Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/13/24
Area Forecast Discussion
National Weather Service State College PA
1104 PM EST Thu Dec 12 2024
.SYNOPSIS...
*Brief cold snap lasts into the weekend followed by mixed
precipitation changing to rain on Sunday
*Milder pattern expected to start next week with rain most
likely on Monday and Tuesday
&&
.NEAR TERM /UNTIL 7 AM FRIDAY MORNING/...
Fair and cold weather with a diminishing breeze is expected
tonight across the bulk of Central PA associated with surface
ridging building in from the Lower Grt Lks. However, a weakening
and moisture-starved clipper tracking into the Ohio Valley will
spread increasing clouds across the region late this evening,
with a bit of light snow over the Laurel Highlands late
tonight. Model qpf indicates snow amounts early Friday morning
of a half inch or less across the Laurels. Elsewhere, veering
boundary layer flow behind the exiting shortwave will probably
spread scattered lake effect snow showers into the NW Mtns very
late tonight, but low inversion heights suggest nothing more
than a fresh dusting across the snowbelt of NW Warren County.
Have nudged min temps a bit higher than NBM overnight across the
southern counties, where model output indicates the cloud cover
will be thickest.
&&
.SHORT TERM /7 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
Any light snow over the Laurel Highlands should end by mid
morning Friday, as the weakening clipper passes south of PA.
High pressure building southeast from the Grt Lks should then
ensure fair and cold weather the rest of the day with
increasing sunshine.
See no reason to deviate from NBM max temps, which range from
the low and mid 20s over the N Mtns, to the low and mid 30s
across the Lower Susq Valley.
Clear skies, a calm wind and dry air associated with the surface
high passing across the southern tier of NY State should result
in nearly ideal radiational cooling across much of Central PA
Friday night, with min temps likely falling below NBM guidance.
However, much of the latest model guidance indicates an
easterly flow ascending the higher terrain of South-Central PA
could result in broken low clouds, which would hold temps up in
that part of the state. The northern valleys are likely to go
below +5F, while the southern tier may struggle to get colder
than 20F if clouds materialize.
&&
.LONG TERM /SATURDAY THROUGH THURSDAY/...
*Wintry mix/ice possible Sunday into Sunday night/AM Monday
*Mild warming trend early next week with periods of rain
*Break in precip into midweek; colder temp trend Dec. 19-21
Bitter cold start to the weekend with sunrise temps Saturday in
the +single digits and teens - thanks to +3SD 1045 to 1050mb
sfc high pressure centered over northeast PA/Poconos. This very
anomalous dome of high pressure will put record high December
SLP within reach at IPT/1048.8mb MDT/1049.4mb and AVP 1049.4mb.
The shallow cold air associated with the massive and retreating
arctic high should be very difficult to dislodge and should
become entrenched along and to the east of the Allegheny Mtns.
This signals a rising risk for a light overrunning mixed/wintry
precip event Sunday into Sunday night. With timing still a
little uncertain, we were keen to add wintry mix threat into the
HWO with the highest odds for freezing rain and potential icing
impacts over the Laurel Highlands. Given the magnitude of the
sfc high, models may be too bullish on transition to rain early
Monday however stronger WAA and southwest flow should push llvl
thermal profiles far enough to the right to favor dominant rain
ptype in most locations by Monday afternoon.
Latest guidance continues to support a brief lull in the
precipitation Monday in between shortwaves with a next round of
overunning rain Monday night. Most likely rainfall Monday night
based on ensemble plumes is in the 0.25 to 0.33 inch range.
Both the EPS and GEFS signal dry and mild conditions Tuesday PM
into Wednesday, as a cold/occluded front sweeps east of the
state and an area of high pressure builds in from the Ohio
Valley. Medium range guidance indicates an upstream trough will
will approach by Wed night. However, plenty of uncertainty
remains regarding how deep this trough is and the associated
prospects for precip.
&&
.AVIATION /04Z FRIDAY THROUGH TUESDAY/...
VFR conditions are expected at all airfields outside of BFD/JST
through 00Z Saturday with very high (~80-90%) confidence as
winds continue to decrease overnight and throughout the entire
TAF period. MVFR restrictions appear the most plausible solution
at BFD/JST with scattered upslope (JST, ~40% probability) and
lake effect snow (BFD, < 20% probability) in the 05-11Z Friday
timeframe based on a combination of RAP/HREF guidance. It is of
note that RAP model soundings do outline more saturation in the
lower-levels during this timeframe and push BFD/JST closer to
(yet slightly above) IFR thresholds; however, comparing current
observations to RAP initialization seems to outline the model
overestimating T/Td spreads in the near-term. Thus, have higher
(~60-70%) confidence in restrictions staying above IFR
thresholds in this timeframe before slowly lifting above VFR
thresholds by Friday afternoon.
Sustained winds will generally remain in the 5-10KT range with
localized gusts up to 20kts over the next couple of hours before
gradually decreasing overnight. As high pressure begins to
build across the region, light westerly winds will continue
throughout the day on Friday, generally around/below 5KTS.
Outlook...
Sat...VFR. LLWS possible in the west Saturday night.
Sun...MVFR/IFR with rain and possible mixed precip at onset.
Mon-Tue...RA likely. Widespread MVFR and spotty IFR.
Tue PM...Lake effect clouds/SHSN NW. MVFR cigs elsewhere.
&&
.CLIMATE...
