Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 12/28/22

Area Forecast Discussion

National Weather Service Northern Indiana

 637 PM EST Tue Dec 27 2022

.SYNOPSIS...
Issued at 249 PM EST Tue Dec 27 2022

Clouds will continue to plague many areas into the overnight hours
before clearing finally occurs everywhere on Wednesday. Even
warmer air begins to arrive Wednesday night into Thursday with
patchy drizzle expected.

&&

.SHORT TERM...(This Evening through Wednesday)
Issued at 249 PM EST Tue Dec 27 2022

The main challenge for the period will be the battle between drier
air/clearing in the NW and stubborn stratus deck in the SE. ACARS
soundings from FWA show a rather stout layer of moisture in place,
roughly 3500 ft or so deep. Visible satellite shows the NW edge of
this stratus from Logansport to east of Warsaw to Angola and
Hillsdale with some indications of it trying to expand further NW.
Have made adjustments to sky cover to reflect current trends with
normal diurnal trends expected to allow the stratus to
develop/expand back to the NW this evening (how far exactly, we will
see), before the drier air and increasing mixing finally allow the
stratus to break up or shift east late tonight into Wednesday. For
the moment, leaving any fog mention out in S and SE areas with
little change in the boundary layer situation where the stratus
remains in place.

Temperatures climbing above freezing, combined with fair amount of
sunshine should allow many areas to get rid of or significantly
reduce any snow cover. The exception will remain in the far NW where
the greater snowpack exists and will take time to compact and
eventually release.

&&

.LONG TERM...(Wednesday Night through Tuesday)
Issued at 249 PM EST Tue Dec 27 2022

Longwave trough will be entrenched across the western US, with a
series of disturbances and sfc reflections heading northeast through
the period. The first disturbance will begin its journey northeast
with increasing isentropic lift in the 280-290K layers moving in
late Wednesday night into Thursday associated with the arrival of
the much warmer air. Setup continues favorable for some drizzle
across the entire area, possibly extending into Thursday night.
Mixing of low levels may be sufficiently strong enough to
preclude any fog development, especially if we can get rid of
most/all of the snow pack. May need to watch NW areas for more of
a fog potential but for now just kept with mention of drizzle.

Initial wave will take on a bit of a negative tilt but track west of
the area. Chances for rain will increase, but overall QPF threat
looks minimal with maybe a quarter inch or so in S/SE areas. Next
strong wave will be on its heels into Saturday and Sat night with
best chances likely confined to the same general area. The flow will
then relax some as yet another trough moves in from the west coast,
with this feature rapidly deepening and closing off late in the
period (and maybe even outside it depending on your model of
choice).

With no real cold air in sight again, highs will remain above to
well above normal in the 40s and 50s.

Initial concerns for hydro appear to be more limited, if at all,
with lower QPF and plenty of time for any trapped moisture in the
snowpack to release and runoff. An ESF was issued earlier today for
NW parts of the area where at least a non-zero risk for some ice
jams exists. With flows overall rather low, not expecting major
issues but something to watch.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday Evening)
Issued at 637 PM EST Tue Dec 27 2022

Sfc analysis indicated a low pressure system over the northern
plains with ssw flow becoming established across the ohio valley
and gtlks region. Satellite trends have been showing llvl clouds
shifting nwwd across northern IN and should impact KSBN in the
first couple of hours of the fcst period. Winds have not increased
yet, however expect this to change around 02Z with gusts to 25
kts or more and continue through the rest of the fcst. Also
included wind shear starting around 11Z at KSBN and 14Z at KFWA.
With mixing expected on Wednesday, cigs will rise and mix out
during the aftn on Wednesday.


&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...Gale Warning until 1 AM EST Thursday for LMZ043-046.

&&

$$

SYNOPSIS...Fisher
SHORT TERM...Fisher
LONG TERM...Fisher
AVIATION...MF


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Area Forecast Discussion

National Weather Service Phoenix AZ

 533 PM MST Tue Dec 27 2022

.UPDATE...
Updated Aviation section.

&&

.SYNOPSIS...
A moist Pacific disturbance will move through the area Wednesday
and Thursday bringing cooler temperatures and rain to the area.
Somewhat more tranquil weather will return Friday and Saturday.
Another system will pass through the region late Saturday into
Sunday, bringing additional rain. Afternoon temperatures will be
at or slightly below normal with overnight temperatures at or
slightly above normal.

&&

.DISCUSSION...
GOES-17/18 water vapor channels depict a well-developed cyclone
moving into the PacNW with a strong jet streak of 175kt on the
southern periphery. This is driving copious moisture into the
central California coast, where IVT is currently maximized and
moderate precipitation is falling. Over the Desert Southwest,
broadly diffluent upper level flow is resulting in ample high
level clouds, with vertical profiles indicating relatively dry
conditions persist below 400 mb (27.12Z RAOBs and more recent
ACARS data measured PWATs in the 25-50th percentile). The airmass
also remains fairly warm, with 850/700 mb temperatures in the mid
teens/mid single digits (~90th percentile). Thus despite the
increase in clouds, surface temperatures are above normal this
afternoon.

Conditions will rapidly change beginning late this evening across
our western CWA as the aforementioned jet and cyclonic energy
move into our region. The IVT plume will pass across our CWA
tonight into early Wednesday, though will be decaying as it does
(peak IVT values near 500 kg/ms). In fact, for our far western CWA
(JTNP, Salton City) the rain-shadowing of the coastal mountains
will be strong enough for a 10-30% potential of no rain.

