Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/25/18
Area Forecast Discussion
National Weather Service Austin/San Antonio TX
815 PM CST Mon Dec 24 2018
.UPDATE... /EXPAND FOG TONITE, LIGHT RAIN TUESDAY/
Mesoscale and rapid refresh models show an increased potential for
fog to expand NW overnight as some dewpoints are already warming to a
few degrees above forecast min temps. With this influx of moisture
relfects more an advection fog property, have also expanded the
potential for light rain or drizzle to form farther west as well for
Tuesday morning. Some periods of dense fog could develop so will
monitor trends for the potential need of a dense fog advisory.
&&
.PREV DISCUSSION... /ISSUED 618 PM CST Mon Dec 24 2018/
AVIATION...
VFR conditions this evening will quickly deteriorate to MVFR/IFR
overnight as a 30 knot low level jet spreads stratus across the
South Central Texas terminals. RAP forecast vertical wind profiles
show the jet strongest near SAT/AUS between 04-10Z and would expect
to see ceiling development begin during that time. Lighter near
surface winds will allow for stratus to build down by sunrise,
producing fog and LIFR to IFR visibilities. With IFR ceilings
lingering into mid to late morning, delayed heating may allow for fog
to linger at the terminals as late as 15-18Z. Ceilings are expected
to lift to low-end MVFR during the afternoon with IFR possibly
resuming after 00Z Wednesday.
PREV DISCUSSION... /ISSUED 246 PM CST Mon Dec 24 2018/
SHORT TERM (Tonight through Tuesday Night)...
Mid level shortwave moving across the Central Plains has allowed a
southerly lower level flow and low clouds to return to South Central
Texas today. An upper level trough approaching northern California
moves southeast across California tonight to the Arizona/New Mexico
region Tuesday night. Patchy fog is expected overnight into Tuesday
morning across eastern areas. Deepening moisture and increasing
upward forcing Tuesday into Tuesday night lead to the development,
and then increasing coverage of showers. Well above normal
temperatures are expected tonight through Tuesday night.
LONG TERM (Wednesday through Monday)...
The upper level trough will move across the Southern into Central
Plains Wednesday through Thursday with the axis and associated
Pacific cold front moving across South Central Texas Wednesday
night. Upward forcing continues to increase ahead of the axis/front.
Weak instability develops on Wednesday allowing for isolated sub-
severe thunderstorms in the afternoon. Parameters become favorable
for a squall line with isolated storms out ahead of it Wednesday
night. CAPEs around 2K J/KG, steep 850 to 500 MB lapse rates of >7
C/km, and 0-6 km shear of 60 m/s indicate a potential of strong to
severe thunderstorms with all types possible. The timing is expected
from the evening into the overnight hours of Wednesday. In the wake
of the trough/front passage, lower level ridging makes for a dry
Thursday and Friday. Over the weekend, an upper level trough deepens
over northern Baja California and Sonora state of Mexico while cold
surface high pressure builds south across our area. Impulses moving
in the southwesterly flow aloft over our area generate upward forcing
for low chances of showers for Saturday into Sunday. There are
significant disagreements with the timing of trough over our area on
Monday as showers will end with its passage. The ECMWF/GEM bring it
across early Monday with the GFS Monday evening which would lead to
possible impacts to New Year`s Eve activities. There is a potential
for thunderstorms across eastern areas, as well as, winter type
precipitation across far northern reaches of the Edwards Plateau and
Hill Country. Will leave out mention, for now, as chances are
currently slight, at best. Above normal temperatures for Wednesday
through Friday turn below well normal for Saturday through Monday.
