Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/22/17
Area Forecast Discussion
National Weather Service La Crosse WI
534 PM CST Thu Dec 21 2017
.SHORT TERM...(This evening through Friday)
Issued at 240 PM CST Thu Dec 21 2017
For the bulk of the day, a narrow frontogenetical snow band has been
set up near and just north of the I-90 corridor across southern
Minnesota eastward into Wisconsin, with little in the way of precip
outside of this focused area. Through early afternoon, up to 1 to
2 inches has fallen north of I-90 in west-central Wisconsin.
Much of the short term high-res model guidance indicates this band
will slowly shift northward through the evening, with perhaps
another inch within the band. The RAP suggests precip will focus
near another area of mid-level frontogenesis this evening,
possibly impacting portions of northeastern Iowa and far southwest
Wisconsin. While early on this evening, the moisture depth will
be limited across the extreme southern portion of the area, deeper
saturation is expected to develop through the evening. Similar to
what has occurred farther to the southwest over Iowa today, a
short period of drizzle/freezing drizzle is possible especially
Fayette, Clayton, and Grant Counties this evening before any
precip switches to snow with the introduction of ice in cloud. It
likely would be a very small time/space window of overlap with
sufficient moisture depth for drizzle and no cloud ice, but will
have to closely monitor for any freezing drizzle this evening.
Outside of these two areas, any snow would be quite light
overnight. A few flurries could persist into Friday within a
rather deep saturated layer before mid-level drying begins to
spread across the area. One more mild day is expected, with highs
Friday in the 20s and 30s.
.LONG TERM...(Friday night through Thursday)
Issued at 240 PM CST Thu Dec 21 2017
The advertised turn to colder weather is still on track heading into
the weekend. Steady low-level cold advection Friday night into
Saturday ahead of surface high pressure nosing eastward from the
plains will keep highs in the teens to low 20s on Saturday. Similar
temps are expected for Christmas Eve Day ahead of a cold front that
will drop through overnight with a reinforcing surge of cold air
as 850 mb temps fall towards -20C in its wake by Christmas Day.
Could not rule out some light snow or flurries with the frontal
passage and an associated upper shortwave overnight Christmas Eve,
but if any snow does occur, it won`t amount to much. The main
impact will be the cold temps, with highs in the single digits and
teens and lows in the single digits above to low teens below zero
through the middle of the week. Wind chills will fall to 10 to 25
below zero at times Sunday night through Wednesday, especially
during the overnight and early morning hours. The lack of deep
snowcover across parts of the area may at least keep temps a bit
warmer than they would be with a more widespread, deep snowpack.
There is consensus that the cold upper trough will remain
anchored over the area through much of next week keeping a west
to northwest flow in place for the week. Surface high pressure
will help maintain primarily dry weather over the region through
mid-week. Model guidance has been very inconsistent with timing
and amplitude of shortwaves late next week, so confidence in
precip is quite low at this time given the large model spread.
Consensus solution favors dry weather Wed/Thur at this time.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 534 PM CST Thu Dec 21 2017
A persistent band of light to moderate snow has remained across
southeast Minnesota into central Wisconsin. There has been some
recent expansion on the south side of this band and expect this
band to maintain itself into the middle of the evening ahead of a
northern stream short wave trough moving across the Upper Midwest.
The 21.22Z HRRR and 21.19Z HRRR-EXP both show the band maintaining
until about 22.04Z or 22.05Z and then quickly diminishing. Based
on this, have kept MVFR/IFR visibilities in at both airports
through much of the evening before improving to VFR with some
flurries. Ceilings, however, will stay MVFR through the evening
before most likely going down to IFR overnight as the low levels
remain saturated underneath the low level inversion. These
ceilings should break up Friday afternoon and will detail that
with the next set of forecasts.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&
$$
SHORT TERM...JM
LONG TERM...JM
AVIATION...04
Area Forecast Discussion
National Weather Service Taunton MA
1006 PM EST Thu Dec 21 2017
.SYNOPSIS...
Cool and dry weather continue most of the overnight hours. A
series of storm systems tomorrow into Monday will deliver
periods of wintry weather and impact travel for the holiday
weekend. Very cold conditions follow through the middle and end
of next week.
&&
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
10 PM Update...
Mid and high clouds beginning to stream across the region as WAA
pattern evolves from the west. Light northerly flow continues to
drain cold air from northern New England into our area. Not much
change from previous forecast, just adjusting hourly temps to
reflect current conditions.
00z NAM/ARW/NMM and latest runs of the HRRR and RAP continue to
slow the arrival time of snow tomorrow morning to after 12z
across northern MA and not until the afternoon for the remainder
of the region. Deep dry layer will preclude the column from
saturating quickly. Thus later onset time. Earlier discussion
below.
&&
.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
*** Wintry Mix Will Make For Hazardous Conditions Fri-Sat ***
Initially, warm front associated with nose of weak LLJ will
lead to broad isentropic lift across the region early morning
into Fri afternoon. Lift and moistening through the -12C to -18C
DGZ is expected through early afternoon however, soundings show
relatively dry air below H8 particularly S of the Mass Pike
through much of the day, which should limit snowfall
accumulations there. Areas where best dendritic growth, moisture
and lift coincide remains along and north of Route 2 in MA,
with SN beginning around 3-5AM and shifting ESE through 15Z.
Will feature an area with 2-4 inches along/N of Route 2, 1-3
along the Mass Pike to Route 2, with a coating to an inch in N
CT/RI and SE MA. Areas along the immediate S coast will likely
be too warm by the time afternoon precip begins.
Fri afternoon and evening, there is a gradual shift as a meso
low pres develops along the warm frontal boundary which
continues to attempt a N shift. At the same time, noting a dry
slot aloft, which will limit moisture in the DGZ while the lower
lvls moisten. This will lead to less ice through the column and
lack of dendritic growth should allow for a S-N switch to sleet
then to light FZRA through the evening hours. Meso-low will
also enhance isallobaric drainage flow with winds shifting more
NNE through the evening and overnight within a regime signaling
a classic cold air damming signature (inverted ridge, N flow).
While temps through the day will likely be below freezing away
from the coast thanks to this CAD signature, the enhanced
northerlies provided by the mesolow could even lead to an
overnight cooling effect, leading to more widespread freezing.
Final QPF totals through Fri night rest between the 0.25 to 0.5
mark, and given temps will be in the 20s along the MA NH/VT
border, this is where highest ice accums are likely. Will
highlight 0.1-0.25in ice accums mainly N of the Pike, with a
T-0.1 further S.
