Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/05/17
Area Forecast Discussion...corrected date
National Weather Service La Crosse WI
549 PM CST Mon Dec 4 2017
.SHORT TERM...(Late Afternoon through Tonight)
Issued at 304 PM CST Mon Dec 4 2017
High Impact Weather Potential: First things first, can`t rule out
an isolated severe storm through 7 pm as the front arrives.
Thereafter, wind remains the big story through the night, but
also watching the potential for a little accumulating snow for a
time this evening, especially north of a line from about Charles
City, IA to Black River Falls, WI.
A true tale of two seasons ongoing across the region at the
moment, with very mild air drawn northward into our area ahead of
an approaching strong cold front, just pushing into parts of
southeast MN and northeast IA as of 20Z. That feature is of course
tied to a strengthening surface cyclone expected to lift north
over western Lake Superior this evening, sending much colder air
in our direction along with a rapidly tightening pressure
gradient. Temps in many areas have approached (or will approach
shortly) record values well into the 50s and lower 60s for
December 4th (wow!), with a broken line of convection now
developing along the incoming sharp wind shift, aided by 500-750
J/kg MUCAPE pooled ahead of the front. As this line progresses
east, would anticipate it continuing to develop through 6-7pm, and
with strong 0-2km shear in place, can`t rule out a few stronger to
severe storms, especially east of the Mississippi River, though
we`ll have to overcome some residual surface-based inhibition as
well as a notable warm layer up around 800mb. RAP soundings
suggest we just may do this across far southern areas, and do have
a small concern for low-topped supercell development so definitely
something to watch closely.
That severe threat will end quickly just after 00Z as the cold
front clears the area, with steepening low level lapse rates in
strong cold advection through the evening promoting mixing up to
850-800mb. Solid area of 40-50 knots through the mixed layer
continues to suggest many areas will see surface gusts of 45-50
mph, especially for a few hour period just behind the front. Can`t
rule out a few gusts to 55 mph, especially west of the
Mississippi River in the tightest gradient but overall, just a
windy period through the evening and night, with speeds gradually
subsiding later tonight with slowly weakening mixed layer flow.
Also of interest is the potential for a few hour period of snow to
impact western and northern areas this evening, associated with
deformation forcing as the upper shortwave swings across the area.
Recent trends suggest this feature may be a little more robust
farther east into our area, with the potential for a half-inch to
maybe one inch of accumulation north of a Charles City, IA to Black
River Falls, WI line. This should be short-lived, but it`s possible
snow could fall heavily for a brief period, with some messy travel
possible while snow is ongoing given the gusty winds as well. At the
moment, don`t see the need for a Winter Weather Advisory just yet
but will hit the potential impacts a little harder in graphical
form/social media.
.LONG TERM...(Tuesday through Monday)
Issued at 304 PM CST Mon Dec 4 2017
Steady as she goes in the temperature department right on through
the weekend, with our well-discussed and rather stable western North
America ridging pattern teleconnecting well to broad upper troughing
centered over the Great Lakes. That of course opens the doors to
persistent shots of colder air working down across the area, as well
as the likelihood for periodic shortwaves to also traverse the flow.
As is typical is such setups, the timing and placement of each wave
remains rather low confidence beyond about 2 days, with already
plenty of change noted in the position or even existence of said
waves from just 24 hours ago.
Given such uncertainty, a blended approach remains best with regard
to any precipitation chances, but overall the pattern will not be
very conducive to any big chances for significant wintry
precipitation the next 7 days. With that said, a few stronger waves
could certainly put down some light snow accumulation, with one
target toward later Thursday night or Friday with consensus guidance
hinting at a stronger wave crossing the area with a modest
frontogenetic response somewhere nearby. Outside of that, periodic
flurries or light snow showers could occur with just about any
shortwave, but with the larger message being steered toward an
extended stretch of near to below normal temperatures for early and
mid December (a HUGE change from the past 2 weeks).
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 549 PM CST Mon Dec 4 2017
Through 7 PM, a line of showers and scattered storms located along
and ahead of a cold front will move east through western
Wisconsin. With this line already east of the TAF sites, the
showers and storm were not added to the TAFs. In the wake of this
front, ceilings will become MVFR. These MVFR have already moved
into KRST and they will move into KLSE around 05.01z.
Overall, the HRRR is handling the deformation band the best. It
shows that some light snow may fall at KRST between 06.04z and
06.06z. As a result, included a MVFR visibility at that time. By
06.09z, the deformation will be pulling out of the TAFs and the
ceilings will become VFR.
Strong west winds will be seen at the TAF sites into Tuesday.
The strongest winds will be from 05.03z and 05.13z when the wind
gusts will be in the 35 to 45 knot range.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...Wind Advisory until 6 AM CST Tuesday for WIZ017-029-032>034-
041>044-053>055-061.
MN...Wind Advisory until 4 AM CST Tuesday for MNZ079-086>088-094>096.
IA...Wind Advisory until 4 AM CST Tuesday for IAZ008>011-018-019-029-
030.
&&
$$
SHORT TERM...Lawrence
LONG TERM...Lawrence
AVIATION...Boyne
Area Forecast Discussion
National Weather Service Duluth MN
916 PM CST Mon Dec 4 2017
.UPDATE...
Issued at 904 PM CST Mon Dec 4 2017
Based on latest trends of RAP and HRRR which move snow into
Wisconsin rather than Minnesota decided to replace portions of
the winter storm warnings with advisories in Minnesota. Meanwhile
in Wisconsin, replaced the wind advisory with a winter weather
advisory as more snowfall is expected there in addition to the
winds so wrapped those two into one product. Latest water vapor
imagery shows a comma head forming over Minneapolis with a
deformation band extending northward. This is progged to move
across NW Wisconsin, so upped snowfall totals there by quite a bit
and am still probably too low with 2-4 inches expected.
Considered moving to just winter weather advisories in Minnesota,
but a little concerned that the deformation band may move
northward and thus decided to keep the arrowhead in the wsw, but
the probability of that happening is less than 50 percent; though,
there is a strong northward surge in WV imagery though, so we`ll
see.
&&
.SHORT TERM...(This evening through Tuesday)
Issued at 408 PM CST Mon Dec 4 2017
Things are evolving very rapidly this afternoon as a rapidly
deepening low pressure area is centered between the Twin Cities
and Duluth. This low is forecast to deepen around 20 mb to
somewhere around 970 mb by midday tomorrow north of Lake Nipigon.
