-044>046-048>051.
&&
$$
SHORT TERM...Barjenbruch
LONG TERM...RJK
AVIATION...Barjenbruch
Area Forecast Discussion
National Weather Service Cheyenne WY
505 PM MST Thu Dec 26 2019
.UPDATE...
Issued at 500 PM MST Thu Dec 26 2019
Southeast winds here at Cheyenne this evening could create some
upsloping stratus and fog conditions here. Had a report of fairly
widespread fog and low visibility in eastern Cheyenne already,,,so
went ahead and added areas of fog into the forecast for the
Cheyenne area this evening. GFS sounding for Rawlins showing a
great setup for fog out there as well...so added areas of fog out
there. Updates have been sent.
&&
.SHORT TERM...(Late this afternoon - Friday)
Issued at 210 PM MST Thu Dec 26 2019
Afternoon WV/IR imagery showed a powerful closed upper low
affecting southern CA/NV and western AZ. Pacific moisture from
this system was spreading northeast into the Four Corners, with
a veil of high clouds over the central Rockies. A cold front
extended from Lake MI across eastern MO, central OK, and northwest
into southeast WY. Low clouds covered much of western NE into
portions of southeast WY. Isolated light snow showers over the
higher terrain will end later this afternoon.
Dry and cool conditions are forecast tonight and Friday morning.
Light rain and/or snow showers will develop and spread north into
extreme southeast WY and the southern NE Panhandle Friday afternoon.
High temperatures Friday will be near seasonal normals.
.LONG TERM...(Friday Night - Thursday)
Issued at 319 AM MST Thu Dec 26 2019
Winter storm concerns quickly take over as we head into Fri night/
Saturday. This is an extremely complicated forecast scenario, with
very low overall confidence for this time range. Models are coming
into better agreement w/ the overall evolution of the storm, but a
few considerable discrepancies still exist concerning the track of
the storm and resulting QPF over our CWA. On Friday, a significant
northern stream short wave will dive quickly south across Montana/
western Wyoming, a continued westward trend. Meanwhile, a vigorous
closed low will be drifting from southern California and along the
AZ/Mexico border. This will eject into the 4 Corners & will become
absorbed by the northern stream system by late Friday. Models then
show significant deepening over Colorado with surface cyclogenesis
likely to occur from southeast CO into western KS. The 0z ECMWF is
still the most concerning being the furthest west with the track &
its H7 low tracking directly over the Panhandle. The GFS & NAM are
considerably further east, but other foreign models including both
the GEM and UKMET are closer to the ECMWF albeit not quite as well
organized as the ECMWF. Ensembles are virtually all over the place
for the storm track w/ extremely high standard deviations for this
being less than 48 hours out.
Here is what we know. The majority of southeast WY and the western
NE Panhandle will see accumulating snowfall. The heaviest snowfall
will begin by late Friday night and will likely persist through at
least late Saturday night. A blended approach to QPF places higher
chances for 4+ inches of snow over the southern Nebraska Panhandle
and areas along the Pine Ridge from Lusk-Chadron. This makes sense
even with some of the more eastern storm tracks. The ECMWF remains
the most aggressive with QPF, but is a favored model in the eye of
our national centers. Significant discrepancies exist for the Pine
Ridge, but feel confident that strong northerly low-lvl winds will
lead to topographic enhancement in that area. ECMWF ensemble probs
are around 40-50 percent for 6+ inches along/east of the Wyoming &
Nebraska line, nudging west along the Cheyenne/Pine ridges. Values
increase to 70-80 percent for 3+ inch probabilities. One important
factor here will be that winds are likely to be fairly strong with
excellent low-level gradients in place. Widespread gusts up to 30-
40 MPH would create problems even w/2-4 inches of snow, especially
while the snow is falling.
Given extensive collaboration w/ WPC and neighboring WFOs, we have
agreed that a unified message is critical due to this being a very
busy travel weekend following Christmas. A Winter Storm Watch will
go into effect from Friday evening through early Sunday, for areas
along/east of a Lusk-Torrington-Pine Bluffs line.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 500 PM MST Thu Dec 26 2019
Tricky forecast tonight as lower atmosphere still moist from
recent precip and upsloping winds for a time. Followed latest HRRR
guidance on the 00Z TAFs...which shows lowering conditions at KRWL
and KCYS. Will continue to monitor.
