Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/25/17
Area Forecast Discussion
National Weather Service La Crosse WI
537 PM CST Sun Dec 24 2017
.SHORT TERM...(Tonight through Monday)
Issued at 300 PM CST Sun Dec 24 2017
Transition for this Christmas Eve as Arctic cold front continues to
approach. Already seeing some convective looking snow showers
forming in parts of the region as weak short waves rotate into the
area within larger upper trough. One band of snow showers showing up
near and ahead of the main front will pass through north of
Interstate 90 early this evening, while focus will be on next
upstream wave that is sparking more snow showers across eastern
Dakotas.
Expect this secondary wave to pass through tonight bringing some
light snow accumulations. Not expecting much in the way of impact,
but a few locales could see quick bursts of snow. Brief window of
steeper lapse rates passes through with feature.
Main focus for Christmas day will be colder air funneling in and
developing wind chill dangers. Criteria first met in northern
Wisconsin so will begin Wind Chill Advisory early for areas north of
Interstate 94. But after coordination with neighboring forecast
offices, have settled on adding additional counties, except far
south, late in day. Obviously exact headline times may get adjusted
based on trends, but either way, it will feel much colder.
.LONG TERM...(Monday night through Sunday)
Issued at 300 PM CST Sun Dec 24 2017
Wind Chill Advisories will be going at start of period. Lots of
coordination today on where and how long to extend these headlines
but I`m sure adjustments will be coming. Tried to find a period
where advisories could be stopped at least for a time due to weaker
wind speeds, but main story is it will be coldest on Tuesday before
some moderation. Early Tuesday morning wind chill values could
be -25 to -35.
Fairly benign weather expected going into mid week but medium range
guidance still advertising weak short wave as temperatures moderate.
This will be next precipitation risk with discrepancies on
location, but could see several inches of snow if feature
materializes.
Flow amplifies again towards next weekend with Arctic low predicted
to pass through Great Lakes bringing even colder shot of air. Will
likely be looking at more wind chill related headlines during later
periods.
&&
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 537 PM CST Sun Dec 24 2017
A short wave trough was over western Minnesota early this evening.
Regional radars and observations showing an area of light snow
with this short wave trough producing IFR conditions. The 24.22Z
HRRR and 24.21Z CR-HRRR both show this area of light snow moving
across the area and impacting both airports this evening, but they
have it weakening as it comes in bringing into doubt whether there
will be IFR conditions or not. For now, will maintain continuity
with previous forecast and upstream observations and bring in the
IFR conditions. There will also be a period of gusty northwest
winds with the passage of the light snow. Once this short wave
trough moves past, satellite imagery shows strong subsidence
allowing the clouds to quickly scatter out for VFR conditions.
Another short wave trough over North Dakota will move across
Monday that may produce a short period of VFR ceilings but not
expecting it to have any snow with it.
&&
.CLIMATE...
Issued at 300 PM CST Sun Dec 24 2017
High temperatures on Christmas day will likely be early in the day,
but still one of the coldest since 2000. If high temperatures end up
in the Teens it would end up being in the top 15 to 25 coldest, so
clearly not any kind of record.
Last subzero high temperatures on Christmas were in 1996.
All-time coldest high temperatures on Christmas include -6 at
Rochester, MN in 1996, and -11 at La Crosse, WI in 1884.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Wind Chill Advisory from 6 PM Monday to noon CST Tuesday for
WIZ032>034-041>044-053-055.
Wind Chill Advisory from 5 AM Monday to noon CST Tuesday for
WIZ017-029.
MN...Wind Chill Advisory from 6 PM Monday to noon CST Tuesday for
MNZ079-086>088-094>096.
IA...None.
&&
$$
SHORT TERM...Shea
LONG TERM...Shea
AVIATION...04
CLIMATE...Shea
Area Forecast Discussion
National Weather Service Taunton MA
1009 PM EST Sun Dec 24 2017
.SYNOPSIS...
Low pressure developing off the North Carolina coast will
move rapidly northeast tonight, passing near Nantucket, the
intensify Monday over the Gulf of Maine. This will bring
moderate to heavy snow to northwestern portions of southern New
England and a mixed bag over the rest of the interior. Mainly
rain is expected in southeast areas. Strong to damaging winds
will follow in its wake Monday afternoon. Arctic air will
dominate the week ahead with mainly dry weather, but low
pressure tracking off the coast may bring snow later Friday into
Saturday.
&&
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
10 pm update...
Storm taking aim on S New England. Primary low over the E Great
Lakes meeting up with secondary energy off the Mid-Atlantic. The
E inflow apparent as pressure falls begin to emerge. The parent
H5 trof beginning to undergo a negative-tilt as the parent potent
vortmax rounds through the base increasing the cyclonic curvature.
QG-forcing just starting to emerge, frontogenesis and moisture
convergence pulling together and tightening, deformation evolving.
Anticipating a system that will pack a wallop across S New England
tonight going into Monday.
