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

Area Forecast Discussion

National Weather Service Indianapolis IN

 826 PM EDT Fri Sep 22 2023

.Forecast Update...
Issued at 826 PM EDT Fri Sep 22 2023

Skies have cleared over all but parts of the upper Wabash Valley.
This has allowed temperatures to drop quickly after day with light
ESE winds, the clear skies and drying a good setup for radiational
cooling. Would not rule out brief fog in sheltered, low lying area
and areas near water sources and corn fields. However, ACARS and
BUFKIT soundings continued to show a dry boundary layer, so any fog
will be very shallow near the surface.

Temperatures should have no problem falling to the 50s by daybreak.
Would not even rule out upper 40s over northeastern sections based
on the dew points there.

&&

.Short Term...(This evening through Saturday)
Issued at 259 PM EDT Fri Sep 22 2023

* Summer-like Weather for the First Day of Fall
* Dry stretch of weather continues

.This evening and tonight...

Current satellite imagery shows high clouds from convection in
Illinois making its way into Central Indiana. With the increase in
cloud cover, highs may remain a degree or two below forecast highs;
however most locations have already hit the 80 degree mark so far
this afternoon. Expect cloud cover to quickly diminish after sunset
as convection to the west begins to dissipate.

The region is still sandwiched in between two systems, TS Ophelia
near the NC coast and another area of low pressure in the Plains.
High pressure centered over the NE CONUS and SE Canada extends
southward into the Great Lakes and Ohio Valley in between these two
systems leading to relatively quiet and dry conditions persisting
for Central Indiana. Subsidence under the high and dry air through
much of the column will lead to another mainly clear night outside
of a few high clouds. A weak easterly pressure gradient over the
region will likely keep winds from becoming completely calm
overnight, limiting how far temperatures plummet. With such a dry
airmass in place and dew points in the 50s, expect temperatures to
fall into the low to mid 50s in the east and upper 50s to near 60
further west. Not expecting widespread fog, but patchy areas of fog
are possible in the Wabash River Valley closer to sunrise.

.Saturday...

The same weather pattern repeats itself on Saturday with Indiana
remaining under the influence of high pressure aloft with areas of
low pressure on either side of the region. CAMs guidance keeps
convection further west tomorrow, which will likely limit upper
level cloud blow off into the region. Continued subsidence under the
high and a dry environment will result in a sunny and relatively hot
first day of Fall with highs likely reaching the 80 degree mark once
again. Easterly low level flow will also work to advect in drier air
at the surface leading to lower dew points and RH values tomorrow.
The only weather concerns in the near term would be possible
elevated fire threats due to such dry grounds and low humidity
values. Winds are expected to stay at or below 10 kts which will
limit the overall fire threat, but still will be something to
monitor as some burn bans are in place around the state.

&&

.Long Term...(Saturday night through Friday)
Issued at 259 PM EDT Fri Sep 22 2023

A developing tropical low pressure system just southeast of the
Carolinas is forecast to move northward onshore later today. This
system should then slowly slide northward along the Atlantic
seaboard and slow down. As it does so, it will largely prevent
systems to our west from freely advancing eastward. As such,
subsidence between the two will lead to relatively quiet conditions
this weekend.

Surface flow will primarily be influenced by the tropical system
with surface winds out of the east or northeast beginning Saturday.
This should allow for some weak cold air advection leading to a
reduction in high temperatures through the period. Expect highs in
the mid 70s for most locations as opposed to the lower 80s we are
seeing today. Less-than-ideal radiative cooling conditions may help
moderate low temperatures a bit and limit morning fog potential.

Clouds begin to increase late Saturday and into Sunday as a west
coast trough ejects into the Plains. Most guidance stalls and
eventually breaks down the trough before it reaches Indiana.
However, guidance is trending in the direction of a weak cut-off low
developing from the dying trough and drifting eastward. Moisture
appears limited with continued east/northeasterly flow at the
surface, but enough forcing may be present for some isolated showers
or thundershowers. As such, slight chance PoPs are introduced from
Tuesday onward. Ensemble guidance is is better agreement with the
formation of the weak cut-off low than its subsequent evolution.
Forecast uncertainty therefore increases late in the week.

Despite differences in guidance regarding the departure of the
aforementioned upper-low...enough agreement exists for increased
confidence in quieter weather by Friday/next weekend.

&&

.Aviation...(00Z TAF Issuance)
Issued at 605 PM EDT Fri Sep 22 2023

Impacts:

Small chance for brief MVFR and worse fog at the smaller airports
07z-12z, otherwise VFR flying conditions will dominate

Discussion:

The terminals will be most influenced by broad surface high
pressure, centered over Ontario and Quebec, and a dry column per
BUFKIT soundings. Light ESE winds will should keep the surface dew
points low enough to avoid lingering fog issue, although brief
shallow MVFR and worse fog can not be ruled out overnight until just
past daybreak as occurred at KBMG last night and early this morning.
Otherwise, should see the diurnal cu ending at or shortly after
issuance time and after that only see some passing, thinning cirrus.


