Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 07/09/23

Area Forecast Discussion

National Weather Service Denver/Boulder CO

 953 PM MDT Sat Jul 8 2023

.UPDATE...
Issued at 940 PM MDT Sat Jul 8 2023

Convection is continuing across the northern half of the CWA at
this time. A significant outflow boundary pushed southwestward
across the Greater Denver Area earlier this evening. Winds gusted
to 40 knots with the outflow.

Most of the models have the convection done for all the forecast
area by 07Z tonight.  Models are all over the place regarding the
cloud cover overnight and the height of the ceilings as well. I
will go with slowing partial clearing from west to east overnight,
with the eastern half of the plains to still have broken ceilings
at 12Z.

&&

.SHORT TERM...(This evening through Sunday)
Issued at 250 PM MDT Sat Jul 8 2023

Conditions are shaping up for an all too familiar active weather
pattern across northern Colorado this afternoon and evening. Under
mostly clear skies, temperatures have been able to climb quickly,
even creeping into the low 80`s in the Denver metro. A stable cap
eroded early and SPC Mesoanalysis suggests MLCAPE values above
1,500 J/Kg will become relatively widespread in the coming hours.
This appears reasonable, with the latest ACARS (aircraft)
soundings calculating ~1,300 J/Kg over Denver.

Considering all the above, and the surge of robust southeasterly
winds advecting abundant moisture into the region (dewpoints in
the low to mid 60`s across most of the lower elevations), it`s no
surprise we`re seeing widespread convective development at this
time. Impressive bulk shear values exceeding 50 kts will help
support the development of a few supercells and elevate the
threat of large hail, which could push 2-3" in diameter with the
stronger storms. Coordinated with SPC for the issuance of a Severe
Thunderstorm Watch for all of our lower elevations, including the
urban corridor (although the highest severe weather threat will
be focused east of I-25). One factor that bears watching is the
position of the Denver Convergence Vorticity Zone (DCVZ) today
(fancy term for an area of circulating wind and associated surface
boundary in the Denver area), which so far has set up farther
west than hi-res model guidance had indicated. This should nudge
southeastward a little throughout the afternoon, but how quickly
and how far it does so is questionable. Either way, it`ll present
a favorable environment for the development of brief landspout
tornados, so another hazard to watch out for, particularly for the
southeastern Denver metro and areas near and SE of Denver
airport.

The bulk of the strong to severe thunderstorms will likely push
east of the urban corridor after 6-7 PM, although one or two
smaller storms could linger behind. Thus, the severe threat will
focus over the eastern plains later this evening, and could
sustain storms will damaging hail through about 10 PM, especially
for Lincoln County.

Conditions tonight will be favorable for the return of low clouds
with abundant surface moisture in place in the wake of today`s
storms. The potential for some areas of fog tonight into early
Sunday morning appears higher than previous days with lighter
winds and a more northerly flow direction.

For Sunday, it seems we are finally in store for a lull in our
incessant severe weather. An expanding ridge of high pressure
over the Intermountain West will shift east and bring warmer and
drier conditions to the region. Have increased forecast highs as
bias- correction is likely not ideal with the anticipated pattern
change. Low to mid 80`s are likely for all of the lower
elevations, with the Denver metro being the warmest. There will
still be some moisture and instability around which could feasibly
sustain an isolated shower or thunderstorm in the afternoon, with
the highest chances of this over the higher terrain and northern
plains. Most, if not all, will stay dry though, and severe weather
is unlikely.

.LONG TERM...(Sunday night through Saturday)
Issued at 250 PM MDT Sat Jul 8 2023

A warm and dry period is in store for most of this week. We can`t
be completely devoid of PoPs as the low level moisture east of the
mountains never goes away and there are lots of little things that
could cause a few storms. Shortwaves in the westerly flow aloft
north of Colorado should drag weak boundaries into the state at
times, and we may also be on the edge of the lift from these. Our
expectation is that most of the plains MCS activity will remain
northeast and east of Colorado through Wednesday, but this isn`t a
sure thing, and there could be an isolated strong late day storm
on the plains anyway. There will also still be a little moisture
left on Monday associated with a little warming aloft. This may be
capped and just be a nice deck of altocumulus, but there may be
enough moisture for some isolated late day storms from the Front
Range east. Any of this activity should be weak.

Tuesday should be the warmest day as drier and warmer air aloft
moves in from the west. Temps could approach 100 is we weren`t so
green, but the vegetation/soil moisture will likely hold us back
to mostly mid 90s.

