Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/16/16
Area Forecast Discussion...UPDATED
National Weather Service Lubbock TX
624 PM CST Thu Dec 15 2016
Quick update to expand low clouds north more aggressively this
evening and also to insert fog mention for all but our far NW
counties. Regional METARs, webcams and IR low cloud imagery
confirm the themes of the HRRR and RAP regarding a bullish
northward surge of very low stratus with lowering visibilities.
Will monitor trends for a possible dense fog advisory later this
.PREV DISCUSSION... /issued 552 PM CST Thu Dec 15 2016/
Conditions are likely to fall to IFR by 8-10 PM at LBB and PVW,
and closer to midnight at CDS. Upstream observations at SWW and
BPG already show MVFR-IFR CIGs on very moist southerly winds, and
this will expand north through the evening likely accompanied by
some fog at times.
VFR should resume toward daybreak as winds veer more SW, before
ramping up to windy levels from the WSW after 12 PM. An AWW for
30+ knot winds may be issued for LBB as soon as the onset of these
winds is more clear.
PREV DISCUSSION... /issued 313 PM CST Thu Dec 15 2016/
Low clouds have been slow to burn off from west to east but were
finally making slow progress eroding this afternoon. This has
impacted temperatures and wind speeds this afternoon with areas
under the cloud cover not warming up as fast as forecast and areas
that have cleared seeing wind speeds increase a bit higher than
previously thought. Forecast for tonight is once again challenging
as the coarser model resolutions do not show low clouds returning
while all of the high-resolution models (RAP, HRRR, TTU WRF) have
some hints of another round of low clouds tomorrow morning. Will
keep low clouds in the forecast but uncertainty remains high on when
the clouds will dissipate. 18Z RAP indicates that the clouds should
clear out earlier in the day Friday as southwest wind develops in
the morning pulling in drier air from the southwest.
Friday also has it`s share of forecast concerns as well, mainly the
potential for high wind warning speeds as well as the potential for
fire weather concerns. Timing will be critical tomorrow for both
these elements. Models are showing a batch of fairly thick high
clouds that will be across the area by sunrise Friday. These will
be slow to move east but will clear the northwestern counties of the
forecast area by mid-day. Clearing skies will help to deepen the
boundary layer while also helping to mix stronger wind speeds aloft
down to the surface. Lee surface trough gradient will also tighten
through the day as wind speeds through the depth of the atmosphere
increase with the passage of a weak shortwave. Models have the
strongest 850 hPa wind speeds just north of the forecast area but
close enough that we could see sustained speeds at or above high
wind warning criteria across much of the Caprock. Uncertainty
remains high enough that we will keep the high wind watch in place
in hopes that the incoming shifts can possibly narrow down both the
timing and aerial coverage needed for a possible warning. As for
the Rolling Plains, wind speeds will likely be lower as cloud cover
will keep mixing to a minimum until late in the afternoon. Narrower
window for daytime mixing could mean that there is a pretty sharp
gradient in wind speeds from west to east across the area. Southwest
to westerly wind direction will provide good downslope warming
potential and we will see high temperatures in the mid to upper 70s
across the area. Unfortunately the strong wind speeds also means
areas of blowing dust across the Caprock as well. See the fire
weather discussion below for more details in how the forecast for
tomorrow will impact fire weather concerns.
The one thing that is for certain on Saturday is that a strong cold
front will push through, it will be windy, and it will get cold.
Models still seem to be a bit slow on the fropa with the ECMWF being
the closest to what is expected with the front being south of the FA
by the mid to late afternoon. Temps will drop off sharply after the
fropa with our northern zones dropping below freezing around or just
after noon with the rest of the FA being below freezing by the early
evening. A tight surface pressure gradient along and behind the cold
front will allow for winds to be in the 20-25 mph range during the
day. Winds will gradually decrease overnight Saturday into Sunday
morning, but winds will still be in the 10-15 mph range while temps
are in the teens and single digits allowing wind chill values to dip
below zero. What continues to be the forecast issue for Saturday is
precipitation. There should be low level and some mid level (mostly
lower mid level) moisture that will be present mainly across our
northern zones during part of the day. Frontogenetic forcing will be
more than enough to provide enough lift for possibility rain to fall
in the late morning before turning to snow in the early afternoon.
The window of opportunity will be fairly short lived to see
precipitation, and what precip we can see will be light at best.
Flurries will be possible across the southern half of the FA as
there should be enough low level moisture available during the fropa
to squeeze out a few flakes.
Sunday will be a cold day with morning lows dipping into the single
digits to the low teens while highs will struggle to get into the
upper 20s/low 30s. Monday may not be much better as lows will still
be near 10 degrees and highs will only be in the mid to upper 30s.
Beyond Monday the only clear part of the forecast is that we will
warm up gradually. Models have been inconsistent to say the least
with the evolving pattern into mid week. The GFS still has high
hopes that a low will develop somewhere across northwestern Mexico
which may or may not make it to West Texas. The ECMWF meanwhile has
decided to keep the low offshore in the Pacific and have a rather
benign pattern before pushing a cold front into the region by next
Thursday. Consulting the in-house dart board model yielded a
scattered plot emphasizing the unknown. For now the forecast for
next week will reflect the superblend for a middle of the road
Critical fire weather conditions remain iffy at best across the
caprock due to two major concerns. The first is the timing on when
wind speeds will increase. Second is minimum RH values are not
expected to meet the length of time at or below 15 percent criteria.
