IND issues Area Forecast Discussion (AFD) at Nov 19, 10:15 PM EST336
FXUS63 KIND 200315
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
1015 PM EST Tue Nov 19 2024
.KEY MESSAGES...
- Dry and cooler tonight and Wednesday.
- First snow possible on Thursday and Thursday night, possibly
impacting Thursday evening rush hours.
- Small snow accumulations possible Thursday and Thursday Night,
resulting in slick surfaces.
- Mainly dry and not as cold this weekend.
- Rain chances return late Monday and Tuesday.
&&
.FORECAST UPDATE...
Issued at 1014 PM EST Tue Nov 19 2024
The forecast remains in good shape with only minor adjustments
needed. Expect quiet weather conditions to continue through tonight
before a quick moving system approaches towards daybreak Wednesday.
MOre details on this system can be found in short term discussion
below. Latest guidance suggests there will be stronger forcing
Wednesday morning with the approaching disturbance supporting
better chances for precipitation. Rainfall chances were increased
using CAMs to account for this.
Current observations show winds across much of central Indiana are
near calm tonight as the PBL has decoupled quickly under clear
skies. Rainfall early this morning combined with light winds and
clear skies could lead to some patchy fog development later tonight.
Only minor visibility reductions are expected at this time.
Temperatures will generally fall into the low-mid 40s overnight
which is still above normal for this time of year.
&&
.SHORT TERM (This evening through Wednesday)...
Issued at 304 PM EST Tue Nov 19 2024
Clearing has taken place across all of Central Indiana this
afternoon as the dry slot of an occluded low in Minnesota
overspreads the region. Cold air is lagging behind in the upper
Midwest, resulting in what likely will be one of the last warm days
of the year. Latest IND ACARs sounding shows steep lapse rates in
the lowest 1km agl working to mix down stronger winds from the low
level jet. While the southwesterly low level jet weakens and pushes
east, still expect gusts to 20mph through the afternoon, diminishing
as the evening progresses. Increased high temperatures slightly for
today with upper 60s to near 70 likely for the southern half of the
state as ample sunshine heats the boundary layer. Humidity values
will continue to diminish as dry air is advected in and daytime
mixing takes place. Dew points have already fallen about 10 degrees
into the low 50s and will continue to drop another 20-30 degrees
through tomorrow as a much colder and drier airmass moves in.
Cloud cover will begin to increase again late tonight as a large,
complex upper low moves into the Upper Midwest and Great Lakes
region by tomorrow. Cannot completely rule out a few sprinkles with
a vort lobe swinging into the area near daybreak Wednesday, but
forecast profiles suggest this should hold off until near or just
after 12Z, and will keep a dry forecast throughout tonight.
Wednesday through Thursday night...
FIRST SNOWFALL OF THE SEASON FOR CENTRAL AND NORTH CENTRAL INDIANA
The most impactful portion of the short to mid range forecast will
be Wednesday night through Thursday night where much of the region
will experience the first snowflakes and coldest air of the season.
The set up over the next 1-3 days is complex with an unusual pattern
setting up, making for a complicated forecast. A deep complex 525dm
upper low moves from Fargo, ND to around Central PA Wednesday
morning through late Thursday night with multiple shortwaves
rotating about it. Cold air advection through the column arrives
Wednesday as the first vort max, associated with the trough axis,
pushes east through the state. Lift ahead of the vort max combined
with steepening lapse rates and sufficient moisture should lead to
scattered showers during the morning hours Wednesday. Surface
temperatures will struggle to get out of the 40s with brisk WNW
winds gusting 20-30mph strong cold air advection ushered in by a
35kt low level jet. Potential is there for graupel with showers
Wednesday morning, but the primary P-type will be rain.
A brief dry break occurs midday Wednesday before even colder air
arrives with the chance for snow showers. This is where the forecast
becomes interesting. A strong 120kt upper jet rounds the negatively
tilted trough Wednesday evening inducing surface cyclogenesis over
the thumb of Michigan. Guidance is in good agreement with this low
strengthening to near 990mb as it retrogrades around Michigan and
then heads southward down the eastern shore of Lake Michigan on
Thursday. The low is expected to reach peak strength around Traverse
City, then becomes stacked and begins to slowly fill as cold air
advection wraps around the low. On the southside of this low, cold
air from Canada will continue to advect into Indiana with 850mb
temperatures reaching -10C by Thursday afternoon. Cyclonic flow
around the low in addition to multiple Vort maxes rotating about it
will bring multiple periods of showers and snow showers to the
region. First round of rain/snow showers arrives late Wednesday
night with the best chance for precip along and north of the I-74
corridor. Temperatures will be marginal for accumulating snow;
however forecast soundings to indicate enough of a saturated layer
within the dendritic growth zone to support snow showers. Warm
ground temperatures should inhibit much accumulation; however a
heavier snow shower could briefly coat the ground, especially in
North Central Indiana.
The aforementioned low in Michigan takes a very unique track during
the day Thursday, down the eastern short of lake Michigan and into
Indiana or Ohio. This is a very unique track and guidance has has a
difficult time pin pointing its exact track with some guidance
bringing it over Indianapolis and some keeping it further east
toward the IN/OH border. This will ultimately impact where the
heaviest snow band sets up ahead of the low dropping south into the
area. The time period to watch for potential accumulating snow is
late Thursday afternoon into Thursday night as the low approaches.
