Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/11/16
Area Forecast Discussion
National Weather Service La Crosse WI
911 PM CST Sat Dec 10 2016
Issued at 911 PM CST Sat Dec 10 2016
Well...here we are with the event underway and some questions
still remain regarding snow amounts overnight. Overall, am
starting to get a little nervous that our snowfall amounts may be
a touch too high across southern areas and thus a little too low
near the I-90 corridor. Radar trends the past 2 hours are telling,
with a pronounced narrow but intense frontogenetic snow band laid
out across southern MN and WI, and really stretching back into
western SD as well. Recent RAP trends seem to have caught onto
this feature, most pronounced in the 700-500mb layer, which also
just happens to be completely in the DGZ, supporting the growth of
dendrites and thus some pretty high snow-liquid ratios. Per
reports/observations under this band, snow ratios are generally
20-25+ to 1 (not surprising at all with a 300+mb deep DGZ), while
outside of it where there is minimal lift through the DGZ, ratios
are much closer to 12 to 1. That makes for a very tough forecast
heading through the night, not only with regard to snowfall
amounts but also placement of the narrow FGEN band, especially
considering some spots under that band have already picked up 2-4"
of fluffy snow the past 6 hours.
Hard to ignore reality and short term model trends which agree
that the FGEN axis may well end up a little farther north than
earlier thought. This is especially true with recent RAP runs,
showing the elongated FGEN axis pretty much stationary as a subtle
lead 700mb wave passes the next few hours, followed by the more
pronounced upper feature toward morning, with the latter also
helping induce a nice deformation field bisecting the CWA near the
I-90 corridor. That setup does leave some question about how far
south additional precip redevelopment will occur, especially too
far south of the FGEN axis (as well as areas north of I-94 on the
downward branch side...also fighting some dry air). All told, not
ready to bite on the need for any upgrades to the current advisory
area farther north, but it may be needed with little advance
notice pending trends overnight.
Ahhh...the joys of winter weather forecasting!
.SHORT TERM...(This evening through Monday night)
Issued at 220 PM CST Sat Dec 10 2016
It now appears that the southern parts of the forecast area will
have a decent shot of getting some heavier snow and plan to
upgrade to a warning to handle this. The 10.12Z models have come
in with a slightly stronger short wave trough to cross the area as
it deepens once it crosses the northern Rockies tonight. This
allows the frontogenesis zone to become stronger, especially in
the 06Z to 12Z time frame tonight in the 750-600 mb layer. With
this stronger forcing signal, the resulting qpf amounts and snow
amounts will be bumped up and it now appears that 8 inches of snow
could fall in a 24 hour period. In addition, the surface low looks
like it will take a more northeast track Sunday which could linger
some light deformation snows a little longer over southwest
Wisconsin. This may not add all that much snow as the qpf amounts
look to be pretty light in the deformation zone, but again, could
be enough to bump some areas into the warning category. Thus will
take all of our northeast Iowa counties along with the 3 southwest
Wisconsin counties and upgrade to a winter storm warning through
Sunday. Otherwise, very little overall change in the expected
conditions for the remainder of the area. Snowfall amounts of 6 to
8 inches north of the warning up to Interstate 94 still look on
track as does the 4 to 6 inches for north central Wisconsin.
There may also have to be some adjustments made on the back side
of the system to the end times for the Wisconsin part of the
advisory. It looks like the snow could be winding down by late
afternoon or early in the evening, which could necessitate ending
the advisory a little sooner. There is also a signal on the back
side of the system of a potential loss of ice before the
precipitation ends. However, think the models have a bit of a bias
toward taking the ice out too fast as systems are pulling away
from the region and will stay with just snow for now.
Cold, arctic air is still on track to spill into the Upper
Midwest early next week. The arctic cold front will move through
the region Monday afternoon and evening. Another pacific short
wave trough looks like it will zip across the region in
conjunction with the cold front. This wave looks to be strong
enough to generate a short period of weak to moderate pv advection
in the 500-300 mb layer. The QG convergence looks to be weak but
extend through a deep layer from 1000 up to 300 mb. This may be
enough to squeeze out some light snow as the cold air moves in and
will carry a small 20 to 30 percent of snow Monday afternoon and
evening. Temperatures Monday night look to bottom out in the
single digits above and below zero. Wind chill values will become
a concern with values dropping into the single digits and teens
below zero. However, it does not look like an advisory would be
needed at this time.
.LONG TERM...(Tuesday through Saturday)
Issued at 220 PM CST Sat Dec 10 2016
The cold air will remain for much of the week with some slow
moderation expected by the end of the week into the upcoming
weekend. Wind chill advisories may be needed Tuesday
night/Wednesday morning across north central Wisconsin and again
Wednesday night/Thursday morning for much of the area. Overnight
lows during this period generally look to be in the single digits
below zero with west winds of 5 to 15 mph. The next chance for
snow will come for the end of the week into the weekend as the
arctic high pressure moves off to the east. The models are
currently showing a positive tilt long wave trough moving across
the Rockies with southwest flow and embedded short wave troughs
over the Midwest. Decent agreement that a surface low in the
pattern will track between the local area and the Ohio River
Valley into the eastern Great Lakes with the potential to drop
some more snow on the area.
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 530 PM CST Sat Dec 10 2016
Periods of snow have begun across the area and will continue
overnight and into Sunday, with the heaviest period of snow still
expected later tonight into Sunday morning. Overall, IFR
conditions will prevail (especially visibility), though a few
periods of LIFR are possible during any bouts of heavier snowfall.
It still appears that RST and LSE will pick up between 5 and 8
inches of snow by the time it tapers off Sunday afternoon, with
the snow initially of a lighter, more fluffy variety gradually
replaced by a slightly wetter snow with time. As the snow departs
(or at least lightens up in intensity) Sunday afternoon and
evening, widespread IFR ceilings appear probable, with even a
small risk for a little freezing drizzle, though confidence in
that is very low.