&&
.FIRE WEATHER...
Issued at 210 PM MST Thu Dec 26 2019
No fire weather concerns are anticipated through early next week
due to cooler than normal temperatures, widespread snowfall, and
non-critical humidities.
&&
.CYS WATCHES/WARNINGS/ADVISORIES...
WY...Winter Storm Watch from Friday afternoon through late Saturday
night for WYZ102-108-119.
NE...Winter Storm Watch from Friday afternoon through late Saturday
night for NEZ002-003-019>021-054-055-095-096.
&&
$$
UPDATE...GCC
SHORT TERM...MAJ
LONG TERM...CLH
AVIATION...GCC
FIRE WEATHER...MAJ
Area Forecast Discussion
National Weather Service Dodge City KS
522 PM CST Thu Dec 26 2019
...Updated Aviation Discussion...
.SHORT TERM...(This evening through Saturday)
Issued at 348 PM CST Thu Dec 26 2019
A major storm system will bring prolonged precipitation to western
Kansas beginning tomorrow morning. There are still a lot of question
with this storm, but the focus is narrowing on pretty much a pure
cold rain event for much of our southwest Kansas region. The big
question initially, will be out west tomorrow morning through early
afternoon as short-term higher resolution model consensus suggests
surface temperatures 31 to 34F from onset of precipitation through
the afternoon. The official forecast will reflect mixed
precipitation, mainly in the form of freezing rain should the
surface temperature be 32F or just below. All the CAMs shows the
first wave of precipitation mainly along/west of U83 to the Colorado
border. The storm has slowed down enough to the point that areas
east of U83 and especially east of U283 will likely not see much
precipitation at all until very late in the afternoon. As the main
body of the warm conveyor precipitation event translates east late
Friday and Friday Night, the boundary layer will continue to
slowly warm, however initial wet-bulb effect could bring the surface
temperature precariously close to the 32F point Friday evening. It
will be close, but for now, the official forecast is a cold rain
with temperature in the mid 30s, slowly warming to the upper 30s
Friday Night through early Saturday.
Going beyond Friday Night, the main warm conveyor precipitation
event will come to an end, however given the slow movement of the
whole upper trough, and with some indication of another potential
vorticity anomaly rounding the base of the trough across eastern New
Mexico early Saturday, there could be another round of warm conveyor
precipitation developing across the Texas Panhandle and moving on
north-northeast into portions of southwest and/or south central
Kansas. As far as precipitation amounts go, we are still going with
a widespread three-quarters inch plus, with an axis of one-inch
plus, focused mainly on the U283 corridor north-northeastward up
toward Ellis County. Some areas within this axis still may see up to
1.5 inches of rain given the expected training nature of heavier
showers and even a lightning flash or two. Any thunder potential
should be confined to areas closer to the Oklahoma border. As the
main surface low and 700mb mature and develop northeast of here, the
"comma head" deformation axis will likely develop well to our north
across far northwest Kansas into central Nebraska. The big snow
storm with this system will be confined to areas of northeast
Colorado, far northwest Kansas into much of the western half of
Nebraska, and continuing on into the Dakotas.
We collaborated with NWS Pueblo and Amarillo about a Winter Weather
Advisory in the western counties against their NWS areas, but given
the remaining high uncertainty in whether the temperature will be 32
degrees long enough out there in the west, we decided to hold off.
The following shifts will really need to watch these temperature
trends closely, and see how actual observations are matching short-
term surface temperature progs off the HRRR and other high-
resolution models.
.LONG TERM...(Sunday through Thursday)
Issued at 348 PM CST Thu Dec 26 2019
After the weekend storm is out of here by Sunday, temperatures will
slowly moderate back into the 40s by early next week, with Wednesday
likely being the warmest day of the upcoming week. The global models
continue to show a rather active polar jet stream entering the CONUS
off the Pacific, but right now, there are no indications of another
major mid-latitude cyclone affecting western Kansas. Things can
change fairly quickly in this active regime, so we will continue to
monitor daily changes and trends in the global numerical prediction
for our next potential precipitation event.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 509 PM CST Thu Dec 26 2019
Clear skies this Thursday evening will give way to increasing MVFR
ceilings along with areas of fog after midnight in the Garden
City, Liberal and Dodge City areas. IFR or even a period of LIFR
ceiling will be possible at Garden City and Liberal between 09z
and 15z Friday. Winds overnight and Friday will be east to
southeast at 10 knots or less. As an upper level trough
approaches early Friday the chance for a cold rain will be
possible in the Garden City and Liberal areas after 15z Friday
and this area of cold rain will then begin to spread east into the
Dodge City and Hays areas during the afternoon. Confidence is not
high at this time but a few models models do suggest that there
may be some patchy very light freezing rain/drizzle at or just
west of the Garden City and Liberal areas briefly between 12z and
15z Friday. Ceilings during the day on Friday will range from 500
to 2000ft AGL.