Large scale forcing for ascent is becoming intense as the primary
upper vort max approaches the region from the northwest
Iowa/northeast Nebraska/southeast South Dakota area. Rather
significant instability is in place in both terms of CAPE and EPV,
which will result in robust vertical motion fields for the next 12
to 18 hours as the main lobe of forcing moves across northern
MN/northwest WI. The other result of this is that thunderstorms
will be somewhat widespread across northwest WI thru this evening,
and with the lower troposphere being so cold this time of year,
it will not take much to get hail out of the stronger updrafts.
The rain/snow line is currently roughly from near Lake
Winnibigoshish to just east of International Falls, and this
transition zone will rapidly collapse eastward over the next 3-6
hours as the surface low deepens and moves across Duluth and on to
western Lake Superior coincident with the collapse of the inverted
trof across NCent MN that has thus far kept the colder air at bay.
While the period of intense lift and heavy precip will be
relatively short, there will be a 6-9 hour period if strong to
intense precip/snow rates. We have tried to reflect a majority of
the precip falling tonight and early Tuesday morning with the
primary deformation area, but light snow will persist for much of
Tuesday within a large area of wrap around saturation.
The other big story with this system will be a 9-15 hour period
of very strong northwest winds later tonight and Tuesday morning
when the super-position of strong cold advection, a very strong
gradient, and very strong pressure rises will be bullseyed over
northeast MN. The initial heavy wet snow will cling to trees and
power lines, and the winds would likely be strong enough to bring
down some weaker branches/trees anyway, so some power outages with
this system seem likely.
We will also need to keep a close eye on the potential for a
gravity-wave forced snow band late tonight/Tuesday morning across
Douglas/Bayfield Counties as the intense low level/cross
northshore ridge and strong cold advection are ideal for trapping
gravity wave energy. We may need to up snow totals in these areas
if this feature sets up over land.
.LONG TERM...(Tuesday night through Monday)
Issued at 408 PM CST Mon Dec 4 2017
Winter is back and it`s here stay. Much colder temperatures are
expected mid week through this weekend across the Northland with
highs as cold as the teens as lows below zero towards late-week.
Lake effect snow will linger across the Wisconsin snow belt region
Tuesday night through Wednesday night, then the next chance for
widespread light snowfall arrives Thursday night into Friday when a
clipper will bring light snow to the region and a round of lake
effect snow afterwards continuing through the weekend.
Mid to late week the primary concern will be the cold temperatures
across the Upper Midwest. Tuesday night into Wednesday the stacked
low that brought the return of the winter weather will be over far
northeast Ontario tracking northeast towards Hudson Bay. Meanwhile a
strong mid/upper level ridge will be building over the west coast
leading to strong north-northwest flow across the Great Plains and
Upper Great Lakes at low, mid, and upper levels of the atmosphere. A
reinforcing wave of colder air will arrive Wednesday night into
Thursday, then a subtle mid-level trough will track almost due south
across northern Manitoba and northwest Ontario to bring another
chance of light snow and even colder temperatures Thursday night
into Friday. By Friday night 850mb temps will be the coldest for
this stretch with -20C to -25C air aloft. The parade of weak
disturbances continues into the weekend as some weak ridging and
slight warming at low levels across the Upper Midwest precedes yet
another mid-level shortwave trough, this time coming out of Canada
Prairie into the Upper Great Lakes Sunday into Monday. Behind this
disturbance, extremely cold air on the order of -25C to -30C at
850mb is possible Monday night into Wednesday which would result in
frigid, well below normal temperatures - perhaps *high* temperatures
below zero by Wednesday.
High temperatures in the teens to 20s Wednesday through Monday,
except on Sunday when highs may reach the low 30s for parts of east-
central MN into northwest Wisconsin. Lows in the single digits above
zero Tuesday night, then single digits below or above zero
Wednesday, Thursday, and Friday nights, coldest in far northern
Minnesota. Lows "warmer" in the single digits to teens above zero
Saturday and Sunday nights. While these temperatures really aren`t
that out of the ordinary for mid December (average highs are in the
low 20s, lows in the mid-upper single digits for Duluth), the very
warm weather over the past two weeks will make this rapid change
from warm to cold feel more extreme.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 534 PM CST Mon Dec 4 2017
A strong deepening low pressure is crossing the area this evening.
Prevalent IFR expected through 07Z despite improving ceilings,
snowfall coupled with blowing snow should drop vsbys down to 1 SM
in snow bands. Winds will be strong and gusty with gusts to 35 kt
possible throughout the period - a wind shift will occur as the
low passes overhead changing direction to be predominately nwly as
it exits Tuesday.
&&
.PRELIMINARY POINT TEMPS/POPS...
DLH 13 16 8 18 / 90 30 20 10
INL 10 13 5 14 / 100 60 40 20
BRD 11 15 9 19 / 100 10 10 10
HYR 15 17 9 20 / 80 30 30 30
ASX 19 22 13 22 / 90 40 50 50
&&
.DLH WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until noon CST Tuesday for WIZ001>004-
006>009.
Winter Weather Advisory from midnight Tuesday night to 6 PM CST
Wednesday for WIZ004.
Lakeshore Flood Advisory until 6 PM CST Tuesday for WIZ002.
MN...Winter Weather Advisory until noon CST Tuesday for MNZ025-026-
033>038.
Winter Storm Warning until noon CST Tuesday for MNZ011-012-
019>021.
Winter Storm Warning until 6 AM CST Tuesday for MNZ010-018.
LS...Small Craft Advisory until 10 PM CST this evening for LSZ121-
143>148.
Gale Warning until 10 PM CST Tuesday for LSZ121-140>145-148.
Storm Warning until 10 AM CST Tuesday for LSZ146-147.
Gale Warning from 10 AM to 10 PM CST Tuesday for LSZ146-147.
&&
$$
UPDATE...Wolfe
SHORT TERM...Miller
LONG TERM...JJM
AVIATION...Wolfe
Area Forecast Discussion
National Weather Service Des Moines IA
616 PM CST Mon Dec 4 2017
...Updated Aviation Discussion...
