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Area forecast discussion 
National Weather Service northern Indiana
850 am EDT Tuesday Oct 21 2014

issued at 351 am EDT Tuesday Oct 21 2014

Low pressure will drift slowly east out of the Great Lakes into
the Carolinas by Wednesday. Skies will clear across western areas
by late afternoon with mostly cloudy skies holding until tonight
in the east. Highs will climb into the 50s today with lows tonight
into the lower to middle 30s.


issued at 850 am EDT Tuesday Oct 21 2014

Midlevel vorticity maximum and associated broad surface trough are currently
pushing south into the area. Latest radar mosaic and surface observation
indicate several locations are receiving light...but measurable...
rainfall. Precipitation is being forced by modest DCVA and low level
convergence but is also being aided by some lake induced
instability off of Lake Michigan. Have therefore increased probability of precipitation
for the morning hours. Still expecting mainly dry conditions by
the afternoon as shortwave exits and drier air is advected south.
Latest rap and hrrr support this idea so no major changes for the
afternoon period.


Short term...(today and tonight)
issued at 351 am EDT Tuesday Oct 21 2014

Upper level trough will continue to deepen as it moves slowly
southeast out of the Great Lakes and towards the Carolinas. Lake
effect clouds and limited shower activity should quickly diminish by
late afternoon as flow becomes more north and NE. While skies will clear
in western areas later today into cover will linger
longer as cyclonic flow remains across eastern areas with some
contribution from Lake Huron. The result will be partly if not
mostly cloudy skies lingering into tonight along/east of I-69.

As skies clear...temperatures should be able to rebound somewhat but
will still remain below normal with highs in the low to middle 50s.
Clearing in the west will set the stage for a cold night with NE
flow ushering in dewpoints in the lower 30s and lows in a similar
range (low to middle 30s). Frost will be possible...but with end of
climatological growing season no headlines will be issued.


Long term...(wednesday through monday)
issued at 351 am EDT Tuesday Oct 21 2014

Slightly below normal temperatures to begin the period will moderate
to near normal or slightly above normal for this weekend into the
early parts next week.

On Tuesday...upper trough digging across the eastern Great Lakes
will eventually develop into a closed off upper level circulation
across the Middle Atlantic States. This will place local area into
upper level inflection zone with the possibility of some stratocu
persisting across mainly eastern locations. Middle level height rises
building in more aggressively for Tuesday night should result in
mainly clear skies. Slow progression of closing off system across
middle Atlantic will result in only a very slow eastward migration of
upper level ridging...which will keep low level anticyclone anchored
across the region through Wednesday night. This setup should provide
highs in the middle to upper 50s...and a few good nights of radiational
cooling conditions with lows in the middle 30s (possibly lower 30s in
cool spots). Per public information statement sent
yesterday...frost/freze headlines have been discontinued for local
area due to effective ending of the growing season.

Next feature of interest for Thursday will be upper pv anomaly
approaching the area from the northern plains. Upper level
deformation associated with slow moving upper level ridge should
attenuate this pv anomaly across the Great Lakes region Thursday
night into early Friday resulting in waning upper forcing.
Nonetheless...another narrow low level moisture axis will precede
this upper pv anomaly with weak low level warm air advection/moisture advection and
weak low level convergence axis overspreading the area. No change
needed to previous slight chance rain shower probability of precipitation across the west
Thursday night...with lesser confidence across the east due to
weakening nature of upper pv anomaly.

Upper ridge should eventually get pinched off from aforementioned
two systems...with renewed middle/upper level height rises working into
the region for the weekend. This will mark a more distinct warming
trend for Saturday/Sunday...although medium range guidance continues
to indicate southeast Canadian upper short wave providing more
substantial low level cold advection push across the eastern Great
Lakes. Only adjustment to previous forecast was for slightly warmer
conditions on Sunday...with a bit sharper southwest to northeast
gradient in maximum temperatures although still a good deal of uncertainty in
how far south stronger low level cold advection is able to push
across the eastern Great Lakes.

A slightly flatter and more progressive pattern should set up early
next week with next broad eastern Pacific wave bringing the next
chance of rain showers toward the end of the period.


Aviation...(for the 12z tafs through 12z Wednesday morning)
issued at 646 am EDT Tuesday Oct 21 2014

Scattered light lake effect rain showers will continue this
morning with marginal lake induced instability. A sheared upper
level vorticity associated with upper jet streak will also be
shifting south across the region over next several hours providing
some synoptic enhancement. May include a tempo -shra mention for
ksbn with the 12z tafs along with the possibility of short lived
2-3k feet ceilings. Otherwise...generally VFR stratocu today...and
should diminish in coverage later this afternoon into this evening
as upper ridge axis begins to build across the area. Northwest
winds around 10 knots will veer to the north this afternoon...and
become light northeast tonight as low level ridge axis overspreads
the western Great Lakes.


Iwx watches/warnings/advisories...
Lm...Small Craft Advisory until 5 am EDT Wednesday for lmz043-046.



short term...Fisher
long term...marsili

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