Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 07/21/23

Area Forecast Discussion

National Weather Service Denver/Boulder CO

 954 PM MDT Thu Jul 20 2023

.UPDATE...
Issued at 954 PM MDT Thu Jul 20 2023

The forecast is performing well with only minor updates this
evening.

We had widespread strong thunderstorms this afternoon and evening
which produced large hail and damaging gusts, mostly northwest to
southeast across the forecast area. There is a bit of lightning
up around the Divide but it hasn`t been surviving to the plains.
On the plains, this afternoon`s convection is slowly exiting
southeast and there is stratus in its wake. There will be more
light to moderate rainfall under those showers early tonight.
There is mist and fog under the stratus, which is reducing
visibility around the urban corridor. So far, it has not been
persistent nor widespread enough to warrant a highlight, and we
will continue to monitor it.

Our partners at CDPHE have issued another Air Quality Alert for
the Front Range Urban Corridor valid until 4 PM MDT tomorrow, as
hot temperatures and light winds will allow ozone concentrations
to reach unhealthy levels. More information is available in our
AQABOU.

&&

.SHORT TERM...(This evening through Friday)
Issued at 231 PM MDT Thu Jul 20 2023

Strong thunderstorms have already developed over the mountains,
foothills and adjacent plains early this afternoon. These will
continue to develop and spread eastward over the plains through
the evening hours. Severe thunderstorm watch has just been issued
for much of the eastern plains of Colorado with the exception of
Phillips and Sedgwick county until 03z. Instability is improving
with ML CAPE at Denver at 1200j/kg of latest ACARS sounding with
just a small inversion left at 750mb. The scarcity of storms over
the Denver area maybe due to the morning cloudiness and showers
that occurred early this morning. Current precipitable water
values closing in on 1.20" of water with continued threat of very
heavy rain with storms. Expect the deepest moisture farther east
with pw values close to 1.50". Rainfall rates up to an inch in 30
minutes or less is expected with strongest storms.

The features responsible for the severe weather today is an upper
wave now entering northwest Colorado with noted drying occurring
behind the wave across Utah and Nevada. RAP Analysis showing 60kt
speed max slicing across central Colorado. Given latest HRRR showing
a second round storms early this evening from the back edge of the
upper wave this looks like a reasonable solution. Substantial dry
and subsidence kicks in behind the wave with drying and storms
ending from northwest to southeast through the night. Drier airmass
along with warmer temperatures expected for Friday. Looks like
enough moisture for isolated showers/thunderstorms over the
mountains and adjacent plains.

.LONG TERM...(Friday night through Thursday)
Issued at 231 PM MDT Thu Jul 20 2023

An upper level high amplifies while sitting over the Four Corners
this weekend. This pattern will keep northwest flow bringing drier
air into the region. Low levels will have enough moisture Saturday
due to shortwave in the southern Rockies. This could lead to
isolated weak high based showers mainly in the foothills and South
Park Saturday afternoon. These high based showers will likely
produce strong wind gusts and light rain until Saturday evening.
Additionally, without much cloud cover, temperatures will begin to
warm. Parts of the foothills, urban corridor and plains increase
near mid 80s to lower 90s. Mountains and valleys trend near the low
to upper 70s Saturday afternoon. Clear skies continue through Sunday
morning.

Relative humidity across the region decreases near 15-20 percent
for the higher elevations. Northwest winds remain weak near 10-12
mph thus fire weather conditions should remain low. With MLCAPE
near 100 J/kg for the foothills and mountains, decided to decrease
NBM PoPs Sunday keeping less than 20-25 percent for the foothills
and majority of Park County. Additionally, without much cloud
cover, temperatures will begin to warm. Parts of the foothills,
urban corridor and plains increase near mid 80s to lower 90s.
Mountains and valleys trend near the low to upper 70s Saturday
afternoon.

Moisture continues to wrap around the upper level system which
increases our chances for diurnal showers and storms next week. Most
guidance favors the higher elevations for scattered showers and
storms but a stray shower or storm cannot be ruled out for the
Palmer Divide. ECMWF ensembles display increasing temperatures
Monday through Wednesday all areas.  Both GFS and ECMWF ensembles
present KDEN reaching 98-99 for a high temperature both Monday and
Tuesday. With increasing cloud cover

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 538 PM MDT Thu Jul 20 2023

Expect generally VFR conditions through the period, intermittent
MVFR conditions are possible with passing storms, and cloud bases
below 6000 feet. Much of the threat has cleared our around the
terminals for the moment, with a little development near APA and
just a few more storms upstream. Those could bring impacts in the
next few hours but should not be as significant as the activity
from this afternoon. Following the convection, expect a stratus
deck for the night which should diminish by mid morning. Winds are
highly variable with outflow and do not look to turn to typical
drainage tonight. Winds should come around southeasterly and
easterly tomorrow, isolated thunder in the vicinity is possible in
the afternoon, then winds should come around to drainage in
evening.


&&

.HYDROLOGY...
Issued at 231 PM MDT Thu Jul 20 2023

Deeper moisture today will enhance the risk of flooding in the
burn scars. Rainfall rates up to an inch in 30 minutes or less
may occur with the stronger storms. Storm motions will be moving
at a decent clip which may help to minimize flash flooding as long
as training storms don`t develop. Flash flood watch has been
extended until midnight tonight for the Palmer Divide region,
including Washington county.

The flash flood threat remains little to none over the burn areas
this weekend.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Flood Watch until midnight MDT tonight for COZ046-047-049.