The moisture band re-asserts itself as it gets to the Colorado
River overnight, overcoming the dry atmospheric column. Initially
as atmosphere saturates just ahead of the front, there will be a
brief window for gusty (~20kt) winds to mix to the surface. As of
now, most reasonable timing (primarily leveraging 27.12Z HREF
mean) for precipitation onset as it sweeps in from the west is 12
AM (MST) for El Centro/Blythe/Parker, 2 AM for Wickenburg, 3 AM
for Yuma, 4-6 AM for the Phoenix Metro, and 6-7 AM for Casa
Grande/Globe 6-7 AM. Light to moderate rain will continue for
about ~6 hours at each location.

Once the main band moves through, low (20-40%) chances for post-
frontal convective shower redevelopment continue in the afternoon
for central Arizona. Just enough instability may exist for some
thunder (10%) with the convective showers that develop. Shower
potential continues Wednesday night into Thursday for central
Arizona as trailing PVA moves through the cyclonic upper level
flow, acting on the saturated airmass in place and promoting more
orographically enhanced showers.

Current deterministic QPF for this first system (tonight through
Thu night) ranges from 0.1" or less for our far western CWA,
0.2-0.5" for lower elevations of La Paz/Yuma/SW Maricopa counties,
0.5-1.0" in the Phoenix area, and 1-2" for elevated areas of our
eastern CWA. The potential for notably higher amounts, 2" or more,
is below 5% for the Phoenix area increasing to 30-40% for Pinal
Peak and the Mazatzals. Record rainfall will be possible at KPHX
with Wednesday`s current value being 0.79" from 1972. Little snow
is expected, with snow levels around 8 kft to start, lowering to
6.5 kft post frontal. For a few days following, there will be a
low (10%) chance of fog, primarily lower elevation/valley areas
that receive 1/4" or more of rain, though forecast soundings
suggest low/mid clouds are more likely and would inhibit fog
formation.

Friday and Saturday look to be dry but the next system will move
in Saturday night and last through Sunday. This one does appear to
be a more potent/colder short wave than the first system, though
carrying slightly less moisture content. GEFS members are
generally a little more aggressive than their EPS colleagues
(confirmed through cluster analysis). Overall the probability of
250+ kg/ms of moisture flux is 60%+ (less than 30% for 500+). With
the front on Sunday, there is modest ensemble support for a low
end (10%) thunder potential.

Snow levels will have rebounded ahead of this system, up to 8
kft. Right now the resultant deterministic QPF looks very similar
to the first system save for slightly higher values in the eastern
third of our CWA. Given the wet antecedent conditions, we may see
more of a hydrologic response with the second system. Snow levels
will come down towards 6 kft post frontal late Sunday and below 5
kft into Monday. This could bring some snow impacts to our more
elevated S Gila Co locations (including Hwy 77 to Show Low).

One other potential impact will be wind on Sunday. The EPS-based
EFI data indicate breezy/windy conditions possible, and NBM v4.1
based 50th percentile peak wind gusts on Sunday are 25-40kt CWA-
wide. And to touch on temperatures, afternoon highs will remain at
or slightly below seasonal normals but overnight lows will
actually be at or slightly above seasonal normals due to the high
humidity and cloud cover.

Beyond the second system (Monday/Tuesday), there is general
ensemble support for weak ridging to build over the region leading
to drier conditions. This is not a high confidence projection
though as a scenario with another passing shortwave certainly
exists within EPS/GEFS/CMC members. As long as the East Asian jet
remains robust and extends considerably eastward into the central
Pacific, the potential remains for additional short waves/breaking
Rossby waves to impinge on the West Coast.

&&

.AVIATION...Updated 0033Z.

South-Central Arizona including KPHX, KIWA, KSDL, KDVT:

A low pressure system will move through the Western states
tonight through Thursday. For the Phoenix area, it will bring
rain showers and a prolonged period of impactful ceilings. The
main window for precipitation and reduced visibilities (AOB 6SM)
will be roughly 10Z-18Z. Ceilings AOB FL060 will have a similar
onset but are expected to last at least through 00Z Thursday and
likely beyond that. In fact, expect conditions on the low end of
MVFR for both ceilings and visibility between roughly 11Z-17Z with
pockets of IFR (most likely at KDVT and KSDL). Anticipate
widespread MVFR ceilings to continue for much of the afternoon -
especially in the isolated showers.

Winds will be light overall and favor southwest directions early
this evening then southeast for much of the night. With the
arrival of the showers, anticipate an initial push west/northwest
winds (possibly with brief gusts of 10-20kts) followed by a lot of
variability associated with the showers. From mid morning on-
ward, southeast directions will be favored again.


Southeast California/Southwest Arizona including KIPL and KBLH:

A low pressure system will move through the Western states
tonight through Thursday. For far southeast CA, it will bring
scattered rain showers and reduced ceilings. The main window for
precipitation and reduced ceilings (FL060-080) will be roughly
06Z-12Z. The showers will likely reduce visibilities below 10SM
but overall anticipate ceilings to remain AOA 6SM. Anticipate
scattered stratocumulus (FL050-070) to linger through the day
Wednesday.

&&

.FIRE WEATHER...
A series of Pacific storm systems will move across the districts
through early next week resulting in cooler temperatures and
periodic rainfall. Wetting rainfall is almost a certainty
Wednesday in eastern districts with a modest 25% chance in western
districts. A stronger disturbance and additional rainfall will
move through the region Sunday and Monday. As Pacific moisture
streams into the region Wednesday, minimum humidity levels will
only fall into a 50-75% range with widespread saturation
overnight. Winds will remain seasonally light throughout the week
with just some isolated gusts along the passing frontal
boundaries.

&&

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

$$

DISCUSSION...Iniguez
AVIATION...AJ
FIRE WEATHER...18