Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/26/21
Area Forecast Discussion
National Weather Service Boston/Norton MA
1005 PM EST Sat Dec 25 2021
.SYNOPSIS...
Low pressure lifts offshore tonight with an inverted trough
nudging into the region. Will still have some spotty rain and
freezing rain perhaps changing to a brief period of snow before
ending by daybreak across north central and northeast
Massachusetts. High pressure builds in bringing drier weather
Sunday and Sunday night. Slightly above normal temperature are
expected for much of next week. Spotty light wintry mix/rain
showers are possible at times with the best chance for a period
of steady precipitation sometime Thursday into Thursday evening.
&&
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
10 PM update...
Areas of light rain and freezing rain have filled in a bit more
over the last hour for the farthest reaches of northern MA
where temperatures are hovering right around the freezing mark
for most locations. No significant changes needed with this
evening`s update.
Previous Discussion...
* Rain may change to a brief burst of snow after midnight across
north central/northeast MA with a coating to 2" possible
* Patches of Black Ice possible overnight northwest of I-95
We are in a bit of a lull right now with mainly spotty light
rain/drizzle and fog this evening. A few spots northwest of I-95
remained around 32, so some patches of black ice are possible on
untreated roadways especially bridges and overpasses. Most
locations though were a degree or two above freezing this
evening with just light rain/drizzle.
The main concern overnight will be the approach of shortwave
energy/cold pool aloft. This should combine with an offshore
low to generate an inverted trough. This will result in a few
hours of fairly widespread precipitation very late this evening
until just before daybreak.
The latest HRRR along with with the 18z NAM/GFS/RGEM show that
the soundings become isothermal after midnight across north
central and northeast MA. There is also modest snowgrowth
depicted in the soundings for 1 to 3 hours with even a bit of a -EPV
signature. Given the soundings are right on the cusp of rain vs
snow there is uncertainty on how exactly this unfolds. However,
the potential for a brief burst of snow exists across north
central and northeast MA after midnight through about 4 or 5 am.
If this materializes...a coating to 2 inches of snow would be
possible with even the low risk for localized 3 inch amounts.
Greatest risk for these snow accumulations would be across
Middlesex and Essex counties. This will be somewhat of a nowcast
situation, but may even see a very brief period of snow impact
the Boston metro area. Something will have to monitor closely
overnight.
Given temps still near freezing in a few locations this evening
with spotty freezing drizzle; followed by the risk for a brief
burst of snow overnight opted to continue Winter Weather
Advisory for much of northern MA.
Bulk of any precipitation should be offshore by daybreak. We
will have to watch for patches of black ice overnight,
especially if temps drop a degree or two just before daybreak.
&&
.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
Highlights...
* Could perhaps have some spotty rain showers across
Cape/Islands early on Sunday, but clearing skies with gusty
winds for most on Sunday.
* Still breezy at times Sunday night with relatively clear
skies.
Shortwave trough lifts further offshore on Sunday while a weak
ridge builds in. The ridge flatten out a bit giving way to
another shortwave trough swinging through Sunday evening, but
will have a more substantial ridge building into the
central/eastern Great Lakes late on Sunday. At the surface the
inverted trough moves well offshore and high pressure nudges on
from Ontario on Sunday. The high builds into Quebec late Sunday
night and nudges into southern New England.
Sunday...
As the inverted trough is lifting offshore will still have some
rain showers lingering across mainly the Cape/Islands early on
Sunday. Could take a bit for skies to clear here, but for most
the high will nudge in enough to clear things out to bring a
mostly sunny day for most. Will have blustery NW/N winds with
colder air advecting in. Will not be too difficult to mix down
the 25 kt gusts, but may need to nudge gusts up to the 25-30 kt
range in future updates. Given this did bump temps up to the
75th percentile due to downsloping. Highs top out in the upper
30s to low 40s for most.
Sunday night...
Dry and quiet weather anticipated as high pressure nudges into
the region from Quebec. Still will be a bit breezy at times due
to the tightened pressure gradient between the high and low
pressure well offshore. Went with the 25th percentile of
guidance for low temps which results in readings in the 20s for
most. The only exception is the Cape/Islands where readings
bottom out in the low 30s.
&&
.LONG TERM /MONDAY THROUGH SATURDAY/...
Highlights...
* Slightly above normal temps next week, particularly with low temps
* Brief rounds of spotty light wintry mix/rain showers at times with
a better chance for a period steady precipitation Thu/Thu evening
* No major winter storms expected for the last week of December
Details...
Highly anomalous -PNA across the western United States coupled with
an upper level ridge of high pressure across the Caribbean will be
the main story next week. This will result in relatively fast zonal
flow across our region. Slightly above normal temperatures are
anticipated and with the lack of upper level amplification across
the northeast...no major winter storms are expected. We will break
it down a bit more below.
Monday and Monday night...
Dry and chilly weather expected Monday with highs in the 30s to near
40. A warm front approaches Monday night, which may result in a
period of spotty light precipitation. Greatest risk is south of the
MA Turnpike where somewhat better forcing exists. Saturation is
fairly shallow, so mainly looking at light showers or perhaps light
freezing rain/freezing drizzle depending on surface temperatures.
Tuesday and Wednesday...
Upper level ridging noses a bit further northward Tue into Wed which
should allow for above normal temps. Highs should mainly be in the
40s to near 50 on Tue and probably a few degrees cooler Wed. We will
have to watch for a period or two of light showers/wintry mix Tue
night into Wed with fast moving shortwave in zonal flow. Any
precipitation that falls should be rather light and much of this
time should feature more in the way of clouds than precipitation.
Thursday and Thursday night...
Appears the best chance for a period of steady precipitation will be
Thu into Thu evening. Upper level ridge off the southeast coast is
suppressed a bit, perhaps allowing a bit more amplification of
shortwave energy. Still not expecting a big storm and probably will
be dealing with a fast moving wave of low pressure. Airmass is not
cold at all for late December standards, so favoring more rain than
snow at least across the coast. However, if the low cuts underneath
us some snow will be possible with the best chance in the higher
terrain.
Friday and Saturday...
Dry and seasonably chilly weather follows Friday into the first part
of Saturday. Long range guidance is indicated the potential for
unsettled weather returning late Saturday into Sunday, but still a
ways out in the future.
&&
.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
00Z Update...
Tonight...High confidence in trends, moderate in timing.
Mainly IFR/LIFR overnight but improvement to MVFR is expected
toward daybreak across the interior. Spotty light rain/drizzle
and fog patches this evening will give way to a few hours of
steady/widespread precipitation very late this evening into the
overnight hours. Ptype will mainly be rain, but a change to a
brief burst of snow is possible between 5z and 10z across north
central and northeast MA; where a coating to 2 inches of snow
is possible.
Sunday...High confidence.
MVFR conditions across the interior with IFR along the coastal
plain early in the morning should pretty much improve to VFR in
all locations by afternoon. The exception will be the
Cape/Islands where some lower ceilings may linger a few hours
longer. Winds out of the NW around 10-15 kts with gusts of
20-25 kts.
Sunday night...High confidence.
VFR with NW winds at 5-10 kts. Gusts of 15-20 kts during the
evening diminishing to around 15 kts toward daybreak.
KBOS Terminal...High Confidence in trends, moderate confidence
in timing. Biggest uncertainty is does the rain change to a
brief period of snow before ending between 07z and 10z.
KBDL Terminal...High Confidence in trends, moderate confidence
in timing.
Outlook /Monday through Thursday/...
Monday: VFR. Breezy. Slight chance FZRA.
