Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 01/12/18
Area Forecast Discussion...Updated
National Weather Service Billings MT
832 PM MST Thu Jan 11 2018
Not much to update. Earlier update took care of quick temperature
drop over the west. Temperatures have steadied out at Livingston
and do expect rising readings overnight there. Snow was filling in
on the radar, but at this time, snow was rather light. Strong
shortwave was entering northern Idaho, so expect snowfall to
intensify over the next several hours. Adjusted PoPs up a bit as
snow started a little earlier than expected at Miles City. Latest
high resolution models have the bulk of the snowfall tonight, with
a definite tapering off trend during the morning. This was hinted
at by the GFS as well. Expect a lull early Friday, before the
next round moves in late Friday afternoon into Friday evening.
Will have to watch Livingston closely as the RUC pointed to higher
snow amounts than existing forecast. Snow has been rather light
there so far, and with expecting winds switching to the southwest
with rising temperatures overnight, will leave totals alone for
now. Advisories in good shape. TWH
.SHORT TERM...valid for Fri and Sat...
Arctic airmass over the region today kept many places in the
single digits above and below zero, while some of the foothill and
mountain locations were in the balmy teens and twenties above
zero. Winds have been a challenge today along the western
foothills, with a baroclinic zone hugging the slopes of the
mountains. Winds may turn southwest for a time late this evening
and overnight at Livingston with perhaps a bit of blowing and
drifting snow. Otherwise, snow will overspread the area this
evening and overnight as the next system moves into the region in
the form of a shortwave trough. Pacific moisture will overrun the
colder air near the surface, with a surface low diving south and
east into Wyoming continuing upslope flow, producing periods of
accumulating snowfall. Snow looks to end across portions of the
area during the day Friday, but continue through the afternoon and
into the evening for areas west of a Forsyth to Broadus line as a
baroclinic zone pushes south and west. When all is said and done,
the western mountains could pick up 10 to 15 inches of snowfall,
highest on south and west facing aspects, with significantly less
amounts on north and east facing aspects. For the lower
elevations, locations west of a Forsyth to Broadus line and areas
north of I-90 and I-94 could see amounts of 2 to 5 inches, with
locally higher amounts possible. Given winds aloft look to remain
out of the southwest, locations along the southwest foothills are
not expected to receive much snow. Have continued the Winter Storm
Warnings for the western mountains, and expanded the Winter
Weather Advisories across the rest of our Montana zones, with the
exception being the southwest foothill locations. Went with Winter
Weather Advisories for our far eastern areas tonight into Friday
instead of a Wind Chill Advisory because we are expecting a couple
inches of snow along with wind chill values down near 35 degrees
below zero. The rest of the Winter Weather Advisories go into
A mainly dry day can be expected for Saturday with shortwave
ridging building over the area. A jet max moving overhead may
bring some snow showers to eastern areas during the evening and
night. High temperatures will range from the twenties across
western foothills, to near zero degrees across the east on
Friday, with thirties across the west and central zones on
Saturday, with twenties across the far east. Lows will continue
to be coldest east (lows below zero) and warmest west (teens to
near twenty above zero). STP
.LONG TERM...valid for Sun...Mon...Tue...Wed...Thu...
Next clipper dropping out of Canada in amplifying flow aloft will
bring our next chance of snow and next surge of colder air Sunday
afternoon and night. There is time for downslope warming ahead of
this wave...so 30s to lower 40s expected in our west, with gusty
winds along the foothills. Backdoor front arrives in the afternoon
and evening and temps should fall sharply with the wind shift to
NE-E. Models have differed with the strength of the energy and
magnitude of cooling, with the ECMWF being colder than the GFS,
but the 18z GFS has trended colder. Have kept temps sided with the
more consistent colder model, which is given further credence by
the large area of snow cover in the lee of the mountains and
strong high pressure dropping out of Canada. As for snowfall,
could see an inch or two in central/eastern zones with mostly weak
upper level forcing but a favorable dendritic layer along a low
level baroclinic zone. Snow could push all the way to the
foothills by late Sunday night, but this is more uncertain. Temps
will drop and highs on Monday should range from the single digits
in our east to maybe 30s in our west, depending on when downslope
winds kick back in.
The trend for the remainder of the extended period is for more
zonal flow as the west coast ridge breaks down. Tuesday looks like
a dry day. Could see some showers Wednesday with a Pacific
shortwave. Another shortwave and lower heights expected by
Thursday. Temperatures should moderate to the 30s to lower 40s in
this regime, and that should begin to melt some lower elevation
snow cover. Expect some gusty west winds as well, which could
cause blowing/drifting snow, especially Tuesday which is the
transition day from colder temps. JKL
Snow will develop by this evening and continue into Friday across
most of the region. Poor flight conditions will become
widespread. Expect IFR or lower, and mountains will be completely
obscured. Snow will become lighter on Friday afternoon with MVFR-
IFR persisting. KLVM could see a period of gusty SW-W winds late
tonight and early Friday, but there is uncertainty with winds
along the foothills, with east winds across the lower elevations
and west winds over the high terrain. JKL
.PRELIMINARY POINT TEMP/POPS...
Fri Sat Sun Mon Tue Wed Thu
BIL 903/007 004/038 026/038 011/025 013/037 027/041 026/041
97/S 52/O 12/S 52/S 00/B 12/J 11/B
LVM 003/032 025/041 031/040 017/037 024/043 028/042 029/044
95/S 32/R 11/N 21/B 00/N 22/J 12/W
HDN 905/004 903/037 019/034 006/022 005/034 021/042 026/044
95/S 42/O 12/S 51/B 00/U 02/J 11/B
MLS 913/905 913/024 015/027 907/006 902/025 017/037 022/038
+5/S 13/S 14/S 30/U 00/U 01/B 11/B
4BQ 907/005 906/034 021/033 901/017 002/031 020/041 024/044
85/S 22/S 24/S 40/U 00/U 01/B 11/B
BHK 915/000 915/023 013/026 913/007 910/023 012/036 021/041
85/S 13/S 25/S 20/U 00/U 01/B 11/B
SHR 001/015 006/039 024/039 014/028 010/039 024/042 026/046
54/S 32/O 12/S 52/S 00/U 01/B 01/B
MT...Winter Weather Advisory in effect until 11 PM MST Friday FOR
Winter Weather Advisory in effect until 11 AM MST Friday FOR
Winter Storm Warning in effect until 11 PM MST Friday FOR
Area Forecast Discussion
National Weather Service Charleston SC
1041 PM EST Thu Jan 11 2018
...DENSE SEA FOG LURKING ALONG THE GEORGIA AND FAR SOUTHERN
SOUTH CAROLINA COAST...
A coastal trough will shift inland through tonight. A cold
front will move through Friday evening, followed by a secondary
front Saturday night. Cool high pressure will settle over the
area Sunday through much of next week.
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
No major changes were made for the late evening forecast. Did
nudge overnight lows up a few degrees for most areas as elevated
winds and low T-Td depressions should keep conditions rather
warm and humid for January.
The coastal trough has pushed inland and surface dewpoints have
climbed into the upper 60s for most areas. Bands of rain will
continue to rotate inland across mainly the Charleston Tri-
County area for the next few hours and the highest pops (up to
50%) remain clustered in this area. The risk for measurable
rains has generally ended for the remainder of Southeast South
Carolina and Southeast Georgia, except far interior Southeast
Georgia where a few showers could still brush those areas as
weak low pressure moves north. Maintained low-end mentionable
pops for the next few hours to account for this.
The main concern for the overnight period is centered on the
potential for dense fog. Widespread sea fog has already
developed across the coastal waters early this evening as upper
60 dewpoints advect over chill Atlantic waters well into the
40s. Although surface winds will remain elevated through the
night, the advection of sea fog inland will bring the risk for
low visibilities for much of the coast as surface winds veer to
the south and increase parcel residence times over the cold
shelf waters. It is unclear how far inland the sea fog will
spread given the elevated winds atop the marine/boundary layer
and much of this could very well transition to low-stratus.
However, high resolution guidance members, including the H3R,
RAP and the Time-Lagged Rapid Refresh Ensemble (NARRE-TL) have
been consistent in showing very high probabilities for dense fog
spreading as far inland as the I-95 corridor by daybreak. A
Dense Fog Advisory may very well be needed over the coming hours
for portions of the Georgia and far southern South Carolina
coast. Adjusted near term pops, weather and temperatures to
reflect going trends. Also expanded mention of dense fog with
vsbys 1/4 mile or less into most the coastal zones.
.SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/...
An upper trough will lift from the northern Gulf of Mexico into
the Carolinas late Friday, pushing a cold front through Friday
night. Immediately ahead of the front, deep southerly flow will
bring in unseasonably warm and moist air. We anticipate another
day with high temperatures climbing into the low to mid 70s with
surface dewpoints in the low to mid 60s. PWATs are forecast to
rise to 1.6-1.7" which is around the daily climatological
maximum for CHS. There continues to be fairly good model
agreement on the main frontal precip band moving into our
southeast GA zones during the mid afternoon, then through
southern SC by early Fri evening. Although Lifted Indices and
CAPEs will be marginal, we maintained a slight chance for tstms
during the afternoon and evening.
Much colder, drier air will shift in late Friday night into
Saturday, followed by a secondary cold front Saturday evening.
