IND issues Area Forecast Discussion (AFD) at Dec 4, 8:33 AM EST054
FXUS63 KIND 041333
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
833 AM EST Wed Dec 4 2024
.KEY MESSAGES...
- Wind Advisory this evening & tonight for wind gusts over 45 mph
- Snow showers 7pm-12am tonight may create hazardous travel
conditions at times
- Wind chills as low as -5 degrees tonight and tomorrow morning
- Warming trend this weekend and rain late this weekend into early
next week
&&
.FORECAST UPDATE...
Issued at 833 AM EST Wed Dec 4 2024
Stratus has at least temporarily moved out of much of the area this
morning. Fairly high surface temp/dewpoint spreads and strong
surface winds appear to have prevented any freezing drizzle, and
have removed the last mention of -FZDZ through the morning. Breezy
conditions are expected through this afternoon, with the Arctic
front sweeping quickly through the area this evening and bringing
stronger wind gusts, snow showers, and possible squalls.
&&
.SHORT TERM (Today and tonight)...
Issued at 333 AM EST Wed Dec 4 2024
An active short term period is in the forecast for all of Central
Indiana featuring strong winds, rain, snow, and crashing
temperatures.
Early this morning, satellite imagery shows an area of stratus
pushing eastward across the state. Weak isentropic lift ahead of an
approaching trough may be enough to squeeze out a few drops out of
this stratus deck early this morning. Temperature profiles in the
near surface layer do not support the formation of dendrites; so
anything that does fall would be super cooled droplets... aka
freezing drizzle/sprinkles. Usually this would not be impactful,
however with surface temperatures lagging beneath the warm air
advection aloft, this drizzle may freeze on contact with frozen
objects/ground. Overall this shouldn't result in more than a
hundredth on ice accumulation, but that can still produce slick
spots on roadways. Greatest chance of occurrence will be over the
southern half of central Indiana between 4AM and 9AM.
Once this stratus layer pushes off to the east, the rest of
Wednesday should relatively mild as temperatures quickly rise
beneath strong warm air advection. Main impact during the mid
morning to afternoon hours will be winds gusting over 35mph at
times. A strong 50kt LLJ just above the surface may mix down a few
strong wind gusts over 40mph; however the inversion aloft should
prohibit widespread stronger gusts from mixing down. Broken cloud
cover is likely within this WAA regime, but precipitation should be
minimal until a shortwave trough approaches from the north later
this evening. Most of the precipitation associated with this low
should be after 00Z, but a few sprinkles are possible as the frontal
boundary nears, mainly over far NE portions of central Indiana.
Now to the more impactful portion of the forecast...Rain, snow, and
strong winds tonight. An intense cold front approaches from the
northwest, extending from a 992mb low just north of Lake Huron. A
1040+mb high at the same time dives southward into the Upper Midwest
with a very tight pressure gradient between that and the
aforementioned low. In addition to the tight gradient, the front
will usher in very cold and very dry air with a 30F degree dew point
drop at the surface and crashing temperatures into the lower teens.
Strong cold air advection aloft will rapidly steepen low level lapse
rates within the 23z-09z timeframe allowing for strong LLJ winds to
mix down to the surface. This pattern is notorious for overachieving
on wind gusts, especially with such a sharp temp and dew point drop.
Therefore will go ahead an issue a Wind Advisory for the northern
2/3 of Central Indiana late this evening through the overnight hours
for widespread gusts over 45mph with sporadic gusts to 50 mph.