Monday Night: Mainly VFR, with areas MVFR possible. Breezy.
Slight chance FZRA.
Tuesday: Mainly VFR, with local MVFR possible. Breezy.
Tuesday Night: MVFR/IFR conditions possible. Breezy. Chance
SHRA, chance SHSN, slight chance FZRA.
Wednesday: Mainly MVFR, with local IFR possible. Chance SHRA,
slight chance FZRA.
Wednesday Night: MVFR/IFR conditions possible. Slight chance
SHRA, slight chance FZRA.
Thursday: MVFR/IFR conditions possible. Breezy. Chance RA.
&&
.MARINE...
Forecaster Confidence Levels.
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Tonight through Sunday night...High confidence.
Expanded and extended the Small Craft Advisories due to mainly
strong NW wind speeds/gusts due to colder air advection. Will
have some spots of 4-7 ft waves across the southern and eastern
waters.
Winds tonight shift to the N/NW late tonight. Winds become
stronger and gusty Sunday into Sunday night. Gusts of 20-25 kts
on Sunday and 25-30 kts Sunday evening.
Outlook /Monday through Thursday/...
Monday: Winds less than 25 kt. Seas locally approaching 5 ft.
Monday Night: Winds less than 25 kt. Slight chance of rain
showers, slight chance of freezing rain.
Tuesday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt.
Tuesday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas locally approaching 5 ft. Chance of
rain showers.
Wednesday: Winds less than 25 kt. Seas locally approaching
5 ft. Chance of rain showers.
Wednesday Night: Winds less than 25 kt. Areas of seas
approaching 5 ft. Slight chance of rain showers.
Thursday: Winds less than 25 kt. Seas up to 5 ft. Chance of
rain.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...Winter Weather Advisory until 5 AM EST Sunday for MAZ002>006-
026.
RI...None.
MARINE...Small Craft Advisory from 1 PM Sunday to 4 AM EST Monday for
ANZ230-232>234.
Small Craft Advisory from 1 PM Sunday to 7 AM EST Monday for
ANZ231-250-251.
Small Craft Advisory until 7 AM EST Monday for ANZ235-237-
254>256.
&&
$$
SYNOPSIS...Frank/BL
NEAR TERM...Frank/BW
SHORT TERM...BL
LONG TERM...Frank
AVIATION...Frank/BL
MARINE...Frank/BL
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
702 PM EST Sat Dec 25 2021
.AVIATION...
Robust dry air advection on the 280-288Ke surfaces has occurred at
the Detroit area terminals within the hour. Model data supports some
continued isentropic downglide at roughly 3.5 kft agl throughout the
next 6 hours or so, which increases confidence that low clouds will
not be much of a concern this evening. Upper level moisture across
Wisconsin is timed to push through Southeast Michigan tonight after
05Z. Just expecting residual cloud to advect through with models
showing the active subsidence. Despite the look of the saturation in
the NAM solutions, the decision was made to go much more optimistic
with clouds Sunday. System relative trajectories show no isentropic
lift so difficult to really understand where the cloud is going to
come from. There is some modest cold air advection but that is
within the subsidence inversion. Did include a FEW category for sub
2.0 kft agl clouds for any diurnal cloud development. High cloud in
advance of the next system is expected to hold off until the evening
hours tomorrow.
.DTW THRESHOLD PROBABILITIES...
* Low for ceiling at or below 5000 feet late tonight and Sunday
morning.
* Low for visibility of 1/2SM or less with br/fg.
&&
.PREV DISCUSSION...
Issued at 357 PM EST Sat Dec 25 2021
DISCUSSION...
Morning passage of the surface cold front brought temperatures down
from the mid 40s to lower 50s that were reported from most locations
around sunrise. A slowly falling temperature trend continues this
afternoon with several degrees of cushion above freezing still
available in the Tri Cities area heading into sunset. A larger
margin of lower to mid 40s is reported south of I-69 as the last
patches of light rain exit eastward leaving just a low potential for
freezing before adequate drying of surfaces occurs this evening. The
rest of tonight is dry with a range of cloud cover by mid evening
into Sunday morning as surface high pressure builds from the Midwest
into Lower MI. The incoming dry air mass helps scour out low clouds
during the evening while mid and high clouds thicken after midnight
from the low amplitude mid level wave tracking over Lake Superior.
These clouds in turn quickly exit eastward followed by the influence
of a larger scale short wave ridge for Sunday that helps start things
off under mostly sunny sky during the morning. High clouds then
increase during the afternoon as reinforced surface high pressure
rolls across Lower MI. Guidance high temperatures in the mid to upper
30s are on target with the help of a little late December surface
heating and dwindling snow cover.
The Sunday afternoon high clouds are a precursor to the next low
pressure system organizing across the Plains states. It remains set
to bring our next wintry precipitation event in which the 12Z model
data shows some convergence of solutions on a snow to rain scenario
with a brief wintry mix during the transition. Thicker cirrus helps
curtail any big temperature drop during the night, especially as SE
surface wind sets up after midnight. Guidance projections are
preferred that allow lows in the upper 20s in the Tri Cities and
interior Thumb with readings settling into the lower 30s Detroit
metro to the Ohio border. The Plains low pressure system appears
plenty large and deep enough to displace the surface high from the
eastern Great Lakes farther toward the Atlantic coast during the
night leaving less temperature influence from that air mass. There
is still room for surface/boundary layer wet bulb cooling at the
onset of precipitation as mid level moisture transport surges into
the region late Sunday night into Monday morning. Model soundings
from the GFS and available time ranges from the RAP and ARW indicate
a distinct snow profile at onset before the mid level warm nose
punches in followed closely by the dry slot with the surface
occlusion. This process forces a rapid progression from snow to a
wintry mix of sleet/pellets and a brief period of freezing rain. The
above mentioned soundings do not show surface temperature locked at
or below freezing during this transition. This will be a crucial
aspect of the event to further evaluate, but at this point surface
temperatures rebound above freezing as precipitation rate drops off
to a drizzle pattern within the low level occlusion before ending by
Monday evening.
A break in precipitation coverage occurs Monday night and Tuesday
before the next wave moves in from the parent Rockies long wave
trough. This system looks very similar to the Monday version with
the possible exception of a farther south occlusion and greater
convective activity in the Ohio valley. This has potential to
disrupt precip production in Lower MI or at least reduce it to
another light snow to rain scenario with a brief wintry mix
transition heading into the mid week period.
MARINE...
Low pressure continues to pull away toward the mid Atlantic coast
today while high pressure builds in from central Canada. This will
keep a northerly wind across the lakes through Sunday with speeds
generally 20 knots or less. There are some waves around 3 feet
lingering around the Thumb but will decrease over the next few
hours. A push of cold air will arrive later tonight, bringing a
slight increase in northerly winds for Sunday, but again remaining
below 20 knots. The next storm system will enter the Midwest early
Monday with a warm front sliding north through the region through
the morning and afternoon. Winds will increase out of the southeast
in the morning reaching 25 to 30 knots which will likely lead to
small craft advisories around the Thumb for building wave heights.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&
$$
AVIATION.....CB
DISCUSSION...BT
MARINE.......DRK
You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.
AREA FORECAST DISCUSSION
National Weather Service Eureka CA
247 PM PST Sat Dec 25 2021
.SYNOPSIS...Another round of showers is expected tonight with heavy
snow above 1000 ft and small hail near the coast. 1 to 3 inches of
snow could fall as low as sea level early Sunday morning.
Precipitation will continue Sunday afternoon with snow levels above
1500 ft. Cold air will move back in Monday morning with more
possible sea level snow as showers taper off. Cold weather is
expected to persist all week.