All this warrants expansion of Winter WX Advisories. Will be
hoisting for all of N CT/RI and the remainder of MA outside of
the SE coastal plain (Bristol/Plymouth, Cape/Islands).
Timing...Snow begins early AM in N MA, shifting to the
remainder of S New England after sunrise through mid day.
Transition to ice occurs late afternoon and evening, with peak
accretion expected during the evening and overnight hours Fri.
Uncertainty...As in any mixed precip event, the transition
times may be off a bit as well as the exact location of the
rain/snow/ice lines. These will continue to be better defined,
but have enough certainty in the details now to expand
advisories. Even a T of ice will make untreated surfaces
slippery and hazardous.
Another layer of uncertainty rests particularly along E coastal
MA. Should sfc lvl flow take on a more E component, it would
draw in marine air where SSTs are around 40-43F. This may warm
sfc temps sufficiently to limit ice accretion. This will need to
be watched.
&&
.LONG TERM /SATURDAY THROUGH THURSDAY/...
* Highlights...
- Icing slowly ends Sat morning across interior, warmup into 50s
in SE New England.
- Accumulating snow likely late Christmas Eve into Christmas Day.
- Very cold and mainly dry next week.
* Details...
Larger scale pattern features persistent closed low over southern
Canada into next week which keeps northern tier of states under
broad cyclonic flow and results in below average temperatures for
much of period, as SE Atlantic ridge (and any hopes of early winter
warmth) are shunted well south into Caribbean. Coldest of airmass is
slated to arrive after Christmas Day with highs in teens and 20s
most of next week, although core of coldest air appears to stay to
our west and undergoes some "modification" as it arrives here.
Saturday...
Temperatures slowly warm across interior as low level ageostrophic
flow weakens and cold air damming slowly loses its grip. For much of
area from northern CT into western and central MA, transition to
rain probably won`t take place until late morning or early
afternoon. Meanwhile, warm front lifting north across region will
bring significant warmup to much of RI and southeast MA, where model
2-meter temperatures are in good agreement that readings will rise
into 50s Saturday afternoon. Question is how far north warmer air
will get - as it`s entirely possible it stays closer to Providence-
Plymouth corridor or manages to make it farther north into Metro
Boston. Big bust potential here with high temperatures, but right
now we are more confident that 50s will stay just to south of
Boston. However at 48-60 hours out in time, this will need to be
adjusted in later forecasts.
Christmas Eve into Christmas Day...
Ensembles and 12z models are showing fairly decent potential for
accumulating snowfall, mainly from later at night on Christmas Eve
into Christmas morning. Models are keying on short wave energy
rounding base of broad upper trough, which are highly subject to
timing differences and errors at 3+ days out in time. What we have
been seeing over past few model runs is an open wave at 700 mb that
eventually closes off to our east, with a range of surface low
tracks from just off SNE coast (12z GFS) to well outside 40/70
benchmark. Even if more offshore track (12z ECMWF) verifies presence
of an inverted trough extending back toward coast would still bring
accumulating snow to much of SNE, especially to RI and eastern MA.
These inverted troughs can easily "overperform" and bring more snow
than one would normally expect with a more offshore track. That
said, overall pattern with an open wave aloft which is progressive
would suggest most likely snowfall accumulations somewhere in Winter
Weather Advisory range (perhaps 2-5") and not an extreme event,
although a few spots could come in with slightly higher totals.
Certainly something we will fine tune in next day or so, especially
once models are able to determine this short wave`s interaction with
what occurs Fri-Sat. Certainly enough to provide some holiday cheer,
however.
Tuesday through Thursday...
Overall very cold and mainly dry. Setup favors bands of ocean effect
clouds and snow showers, primarily over coastal waters east and
southeast of New England due to prevailing NW flow.
&&
.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Short Term /through Friday Night/...
03z update...
No major changes from previous TAFs. VFR and dry overnight.
Latest guidance delays onset of snow until after 12z for
northern MA and not until the afternoon for the remainder of
MA/RI and CT. Earlier discussion below.
=============================================================
Through 06Z tonight...High confidence.
VFR. Light/variable or calm winds will gradually shift around
to N through around midnight.
After 06Z tonight into 18Z tomorrow...Moderate confidence.
CIGS lower to MVFR across NW MA and CT mainly between 09Z and
12Z, along with some -SN with minor accums on runways. SN/MVFR
conditions then spread E mainly N of the Mass Pike, with
less/lighter SN further south. Some accumulation likely, mainly
1-4 inches N of the Pike with an inch or less south. Widespread
MVFR by mid-late afternoon.
Tomorrow evening and tomorrow night...Moderate confidence.
SN will gradually transition from S-N to a wintry mix of PL/FZRA
into the overnight hours, this wintry mix is most likely across
interior MA/RI and CT, but coastal areas could transition
predominantly to RA. Light ice accumulations are likely.
MVFR/IFR conditions.
KBOS Terminal...High confidence in TAF thru tonight then
diminishing somewhat tomorrow given uncertainty on precip timing.
KBDL Terminal...High confidence in TAF thru tonight then
diminishing Friday given uncertainty on precip type.
Outlook /Saturday through Tuesday/...
Saturday: Mainly MVFR, with areas IFR possible. Breezy. RA
likely, FZRA likely.
Saturday Night: MVFR/IFR conditions possible. Breezy. Chance
RA, chance FZRA.
Sunday: VFR. Breezy.
Sunday Night: MVFR/IFR conditions possible. Breezy. SN likely,
RA likely.
Christmas Day: MVFR/IFR conditions possible. Windy with gusts
to 35 kt. SN likely.
Monday Night: VFR. Windy with areas gusts to 30 kt.
Tuesday: VFR. Breezy.
&&
.MARINE...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Short Term /through Friday Night/...High confidence.
Tonight and tomorrow...
Winds will gradually be veering from the NW to the N and NE late
tonight into tomorrow but remain at or around 10 kt most of this
period. Seas too should remain below SCA criteria. Some light
rain/fog will impact mainly the E waters during the day
tomorrow.
Tomorrow night...
A small scale low pres center will move across S New England.
This may provide a brief period of winds shifting and gusting to
around 25 kt with seas building to near 5 ft. A short fused
small craft advisory may be needed. However, given the
uncertainty will wait before issuing.
Outlook /Saturday through Tuesday/...
Saturday: Low risk for Small Craft Advisory winds with gusts up
to 30 kt. Local rough seas. Rain likely, freezing rain likely.
Saturday Night: Low risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 12 ft. Rain likely.
Sunday: Winds less than 25 kt. Areas of rough seas. Slight
chance of rain.
Sunday Night: Winds less than 25 kt. Seas up to 5 ft. Rain
likely.