.SHORT TERM.../Tonight through Tuesday/
Issued at 317 PM CST Mon Dec 4 2017
Confidence: Medium to High
Models handling of current system overall decent with elongated
trough over MN/IA and two low centers expected to consolidate into
one as the storm deepens through 12z Tuesday. At 19z cold front
nearing the I35 corridor with warm sector beginning to be pinched
off to the west and strong cold air advection replacing the mild
air. Surface moisture plume/axis of 50 to 55F dewpoints advecting
east/northeast with the surface front. Current SPC mesoanalysis
shows sufficient shear along with up to 500 J/kg MLCAPE just
ahead of the boundary. However a weak cap remains of 25 to 50 j/kg
MLCIN. SPC upgraded the far southeast to slight risk through
day1. Though it will be close...with the current convective
initiation just northwest of Kansas City it is likely that the
bulk of any stronger storm development this afternoon/early
evening will track east northeast and just miss our forecast area
in the southeast... tracking into eastern Iowa and western
Illinois/Missouri. The window of opportunity for any severe storms
will be very short...from roughly 3 pm to 6 pm as front slides
east. Will monitor for any development further west...but current
trends/SPC HRRR forecast both suggest this evolution. Winds remain
the big story and soundings continue to confirm strong northwest
winds with strong subsidence this evening into the overnight
hours. Sustained northwest winds to 30 to 35 mph with gusts to 50
mph still in the offing so will not make any changes to wind
advisory. Farther northwest in the forecast area...departing low
still expected to develop deformation axis which just clips the
northwest counties east to near KMCW. Though snow amounts are
forecast to be rather light and less than an inch ...some blowing
snow may occur due to the strong winds expected to accompany the
snowfall. Warm ground due to today`s high temperatures will likely
temper some of the blowing snow as it either melts or sticks more
readily for a time prior to lowering temperatures below 30
degrees. Window of opportunity for snowfall will be around 2 to 3
hours from just after 01z through 04z. Cold air quickly follows
the departing system tonight into tomorrow. After lows in the
teens northwest to the upper 20s southeast...highs tomorrow will
likely only recover to the mid 20s northwest to the upper 30s
southeast. Winds will remain brisk and again mix well into the
afternoon. Model continue to depict a weak shortwave with little
moisture...tracking southeast on the back side of the wave
tomorrow morning/early afternoon. Have kept isolated flurries with
passage of mid level clouds as destabilization may briefly add to
snow shower/flurry chances tomorrow.
.LONG TERM.../Tuesday night through Monday/
Issued at 317 PM CST Mon Dec 4 2017
Main change in upper pattern will have nearly been completed by
the beginning of this period with broad amplified eastern trof in
place. This will ensure that flow from Canada will be essentially
unabated for the remainder of the week. Average temperatures will
be from 20 to 30 degrees cooler than last week and back to below
normal for the first time since mid November. Main concerns will
be the various waves that drop into the western side of the trof
and their timing and impact on the state. Models indicate a wave
passing through on Tuesday night with sufficient lift for some
deeper saturation. The production of some flurries appears
somewhat likely across central portions of the state and have
continued the threat.
The thermal trof and cool north winds will persist on Wednesday
and Thursday with deep northwesterly flow. Next system drops down
for Friday into Friday night with some threat of light snow and
some slight moderation in temperatures. After the passage of this
system, some warmer air is expected to begin pressing eastward
from the Plains into the weekend with slowly moderating
temperatures. However, a reinforcing shot of colder air is
expected by the end of the weekend as another wave dropping
southeast reinforces the eastern trof. Overall, temperatures will
remain at or below normal for much of the later half of the
forecast.
&&
.AVIATION.../For the 00Z TAFS through 00Z Tuesday evening/
Issued at 613 PM CST Mon Dec 4 2017
MVFR stratus with intermittent IFR stratus impacting northern Iowa
this evening with the CAA. The strong winds will persist
throughout the period with a possible lull or slight decrease in
the winds Tuesday morning before the deep mixing develops again by
the afternoon. However, the gradient winds seem to remain strong
enough through Tuesday morning to keep at least wind gusts from
25-30 knot mentioned. This evening, expect some periodic wind
gusts to 45-50 mph.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 3 AM CST Tuesday for IAZ004>007-015>017-
023>028-033>039-044>049-057>060-070.
&&
$$
SHORT TERM...REV
LONG TERM...Cogil
AVIATION...Podrazik
Area Forecast Discussion
National Weather Service Sioux Falls SD
526 PM CST Mon Dec 4 2017
.SHORT TERM...(This evening through Tuesday)
Issued at 318 PM CST Mon Dec 4 2017
Well advertised potent surface low and upper level trough will
continue to dig across the northern and central Plains into tonight.
This fast moving system will be a strong punch of colder air and a
band of precipitation. The main precipitation player will be
associated with the deformation band which currently extends from
south central SD into eastern North Dakota. This band will continue
to slide eastward through the evening hours, exiting to our east by
midnight tonight. Frontogenetic forcing ahead of the deformation
band has not really materialized as expected, which had delayed the
onset of precipitation across the forecast area. The cold air
advection and strong winds however remain on track. Winds will
continue to gust to 35 to 45 mph with locally higher gusts to 55 mph
possible through the evening.
With the initial push of precipitation into south central SD and the
highway 14 corridor in SD over the past few hours, we have received
reports of rain freezing on powerlines and causing outages when
combined with the strong winds. With the low and mid levels cooling
rapidly this evening, expect the patchy freezing rain threat in
these areas to quickly switch over to snow. Will add mention of
freezing rain to the winter weather advisory in south central and
east central SD.
High res models such as the HRRR and NAM derivatives indicate the
potential for localized convective enhancement with the stronger
forcing arriving as the band of snow move approaches the I-29
corridor, then into southwest Minnesota. Think that brief heavy snow
will be possible for areas mainly along and north of I-90, however
the progressive nature of this system will limit snowfall amounts
from piling up more than than 2 to 4 inches. Most locations will be
closer to the 1 to 2 inch range, while amounts will generally be an
inch or less in northwest Iowa. With the strong winds and "flash
freeze" type conditions as the temperatures cool rapidly, travel
conditions will be hazardous. Blowing snow and reduced visibilities
will be a huge concern with near blizzard conditions possible during
snowfall. Timing places the snow band in the FSD and SUX areas
during the evening commute. Decided to expand the winter weather
advisory further east into MN and southeast SD, generally following
where an inch or more of snow is possible. Again, amounts are not as
big of a factor in the advisory as the blowing snow and poor
visibility conditions. Elsewhere, the wind advisory remains in
effect for northwest Iowa and northeast NE where the winter weather
advisory is not in effect.
Skies will clear behind the exiting system tonight, with strong
winds only decreasing a small amount overnight. Northwest winds
remain windy into Tuesday, averaging 15 to 30 mph with higher gusts.
Clouds will be on the increase late tonight and Tuesday as a
reinforcing shot of cold air arrives with a trailing wave. Lows
tonight reach the teens with highs in the 20s to near 30 on Tuesday.
with the strong winds, wind chills will drop to near zero or a few
degrees below zero late tonight.
.LONG TERM...(Tuesday night through Monday)
Issued at 318 PM CST Mon Dec 4 2017
With the focus on the ongoing storm system, did not make any
alterations to the blended forecast in the mid and long range.