&&
.DISCUSSION...Several small showers have moved on shore today
bringing sporadic rain. Even very small showers have generated
reports of small hail, highlighting just how cold air is in the low
levels. Outside of small showers, conditions have been calm and
partly sunny, making for a relatively pleasant holiday. CAMs show
another wave of stronger showers this evening as a shortwave starts
to pass overhead. Timing on the line varies from late afternoon to
near midnight. Small hail is expected to be an ongoing occournce
with these cells. This will bring even more heavy snowfall to
interior mountain above 1000 ft. As wind continues to turn westerly,
snowfall will become increasingly focused on the western ridges of
the Klamath mountains. Over the next 24 hours, NBM 4.1 shows a 90%
chance or more of over a foot of snow on high elevation passes with
50% chances along the low elevation valleys of Trinity and Eastern
Humboldt Counties.
A lobe of cold air will move in behind the trough. Hysplit modeling
shows the air coming form interior British Columbia and as far north
as SE Alaska. This cold air will pick up moisture from the ocean but
move too fast to substantially warm. Models look even colder today
than yesterday with 700 mb temperatures reaching -16 to -18C over
the area tonight. Sporadic convective showers are expected to reduce
but persist as cold air moves in. While most deterministic model
guidance shows snow levels bottoming out around 800ft, NBM 4.1 still
has about a 25% chance of 2 inches of snow at sea level tonight
through morning. Up just a couple hundred feet along many passes of
101 in Humboldt and Mendocino counties that probability increases to
40 to 70%. Model soundings consistently show the freezing level just
a few hundred feet from the surface, even at the coast. Meanwhile,
cold air aloft is helping support sustained periods of CAPE in
excess of 100 J/kg. This may allow snow levels to drop to sea level
in the midst of convective cells, supporting accumulating snow. The
HRRR even now shows snow levels around 100 ft in modeled convective
cells.
Low elevation snow looks strongest on the Humboldt and Del Norte
coasts where a Winter Storm Warning has been issued tonight. Snow is
most likely between midnight and 4 am. At this time, air aloft will
be coldest while models such as the NAM show dry air at the surface.
This would allow snow to freely fall. Since snow levels will vary
widely within cells, snow is expected to be wet and sporadic. While
chances of more than an inch of snow are not great in Eureka proper,
chances of 2 or more inches is much high just a couple hundred feet
ASL in Blue Lake, Micklinyville, and Fortuna.
Snowfall will be patchy but highly impactful where it does fall.
Thankfully snow levels will start to rise around sunrise, which
should help quickly melt any accumulated snow. These impacts and
potentially high accumulations justify an upgrade to a Winter Storm
Warning and an Advisory around Ukiah where snow amounts are lower.
Snow levels will briefly rise above 1500 feet Sunday afternoon and
evening before another lobe of cold air crashes down early Monday
bringing 700mb temperatures as cold as -19 C. This will help bring
snow levels back down to sea level, much more consistently than
Sunday as the air mass settles in. Though there are likely to be
fewer showers, CAPE has increased in models today, lingering near
100 J/Kg until noon. The colder temperature will help any
accumulation stick better. NBM 4.1 puts a 40 to 60% chance of
atleast 1 inch of snow on the Humboldt and Del Norte beaches with a
30 to 40% of 4 inches above 500ft on highway 101. Models today have
shifted snow further south putting a higher risk of more than 2
inches in Ukiah. High elevation snow will start to taper of Monday,
but accumulation in excess of a foot is still possible on the
western side of the Klamaths. There is still some uncertainty in the
relative timing of lingering showers and lowering snow levels, which
could substantially change low elevation snow. This in mind, a
winter storm watch has been left for low elevation locations for now.
Calmer weather will settle in beyond Monday alongside cold arctic
air. All clusters have cold air sitting over Northwest California to
some degree through the week. This will lead to very cold
temperatures. Tuesday will probably have the strongest cold air
advection. Alongside fresh snow, NBM 4.1 places less than a 50%
chance of most interior valleys even breaking above freezing. NBM
has a 60% chance of the low below 28 on Tuesday along the coast,
likely signaling a hard freeze. NBM hints at clear skies Monday
night, which could drive some interior areas like Hayfork into the
single digits. Low temperatures below freezing are likely all week,
even along the coast where multiple killing frosts seem almost
certain.
Light snow and rain showers are possible through Wednesday. Models
continue to struggle with a cutoff low off the coast next Wednesday
and Thursday. NBM show little to no precipitation while the
deterministic Euro and GFS both show QPF up to 0.5 inches. With
persistent low snow levels, even small amounts of QPF could prove
impactful. 80% of cluster ensemble members show at least mildly cool
weather persist into next weekend. /JHRW
&&
.AVIATION...Another round of convective weather and the
threat of winter storms are to be expected for the forecast area.
The coastal terminals have had intermittent rain and thunderstorms
with a constant threat of hail. Hail threats for KCEC and KACV will
persist until midnight with showers continuing through tomorrow.
Southwesterly winds at KCEC will prevail. Gusty southerlies at KACV
will veer west in the morning with MVFR conditions degrading to IFR
or less as ceilings and visibility come down. KUKI also has had
periods of rain which may continue into tomorrow. Westerly winds at
KUKI are at a gentle breeze and will veer to the south in the
morning. MVFR/VFR categories otherwise. /EYS
&&
.MARINE...Winds out of the NW will build from gentle to a strong
breeze, just under Gale strength, by early Sunday morning. Winds
will diminish by Sunday afternoon, especially in the southern
waters. Small craft advisories are in place for all area waters
through Monday, despite the fluctuating wind regimes. This is due to
a persistent swell out of the NW which will peak Sunday 16 to 20
feet by 13 seconds and will linger into the early work week.
Otherwise, tidal anomalies could bring coastal flooding on January
2nd with gravitational influence by a new moon. /EYS
&&
.EKA WATCHES/WARNINGS/ADVISORIES...
CA...
Winter Weather Advisory from 10 PM this evening to 10 AM
PST Sunday for CAZ109-112-113-115.
Winter Storm Watch from Sunday evening through Monday
morning for CAZ101-103-109-112-113-115.
Winter Storm Warning until 10 AM PST Monday for CAZ102-
104>108-110-111-114.
Winter Storm Warning from 10 PM this evening to 10 AM PST
Sunday for CAZ101-103.
NORTHWEST CALIFORNIA COASTAL WATERS...
Small Craft Advisory until 3 AM PST Monday for PZZ450-455-
470-475.
&&
$$
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For forecast zone information
see the forecast zone map online:
https://www.weather.gov/images/eka/zonemap.png
AREA FORECAST DISCUSSION
National Weather Service Hastings NE
951 PM CST Sat Dec 25 2021
...Short Term Update...
.UPDATE...
Issued at 951 PM CST Sat Dec 25 2021
Quick comments solely regarding the overnight forecast:
- Albeit minor, nudged down low temps 1-3 degrees from "original"
afternoon forecast package, and would not be surprised if we
still aren`t cold enough in some spots. More specifically, this
latest update now has the vast majority of the CWA (especially
Nebraska zones) bottoming out somewhere in the 21-29 range, with
any lows as "warm" as the low 30s most favored in parts of (not
all) our KS zones.
- If anything, satellite and model trends this evening have
indicated an overall-clearer overnight, with only a modest,
gradual increase in mid-high level clouds through daybreak.