Expanded winter weather headlines. The storm system expected to
over-perform, the concern is with the tandem low pressure centers
evolving and deepening along the secondary off the Mid-Atlantic
that we`ll see strong deformational banding on the backside in a
region of dynamic cooling and steep mid-level lapse rates supportive
of upright-convection / thundersnow. Per the HWRF / HRRR / NCAR
ensembles, reason to believe that this band has the potential of
producing 1-3"/hr snowfall rates where snow-ratios modify higher
with the influx of colder air, winds picking up out of the W
behind the band such that considering the fluffy snow we could
be dealing with blowing and drifting, potential for near-blizzard
criteria with white-out conditions.
WINTER STORM WARNINGS along the E-slopes of the Berkshires and
within the NW corridor of the 495 beltway.
WINTER STORM ADVISORIES expanded S/E towards the I-95 corridor
outside of Boston.
Continued concern for the SW-NE transition line of a wintry mix
in addition to the depth and magnitude at which later snow-
banding can swipe Northeast MA. Quite possible that for the
Boston-metro that the W-metro will meet or exceeding advisory
criteria while out at Logan airport it may not crack 1 to 2
inches. If the depth of cold air and precipitation is able to
swing further S, then we`ll have to update headlines accordingly
and the area at most risk at this time is Northeast MA including
the Boston-metro area.
Previous Discussion...
System will phase with the upper support moving in from the
west and lead to rapid intensification of the coastal storm on
Monday, aided by a 150-160 kt jet at 300 mb. The low will be
near or just east of Nantucket early Monday morning then rapidly
deepen in the Gulf of Maine during the day on Monday.
Cloudiness will be lowering and thickening across our region
this evening and precipitation will begin breaking out by
midnight. Thermal profiles support snow in the northwest half of
the region and a mix of rain and snow from Boston to Providence
at the start, with rain along the coast. However, warmer air on
increasing easterly winds, should change mixed precipitation to
rain from northeast CT to Boston and points southeastward
overnight. There could be an area of freezing rain and sleet
from northern CT to southern Worcester County, northeastward
into central Middlesex County. There could also be freezing rain
and sleet in portions of northwest RI and Norfolk County, MA.
Snow is expected in northwest MA and north central MA for most
of the storm. The snow may be moderate to heavy at times.
Total snow accumulations are expected to reach 4 to 7 inches in
the Warning area, with a localized 8 inch amount possible
nearest to the Vermont and New Hampshire borders. Where there is
mixed precipitation, only 2 to 4 inches is expected. And in
Boston and Providence we are expecting anywhere from a coating
to as much as 1 or 2 inches.
Have blended high resolution temperature guidance to arrive at
minimums for tonight...ranging from mid and upper 20s northwest
and central sections to the mid and upper 30s in coastal MA and
southern RI, helped by winds off the water.
&&
.SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
* Short burst of heavy snow possible in the morning
* Strong to damaging winds from mid-day through the afternoon
The low deepens to 980-985 mb in the Gulf of Maine Monday
afternoon. On the tail end of the storm, we are expecting a
line of convective snow showers, possibly even accompanied by a
rumble of thunder, to cross the region between 6 AM and 10 AM.
This is indicated on multiple high resolution models. The
atmosphere will be unstable with Total Totals indices of 50 and
negative Equivalent Potential Vorticity. This narrow band could
produce heavy snowfall rates...and could potentially be moving
through Hartford/Springfield at 6-7 AM, Worcester at 8-9 AM, and
Boston and points north from 9-10 AM.
A very strong low level jet will develop with mainly westerly
winds in the wake of the low. Cold advection mixing will be
occurring all the way to 800 mb or higher up in the atmosphere.
This should result in winds gusting to 40 to 60 mph, with gusts
to 65 mph even possible over Cape Cod and the Islands.
There will likely be a lot of power outages, both in southeast
areas where the winds are strongest and in northern and western
areas where fresh snow and any additional ice will cling to
some lines.
Skies will become partly sunny in the afternoon but temperatures
will remain in the upper 20s and 30s.
&&
.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
Highlights...
* Arctic air dominates.
* Snow possible later Fri and Sat.
Fairly high confidence in overall pattern this week as broad
cyclonic flow dominates with upper low remaining parked over south
central Canada. Series of short waves rounding trough will bring
reinforcements of arctic air, but moisture looks to be limited so
dry weather is expected for much of week. Cannot rule out a few
LES streams for western MA if there is enough low level
moisture.
While record lows look to be out of reach, we may be challenging
record cold high temperatures on Thu 12/28 which include 21 degrees
at PVD in 1976, 18 degrees at BOS and BDL in 1924, and 15 degrees at
ORH in 1976. Forecast highs are a few degrees colder for each
location.
