Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 251619
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1219 PM EDT Mon Mar 25 2024

.KEY MESSAGES...

- Wind Advisory Tonight and Tuesday
- Increasing Clouds Today; Windy and warm.
- Elevated Fire Danger this Afternoon
- Windy with rain Tonight
- Showers and few t-storms Tuesday...isolated severe storms possible
- Frost possible Wednesday night

&&

.FORECAST UPDATE...
Issued at 1006 AM EDT Mon Mar 25 2024

Breaks in the cloud cover will allow for downward transfer of higher
winds from 3K feet to the ground this afternoon. That in addition,
the tight surface low pressure gradient ahead of the strong Plains
system along with mixing will allow temperatures to surge into the
60s or some 10 degrees above normal this afternoon. The windy and
dry conditions will also result in an elevated fire danger. Will add
this to the HWO.

&&

.SHORT TERM (Today and tonight)...
Issued at 246 AM EDT Mon Mar 25 2024

Synopsis:

Surface analysis early this morning shows deep low pressure over
southwest KS, with an inverted trough axis stretching north across
eastern NB to western MN. Strong high pressure was found over the
east coast of the United States. This was resulting in a moderate
easterly flow of mild, dry air to Central Indiana. A strong pressure
gradient was found across Illinois, building east toward Indiana
with the eastward progression of the associated low pressure system.
Dew points across the area remained very dry, in the lower 20s,
indicative of the very dry air mass in place within the lower
levels.  GOES16 showed abundant cloud cover across the Mississippi
and Ohio River valleys, streaming into Indiana. These clouds were
mainly of the mid and high type variety.

Aloft water vapor showed a deep upper trough over the high plains,
just east of the Rockies. This was resulting in southwest and
southerly flow aloft ahead of the trough. A moist conveyor belt
appeared to beginning to form with showers and storms developing
over OK and TX.

Today...

A windy day is in store today. The upper trough over the high plains
is expected to push east today along with the associated area of
surface low pressure. This will push the already tight pressure
gradient across MO and IL across Indiana through the course of the
day. This southerly flow aloft also shows a 40 to 50 knot LLJ
streaming across Indiana through the course of the day. Forecast
soundings keep the lower levels quite dry, while saturation is seen
aloft. Given the very dry dew points across the area, this seems on
target, with high clouds as seen on GOES16 streaming across Central
Indiana through the course of the day. However, with limited lower
level moisture present and the arrival of the LLJ through the day,
heating and mixing should result in a windy day with gusts around 35
mph possible through the day. Thus expect filtered sunshine today
due to mainly high clouds with cloud opaqueness increasing through
the afternoon.

Given the strong warm air advection today with winds becoming
southerly, highs in the middle to upper 60s will be expected, which
is well above the seasonal normals.

Tonight...

Active weather is in store for tonight. The surface low pressure
system is expected to push toward MO/IA overnight, keeping Central
Indiana within the warm sector through the overnight hours. Models
suggest a developed warm and moist conveyor belt ahead of the low
will quickly push across Central Indiana through the late evening
and overnight hours. Ample forcing will supplied through a strong
LLJ around 70 knts aimed at Central Indiana. Forecast soundings show
deep saturation present tonight as these features pass with pwats
over 1.2 inches. The 300K GFS isentropic surface shows favorable up
glide with specific humidity over 6 g/kg. HRRR is also on board,
showing a wave of showers push across Indiana tonight associated
with the passing of the warm conveyor belt. Thus confidence for rain
is high tonight and high pops will be used through the overnight
hours.

Indiana will remain in the warm sector after the departure of the
wave of moisture overnight. Thus lower pops will still be needed for
any light...stray showers that could be possible.

Given the expected favorable mixing and precipitation, lows will
only fall to the middle 50s across much of the forecast area.
Furthermore with the strong LJJ passing aloft, gusts around 40-45
mph will be possible. This will continue to be handled with the
ongoing wind advisory.

&&

.LONG TERM (Tuesday through Sunday)...
Issued at 246 AM EDT Mon Mar 25 2024

Tuesday and Tuesday night...

The long term will start with central Indiana amid the warm sector
of a potent 990 mb occluded surface low over the Upper Midwest that
will slowly fill while slowly lifting towards Ontario.  Despite the
main slug of rainfall having ended pre-dawn when better deep
moisture advanced into Ohio...continued rain chances and more
notably a marginal severe risk will accompany the storm system`s
cold frontal passage during the day Tuesday.  Rain or not, the
strong gradient will maintain southerly winds sustained to 20-30
mph, with near-advisory criteria gusts...under what should be a
broken to, likely at least briefly, scattered-out cloud deck that
would allow readings to reach generally the mid-60s.