WI...Winter Storm Warning until 6 PM CST Sunday for WIZ054-055-061.
Winter Weather Advisory until 9 PM CST Sunday for WIZ032>034-
Winter Weather Advisory until 9 PM CST Sunday for WIZ017-029.
MN...Winter Weather Advisory until 6 PM CST Sunday for MNZ079-086>088-
IA...Winter Storm Warning until 6 PM CST Sunday for IAZ008>011-018-
Area Forecast Discussion...UPDATED
National Weather Service BROWNSVILLE TX
638 PM CST Sat Dec 10 2016
.DISCUSSION...Updated for latest aviation discussion below.
.AVIATION...The 00z BRO sounding shows a pretty saturated airmass
in place this evening with a fairly strong low level inversion
persisting. This is resulting in a mixture of VFR/MVFR conditions
around the RGV early this evening. The latest NAM forecast
soundings maintains the saturated low level inversion in place
over the region through the night which will reduce the ceilings
back down to IFR levels. Some fog has started to form over the
northern and western counties and as the surface winds start to
slacken later tonight expect this fog to progress further south
lowering vsbys for the RGV airports. The low level wind flow
tomorrow will finally shift around from the south which will
increase the WAA and the low level mixing allowing for the
ceilings/vsbys to improve back up to VFR levels.
.PREV DISCUSSION... /issued 250 PM CST Sat Dec 10 2016/
SHORT TERM (Now through Sunday night): Zonal flow aloft will
dominate Deep South Texas, and indeed, most of the CONUS, through
the short-term period. After one more cool night, southerly winds
return on Sunday for a quick warm-up.
For the near-term, through 00Z, trimmed back PoP`s per recent radar
trends. Picking up some light (15 dBZ) echoes near the Lower Valley
and coast...in association with convergence into the coastal
trough...but have yet to see any evidence of this reaching the
ground. Mid-Lower Valley locations warmed up a few degrees more
than expected today, when the sun shone for a couple hours, as per
previous AFD update.
Forecast trend overall has remained the same, but 12Z runs of NAM
and GFS showing some timing differences with regard to SSE flow
setting up overnight. Both models show NW winds of past couple of
days finally backing around to light SW this evening, which allows
temps to actually rise a few degrees through the night. However,
GFS brings the more moist flow back inland around 03-06Z, whereas
the NAM is about 6 hours slower...and shows a more sudden jump in
dewpoints mid-morning on Sunday. Latest RUC and HRRR lend more
support to the NAM solution, so based on that, and the fact that
it`s capturing current temps/dewpoints better, will lean pretty
heavily on it for the forecast.
With the slower moisture return, have backed off some on fog
potential tonight. Will still word patchy coverage over most areas,
but delay onset until after 06Z. Can`t rule out some isolated light
rain overnight along the coast, but all other areas should stay dry.
Moving into Sunday, the spring-like warmup kicks in, especially once
a weak trough aloft passes during the morning, swinging upper winds
to more WNW. H85 winds turn SW, ahead of a front moving into the TX
Panhandle. Depth of moisture will trend down from its current 700-
mb level down to 850mb or perhaps even lower. Upshot will be more
sun with temps reaching the low 80s in the mid-Valley with mid-upr
70`s elsewhere. Dewpoint in Brownsville reaches 70F by late
afternoon, so the muggy feel will return. Low temps for early
Monday looked good and so were retained...from near 60 NW to near 70
SE. MOS guidance hitting fog potential pretty hard for late
tomorrow night as well. Will introduce areas of fog across all land
areas and the Laguna Madre for now. Dense fog potential would seem
to be better over the NW counties where winds will die off more so
than nearer the coast.
Continued 8 to 10 second swell period with a still brisk east to
northeast onshore flow has continued tidal run-up to the dune line
at high tide this afternoon per webcams on S. Padre Island. Don`t
see a need to extend the Coastal Flood Statement at this juncture as
water levels (both observed and residual vs. prediction) are running
a bit lower than this time yesterday. Next high tide will be minor,
and by then winds offshore should have shifted to SE, which should
calm down the swell.
LONG TERM (Monday through Saturday): The lastest GFS/ECMWF are
in better agreement through the forecast period. A nearly zonal
flow aloft will prevail through much of the week. Southerly flow
at the surface will allow moisture to increase across the area and
warming temperatures through mid week. A cold front will move
into central Texas on Monday but will stall well north of the
area. Another cold front will approach Deep South Texas Wednesday
night before stalling near the northern Ranchlands on Thursday. By
late week, a sharp 500 mb short wave trough will dive south
through the Pacific Northwest and lift across the Great Basin.
This will result in mid level flow becoming southwest over the
Above normal temperatures will prevail Monday through Wednesday.
High temperatures each day will be in the 80s with overnight low
temperatures generally be in the 60s. Slight chance of rain will
develop Wednesday night through Thursday night with increasing cloud
cover as a cold front approaches and stalls across area.
Temperatures will recover Friday and Saturday as southeast winds
return and push warm Gulf air back over the area.
MARINE (Now through Sunday): Conditions at Buoy 020 as of 150pm
CST were reported as E winds of 18G21KT, with seas near 7 ft.
Extended SCA for the outer Gulf Waters only through 9pm. Winds veer
SE by this evening, but stay at around 16-20 knots. SCA may need to
be extended, again for the outer waters, into Sunday morning as
latest wave guidance keeps seas right around 7 ft. out there. SCEC
likely for the nearer-shore waters. Conditions on the Laguna Madre
should remain relatively favorable with some moderate southerly
breezes by Sunday afternoon. Seas on the Gulf finally subside to
around 5 ft. by later Sunday night, though moderate S winds may
Monday through Thursday...Broad surface high pressure across
the Gulf will support light to moderate south to southeast winds and
low to moderate seas through the period. Isolated to scattered
showers are expected across the coastal waters Wednesday night into
Thursday as a front approaches and stalls across the area.