Subzero temperatures are forecast across parts of interior SNE
Wednesday night/Thursday morning and again Thursday night/Friday
morning. Wind chills may reach 15 below zero, which may eventually
require Wind Chill Advisories. Area of greatest concern is near east
slopes of Berkshires and in north central MA.
We are watching the potential for snow late in the week as
southern stream short wave develops low pressure off East Coast.
Expect to see run-to-run variations among models over next few
days as they struggle with timing issues of energy rounding base
of upper trough, so it will probably be another couple of days
at least until we begin to see some agreement. In meantime,
ensemble probabilities show greater potential for coastal low
develop later Friday and especially Saturday with anomolous
surface pressures.
&&
.AVIATION /03Z MONDAY THROUGH FRIDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Short Term /through Monday/... Moderate confidence.
Deteriorating conditions tonight and Monday down to IFR/LIFR
across the N/W interior with snow beginning 03z through roughly
18z. MVFR/IFR S/E with a wintry mix along and around a LWM-SFZ-
IJD line, even out of HFD. Mainly rain S/E of this line. A burst
of heavy snow showers is likely to cross the region from 11Z in
western MA and northern CT to 15Z in northeast MA.
Strong to damaging west winds with gusts in excess of 50 kts
over southern RI and southeast MA, with 55 to 60 kts possible
Cape Cod and Nantucket. Wind gusts to 40 to 45 kts elsewhere
from mid morning Monday into Monday evening.
KBOS Terminal...Moderate confidence. Rain to start, switch over
to snow around 12z. Focus then turns to increasing W winds
which can gust as high as 45 kts.
KBDL Terminal...Moderate confidence. Conditions lowering to IFR
in snow overnight. Could mix with sleet and possibly freezing
rain at times. A very brief period of heavy snow showers
possible shortly after sunrise Monday morning. Focus then turns
to increasing west winds towards evening with potential gusts
up to 45 kts.
Outlook /Monday Night through Friday/...
Tuesday Night: VFR. Windy with areas gusts to 30 kt.
Wednesday through Thursday: VFR. Windy with gusts to 30 kt.
Thursday Night: VFR. Breezy.
Friday: Mainly VFR, with areas MVFR possible. Slight chance SN.
Friday Night: Mainly MVFR, with areas IFR possible. Chance SN.
Saturday: Mainly MVFR, with local IFR possible. Breezy. Chance
SN.
&&
.MARINE...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Short Term /through Monday/...
Tonight into Monday...
* Dangerous conditions for mariners
STORM WARNINGS remain in effect southeastern waters. We have
added Narragansett Bay and Cape Cod Bay to the Storm Warnings.
As the storm system rapidly deepens over the Gulf of Maine
Monday morning, WSW to W winds will gust to 50 kts...and
potentially to 60 kts in the Storm Warning area. Gale Warnings,
for gusts to 40-45 kts are in effect for all other coastal
waters.
Seas rapidly building to 15 to 20 feet on the southeastern
outer waters and to 10 to 15 ft over the northeastern outer
waters early Monday and continuing through the day.
Outlook /Monday Night through Friday/...
Tuesday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Areas of rough seas.
Wednesday: Low risk for gale force winds with gusts up to
35 kt. Areas of rough seas.
Wednesday Night: Low risk for gale force winds with gusts up to
35 kt. Rough seas up to 10 ft. Chance of freezing spray.
Thursday: Low risk for gale force winds with gusts up to 35 kt.
Areas of rough seas. Chance of freezing spray.
Thursday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas locally approaching 5 ft.
Friday: Winds less than 25 kt. Chance of snow.
Friday Night: Winds less than 25 kt. Seas locally approaching
5 ft. Chance of snow.
Saturday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of rough seas. Chance of snow.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Wind Advisory from 10 AM to 7 PM EST Monday for CTZ002>004.
Winter Weather Advisory until 1 PM EST Monday for CTZ002>004.
MA...High Wind Warning from 7 AM to 4 PM EST Monday for MAZ019>024.
Wind Advisory from 10 AM to 7 PM EST Monday for MAZ002>018-026.
Winter Weather Advisory until 1 PM EST Monday for MAZ007-
011>014.
Winter Storm Warning until 1 PM EST Monday for MAZ002>006-
008>010-026.
RI...High Wind Warning from 7 AM to 4 PM EST Monday for RIZ006>008.
Wind Advisory from 10 AM to 7 PM EST Monday for RIZ001>005.
Winter Weather Advisory until 1 PM EST Monday for RIZ001.
MARINE...Storm Warning from 7 AM to 4 PM EST Monday for ANZ231>237-250-
254>256.
Gale Warning from 7 AM Monday to 4 AM EST Tuesday for ANZ230.
Gale Warning from 7 AM Monday to 7 AM EST Tuesday for ANZ251.
&&
$$
SYNOPSIS...JWD/GAF
NEAR TERM...Sipprell/GAF
SHORT TERM...GAF
LONG TERM...Dunten
AVIATION...Dunten/GAF
MARINE...Dunten/GAF
Area Forecast Discussion
National Weather Service Caribou ME
1020 PM EST Sun Dec 24 2017
.SYNOPSIS...