Highs on Saturday will be about 20 degrees cooler than Friday,
then Sunday will be another 8-10 degrees cooler than Saturday.
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Quiet weather is expected to continue through the long term period,
with no mentionable PoPs in the forecast. Upper troughing will
persist over the eastern half of the country. Meanwhile at the
surface, high pressure will largely dominate the weather pattern,
although a dry cold front will quickly cross the area late Tuesday.
Temperatures will be cooler than normal, especially beyond Tuesday
as strong cold advection takes place.
.AVIATION /04Z FRIDAY THROUGH TUESDAY/...
KCHS: A band of showers moving north across the Tri-county area
should be clear of the terminal by 00Z. Will maintain VCSH
through 04z to account for any additional showers that could
move inland from off the Atlantic. Sea fog has developed along
the Georgia and far southern South Carolina coast this evening.
Some of this could get into the terminal early Friday, but
guidance is consistent in keeping the higher dense fog
probabilities to the south. Will show MVFR cigs developing
overnight with vsbys limited to right at alternate minimums to
trend. The fog/status should lift by mid-morning with VFR
conditions returning. The risk for showers will increase at the
end of the 00Z TAF period.
KSAV: Sea fog has developed along the Georgia coast this evening
and will spread inland this evening into the terminal. Current
progs suggest fog could being to impact the terminal as early as
03Z with dense fog developing by 05Z. Given the consistent
trends noted in the various high resolution data, will go ahead
and bring prevailing dense fog with both vsbys and cigs below
airfield minimums into the terminal by 05Z and keep these
conditions in place through 14-15Z Friday. Conditions should
rapidly improve thereafter. The risk for showers will increase
at the end of the 00Z TAF period.
Extended Aviation Outlook: Flight restrictions possible Fri
afternoon/evening as showers and isolated thunderstorms move
Expanded the Marine Dense Fog Advisory to include Charleston
Harbor. Webcams and Charleston Harbor Control report dense fog
expanding in the harbor.
Webcams and satellite data show dense sea fog has developed
across the Georgia nearshore waters up to near Edisto Beach, SC.
Have issued a marine Dense Fog Advisory for all nearshore legs
through late morning Friday. Patchy sea fog will continue in the
Charleston Harbor this evening with the risk for more widespread
fog increasing by late evening. The advisory may very well need
to be expanded to include the harbor over the coming hours.
Tonight: A coastal trough will push inland as southerly winds
strengthen ahead of an approaching cold front. Winds will mainly
be 15 kt or less but seas continue to be high mainly due to ESE
swells. Significant wave heights should remain at least 6 ft
across all waters most of the night and thus Advisories will be
in effect everywhere outside Charleston Harbor. By daybreak seas
should subside below 6 ft for at least the nearshore GA waters.
Friday through Tuesday: Gusty south winds on Friday will become
westerly late Friday night behind the cold front, then
northerly Saturday night into Sunday after another front drops
through. Winds will remain somewhat elevated into next week as a
modest gradient persists and cold air advection provides decent
mixing over the waters. Small Craft Advisories continue for the
Charleston nearshore waters and GA offshore waters through
Saturday afternoon after which the 6 ft seas should subside.
Sea fog: Very warm, moist air will flow across the cool shelf
waters through Friday, likely maintaining a bank of sea fog over
the nearshore waters. We kept areas of dense fog in the forecast
in these areas and Dense Fog Advisories will be possible. The
fog should begin to clear out by Friday evening as winds turn
MARINE...Dense Fog Advisory until 10 AM EST Friday for AMZ330-350-352-
Small Craft Advisory until 7 AM EST Friday for AMZ352.
Small Craft Advisory until 4 PM EST Saturday for AMZ350.
Small Craft Advisory until 7 PM EST Saturday for AMZ374.
Small Craft Advisory until 4 AM EST Friday for AMZ354.
Area Forecast Discussion
National Weather Service State College PA
1001 PM EST Thu Jan 11 2018
A complex winter storm will bring rain, ice and snow to Central
Pennsylvania, causing significant travel disruptions into the
weekend. The mild air and heavy rain will increase the risk of
ice jam and low-lying area flooding.
After the brief January thaw, progressively colder air will
return to the area with sharply falling temperatures and freeze-
up possible on Saturday. Below average temperatures will persist
into early next week.
.NEAR TERM /THROUGH FRIDAY/...
The first round of rain is progressing smartly north and has
reached my central zones. The HRRR shows the rain continuing to
progress eastward overnight.
Models are in agreement in depicting an axis of 1-2 inches over
northwest 1/3 of the CWA through 12Z/7AM tomorrow. Lighter
rains are expected during the day Friday with areas of fog
before the next round of precipitation arrives Friday night.
Temperatures will be unseasonably mild with 50-60F highs feeling
very spring-like to end the week.
.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/...
Increasingly negative tilt shortwave pivoting across the
Southeast will track a more pronounced surface low from the
southern Appalachians toward the northern Mid Atlantic coast.
The consensus model (GFS/ECMWF/CMC/NAM) track continues to be
east of the Appalachians and Blue Ridge Mountains with 12z UKMET
west of the WPC preferred blend. The NAM is a bit faster than
the other models.
As arctic air impinges on a robust baroclinic zone, overall
confidence continues to increase in a swath of moderate to heavy
snow on the northwest edge of the precipitation shield across
far northwest PA within zone of enhanced UVVEL and low to mid
level FGEN. Upgraded to warning for Warren and McKean Counties
with 6-12 inches expected. The heavy snow will be preceded by a
transition from rain to wintry mix which will shift to the
southeast with time. The shallow cold air will initially
undercut the warm/moist air with a significant icing zone
possible over parts of Central PA before changing to snow as
cold air deepens through the column. Expanded winter storm watch
to the Laurels and adjacent Pocono Counties given uptick in WWD
deterministic forecast and overall potential for more snow/ice.
Also have some concern over parts of south central PA between
I-99 and I-81 which seems to be in the tightest gradient or area
of max uncertainty. The 12/00Z HREF should provide valuable
insight on thermal profiles and snow/ice accumulation potential
with winter weather advisories likely to be issued on the next
shift cycle. A very messy start to the weekend for sure, with a
glaze of ice and coating of snow/sleet possible as far south as
the Route 30 corridor.
It will turn sharply colder Friday night into Saturday with a
drastic swing from very mild temperatures to arctic cold. This
may result in a rapid freeze-up of standing water/slush on
untreated surfaces. Wind chills will range from around 10 below
in the west to the low single digits in the Lower Susq. Valley
by Sunday morning.
.LONG TERM /SUNDAY THROUGH THURSDAY/...
Winter conditions for much of the extended. Cold and windy
Sunday with temperatures below average everywhere. Cold for the
first half of the work week. Will keep low pops for light snow
across the western half of area. Next weather system later on
Wednesday with a period of snow possible for much of the region.
Some snow accumuations are possible with this.
.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
Expect aviation ceilings and visibilities to lower from west to
east overnight, as rain and deep moisture overspreads Central
Pennsylvania. The result will be widespread IFR/LIFR ceilings
and visibilities developing in most areas overnight, and
continuing through Friday. LLWS likely in all areas overnight,
lasting into Friday in eastern areas.
Periods of rain continue Friday along with significant flying
restrictions and gusty south winds, with an eventual changeover
from rain to snow from northwest to southeast during the
afternoon and evening. Winds too will shift from south to
northwest with the passage of a strong cold front later Friday
into Friday Night.
Low ceilings and reduced visibilities likely through Saturday
morning. Improving weather for the weekend, though winds will
Sat...AM rain/low cigs poss east. AM snow/ice poss central/west.
Sun...No sig wx expected.
Mon...PM light snow poss west. PM low cigs poss east.
Tue...Morning snow ending. Becoming VFR south and east,
lingering snow showers and restrictions over the mountains.
Wed...Snow showers and restrictions N and W, VFR elsewhere.
A mild surge in temperatures combined with 1-3 inches of rain
will produce significant rises on rivers and streams with the
potential for ice jams and low-lying flooding. Streamflows are
currently low, but many waterways are choked with ice. The
greatest risk of flooding is in the Watch area over north-
central PA where snowmelt will be a contributing factor.
Temperatures are expected to fall sharply below freezing by
Saturday and could reinforce ice jams.
Flood Watch through Saturday evening for PAZ004>006-010>012-
Winter Storm Watch from Friday evening through Saturday
afternoon for PAZ042-053-058.
Winter Storm Watch from Friday afternoon through Saturday
afternoon for PAZ006-010>012-017-018-037-041.
Winter Storm Watch from Friday evening through Saturday
afternoon for PAZ024-033.
Winter Storm Warning from 4 PM Friday to 4 PM EST Saturday for
NEAR TERM...La Corte
Area Forecast Discussion
National Weather Service Duluth MN
417 PM CST Thu Jan 11 2018
Issued at 414 PM CST Thu Jan 11 2018
A gravity wave induced narrow band of moderate to heavy snow has
developed along the North Shore into parts of Duluth to eastern
Carlton County. This band is further west than typically seen from
a gravity wave and snowfall rates around an inch per hour will be
possible under this band. The RAP continues to suggest drier air
will move in and this band of snow should weaken then dissipate
after 6 pm.
