Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service northern Indiana
148 PM EDT sun Aug 30 2015

Synopsis...
issued at 142 PM EDT sun Aug 30 2015

A trough axis over the region will continue to weaken today into
tonight. This will result in low chances for scattered showers
this afternoon. Highs today are forecast to reach the upper 70s
to lower 80s...with lows tonight dropping back into the 60s. Next
week will feature above normal temperatures and mainly dry
conditions as high pressure builds in.

&&

Short term...(today and tonight)
issued at 352 am EDT sun Aug 30 2015

Middle-upper level shear axis will continue to edge/decay slowly
east into eastern portions of the forecast area today...while at
the surface a subtle/diffuse trough (enhanced by Lake Michigan over
northern Illinois/Southern Lower Michigan as of this writing) sinks into
northern Indiana. Drying aloft over very moist low levels will
likely support low stratus and areas of fog through late morning
across northwest in/SW lower Michigan in the vicinity of the low level
trough...with latest observational trends suggesting the better
potential for dense fog will be along the immediate Lake Michigan
shoreline.

Chances for additional showers (isolated at best) appear rather low
(5-15%) through the early afternoon given radar trends and waning
lift/moisture quality associated with the above mentioned middle-
upper level shear zone (drier air aloft definitely making inroads
per morning water vapor). Scattered shower/isolated thunder chances increase
a bit (15-35 percent...highest along and southeast of the Highway 24
corridor) middle afternoon through early evening given expectations
for weak surface based destabilization/heating (near 1000 j/kg
possible if afternoon highs reach the low 80s and dewpoints linger in
the middle-upper 60s) and weak forcing mechanisms mentioned above. As
for later tonight...light/calm winds, clearing skies, and residual
near surface moisture may support some fog development.

&&

Long term...(monday through saturday)
issued at 352 am EDT sun Aug 30 2015

The upper level short wave which will decay across the region on
Sunday will remain sprawled across the Ohio River valley on
Monday. This very weak forcing combined with daytime heating and
weak surface based instability may be sufficient for an isolated
shower or thunderstorm south across extreme southern portions of
the forecast area Monday afternoon. Will keep the forecast dry at
this point with expectation that any better chance for any
isolated shower may remain south/southeast of local area.
Middle/upper level ridge amplification will be underway to the west
of the area on Monday...with this upper ridging gradually folding
over the weak sheared upper pv anomaly across the Ohio River
valley Monday night. While a pocket of slightly cooler low level
temperatures will persist in association with this weak upper
wave...better insolation on Monday should support highs back into
the lower to middle 80s for most locations.

By Tuesday...remnants of this weak pv anomaly will begin to lift
back northward across the local area with sufficient near surface based
moisture available for at least weak afternoon surface based
instability. Have not strayed far from previous forecast and will
maintain slight chance thunderstorms and rain probability of precipitation for Tuesday due to combination of
this weak upper forcing during peak heating. Did contemplate
removing weather mention for Wed/Thu...but have also maintained isolated
daytime probability of precipitation for this period as a series of weak Pacific
perturbations temporarily suppress building central Continental U.S. Ridging...
which could be enough to generate some isolated afternoon convection
each day. Continued temperature moderation should be somewhat tempered
Tuesday/Wednesday by some warm air advection induced cloudiness...but still into the middle to
upper 80s for both days.

Reamplification of upper level ridging should tend to suppress any
additional low end precipitation chances by Friday/Sat with some indications
in medium range models of low level easterly flow setting up toward
the end of the period as upper ridge axis remains just west of the
area. This should allow to keep further temperature moderation in check
with highs generally in middle 80s and lows in middle 60s for this period.

&&

Aviation...(for the 18z tafs through 18z Monday afternoon)
issued at 142 PM EDT sun Aug 30 2015

Light low level flow along with slow mixout across northern Illinois/northwestern in
lends difficult forecast with respect to br/stratus redevelopment
late in forecast period. By daybreak 10-15 kts coincident with
high 925mb relative humidity suggest that low clouds to likely reform around
08-10 UTC...especially in light of slow improvement seen upstream
today. Br/fog also a concern as well...espcly at ksbn with higher
xover temperature.

&&

Iwx watches/warnings/advisories...
in...none.
Michigan...none.
Ohio...none.
Lm...none.
&&

$$

Synopsis...Murphy
short term...steinwedel
long term...marsili
aviation...Murphy



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

Follow US on facebook...twitter...and youtube at:
www.Facebook.Com/nwsnorthernindiana
www.Twitter.Com/nwsiwx
www.Youtube.Com/nwsnorthernindiana

National Weather Service Glossary of Abbreviations