IND issues Area Forecast Discussion (AFD) at Dec 15, 2:54 AM EST742
FXUS63 KIND 150754
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
254 AM EST Sun Dec 15 2024
.KEY MESSAGES...
- Rain and drizzle today, diminishing late
- A second round of rain with the potential for embedded
thunderstorms arrives early Monday morning.
- Milder temperatures through Monday
- Cooler temperatures arrive from Tuesday onward
&&
.SHORT TERM (Today and tonight)...
Issued at 254 AM EST Sun Dec 15 2024
Early This Morning through Today...
Early this morning, an upper level low was across central Illinois,
with a surface low across western Illinois. An 850mb jet was pumping
moisture into the area. These were working together to produce rain
across much of the forecast area.
The 850mb jet will move off to the east during the remainder of the
pre-dawn hours, taking the solid area of rain with it. However, as
the upper low moves northeast, additional areas of rain will develop
ahead of it and move into the area.
This will continue past 12Z as the low moves into lower Michigan.
Will go at least likely category PoPs across much of the area
through 12Z, then gradually push these PoPs east through the morning
as the upper low continues its journey northeast.
Upper moisture will diminish as the low moves northeast, but low
level moisture will linger. Some weak forcing may remain in this
layer, which will likely lead to some drizzle. Will continue with a
drizzle mention into the afternoon.
In addition, will have to watch for some fog in the northern
forecast area this morning as the upper low moves by, based on what
is ongoing upstream.
Even with the clouds and rain/drizzle, southerly flow will allow
temperatures to peak in the middle 40s to middle 50s.
Tonight...
Brief upper ridging will move in for this evening ahead of the next
system. This will keep the area dry during the evening. However,
forcing from the next upper trough will move in overnight. An 850mb
jet will return as well, bringing in deeper moisture once again.
There are some questions though about how fast forcing and moisture
return, which will impact how far east the rain will get by 12Z
Monday. Given the uncertainty, will keep the eastern part of the
area in chance PoPs, with higher PoPs to the west.
Some weak instability will move into portions of the southern
forecast area, so a rumble of thunder will be possible there
late tonight.
Little change in airmass plus continuing cloud cover will keep low
temperatures in the 40s most areas.
&&
.LONG TERM (Monday through Saturday)...
Issued at 254 AM EST Sun Dec 15 2024
Monday/Monday Night:
By Monday morning, a moisture tongue associated
with a modest WSW LLJ streak will be breaching central Indiana,
initiating a new round of precipitation. Trends continue to shift
this initial LLJ streak southward, now with HREF clusters generally
just south of the Ohio River. This has placed the greatest
precipitation axis (1.5-3") to over the Ohio River, with generally
0.5-1.0" over southern Indiana. Within the LLJ, strong differential
WAA also looks to create steep 850-500mb lapse rates, creating an
elevated, embedded thunder threat through Monday morning. This
threat would likely stay confined to far southern portions of
central Indiana.
Even with some increasing HREF continuity, there are still some
uncertainties with Monday's system. This mostly resides with the
magnitude of northward theta-e advection out ahead of the wave
during the day on Monday. The greater the advection, the greater the
baroclinicity will be ahead of the pressure trough, leading to
chances for convective showers and thunderstorms in the
afternoon/evening (Currently being modeled by the HRRR/RAP).
However, looking at the whole HREF suite, along with model trends,
there looks to be a greater than 50% chance the low level flow will
remain SW/WSW ahead of the pressure trough, mitigating northward
advection, and therefore limiting afternoon convection chances (More
aligned with the NAM). We will continue to monitor this in the
coming issuances, as this could also impact total QPF and afternoon
high temperatures, along with potential low end convective hazards.
Tuesday Onward:
After the passage of the wave on Monday, latest model guidance
remains steadfast with a marginal cooling trend late Monday through
Tuesday. Without a large upper level trough, this change in airmass
will be much more marginal, with temperatures falling back towards
seasonal (vs the arctic-like airmass we had in previous weeks). This
begins to change some mid-week as another wave further taps into air
over the Canadian Plains. This wave will likely still be early in
its life cycle as it arrives Tuesday night into Wednesday, without a
true cold conveyor belt formed. Therefor, p-type issues are not
expected with the midweek system initially; there is a low chance of
some frozen precip on the backside of the wave Wednesday evening.
Outside of general temperature continuity, there is little in the
way of model consistency regarding this system's track and
magnitude, leading to low confidence on specific timing and QPF
amounts.
Days 6-10: A signal for broad East Coast troughing remains within
ensemble guidance beginning late next week. Such a pattern typically
leads to a cooler and drier pattern in Indiana under northwesterly
flow. Guidance dampens the troughing signature by about Christmas
which is likely due to uncertainty between the various members.
&&
.AVIATION (06Z TAF Issuance)...
Issued at 1209 AM EST Sun Dec 15 2024
Impacts:
- Conditions will deteriorate to IFR overnight
- IFR and potentially worse continuing through at least midday
- Winds tonight occasionally gusting to 18-22KT into the morning
Discussion:
Although ceilings have been slow to lower, still expect them to
reach IFR category overnight from west to east. These conditions
will persist at least through midday, and some lower ceilings are
possible. MVFR ceilings may return by 21Z.
Rain will continue at times through mid-morning or so before
transitioning to drizzle. Visibility will dip into MVFR at times.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SHORT TERM...50
LONG TERM...Updike
AVIATION...50
Source:
IND issues Area Forecast Discussion (AFD) at Dec 15, 2:54 AM EST---------------
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