Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 08/18/23

Area Forecast Discussion

National Weather Service Denver/Boulder CO

 214 PM MDT Thu Aug 17 2023

.SHORT TERM...(This evening through Friday)
Issued at 214 PM MDT Thu Aug 17 2023

Current satellite shows all convective clouds and so far only
isolated showers and storms are confined to the mountains and
foothills. The plains are firmly capped as of mid afternoon per
the latest ACARS soundings. At this point, there is a relatively
small chance we`ll still get hot enough to support a couple
storms onto the nearby I-25 Corridor by late afternoon/early
evening. Mountain showers/storms could linger into the evening
hours, but mostly only gusty winds and light rainfall expected.
Southerly winds increase on the plains and Palmer Divide this
evening, so a relatively mild/warm night expected especially in
those breezy locations.

On Friday, the existing area of deeper monsoonal moisture will
spread from the Four Corners area north/northeast into our
forecast area. This occurs as flow aloft turns more southwesterly
as the upper high builds southeast into the Southern High Plains.
Therefore, storm coverage and intensity is expected to increase.
The highest coverage is still expected over the high country, but
we`ll also see a few storms spread east across the I-25 Corridor
and onto the plains for a change. Strong, gusty outflow winds can
be expected given DCAPE of 1500-1600 J/kg, but also brief moderate
to heavy rain given the increase in precipitable water.

Finally, as the thermal ridge shifts this way, temperatures will
be heating up again. Mid 90s to near 100 degree readings can be
expected over most of the I-25 Corridor and plains.

.LONG TERM...(Friday night through Thursday)
Issued at 214 PM MDT Thu Aug 17 2023

A strong ridge amplifies across the southeastern United States
extended to the Central Plains. Models are in agreement with above
normal temperatures continuing throughout northeastern Colorado
in the long term forecast. Strong temperature anomalies are
displayed from the ECMWF and GFS this weekend into next week. With
multiple days of mid 90s-100 for the urban corridor and plains,
this could lead to increasing heat risk especially for those
vulnerable to heat.

Majority of the plains will likely remain dry Friday night. A few
showers and storms could occur from the southern foothills to the
Palmer Divide producing mainly strong wind gusts. Saturday, in terms
of precipitation, should be favorable to thunderstorms in the
mountains and valleys then extending to the Cheyenne Ridge and parts
of northern Weld. MLCAPE values near 500-800 J/kg and daytime
heating should allow for scattered thunderstorm development but weak
shear between 15-20kts. As lapse rates approach 7-8 C/km and
PWATs between 0.60-0.70 inches, it is possible these storms could
produce small hail and brief heavy rainfall.

Drier air enters the 500-700mb layer early Sunday morning. A lack of
synoptic forcing and instability should create partly cloudy
skies for the entire region. A few high clouds shouldn`t limit
daytime heating, thus expect rapid heating into the afternoon.
Parts of the mountains and valleys could reach mid 70s to low 80s.
The urban corridor and plains trend near mid to upper 90s. A few
spots could reach 100 across the far eastern plains easily. By
Sunday night into Monday morning, overnight lows will remain warm
due to strong southerly flow along the Palmer Divide and adjacent
plains. It may be uncomfortably warm overnight for parts of these
areas as lows sit near 70.

Generally, Monday will be similar to Sunday meaning dry and above
normal temperatures continue. Another round of scattered showers and
storms will occur for the higher elevations Tuesday afternoon; these
showers will likely decrease in coverage along the urban corridor
becoming isolated. Beyond Tuesday, 500mb height ensembles differ
in placement of the upper level high. If this system pushes
eastward, our entire region could receive moisture once more. It
is also possible for this system to strengthen leading to another
cut off of monsoonal moisture. With so much uncertainty, this
forecast package includes a decrease to NBM PoPs both Wednesday
and Thursday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1017 AM MDT Thu Aug 17 2023

VFR through the period, and any (low) risk of storms should stay
confined to KAPA and KBJC 22Z-02Z. KDEN should be far enough east
to avoid any variable wind threat. Winds have already become more
southeasterly, and will stay there through the afternoon with a
slight bump in speeds closer to 15 knots by 22Z-00Z. Winds are
expected to increase further this evening as they turn more
southerly by 01Z, and gust to 20-25 knots at KDEN and KAPA. Winds
slowly relax later tonight and turn more southwesterly 12Z-15Z
Friday.

