169
FXUS63 KIND 281859
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
259 PM EDT Fri Jun 28 2024

.KEY MESSAGES...

- Rain showers/isolated thunderstorms overnight and early Saturday
- Becoming partly sunny on Saturday afternoon.
- Cooler Sunday and Monday, heat returns on Tuesday and Wednesday.
- Rain/storm chances return Wednesday onward.

&&

.SHORT TERM (This evening through Saturday)...
Issued at 258 PM EDT Fri Jun 28 2024

Surface analysis early this afternoon shows strong high pressure
centered over eastern NY and NJ. This high was influencing the
weather across the eastern third of the country, including Indiana.
The high was providing southeasterly to southerly flow across
Central Indiana. Surface low pressure was found over NB. Warm and
moist southerly flow was found streaming northward through the
Mississippi river valley, where abundant cloud cover was found. This
cloud cover was advecting east toward central Indiana.  A large area
of showers with a few thunderstorms were found over IA/Northern IL
and MO. Water vapor imagery showed a mainly zonal flow in place
across the CONUS, with a wave of moisture in place from the southern
plains to middle Mississippi valley to the western Great Lakes. A
short wave within this flow was found over SW MO. Dew points across
central Indiana were mainly in the lower 60s.

Tonight...

Models suggest that within the upper flow several weak upper
disturbances will pass across Indiana tonight and on early Saturday.
Meanwhile within the lower levels the low pressure system over NB
pushing toward the Great Lakes tonight dragging an elongated cold
front across the Mississippi Valley toward Central Indiana. Forecast
soundings this evening remain dry as these features approach.
However the forecast soundings show deeper saturation arriving after
09Z with pwats near 2.25 inches. Instability appears quite limited
as CAPE remains mainly below 500 J/KG.  HRRR shows showers mainly
arriving after 08Z, then passing into the forecast area by 12Z. Thus
will have a dry forecast this evening, but begin ramping up pops
overnight as the forcing and moisture begin to arrive in the area.
Confidence for rain is high. Given the expected clouds and
precipitation and the cold front not passing until after 12Z expect
lows in the lower 70s, with some middle 70s south.

Saturday...

Models suggest that at 12Z forcing and the associated cold front
will be over Central Indiana. This should then continue to exit to
the east through the morning hours on Saturday, with the focus
mainly along and south of an I-70 line. By 18Z, forecast soundings
lose their deep saturation and winds become westerly in the wake of
the cold front. Aloft forcing is lost as it pushes east by the
afternoon. Again, instability appears limited as little CAPE is
available, however a stray thunderstorm cannot be ruled out. Thus
will continue high pops through the morning hours, mainly across the
southern half of the forecast area and trend toward a dry forecast
by afternoon. Minimal overall temperature advection is expected
until Saturday night. This will lead to a quick recovery of high
temperatures on Saturday afternoon to the middle 80s.

&&

.LONG TERM (Saturday night through Friday)...
Issued at 258 PM EDT Fri Jun 28 2024

Generally quiet weather through much of the long range as broad
ridging takes hold early next week. Rain chances return late in the
period.

Saturday Night and Sunday

Any lingering showers from Saturday`s cold front / shortwave will be
slowly exiting the area by Sunday morning. Much cooler conditions
will follow, as surface high pressure builds in from the north.
Model temperatures in the 850mb level drop to around 11C in most
guidance, with some members showing as low as 8C by Sunday night.
Around the same time, the surface high moves directly overhead with
large-scale subsidence. Clear skies, light winds, and a cold air
mass should promote temperatures well-below normal Sunday night into
Monday morning. Lows should drop well into the 50s with perhaps some
rural areas dropping into the 40s. Normal lows are around 65 for
this time of the year.

Monday Onward

Cooler than average temperatures linger into Monday with highs
climbing into the 70s for the most part. A few locations may reach
80, especially further south away from the core of the now-departing
cold air mass. As high pressure slides eastward, low-level flow
turns southerly and a warming trend looks to commence. By Tuesday,
850mb temps rise by about 5-10 degrees, which under full sun and
efficient mixing corresponds to highs in the mid to upper 80s. The
primary axis of warm air advection remains to our west, however.
This warm air advection enables a ridge to build over the Plains
which then drifts eastward through the week. As such, generally
above-normal temps in the upper 80s / low 90s should persist through
the remainder of the week. Low temps should also be a bit above
normal, reading in the high 60s to low 70s for most locations.

Turning our attention to precipitation chances, we`ll see quiet
weather associated with high pressure persisting through Tuesday.
Most guidance shows a cold front attempting to infiltrate the
aforementioned ridge by Wednesday night or Thursday. This front
combined with increasing humidity from the south could allow for
repeated shower/storm chances. Ensemble guidance shows the ridge
axis moving eastward a bit allowing flow to be south/southwesterly
through the column across Indiana. Since the front is diving down
from the northwest and encountering largely boundary-parallel
flow...most guidance stalls the front somewhere nearby (most show
central or southern Indiana). Shower and storm chances could then
linger through the rest of the week if this is the case.

Ensemble guidance is in fairly good agreement through Wednesday but
diverges thereafter. And this is probably due to how individual
members handle the front impinging on the departing ridge.
Therefore, confidence in forecast temperatures and precipitation
decreases by late Thursday and Friday.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 1215 PM EDT Fri Jun 28 2024

Impacts:

- VFR expected for much of the TAF period.
- Showers with isolated TSRA possible after 07Z.

Discussion:

Clouds over IL and MO will continue to increase and thicken this
afternoon, however cigs will remain VFR through most of the period.
Low pressure over NB is expected to advance northeast and push a
cold front across Central Indiana late tonight and early Saturday
morning. Forecast soundings suggest a nearly saturated column as the
front approaches and passes through Central Indiana. HRRR also shows
an area of showers passing with the approaching dynamics and cold
front overnight and early on Saturday. Thus confidence is high for
showers passing across Central Indiana late tonight and early on
Saturday, however confidence on specific timing and locations is
low. Thus will include a large window of VCSH late tonight. Have
used a tempo group on Saturday morning as the best forcing is
expected to pass.

Although a thunderstorm will be possible, the time of day and
limited instability are unfavorable for convection. For now have
left thunder out due to low confidence.


&&

.IND WATCHES/WARNINGS/ADVISORIES...None.

&&

$$

SHORT TERM...Puma
LONG TERM...Eckhoff
AVIATION...Puma