Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/05/16
Area Forecast Discussion
National Weather Service La Crosse WI
546 PM CST Sun Dec 4 2016
.UPDATE...
Issued at 546 PM CST Sun Dec 4 2016
Local radar and observations indicate all the significant snow has
moved out of central Wisconsin. There could be some remaining
flurries or drizzle for a couple hours this evening. Temperatures
are near freezing, so the drizzle could put a very light coating
of glaze on any untreated surfaces. Not expecting this to last
long enough to pose any significant problems. Will let the winter
weather advisory expire at 6 p.m. as scheduled.
&&
.SHORT TERM...(Tonight through Tuesday)
Issued at 300 PM CST Sun Dec 4 2016
Concerns are 2-fold:
1) Dense fog and/or low stratus tonight
2) Precipitation chances Monday night-Tuesday
Snow has made steady progress east, but probably won`t clear
Adams/Juneau WI counties until 6 pm. Opted to extend to advisory for
those counties, letting it expire elsewhere. Expect some impacts
through the evening for travel with many roads snow covered, slushy
and slick.
The challenge for the rest of tonight is the potential for fog
and/or stratus development. Current cloud mass is progged to shift
northeast through the nighttime hours, although it could hang tough
in the I-94 corridor. RAP more pessimistic, compared to the
NAM12/GFS, with slower clearing. Some high clouds then start to
spill in from the west near 12z ahead of a shortwave trough over the
Northern Plains. Meanwhile, winds stay fairly stiff through the
night - both at and just above the surface. That said, the fresh wet
snow pack will be a great moisture source, and hrrr/rap/nam bufkit
soundings keep a saturated near sfc layer through the night.
Certainly suggestive of either thick fog or low stratus. Winds would
usually point to more stratus, but could be an advective type fog
scenario.
Confidence not high on which way it will play out, but too much
consensus to dismiss the potential. Will go with areas of fog for
now...especially west of the Mississippi where the clearing is more
likely. If fog manifests, it could become dense - which would result
in a dense fog advisory. Something to watch.
That next shortwave swings across the region Monday night-Tue with
the bulk of its forcing holding to the north. It will drag a sfc
front through the local area though and that looks to have a
relatively strong, but very narrow band of frontogenetic forcing.
Saturation could be an issue, at least with pcpn type potential.
North-south running x-section keeps the deepest saturation generally
north of I-94. To the south it quickly shallows out, and loses any
ice in the cloud. Pcpn type would be liquid - and depending on sfc
temps - freezing rain/drizzle would be possible. Whatever falls
looks to be short lived - but a quick 1/2 inch of snow in the north,
and that freezing potential in the south - allude that it won/t
necessarily be an impact-free frontal passage.
.LONG TERM...(Wednesday through Sunday)
Issued at 300 PM CST Sun Dec 4 2016
Temperatures are going to be the big story for the later half of the
week. Significantly colder air will funnel southward across the
Upper Mississippi River Valley post the Tue system. The GFS and EC
drop 850 mb from around +2 C at 00z Tue to -16 C by 00z Fri. NAEFS
850 mb temp anomalies are around -1 to -2. The cold air starts to
moderate a bit by the end of the weekend as the next potential snow
maker moves in from the west. Highs look to hover near 20 Wed-Sat.
The weekend is showing some promise for accumulating snows as both
the GFS and EC want to drive an upper level shortwave trough across
the northern plains and then through the local area sat/sun.
Previous GFS run was more robust/quicker compared to the EC, and
would have favored more accumulations. 12z run came in weaker
though, more like the EC. Something to watch for now.
&&
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 546 PM CST Sun Dec 4 2016
The back edge of the clouds has been working across southern
Minnesota this afternoon and is expected to move through both
airports this evening. Until the clearing does move in, expect
the ceilings to remain MVFR. Some concern for fog overnight as the
forecast soundings show the lowest levels of the atmosphere remain
saturated. However, countering this, should be the southwest winds
of 5 to 10 knots. Will include some MVFR visibilities at KRST but
for now keep KLSE clean. VFR conditions then expected from Monday
morning through the afternoon, but the next system will be
quickly advancing across the northern plains that could bring in
some MVFR ceilings right around 06.00Z.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&
$$
UPDATE...04
SHORT TERM...Rieck
LONG TERM....Rieck
AVIATION...04
Area Forecast Discussion
National Weather Service Denver/Boulder CO
852 PM MST Sun Dec 4 2016
.UPDATE...
Issued at 841 PM MST Sun Dec 4 2016
Have updated the grids for tonight, slowing down the onset of
any snow in the mountains until after midnight, primarily
impacting zone 31 based on the last few HRRR runs. Also made some
wind adjustments in the the foothills. Still expected strong winds
overnight and Monday morning, but no highlights with gusts
primarily in the 50-65 mph range.
&&
.SHORT TERM...(This evening through Monday)
Issued at 328 PM MST Sun Dec 4 2016
Westerly flow aloft will be increasing over northern Colorado
tonight as an upper level jet moves in from the Pacific Northwest.
Moisture associated with the developing flow pattern will also be
on the increase over the mountains by 06z and continuing through
Monday. The core of the upper level jet will be staying over
Wyoming with ridgetop flow in Colorado peaking out at around 70
knots. Model cross sections indicate that the fastest flow will
remain over the ridges, without much of a lee-slope mountain wave
developing. Quasi-geostrophic diagnostics also show a lack of
strong subsident forcing overnight, which may be why a strong wave
does not develop. At any rate, the strongest winds are expected to
remain above 10,000 to 11,000 feet, with lesser impacts down in
valleys and population centers. No highlights will be issued.
Light snow will also be developing in the mountains overnight, but
only light amounts, up to about 4 inches, are expected through
tomorrow afternoon.
On the plains, one last mild day will be in store, but by mid-
afternoon cooler air is expected to begin moving in from the
north. High temperatures in the mid 40s to lower 50s will be
possible, primarily by the lunch hour. Dry conditions will prevail
through later Monday night. Afternoon gusts on the plains will be
in the 25 to 35 mph range.
.LONG TERM...(Monday night through Sunday)
Issued at 328 PM MST Sun Dec 4 2016
A dramatic change in the wx ptrn will occur Tue into Wed as an upper
level trough moves along with a couple of cdfnts. Mtns will see
some snow Mon night into early Tue however best chc of heavier snow
will be Tue aftn and night when best QG ascent moves across in
association with deeper moisture.
Across nern CO first shot of colder air will move in Mon night into
early Tues with a brief shot of upslope flow Mon night. Overall
with lack of QG ascent Mon night thru Tue morning and a dry lyr in
the lower levels will only see a chc of light snow mainly in and
nr the foothills. Highs on Tue will be in the mid 20s to around 30
across the plains.
