IWX issues Area Forecast Discussion (AFD) at Sep 5, 7:00 PM EDT333
FXUS63 KIWX 052300
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
700 PM EDT Thu Sep 5 2024
.KEY MESSAGES...
- Scattered showers and an isolated storm possible tonight in
association with southward sinking cold front.
- Scattered showers continue Friday, but should diminish later
in the day transitioning to mainly lake effect rain showers
by evening.
- Turning much cooler this weekend with highs in the 60s
Saturday.
- Much warmer next week with prolonged dry period aggravating
drought conditions.
&&
.DISCUSSION...
Issued at 323 PM EDT Thu Sep 5 2024
Upper level ridging across the Ohio River Valley will continue to
get dampened into this evening as broad negative height anomaly
strengthens and digs across the Upper MS Valley and eventually to
the southern Great Lakes on Friday. A couple of areas of stronger
low level theta-e advection are evident in model
initialization/short term progs. A lead narrow band of moisture
advection is working across NW Ohio this afternoon while a
second low level theta-e ridge is building across northwest
Indiana. These pockets of weak advective forcing an MLCAPES in
the 1000-1500 J/kg have been sufficient for some isolated
showers/storms across the area this afternoon. Expecting this
trend to continue into the late afternoon hours as some weak
mid/upper perturbations may also drift across the southern Great
Lakes region via a weak upper level upstream deformation axis.
The afternoon showers should tend to diminish early this evening
with loss of diurnally enhanced instability and then focus will
shift across the far north/northwest as low level frontal boundary
and stronger upper height falls begin to approach. Some question
persists as to the strength/coverage of these frontally induced
showers tonight as stronger upper forcing should remain slightly
displaced to the north across the Great Lakes region. While stronger
positive vorticity advection should reside to the north across the
Great Lakes, decent signal in near term model guidance of increasing
forcing for vertical motion via frontogenetic processes later this
evening into the overnight. This should tend to yield at least
scattered showers during the overnight hours, with a potential
of this precip to be post-surface frontal in nature. However,
given rather subdued low level convergence fields, not
expecting a good deal of rain tonight.
The timing of the frontal forcing and later arriving upper dynamics
on Friday lead to a rather disjointed picture in terms of any
organized convective potential. Sfc cool front will likely push
southeast of the forecast area by late Friday morning, but given
strength of lagging mid/upper forcing would expect 900-800 mb
frontal zone to become active across approximately southeast third
of the area. Overall severe potential appears minimal as local
area would be characterized by robust shear, but weak to modest
instability fields in the above scenario. The potential for
stronger, sfc-based convection still appears to be maximize east
and southeast of the local area Friday afternoon.
Dramatic post-frontal cooling is expected Friday night into Saturday
with anomalously cold low level air mass sinking across the
southern Great Lakes. Initial fetch considerations would point
to northwest Indiana having best chance of lake effect rain
showers Friday night into early Saturday before shifting east
Saturday morning. However, most optimal lake effect parameters,
and better land breeze convergence early Saturday morning would
favor northwest IN to extreme southwest Lower MI for greater
lake effect rain shower potential. Fairly dry mid level air may
tend to keep a more cellular nature to the lake effect rain
showers, with best chances of more organized lake effect rain
shower bands in the 09Z-15Z window Saturday when thermally
induced wind fields would be more supportive. Breezy/windy
conditions along with highs only in the low-mid 60s are expected
on Saturday.
Saturday night should feature the coldest conditions (lows in lower
40s) of this forecast with sfc anticyclone building into the area,
and decreasing clouds expected allowing for good radiational cooling
setup. Some residual lake effect clouds could persist into Saturday
evening across southwest Lower MI as low level winds back more
northwest.
The remainder of the forecast is uneventful with the main story
being a sharp warming trend into the middle parts of the work week.
Longwave western CONUS upper ridge will shift east and show some
deamplification allowing low level thermal ridge to build east. This
should support highs back into the mid 80s for Tuesday-Thursday.
&&
.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 700 PM EDT Thu Sep 5 2024
Cold front will sweep across the area overnight with some light
rain showers and roughly 6 hours of MVFR conditions. Fuel-
alternate conditions are possible but will be brief and
confidence is low on ceilings dropping that low. An isolated
thunderstorm also cannot be ruled out but the chances are very
low. Precip exits by Friday morning and ceilings slowly improve.
Lake effect rain showers are possible at KSBN late Friday but
the best chances are west of the terminal through this forecast
period.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...Beach Hazards Statement from 4 AM CDT Friday through late
Saturday night for INZ103.
OH...None.
MI...Beach Hazards Statement from 5 AM EDT Friday through late
Saturday night for MIZ177-277.
MARINE...Small Craft Advisory from 5 AM Friday to 5 AM EDT Sunday for
LMZ043-046.
&&
$$
DISCUSSION...Marsili
AVIATION...AGD
Source:
IWX issues Area Forecast Discussion (AFD) at Sep 5, 7:00 PM EDT---------------
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