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Area forecast discussion
National Weather Service northern Indiana
651 am EST Tue Jan 23 2018

Synopsis...
issued at 650 am EST Tue Jan 23 2018

Scattered rain showers will transition to rain and snow showers
today, especially downwind of Lake Michigan where minor snow
accumulations of less than an inch are possible. Rain and snow
shower coverage should diminish later this afternoon. Otherwise for
today, morning temperatures in the mid to upper 30s will slowly fall
through the day as blustery west to northwest winds bring cooler air
back to the region. Dry weather is then expected for tonight through
Friday afternoon with temperatures moderating once again for
Thursday and Friday.

&&

Short term...(today and tonight)
issued at 257 am EST Tue Jan 23 2018

Unsettled pattern to continue today with several disturbances
rotating through parent upper low across the mid MS valley this
morning.

One vort lobe is current working across east central Illinois this
morning which will provide some light rain showers for areas
especially along and south of Route 24 through daybreak. Cold air
advection across east central Illinois into Central/Northeast
Indiana will be a bit more pronounced early this morning as colder
air wraps into this system, which could allow rain/snow shower mix
through daybreak across these locations. No snow accumulation is
expected at this time in association with this area of precip
through daybreak. Passage of this vort will then allow a small
scale mid/upper wave across northeast Illinois to drop across
northern Indiana in the 12z-16z timeframe with better chance of
rain/snow showers transitioning to mainly snow showers with brief
period of lake enhancement expected.

Some light snow accumulations still appear possible this morning
with stronger forcing and deeper mid level moisture in place. Wet
nature of snow and initial rain/snow mix potential should cut down
on ratios however, and still only expecting limited snow
accumulations of less than an inch across the northwest. For this
afternoon, dgz does indicate some drying, although deepening mixing
with cold air advection should begin to saturate lower portions of
the dgz again. A smaller scale wave rotating through western
periphery of this upper low across southeast Minnesota/eastern Iowa should
track across southern Great Lakes region later this afternoon into
this evening with continued isolated/scattered snow showers. Bulk of
any snow accumulations should occur through 18z however.

Otherwise for today, high temps expected to be reached early in the
day with steady to slowly falling temperatures. Deepening mixing
will allow west-northwest gusts in the 25 to 30 mph range late
morning/afternoon. Quiet weather tonight as upper low finally
lifts out of the area with short wave ridging building into the area.

&&

Long term...(wednesday through monday)
issued at 257 am EST Tue Jan 23 2018

Weak Pacific upper trough will dig across the area on Wednesday,
with maybe a few flurries in the morning, but meager moisture will
limit any accumulating precip potential. Low level thermal trough
will be slightly reinforced by this wave providing near
seasonable temperatures. For late Wednesday/Thursday Great
Lakes/Ohio Valley become positioned in upper level inflection zone
which will mark onset of moderating temperatures for Thu-Fri as
long wave upper ridging across central Continental U.S. Approaches. Air mass
will remain dry across the area through Friday as southeast US
anticyclone allows low level southwesterlies to feed drier low
level air northeast across the Ohio Valley. A series of Pacific
waves will allow for weak cyclogenesis across northern plains
late this work week with fairly robust southwest gradient in place
by Friday. Breezy/windy conditions are possible Friday, but this
should also provide highs back close to the 50 degree mark.

Rain chances should increase again for late Friday-Saturday as low
level flow trajectories become more favorable for better low level
moisture transports in advance of approaching Pacific wave. Medium
range models still exhibiting quite a bit of spread in terms of
phasing southern/northern stream and resultant amplification with
this pattern, and thus will keep previous forecast idea of limiting
to chance pops, with possible transition to snow before precip ends.
Temps should transition back closer to normal by late
weekend/early next week.

&&

Aviation...(for the 12z tafs through 12z Wednesday morning)
issued at 650 am EST Tue Jan 23 2018

Rain and snow showers are just now coming onshore from Lake
Michigan, and will impact ksbn through the morning. MVFR/IFR
visibilities/ceilings have been observed upstream, along with a wind
shift from SW to northwest associated with the backside of the low pressure
system. Expect this to be the case today at ksbn, with gradual
improvement into higher-end MVFR tonight. A little bit trickier
situation at kfwa this morning, as a shortwave generated some light
rainfall ahead of the main line, and is now heading eastward. It
looks like the heaviest of the precipitation is to the north of
kfwa, but have observed some increasing reflectivities on the
southern end of the line. Think this may move through the
Airport, but don't expect much of an impact other than continued
fluctuation between scattered/bkn006 and maybe some lower visiblity
again. Included a tempo for this through the morning. Expect the
precip. To the west (that impacts ksbn) to die out just as it
reaches kfwa per latest high res guidance, so kept only vcsh in
the taf for now (16z-02z). If it does reach the Airport, it will
likely be early this afternoon. Overall, expect MVFR conditions
to prevail, with brief reductions to IFR during the precipitation.
Could see some snow flakes mix in with rain at kfwa, but expect
it will be mostly rain.



&&

Iwx watches/warnings/advisories...
in...none.
Michigan...none.
Ohio...none.
Lm...Small Craft Advisory until 9 am EST Wednesday for lmz043-046.

&&

$$

Synopsis...marsili
short term...marsili
long term...marsili
aviation...mesoscale discussion



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