&&

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

$$

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



Area Forecast Discussion

National Weather Service Phoenix AZ

 503 PM MST Fri Sep 22 2023

.UPDATE...Updated Aviation Discussion.

&&

.SYNOPSIS...
Increased cloud cover will allow for slightly below normal
temperatures today. As conditions begin to dry out Saturday
afternoon, mostly clear skies will prevail through at least early
next week. High pressure is expected to strengthen heading into
next week as well, resulting in a gradual warming trend and above
normal temperatures. Temperatures will peak Tuesday- Wednesday
before cooling down slightly the latter half of next week.

&&

.DISCUSSION...
A low pressure system situated over southern Idaho will weaken in
the coming days as an upper level ridge continues to dominate the
overall weather pattern through the middle of next week.
Southwesterly flow aloft will allow remnant mid to upper level
moisture from Post-Tropical Cyclone Kenneth to push into portions of
the Desert Southwest today. This will result in increased cloud
cover over the region, as depicted on water vapor satellite imagery.
These thick mid to high clouds with ceilings between 12-15 kft
will cause temperatures to be slightly below normal today.
Afternoon highs are expected to range between the low to mid 90s
across the lower deserts as light, diurnal winds persist.

PWATs are anticipated to continue rising throughout the day, peaking
at 1.2-1.3" in southeast California overnight. However, latest ACARS
soundings indicate a substantial amount of lower level dry air in
place which will make it difficult to produce rainfall. The best
chances are mainly over Riverside County, where NBM PoPs reach over
15% and sprinkles/isolated light showers are possible through this
evening. Thus far, sprinkles have been shown on radar imagery but no
measurable precipitation has been recorded. Otherwise, mainly virga
is expected across the region before conditions dry out beginning
late Saturday afternoon through at least the middle of next week.

The subtropical high pressure system over Mexico will strengthen and
expand this weekend leading to a warming trend and near normal
temperatures. H5 heights are anticipated to peak around 590-592 dam
during the first half of the week as temperatures reach 4-6 degrees
above normal as early as Monday. Highs are forecast to peak Tuesday
and/or Wednesday, reaching between 99-103 degrees in south-central
Arizona each afternoon. Although Minor HeatRisk will prevail,
temperatures will be above the 90th percentile of climatology so
continue to stay hydrated.

Ensemble spread increases the latter half of next week due to
uncertainty regarding the amplitude and trajectory of a trough
originating in the eastern Pacific. Looking at Day 7 cluster
analysis, EPS and GEFS members indicate that the trough will deepen
and push southward across the western CONUS, while Canadian members
favor a more shallow trough solution. Regardless, the trough is
expected to bring slightly cooler temperatures and breezy to windy
conditions to late next week. Less than 10% of ensemble members also
suggest that moisture will increase towards the end of the period,
however uncertainty remains high at this time.

&&

.AVIATION...Updated at 0000Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
No major aviation weather concerns are expected through the TAF
period. Winds will generally follow light, diurnal tendencies
becoming variable at times. By tomorrow afternoon, W/SW winds will
increase with sustained speeds around 8-11 kts along with a few
gusts into the teens possible before subsiding in the evening.
Isolated virga can`t be ruled out, which could create some erratic
breezy winds, but expect this to mostly remain confined to the
north of the terminals. SCT-BKN clouds aoa 12 kft will continue
before clearing out by tomorrow evening.

Southeast California/Southwest Arizona including KIPL and KBLH:
No major aviation weather concerns are expected through the next
24 hours. Light W to NW winds are favored at KIPL through the
period, while winds at KBLH will bounce between the NNW and SSW. A
few passing virga showers will remain possible through the
overnight hours, which could create some erratic breezy winds at
times. SCT-BKN mid and high clouds aoa 12 kft will continue before
clearing out going into tomorrow afternoon.

&&

.FIRE WEATHER...
Tranquil weather will prevail through at least the middle of next
week as the chances for wetting rain remain neglible. Near to slightly
below normal temperatures will warm to slightly above average as
early as Monday. The warmest days expected next week are Tuesday-
Wednesday, followed by a cooling trend the latter half of the
week. Afternoon humidity values will mostly fall into the teens
with fair to good overnight recoveries of 30-60% this week,
however larger expanses of single digit minimum RH and poor
recovery will begin to develop next week. Lighter winds are
expected through at least mid week with only daily periodic
afternoon upslope breeziness.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

$$

DISCUSSION...Leffel
AVIATION...Smith
FIRE WEATHER...Kuhlman/Leffel