Pattern remains cold in comparison to the recent weather pattern,
but not extreme, with highs in the 20s and 30s. Northerly upper
level flow pattern stick around through the end of the week, with
a sharp ridge over the west coast and troughing over the Great
Lakes region. Models hint at several weak waves dropping
southward through the northern Plains during the week, however
model timing of these waves remains uncertain. Precipitation
chances remain spotty at best.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 520 PM CST Mon Dec 4 2017
Band of snow along the I-29 corridor as of 23Z will shift east
into southwest Minnesota and northwest Iowa through 02Z...and
shift further east into Central Iowa/Minnesota after 04Z. Strong
northwest winds gusting to 45kts will reduce visibilities in band
of snow.
Northwest winds will gradually decrease overnight...but remain in
the 15-30 mph range through much of the forecast period.
&&
.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Winter Weather Advisory until 8 PM CST this evening for
SDZ038>040-050-052>070.
Wind Advisory until midnight CST tonight for SDZ071.
MN...Winter Weather Advisory until 8 PM CST this evening for MNZ071-
072-080-081-089-097-098.
Wind Advisory until midnight CST tonight for MNZ090.
IA...Winter Weather Advisory until 8 PM CST this evening for IAZ001.
Wind Advisory until midnight CST tonight for IAZ002-003-012>014-
020>022-031-032.
NE...Wind Advisory until midnight CST tonight for NEZ013-014.
&&
$$
SHORT TERM...
LONG TERM...
AVIATION...BT
Area Forecast Discussion
National Weather Service Green Bay WI
516 PM CST Mon Dec 4 2017
Updated aviation portion for 00Z TAF issuance
.SHORT TERM...Tonight and Tuesday
Issued at 238 PM CST Mon Dec 4 2017
The latest RAP analysis and satellite/radar imagery show a
strengthening area of low pressure moving northeast over east-
central Minnesota early this afternoon. Widespread showers and
isolated thunderstorms within the warm advection zone have mostly
exited to the Upper Peninsula, though a few spotty showers and
some drizzle remain. Expect this lull in the precip to continue
for the rest of this afternoon, until a strong cold front,
currently over southern Minnesota and central Iowa, moves across
the region this evening. With the clouds and rainfall, winds have
struggled to increase, but could still see some gusts to 30 kts
through the start of the evening. As the cold front races across
the area tonight, precip trends, and potential for strong gusty
winds are the main forecast concerns.
Tonight...As low pressure lifts northeast across western Lake
Superior, a dynamic shortwave will push a cold front across the
region during the evening. The latest HRRR suggests a broken line
of showers will develop along the boundary, which should impact
much of the area. Cannot rule out some thunderstorms along the
front, given modest but sufficient elevated instability in place.
Tend to think the wind gusts will continue to struggle in the
warm sector ahead of the front, but the showers that are expected
to develop could be capable of bringing down the stronger winds
aloft. But the main push of wind will arrive behind the cold
front, mainly after midnight. Bufkit soundings continue to
indicate that wind gusts of 35 to 45 mph are likely, with some
gusts up to 50 mph possible. The highest gusts should occur over
central to northeast Wisconsin coincident with the highest
boundary layer winds. As the comma head rotates through the area
and temperatures fall below freezing, some snowfall is likely over
parts of central and north- central WI late. Amounts should be
relatively light, perhaps up to an inch over western Oneida and
Vilas Counties. Temps in the upper 40s to mid 50s in the evening
will fall into the 20s and 30s by daybreak.
Tuesday...Wrap around snow showers will likely continue for most
of the day across northern WI. Up to another inch looks possible.
Otherwise, a tight pressure gradient to go along with cold
advection and steep low level lapse rates will keep the strong
gusty winds going through the day. Highest gusts should again
occur over eastern WI where bufkit shows 35 to 45 mph will be
possible. With coordination from surrounding offices, will extend
the wind advisory for counties along and to the east of a Wautoma
to southern Marinette line. High temperatures will be much colder
than todays unseasonable readings, and range from the lower 20s to
lower 30s.
.LONG TERM...Tuesday Night Through Monday
Issued at 238 PM CST Mon Dec 4 2017
The strong low pressure system will continue to influence the
beginning of the long term period as it moves out towards the
northeast. A few snow showers will linger on late Tuesday night
into Wednesday morning, as lake effect mechanisms dominate the
region with the wind flow across Lake Superior. Winds will remain
primarily from the W/NW which will keep the heaviest snow showers
concentrated in the Upper Peninsula of Michigan, but far northern
Wisconsin could still see some isolated snow showers. Left flurry
chances in the region through Wednesday until the mid levels begin
to dry out overnight. Winds will slowly diminish starting Tuesday
night, but some weaker gusts are still likely in the region.
A drier and possibly more clear day is in store for Thursday,
especially away from the influence of Lake Superior. Lake enhanced
snow showers and flurries may continue to touch into northern
Wisconsin, but otherwise a cooler and drier day is expected.
Although timing may yet vary, a stronger piece of upper level
energy is expected to come through on Friday for a brief chance
to see some widespread snow showers. Due to the lack of available
moisture and the anticipated speed of this system, overall
accumulations are expected to be minimal. An additional chance
will be over the weekend, again with a lack of moisture before we
see a better chance of accumulations early next week with the
third shortwave. Timing and placement on this third event is still
too variable to determine.
Temperatures through the extended will be much cooler than the
start for December, and be 5-10 degrees below normal.
&&
.AVIATION...for 00Z TAF Issuance
Issued at 515 PM CST Mon Dec 4 2017
The lull in precipitation will come to an end as scattered
showers and isolated storms develop along a strong cold front this
evening. Strong south winds this evening will become southwest
then west behind the cold front with gusts approaching 40 kts
later tonight. A few hours of light snow is possible over north-
central WI overnight within the comma head of the strong cyclone.
Windy conditions will continue on Tuesday, with only light snow
over far northern WI. Conditions are expected to mainly be IFR
across the north, improving to MVFR later tonight into Tuesday.
Further south mainly MVFR conditions are expected with VFr
possible at times.
&&
.MARINE...
Issued at 238 PM CST Mon Dec 4 2017
South winds will continue to gradually increase this afternoon...with
gale force gusts possible. Subsidence in the cold advection and
dry slot tonight will produce southwest then west gale gusts with
the potential of storm force winds toward the open waters. These
conditions will persist into Tuesday before gradually tapering
off on Tuesday night.
&&
.GRB WATCHES/WARNINGS/ADVISORIES...
Wind Advisory until 6 PM CST Tuesday for WIZ022-038>040-048>050.
Wind Advisory until 6 PM CST Tuesday for WIZ031-037-045-073-074.