&&
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 54 69 60 68 53 / 10 20 50 90 100
Austin Bergstrom Intl Airport 53 71 60 70 53 / 10 30 40 90 100
New Braunfels Muni Airport 53 71 61 71 54 / 10 20 50 80 90
Burnet Muni Airport 50 66 58 67 49 / 10 20 50 90 100
Del Rio Intl Airport 48 65 57 72 47 / 10 10 40 50 60
Georgetown Muni Airport 52 67 60 68 51 / 10 20 50 90 100
Hondo Muni Airport 50 72 60 73 49 / 10 20 50 70 90
San Marcos Muni Airport 54 71 61 71 53 / 10 30 50 80 100
La Grange - Fayette Regional 56 71 61 70 58 / 10 20 30 70 90
San Antonio Intl Airport 54 70 61 71 53 / 10 20 50 70 90
Stinson Muni Airport 54 72 63 73 55 / 10 20 50 70 90
&&
.EWX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Aviation...Huffman
Short-Term/Long-Term...Oaks
Area Forecast Discussion
National Weather Service Hastings NE
525 PM CST Mon Dec 24 2018
.SHORT TERM...(This evening through Tuesday)
Issued at 252 PM CST Mon Dec 24 2018
After a quiet day this Christmas Eve, the weather pattern will
turn more active for the middle/latter part of the week. The
pattern aloft was fairly zonal today and the system which will
impact our area Wed/Thur was just off the coast of Oregon and
northern California. Ahead of this system, a subtle disturbance
will translate across KS/southern Neb late this afternoon and
evening. The majority of models suggest any precip associated with
this system will develop just east of our cwa, however HRRR runs
occasionally suggest precip may develop in Thayer County near
Hebron and will need to monitor.
Fog potential tonight...Low level moisture increases across eastern
Kansas/Nebraska tonight which advects into our area late
tonight/Christmas Day morning. Models suggest the development of low
clouds/fog and latest SREF/high resolution models suggest that the
fog may become dense, with the lowest visibilities expected
mainly along/east of Highway 281. Overnight low temps will be
below freezing and if dense fog does develop, will need to monitor
for light icing.
If fog does develop tonight, it is expected to erode mid/late
morning Tuesday, then a fair amount of cloud cover is forecast
Christmas Day. The NAM is the most robust with persistent low cloud
cover and therefore reflects colder temps than the GFS which
suggests more mid/high level clouds and warmer temp guidance. Given
the spread in guidance for temps Christmas Day have went with a
blend which reflects slightly cooler readings than previous
forecast.
.LONG TERM...(Tuesday night through Monday)
Issued at 252 PM CST Mon Dec 24 2018
A storm system is still on track to produce widespread
precip(rain/snow) Wednesday and Thursday.
Models...Have disregarded GFS solution with its southern track
solution in favor of other model solutions...which emerge the system
from the south central Rockies Wednesday night, with the upper low
tracking through NW KS, central/northeast Neb, into southern MN
Thursday.
Tuesday night...clouds thicken/lower and light precip develops in
isentropic lift ahead of the approaching upper low/storm system
reaching the four corners region. Precip type favors a messy mix at
the onset with the potential drizzle/freezing drizzle or
rain/sleet/snow before transitioning to rain as temperatures rise
Wednesday. Light icing may occur.
Wednesday...Wet weather expected with periods of widespread rainfall
ahead of the upper system over the Rockies. Precipitable water
values range from around a half inch in our western zones to near an
inch in our southeast...high for this time of year. Model
instability parameters indicate several hundred j/kg of MUCAPE
across north central KS into southern Neb from late morning
Wednesday through Wednesday evening and have included thunder in the
forecast for non-severe storms.
Rainfall amounts and impacts...Precipitation amounts (rain and
melted snow) are expected to range from an inch to an inch and a
half, with the majority of the precipitation falling as rain. These
amounts are significant and to put in perspective, normal
precipitation for the entire month of December ranges from a half
inch to just over three quarters of an inch across our cwa. The
ground is frozen, with a frost depth of two inches measured at NWS
Hastings this morning. Rainfall on the frozen ground is expected
to lead to runoff, ponding, and rises in streams and
rivers...similar to the December 1st event when several areas
received an inch of rain or more.
Snow...Cold air is slow to arrive, reaching our western zones
between 03Z and 06Z Thursday with rain changing over to snow. All
but our far southeast zones are expected to change to snow by
Thursday morning, with the southeast areas expected to transition to
snow Thursday before the precip ends. Snow amounts are tricky
given the wet ground from the initial rainfall and it may take
some time to accumulate. The current track of the system orients
the heaviest snowfall across our western zones roughly from Ord to
Lexington and west where amounts of 2 to 5 inches (and locally
higher amounts) are possible. Snow amounts are expected to drop
off sharply to the southeast where more rain vs snow is forecast.
Snow amounts south of the tri-cities and into north central Kansas
are expected to average an inch or less. Snow tapers off during
the day Thursday as the system lifts northeast and dry slot moves
in.