Christmas Day: Low risk for gale force winds with gusts up to
40 kt. Areas of rough seas. Rain likely. Local visibility 1 to
3 nm.
Monday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Local rough seas. Local visibility 1 to
3 nm.
Tuesday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of seas approaching 5 ft. Local visibility 1 to
3 nm.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Winter Weather Advisory from 11 AM Friday to 10 AM EST
Saturday for CTZ002>004.
MA...Winter Weather Advisory from 7 AM Friday to noon EST Saturday
for MAZ002>008-010-026.
Winter Weather Advisory from 11 AM Friday to noon EST Saturday
for MAZ009-011>016.
RI...Winter Weather Advisory from 11 AM Friday to 10 AM EST
Saturday for RIZ001.
MARINE...None.
&&
$$
SYNOPSIS...Doody/JWD
NEAR TERM...Nocera/Doody/EVT
SHORT TERM...Doody
LONG TERM...JWD
AVIATION...Nocera/Doody/JWD
MARINE...Doody/JWD
Area Forecast Discussion
National Weather Service Columbia SC
1046 PM EST Thu Dec 21 2017
.SYNOPSIS...
Weak surface high pressure expected to remain over the region
through Friday. A cold front will move through the region this
weekend. Dry and cooler conditions expected early next week
behind the front.
&&
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Latest satellite loop indicating lower clouds over much of the
CSRA late this evening, but clouds are expected to spread across
much of the entire area overnight. HRRR and RAP models showing
that the lower cloud cover will continue to increase over the
Midlands and CSRA during the overnight hours. Lows overnight
will range from around 40 degrees to the mid 40s with the
coolest temperatures to the northeast.
&&
.SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/...
High pressure will remain over the region on Friday and dry
conditions will prevail, with temperatures above normal and
highs in the 60s. The high will shift east on Friday night as
large scale broad troughing and a frontal system approach from
the west. Strong southerly flow ahead of the front will allow
Saturday`s temperatures to rise into the 70s. There continue to
be timing differences among the models, but rain should arrive
by Saturday evening. The best chance for rain will be Saturday
night. The GFS pushes the front east of the area on Sunday
morning, but the ECMWF is slower. Therefore, have kept a chance
of rain for Sunday, with the better chances to the east.
Sunday`s temperatures will be cooler, with highs in the upper
50s to mid 60s.
&&
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Cool, dry high pressure is expected to build in for early next
week. Temperatures will likely be below normal for Christmas day
with highs only in the upper 40s to low 50s. These cool and dry
conditions will continue through Wednesday. Overnight lows
during this period will be in the mid 20s to mid 30s. Southwest
flow aloft could bring another weather system and more rain on
Thursday, but there is still alot of uncertainty at this time.
&&
.AVIATION /04Z FRIDAY THROUGH TUESDAY/...
High pressure will extend south over the region through Friday
with dry conditions expected. Although ceilings are currently
VFR, low clouds have overspread the CSRA and are moving into the
Midlands. Expect ceilings to drop to MVFR over the next couple
of hours and continue through the overnight period as weak warm
advection overruns the cool low level airmass. Despite calm
winds overnight, expect cloud cover to limit fog potential, so
have kept visibilities VFR. All TAF sites will likely return to
VFR conditions after 16Z Friday morning as light SW flow
develops.
EXTENDED AVIATION OUTLOOK...The next low pressure system will
move through the region Saturday afternoon through Sunday with
chances of rain and associated restrictions.
&&
.CAE WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
&&
$$
Area Forecast Discussion
National Weather Service Charleston SC
1045 PM EST Thu Dec 21 2017
.SYNOPSIS...
High pressure will prevail into Friday, with a trough of low
pressure offshore. High pressure will shift southeast, with a
cold front expected to move through the region Sunday night,
followed by cold high pressure for most of next week.
&&
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
As of 1040 PM: I will issue a quick update to increase sky cover
through the rest of tonight. In addition, I will make minor
adjustments in hourly temperatures into the early morning hours.
As of 920 PM: IR satellite indicated that most of the forecast
area was under a low ceiling, with a few holes across portions
of inland SC. HRRR and NAM12 surface condensation pressure
deficits drop to fog supporting values across inland GA. I will
update the forecast to adjust sky and refine timing and
placement of patchy fog.
As of 635 PM: Clouds continue to advance from the coastal
waters, moving westward at 15 kts. I will update the forecast to
adjust sky placement and timing. Otherwise, the current forecast
appears in good shape.
As of 535 PM: Recent IR satellite images indicated that stratocu
clouds pushing onshore along the SC coast. Otherwise, overcast
conditions existed across SE GA and inland SC. I will update the
forecast to adjust the sky forecast through this evening.
Previous Discussion:
Deep layered ridging will exist throughout the troposphere across
the Gulf of Mexico, Florida, the Bahamas and NW Caribbean. Our
forecast zones will lie to the north with flat ridging and a slow
rise in heights to occur. At the surface we find an in-situ wedge of
high pressure with the gradual development of an inverted trough
across the coastal waters out near the Gulf Stream.
Sky cover will be the most difficult aspect of the forecast as there
are conflicting signals as to what becomes of the extensive stratus
across our central and southern counties, and to how quickly the
mostly clear skies over the Charleston tri-county district fills
back in. But given some warm advection atop the cooler low level air
mass, and considerable moisture stuck beneath a solid inversion, we
anticipate that the pre-existing low stratus will hold in place.
Also, stratus will return to Charleston, Berkeley and Dorchester
counties during the mid evening hours, with some of it still lurking
nearby. There looks to be enough of a build-down of the stratus
south of I-16 in Georgia to generate at least patchy fog after
midnight.
Models depict isolated to scattered showers in proximity to the
coastal trough, but these are expected to stay over the Atlantic.
Thus we have no mention of rainfall in the forecast, instead showing
5-10% PoP in northern Charleston County, with nil PoP elsewhere.
Temps will radiate quickly in the northern zones this evening with
clear skies and light wind, with a slower decline elsewhere due to
the extensive cloudiness. Lows will reach the mid and upper 40s most
communities, with island locations around 50F.
&&
.SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/...
Friday: A mid/upper lvl ridge of high pressure centered over Cuba
will gradually build north/northeast with an axis extending over the
western Atlantic by the evening. At the sfc, high pressure extending
south over the area will weaken, then gradually shift offshore well
ahead of a low pressure system tracking over the South-Central
United States. The setup will result in dry conditions while a
light north/northeast wind becomes southeast by late afternoon.
The change in wind direction along with decreasing cloud cover
will help temps warm into the upper 60s to around 70 for most areas.