&&
.PRELIMINARY POINT TEMPS/POPS...
DDC 26 38 33 50 / 0 90 90 30
GCK 25 36 32 45 / 0 90 90 20
EHA 29 36 31 45 / 20 90 70 20
LBL 29 36 33 47 / 10 90 90 20
HYS 25 39 32 48 / 0 80 90 60
P28 30 44 39 56 / 10 50 90 70
&&
.DDC WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...Umscheid
LONG TERM...Umscheid
AVIATION...Burgert
Area Forecast Discussion
National Weather Service North Platte NE
642 PM CST Thu Dec 26 2019
.SHORT TERM...(This evening through Friday night)
Issued at 308 PM CST Thu Dec 26 2019
The models continue to advertise a vigorous warm air advection
driven precipitation event Friday night. The short term model blend
plus bias correction, where appropriate, was the basis for rain
changing to snow and freezing rain Friday evening. Ice accumulations
are about the same as the previous forecast and around 1/10 of an
inch of ice is predicted along and east of highway 83 with highest
ice accumulations near highway 183. Snow accumulations of up to 2
inches are in place Friday night throughout wrn and ncntl Nebraska
but given the strength of the forcing, locally higher amounts could
develop.
The forecast Friday night could go a variety of ways as the GFS,
known for deep mixing and warmer temperatures, suggests mostly rain.
Meanwhile, the NAM indicates a mix of rain and freezing rain
changing to snow and the 15z 39hr solution of the RAP model
indicated rain changing to snow. The blended forecast appears
similar to the NAM and the forecast suggests about 1/3 of an inch of
liquid should fall in the form of rain, snow and freezing rain.
All models indicate this area of precipitation will lift rapidly
north Friday night followed by a weakening or lull in the
precipitation early Saturday morning. This is the result of the
forcing on the h700mb warm front lifting in South Dakota and deep
convection across Kansas and eastern Nebraska blocking moisture
transport into western Nebraska.
.LONG TERM...(Saturday through Thursday)
Issued at 308 PM CST Thu Dec 26 2019
The models are beginning to congeal on the development of a wrap
around band of moderate to heavy snow Saturday across wrn
Nebraska. This band of snow will either lift north through wrn and
ncntl Nebraska as indicated in the ECM or translate northeast
through ncntl and northeast Nebraska as suggested by the GFS, the
GFS ensemble and the 12z NAM. The forecast follows a blended
approach but limits snow to liquid ratios to 14 to 1 which might
still be too high given the strong winds that are expected to
develop Saturday afternoon and last through Sunday night. This
snowfall forecast is close to the ECM and WPC with 6 to 10 inches
of snow throughout wrn and ncntl Nebraska. Highest amounts are
predicted along the SD border. Note that the 18z NAM does not show
this band of snow developing. The upper level low in the model is
still organizing Saturday evening and the model will skip over
Nebraska producing the heavy snow north of the region.
The wind forecast Saturday through Monday uses a blend of the
consensus MOS plus bias correction. This produced speeds of 25 to 30
mph and gusts to 45 mph which is close to the 30 mph surface speeds
suggested by the 500m AGL winds indicated in the models. The
prospect of blizzard conditions developing appears on the low side
as this storm will be operating in a very high moisture environment
with temperatures mainly in the upper 20s to around 30. This tends
to produce a sticky snow which generally hugs the ground.
Nonetheless, it appears this storm will approach the upper limit for
winter storms.