Wind Advisory until 6 AM CST Tuesday for WIZ005-010>013-018>021-
030-035-036.
&&
$$
SHORT TERM.....MPC
LONG TERM......Uhlmann
AVIATION.......Kurimski
MARINE.........MPC
Area Forecast Discussion
National Weather Service Grand Rapids MI
1003 PM EST Mon Dec 4 2017
LATEST UPDATE...
Update
.SYNOPSIS...
Issued at 330 PM EST Mon Dec 4 2017
Southwest Michigan will see significant weather changes over the
next 24 hours. Tonight will see rainshowers and even a few
thunderstorms. Temperatures will stay in the 50s through midnight,
then temperatures will fall quickly late tonight as a cold front
comes through. The mercury will fall through the 30s on Tuesday,
and into the 20s Tuesday night. The rain will change to snow late
tonight into Tuesday, but it will remain light through Tuesday
night. Accumulations will be less than an inch through Wednesday
morning.
A stronger push of snow showers is expected by Wednesday afternoon
and Wednesday night when an inch or two is expected, localized
amounts of four inches will be possible.
The rest of the week will remain cold with high temperatures only
around the freezing mark each day. Periodic snow showers will
occasionally result in additional accumulations.
&&
.UPDATE...
Issued at 1003 PM EST Mon Dec 4 2017
Latest HRRR guidance has the line of convection currently over
WI/IL weakening as it moves east. Skinny area of sfc based cape
near 500 J/KG helping to fuel the line falls off by the time it
hits lk MI. However elevated instability will still be present as
the convection moves east overnight with a few hundred joules of
MUCAPE progged. So a few rumbles may still occur overnight and
some locally stronger wind gusts to 50 mph are possible if the
stronger winds just above the sfc can be mixed down by the
convection. Winds after fropa will be gusty as well as deeper
mixing develops in the colder air. Strongest gusts near lk MI.
&&
.SHORT TERM...(This evening through Wednesday night)
Issued at 330 PM EST Mon Dec 4 2017
Major change to the region`s weather is on the horizon as a cold
front comes through late tonight. Temps will fall through the 30s
on Tuesday and into the 20s Tuesday night. Snow showers will began
to add up, especially Wed afternoon and night.
The very mild air with temps in the mid and upper 50s will hold
through the evening, but then come crashing down once the front
passes through about 09Z. The front could bring a brief period of
gusty thunderstorms tonight too.
The 40s will quickly vanish behind the front and much of Tuesday
will fall through the 30s. There will be a bit of moisture
immediately behind the front so we should see a few rain/snow
showers early Tuesday, that will dry up toward mid day. The rest of
day will be windy, but with just some flurries. The moisture
continues to look less favorable for Tuesday night. Thinking the
snow showers will continue, but they`ll be light. Any accums by
daybreak Wed should be under an inch.
A short wave swings through the upper trough over the Great Lakes
Wed afternoon and Wed night when the lake effect snow will increase.
This is the period when better accums should occur. Figuring an
inch or two in most places along and west of U.S. 131, with isolated
four inch amounts. An inch or less to the east of U.S. 131.
Will issue a wind advisory for the lakeshore counties starting
late this afternoon. Warm sector winds have already approached
criteria and as the front moves in, the winds should only
increase. Will run the advisory through Tuesday too as the cold
advection continues to produce winds to 40 knots or greater. This
is most likely for the lakeshore itself, as winds 10-15 miles
inland may not make it to the 40 knot criteria.
.LONG TERM...(Thursday through Monday)
Issued at 330 PM EST Mon Dec 4 2017
Not much of a change in the long term forecast. The main themes
remain colder than normal temperatures and periodic lake effect
snow. A long wave upper trough is forecast to remain entrenched over
the Great Lakes region through the period. Upper shortwaves will
periodically dive through the Western Great Lakes so there will be
periods of moderate to heavier snow. Timing these episodes are
problematic at this time range but we should see periodic heavier
lake effect snow right into the weekend and likely beyond. 850mb
temperatures have remained fairly consistent from run to run with
-12C to -16C temps common. Sunday looks a bit warmer now but still
cold enough for lake effect snow to continue. Just beyond this
forecast period out in the Tuesday through Thursday time frame of
next week even colder air is forecast with -20C air rotating in from
the north.
Bottom line: periodic lake effect snow and colder than normal
temperatures. Main impacts will likely be along and west of U.S.
highway 131. Accumulating snows are likely in Western Lower Michigan.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 700 PM EST Mon Dec 4 2017
Line of tstms now getting into wrn WI and IL at 7 PM EST is
expected to weaken once it gets to Lk MI later this evening.
However we may still get some thunder and gusty winds as this
convection comes through the area between roughly 04Z and 08Z.
Also MVFR to IFR cigs and vsbys could accompany the heavier
showers.
Once the cold front comes through late tonight, the showers will
end but MVFR cigs and gusty southwest winds will continue. Some
light snow showers or flurries may develop Tuesday afternoon which
could create reductions in vsbys, particularly at MKG and GRR.
&&
.MARINE...
Issued at 330 PM EST Mon Dec 4 2017
Gale warning will continue into Tuesday night. A few gusts toward
45 knots will be possible toward the Sable Points region, with 35 to
40 elsewhere.
&&
.HYDROLOGY...
Issued at 1257 PM EST Mon Dec 4 2017
Precipitation will fall as rain through tonight before colder air
rushes in behind a strong cold front and precipitation transitions
to snow. Total rainfall from this morning through Tuesday morning is
expected to range between 0.25 and 0.70 inches, which will not be
enough to cause significant rises on rivers and streams. Totals
exceeding 0.5 inches will most likely occur along and north of I-96.
A few thunderstorms may develop late this evening and overnight.
These would produce locally heavier rainfall amounts, and could
result in water ponding on roadways and low-lying areas.
Precipitation from Tuesday afternoon into the weekend will fall as
snow as temperatures remain below freezing. High snow-to-liquid
ratios will result in some snow accumulations (especially near the
lakeshore), but no significant liquid-equivalent accumulations.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Wind Advisory until 4 PM EST Tuesday for MIZ037-043-050-056-064-
071.
LM...Gale Warning until 4 AM EST Wednesday for LMZ844>849.
&&
$$
UPDATE...Meade
SYNOPSIS...JK
SHORT TERM...JK
LONG TERM...Duke
AVIATION...Meade
HYDROLOGY...HLO
MARINE...JK
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
857 PM CST Mon Dec 4 2017
.UPDATE...