Yesterday there was uncertainty about a stronger shortwave trough
on Thursday or Friday, along with a tendency towards northwest
flow about then. The shift in the upper air pattern is now looking
more like Friday or Saturday, but there`s still decent agreement
on a surge of cooler moist air at low levels Thursday night or
Friday morning. We were anticipating increased storm activity
then, but if this winds up being a low level feature it may be
stable behind it on Friday, with increased activity Friday night
or maybe not until Saturday. For now, the NBM temps and PoPs look
reasonable with low PoPs in the northeast corner during the
nighttime hours, then introducing higher foothills/plains PoPs
along with cooler temperatures starting Thursday night.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 945 PM MDT Sat Jul 8 2023

A strong surge of easterly winds from convection moved across the
airport around 02Z. Some low Stratus moved in as well, but has
since scattered out. Models are in poor agreement on whether or
not the low clouds will stick around overnight or not. I will go
somewhere in the middle and keep some ceilings in the
BKN015-BKN030 range through 12Z. We`ll see. Low visibilities
should not be an issue overnight. We will also see on that.

&&

.HYDROLOGY...
Issued at 250 PM MDT Sat Jul 8 2023

Scattered to widespread thunderstorms are ongoing across the
region at this time, and will continue with a gradual eastward
shift throughout the afternoon and into the evening. There will be
an elevated threat of flash flooding for the Cameron Peak burn
scar over the next 2-3 hours, and any locations in the plains that
see training storms or successive rounds of storms will also be
susceptible to flooding issues. Storms are moving slightly slower
than prior days as well, which will also contribute to a slight
increase in flooding potential.

The pattern turns considerably quieter and drier starting Sunday.
Although isolated showers and storms won`t be out of the question
on almost any day, especially over the higher terrain, they should
not be particularly strong or carry much of a flood threat. Some
increase in the burn area threat is expected about Friday as
thunderstorm activity increases again.

&&

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

$$

UPDATE........RJK
SHORT TERM....Rodriguez
LONG TERM.....Gimmestad
AVIATION......RJK
HYDROLOGY.....Rodriguez/Gimmestad



Area Forecast Discussion

National Weather Service Indianapolis IN

 1006 PM EDT Sat Jul 8 2023

.Forecast Update...
Issued at 1006 PM EDT Sat Jul 8 2023

A few updates to the forecast with this evening`s update.

Latest satellite and radar imagery show the last of the diurnal
convection waning as it exits the CWA in Southeastern Indiana. The
main cold front is already south of the Ohio River with light
northwest flow across the entire region. Clouds are already thinning
and beginning to clear across North Central and Western Indiana at
this hour as drier air filters in from the north. High pressure will
be centered over the Central Plains tonight and tomorrow keeping the
dry conditions and light northerly flow around. Overnight,
conditions may become conducive for patchy fog formation as skies
clear and winds diminish across Western and North Central Indiana.
Added patchy fog for the early morning hours around sunrise from
Indianapolis to Terre Haute to Lafayette to Kokomo. Any fog that
does develop will diminish quickly after sunrise. Other than that, a
warm, dry, and not nearly as humid end to the weekend is expected
over the next 24 hours.

&&

.Short Term...(This afternoon through Sunday)
Issued at 152 PM EDT Sat Jul 8 2023

Post-MCS environment is characterized by slight overturning of
low-level thermodynamics and also wake subsidence. ACARS shows
relatively warm/dry lower troposphere as a result and shallow
mixing with stratus near and north of the cold front. The
combination of (1) diabatic surface heating and growing PBL depth,
(2) weak ascent from upstream shortwave trough, (3) frontal
convergence, could lead to isolated to scattered diurnal
convection later this afternoon across roughly the southern third
of the area. This is conditional on if there`s enough ascent to
lift aforementioned dry subsident capping layer. If thunderstorms
develop, exact spatial coverage will need to be adjusted based on
observational trends on placement of the front and associated
convergence. North of the front, stratus is limiting diabatic
heating and lower theta-e air mass is moving in. This will
preclude convective development.

If thunderstorms develop, flow aloft should be strong enough for
quasi-organized/sustained cells and instability magnitude may
support marginally severe wind and hail. The overall severe threat
is low however, given marginal magnitude and limited spatial
coverage.

Any convection should diminish with nocturnal stabilization and/or
as the front moves southLong term AFD section below will be
updated by 3:00pm.  of the area. The post-frontal air mass is
slightly cooler and drier. It appears we would need a longer
period of more optimal radiational cooling for fog, though can`t
rule out patchy fog in a few sheltered areas, especially if
stratus and cirrus clear quicker.