.SHORT TERM...(This evening through Friday)
Issued at 151 PM CST Thu Jan 11 2018
Surface low pressure was centered near or just east of Lake
Superior as of 130 pm. A well defined shortwave was seen on water
vapor imagery moving north out of eastern Iowa. Area radars showed
moderate to heavy snow over parts of northern Wisconsin and
adjacent eastern Minnesota with more moving out of western
Wisconsin and southeast Minnesota. Snowfall rates will be around
an inch per hour at times. The snow also continued to diminish
from the west with light snow or flurries over most of Aitkin and
far western Saint Louis Counties. Most of the snow will diminish
or end around 00Z Friday, except over far northern Wisconsin.
Lake effect snow and a gravity wave induced band of snow should
continue to produce snow along much of the South Shore, all the
way west into northern Douglas County. We extended the Winter
Weather Advisory for Douglas and Bayfield County through 03Z,
after which time enough dry air should move in to shut down the
gravity wave snow. Lake effect snow will continue all night in
Iron/Ashland Counties due to northerly winds. However, the snow
intensity should diminish late tonight as inversion levels lower
and more dry air moves in. Additional accumulation tonight twill
range from 1 to 4 inches with the higher amounts in the Gile,
Montreal, and Hurley areas.
Tonight will be cold with lows 25 to 30 below zero along the
International Border to the single digits below zero over the
South Shore toward Price/Sawyer Counties. There will be enough
wind to create wind chill values from 25 below to around 40 below
over much of northern Minnesota into far northwest Wisconsin. We
will likely issue a Wind Chill Advisory for those areas. There may
be a few wind chills below 40 below but confidence in that
occurring and the need for Wind Chill Warning is low.
Friday will be cold with highs in the single digits above and
below zero. It should be mostly sunny with more lake clouds and
light snow showers in the snowbelt along the South Shore.
.LONG TERM...(Friday night through Wednesday)
Issued at 151 PM CST Thu Jan 11 2018
For the long-term forecast, no major winter storm systems look to be
on the horizon, but temperatures will be much colder compared to
what we experienced earlier this week. The best chances of
widespread snowfall will be on Sunday.
Friday night through Saturday will be dry across nearly all of the
Northland as surface high pressure builds across North Dakota. A
very dry air mass will also be place, so expecting a very cold night
over the region. Decreased overnight lows slightly to better
accommodate the radiational cooling as the consensus blends were a
bit too high. Lows look to drop to between -15 to -30, with the
coldest temperatures over north-central Minnesota. Wind Chill
Advisories will very likely be needed, with perhaps winds chills
pushing warning criteria over Koochiching county. The only
precipitation during this time might be some lake enhanced snow over
the snowbelt of Iron county in northwest Wisconsin as low-level
lapse rates remain steep and favorable northwest flow and little
The best chances for widespread light snow will return Sunday
morning, continuing through Monday morning as a mid-level shortwave
trough dives southeast from Manitoba and over the Northland. Pretty
good large scale lift will be associated with the wave as indicated
by the Thaler QG 850-300 mb omega progs. GFS/NAM model soundings
indicate a fairly deep layer of saturation in the dendritic snow
growth zone, but the isentropic lift within that zone looks to be
minimal, so high snow fall rates should be limited. Given the amount
of QPF from the models, total snow through Sunday night could range
between 1 to 2 inches, with possible higher amounts along the
Gogebic Range of northern Iron county due to lake enhancement. This
lake enhancement over the Lake Superior snowbelt could continue
through the early part of next week. One concern for this lake
enhancement is that the GFS model is bringing a very favorable 1000-
850 mean flow fetch along the length-wise direction of Lake
Superior, which could bring the potential for several inches of lake
effect snow. However, uncertainty still exists as the ECMWF/GEM
models don`t show this, so not putting much stock into the GFS
solution for now, but will need to be monitored.
.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1138 AM CST Thu Jan 11 2018
A range of MVFR to LIFR conditions continue across the Northland
as a potent surface low makes its way over Lake Superior.
Conditions should gradually improve from west to east as the low
exits the region this afternoon. Gusty northwest winds and light
snow will maintain lower visibilities due to blowing snow through
at least the middle afternoon. It`s possible that lower
visibilities could linger later than what is in the TAFs due to
these gusty winds but are still expected to improve by the evening
hours. Ceilings could also approach MVFR or lower in some
locations across the area as well.
.PRELIMINARY POINT TEMPS/POPS...
DLH -13 1 -17 1 / 50 0 0 0
INL -29 -4 -28 -2 / 0 0 0 0
BRD -17 2 -22 1 / 0 0 0 0
HYR -9 6 -18 2 / 50 0 0 0
ASX -2 7 -10 4 / 60 20 0 10
WI...Wind Chill Advisory until noon CST Friday for WIZ001-006.
Winter Weather Advisory until 6 PM CST this evening for WIZ006-
Winter Storm Warning until 6 PM CST this evening for WIZ008-009.
Winter Storm Warning until midnight CST tonight for WIZ003-004.
Winter Weather Advisory until 9 PM CST this evening for WIZ001-
MN...Wind Chill Advisory until noon CST Friday for MNZ010>012-018>021-
Winter Weather Advisory until 6 PM CST this evening for MNZ012-
LS...Small Craft Advisory until 4 AM CST Friday for LSZ121-142>148.
Heavy Freezing Spray Warning until 10 PM CST this evening for
Gale Warning until 6 PM CST this evening for LSZ140-141.
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
951 PM EST Thu Jan 11 2018
Well defined arctic boundary now seen exiting the eastern shores of
lake Michigan on pace to rapidly sweep across southeast Michigan
during the early morning period /04z-08z/. Extremely moist resident
environment will continue to contribute to periodic bouts of rain
overnight, both within the existing mild pre-frontal environment and
accompanying the frontal passage. Pronounced downward spiral in
temperatures with the fropa, as witnessed by the 19 degree drop in 2
hours at Chicago-Midway Airport. These trends continue to lend
confidence in expectations for a high magnitude of low level cold
air advection to eventually cool the near surface profile enough to
leave a brief window for freezing rain, before the entire column
drops below freezing and ptype moves to snow. Latest hi res
guidance holding in support of this transition timeline. Primary
area of uncertainty remains the behavior of the fgen response mid
morning through early afternoon Friday, highlighted by the potential
for a localized stronger axis of ascent to emerge should the forcing
contract. No definitive signal yet per recent model evidence, which
isn`t surprising given the scale, so no plans to provide any
refinements to the going snow forecast with the evening update.
Issued at 725 PM EST Thu Jan 11 2018
A warm and increasingly moist deep layer southwest flow will
maintain an extensive low stratus and periodic light to moderate
showers and drizzle early tonight. An associated reduction in
ceiling will favor predominate IFR conditions through the latter
half of the evening, but with the higher terrain contributing to
marginal LIFR conditions at PTK. The passage of an arctic front will
then bring a transition in precipitation type from liquid to frozen
Friday morning, as colder air surges in under developing northwest
winds. The strength of the low level cold air advection will provide
a 2-3 hour window mid morning where conditions become favorable for
freezing rain, before the entire column cools sufficiently enough to
support the transition to snow. A period of accumulating snowfall
then expected from mid-late morning into the early afternoon.
Current forecast will continue to highlight IFR level conditions in
falling snow. However, the potential does exist for a localized
heavier axis of snow to develop, which could result in a period of
LIFR conditions. Confidence in placement of a heavier axis remains
low at this time. Total snowfall accumulation of 2 to 4 inches,
before snowfall tapers from northwest to southeast through the
For DTW...Short window for potential freezing rain remains centered
12z-15z Friday morning. Transition to accumulating snowfall
thereafter through early afternoon. Current forecast calls for total
accumulation of 2 to 4 inches. Firm southerly winds early tonight,
turning northwesterly and increasing Friday morning. This may
necessitate the eventual shift to northeast operation early Friday.
//DTW THRESHOLD PROBABILITIES...
* High for ceiling at or below 5000 ft through Friday.
* Moderate for the occurrence of light freezing rain Friday morning
* High in the transition from rain/freezing rain to snow late
morning /after 14z-15z/.
Issued at 455 PM EST Thu Jan 11 2018
An extremely fluid forecast exists during the next 24 hours as an
arctic boundary will impinge upon the area. The cold air will lead
to the changeover of precipitation type from all rain to a period of
freezing rain/sleet, eventually changing over to an all snow.
Compounding matters is that shallow cold air advection will lead to
rapidly falling temperatures across all of Southeastern Michigan
Friday, resulting in high impact winter weather both with the
expected snowfall amounts and the the flash freezing of earlier
fallen precipitation. A Winter Weather Advisory is now in effect for
all of Southeast Michigan between 09Z Friday-00Z Saturday. This will
include both of the morning and evening commute times. It is likely
that mixed precipitation and negative impacts would hold off until
after the main morning rush hour push for a portion of metro
Detroit. However, confidence is too low at this time to emphasize
that message. Thus, the Winter Weather Advisory start time will
begin at 09Z for all of the CWA.
