IND issues Area Forecast Discussion (AFD) at Aug 29, 1:25 AM EDT346
FXUS63 KIND 290525
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
125 AM EDT Thu Aug 29 2024
.KEY MESSAGES...
- Heat Index values near 100 on Friday
- Rain-free weather to oversee a slow transition to milder, and then
lower humidity conditions through the holiday weekend
&&
.FORECAST UPDATE...
Issued at 936 PM EDT Wed Aug 28 2024
- Partly Cloudy and mild
- Patchy Fog overnight
Surface analysis this evening shows a poorly organized and diffuse
boundary across southern Indiana, near where earlier thunderstorms
resided. A larger, stronger area of high pressure was found over
Ontario, providing easterly flow to the Great Lakes and weak
northerly flow to Central Indiana. The air mass across Central
Indiana remained rather humid, with dew points in the upper 60s and
lower 70s. GOES16 this evening shows some dissipating CU clouds
along with some mid and high clouds streaming well aloft due to a
tropical plume near the area and left over convective debris
clouds. SPC meso analysis pages shows falling CAPE across the area
and CIN developing and instability is being lost with a loss of
heating. The nears storm system to Central Indiana was near SW
Illinois.
Overnight, little forcing is expected to pass across Central
Indiana. Best area for possible convection would be near the surface
trough area near southern Indiana and the Ohio river, south of our
forecast area. Still the plume of moisture found across Indiana as
seen within the water vapor imagery will remain across Central
Indiana overnight. This will provide some high passing clouds from
time to time. Forecast soundings overnight maintain a very warm and
moist column, but fail to show deep saturation at any time.
Meanwhile the HRRR keeps the area dry through the overnight hours.
Thus will try and trend toward a dry forecast overnight under partly
cloudy skies. The weak surface pressure pattern across the area will
lead to light to calm winds. This along with the very high dew
points allow dew point depressions to fall to 2F or less. Thus
will trend lows in the upper 60s and lower 70s, with patchy fog
expected, particularly in more rural areas.
&&
.SHORT TERM (This evening through Thursday)...
Issued at 300 PM EDT Wed Aug 28 2024
Relatively benign weather has been observed this afternoon across
Central Indiana with only small chances for rain into tonight. An
area of dying convection this morning brought rain and a few storms
to areas along and west of the I-69 corridor in South Central
Indiana. Canceled the Heat Advisory for areas along and north of a
line from Putnam to Delaware Counties as clouds from this morning's
storms has kept temperatures down in the upper 70s and low 80s in
those areas. There was concern there would be an area within Central
Indiana that this would happen to today, so this does not come as a
surprise. A Heat Advisory remains in effect until 8 PM EDT for
counties along the I-70 corridor and points south. Within the Heat
Advisory, temperatures are making a run for the 90s again by this
evening with dew points in the upper 60s to low 70s and heat
indices over 100.
Rainfall and thunderstorm chances have diminished somewhat across
the region for the rest of the evening and into the overnight hours.
While satellite imagery shows the remnant circulation from an MCV in
Central IL moving toward the IL/IN state line, the environment
ahead of it may be too dry and stable for convective development.
Satellite imagery does not show the presence of developing cumulus
across most of Indiana and ACARs soundings confirm dry air in the
lower and upper levels. Leftover clouds have made it difficult
for the low levels to destabilize through much of the day. Just
within the past hour it appears low level lapse rates have
steepened some with instability beginning to increase. Will have
to watch trends over the next couple hours as the potential is
there for a few showers or storms to develop as the MCV nears and
a front sags south from the north. Kept 20-30 PoPs in through this
evening (lowering them from 50-60) to account for the slight
chance of a stray shower or storm. Confidence remains low and most
places will likely stay dry this evening.
The aforementioned front will sag south across the region overnight
and become quasi-stationary with light winds shifting to the NE and
then E by tomorrow morning. Little change in airmass is expected
with relatively humid conditions persisting into the day tomorrow.