By late aftn into Tues night upslope flow will gradually increase as
a sfc low forms over srn CO and a secondary shot of colder air moves
into nern CO. Meanwhile QG ascent will increase across the area
which will lead to a gradually increase in snow in and nr the
foothills and across the rest of the plains Tue night. Based on
current data and timing of upper level trough snow may linger into
Wed morning as well before gradually ending in the aftn. As for
amounts HI RES WRF and SREF Plume data indicate advisory amounts fm
the foothills across the plains with the potential for heavier
amounts around the Denver area. Confidence is not high enough to
issue a watch at this point since the heaviest snow at lower
elevations will be from Tues night into Wed morning. Meanwhile
highs on Wed will only be in the teens across the plains.
For Wed night into Thu drier air will spread across the area in nw
flow aloft. Outside of a chc of light snow in the mtns Wed night it
will be dry thru Thursday. Morning lows on Thu will likely be below
zero across much of the area. As for highs on Thu readings will
only be in the upper teens to lower 20s across the nern Co.
For Fri and Sat the flow aloft will become more wly with moisture
affecting the mtns both days with a good chc of orographic snow.
Across nern CO it will be dry with moderating temps on Fri as
downslope flow develops with readings mainly in the 30s. On Sat a
wk fnt may move across nern CO which would keep readings in the 30s.
On Sun a weak upper level trough is fcst to move across bringing
another chc of snow to the mtns. Across nern CO will not mention
any pcpn and will keep highs in the 30s.
&&
.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 841 PM MST Sun Dec 4 2016
VFR conditions through 06z Monday night but could see the
potential of some ils restrictions with bkn cigs 050-060 kft agl
developing after 00Z. Winds will be out of the west or southwest,
especially over the western portions of the Denver area where
gusty winds are expected at times overnight, primarily impacting
KBJC. Winds are expected to increase Monday afternoon and evening
as an initial surge of cold air begins moving into northeast
Colorado. Northwest to northerly in the afternoon, then north to
northeasterly Monday evening.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...Cooper
SHORT TERM...Dankers
LONG TERM...RPK
AVIATION...Cooper
Area Forecast Discussion
National Weather Service Duluth MN
703 PM CST Sun Dec 4 2016
.UPDATE...
Issued at 629 PM CST Sun Dec 4 2016
Have sent out updated to allow a portion of the winter weather
advisory to expire. On the southwest flank of the exiting
precipitation we have lost enough ice aloft to cause freezing
drizzle to affect areas where we still have low stratus and a
little lift. Have updated the forecast to include this freezing
drizzle. Since our roads are all well treated from the exiting
snow, the freezing drizzle should not affect more than some
elevated surfaces. See no reason at this time to extend the
advisory since the accumulating snow is coming to an end.
Also, updated aviation section below.
&&
.SHORT TERM...(This evening through Monday)
Issued at 306 PM CST Sun Dec 4 2016
The focus remains on the snow moving through the Northland this
afternoon with the deep low pressure trough lifting through the
region. Earlier this morning, we had increased snowfall amounts
across parts of the Northland after reviewing the latest higher
resolution model guidance, seeing snowfall reports come in with
higher amounts than anticipated, and seeing a period of decent
dendritic growth here in Duluth. The most significant increases
to the snowfall forecast were made for areas from Duluth up the
North Shore, which prompted expanding our earlier winter winter
advisory for the Shore of Cook County down to include the Shore of
Lake County and even the Duluth area. The advisories are in effect
through 6 pm and 9 pm, with the latter time for Cook County. The
snow is continuing to fall along the North Shore, so will
definitely maintain the current advisories for the Shore. As for
Duluth, while there has been a break in the snow, additional bands
of snow are approaching from the west and southwest, which should
bring additional light snow through early this evening. Therefore,
will maintain the advisory for Duluth, too.
The axis of a deep low pressure trough, extending from west
central Manitoba to at least eastern Missouri, will lift through
the Upper Midwest and Great Lakes through the rest of today and
into early Monday. Its synoptic lift, combined with relatively
deep moisture ahead of the trough, will continue to result in
light to moderate snowfall rates across northeast Minnesota and
parts of northwest Wisconsin today and this evening, with the snow
gradually spreading and exiting to the north and east. There will
be widespread snowfall totals, including what fell earlier today,
of 1 to 3 inches across the Northland. The greatest amounts, of
about 3 to 6 inches, will be along the higher terrain of the
Minnesota North Shore, from the eastern outskirts of Duluth to
Grand Portage. This is because of a few factors, including the
moisture lake enhancement from the strong southerly flow over
western Lake Superior, the orographic lift up the higher terrain,
and the good potential dendritic growth because of good vertical
motion within the secondary key thermal layer for dendritic growth
near -2 to -5 degrees Celsius.
The snow will gradually shift north and east later this afternoon
and evening, exiting and tapering off for the Northland. A warmer
air mass will filter into the Northland from the south and
southwest, in the wake of the passing trough. Some clearing of the
skies across the west and south, as well as the fresh snowpack and
light winds, will likely let temperatures to drop to the middle
20s.
The surge of warmer air from the south late tonight and Monday
will likely result in low-level stratus moving into the region.
The soundings are showing a decent inversion by late tonight with
low-level saturation. Some models, such as the HRRR experimental,
are suggesting this will result in fog. Not convinced yet if this
stratus layer will dramatically reduce visibility, but will need
to reevaluate the threat of fog later on. It is certainly possible
if warm enough air overrides the snowpack and results in some
melting of the snowpack and help the boundary layer saturate. If
the skies clear better tonight, then the radiational cooling could
strengthen that inversion and provide a better setup for fog.
A not-so-stacked low will move through the North Dakota region
Monday, likely resulting in light snow across parts of the
Northland, especially northern Minnesota, Monday afternoon.
Temperatures in the lower and middle 30s, though, will limit
accumulation to little amounts until the evening.
.LONG TERM...(Monday night through Sunday)
Issued at 306 PM CST Sun Dec 4 2016
The long-term period will begin with another mid-level shortwave
trough associated with a broad swath of positive vorticity
advection evident in all of the synoptic scale models. A strong
push of a 700- 500 mb layer deformation zone sets up along the
leeward side of the trough. The 04.12z synoptic models have taken
the sfc low pressure center slightly southeast compared to
yesterday`s corresponding runs, but overall uncertainty still
exists on the exact track of the low, but the overall agreement is
to bring the center of the low across North Dakota, and into
southern Manitoba and southwest Ontario, Canada Tuesday morning.
The models are bringing the sfc low pressure over Canada, which
should place the Northland within the cyclonic flow aloft. There
are some questions based on the model QPF as to where exactly an
precipitation that develops will be. The GFS is once again more
bullish than the NAM/ECMWF models. Generally, those in the
furthest north counties will be more likely to see precipitation.