GM...Small Craft Advisory until 9 PM CST this evening for GMZ170-175.
This product is also available on the web at:
Area Forecast Discussion
National Weather Service Wilmington OH
925 PM EST Sat Dec 10 2016
A low pressure system will eject northeast from the Plains into
the Great Lakes Sunday into Monday. Snow will develop ahead of
this system tonight and then a mix of rain and snow is expected
Sunday before precipitation ends early Monday. High pressure
returns late Monday.
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Not many changes to current forecast as widespread WAA/ isentropic
upglide has allowed a band of snow to move into our northern zones
with a couple of sites already reporting. The main question is
that dry air remains in the low levels and will take a little bit
of time to saturate as the band heads north. Latest HRRR run then
has snow filling back in across the northern zones early Sunday
morning. Latest run of the NAM also hints at this while
advertising a sharp cut off. Have kept forecast advertising
accumulating snow along and north of Interstate 70. New zones out.
Still have a few flurries flying across the CWA this afternoon,
particularly across west central Ohio and east-central Indiana. No
accumulation is expected from the flurries through sunset.
Focus then shifts to the next system which will begin to affect
portions of the CWA tonight. Low pressure will eject out of the
Rockies and into the central Plains tonight. And as high pressure
over the Ohio Valley moves into the Mid-Atlantic, a return flow
will set up, allowing the low levels to moisten up and warm
advection will also start to kick in and produce more clouds.
Isentropic lift will also promote the development of snow,
although much of our guidance suggest a fairly sharp southern cut
off where accumulating snow will occur. At this point in time,
the highest confidence in accumulating snow looks to be just north
of the Interstate 70 corridor, favoring a GFE/SREFS blend.
Highest snowfall accumulations are forecast to reside across our
northern most counties, namely Auglaize, Mercer and Hardin and a
Winter Weather Advisory has been issued. Further south of this
area toward the Interstate 70 corridor, snowfall accumulations are
expected to remain below Advisory criteria but enough to
potentially result in slick travel late tonight/early Sunday.
.SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY/...
Snow continues Sunday morning mainly across the far northern
portion of the CWA, but precipitation will overspread the entire
area during the afternoon/evening as a favorable jet develops
over the CWA ahead of low pressure which will move into the upper
Midwest by days end. In addition to supporting precipitation, the
southwesterly jet will also result in the rain/snow line shifting
north through the day where much of the CWA is likely to
experience rain by late afternoon, except for perhaps the extreme
northern counties within the Advisory area.
Surface temperatures will likely continue to rise into the
overnight hours, with rain being the primary p-type across the
CWA. Then, as low pressure moves through the Great Lakes late Sunday
night, this will allow a cold front to move through from the west,
ending the precipitation chances Monday morning. The remainder of
Monday dries out and clouds may even break for some sunshine later
in the day.
.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
With the departing frontal system leaving the area becoming under
the influence of a shallow ridge over the southern CONUS...but low
level moisture will linger for Monday night. So despite Cold air
advection over especially the northern half of the forecast
area,there will only be occasional breaks in cloud cover. There will
be a pretty tight gradient of temperatures on especially Tuesday
into Tuesday night with the passage of the upper low over central
and then SE Ontario, with the weak ridging in the south. The only
potential for precipitation will come in the form of light snow
showers in NW flow with the passage of the upper low, but limited
More significant Cold advection and dry conditions will continue the
below normal temperatures through the work week, with single digit
overnight lows Wednesday night and Thursday night. For Friday into
Saturday, moisture returns to the region with the passage of
another shortwave, with precipitation onset beginning as snow and
then changing over to rain during the day on Saturday.
.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
Light returns are moving across the western taf sites this evening
with no snow being reported. There are some reports of snow in the
KIND area. Looking at MPING reports are sparse. Widespread WAA
lift will continue this evening with most of the snow remaining
north of the TAF sites. Looking at forecast soundings KDAY and
KCMH/KLCK have the greatest chance of observing snow with KCVG/
KLUK likely remaining south of the snow. As this initial band of
snow heads northeast it will push north of all the TAF sites by
12z. Looking at high res guidance shows all TAF sites remaining
VFR with this initial band. In any heavier snow bands that due
form reductions in visibilities will be possible.
Sunday afternoon surface low pressure will head northeast towards
the Great Lakes with another band of precipitation moving in from
the west. Looking at GFS and NAM forecast soundings thermal
profiles quickly warm Saturday afternoon with precipitation
starting right on the border of the rain/ snow line across the
north. The precipitation will then continue into early Monday
morning. Cigs and visibilities will then start to fall Sunday
OUTLOOK...MVFR/IFR ceilings and visibilities possible Sunday
night into Monday morning.
OH...Winter Weather Advisory until 6 PM EST Sunday for OHZ026-034-
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
859 PM CST Sat Dec 10 2016
855 PM CST
No changes planned to forecast or headlines at this time, though
will be making some minimal changes to near term pops based on
Initial region of warm-advection forced light snow overspread the
region late this afternoon as anticipated, with heavier (mainly
moderate) snowfall within a region of frontogenetically-forced
northwest-southeast bands. Recent radar trends show this banding
has weakened and lifted northeast across southeast WI, Lake
Michigan and northern IN at this time. However, 00Z DVN sounding
depicts a fairly deeply saturated column with nice veering wind
profile signature associated with strong warm-advection. Within
this region of persistent upglide, latest high-res guidance
continues to support regeneration of transient f-gen banding which
should continue to result in periods of moderate or greater
intensity snowfall. While we`re currently in a lull in radar
returns especially across the western parts of the cwa, stronger
returns are blossoming across portions of eastern IA, and would
expect an uptick in coverage and intensity later this
evening/overnight as forcing and moisture advection persist. With
the first band working to moisten initially dry low-levels, will
likely see additional bands more efficient in lowering vis and
producing heavier snow, and latest RAP soundings suggest a decent
period of deeper dendritic growth after 05-06Z.
