IND issues Area Forecast Discussion (AFD) at Dec 2, 9:48 PM EST483
FXUS63 KIND 030248
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
948 PM EST Mon Dec 2 2024
.KEY MESSAGES...
- Very cold temperatures Thursday followed by a warming trend next
weekend
&&
.FORECAST UPDATE...
Issued at 948 PM EST Mon Dec 2 2024
500mb jet and vort max are now southeast of central Indiana, and the
snow has ended other than a few flurries in the southeast. Some
partial clearing has occurred across the northern forecast area, but
additional clouds are already moving into the northeast forecast
area.
Main cloud deck will continue to slowly move south overnight. Have
upped sky cover based on the slower trend of the southern movement
of the clouds. Clouds will also occasionally drift into the
northeastern forecast area as well. A few flurries may accompany the
northeastern clouds at times early in the overnight.
Low temperatures will depend in part on how much clearing occurs and
how long clear skies will linger at any location, especially with a
fine layer of snow across much of the southwestern two-thirds of the
area. Given the uncertainty on the cloud cover, chose to leave low
temperature forecast alone for now. If clear skies last longer than
expected, temperatures would get colder than expected.
HREF and to some extent the SREF are hinting at some fog potential
in the northwest, but given the uncertainty in cloud cover, will
leave out any mention.
&&
.SHORT TERM (This evening through Tuesday)...
Issued at 235 PM EST Mon Dec 2 2024
Scattered snow showers embedded in widespread flurries are
quickly pushing through central Indiana as of 19Z out ahead of a
weak clipper system. This has been despite a 8-12 degree dew point
depression, although there has been slight increases in moisture
as this wave arrives. Within the snow, expect 1-3SM visibilities
with light accumulations. Greatest accumulations are expected to
generally be SW of the I-74 corridor.
The clipper will quickly move southeast of central Indiana late
today and tonight and the trough axis itself will move into the
Appalachians as a reinforcing shot of Arctic high pressure moves
into the middle Mississippi Valley. A drying column should aid in
clearing of skies overnight, but with central Indiana stuck in
broad upper level cyclonic flow, lingering stratus through
portions of the early night hours is possible. Also some lake
enhanced stratus downstream of Lake Michigan could reach northern
portions of central Indiana tonight. For this reason, snow
flurries have been added to Howard and Carrol Counties.
The difference in cloud cover will make for a challenging
temperature forecast overnight. Areas that experience clearing could
drop towards 10 degrees by morning within CAA and efficient
radiational cooling. However, areas beneath cloud cover may stay
closer to 20 degrees tonight.
Tomorrow, conditions are expected to remain cold as winds remain out
of the W/SW aloft and a cold core high in the low levels. Although,
there will be increased sunshine tomorrow, allowing for slight
moderation. Current expectation is for temperatures to top out near
freezing tomorrow afternoon.
&&
.LONG TERM (Tuesday night through Monday)...
Issued at 235 PM EST Mon Dec 2 2024
On the synoptic scale, a persistent eastern trough and associated
negative midlevel height anomalies will result in colder than normal
temperatures until Sunday, when the trough moves northeast and
ridging builds in. Until then models show four perturbations within
northwesterly flow impacting Indiana. Light precipitation amounts
may accompany these.
Wednesday:
An amplifying shortwave trough will move through late in the day,
and be preceded by a period of warm advection. A reasonable worst
case scenario would be a brief period of light freezing drizzle
early Wednesday. This primarily shows up in NAM-based model guidance
where the shallow cold arctic air mass is slower to abate, and low-
levels are comparatively more moist/saturated than other models.
This is a common bias, and may fall more into the less likely
category when moisture return is from modified western gulf air mass
with long continental trajectories through the southern/central
Plains. If even a small amount of drizzle can occur before warm
advection can push temperatures above freezing, antecedent cold
conditions will ensure road surfaces are cold enough for some minor
travel impacts. Again, a reasonable worst case scenario, but worth
monitoring trends closely.
Later in the day, continued low-level moistening and moisture
convergence along the front could bring the best chance of at least
trace amounts of precipitation, and possibly a couple hundredths in
a few areas. Should be warm enough for some liquid, though thermal
profiles do become favorable for snow late afternoon into the
evening. Stratus in the colder post-frontal environment Wednesday
night will be within the dendritic growth temperature range, and
some flurries may continue into the predawn hours.
Thursday:
The post-frontal air mass will have origins in the lee of the
Canadian Rockies, and we will struggle to rise out of the low-mid
20s (~20 degrees below early December climatology). Early in the day
before the MSLP gradient lessens, wind speeds will be high enough to
cause near or just below zero wind chill values. Stratus may be slow
to clear, especially if residual low level moisture is slightly
greater than currently modeled. Cyclonic low level flow with
building subsidence inversions tend to result in stratus lingering
longer than anticipated.
Overnight, stratus will probably clear as ridging shifts the low
level flow to allow for a more dry trajectory, but midlevel clouds
from the next weak perturbation in northwesterly flow will likely
move in. MSLP high center to our south will allow for light winds
and otherwise good radiative conditions if not for clouds.
Nevertheless, low to mid teens will be common.
Friday:
Veering low level flow ahead of the next in the series of transient
shortwave perturbations should moderate temperatures some Friday,
albeit still cold in the low 30s.
Saturday:
Modest forcing on the southern end of aforementioned shortwave
trough amidst neutral moisture anomalies may be just enough for a
period of light precipitation. Minor amounts.
Sunday and Monday:
Ridging quickly builds moderating temperatures to near normal for
early December. A southern stream wave will approach bringing low
precipitation chances, but its timing and alignment of best moisture
and ascent raise question on amounts.
Days 8-14:
Medium-range guidance is out of phase with timing on a potential
deeper trough and precipitation event early in the period. They are
also not totally aligned on the emergence of a slightly warmer
pattern late in the period. Thus, at this time confidence on
above/below normal temperatures and precipitation is low and no
specific weather hazards can be delineated yet.
&&
.AVIATION (00Z TAF Issuance)...
Issued at 607 PM EST Mon Dec 2 2024
Impacts:
- MVFR conditions in snow/fog early in the period. Potential for
freezing drizzle early
- Some potential for MVFR fog late tonight
Discussion:
Radar shows that the back edge of light snow continues to march
southeast. Some flurries will linger behind the snow. MVFR ceilings
and visibility are possible in snow early in the period, with MVFR
ceilings lasting a bit longer than the snow. There may also be some
patchy freezing drizzle, but confidence in impacting a TAF site is
too low to include at this time.
Clouds will gradually diminish from north to south into the
overnight. With the lingering low level moisture and the decrease in
clouds, cannot rule out some patchy fog late. Confidence is not high
enough to include at this time.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...50
SHORT TERM...Updike
LONG TERM...BRB
AVIATION...50
Source:
IND issues Area Forecast Discussion (AFD) at Dec 2, 9:48 PM EST---------------
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