Wind...Northwest winds ramp up with the arrival of the cold air
late Wednesday night and the wind remains strong
Thursday/Thursday night into Friday. Wind speeds are expected to
average 25-30 mph with gusts of 40 mph. Locations which receive
accumulating snowfall may see areas of blowing snow/reduced
visibility especially as the initial wet snow becomes drier as the
cold air deepens.
Headlines...A winter storm watch will be in effect for our northwest
counties late Wednesday night through Thursday evening where the
greater snow accumulations are expected, and the combination of
snow/wind may cause travel impacts. If snow amounts continue to
trend lower, the watch may need to be converted to an advisory,
but if amounts trend higher, a warning may be warranted.
Friday/Saturday...Cold weather settles in with wind chills in the
single digits above/below zero Thursday night/Friday morning and
Friday night/Saturday morning.
The airmass moderates some Sunday/Monday (New Year`s Eve)...then
models suggest another surge of cold air around New Year`s Day
next week.
&&
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Tuesday)
Issued at 523 PM CST Mon Dec 24 2018
Mid and high clouds will move out of the area tonight and the
radiational cooling will allow for some fog to form. KGRI is
expected to have lower visibility than KEAR. The fog will lift in
the morning, but clouds will increase during the afternoon.
&&
.GID WATCHES/WARNINGS/ADVISORIES...
NE...Winter Storm Watch from late Wednesday night through Thursday
evening for NEZ039-040-046-060.
KS...None.
&&
$$
SHORT TERM...Fay
LONG TERM...Fay
AVIATION...JCB
Area Forecast Discussion
National Weather Service Lincoln IL
843 PM CST Mon Dec 24 2018
.UPDATE...
Issued at 843 PM CST Mon Dec 24 2018
Radar returns across Missouri look rather impressive this
evening, though surface obs and mPING reports are indicating the
precipitation has just started to reach the surface. Evening
sounding from our office shows a rather dry layer below 700 mb.
GFS forecast soundings show the lowest 5,000 feet of atmosphere
with a dearth of moisture, while the NAM only has a few hour
window where the low layers moisten. If the precipitation ends up
very light, the evaporative cooling may not take place, which
would favor more of a rain scenario. Latest RAP model actually
keeps us dry the entire night, while the HRRR has only a few small
areas of light rain or snow. Fresh runs of the NAM, ARW and NMM
are also featuring lesser amounts of precipitation, mainly between
midnight and sunrise. Have recently sent out some updated
grids/zones to pull back a bit on the PoP`s and snow amounts, not
that they were that great to begin with.
&&
.SHORT TERM...(This evening through Tuesday)
ISSUED AT 240 PM CST Mon Dec 24 2018
Our next weather system tracking east out of southeast Colorado is
forecast to move across our area late tonight and into Christmas
morning bringing a period of light snow and rain to the area. QPF
amounts not real impressive with mostly less than a tenth of an
inch with any snow accumulations generally less than one half
inch. Most of the forecast soundings indicate our boundary layer
starts out on the warm side as the precipitation approaches later
this evening but with a dry layer indicated from the surface up to
around 8000 feet, there will be enough evaporative cooling once
the rain begins to become a mix of rain and snow. A few locations
north of I-74 may see a brief turn over to all snow, but again,
with the speed of the system and a lack of deep moisture with this
upper wave, it appears precipitation amounts will be on the light
side. Low temperatures should be around the freezing mark most
areas tonight.
The upper wave should push off to our east by afternoon with
upper level ridging building over the central U.S. in response to
the deep upper low pushing across the southwest U.S. This should
bring another round of unseasonably mild temperatures tomorrow
afternoon accompanied by a mix of clouds and sun with highs in the
mid to upper 40s.
.LONG TERM...(Tuesday night through Monday)
ISSUED AT 240 PM CST Mon Dec 24 2018
The southwest storm system is forecast to slowly push east and
northeast into the southern Plains by Wednesday but its associated
precipitation shield is forecast to remain mainly to our west
through most of the day. Rain chances start to increase from west
to east Wednesday night as a strengthening southerly flow draws
moisture north out of the Gulf of Mexico into the Midwest. The NAM
model indicating a 65-70 kt low level (~850mb) jet drawing PWAT
values of over an inch across the northern half of Missouri by
Thursday morning. The deepening surface low will be between Omaha
and Des Moines by Noon Thursday with the axis of deep moisture
(PWAT values approaching 1.25 inches which is well above normal
for late December) aligned from south to north right across our
forecast area Thursday morning.
