Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service northern Indiana
142 PM EDT Wednesday Jul 30 2014

issued at 1049 am EDT Wednesday Jul 30 2014

Another disturbance will move across the region today from a low
centered over James Bay Canada. This will provide once again a
chance for some showers this afternoon with isolated
thunderstorms. This low will also help to keep cool July
temperatures across the region. High temperatures today will
range from the lower 70s in southern Michigan to the upper 70s
along the Ohio River. Then tonight will be dry and partly cloudy
with low temperatures ranging from the lower 50s in southern
Michigan to the upper 50s near the Ohio River.


issued at 137 PM EDT Wednesday Jul 30 2014

Minor adjustments to grids to extend Lake Shadow in a bit further
in northwest parts of Indiana.

Convective temperature now being met with cumulus beginning to pop. Main push
of stronger convergence was still across Southern Lower Michigan
but will drift south into area. Lake Shadow area should remain dry
with stable layer in place as depicted by Storm Prediction Center mesoscale analysis of
little instability. Points east indicate 750 to nearly 1500 j/kg
of surface based cape in a weakly sheared environment. This should
set the stage for isolate to scattered showers and storms to pop much like
yesterday from middle afternoon through early evening. Grids already
reflected this so no need to change that.

Rest of the forecast on track for now.


Short term...(today and tonight)
issued at 446 am EDT Wednesday Jul 30 2014

Anticipate similar scenario as seen yesterday given highly blocked
longwave pattern with deep layer trough axis holding from James Bay
anchor southward to Western Lake Erie. Continued nwrly perturbed
flow amid steep 0-3km lapse rates peaking at 7.5-8.25c/km
midday/afternoon with surface/500 mb differentials again in upper 30c to
near 40c range should be sufficient for renewed convective
development by late morning/midday. Surface dewpoints have crept
upwards per both yesterdays isolated to scattered convection as well
as generous evapotranspiration through corn belt. Modified nam12
point soundings yield generally 600-800 j/kg with middle 70s/middle for only about 250 j/kg downwind of southeast Lake
Michigan. With greater convergence/instability well inland and along
southeast extension of northestern Illinois/northwestern in Lake Shadow...will offer some
spatial detail with coverage type wording...and lower probability of precipitation as well
as Nix thunderstorms and rain mention in northwestern County Warning Area concavity. Again little local/level of free convection
differential should provide fairly rapid low topped convective
development and wet bulb zero heights around 9 kft suggest small
hail within strongest storms possible. Weakening gradient flow and
remnant low level thermal trough suggests another good longwave
radiational evening/early Wednesday night and lowered temperatures
slightly...especially at kbeh with anticipated land breeze/drainage


Long term...(thursday through tuesday)
issued at 446 am EDT Wednesday Jul 30 2014

Continued seasonally cool middle level temperatures on Thursday will allow
afternoon lapse rates to steepen with daytime heating...and should
allow for a slight chance for thunderstorms as weak upper level
disturbances move across the area. Weak unidirectional wind flow but
with low wet bulb zero heights could allow for some very small hail
from a storm or two. Therefore...have kept a slight chance for
thunderstorms Thursday afternoon. Kept a low chance or slight chance
for showers or storms Friday through Saturday as this pattern
continues with additional weak short wave energy rotating around the
upper low that should be over James Bay early this weekend. The
upstream upper level ridge should flatten early next week and allow
a more progressive upper level pattern. Low level Theta-E should
increase Tuesday...and along with weak low level forcing...should
allow for a small chance for thunderstorms Tuesday. As for
temperatures...favor the cooler GFS mean ensemble temperatures which
seem to support cool 850 mb temperatures for this time of year.


Aviation...(for the 18z tafs through 18z Thursday afternoon)
issued at 137 PM EDT Wednesday Jul 30 2014

VFR conditions expected to dominate the ksbn area as Lake Shadow
has now passed over the Airport resulting in a more stable setup.
At kfwa cumulus will conitnue to expand somewhat with potential for
widely scattered to scattered showers and storms to develop from middle afternoon
into the early evening as a weak disturbance moves in. Have left
thunderstorms in the vicinity in place given plenty of instability for convection to form
but low confidence on impact at Airport. Otherwise high clouds
will stream across the sky from time to time.


Iwx watches/warnings/advisories...


short term...Murphy
long term...skipper

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

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

National Weather Service Glossary of Abbreviations