Astronomical winter (solstice) begins on Saturday, December 21st
at 4:19 a.m. EST.
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...Dangelo
NEAR TERM...Fitzgerald
SHORT TERM...Fitzgerald
LONG TERM...Fitzgerald/Steinbugl
AVIATION...NPB
CLIMATE...Steinbugl
Area Forecast Discussion
National Weather Service Dodge City KS
530 PM CST Thu Dec 12 2024
.KEY MESSAGES...
- Except for small shower/t-storm chances in Stafford, Pratt
and Barber counties Friday evening, measurable precipitation
is not expected for the next week to ten days.
- Temperatures will generally be within 5 to 10 degrees of
climatology, except for Sunday when temperatures will be 15
to 20 degrees above average.
&&
.DISCUSSION...
Issued at 159 PM CST Thu Dec 12 2024
A shallow cool air mass moved into southwest Kansas today. The
leading edge of this cool air will stall near the Oklahoma state
line or just south. Expect lows tonight to range from the teens
at Scott City to upper 20s at Medicine Lodge. Meanwhile, an
upper level storm system currently over the western United
States will approach the plains Friday night. Ahead of this
system, a warm advection pattern will develop, along with a low
level jet. Low level moisture over south Texas will rapidly
advect northward into a cooler air mass, leading to low level
stratus formation east of a line from WaKeeney to Dodge City
Friday afternoon. The NAM looks more reasonable with backed
winds north of the front across most of southwest Kansas,
leading to upslope flow and cooler temperatures. Across west
central Kansas, the shallow cool air will stay in place, with
highs only reaching the upper 30s to mid 40s. Across central
Kansas, temperatures will be held down by upslope and cloud
cover, with highs from the mid 40s at Hays to lower 50s at
Medicine Lodge. As mid level cooling arrives ahead of the
disturbance Friday evening, RAP soundings indicate cap removal
between 02 and 04z, with marginal elevated CAPE. The HRRR breaks
out isolated convective precipitation around Pratt and Stafford
during the late evening. Bottom line is that there are small
chances for a shower or t-storm between 10 pm and midnight
across south central Kansas. The moist layer in the NAM and RAP
is too shallow (2000-2500ft) for drizzle formation.
A warming trend will commence Saturday in the wake of the
aforementioned system and plentiful sunshine will allow
temperatures to reach into the mid to upper 50s in the
afternoon. Downslope flow is forecast to develop Sunday ahead
of the next fast moving upper level disturbance. This will allow
temperatures to warm to the 60s to near 70, with the warmest
readings near the Oklahoma state line. This system is forecast
to pass through dry given its rapid movement and low amplitude.
Probabilistically, the various ensemble means including the ENS
and GEPS only indicate 0 to 10% chances for measurable
precipitation. Expect temperatures to cool off a few degrees in
the wake of the associated front on Monday. By Tuesday night,
the next upper level disturbance is expected approach the
southern high plains in positively tilted fashion. Even though
this system will likely be more amplified based on the various
ensemble systems, deep moisture and precipitation is predicted
to stay to the south and east Tuesday night and Wednesday
morning given the system`s positive tilt. Probabilistically, the
various ensemble means only indicate 10 to 20% chances for
measurable precipitation, most likely in the form of rain.
Cooler air will advance into southwest Kansas in the wake of the
associated front, with highs falling from the 50s Tuesday to
the 40s Wednesday.
&&
.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 530 PM CST Thu Dec 12 2024
VFR flying conditions will prevail across DDC, GCK, and LBL this
TAF cycle, while HYS sees a brief window of MVFR late in the
period as low stratus moves into the area from the east. Winds
will generally stay light through tomorrow, although an increase
out of the southeast to southwest into the 10-12 kt range is
expected during Friday afternoon.
&&
.DDC WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
DISCUSSION...Finch
AVIATION...Springer
Area Forecast Discussion
National Weather Service Des Moines IA
540 PM CST Thu Dec 12 2024
...Updated for the 00z Aviation Discussion...
.KEY MESSAGES...
- One more cold night this week with near-zero lows in the
northeast.
- Winter Weather Advisory issued for Friday evening into
Saturday morning. Ice accumulations to bring certain (100%
confidence) travel impacts to the state at times in the
period. Precipitation to gradually transition to all rain.
- Uncertainty in timing of departure of precipitation as drizzle
and freezing drizzle will linger further into Saturday. Any
ice accumulation will be impactful, no matter the amount.
highest confidence in lingering freezing drizzle is in the far
north.
- Milder temperatures on track for Sunday with rain chances now
trending into the eastern part of the area. (~30%)
&&
.DISCUSSION...
Issued at 242 PM CST Thu Dec 12 2024
The near-surface temperature profile resides in the DGZ today,
assisting snow showers in continuing through this afternoon despite
the dryness and weak forcing. Higher accumulations have focused more
into far southeast Iowa where moisture was better aligned. Overcast
skies will lessen this evening and allow for lows in the northeast
to drop to near zero again tonight. Clouds are quick to fill in
overhead Friday and hold temperatures below freezing for much of the
area.
