Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 08/14/22

Area Forecast Discussion

National Weather Service Denver/Boulder CO

 738 PM MDT Sat Aug 13 2022

.UPDATE...
Issued at 729 PM MDT Sat Aug 13 2022

The center of the ridge of upper level high pressure has shifted
east over SW Kansas. Moisture has wrapped around the base of the
ridge with widespread thunderstorms over the region. Storms are
powered by heat with no upper level drivers so will gradually come
to an end by the evening hours. some storms will maintain and hold
together thanks for a robust boundary that is moved east across
the metro area. These storms will be mainly capable of some light
rainfall with lightning and gusty winds given the dry lower levels
across the eastern plains currently. Forecast is on track with
just minor adjustments to winds and temperatures to match current
conditions.

For Sunday, did not alter much with the forecast as PW values will
increase and storm coverage becoming more numerous by the
afternoon.

&&

.SHORT TERM...(This evening through Sunday)
Issued at 216 PM MDT Sat Aug 13 2022

As of 2PM, thunderstorms were developing over the mountains with
locally heavy rain in spots. We have a little more moisture to
work with today, and steering level flow remains very slow (only
about 10 knots), which will bring the potential for high rainfall
rates that could trigger flash flooding for the burn scars. A few
of these are likely to drift off the foothills into the urban
corridor this evening, but dry near-surface conditions will limit
rainfall. Lots of virga will be a good bet, along with a few
wetting cores and a few lightning strikes. Temperature wise, the
heat has struggled to get going with a robust inversion in place
this morning and early afternoon as observed in AMDAR soundings.
Nonetheless, we`ll reach the low to mid 90`s across the urban
corridor and plains this afternoon now that we`ve mixed out.

The high pressure ridge will flatten slightly on Sunday, allowing
for a modest increase in moisture and more widespread thunderstorm
development in the high country during the afternoon. Although
storm motion should increase a touch, thunderstorm activity will
likely be more numerous, and the burn scar flash flood threat will
inch up as a result. The moisture increase will be more
substantial for the plains, where scattered afternoon/evening
thunderstorms will be more likely compared to recent days. Despite
the flattening ridge, the lower levels will remain very warm, and
some guidance even depicts a couple degrees of warming at the
700mb level. With forecast soundings indicating an earlier breakup
of the inversion, temperatures should climb quicker in the
morning and afternoon. However, more widespread convection will
bring an increase in mid- level clouds during the afternoon, and
it wouldn`t be surprising for that to taper the highs along the
urban corridor. With this in mind, erred on the conservative side
for high temperatures along the urban corridor tomorrow, but
maintained mid to high 90`s in the plains where cloud cover should
be less of an issue and the deep mixing will allow for an
efficient warm up. With a dry sub-cloud layer in place,
thunderstorms that drift into the urban corridor and plains will
be capable of producing some decent outflow winds.

.LONG TERM...(Sunday night through Saturday)
Issued at 239 PM MDT Sat Aug 13 2022

Elevated instability (MUCAPE ~250-750 J/kg) will allow
thunderstorms to linger through the early overnight hours on
Sunday night. The focus for thunderstorms should remain over the
high country, but isolated to scattered thunderstorms will be
possible across the plains as well.

Cooler, more unsettled weather is expected for the first two days
of the work week. A very moist post-frontal airmass on Monday is
expected as monsoonal moisture shifts southward back into our
forecast area. Precipitable water amounts increase to 1-1.5 inches
across the plains... which is well above normal for this time of
year. The midnight shift aptly mentioned the battle between
marginal instability/weak capping vs. the upper level support from
a quick moving shortwave and favorable jet placement, and not
much has changed in our overall thought process today. There would
certainly be a heavy rain/flash flooding threat with any storms
that develop Monday - especially across burn areas - but
confidence is still low at time time.

By Tuesday, models begin to push cooler/drier air into the
region. Scattered showers and thunderstorms will be likely across
the southern Foothills and South Park, with lower chances as one
goes north. There wasn`t a noticeable trend between 00z/12z
guidance and thus our PoPs/QPF are largely similar to the previous
forecast.