At this time, accumulations look to be steady, but light, with
about a few tenths of an inch of snow expected every six hours. Of
course, this is depending on the low track, so we will keep an eye
on the latest guidance.
This light snow looks to continue through the day Wednesday as
another quick pulse of energy sweeps south through the area. The
low will eventually take its leave late Tuesday, which will result
in veering sfc winds from west to a more northwesterly direction.
This will set up cold air advection on the backside of the low.
Temperatures look to plummet from Wednesday through Friday as 925
mb temperatures drop between -8 and -13 degrees C across the
forecast area on Wednesday, to as low as -19 degrees C Friday
morning in the GFS. Lows during this period will drop into the
teens and single digits during this time, as highs stay in the mid
to upper teens. Wind chill values are likely to drop into the
single digits, above and below freezing, the mornings of Thursday
through Saturday.
Chances of light snow showers will linger through Friday as we
stay within the cyclonic flow. The northwest flow will help to
support some lake enhanced snow in the Snowbelt region of
northwest Wisconsin. I bumped up the PoPs a little bit in Ashland
and Iron counties in Wisconsin to account for the lake
enhancement. This should begin to ramp up Thursday morning and
last through the day Friday before tapering off Saturday morning
as sfc high pressure moves in, which will weaken the on-shore
flow. Isentropic lift in the 1000-850 mb layer reaches up to -10
ubar/s Thursday afternoon into Friday morning, when the lake
enhancement will be maximized and PoPs are at their highest. 850
mb temperatures will also be at their lowest at that time, which
will range between -17 and -20 degrees C. Otherwise, most of the
rest of the forecast area should stay dry.
Chances of light snow looks to return Saturday and Sunday as
another mid-level shortwave and 850-700 mb warm air advection
makes its way back into the area. Temperatures look to rebound
slightly but should still stay below freezing.
&&
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 629 PM CST Sun Dec 4 2016
Snowfall coming to an end across the terminals, leaving behind IFR
to even LIFR stratus and some patchy freezing drizzle. Expect
these IFR/LIFR ceilings to continue throuh much of the overnight
period, though the visibilities should gradually improve to MVFR
after 05z. After 12z we should see further improvement to MVFR
ceilings and VFR visibilities. After 18z light snow is expected
to move back into the terminals with IFR ceilings, but have put
in VCSH for now as timing and placement are still uncertain.
&&
.PRELIMINARY POINT TEMPS/POPS...
DLH 27 35 24 25 / 40 30 30 20
INL 25 34 22 23 / 50 50 60 40
BRD 25 35 22 23 / 20 20 20 20
HYR 26 37 26 28 / 20 20 30 20
ASX 29 39 29 30 / 40 20 30 20
&&
.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...Winter Weather Advisory until 9 PM CST this evening for MNZ021.
LS...Small Craft Advisory until 10 AM CST Monday for LSZ140.
&&
$$
UPDATE...LE
SHORT TERM...Grochocinski
LONG TERM...JTS
AVIATION...LE
Area Forecast Discussion
National Weather Service Green Bay WI
533 PM CST Sun Dec 4 2016
Updated aviation portion for 00Z TAF issuance
.SHORT TERM...Tonight and Monday
Issued at 301 PM CST Sun Dec 4 2016
The latest rap analysis and satellite/radar imagery show a
relatively sharp shortwave trough moving into the northern
Mississippi Valley early this afternoon. A swath of light to
moderate snow continues to move northeast across the region ahead of
this trough, but accumulations have struggled to occur on the
primary roadways based off of area webcams. Looking at road
temperature forecasts, potential remains for accumulations on
roadways to occur late this afternoon and this evening as pavement
temps cool. Wet pavements could also become icy. The back edge of
the snow is currently pushing across Eau Claire and should start
moving into Wood and Marathon counties between 4 and 6pm. Forecast
concerns revolve around snow accumulation trends and amounts
tonight.
Tonight...Followed the HRRR for timing the back edge of the swath of
snow. This back edge should proceed east across central and north-
central WI between 5 and 8 pm, and northeast WI between 8 and 11 pm
tonight. As road temperatures cool with the sun going down,
anticipate travel conditions to become increasing treacherous late
this afternoon into this evening. This will likely have bigger
impacts to eastern WI than farther west, since an additional inch or
two of accumulations will be possible during this time in this area.
In total, still think 2 to 4 inches looks about right for the
advisory area, perhaps lower right along the Lake Michigan
shoreline. Once the snow departs, roughly around midnight, partial
clearing could arrive from southwest to northeast late. Lows should
not fall much due to the clouds and a persistent southwest wind.
Mins in the middle to upper 20s look about right.
Monday...Weak ridging will move across the area during the morning,
which could result in a few hours of partial sunshine. Then
southwest winds aloft will bring in mid and high clouds in a warm
advection regime late morning through the afternoon. Moisture could
become deep enough for some flurries or light snow over far north-
central Wisconsin during the afternoon. Highs in the mid to upper
30s.
.LONG TERM...Monday Night Through Sunday
Issued at 301 PM CST Sun Dec 4 2016
Upper troughs pass north and south of Wisconsin Monday night and
Tuesday. The one to the north looks strong enough to bring some
snow showers to the region, but no accumulations expected.
Blustery and colder weather arrives Tuesday night and Wednesday as
surface high pressure moves in.
AN upper trough moving slowly across the region Wednesday night
through Thursday night will produce some upper support and shift
low level winds to the northwest and make lake effect snow
possible for far north central Wisconsin. Several inches of snow
possible in Vilas county from early Thursday through Friday. The
remainder of the forecast area should be dry and cold.
There is a chance of a light snowfall Saturday as a trough
approaches from the west.
&&
.AVIATION...for 00Z TAF Issuance
Issued at 526 PM CST Sun Dec 4 2016
Snow will taper off from west to east this evening, and may mix
with light freezing drizzle for an hour or two on the back edge of
the precipitation. Low clouds should gradually improve from IFR
to MVFR this evening. Although clearing skies are not certain,
have hedged bets that clearing will occur as a surface ridge axis
arrives late tonight into Monday morning. There is already a
pronounced clearing line over southwest MN and western IA, so
there is evidence that this may occur. MOS guidance also supports
this scenario. Most locations should have VFR conditions with
mainly mid-level clouds in the late morning and afternoon.
&&
.GRB WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 9 PM CST this evening FOR WIZ019-
020-022-031-037>040-048>050-074.
Winter Weather Advisory until 6 PM CST this evening FOR WIZ018-
030-035-036-045.
&&
$$
SHORT TERM.....MPC
LONG TERM......RDM
AVIATION.......Kieckbusch
Area Forecast Discussion
National Weather Service Wilmington OH
930 PM EST Sun Dec 4 2016
.SYNOPSIS...
