Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 01/10/24
Area Forecast Discussion
National Weather Service Indianapolis IN
948 PM EST Tue Jan 9 2024
.Key Messages...
- Rain will transition back to snow tonight. Up to around an inch
possible in areas.
- Wind gusts up to 40 mph possible overnight.
- Another impactful winter system possible Friday-Friday night with
snowfall accumulation. Exact snowfall amounts remain uncertain.
- Sub zero lows and wind chills possible early next week.
&&
.Forecast Update...
Issued at 948 PM EST Tue Jan 9 2024
Scattered showers continue across the eastern half of the forecast
area at mid evening aided by forcing aloft associated with the
strong upper low over the region currently. Rain remains the primary
precip type but may be starting to see a few snowflakes mix in west
of the Indy metro. The main area of snow on the back side of the low
was pivoting into eastern Illinois and will shift into the Wabash
Valley momentarily. Temperatures had begun to tumble with much of
central Indiana in the mid to upper 30s as of 02Z.
The overall forecast remains in good shape for the overnight with a
few adjustments in order based on current obs and trends. The focus
will be on the wraparound moisture plume that pivots across the
forecast area overnight. As mentioned above...this will fall as snow
as the boundary layer sufficiently cools to support over the next
few hours. Potential is there for a light accum under an inch by
Wednesday morning and as surface temps fall to just below freezing
near daybreak...likely to see roads become slick late tonight into
Wednesday morning in spots.
Winds are the other factor for the overnight. Gusts have not been
quite as strong as originally thought with peak gusts generally at
35 mph and lower. Regardless..it will be windy overnight and those
winds will help to blow snowflakes around and may briefly limit
visibilities in some locations. With the slick spots on roads
mentioned above...there will be some challenges for travelers late
tonight and early Wednesday.
Zone and grid updates out.
&&
.Short Term...(This evening through Wednesday)
Issued at 255 PM EST Tue Jan 9 2024
A strong area of low pressure tracking through northern Indiana this
evening is responsible for the heavy rainfall, gusty conditions, and
snow in the forecast over the next 24 hours. Current observations
show pressure dropping as low as 981 mb at KIND and KLAF as the
center of the elongated low pressure system passes by this
afternoon. One thing to note is that this system is deepening a
little faster than what guidance has suggested. As the low tracks
off to the north and east through the rest of the evening and
overnight hours, expect rapidly changing conditions.
Latest satellite and radar show the dry slot just south of the
occluded low filling in as the system deepens. Latest ACARS
soundings from around the region confirms there is a dry slot with
this system above the 500mb layer; however saturation within the
lowest 3-5km has been sufficient for continued rainfall through the
day. As cold air wraps around the backside of the low, rain is
forecast to transition to snow around or after the 8-11pm timeframe.
With the low track north of the region, Central Indiana will only
see the wrap around snow showers. In these patterns, minor
accumulations are possible in heavier snow showers. Generally
accumulations should remain at or under an inch, with the highest
snowfall totals likely from Lafayette to Kokomo to Muncie. Snowfall
is expected to shut off before sunrise tomorrow as drier air filters
into the lower levels.
Tight pressure gradients with this low and increasing low level
lapse rates will bring gustier wind through the evening and
overnight hours. Highest winds are expected from 10pm tonight
through daybreak Wednesday. Observations upstream today have shown
gusts on the backside of this system maxing out around 40 mph, and
with similar conditions expected locally, have kept max wind gusts
for tonight around 40 mph as well. Potential is there for sporadic
gusts over 40 mph, but confidence is not high enough for frequent
gusts of 45+mph to issue an advisory. Have gone ahead and issued an
SPS for gusty winds near 40 mph in addition to snow showers tonight.
Winds in combination with snow may create low visibility and
hazardous travel conditions at times through Wednesday morning. With
falling temperatures to near freezing, will have to watch for
slick/icy travel conditions during the Wednesday morning commute.
Drying conditions are expected Wednesday with gusty westerly winds
slowly subsiding through the day. A colder airmass in the wake of
the strong low today should result in highs struggling to get out of
the low to mid 30s with wind chills remaining below freezing.
&&
.Long Term...(Wednesday night through Tuesday)
Issued at 255 PM EST Tue Jan 9 2024
Wednesday night through Thursday...
The long term period will begin with a surface low moving across the
Great Lakes region Wednesday night resulting in increasing clouds.
Measurable precipitation looks unlikely as the best forcing for
ascent should remain north of central Indiana. However, cannot
completely rule out a few light snow showers or flurries overnight
across far northern counties. Expect a strong pressure gradient to
keep winds elevated overnight with gusts around 30-35 mph possible.