Tomorrow should be quite pleasant and uneventful weather wise, as
we will be in a subsident regime behind the departing shortwave
trough. There should be enough residual moisture in the PBL for
some cumulus once it deepens during the afternoon. Temperatures
will be 2-3 degrees below normal for early July.

&&

.Long Term...(Sunday night through Saturday)
Issued at 232 PM EDT Sat Jul 8 2023

The long term will start with at least 48 hours of rain-free
conditions before occasional opportunities for typical midsummer
ridge-riding convection through the second half of the week.

Sunday Night through Wednesday...

The long term will begin with a somewhat amplified, yet weaker H500
trough axis extending from the eastern Great Lakes southward through
the Tennessee Valley.  Associated fair weather under seasonably
weak high pressure will remain over central Indiana into the early
work week.  Light surface flow will back from north-northwesterly
Sunday night to southwesterly by Tuesday.  Dewpoints in the upper
50s to around 60F on Monday should mainly prevent convective
temperatures from being reached, promoting plentiful sunshine.

Tuesday will exhibit the greatest transition back to a more summery
pattern.  The surface high aligned over the Appalachians and a
surface trough expanding eastward into the central Plains. Resultant
southwesterly flow gusting to around 15-20 mph will return moderate
humidity levels and at least a few clouds.  Can expect a few
thunderstorms over northwest zones late Tuesday...with then widely
scattered convection expected Wednesday amid more robust SSW flow.
Any severe threat Wednesday will appear to be dependent on enough
instability arriving before the end of peak heating given moderate
levels of vertical wind shear and decent mid-level lapse rates
expected to already be in place. Temperatures are expected to trend
from low to mid-80s early next week to more commonly upper 80s in
the warm advective winds of Tuesday and Wednesday.

Wednesday Night through Saturday...

An upper trough over northern/interior North America will broaden
amid its shift towards southwestern Ontario, bringing a tighter,
zonal gradient from the Dakotas to the Upper Midwest...while the
midsummer subtropical ridge quietly expands eastward across the
southern US. This adjusted pattern will promote mesoscale convective
systems forming over the Middle Mississippi Valley...before flow
towards the east-southeast would potentially bring them into the
western Midwest during late night hours of Wednesday night and/or
Thursday night. Parameters over central Indiana could favor showers
and thunderstorms should they sustain themselves this far
east...with precipitable water often approaching 2.00 inches...and
generally non-zero instability possibly briefly reaching 1000-2000
J/kg over some areas through overnight hours...although any
organized wind shear may stay mainly just north and/or west of the
local area. Nonetheless the threat of stronger winds from any
collapsing MCS may be a concern, especially for western counties.
North-south placement of such convection may be dependent on the
alignment of a corresponding stationary frontal boundary that is
expected to extend from the central Plains to southern Great
Lakes.

The late week may find further subtle pattern adjustments with
ensembles suggesting the interior trough nudging southward which
would lower heights slightly over the central CONUS.  Corresponding
passage of a weak cold front around the Friday timeframe would
continue rain/t-storm chances, although low confidence so far in any
noteworthy upper forcing here.  The long term may end with a small
split in the upper flow near Indiana and at least a decrease in deep
moisture and POPs, if not fair conditions with noticeably lower
dewpoints. Moderate confidence in seasonably warm readings through
the second half of the week.  The normal max/min at Indianapolis
through the long term is 85/67...the highest tandem of the year.

&&

.Aviation...(00Z TAF Issuance)
Issued at 740 PM EDT Sat Jul 8 2023

Impacts:

* Patchy fog possible at KIND, KHUF, and KLAF around sunrise

Discussion:

Latest observations this evening show light northwest flow across
all of Central Indiana as the cold front pushes south of the Ohio
River. Showers and storms have also pushed south and east of all TAF
sites and will diminish shortly after sunset. Expect SCT to BKN mid
to high level clouds through the overnight hours, diminishing
towards the morning hours. With light winds overnight and wet
grounds from recent rains, would not be surprised to see patchy
areas of fog around KHUF, KLAF, and KIND. Fog should quickly
dissipate after sunrise.

For Sunday, expect mainly VFR conditions through the day with
northwest winds of 5-10 kts as surface high pressure is centered
over the Central Plains. Afternoon mixing from daytime heating may
help mix a few gusts of 12-18 kts to the surface after 15z.


&&

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

$$

Update...CM
Short Term...BRB
Long Term...AGM
Aviation...CM