Initial bands of snow have produced 2+" of new snow in many spots
across the warning area, which is in line with going forecast
amounts through 06Z. Thus not inclined to make any big changes at
this time, with expected redevelopment and increase in snow
coverage and intensity later tonight.
309 PM CST
Through Sunday Night...
The main forecast concerns with the winter storm continue to
revolve around total snow amounts, as well as the extent of the
mixing/changing to rain in my far south later Sunday into Sunday
Not much has changed in the overall thinking in terms of snow
amounts, with only minor tweaks made from the updated snow
amounts from this morning. Generally this will continue to result
in the highest totals of generally 8 to 12 inches north of I-80.
Amounts still look to tapper off into the 1 to 4 inch range over
my far southern counties (Livingston, Ford, Iroquois and Benton
counties). As a result, no changes are planned to the current
An impressive band of moderate snow continues to develop east-
northeastward over eastern Iowa and western Illinois in
association with an initial band of frontogenesis along the
leading edge of the increasing isentropic upglide (warm air
advection). This area of snow should begin to result in a quick
onset of moderate snow from west to east over the area within the
next few hours. This could result in up to a quick inch of snow
through early this evening, especially over north central
Illinois. Once this snow onsets, it appears that it will continue
at times through the night and into Sunday morning over northern
Illinois and northwestern Indiana as warm air advection continues.
Mesoscale banding will also continue to be possible over northern
Illinois overnight as steep mid-level lapse rates remain in place
above 650 MB. As a result, snow amounts tonight alone could be in
the 3 to 6 inch range, especially north of I-80 where higher
ratios of around 15 to 1 will be likely.
Periods of moderate snow look to continue Sunday morning, though
there could end up being a break, or a period of lighter snow
during the morning, before another period of wetter snow onsets in
the afternoon in association with the approach of the mid-level
disturbance. This could again result in periods of moderate, to
possibly at times heavy snow over the area into early Sunday
evening. Temperatures still could get warm enough in my far south
for a mix or transition to a period of rain late Sunday into the
evening, though it appears areas farther north would remain
mainly snow. Snow ratios will likely be lower (around 10 to 1)
during the day, but another 3 to 6 inches will still be possible.
The snow should gradually come to an end from west to east during
the evening on Sunday. There could also be some patchy blowing
snow Sunday night as the winds pick up a bit on the back side of
the surface low. However, given the wet nature to the snow on
Sunday, blowing snow would likely be a minor impact.
249 PM CST
Monday through Saturday...
Concerns in the long-term portion of the forecast include the
potential for dangerous cold Tuesday night through Thursday night,
as well as a few opportunities for snow. Late next week, a more
significant storm system could take shape, with accompanying
accumulating wintry precipitation.
Anomalous mid and upper ridging across the Aleutians and
northeastern Pacific near Alaska will favor a very cold pattern
continuing through the upcoming week, as true Arctic air plunges
southward across the country. A piece of the polar vortex will
drop to near Hudson Bay, supporting 500 mb heights of near or
below 480 DM. Meanwhile, the fast progressive jet stream pattern
will remain as well, with low amplitude clipper type disturbances
possible Monday evening and again Wednesday. With the Arctic air
mass in place, any snow from these potential systems will be of
the fluffy/high-ratio variety. Thus, while the current operational
guidance would not suggest any significant events, snow will
easily accumulate on surfaces for at least some travel impacts.
Also, some previous model runs have offered potential for more
energetic disturbances and more notable accumulations, so cannot
rule this out either. Again, latest forecast suggests that period
of interest for potential fast moving snow producers are Monday
evening and Wednesday.
Returning to the potential for dangerous cold in the mid-late work
week period, behind the possible Wednesday system, shortwave
around impressive ~480 DM mid-level low near James Bay will send a
potent thermal trough our way. Models have exhibited run to run
variance in the magnitude of the cold air mass that reaches our
latitude, though there was consistency in today`s guidance in 850
mb temperatures of -20 Celsius or colder Wednesday afternoon
through early Thursday. With deep snow pack in place, this thermal
profile will easily support temperatures barely budging and then
falling Wednesday afternoon followed by widespread subzero
readings Wednesday night/early Thursday. Expansive high pressure
spreading toward area will also add a westerly wind component to
support wind chill values of -20F or colder (advisory criteria or
colder) for at least a portion of the area. Weak "warm" advection
will ensue aloft on Thursday, though frigid start and no mixing
under the high could keep temperatures in the single digits area
wide, if not colder in a few spots.
Finally, despite long lead time, concern is increasing for a
significant winter event later in the week. A very impressive
thermal gradient will exist across the Plains with Arctic high
pressure to the north. At the mid and upper levels, there is
decent guidance continuity in the idea of deep trough carving out
into the intermountain West, with a temporary surge of height
rises for the eastern 2/3 of the CONUS. Associated surface cyclone
will be working with aforementioned impressive thermal gradient,
as well as very strong WAA ahead of it, potentially supportive of
mixed precip for at least portions of the area. This will depend
on low pressure track and how far north warm surge makes it.
Cold northerly flow supplied by Arctic surface high over the
northern Plains, as well as deep snow pack locking in the cold
increase the concern. With it being 5-6 days out, however, have
maintained snow as precipitation type in the Friday-Saturday
period. There is enough confidence in precipitation occurring for
likely PoPs Friday night. Will need to watch this period closely
as it draws closer.
For the 00Z TAFs...
554 pm...Main forecast concern is snow through the period with
significant challenges trying to determine the time periods of
lowest vis/cigs associated with bursts of moderate/heavy snow.