An extremely tight temperature gradient is forecasted along the
arctic front as it pushes eastward over Lower Michigan at 06Z
tonight. Impressive front, as 925mb temperatures of
-22C will exist over portion of extreme eastern Lake Superior while
temperatures of +12C exist near the city of Detroit. High end
equivalent potential temperature/heat content for this time of year
south of the front, as model data suggests PWATs exceeding 1.0 inch
at 00Z this evening (greater than 300% of normal). Models are now
advertising a slight slowing down of the mid to upper level frontal
boundary as it arrives directly over the cwa on Friday. Big player
from a dynamics perspective is a compact, but robust frontogenetic
circulation that will ride northward along the frontal boundary in
the 09-18Z time window. This fgen arises from an outstanding
ageostrophic response from highly organized right entrance region
dyanmics centered over the region. Additionally, pre-existing
midlevel fgen residual to the upper Mississippi River Valley is
expected to be drawn in and merge with the active response here
locally. Two dimensional plan views show some merging of this larger
scale forcing setting the stages for the event here locally.
The overall narrative is one of the changing over of precipitation
type from all rain to a period of freezing rain/sleet and all snow.
Timing of the changeover will transition from the north to the
south. Overall, looking at the period of mixed precipitation to be
generally around 2 hours for any one location. All signs point to a
period of high precipitation rates that brings ice accumulation of
10 inch in play. This includes favorable low static
stability/convective instability above 10 kft agl, amount of
available forcing and the freshening, frontal circulation. Total
snowfall accumulations of 1 to 4 inches is expected on top of the
earlier mix of freezing and rain and sleet.
Some main thinking on this system.
1. One aspect of this forecast that remains highly uncertain is
whether or not the fgen will collapse down in scale. There are some
hi-resolution runs that are suggesting that convective
precipitation, and very high rates will contract down to a single
band on the order of tens of miles. The last forecast trends
suggests possibly north of M59. If there were to occur than
forecasted snowfall and/or icing amounts would need to be increased.
Confidence in this is low at this time, hopefully, later hi-res
runs including the HRRR will offer some useful guidance.
2. Forecast soundings resoundingly suggest that hydrometeors in the
warm layer between 3.0 and 6.0 kft agl will be fully melted. This
supports more in the way of freezing rain. It will be more difficult
to refreeze a full liquid drop to get sleet.
3. Some model solutions suggest that the frontal boundary could slow
down even more, and be slow to exit the forecast area. This could
lead to some additional nuisance snow amounts in the far eastern
cwa. However, bulk of moisture will have exited.
4. Main narrative is that conditions will not be pleasant with rapid
onset of arctic cold and freezing of residual moisture. North winds
of 20 to 30 mph is expected. Windchills are forecasted to fall
into the -5 to -10 degree range Friday night.
5. There are a couple of reasons that Bay and Midland Counties were
left out of the advisory at this time. The first is that overall
system QPF is expected to be lacking, and the likely outcome is
that they will miss the mixed precipitation types of this event.
6. Not completely clear yet how much of the Detroit Metro area will
witness warm rain during the entirety of the morning rush hour.
Arctic airmass in place Saturday (850 mb temps nearing -23C) along
with long fetch northerly flow over Lake Huron will result in an
increased likelihood of a band of lake effect snow to develop over
the eastern Thumb. NAM model soundings still advertising good
convergence/omega at 925mb and decent instability intersecting the
saturated dendritic growth zone. Assuming this band stays
persistent, a few inches of snow will be possible in and near Port
Huron in the morning hours before flow backs to the northwest and
pushes the band into the Canadian side of Lake Huron. Conditions for
the rest of SE Michigan will stay quiet and gusty Saturday with
highs staying in the mid to upper teens.
Sunday will be a benign, cold day for all of SE Michigan. Morning
lows will dip to the single digits as high pressure overhead will
allow for some clearing and efficient radiational cooling to occur.
Highs will recover to the upper teens as the high pressure moves off
to the east and allows for some return southerly flow to filter back
Next chance for snowfall will be Monday as a clipper is still
progged to swoop through the Great Lakes. Model guidance is failing
to reach consensus on the exact placement of the low, with the ECMWF
showing it track over central Michigan and the GFS suggesting a
track further south over central Ohio. Regardless, looking like an
area-wide light snowfall of a couple inches will be possible as the
system pivots through before exiting Tuesday morning. This clipper
will also deliver a reinforcing shot of Arctic air that will keep
temps some 10 degrees below average through midweek. Renewed
northerly flow over Lake Huron will again lead to an increased
chance for lake effect snow over the Thumb Tuesday and Wednesday.
Otherwise, conditions will remain mostly quiet over the region
through the rest of the week before the Arctic air moves off to the
east and a warm up begins in time for next weekend.
Gusts to north northwest gales will develop across Lake Huron
tonight as colder air spreads across the waters. Gale warnings
remain in effect. In addition a heavy freezing spray warning has
been issued to coincide with most of the gale warning
area...including the nearshore zones. Maximum waves heights around
10 feet will be common along the exposed and ice free waters along
the Thumb. Winds and waves will diminish as cold high pressure
settles over the waters for the weekend. Winds will ramp up again
early next week as a clipper moves through the Great Lakes region.
MI...Winter Weather Advisory from 4 AM to 7 PM EST Friday for MIZ049-
Lake Huron...Heavy Freezing Spray Warning from 10 AM Friday to 7 AM EST Saturday
Gale Warning from 3 AM Friday to 7 AM EST Saturday for LHZ441>443-
Gale Warning until 10 AM EST Friday for LHZ361.
Gale Warning until 7 AM EST Saturday for LHZ362-363.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
You can obtain your latest National Weather Service forecasts online
Area Forecast Discussion
National Weather Service Austin/San Antonio TX
1001 PM CST Thu Jan 11 2018
Additional counties have been removed from the Wind Advisory. Based
on recent observations, we have cancelled the advisory for most
areas along and west of Highway 281. No other changes to the forecast
have been made at this time.
.PREV DISCUSSION... /ISSUED 827 PM CST Thu Jan 11 2018/
Winds have been steadily decreasing over the last few hours across
south central Texas. Based on observational trends and hi-res
guidance, we will cancel the wind advisory for areas generally along
and west of Highway 83. Some of the hi-res models suggest gusty
conditions will continue over portions of the Hill Country and along
and east of the I-35 corridor this evening. We will continue to
monitor, but may opt to cancel additional counties in a future
update. Otherwise, updates have been made to the hourly temperatures,
dew points and winds.
PREV DISCUSSION... /ISSUED 553 PM CST Thu Jan 11 2018/
AVIATION... /00Z TAFS/
Nw winds will go from the brink of reaching AWW criteria at SAT to
below 12 knots between 02 and 04Z. Will expect some subtle changes in
wind direction at AUS before the winds become less gusty later in the
evening. VFR skies should otherwise prevail, and the vsby restrictions
from blowing dust look to have abated already.
PREV DISCUSSION... /ISSUED 235 PM CST Thu Jan 11 2018/
SHORT TERM (Tonight through Friday Night)...
Front has cleared the CWA. Windy conditions will continue through
the evening, with highest gusts now through sunset. Will maintain the
Wind Advisory through midnight, although most locations should fall
below criteria before then.
Temperatures have fallen into the upper 40s to mid 50s across the
Hill Country this afternoon. Compressional heating that occurred
along and south and east of the escarpment allowed temperatures to
rise into the mid 70s, however temperatures should begin to fall in
these locations through the late afternoon as cold air advection
increases. Elevated light showers currently moving through the Hill
Country should begin to decreasing coverage approaching the I-35
corridor per HRRR and 4KM Texas Tech WRF.
A light freeze is forecast Friday morning across the Hill Country and
Central Texas. Temperatures rebound into the mid 50s northeast to low
60s southwest for highs on Friday.
A weak re-enforcing surge of high pressure late Friday night will
send lows Saturday morning to freezing across most areas of the CWA,
with the exception of possibly the Rio Grande.
LONG TERM (Saturday through Thursday)...
Cool conditions over the weekend as the aforementioned re-enforcing
ridge settles over the region on Saturday and Saturday night. Highs
Saturday are only forecast in the upper 40s to upper 50s. A hard
freeze is expected Sunday morning. A return flow will setup Sunday
night ahead of the next cold front. Slightly warmer Monday ahead of
the front, but increasing clouds through the day.
A large, deep trough will develop Monday through Wednesday from the
Midwest into the Southeast U.S. and allow a glancing blow of arctic
airmass to spill south into the area. The cold front is currently
forecast to arrive Monday evening by both 12Z operational runs of the
GFS and ECMWF. The ECMWF is a little more robust with developing
light rain behind the front Monday night into Tuesday morning than
the GFS. Will continue the 20-30 PoPs forecast during this time.
Will have to watch temperatures closely for light freezing rain
potential across northern areas of the CWA Tuesday morning if precip
does linger longer and temps trend cooler, however am keeping this
mention out of forecast for now. Much colder Tuesday, with highs not
making it out of the low to mid 40s. Some of the raw guidance
suggests highs could remain in the mid and upper 30s in across he
northern CWA. The cold airmass will remain in place into Wednesday.
