IND issues Area Forecast Discussion (AFD) at Aug 7, 8:56 AM EDT441
FXUS63 KIND 071256
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
856 AM EDT Wed Aug 7 2024
.KEY MESSAGES...
- Cooler and less humid Wednesday
- Much cooler and low humidity this weekend
&&
.FORECAST UPDATE...
Issued at 854 AM EDT Wed Aug 7 2024
A few updates have been made regarding theh ongoing stratus deck
over the Ohio Valley. Patchy drizzle has sustained itself over S/SE
portions of central Indiana, but should become more isolated and
eventually end over the next few hours as LCLs rise within increases
in sensible heat fluxes.
The other change to the forecast is a decrease in expected
temperatures this afternoon. This thick stratus deck will have a
difficult time breaking apart, reinforced by continued cyclonic flow
aloft. This should subdue temperatures siginificantly with highs in
the upper 70s for most of central Indiana.
Zone and grid updates out.
&&
.SHORT TERM (Today and tonight)...
Issued at 140 AM EDT Wed Aug 7 2024
A modest push of cooler and slightly drier air has moved into
central Indiana behind departing midlevel perturbation and
associated surface wave. Moisture under the frontal inversion and
subsident layer is resulting in stratus this morning. This should
gradually decrease through the day, but will delay surface heating
some holding temperatures a few degrees above early August climo.
Clearing and decoupling should be enough for good radiative
conditions, especially across the north tonight. Much of the high
resolution and statistical model guidance is cooler than a blended
mean, and so it appears mid-50s for minimum temperatures are
achievable in rural portions generally north of I-70. There could be
some patchy fog but coverage is expected to be less than the
pattern over the last few days.
&&
.LONG TERM (Thursday through Tuesday)...
Issued at 140 AM EDT Wed Aug 7 2024
The new air mass in place through Friday is fairly standard for
early August. Humidity will be lower than recent days since a
modified push of continental air has now arrived. But it is still
augmented by seasonally high levels of evapotranspiration. So, while
less oppressive as the air mass it replaced, it's moisture content
is still fairly high.
Weakening of western ridge will be coincident with deepening Great
Lakes low. This low will be more effective at displacing drier and
cooler continental air mass down to our latitude this weekend.
Differences among medium range guidance do emerge by then, with
ECMWF/EPS-weighted cluster not as deep compared to the GEFS-weighted
cluster.
It appears several days of warm advection-driven convection
at the nose of a quasi-permanent low-level jet across the Plains
will start up early next week. While the GEFS camp is more
progressive with the trough and also more perturbed with the
northwesterly flow, it still holds continental air mass over Indiana
and thus has only a weak QPF signal early next week. Due to the
synoptic-scale differences in models, EPS-camp is drier and
suppresses Plains convection further southwest.
The pattern into next week will support gradual displacement of
anomalously cool continental air mass, and we should moderate back
to near seasonal levels by the middle of next week.
Medium range ensemble data shows strengthening broad ridging across
the central CONUS during the Day 8-14 period. This will keep us in
northwesterly flow and may shift the aforementioned Plains warm
advection regime further east, offering at least normal if not
slightly above normal precipitation chances. Temperatures should be
near or just above normal in this pattern.
&&
.AVIATION (12Z TAF Issuance)...
Issued at 535 AM EDT Wed Aug 7 2024
Impacts:
- IFR or lower ceilings and visibility this morning
- Low probability of fog again tonight
Discussion:
Low stratus should gradually increase later this morning and a
return to VFR conditions should occur early this afternoon. Moderate
forecast confidence on cessation of ceiling restrictions. We used
TEMPO groups to communicate uncertainty.
Wind gusts 15-20 knots are possible once mixing deepens, given
residual MSLP gradient. These would subside this evening once mixing
decreases.
There is some conditionality on fog potential tonight. Cooler
starting point for temperatures at onset of nocturnal cooling, and
probably enough low-level moisture. Where winds go calm, chances are
higher. New 12z TAFs include fog tonight only where confidence is
currently highest, but all sites have some risk.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...Updike
SHORT TERM...BRB
LONG TERM...BRB
AVIATION...BRB
Source:
IND issues Area Forecast Discussion (AFD) at Aug 7, 8:56 AM EDT---------------
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