We are still expecting strong southwest to westerly wind speeds to
develop in the afternoon tomorrow across all of the Caprock. Speeds
will start to increase around noon, peak around 4 pm, and then start
to decrease slowly after that. This will help to mix the atmosphere
enough that moisture levels will potentially rise a bit in the
afternoon as well. Current forecast has minimum afternoon RH values
briefly falling to near 14 percent across the central South Plains
for one hour before starting to climb while the rest of the South
Plains and all of the Rolling Plains keeps minimum RH values above
15 percent in the same time frame. This does not meet the criteria
for critical conditions. Texas Forest Service data show that energy
release components are near normal for this time of year and fuel
moisture levels are not in the critical range either. However,
ample time for fuels to cure and strong winds should help drop fuel
moisture levels in grasses in the strong winds. At the very least,
elevated fire weather conditions will develop but will hold off
issuing a Red Flag Watch for now.
High Wind Watch Friday afternoon for TXZ021>024-027>029-033-034.
Area Forecast Discussion
National Weather Service Medford OR
243 PM PST Thu Dec 15 2016
.SHORT TERM...Tonight through Sunday...A cold and relatively dry
air mass will move into the forecast area behind a front stretched
from Northern California into Eastern Oregon. A wave has
developed along the front which has slowed its movement, but
latest satellite trends and HRRR model output suggest the front
and precipitation over Eastern Siskiyou and Modoc Counties will
shove east quickly tonight. Some moderate to heavy precipitation
has fallen in these areas and more rain is expected this evening,
so an Areal Flood Watch continues for Eastern Sikiyou and Modoc
Counties through the evening.
As the precipitation moves out of Modoc County, cold air will
briefly meet up with the lingering precipitation, and a few inches
of snow is possible there later tonight.
A shortwave moving in from the northwest and some lingering
moisture prompted us to keep a slight chance of mainly snow
showers in for much of the area tonight, though little to no
accumulation is expected with any snow.
Near-freezing to freezing temperatures will affect the entire
forecast area tonight, which could quickly freeze any lingering
water on roadways, so travelers should be aware of the potential
for ice on roadways. West side areas will likely take most of the
night to reach freezing, and there is slight potential for
freezing fog though conditions suggest low clouds instead of fog
at this point. At the coast, with lows expected to be in the low
30s, a Frost Advisory at NPWMFR has been maintained for that area.
Tomorrow night, clearing skies and light winds, along with 850mb
temperatures around -7C over Medford (which is about the coldest
5% for this time of year) will likely yield the coldest night of
the next several. Fresh snowpack will help East Side temperatures
dip well below zero in favored locations like Chemult. West of the
Cascades, barring any widespread freezing fog forming early in the
night, temperatures will dip to the upper teens to low 20s.
Residents should take precautions to mitigate any impacts this
cold weather might have.
Cold nights are expected through Sunday night at least.
.LONG TERM...Monday through Thursday...After a brief break in the
precipitation over the weekend, the storm track will become active
again next week. The models are in good agreement that two
significant frontal system will affect our area next week, and while
there are some differences in timing and strength, the differences
are not significant enough to worry about at this time. System
number one may bring rain to the north coast as early as Monday, but
all areas should see some precipitation Monday night and Tuesday.
Snow levels will surge ahead of this system, so while precipitation
may start as snow in the colder east side locations, it will likely
be rain over all but the higher mountains most of the time.
There will be a break Wednesday, then system two arrives Thursday.
Snow levels will be a little lower ahead of this system, so much of
what falls from the Cascades east will be snow with rain on the west
side. Models are consistent in showing cooler air moving in Friday
with lowering snow levels and continued precipitation. This may
result in some impacts from snow at lower elevations from Friday
into next weekend. While this is beyond the current forecast window,
that will be right in the heart of the Christmas travel window, so
it`s worth keeping an eye on if you plan to travel through southern
Oregon or northern California for Christmas. -Wright
.AVIATION...15/18Z TAF CYCLE...Low clouds will be stubborn in many
areas today, but should gradually lift to MVFR and local VFR at the
terminals this afternoon as a front moves off to the east. Far
eastern areas in Lake and Modoc counties will see rain with reduced
CIGs/VIS as the front crosses the area, then conditions will worsen
briefly tonight as rain changes to snow before ending. At the
terminals tonight, clouds will likely lower and BR/FZFG will re-form
reducing conditions to IFR or LIFR. There is even a slight chance
of a brief snow shower at the terminals tonight. -Wright
.MARINE...Updated 845 AM PST Thursday 15 December 2016...Offshore
high pressure will build west of the waters today with light to
moderate north winds. A mix of wind waves and fresh south swell will
keep waters choppy, but below small craft advisory levels over much
of the area today. However, borderline small craft conditions are
possible in the southern outer waters late this afternoon and
evening. Calmer conditions are expected Friday into next weekend. A
cold front may bring strong south winds and seas early next week
followed by a very high and very long period swell.
OR...Frost Advisory from 2 AM to 9 AM PST Friday for ORZ021-022.
Frost Advisory from 1 AM to 9 AM PST Saturday for ORZ021-022.
Freeze Watch from late Friday night through Saturday morning for
CA...Flood Watch until 6 PM PST this evening for CAZ081>083.
Flood Watch until 10 PM PST this evening for CAZ084-085.
Pacific Coastal Waters...Small Craft Advisory for hazardous seas from 1 AM to 10 AM PST
Friday for PZZ356-370-376.