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Area forecast discussion 
National Weather Service northern Indiana
729 PM EDT Sat Aug 30 2014

issued at 729 PM EDT Sat Aug 30 2014

Scattered showers and thunderstorms will continue to move across
northwest parts of the area this evening as low pressure tracks
into the northern Great Lakes. Drier air will briefly work into
the area on Sunday before a cold front brings renewed chances for
showers and thunderstorms on Monday. Lows will be near 70 with
highs on Sunday and Monday in the low to middle 80s.


Short term...(this evening through sunday)
issued at 335 PM EDT Sat Aug 30 2014

Convective development has triggered where the clouds cleared
earlier today...mainly over central Illinois to Lower Lake
Michigan and into northern Michigan. Best synoptic scale forcing
associated with the low/trough in Wisconsin. Flow regime is such
that the convection has developed in a stretching deformation
axis. Hrrr and local WRF show the surface based frontogenesis in this

Lapse rates and wind profiles support the potential for convective
lines and individual line segments. Isolated threat for severe wind
gusts. Do not expect to see sustained convective development as the
boundary layer forcing does not persist much past 04z.

Low level jet kicks in overnight and this should be enough to
sustain more organized rain showers/thunderstorms and rain across the southeastern half of the
forecast area. While there is discrepancy in timing and intensity
between the models...the boundary layer cape and wind profiles are
very similar and do support persistent/lingering showers through
Sunday morning. With abundant moisture tap and a long fetch of
isentropic assent...some of the showers could produce moderate to
locally heavy rainfall.

As the low level jet decreases and the trough/deformation axis shifts
eastward...expect improving conditions during the day Sunday ahead
of another more robust synoptic system approaching the area for


Long term...(sunday night through saturday)
issued at 335 PM EDT Sat Aug 30 2014

Main focus of long term is on precipitation/severe weather chances Monday
into Monday night. Well defined middle/upper level trough currently
digging into the Pacific northwest will swing through the Great
Lakes late Monday. Trough will be lifting as it moves through the
region but strong push of height falls and cva will support a decent
surface cyclone and attendant cold front. Precipitation chances will be
further aided by good right entrance jet dynamics over the southern
Great Lakes. Deep and strong southwest flow ahead of the trough will
easily advect high Theta-E airmass back into our area on Monday.
Afternoon SBCAPE values expected to reach the 2-3 kj/kg range as
high temperatures climb into the middle...or perhaps upper...80s with surface
dewpoints in the low 70s. Very dynamic wave will likely support
numerous showers and thunderstorms but timing will be critical to
severe weather chances. Latest 12z nwp suite keeps surface boundary
west of our County Warning Area until Tuesday morning. Isolated/scattered convection may
develop in the warm sector Monday afternoon along weak prefrontal
trough as suggested by the latest nam12 but expect bulk of the
activity will be tied to the actual cold front late Monday night.
Better wind profiles...with 0-6km shear of 30+ knots...will also be
tied closer to the front. Despite more than adequate
shear...midlevel lapse rates of 6-7 c/km are only weakly supportive
of a nocturnal severe weather threat. Forecast soundings indicate
only around 1000 j/kg of elevated instability Monday night....plenty
for widespread thunderstorms but severe potential is less clear.
There will be a threat for severe winds...and potential
rotation...with any substantive updrafts that manage to develop but
late arrival of front may limit chances for a widespread severe
weather event. Pushed back timing of probability of precipitation but also increased them a
bit based on latest model solutions. Could also be a threat for
stronger storms in our far southeast counties late Tuesday morning
if surface boundary is slow enough to exit the County Warning Area.

Quiet weather expected midweek before another trough approaches next
weekend. Scattered convection may be possible Thursday into Friday as warm
front lifts north once again but best chances look to hold off until
the weekend. After a brief break Tuesday and Wednesday...heat and humidity
will return for the end of the week as active weather pattern


Aviation...(for the 00z tafs through 00z Sunday evening)
issued at 729 PM EDT Sat Aug 30 2014

VFR conds this evening will give way to a period of MVFR/IFR conds lt
tonight as weak surface trough stall across the area. Forcing along trailing
boundary associated/west parent SW shifting eastward through northern WI has so far been
generally poor W/fractured...poorly developed convective line extending
from eastern Illinois northeastward through northwest in/southern Michigan. Doubt this will improve
overnight as near term highres guidance weakens veered low level jet after
midnight and west/no real push to surface boundary doubt convn makes it out of
northwestern zones. Thus will keep west/prior tempo thunderstorms and rain mention at ksbn which
may need to be extended a bit further. However convn expected to remain northwest
of kfwa and dropped previous thunderstorms in the vicinity mention there. High boundary layer moisture
remains in place and west/decaying surface gradient and some clearing overnight
expect some fog to develop.


Iwx watches/warnings/advisories...
Lm...Small Craft Advisory until midnight EDT tonight for lmz043-046.



short term...Lewis
long term...agd

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