Warmest temps are expected south of I-16 in Southeast Georgia.
Overnight lows will be slightly warmer than the previous night
as a light southerly wind persists. In general, lows will range
in the low/mid 50s, coolest away from the coast. These temps
along with sfc dewpts in the upper 40s/lower 50s could produce
some patchy fog over the area late, especially in southern areas
of Southeast Georgia away from the coast.
Saturday: Aloft, a mid/upper lvl ridge of high pressure will expand
across the region in advance of a low pressure trough to the west.
The setup will result in temps well above normal as a deep southwest
flow occurs well in advance of a cold front approaching from the
west. Warm air advection and ample sfc heating will likely lead to
afternoon temps in the mid/upper 70s for most areas. Temps could
approach 80 south of I-16 away from the coast. Clouds should then
gradually increase late afternoon into evening hours as deep
moisture characterized by PWATs near 1.5 inches and isentropic
ascent enter western zones. Showers should spread from west to
east during overnight hours, likely reaching the coast by daybreak
Sunday. Overnight lows will remain mild under cloud cover ahead
of the approaching cold front. In general, lows will range in
the mid/upper 50s. A few locations could stay in the lower 60s
along the coast in Southeast Georgia.
Sunday: Conditions should start off fairly wet as a plume of
moisture characterized by PWATs near 1.5 inches persists over the
Southeast near/along a slowly advancing cold front. At this time,
precip coverage should be greatest during morning to early afternoon
hours over parts of Southeast South Carolina where forcing associated
with the front coincides with the strongest upper-lvl divergence
associated with the right-rear quadrant of a passing h25 jet
aloft. Showers should begin to shift offshore during the evening
as fropa occurs. Ahead of the front, temps should peak in the
upper 60s for most areas. A few locations could see temps in the
lower 70s in Southeast Georgia.
&&
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
A cold front will be moving offshore Sunday night. Strong high
pressure will build into the region on Christmas, leading to dry
conditions and seemingly cold (but near normal) temperatures.
High pressure and dry conditions will prevail into Wednesday.
&&
.AVIATION /04Z FRIDAY THROUGH TUESDAY/...
Prior to the 0Z TAFs, IR satellite indicated widespread MVFR
ceilings advancing over KCHS from the coastal waters. KCHS
should remain MVFR through mid Friday morning. KSAV remains
under uniform 1kft, however, a few breaks may reach KSAV by mid
evening. MOS and forecast soundings indicate that restrictive
ceilings will redevelop within the breaks. In fact, if breaks do
occur, then the probability of fog will increase during the
late night hours. At KSAV, I will indicate IFR fog in a TEMPO
from 9Z-13Z. Conditions should return to VFR by 16Z.
Extended Aviation Outlook: VFR conditions should prevail Friday
afternoon into much of Saturday. Flight restrictions are then
possible Saturday night into Sunday as showers and low clouds
develop/occur with a passing cold front. VFR conditions will
likely return at both terminals Monday.
&&
.MARINE...
Tonight: A 1032-1034 mb high centered over eastern Canada will
extend through New England and the mid-Atlantic region, and finally
into the southeast and eastern Gulf of Mexico. At the same time an
inverted trough will develop near the Gulf Stream east of the local
waters. This keeps a NE fetch in place, backing more northerly with
land breeze influences late. On average winds will be at or below 15
kt (a little higher initially on the AMZ350 waters), with seas
mainly in the range of 2-4 ft.
Friday through Monday: North/northeast winds will prevail within
high pressure early Friday, but winds are expected to weaken and
veer to the southeast Friday afternoon and evening. Winds/seas will
remain well below Small Craft Advisory levels through Friday night,
but an uptick in southwest winds and seas is anticipated Saturday
into Sunday ahead of a cold front approaching the coastal waters
Sunday night. Wind gusts could approach marginal Small Craft
Advisory levels as strong high pressure builds behind the front
Sunday night into early Monday. Small Craft Advisories could be
needed for northern South Carolina waters and offshore Georgia
waters.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.
&&
$$
NEAR TERM...NED
SHORT TERM...
LONG TERM...MS
AVIATION...NED
MARINE...
Area Forecast Discussion
National Weather Service Duluth MN
957 PM CST Thu Dec 21 2017
.UPDATE...
Issued at 955 PM CST Thu Dec 21 2017
Expired the winter weather advisory for freezing drizzle. Silver
Bay is still reporting rain, but none of the spotters have
corroborated that report. Elsewhere, obs have switched to plain
-sn.
UPDATE Issued at 535 PM CST Thu Dec 21 2017
Many reports of fzdz out there tonight, so issued a winter weather
advisory for freezing drizzle this evening. Light ice accumulations
have already been observed mixed with flurries.
&&
.SHORT TERM...(This evening through Friday)
Issued at 246 PM CST Thu Dec 21 2017
Mid level and surface ridging covered much of the forecast area at
20Z. A lake effect snow band was propagating around the western end
of Lake Superior. However, have yet to see it make landfall as it
encounters the drier air over the region. Regardless, will continue
to follow the HRRR for trying to resolve pops as to where the band
may make landfall. The northeast flow over Lake Superior has led to
a low cloud shield covering the north shore and inland as far as
EVM/ELO/COQ, and along the south shore affecting SUW/DYT. Plenty of
low, mid and high clouds moving over northwest Wisconsin from the
system to the south. There will not be much of a change in the cloud
cover tonight from what is currently seen on satellite. With the
ridge axis nearby, will see min temps tonight as cold as last night,
but colder near the Brainerd Lakes region with the mainly clear sky
and light wind. Expect the aforementioned lake snow band to
eventually move up the north shore through the night, occasionally
making its way inland. Snow amounts should be fairly light due to
the dry air and the shear just off the surface are the limiting
factors.
On Friday, a slow moving upper and mid level trof, and its surface
cold front will move into northeast Minnesota in the afternoon, and
reach the border of northeast Minnesota/Lake Superior/northwest
Wisconsin by 00Z Saturday. The best moisture is found along and
behind the front, and dissipates as it reaches the aforementioned
border area. Upper level support is lacking, and therefore only
expect minor snow accumulations, less than one inch. There may be
some additional lake enhanced light snow along the north shore from
Lutsen to Grand Portage and adjacent inland areas, due to a
southwest wind.
.LONG TERM...(Friday night through Thursday)
Issued at 246 PM CST Thu Dec 21 2017
The main concern for the long term continues to be the blast of
Arctic air arriving Christmas eve and lingering into mid-week.