The winter system to start the weekend include definite (100%
confidence) travel impacts from freezing rain in the time range of
Friday evening into Saturday morning. Expect treacherous travel to
begin right as freezing precipitation begins, especially on
untreated surfaces. Ice accumulations will be highest north of
Interstate 80. Accumulations here will be between 0.1 and 0.2 inches
with impacts lasting into Saturday morning. Areas to the south can
expect to see under a tenth of an inch of ice with the window of
highest impact primarily taking place before midnight Saturday. A
Winter Weather Advisory has been issued for the area in response to
these expected impacts. Detailed forecast information below:
The well advertised system continues to trend slower. Moisture
increases across the southwest Friday afternoon with PWATs over a
half inch present by 3pm. All of the moisture, at least to start,
will be constrained in the lower levels, making for a scenario of
drizzle or light precipitation. There remains noticeable discrepancy
in when the lowest thousand feet or so of the column will saturate,
making start time tricky for the far southwest. Highest confidence
start time would be around 6pm. Surface temperatures at this point
will be below freezing, but with a warm nose aloft on the magnitude
of around +2C at 850mb. Moisture advection will quickly expand
northward with an initial window of precipitation include freezing
rain across the far south and brief window of sleet from around
Highway 30 and northward. Between 6pm and Midnight, WAA from
southeast flow will continue to warm temperatures after dark,
transitioning the south gradually to rain and the remainder of the
area to freezing rain. The lack of deeper saturation in this 6 hour
time window makes accumulations less efficient, but one can expect
travel impacts Friday evening, especially since the frozen ground
will already be primed for ice accumulations thanks to the cold
temperatures and lack of sun for the latter half of the week. Air
temperatures in the south will rise above freezing at the end of
this time period, impacts may linger longer despite air temperatures
being above freezing due to the cold ground.
Beyond midnight, moisture continues to progress northward. Between
midnight and 6am is when highest QPF is placed everywhere, so this
is an important time period to watch in the forecast, especially
since some discrepancies exist in the QPF which will be covered
here. A cursory glance at the QPF output for all models shows the
highest amounts focused across eastern to southeast Iowa. This
placement makes sense as the main moisture axis extends this
direction. However, there are a small camp of models, generally
those that are NAM and ARW based, that bring higher accumulations to
northern and especially northwest Iowa. The reasoning is how the
model cores mature the cyclone over time, with the aforementioned
cores deepening the cyclone and modeling the occlusion stage
earlier, allowing the warm conveyor belt to extend north and
northwestward around the low center. Models such as the GFS, ECMWF,
and RAP delay this process, preserving a uniform southwest-northeast
moisture advection. Less moisture pivoting northwestward means lower
QPF. If the latter solution is correct, that would mean the current
QPF in the north and northwest is overdone. Better consensus
should be seen in the next couple of issuances. It`s important
to note that even if there is less ice accumulation, impacts to
travel will approach a similar magnitude.
At 6am Saturday, the main moisture axis will push into eastern Iowa
with much of the southern half of the state above freezing. Liquid
rain accumulations will be maximized from this time to noon with
places like Ottumwa potentially seeing rainfall amounts approach an
inch. Meanwhile, colder temperatures hang on in the north and
northwest. Taking a look at the soundings in the northwest quadrant,
ice introduction never occurs consistently, but the low levels
remain saturated. Weak lift and low condensation pressure
deficits paired with the increasing shear from the nearby low
center are collocated. All these ingredients point towards an
extended period of drizzle/light precipitation on Saturday apart
from the main axis of rain. In areas that remain below
freezing, ice will continue to accumulate and prolong impacts.
This scenario is most likely in the northern half of the state.
We will have monitor temperature trends to determine the
southern extent of the prolonged freezing drizzle. Thankfully,
at some point Saturday afternoon, the WAA wins out and yields
all liquid rain for the area.
WAA continues into Sunday and Monday which will push highs into the
40s across the southern half of the state. An approaching system
Monday has slowed its progression in the latest model runs, bringing
some rain chances to the east and southeast. Details will be better
refined upon the current winter system`s passing.
&&
.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 538 PM CST Thu Dec 12 2024
VFR conditions in 4000-9000ft ceiilngs were in place across
much of the area at 00z and are expected to persist into at
least mid evening. VFR conditions are expected to persist
through the remainder of the period as well, with CLR-SCT
conditions overnight giving way to increasing mid and high
cloudiness Friday afternoon. The potential for a wintry mix of
precipitation, mainly freezing rain or sleet, will increase
sharply beyond the valid period Friday evening however.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 4 PM Friday to 9 AM CST Saturday
for IAZ004>007-015>017-023>028-033>039-044>050-057>062-070>075-
081>086-092>097.
&&
$$
DISCUSSION...Jimenez
AVIATION...Small
Area Forecast Discussion
National Weather Service Hastings NE
614 PM CST Thu Dec 12 2024
...Aviation Update...
.KEY MESSAGES...
- Mixture of rain and freezing rain moves into the area Friday
afternoon/evening, lasting through the night before exiting
the area Saturday AM.
- Light sleet/snow is also possible, but the main impact is
expected to be ice.
- A Winter Weather Advisory has been issued for areas along and
east of Highway 281 in Nebraska. These areas are most favored
(50-80% chance) to see at least a glaze of ice.
- Overall ice accumulation and resulting impacts will be
heavily dependent on low level temperatures, which remain
somewhat uncertain for areas near and south of the KS/NE state
line.
&&
.DISCUSSION...
Issued at 315 PM CST Thu Dec 12 2024
The main concern in this forecast package is the winter storm
expected to bring a wintry mix (primarily freezing rain) to the
area Friday afternoon through Friday night. Clouds will
increase tonight in advance of this system. With the cold
airmass in place, temperatures are expected to dip into the
single digits and teens by Friday morning.