- Given the predominantly clear skies and light winds through most
of the night (solidly under 10 MPH until closer to sunrise), the
stage is set for a slightly-colder-than-expected night, and
despite this latest temp update, could easily foresee a few
spots dropping even colder yet (which admittedly has been the
case each of the past few nights as well).
&&
.DISCUSSION...(This evening through Saturday)
Issued at 355 PM CST Sat Dec 25 2021
Main forecast issues are fire weather for Sunday, and
temperatures over the next several days.
Summary...
Mild, but breezy, conditions will continue through the holiday
weekend and promote areas of near-critical fire weather
conditions. A cold front will usher in windy conditions Sunday
night and set the stage for an overall cooler week (compared to
this last week) to close out 2021, but one that will still
feature some ups and downs. The coldest days of the next week or
so will come on Wednesday and Saturday (New Year`s Day) behind a
pair of storm systems. Precipitation chances with these storm
systems, however, look to remain on the low side as the best
moisture is shunted east of the High Plains.
Forecast Details...
Today has largely played out as expected as morning clds over far
N have given way to sunny skies and a late day surge in temps, and
wind, owing to bump in mixing on Wrly downsloping winds. In fact,
ODX has recently shot up to 61F and RH has dipped to 15 percent on
brzy W winds. Fire weather concerns are discussed below.
Brief shortwave ridging this eve will give way to a backdoor cold
front moving in from the N/NE late overnight. This front should stall
out towards daybreak and eventually lift N on Sun as low pressure
deepens over the High Plains. Tightening pressure gradient will
result in brzy and fairly chilly conditions for the AM hrs under
what could be fairly thick cld cover. The sfc trough axis should
set up from NE WY into SW NE by late aftn, allowing the warm front
to make some northward progress. Exactly how far N the front
makes it, along with lingering effects from potential AM stratus,
makes for a tricky high temp forecast on Sun and would not at all
be surprised if there`s a 20+ deg gradient from N to S. Latest
forecast calls for upper 40s N, where clds linger longest and
winds remain more SErly. Models are in pretty good agreement that
the warm/dry air (air temps potentially near 70F) will have best
chc to make a LATE afternoon surge into SW zones (similar to
what`s happening today near ODX)...and related fire weather
concerns are discussed below. As mentioned above, brzy conditions
are expected much of the day, ranging from SE to SW, so it
probably won`t feel quite as pleasant as today, esp. N of I-80.
A cold front will pass quickly through the area from W to E Sun
night, and some models continue to indicate potential for wind
gusts around 35-45 MPH for at least a couple of hrs immediately
behind the front, strongest over far NW zones. This front will
usher in colder air and make it feel like teens Mon AM. Highs will
struggle to rally into the 40s Mon aftn for areas along and N of
I-80, but should see mid to upper 40s near/S of the state line.
Upper pattern will gradually transition to broad troughing over W
third of CONUS and broad ridging over the SE CONUS. This will
result in relatively fast SW upper flow and tight low level
baroclinic zone over the Central Plains, with several upper
perturbations riding NE along this zone through the upcoming week.
The first system will deepen along the High Plains Mon night and
give us relatively mild conditions to start the day Tue. However,
by aftn the sfc low is forecast to quickly shift E across either N
KS or S NE, with strong CAA kicking in for the aftn. GFS and EC
are in good agreement on this, with the NAM being a slower
outlier. Depending on the exact depth and timing, Tue could again
be a difficult temp forecast day as latest GFS/EC suggest another
25+ deg gradient from NW to SE. It seems that regardless of exact
timing/strength, pcpn chcs from this system remain quite low.
Can`t rule out some lgt WAA driven pcpn over far E/NE Tue AM, but
models keep any appreciable QPF off to the E. IF the system can
slow down, closer to the NAM, and maintain strength from GFS/EC,
then perhaps chcs could incr. Main impact, though, looks to be
cold, brzy conditions Tue PM.
Some of the coldest temps of the week will come Tue night into
Wed as sfc high pressure noses S out of Canada. Wind chill values
could fall to -5 to -15F by Wed AM, with aftn air temps struggling
through the mid/upper 20s.
Temperatures will rebound Thu into Fri ahead of another potential
storm system for New Year`s Eve into New Year`s Day. Pcpn chcs may
be marginally better with this system, but definitely too soon to
get into too much specifics. Could see another dip in highs into
the 20s behind this system for New Year`s Day.
&&
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Monday)
Issued at 659 PM CST Sat Dec 25 2021
General overview:
High confidence in VFR visibility and precipitation-free weather
throughout the period, and high confidence in VFR ceiling through
the vast majority of it. However, there will be at least a 3-hour
window-of-opportunity for MVFR ceiling during the day Sunday. The
other main concern is a 4-hour period of mentionable low level
wind shear (LLWS) Sunday morning. Details on both of these
potential issues follow.
Ceiling details:
Very high confidence in VFR through at least these first 14 hours,
with only a gradual increase in mid-high level clouds. However,
particularly between about 16-19Z, there remains a decent signal
for at least a sporadic MVFR ceiling, and have indicated BKN015
during this time. For what it`s worth, one model (NAM) appears to
be up to its often-over-aggressive habits in suggesting not only
a longer duration of MVFR potential (well into the afternoon), but
also a chance of IFR. At this time (and after seeing how
overblown the 18Z NAM ended up being with low cloud potential last
night), have opted to shy away from this more pessimistic
solution but later forecasts will obviously need to monitor, just
in case.
Wind details (including LLWS):
- Surface winds: The lightest speeds of the period will focus
right away these first roughly 9 hours (direction somewhat
variable/speeds mainly at-or-below 6KT). However, during the day
Sunday breezes will be on the increase, initially out of the
east-southeast but then trending more southerly as a warm front
lifts through. The overall-strongest winds will focus 16-22Z
(commonly sustained 15+KT/gusts 20-25KT).
- LLWS: Made only minor adjustments to previous TAFS here,
focusing all LLWS 12-16Z, during which time as much as 30-35KT
of shear magnitude will exist between the surface and roughly
1,500 ft AGL, thanks to southeast winds slightly above the
surface increasing to as much as 40-45KT.
&&
.FIRE WEATHER...
Issued at 355 PM CST Sat Dec 25 2021
Fire weather conditions briefly spiked into the critical range
near ODX with an RH in the teens and gusts near 30 MPH. This looks
to be brief, however, as winds are already dying off.
At least near-critical fire conditions will become a strong
possibility over SW zones on Sun aftn. This is supported by latest
SPC Day 2 Fire Weather outlook. However, uncertainties still
remain owing to differences in model placement of sfc low/fronts.
Areas SW of Arapahoe to Osborne line have greatest chc for near-
critical fire wx, though this could extend further NE if 18Z HRRR
pans out. Official forecast isn`t quite that low with RH, but
there`s still an hr or two of critical conditions in mainly Rooks
Co. Will have to keep an eye on this for potential Red Flag
Warning, but confidence on coverage/duration of critical fire wx
conditions too low to issue attm. There`s hints that cld cover
could be stubborn and limit the mixing/warming potential further
E/NE toward Mankato/Hebron. Worth noting that IF there are any
fire starts tmrw aftn that linger into the overnight, RH recovery
will be pretty slow, and expect a surge in NW wind gusts with a
cold front around 03-06Z.
&&
.GID WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
KS...NONE.
&&
$$
UPDATE...Pfannkuch
DISCUSSION...Thies
AVIATION...Pfannkuch
FIRE WEATHER...Thies
Area Forecast Discussion
National Weather Service Huntsville AL
857 PM CST Sat Dec 25 2021
.NEAR TERM...(Tonight)
Issued at 858 PM CST Sat Dec 25 2021
A weak front is slowly pushing southeast into northwestern Tennessee
at this hour. Models slowly but surely push this front further
southeast into northern Alabama and southern middle Tennessee by
daybreak on Sunday. Winds have become light over the last few hours.