Then the ridge shifts east and a warming trend and return flow is
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 33 56 30 50 28 / 0 0 0 0 0
Austin Bergstrom Intl Airport 33 55 27 50 22 / 0 0 0 0 0
New Braunfels Muni Airport 33 58 29 52 24 / 0 0 0 0 0
Burnet Muni Airport 29 54 26 47 24 / 0 0 0 0 0
Del Rio Intl Airport 35 62 35 59 32 / 0 0 0 0 0
Georgetown Muni Airport 30 54 26 48 23 / 0 0 0 0 0
Hondo Muni Airport 33 62 29 57 25 / 0 0 0 0 0
San Marcos Muni Airport 33 57 28 51 25 / 0 0 0 0 0
La Grange - Fayette Regional 32 52 29 50 26 / 0 0 0 0 0
San Antonio Intl Airport 36 60 31 54 27 / 0 0 0 0 0
Stinson Muni Airport 36 60 32 55 27 / 0 0 0 0 0
Wind Advisory until midnight CST tonight for the following
counties: Bastrop...Caldwell...Comal...De Witt...Fayette...
Public Service/Data Collection...33
Area Forecast Discussion
National Weather Service Grand Rapids MI
1049 PM EST Thu Jan 11 2018
Issued at 330 PM EST Thu Jan 11 2018
A cold front will bring rain showers this evening that will become
mixed with and then change over to light snow showers. Light snow
and sleet accumulations of an inch or two are expected through
midday Friday with relatively highest accumulations southeast of
Grand Rapids. Temperatures will plummet into the 20s behind the cold
front tonight. The cold air will stick around this weekend through
next week with occasional snow showers.
Issued at 1049 PM EST Thu Jan 11 2018
I continued the headlines as they are but I am very concerned that
snowfall amounts will be more like 3 to 6 inches in the I-69 area
by mid afternoon. This is supported by the latest runs of HRRR,
HRRRX, RAP model, SPC SREF plums, NAM12 00z run just to name a
few. The wave looks really good on the water vapor image loops and
that wave is heading north northeast. We have a negative tilt
upper wave over MS and AL this evening and those type systems tend
to track north and west of where the models show them. This system
should be coming into our area just as the deeper cold air
arrives. Thus most of the precipitation should be snow. There will
be strong winds with this system since the cold air is just
starting to come in. Thus if we really get that FGEN band of
heavier snow near I-69 the heavy falling snow and strong winds
will make for dangerous driving conditions. The good news is the
storm moves through quickly and in all areas the snow should be
done by 4 pm or so.
.SHORT TERM...(This evening through Saturday night)
Issued at 330 PM EST Thu Jan 11 2018
The cold front will bring rain showers into this evening that will
change over to snow showers overnight as strong caa occurs after
fropa. A very brief period of sleet is also possible. Based on a
consensus of latest higher resolution short range guidance and qpf
we expect snow accumulations of around an inch in our central
fcst area. Snow accumulations of up to around two inches are expected
over our se fcst area by midday Friday with locally higher amounts
to near 3 inches possible near KJXN.
Given plummeting temperatures after fropa and the precipitation
and expectations for snow overnight into Friday morning we
decided to hoist a winter wx advisory for the southern two thirds
of our fcst area where travel conditions will likely become rather
hazardous for the Friday morning commute. Decided against an
advisory for our northern two rows of counties where very little
snow (under an inch) is forecast and based on coord w/DTX and
APX (thanks for extensive coordination on headline decisions
Cold and dry/tranquil wx is fcst for the vast majority of our
fcst area Friday afternoon through Saturday night as high pressure
gradually builds in from the northwest. A few flurries or light
lake effect snow showers will just clip areas right along the Lake
.LONG TERM...(Sunday through Thursday)
Issued at 330 PM EST Thu Jan 11 2018
Models are in relative agreement in tracking down a clipper low
starting Sunday Night and lasting through Monday. Widespread
accumulations look likely with some at least low impacts expected. I
have increased POPs for this event given the better confidence.
A reinforcing shot of arctic air moves in behind this departing
system. Based on the low level flow...lake effect if any will be
confined to the immediate lakeshore region. I do feature this
highest POPs there with some potential for accumulations. Well below
normal temperatures will continue.
Mid level ridging arrives for the end of the week. The Gulf looks
cut off through Friday. This pattern typically leads to moderating
temperatures and less than normal precipitation. That could change
next weekend as the Gulf is shown to open up as a Southern Rockies
low kicks out into the Southern Plains.
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 628 PM EST Thu Jan 11 2018
IFR conditions continue to prevail at all of our TAF sites this
evening. The cold front will be passing through by 03z or so and
that will bring the winds to the west then northwest. Normally
this would bring some clearing (behind a strong cold front) but
this time there is a wave on the front. So even through the rain
should end around 03z or so from the frontal system, then
precipitation from the wave on the front will move in around 06z.
Since by then the cold air will be in place I expect freezing
rain, sleet and snow to start the precipitation again around 06z
or so then it should change to all snow by 09z or so. I could see
several hours of moderate snow at AZO, BTL, LAN AND JXN. For the
western TAF sites skies will clear by 18z or so. The more eastern
TAFS may stay in snow till late afternoon.
Issued at 330 PM EST Thu Jan 11 2018
The small craft advisory was extended through early Saturday
Issued at 330 PM EST Thu Jan 11 2018
Snowmelt is expected into tonight, as warm moist air continues to
invade the region. Most of the snow pack should melt, but not all of
the melt water will make it into the river system before the cold
air moves back in and locks it down later tonight through the
There is still 1 to 2 inches of snow, mainly north of Grand Rapids.
No excessive rainfall is expected with the warmup and amounts should
be generally under one half inch through the warm period. This has
resulted in minor river flooding scattered across Southwest Lower
Michigan. Some ponding of water, away from the rivers, will be
possible. The rivers will need to be closely monitored for ice
breakup and potential ice jam flooding.
MI...Winter Weather Advisory from 3 AM to 6 PM EST Friday for MIZ059-
Winter Weather Advisory until 1 PM EST Friday for MIZ050>052-
LM...Gale Warning until 4 AM EST Saturday for LMZ844>849.
Area Forecast Discussion
National Weather Service San Joaquin Valley - Hanford CA
408 PM PST Thu Jan 11 2018
.UPDATE...Updated air quality issues.
High pressure will build over the region for dry weather through
at least next Monday. Late night and early morning dense fog is
possible in the San Joaquin Valley through Monday. A cold front
will move through the region next Tuesday bringing a slight chance
of showers to the Sierra Nevada around Yosemite.
Some patchy dense fog formed just before sunrise this morning then
burned off by 10 AM. Large stratus deck over the San Joaquin Valley
eroded from the east earlier with scattered to broken stratocumulus
over mainly the southern SJ Valley now. The clearing led to warmer
temperatures than expected with lower 60s across most of the Valley.
A s/wv trough is passing over the Pacific Northwest as a ridge of
high pressure sits just west of Baja CA. The ridge will build over
the west through the weekend for dry and stable conditions. The
big weather concern will be Tule Fog development the next several
nights. The stage seems set for a good chance of more dense fog
tonight but there is still some uncertainty regarding development
time and coverage. The latest HRRR visibility forecast does paint
a good portion of the Valley with dense fog forming after midnight,
but other guidance is less bullish. We`ll be monitoring conditions
this evening to determine the need for a Dense Fog Advisory. Safe
to say there will be at least some patches of dense fog by early
tomorrow morning. It is always a good idea during Tule Fog season
to be prepared for hazardous travel conditions during the morning
commute and allow for extra travel time. The pattern will remain
favorable for fog through the weekend and probably Monday morning
There is good model agreement with the ridge giving way early next
week as an upper trough moves over the Pacific NW and northern CA
Monday night and Tuesday. There remains a slight chance for some
light precipitation, mainly around Yosemite NP, but the trend is
farther north with precip. Brief short wave ridging is progged to
slide in next Wednesday, followed by a deeper trough Thursday and
Friday. It is still a week away, but the models are indicating a
return to wet weather for central California.
MVFR visibility and ceilings and mist across the San Joaquin Valley
through 18Z Friday. Patchy IFR conditions possible after 08Z Friday
in Fog. VFR conditions will prevail elsewhere across the Central
California Interior during the next 24 hours.
.AIR QUALITY ISSUES...
On Friday January 12 2018... Fireplace/Wood Stove Burning Status
is: No Burning Unless Registered in Kern... Kings and Tulare
Further information is available at Valleyair.org
The level of certainty for days 1 and 2 is medium.
The level of certainty for days 3 through 7 is medium.
Certainty levels include low...medium...and high. Please visit
www.weather.gov/hnx/certainty.php for additional information
an/or to provide feedback.
Area Forecast Discussion
National Weather Service Northern Indiana
849 PM EST Thu Jan 11 2018
Issued at 313 PM EST Thu Jan 11 2018
A winter storm will bring a mix of precipitation to the forecast
area tonight into Friday, with freezing rain, sleet both possible.
Mixed precipitation will change over to all snow from northwest to
southeast as a cold front moves through tonight, with snow
gradually tapering off by Friday afternoon and evening. Expect 1
to 3 inches of snow and minor ice accumulations. Both the Friday
morning and evening commutes will be impacted. See the latest
winter weather statement for details.