Precipitation then is expected to develop Friday afternoon
(roughly 2-4pm) as the deepening upper low moves into the
central Plains. With warm air aloft, precipitation is expected
to begin as a mix of rain and freezing rain...dependent upon the
surface temperature. Areas near/north of I-80 have a high
chance (90% or higher) for temperatures to be below freezing at
onset, but near/south of the KS/NE state line, there is only a
30-40% chance for subfreezing temperatures at onset. As such,
the current expectation is that MOST of Kansas will remain ice-
free, but this could change if temperatures trend cooler
tomorrow. Unfortunately, there is still quite a bit of spread
amongst models, and therefore quite a bit of uncertainty on
temperatures/impacts.
Continued warm advection ahead of the surface low could
actually lead to rising temperatures in our southeastern areas
through Friday evening. There may even be enough instability
aloft to hear a few rumbles of thunder from the Beloit area up
to around Hebron, which is reflected in the 12 and 18Z HRRR
runs.
If some of the colder model solutions (NAM, NAMnest, WRF-NSSL)
verify, it is possible that some sleet/snow may mix in later
Friday night into Saturday morning. That said, accumulation is
expected to be minimal, and ice is still expected to be the
primary impact.
By Saturday morning, the upper low is forecast to be overhead,
and precipitation should be winding down over western parts of
the area, but a light wintry mix may persist in northeastern
parts of the area until at least 8-9am Saturday.
In total, ice accumulations are expected to remain below 0.10"
for most areas. These light amounts, combined with the lack of
strong winds, should prevent any major impacts to electricity
infrastructure, but even just a light glaze of ice can lead to
significant travel impacts. Heaviest precipitation is expected
to occur over the eastern half of the area. This is why the
Winter Weather Advisory was confined to these areas but some
light icing is also possible further west (along with spotty
travel impacts).
As skies clear on Saturday, temperatures are expected to climb
above freezing Saturday afternoon, hopefully melting off any
remaining ice off of roadways. Southwestern zones could actually
approach 50 degrees!
Even warmer air arrives for Sunday, with widespread
temperatures in the upper 40s and 50s. A cold front then moves
through for Monday, ushering in gusty northwest winds...but only
slightly cooler air. Any precipitation associated with this
front should stay primarily to our north and east.
After near to slightly above-normal temps on Monday/Tuesday,
another cold front moves through Tuesday night, pushing in
colder air for Wednesday. Temperatures return to near normal
for Thursday before another push of arctic air pushes in for
next Friday/Saturday.
&&
.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 614 PM CST Thu Dec 12 2024
For KGRI/KEAR Airports:
- General overview:
High confidence in VFR ceiling/visibility and precip-free
weather through at least the first 18 hours. However, a
marked/rapid deterioration of ceiling (to at least MVFR) is
likely late in the period Friday afternoon, along with eventual
onset of light freezing drizzle. Winds out of the east and not
overly-strong, with even gusts holding under 20KT.
- Ceiling/visibility/precipitation:
Very high confidence in VFR/precip-free through at least 18Z,
with only a gradual increase in mid-high clouds mainly at-or-
above 15K ft. However, by around 20Z expect a rapid onset of
high-end MVFR ceiling, with further lowering toward low-end MVFR
likely especially 22-00Z (IFR cannot be ruled out, but appears
more likely JUST beyond this valid period).
Precipitation-wise, have introduced prevailing light freezing
drizzle (-FZDZ) starting 22Z, as various models are quite
insistent on this being the predominant precip type (instead of
snow). Any ice accumulation through this valid TAF period should
only be a very light glaze, but just beyond this valid period
into Friday evening there will likely be a bit higher potential
for measurable light icing (at least a few hundredths of an
inch...causing slick untreated surfaces).
- Winds:
No significant issues here. Direction will remain quite
consistent from the east. The overall-lightest speeds sustained
at-or-below 10KT will occur this evening-overnight. However,
Friday daytime will see a modest uptick to sustained
12-15KT/gusts up to around 20KT.
&&
.GID WATCHES/WARNINGS/ADVISORIES...
NE...Winter Weather Advisory from 2 PM Friday to 9 AM CST Saturday
for NEZ040-041-047>049-062>064-075>077-085>087.
KS...None.
&&
$$
DISCUSSION...Mangels
AVIATION...Pfannkuch
Area Forecast Discussion
National Weather Service Goodland KS
241 PM MST Thu Dec 12 2024
.KEY MESSAGES...
- Continued low chance (15%) of a light wintry mix or freezing drizzle
across Norton/Graham counties Friday evening.
- Chilly and cloudy day Friday with temperatures struggling to
get out of the 30s for most; maybe even struggling to get
above freezing.
- Near to above normal temperatures return Saturday through
Wednesday with continued dry conditions.
&&
.SHORT TERM /THROUGH SATURDAY NIGHT/...
Issued at 112 PM MST Thu Dec 12 2024
A backdoor cold front has stalled from roughly a Benkelman to the
Monument Rocks line which will lead to a wide range of temperature
across the area with highs across eastern Colorado in the 50s to
eastern portions of the east struggling to get above the freezing
mark. Overall mainly clear skies will be in place due to dry air but
cloud cover will slowly increase through the afternoon as a
wave approaches the Rockies and upper level moisture increases.