An upper level disturbance will move across the region today
bringing mostly rain with snow possibly mixing in across the
north. Drier conditions are expected on Monday, as high pressure
moves into the area. On Tuesday, an area of surface low pressure
is expected to move into the Ohio Valley, bringing rain to the
area. Behind a cold front on Wednesday night, much colder
conditions are expected through the end of the week.
&&
.NEAR TERM /THROUGH MONDAY/...
Mid level shortwave evident on water vapor imagery pivoting into
srn lower MI. With this progressive system, precipitation is
ending quickly from west to east across ILN/s FA. Northern
periphery of this pcpn band producing a light snow accumulation of
less than an inch on grassy areas. All pcpn to end by midnight
with skies remaining cloudy through the night. Expect lows to
range from the lower 30s nw to the upper 30s se.
Previous discussion...
Starting to get reports of light rain across our northwestern
zones (and sleet in Wayne County, IN). This is thanks widespread
isentropic lift across the area along with a shortwave approaching
from the west. Looking at the latest high res models confidence
has built that rain will likely transition to a rain/snow mix and
then transition to all snow possibly across our far northern
counties (Mercer, Hardin, Auglaize). This transition will likely
be driven by stronger upward motions and adiabatic expansion from
lower pressures (dynamic cooling). The latest HRRR run shows
these northern counties actually transitioning to all snow around
23z with some light accumulations on grassy surfaces possible.
There may be some accumulations on roadways (esp. elevated
surfaces) which could cause some slick spots but this should be
transient. Have covered this in the HWO. All the three metro areas
and south should stay all rain. The upper level shortwave will
start to take on a negative tilt and eject northeast late this
evening with precipitation coming to an end across the area around
midnight.
&&
.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
Monday morning a weak surface high pressure will move overhead
behind the shortwave trough that moved through the area Sunday.
Global models are showing some clearing Monday but there remains a
sharp inversion in both GFS and NAM forecast soundings around 920
mb which could help trap some low level moisture. Looking at
ECMWF, GFS, and NAM rh fields a potent surge of dry air is
expected to move into the area and have allowed skies to clear a
bit. High temperatures Monday will likely have trouble getting
much above the mid 40s as 1000/ 850 mb thicknesses (~1305 m)
support highs only in the mid 40s. Given the above mixing is only
forecasted to be around 925mb so have backed off on high
temperatures a bit for Monday.
The weather pattern will be quick to change Monday night as an
upper level low currently over northern Mexico (as of Sunday
afternoon) will begin to head northeast Monday afternoon with a
coastal low forming. This surface low will be near the Tennessee
valley Tuesday morning and move just southeast of the area Tuesday
afternoon. Current thermal profiles support rain across most of
the area with the NAM and GFS trying to show a brief change over
to snow across the far northern zones. Overall the GFS, ECMWF, and
NAM are in pretty good agreement with the timing of the surface
low which would still support non- diurnal temperatures. Have
adjusted the timing of the precipitation onset a bit for Tuesday
while also adding a brief period of rain/snow for our far northern
counties.
The surface low will also help bring deep gulf moisture northwards
with PWATs on GFS/ NAM forecast soundings rising to above 1"
Tuesday. These PWATs are also shown on the NAEFS which are 1 to 2
SDs above normal for this time. Given the above have kept PoPs
categorical with storm total amounts of 0.50" - 1.00" of rain
possible Tuesday.
&&
.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
This period will be characterized moreso by temperature impacts
rather than precipitation impacts - though the latter will still
need to be watched on late Wednesday night/Thursday morning...and
again later next weekend.
Confidence assessment - there`s really pretty decent agreement in
larger scale evolution of the flow into next weekend between higher
resolution deterministic runs and parent ensemble means. There`s
much higher confidence on temperature evolution Wed-Sun vs.
precipitation...with the season`s first /well advertised/ cold spell
centering on Friday with temp departures some 10-20 degrees below
normal. Wednesday/Sunday can be viewed as transition days into /Wed/
and out of /Sun/ the thermal trough but this entire period will
average out well below normal. Precipitation type/timing is much
more problematic and of much lower confidence - with notably two
decent changes at synoptic scale forcing/vertical motion. The first
is with shortwave energy rippling along the advancing cold front
Wednesday night/Thursday morning...the second is progressive
shortwave energy across the Great Lakes next weekend. Very low
confidence with the forecast next Sat/Sunday - as it is noted that
ensemble plumes /GEFS and ECMWF/ get extremely noisy in Days 7-10
suggesting the pattern is of very low confidence with how the energy
next weekend evolves. Both data show the deterministic runs trending
away from their respective ensemble means by Day 8...suggesting
caution in next weekend`s forecast.
All that being said - however - Wednesday there is rather high
confidence in a dry day downstream from approaching height falls
moving through the Plains. Most recent /04.12z/ ECMWF has caught up
in speed to GFS/GEFS which was a disagreement source early on.
Advancing strong cold front and strengthening shortwave trough have
had hints of developing a weak frontal wave as it approaches the
area Wed night/Thursday morning...with deterministic ECMWF /04.00Z
and 04.12Z/ consistent with a stripe of modest QPF enhancing on the
cold side of the strong cold front which may be worthy of some light
snow accumulations north of the Ohio River...but agreement in this
scenario has less /GFS/ to much less /CMC/ agreement outside the
ECMWF/ECMWF ens spectrum for anything more than mid-range snow
chances at this time.
Once this front/frontal wave passes...cold air blasts in but is
progressive. -16C at 850mb is significant for mid-December on Thurs
night and thus have no problem accepting mid/upper teens for lows
and mid/upper 20s for highs Fri through this brief cold spell.
Moderation begins on Saturday with temps back toward 30 on Saturday.
Some cold advection flurries/snow showers are possible both
Thursday/Friday...particularly across central Ohio in favorable
trajectory off Lake Michigan...but coverage expected to be spotty.
Per confidence assessment above - not a great deal of confidence how
shortwave energy and associated rain/snow chances look for Sunday
and this lingers beyond Day 7 depending how energy ejects within the
upper trough. For right now have middle-range snow chances
developing Sunday with transition from south to north given warm
advection...but we`ll need to see more data before any potential
impacts are.
&&
.AVIATION /02Z MONDAY THROUGH FRIDAY/...
Rain associated with a trough of low pressure has overspread all TAF
sites late this afternoon. Ceilings and visibilities have lowered
into the MVFR category, with IFR ceilings likely and LIFR possible
tonight as rain departs to the east. A period of Mixed snow in at
kCMH and kLCK is possible late this evening prior to ending.
Slow improvement to MVFR will occur Monday morning with lingering
low level moisture. Clouds will clear from the southwest to
northeast with VFR developing Monday afternoon.
OUTLOOK...MVFR/IFR ceilings and MVFR visibilities expected
Tuesday with rain. MVFR ceilings to linger Tuesday night into
Wednesday morning.