857 PM CST
No big changes planned to going forecast this evening. Strong cold
front has breached our western CWA border and will sweep rapidly
across the remainder of the CWA over the next 3-4 hours. Ahead of
the front, have seen several sites tag wind advisory criteria
gusts this evening as the low level jet ramped up. An area of
showers and some t-storms will continue ahead of the front, though
convection has been quickly weakening and lightning activity
diminishing as the storms out run the narrow instability axis.
Still could see some 50+ mph gusts in the heavier shower activity
as it transports the higher momentum air to the sfc.
Biggest change to going forecast was to beef up sky cover
overnight into tomorrow morning as GOES-13 imagery shows expanding
area of stratus over Iowa spreading quickly east behind the front.
Have seen reports of flurries in the stratus deck, but as upper
low lifts northeast would expect the flurry threat from this deck
to diminish as it moves into northern IL. Other than the MET, most
guidance is largely unaware of this stratus, leading to low
confidence in how long it persists Tuesday. For now, just hung on
to the lower clouds through mid-morning, but will need to monitor
satellite trends overnight to see how it evolves. Forecast
soundings for Tuesday show drying beneath the sharp frontal
inversion, but given most models poor initialization of this
cloudiness, not convinced they are handling the post frontal low
level moisture well tomorrow either.
No changes planned to the wind advisory. Could see a short period
of slightly lower winds immediately behind the front, but as axis
of strong pressure rises shifts east and low clouds prevent any
decoupling, think it is possible we could see some near advisory
level gusts again later tonight.
- Izzi
&&
.SHORT TERM...
254 PM CST
Through Tuesday...
Main forecast concerns/challenges are with the thunderstorm
potential late this afternoon through mid/late evening, which now
includes an increased threat for isolated strong to severe
thunderstorms mainly across north central Illinois. Also,
strong/gusty winds will continue into tonight with current wind
headline still on track.
In the near term, dry conditions in place as lacking focus in the
area continues. However, this will likely change by mid to late
afternoon as system to the west draws near. Have been monitoring
convective trends over the last couple hours, with concerns
growing for an increased threat of strong to severe storms across
the region. Some limiting factors such as thick cloud cover and
weaker instability are still noted and valid items to consider,
but these trends have been showing that these could become offset
later today into this evening at least across a portion of the
CWA. Surface low continues to deepen across the midwest ahead of
large upper level trough and strong vort max swinging across the
region. Expect this low to further deepen through the night as it
lifts across the western Great Lakes, with associated surface
front pushing east the region. As large scale forcing quickly
increases over the next couple of hours, will see convection
develop over eastern Iowa into west central Illinois along and
ahead of this front.
While instability is in place across the region, observational
trends and rap analysis indicating a narrow ribbon of MLCAPE
situated right along this front. What`s also in place is weakening
CIN, with short term guidance indicating this trend of weakening
CIN may continue into this afternoon and evening into northern
Illinois. Cloud cover in place may limit this trend, but strong
forcing ahead of this system could offset this and allow further
erosion. This is concerning, as this front/environment along with
precip development push east towards the CWA later this afternoon.
Now, while the highest instability and higher threat for more
robust development is situated just to the west of the CWA at this
time, areas along and west of I-39 in northern Illinois still
have a threat for this stronger development before MLCAPE weakens
and CIN increases. Guidance has struggle to catch up on trends,
and think its also still struggling to the most eastward extent.
This will occur, while bulk shear will be more than sufficient for
organized development and while low level flow continues to
increase.
Showers/thunderstorms will likely reach the I-39 corridor in the
5-7 PM CST time frame, with the highest threat of strong to severe
thunderstorms along this corridor and with the main hazards
damaging winds. This is especially as the low level flow
increases, strong flow that is just right above the surface.
Although the main hazards would be strong damaging winds, could
not rule out an isolated tornado threat. This threat should be
higher to the west, but cannot rule out this threat reaching the
CWA. As these showers/storms push further to the east in the
evening, intensity of any storms should diminish. However, will
need to monitor for a continued threat further to the east as this
convection moves into northeast Illinois and northwest Indiana.
Southerly winds/gusts have continued to increase this afternoon,
and will likely continue this trend this afternoon into the
evening. Gusts of 45-50 MPH will remain a possibility but with
FROPA later this evening, could see a slight quick increase. Also,
outside of the thunderstorm threat, high wind gusts will be
possible with any shower.
Rodriguez
&&
.LONG TERM...
223 PM CST
Tuesday night through Monday...
Main message for the extended is colder and mainly dry. Blustery
winds continue through Wednesday, although winds will not be as
gusty as they were today (Monday). A clipper system could bring a
chance of snow Friday evening/Saturday.
The surface low driving the strong winds will continue northeast to
James Bay, but gusty winds will continue thanks to a tight pressure
gradient. 35 MPH gusts are expected Tuesday night followed by gusts
to 25-30 MPH Wednesday. Low temperatures Wednesday morning will be
in the low 20s while wind chills will be around +10 or in the single
digits above zero. Highs Wednesday will be in the low 30s, but wind
chills will make it feel around 20 degrees.
An upper level vorticity streamer may force flurries south of I-80
Wednesday morning, but no impact is expected. Cold and dry
conditions continue under the upper level trough through late week.
A clipper system rotates around the trough and may bring snow to the
region Friday evening/Saturday. A punch of colder air may accompany
the snow with forecast 925mb temps of -12 to -10 C. This could
result in colder temperatures than currently forecast Saturday.
Models then show a slight warming trend early next week.
JEE
&&
.AVIATION...
For the 00Z TAFs...
Southerly winds (190-200) should continue ahead of the front this
evening with prevailing gusts in the 30-38kt range expected.
Narrow line of SHRA/TSRA and associated strong cold front
currently approaching the MS River will move across the terminals
this evening. Current timing suggests 04-05z at ORD/MDW, but given
the potential for some additional development ahead of the line,
maintained a 2 hour TEMPO window. Given the strong wind fields,
even a moderately heavy shower could mix 40kt+ gusts to the sfc.
Expect the current TSRA activity to weaken as it moves across
northern IL, but still some robust SHRA and ISLD TSRA look are
expected. Behind the front, winds will remain strong and gusty
from the west, with gusts near or above 30kt likely overnight and
through the day Tuesday. Guidance suggests that skies should clear
out behind the front, though will need to monitor an area of MVFR
CIGS over western IA for potential of those clipping the terminals
late tonight/early Tues AM.
- Izzi
&&
.MARINE...
223 PM CST
Gale warnings remain in effect, and the only adjustment was
extending the open water gale warning into mid Wednesday morning.