A shortwave trough will move through the Northland Friday night
with snow showers lingering over northeast Minnesota and portions
of northwest Wisconsin. Snow accumulation should be light, less
than an inch. A cold front will slowly move southward through the
Northland Saturday afternoon and Sunday. There is a slight chance
of snow showers along the front over northern Minnesota and a
chance of flurries farther south. Lake effect snow showers are
expected for portions of Bayfield, Ashland, and Iron Counties
through the weekend, but especially behind the front Sunday.
Arctic air arrives in the Northland Sunday night (Christmas
Eve). The GFS, GEM, and ECMWF are in good agreement with the
timing of the airmass arrival aloft, but there are differences in
the intensity. The GEM is the coldest and features a 925 mb core
of nearly -40 Celsius into northwest Ontario while the GFS and
ECMWF are about 5 degrees warmer. By 18Z Monday (Christmas Day),
the GEM features 925 mb temperatures around -36 Celsius to
International Falls while the GFS and ECMWF are around -30
Celsius. With the fresh snowpack in place across the area, we
will likely experience bitterly cold overnight lows Sunday night
of -25 to -10 degrees Fahrenheit and even colder temperatures
Monday night of -25 to -15 degrees Fahrenheit. Daytime highs will
be cold as well with readings from near 0 to -10 Christmas Day
and Tuesday. Relatively strong winds will accompany the Arctic
airmass resulting in wind chill values between -25 and -40 degrees
Fahrenheit Monday and Tuesday mornings. The wind chills will only
recover slightly during Christmas day with readings between 15 and
25 below zero. These values will present a dangerous scenario for
travelers and anyone outdoors over the holiday.
Temperatures will gradually moderate through the remainder of
the week but will remain below normal for late December. Lake
effect snow showers will be possible over northwest Wisconsin
snowbelt areas through Wednesday night and likely through the
remainder of the week. High pressure will be in charge elsewhere.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 535 PM CST Thu Dec 21 2017
Some fzdz expected through 04Z at DLH. Otherwise MVFR stratus and
the occasional flurry. Conditions improve to VFR Friday afternoon
before trending back towards MVFR with the next weak system.
&&
.PRELIMINARY POINT TEMPS/POPS...
DLH 5 20 2 12 / 20 20 20 0
INL -14 15 -3 9 / 10 40 10 20
BRD -6 19 2 13 / 0 20 10 0
HYR 7 23 5 11 / 10 10 20 0
ASX 6 25 8 13 / 20 20 20 20
&&
.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...None.
&&
$$
UPDATE...Wolfe
SHORT TERM...GSF
LONG TERM...Huyck
AVIATION...Wolfe
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
925 PM EST Thu Dec 21 2017
.UPDATE...
Regional radar has shown some light returns developing across nrn
Illinois. This is supportive of model solutions which suggest an
increase in frontal forcing a little lower in the troposphere than
what has produced the snow across the tri cities and thumb. Given
model soundings continue to suggest some loss in moisture in the ice
nucleation region, high probabilities of some light freezing
rain/drizzle still looks reasonable late tonight through much of
Friday morning. Sfc wet bulb temps are expected to hold at or below
32 deg F well into the morning, mainly along/north of the Irish
hills. Therefore, a winter weather advisory for the potential for
a glazing of ice due to freezing drizzle has been issued south of the
previous advisory. Boundary layer temps are expected to hold at or a
couple degrees above freezing along/south of an Ann Arbor to Detroit
line, thus no advisory has been issued in this region. The chances
for freezing drizzle will diminish markedly north of the I-69
corridor, deeper into the colder air.
The mid level fgen band which impacted the northern Saginaw Valley
and thumb earlier continues to linger across Huron County. The region
of mid level forcing is still expected to weaken as it lifts east of
the thumb region over the next couple of hours. Another round of
widespread light snow is still expected Fri morning with the second
influx of moisture/forcing. So some additional minor snow
accumulations are possible in the north.
&&
.PREV DISCUSSION...
Issued at 717 PM EST Thu Dec 21 2017
UPDATE...
Mid level frontal forcing has increased substantially over the last
couple of hours along an axis from Midland to Sandusky. While the
overall trend has been for a slight northerly transition to the
better forcing, recent RAP and HRRR suggest the forcing will become a
little more stationary across the nrn Saginaw Valley and thumb
through 03Z before weakening and lifting off to the northeast, when
the lower tropospheric sections of the frontal boundary become more
active. Based on current radar and latest hi res solutions, three
inch accumulations within a six hour period look reasonable,
primarily extending north of a Midland to Bay City to Sandusky line.
Therefore a winter wx advisory for snow has been issued. Given the
potential for a secondary surge in forcing Fri morning, possibly
adding an additional light accumulation, the advisory will be
carried through the morning, also matching surrounding WFOs. So
total snowfall of 2 to 4 inches is expected in the advisory area,
again with the bulk of it occuring this evening.
Temperature trends will be monitored for the next couple hours to
address any light icing potential with expected freezing drizzle
(mainly along the M 59 corridor) Friday morning.
PREV DISCUSSION...
Issued at 605 PM EST Thu Dec 21 2017
AVIATION...
Ongoing elevated frontal forcing will persist through the night and
through Fri morning north of a low pressure system that will be
sliding across the nrn Ohio Valley. A band of more focused ascent
will remain present across the MBS region through much of the
evening, sustaining occasional light snow. This region of enhanced
forcing is expected weaken later this evening, with forcing expected
to develop farther south and closer to the approaching sfc low. Both
RAP and NAM model soundings suggest ice nucleation will not be
present farther south, leading to expectations of more freezing
drizzle/drizzle late tonight through Fri morning. An influx of low
level moisture during the night with the approaching sfc low will
also lead to steadily lowering ceiling heights.
For DTW...There is a fairly high probability for a period of drizzle
in the 09Z to 15Z time frame. Recent RAP and HRRR models suggest sfc
wet bulb zero temperatures holding at or just above freezing at the
onset of light rain, with temperatures then slowly warming a degree
or two above freezing during the course of the morning. Therefore
there is just a low chance for an interval of freezing drizzle late
tonight.
//DTW THRESHOLD PROBABILITIES...
* Moderate in ceilings below 5000 ft late this evening, high
late tonight through Friday.
* Low confidence in precipitation type as the boundary layer
conditions suggest borderline -dz/-fzdz late tonight/early Fri
morning.
PREV DISCUSSION...
Issued at 309 PM EST Thu Dec 21 2017
DISCUSSION...