However, thick low and mid level cloud cover is in place and should
only lower towards daybreak.
Area radars show some showers developing along and ahead of the front
over southern Kentucky and central Tennessee over the past 2 hours.
HRRR has been forecasting this even this afternoon. This model
continues to push isolated to scattered showers southward along the
front into southern middle Tennessee and northern Alabama after 10
PM. These look to continue until just after daybreak before weakening
and pushing southeast of the area around 8 AM. Could see some patchy
fog and rain during that period, especially near and east of the
I-65 corridor. Adjusted lows to reflect the front making it into the
area and some lower dewpoints filtering in. Expect lows still in the
mid 50s to around 60 degrees in most locations.
.SHORT TERM...(Sunday through Tuesday)
Issued at 234 PM CST Sat Dec 25 2021
The regime discussed above should come to an end by Sunday
afternoon, as mid-level heights begin to rise across much of the
southern CONUS downstream from an amplifying longwave trough
extending from western Canada into the eastern North Pacific.
Furthermore, the cold front (which should be located immediately
north of the CWFA at 12Z tomorrow) is predicted to retreat northward
throughout the day, as a deepening shortwave trough lifting across
the northern Plains initiates lee cyclogenesis across northeastern
CO/southwestern NE. Low-level southerly flow will begin to strengthen
across our region once again during the afternoon as the warm sector
builds northward, with broken-overcast stratus clouds expected to
spread back into the region, keeping highs in the u60s-l70s. Strong
southwesterly gradient flow is expected across the TN Valley once
again on Sunday night/Monday, but as the weakening frontal low
travels eastward from northern IL into the eastern Great Lakes late
in the day, winds will begin to subside as the trailing cold front
drifts southeastward into the OH Valley. Lows on Monday morning will
be in the u50s-l60s, with afternoon highs in the u60s-l70s, and
chances for showers will begin to increase late in the day
(especially across northern zones) as moisture advection strengthens
ahead of the front.
During the period from Monday night-Tuesday, the subtropical ridge
to our south is predicted to shift further eastward across south FL
and the Bahamas, inducing a return to southwesterly flow aloft. At
the surface, the polar front drifting southeastward into the Lower OH
Valley Monday evening should begin to retreat northward once again,
as another shortwave lifts northeastward out of the longwave trough
to our west, leading to renewed cyclogenesis across eastern
CO/western KS. Due to some uncertainty regarding the position of the
front, we have maintained a low chance for showers Monday evening
(focused across our northern zones). However, the coverage of showers
is expected to increase on Tuesday, as deeper moisture begins to
return to the region and potentially interacts with a weak upper-
level wave lifting northeastward from the western Gulf of Mexico.
Temperatures will not change much (if at all), with lows in the u50s-
l60s and highs in the l-m 70s.
.LONG TERM...(Tuesday night through Friday)
Issued at 234 PM CST Sat Dec 25 2021
The weather shifts to a more active pattern through the second half
of next week. It starts with the shift of the subtropical high
eastward out over the Atlantic, with a deepening trough over the
Rocky Mountains. As this trough shifts eastward into the Missouri
River Valley, the subtropical jet pushes into the Southeast, bringing
with it a track of shortwaves that will bring periods of rain
through the end of the week. The first of these waves will generate
showers across the Tennessee Valley on Tuesday into Wednesday. During
this time, a low pressure system picks up the frontal boundary
draped across Tennessee and ramps up moisture advection ahead of its
associated cold front. During this time frame, we see PWAT increase
from 0.7-0.8 on Tuesday to 1.3-1.5 on Wednesday. Depending on how
high PWAT gets, the record for Dec 29 is 1.62 in. according to
historical BMX soundings. This indicates a pretty good chance for
heavy rainfall associated with showers starting Wednesday morning.
The greater threat for heavy rainfall, however, will be as the cold
front moves through Wednesday night into Thursday morning due to
stronger synoptic-scale forcing.
Though we`ll remain fairly cloudy on Wednesday, moisture advection
will help to destabilize the environment ahead of the cold front,
starting Wednesday morning. This will lead to a threat for
thunderstorms all day on Wednesday, with the best chance as the cold
front moves through. As previously mentioned, the primary threat will
be for moderate-heavy rainfall, but we`ll need to watch for how much
we can destabilize ahead of the cold front for the potential for a
few stronger storms as it moves through Wednesday night-Thursday
morning. Enough shear will be present for organization if storms can
get tall enough.
Beyond Thursday, high pressure slides in behind the cold front,
likely bringing us a dry period just in time for outdoor New Years
Eve plans. Left a slight chance of showers due to uncertainty in the
timing of the warm front bringing more rain ahead of the next surface
low moving across the Central Plains. That`s more likely to spread
into the area late Friday/Saturday.
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 508 PM CST Sat Dec 25 2021
VFR CIGS are in place at both terminals at this time and should
remain in place much of the evening, as winds quickly become much
lighter around 4 knots after 1Z. Closer to 10Z, as a front approaches
the region, CIGS are expected to become IFR or lower as they drop
below 1000 feet. Some fog or drizzle could reduce visibilities to
1SM or lower between 10Z and 14Z as a result. For now, leaving DZ
out of the forecast and not going lower than 1SM with VSBYS. However,
lower VSBYS or DZ may need to be added in the 06Z issuance of TAFs.
Expect VFR CIGS to become MVFR after 18Z at both terminals and VFR
after 20Z.
&&
.HUN WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
TN...NONE.
&&
$$
NEAR TERM...KTW
SHORT TERM...70/DD
LONG TERM...McCoy
AVIATION...KTW
For more information please visit our website
at weather.gov/huntsville.
Area Forecast Discussion
National Weather Service North Platte NE
642 PM CST Sat Dec 25 2021
.UPDATE...
Issued at 642 PM CST Sat Dec 25 2021
The Sunday forecast wind gust forecast gets a boost from the RAP
model which shows 50 mph wind gusts across wrn Nebraska. The
culprit, a strong Pacific cold front moving in late in the
afternoon and during the evening. Bufkit-GFS suggest stronger
gusts to near 60 mph. This is in response to a PV1.5 anomaly and
65 kt winds aloft at h700mb. Later forecast might include a High
Wind Watch. For now, we will have to wait on the 00z HRRR model
run for conformation. The 00z model run will run out through
Sunday evening.
&&
.SHORT TERM...(This evening through Sunday night)
Issued at 316 PM CST Sat Dec 25 2021
Mild conditions prevail across the area today, with clear skies and
elevated wind gusts from the west. Temperatures this afternoon are
ranging from the 50s across southwest Nebraska to the 40s for the
remainder of central and north central Nebraska. Aloft, zonal flow
yet again reins supreme across the CONUS today.
Cloud cover is anticipated to build in overnight, and will be a
higher point of uncertainty with regards to temperatures. This is a
response of warm advection, as a surface warm front approaches and
increases isentropic ascent overnight into tomorrow morning. Clouds
should begin to overspread the area around midnight with an increase
to ascent noted on the 295-305K surfaces. This cloud cover will be
maintained through much of tomorrow morning as well, especially
across north central Nebraska, where ascent lingers longest. This
should keep lows warmer, and the going forecast reflects this.
By late tomorrow afternoon a surface low will begin to eject
northeast across the Panhandle, dragging a cold front into the area.