Upper ridging will build to the west of the region for the second
half of the week, with north/northwesterly flow aloft developing
by Wednesday. With the best moisture shunted off to the south of
our forecast area (with the exception of South Park), the pattern
will be much drier. Storm chances will gradually increase towards
next weekend as a couple shortwaves try to track through the area.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 729 PM MDT Sat Aug 13 2022

Winds will continue out of the northwest with thunderstorms
developing to the north of the field off the boundary and bringing
variable wind gusts up to 30kts. These storms are expected through
04z where winds will gradually go to drainage overnight. Another
round of thunderstorms will be possible Sunday between 22 and 02z
with increased variable wind gusts up to 32kts. Ceilings will
remain VFR for area terminals through the TAF period.

&&

.HYDROLOGY...
Issued at 216 PM MDT Sat Aug 13 2022

There will be a limited threat for flash flooding across area burn
scars this afternoon and Sunday afternoon, with modest moisture in
place and relatively slow storm motions. Rainfall rates up to 1
inch/hour will be possible with stronger thunderstorms.

An elevated threat of burn area flash flooding is forecast for
each of our burn areas on Monday as moisture increases. There is
still some question regarding overall storm coverage, but
ingredients appear to be in place for heavy rainfall (Up to 2
inches in 30 minutes). Depending on the amount of instability
available across the plains, heavy rain could also spread into the
I-25 corridor.

As moisture shifts southward on Tuesday, the heavy rain threat
will be confined to South Park and portions of the southern
Foothills. A few showers and storms will still be possible north
of I-70, but the flash flooding threat should stay limited. A
drier pattern will take over by Wednesday and continue through the
rest of the week.

&&

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

$$

UPDATE...Bowen
SHORT TERM...Rodriguez
LONG TERM...Hiris
AVIATION...Bowen
HYDROLOGY...Rodriguez/Hiris



Area Forecast Discussion

National Weather Service Chicago/Romeoville, IL

 845 PM CDT Sat Aug 13 2022

.MESOSCALE DISCUSSION...
Issued at 845 PM CDT Sat Aug 13 2022

Severe threat has diminished, with only isolated thunderstorm
coverage likely remainder of late evening/overnight.

Surface low pressure was analyzed near the Quad Cities at 00Z,
with a cold front trailing through northern MO into far northern
KS. A warm front curved southeast and south of the low through
western IL into eastern MO. While a few convective attempts were
made along the front in eastern IA late this afternoon/early this
evening, the warm mid-level temps and resulting inhibition/capping
mentioned in the previous mesoscale update appear to have proven
too much to overcome. Farther east, elevated isolated to widely-
scattered showers have developed across northern IL in warm
advection/isentropic upglide above the warm frontal slope. AMDAR
aircraft ascent soundings from MDW at 0030Z/730 PM depicts
relatively poor lapse rates through the column, though some
shallow instability was noted above ~880 mb likely supporting
current showers. DVN 00Z RAOB (in the warm sector west of the
surface warm front) looked a little better, though sampled a warm
layer of +14C around 740 mb, with a fairly dry profile through and
above that level.

Given above, it appears that severe threat has diminished greatly
across the region this evening. While some increase in scattered
showers is likely across the area late this evening into the
overnight, thunderstorms look to be more isolated and likely along
the cool side of the surface warm front as it tracks east-
southeast across the cwa into the pre-dawn hours. Occasional cloud
to ground lightning, brief downpours and small hail will be
possible with these isolated storms.

Ratzer

&&

.SHORT TERM...
Issued at 301 PM CDT Sat Aug 13 2022

Through Sunday night...

Aside from a few widely scattered showers ongoing across parts of
northern IL, all is quiet across the area. This is likely to
change, however, as we head into this evening. Currently our main
area of focus is with an approaching surface cold front and
compact surface low. This front is located northwest of the area
over eastward IA into far southwestern WI, just northwest of KDBQ
and KCID. It is within this area that we will be monitoring for
the initial development of isolated to widely scattered
thunderstorms after 5 pm.