Light snow continues to spread across the terminals this evening
and while this timing and trends have worked out well...colder
temps and lower dewpoints have resulted in a dry snow which has
struggled to lower vis below 1sm. There may still be some vis
reductions below 1sm this evening but not confident on how
prevailing vis under 1sm will become.
Models seem to be converging on additional bands developing later
this evening which may continue to support vis around 1sm or
perhaps lower as the low levels fully saturate. Will need to
monitor trends this evening and may need to make changes with the
03z updates. If this banding...more moderate snow doesn/t
materialize later this evening...it will likely develop overnight
toward dawn. Added a tempo for lower conditions during this time
period but confidence remains low and changes here can be
expected. Beyond this time period...maintained previous forecast
as trying to pin down periods of moderate/heavy snow is difficult.
Trends would support a lull mid/late Sunday morning with perhaps a
period of heavy snow Sunday afternoon but not confident enough to
make any changes with this forecast. Even if a lull does occur...
its likely vis/cigs would improve no more than low ifr. Back edge
of the snow does appear to become fairly progressive Sunday
evening with snow ending after 00z but this timing will likely
need adjustment with later forecasts.
Winds have become south/southeast at most locations and will
remain southeast through Sunday morning with speeds gradually
increasing overnight into Sunday morning. Winds will eventually
turn more to the southwest Sunday afternoon but confidence on this
timing remains low. Some gusts into the upper teens/near 20kts are
possible Sunday morning into Sunday afternoon. cms
330 PM CST
An active pattern is in store on the lake through the upcoming
week. The pressure gradient between a weak surface low approaching
the lake from the west and high pressure departing to the east
will support south-southeast winds increasing tonight and topping
out at 30 kt on Sunday. The low will track northeast Sunday night,
with trailing cold front sweeping across the lake and resulting in
winds shifting to west-northwest up to 30 kt, though likely
remaining sub-gale. Westerly winds will diminish on Monday and
briefly shift southwest ahead of another cold front Monday night,
bringing another period of west-northwest winds to 30 kt. A brief
period of gales can`t be ruled out in this period given the very
cold air mass and deeply mixed unstable conditions.
Yet another Arctic front will cross the lake Tuesday evening, and
this frontal passage could set the stage for a fairly extended
period of westerly gales through early Thursday. An even colder
air mass will support very unstable conditions and deep mixing,
along with the pressure gradient remaining tight as high pressure
spreads eastward from the northern Plains. Despite the lake waters
still being mild for mid December, will need to watch for freezing
spray potential Wednesday and Thursday. Finally, to close out next
week, a stronger storm system could take shape and affect the
region as expansive high pressure spreads southeast across the
Regarding headlines, have issued a Small Craft Advisory from early
Sunday morning into Monday, for the strong southerly winds
shifting to westerly. Hazardous conditions for small craft will
subside by mid to late Monday morning for the Illinois shore as
west winds diminish, and by mid to late afternoon for the Indiana
shore after winds and waves diminish.
IL...Winter Storm Warning...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
UNTIL MIDNIGHT Monday.
Winter Weather Advisory...ILZ023 UNTIL MIDNIGHT Monday.
IN...Winter Storm Warning...INZ001-INZ002 UNTIL MIDNIGHT Monday.
Winter Weather Advisory...INZ010-INZ011 UNTIL MIDNIGHT Monday.
LM...Small Craft Advisory...LMZ740-LMZ741-LMZ742...4 AM Sunday TO 9
Small Craft Advisory...LMZ743-LMZ744-LMZ745...4 AM Sunday TO 3
VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)
FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
Area Forecast Discussion
National Weather Service Medford OR
301 PM PST Sat Dec 10 2016
.DISCUSSION...The latest IR image shows the front that brought
steady precipitation last night and this morning is just south of
the area. Meanwhile a shortwave is swinging through Vancouver Island
and a surface trough is just offshore. This feature will move inland
in the next couple of hours and places like Coos County and
northwest Douglas County will have an uptick in shower activity.
Elsewhere at the moment showers are far and few in between. A look
at the high res short range HRRR model shows showers increasing
along the coast late this afternoon, then moving inland early this
evening west of the Cascades. Snow levels this evening will be
around 3500 feet along the Cascades, so accumulating snow is most
likely to occur at Crater Lake and Diamond Lake where showers are
expected to be most frequent. Could not rule out a inch or two near
Lake of the Woods and an inch or less at Siskiyou Summit tonight.
A strong westerly 100+ kt jet at 300mb will remain over the region
through early next week. This will keep our weather active most of
the time. The flow at the mid levels will also remain westerly with
disturbances riding along it. Therefore we can expect showers to
continue mainly west of the Cascades Sunday into Monday morning.
Snow levels are expected to start out around 3000 feet Sunday the
morning, then rising to around 3500 feet Sunday afternoon. Same for
Monday morning and Monday afternoon. This type of flow at the mid
levels typically results in higher precipitation amounts along and
west facing slopes of the Cascades. However its not expected to be
excessive, even for areas like Crater Lake and Diamond Lake.
We`ll catch a relative break in the action Monday afternoon into
Monday night with weak ridging building into the area, then a good
slug of moisture (IVT related) could impact Northern Cal Tuesday
morning. The models vary with respect to the tining and northward
extent of the heavier precipitation. However they do agree that the
heaviest precipitation should remain south of our area. If the core
of the heavier precip ends up further north, say into southern Modoc
and Siskiyou county, then we could be dealing with significant snow
accumulations. As previously mentioned, it`s still a ways out so
we`ll have to keep a close eye on this in the days to come.
.Long Term...Wed, Dec 14th - Saturday, Dec 17th...