Overall the models are tracking the storm through Nebraska and
stalling it for a period of time across the Upper Midwest. This
slower motion is allowing for stronger winds and more moisture to be
ingested into the system. Storm total QPF across western and north
central Nebraska has increased to 1/2 inch to 1 and 1/4 inches. The
Winter Storm Watch will remain in place as the models are showing
east and west storm track differences which could ultimately exclude
some areas from winter storm conditions.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 533 PM CST Thu Dec 26 2019
Latest satellite imagery and surface obs show a few patches of low
stratus across the Panhandle, elsewhere generally partly cloudy
skies overhead with VFR ceilings. Current thinking is partly
cloudy skies will persist overnight across northern NEB with
increasing sky cover across southwestern NEB. Increasing concern
in the potential development of low stratus late tonight-early
morning earlier than presently advertised across far southwest
NEB. Confidence is below average at this point but may need to
update. Thinking at least low-end VFR ceilings (less than 7 kft)
spreading across western NEB early morning to north central NEB
by late afternoon. Ceilings will lower to MVFR-IFR late morning-
afternoon across southwestern NEB and the western Sandhills. Storm
system then moves into the region Friday night bringing ahead of
it increased rain chances Friday afternoon with potential for a
wintry mix starting late afternoon.
&&
.LBF WATCHES/WARNINGS/ADVISORIES...
Winter Storm Watch from Friday evening through late Saturday
night for NEZ004>010-022>029-035>038-056>059-069>071-094.
&&
$$
SHORT TERM...CDC
LONG TERM...CDC
AVIATION...ET
Area Forecast Discussion
National Weather Service Memphis TN
839 PM CST Thu Dec 26 2019
.UPDATE...
Light rain or drizzle continues across portions of North
Mississippi and West Tennessee this evening. Will update to add
20 POPS. The latest HRRR continues to show dense fog development
along and west of the Mississippi River during the overnight
hours. Will change patchy wording to areas of fog and will monitor
for fog development. A Dense Fog Advisory will likely be needed
at some point tonight. The combination of clouds and fog will keep
lows from dropping as much as previously thought. Will also bump
up lows a tad. Update will be out shortly.
KRM
&&
.DISCUSSION.../issued 218 PM CST Thu Dec 26 2019/
.SHORT TERM (Tonight through Friday Night)...
Persistent low clouds, light rain and drizzle has managed to
produce minor accumulations at Memphis, and the surrounding areas.
Coverage seems to be diminishing over the last couple of hours.
We may see some breaks in the clouds prior to sunset but low
clouds and fog is expected to return overnight. Persistence is
often one of the best forecast tool. With that in mind, expect
clouds to linger through much of the day again tomorrow, keeping
temperatures in check.
30
&&
.LONG TERM (Saturday through Thursday)...
Numerical models are converging their solutions for a major storm
system over the Central US this weekend. Northern and Southern
streams of the jet combine on Saturday leading to cyclogenesis over
the Plains. A mild and humid airmass is in place over the Mid-
South leading us to focus on the potential for severe weather and
heavy rainfall.
Based on current model trends the significant brunt of showers and
thunderstorms should hold off until Saturday night. Although dew
points creep into the 60s and a powerful jet moves into the Plains
an orientation so far west is not conducive for increasing amounts
of instability. Consequently, the models struggle to muster up only
a few hundred J/KG of CAPE.
On Sunday another strong jet streak rotates through the base of the
trough, which does prove worrisome, however the pre-frontal surface
trough is already located in the eastern portion of the CWA by
Sunday morning. Instability in our forecast area again proves
difficult to generate. Although the evolution of this jet streak
will need to be watched.
The end result of all this lack of instability suggests that a
marginal risk for severe weather is appropriate despite the shear.
Additionally rainfall amounts as the trough progressively rotates
through the region should remain generally from 1 to 2 inches, with
localized 3 inch amounts, most likely in north Mississippi.
This trough dominates our weather into early next week with more
average temperatures before yet another shortwave ejects from the
Southwest US. This next weather system shows promise for bringing
us a wet 2020 New Year.
Belles
&&
.AVIATION...
A mix of MVFR/VFR cigs prevail across the Mid-South this evening.
Drizzle/light rain has pretty much come to an end for the time
being. A weak cold front will drop into northern areas of the
Mid-South early Friday morning. Expect IFR/LIFR cigs to develop
along and ahead of the front with dense fog likely over parts
eastern AR, the Bootheel and NW TN. Drizzle is also possible.
Expect the LIFR conds to impact MEM and JBR later tonight into
Friday morning with somewhat better conds at KMKL and KTUP. Winds
will be light through the period.