&&
.ILN WATCHES/WARNINGS/ADVISORIES...
OH...None.
KY...None.
IN...None.
&&
$$
SYNOPSIS...Haines
NEAR TERM...Haines/AR
SHORT TERM...Haines
LONG TERM...Binau
AVIATION...AR
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
735 PM CST Sun Dec 4 2016
.UPDATE...
735 PM CST
Allowed the winter storm and winter wx advisory to expire at 6 pm
as scheduled. Still had some accumulating snow falling at 6 pm,
but knew it was winding down quickly and didn`t see a need to
extend advisory an hour. Radar would suggest accumulating snow has
ended and will fire out one more ZFP shortly to pull all snow.
Have made some adjustments to going forecast beyond this evening.
1) Have hit dense fog/dense freezing fog potential harder in the
grids. Really a pretty atypical set-up, but many signs are
pointing to the potential for a potential widespread dense fog
event late tonight and particularly Monday morning. Typically,
following a big snow, we see dry/cold air advection in its wake,
however all of the forcing with today`s big snow came from aloft.
This evening, however, a narrow surface ridge is over the area now
and will scoot off to the east and allow for weak low level
warm/moist advection. So fresh snow cover will work to hold temps
in check and perhaps try and fall a degree or two, while
developing southwest winds attempt to advect in mid 30s dewpoints,
setting stage for what appears to be a good dense fog set up. I`ve
seen many seemingly perfect dense fog set-ups bust with no fog, so
plan to take a wait and see approach regarding any headlines, but
did hit the fog harder in the grids/text products. Assuming fog
does indeed develop as expected, then it would likely peak after
sunrise Monday and could even linger into the afternoon.
2) Most guidance high temps for tomorrow were not based on the
deep snow pack that now blankets the region. The combination of
the deep snow pack and the potential for dense fog and likelihood
of a low overcast would all suggest that our temps tomorrow aren`t
going much of anywhere. Have run with the NAM 2m temps for highs
tomorrow, which basically suggests only a rise of a couple degrees
diurnally, more reason why if dense fog forms as expected, that it
could linger much of the day.
3) Finally, haven`t added it to the forecast, but also will need
to watch for some drizzle/freezing drizzle late tonight and
Monday. Confidence is low, since model guidance varies on the
depth of the stratus/low level moisture. NAM/HRRR look more
supporting with cloud depth nearing 2000ft agl with 20-25kt winds
at the top of the cloud layer. This would result in 15-20kt of
shear within the stratus promoting collision & coalescence and
drizzle production. Temps could inch above freezing, lessening the
freezing potential Monday if drizzle does fall, but it is
something to keep an eye on.
Izzi
&&
.SHORT TERM...
209 PM CST
Through Tonight...
Moderate to heavy snow continues mid afternoon across northern
Illinois and northwest Indiana. This morning, a slow moving band
of snowfall set up across western portions of the CWA where over
6 inches of snow has fallen and that area had to be upgraded to a
Winter Storm Warning. The band eventually shifted east across
portions of the Chicago metro area where a few inches of snow
quickly accumulated and the band is now in the process of
reorienting along the I-80 corridor. Latest RAP shows the best
F-Gen focused along this corridor and shifting east out of the CWA
by late this afternoon or early evening. Already seeing some signs
of improvement west of the I-39 corridor and expect improvement
into the Chicago metro by around 23-00Z. There is some possibility
eastern counties may need a brief extension in headlines for an
hour or two but going to let the timing ride for now. Storm total
snow of 3 to 6 inches appears likely within the advisory area
including the Chicago metro with 1 to 4 inches south of the
advisory. Meanwhile, the warned counties of Ogle, Lee and Dekalb
are expected to finish out in the 5 to 9 inch range.
Expect overcast to mostly cloudy conditions to persist overnight
with temperatures only dropping off a little...into the mid to
upper 20s west of the Fox River Valley and low 30s farther east.
Areas of fog appear possible, especially in the west with weak
surface ridging building into that area. BMD
&&
.LONG TERM...
Monday through Sunday...
231 pm...Forecast concerns included potential for mixed precip
Monday night/Tuesday morning...chance of snow Wednesday night/
Thursday morning and much colder for the middle/end of the week.
High pressure over the Ohio Valley will be moving east Monday
afternoon into Monday night. With the new snow pack and low sun
angle...expect high temps Monday to be below guidance levels even
if some sunshine develops though low level moisture fields would
suggest that some low cloud cover could remain with increasing
mid/high clouds later Monday.
Models remain fairly similar with one low moving northeast
through the Ohio Valley/Mid Atlantic Tuesday and a second low
moving across the upper midwest Monday night and into Ontario
Tuesday...with a trailing cold front moving across the area on
Tuesday. There has been some consistency with the low moving
across the Ohio Valley remaining far enough to the southeast that
precip would only reach the far southeast cwa late Monday night
into Tuesday morning. Only the NAM remains further northwest
across the cwa and confidence with this solution is low. Mainly
chance pops with this system but confidence regarding where the
precip actually occurs is low. Thermal profiles continue to
suggest that precip would be a mix and possibly rain or freezing
rain depending on surface temps. With the new snow pack...its
likely that temps will drop to then hover near freezing Monday
night into Tuesday morning...before slowly warming. Too close to
call from this distance but some mention of light freezing rain
seems prudent at this time. If temps end up a few degrees warmer
or the precip shield continues to shift to the east...then changes
to precip type/timing can be expected.
Cold air begins to spread into the area Tuesday and continues
through the end of the week. Models continue to try to develop
light snow across the area Wednesday afternoon into Wednesday
night as the coldest air arrives. The Ecmwf is most developed...
though still a weak surface low through the Ohio Valley.
Confidence regarding system development and associated snow
remains low with just chance pops for this time period.
Another wave rotates across the area Thursday/Thursday evening
that could bring some snow showers or light snow to the area.
Wind direction with the colder air should keep any significant
lake effect snow east of Porter County but still chance mention
for far northeast Porter County later in the week. A clipper like
system is possible next weekend but too early for any specifics
with this system. cms
&&
.AVIATION...
For the 00Z TAFs...
The heaviest of the snow is pushing off to the east, with just
some lingering light snow expected for a few hours. Vis has
improves to 1sm or higher at all TAF sites except RFD which
remains at 3/4sm at issuance time. Latest satellite imagery shows
the layered high cloud over far nern IL/nwrn IN with a widespread
area of st/fg to the west. Expect that over the next few hours,
the higher cloud will push to the east, with the lower st/fg
spreading over the entire area. Have made some adjustments to the
cig/vis for the overnight and morning hours. With a blanket of 5
inches or more snow on the ground and temps expected to trend down
to just below freezing, and no drier air likely to move in
overnight, have trended cigs/vis back down to ifr, with the
potential for lifr conditions for the early morning hours. The
highest probability of 1/4sm will be for the more rural areas,
but with the snow cover in place, do not expect much of an urban
heat island effect overnight, so even the more urbanized area will
have the potential for fg/fzfg to develop. Given some uncertainty
in the situation for the the urban areas, have only gone with a
tempo 1/2sm for ORD/MDW with prevailing 1/4sm for RFD/DPA/GYY.