Issued at 840 PM EST Thu Jan 11 2018
Sfc cold front is quickly advancing into northwest portions of the
area this evening with a thin line of enhanced showers developing
along the stronger low level convergence from South Bend to
Lafayette. Temperatures to sharply drop with approach of this
front. Precipitation type/amounts obviously remain the primary
forecast issue for tonight. Arctic air mass will continue to
undercut warmer low level air this evening resulting in transition
to freezing rain late this evening and early overnight. The
approach of disjointed the upper level trough tonight should tend
to strengthen low level fgen fields over the next several hours,
with post-frontal 900-700 mb forcing becoming more prevalent in
the 04Z-10Z timeframe. Tightening low level thermal gradient in
response to strengthening low level fgen will be a challenge to
resolve in terms of warm layer magnitude and accompanying precip
types, with some slowing of tight thermal gradient for the
overnight hours across central/eastern portions of the forecast
area. There still appears to be a 2 to 4 hour window of freezing
rain potential before warm layer is eroded to more of a sleet
profile, with eventual changeover to snow.
Near term forecast profiles suggests arctic intrusion across
western half of area may marginally support some refreezing of
melted hydrometers aloft, that would be even more supportive of
sleet over freezing rain. Latest HRRR trends even a bit more
bullish in maintaining weak warm layer across the west through
most of the warm overnight hours that may prolong sleet a bit more
than previously indicated.
Uptick in precip/coverage intensity noted over past several hours
across western Kentucky/southern Illinois, although LLJ
orientation would tend to favor best narrow theta-e advective
forcing lifting north-northeast across eastern portions of the
forecast area during the early overnight. However, expecting
additional post sfc-frontal development overnight given the above
Previous forecast seems to have overall situation in hand, and
only tweaks that will be made at this time may be to slightly
prolong sleet mention across western half of the area overnight
before changeover to snow. Will maintain general distribution of
snow/ice accumulations, although may be seeing increasing
tendencies of a good deal of sleet overnight/early Friday morning
for many locations. Far east/southeast will be slow to changeover
to wintry mix overnight, with extreme southeast more in the after
.SHORT TERM...(This Evening through Friday)
Issued at 313 PM EST Thu Jan 11 2018
...Wintry Mix of freezing Rain, Sleet, and Snow Expected...
Headline Decision: Winter Weather Advisory for all counties in the
CWA. See the latest winter weather statement for details on timing,
Well we`ve finally reached decision time. Thankfully, models are
still in agreement with regards to keeping the axis of heaviest
precipitation to our east. That being said, we still have a
winter weather situation on our hands with the wintry mix expected
tonight, and the transition to snow by late Friday morning. Snow
will continue through early afternoon in the west, and by the
evening in the east. Lake effect snow will develop with north-
northeasterly winds in the wake of the system Friday afternoon
into the remainder of the period.
The real tricky aspect: We`ll only have a short window of freezing
rain/sleet, up to about 2-3 hours for most locations. How much of
this will be freezing rain before it turns to sleet/snow, and how
much ice? From latest model runs, thinking it will be brief enough
that we won`t have more than 0.10" of ice accumulation...and this is
probably a higher-end scenario because we will could see a greater
mix of sleet than what we have in the forecast.
Adding to concerns, the 12Z NAM develops a bullseye of QPF over
our east-central CWA in response to the enhanced forcing in the
right entrance region of a strengthening 300MB Jet between 9-15Z,
which stretches over northern Lower Michigan/Ontario/Quebec. The
enhanced upper level divergence works to tilt our trough
negatively and contract (strengthen) the frontal zone across our
area. Looking at a cross section through the frontal zone, we see
a brief period of decent instability/CSI. If it occurs, this will
favor the development of heavier bands of snow, which supports the
idea of the NAM`s increase in QPF (including the FWA area).
Overall, however the time the ingredients come together is pretty
short-lived, and don`t expect too much in the way of additional
ice accumulations beyond those forecasted at this point.
Furthermore, thinking it will largely be more snow/sleet than any
freezing rain at the times of greatest instability. In the end,
put 2-3" snow in the forecast for the eastern half of the advisory
given the potential.
Adding to concerns, observations of the impending cold front rapidly
progressing across IL shows a large temperature gradient and sharp
wind shift to the northwest. Temperatures across eastern IL are in
the upper 50s to around 60F, but behind the front they quickly drop
to around 15-20F...which brings the concern for a flash-freeze
scenario. With recent snowmelt/ongoing rain, this brings the slick
road concern to the forefront (regardless of how much freezing rain
Overall, expect only 1-3" of snow accumulation as forecast
soundings suggest riming and low snow ratios will probably cut
down snow totals. Icing will be less than 0.1" total.
If you must travel tonight or Friday...DRIVE SLOW ON ICE AND
.LONG TERM...(Friday Night through Thursday)
Issued at 412 PM EST Thu Jan 11 2018
...Winter is Back: Cold Air and Lake Effect...
Cold air filters in behind the strong low pressure system to our
east, bringing highs into the teens and 20s, and lows into the
single digits and teens through next week. As far as the pattern
aloft, we`ll see our broad upper level trough shift overhead, with
several embedded shortwaves pinwheeling through the flow into Sunday.
At the surface, strong arctic high pressure to our northwest (1044
mb high) will impinge southeastward into our area as low pressure
that caused our recent winter weather shifts out of the area. This
will give us a pretty decent north-northeast wind that will continue
into Saturday before shifting northwest and weakening Saturday
evening. With our arctic airmass sliding across the lake, we`ll
see some lake effect potential, with models appropriately
suggesting the development of a single band down the axis of Lake
Michigan through Saturday. While instability is favorable, with
delta theta e values between -3 and -5, the moisture is lacking.
Dewpoint depressions of 10-15C move in pretty rapidly,and
inversion heights sit at around 3000-5000 feet. Right now, have
around 1" or so of accumulation from late Friday afternoon into
Saturday, with other areas near the lakeshore even less than that.
We`ll see how things develop after the system exits our area
tomorrow to add more detail in. Things will wind down as winds
back around to the west southwest Sunday morning, we`ll see things
fall apart as they move onshore into our Michigan Counties, with
some of the Michigan areas seeing light accumulations.
Otherwise, Monday into Tuesday we`ll see an upper level low plummet
into the Great Lakes Region, with our CWA in the left-exit region of
a decent upper level Jet. We see decent 850-500mb qvector
convergence enter into our western CWA by Monday morning, shifting
eastward through the afternoon. Given the cold temps, this will be
snow. ECMWF/GFS still place the surface low center in slightly
different locations, but it is something to keep an eye for this
A northerly fetch will develop over Lake Michigan Wednesday into
Wednesday night as Monday/Tuesday`s surface low pressure system
exits the area and high pressure inches in from the northwest. This
will bring yet another single band set up to Lake Michigan, which
will impact the northwest portions of our forecast area until flow
becomes more west-northwesterly Thursday into Friday. Snow showers
will gradually taper off as an upper level ridge builds in.
.AVIATION...(For the 00Z TAFS through 00Z Friday Evening)
Issued at 702 PM EST Thu Jan 11 2018
Sfc cold front is approaching the IL/IN stateline at this hour
and should reach the KSBN vicinity around 03Z, and KFWA in the
05Z-06Z period. Temperature gradient with this front is very
strong and current temperatures in the mid to upper 50s will
rapidly cool into the upper 30s by late evening, and then into the
mid and upper 20s overnight. This strong arctic air mass
undercutting warmer air will lead to about a 2 to 3 hour window of
freezing rain potential, followed by period of sleet before
changing to snow late tonight from west to east. Timing of
previous TAFs with this precip type evolution still appears to be
very reasonable when considering current trends and no
significant changes were made for the 00Z TAFS. While the duration
of the freezing rain is expected to be small, some impressive
precip rates could occur during this short window. Accumulating
snow expected at terminals late tonight into Friday morning before
tapering at KFWA for the afternoon hours. Gusty south-southwest
pre-frontal winds will remain gusty behind the front from
northwest in strong cold advection through this period. IFR cigs
in vicinity of frontal boundary and just behind the frontal
boundary are expected, before transitioning to MVFR cigs deeper
into the cold air late tonight/Friday. However, periods of IFR/LIFR
conditions may hold through much of Friday morning due to vsby
restrictions in changeover to snow.
IN...Winter Weather Advisory from 3 AM to 7 PM EST Friday for INZ007-
Winter Weather Advisory until 1 PM EST /noon CST/ Friday for
MI...Winter Weather Advisory from 3 AM to 7 PM EST Friday for MIZ080-
Winter Weather Advisory until 1 PM EST Friday for MIZ077>079.
OH...Winter Weather Advisory from 3 AM to 7 PM EST Friday for OHZ001-
LM...Small Craft Advisory until 4 AM EST Saturday for LMZ043-046.
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Area Forecast Discussion
National Weather Service Louisville KY
1018 PM EST Thu Jan 11 2018
Issued at 1018 PM EST Thu Jan 11 2018
Another complex Ohio Valley winter storm, with a variety of model
solutions from which to choose.
A cold front extends from Michigan to the Wabash Valley to the lower
Mississippi Valley. This front is pushing eastward quickly. However,
the 18Z and 22Z RAP runs verified well with its 01Z placement, as
did the WRF-ARW. These models showed the band of heaviest snow, and
the best ice potential, within the warning that is already in
effect. They did suggest a slight eastward trend, however, with the
SREF plumes show a wide variance in snowfall totals, with an average
of about three inches at Louisville, roughly in line with the
The most recent NAM is showing a couple bands of heavy snow,
including one over the Blue Grass. However, the NAM has shown little
run-to-run consistency over its last 4 runs, leading to somewhat
less confidence in its solution. It actually had better consistency
5 to 7 runs ago, at which time it painted the snow farther west. The
CMC has told a similar story, with inconsistencies over its past
couple runs but better agreement in earlier runs, placing the band
So, going with the short term models that have verified well lately
and are showing a similar trend, have bumped up snowfall amounts in
the Blue Grass and have pushed the warning one more tier of counties
eastward. This was coordinated with ILN and JKL. Kept the ice
amounts and placement the same for now.