Not much in the way of instability noted on the latest NAM but
0-6km shear values of 60-65 kts is a concern for Thursday late
morning through the mid afternoon hours using the timing of the
current NAM model, which does depict a narrow squall line racing
northeast across southern Illinois at this time. Models continue
to indicate widespread deep convection across the lower Mississippi
Valley in addition to the rain and extensive cloud cover further
to the north in our area. Will see what affect, if any, this has
on our chances for more organized strong convection Thursday
afternoon, especially over our south and southeast counties. The
warmest temperatures this week will be Thursday just ahead of the
storm and associated cold front with highs well into the 50s with
60s not out of the question over the southern half of the forecast
area.
The mid level dry slot will race across our area late Thursday
afternoon or early evening taking any threat of rain off to our
east and northeast. Gusty southerly winds, of 20 to 30 mph will
shift more into a southwest to west direction overnight Thursday
ushering in cooler weather overnight, but lows are only forecast
to drop off into the mid 30s to mid 40s from north to south. Those
are our average high temperatures for this time of year. Much
quieter weather forecast to move in for the end of the week but
additional shortwave energy ejecting out of the mean longwave trof
over the southwest U.S. is forecast to drift northeast into the
region later Saturday into Sunday with low chance POPs introduced
with the threat for some light snow Saturday night and a slight
chance for a rain snow mix on Sunday with temperatures closer to
where they should be for the end of December, mostly in the 30s
for daytime highs with early morning lows dropping into the 20s.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 516 PM CST Mon Dec 24 2018
Main focus will be the period from about 06-15Z, as a storm system
brings light rain and snow to the area. Lower levels below 8,000
feet are dry and will cut down some on the precipitation, at least
at the start. Will continue with the VCSH mention and keep
conditions VFR for now, though a switch to snow could at result in
some MVFR conditions at times. Precipitation will lift northeast
of the area after 15Z, with VFR conditions expected to prevail
after.
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...Geelhart
SHORT TERM...Smith
LONG TERM...Smith
AVIATION...Geelhart
Area Forecast Discussion
National Weather Service Lake Charles LA
1002 PM CST Mon Dec 24 2018
.DISCUSSION...
Dense fog is developing and will become more widespread across
Southwest Louisiana and Southeast Texas, as well as the inland
lakes tonight. Latest HRRR and NAM12 guidance shows the dense fog
affecting SE TX and portions of SW LA for the remainder of
tonight. With dense fog forming further east across most of
Cameron and Calcasieu parishes, included dense fog across Jeff
Davis, spreading inland across Beauregard, ALlen, and Vernon
parishes, as well as the remainder of SE TX, overnight. Thus,
issued a Dense Fog Advisory for these areas through 9 am Christmas
morning.
&&
.PREV DISCUSSION... /issued 508 PM CST Mon Dec 24 2018/
AVIATION...Lower ceilings and vis are expected across the region
this evening through mid Tuesday morning. The MVFR and IFR
conditions will spread from SW to NE. Winds will be light and
generally southeast.
PREV DISCUSSION... /issued 316 PM CST Mon Dec 24 2018/
DISCUSSION...
Return flow already ongoing this afternoon and this will continue
into through the short term resulting in increasing clouds
overnight and warmer temperatures. Areas of fog are also expected
to develop during the overnight and some could be dense. The
evening and overnight shifts will need to monitor for dense fog
advisory potential. Fog should gradually burn off Tuesday morning
with some light showers possible through the day with warm
temperatures expected.
The main concern for this forecast continues to in the Wednesday
through Thursday time frame as the system entering the west coast
today moves towards the east. There has been a slight slowing
noted in the guidance today and thus Wednesday rain chances have
been lowered a bit from the previous forecast, however showers
should overspread the area Wednesday afternoon with breezy
conditions developing as well. The main forcing will move through
Wednesday night into Thursday. There will be a potential for
strong to severe storms along with a heavy rainfall threat in
addition to strong southerly winds.
Front pulls up stationary Thursday night and while there may be a
brief lull in the rain Friday off and on showers and possibly
Thunderstorms is possible much of the weekend into early next
week. Guidance continues to waffle on the details, so still lots
of room for tweaks beyond Friday.
&&
.PRELIMINARY POINT TEMPS/POPS...