Sheared out upper level energy tracking through the northern Great
Lakes through tomorrow, with surface low ejecting out of the Central
Plains this afternoon, tending to weaken as it approaches the
southern Great Lakes tomorrow. Low level jet (55+ knots) tracking
through the northern Ohio Valley with pretty good isentropic
ascent/mid level FGEN over southeast Michigan this evening/tonight,
mainly north of M-59, with around 3.5 G/KG of specific humidity at
700 MB to work with. However, lot of warming/drying in the mid
levels sneaking past the southern Michigan border, and ice nuclei
will become an issue along/south of I-69 by Friday morning. Low
level convergence with the surface low may be sufficient to generate
drizzle/very light precipitation during this period, with
temperatures flirting around the freezing mark, and certainly looks
like areas of freezing drizzle are possible in and around the M-59
corridor. However, elected to wait on possible advisory, as
confidence in timing (although 5 AM-10 AM looks to be the main
window), along with surface temps likely above freezing toward the
Ohio border making exact location/counties uncertain. North of I-69,
mainly snow, but better thermal profiles and forcing looks to be
lifting into northern Lower Michigan into northern Lake Huron
overnight, and still think 1-2 inches looks good across far northern
reaches of the CWA (M-46 north), with up to 3 inches possible across
the northern tip of the Thumb region as we potentially grind out a
little more snow Friday morning. With the snow covered roads expected
up north, any brief changeover to freezing drizzle should not cause
as much of an impact on the roads. Temperatures are expected to rise
above freezing across all of southeast Michigan during Friday.
Low level baroclinic zone straddling the southern Michigan border
late Friday with strong upper level wave/energy coming out of the
Four Corners region, becoming absorbed by the polar trough tracking
through the northern Plains Friday night. Good convergence of
Pacific and Gulf of Mexico moisture, but mostly aligned along the
Ohio River, and 12z Euro has come in line with majority of guidance
indicating precipitation shield Friday night-Saturday mostly missing
southeast Michigan to the southeast with colder air streaming back
into southern Lower Michigan, as 850 mb temps fall into the negative
lower teens by 12z Sunday.
Attention in the long term remains on the potential for light snow
Sunday evening into Monday, possibly impacting Christmas travel
plans. A spoke of potent shortwave energy rotating around the base
of the longwave trough will pass over the Ohio Valley Sunday
evening. The associated PVA will allow for an area of snow to
develop over Ohio, the northernmost extent potentially reaching SE
Michigan during the evening/overnight. For now, have kept PoPs in
the 50-60% range with the greatest chance for the light snow to
affect the eastern counties and areas closer to the Ohio border,
with accumulations around an inch or so.
Arctic front will push through the Great Lakes late on Monday. Cold
advection and an increased pressure gradient will allow for gusts to
reach 30 mph, resulting in wind chills in the single digits most of
the day as actual high temperatures stay in the 20s. Tuesday will be
even colder as the dome of cold air settles more into the region -
850mb temps falling to the -20s C. Gusts will ease up on Tuesday,
however, wind chills remain in the single digits as highs struggle
to reach the upper teens. Overnight lows will fall to the single
digits. Lake effect flurries will be possible in this cold airmass
on Monday and Tuesday, and a chance exists for some more light snow
for areas near the Ohio border Tuesday as another wave traveling
around the longwave trough passes to the south. Wednesday and
Thursday will be quiet as surface high pressure slides through the
Ohio Valley. Highs will remain very cold as the arctic air stays
parked over the region.
MARINE...
Easterly winds will increase tonight into Friday morning as weak low
pressure moves through the northern Ohio Valley on Friday while high
pressure slides east over Quebec. Easterly winds will turn northwest
on Saturday morning as the low departs the region. Colder air will
then filter across the region through the rest of the weekend
bringing the potential for heavy freezing spray to accompany
possible gales.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory until 10 AM EST Friday for MIZ047>049-054-
055.
Winter Weather Advisory from 3 AM to 10 AM EST Friday for MIZ053-
060>063-068>070.
Lake Huron...Small Craft Advisory until 5 PM EST Friday for LHZ421-441-442.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&
$$
UPDATE.......SC
AVIATION.....SC
DISCUSSION...SF/TF
MARINE.......JD
You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.
Area Forecast Discussion
National Weather Service Wilmington NC
709 PM EST Thu Dec 21 2017
.SYNOPSIS...
A coastal warm front will lift northward during the day Friday,
bringing patchy light rain and drizzle. This feature will usher
unseasonably warm temperatures into the region this weekend
ahead of an approaching cold front. The front will cross the
coast Sunday, resulting in noticeably cooler temperatures on
Christmas Day. Tuesday morning may begin with air temperatures
below freezing.
&&
.NEAR TERM /THROUGH FRIDAY/...
As of 708 PM Thursday...Main edit this update was expanding
extent and opacity of encroaching coastal cloud cover, evident
in the GOES-E fog/stratus channel early this evening. KLTX Vad
Wind Profile shows NE wind around 25 KT off the surface up to
2000 feet. The pressure gradient is still crunched up a little
bit into the coast because of the offshore low around 32N, but
it is loosening, as the low continues a weakening trend. Weak
directional wind convergence in the Gulf Stream was setting of
light showers, otherwise the radar should remain clear overnight
over and near land.
As of 300 PM Thursday...High pressure will continue to wedge
in from the north tonight as it shifts farther east moving off
the New England coast by Fri morning. The shallow cool air will
remain in place as a coastal trough develops offshore. Winds in
the low levels above the sfc will shift around to an on shore
direction allowing for some marine moisture to make it on shore,
with an increase in lower clouds and possibly a stray shower
mainly right along coast and off shore overnight into Fri
morning.
The coastal trough/warm front will push inland and north with
time. Looking at moisture profiles and sounding data, there is a
layer of moisture that develops right around 5 to 7k ft into
this evening and deepens down closer to the sfc overnight with
a decent layer of low clouds developing. Basically will see
a saturated layer below 5k ft reaching inland through Fri
morning. Therefore expect clouds to develop tonight and hold on
into Fri before coastal trough/warm front lifts north by the
end of the day. Clouds should prevent much radiational cooling
tonight and will help to produce above normal overnight lows in
the low to mid 40s. Cloud cover should thin out by the end of
the day on Fri with winds coming around to the south. Temps
should make it into the 60s most places.
&&
.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/...