The long term period will bring with it the possibility of
significant precipitation amounts across Northern California and
portions of the East Side, followed or accompanied by the intrusion
of an Arctic airmass into the region. This will set the stage for
the possibility of low elevation snowfall west of the Cascades late
int the week. However, it should be noted that there has been a
tremendous amount of run to variability in the forecast models on
timing and amount related details for this entire extended period.
What there is fairly high confidence in is Arctic air spilling onto
the East Side late week and moderate confidence in this also
affecting the West Side.
More specifically, on Wednesday, ESRL reforecast analog data from
the 00Z GEFS indicates a 90th percentile (of climatology for this
time of the year) precipitation event for the Northern Sierras from
Monday night through Thursday afternoon, while, for our area, it
indicates a 50-70 percent chance of a 90th percentile event in
portions of eastern Siskiyou and Modoc Counties. Meanwhile, for
Wednesday, the operational GFS and ECMWF 12Z runs indicated an
atmospheric river affecting the Northern Sierras with precipitation
pushing northward into our area into at least Eastern Siskiyou and
Modoc Counties. During that time period snow levels appear they will
be in the 4.5-5.5kft range. How much precipitation falls in our area
certainly depends on the details and, while the operational models
and reforecast analogs look promising for significant amounts,
guidance has wavered on whether or not this will be a significant
event. The 18Z GFS has just come in, and indicates 0.50" to 1" of
water late Wed afternoon through late Thu afternoon for the
mentioned areas in northeastern California. I would not be surprised
if the guidance continues to waiver here for a couple more days.
On Thursday and Arctic airmass intrudes from the north, spilling
mostly out of the Columbia Basin, but also in modified form on the
West Side. Models have periodically indicated (every other run or
more for the day) a shortwave trough riding through Thursday night
into Friday with 850mb temperatures falling from -4C to -8C. This
brings a possibility of another round of West Side snowfall,
possibly lower than was observed in the past week. It should be
noted that some guidance simply shows the cold air working in on the
West Side and not much else.
A very cold air mass will then settle in for the weekend, with the
next frontal system expected to dive in from the northwest early
next week. It appears that temperatures on the East Side are very
likely to fall into the single digits or lower for lows this
upcoming weekend, with low in the 10s to lower 20s expected for
most of the West Side. BTL
.AVIATION...10/18Z TAF CYCLE...VFR along the coast and in the Umpqua
Basin is expected to lower to MVFR mid-afternoon as another round
of showers move in, likely falling to IFR overnight into Sunday
morning. Across the remainder of the West Side IFR to MVFR is
expected to improve to VFR this afternoon and then IFR to LIFR is
expected to develop overnight into Sunday morning. All high
terrain areas west of the Cascades will experience at least
partial terrain obscurations. East of the Cascades VFR and partial
terrain obscurations will generally prevail, though areas of MVFR
area expected this morning. The freezing level, between 5,000 and
6,000 feet, late this morning, is expected to lower to 4,000 to
5,000 feet through this evening. BTL
.MARINE...Updated 905 AM PST Saturday 9 December 2016...Periods of
enhanced west to southwest winds are expected through Sunday
evening. Winds will remain at or just below small craft advisory
levels throughout this time. Meanwhile, west swell will combine with
the resulting wind waves to produce steep seas in nearly all of the
coastal waters. Have maintained a small craft advisory for both
winds and seas throughout this time period, as conditions will be
hazardous to small craft, but the confidence in the exact location
and timing of winds is low.
Beyond Sunday, winds and seas will become relatively calm for much
of the week under high pressure and east winds, with a stronger
system forecast to arrive by the weekend. BTL/BPN
Pacific Coastal Waters...Small Craft Advisory until 10 AM PST Monday for
Area Forecast Discussion
National Weather Service Melbourne FL
920 PM EST Sat Dec 10 2016
Tonight...Surface high pressure center will push to the middle
Atlantic coast and cause low level winds to slowly veer to easterly.
This will gradually raise dew points, then some isentropic lift will
occur especially across the south half. This should support an
expansion north of the stratocumulus that have been rather prevalent
along the Treasure Coast. Satellite imagery did not support our
previous cloud forecast though and have trimmed values except in the
south. Precipitable water values are forecast to rise to about 1.3
inches along the Treasure Coast and support small rain chances, but
it looks too dry farther north for any POPs. Don`t anticipate much
change for min temps, though the evening mostly clear skies in the
north will necessitate a downward tweak.
Sunday...Surface high shifting offshore will cause winds to veer to
east/southeast at the surface and southerly in the 850-700 mb layer.
This will allow higher precipitable water values to lift northward,
but the 18z GFS only showed values 1.4-1.5 inches along the south
coast and 1.3-1.4 inches along the Brevard coast. The HRRR model is
rather skimpy on shower coverage spreading north while the local WRF
is more generous especially south of Orlando and Cape Canaveral. The
ECMWF showed a 1.5 inch bullseye of precip along the Treasure Coast.
Our forecast hitting coastal areas south of Canaveral with 40
percent chances looks good for now. Cannot rule out locally heavy
rain amounts with the breezy low level flow possibly enhancing
convergence. Elsewhere rain chances look low but expect more
cloudiness. Overall air mass moderation should result in max temps
about 3-5 degrees more mild than today.
Stratocumulus ceilings expected to be most prevalent KMLB-KSUA and
especially so KFPR-KSUA where some showers may produce MVFR tonight.
Chances for showers will elevate in those areas Sunday morning into
afternoon and a few periods of MVFR should occur. Elsewhere, expect
mainly VFR, but there should be more extensive ceilings at or above
Tonight-Sunday...Pressure gradient has decreased in the north due to
the proximity of an inverted trough. The gradient is tighter in the
south, as evidenced by some still gusty coastal winds. The inverted
trough is forecast to dissipated by Sunday morning and the overall
pressure gradient should tighten over most of the waters. The small
craft advisory expiring at 4 am for the central zones may need to be
extended through the day. Even in the north conditions for small
craft operation look poor, and possibly hazardous offshore.