A Nor`easter will track across the Gulf of Maine on Christmas.
Arctic high pressure builds in Tuesday through the end of the
week.
&&
.NEAR TERM /THROUGH MONDAY/...
1020 pm update...
Update to ingest latest mesonet observations into forecast.
Estcourt Station has dropped to -11F as of 02z as clds are vry
thin and allowing excellent radn`l cooling conds. Clds are
gradually thickening up and think temps acrs the area wl be
fairly steady or drop just slightly (2-4F) ovr the next 3-4 hrs
bfr beginning to rise again.
00z NAM has been very consistent the last several runs with
location of coastal low by 18z Mon. 1012mb sfc low located just
off the Delmarva is a tad deeper than latest models indicate
with greatest pressure falls to the north twd Long Island. 02z
RAP indicating new low dvlpmnt in the next few hrs off of the NY
Bight and heading northeast and deepening from there. Coastal
low wl bomb out ovr the Gulf of Maine in the aftn with a 14-16
mb drop being indicated in a matter of 6 hrs. Fortunately the
low wl be progressive with H7 low dvlpng in the aftn and quickly
mvg into New Brunswick by evening. Expecting a fairly dry snow
with ratios north of Downeast > 13:1. With low deepening this
wl lkly result in gusty winds fm the northeast in the morning
bcmg nw in the aftn and leading to areas of blowing snow
throughout the course of the day. Depending on track of coastal
low, may see warm air mv in aloft acrs the immediate coast.
This may allow sleet to mix in for a time in the aftn and lower
snow ratios, leading to slightly lower snow totals. Overall
current snow fcst looks to be right on target for Christmas Day.
Prev discussion blo...
Cold surface high pressure across the region this evening will
move to the northeast overnight. Upper level energy moving
eastward from the Great Lakes region this evening will result in
low pressure developing off the mid atlantic coast late
tonight. The low will intensify as it tracks northeast toward
Cape Cod by daybreak Christmas morning. Precipitation will
gradually spread northeast across down east areas late tonight.
Precipitation will then continue to expand across the remainder
of central portions of the region toward daybreak, reaching far
northern areas and the St. John Valley after daybreak on
Christmas. All areas will see snow on Christmas Day as the low
continues to intensify and tracks northeast into the Canadian
Maritimes by early Monday evening. There is the potential for
snow to change to all rain for a brief time along down east
coast, especially the outer islands, before precipitation
changes back to all snow before ending Monday afternoon. As the
low intensifies on Monday, expect winds to increase to 10 to 20
mph, with gusts up to 35 to 40 mph at times. This will result in
areas of blowing and drifting snow on Monday. Total snowfall
accumulations by the time the snow winds down late Monday are
expected to range from 6 to 10 inches across most of the area,
except along the down east coast where somewhat lesser amounts
are expected due to the potential change to rain.
&&
.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
Intense low pressure will move northeast away from the region
Monday Night. Expect some snow showers to remain into Monday
Evening in the north as the low pressure system moves away,
while in the south skies are expected to become partly cloudy.
Windy and colder conditions are expected Tuesday and Tuesday
Night as a colder air mass moves in behind the intense low. Cold
and breezy conditions are expected to persist into the day
Wednesday.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
High pressure will approach the region from the northwest
Thursday and will move across the northern portion of the region
Friday. Low pressure will develop over the Atlantic south of
New England Friday Night then move to the northeast. Current
indications are that this system will stay east of the region
and only produce precipitation in coastal areas Friday Night
into Saturday. High pressure will then build in from the west
Sunday.
&&
.AVIATION /03Z MONDAY THROUGH FRIDAY/...
NEAR TERM: VFR will quickly give way to IFR by mid-morning at
northern terminals and around 10z at BGR and BHB. IFR/LIFR
throughout the day tomorrow in snow and blowing snow. Expect
conds to improve to IFR after 21z at southern terminals.
SHORT TERM: Expect VFR conditions Tuesday through Friday.
&&
.MARINE...
NEAR TERM: Have issued a Storm Warning for the outer waters
beginning after day break Monday as low pressure intensifies and
moves northeast toward the maritimes. A Gale Warning is in
effect for the intra coastal waters. Visibility will decrease
to 1 NM or less in snow, and in snow or mixed precipitation on
Monday.
SHORT TERM: For sustained winds have used the NAM for Tuesday
and Wednesday then transition to the Super Blend later
Wednesday. For Waves: A strong southerly fetch will develop
Monday as rapidly intensifying low pressure moves along the
coast. The waves will slowly subside Monday Night into Tuesday
and Wednesday as winds veer into the west. The long period swell
is expected to be the primary wave system into Wednesday with a
secondary off-shore wind wave system. Will use the NWPS to
initialize wave grids.
&&
.CAR WATCHES/WARNINGS/ADVISORIES...
