Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 12/23/23
Area Forecast Discussion
National Weather Service Indianapolis IN
904 PM EST Fri Dec 22 2023
.Key Messages...
- Widespread rain mainly north of I-70 into Saturday morning
- Temperatures 10 to 20 degrees above normal through next Tuesday
- Widespread light to moderate rainfall expected Christmas day and
evening
&&
.Forecast Update...
Issued at 903 PM EST Fri Dec 22 2023
Just some minor adjustments to ongoing forecast this evening. Light
rain coverage across much of northern half of CWA with southern half
more isold to scattered as lower levels still remain quite dry.
Looks like one to two tenths of rain has fallen so far in the north.
Regional radar mosaic indicating back edge of larger pcpn shield
moving into eastern IL with scattered coverage behind. A small
mesoscale circulation aiding in higher reflectivity returns between
HUF and CMI. Another couple tenths of an inch of much needed
rainfall looks likely across the northwest third of area before
tapering to drizzle overnight.
Stratus deck is lowering in wake of rain and visibilities across
western and northwestern IL below 2 miles in many areas. Some
concern upstream fog could expand farther southeast and get close
to northwest areas late tonight so will have to keep an eye on
this into the overnight period.
&&
.Short Term...(This evening through Saturday)
Issued at 300 PM EST Fri Dec 22 2023
Expansive cloud cover across the region this afternoon, and ACARS
soundings over the last few hours supporting a slow moistening to
the lower levels. SFC OBS equally support this as ceilings are
beginning to be reduced to sub 6KFT AGL heights. Meridional flow
continues to be advecting a moist axis north from the Western Gulf
of Mexico, with the channel still displaced to the west of Indiana.
Precipitation from earlier this morning was realizing the dry
environment over Central Indiana and as a result most was either
virga or small droplets that were just wetting the surface. T/Td
spreads have been slowly decreasing as well, and expect this to
continue this evening as the upper level wave drifts east towards
the region.
Guidance has continued to focus on steadier rain developing form the
enhancement to the low-level jet during the nocturnal hours. Expect
that as the moist axis pivots east, the steadier rain should develop
upstream in Central Illinois and push east towards the Lafayette
area around 21Z, then persist into the overnight hours as the
boundary sags southeast. Timing for the steadier precip reaching the
Indy metro appears to be more focused in the 2-6Z timeframe, but
some of the hi-res solutions differ on precise timing and also QPF
values. Touching a bit more on the QPF totals and the median has
been around .25" with a max much higher; however, some caution
should be used when looking at the QPF values as there`s a wide
range in all NWP output. So the confidence is hovering higher with
respect to roughly a .25" value for Central Indiana and perhaps
where precip arrives earlier this evening in the Northwest forecast
area will approach .4".
Parcels will continue to be ascending overnight, but the lift or
omega isn`t too robust. So the concern is that perhaps some patchy
fog could develop should the precip shield not be as expansive as
some guidance is indicating. Bufr soundings still indicate a
decoupled low-levels so some of the steadier rain may transition
over to a heavy drizzle for a few hours with the very moist
environment.
Saturday... It does appear heights will try to rise marginally in
the mid-levels midday, with the deeper moisture peeling east of the
region. This should be enough to support an end to the precip
shield; however, that likely will keep the low-levels trapped with
clouds for much of the day. Flow does remain southerly and there
should be enough warm air in place to support allowing temps to push
into the 50s for much of Central Indiana.
&&
.Long Term...(Saturday night through Friday)
Issued at 309 PM EST Fri Dec 22 2023
Saturday Night and Sunday...
Upper ridging will amplify while slowly crossing the Midwest into
Sunday...while the surface exhibits a strengthening gradient between
very broad high pressure centered along the North American Atlantic
coast and an north-south elongated trough of low pressure slowly
crossing the Plains. Winds will back while increasing slightly over
central Indiana, with the approaching surface low actually filling
slightly courtesy of a convoluted supporting trough over the western
US...with local southeasterly winds expected to gust to 15-20 mph by
Sunday afternoon.
Can`t rule out some lingering light rain or drizzle Saturday night,
but most areas should stay precipitation-free. Guidance is still
promising decreasing clouds late Sunday, albeit with latest data
trending later with this at-least-partial clearing. Unseasonably
mild readings under anomalously high heights for December...will
range from lows in the mid to upper 40s Sunday night to afternoon
highs Sunday in the upper 50s to mid-60s. While Indianapolis may
not reach 2021`s Christmas Eve maximum (62F), the current forecast
of 60F would nonetheless be a an all-time top 10 mark for the day.
The next system`s approaching rain should not reach the CWA until
pre-dawn Christmas morning.
Christmas Day through Friday...
The evolution of the broad trough over the central CONUS will come
to include a occluded/stacked surface low over the Middle Missouri
Valley...prior to the trough filling before slowly dragging its
broad presence eastward and finally out of the region by the end of
the long term. This will include two main phases for central
Indiana...continued well above normal temperatures through Tuesday,
led by organized light to perhaps moderate rainfall on Christmas
Day...before a steady downward temperature trend to near normal
chill by week`s end amid lingering low chances of precipitation
under the system`s rotating center.
As has been the pattern with most rainfall opportunities since this
fall, once-impressive QPF progs have now settled into a better 0.25-
0.50 inch likelihood...which is reasonable given weaker phasing
between the lower and upper portions of the system. Impressive
moisture flux off of the eastern Gulf and even Atlantic will
approach Indiana from the southeast, yet it appears more substantial
rains are not likely to advance farther north/west than the Ohio
Valley. Still, periods of rain should be the rule through most of
Christmas...with lingering POPs into Christmas evening likely
bringing an additional 0.10 inches or less for most locations.
Moderate rainfall totals (0.50+ inches) would be possible south/west
of I-74 should better phasing/duration be realized.
Embedded vort maxs will bring occasional chances for further light
rain through the mild-week. Tuesday will be the final very mild day
as broad dry conveyor streams into Indiana from the SSW. Lower
confidence in timing of the trough`s departure as it slowly spins
east over the Midwest. Lower heights and clouds will oversee light
to moderate breezes slowly veering through westerly directions,
dropping temps most closer to normal for the Wednesday-Friday time
frame. Should some bits of northern energy attempt to plunge
through the Great Lakes towards the region, then a few snow showers
could be ruled out during the late week on the back end of the
departing system...with this so-far smaller potential to be refined
in later updates. The normal max/min at Indianapolis through the
long term is 38/24.
&&
.Aviation...(00Z TAF Issuance)
Issued at 640 PM EST Fri Dec 22 2023
Impacts:
- Showers through the night with CIGs and VIS lowering
- MVFR conditions spreading east this evening and becoming IFR
- LIFR CIGs Possible toward daybreak with drizzle
Discussion:
Radar showing a lot of returns across the region early this evening
with lower levels slowing moistening. KLAF has dropped to MVFR and
upstream observations along with short term guidance supports IFR
cigs moving in next few hours and should maintain through the night.
LIFR looking more likely at KLAF with upstream CIGs already in the 3-
5hft range. The MVFR CIGs and VIS with light rain expected to slowly
work east through the night and lowering to IFR most locations late
tonight with lower levels saturating. Expect transition to drizzle
toward daybreak which will linger into the daylight hours. Tried to
be optimistic with CIGs lifting to lower MVFR range Saturday
afternoon but IFR could linger later into the afternoon.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Update...Lashley
Short Term...Beach
Long Term...AGM
Aviation...Lashley