Tonight, low level moisture will slowly increase around the 850mb
level which may lead to some stratus across eastern Colorado and far
western portions of NW Kansas. Overnight temperatures are a little
challenging as a chunk of the colder air mass will remain across the
area but with the clouds temperatures may not be able to fully
realize the potential. I`m leaning towards trending lower with
the temperatures due to the continued cold air advection into
the area.
Tomorrow, I continue to trend towards some the coldest guidance
such as the NAM as cloud cover is forecast to remain and may be
thick at times especially if the stratus does end up occurring.
There is however a fairly large spread of temperature potential,
if the stratus isn`t as thick then temperatures may end up
being around five degrees warmer than currently forecasted;
currently highs are forecast in the low 30s across the east to
the upper 30s/low 40s across eastern Colorado.
Above I mentioned a wave approaching the Rockies which will lead to
the increase of cloud cover for today, for tomorrow this wave is
forecast to quickly develop into a low pressure system. This will be
the tricky part of the forecast as there is the potential for
freezing drizzle and/or light snow across mainly Norton and Graham
counties. A further east development of the low will lead to all the
precipitation chances remaining east of the forecast area;
whereas on the other hand a further west low would increase the
threat for light snow and freezing drizzle. Thus far the NAM
remains favorable of the more westerly track whereas most other
deterministic guidance favors a more eastern track. The good
majority of ensemble members as well favors the easterly track
but there are still a few that keep the western track which is
what is driving me to keep at least the slight chance wording in
the forecast. At this time as well the potential for any
potential seeder feeder effects occurring to help increase the
potential for precipitation looks to be low given the overall
depth of the dry layer in the mid levels. I am noticing that the
15Z RAP is trying to develop some frontogenesis within the
stratus for tomorrow morning around 13-15Z across eastern
Colorado and far western Kansas. The overall amount of lift does
look to be fairly weak so far but it may be worth trying to
keep an eye on for the next few model runs to see if its the
start of trend towards freezing drizzle or flurries.
As for precipitation types light snow or freezing drizzle
continues to be the most likely to occur. Currently, I`m leaning
towards the freezing drizzle route due to the shallow moist
layer only up to around 1 km. The overall forcing at within the
moist layer is relatively weak as well around 3 micro bars of
omega seen on cross sections. This source of lift looks to be
from a period of isentropic lift in the 285K level as well. At
this time, should the freezing drizzle occur a light glaze of
ice would be possible. The favored time frame for this to occur
continues to look to be from roughly 6pm CT through 12am CT. At
this time my confidence for any wintry precipitation occurring
continues to remain around 15%.
To start the weekend the quick moving system on Friday will move out
as the start of more progressive pattern develops. Ridging will be
in place across the area leading to a return to more mild
temperatures and clear skies.
&&
.LONG TERM /SUNDAY THROUGH THURSDAY/...
Issued at 100 PM MST Thu Dec 12 2024
An amplified, progressive synoptic pattern with regular/
periodic waves.. wavelength ~1500 miles (trough to trough),
period ~30-36 hr.. will prevail over the CONUS early-mid next
week. Long range guidance suggests that the main belt of mid-
latitude westerlies will be relegated to the northern half of
the CONUS (~35-50N).. and that waves therein will be progressive
/fast-moving/ in nature. If this is the case, low-level
moisture return from the Gulf of Mexico will likely be confined
to the Southern Plains and Southern-Central MS River Valley. In
other words, in this pattern.. progressive waves/troughs are
unlikely to be accompanied by precipitation in the lee of the
central Rockies. While day-to-day fluctuations in temperature
and wind direction (cooler/northerly to warmer/southerly) are
likely.. temperatures, on the whole, are anticipated to be
near-average.
&&
.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 239 PM MST Thu Dec 12 2024
VFR conditions continue to remain forecast for the TAF period.
Increasing upper level clouds will overspread the region
overnight. Some guidance still continues to hint at some stratus
potential near the KGLD terminal Friday morning but overall
confidence still low so will continue with the SCT035. Winds
will continue to be primarily from the ESE around 08-10 knots
before becoming more variable later on in the period as a low
pressure system moves near the area.
&&
.GLD WATCHES/WARNINGS/ADVISORIES...
KS...None.
CO...None.
NE...None.
&&
$$
SHORT TERM...Trigg
LONG TERM...Vincent
AVIATION...Trigg
Area Forecast Discussion
National Weather Service Indianapolis IN
928 PM EST Thu Dec 12 2024
.KEY MESSAGES...
- Light snow mainly north of I-70 ending by early Friday morning.
- A warming trend commencing on Friday
- Rain returns late Saturday through early Sunday, and again on
Monday, with warm temperatures
&&
.FORECAST UPDATE...
Issued at 926 PM EST Thu Dec 12 2024
Radar this evening shows a band of snow showers stretching across
the northern half of Central Indiana, with the heaviest band
stretching from Lafayette to Tipton and then to Muncie. The back
edge of the snow was found over central Illinois, making steady
progress eastward.
High pressure was found at the surface, centered over WI/MN, nosing
southeast toward northern Indiana and Ohio. A warm front was found
stretching across southern MO to Kentucky. These two systems were
resulting in a north to northeast lower level flow across Central
Indiana.
HRRR suggests a continued easterly progression of the area of snow
showers with an eventual exit by 04z-05Z. Clouds within the flow
aloft will linger across the northern areas overnight, but eventual
clearing should arrive toward daybreak as ridging aloft over the
upper midwest pushes toward Indiana.