AM...Small Craft Advisory until 4 AM EST Sunday for Volusia-Brevard
County Line to Sebastian Inlet 0-20 nm-Volusia-Brevard
County Line to Sebastian Inlet 20-60 nm.
Small Craft Advisory until 4 PM EST Sunday for Sebastian Inlet
to Jupiter Inlet 0-20 nm-Sebastian Inlet to Jupiter Inlet
Area Forecast Discussion
National Weather Service Marquette MI
1019 PM EST Sat Dec 10 2016
Issued at 1018 PM EST SAT DEC 10 2016
...Warnings for Alger and Luce Counties cancelled...
The MQT radar indicates the les bands that have been impacting ern
Alger and nrn Luce Counties are shifting offshore as the llvl winds
at even Grand Marais have turned to the sw, shifting the axis of
stronger llvl cnvgc out over the open lake. So the warnings that
were in effect until 05Z for Alger and Luce Counties have been canx.
.SHORT TERM...(This evening through Sunday)
Issued at 409 PM EST SAT DEC 10 2016
...Lake effect snow ends tonight then widespread system snow moves
in on Sunday...
Lake effect snow continues but the areas affected have become less
over the last 24 hours. Persistent sfc trough over southern Lk
Superior is main focus with one or two dominant bands of snow over
parts of Keweenaw and multiple dominant bands with some connection
to Lk Nipigon converging over eastern Alger and northern Luce. Over
water instability remains favorable for lake effect with inversions
over western Lk Superior around 5kft/h85 with inversion top temps to
-20c and up to 8kft/h75/-25c over eastern Lk Superior. Winds back
steadily to the WSW-SW this evening over Keweenaw so expect heavier
snow to remain on the move and will not extend the warning or advy
there. However, convergence remains strong into far eastern Alger
and northern Luce so extended warning there until midnight when HRRR
indicates blyr winds turn SW enough to push heavier lake effect
offshore. Away from the lake effect this evening skies should be
mostly clear allowing temps to fall off toward zero this evening for
the interior west. Mid-high clouds increase overnight as low
pressure system over eastern WY and CO this aftn pushes across the
central Plains. Min temps will depend how quickly the clouds move in
but a few zero to 5 below readings for favored cold spots seems
Low pressure system crosses IA and WI/northern IL on Sun morning.
WNW flow aloft and lack of very tight baroclinic zone at h85 should
keep stronger isentropic ascent snow mainly south of cwa into Sun
morning. However by aftn shortwave trough that is currently over
Pacific NW moves across Dakotas and northern MN. Deep layer q-vector
convergence increases markedly through the aftn and that forcing
along with increasing moisture advection ahead of low pressure
trough over WI (mixing ratios at h7 up to 2g/kg) running into cold
airmass should start to produce light to moderate snow. H85 low
tracking across northern WI as the shortwave moves through also
increases larger scale lift and there is some mid-level fgen on
northern edge of this low. That forcing along with SE winds off Lk
Michian and E winds off Lk Superior should result in lake
enhancement with h85 temps -8c to -10c and water temps around 5c.
Overall snow amounts with this system should fall into advy range of
3 to 5 inches in 12 hours (12z-24z/7 am ET to 7 pm ET) along WI
border, but lake enhancement could add to the totals for scntrl
Upper Michigan and across the Keweenaw Peninsula. Highlighted this
potential in the WSW statement and it is possible eventually could
need warnings but will start with advy for now. Does look like after
this event all areas of Upper Michigan will have at least light
.LONG TERM...(Sunday night through Saturday)
Issued at 435 PM EST SAT DEC 10 2016
The medium range models suggest that the blocking ridge through
Alaska will favor pattern amplification with an intrusion of very
cold arctic air into the CONUS as the deep mid level low moves into
nrn Ontario. This will bring an extended period of wrly flow LES and
low wind chills across the region.
Sunday night, although the stronger isentropic lift will shift off
into the ern cwa during the evening a period moderate to strong 700-
300 mb qvector conv associated with the shrtwv moving out of the nrn
plains will help sustain the light to moderate snow through the
evening. In addition, convergent se winds off of Lake Michigan and
easterly winds on Lake Superior will bring some higher snow amounts
into s cntrl Upper Michigan and the Keweenaw. As the sfc trough
moves off to the east another period of lake enhanced snow may
affect the nw cwa. QPF values in the 0.10-0.15 inch range will
favor another couple of inches for most of the cwa with local
amounts of 5 inches or more over the Keweenaw.
Monday, once the lingering snow over the nw ends expect mainly dry
weather. Winds backing to the sw will keep most of the additional
LES potential west of the Keweenaw.
Monday night into Tuesday, the arctic front is expected quickly
move through the nrn Great Lakes. A period of light snow associated
with qvector conv ahead of the mid level trough may bring a period of
light snow through the cwa Monday night with heavier lake enhanced
snow or LES over the Keweenaw as winds veer to the west. Temps will
fall or remain steady through the single digits Tuesday.
Wednesday-Friday, after the initial surge of arctic air, a
reinforcing batch is expected to move in wed into wed night. This
will bring a slight veering trend with the low level flow which may
push the LES into a greater portion of the nrn cwa, especially from
p53 eastward. LES will continue through the period, but the
intensity will be limited as the very cold air limits snow growth.
However, low vsby will prevail through most of the period downwind
of the wrly flow. Wind chill values may approach 25 below both Wed
and Thu, especially inland west, farthest from any moderating
influence of Lake Superior.
Saturday, GFS/GEFS/ECMWF maintain the idea of that sw mid level flow
in response to trough into the Rockies will favor the development of
a broad waa pattern which could bring widespread snow into the
region. However, confidence in any details is low.