One potential challenge with the forecast is the warm lake waters of
Lake Michigan. Guidance shows a long fetch of northerly winds
running down lake Michigan, adding moisture and warmth to the
environment. While this could help increase moisture and QPF
locally, it may work to warm the lower troposphere enough for a
changeover back to rain. BUFKIT cross sectional profiles do show a
rising DGZ during the evening and overnight hours, with the DGZ
drying out overnight as moisture remains in the lower levels. This
could be a scenario where a band of snow ahead of the low pushes
south into Indiana late Thursday afternoon then changes over to
light rain or drizzle overnight. 1000-850mb heights, low level
temperatures, and a saturated DGZ support an initial P-type of snow,
which is reflected in the forecast. Uncertainty lies with how quick
the transition to rain will be. As the warmer air from Lake Michigan
pushes in, the potential is there for the "warm" air to rise up and
over colder air at the surface, leading to enhanced lift and
frontogenetical forcing and heavier snow bands. In this case,
heavier bands of precipitation may keep the column cooler longer,
leading to a few inches of snow accumulations for portions of North
Central and North East Indiana. If surface temperatures remain
marginal in the 32-35 degree range, there may not be much
accumulation. Mesoscale processes, snowfall rates, and surface
temperatures will greatly affect snowfall accumulations. Currently,
highest confidence in accumulating snow of an inch or greater lies
from Lafayette to Kokomo to Muncie to the Ohio Border. Confidence is
marginal in accumulating snow further south along the I-70 corridor,
including the Indianapolis metro area. Do think Indianapolis will
get a period of good snow rates late on Thursday, but urban heat
island effects, warmer grounds, and a transition to rain overnight
should limit overall accumulations. A dusting to a trace of snow is
likely further south and east.
In addition to falling snow, winds will be quite gusty as this low
approaches. BUFKIT soundings and guidance show sustained westerly
winds of 15-25mph with gusts 25-35mph Thursday leading to wind chill
values remaining in the teens and lower 20s during the day. In
addition, wind blown snow may reduce visibility under any snow
shower. Since this is the first snow of the year, take extra
precautions while traveling even if roads are not snow covered.
Highs will struggle to get out of the mid 30s for many areas. Once
heavier precipitation begins later in the day for areas across the
north, temperatures will likely fall to near freezing. Do not expect
a normal diurnal temperature curve Thursday into Friday morning as
the aforementioned area of low pressure moves through the region.
Temperatures will likely remain near freezing as it snows, then
potentially hold steady in the mid 30s overnight as precipitation
ends.
&&
.LONG TERM (Wednesday night through Tuesday)...
Issued at 304 PM EST Tue Nov 19 2024
Friday -
Quieter and cold weather is expected to arrive on Friday. The
strong upper low associated with the Thursday system will have
departed to east coast. Meanwhile models suggest stronger ridging
building across the high plains, leading to the arrival of
subsidence amid northerly flow on Friday. Lower level cyclonic flow
continues to show a favorable fetch across Lake Michigan for
potential clouds and Lake Effect showers across northern Central
Indiana through the day. Trajectories suggest an initial northerly
flow, impacting places like LAF and CRW in the morning, shifting to
become more northwesterly by Friday afternoon. This would change the
impacts location to places farther east, including OKK, Anderson and
Muncie. Forecast soundings on Friday suggest saturated lower levels
amid ongoing cold air advection and dry air aloft. Thus a mostly
cloudy and colder day will be expected, with chances for showers
mainly across the northern parts of the forecast area.
Saturday through Monday -
Models suggest the strong upper ridging building across the plains
on Friday slowly transitions to a more zonal flow through the
weekend, with little in well defined forcing dynamics passing.
Models differ a bit on a couple upper disturbances passing within
the flow aloft here, diminishing confidence in any potential
precipitation pops. Forecast soundings through the weekend mainly
suggest a dry column with periods with shallow areas of saturation,
indicative of just some passing clouds within the flow. Thus focus
will be mainly for dry weather this weekend, with a warming trend,
as stronger warm air advection builds across Indiana. Highs by
Sunday and Monday should recover into the 50s at most locations.
Models suggest some precip chances due to warm air advection alone
on Monday, but with little in the way of forcing aloft. Confidence
for rain here is low.
Tuesday -
The best chances for precipitation during the extended will be on
Tuesday. A weak wave aloft is expected to pass at that time, along
with an associated passing low pressure system across Central
Indiana, of the panhandle hook variety. At this time sufficient
forcing and moisture appear present for pops and precip type will be
rain, as lower levels remain quite warm after southerly flow and
time in the warm sector ahead of this system.
&&
.AVIATION (00Z TAF Issuance)...
Issued at 642 PM EST Tue Nov 19 2024
Impacts:
- VFR conditions expected through tonight
- MVFR conditions possible on Wednesday morning
- 20-28kt gusts possible during the day Wednesday
Discussion:
VFR conditions are expected through tonight. A quick moving system
arrives in the area on Wednesday morning. This will bring a wave of
clouds arriving from the northwest. MVFR ceilings are possible as
these clouds move in, especially near KIND. MVFR ceilings are
possible near KLAF/KBMG though confidence is lower.
Look for rain showers to accompany the front before VFR conditions
return later in the day. The best chance for precipitation will be
near KLAF/KIND. Winds are currently light and out of the southwest.
Look for a wind shift to 270-290 degrees this evening as a weak
front moves through. Winds will increase during the day Wednesday
with strong gusts around 20-28kts possible.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...Melo
SHORT TERM...CM
LONG TERM...Puma
AVIATION...Melo
Source:
IND issues Area Forecast Discussion (AFD) at Nov 19, 10:15 PM EST---------------
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