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Area forecast discussion 
National Weather Service northern Indiana
839 PM EDT Friday Jul 25 2014

issued at 305 PM EDT Friday Jul 25 2014

Periodic chances for showers and thunderstorms will return later
tonight into this weekend as a frontal boundary settles into the
region. Lows will generally be in the 60s...with highs expected to
reach the 80s on Saturday and Sunday. Much cooler weather will
return early next week as an upper trough settles in.


issued at 800 PM EDT Friday Jul 25 2014

A well pronounced short wave tracking across northern
Indiana/Southern Lower Michigan this evening will exit the area
late this evening. Light rain/sprinkles have expanded in coverage
across southeast lower Michigan ahead of this vorticity maximum...but with
strongest DPVA departing east of the area over the next few hours
will maintain just slight chance -rw probability of precipitation. Progressive and lower
amplitude additional short waves are expected to shift into the
western Great Lakes region overnight into early Saturday with
westerly low level jet helping to advect more substantial low level
thetae nose eastward overnight...particularly across western half
of the area. Increased low level moisture should allow for
increased depth to elevated instability particularly after 09z.
Thus...have made few if any changes to previous probability of precipitation with west to
east gradient setting up overnight...highest chance across the


Short term...(this evening through saturday)
issued at 305 PM EDT Friday Jul 25 2014

A weak shortwave now into southern WI per latest water vapor imagery will
propagate southeast through the lower lakes late this
afternoon/early evening. This timed with initial 850-700mb Theta-E
surge/weak isentropic ascent may be enough to generate a few
sprinkles/light showers into mainly our far northwest during this
time...although kept probability of precipitation for measurable precipitation low given very
dry/deep sub-cloud layer.

Chances for showers/elevated convection will increase later tonight
into Saturday morning as low level Theta-E ridge folds southeast in
advance of an upper Midwest low level trough axis. This feature will
eventually be forced into the central/lower lakes on the leading
edge of a strengthening northern plains to western Great Lakes
middle-upper jet streak. Associated boost of precipitable water values
to greater than 1.6 inches within a modest 30 knots low level jet...and added
moisture convergence along an approaching warm front support
inherited middle chance probability of precipitation...although coverage remains in question given
lack of height falls/support aloft. Expected increase in MUCAPE to
greater than 1000 j/kg and 40 kts of deep layer shear suggests a low
risk for severe hail into our far western zones Saturday morning.
Otherwise...temperatures warm closer to normal tonight into Saturday.

Surface trough/instability gradient looks to lay out more west to east
over central/southern portions of the forecast area by middle-late afternoon
Saturday...within the southern fringe of strong middle-upper level jet
core. The eastward advancement of a plains eml over an increasingly
juiced boundary layer should yield SBCAPE values in excess of 3000
j/kg along/south of boundary if highs into the low/middle 80s are
attained (dependent on lingering convective cloud debris)...with
extreme instability possible into southwestern portions of the forecast area
where warm sector may become briefly established. With 0-6 km
shear/flow prognosticated to be sufficient for upscale growth/organization
will have to closely monitor the severe weather potential (discrete
supercells develop across central Illinois and role east into Indiana as a
mcs?) Later Saturday afternoon into Saturday chances
south of the Highway 30 corridor in Indiana/Ohio.


Long term...(saturday night through friday)
issued at 305 PM EDT Friday Jul 25 2014

Potent SW trough along the British Columbia/ab border will dig southeastward into the western
lakes this weekend concurrent west/deep meridonal follow amplification
across noam. Active surface frontal zone/composite outflw boundary position
still very uncertain and poses the greatest quandary this period. However
would certainly prefer to see more sig ridge amplification northeastward of
upper ridge centered over the Southern Plains to justify a more northward frontal/outflw
position this weekend. Regardless loose model consensus fvrs southern
zones Sat evening and eastern zones sun for greater pop weighting however
will refrain from elucidating likely or higher probability of precipitation at this range.

This system will become absorbed in larger scale trough amplification
through eastern Canada of which will drive another unseasonably cool
airmass southward across the eastern US. Strongly prefer cooler guidance temperatures
Monday-Tuesday before moderating back toward normal lt period. Otrws remainder of the
period beyond sun expected to be dry as sig Theta-E sink develops southward into the
Ohio Valley.


Aviation...(for the 00z tafs through 00z Saturday evening)
issued at 800 PM EDT Friday Jul 25 2014

A fairly strong short wave tracking across northern Indiana has
struggled to produce measurable precipitation with an initially
dry subcloud layer. Strongest forcing with this wave is already
shifting into Northwest Ohio at 00z...and thus expecting terminals
to remain dry through the remainder of the evening and into the
early portion of the overnight hours. Additional small scale waves
across the Central Plains/corn belt are expected to shift into the
region overnight. Gradually veering low level flow will also allow
for strong low/middle level thetae advection overnight into early
Sunday in association with westerly low level jet. This will
result in some low chance of thunderstorms and rain at particularly South Bend late
tonight into early Sunday but confidence is too low for inclusion
for 00z tafs at this time. Moderate to strong instability to
develop for Saturday...particularly south of Route 30. Potential of
scattered thunderstorms will exist Saturday afternoon/evening in
association with warm frontal boundary tracking northward...and
have included thunderstorms in the vicinity mention at kfwa after 18z.


Iwx watches/warnings/advisories...


short term...steinwedel
long term...T

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