Limited diurnal cooling should keep temperatures in the upper 20s to
low 30s. Quiet weather conditions are expected for Thursday once
upper ridging builds in. Increasing subsidence aloft will help to
break up clouds promoting warmer temperatures. The southern half of
the area should reach the low-mid 40s. Further north, clouds may
take longer to break up which may keep highs in the 30s.
Thursday night through Saturday...
Confidence continues to grow in the potential for an impactful
winter system towards the end of the week. Guidance shows an
amplifying trough across the southern plains becoming negatively
titled as it approaches the Ohio Valley. Strong diffluence and PVA
should lead to intense cyclogenesis near Indiana. However, latest
guidance is still struggling to determine exactly where the surface
low will develop and track which leads to lower confidence in exact
details. ECMWF ensemble guidance favors a track near the the I-70
corridor and the GFS is farther southeast towards the Ohio River
Valley. A more northern track would support stronger warm air
advection resulting in more rain and a slower transition to snow. If
a more southern track occurs, then more snow with an earlier
transition would be expected.
There is high confidence that widespread precipitation and windy
conditions are going to occur, but the main question that remains is
total snowfall accumulations, especially across the southern half of
central Indiana. While there are differences in model solutions,
both ECMWF and GFS ensemble members show a good signal (40%-60%
chance) for greater than 3 inches of snowfall accumulation across
north/northwest counties Friday night. Confidence in snowfall
amounts decreases further south and east as the warm conveyor belt
with this system lifts north into the area Friday. This leads to
uncertainty on how quickly cooler air filters in during the evening
to allow precipitation to changeover to snow. Make sure to check up
on the latest forecast frequently over the coming days as details
for this event become clearer.
Saturday night into early next week...
There is high confidence that the coldest temperatures of the season
will occur this weekend into early next week. Strong cold air
advection behind the departing late week system will likely drop
lows into the single digits for most by Saturday night. Highs may
then struggle to get out of the single digit s across some
locations next week with widespread lows below zero expected
Monday night. In addition, a strong surface high near the central
Plains and the aforementioned late week system retrograding into
Canada could allow breezy conditions to persist. This leads to
growing concerns for dangerous wind chills during the period.
There have been signals at the potential for another winter system
to impact the region Sunday into Monday, but diverging model
solutions results in low confidence this far out.
&&
.Aviation...(00Z TAF Issuance)
Issued at 653 PM EST Tue Jan 9 2024
Impacts:
- MVFR lowering to IFR ceilings through 12z Wednesday morning
- Visibility varying between IFR and VFR in -SHSN tonight
- Gusts to 34-37 kts 03z-12z tonight
Discussion:
Strong low level jet on the backside of this low in addition to
steepening low level lapse rates will create an environment
conducive for stronger wind gusts of 30-38 kts to make it down to
the surface. Best timing for this is 03z-12z tonight
Ceilings will bounce around between IFR and MVFR levels this
evening, before maintaining IFR overnight. VIS will depend
greatly on current weather, with rain showers transitioning to snow
showers overnight. Within heaviest snow showers, IFR to even LIFR
VIS will be possible
&&
.IND WATCHES/WARNINGS/ADVISORIES...None.
&&
$$
Update...Ryan
Short Term...CM
Long Term...Melo
Aviation...Updike
Area Forecast Discussion
National Weather Service Phoenix AZ
457 PM MST Tue Jan 9 2024
.UPDATE...Updated Aviation Discussion.
&&
.SYNOPSIS...
Well below normal temperatures will persist this week with local
subfreezing morning readings across the region. Another quick moving
storm system will dive south across the Great Basin Thursday
bringing a period of breezy conditions to southeast California and
southwest Arizona, and chances of light rain and snow to south-
central AZ. A more district warming trend should spread over the
area next week allowing temperatures to rebound near and above
normal.
&&
.DISCUSSION...
Early afternoon WV imagery depicts a pair of visually impressive
midlatitude cyclones impacting the Conus: 1) a classic lower Ohio
River valley storm producing SE Conus severe weather and near
blizzard conditions through parts of the Upper Midwest, and 2) a
weakening occluded low punching into the Pacific NW yielding strong
onshore flow and heavy mountain snowfall. Upstream high amplitude
ridging over the NE Pacific will ensure longwave troughing is
maintained through the country throughout the week with
consolidation of PV into an expansive negative height anomaly and
equatorward shift of the polar vortex into the Northeast. This
common winter pattern will ensure NW flow continues over the
forecast area through the weekend with at least one low amplitude
shortwave passing into the Four Corners and reinforcement of cooler
than normal temperatures.