ME...Winter Storm Warning from 4 AM to 7 PM EST Monday for
MEZ001>006.
Winter Storm Warning from 3 AM to 5 PM EST Monday for MEZ010-
011-015>017-031-032.
Winter Storm Warning from 2 AM to 3 PM EST Monday for MEZ029-
030.
MARINE...Gale Warning from 7 AM to 9 PM EST Monday for ANZ052.
Storm Warning from 7 AM to 9 PM EST Monday for ANZ050-051.
&&
$$
Near Term...Duda/Farrar
Short Term...Mignone
Long Term...Mignone
Aviation...Duda/Farrar/Mignone
Marine...Duda/Farrar/Mignone
Area Forecast Discussion
National Weather Service Melbourne FL
825 PM EST Sun Dec 24 2017
.UPDATE...
Tonight-Christmas Day...A cold front in the Florida Big Bend region
is moving slowly southeast but a gradual acceleration is indicated
overnight as low pressure develops along the mid Atlantic coast and
lifts northeast. The latest HRRR model shows the front reaching
northern sections around 06z, Sebastian Inlet around 12z and Jupiter
Inlet around 15z. There is a thin moisture band along the front and
precipitable water values are forecast to be around 1.4 inches.
However, convergence will be weak and with nighttime stability, any
chance for brief showers will be small. Won`t change the 20 percent
values we have for all but southern sections tonight. Partly cloudy
skies in the south and rather light boundary layer winds may allow
for patchy fog in the early morning hours. Lows will be similar to
recent nights in the south half, upper 50s to lower 60s. Northern
sections will realize a little cooling into the middle 50s behind
the front.
Post-frontal conditions look to be quite cloudy on Christmas Day, so
high temperatures will be in the 60s, except for southern sections
which might be able to eke out some lower-mid 70s early before the
front moves through. Skies should gradually clear out in the north
during the afternoon.
&&
.AVIATION...Conditions will be VFR ahead of an approaching front
tonight, then a period of MVFR ceilings should affect areas
northward from about KISM-KMCO-KMLB, near and just north of the
boundary. The frontal band cloudiness should then shift to KVRB-
KSUA after sunrise. The models indicate MVFR ceilings may persist
into afternoon there.
&&
.MARINE...
Tonight-Christmas Day...Boating conditions will deteriorate behind a
cold front in the north late tonight and across all of the waters on
Christmas Day. North winds are forecast to pick up to around 20
knots across most of the waters. A small craft advisory is
warranted, especially over the Gulf Stream where seas will build to
6-8 feet.
&&
.MLB WATCHES/WARNINGS/ADVISORIES...
FL...None.
AM...Small Craft Advisory from 10 AM to 4 PM EST Monday for Flagler
Beach to Volusia-Brevard County Line 0-20 nm-Volusia-
Brevard County Line to Sebastian Inlet 0-20 nm.
Small Craft Advisory from 4 PM to 10 PM EST Monday for Sebastian
Inlet to Jupiter Inlet 20-60 nm.
Small Craft Advisory from 10 AM to 10 PM EST Monday for Volusia-
Brevard County Line to Sebastian Inlet 20-60 nm.
Small Craft Advisory from 4 AM to 10 PM EST Monday for Flagler
Beach to Volusia-Brevard County Line 20-60 nm.
&&
$$
FORECASTS...Lascody
IMPACT WX...Ulrich
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
549 PM CST Sun Dec 24 2017
.SHORT TERM...(This evening through Monday)
Issued at 234 PM CST Sun Dec 24 2017
There are several items of interest during the short term period.
The first is regarding snow chances over the next 12 hours.
Afternoon water vapor imagery shows a couple notable features.
The first is a faint elongated wave that stretches from Lake
Superior across central Minnesota. This wave proved to be strong
enough to generate a healthy band of snow showers that lowered
visibilities down to about 2 miles briefly during the late morning
and early afternoon hours. By 00z said band is expected to have
shifted east of the area, but then attention will shift to the
next upstream wave (currently over eastern North Dakota). The best
forcing with this feature looks to pass from west central to
southern MN this evening (a bit farther southwest of earlier
progs), so have included the highest POPs there, with 20 POPS
elsewhere. Any snow accumulations still look to be around or under
1 inch given the quick-moving nature of the forcing, and by 09z
most areas should be precip-free.
The other concern is of course associated with our first taste of
the arctic blast that`s setting in tonight and on Christmas.
Christmas morning lows look to dip between zero and 10 below,
possibly a few degrees above zero in southern MN. With healthy
northwest winds behind the front in the 12-15 knot range, wind
chill readings look to reach Advisory criteria (-25F) across west
central MN overnight, and generally north of I-94 on Christmas
Day. Have issued Wind Chill headlines with staggered start times
based upon when criteria will be met.