As if the crashing temperatures and strong winds aren't enough,
guidance shows enough saturation in the lower layers and dendritic
growth zone to support the formation of precipitation along and
behind the front, specifically for the northern and eastern 2/3 of
the state. Warm air advection ahead of the front may result in a
rain/snow mix initially; however P-type should turn to snow rather
quickly, especially after 8pm. While Hi-res models do show low level
saturation and a lowering DGZ all night, such strong dry air
advection at the surface may result in precipitation not reaching
the ground. Keeping the chance for snow showers and flurries in as
the night goes on; however the highest confidence in snow will be
during the 7pm-midnight timeframe. Strong winds through the column
will likely lead to fracturing of dendrites and widespread blowing
snow. Any accumulations will likely be light, under an inch, with
snow blowing and drifting against objects. Will have to watch for
the possibility of snow squalls with this front in the 8pm-12am
timeframe as this is a great set up for low topped convective snow
showers resulting in brief periods of low visibility, strong gusts
over 45mph, near whiteout conditions, and slick surfaces. Strong
winds will help keep surfaces rather dry as snow will be blowing
around more than accumulating; however with how cold temperatures
will be tonight, would not be surprised to see a few slick spots.
&&
.LONG TERM (Thursday through Tuesday)...
Issued at 333 AM EST Wed Dec 4 2024
Thursday...
The long term will start off cold and blustery in the wake of an
Arctic front. A tight surface low pressure gradient in between the
departing low pressure system and Arctic high pressure, over the
northern Plains, will result in northwest winds that will gust to 25
to 30 mph Thursday per momentum transfer from Hi-Res soundings. The
combination of the Arctic airmass and breezy conditions support
early day below zero wind chills over much of central Indiana,
especially if the stratus doesn't hang around as it often does this
time of year, underneath strong inversions. Even if the stratus does
hang around, the combination of strong cold advection and winds will
at least result in morning wind chills near zero. Would not be
surprised to see thicker cloud cover and lake enhanced snow showers
over far northeastern sections, well into the day, with the strong
cyclonic boundary layer flow off Lake Michigan.
Thursday night through MOnday...
The Arctic high will quickly settle southeast across the southern
states by Friday as the persistent broad upper trough finally moves
into Quebec and New England. This will allow for a modifying
southwest low level flow off the Gulf of Mexico which will l allow
temperatures to bounce back to around normal by Saturday and well
above normal Sunday into Monday. In addition, deep moisture return
and an approaching southern Plains system will bring a good chance
for a soaking rain to the area late in the weekend into early next
week. Reasonably well clustered models and ensembles support the
best chances of rain Sunday night into Monday.
Later next week, there is a strong signal that a northern Pacific
system will bring in cooler, close to normal temperatures and the
potential mainly light rain.
&&
.AVIATION (12Z TAF Issuance)...
Issued at 549 AM EST Wed Dec 4 2024
Impacts:
- Low Chance -FZDZ at KHUF and KBMG early Wednesday morning
- Low level wind shear impacting all terminals predawn through mid
morning
- W/SW winds gusts 25-30kts increasing to 30-38kts tonight
- Snow showers reducing cigs and vis at KLAF and KIND tonight
Discussion:
Latest satellite imagery shows VFR stratus over the state and
pushing east; however as low level moisture increases, the backside
of the clouds should continue to build and expand over the area
through the morning. Cigs should be largely VFR the first half of the
day.
Main impacts will be windy conditions today and tonight. SW wind
gusts upwards of 20-30kts expected mid morning through mid
afternoon. A cold front approaches from the northwest, shifting
winds to the WNW this evening. As the front passes through, expect
an increase in winds with sustained winds of 15-25kts and gusts 30-
38kts from around 23z to 09z, with a slow diminishing trend at the
end of the TAF period.
Snow showers may accompany the frontal passage after sunset this
evening, with the best chance of any impacts at KLAF and KIND in the
00z-06z timeframe. Expect cigs to drop to MVFR levels later this
evening and remain there through the rest of the night. Brief
periods of IFR or worse cigs and vis from passing snow showers are
expected and will be reflected in the TAFs with more detail later
today as they develop.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
Wind Advisory from 6 PM this evening to 4 AM EST Thursday for
INZ021-028>031-035>049-051>057.
&&
$$
UPDATE...Nield
SHORT TERM...CM
LONG TERM...MK
AVIATION...CM
Source:
IND issues Area Forecast Discussion (AFD) at Dec 4, 8:33 AM EST---------------
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