AEX 48 66 54 67 / 10 20 10 30
LCH 54 70 57 69 / 10 20 10 50
LFT 53 69 56 68 / 10 20 10 40
BPT 56 70 58 69 / 10 20 10 60
&&
.LCH WATCHES/WARNINGS/ADVISORIES...
LA...Dense Fog Advisory until 9 AM CST Tuesday for LAZ041-073-074.
Dense Fog Advisory until 9 AM CST Tuesday for LAZ027-030-031-042.
TX...Dense Fog Advisory until 9 AM CST Tuesday for TXZ215-216.
Dense Fog Advisory until 9 AM CST Tuesday for TXZ180-201-259>262.
GM...Dense Fog Advisory until 9 AM CST Tuesday for GMZ430-432.
&&
$$
PUBLIC...08
Area Forecast Discussion
National Weather Service Paducah KY
922 PM CST Mon Dec 24 2018
.UPDATE...
Issued at 920 PM CST Mon Dec 24 2018
A look at VAD Wind profiles from KSGF, KLZK, and KPAH suggest that
very light precipitation is slowly working toward the ground.
Lowest wind estimates detected is near 2kft msl at KSGF and KLZK
and near 10kft AGL. Differential reflectivity and Correlation
Coefficient from north of the KSGF radar suggest some ice crystal
development aloft, but given the level of warm advection,
anticipate further rain further west initially.
The 13 km RAP sounding over western sections of southeast Missouri are
suggestive of decent ice nucleation in the favorable dendritic
growth zone (-13 to -18 C) as of 9 pm CST this evening. The
challenge is the degree of evaporative cooling through midnight in
the face of lower level warm advection. Most locations may not see
any precipitation reaching the ground through midnight. However,
where weak or non-existent southerly surface flow is in place, a
few locations may see trace precipitation reach the surface as
snow flurries or sprinkles of rain, especially in the northern and
eastern sections of the WFO PAH forecast area. The most intense
period of lift and precipitation potential will likely be between
06z (midnight) and 10z (4 am).
As cloud ceilings drop down near 5-7kft between 5 am and 7 am CST,
may see more sprinkles of rain than snow flurries. At the same
time, the depth of moisture across the area will be shrinking, so
even trace precipitation amounts should be waning by mid-morning
Tuesday.
Do not anticipate any trace precipitation (sprinkles or flurries)
to cause any travel impact for the holiday at this time.
UPDATE Issued at 608 PM CST Mon Dec 24 2018
&&
.SHORT TERM...(Tonight through Wednesday night)
Issued at 308 PM CST Mon Dec 24 2018
A fast moving, upper level disturbance will race westward to
eastward across the area late tonight-early Christmas day. It
should have little to no impact, with gridded time/height cross
sections and sounding data showing a very dry layer below about
10K FT AGL. The 12Z Nam and Gfs both produced zero for most of the
FA, with some .01" qpf pixels in the Ozarks. The thermodynamic
profile suggests sprinkles/flurries or, collaboratively, slight
chance mention in the 10-14z time frame of vort passage.
Preceding the system will be increasing/lowering clouds, and
these should decrease generally later Christmas day and night, in
the wake of its departure. Clouds will increase again fairly
rapidly Wednesday, from the southwest toward the northeast. This
will occur as the column starts to pre-saturate ahead of our next
incoming weather system, which impacts the area later in the week.
Lows in the 30s tonight and tmrw night rise into the 40s with the
saturation column Wed night, as Pcpn sets in late. Christmas day
highs largely in the 40s, will bump into the 50s the day after.
.LONG TERM...(Thursday through Monday)
Issued at 308 PM CST Mon Dec 24 2018
A strong storm system will move northeast across the Plains Thursday
and Thurs night. This system may have some impacts on our area,
primarily in the form of wind and/or strong convection. The
potential for either hazard still appears rather low.
Regarding wind potential, a southerly low level jet will increase to
over 70 knots at 850 mb Thursday morning. The 12z nam showed its
typical high bias, with a few winds to 90 knots at 850 mb Thursday.
As usual, the question is how much wind will actually reach the
surface. The models indicate widespread rain during the period of
strongest winds aloft, which should minimize mixing. However, any
convective elements would potentially contain very strong winds.
There could also be strong surface winds if the models are too quick
to bring in the widespread rain. A conservative estimate of peak
wind gusts Thursday is 30 to 40 mph. Much will depend on the low
level lapse rates, and those will depend on the timing of the
stratiform rainfall.