&&

.HYDROLOGY...
Issued at 214 PM MDT Thu Aug 17 2023

There is a very low/almost nil threat of burn area hydrology
issues this evening as the airmass is relatively stable and
moisture content is limited. On Friday, storm coverage and
intensity will increase by afternoon in the mountains as a deeper
plume of moisture arrives from southwest Colorado. There will be
enough ingredients and moisture content for a limited threat of
flash flooding in burn scars.

Precipitable water values range from 0.60-0.70 Saturday
afternoon thus a limited flash flood threat exists for the burn
areas. Drier conditions will occur Sunday and Monday.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

SHORT TERM...Barjenbruch
LONG TERM...AD
AVIATION...Barjenbruch
HYDROLOGY...Barjenbruch/AD



Area Forecast Discussion

National Weather Service Indianapolis IN

 809 PM EDT Thu Aug 17 2023

.Forecast Update...
Issued at 809 PM EDT Thu Aug 17 2023

A strong storm that earlier produced an inch and a quarter size hail
over Grant county, just north of the IND CWA, was moving southeast
over northern Randolph county this evening. This storm developed in
the higher CAPE environment over northern Indiana. Otherwise, the
strong deep shear of 60-70 knots has overwhelmed the weak to
moderate CAPE over central Indiana, resulting in updrafts not being
able to grow sufficiently. The Randolph county still has the
potential to produce marginal winds and or hail over the next half
hour. Otherwise, with sunset approaching and strong shear in place,
there is very little chance of any additional cell producing severe
weather. The cold front was near the I-69 corridor and will sweep
through this evening with clear skies and northwest winds to usher
in cooler temperatures with good confidence on overnight lows in the
50s. Any lingering showers will move southeast of the area before
Midnight. With northwest winds bringing in cooler and drier air, fog
is not expected.

&&

.Short Term...(This evening through Friday)
Issued at 200 PM EDT Thu Aug 17 2023

The line of showers and embedded thunderstorms mentioned in previous
forecast updates continues into Central Indiana. This line is driven
by an amplifying longwave trough over the Great Lakes. At the
surface, a deep low pressure center is located over south central
Canada. A cold front associated with the low is dropping southward
through the Midwest, and is acting as the primary forcing mechanism
for today`s convection.

Deeper moisture is currently confined to immediately along the cold
front itself. As the front continues to lag behind this morning`s
convection, an opportunity for boundary layer destabilization will
occur. As such, a new round of more surface-based shower and storm
activity is expected this afternoon. Latest satellite shows a
developing band of cumulus from Chicago southwestward to the
Illinois/Missouri border. This marks the location of the surface
front, which is now far behind the ongoing convection in the
northern parts of our CWA.

Ample sunshine has broken out between the front and ongoing
convection, and is allowing for boundary layer instability to
develop. SPC analysis shows surface CAPE approaching 1000 J/kg along
the boundary. ACARs soundings out of Peoria IL, which is fairly
close to the front, show increasing instability and an eroding low-
level inversion. The inversion is still present, as of 17z, but is
expected to erode completely as the afternoon progresses. CAMs
depict convective initiation in northern Indiana around 19z-21z.