The strong low over the upper Mississippi Valley will continue to
deepen as it moves to central Ontario by mid-day Tuesday. The low`s
cold front will push across the lake after midnight, and storm force
gusts are expected over the northern end of the lake. I did not
have enough confidence in persistent storm force winds to go with a
storm force warning.
The low will continue northeast, and west gales will continue into
Wednesday morning. West to northwest winds 20-30 kt persist through
Friday. A surface low/cold front turn winds north late Friday night
into Saturday morning. A brief period of gales is possible, although
confidence is low. A weak surface ridge passes over the region
Saturday night quickly followed by another low and cold front Sunday
night.
JEE
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Wind Advisory...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-ILZ011-
ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-ILZ022-ILZ023-
ILZ032-ILZ033-ILZ039 until 6 AM Tuesday.
IN...Wind Advisory...INZ001-INZ002-INZ010-INZ011-INZ019 until 6 AM
Tuesday.
LM...Gale Warning...nearshore waters until 6
AM Wednesday.
Gale Warning...LMZ777-LMZ779 until 9 AM Wednesday.
&&
$$
VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)
FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO
Please see the 05/00Z aviation forecast discussion below.
&&
.AVIATION...
VFR conditions are forecast. A cold front will slide southward
across west Texas and southeastern New Mexico overnight, with
initial FROPA expected at KHOB around 05/06Z with the remainder of
the terminals in the next 2-3 hours. Light and mostly variable
winds this evening will become northeasterly and gust to near
30kts behind this front. Winds will begin to lay down during the
morning hours, with 10-12 kts forecast after 05/18Z. Clouds will
begin to thicken and ceilings lowering after 06/00Z.
&&
.PREV DISCUSSION... /issued 245 PM CST Mon Dec 4 2017/
DISCUSSION...
One last warm day in West Texas and Southeast New Mexico, w/temps
already set to top out close to 20F above-normal before the
afternoon is out. Unfortunately, this will come to an end overnight
as a strong cold front backdoors into the region, courtesy of an
upper trough currently moving thru the upper midwest as per WV
imagery. Latest sfc analysis has the front in the Panhandles,
w/hi-res models putting fropa at KMAF ~ 04Z. This will take temps
well-below normal thru at least Friday.
In the meantime, WV imagery shows a secondary trough developing over
the west coast, which is set to settle se into the SW CONUS by 12Z
Wed. As it does so, an upper jet will move north of the area,
putting the FA under the RR quadrant by Tuesday night. Isentropic
upglide is forecast to begin after 00Z Wed...about 12 hrs earlier
than models were forecasting 24 hrs ago. The frontal AMS is pretty
shallow at first, w/precip expected to begin as all RA. However, as
the night wears on, the warm nose diminishes N-S, w/a changeover to
SN across the nrn-tier zones, a wintry mix further south, and a
RA/FZRA mix across the Davis Mtns/lwr Trans Pecos. As temps warm a
little Wed, frozen precip will try to change back over to RA, but
forecast soundings go south of the freezing lvl from near the sfc
all the way up by 00Z Thu, for a changeover to all SN everywhere but
the Rio Grande Valley and Big Bend Wed night.
The above scenario comes w/several caveats. NAM Forecast soundings
lean toward a wintry mix of precip, and dry things out rather early,
whereas the GFS saturates the column faster and transitions
everything to snow faster than the NAM, and also is slower to dry
things out. Models tend to scour out the PBL rather early in these
events, so the slower solutions seem favorable. If the NAM pans
out, precip types will be hard to nail down, as forecast soundings
ride the 0F isotherm up thru the warm nose. If reality favors the
GFS, SN will be favored. Attm, confidence is mediocre.
Higher QPFs look to be in the south, but w/antecedent ground temps
where they are, significant wintry precip accumulations are not
expected in the short term. The timing of the changeover to wintry
precip is too far out for a watch attm, and we`ll continue to handle
this in the HWO and SPS.
Precip should taper off in the south Thursday night, w/dry
conditions thereafter. Temps recover to above-normal by Saturday.
&&
.PRELIMINARY POINT TEMPS/POPS...
Big Spring 39 47 34 45 / 0 0 20 50
Carlsbad 39 46 32 42 / 0 0 20 50
Dryden 50 56 38 46 / 0 10 20 70
Fort Stockton 44 49 35 39 / 0 0 30 70
Guadalupe Pass 39 42 29 37 / 0 0 30 60
Hobbs 37 44 31 44 / 0 0 20 40
Marfa 37 54 29 43 / 0 0 30 70
Midland Intl Airport 41 48 35 44 / 0 0 20 60
Odessa 41 48 34 43 / 0 0 20 60
Wink 39 51 33 41 / 0 0 30 60
&&
.MAF WATCHES/WARNINGS/ADVISORIES...
NM...None.
TX...None.
&&
$$
70/84/70
Area Forecast Discussion...UPDATED
National Weather Service Twin Cities/Chanhassen MN
934 PM CST Mon Dec 4 2017
.UPDATE...
Issued at 934 PM CST Mon Dec 4 2017
Blizzard conditions are occurring along the MN river this evening.
New Ulm recently gusted to 58 mph with 1/4 mile visibility. There
have been several other reports of 50 mph gusts over the past
couple hours. The snow is not expected to last long enough to
warrant an upgrade to a Blizzard Warning, with the back edge of
the snow already approaching Redwood Falls.
A well developed deformation band of snow is rotating eastward
across Minnesota. Increased snow totals across eastern MN and
western WI per latest trends. The HRRR has been advertising
greater than 4 inches from the metro northeastward, which isn`t
impossible, but it would need to snow faster than an inch per hour
in order for that to occur. The better bet is for 2 to 3 inches.
Travel conditions are treacherous where temperatures have fallen
below freezing. Deteriorating road conditions can be expected to
spread eastward as the evening progresses.
&&
.SHORT TERM...(This evening through Tuesday)
Issued at 313 PM CST Mon Dec 4 2017
The main change to the short term involved attempting to capture
the potential for an enhanced (narrow) band of snowfall over
central MN where favorable dendritic growth zone intersects
impressive omega as an impressive pocket of PV advection lifts
across east central MN and west central WI this evening. Did
increase snowfall ratios as well. All these factors considered led
to most locations west of I-35 (with the exception of along I-90)
having the potential for 2-3+ inches of snow falling in a
relatively short period of time, creating reduced visibilities and
slippery roads. Therefore transitioned much of central/west
central MN and a small portion of west central WI that was in a
wind advisory to a winter weather advisory...to better capture all
anticipated impacts. We also look to have some upright
instability so thundersnow will be possible this evening as well,
which could also enhance amounts.
.LONG TERM...(Tuesday night through Monday)
Issued at 313 PM CST Mon Dec 4 2017
Very few changes were made in the long term forecast period.