Thus will keep high pops in place for the next few hours across the
northern parts of Central Indiana as the snow showers slowly exit.
Zero pops and limited clouds will be found across southern parts of
Central Indiana. Central Indiana remains engulfed in this cold air
mass and and the warm front is not expected to make any progress
northward overnight. Low temps in the teens and lower 20s in the
ongoing forecast appear on the mark.
&&
.MESOSCALE UPDATE...
Issued at 306 PM EST Thu Dec 12 2024
A compact midlevel shortwave trough interacting with and east-west
midlevel thermal gradient is causing a frontogenesis snow band this
afternoon. Limitations for a more significant band of snow will be
1. only modest strength of midlevel frontogenesis, 2. deep
isothermal layer warmer than the dendritic growth temperature range
(columns and needles may dominate), 3. initial period of moistening
the lower troposphere may delay heavier rates.
Nevertheless, the slowly northward drifting band should be enough
for up to an inch of snow accumulation generally near/north of a
line from Newport to Crawfordsville to Noblesville. It appears the
band`s residence time may be most supportive of locally 1-2 inches
of snow accumulations near Williamsport, Lafayette, and Kokomo.
&&
.SHORT TERM (This evening through Friday)...
Issued at 217 PM EST Thu Dec 12 2024
Snow is now reaching the ground across central Indiana, with light
snow currently (2pm) falling here at the WFO Indy office. Light snow
should continue to build eastward with time, reaching the Ohio state
line by 4pm or so. Snow will be light to start, but increase in
intensity with time. Radar trends show a heavier band taking shape
across central Illinois which should translate eastward as well (see
below for details on this narrow band of heavier snow).
Model analysis shows sloped frontogenesis ahead of the wave, with
favorable jet dynamics aloft (right entrance). Additionally, modest
warm advection / upglide aligns with these as well. Therefore, the
potential exists for a more focused band of moderate to heavy
snowfall. Amounts within this band could range from 1 to 2 inches,
with some of the more aggressive models having almost 3
inches...though that is an outlier as of right now. A limiting
factor may be that optimal saturation and lift are just outside of
the dendritic growth zone (DGZ), roughly along the -10C isotherm.
However, there is saturation within the DGZ in portions of the
column so the possibility for dendrites and larger aggregates and
therefore higher accumulation rates remains.
So, what can we expect based on the latest data? Snowfall values
from 0.5 to 1 inches should be the most common, especially along and
north of I-70. A narrow area of 1 to 2 inches is likely to occur
somewhere across the northern half of our CWA. It`s a bit more
difficult to pin-point this as it is a mesoscale feature.
Regardless, expect snow to begin within the next hour near the
Illinois border and spread eastward with time...reaching the Ohio
state line by 5-6pm. Cold ground temperatures will help snow
efficiently accumulate upon onset, leading to slick conditions and
hazardous driving conditions this evening...especially on untreated
roadways.
Temperatures should remain largely steady this afternoon and through
tonight with little change between this afternoon`s high and
tonight`s low.
Tonight
Once the snow ends by 10pm across our eastern counties, skies should
clear but may be slow to do so. Nevertheless, most of the low
stratus should depart by sunrise leaving us with mainly clear skies.
This could be very short-lived however as high cirrus arrives from
the southwest ahead of the next weather system that will bring rain
to Indiana over the weekend. See the long range discussion for
details on that system.
Friday
Otherwise, Friday will be a bit warmer as an upper trough axis
slides further east. Modest warm advection feeding today`s snow will
continue thereafter allowing temps to rebound into the 30s and low
40s. The only exception may be there the heaviest snow occurs
today...temperatures may be a bit muted up there and fail to reach
freezing.
&&
.LONG TERM (Friday night through Thursday)...
Issued at 217 PM EST Thu Dec 12 2024
Two waves of rain are expected in the long term period, with a
third possible.
#1 will occur with isentropic ascent preceding a midlevel shortwave
trough late Saturday into Saturday night. Ensembles are fairly
tightly clustered on around 0.50" QPF with no significant outliers.
Light rain showers or drizzle may continue much of the day Sunday as
low levels remain moist beneath the system`s dry conveyor belt. Most
of the rain will fall before the trough axis passes late
morning/midday, however.
#2 will be another shortwave trough and associated ascent that
interact with richer moisture (i.e., 2-3-sigma PWAT anomalies) on
Monday. Although there are some phase/amplitude difference in the
ensemble, they aren`t substantial and should only impact onset and
cessation timing. Thus, will go ahead and extremize precipitation
probabilities to 100 percent. Warm advection pattern should hold
temperatures above 10-15 degrees above mid-December climatology and
keep precipitation type all rain for the duration.
The amplified, progressive, short wavelength pattern continues
midweek. The opportunity for stronger cold advection is minimal, but
it appears there may be enough cold advection for a marginal
rain/snow precipitation type late Wednesday/Wednesday night with the
next in a series of waves. This is conditional on the trough`s
characteristics and track, as are precipitation amounts. There is
quite a spread with regards to amplitude and how much phasing occurs
with this system, so confidence on timing, precipitation amounts,
and precipitation type is low at this time.
Day 8-14: Medium-range ensemble data shows initial troughing and
colder than normal temperatures, moderating toward the end of the
period, along with near or below normal precipitation.
&&
.AVIATION (00Z TAF Issuance)...
Issued at 546 PM EST Thu Dec 12 2024
Impacts:
- Light snow north of a Attica to MIE Line through 02Z-03Z.
