Scientific Forecaster Discussion
Area forecast discussion
National Weather Service northern Indiana
408 am EST Monday Nov 30 2015
issued at 406 am EST Monday Nov 30 2015
Mostly cloudy conditions can be expected today as an upper level
disturbance and low pressure area approach the region. There is a
chance of rain late Monday afternoon...mainly west of Route 31.
More widespread rain will then overspread the entire area Monday
high temperatures today will reach into the middle to upper 40s.
Short term...(today and tonight)
issued at 403 am EST Monday Nov 30 2015
Richer moisture laid out far south of County Warning Area across Tennessee Valley into
Ozarks. Deep easterly component flow should maintain moisture at
abeyance until evening. Thereafter...County Warning Area quickly enveloped from
south and west with 6 g/kg 1000-850mb layer isohume surging into
far northestern County Warning Area by 03 UTC. Two focused areas of isentropic lift
appear to split County Warning Area with one focus area across northern
Illinois/southern WI with ardent orthogonal flow to i295k isentropic
surface and a more veered lower level/i300k axis surging northeastward from
Tennessee/Kentucky into middle Ohio Valley region. While some concern of split
between system...suspect overall magnitude of sudden/deeply
vertical moisture flux convergence /with a lessened role placed
upon high antecedent low level condensation pressure deficits/ to
provide high probability/rather low quantitative precipitation forecast event. Highest probability of precipitation/quantitative precipitation forecast 30-09 UTC
across northwestern half County Warning Area proximal to better focus for deep layer
ascent/eastern fringe of dynamic 200m/12 hour 500 mb height fall
centroid as central rockies cutoff low emerges east-northeastward to northwestern Iowa by
daybreak Tuesday. Derisive effect of dry slot as it surges from
central Illinois into southwestern County Warning Area around daybreak may may start to
erode back edge/southwestern extent of rain shield by daybreak...
especially across southwestern/southern County Warning Area.
Long term...(tuesday through sunday)
issued at 403 am EST Monday Nov 30 2015
Strong push of isentropic descent and negative Theta-E advection
to bring a quick end to precipitation chances from west to east Tuesday
morning. A few residual showers possible east of I-69 from 12-15z
but by and large expect Tuesday to be primarily dry. Should even
see some areas of sun by the afternoon due to strength of dry air
advection. Latest GFS still indicating some potential for a few
decent wind gusts midday Tuesday with abrupt descent and mixing
from 285k/875mb where wind speeds are around 30 kts. Certainly
nothing hazardous but could see a few gusts of 25-30 miles per hour.
Main trough axis/vorticity maximum then rotates over our area late Tuesday
night into Wednesday and will light up a round of lake enhanced
showers. Deep moisture and cyclonic flow working in concert with
some marginal lake instability and Theta-E flux will lead to num
showers north of the toll Road with lower chances the further
south you go. Best chances look to be roughly 09z-21z Wednesday.
Left Wednesday night dry but some concern for a few lingering
showers in the 00-03z timeframe. Quantitative precipitation forecast amounts will be light and
marginal surface wet bulb temperatures...particularly during the
afternoon...will prevent any real accumulation. Still think some
rain could mix in during the afternoon based on model forecast
soundings and expected surface wet bulbs. Our Michigan counties
west of I-69 could see a light dusting Wednesday morning if precipitation
arrives early enough and rates are high enough to overcome
marginal surface/ground temperatures. Any amounts should be light
though...less than a half inch. Winds will gust up to 25 miles per hour again
on Wednesday and will add to the "raw" feel. Dry weather then
expected through the weekend with temperatures climbing to slightly above
normal as longwave ridge slides over the Great Lakes.
Aviation...(for the 06z tafs through 06z Monday night)
issued at 102 am EST Monday Nov 30 2015
Focus primarily on deteriorating conditions late in forecast period.
An upper level cyclone will lift northeastward from the central rockies to
near ksux by the end of the forecast period. Meanwhile...latent
surface boundary across Tennessee Valley will surge northward with anticipatory
stratiform rain shield spreding into northern in. Also suspect ceilings to
lower even further from around 06 UTC into daybreak
Tuesday...near/just beyond current forecast period. Later forecast to
delve more into potential IFR conds developing late Monday night.
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