In-situ ACARS sounding data indicates lower and middle tropospheric
warming this morning with the sfc-H7 column completely warming above
0C as the flow pattern temporarily becomes more quasi-zonal. While
this typically suggests morning freezing temperatures relegated to
sheltered valleys most susceptible to cold air drainage, clear skies
and a very dry airmass during the long winter night will support a
third night of Freeze Warning/Hard Freeze warnings, albeit with
readings not nearly as cold as the past 2 morning. Otherwise, modest
thermal increases through the atmospheric column Wednesday will
yield a few degrees of warming, yet still hovering in a below normal
category awaiting the next shortwave diving into the Great Basin.
Models remain very consistent showing a strong, meridional 100+kt
upper jet digging into the western Conus Thursday allowing marginal
amplification of embedded wave energy with a brief period of
favorable cyclonic flow washing across the CWA. A steep cold front
associated with this system will quickly propagate into the region
with fairly tight pressure packing and moderate height falls aloft.
Westerly pre-frontal H8-H7 winds 40-50kt should align very favorably
for strong, gusty downsloping in far southwest Imperial County
Wednesday night. While the post-frontal gradient briefly remains
tight during the day Thursday, height falls will quickly migrate
away from the area with rapidly weakening winds through the sfc-H7
layer.
In addition to the strong winds, ample vorticity forced ascent along
the aforementioned front and marginal moisture levels (PWATs no
greater than 0.50") will support a narrow band of precipitation
across south-central AZ. Much like the most recent weather
disturbance, the frontal boundary will be quick moving such that any
precipitation will be short-lived and accumulations remaining very
light (i.e. no more than 0.10" in lower elevations with slight
enhancement due to orographic effect east of Phoenix). The lower
amplitude nature of this wave may preclude snow levels from lowering
substantially with this system, however the official NBM output
yields 2-5" advisory level totals above about 4500ft. However, there
are some clues that snowfall totals may be even more muted with this
disturbance as 1) forecast soundings show an unsupportive
midtropospheric subsidence inversion ahead of the wave, 2) moisture
appears to be channeled in a very narrow band around the H8 layer,
and 3) a significant amount of dry air seems to be intruding into
the -10C to -20C dendrite layer. Nevertheless, the rapid forward
motion to the shortwave will ensure quickly clearing conditions by
Thursday evening.
After the storm system exits the region Thursday, cold air will
filter into the Southwest Friday yielding another freeze event for
lower elevation communities. The synoptic setup does not look nearly
as favorable as the current freeze event though probabilistic
data strongly suggests a light freeze for many non-urbanized
areas. With a widespread subfreezing readings the past couple
nights (and many areas with a killing freeze), only the most
susceptible impact areas would necessitate any additional
headlines the remainder of the winter season. Forecast confidence
is very good that below normal temperatures will continue into the
weekend with some magnitude of warming beginning early next week.
Several CMC and EPS members attempt to maintain a greater
magnitude of cool, NW flow with additional embedded, low
amplitude shortwaves, while the vast majority of GEFS membership
translates East Pacific ridging inland creating a more rapid
warming regime.
&&
.AVIATION...Updated at 2356Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Very light diurnal winds will prevail through the next 24 hours at
all terminals. Speeds will mostly stay below 7 kts and there will
be extended periods of light variability. SCT high clouds will
pass over the area tonight and clear by sunrise Wednesday.
Southeast California/Southwest Arizona including KIPL and KBLH:
Light diurnal winds will prevail through the TAF period at both
terminals, with extended periods of variability. High clouds will
pass over the area this evening and clear out early Wednesday
morning.
&&
.FIRE WEATHER...
Well below normal temperatures will persist through this weekend
with near freezing to sub freezing temperatures possible each
morning across the lower desert elevations and sheltered valleys.
Minimum humidity will range from 15-20% across southeast CA and
around 25-40% across most of southcentral AZ over the next several
days. Another quick moving weather system will arrive on Thursday,
bringing gusty winds to the western deserts, especially in southeast
California and southwest Arizona where gusts could reach 40-45 mph.
Precipitation chances will increase Thursday morning with light rain
possible over the lower deserts and potential accumulating snowfall
in the higher terrain, mainly above 4000 ft.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Freeze Warning from 1 AM to 9 AM MST Wednesday for AZZ530-531-
533-534-536>544-546>550-554-559.
Hard Freeze Warning from 1 AM to 9 AM MST Wednesday for
AZZ551>553-555-556-560>562.
Winter Weather Advisory from 5 AM to 5 PM MST Thursday for
AZZ557-558-563.
CA...Freeze Warning from midnight tonight to 8 AM PST Wednesday for
CAZ567-569.
Wind Advisory from 7 PM Wednesday to 10 AM PST Thursday for
CAZ562.
&&
$$
DISCUSSION...18/Salerno
AVIATION...Benedict
FIRE WEATHER...18/Salerno