.LONG TERM...(Monday night through Sunday)
Issued at 234 PM CST Sun Dec 24 2017
On Monday night the arctic air becomes even more entrenched across
the area. The coverage of the Wind Chill Advisory will expand to
include areas generally east/southeast of the MN River Valley. The
area will likely need to be expanded to include all of southwest
MN.
On Wednesday into Thursday the trough and pool of cold air shift
east and allow for temperatures to moderate a tad for Thursday,
but even then they`ll still be averaging 10-15 degrees below
normal. This shift will also allow for a clipper to move across in
the northwest flow and bring snow for Wednesday night and
Thursday.
Then on Friday the trough that was spinning over northern
Saskatchewan/Manitoba will plummet southeast across the Great
Lakes. We could see some more light snow with this, but for
certain will get another reinforcing shot of bitterly cold air
for the weekend, with a very cold New Year`s Eve anticipated.
&&
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 549 PM CST Sun Dec 24 2017
Another subtle wave in the northwest flow near RWF to start this
period will track toward LSE through 6z. HRRR has a good handle
on this snow, only it`s about 2 hours too slow, so sped up the
hrrr a couple of hours to get the snow seen in the TAFs for
RWF/MSP/MKT. Not a lot of cloud cover upstream of this wave,
though there is another weak cold front currently dropping through
NODAK that will swing through the MPX area between about 8z and
13z. This may result in another round of light snow, with
increased cloud cover as well. Not much expected for clouds behind
the second wave, with not much cloud cover expected for Christmas
day to go along with brisk and bitterly cold northwest winds.
KMSP...Quick burst of snow west of MSP will get there by 1z, but
should be gone by 3z. Expect mainly MVFR vsbys, with heavier snow
(more consistent IFR vis) going south of MSP. Top end
accumulation potential with this round of snow will be 0.3". We
may see another burst of light snow and lower clouds around 12z,
but each successive wave we see has less and less moisture to work
with, so this one shouldn`t have as much snow to go around.
/OUTLOOK FOR KMSP/
Tue...VFR. Wind NW 5-10 kts.
Wed...VFR. Wind variable 5 kts or less.
Thu...CHC MVFR/-SN. Wind SE 5-10 kts.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
WI...Wind Chill Advisory from 6 PM Monday to noon CST Tuesday for
WIZ024-026.
Wind Chill Advisory from 5 AM Monday to noon CST Tuesday for
WIZ014>016-023-025-027-028.
MN...Wind Chill Advisory from 6 PM Monday to noon CST Tuesday for
MNZ056>063-065>070-075>078-084-085-093.
Wind Chill Advisory from midnight tonight to noon CST Tuesday
for MNZ041>045-047>051-055.
Wind Chill Advisory from 5 AM Monday to noon CST Tuesday for
MNZ052-053.
&&
$$
SHORT TERM...LS
LONG TERM...LS
AVIATION...MPG
Area Forecast Discussion
National Weather Service San Francisco Bay Area
425 PM PST Sun Dec 24 2017
.SYNOPSIS...The southern end of a dissipating weather system
moving across the region this afternoon and evening could bring a
few sprinkles to areas from San Francisco northward. Otherwise,
dry weather is expected to persist through the end of the year.
&&
.DISCUSSION...as of 1:41 PM PST Sunday...Thickening high clouds
over northern California today are resulting in less sunshine and
cooler temperatures across the district. As of 1 PM current
temperature readings were in the lower to middle 50s across the
area, which generally were cooler than yesterday at this time by a
few degrees. Latest scans from local radars show areas of virga
moving across. No reports of any measurable rain in the area thus
far.
Latest models indicate mostly dry conditions through the period.
The latest HRRR runs bring a brief blip of possible precip across
the San francisco Bay Area overnight from the southern part of a
system affecting the PacNW. Keeping in low-end pops through
tonight for San Francisco zones northward. This "threat" will move
through overnight.
Looking ahead, medium range models continue to build high pressure
over the area through the coming week keeping the area dry with
seasonable temperatures.
&&
.AVIATION...As of 4:15 PM PST Sunday...Abundant mid-level
moisture from 700mb up to 300mb could produce some sprinkles or
light showers from SFO north. But lower levels remain very dry so
no low cigs are expected.
Vicinity of KSFO...VFR with mid and high clouds and the
possibility of a sprinkle or light shower early this evening.
SFO Bridge Approach...Same as KSFO.
Monterey Bay Terminals...VFR with mid and high cloudiness.
KMRY ASOS will remain down until Monday at the earliest.
AMD NOT SKED.
&&
.MARINE...as of 03:45 PM PST Sunday...A weak upper level
perturbation may bring a slight chance of showers tonight for the
northern waters. Light to moderate northerly winds will continue
through Tuesday morning, strongest along the Big Sur Coast. Winds
will increase Tuesday afternoon as a coastal trough develops. A
longer period northwest swell arrives this evening and peaks late
tonight into early Christmas Day.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
.Tngt...None.
$$
PUBLIC FORECAST: Sims
AVIATION: W Pi
MARINE: BAM
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Area Forecast Discussion
National Weather Service Blacksburg VA
904 PM EST Sun Dec 24 2017
.SYNOPSIS...