Model soundings show substantial dry air in the mid-levels, which is
confirmed by CIRA Advected Layered PWAT...showing little in the way
of moisture between 850mb and 500mb, and little in the way of
moisture advection. As mentioned before, deeper moisture will be
confined to the boundary itself, so storms are expected immediately
along the front. Model soundings also show fast flow / strong shear
through the column (50kts bulk shear, straight hodographs), which
may lead to some organized updrafts. Shear vectors are oriented
roughly perpendicular to the boundary so storms should be discrete
or in the form of broken line segments. CAPE profiles are relatively
shallow so large hail is not currently expected. An isolated
instance of marginally severe hail is possible within strongest
cells, however. The primary hazard today would be isolated strong to
severe winds, as the dry air in the mid-levels promote modest to
large amounts of DCAPE (500 to 1000 J/kg). Overall, the severe
potential today seems rather limited given marginal lapse rates,
modest instability, and the generally dry environment.

Once the front exits, drier air looks to flow into the region. Dew
points drop from the mid 60s this afternoon into the lower 50s or
possibly upper 40s by tomorrow. Surface high pressure quickly
arrives, which will allow winds to calm down as well. Strong
subsidence should allow clear skies to prevail for the next couple
of days. Lows tonight should drop nicely into the low to mid 50s
under decent radiative conditions. Wouldn`t be surprised if some
patchy ground fog forms by morning, especially over corn fields and
other fog-prone locations. Highs on Friday are expected to rise into
the mid 70s, and combined with clear skies and low humidity, should
lead to essentially perfect weather as we end the week.

&&

.Long Term...(Friday night through Thursday)
Issued at 200 PM EDT Thu Aug 17 2023

* HOT conditions return late weekend into the middle of next week

Models are in decent agreement that the large upper high will move
east and be the primary influence for central Indiana into next
week. Hot air will accompany the high, with 850MB temperatures in
the middle to potentially upper 20s (degrees C).

Surface high pressure will rule through the weekend, and dewpoints
will be low for August (into the 50s). This will help dry out the
ground a bit, setting the stage for a better response for
temperature rises early next week.

High temperatures on Friday and Saturday will be a little below
normal, but as the upper high`s influence is exerted Sunday into
early next week, high temperatures will top out in the lower and
middle 90s (GFS still suffers from issues and its 2 meter
temperatures look too warm at times).

A couple of uncertainties for the next work week remain. First is
what a cold front will do early in the period. With the upper high
in place, believe that the models that have it dropping south into
central Indiana as early as Monday look too aggressive. Most likely,
the front will move in mid-week. When it does move through,
temperatures will dip back into the upper 80s and lower 90s, not
much relief from the heat.

The other uncertainty is how high moisture content will get, which
will influence any rain chances as well as apparent temperatures.
Best Gulf moisture will be cut off to the south of the area with
another decaying front. Thus, for now, expect relatively lower
dewpoints, keeping apparent temperatures below 105 degrees.

The lower moisture content throughout much of the atmosphere with
the upper high in place should keep rain chances below mentionable
criteria, even with the cold front moving in.

&&

.Aviation...(18Z TAF Issuance)
Issued at 550 PM EDT Thu Aug 17 2023

Impacts:

- No impacts are expected

Discussion:

Surface high pressure will spread across the terminals this evening
in the wake of a departing cold front. Subsidence and a dry post
frontal column will result in clear skies. Meanwhile, dry advection
with winds shifting from WSW to NW along with wind speeds 5-9 knots
should result in no fog.


&&

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

$$

Update...MK
Short Term...Eckhoff
Long Term...Updike
Aviation...MK



Area Forecast Discussion

National Weather Service Louisville KY

 1041 PM EDT Thu Aug 17 2023

.Forecast Update...
Issued at 1040 PM EDT Thu Aug 17 2023

Showers along the cold front have been resilient, and hi-res
guidance suggests that they could sustain themselves for at least
another few hours. Accordingly, have increased near term PoPs
farther south and west from where they were in the previous update.
Still, many will miss out on receiving precipitation, with those who
are impacted by these showers generally receiving less than 1/4
inch. Otherwise, the forecast is on track at this time.


