Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 12/30/22
Area Forecast Discussion...UPDATED
National Weather Service Indianapolis IN
809 PM EST Thu Dec 29 2022
.Forecast Update...
Issued at 809 PM EST Thu Dec 29 2022
Only a few minor adjustments were needed. We held temperatures up
through the night given the magnitude of the warm advection pattern.
We may even see temperatures trend a couple degrees warmer by
daybreak given upstream observations near the Ohio River and into
Kentucky.
We will retain "drizzle" wording this evening and early tonight, as
this is a classic drizzle scenario with deepening moist layer and
lowering ceilings beneath residual subsidence inversion/capping
layer. Collision-coalescence within the warm clouds layer should
make for small drops and for a while just sub-measurable amounts are
expected. There is a small amount of very shallow instability for
parcels within the warm nose beneath the cap that should enhance
drizzle intensity and/or shallow convective showers. We will use VCP
31 on KIND radar for a while this evening since it is more sensitive
and should show drizzle more readily.
Later tonight, large scale ascent and a deeper precipitation process
will become dominant with widespread rain evolving toward daybreak.
All other forecast elements look good.
&&
.Short Term...(This evening through Friday)
Issued at 247 PM EST Thu Dec 29 2022
* Areas of drizzle developing tonight
* Steadier rainfall moves in by Fri morning, persists through the day
* Slight chance of thunder in southwest Indiana
* Wind gusts around 30 to 40 mph through this evening
.This evening through Friday...
Current surface analysis late this afternoon shows low pressure and
its associated frontal boundary across the Plains with high pressure
over the Mid Atlantic States. Low level jet ahead of the front
continues to pump in much warmer and moist air northward into the
Ohio Valley. Surface observations show the 50 degree dew point line
already in SW Indiana and is expected to continue its northward
progression through the state tonight. Satellite imagery and IND
ACARS soundings show abundant low level moisture streaming northward
under a mid level inversion leading to stratus around 2000ft agl
across the entire region.
Very dry air is still evident on soundings through the mid levels,
however as isentropic lift increases this evening and the low level
saturated layer thickens, expect areas of drizzle to develop. Added
"Areas of Drizzle" wording to the entire forecast area from 00z-06z
tonight. Short term guidance and time height cross sections show
much deeper moisture advecting into the region after 06z tonight, so
expect drizzle to gradually transition to light rain by 12z. Best
lift and deep moisture move into the area during the day Friday as
the front approaches Indiana from the west resulting in moderate to
heavy rainfall at times. Forecast soundings do show areas of
elevated instability for SW portions of Indiana, so have included
slight chance of thunder from Terre Haute to Bedford to Vincennes
early Friday morning.
Ensembles continue to show PW upwards of 300% of normal for this
time of year as a healthy fetch of moisture is advected northward
ahead of this system. Moderate to heavy rainfall at times may lead
to ponding in low lying areas, especially areas where the ground is
still frozen. Ensembles now show a large swath across Central and
South Central Indiana where the probability of rainfall exceeding 1"
by Sunday is near 100%, which makes sense with how anomalously high
PW is for this time of year. Through Friday evening expect around
0.50" to 1" along and south of I-70 with around 0.25 to 0.50" in
North Central Indiana. More heavy rain moves in Friday night as a
wave moves up along the front enhancing rainfall rates and coverage.
More on this is explained in the long term section below.
Aside from the rain, winds and temperatures will be another topic
over the next day or so. Strong low level jet around 50 kts is
aiding in bringing a much warmer and moist airmass northward into
the region. ACARS soundings do show an inversion above 0.5-1km agl
continuing through tomorrow, which will limit the highest winds in
the LLJ from mixing down to the surface. However, gradient winds are
still strong enough for wind gusts at the surface to exceed 30mph at
times. Gusts should diminish late tonight into tomorrow as the
gradient relaxes and the low level jet moves off to the northeast.