A strong cold front moves through the region tonight with gusty
winds, falling temperatures and some mountain snow showers.
Cold high pressure will dominate the area from Monday through
Wednesday.
&&
.NEAR TERM /THROUGH MONDAY/...
As of 900 PM EST Sunday...
Previous forecast still appears to be on track. Light pre-
frontal precipitation has developed in the past couple of hours
along and west of the Blue ridge as weak isentropic lift and QG
forcing supporting sufficient weak upward vertical motion
through now saturated lower tropospheric column. Precipitation
mainly falling as light rain, or mixed rain/snow, but this
expected to rapidly change over to all snow as strong cold front
pushes east through mountains by midnight, and shortly
thereafter east of the Blue Ridge.
Rapid post-frontal increase of winds from the west and
temperatures falling quickly to below freezing may result in
flash freeze in the mountains where pre-frontal precipitation
fell - which will only be compounded by any post-frontal snow
showers, especially west of I-81. Have therefore called
attention to possibility of developing slippery roads in
mountain areas before midnight via release of a Special Weather
Statement. Overall threat temporally, spatially, and with
respect to potential impact not yet to the point where a short-
notice Winter Weather Advisory is warranted, but will be
watching this closely during the next several hours, and will
respond accordingly.
As of 638 PM EST Sunday...
Make some tweaks to PoPs/Wx, essentially to sharpen up/delaying
the timing of highest PoPs a little more. Low pressure still
making eastward inroads across the eastern Ohio Valley, leading
to periods of warm-sector rain, mixing with snow in the post-
frontal cold advection NWlys across eastern KY, southern OH and
western WV. As temperatures in southeast WV to the Blue Ridge in
VA/NC are all several degrees warmer than freezing, and with
little significant fall anticipated, would expect a cold rain to
be initial p-type as frontal zone approaches western
Appalachians between 01-03z (8-11 pm). Have discounted the past
several 3-km NAM runs as it is several hrs too fast. Shaped PoPs
heavily on the 18z regional GEM and the past couple HRRR runs,
each of which indicate the mid/late evening timeframe for start
time of precipitation. As temperatures can cool and wet- bulb
with dry advection behind the front, a mix of rain and snow then
becomes dominant as far east as the I-81 corridor, with the
best chance of snow being from the New River Valley into
southeast WV. After 1 AM, focus then shifts to the VA/WV border
and points west for potential light accumulations of wet snow.
Overnight tonight, there`s the potential for any wet pavement
either from rain or melted snowflakes to refreeze as
temperatures fall through the mid/upper 20s, with the best
chance of this occurring mostly west of the New River Valley.
Increased winds (more on that below) will help to evaporate any
damp spots on pavement, but if traveling overnight tonight west
of the New River Valley be cautious as there may yet be patchy
slick spots.
Northwesterly winds should turn gusty again, but not until after
frontal passage. Per 18z GFS, appears favorable
overlap of pressure rises and northwesterly 45-50 kts jet is
after 1 AM into mid-morning Christmas Day. Would expect
strongest winds/gusts in the overnight/pre-dawn hrs. These
ideas all indicated well in going fcst.
Previous discussion issued at 230 PM EST Sunday...
An upper level trough over the upper Mississippi Valley will
push a cold front across the region tonight. This front will
bring rain/snow showers across the mountains, windy conditions
and very cold temperatures to the area tonight into Christmas
day.
Winds back ahead of the front this evening, which will help increase
moisture over the region. Rain showers will accompany the front late
this afternoon into early evening, then as cold air filters into the
area, precipitation will change over to snow. Higher elevations will
likely not see any rain but we will see snow. Snow accumulations
will remain light as bulk of the moisture stays with a surface low
tracking northeast towards Lake Erie tonight. As the upper level
trough moves east over the Ohio Valley, a weak short wave will track
along the VA/NC border. This wave will bring snow showers as far
south as Boone NC and east to the Blue Ridge. Once this wave moves
east of the area during the early morning hours, snow showers areal
coverage will shrink to western slopes of SE WV while continuing
into Monday morning. Accumulations will range from a dusting in the
mountain valleys to an inch along higher ridges across SW VA, SE WV,
NW NC mountains. Western Greenbrier county will see a longer
duration of snow and more orographical lift with amounts ranging
from 2 to 4 inches, maybe a few spots approaching 6 inches. As winds
increase overnight, blowing snow will also cause problems. A winter
weather advisory for snow and blowing snow will be in effect from 6
PM this evening to noon tomorrow.
The more widespread threat will be strong and gusty winds tonight
into Monday morning. Strong pressure rises and a 40-50 knots cross
barrier jet will bring wind gusts of 40 to 50 MPH across the
mountains. There maybe a few hours early in the morning where gusts
along the Blue Ridge (Floyd county south) could peak above 50 MPH.