Ahead of this low, southeasterly flow (in association with the
aforementioned warm front) increases and will lead to low end
precipitation chances across portions of north central Nebraska.
Forecast soundings indicates the moist layer will largely remain
above -10C, leading to the potential for mixed precipitation with
supercooled liquid water in the cloud bearing layer. That said,
ascent remains weak in the warm frontal zone and any precipitation
looks to be very light. Additionally, some guidance suggests a dry
layer near the surface leading to further uncertainty. Still, enough
potential exists for flurries/drizzle to add some low end POPs to
Boyd and Holt counties through tomorrow afternoon. Temperatures will
need to be monitored closely, as some guidance supports a brief
period of freezing drizzle tomorrow morning before gradual warming
and drying of the column occurs. Temperatures will struggle to rise
out of the 30s across north central Nebraska where the lingering
cloud cover remains. Temperatures in the upper 50s will be possible
across southwest Nebraska where clearing is anticipated.
The cold front clears the area overnight, leading to a period of
stronger westerly winds behind the boundary. This is largely due to
quickly increasing H7-H85 flow, on the order of 50 to 60kts. How
much of this can mechanically mix to the surface overnight leads to
uncertainty in the strength of surface wind gusts. Cold advection
does not look overly strong behind the boundary, but decent surface
pressure rises (2-3mb/hr) and a unidirectional wind profile could
counteract this some. Widespread gusts in the 40 to 45 mph range are
expected across the Panhandle and western Sandhills. However, this
will need to be monitored for the potential for locally higher
gusts.
.LONG TERM...(Monday through Saturday)
Issued at 316 PM CST Sat Dec 25 2021
A pattern shift remains on tap for the long term period with a
reinforcing cold shot expected Tuesday.
Elevated fire weather concerns will be possible Monday, as RH values
drop into the upper teens, though there looks to be very limited
overlap in low humidity and gusty winds. H85 flow briefly
transitions southerly Monday afternoon in response to a deepening
lee side low over eastern Wyoming/Colorado. This leads to WAA
through the day though H85 temps only climb to around and just above
freezing. This will promote a cooler day Monday, with highs some 10
to 15 degrees cooler than Sunday.
The next cold shot arrives as the aforementioned low ejects across
the Plains. This will bring in some of the colder air we`ve seen yet
this season, though not quite as cold as guidance had indicated the
last few forecast cycles. Still, a stretch of below freezing highs
are anticipated along and north of Interstate 80 Tuesday through
Thursday and single digit lows. Some light precip will be possible
across far northern Nebraska with the passage of the front, though
confidence remains low in this. Moisture will quickly be ushered out
of the area with FROPA, leading to a limited window for any
precipitation.
Another system is possible near the end of the week, though spread
increases substantially in ensemble/deterministic guidance. An upper
low is progged to drop into the Four Corners region late week and
eject northeastward. Colder temps and precipitation appear possible,
but trends will need to be monitored.
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 520 PM CST Sat Dec 25 2021
Currently, winds are a bit variable across the southern terminals,
generally from the SE. For northern terminals, winds are from the
NE ATTM. Some LLWS is expected across the Sandhills from about
9-18Z. Overnight, winds will generally be from the SE, and into
tomorrow they will transition to be from the SW. There is a chance
at the end of the TAF period for northern terminals to see some
low CIGS. At this time have left as MVFR. Will continue to
monitor and update as needed.
&&
.FIRE WEATHER...
Issued at 315 PM CST Sat Dec 25 2021
A surge of warm dry air has spread east across the area this
afternoon. There is a small corridor, near I-80, where near
critical to briefly critical fire weather conditions are being
met this afternoon. These conditions will improve quickly by late
this afternoon as winds quickly diminish and humidity values rise.
Elevated fire weather conditions will be possible across far
southwest Nebraska and portions of the Panhandle late Sunday
afternoon. On Monday, low relative humidity is expected all areas
but winds should remain mostly light.
&&
.LBF WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...CDC
SHORT TERM...Brown
LONG TERM...Brown
AVIATION...Sinclair
FIRE WEATHER...Taylor
AREA FORECAST DISCUSSION...UPDATED
National Weather Service Morristown TN
1003 PM EST Sat Dec 25 2021
.UPDATE...
EVENING UPDATE.
&&
.DISCUSSION...
A few showers are moving into northern portions of the area just
ahead of a cold front. The HRRR seems to have the best handle on
these showers, though it is a little overdone in coverage. The
expected trend over the next few hours is for the showers to track
south and gradually decrease in coverage. The current forecast has
chance PoPs in SW VA and NE TN, with a slight chance in the
central Valley, and no PoPs across the southern counties. This
appears on track, so no major changes are planned. Temps/dewpoints
also are running close to obs in most spots, with only a few
tweaks needed.
DGS
&&
.AVIATION...
00Z TAF DISCUSSION.
Forecast confidence is low this period as several factors will
influence cig/vis at the terminals. A mild and moist air mass is
over the area due to a breezy SW wind. Winds should drop to less
than 10 kts after minight. A front is approaching from the north,
with a few showers along it. This front will move through
overnight, but the chance of showers is low. With temps cooling
but low level moisture remaining high, some low cigs seem likely
at all sites, so will have IFR conditions in the TAFs. Models
point toward fog as well, IFR or lower, but the question is how
much wind will stay up to prevent fog. Will forecast predominant
MVFR vis for now.
DGS
&&
.PREV DISCUSSION...
/ISSUED 320 PM EST Sat Dec 25 2021/
SHORT TERM...(Tonight and Tomorrow)...
Key Message:
1. Fairly low chances of light rain late this afternoon through
this evening, with the highest chances being north of Interstate
40.
Discussion:
In the upper levels, nearly zonal flow will be over the region. At
the surface, low pressure off the Northeast Coast will bring a
weak cold front through the region late tonight. High pressure
will be over the Ohio Valley and Southeast tomorrow. Model
guidance has consistently overdone POPs this morning and so far
this afternoon, so I kept POPs fairly low and confined to north of
Knoxville and along the higher elevations of the Smokies. Timing
of light rain will be late this afternoon and through the evening.
Winds will decrease significantly around sunset this evening.
Patchy fog will be possible overnight and in the early morning but
confidence is low. Model guidance has not been performing well
today, winds were stronger than forecast and rain showers have not
developed ahead of the cold front (Some light rain is observed
along the front in Indiana). So this has been a tricky forecast
with lower than usual confidence.
Frontal passage will bring only a brief wind shift and drop in dew
points. Temps will remain warm with highs in the 60s expected
tomorrow with clearing skies in the afternoon.
McD
LONG TERM...(Sunday Night through Saturday)...
Key Messages:
1. Unseasonably mild temperatures are expected through the entire
period.
2. Widespread, moderate rainfall expected mid week. Otherwise, just
occasional showers expected and mainly in the north.
Discussion:
Weak upper ridging will be in place over the southern Appalachians
Sunday night into Monday morning, with a shortwave topping the ridge
and moving through the upper midwest and Great Lakes. Associated
surface low will trek through Missouri and Illinois during this
time, dragging a front south into Kentucky. Have some slight chance
to chance PoPs in the forecast on Monday to account for this, with
the best chances being up in Virginia. Given the front will likely
remain to our north, and upper forcing will be pulling away, I
wouldn`t be surprised if we wind up dry. For now however, will keep
the light rain chances in the forecast.