Another thing to consider here is the wind. Northwest and north
winds will be in the 10 to 20 mph range, with gusts to 30 mph Friday
afternoon and evening. Ice covered branches will be vulnerable to
such winds, and blowing snow may become a problem in the evening.
Wind chills will fall into the teens by evening.
Nothing is set in stone with this forecast, and it is likely that
further alterations will be made by the overnight shift as new data
.Short Term...(Tonight through Friday night)
Issued at 255 PM EST Thu Jan 11 2018
...Wintry Precipitation Will Impact Travel Friday and Friday Night...
Deep southerly flow continues to feed unseasonably warm and humid
air into the Ohio Valley. Weak isentropic lift touched off scattered
showers earlier, but we are now mainly dry. Temps generally in the
60s this afternoon, and will initially be slow to fall this evening.
Winter storm is still poised to have substantial impacts Friday into
Friday night. Main challenges are timing of the transitions to
freezing rain and eventually to snow, and amounts of ice and snow
Still expect the transition to freezing rain during the morning
along and west of Interstate 65 as the cold low-level air undercuts
the warm SW flow aloft. The duration of the freezing rain in this
area is longer than previously advertised, and opens a wide window
to pick up a quarter inch of ice accumulation. As the Arctic air
heads farther east, low pressure over the Tennessee Valley will hang
up the cold front, allowing the cold air aloft to catch up, and
narrowing the window for freezing rain as the transition happens in
the Bluegrass late in the afternoon.
Should be mostly snow by late afternoon as the upper low swings
across Kentucky, with a potential deformation band setting up
somewhere over north central Kentucky or southern Indiana. Snow
totals of 2-4 inches are expected along and north of the Western
Kentucky and Bluegrass Parkways, with the majority of that area
trending toward the low end but locally exceeding 4 inches where the
heavier band sets up.
Winter Storm Warning has been posted west of I-65, and one tier of
counties farther east. To the east of the warning area, a Winter
Weather Advisory has been posted. Gave some thought to expanding the
warning into the Bluegrass, as there is an outside shot of the
deformation band setting up that far east, especially if the weaker
and faster ECMWF is right. However, this is also where uncertainty
remains the highest, as loss of ice aloft will cut into snow amounts
as well as QPF, especially southward toward Lake Cumberland.
While there are still question marks about precip types and amounts,
impacts to travel are likely along and west of I-65 during the
morning commute, and a virtual certainty throughout the area by
.Long Term...(Saturday through Thursday)
Issued at 305 PM EST Thu Jan 11 2018
Arctic high pressure builds in on Saturday, plunging the Ohio Valley
back into the deep freeze. Clipper system swings through on Monday,
and could bring minor snow accumulations. Very cold temps through
the period, with highs below freezing. Coldest temps Mon night and
Tue night, when snow cover may allow temps to radiate down close to
zero. Sub-zero wind chills likely those two mornings.
.Aviation...(00Z TAF Issuance)
Issued at 649 PM EST Thu Jan 11 2018
A line of scattered showers has pushed east of HNB this evening, so
dry conditions prevail for the moment at all TAF sites. HNB has
dropped to the Fuel Alternate MVFR range, and ceilings will
gradually lower to MVFR tonight and IFR during the Friday morning
hours. Timing on the IFR is around 02z for HNB, 08-09z for SDF/BWG,
and 13z for LEX. IFR is then likely through much of Friday with
As colder air pours into the region Friday morning and afternoon, a
changeover to wintry precip is expected. FZRA is possible at HNB as
early as 10z and 14z at SDF. As the atmosphere continues to cool,
sleet will mix in with freezing rain. Sleet should become more
common from west to east between 14-20z. Finally, a changeover to
all snow is likely from west to east between 16-22z. By midday,
icing could start to cause issues on pavement as well as elevated
surfaces and power lines. The worst impacts are expected during the
afternoon and evening hours, when the bulk of the wintry weather
will occur. Storm total ice accumulations of 0.10-0.25 inches are
expected, followed by 2-4 inches of snowfall. A couple of the
northern TAF sites could be impacted by a localized heavier band of
snow that results in more than 4 inches.
Ceilings : High
Winds : High
Precip Type : Moderate
IN...Winter Storm Warning from 4 AM EST /3 AM CST/ Friday to 1 AM EST
/midnight CST/ Saturday for INZ076>079-083-084-089>092.
KY...Winter Storm Warning from 4 AM EST /3 AM CST/ Friday to 1 AM EST
/midnight CST/ Saturday for KYZ023>035-038-039-045-046-053-
Winter Weather Advisory from 10 AM EST /9 AM CST/ Friday to 7 AM
EST /6 AM CST/ Saturday for KYZ036-037-040>043-047>049-
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
821 PM CST Thu Jan 11 2018
821 PM CST
In coordination with DVN, ILX, and MKX have opted to cancel the
winter wx advisory early. No additional measurable precipitation
is expected tonight roughly north and west of I-55. There had been
concern about a flash freeze and "black ice" forming this evening,
however have not had any reports of this yet and after spending
nearly 2 hours below freezing here at the WFO, pavement is mostly
dry with just a few moist patches that have yet to freeze. The
recent warm spell where dewpoints rose into the mid-upper 50s
likely sent pavement temps well into the 40s and lower 50s and
current pavement temperatures in Chicago and northwest IN remain
in the 40s, even in the upper 40s on the warmest sensors in
Chicago. By the time the pavement temps cool to freezing, it is
likely they will have had ample time to mostly dry out. Could
still eventually be some icy spots develop tonight, mainly on
bridges and overpasses, but with no measurable precip expected,
felt comfortable canceling the advisory early.
Farther southeast, mainly to the east of I-57, a secondary surge
of precip is expected to light north into the area late this
evening and especially overnight. Forecast soundings suggest that
the bulk of this precipitation could fall as sleet with some
freezing rain or snow possible. Did add Livingston County to this
advisory grouping and kept them going until 1 am as the HRRR still
shows SE Livingston being clipped by some precip late this
evening. Snow/sleet combination could accumulate up to a quarter
to a half inch over NW IN and adjacent areas of EC IL, with a
glaze of up to a tenth of an inch possible. As alluded to earlier,
pavement temps remain well above freezing, which could limit the
impacts to travel from this precip, especially the freezing rain,
but eventually temps should cool enough for freezing/frozen precip
to stick on roadways especially late tonight.
Overall, going forecast is in good shape and no big changes needed
111 PM CST
Messaging for today`s weather continues to center on a window of
mixed precipitation this afternoon across north central Illinois,
getting close to the Chicago metro area, a dramatic drop in
temperatures creating hazardous road conditions due to wet roads,
then a resurgence of mixed precipitation in the form of snow and
sleet across northwest Indiana.
Very mild conditions are currently in place with several bands of
rain occurring. A well defined upper level low/shortwave is tracking
through Iowa and this wave is driving a more significant band of
precipitation. It is this second wave that will present concerns for
areas across north central Illinois this afternoon as a strong cold
front comes crashing in.
Upstream observations depict a rapid transition to wintry
precipitation, with some sites headed to freezing rain, others
quickly heading to sleet snow. Expect a similar situation in
parts of our area as such strong low level cooling would likely
transition from a window of freezing precip to sleet. Areas
northwest of the Chicago area will have the cold air arrive in
time this afternoon to present the highest concern for mixed
precipitation. The concern begins after about 3 pm across north
central Illinois through about early evening, which would present
concern during busy travel times. Once the cold air arrives in the
Chicago metro this evening, there may not be much precipitation
left. But with damp/wet conditions today and upstream locations
already reporting significant travel problems just from the rapid
freeze of the wet surfaces, this may end up being the more
significant concern for the Chicago area. The period of highest
concern for metro area is after 6-7pm for several hours. Strong
pressure rises behind the front will lead to blustery northwest
winds which will get to 30-35 mph. Wind chill readings this
evening will correspondingly plummet to the single digits through
the evening, and it is likely temperature trends are too slow
with the speed of the drop.
Areas southeast of I-57 stand the best chance for what will largely
be sleet to snow overnight where accumulations still look on track.
QPF numbers are a tad higher over northwest Indiana, peaking
overnight as the next wave of moisture still well south of the area
but embedded in the southwest flow ahead of the upper trough shifts
into Indiana, where sleet and snow accumulations do still appear
likely. Some of this precip may sneak back into northeast Illinois
but it would be light. Temperatures continue to fall and will end
the night with lows in the lower teens toward RFD to near 20
across northwest Indiana, and wind chills in the single digits to
Cold north winds will transition the area to lake effect concerns,
which we will address in the long term discussion.
234 PM CST
Friday night through Thursday...
Main forecast concerns include lake effect snow Friday evening
through Saturday afternoon... next round of light snow with
clipper type system Sunday evening through Monday... and return to
below average temps through much of the period.
Expect period of light to perhaps locally moderate lake effect snow
to develop Friday afternoon and continue into Saturday afternoon
before shifting off to the east of the forecast area by evening.
