Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service northern Indiana
347 am EDT Tuesday Jul 28 2015

issued at 344 am EDT Tuesday Jul 28 2015

A ridge of high pressure across the Great Lakes will continue to
provide warm and humid conditions to the region today. This high
will begin to shift off to the east tonight which will allow
increased moisture to move into the area...along with a chance of
showers and thunderstorms across portions of northern Indiana and
southwest lower Michigan late tonight. An upper level disturbance
tracking out across the northern tier of the United States will
push a cold front into the region on Wednesday providing the next
chance of thunderstorms. High temperatures this afternoon will
reach into the upper 80s to around 90. Low temperatures tonight
will range from the middle 60s to around 70.


Short term...(today and tonight)
issued at 344 am EDT Tuesday Jul 28 2015

Another quiet day weather wise is in store with main story in the
short term on the heat/humidity followed by shower/thunderstorm
chances late tonight.

Overall synoptic pattern has changed little in comparison to past
few days with Great Lakes anticyclone continuing to provide low
level easterly flow. This pattern has led to a sharp southwest-
northeast moisture gradient which should be the case once again
today. Rather stagnant middle level pattern will allow for continued
middle level ridging/synoptic scale subsidence in place for today.
Continued moderation of low level air mass with history of
subsidence and good deal of insolation should allow for slightly
warmer maximum temperatures today in comparison to yesterday. Previous forecast
appears to be in good shape with highs generally in the upper
80s...although would expect some spots to hit the 90 degree mark.
With easterly flow remaining weak today...have trended more toward
rap wind fields closer to Lake Michigan which are more supportive of
a weak synoptically modified north-NE lake breeze developing again this
afternoon. Even closer to the Lakeshore...would expect highs to top
out in the upper 80s before some cooling late afternoon with the
modified lake breeze. With the aforementioned southwest to northeast
moisture gradient...highest afternoon heat indices in the middle 90s
are still expected across southwest half or southwest third...and
generally in the lower to middle 90s elsewhere. Extreme southwest
locations could make a run at the upper 90s for heat indices this
afternoon but will continue to hold off on any heat headlines at
this time.

In terms of precipitation potential...ongoing mesoscale convective system early this morning across
the eastern Dakotas is expected to drop southeast this afternoon
with higher res models suggesting this convection decaying across
the middle MS River Valley into northeast Illinois late afternoon/early
evening. Given Stout middle/upper ridging in place across Great
Lakes/Ohio Valley...have generally bought in on this scenario. A
strong upper level trough lifting northeast out of the northern
plains late tonight will allow for eastward progression of cold
front to middle/upper MS River Valley by daybreak Wednesday. A narrow
but significant low level moisture axis will advect into western
portions of the area late tonight ahead of this front as low level
winds begin to veer. In addition to low level thetae
advection...some residual vorticity maximum enhanced by northern plains
convection this morning may be slowly progressing through mean flow
to the western Great Lakes by later have continued low
chance thunderstorms and rain mention across western third of the area after 09z


Long term...(wednesday through monday)
issued at 344 am EDT Tuesday Jul 28 2015

Period will start focused on weakening cold front passing through
the region. Isolated to scattered convection may already exist along
the front...supported by weak convergence and abundant moisture.
Some of the hi res models would suggest a decent eml potential...but
good degree of warm air likely capping much of this off...limiting
severe potential. At this point middle to high end chance (sct) probability of precipitation still
warranted with continued passing mention of strong to isolated
severe storm. Temperatures prior to frontal passage may be tricky depending on
amount of cloud cover as well as timing of front. Warmest readings
southeast still look most reasonable.

Semi active northwest flow will continue the remainder of the period with
several weak ripples and surface reflections making their way into
the region. Chances for showers and storms exist during the period
in more Summer like...isolate to scattered convective pattern at best with
best dynamics remaining removed from the region. Timing of each
system likely to vary in the coming days so only made minor changes.


Aviation...(for the 06z tafs through 06z Tuesday night)
issued at 127 am EDT Tuesday Jul 28 2015

Overall quiet pattern to continue through this forecast cycle with
Great Lakes anticyclone continuing to be the dominant feature
across the region. High clouds should gradually thin overnight
transitioning to mainly few-scattered VFR cumulus during the day Tuesday. Dry
conditions to persist through this forecast period but as low
level winds slowly begin to veer southeast toward the end of the
period...low level moisture will be on the increase. Primary low
level moist tongue will advect into northern Indiana after this
forecast valid period early Wednesday morning...with any
associated shower/thunderstorm chances holding off until after 06z
Wednesday. East winds less than 10 knots to continue today due to
persistence of high pressure across the Great Lakes.


Iwx watches/warnings/advisories...


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

Visit US at www.Weather.Gov/iwx (all lower case)

Follow US on facebook...twitter...and youtube at:

National Weather Service Glossary of Abbreviations