IWX issues Area Forecast Discussion (AFD) at Mar 5, 3:25 PM EST314
FXUS63 KIWX 052025
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
325 PM EST Wed Mar 5 2025
.KEY MESSAGES...
- Rain showers will change to snow showers this evening as
colder air builds in from the west. Snow accumulations are
expected to be less than an inch with a possible exception
across northwest Indiana into southwest Lower Michigan where 1
to 2 inches is expected.
- West to northwest winds increase to 20 to 25 mph this evening
with gusts to 40 to 45 mph. A Wind Advisory is in effect
tonight into early Thursday morning.
- The snow showers and temperatures dropping into the mid and
upper 20s may result in some minor travel impacts tonight.
Most of the snow is expected after this evening's commute and
before the Thursday morning commute, but slick roads are
possible Thursday morning due to the potential of refreezing.
&&
.DISCUSSION...
Issued at 324 PM EST Wed Mar 5 2025
The next in the series of strong short waves rotating through
upstream parent low is making its way across east central
Indiana as of 19Z. Widespread showers with this feature should
be shifting east of the area over the next few hours. An
isolated thunderstorm is still possible through late afternoon
far east/northeast where sfc temperatures are sill in the lower
50s contributing to a few hundred J/kg of sfc based CAPE.
Scattered convective showers will be possible through the
remainder of late afternoon into early evening, but overall a
break in the greater precip coverage is expected late afternoon.
After 23Z, attention will turn to next more vigorous upper level
vort max associated with primary upper level level low across
Illinois. An associated sfc trough with this feature will be
tied to stronger push of low level cold air eastward this
evening.
One subtle observational trend as of late is for more dominant sfc
low track to be a bit weaker and farther north across central
Lake MI vicinity. This is likely tied into more robust
development of northward-displaced 950-800 diabatic PV anomaly
which has evolved over the past 12-18 hours. This northward
track appears to favor onset of low level cold advection a bit
quicker.
In terms of headlines, did slightly move up the onset of Wind
Advisory to 01Z as associated rise/fall couplet is quicker to push
across the western Great Lakes. This could provide a period of near
advisory criteria wind gusts before deeper mixing later this evening
promotes wind gusts in the 40-45 mph range. Some modest deepening
of low level heights across the Great Lakes this evening should
support strongest low level winds from northeast Indiana into
southeast Lower Michigan where the greater confidence in 45 mph
wind gusts persists. These low level winds are appear to be
augmented by tightening low level baroclinicity as the upstream
sfc trough swings through. Reaching advisory criteria will
likely be more marginal across the south/southwest and more
confined to a 01Z-06Z temporal window.
Progression of features tonight should limit snow accums to less
than an inch most locations, with possible exception of lake
enhancement across favored areas. The combination of these light
snow accumulations and sharply falling temperatures into the 20s
late evening/overnight could result in some minor travel impacts,
particularly for lake enhancement areas. Did contemplate needs for
advisory across the northwest given combined impact of snow/wind,
but given low confidence in snow amounts will handle with SPS.
Bulk of snow will have diminished by Thursday morning commute
period, but SPS will also cover possibility of slick roads with
potential re-freezing.
Gusty winds persist Thursday with seasonable or slightly below
normal temperatures. Wind gusts will drop off more sharply heading
into Thursday evening with approach of low level ridge axis.
Next system of interest will be on Friday as western CONUS split
flow regime results in downstream confluent zone across the Great
Lakes. Guidance has been consistent with low/mid level fgen band
affecting the region during the day Friday. While confidence in this
system is high in regional sense, narrowing down band placement in
confluent flow regime with sharp moisture gradient is difficult at
this forecast distance. The rate at which upstream mid level wave
decays in this confluent zone will have a large say in where
favored fgen zone sets up. This setup does appear to support
some decreased stability above fgen layer, so certainly worth
watching for at least narrow zone of some snow accumulation. A
couple of negative factors could be marginal low level wet bulbs
and time of day limiting more efficient accums.
Weak reinforcing cold advection builds in Friday night behind this
wave, with a relatively quiet weather pattern expected to follow
into the weekend. Eastward progression/dampening of upstream
longwave ridge axis will allow for moderating trend through the
weekend, and especially into early parts of next week as highs
into the mid/upper 60s are possible Tue/Wed. Medium range
guidance indicates better potential of more substantial eastern
Pac wave toward the end of this period with next chance of rain.
&&
.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1141 AM EST Wed Mar 5 2025
Scattered showers will persist this afternoon as several more
smaller scale impulses lift through with times of reduced
visby's and cigs lowering into mainly MVFR. Colder air quickly
wraps into KSBN around 00z, and by ~02z at KFWA, on the
backside of an impressive low pressure center filling into
Michigan. WNW winds will ramp up thanks to strong pressure rises
and cold advection with gusts 30-40 knots at times this evening
into early Thursday. Rain showers will also change over to a
period of snow showers with reduced visibilities tonight,
particularly at KSBN where there will be some lake contribution
with consistent IFR to low MVFR conditions.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Wind Advisory from 8 PM EST /7 PM CST/ this evening to 9 AM
EST /8 AM CST/ Thursday for INZ005>009-012>015-017-018-
020-022>027-032>034-103-104-116-203-204-216.
OH...Wind Advisory from 8 PM this evening to 9 AM EST Thursday for
OHZ001-002-004-005-015-016-024-025.
MI...Wind Advisory from 8 PM this evening to 9 AM EST Thursday for
MIZ078>081-177-277.
MARINE...Gale Warning until 7 AM EST Thursday for LMZ043-046.
&&
$$
DISCUSSION...Marsili
AVIATION...Steinwedel
Source:
IWX issues Area Forecast Discussion (AFD) at Mar 5, 3:25 PM EST---------------
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