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 620 PM EST SAT DEC 10 2016
As the llvl winds shift to the sw over the Keweenaw this evng, band
of heavier les impacting CMX wl shift to the n and allow for VFR
conditions to dvlp at that site later in the evng. Dry llvl air at
SAW and IWD wl result in VFR conditions at both those locations even
as mid/hi clds begin to increase overngt ahead of the next lo pres
advancing toward the Upr Midwest. Sn in advance of this lo pres wl
overspread Upr MI on Sun, resulting in IFR conditions by the aftn at
all 3 sites.
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 435 PM EST SAT DEC 10 2016
Expect NW winds up to 25 kts to diminish under 20 kts tonight but
may increase to around 25 knots as a trough lifts into Upper
Michigan Sunday. A steady WNW wind to 30 kts with potential for
brief periods of gales Mon night into Thu following a strong cold
frontal passage that will introduce arctic air into the Upper Lakes.
Expect some heavy freezing spray over at least portions of the Lake
on Tue night/Wed as this arctic air moves into the area and waves at
the end of fetch build to at least 10 feet.
Winter Weather Advisory from 10 AM EST /9 AM CST/ Sunday to 1 AM
EST /midnight CST/ Monday for MIZ002-004>007-009>014-084-
Winter Weather Advisory from 1 PM Sunday to 7 AM EST Monday for
Area Forecast Discussion
National Weather Service Charleston WV
1013 PM EST Sat Dec 10 2016
A low pressure system crosses Sunday night and Monday. A cold
front crosses toward midweek bringing another arctic blast and
ushering in a more unsettled pattern through next weekend.
.NEAR TERM /THROUGH SUNDAY/...
As of 1010 PM Saturday..
Used the latest runs of the HRRR and RAP to give the POPs, QPF,
and snow grids some TLC along the far northern tier of the CWA
beginning tonight through 18Z Sunday. The changes do not amount to
all that much, and max out the totals to around 1.5 inches, but
for only a very small area up in far northern Perry County.
As of 200 PM Saturday...
Clouds will be increasing tonight as mid and high level moisture
advect into the area ahead of the next system. WAA will be
increasing over the upper Ohio Valley on low level SW flow. Some
good isentropic lift will develop as well, which will allow snow
to overspread portions of the upper Ohio Valley. It still appears
most of this will fall just north of the RLX CWA, perhaps clipping
Perry/Morgan over to Clarksburg/Elkins later tonight. The
consensus in the hi res models though keeps all of precip north
of the CWA with the GFS/ECMWF showing QPF over the aforementioned
areas. Given the amount of low level dry air in place...tend to
favor keeping the precip north of the area but will leave a tight
gradient of POPs across our northern fringe counties for some
wiggle room. The best chance for any accumulations would across
Perry/Morgan where a tenth or two is possible.
This all pushes north Sunday morning with mainly a dry forecast
for the daylight hours in broad SW flow aloft/SE flow at the
surface. Expect some sunshine in the afternoon across SW VA and a
good portion of WV. This along with downsloping should allow temps
to approach 50 in the typical banana belt areas along US 119/I 79
.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
As of 250 PM Saturday...
The period starts with another front knocking on our doorstep.
Continuing WAA will push H85 temps to near +10C ahead of this
system, so predominantly a rain event for most areas. There will be
a small window for brief frozen precip in/near the mountains from
late Sunday evening into the pre-dawn hours Monday before too much
warm air moves in aloft. Forecast soundings show low level
thermal profiles favoring brief SN along the taller ridges with ZR
possible in mountain valleys. While a light glaze of ice is
possible, the changeover to rain should occur relatively quickly
Monday morning with all rain across the area before dawn.
Temperatures will remain cool but relatively mild compared to the
previous several days and rain should end west-to-east late
Monday into Tuesday with sfc high pressure building back in.
.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
As of 250 PM Saturday...
Confidence remains low concerning overall pattern evolution for the
long term. Regardless of spatial and temporal discontinuities in
model guidance, it does appear that another arctic airmass will
filter in by mid week. Multiple rounds of precipitation are also
possible through the period with any waves embedded in the larger
.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
As of 630 PM Saturday...
For the area terminals, forecast is VFR ceilings and visibilities with
winds turning southerly less than 10kts.
Off the surface, low level flow to increase steadily through the
Warm front will develop north of the terminals with light snow
overspreading the region. Again, this will fall north of the PKB-
CKB-EKN line, and will end up in warm advection warm sector flow
through the period. Rain will move in from the west northwest
towards the end of the period, but will lie just beyond the
temporal scope of the TAFs.
FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 00Z MONDAY...
FORECAST CONFIDENCE: Medium SE OH/N WV. High elsewhere.
ALTERNATE SCENARIOS: Light snow tonight may sneak into northern
TAF sites which would bring MVFR into play.
EXPERIMENTAL TABLE OF FLIGHT CATEGORY OBJECTIVELY SHOWS CONSISTENCY
OF WFO FORECAST TO AVAILABLE MODEL INFORMATION:
H = HIGH: TAF CONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL.
M = MEDIUM: TAF HAS VARYING LEVEL OF CONSISTENCY WITH MODELS.
L = LOW: TAF INCONSISTENT WITH ALL MODELS OR ALL BUT ONE MODEL.
DATE SUN 12/11/16
UTC 1HRLY 03 04 05 06 07 08 09 10 11 12 13 14
EST 1HRLY 22 23 00 01 02 03 04 05 06 07 08 09
CRW CONSISTENCY H H H H H H H H H H H M
HTS CONSISTENCY H H H H H H H H H H H M
BKW CONSISTENCY H H H H H H H H H H H M
EKN CONSISTENCY H H H H H H H H H H H M
PKB CONSISTENCY H H H H H H H H H H H M
CKB CONSISTENCY H H H H H H H H H H H M
AFTER 00Z MONDAY...
IFR possible in rain developing Sunday night.