With the frontal boundary over the region, mid to high clouds should
stick around for a while keeping overnight lows elevated in the
upper 60s to low 70s.
Despite an increase in clouds tomorrow, another warm to hot today is
expected with highs approaching or exceeding 90 degrees in South
Central Indiana and mid to upper 80s further north. With the frontal
boundary hanging around the region, there is a very slight chance
for a rogue shower or storm to develop; however with ridging
building overhead ahead of the next approaching system in the Upper
Midwest, conditions may be too dry to support much convective
activity. Kept 20 PoPs for tomorrow afternoon and evening to account
for this, but at the moment most areas should stay dry.
&&
.LONG TERM (Thursday night through Wednesday)...
Issued at 305 PM EDT Wed Aug 28 2024
Thursday night through Sunday...
Summer's final push of several humid days across central Indiana
will continue into Saturday under a retracted jet stream...with weak
surface low pressure approaching from the central US lifting towards
the southern Great Lakes Friday, which will help maintain the
oppressive flow from occasional southwest breezes. Maximum Heat Index
values Friday should again approaching Advisory criteria with
widespread 95-104 values. A faster arrival of clouds/convection thru
midday/early afternoon hours could mitigate this risk.
The boundary accompanying the weak wave Friday will bring another good
chance of rain to the region, especially during afternoon and evening
hours. Diurnally-driven convection Friday, courtesy of 1000 or so J/kg
of CAPE...will have the potential for marginally strong/severe wind
gusts amid a well-mixed boundary layer that should be sporting 1500
J/kg of DCAPE. This threat so far appears to be favored near/north
of the I-70 corridor.
Wind direction will shift to a light northwesterly flow for
Saturday, which will couple with slowly-clearing clouds to hold max
temperatures to only seasonably warm levels. However, the lack of
solid advection of drier air will maintain high humidity for one
more day, especially south of I-70. The arrival of moderate
humidity should be the rule for Saturday night and Sunday. Lower
dewpoints and light westerly breezes Sunday will attempt to bring in
the northeast corner of the hot, western ridge...which should result
in one final day of above normal temperatures with widespread mid-
80s giving a final taste of August. Rain-free conditions are
expected through the weekend amid this slow transition from hot and
humid to a more pleasant Labor Day.
Labor Day through Wednesday...
A secondary boundary is expected to cross Indiana around the Sunday
night timeframe...with subsequent Canadian high pressure's
noticeably lower dewpoints completing the transition to early fall
conditions. The broad dome's center will slowly cross the Great
Lakes...with the local region the benefactor of several days of
northeasterly to easterly surface winds, which should gust above 15
mph for most locations Monday afternoon. This flow will combine
with FEW/SCT daytime clouds to promote slightly below normal
afternoon highs, with mainly upper 70s through at least Tuesday.
Drier air should allow widespread morning lows in the 50s starting
Saturday morning, with the potential for isolated upper 40s across
the CWA's northern tier Monday night. Lack of forcing and
precipitable water values generally suppressed below 1.00 inch will
maintain rain-free conditions into the mid-week. The long term
normal max/min at Indianapolis is 83/63.
&&
.AVIATION (06Z TAF Issuance)...
Issued at 123 AM EDT Thu Aug 29 2024
Impacts:
IFR/MVFR fog likely between 09z-13z at LAF, HUF and BMG
Discussion:
Weak high pressure across the area will remain in place as ridging
aloft begins to re-establish. High dew points across the area along
with clear skies and light winds will allow for the formation of
patchy fog overnight, particularly at BMG/LAF/HUF. A tempo group was
used to account for this.
After sunrise, heating and mixing will allow for fog burn off and a
return to VFR, as weak high pressure remains across the area.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...Puma
SHORT TERM...CM
LONG TERM...AGM
AVIATION...Updike
Source:
IND issues Area Forecast Discussion (AFD) at Aug 29, 1:25 AM EDT---------------
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