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000
FXUS63 KIND 241250
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
850 AM EDT Wed Apr 24 2024

.KEY MESSAGES...

-  Cooler mid-week, some frost possible Wednesday night for North
Central and Eastern Indiana

- Active pattern returns Friday into next week with above normal
  temperatures and frequent storm chances

&&

.FORECAST UPDATE...
Issued at 850 AM EDT Wed Apr 24 2024

Area of lower clouds has spread across the northern half of the area
and continues to work its way south this morning. Upped sky cover as
needed based on latest satellite images.

The cloud deck will continue to work south before eventually
stalling out as mixing increases. Mixing should break up the lower
clouds later today. Based on latest guidance, slowed this down some,
keeping skies mostly cloudy longer.

Left temperatures alone for now, but will monitor for needed changes
based on how the cloud cover behaves.

&&

.SHORT TERM (Today and tonight)...
Issued at 306 AM EDT Wed Apr 24 2024

Latest satellite imagery and observations showing mainly clear skies
across the region with the main cold front still stretched across
Northern Indiana and Illinois. Patchy areas of fog and low stratus
have been observed across the state as recent rainfall has left the
boundary layer nearly 100 percent saturated. A developing low level
inversion is trapping a lot of the moisture at the surface, so
expect continued areas of patchy fog and low stratus through the
morning hours, especially in the Wabash River Valley and in wind
sheltered low lying areas. Satellite imagery does show that this fog
is widely scattered in nature, so not expecting widespread impacts
from it.

With the cold front still north of the area and the boundary layer
saturated, temperatures have been slow to fall overnight with
observations still indicating upper 40s to low 50s across the area.

Today...

Upper trough departs to the east while strong ridging builds across
the Rockies, resulting in NW flow aloft. Surface high pressure over
NW Ontario slides southeast through the day becoming centered near
Upstate NY by Thursday morning keeping surface winds out of the
north today then becoming light out of the northeast by tonight.

Overall guidance has backed off on the strength of the cold air
advection as this area of high pressure settles in over the region.
However, model soundings do indicate lower mixing heights today due
to a low subsidence inversion, which may keep temperatures on the
cooler side anyways. Temperatures aloft at 850mb fall to 0-3C today,
then begin to rise overnight as low level ridge axis moves in aloft.
Expecting below normal highs today ranging from the low to mid 50s
across the north where cloud cover may be thicker to low to mid 60s
across the south where the front will take longer to push through. A
saturated boundary layer and cold air advection aloft may lead to
low level cumulus developing during the day today.

Focus shifts to the potential for frost tonight across portions of
North Central and Eastern Indiana. With the center of the high well
the the northeast of the region, winds may not go completely calm to
allow for optimal radiational cooling. Guidance also shows some high
level clouds pushing in towards sunrise Thursday morning, which may
also work to limit frost potential. Nonetheless, diminishing winds
and a saturated boundary layer may allow for frost formation in low
lying and wind sheltered locations away from urban areas with
temperatures falling into the mid 30s. Confidence is not high enough
to issue a Frost Advisory and frost coverage is expected to be
patchy and isolated. Still something to watch out for, mainly for
those with agricultural interests in Eastern and North Central
Indiana.

&&

.LONG TERM (Thursday through Tuesday)...
Issued at 306 AM EDT Wed Apr 24 2024

Modest warming will occur Thursday but deeper warm plume and surface
warm front will still be southwest of central Indiana. By Friday,
mean ridge axis will pass over bringing deep southwesterly flow and
warm advection and a broad conveyor of deep moisture into the
region. A band of rain is expected to move northeastward across
central Indiana midday or afternoon Friday with warm frontal
forcing, bringing up to around one quarter inch of rainfall. The
core of the warm conveyor belt and pronounced IVT with anomalous
moisture values peaks Friday night, but a weakening/occluding mid-
latitude system to the west means steeper lapse rates and stronger
ascent is displaced, and thunder may be hard to achieve.

Models generally agree that the core of the most anomalous moisture
will shift away Saturday and we will be fully within the warm sector
with limited forcing, and thus limited precipitation coverage.
Positive 2-m temperature anomalies of 10-15 degrees are expected.

Another mid-latitude system will take a similar track Sunday with
forcing for ascent more noteworthy this far east and maximizing
Sunday night. Steeper midlevel lapse rates with this second system
coupled with another plume of anomalous moisture will result in
enough instability for thunderstorms. The CAPE/shear parameter space
looks to be marginal for severe, but CSU machine learning does have
low probabilities. The most likely outcome will be a band of rain
and some deeper convection moving through either Sunday night or
Monday, depending on models. Ensemble spread is still insufficient
to narrow the time window down and we will be able to refine
further, as well as speak more about potential convective hazards,
as this event nears and model spread decreases.

System track is not favorable for noteworthy wake cold advection,
and temperatures should be just above late April normals Tuesday and
Wednesday.

Day 8-14: Multi-model ensemble mean shows anomalous ridging and
warmer than normal temperatures for much of this period.
Precipitation opportunities will still be present within less
dramatic forcing regime, but with sufficient moisture
and instability, leading to some convection.

&&

.AVIATION (12Z TAF Issuance)...
Issued at 642 AM EDT Wed Apr 24 2024

Impacts:

- Pockets of IFR cigs and fog through sunrise, mainly for KLAF and
KBMG

- MVFR cigs pushing in from the north through 18z

- Winds shifting from SW to N, sustained at 7 to 10 kts. Gusts 15 to
20kts mid morning to early afternoon.

Discussion:

Latest satellite imagery shows a large area of MVFR stratus pushing
southward from Michigan into Indiana. Subsidence under the incoming
high will keep moisture and low clouds trapped within the boundary
layer. Expect this area of stratus to continue to push southward
toward the I-70 corridor through the morning hours, with low
ceilings expected at KLAF, KHUF, and KIND. After 16-18z, expect
enough boundary layer heating to occur to allow the stratus deck to
begin to lift and mix out. Confidence is semi-low on how long it
will take the low clouds to rise and break up; however guidance
suggest it to be around the 16-18z timeframe. Higher confidence in
improving conditions to VFR at all sites late afternoon and into the
evening hours.

Winds will shift from SW to NW to N behind the front through the
morning hours. Wind shift line looks to be around the I-70 corridor
and will continue to move southward through the morning. Guidance
shows an increase in speeds to 10-15 kts through early afternoon as
the main front/wind shift passes through the region. Expect winds to
begin diminishing late afternoon to around and under 10 kts.


&&

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

$$

UPDATE...50
SHORT TERM...CM
LONG TERM...BRB
AVIATION...CM