SJM
&&
&&
.MEG WATCHES/WARNINGS/ADVISORIES...
AR...None.
MO...None.
MS...None.
TN...None.
&&
$$
...Update to aviation forecast discussion...
.SHORT TERM...(This evening through Friday)
Issued at 300 PM CST Thu Dec 26 2019
For tonight, the question is what will the stratus do and is
there a chance for fog to develop overnight. The NAM has generally
been the only model solution to hold onto the stratus this long,
and the RAP has started to catch onto this as well. Forecast
soundings from both models suggest the stratus will dissipate
during the evening and the the boundary layer could saturated as
radiational cooling occurs. Although I`m not sure what would cause
the inversion and stratus to dissipate after sunset. So there is
a large amount of uncertainty with the low level humidity. Have
inserted some patchy fog across the north where skies are more
likely to be clear for a period of time this evening. Also have
held onto the stratus across eastern KS well into the evening.
Lows are expected to range from the lower 20s along the NEB state
line to the lower 30s over east central KS. If the clouds hold on
all night, lows could easily be a few degrees warmer.
Friday should start to see moisture return as the upper low over the
southwest moves into the souther Rockies. Forcing for vertical
motion will be on the increase through the day, but it appears to
be at its strongest after Friday. So think Friday will be a mostly
cloudy or overcast day with highs slowly climbing into the mid 40s
to near 50. Precip chances should increase across central KS and
spread east as the day progresses.
.LONG TERM...(Friday night through Thursday)
Issued at 300 PM CST Thu Dec 26 2019
Have categorical POPs for Friday night through Saturday. This is
when models show a consensus for the best forcing and moisture to
come together before a dry slot works its way into the state by
Saturday evening. With good warm air advection and the forecast
area remaining on the warm side of the system through Saturday,
precip should be in the form of rain for all of the area. Models
show some weak surface based instability developing across eastern
KS Saturday afternoon. Lapse rates remain pretty marginal and
near the moist adiabat, but low level and deep layer shear are
progged to be good enough for possibly some organized convection.
We may have to keep an eye out for a strong thunderstorm Saturday
afternoon. The dry slot eventually works in Saturday evening
bringing a break from precipitation. Then there may be enough wrap
around moisture for some precip within the deformation band on
the back side. Forecast soundings suggest a wintry mix could be
the most likely precip type since saturation within the dendritic
growth zone is hard to come by. However any precip looks to be
very light so the forecast doesn`t anticipate a lot of impacts
from this just yet. Highs Saturday over eastern KS are forecast to
be near 60 thanks to persistent low level warm air advection.
Further west across north central KS, highs may only make it into
the lower 50s since the temp advection shouldn`t be as strong.
Colder temperatures are likely Sunday as gusty northwest winds
advect cold air into the region.
The forecast remains dry for Sunday night through Tuesday night. Dry
air is forecast to be over the area with no well organized
disturbance progged by the models. There are some slight chance POPs
in the forecast for Wednesday and Thursday as models show energy
over the southwest trying to phase in with a northern stream trough
moving through the plains. Moisture availability looks to be a
limiting factor for POPs at this point. Temps are forecast to see a
gradual warming trend, but remain generally seasonable with lows in
the 20s and highs in the 40s.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 529 PM CST Thu Dec 26 2019
The deck of MVFR stratus continues to linger over terminals at
the 00Z TAF issuance time. Forecast soundings and high res models
show scattering of the cloud deck occurring around 02Z at KMHK
and a few hours later at KTOP/KFOE. Confidence is not high,
however, that CIGS will scatter that quickly so amendments will be
possible this evening. Patchy fog is looking possible early
tomorrow morning, especially if skies clear through the night.
&&
.TOP WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SYNOPSIS...Wolters
SHORT TERM...Wolters
LONG TERM...Wolters
AVIATION...Teefey
Area Forecast Discussion
National Weather Service Las Vegas NV
345 PM PST Thu Dec 26 2019
.SYNOPSIS...A potent storm over southern California is pushing
eastward towards southwestern Arizona and will continue to do so
through Friday morning. This storm will continue produce
widespread moderate to occasionally heavy rain and winter weather
impacts across southeast California, southern Nevada and
northwest Arizona followed by dry conditions over the weekend.
Another system dropping south late Sunday into Monday will bring
a quick chance of precipitation followed by gusty north winds
Tuesday.