Issued at 855 PM EDT Thu Aug 17 2023

The surface cold front will move through the area tonight clearing
the skies and allowing a rather pleasant airmass to settle in. As of
this hour, LVX shows sporadic weakening showers along the frontal
line with an absence of any vertical growth or lightning given the
limited instability, poor mid-level lapse rates and establishing
subsidence aloft (evidenced in the SDF ACARS). Thus, decreased rain
chances for the next couple of hours and removed any thunder
wording. Expect few sprinkles or isolated/brief light shower before
midnight , most likely over the Bluegrass where chances are higher
(~20%). Otherwise, clear skies and light northerly winds for the
rest of tonight with a small possibility of patchy valley fog
towards the Lake Cumberland area. Mins will be range from the upper
50s in southern Indiana to low 60s in southern Kentucky.

&&

.Short Term...(Tonight through Friday evening)
Issued at 250 PM EDT Thu Aug 17 2023

Area radar mosaic shows pre-frontal showers/t`storms across central
IN stretching from around Terre Haute to Muncie to Toledo this
afternoon. The main cold front was located over Chicago stretching
into central IL and north central MO. This activity has been
weakening over the past several hours as it continues to move east-
southeast. AMDAR soundings across the area shows good amount of low-
level dry air and strong inversion between 850-700mb. MUCAPE was
fairly meager between 100-200 J/kg and the best dynamics associated
with the LLJ was across northern OH and Lake Erie. Given the current
trend, think a few scattered showers and even a few isolated rumbles
of thunder are still possible later this afternoon into early
evening but I wouldn`t be surprised if there were some people who
don`t see a single drop of precipitation. The best chance will be
across southern IN and north central KY. Main cold front will push
through between 03-06z. There could be a few isolated light showers
along the boundary but they would be isolated at best. Winds this
afternoon and evening ahead of the front will remain gusty between
15-25 mph out of the southwest then shift to more north-northeast
overnight allowing for cooler and drier air to advect into the
region by tomorrow morning. Lows will range from the mid/upper 50s
to near 60 north of the parkways to the low/mid 60s to the south.

Tomorrow looks like an absolutely fantastic day for mid August with
low dew points(upper 50s), lots of sunshine and highs around 10
degrees below normal in the upper 70s to near 80. A true Chamber of
Commerce weather day across the area for the end of the week.

&&

.Long Term...(After midnight Friday night through Thursday)
Issued at 222 PM EDT Thu Aug 17 2023

Key Messages:

- Dry and increasingly hot temperatures much of next week

Surface high pressure will gradually move from the Ohio Valley
toward the east coast over the weekend, setting up southerly return
flow across the region. Low level humidity/dewpoints will gradually
increase with the southerly flow and likely become more impactful by
early next week. Temperatures on Saturday will still be slightly
below climo norms, but the heat will become more noticeable by
Sunday as the core of a very strong upper level ridge meanders from
the Plains into the Missouri Valley and Midwest.

Much of next week will likely feature high temps in the low to mid
90s as we remain under the influence of the large upper level ridge.
Depending on dewpoints, heat indices could exceed 100 degrees during
the afternoon hours. Strong subsidence associated with the ridge
will suppress any shower/storm chances. There are signs within the
long range ensemble guidance we may see the upper level ridge
retrograde back to the west a bit by late week which could allow
for the passage of a front to drop us to more normal temps, but
confidence is low in the specific timing and evolution of the upper
air pattern.

&&

.Aviation...(00Z TAF Issuance)
Issued at 740 PM EDT Thu Aug 17 2023

Discussion...Terminals will remain VFR during this TAF period.
Current surface observations and satellite imagery show the cold
front moving across southern Indiana associated with sporadic shower
activity and an overcast stratus layer ahead of it. Those showers
will most likely dissipate before moving through the forecast area
while the cloud base remains well above MVFR criteria. As a result,
the most impactful change tonight will be the wind shift to a weaker
northerly component. Last but not least, models are hinting at fog
development later tonight, but any fog instance will stay far from
the terminals.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...None.
&&

$$

Update...CSG
Short Term...BTN
Long Term...DM
Aviation...ALL