IND issues Area Forecast Discussion (AFD) at Nov 26, 3:02 AM EST687
FXUS63 KIND 260802
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
302 AM EST Tue Nov 26 2024
.KEY MESSAGES...
- Becoming sunny, but cold today
- Increasing clouds tonight.
- Potential rain/snow Wednesday and Thursday; limited accumulation
and travel impact currently expected
- Much colder Friday into the weekend.
- Light snow possible on Saturday.
&&
.SHORT TERM (Today and tonight)...
Issued at 301 AM EST Tue Nov 26 2024
Synopsis:
Surface analysis early this morning shows deep low pressure in place
over southern Ontario, with a cold front extending south through the
Appalachian mountains. Strong and cold high pressure was found over
KS and OK. This was resulting in cold northwest flow across Central
Indiana. GOES16 shows a cold air advection cloud deck in place over
our region, with clearing found over IL and points west. Aloft,
water vapor showed an upper low over western Ontario, with a trough
axis nosing SE toward Ohio. Subsidence was found across Indiana and
Illinois. Looking west, weak ridging was found over the Rockies,
aiding surface high pressure development.
Today -
Quiet but cool weather will be expected today. Models suggest the
upper flow to become more zonal today, with little in the way of
upper support in play. Forecast soundings show a dry column in place
through the day. This is indicative of the strong subsidence that
will be in play today as the surface high pressure system to the
southeast drifts east to the Ohio valley. Thus we will expect sunny
skies today as the current cloud cover is expected to depart to the
east early this morning. As the high pressure system arrives across
the area and the low to the northeast departs, the pressure gradient
across the areas will diminish, leading to lighter winds through the
day. Given our ongoing cold air advection highs in the lower to
middle 40s will be expected.
Tonight -
More dry and quiet weather will continue tonight. The zonal flow
aloft is expected to remain in place for much of the night, but
changes are starting to arrive late. A trough within the upper flow
will emerge from the northern plains late tonight. This system will
begin to deepen, and be our weather maker for Wednesday and into
Thursday, however tonight it will not have much impact across
Central Indiana. A lack of dynamics aloft along with plentiful dry
air within the lower levels, and departing surface high pressure
will lead to a mostly clear evening. Mid and high cloud are expected
to arrive overnight as they are ejected from the approaching upper
trough over the plains. Thus expect increasing clouds overnight,
with cold temperatures. Lows will fall to the lower and middle 30s.
&&
.LONG TERM (Wednesday through Monday)...
Issued at 301 AM EST Tue Nov 26 2024
All eyes are on a system expected to arrive on Wednesday. Guidance
has largely come into consensus on its evolution and timing, though
some differences remain (primarily in the mesoscale). Thermal
profiles suggest that both rain and snow are possible for portions
of central Indiana. Minor accumulations are also possible...which
will be discussed below along with associated impacts.
As of 06z Tuesday, satellite imagery shows a large plume of moisture
advancing inland over the California coast. This feature should
progress eastward, ejecting into the Plains late tonight into
Wednesday. A broad baroclinic zone will simultaneously reside over
the Midwest, emplaced by yesterday's cold front. The approaching
system should act upon this baroclinic zone leading to an east-west
oriented area of frontogenesis. Guidance shows precipitation
breaking out in response to the frontogenetical forcing. However, a
very dry lower atmosphere may prevent much of this initial precip
from reaching the ground. It may take several hours before the lower
column saturates enough for precip to begin at the surface. Wet bulb
temperatures may be right around freezing, where precip begins as
rain before transitioning to snow due to evaporational cooling. Best
chances for snow Wednesday afternoon are north of I-70, as
temperature profiles are warmer with southward extent. Regardless,
not much precipitation may end up reaching the ground south of I-70,
at least initially, as the best frontogenesis may be in the northern
half of our CWA. Heavier rates may be an important factor for
overcoming the dry lower atmosphere for much of the day.
Further west, lee cyclogenesis ahead of the parent vort max should
be ongoing during the day Wednesday. The shortwave and resulting
surface cyclone, though weak, should progress eastward passing south
of Indiana through Kentucky. Precipitation expands in coverage as
the low approaches Wednesday evening. In locations that escaped the
initial round of precipitation, that changes around and after
sunset. Thermal profiles south of I-70 still look quite marginal, at
best, and rain is the preferred precip type here. Snow may briefly
mix in before the system exits Thursday morning. Across the northern
portions of our CWA, precipitation may switch over to snow and
remain snow for the duration of the event. Even here, thermal
profiles are marginal...with most guidance showing surface temps a
degree or two above freezing. Fresh cold air will not be ingested
into this system, so snow will depend on diabatic processes along
with evaporational cooling. Accumulations and impacts may be rate-
driven, especially where one or more mesoscale bands set up (03Z RAP
shows such a scenario). Areas that find themselves under a mesoscale
band may "over-perform" compared to surrounding locations by a
couple of inches. On average, however, amounts will be light
(generally under 2 inches) due to the marginal temperatures (lower
snow-liquid ratios and some melting) and limited duration of
precipitation. Accumulations should primarily occur on elevated and
grassy surfaces.
Strong cold air advection ensues once the system departs on
Thursday. Temperatures fall into the 20s Thursday night and may
struggle to reach freezing again Friday afternoon. Cold
northwesterly flow is expected to persist through the weekend. Multi-
model ensemble guidance retains a strong signal for continued east
coast troughing. Therefore, well-below average temperatures are
likely through the first week of December. Such patterns are
typically dry, though a few periodic light precipitation events may
occur.
&&
.AVIATION (06Z TAF Issuance)...
Issued at 1220 AM EST Tue Nov 26 2024
Impacts:
- Cigs improve to VFR after 09Z
Discussion:
GOES16 shows the back edge of clouds over eastern IL, making stead
progress eastward. These clouds should exit the TAf sites during the
first 3-4 hours of the Taf period, leading to VFR Conditions
thereafter.
Forecast soundings and time height show a dry column through the day
on Tuesday, but higher clouds begin to invade this evening as the
next system approaches.
Strong pressure gradient across the area will allow for continued
gusty winds overnight. As high pressure arrives on Tuesday, winds
will lessen as the gradient relaxes.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SHORT TERM...Puma
LONG TERM...Eckhoff
AVIATION...Puma
Source:
IND issues Area Forecast Discussion (AFD) at Nov 26, 3:02 AM EST---------------
If I'm using your data in a way that is against your terms please email the team at "threatweb@pupswoof117.com"! I am a bot who will not respond in the comments at all and is only designed to post RSS feeds!