However, there is some potential for ORD/MDW to see the prevailing
1/4sm, but confidence is too low at this point to include this in
the TAFs at this time. Expect that ifr cigs should remain at least
through the morning and into early afternoon. Have gone with
improving conditions to mvfr by early afternoon, but there is a
high probability that the timing of improvement may be too fast.
&&
.MARINE...
342 pm...A trough of low pressure will move across the lake this
evening as high pressure moves across the Ohio Valley overnight
into Monday. The gradient will tighten this evening with southerly
winds turning westerly and increasing into the 15-25kt range and
there could be some gusts to 30kts. Low pressure will move across
the upper midwest Monday afternoon and into Ontario Tuesday. Winds
will turn southerly ahead of this low and may increase to 30 kts
as the gradient tightens Monday night. High pressure will spread
across the northern and central plains Tuesday into Wednesday and
then strengthen as it moves across the central part of the country
Thursday into Friday. A tight gradient along with much colder air
spreading across the lakes region will allow strong west/northwest
flow to develop mid week and continue through late week with a
period of gales possible Thursday into Friday. cms
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&
$$
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Area Forecast Discussion
National Weather Service Newport/Morehead City NC
957 PM EST Sun Dec 4 2016
.SYNOPSIS...
High pressure will move offshore tonight. Low pressure will move
quickly up the coast late tonight and then offshore Monday,
followed by high pressure late Monday. Complex low pressure will
develop across the area Tuesday and move offshore Wednesday. A
strong cold front will move through Thursday evening.
&&
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
As of 10 pm Sunday...Light rain covers the forecast area this
evening. As the lower layers saturate and dewpoints rise from
current levels in the lower/mid 40s, expect intensity and
coverage of rain to increase which is forecast by latest HRRR
model. Have categorical PoPs through the night as rain becomes
steadier. Fairly uniform low temperatures expected tonight with
lows in the mid 40s at most locations.
&&
.SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
As of 310 PM Sunday, as surface low moves along then offshore of
the northern Outer Banks, some drier air will get advected into
the region during the morning hours on Monday, mainly inland. Rain
may linger along the coast during the early part of the day and
will taper the PoPs inland. Some partial sunshine is possible over
much of the area during Monday afternoon as most of the rain moves
offshore. High temperatures will range in the upper 50s to lower
60s for Monday.
&&
.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
As of 316 AM Sun...Another round of rain moves through late
Monday night through Tuesday. Dry and warm mid week followed by a
strong cold front and arctic air Friday into next weekend.
Monday Night into Tuesday...Strong compact shortwave trough will
eject out of the southern plains Monday night and move through the
TN/OH valley Tuesday. 04/00Z model suite remains in good
agreement with this system bringing another round of rain during
this time frame. Strong omega develops late Mon night as
strengthening S flow develops on 50 kt LLJ. The region will be in
RRQ of upper jet and will induce large area of div q over the
region. Deep southerly flow downstairs combined with large area of
omega advancing towards E NC will spread in rain from west to
east after midnight and have an increasing pop trend through the
overnight as a result. First half of Tue will be a washout as deep
moisture/lift is maximized over the area. Second area of
cyclogenesis progged to develop along the NC coast and quickly
exit on Tuesday with winds becoming NW behind the exiting system.
It will be warm despite the rain with highs in the 60s east to
mid/upr 50s coastal plain which should remain in northerly flow on
cool side of the low.
Tuesday Night through Thursday...Dry conditions return with
subsidence and advancing high pres behind the departing system.
It will continue to be mild as upr ridge amplifies across the
eastern CONUS in response to deepening trough across the
Intermountain West and Plains states. Temps above climo expected
with highs in the 60s and lows in the mid 40s to lower 50s.
Friday through Sunday...Aforementioned trough across the
western/central CONUS will translate eastward bringing coldest
air mass of the season to much of the eastern 2/3 of the CONUS.
Strong cold front will push through E NC by Fri with strong CAA
ensuing behind it. Blustery and cold conditions expected Friday
through Sat with high temps in the 40s and lows 20-25 interior to
low 30s OBX.
&&
.AVIATION /03Z MONDAY THROUGH FRIDAY/...
Short Term /Through 18Z Monday/...
As of 7 pm Sunday...VFR conditions are slowly giving way to MVFR
and IFR conditions, which will eventually become widespread
overnight. Ceilings will gradually lower throughout the rest of
the evening. Heavier rain will hold off until overnight. Rain and
low clouds will exit the airspace quickly Monday morning and VFR
conditions should return by mid morning.
Long Term /Monday Night through Friday/...
As of 316 AM Sun...Ceilings will lower again Monday night into
Tuesday with strong low pressure moving across the area and more
widespread rain. The low will exit Tue afternoon and evening
though low clouds and fog may persist on Tue night. High pres
builds in for Wed into Thur bringing return to VFR conditions.
Strong cold front will push through Thur night into Fri with gusty
NW winds developing behind it.
&&
.MARINE...
Short Term /Tonight and Monday/...
As of 10 pm Sunday...Presently seeing E/NE winds at 5-15 knots.
Seas are in the 3-4 foot range. Latest local SWAN/NWPS model shows
some 6-foot seas into southern waters south of Ocracoke starting
Monday into late Monday afternoon. These higher seas will be
mostly in the offshore waters driven by gusty S/SW winds offshore
around surface waves moving near or just offshore. As a result,
have initiated a Small Craft Advisory from 12z-21z Monday for the
waters south of Ocracoke. Increased seas will affect northern
waters from 18z Monday through 06z Tuesday. NE winds of 5-15 knots
tonight veer to SE late tonight and around to West 10-20 knots for
Monday.
Long Term /Monday Night through Friday/...
As of 316 AM Sun...A stronger low pres area develops and moves up
the coast on Monday night and Tue, bringing strong gusty winds
and probable SCA conditions. Tough to pin down the speed and
direction of winds at this time as the low will be passing through
the marine domain making timing of wind switch difficult this far
out in time, but it appears gusty easterly winds ahead of the low
will then switch to the NW and remain gusty as the low exits. The
low will exit Tue night with winds diminishing on Wednesday. Winds
back to the SW or W by Thur with approach of strong cold front
that will move through the waters Thur night or Fri bringing
another round of gusty 20-30 kt winds in its wake.
&&
.MHX WATCHES/WARNINGS/ADVISORIES...