Rain chances don`t go away however as the upper pattern becomes more
amplified through midweek, with deeper troughing developing out west
and several impulses ejecting northeast through the central and
southern plains. This keeps the aforementioned frontal boundary
locked in place across Kentucky and likely back through western
Tennessee, with waves of precip moving along and southeast of the
front. Tue night into Wed in particular, look quite rainy across the
CWA. Ramp PoPs up to categorical levels during that time frame. The
pattern, if it were persistent or featured a lot of training
convection, would represent a flooding concern. It is definitely
worth monitoring, but currently it appears the duration of the event
combined with a lack of convective QPF poses a low flooding risk for
the time being. It will be a good soaking rain however, with a
general 1-2" of rain expected across the area in general.
The NBM guidance keeps rain chances in the forecast Thu night and
Fri. Tapered those down a bit as operational runs show the frontal
boundary finally pushing off to the southeast. This will likely be
short lived however as the next trough out west ejects into the
central US and the front pulls back north through the forecast area.
Temperature wise, the warm winter temperatures continue. Guidance
continues to show temperatures 10-15 degrees above normal through
the entire long term period. Even behind the front on Thu/Fri, lack
of amplified upper flow means no cold air crashed in from Canada and
we`re only down to 5-10 degrees above normal instead of 15.
CD
&&
.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN 55 70 57 69 59 / 10 0 0 20 20
Knoxville McGhee Tyson Airport, TN 54 67 53 68 59 / 20 0 0 20 30
Oak Ridge, TN 53 66 52 66 58 / 20 0 10 20 30
Tri Cities Airport, TN 51 62 45 65 53 / 30 10 10 30 40
&&
.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...NONE.
VA...NONE.
&&
$$
Area Forecast Discussion
National Weather Service Pueblo CO
338 PM MST Sat Dec 25 2021
.SHORT TERM...(This evening through Sunday)
Issued at 338 PM MST Sat Dec 25 2021
Key messages:
- Snow, along with periods of very strong winds, will
redevelop along the Continental Divide overnight and persist
through Sunday.
- Strong/damaging winds with gusts 60-80 mph likely over the
San Luis Valley and southern mountains beginning early Sunday
morning, with risk spreading across the southern I-25 corridor
and southeast plains after sunrise.
- High Fire Danger expected over the I-25 corridor and
southeast plains Sunday afternoon.
Currently...Most locations experiencing a brief break between
winter storms this afternoon, though still some gusty winds and
patchy Red Flag conditions over portions of the Arkansas Valley and
El Paso County, where winds were gusting 25-30 mph at times.
Tonight...Next strong upper level trough moves onshore along the
Pacific Coast, while 180 kt 250h jet streak moves into wrn Colorado
by early Sunday morning. Increasing swly mid-level flow and
accompanying moisture will begin to generate some snow showers over
the eastern San Juans this evening, then snowfall spreads to the
remainder of the Continental Divide early Sunday morning. By
sunrise, snowfall will become heavy around Wolf Creek Pass, with
lighter snow farther north in the central mountains. As mid/upper
level winds increase, potential for strong and damaging winds
develops over the San Luis Valley, southern mountains and southern
Interstate 25 corridor by sunrise, with progged 700h flow of 50-60
kts spreading across the area. Have converted Winter Storm Watches
to Warnings over the higher terrain and advisories at lower
elevations, with High Wind Watch converted to a warning as well.
Sunday...Very windy with periods of heavy snow along the Continental
Divide through the day as upper trough moves across and strong jet
rotates through the state. Expect difficult travel over high
mountain passes, with Wolf Creek and Monarch Passes most impacted.
High winds will spread from the mountains onto the plains early in
the morning, with strong/damaging winds continuing into the
afternoon. Added Fremont County to the High Wind Warning, as flow
briefly lines up with the Arkansas Valley in the afternoon,
suggesting gusts over 60 mph possible, especially around Canon
City. Biggest question mark on Sunday will be potential for strong
wind outside the current warning area, with upper Arkansas Valley,
El Paso County and far eastern plains getting close to 60 mph for a
period in the afternoon. Given HRRR forecasts keeping stronger gusts
generally south and west of these areas, didn`t expand the warning
yet, but does need monitoring. Humidity marginal for a Red Flag
highlight, though with many locations along and east of I-25 getting
close to 15 percent by mid-afternoon, will go ahead and upgrade the
Fire Weather Watch to a warning. Could see some blowing dust over
the San Luis Valley and across the eastern plains Sunday, especially
from mid-morning through mid-afternoon, when thermal mixing will
aide in lofting loose soil in open areas. Away from the snowfall
near the Divide, max temps will again be above average, though wind
will make for a rather ugly day at many locations.
.LONG TERM...(Sunday night through Saturday)
Issued at 338 PM MST Sat Dec 25 2021
Key Messages:
- Snow continues along the Continental Divide sporadically through
the upcoming week
A longwave trough of low pressure over the western US will
persist well into next week, with multiple embedded shortwaves
within the larger scale flow sweeping across the region. This
pattern will continue to bring sporadic snow to the higher
terrain, and especially along the Continental Divide, while the
eastern plains will essentially just get more wind and persistent
dry conditions.
Sunday night and Monday...The first upper shortwave will exit the
region Monday morning, allowing the stronger wind gusts to
lessen, as snow diminishes across the mts through Monday morning.
Additional snow amounts across the sw and central mts should
amount to around 3 to 4 inches, and all highlights will likely be
allowed to expire by 12z Mon. Temps will be a bit cooler and more
seasonal, with highs Mon in the 30s to around 40F for the high
valleys, and 40s to around 50F for the plains.
Monday night through Wednesday...Another shortwave is forecast to
sweep across the Pacific NW and the Great Basin early Monday, then
across Colorado Monday night through Wednesday. This will bring
another round of significant snow to the mts, and wind to the
eastern plains, and highlights will likely need to be hoisted once
again for the forecast area. Current forecast snow amounts are in
the 18 inch range for the sw mts, and 8 to 10 inches for the central
mts. As the shortwave passes to the east late Tue into Wed, much
cooler air is expected to filter in for Wed. Therefore, plan on
highs in the 30s for the high valleys both days. Across the plains,
look for 40s to lower 50s on Tue, then 30s to around 40F for Wed.
Wednesday night and Thursday...A closed upper low breaks off from
the main flow aloft and pushes just off the CA coast late Wed. This
will produce a lull in activity across CO into Thu, with just some
light lingering snow along the Divide and about 10 degrees of
warming for the plains.
Friday and Saturday...Another shortwave pushes southeast out of the
Pacific NW, while the closed low off the CA coast weakens and start
to move north. Both of these features merge over the desert SW and
cross the Four Corners, bringing another round of snow to the mts
Friday into Saturday morning. Temps will warm by another 5 degrees
for Fri, then bottom out in the 30s for most areas for the first day
of the new year. Moore
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 338 PM MST Sat Dec 25 2021
VFR at all taf sites the next 24 hrs. W-SW winds will be strong at
all terminals until 00z, then lighter winds expected overnight. On
Sun, strong W-SW winds will redevelop, with some gusts to 50 kts
possible, especially after 18z. Low risk of a vcsh at KALS during
the day Sun, though heavier precip will stay back west over the
higher terrain. Also a low risk of blowing dust briefly limiting
visibility at all terminals for a few hrs Sunday afternoon.
&&
.PUB WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from 11 AM to 5 PM MST Sunday for COZ226>237.
Winter Weather Advisory from 2 AM Sunday to 5 AM MST Monday for
COZ058-059-061-066-067.
High Wind Warning from 2 AM to 8 PM MST Sunday for COZ069>075-
078>080-087-088.
Red Flag Warning until 5 PM MST this afternoon for COZ222-
226>228.