IFR/MVFR Conditions possible at LAF through 02Z.
- Improvement to VFR at all locations overnight.
Discussion:
Radar shows an area of snow north of the IND-BMG and HUF, continuing
to push north and east. This area is expected to remain across
the northern parts of Central Indiana for the next few hours,
impacting LAF with IFR to MVFR conditions.
Snow diminishes by 05z across the entire area after 05Z but
lingering stratus will persist into the night. Clouds clear up by
morning with higher level clouds moving in after sunrise.
Winds should remain under 10kt through the TAF period, direction
will shifting to the northeast and then east on Friday as high
pressure moves north of Indiana.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...Puma
SHORT TERM...Eckhoff
LONG TERM...BRB
AVIATION...Puma
Area Forecast Discussion
National Weather Service Marquette MI
650 PM EST Thu Dec 12 2024
.KEY MESSAGES...
- Heavy lake effect snow continues near Lake Superior east of
Munising tonight. Heaviest totals of 5-10 inches expected
north of M- 28 through tonight. Visibility less than half a
mile in the heaviest bands.
- 2-5 more inches of lake effect snow is expected along the
western UP shoreline into the Keweenaw through tonight, which
could prolong difficult travel conditions.
- Another cold night is expected tonight with lows ranging from
near 5 above in the east and Keweenaw to 15 below in the
interior west.
- Above normal temperatures with highs above freezing expected
over the weekend into early next week
&&
.SHORT TERM /THROUGH FRIDAY/...
Issued at 247 PM EST Thu Dec 12 2024
Early afternoon water vapor imagery and RAP analysis shows expansive
cyclonic circulation over the Great Lakes basin and much of
eastern/central Canada. 12Z KINL sounding appeared to measure the
heart of the cold airmass with an 850 mb temp of -26C. The longwave
trough will gradually shift away from the local area through Friday.
Surface high pressure on the SW flank of the upper trough over MN
will gradually expand into the Upper Great Lakes through Friday.
Frigid airmass has snuck around Lake Superior from the southwest,
with Ironwood feeling the brunt as apparent temps are still close to
-25F, which is the warmest they`ve been all day. Meanwhile, the
assertion of the arctic high has shifted lake effect snow closer to
the shorelines of the western UP, Keweenaw, and east of Munising.
Dominant convergent band is setting up east of the Keweenaw into
eastern Alger County as of early this afternoon. This band should
continue to impact areas east of Munising and mainly north of M-28
through the night. In fact, forecast soundings show low-level temps
at Grand Marais actually warming a bit tonight such that the profile
becomes more favorable for lift within the saturated DGZ just above
the surface. Winter Storm Warnings remain in effect through the
night here, where 5-10 additional inches of snow could fall, with
snowfall rates around 1"/hr and very low visibility within the
heaviest band(s). In the western UP/Keweenaw, inversion heights are
lower, but multi-band LES should continue through the night, with 2-
5 more inches expected. The Winter Weather Advisory has been
extended through the night here, although there is some indication
that bands will weaken late tonight into early Friday morning.
As for temperatures, the proximity of surface ridging should promote
good radiational cooling conditions outside of the LES plume,
especially where there is fresh snowpack. Went toward the minimum of
all guidance here, with lows from near zero interior east to near 15
below interior west (wouldn`t be surprised to see a few 20 or 25
below readings in the coldest spots). The good news is that wind
chill will be less of a factor, so no cold weather products are
anticipated.
Friday, lingering LES near the shorelines should gradually dissipate
by the afternoon as winds finally go offshore as a result of the
surface high being positioned to our south. It will be sunny for the
majority of the UP and temps, while still below normal, will be
warmer than today with highs mainly 15-20F.
&&
.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Issued at 245 PM EST Thu Dec 12 2024
Surface ridge axis will be over the far eastern U.P. Friday evening.
With clear skies and light winds, temperatures will drop quickly
again Friday evening especially across the central and east. Lows
will probably be reached prior to midnight. After midnight, high
clouds will begin to increase from the southwest and southerly winds
will begin to pickup across the area as the surface ridge moves into
New England and low pressure moves into the Missouri Valley.
Weakening surface low will lift northeastward into the lower Lakes
Saturday and Saturday night passing south of the U.P. Warm advection
ahead of it may be enough to squeeze out some light rain/snow
showers across the south but any qpf amounts will be light, perhaps
a couple hundreths. With recent cold snap, ground is quite cold so
can`t rule out any liquid precipitation freezing on some surface but
impacts should be pretty minimal. As Saturday`s system fizzles over
the eastern Lakes by Sunday, warm advection will continue across the
Great Lakes as main upper trough begins to emerge from the Central
U.S. With surface dewpoints climbing above freezing on Sunday with
light southeasterly winds expect a dreary, low clouds, and patchy
fog kind of day.
Models still not in complete agreement with how system will evolve
early next week but seems to be converging on a northern surface low
track across the northern MN and Lake Superior. This track would
yield some warm advection rain for most during the day Monday
followed by dry slotting and then some marginally cold air by
Tuesday night for some light northwest wind lake effect lasting into
Wednesday.
All in all, temperatures will average above normal for much of this
forecast period. While record highs probably aren`t attainable
Sunday and Monday, record warm lows may be Sunday night and Monday.
Temperatures will cool closer to normal by later next week before
climbing above normal again prior to Christmas.
