Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 04/12/23

Area Forecast Discussion

National Weather Service Indianapolis IN

 936 PM EDT Tue Apr 11 2023

.Forecast Update...
Issued at 936 PM EDT Tue Apr 11 2023

Forecast is in good shape this evening. Some thin cirrus was
spilling down across the area from lower Michigan and northern
Indiana. Temperatures were mainly in the 60s.

The thin cirrus will continue to move south. That plus some light
southerly winds will keep temperatures from bottoming out in the dry
air across the area. Forecast low temperatures reflect this and look
good.

&&

.Short Term...(This evening through Wednesday)
Issued at 319 PM EDT Tue Apr 11 2023

Quiet conditions will continue into the overnight hours tonight with
a broad ridge of high pressure currently situated over the Central
United States Region. This ridge will gradually shift eastward
tonight into tomorrow with forecast soundings showing a dry column
and allowing for clear skies.

Main focus for the period will be on forecasting the afternoon
dewpoints and high temperatures. Conditions so far today have
generally evolved as expected with ACARs soundings showing dry
adiabatic conditions through 850mb with the PBL expected to deepen
another 1500ft or so by late afternoon. Those lapse rates will then
relax after sunset as diurnal cooling works in.

Similar conditions are expected for tonight as in recent nights with
the dry near surface air and fairly light winds allowing for
efficient radiational cooling. Slightly higher dew points will keep
temperatures from falling into the 30s thought with mid to upper 40s
more likely.

Similar conditions are expected for tomorrow with slightly stronger
winds at the top of the boundary layer which may allow for some
occasional wind gusts to 20kts. There remains a fair amount of
uncertainty as to how much the dewpoints will crash as mixing ensues
during the afternoon hours tomorrow with a 5-10 degree difference
between models.  Leaning more towards a slightly higher dew point
spread for tomorrow compared to today with better moisture flow near
the surface expected. If dewpoints end up on the lower end, fire
weather concerns will increase with marginal Red Flag conditions.
Will continue to monitor these moisture trends for any potential
Fire Weather headlines, but currently do not expect a need for one.
Temperatures should have no issue rising back into the upper 70s to
near 80 again.

&&

.Long Term...(Wednesday night through Tuesday)
Issued at 319 PM EDT Tue Apr 11 2023

* Monitoring Saturday afternoon/evening for at least isolated severe
  potential.

* Warm through Saturday, sharply cooler thereafter.

* Dry through early Friday, rain chances return Friday afternoon
  into the weekend.

The brief mid-week Rex block pattern over the central US,
characterized by broad upper level ridging centered over the
Mississippi Valley poleward of a quasistationary upper level closed
low over the Louisiana Gulf coast, will be breaking down at the
start of the long term period, with the upper low weakening and
opening up as it gets pulled northeastward and reabsorbed back into
a broader upper level trough pushing into the Intermountain West.

As this disturbance lifts northeastward through the Tennessee and
Ohio Valleys, modest moisture transport and afternoon heating will
result in very weak instability developing Friday afternoon, and
isolated showers will be possible. Have my doubts given the paucity
of instability that thunder will be a significant threat, but K
index values in excess of 30 may merit a continued mention. Briefly
heavy downpours and lightning would be the primary concerns with
these showers and storms.

With the departure of this leading wave and diurnal cooling, precip
threat will come to an end overnight Friday night before returning
Saturday as we move into the warm sector of the approaching low
pressure system, which looks to be weakly negatively tilted during
the day on Saturday before quickly wrapping up and beginning to
occlude Sunday night onward.

Models have generally sped the system and cold front arrival up
about 6 or so hours, now bringing it through the region at a more
diurnally favored time of day for severe storms, sometime Saturday
evening. This improved timing, along with decent poleward moisture
transport, daytime heating, and increasing values of deep layer (30-
40+KT) and low level shear (20+KT), along with potential for some
modest low level directional shear, could possibly put all hazards
on the table, as mean shear vectors look to be at least partially
oblique to the front. This could give potential for both discrete
storms along with more linear modes with the frontal forcing. This
is several days out, however, and with strong, wrapped up lows,
minute changes could easily lead to more boundary parallel flow and
less tendency toward discrete cells.

Both Colorado State experimental machine learning guidance and SLU
CIPS Severe Analogs point toward some severe weather threat in the
region, at this point likely maximized a bit to our west or
southwest, with the tail end of the event possibly impacting central
Indiana Saturday evening. This appears quite reasonable based on
above analysis and pattern recognition, and will bear monitoring
through the week.

In the wake of the cold front, the strong, closed upper level low
will pinwheel slowly eastward through the Great Lakes into early
next week, keeping low shower chances in place through the weekend,
with temperatures turning sharply (15-20 degrees or so) colder
late in the weekend into early next week. Fortunately, at this
time the cold snap appears relatively brief, with temperatures
beginning to moderate by mid week next week.

&&

.Aviation...(00Z TAF Issuance)
Issued at 602 PM EDT Tue Apr 11 2023

Impacts:

*A few gusts into the 15-20kt range possible at times.

Discussion:

Dry and quiet conditions will continue. A few cumulus may pop up on
Wednesday. Otherwise a few high clouds can be expected. Winds will
generally be 5-10kt through the night but a few gusts remain
possible this evening. Sustained winds of 10-15kt will occur on Wed.


&&

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

$$

Update...50
Short Term...White
Long Term...Nield
Aviation...50