&&
.SHORT TERM...Through Tomorrow.
With the forecast more or less on track this afternoon, not many
significant changes were made to the forecast through 12Z tomorrow
morning.
Of note, looking at the latest HRRR and 12Z HREF trends as well as
satellite trends, felt fairly confident snowfall cessation for
both the Spring Mountains/Mountain Springs area as well as
Mountain Pass should be over between 06-12Z. Thus, trimmed back
the end time of those respective WWAs to 12Z instead of 15Z.
However, snowfall expectations have not changed much and thus did
not see the need for further upgrades or amount updates.
Farther east to Hualapai Mountain, did increase QPF a bit there
(and thus snow totals) due to enhancement in the deformation zone
seen on satellite as of 15Z over Mohave County. Hualapai Mountain
Rd has been closed already where the majority of impacts are
expected. Even with the higher totals though, expectations are on
the high end of advisory level and feel fairly comfortable that
this is appropriate.
Still believe flash flood impacts will be isolated in nature, if
any but can`t rule this possibility out due to the aforementioned
enhancement seen on satellite. QPF totals have been impressive in
the Twentynine Palms area (~1.25+") and with another 12ish hours
of rainfall possible in the lower deserts across the Colorado
River Valley and southern Mohave, did not feel comfortable
canceling the watch.
Latest HRRR trends quickly dissipate PoPs by 18Z tomorrow but this
is on the faster end of solutions this afternoon so lingered low
end chance PoPs for eastern Mohave county through 00Z tomorrow.
However by this point, the bulk of the lifting associated with the
low should be well east of the region and only light precip is
expected, thus did not feel a extension in the watch or advisory
was needed.
.LONG TERM...This Weekend through New Year`s Day.
Overall, weekend weather expectations have not changed much.
However, looking at our next system late Sunday into Monday
morning, a few intriguing details are worth noting...
Looking at the deterministic GFS/ECMWF/Canadian, there suggests
significant difference in the southward progression of the next
low pressure system. While both are very cold lows, one is
positioned along the California coast, and the other is much
farther east, passing directly over southern Nevada by Monday
morning. Diving into ensemble cluster analysis, there suggests
evidence that about 20% of the GFS ensembles favor the 12Z ECMWF
while there is much more agreement in the ECMWF ENS. Thus,
the forecast overall favored this more eastward progression. What
is that interesting? It would be the best possibility for snow
levels to reach desert valley floors. However, this also would
mean it would move through quickly, moisture would be lacking, and
low temperatures Monday morning look to stay in the mid to upper
30s, so no accumulations would be expected. Also, snow levels
would recover quickly by late morning, so the opportunity would be
short and marginal, but not-zero.
By Tuesday, it appears that the aforementioned low should be well
south of the region and a drier forecast is expected. By New
Year`s Day, there could be a quick opportunity for snow across
Lincoln county, but details are still quite hazy.
&&
.AVIATION...For McCarran...Vicinity light showers expected for the
Las Vegas Valley through much of the overnight hours with increased
chances of rain at the terminal before midnight. Winds will be
fairly consistent through the majority of the TAF period with
speeds 10-15 kts from the northwest until Friday mid-afternoon
when they decrease to generally below 5 kts. CIGs will gradually
improve through the overnight hours. CIGs aoa 4 kft should only
persist through around midnight with OVC aoa 12 kft expected by
daybreak. Moderate confidence on the exact timing of the lift, but
ceilings expected to continue to improve throughout the day
Friday as dry conditions return.
For the rest of southern Nevada, northwest Arizona and southeast
California...Light rain showers expected to continue through the
overnight hours at KDAG, KIFP and KEED with ceilings below 5 kft at
times. As daybreak approaches, CIGs will gradually improve as
precipitation chances within the vicinity of the terminal decrease.
CIGs will continue to improve throughout the day on Friday while dry
conditions return. Gusty northerly winds down the Colorado River
Valley will relax after sunset tonight with speeds around 10 kts
prevailing overnight. Otherwise, area-wide improvements through the
day Friday expected with breezy-to-gusty northerly winds setting
back up around sunrise.
&&
.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant winter weather or flooding impacts according to
standard operating procedures. Measured snowfall accumulations are
also encouraged.
&&
$$
DISCUSSION...TB3
AVIATION...Berc
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