Despite the inordinately highly-sheared profile, with 0-6 km bulk
shear of 70-90 kts ahead of the frontal passage, mainly near-zero
instability will be the factor limiting stronger convection.  CAPE
(essentially all sfc-based) may briefly approach 500 J/kg for a 2-4
hour period during the late morning to afternoon ahead of the
boundary, with the 3-4 hour durations only over southeastern
counties.  This marginal potential, is also conditional with
adequate 700-500 mb lapse rates lagging behind the brief CAPE until
perhaps late day when they may finally meet over far eastern
counties, albeit likely after peak heating. Suspect a broken north-
south line of showers and embedded thunder over western zones by
late morning...that will slide east into the afternoon. Uncertainties
on peak intensity of rainfall rates and winds in stronger cells...
although with surface flow already gusting to 40-45 mph it would not
take too strong of convection to produce isolated severe gusts.
Latest CAMs depict the broken cluster of (T)RW`s diminishing while
crossing the CWA - which may be a reflection of the main plume of
deep moisture continuing to dwindle ahead of the front...with
precipitable water possibly falling to under 0.70 inches along the
front edge of showers by 18z.

Suspect any additional rainfall Tuesday will be mainly under 0.25
inches, with chances for locally double that under the few heavier
downpours. Flooding threat should be low/zero with less than 0.75
inches expected from the preceding overnight. Any remaining showers
should be fading and/or departing the region by late day with the
front nearing the Ohio line.  The long-awaited decrease in wind
speed should be noticeable before sundown...with gusts probably down
to the 15-20 mph range by midnight.  The southeastern most portions
of chilly Canadian surface high pressure will begin building into
Indiana as the storm center slowly crosses Lake Michigan.  At least
a 30-degree drop behind the front will bring lows in the 30s Tuesday
night...although considerable cloudiness trapped within the
subsidence inversion should deter any freezing readings.

Wednesday through Sunday...

The remainder of the workweek will be a slow transition from the
lingering broad, split, yet filling upper trough to a building ridge
pattern by Friday.  The amplified surface ridge extending from
interior Canada to much of the southeastern CONUS will block the
return of Gulf moisture.  The resultant dry column should promote
ample sunshine for much of the Wednesday-Friday period.  The
greatest frost/freeze concern is expected to be Wednesday night when
diminishing breezes and mostly clear skies should allow lows around
30F for most locales...and a possible hard freeze in the typical
colder areas N/NW of the Indianapolis Metro and SE of the Muncie
area.  Readings will trend from slightly below to near normal
through Thursday night.

Passing chances for showers and probably a few thunderstorms will
then be the rule through the weekend`s time frame...when surface low
pressure slowly ejecting across the central Plains, likely phases
with some northern stream energy while tracking into the southern
Great Lakes.  While upper forcing appears to be rather weak as far
south as central Indiana...residence in this next wave`s warm sector
and then probably a cold frontal passage...could set off a couple
rounds of scattered showers.  Otherwise above normal temperatures
are expected under retracted heights with diurnal spreads ranging
from mainly the 40s to 60s.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 1218 PM EDT Mon Mar 25 2024

Impacts:

- SSE winds to 20+ knots and gusts to 30+ knots.

- Non-convective low level wind shear 05z-12z or so

- MVFR and possibly briefly worse flying conditions
  in rain 05z-12z

- Thunderstorms and gusts to 50+ knots can not be
  ruled out 15z-19z Tuesday

Discussion:

A strong low pressure system will result in windy conditions through
the TAF period along with rain tonight and perhaps some strong to
severe thunderstorms late Tuesday morning and afternoon. Flying
conditions will also deteriorate to MVFR and possibly briefly worse
tonight and Tuesday in rain or showers.

&&

.FIRE WEATHER...
Tight surface pressure gradient ahead of the upstream strong low
pressure system, a 40+ knot low level jet and breaks in the mid and
high clouds allowing for mixing down of higher gusts from 3K feet
will result in another windy and dry day and elevated afternoon fire
danger. Used the NBM10 percent to adequately capture the drier air
mixing down as the blend typically doors poor with mixing.

Fuel moisture was already 8% or less from local RAWS and
expected to drop further to 6-7% late in the day as it did
yesterday.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
Wind Advisory from 6 PM this evening to 6 PM EDT Tuesday for
INZ021-028>031-035>049-051>057-060>065-067>072.

&&

$$

UPDATE...MK
SHORT TERM...Puma
LONG TERM...AGM
AVIATION...MK
FIRE WEATHER...MK


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