As far as convective potential, there has been little change in the
model parameters. A narrow axis of marginally unstable air will nose
into our region Thursday. A few recent runs of the gfs indicate this
instability will be surface-based, while the ecmwf has shown
slightly elevated instability. In either case, the values of cape
are below 500 j/kg. Given the extremely strong winds aloft, these
small values are still a concern. Another complicating factor is a
pronounced mid-level dry slot that will surge northeast across the
Ohio Valley. The models indicate this would occur in the afternoon,
ending the widespread rainfall. This looks somewhat similar to the
December 1 storm system, when a dry slot inhibited convection over
our forecast area despite sufficient instability. However, the fine
details such as the depth of the dry air can make a big difference.
The dry air will win out by Friday morning, when all precipitation
will come to an end. West winds will become northwest during Friday,
bringing cooler air. Highs will still reach the 50s due to the mild
start to the day. The cooling trend will continue through Saturday,
when highs will be mainly in the 40s.
The models are still hinting that southwest flow aloft will bring
precipitation sometime Saturday night into early next week. The 12z
gfs is especially bullish with precipitation Saturday night. The
forecast will contain chance pops for Sat night. This precip will
most likely not be all liquid as lows fall to around 30.
There is good model agreement (including the ensemble means) that
the western US trough will deepen early next week. Some
deterministic runs are ejecting a 500 mb shortwave northeast out of
this trough, bringing precip to our area. The track and strength of
any such system will determine precip type and intensity. Based on
the faster gfs timing, the forecast will contain chance pops for
Monday.
&&
.AVIATION...
Issued at 608 PM CST Mon Dec 24 2018
Cigs may flirt with MVFR levels west of the MS River late Tue
morning; otherwise VFR conditions can be expected throughout the 24
hour TAF period. An eastward-moving disturbance aloft will probably
generate some showers of light rain or snow, mainly west, early on
Christmas Day. However, with plenty of dry air near the surface,
significant vsby restrictions are not likely, as much of the pcpn is
not expected to reach the ground. Winds will be quite variable in
direction, but mostly out of the southeast, and light.
&&
.PAH WATCHES/WARNINGS/ADVISORIES...
IL...None.
MO...None.
IN...None.
KY...None.
&&
$$
UPDATE...Smith
AVIATION...DB
Area Forecast Discussion...UPDATED
National Weather Service Reno NV
500 PM PST Mon Dec 24 2018
.UPDATE...
The latest HRRR and 3KM NAM show front/NCFR band pushing quickly
east across the area early this evening. It is behind these
features that wet bulb temperatures will finally cool and allow
snow levels to begin falling. Much of the precipitation from
about 6500 feet and lower is in the form of rain as of 5 pm but
dewpoints are slowly inching down in the Tahoe Basin. So the rain
should turn over to snow by 7 pm at lake level but intensity may
decrease considerably once the NCFR passes to the east - thus
limiting snowfall amounts at lake level. Areas above 6500 feet,
especially west of Highway 89, are going to see some appreciable
snowfall before the snow begins to taper off later tonight. We
only made a minor update to adjust rain/snow at lake level through
7 pm. We kept the snow amounts as is, although at lake level,
latest trends are favoring less accumulations due to the late
drop in snow levels. Hohmann
&&
.PREVIOUS DISCUSSION... /Issued 229 PM PST Mon Dec 24 2018/
SYNOPSIS...
The second half of a moderate winter storm will move through the
region tonight bringing continued travel impacts into Christmas
morning due to rain and snow. Temperatures will fall tonight and
drop snow levels to near the lowest valley floors. This will be
followed by much colder temperatures and periods of snow showers
later this week through next weekend.
SHORT TERM...
The first wave associated with a broader upper level area of low
pressure has pushed through much of the forecast area early this
afternoon. This first wave brought rain and snow...briefly
moderate to heavy in the Sierra...with snow levels dipping below
6000 feet in the heaviest precipitation. As the precipitation
intensity decreased...snow levels rose.
The main upper low remains just off the coast. Satellite imagery
shows convection forming east of the low as it pushes toward the
coast of California. As this low moves onshore and into our region
this evening and overnight...we expect another round of moderate
to heavy precipitation in northeast California and the Sierra.