NC...None.
MARINE...Small Craft Advisory from 1 PM Monday to 1 AM EST Tuesday for
AMZ150-152-154.
Small Craft Advisory from 7 AM to 4 PM EST Monday for AMZ156-
158.
&&
$$
SYNOPSIS...CTC
NEAR TERM...HSA/CTC
SHORT TERM...CTC
LONG TERM...TL
AVIATION...HSA/TL/SGK
MARINE...HSA/CTC/TL
Area Forecast Discussion
National Weather Service Marquette MI
706 PM EST Sun Dec 4 2016
.SHORT TERM...(This evening through Monday)
Issued at 405 PM EST SUN DEC 4 2016
12Z raobs/latest wv imagery and RAP analysis show a fairly strong
shrtwv moving e thru srn MN/Iowa toward the the wrn Lower Lks,
accompanied by 12hr h5 hgt falls close to 100m. Although the sharper
dvpa/deep lyr qvector cnvgc/upr dvgc are passing to the s closer to
the shrtwv track, widespread snow has overspread the cwa under the
the colder cld tops expanding into the Upr Lks under the general upr
diffluence/waa ahead of the shrtwv. The pcpn is beginning to
diminish over much of MN/wrn WI as the colder cld tops pass to the
ne of those areas.
Main fcst concerns in the short term focus on pops/sn amounts/going
headlines into tngt associated with shrtwv passing to the s.
Late Today/Tngt...The nrn edge of the sharper forcing wl impact the
se half of the cwa thru this evng, when a steady s wind off the
relatively warm waters of Lk MI under h85 temps remaining as low as
-6 to -7C wl result in some lk enhancement. Thus carried the more
persistent, hier pops in that area. Some of the hier res models
indicate over 0.50 inch of liquid equivalent pcpn wl fall in some
areas under the heavier bands that could impact the cwa e of a line
fm about Escanaba to Munising into Schoolcraft County. Relatively
hi/narrow dgz shown on the fcst sdngs wl result in sn/water ratios
10-15:1, butnot out of the question some places in this area could
see up to 5-6 inches of wet snow. The sly flow off the relatively
warm waters of Lk MI and the Green Bay may result in a mix with rain
at some places along the shore and hold down accums in those areas.
Away fm the area of enhancement, expect up to 2 to 3 inches of wet
sn under axis of 2g/kg of h7 specific humidity in the mid lvl mstr
surge ahead of the shrtwv to the s. Going winter wx advys include
Delta, Alger, Schoolcraft and Luce Counties until 06Z, when the
larger scale forcing wl exit to the e and give way to dnva/deep lyr
qvector dvgc/subsidence/mid lvl drying ahead of trailing shrtwv rdg
axis. There could be some drizzle/freezing drizzle over mainly the
hier terrain fm the Porcupine Mtns thru the Keweenaw as the incrsgly
shallow mstr wl occur under the dgz in the presence of an upslope
wsw wind behind the passing sfc lo pres trof.
Mon...Although some lgt pcpn may linger in the mrng over mainly the
Keweenaw with the upslope wly flow ahead of an aprchg hi pres rdg,
the arrival and passage of this rdg axis should end that pcpn and
allow for at least partial sunshine at many places under the mid lvl
drying associated the passing shrtwv rdg axis. But many of the
models show more waa clds arriving in the aftn as the llvl flow
shifts to the s following the passage of the sfc hi pres to the e.
Some of the models even generate some light pcpn over the wrn cwa
where the sharper isentropic ascent and some pva ahead of a shrtwv
moving thru the nrn Plains results in some deep lyr qvector cnvgc/
greater mid lvl moistening. H85 temps recovering to near 0C wl
support abv normal max temps well into the 30s and perhaps the lo
40s, especially over the w with a downslope s wind.
.LONG TERM...(Monday night through Sunday)
Issued at 258 PM EST SUN DEC 4 2016
Late Mon into Mon night the Great Lakes will be within shortwave
ridging btwn the shortwave trough (bringing the snow to Upper
Michigan this aftn) exiting across New England and rather strong
shortwave trough crossing the northern Plains and pivoting north
into southern Manitoba and northwest Ontario. Could see light snow
showers into far west cwa Mon night as h7 moisture/h7-h5 q-vector
convergence pass by mainly to the west. Associated sfc low deepens
blo 1000mb along the SE Mantioba/Ontario border by 12z Tue which
sends a sfc cold front toward western Upper Michigan. Could be light
rain/snow around on Tue over parts of Upper Michigan as the front
crosses especially if the GEM and ECMWF are on track showing
stronger shortwave/h7-h5 q-vector convergence lifting across WI and
Upper Michigan Tue aftn into Tue evening. Temps should be steady or
even fall slightly over the west as colder air works in from the
northern Plains. Could be lake effect on the Keweenaw but should be
light as inversion remains less than 5kft and winds are more SW than
W.
Shortwave trough becomes more of an upper low Tue night into Wed
with sfc low slowly crossing northern Ontario. As this occurs,
another shortwave trough will be tracking across the southwest conus
to the southern Plains with a sfc low crossing vcnty of northern
TX/OK. On Wed, expect lake effect to affect more of the northwest
cwa as colder air moves in with h85 temps down blo -12c and as sfc-
h85 winds veer more W or even NW if the more aggreesive GFS is
correct. Inversion heights around 5kft increase to 6-8kft bringing
dgz into much of lake convective layer so there should be moderate
les. Snow showers over the west could become heavy at times if
stronger low-level convergence develops. Away from the lake effect
the cooldown will be well underway with daytime highs in the 20s
most areas. Could be breezy especially near Lk Superior.
Deep trough aloft with widespread cold air will continue to occupy
much of the eastern half of the Conus late this week with the cold
reaching the deep south and Gulf coast by Fri. Over the Great Lakes,
lake effect snow will be the main story. Areas favored by NW winds
will see the the most snow across Upper Michigan as h85 temps
continue to fall to around -15c by late Thu into Fri. Plenty of deep
moisture to h7/10kft with large scale troughing and low level
cyclonic flow so lake effect may be moderate to even heavy depending
on when shortwaves work through to enhance the snow further. Though
the TX/OK wave and sfc low look to stay south of Upper Lakes
limiting widespread system snow, once that system lifts across New
England late Thu into Thu night it should help a reinforcing cold
front drive across the Upper Great Lakes. GFS continues to be on the
faster side with the fropa (Thu aftn) and ECMWF is slower (Fri
morning into early Fri aftn). As this front moves through winds
could become more NNW or N so lake effect could shift around from
the northwest flow areas to the northerly flow areas for a time.
Unlike the regime we have been in the last week or so with only
marginally cold low-level temps, low-level temps late this week will
be sufficiently cold for snow, so should see snow all areas, even
near the Great Lakes shorelines.