As of 300 PM Thursday...Coastal trough will extend slightly
inland from the NC coast during Friday night basically from Cape
Fear northward. Weak dynamics along the trough but very limited
moisture except for the lower levels. For now will keep it pcpn
free but would not be surprised for an isolated shower or
patchy drizzle. The coastal front basically washes out by
Saturday daybreak with synoptic south to southwest flow
increasing ahead of the cold front that will be crossing the NC
and SC Appalachians during daylight Saturday. Any residual low
clouds and fog across the FA Sat morning will also scour out
leaving mid and high level clouds approaching from the west. The
parameters for sea fog to develop Saturday are not all that
conducive but enough to place patchy sea fog occasionally moving
onshore and affecting the immediate coast during Saturday. Much
will depend on the direction of the winds. For Saturday evening
and night look for the slow eastward progression of the front,
having reached the far western portions of the FA around
midnight Sunday and only making it to the immediate coast by
daybreak Sunday as the front itself temporarily becomes parallel
with the flow aloft. Cloud coverage along with POPs will
increase Sat night to good chance or possibly likely category by
daybreak Sun. As for temps, the FA will experience above normal
readings thruout this period. Night time lows will run 10 to 15
degrees above normaL and for daytime Saturday 15 to possibly 20
degrees above normal away from the immediate coast, For the
immediate coast, any onshore flow across 50s SSTs will limit Sat
high temps to the 60s.
&&
.LONG TERM /SUNDAY THROUGH THURSDAY/...
As of 300 PM Thursday...Looks like it is trending cooler and
drier for Christmas day. A cold front will move slowly through
the forecast area from the northwest on Sunday. The deep mid to
upper trough will remain west of the forecast area leaving front
aligned with deep SW flow aloft and therefore will take its
time moving through on Sunday. A wave of low pressure may
develop along the front as it bisects our forecast area Sun aftn
enhanced by energy rotating around the upper trough with strong
jet dynamics aloft. The GFS shows pcp water values up to 1.7
inches Sun morning. This will maintain clouds and showers across
the area on Sun. The NAM and GFS are slightly more bullish with
pcp over the drier ECMWF model QPF for Sunday. Overall will go
with lower end QPF amounts. Forecast highs for the day may come
early on Sunday for places north of the front and will also be
hampered by clouds and pcp but for now will go with highs
reaching near 60 early north of the front and into the 60s south
of the front.
By Sun night, the mid to upper trough will swing east and lift
north allowing a deep W-NW flow to push this cold front off the
coast around midnight. This will scour out the clouds and pcp
allowing a rush of cooler and drier air in. CAA will be in
force with gusty northerly winds. 850 temps up near 11C Sun
morning will drop below 0c by Mon aftn. Overnight lows will drop
down near 40 and may end up in the mid 30s by Mon morning in
deep NW flow with plenty of CAA.
Cold and dry high pressure will build into the area Mon
remaining over the area through mid week. A broad mid to upper
trough will take residence over the ern CONUS next week with
cold and dry high pressure at the surface. This will maintain
below normal temps and dry, sunnier weather Mon through Wed.
A low pressure system may affect the area Thursday into Fri
with increasing clouds and chance of rain.
&&
.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
As of 23Z...Watching StratoCu deck work its way into the region
from off the coast moving west. Goes16 fog 10.3-3.9um shows it
well with nice color enhancements that makes the stratocu stand
out. Will watch expansion westward over the next few hours and
forecast sct deck going to bkn across the inland terminals with
bkn-ovc deck across the coastal terminals. clouds are forecast
to stay across the region especially the coastal terminals on
friday as coastal trough lines up across the coast. HRRR keeps
most of the showers near ILM and points e and N so will only
mention vcsh in the KILM taf after 22/16z. Moderate chance of
MVFR in tempo group after 08z coastal TAFs with better chance
coastal terminals after 16z. VFR to prevail across the inland
terminals. NE flow to prevail through the forecast period.
Extended Outlook...VFR Friday. Patchy fog with IFR/LIFR Sat
morning, otherwise VFR. VFR/tempo MVFR with showers Sunday. VFR
developing early Monday. VFR Tues.
&&
.MARINE...
NEAR TERM /THROUGH FRIDAY/...
As of 708 PM Thursday...A SCEC was needed because of the
continued gusts to 20 kt and seas of 5, almost 6 feet offshore.
Extended the `Caution` headline until 600 AM, but it could be
pulled earlier since the pressure gradient is loosening
presently and is expected to keep trending this way, as the low
off shore along 32 N weakens. E waves will dominate the spectrum
in 5-6 second intervals, making moderate wave steepness.
As of 300 PM Thursday...Winds and seas are just beginning to
diminish this aftn. On this trend, both should drop below SCA
thresholds by early this evening across the northern waters,
allowing the SCA to expire on time, at 6pm. Precautionary
headlines for the southern waters have been dropped with winds
near 15 kts and seas 3 to 5 ft this aftn.
A weak coastal trough will develop tonight as high pressure to
the north begins to shift off the Northeast coast. This will
allow gradient to relax and leaves N-NE winds down to 10 to 15
kts across most of the waters tonight. The trough shifts toward
the coast or just inland early on Friday which will shift the
winds around to the E-SE and eventually south by the end of the
day as trough lifts north as a warm front. Seas up to 4 to 6 ft
this aftn will be down to 2 to 4 ft by morning and will may rise
slightly in the on shore push through the aftn.
SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/...
As of 300 PM Thursday...Winds will generally run below 10 kt Friday
Evening with a mesoscale coastal trough having partially moved
onshore from Cape Fear northward. This will result with wind
directions E-SE east of the trough and for the waters west of
the NE 5 to 10 kt. During the pre-dawn Sat hrs, the coastal
trough will wash out by daybreak Saturday as synoptic S to SSW
flow ahead of the approaching cold front ramps up. Saturday thru
Saturday night winds will veer slightly to the SW and increase
due to a tightening sfc pg. Have kept winds mainly just at or
below 20 kt due to the cool marine layer just off the deck,
eventhough just above this layer windspeeds are progged at 30+
kt. Sea fog may become an issue during Sat with parameters not
all that conducive but enough to mention patchy sea fog lowering
VSBY to at least 2nm. By Sunday daybreak, the cold front will
be nearly overhead with winds having already started a veering
trend to the W and NW by daybreak Sun.
LONG TERM /SUNDAY THROUGH TUESDAY/...
As of 300 PM Thursday...A cold front approaching the waters
early Sunday will finally cross the waters by Sun night. The
wind direction will be SW ahead of the front early Sun and then
shift to W and NW behind the front, becoming N by Mon morning.
Winds should become more variable on Sunday, 15 kts, but will
increase in northerly surge behind front, up to 15 to 20 kt Sun
night into Mon. Seas of 2 to 4 ft Sun may reach near SCA
thresholds Sun night into early Mon before subsiding to less
than 3 ft Mon afternoon and dropping even further into Tues.
&&
.ILM WATCHES/WARNINGS/ADVISORIES...
SC...None.