Northerly flow will prevail, which will mean the door will open
for cold air to move in from Canada. Temperatures through the
weekend will generally range around 5-10 degrees below normal.
Occasional shortwaves will clip the region, but little to no
attendant moisture and their quick- moving nature will limit
snowfall potential.
&&
.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 614 PM CST Mon Dec 4 2017
Generally IFR conditions are in place, with rain advancing
northeast from south central MN and snow across western MN. The
precip will transition to snow from west to east this evening with
periods of moderate snow (1/2SM vis) possible. The snow should end
about 4 or 5 hours after its onset. Strong northwest winds
expected tonight with some gusts to 45 kts possible, especially
across western MN.
KMSP...Rain will become steady within the hour, then transition to
snow between 02-03Z. Visibility may drop to LIFR levels and
accumulations of 1 to 3 inches are expected.
/OUTLOOK FOR KMSP/
Wed...VFR. Wind NW 10-15G25kts.
Thu...VFR. MVFR possible late with Chc -SN.Wind NW 5-10kts.
Fri...VFR. MVFR possible early with Slgt Chc -SN. Wind NW 5-10kts.
&&
.MPX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until 4 AM CST Tuesday for WIZ014>016-
023.
Wind Advisory until 6 AM CST Tuesday for WIZ024>028.
MN...Winter Weather Advisory until 4 AM CST Tuesday for MNZ043>045-
049>053-057>063-065>070-073>077-082>084-091-092.
Winter Weather Advisory until midnight CST tonight for MNZ041-
042-048.
Winter Storm Warning until midnight CST tonight for MNZ047-
054>056-064.
Wind Advisory until 4 AM CST Tuesday for MNZ078-085-093.
&&
$$
UPDATE...BORGHOFF
SHORT TERM...LS
LONG TERM...LS
AVIATION...BORGHOFF
Area Forecast Discussion
National Weather Service Paducah KY
859 PM CST Mon Dec 4 2017
.UPDATE...
Issued at 859 PM CST Mon Dec 4 2017
Updated the public forecast to delay the arrival of the convective
line by an hour or two. Radar trends through the evening have been
steadily downward and lightning activity has also been dwindling.
Given the strength of the wind field, especially in the low-
levels, a few gusts up to 40 mph will be possible, but severe
weather is unlikely. Of course gusts up to 35 mph will continue to
be possible ahead of the line.
&&
.SHORT TERM...(Tonight through Wednesday night)
Issued at 1253 PM CST Mon Dec 4 2017
Early this afternoon, a deep surface cyclone was over southern MN
with a trailing cold front extending south into the southern
Plains, still well to our west. Sharp s/wv energy was moving
across the northern Plains, with a nice fetch of moisture seen on
wvapor moving NE along a 75-90 kt upper level jet. Radar showed an
increase in light showers over the past hour. Members of the HREF
and HRRR show an uptick in scattered convective activity this
afternoon. The activity should head NE 40-45 mph, with isolated
thunder possible. The models depict a lull after this initial area
of WAA convection driven by weak mid level support and low level
moist transport. Gusty south winds to continue.
Focus for convection tonight will be along the aforementioned
cold front, that will move across the area. Continued with
categorical 100 PoPs for showers and scattered thunderstorms.
PWAT`s will be unseasonably high as the front moves through. So
some decent and much needed rain is forecast. The chance of strong
and isolated severe will stay to our west. Even with a decent low
level jet, the low level lapse rates are not conducive to
downward momentum. Just gusty surface gradient winds ahead of and
behind the front.
The precipitation will move out quickly from west KY Tuesday
morning, with dry weather from Tuesday afternoon through Wednesday
night, as a surface ridge axis moves southeast across the area,
with dry NW flow aloft forecast. It will be colder behind the
front, but not too far from norms. Colder air arrives later in the
week. Stayed close to persistence and MOS for temps. Decent model
agreement overall in the short term. Precip/PoP trends will be
derived from the HRRR, and members that make up the HREF, and
some NAM incorporation.
.LONG TERM...(Thursday through Monday)
Issued at 1253 PM CST Mon Dec 4 2017
Confidence remains high that a high amplitude flow pattern will
prevail through the long term. The overall pattern will be a
strong mid level ridge over the west U.S., and deep trof over the
east 1/2 of the nation. The mean trof axis positions are similar
longitudinally to 24 hours ago, perhaps slightly slower per the
latest ensemble mean solutions. Significant negative anomalies
continue to be seen with this trof over our area. This will result
in below normal temperatures, as much as 5 to 15 degrees, and
unsettled weather, as impulses head SSE, bottom out in the base of
the trof and then head on east. Despite the very low heights
aloft, surface pressures are not terribly high, negative
anomalies minimal.
It continues to look dry Thursday. The models for two days now
show a lead wave that will move across the area late Thursday into
Thursday night then dampen. The uncertainty lies with forecast
moisture. The GFS is persistent suggesting some very light snow
showers or flurries may move across the area. However the EC and
CMC solutions remain dry. Sometimes the EC and CMC are too
conservative in this regard. So we prefer to keep a slight chance
20 PoP going.
The models depict a lull Friday. A consistent signal remains for
Friday night. Another s/wv will move SE across the area resulting
in additional h5 height falls, and greater moisture. There is
generally agreement across the board, that light snow will
accompany this system, with the best chances across the NW 3/4 of
the area. Bear in mind this is a late day 5 into early day 6
forecast, and the details may change. For now, conservative and
appropriate wording is we may see some snow, and possibly light
accumulations should the signal remain. Adjustments in timing and
such will continue to be made over the next few days. Will there
be any impacts? Way too early to tell. Other than maybe some
lingering light snow showers or flurries early Saturday SW Indiana
and KY Pennyrile, dry weather on through Sunday and most of
Monday. Temperatures will moderate Sunday into Monday as the mean
mid level trof axis moves on east.
&&
.AVIATION...
Issued at 536 PM CST Mon Dec 4 2017
Little variation in timing and lowering of ceilings and
visibilities from VFR to MVFR (with locally brief IFR visibilities
possible) from 18z Monday WFO PAH TAF issuance. Current pre-
frontal and main cold front convection and cloud cover following
closely to the NAM-WRF model guidance. May have trended in the
wrong direction, but returned ceilings and visibilities back to
VFR category between 7z and 10z Tuesday as frontal boundary moves
east of the WFO PAH TAF sites. Will monitor.
&&
.PAH WATCHES/WARNINGS/ADVISORIES...
IL...None.
MO...None.
IN...None.
KY...None.
&&
$$
UPDATE...DRS
AVIATION...Smith