Expect a transitory and evolutionary nature of the lake effect
snow... beginning as a wind parallel banded event... with then
perhaps a more dominant band setting up in the north flow
overnight Friday into Saturday morning for several hours... before
evolving back to a more multiple banded event.
Model guidance continues to oscillate a bit on the boundary layer
wind orientation with this event... which is of course critical
to where the snow will set up. Latest runs of the NAM/3 km NAM
nest trending slightly more northerly in low level wind direction
(rather then NNE) which would impact more just the eastern
portions of Cook and Will Counties along with Indiana. Expect this
at the onset of the event... when the lake surface to 850 mb temp
difference exceeds 15-17 deg C... which increases to 20 by Friday
evening. Limiting factor in lake snow band development however
will be low inversion heights... around 4500 ft through Friday
Most impressive snow of the episode appears possible overnight
Friday into Saturday morning as thermal instability peaks and
inversion heights rise slightly. During this time model low level
wind fields suggesting some along shore/coastal convergence
setting up which may enable a more dominant band. By this
evolution of the event it would be Lake and Porter Counties in
Indiana where concern would be greatest. May see accumulations of
a few inches from this band with a moderate snowfall rate at
Inversion height is lowering again somewhat by Saturday afternoon
with boundary layer winds turning more west of north. With this
expect nature of the lake effect snow to transition back to more of
a wind parallel banded (and hence lighter snowfall) with the snow
at this time all in northwest Indiana and on an eastward moving
All the above being said... conditions and guidance will be
monitored closely the next 24-36 hours since very subtle changes in
the low level winds will play a key role in where snow falls and
hence who gets it. Will maintain high pops and snow accumulations of
1-3 inches with this event through Saturday evening... with some
isolated 4-5 inch amounts possible under where any more dominant
band sets up... in Lake and Porter Counties in Indiana. This
forecast will continue to be refined however as the event draws
Expect lake effect snow to shift east of Porter County by Saturday
evening. A brisk north wind will contribute to blowing and drifting
snow throughout this episode and help cause sharply reduced
visibilities at times. Hence significant travel impacts can be
Progressive upper pattern early next week as large trough/upper low
rotates into the western Great Lakes Monday. Low then cuts off
Tuesday however in response to amplifying pattern with strong
height rises over the Atlantic seaboard. This maintains broad
cyclonic flow across the region through mid week.
Fast moving clipper like system moves quickly southeast into the
area Sunday evening via evolving northwest flow aloft. Expect broad
area of light snow along/ahead of the wave with strong divergence
aloft given favorable upper jet positioning helping produce broad
ascent. Will maintain high pops with accumulating snow a good bet
at this point.
As surface low stalls over lower Michigan by Monday evening in
response to evolving cut off low and system becoming vertically
stacked... the local area comes under an extended period of broad
cyclonic flow. The potential for a lake enhanced snow episode
then comes into the picture... especially Tuesday given continued
favorable thermal instability (lake surface to 850 mb temp
difference remaining 18-20 deg C) and a disappearing capping
inversion. Considerable differences in the low level wind fields
between the models however raises considerable uncertainty as to
what degree this may take place and if it does, exactly where.
Hence will need to continue to closely monitor this period. In any
event a return to below average temperatures is certain for next
week with highs mainly in the teens early in the week...
moderating to the 20s by Thursday.
For the 00Z TAFs...
608 pm...Forecast concerns include freezing drizzle this
evening... light snow/flurries early Friday morning and then lake
effect snow showers Friday afternoon into Friday evening.
The back edge of light rain will move northeast of ord/mdw in the
next hour or so with the chance of a little sleet as colder air
continues to spread into the area. It appears this light rain will
end prior to air temperatures falling below freezing. However...
further southeast at gyy...light rain or rain showers may continue
through the mid/late evening with air temperatures below freezing
with freezing rain possible there. Elsewhere...chances for
prevailing precip look low and have maintained tempo freezing
drizzle but confidence for precipitation west of gyy is low.
Short term guidance is showing a band of light snow or flurries
developing over northeast IL prior to sunrise and while confidence
for exactly how strong this precip may be is low...added flurries
for a few hours toward sunrise to account for this potential.
Lake effect snow is expected to develop Friday morning and
continue into Friday night but there remains uncertainty regarding
how far west and potentially into northeast IL...this lake effect
snow may move. For now have kept ord dry with prob mention at mdw
and tempo mention at gyy.
Gusty west/northwest winds will slowly turn more north/northwest
tonight and then northerly Friday morning with gusts increasing
toward 30kts Friday morning. Wind directions may favor a more
north/northeast direction later Friday morning into Friday
afternoon but confidence for specific wind directions is low.
Winds are expected to slowly turn back north/northwest Friday
308 PM CST
A very strong cold front will move west to east across Lake
Michigan late this afternoon/early evening... with a rapid wind
shift and increase in wind speeds to gale force by early to mid
evening. Northwest gales become North overnight and continue
Friday and Friday night as strong low pressure moves east into the
Appalachians and strong high pressure builds into the upper
Midwest by Saturday morning.
The ridge of high pressure will move across the lake Sunday... as
a clipper type low pressure area then moves quickly across the
southern Great Lakes Monday and slows over the eastern Great Lakes
IL...Winter Weather Advisory...ILZ023-ILZ033-ILZ039 until 6 AM Friday.
Winter Weather Advisory...ILZ032 until 1 AM Friday.
IN...Winter Weather Advisory...INZ001-INZ002-INZ010-INZ011-INZ019
until 6 AM Friday.
LM...Gale Warning...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745...3 AM
Friday to 6 AM Saturday.
Small Craft Advisory...nearshore waters
until 3 AM Friday.
Small Craft Advisory...LMZ740-LMZ741-LMZ742...6 AM Saturday to 3
Small Craft Advisory...LMZ743-LMZ744-LMZ745...6 AM Saturday to 6
Gale Warning...LMZ777-LMZ779 until 3 AM Saturday.
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Area Forecast Discussion
National Weather Service Shreveport LA
928 PM CST Thu Jan 11 2018
Very strong cold air advection in the wake of the cold front now
which extends from near ELD to just west of IER as of 03z. Most of
the more moderate rainfall is out ahead of the frontal boundary
across portions of South Central Arkansas into North Central and
Northeast Louisiana but post frontal light rain continued to be
observed across portions of Northwest Louisiana into Southwest
Arkansas. Calling around to our west and northwest, it does not
appear that echoes near and to the west of TYR are making it to
the ground as ceilings ranging from near 8-12kft along the back
edge of the cloud cover to the west of TYR with the ceiling at TYR
coming up rapidly.
Newest 00z runs including the latest run of the HRRR continue to
be in good agreement with the center of the trough extending from
near NE OK into NW LA and SE TX by 06z this evening and near the
Tenn and Lower Miss River Valley by 12z Fri morning. Area of mid
level lift in association with the left front quadrant of 90kt
upper jet along the back side of the trough of low pressure should
continue to produce enough forcing for some precipitation to
continue through the remainder of the night but mainly across
Northern Louisiana into Southern Arkansas.
Hourly trends were not keeping up with the rapid post frontal CAA
in place so had to lower temperatures a few degrees for the
overnight period which resulted in needing to make some necessary
changes to precip type. Transitioned from rain to light freezing
rain/sleet and/or light snow a little quicker as well in addition
to needing to add the mention of light freezing rain to our
extreme eastern parishes but this would be closer to sunrise or
shortly thereafter if the temperature can get to freezing before
the precipitation exits the region.
Contemplated hoisting a Winter Weather Advisory but the window of
opportunity is very brief if at all before the precip exits our
region to the east. Did make the change from no accumulation to
little if any accumulation expected for the above mentioned areas
and we will continue to monitor the transition when it happens. If
intensities pick up under this strong CAA pattern, then a quick
Winter Weather Advisory may be necessary during the overnight
Updated forecast package already sent...13.
.PREV DISCUSSION... /issued 521 PM CST Thu Jan 11 2018/
TSRA conditions expected across MLU/ELD in conjunction with a
cold front that is moving east across the region. Northwest winds
to increase to 25 to 30 knots with higher gusts across
TYR/GGG/TXK/SHV terminal sites with slightly lower wind speeds
elsewhere. Otherwise, -SN conditions possible from 12/08Z-12/12Z
across SHV/ELD/MLU/TXK terminal sites. Otherwise, winds to
gradually decrease on Friday. /05/
.PRELIMINARY POINT TEMPS/POPS...
SHV 28 44 27 42 / 50 0 0 0
MLU 33 42 25 40 / 70 20 0 0
DEQ 24 42 22 40 / 20 0 0 0
TXK 26 42 24 39 / 30 0 0 0
ELD 30 42 23 39 / 60 10 0 0
TYR 26 44 26 42 / 20 0 0 0
GGG 27 45 25 42 / 20 0 0 0
LFK 29 47 27 46 / 20 0 0 0
AR...Lake Wind Advisory until noon CST Friday for ARZ050-051-059>061-
LA...Lake Wind Advisory until noon CST Friday for LAZ001>006-010>014-
OK...Lake Wind Advisory until noon CST Friday for OKZ077.
TX...Lake Wind Advisory until noon CST Friday for TXZ096-097-108>112-
For frequently asked questions about the Area Forecast Discussion