High Wind Warning from 7 AM to 8 PM MST Sunday for COZ076-077-
083-086-093-094.
Winter Storm Warning from 2 AM Sunday to 5 AM MST Monday for
COZ060-068.
&&
$$
SHORT TERM...PETERSEN
LONG TERM...MOORE
AVIATION...PETERSEN
Area Forecast Discussion
National Weather Service Blacksburg VA
922 PM EST Sat Dec 25 2021
.SYNOPSIS...
A cold front will cross the area tonight, gradually reaching a
west to east oriented state across the Tennessee Valley into the
Carolinas Sunday. This front will lift back north early next
week and the overall weather pattern will change little through
the remainder of the year, with warmer than normal weather
persisting through Friday. The best chance of rain will be on
Wednesday and Thursday across the region.
&&
.NEAR TERM /THROUGH SUNDAY/...
As of 915 PM EST Saturday...
Expect Winds To Stay Gusty Through Early Overnight...
Coverage of strongest winds continues over the higher ridges of
southwest VA into the NC mountains. Trend is for low level jet
to head east toward midnight, so after collaborating with WFO
GSP will keep wind advisory going as still getting gusts 40-45
mph in the advisory area at times.
Otherwise, leading edge of showers along the front has made into
the Greenbrier Valley and Alleghanys. Could see some gusty winds
from these showers as well. Meanwhile, temperatures running mild
late this Christmas evening with upper 50s to mid 60s, feeling
more like late Spring.
Temperatures will eventually drop into the upper 40s to mid 50s
by dawn which is about 20-25 degrees above normal.
Previous discussion from early evening...
Winds to diminish through the night...
Gusts over 35 mph still persist at elevations above 4000 feet,
with some gusts over 30 mph above 2500 feet. As we head through
this evening, the core of the low level jet tracks east, so
aside from the highest elevations this evening, the advisory
area should stay mainly below 45 mph gusts, so planning on
cancelling the advisory early, once that 8h jet shifts east
this evening.
Other changes to the forecast were to keep it drier earlier this
evening as main lift is along the front across northern WV into
the KY/OH area. Should start to see these showers shift
southeast to the Alleghanys of SE WV by mid evening, but
limiting rainfall east of the WV/VA border.
Previous discussion from Saturday afternoon...
Very zonal 500 mb pattern slowly becomes more northwest on
Sunday. 50-60 knot west 850MB winds turn to the northwest and
gradually diminish after midnight.
Band of relatively deeper moisture along the front crosses from
central Virginia into central North Carolina between 00Z/7PM
and 12Z/7AM. This will be the best chance for showers in the
mountains and a few sprinkles are possible east of the Blue
Ridge. Clouds erode in the morning on Sunday and even in the
favorable upslope areas, the air mass dries by afternoon. Timing
of the front and associated precipitation varies slightly in
the guidance with the NAMNest faster than the HRRR and FV3.
Surface dew points stay in the mid 40s to mid 50s until a weak cold
front crosses through the region from northwest to southeast
tonight. This will result in a non-typical diurnal hourly
temperature trend. Cold air advection is weak behind the front so
maximum temperatures on Sunday will still be well above normal.
&&
.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
As of 215 PM EST Saturday...
Warming temperatures and increasing chance of rain heading into
early next week
High pressure will shift east of the region Sunday night with the
approach of an upper level shortwave through the Great Lakes region.
This system is expected to continue on an eastward track, and
progress into PA/NY by Monday afternoon. Southwest flow will
increase across the area as the system passes to our north, helping
to advect Gulf of Mexico moisture into the region. The associated
cold front is expected to reach the area by Tuesday morning.
There is some question as to how far the front will push south of
the area, or even if it will. Most guidance is offering the latter
solution, with the feature setting up a weakness over the area that
will remain there through Tuesday night.
The result for our region will be temperatures still on the mild
side, but with Tuesday milder than Monday. Also, rain chances will
also increase across the region from west to east, arriving last
across the far southeast portion of the area late Tuesday night.
Confidence in the above weather scenario is moderate to high.
&&
.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
As of 100 PM EST Saturday...
Temperatures will start trending cooler, but still remain above
normal for this time of year.
On Wednesday, we will see the front to our west heading our way,
with mild conditions and good moisture flow off the Gulf of Mexico.
We are expecting probably the mildest day of the week, with
increasing chances of rain across the region, with the best coverage
in the west.
Wednesday night into Thursday, the front to our west either moves
across the region and then parks over the Carolinas, or stalls and
washes out over the region. Guidance has an amount of variability on
this. Either way, rain chances continue across the area, with the
best probabilities shifting to the southern half of the area.
By Thursday night into Friday night, the latest guidance is offering
a pattern that trends flow aloft across the area to zonal, while a
surface ridge moves over, then east of the area. While precipitation
chances are trending downward as compared to the previous solution
based upon this trend, we are not ready to say a zero percent quite
yet. Will continue with a token slight chance to reflect trend
towards no precipitation, not an abrupt chance.
For Friday into Saturday, guidance varies as to the degree to which
the next Pacific-based low pressure evolves over central CONUS.
Likewise, this will impact weather across our region depending
upon the degree of deepening and path this low takes. Our
current forecast will reflect increasing chance of precipitation
Friday night into Saturday, especially over western parts of
the region.
Temperatures during this part of the forecast will trend from
readings around twenty-five degrees above normal on Wednesday to
values about ten degrees above normal on Saturday.
Confidence in the above portion of the forecast is low to moderate
with the timing and location of the precipitation the biggest
questions.
&&
.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
As of 625 PM EST Saturday...
Expect gusty southwest to west winds at most terminals through
tonight, with sub-VFR cigs impacting BLF/LWB and at times BCB.
Gusts over 25kts are likely at BLF/BCB, maybe LWB, and could see
some higher gusts as showers move in, but will not try to time
this as of this issuance, but based on high-res models, LWB
could see these showers over northern WV arrive by 02-03z. Wind
speeds gradually diminish throughout the day Sunday. Some gusts
of 15 to 25 knots are still possible once mixing begins in the
morning Sunday.
Showers are expected along and ahead of the front from the Ohio
Valley into the mountains of WV/VA. These showers are not
expected to make it east of the Alleghanys and NC mountains due
to the strong downslope wind flow.
Drier air moves into the region Sunday morning and clouds over
the mountains erode, with BLF/LWB becoming VFR by 16-19z.
Average confidence for ceiling, visibility and wind.
.Extended Aviation Discussion...
Sunday night will be VFR, with another chance for showers and
MVFR ceilings across the mountains Monday into Tuesday.
Another period of MVFR clouds and a chance of precipitation for
the mountains is expected Tuesday night and Wednesday, along
with the potential for gusty winds.
Sub-VFR may impact most sites into Thursday as a frontal
boundary moves across.
&&
.CLIMATE...
As of 600 PM EST Saturday...
Record high temperatures were set at Roanoke today, and tied at
Lynchburg. Roanoke reach 69, which brought the Christmas record
of 68 set in 1964. Lynchburg reached 72, which tied the record
from 1982.
&&
.RNK WATCHES/WARNINGS/ADVISORIES...
VA...Wind Advisory until 1 AM EST Sunday for VAZ007-009-010-012-015.
NC...Wind Advisory until 1 AM EST Sunday for NCZ001-018.
WV...Wind Advisory until 1 AM EST Sunday for WVZ042.
&&
$$
SYNOPSIS...AMS/WP
NEAR TERM...AMS/WP
SHORT TERM...DS
LONG TERM...DS
AVIATION...AMS/WP
CLIMATE...WP