Temperatures will not fall much tonight with persistent southerly
flow and clouds. Some areas may not fall below the 50 degree mark
until tomorrow evening, which is pretty "warm" for late December in
Indiana. With abundant rainfall for tomorrow, highs may not rise too
much either, remaining in the mid 50s for most areas.
&&
.Long Term...(Friday night through Thursday)
Issued at 247 PM EST Thu Dec 29 2022
* Periods of rain Friday night. Limited Flood Risk
* Potential for moderate-heavy rainfall, embedded thunder Mon night
* Breezy and Warm Tuesday
Friday night into Saturday...
As an upper trough approaches central Indiana from the southwest, a
surface low will develop and move along the front in the area Friday
night.
Plentiful moisture will remain in place from the low level
jet from during the day Friday. Some moisture transport will
continue Friday night as well, but not as strong as previously.
Precipitable water values will be around an inch in the southeast
Friday night.
The broad forcing with the upper trough/surface low combined with
the plentiful moisture will continue rain across central Indiana, so
will go with likely category or higher PoPs all areas, with the
highest PoPs southeast closer to the front.
Rain amounts may be enough for some minor flooding, mainly southwest
where higher amounts are expected. Shallow ground temperatures are
warming thanks to the warm air temperatures, so some of the rain
will able to soak in.
As the system exits on Saturday, some rain will linger in the
morning, mainly east. Most areas will be dry Saturday afternoon.
Temperatures will vary from cooler northwest to warmer southeast
with the front in the area, but readings will remain above normal.
Saturday night through Sunday night...
Quiet weather will rule during this period with quasi-zonal flow
aloft in between systems. Surface high pressure will briefly build
in, but a warm front will approach the area from the southwest
Sunday night. Forcing from this will be weak enough at this time to
continue a dry forecast.
Above normal temperatures will continue with the colder air bottled
up to the north.
Monday through Tuesday...
A large upper trough across the western half of the country will
develop a strong surface low that will move into the upper
Mississippi Valley. There are some uncertainties on the track of
this low, but central Indiana will remain on the warm side of the
system.
A 60kt low level jet will pump in moisture straight from the Gulf of
Mexico into the area (this is near the 99th climatological
percentile). Ensemble guidance indicates that precipitable water
values will be near climatological maximum by Monday night as well.
Strong forcing will accompany an initial upper wave that will
move through on Monday night. Will have chance PoPs Monday as the
the system approaches, and then categorical PoPs Monday night as the
it moves through. PoPs will diminish on Tuesday as the initial upper
energy exits.
Rainfall amounts could cause some localized flooding issues. Will
continue to monitor.
Enough instability will work north to mention thunder Monday night.
Potential for severe weather looks to remain south of the area.
Gradient winds will increase as the surface low deepens and the
surface front approaches. 40mph gusts are possible Monday night and
Tuesday.
Above normal temperatures will continue, with highs in the 60s
ahead of the cold front on Tuesday.
Tuesday night onward...
Some low PoPs will linger into Wednesday as the surface front moves
through and perhaps a surface trough will rotate in behind the low
pressure system. The upper trough will linger on Thursday, but
forcing may be weak enough to go with a dry forecast then.
Temperatures will cool to closer to normal by Thursday as the upper
trough moves in.
&&
.Aviation...(00Z TAF Issuance)
Issued at 631 PM EST Thu Dec 29 2022
Impacts:
* Southerly winds remaining gusty overnight into early Friday
* Non-convective low-level wind shear diminishing by early morning
* MVFR ceilings lowering to IFR late evening or early tonight.
* Drizzle transitioning to a steadier rain for much of Friday.
Discussion:
Initial surge of moisture is deep enough with sufficient low-level
ascent for drizzle, which is already being observed as of this
writing at BMG and will spread northward shortly to all other TAF
sites. Intensity of precipitation will increase and visibilities
will fall into the MVFR range later tonight as deeper moistening and
increased synoptic scale ascent occur. Ceilings will lower to MVFR
as well. Conditions will not improve much Friday, perhaps slightly
toward the end of the TAF period.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Update...BRB
Short Term...CM
Long Term...50
Aviation...BRB