&&

$$

UPDATE...EJD
SHORT TERM...Entrekin
LONG TERM...AD
AVIATION...EJD
HYDROLOGY...Entrekin/AD



Area Forecast Discussion

National Weather Service Indianapolis IN

 1016 PM EDT Thu Jul 20 2023

.Forecast Update...
Issued at 1016 PM EDT Thu Jul 20 2023

It has been a largely underwhelming evening on the convection front
as storms just were never able to really take off across central
Indiana like they have done to our east across Ohio. The capping
inversion and clouds from earlier today served as a mitigating
factor for convection and even as ACARS and LAPS soundings showed
the cap largely diminishing by early this evening...remnant
inhibition within the boundary layer and warmer air aloft kept cells
subsevere.

All that now remains as of mid evening is a convective band with
gusty winds along the cold front running from near Columbus
southwest to Washington. This will continue to progress southeast
and should be clear of the forecast area by 04Z. Over the rest of
the forecast area...winds have veered to the northwest in the wake
of the frontal passage. Some clouds are lingering but as the night
progresses...skies should largely become mostly clear with light
northwest flow. Dewpoints are already beginning to fall back from
their earlier oppressive levels and should drop back close to 60 by
daybreak. Lows in the low to mid 60s look reasonable.

Zone and grid updates out.

&&

.Short Term...(This evening through Friday)
Issued at 256 PM EDT Thu Jul 20 2023

- Severe thunderstorms possible remainder of the afternoon through
  the first half of the evening

- Dry and not as warm Friday

Radar loop was showing scattered strong thunderstorms developing
along a pre-frontal boundary from near Lafayette to Danville,
Illinois. These storms were developing ahead of a cold front and
upper trough, underneath a seasonably potent 90-110 knot, jet
aligned from South Dakota into northern Kentucky. The airmass was
rich with low level moisture and instability, accompanied by
seasonably strong 40 knot 0-6km shear. Mixed layer CAPEs have
climbed to over 2500 J/kg over northern sections where some sunshine
is occurring. Further southeast, ACARS sounding at IND was still
showing a decent CAP around 800 millibars. Additional diabatic
heating along with moisture convergence along the pre-frontal
boundary will overcome the cap as well as the storms move ESE 35-40
knots. The cold front itself, currently from near a Chicago to St.
Louis line, will sweep southeast with additional convection possible
along and just ahead of it. The current and expected activity has
necessitated a mesoscale discussion, conference call and looming
watch issuance over roughly the northern half of central Indiana.
Areas further south have been slower to warm with the extensive
cloud cover. Temperatures over this area was only in the lower 80s
with upper 80s further north. Very moist low levels with dew points
in the lower and mid 70s, steep lapse rates, dry air aloft and the
strong instability will allow for significant vertical growth, large
hail and damaging wind threat. BUFKIT IND sounding is showing 0-3km
SRH around 100 m2/s2, so would not rule out a brief tornado or two
late this afternoon and early evening.

The cold front will move quickly southeast across the terminals with
the convection expected to clear south central Indiana toward
Midnight. Much drier air will filter in behind the front along
allowing for clearing and post frontal winds will shift to north and
northwest. This should allow temperatures to fall to the lower to
mid 60s overnight. Meanwhile, high pressure will provide subsidence
and  dry and pleasant weather on Friday. The only cloud cover
will be passing cirrus in persistent northwest flow aloft and
perhaps scattered diurnal fair weather cu. Low level thermals
combined with a mix of clouds and sunshine, suggest temperatures
will not make it any higher than the lower 80s during the afternoon.

&&

.Long Term...(Friday night through Thursday)
Issued at 256 PM EDT Thu Jul 20 2023

The synoptic pattern in the long term will remain meridional, with
an upper level trough axis over Indiana by Saturday night into
Sunday. This upper level pattern will become fairly stagnant as a
quasi-blocking pattern develops. This should keep central Indiana in
a relatively negative upper level height anomalies for the rest of
the long term.

The lower levels will be much more progressive, with multiple waves
expected. The first of which is expected on Saturday. Moisture
content looks modest ahead of the wave, with only isolated showers
and thunderstorms expected in the afternoon and evening. This
shortwave will have a larger impact on near surface temperatures,
moving an slightly above seasonal airmass over the region. This
should push temperatures into the 90s by as early as Monday,
continuing the rest of the week. Dew points will increase gradually
through week, but generally will remain in the low to mid 60s. This
should allow for heat indices to stay bellow 100, and nighttime lows
in the 60s.

The combination of high low level temperatures and low heights aloft
will lead to continuous afternoon destabilization with CAPE routinely
exceeding 2000 J/kg. Dynamic support looks limited at this time,
leading to mainly sub-severe weather expected. However, with that
said, mesoscale influences in the near term could alter the dynamic
environment, so stay up to date with current forecasts for the
latest information.

&&

.Aviation...(00Z TAF Issuance)
Issued at 646 PM EDT Thu Jul 20 2023

Impacts:

* Scattered convection lingers for a few hours this evening mainly
  at KBMG and KIND

* Diurnal cu develops Friday afternoon within N/NW flow

Discussion:

Scattered convection has had difficulty maintaining intensity since
mid afternoon but the arrival of the cold front now into the
northern Wabash Valley may enable an uptick in coverage for the next
few hours as the boundary slides southeast. KLAF is just about in
the clear and KHUF should be near or just after 00Z. KBMG and KIND
will be clear by mid evening as the front shifts south of the area.

Once the front clears...winds will veer to northwest with skies
clearing into the overnight. Mid and high level clouds will drift
back into the area by early Friday with the addition of diurnal cu
for the afternoon within a cold advection regime in the post
frontal airmass. N/NW winds will be around 10kts Friday afternoon.

&&

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

&&

$$

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