IWX issues Area Forecast Discussion (AFD) at Jun 27, 4:23 AM EDT326
FXUS63 KIWX 270823
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
423 AM EDT Thu Jun 27 2024
.KEY MESSAGES...
- Hazardous swimming conditions are expected on Lake Michigan
today. Dangerous currents are likely, in addition to waves of
3 to 5 feet.
- Patchy fog is possible this morning, predominantly south of US
30. Otherwise, expect partly to mostly clear skies today with
highs in the 70s. Lows tonight will be in the 50s and low 60s.
- Friday we'll see increasing clouds from west to east through
the day, with highs in the upper 70s and low to mid 80s.
Chances for showers and thunderstorms begin Friday evening and
persist through Saturday night.
&&
.DISCUSSION...
Issued at 422 AM EDT Thu Jun 27 2024
Patchy fog developed this morning along US 30 and southward, with a
couple locations in Cass and White Counties in IN dropping to about
1/4 to 3/4 of a mile for a couple hours. Was considering an SPS,
however in the last hour there was rapid improvement, likely due to
a very slight increase in wind speed and drop in humidity behind a
weak surface trough. Winds are expected to continue to stay up
around 5 mph or greater through morning hours in the north and west,
with the far southern CWA near Grant/Blackford/Portland, IN Counties
still showing calm winds with visibility between 1SM or less on the
observations. It is possible some fog re-develops, or becomes more
widespread in the area, especially where winds stay on the calm side
further south for longer. I will hold off on any SPS until I see
more consistent observations of 1 mile or less. Otherwise, I think
most places will linger between 2-5SM until sunrise at worst, then
improve.
Quiet weather conditions today and during the day on Friday thanks
to the upper level ridge and surface high building over the Great
Lakes. Highs will be in the 70s today, then rise into the upper 70s
and low to mid 80s Friday. Lows will be around 60 degrees.
Otherwise, northerly winds behind the trough that is moving through
right now have picked up on Lake Michigan to around 10 to 20 mph
with gusts up to around 25 mph. Surface high pressure builds in
rapidly behind the trough through the day, and is will be favorably
positioned to allow for slightly gustier N-NE flow and longer fetch
on Lake Michigan. Waves quickly came up to around 4-5 feet per the
latest observations at Michigan City, IN Buoy and Bridgman, MI-with
wave periods around 4-5 seconds. Wave direction will be more shore-
parallel further north and become more oblique in La Porte county,
IN. This will generate a strong southward flowing longshore current,
which will re-direct offshore as a structural current on the north
side of any piers or breakwalls. Rip currents are possible, but more
likely further south in LaPorte where the wave angles of approach
relative to shore fall more into the 30-59 degree range.
Furthermore, if winds shift more N-NW this afternoon with the lake
breeze, the more direct wave angle of approach, in combination with
wave heights of 2 to 5 feet (lesser this afternoon), will make rip
currents more likely within the sandbars. Maintained the going high
swim risk and left the beach hazards statement as is (ending at 21z
today). It's possible if winds stay stronger than forecast and have
a more NW-component to the wind/wave direction (vs N-NE) we may need
to extend the beach hazards statement through this evening,
particularly at La Porte where the conditions are most favorable
longer into the day. Stay dry when waves are high, and steer clear
of the piers! Waves could wash you off the pier and into the water,
where you will most certainly be met with a staunch structural
current that pulls you to deeper water. Those visiting the beaches
should plan to stay out of the water.
Last but not least SPC has added our entire CWA to a Marginal Risk
for strong to severe storms on Saturday, which is reasonable given
the forecasted synoptic pattern. It's somewhat convoluted this far
out, however it appears there are two potential rounds of storms,
the first with the surface warm front lifting northward Friday night
into Saturday morning (with a weak shortwave rippling through the
upper level flow). The second round would be from around 15z -21z
Saturday when a cold front moves west to east across our CWA. In
terms of severe weather, the best potential will be with the cold
front in the afternoon hours. The first round may not even develop
over our area (some of the guidance pops it just east of us, some
have little to no precipitation with it. Strong moisture transport
will be ongoing from the gulf thanks to return flow over our exiting
high pressure system (Sitting over the Atlantic by 6z Sat), with
pwats reaching 150 to 200 percent of normal! Second, we have decent
synoptic forcing with the cold front, 0-6 km bulk shear of 35 to 45
knots, and lastly-we will likely have some instability (models have
between 400-1200 J/kg. This is of course conditional upon the first
round-if it develops, how much convective debris is leftover, and
how quick we can recover. It will also depend on timing, some
of the models suggest the cold front coming through in the
12-15z time frame, which could limit the intensity of the storms
(versus when instability is maximized further east as they have
the best chance to recover from morning convection). Mid level
lapse rates aren't that great-around 5-6C/km, which could limit
intensity as well, but it's definitely worth watching.
Sunday into Monday will be cooler and dry with highs in the 70s and
low 80s. Additional rain and storm chances approach for the middle
of next week.
&&
.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 109 AM EDT Thu Jun 27 2024
Some BR/FG has developed on the interface of an east-west
oriented cold front south of KSBN, but in the vicinity of KFWA.
Therefore, no risk of fog at KSBN with their lower dew points
post- frontal. However, 2SM BR perhaps lingers at KFWA for most
of this morning. Dew points have been slowly falling there since
sunset but saturation likely prevails until sunrise. Medium
confidence on the duration and magnitude of visibility
restriction this morning.
Otherwise, high pressure in place today followed by high clouds
late.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Beach Hazards Statement through this afternoon for INZ103.
OH...None.
MI...Beach Hazards Statement through this afternoon for MIZ177-277.
MARINE...Small Craft Advisory until 5 PM EDT this afternoon for LMZ043-
046.
&&
$$
DISCUSSION...MCD
AVIATION...Brown
Source:
IWX issues Area Forecast Discussion (AFD) at Jun 27, 4:23 AM EDT---------------
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