Lake effect will continue at least into Sat morning for NW flow
areas, especially over eastern cwa. Another shortwave works across
north central Conus by next Sun. Sfc low should accompany the
trough. Have to wait on specifics in terms of system snow across
Upper Lakes, but just from a pattern recognition standpoint, should
see lake enhanced snow off Lk Michigan since h85 temps are blo -10c
as the system approaches. Certainly by late next week and next
weekend it will look and feel more like winter across most of Upper
Michigan.
&&
.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 705 PM EST SUN DEC 4 2016
As disturbance that has generated -sn shifts e, expect slowly
improving conditions at KIWD/KCMX/KSAW as -sn ends and drier air
eventually spreads into the area. Arrival of high pres ridge and
anticyclonic flow on Mon will aid the improvement. At KIWD, MVFR
conditions should fall back to IFR for a time overnight, before
improving to VFR Mon morning as low clouds scatter out. At KCMX,
expect LIFR conditions to improve to MVFR by late evening, but will
likely fall back to IFR early in the morning as winds veer to an
upslope westerly direction. Not out of the question that there could
be some -FZDZ under this upslope w wind. Low clouds should scatter
out at KCMX by aftn. At KSAW, IFR conditions this evening will
improve to MVFR overnight. Low clouds will then scatter out in the
morning, leaving VFR conditions for the remainder of the day.
&&
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 258 PM EST SUN DEC 4 2016
S to SW winds 20-30 kts through Mon then as low pressure trough
moves in Mon Night then deepens into to a low pressure system on Tue
northwest of Lk Superior, the tightening pressure gradient will
result in SW gales to 35 kts, especially over the west and north
central portions of Lk Superior. NW winds to 30 kts continue Wed
into Fri as colder air moving in increases over water instability.
The colder air and building waves will result in some freezing spray
by late in the week.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
Winter Weather Advisory until 1 AM EST Monday for MIZ006-007-013-
014-085.
Lake Superior...
None.
Lake Michigan...
None.
&&
$$
SHORT TERM...KC
LONG TERM...JLA
AVIATION...Rolfson
MARINE...JLA
Area Forecast Discussion
National Weather Service Pocatello ID
534 PM MST Sun Dec 4 2016
.UPDATE...
Updated forecast to include upper snake plain in a winter weather
advisory for tonight. Getting reports of icy, difficult to drive
roads on the benches above Rexburg. Very little snow, but given
temperatures, seems to be having some bigger impacts than normally
expected.
Valle
&&
.PREV DISCUSSION... /issued 209 PM MST Sun Dec 4 2016/
SHORT TERM...Tonight through Wednesday. Vigorous shortwave axis
and associated surface cold front slowly shifting through Idaho
panhandle this afternoon per water vapor satellite imagery.
Consolidated moisture stream ahead of feature producing moderate
snows across portions of East Idaho this afternoon. Snow totals
slowly building up in central mountains with precip shield now
pushing east across the remainder of the region. Strong south
winds along south edge of Snake Plain along interstates continuing
to keep areas dry. HRRR paints winds shifting more southwest
around 02Z, give or take an hour, which should be passage of the
front. Precip enhances along that line during this time frame.
Surface wet bulbs likely cold enough to support snow down the
surface by this point though stronger temperature gradient lags
the wind shift by 4-6 hours, coincident with shortwave axis.
Expect snow to continue shifting focus southeast toward the Bear
Lake area after 06z, but concern shifts to blowing snow in
strengthened gradient behind the front. Have highlighted areas
with gusts > 20kts for areas of blowing snow, which matches well
with current headlines and includes some areas of the Snake Plain.
Limited accumulations in the Snake Plain ahead of the front will
likely limit impact, especially with overnight event. Therefore
will hold off on any headline at this time. Model consensus is to
shift feature out of East Idaho early Monday, with most areas
seeing snow end before or around sunrise. Have kept decreasing
orographic snows along Wyoming border through the day tomorrow but
decreasing trend is clear. Have shifted end of eastern zone
headline to end earlier at 18z, but believe an even earlier
cancellation is likely, perhaps even with next forecast package as
conditions decrease overnight.
Northwest flow stays in place but flow generally dry and anti-
cyclonic through Monday night. Very cold temps begin to shift into
the region behind current system and will likely see several below
zero readings. Next system drives through PacNW and arrives in
central mtns by Tuesday morning. Quite a bit of difference between
GFS/NAM in depth of next shortwave and placement of associated
precipitation. Highest precip chances between 06Z Tue-00Z Wed,
then decreasing afterward. QPF amounts not impressive but
increasingly cold temperatures and higher snow ratios could still
lead to a few inches mainly higher elevations. Remnants of system
could linger into Wednesday but have kept precip chances low. DMH
LONG TERM...Wednesday night through next Sunday. The GFS and ECMWF
are still several hours apart with the onset of precipitation for
the storm coming in for Thursday and Friday. The GFS still pushes
moisture into the eastern highlands with the EC only into the
western mountains, although the latter has sped up just a bit.
Despite that, it looks like Thursday night and Friday will be WET
AND WINDY across all of eastern Idaho. While we are still a ways
out, the central and eastern mountains will see quite a bit of snow
again along with blowing snow. This storm will eventually turn warm
at lower elevations for at least a mix for a bit, but we might be
looking for some decent snowfall at those locations as well. The
weekend will be drier at lower elevations but showers will be
possible especially in the mountains. Keyes
AVIATION...We are finally seeing rain and snow affecting valley TAF
sites as of 2pm. Meanwhile, KSUN has been socked in all day with
snow and KDIJ is FINALLY seeing snow and lower ceilings/visibility
developing as downslope effects weaken. Through at least this
evening, we should continue to see conditions worsen at all sites
(except for KSUN which will stay IFR). That means look for IFR
(potentially LIFR) as ceilings and visibility lower. At sites seeing
rain now, that will quickly change to snow as the cold front
arrives, which also may spell blowing snow at KBYI, KPIH, KIDA and
KDIJ. Strong wind shear should also continue until frontal passage
as well with ~50kt winds within 1000ft of the ground. There will be
an abrupt end to the snow within a couple hours of the front
passing. Timing would be as follows: KSUN (4-6Z), KBYI (4-6z), KPIH
(5-7z) and KIDA (6-8z). KDIJ will likely remain at IFR until around
10-13z) due to snow lingering in northwest flow into the Teton
Valley. Conditions will improve, including diminishing winds through
the day tomorrow. Keyes
&&
.PIH WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 6 AM MST Monday for IDZ032.
Winter Weather Advisory until 6 AM MST Monday for IDZ020.
Winter Storm Warning until 11 AM MST Monday for IDZ019-023-025.
Winter Storm Warning until midnight MST tonight for IDZ018-031.
&&
$$