IND issues Area Forecast Discussion (AFD) at May 18, 12:08 AM EDT870
FXUS63 KIND 180408
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
1208 AM EDT Sun May 18 2025
.KEY MESSAGES...
- Dry and seasonable conditions through Sunday
- Showers and thunderstorms chances return Monday through Wednesday
- Severe weather possible on Tuesday, especially over southern
portions of central Indiana
&&
.FORECAST UPDATE...
Issued at 936 PM EDT Sat May 17 2025
Quiet evening ongoing as the diurnal cu has been slow to diminish in
parts of the area. Wind gusts have dropped off with sunsets with
temperatures in the mid and upper 60s across central Indiana at 01Z.
The overall forecast is in excellent shape for the overnight.
Surface ridging will expand into the region tonight as winds veer to
northwest and decrease below 10mph. While the cu has taken longer to
dissipate...anticipate mostly clear skies across the forecast area
by the end of the evening or shortly after. Cool night expected as
lows fall into the lower 50s. Normal cool spots across the lower
Wabash Valley are likely to drop into the upper 40s.
Zone and grid updates out.
&&
.SHORT TERM (This evening through Sunday)...
Issued at 319 PM EDT Sat May 17 2025
Rest of This Afternoon...
Cyclonic flow and colder air aloft will continue keep cumulus and
stratocumulus across much of central Indiana, with the greatest
concentration of clouds expected across northeastern portions of the
area. Mixing will continue to bring down some wind gusts over 30
mph, especially early.
Tonight...
An upper level low will gradually move east, allowing heights to
rise a bit. At the surface, high pressure will nose in from the
northwest. The result will be quiet weather across the area.
Stratocumulus may linger into the night across northeastern
sections of the area, farthest from the influence of high pressure
and closer to lingering cyclonic flow. Otherwise, clouds will
diminish across the area with loss of heating.
Winds will also diminish with loss of heating/mixing and with the
high nudging in. This and fewer clouds will allow temperatures to
dip into the 40s northwest, with lows around 50 to the lower 50s
elsewhere.
Sunday...
High pressure and some upper ridging will continue the quiet weather
across central Indiana on Sunday. Less moisture around will lead to
more sunshine, which will boost temperatures into the lower and
middle 70s.
&&
.LONG TERM (Sunday night through Saturday)...
Issued at 319 PM EDT Sat May 17 2025
OVERVIEW
Our active pattern looks to continue as a slow-moving trough begins
to track eastward out of the Rockies early next week. Multiple
vorticity centers are modeled to rotate around the primary trough
axis, inducing rounds of cyclogenesis over the Plains. At least two
or three lows may quickly spin up and occlude into the trough /
broad upper low. Each of these should produce strong to severe
thunderstorms in their respective warm sectors. Thunderstorm
activity is expected to remain to our west until Monday. Heavy rain
and thunderstorms are likely on Tuesday, with some severe potential.
Cooler than normal conditions follow as the parent trough arrives
and lingers for the remainder of the week.
MONDAY
Guidance shows a warm front lifting northward across the mid
Mississippi Valley ending up somewhere just south of Indiana by
Monday morning. There is potential for upstream convective activity
on Sunday to grow upscale into an MCS and track east southeastward
with time. Some members of guidance bring this convective activity
into our CWA by Monday morning. Any activity would likely ride the
warm front moving parallel to the bulk shear vector, perhaps
deviating slightly southward into the low-level jet (LLJ).
Uncertainty remains regarding whether or not this activity makes it
into central Indiana or just to our south...or dissipates completely
beforehand. Mitigating factors include weakening instability and
decreasing LLJ magnitude with eastward extent.
Should an MCS affect our area early Monday, widespread severe
weather is not expected since lapse rates are poor and CAPE is
modest at best. RAP soundings do however so a bit of dry air in the
low to mid levels, which could enhance DCAPE enough to allow for
some sporadic wind gusts. This appears to be a low-probability
scenario at the moment. Heavy rainfall would be possible, especially
on the southern end of the system where corfidi upshear vectors are
slower than the mean wind.
TUESDAY
As the warm front continues to lift north, it should end up over
central Indiana by Tuesday afternoon. Its parent low should be
sitting over western Illinois. North of the warm front, fairly cool
air will be streaming in from the east northeast with temperatures
only reaching into the 60s. South of the front, highs close to 80
are possible under optimal conditions (more sun than clouds). The
gradient between the two could be fairly tight, more than depicted
by blended guidance. At this point its too soon to determine exactly
where the front will end up, so we will maintain the broader
temperature gradient across the CWA for now.
A severe weather threat exists for Tuesday, especially in the open
warm sector along and south of the warm front. Model soundings show
steep lapse rates with rich low-level moisture, tall and wide CAPE
profiles (1500-2000 J/Kg MLCAPE), and long curved hodographs (40-60
kt bulk shear). Based solely on parameter space, one would think
severe weather is likely...but that's not always the case. There are
mitigating factors in place and some uncertainty to work out. In
terms of mitigating factors, the quality of the warm sector is still
in question. Some guidance shows a lot of precipitation within the
warm sector and along the warm front. This could stabilize the
environment through the remainder of the day. In terms of
uncertainty, we still need to see where the warm front actually ends
up and how upstream convective activity alters boundary placement.
That being said, there is potential on Tuesday for severe weather.
The scenario that would lead to the greatest risk would include a
pristine open warm sector lifting northward into central Indiana.
Minimal morning convection with ample destabilization during the
afternoon hours. CSU machine learning is hinting that the highest
probability of this occurring would be over southern Indiana into
Kentucky and Tennessee. Heavy rainfall and localized flooding is
possible as well with multiple rounds of storms.
Stay tuned for updates as guidance comes into agreement and we
continue to refine the forecast.
WEDNESDAY ONWARD
As the low pressure to our west wraps up Tuesday night and occludes,
the parent trough should be overhead or nearby. Cold air advection
combined with the cold upper low will allow for scattered showers at
times with perhaps some precipitation enhancement on the wrap-around
portion of the departing low. Temperatures likely remain below
average through the remainder of the period as the primary trough
slowly drifts eastward.
&&
.AVIATION (06Z TAF Issuance)...
Issued at 1207 AM EDT Sun May 18 2025
Impacts:
- VFR Conditions expected
Discussion:
GOES16 shows a few lingering stratocu across Central Indiana. These
are expected to dissipate and move east within the next few hours.
Surface high pressure in place over the plains states is will build
across Indiana tonight and dominate the weather through the TAF
period. Forecast soundings continue to show a dry column today and
any CU development will be much more limited as compared to
Saturday. Thus VFR.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...Ryan
SHORT TERM...50
LONG TERM...Eckhoff
AVIATION...Puma
Source:
IND issues Area Forecast Discussion (AFD) at May 18, 12:08 AM EDT---------------
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