A narrow corridor of lower 70 degree dew points now resides
within the frontal boundary, and clouds have cleared across this
area, allowing temperatures to warm into the lower to middle 80s.
While satellite imagery current suggests capping remains in place
near the front, the expectation is that continued surface heating
over the next couple hours and modest height falls/cooling
associated with an approaching impulse will weaken convective
inhibition enough to support at least isolated storm development
late this afternoon after 5 pm over northwestern IL and
southwestern WI. Recent runs of the HRRR continue to support this
idea. Any storms that do develop with be capable of developing
rotating updrafts (super cellular structures) owing to enhanced
and veering mid level flow. Any such structures will increase the
threat for a few isolated instances of hail, and strong gusty
winds. Also cannot rule out a brief window in which a short lived
tornado or two could result with any of these surface base storms
early this evening given the veering low- to- mid level flow. The
window for such would be short lived, and primarily west of I-39.

Storm coverage is expected to increase over northern IL after
sunset this evening as Theta-E advection ramps up owing to an
increasing west-southwestern low-level jet. Storms will become
increasingly elevated after sunset, so the threat of tornados will
quickly subside. However, with the threat of some elevated
supercells, the threat for isolated instances of hail will
continue over eastern IL and into northwestern IN this evening,
along with heavy downpours. The main focus for storms is expected
to become focused across far eastern parts of IL and into
northwestern IN later this evening before shift east-
southeastward out of the area overnight. The primary time period
of possible strong storms will be from about 6 to 10 pm.

Winds will turn northerly and become breezy on Sunday in the wake
of the wave of low pressure shifting over the area tonight.
Temperatures will be on the cool side of average (low to mid 70s) as
lower cloud cover looks to hang on for a good part of the day. The
most notable concern is the likelihood of dangerous swimming
conditions developing along the northeastern IL shores due to
building waves on Lake Michigan. We have opted to issue a beach
hazard statement from late morning Sunday through Monday morning,
though onshore winds through the day Monday will continue at
least a moderate swim risk.

KJB

&&

.LONG TERM...
Issued at 301 PM CDT Sat Aug 13 2022

Sunday night through Friday...

No changes to the extended period this afternoon.

The extended forecast period features pleasant late summer weather
with seasonable to slightly below normal temperatures expected
through the work week. North to northeast surface winds will
limit warming near Lake Michigan to just the mid 70s. Further
inland can expect highs in the upper 70s to lower 80s. There are
occasional weak short-waves embedded within the northwest upper
level flow that move overhead through midweek but think dry
conditions should prevail for most areas under broad surface high
pressure. The eastern periphery of the western ridge will begin
to break down later in the week. Long-range guidance remains
varied in the handling of this. Will maintain blended slight to
low chances for showers/storms Thursday into Friday noting that
our dry stretch could persist. Either way it is not looking like
a wash out heading into the weekend at this range.

Petr

&&

.AVIATION...
For the 00Z TAFs...

Forecast concerns for the terminals...
*Chance for scattered showers and a few thunderstorms this evening

*MVFR ceilings move in behind the cold front late this evening and
 linger through Sunday

*Breezy northeast winds Sunday afternoon

A broad surface low and associated cold front continue to
gradually push eastward across eastern Iowa this evening which
will eventually move through the terminals late this evening.
While nothing more than a few light showers/sprinkles has been
shown on radar so far, forecast soundings continue to show decent
elevated instability present across the area which would support
the development of a few thunderstorms this evening as the front
moves through. Given this possibility I have maintained a formal
TSRA mention at the Chicago terminals starting around 03z which
seems reasonable given the latest observational and guidance
trends. I did decide to go with a VCSH mention for RFD given its
close proximity to the cold front and the limited activity around
the terminal so far which is likely due to some remaining capping
aloft, however; the possibility is still there for an isolated
thunderstorm or two to develop near RFD prior to the frontal
passage around 04z.

Once the cold front moves through this evening winds will turn
northwesterly with speeds around 10 kts persisting through the
rest of the overnight hours. Winds will then become northeasterly
and increase in speed as the pressure gradient tightens behind the
surface low Sunday morning with gusts around 20 kts expected
Sunday afternoon. Ceilings will also be lowing to MVFR behind the
front overnight and are expected to linger throughout the day on
Sunday before gradual improvement begins to occur late Sunday
evening.

Yack

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Beach Hazards Statement...ILZ006-ILZ103-ILZ104...11 AM Sunday to
     10 AM Monday.

IN...Beach Hazards Statement...INZ001...11 AM Sunday to 10 AM Monday.

LM...Small Craft Advisory...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744...11
     AM Sunday to 4 AM Monday.

&&

$$

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