NC...None.
MARINE...None.
&&
$$
SYNOPSIS...8
NEAR TERM...RGZ/MJC
SHORT TERM...DCH
LONG TERM...RJD/RGZ
AVIATION...MAC
Area Forecast Discussion
National Weather Service Omaha/Valley NE
909 PM CST Thu Dec 21 2017
.UPDATE...
Issued at 904 PM CST Thu Dec 21 2017
Extended the Winter Weather Advisory for parts of northeast
Nebraska and western Iowa where light snowfall continues and roads
remain slick. Radar trends show precipitation gradually
diminishing across the area. In addition, both the HRRR and RAP
indicate wintry precipitation coming to an end by around 05Z this
evening in our CWA.
&&
.SHORT TERM...(Tonight through Sunday)
Issued at 254 PM CST Thu Dec 21 2017
A split-flow pattern prevails over the western half of the CONUS
this afternoon, characterized by a mid-level low near the Four
Corners, and a separate polar-branch trough tracking through the
northern Plains. The mid-MO Valley is situated within the
confluence of these two air streams, and on the immediate backside
of a weak perturbation that moved through the area earlier today.
In the low levels, the primary surface cyclone over eastern KS
will continue east into the Ozarks, allowing for the southward
acceleration of a continental-polar air mass through the remainder
of the region tonight.
Large-scale forcing for ascent was enhanced briefly earlier today
with the passage of the aforementioned impulse through the area.
Since that time, the convective elements which produced bursts of
snow, some sleet and freezing rain north of the Omaha metro have
weakened. Latest convection-allowing guidance suggests that there
could be an uptick in precipitation intensity late this afternoon
into early evening across portions of eastern NE into west-
central IA, a notion supported by recent trends in mosaic radar
data to our west. Predominant precipitation type is expected to be
snow over northeast NE with light freezing rain or freezing
drizzle farther south toward I-80. These more-southern areas
could mix with or change over to light snow this evening.
Across southeast NE and southwest IA, temperatures will continue
to fall with light drizzle switching to freezing drizzle before
precipitation ends tonight. As such, road conditions will
deteriorate through the evening commute, and we will maintain the
ongoing winter weather advisory through 9 PM.
Friday into Friday night, a secondary cold front advances through
the area in tandem with a low-amplitude disturbance tracking
across the north-central states. On Saturday into Saturday night,
a vigorous short-wave trough will translate from the northern
Intermountain Region into the mid-MO Valley with a band of light
snow focused along the mid-level baroclinic zone preceding the
disturbance. Current indications are that the best potential for
some light accumulation will be across southeast NE into southwest
IA Saturday night into early Sunday.
High temperatures are expected to be around freezing on Friday and
in the 20s on Saturday.
.LONG TERM...(Sunday night through Thursday)
Issued at 254 PM CST Thu Dec 21 2017
Broad, long-wave troughing will be maintained across much of
North America during the early part of the upcoming week with some
indication we could see flurries or light snow on Christmas day.
Confidence in this scenario remains low enough that we will not
include a mention in the official forecast, though it`s something
worth following. Highs on Monday will range from around 20 north
to lower 30s south.
By the middle to late part of the upcoming week, the medium-range
models diverge on the evolution of the large-scale pattern,
resulting in considerable uncertainty in the forecast during that
time frame. In general, we will continue to indicate below-normal
temperatures with low chances for light snow.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 525 PM CST Thu Dec 21 2017
Mosaic radar data as of 23z indicate a weakly-defined vorticity
lobe progressing through east-central NE with an associated
enhancement of precipitation immediately downstream across the
Omaha Metro and points east. Observations indicate that the
precipitation type is predominantly snow which should continue in
the KOMA vicinity for the next few hours. At KLNK, some light snow
remains possible this evening, though prevailing conditions
should remain dry. Meanwhile in the KOFK area, a slightly longer
period of light snow (with intermittent IFR ceilings/visibilities)
remains possible with conditions improving toward 06z Friday.
Expect predominantly MVFR ceilings to persist until after 12z
Friday.
&&
.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Winter Weather Advisory until 11 PM CST this evening for NEZ015-
018-031>034-043>045.
IA...Winter Weather Advisory until 11 PM CST this evening for IAZ043-
055-056-069.
&&
$$
UPDATE...KG
SHORT TERM...Mead
LONG TERM...Mead
AVIATION...Mead
Area Forecast Discussion
National Weather Service Nashville TN
937 PM CST Thu Dec 21 2017
.UPDATE...
FOR EVENING DISCUSSION.
&&
.DISCUSSION...
Temperatures have fallen into the mid to low 50s this evening
across the mid state. Some sites have fallen just a degree or two
below forecast lows, and while temperatures won`t fall much more
with a strong southerly wind and plenty of clouds in place I did
adjust forecast lows for tonight down a degree or so for the area.
According to the HRRR and latest model runs we should stay dry
through at least 3am, so lowered pops before 09z to reflect this.
Precip will remain light from 09z to 12z with heavier rainfall
rates in the afternoon and overnight hours Friday. No changes to
that portion of the forecast at this time.
&&
.AVIATION...
00Z TAF DISCUSSION.
CKV/BNA/MQY/CSV...Significant rainfall event expected across mid
state region approaching 22/24Z. Several amendments possible thru
22/24Z, especially 22/14Z-22/24Z per potential rapid changes in
vsbys/ceilings. Initial MVFR ceiling conditions, IFR CKV, should
progress to predominately IFR by 22/12Z and then LIFR approaching
22/24Z. Light drizzle may develop ahead of main brunt of pcpn.
Generally, light shwrs starting W 22/14Z spreading E will
transition to mdt shwrs by 22/18Z and then to heavy shwrs
approaching 22/24Z, except CKV which is expected to remain north
of main moisture advection slot. Although some fog formation
potential possible, with the prolonged establishment of sfc
pressure gradient influences thru 22/24Z, and thus sustained winds
5kt- 12kt with gusts potentially to 17kt expected, should
preclude significant fog development at terminals.
&&
.OHX WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch from Friday afternoon through Saturday morning
for Bedford-Cannon-Cheatham-Clay-Coffee-Cumberland-Davidson-De
Kalb-Dickson-Fentress-Giles-Grundy-Hickman-Houston-Humphreys-
Jackson-Lawrence-Lewis-Macon-Marshall-Maury-Montgomery-Overton-
Perry-Pickett-Putnam-Robertson-Rutherford-Smith-Stewart-Sumner-
Trousdale-Van Buren-Warren-Wayne-White-Williamson-Wilson.
&&
$$
DISCUSSION......11
AVIATION........31