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Area forecast discussion 
National Weather Service northern Indiana
447 am EDT Monday Sep 15 2014

issued at 445 am EDT Monday Sep 15 2014

Clouds will be on the increase today as an upper level disturbance
across the northern plains approaches. This disturbance will bring
the likelihood of rain showers later today into this evening. Dry
conditions will return later this evening behind this system...with
a reinforcing push of cool air resulting in continued below normal
temperatures through middle week. High temperatures this afternoon will
reach into the 60s...except lower 70s across central Indiana into
central Ohio. Low temperatures tonight will range from the middle 40s
to around 50.


Short term...(today and tonight)
issued at 445 am EDT Monday Sep 15 2014

The next upper level short wave of interest is well pronounced on
water vapor imagery this morning across the Dakotas. Already have
noted some very weak elevated echoes upstream across
central/northern Illinois where backing of low level winds has
allowed for an increase an isentropic lift. At least over the next
several hours...shower potential seems somewhat minimal due to
highly elevated nature of this forcing and initially quite dry low
levels. Southwesterly low level flow will ramp up somewhat in
advance of this wave allowing broad weak low level thetae ridging
across the middle Mississippi River valley to shift into the Ohio
Valley/southern Great Lakes. Low/middle level frontogenesis will also
be on the upswing in advance of this wave...especially during the
middle to late afternoon hours. Local area will also become
increasingly favored in right entrance region of Great Lakes upper
jet streak. Given fairly strength of upper wave...mid/upper level
frontogenesis...and strengthening isentropic upglide...have stayed
the course with high end likely probability of precipitation. May eventually need to
consider nudging into categorical pop range for portions of the area
however as stronger isentropic upglide/frontal forcing become
established later this afternoon/early evening. Main tweak to
forecast was to push timing of higher probability of precipitation back just a few hours
into the late afternoon hours as approaching frontal forcing should
allow precipitation to continue.

A few thunderstorms have developed across southern Iowa this morning
in zone of stronger isentropic lift/low level mass convergence.
Current forecast thinking is that better thunder potential will
remain southwest of local area in Richer low level thetae airmass.
While cannot completely rule out an isolated thunderstorm
particularly across the southwest...feel prospects are below
mentionable levels at this time.

Axis of more pronounced middle level fronto forcing to linger across
the central/eastern areas early this evening where have carried
likely probability of precipitation...with conditions drying out from west to east. Skies
should clear or partially clear tonight as low level trough axis
clears area...although as has been the case over the past several
days...persistent low level inversion gives some hesitation for more
longevity of stratocu than currently forecasted. Lows should drop
into the middle 40s tonight...but probably more into the upper 40s to
around 50 range where stratus persists longer. Some lake effect low
cloudiness may also provide warmer conditions near the Northwest Indiana
Lakeshore areas...but lake induced instability depths appear to be
too shallow for any precipitation inclusion at this time.


Long term...(tuesday through sunday)
issued at 445 am EDT Monday Sep 15 2014

Tranquil weather is expected for Tuesday into Saturday with
gradually moderating temperatures as the flow becomes more high
zonal and as the airmass over the area modifies. At the start of the
period...the short wave will have moved east of the area by Tuesday
morning...with decreasing clouds expected during the day as
subsidence behind the trough increases. Favorable nocturnal
radiational cooling conditions are expected Tuesday night with lows
dropping well below 50 degrees. Could be some patchy frost in
locally cold spots...but otherwise...frost is not expected and have
not mentioned any frost in the grids/forecast. The GFS has been
reasonably consistent with the warm up this week...and the GFS/mex
mean ensemble MOS temperatures appear on track. For this coming
weekend...the GFS and European model (ecmwf) have come into a little better agreement
on timing of the next system...with an upper level system and
associated cold front moving across the area by late in the weekend.
For now...kept a chance for showers Saturday through Sunday. Thunder
may need to be added at some point...but for now kept thunder out
given cape values very small per GFS/BUFKIT.


Aviation...(for the 06z tafs through 06z Monday night)
issued at 108 am EDT Monday Sep 15 2014

Next upper level short wave across the northern plains will race
eastward across the southern Great Lakes region this afternoon.
Rain is expected to Blossom in advance of this short wave given
fairly strong low level baroclinic zone that this feature will
have to work with. Best chance of rain will be in the afternoon
hours at ksbn...and in the late afternoon into early evening hours
at kfwa. MVFR ceilings are expected by late afternoon with a low end
possibility of brief IFR this evening...but confidence remains too
low for inclusion. Some patchy fog may develop outside of this
forecast valid period as next low level anticyclone settles across
the region.


Iwx watches/warnings/advisories...


short term...marsili
long term...skipper

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