Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service northern Indiana
739 PM EDT Friday Aug 29 2014

issued at 323 PM EDT Friday Aug 29 2014

A warm front will lift northeast into the area today into this
evening bringing increasing chances for showers and
thunderstorms...especially late this afternoon and evening across
Northwest Indiana and southwest lower Michigan. Lows tonight will
fall back into the 60s.

Saturday will feature better chances for thunderstorms and
locally heavy rainfall as a low pressure system tracks into the
Great Lakes region.


Short term...(this evening through saturday)
issued at 323 PM EDT Friday Aug 29 2014

Warm front making quick progress northward this afternoon in association/west SW trough and
attendant surface cyclone lifting northeastward out of the plains. Broad belt of
ll moisture flux tied to low level jet within Theta-E ridge leading to an
expanding area of rain showers/embedded thunderstorms and rain across western zones extending southwestward
into eastern Illinois/western in and expect this will continue to gravitate north/northeastward
through this afternoon. Southeastern half though expected to remain dry given
influence of western periphery of retreating Continental ridge and poor
eastward moisture flux bound.

Otrws west/warm front lifting through this evening do not see much of an
appreciable focus Sans far northwest zones for anything more than a
threshold lower bound slight chance pop mention. On Sat warm sector is
fully entrenched across County Warning Area along west/a very moist airmass. Diurnal heating
shld Foster sig instability by afternoon and west/southern edge of height falls in
association/west ejecting plains SW and approaching surface frontal zone will keep
west/prior likely probability of precipitation although did add some temporal detail to Sat
morning. Some low risk for severe (damaging winds) per modest 0-6km
bulk shear near 30-35kts which combined west/precipitable waters near 2 inches suggestive
of local mass loading and a pulse severe threat. Much warmer west/low to
middle 80s west-east across County Warning Area.


Long term...(saturday night through friday)
issued at 323 PM EDT Friday Aug 29 2014

Main focus in long term remains on timing of precipitation chances and
potential for additional heavy rainfall. Upper trough and associated surface
boundary will be moving across the area Saturday night with rain
chances continuing through the overnight hours. As mentioned by several
previous shifts...localized heavy rainfall remains a threat as
impressive Gulf moisture transport continues into the area (pwats in
the 1.7 to 2 inch range which is near 99th percentile for this time
of year). System will exit during the day Sunday with precipitation
tapering off from northwest to southeast. Latest 12z model runs in agreement with
timing and suspect most of Sunday will be dry...especially in northwest so have
cut probability of precipitation further especially during the afternoon/evening hours. Brief dry period
likely into the start of Labor Day as forcing diminishes and
shortwave ridge moves in ahead of next system.

Aforementioned system prognosticated to move east from North Plains/S Canada
and swing a cold front through the area by late afternoon into the
evening hours. Latest nam12 has sped up timing a few hours from
previous run with front moving through in the 21z timeframe during peak
heating with middle level jet ramping up. 12z GFS/Gem/ECMWF remain
slower with frontal passage in the 00-06z timeframe. Severe threat remains
conditional and will hinge on timing of frontal passage which can be further
nailed down as Labor Day approaches. Lapse rates will remain meager
with marginal shear on the order of 20-30 kts but if destabilization
occurs...expect moderate instability which may be enough to trigger
a few stronger storms. Again heavy rainfall would be biggest threat
as Bountiful moisture transport continues in warm sector. Precipitation
will taper off during the day Tuesday as front departs and stalls
east-west in vicinity of Ohio Valley. Models differ a bit in details and placement of
several shortwaves riding along boundary in zonal upper level flow
through end of period. For now have kept with going dry forecast for
Wednesday through Thursday afternoon until details are better resolved.

Temperatures will remain near normal for the start of the period
before ramping up by end of the week with more muggy conditions
expected. Highs will generally be in the low 80s through Wednesday with middle
to upper 80s possible by end of the week. Overnight lows will be in
the 60s.


Aviation...(for the 00z tafs through 00z Saturday evening)
issued at 738 PM EDT Friday Aug 29 2014

Low level warm front continues to lift north with associated
low level jet/Theta-E surge generating scattered convection over extreme western
Indiana. Storm Prediction Center/rap mesoanalysis indicates around 2000 j/kg of SBCAPE
in this area with much less moisture/instability around kfwa.
Expect thunderstorms to slowly dissipate with loss of daytime
heating. Forecast soundings indicate could be enough instability
for a few isolated storms around ksbn tonight but coverage
should be limited and will refrain from inclusion in the taf at
this time. Much better chances for convection will arrive tomorrow
afternoon...though exact timing is subject to revision. Some
concern for low level wind shear early tomorrow morning but current forecast
wind profiles are too marginal for inclusion in the tafs.


Iwx watches/warnings/advisories...


short term...T

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

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

National Weather Service Glossary of Abbreviations