IWX issues Area Forecast Discussion (AFD) at Mar 7, 12:30 AM EST690
FXUS63 KIWX 070530
AFDIWX
Area Forecast Discussion
National Weather Service Northern Indiana
1230 AM EST Fri Mar 7 2025
.KEY MESSAGES...
- Wind gusts to 30 mph diminish early this evening.
- Light snow will overspread the area Friday into Friday night.
Periods of moderate snow are possible Friday afternoon into
early evening which could make for a hazardous evening
commute Friday.
- The greatest potential for snow accumulations greater than 1
inch is along and north of US Route 6 across northern Indiana
into southern Lower Michigan.
- Warming trend begins this weekend with highs in the 50s by
Monday and in the 60s by Tuesday.
&&
.DISCUSSION...
Issued at 250 PM EST Thu Mar 6 2025
The main highlights of this forecast center on potential of some
banded snow on Friday, followed by a warming trend late this weekend
that will lead to mild conditions early next week.
Low clouds have been stubborn to diminish today with a strong low
level frontal inversion keeping low clouds in place. Diurnal mixing
and strong low/mid level subsidence will continue to erode this low
cloud deck through the early evening hours. Short wave upper
ridging will quickly translate eastward tonight and will be
accompanied by strong mid level warm advection and an associated
increase in mid and high cloudiness.
The next feature of interest to monitor going into Friday is an
upper level short wave across the northern Rockies this afternoon.
This wave will continue to eject east-northeast in southern stream
of split flow pattern. Stronger southwest low/mid level flow
downstream of this feature is already allowing some impressive
precip banding back across Nebraska Panhandle this afternoon.
This upper wave will eventually encounter a very strong upper
level confluent zone across the Great Lakes on Friday that will
attenuate and elongate the upper PV anomaly. This
confluent/deformation flow is being enhanced by stronger
northwest flow in northern stream, downstream of upper ridge
axis across northwest CONUS/southwest Canada. The approach of
this northern Rockies short wave trough and an fgen-friendly
synoptic flow pattern will increase the potential of some banded
precip across the local area on Friday. Isentropic progs
indicate initial lift being spent on saturating low levels, but
290K condensational pressure deficits take a sharp drop toward
12Z and will continue sharp ramp-up in PoPs in the 12Z-15Z
timeframe from the previous forecast.
Confidence continues to increase in banded snow potential for Friday
as much of the frontogenetic nature to the flow is derived from the
large scale mid/upper level synoptic setup. Some inherent
uncertainty persists in exact band placement however which will in
large part be determined how quickly upstream wave gets sheared in
the confluent Great Lakes flow. Model cross section indicate a few
rounds of stronger fgen forcing on Friday, the first during the
morning at leading edge of stronger low/mid level flow, and then in
the afternoon more tied into approaching mid level wave an
interaction with the northern stream. Strongest fgen still appears
to be quite elevated in the 700-500 mb layer, with continued
indication of reduced static stability just atop this fgen forcing.
Southern portions of the area appear to be exhibit more of
convective nature to instability, while some case can be made of
some support for slantwise instability across the north (more
supportive of longer-lived banded precip).
Thermal/moisture profiles still support rather inefficient snow
accumulation scenario with a highly elevated DGZ and low level wet
bulbs right around freezing. One possible factor to make up for this
could be localized better ratios in stronger vertical motion with
banding, and some potential of aggregates given low level thermal
profiles. Early March sun angle/some melting may also cut into
accumulation efficiency. Have maintained idea of previous forecast
with mainly snow ptypes across the north, and rain/snow southern
half. Given low snow:liquid ratios, still feel that 1 to 2 inch
accums are possible along and north of US Route 6, with a low
potential of amounts near 3 inches in better banding. Future
forecasts will certainly need refinement as confidence remains low
to medium in exact placement of better banding potential. Given what
now appears to be a later timing into late afternoon, some potential
of minor impacts exists for the Friday evening commute across
the north/northwest. Fgen forcing diminishes sharply after 00Z
Saturday with diminishing rain/snow as low level front sags back
south.
Quiet conditions are expected for the weekend as mid/upper flow
deamplifies. This will allow for a sharp moderation late
weekend, and especially early next week as core of low level
thermal ridge shifts across Great Lakes and Ohio Valley (highs
in 50s Monday/60s Tuesday). Did maintain blended chance PoPs for
midweek although disjointed southern/northern stream forcing
leads to low confidence. Large scale baroclinic zone should
shift south for Thursday-Friday with cooler but still above
normal temps late next work week.
&&
.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1230 AM EST Fri Mar 7 2025
Approaching shortwave will bring a period of rain and snow to
the area on Friday. Much better convergence/fgen signal at KSBN
where heavier precip rates and a slightly cooler environment
will support primarily snow. IFR is likely during the late
afternoon with brief periods of LIFR possible. Confidence is
much lower at KFWA given better forcing is just to the north
and thermal profiles are slightly warmer. Anticipate a rain/snow
mix if precip occurs during the afternoon becoming all snow
after sunset. Precip and associated lower flight categories at
KFWA may be more intermittent during this period. Improvement
anticipated at both sites around 06Z Friday night.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...None.
OH...None.
MI...None.
MARINE...None.
&&
$$
DISCUSSION...Marsili
AVIATION...AGD
Source:
IWX issues Area Forecast Discussion (AFD) at Mar 7, 12:30 AM EST---------------
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