IND issues Area Forecast Discussion (AFD) at Nov 15, 12:26 PM EST247
FXUS63 KIND 151726
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
1226 PM EST Fri Nov 15 2024
.KEY MESSAGES...
- Low clouds and drizzle through this morning
- Potential for fog and continued low stratus tonight
- Rain chances return Tuesday followed by a trend toward cooler
temperatures by the end of the week.
&&
.FORECAST UPDATE...
Issued at 928 AM EST Fri Nov 15 2024
Cold air advection behind a trough passage has lead to building low
level pressure and subsidence across the Great Lakes and Western
Ohio Valley. The combination of subsidence and remnant surface to
800mb moisture has lead to a large region of low level stratus. This
subsidence is also aiding in squeezing out pockets of drizzle across
Indiana this morning.
Surface level heat fluxes should aid in some mixing and PBL warming
throughout the day eventually raising ceilings heights and ending
drizzle near or shortly after noon. Some model solutions have the
stratus deck eroding some this afternoon, but given consistent low
level moisture profiles remain saturated through the early evening,
it looks likely that this stratus deck will remain into the evening.
For this reason, temperatures have been cut by a few degrees, with
highs now expected to remain in the low 50s for most of the area.
Fog will be a concern tonight given high pressure centered over the
area, but low level moisture remaining. Still many uncertainties
remain regarding coverage and magnitude, but this will be the main
point of focus for the afternoon update.
&&
.SHORT TERM (Today and tonight)...
Issued at 257 AM EST Fri Nov 15 2024
A rather cool and dreary weather pattern continues into Friday for
much of the state. Latest satellite imagery shows widespread low
stratus across the Great Lakes region and Midwest in the wake of an
area of low pressure near Detroit. Latest ACARs soundings align well
with short term model guidance indicating a strengthening subsidence
inversion aloft with a fairly deep saturated layer from the surface
to around 1.5km agl. Weak lift associated with cyclonic flow around
the aforementioned low has resulted in isolated areas of drizzle
across the state early this morning. Keeping the chance for drizzle
in through the rest of the morning hours, with a slight drying trend
likely by the afternoon hours. Keeping the forecast on the
pessimistic side however for the rest of the day. The lower sun
angle this time of year will struggle to heat the boundary layer
through the thick stratus, keeping moisture and low clouds stuck
near the surface under the strengthening subsidence inversion aloft.
This pattern is normal for this time of year where models try to dry
out and heat the boundary layer too fast. Therefore, going below
guidance for highs today, with the coolest areas likely in Northern
and Eastern Indiana, where clouds will stick around the longest.
Depending on how fast the clearing line near the Mississippi River
pushes east today, there may be a good temperature gradient from
west to east across the area. If sunshine is realized for Western
and SW Indiana, highs may reach the mid 50s; whereas areas stuck
under low clouds may struggle to exceed the 50 degree mark.
Surface high pressure moves directly overhead by this evening before
shifting northeastward later tonight. A nearly saturated boundary
layer and high pressure overhead may result in areas of fog and very
low stratus across much of the region overnight tonight. If clearing
does take place in some spots, optimal conditions for radiational
cooling may lead to dense fog and very low visibility in some areas.
Will watch this carefully as headlines may be needed if the threat
for dense fog becomes widespread. Fog and low clouds should keep
lows from plummeting, remaining elevated in the mid 40s.
&&
.LONG TERM (Saturday through Thursday)...
Issued at 308 AM EST Fri Nov 15 2024
A fairly highly amplified pattern will dominate the long term
period, with ridging across the region over the weekend evolving
into a mid to late week pattern dominated by a potent closed low
pressure system, which deterministic models are struggling to come
to consensus on with respect to intensity/positioning and resultant
impacts on advection patterns.
There is much better agreement on evolution of the pattern over the
weekend into the early portion of the week, with continued well
above normal temperatures persisting through at least Tuesday night
into early Wednesday. Additionally, some low rain chances will be
necessary Sunday night into Monday as moisture advection into the
region ramps up ahead of the approaching low pressure system and
some weak isentropic lift develops, but the bulk of rainfall, and
far higher PoPs, can be expected Monday evening into early Tuesday
as the warm conveyor belt associated with the strong low moves
through the area.
Guidance then begins to differ fairly significantly on the
progression of the larger closed low through the Midwest and into
the Northeast during the latter portion of the week, along with the
degree and intensity of any secondary cyclogenesis that may occur in
or east of the Ohio Valley. Nevertheless, precipitation chances will
be necessary most of the remainder of the period between the
influence of the upper low and any potential lake enhancement with
cold advection over Great Lakes waters that are running much above
normal temperature wise for the time of year.
The differences in cold air intrusion into the area in the
deterministic models is a significant complicating factor - and
cannot entirely rule out temperatures cold enough to support a few
snowflakes toward the end of next week, but for the time being the
blend approach is likely the prudent one, which keeps temperatures
below normal but well above freezing during the day and only down to
near freezing overnights. Should be able to refine this as time goes
on and guidance hopefully converges onto a coherent solution, but at
this point the GFS solutions appear to be a bit of an outlier with a
far stronger cold air intrusion into the region.
Nevertheless - some of the coolest conditions of the season thus far
look to be a good bet for late next week, with highs by week's end
not much different than the overnight lows expected this weekend.
&&
.AVIATION (18Z TAF Issuance)...
Issued at 1225 PM EST Fri Nov 15 2024
Impacts:
- MVFR cigs through the evening; improvement early tonight
- Fog and low stratus likely again tomorrow morning
Discussion:
MVFR cigs continue through the afternoon and evening hours at all
TAF sites in Central Indiana. Latest ACARS soundings and satellite
imagery show low level moisture and clouds trapped within the lowest
1km agl with the back edge of the cloud deck still in Central
Illinois.
Lower confidence exists with how fast conditions improve during the
late evening into tonight. Potential exists for MVFR cigs to stick
around through the entire TAF period. Current expectation is for some
breaks in the clouds tonight; however this may result in
additional fog development. Added fog and low stratus to all TAF sites
after 10Z tonight with the assumption breaks occur. Even if
breaks dont occur, subsidence beneath high pressure should lead
to 5SM BR at points tomorrow morning.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...Updike
SHORT TERM...CM
LONG TERM...Nield
AVIATION...Updike
Source:
IND issues Area Forecast Discussion (AFD) at Nov 15, 12:26 PM EST---------------
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