The strongest winds tonight will be along higher ridges, but as the
inversion lowers and breaks in the morning, lower elevations and
locations east of the Blue Ridge will see winds pickup through the
morning. For now, we will maintain a wind advisory for SW VA/NW NC
mountains and foothills. Winds will begin to subside in the
afternoon as high pressure builds over the region.
Temperatures this afternoon warmed into the upper 30s to mid 40s.
Following the front, temperatures by sunrise Christmas morning will
be in the low to mid 20s across the mountains to near 30F in the
east. Combining the winds with the cold temperatures, wind chill
values across the mountains will range between 5F-15F, higher
elevations will be at or below zero. Wind chills in the east will be
in a range from the upper teens to lower 20s. Afternoon temperatures
will warm into the upper 20s west of the Blue Ridge to the upper 30s
east. However, the wind will continue to make it feel a lot colder
than what it actual is.
&&
.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/...
As of 300 PM EST Sunday...
Cold high pressure will dominate the post-Christmas period as an
upper level vortex centered near Hudson Bay allows modified arctic
air to overspread the eastern CONUS. Temperatures will run 5 to
10F below normal through the period but it will be dry through
most of the period.
&&
.LONG TERM /THURSDAY THROUGH SUNDAY/...
As of 300 PM EST Sunday...
Still watching potential system for late Thursday into Friday which
looks fairly benign at this point, but obviously will be watched
closely. GFS and other longer range models show a very weak low or
inverted trough tracking across parts of the southeastern U.S. and
not strengthening much at all until well east of the southeast coast
and then moving more east then north after that. All the models have
trended slightly further south today with their runs and the
deterministic QPF shows generally less than 0.10-0.15 inches of
liquid equivalent, mostly likely snow, and confined to about the
southern half of the CWA. Latest WPC probabilistic runs which
include several model ensembles are just slightly more optimistic
then the deterministic runs about the possibility of accumulating
precipitation. Now showing a 30-50% chance of 0.25 inches of liquid
equivalent winter-type precipitation covering about the southern 2/3
of the CWA, with diminishing pops north. Much of the area remains
badly in need of any precipitation it can get, especially from the
Blue Ridge eastward. December precipitation is running well below
normal after what was also a very dry November and parts of piedmont
are in a moderate drought. Temperatures will continue to be chilly
through the entire long term period as the controlling upper trough
shifts only slowly to the southeast through the upcoming weekend. A
reinforcing shot of cold air is likely late Saturday into Sunday
with some of the coldest air of the season possible especially per
the EC model which is showing some h8 -20C to -24C air.
&&
.AVIATION /02Z MONDAY THROUGH FRIDAY/...
As of 652 PM EST Sunday...
Initial MVFR ceilings should persist ahead of the low pressure
area moving out of the Ohio Valley, with light east winds in the
Piedmont east of the Blue Ridge, with southeast/southwest west
of the Ridge.
Greater operational impact then more likely for western
terminals overnight. Front will introduce initial rain
along/ahead of it between 02-04z from southeast WV to the Blue
Ridge in VA/NC. Unlikely to see any worsening of conditions
initially, but as temperatures cool and precip begins to mix
with snow, visibility may drop to MVFR or IFR levels. Best
chance of restricted visbys being at Bluefield where indicated
TEMPO 1SM SHSN; however some potential as well at Blacksburg and
Lewisburg. See TAFs for specific timing. Frontal passage then
will increase northwest wind speeds and gusts to around 10-15
kts, gusts between 25-35kts highest at Roanoke. Strong cold
advection will help clear ceilings to VFR levels in the
Piedmont, but may also cause any wet pavement from initial rain
or melted snow to refreeze on runways. Bluefield stands best
shot at this occurring. Leftover snow showers then become more
intermittent into Christmas Day.
Should see conditions improving to VFR on Christmas Day, with
aviation operational impact restricted to northwesterly
winds/gusts. Peak gusts should occur through mid-morning before
steadily decreasing, though sustained winds 10-15 kts will
continue.
Extended Discussion...
High pressure builds in Monday afternoon ending the strong
winds and upslope precipitation. No flight restrictions are
expected Monday afternoon through Thursday. Next chance at sub-
VFR conditions is on Friday with an upper-level disturbance
skirting across the Southern states, but confidence is low attm.
&&
.RNK WATCHES/WARNINGS/ADVISORIES...
VA...Wind Advisory until noon EST Monday for VAZ007-009>020-022>024-
032>035.
NC...Wind Advisory until noon EST Monday for NCZ001>003-018-019.
WV...Winter Weather Advisory until noon EST Monday for WVZ508.
&&
$$
SYNOPSIS...AMS
NEAR TERM...AL/RCS/WERT
SHORT TERM...PC
LONG TERM...PC
AVIATION...AL/RCS