This should drive snow levels down again overnight. Snow levels
are quite tricky with this system...not just in northeast
California and the Sierra...but in western Nevada as well.
Much of our internal guidance indicates snow levels should start
higher than we currently show in our forecast...but may be
accounting for better mixing than we have seen in some areas.
While winds have increased in the Mono County area and parts of
the basin and range in western Nevada...the winds overall have not
been quite as strong as advertised. This may have more to do with
the increased moisture and light precipitation over the northern
half of the forecast area than it does with a decreased gradient.
So...for some areas...high temperatures are a little lower than
forecast due to decreased mixing. This would argue for lower
initial snow levels. But the increased moisture in the boundary
layer will inhibit the ability for snow levels to fall this
evening due to a higher wet bulb temperature.
We will show snow levels falling in the evening as the heaviest
precipitation moves into the forecast area...but try to balance
out the factors mentioned above. Varying snow levels could result
in widely varying snow amounts between 5500 and 6500 feet this
evening and overnight. Most areas below 5500 feet will struggle to
see any snow before the main cold front passes Tuesday morning.
So the lowest valley floors are not likely to see much more than
0.5 to 1 inch of snow. Areas above 7000 feet in the Sierra may see
between 8 and 16 inches. That area between 5500 and 7000 feet
could vary from a few inches to as much as 8 inches...depending on
the snowfall intensity and duration.
This is a fast moving storm so most of the precipitation will end
Tuesday morning. There will be lingering showers through the day
and northwest winds are likely to become gusty over parts of
Mineral County where stronger northwest winds are favored. Lake
enhancement of snow showers is possible off Pyramid Lake from
Nixon to Fernley and Lake Tahoe around Stateline across Dagget
Pass.
Temperatures Tuesday and Wednesday should be a little below
normal. By Tuesday night a ridge begins to build with partial
clearing. This is likely to allow for colder low temperatures by
Wednesday morning with teens and 20s common.
LONG TERM...Wednesday night through the New Year...
A secondary cold front is forecast move into the region along the
backside of large scale trough in the intermountain west
Wednesday night into Thursday. This will bring colder
temperatures, breezy north winds, and chances for snow showers
back to the region.
Current simulations have the front moving through from the
northwest to the southeast as it moves through the region creating
only a few snow showers in far western Nevada. However, this is
the pattern where we can get a slider cold front through western
Nevada that can bring snow accumulation to the lower valleys,
especially if the frontal passage takes a more southerly track,
something we`ll have to keep an eye on. On Thursday there is a
pretty good chance of some upslope showers in Alpine and Mono
counties and a chance for some lake enhanced showers south of
Pyramid Lake.
The end of the week will be relatively cold behind the front with
highs likely in the mid 30s on Friday for the valleys. Low
temperatures could be in the teens for much of the region Saturday
morning with single digits in colder valleys. Temperatures will
slowly warm up going into the weekend. -Zach
AVIATION...
The main part of the current storm system will move through the
forecast area through early Tuesday. Periods of IFR in rain and
snow develops for northeast California...northwest Nevada...and
the Sierra this evening. Cigs/vsbys should be no worse than MVFR
for areas east of the Sierra this evening...but could briefly
drop to IFR with the main cold front around the midnight time
frame. Wind shear is also likely...especially near frontal passage
tonight. Mountain obscurations and turbulence are likely as well.
Little in the way of snow accumulation is expected for the
western Nevada terminals; KCXP and KRNO could get between 0.5 and
1 inch of snow in a brief burst. For the Sierra terminals...KTRK
and KTVL have the best chance at accumulating snow with between 3
and 7 inches possible...higher at KTVL than KTRK. KMMH could get
up to 4 inches...but the snow will be lesser in intensity there.
Behind the front Tuesday...snow showers will linger through the
day and decrease in the evening. So there could be isolated areas
of reduced cigs/vsby.
&&
.REV Watches/Warnings/Advisories...
NV...Winter Weather Advisory until 7 AM PST Tuesday NVZ005.
Winter Weather Advisory until 7 AM PST Tuesday NVZ002.
CA...Winter Weather Advisory until 7 AM PST Tuesday CAZ071.
Winter Weather Advisory until 7 AM PST Tuesday CAZ070.
Winter Weather Advisory until 7 AM PST Tuesday CAZ072.
&&
$$
For more information from the National Weather Service visit...
http://weather.gov/reno