&&
.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 649 PM EST Thu Dec 12 2024
Lake effect snow and blowing snow continue at KCMX, with LIFR
conditions expected to persist through this evening. After 06Z,
conditions will improve to IFR and then to MVFR by early Friday
morning as snow tapers off. KIWD will remain on the fringes of
the lake effect snow this evening, with IFR ceilings expected.
Cloud cover will scatter out at KIWD after 06Z brining a return
to VFR conditions. VFR conditions will prevail at KSAW for the
duration of the TAF period.
&&
.MARINE...
Issued at 245 PM EST Thu Dec 12 2024
Northwest gales will diminish over the east Lake by early this
evening. Expect about a 24 hour window from late tonight through
late Friday night where winds will be less than 20 knots across the
Lake. Southerly winds up to 25 knots will develop late Friday night
Saturday. Lighter winds return for Sunday into early Monday before
southerly winds ramp up to around 25 knots on Monday ahead of the
next area of low pressure expected to move across Lake Superior.
After the low passes to the east by late Monday at least low end
northwesterly gales look increasingly likely from late Monday
night through Tuesday.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
Winter Weather Advisory until 7 AM EST Friday for MIZ002-003-
084.
Winter Storm Warning until 7 AM EST Friday for MIZ006-007-085.
Lake Superior...
Heavy Freezing Spray Warning until 7 PM EST this evening for
LSZ250-251-266-267.
Gale Warning until 7 PM EST this evening for LSZ251-267.
Lake Michigan...
None.
&&
$$
SHORT TERM...Thompson
LONG TERM...MZ
AVIATION...RM
MARINE...MZ
Area Forecast Discussion
National Weather Service Topeka KS
531 PM CST Thu Dec 12 2024
.KEY MESSAGES...
-Freezing drizzle remains a possibility for some locations tomorrow
(Friday) midday and early afternoon.
-Rain showers are expected from tomorrow afternoon through
Saturday morning, with a rumble of thunder not totally out of
the question.
-Temperatures warm late in the weekend.
-A few locations could see more light rain Sunday night.
&&
.DISCUSSION...
Issued at 237 PM CST Thu Dec 12 2024
This afternoon, sfc obs show high pressure sitting north and
northeast of the region, and low pressure near the OK/TX
panhandles with a warm front extending eastward across southern
KS. Temperatures across the forecast area range from near 30
degrees in far northern KS to the mid 40s near I-35. Temperatures
south of the warm front are in the 50s. Our air mass is very
dry this afternoon with dew points in the single digits and
teens for much of the area. Aloft, low pressure and an associated
trough axis are moving from the Pacific coastline eastward
toward the Great Basin region. That system will quickly pivot
eastward over the Rockies and toward the central High Plains
tomorrow. This will bring a chance for freezing drizzle and
light rain to the area.
Tomorrow morning, the warm front to our south will slowly move
northward as sfc low pressure moves out over the High Plains
with the approach of the upper low. Sfc temperatures appear to
be one of the more challenging parts of the forecast tomorrow
with models still showing differences in the progression of the
warm front. However, the slower and thus colder solutions
(mainly NAM and NAMNest) seem to still be the outliers with
other models in better agreement on the timing of the freezing
line advancing northward. Moisture advection will also be
occurring as the front moves north and as low level lift begins
to increase with isentropic ascent and approach of the upper
wave. However, forecast soundings from various models primarily
show a dry layer near the surface continuing until temps are
above freezing for areas near and south of I-70. Farther north,
temps may hover closer to freezing midday and early afternoon as
the column begins to saturate, which could lead to a few hours
of freezing drizzle. The temperature trend will need to be
monitored closely to see if a slower progression of the freezing
line could mean freezing drizzle closer to I-70. Any ice
impacts still appear to be minor, but some slippery surface
could develop especially if the drizzle persists for a few
hours. Bridges and overpasses are likely to ice up faster. Have
held off on an advisory at this time until confidence
increases - a possibility with the next forecast package
tonight.
Later in the afternoon and evening, light rain will become the only
precipitation type with temps above freezing area-wide. Some of the
latest runs of the HRRR also show the possibility of small, scattered
storms developing Friday night with some elevated instability. Low
pressure with a trailing cold front will continue to move across
Kansas Saturday morning with light rain showers expected to be
ongoing. POPs decrease into midday and early afternoon as the system
continues eastward. Total QPF still looks fairly low with between a
tenth and quarter of an inch of rain most likely.
High temperatures Saturday should range from the mid 40s west to the
mid 50s east, with even warmer conditions expected Sunday. The next
upper level trough axis will move over the area on Monday. NBM
placed 20-40% POPs in the southeastern forecast area Sunday night
into Monday where moisture will be more available. Otherwise, the
long range forecast is currently dry with a cool down expected
midweek with the arrival of our next cold front. The EC does have
some precipitation with the front, but models do not agree well at
this range.
&&
.AVIATION /00Z TAFS THROUGH 00Z Saturday/...
Issued at 531 PM CST Thu Dec 12 2024
VFR conditions hold through around midday Friday when MVFR cigs
and drizzle/rain impacts terminals. There is a low chance for a
brief period of freezing drizzle before surface temperatures
warm above freezing. Cigs may lower to IFR near or just beyond
the end of this TAF period. North-northeast winds this evening
and overnight become east-southeasterly Friday morning at 10-15kts.
&&
.TOP WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
DISCUSSION...Teefey
AVIATION...Flanagan