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Area forecast discussion 
National Weather Service northern Indiana
534 am EDT Sat Aug 29 2015

issued at 330 am EDT Sat Aug 29 2015

A weakening trough will drop into the lower Great Lakes today into
Sunday causing scattered showers and possibly a few thunderstorms.
Highs each day should reach the middle 70s to low 80s. Next week will
feature warmer and mainly dry conditions as high pressure builds


Short term...(today and tonight)
issued at 330 am EDT Sat Aug 29 2015

Main focus today into tonight will be on shower/isolated thunder chances
as a disjointed middle-upper level trough axis and associated weak low
level trough weaken east-southeast into the lower lakes.

Corridor of deeper moisture (pwats exceeding 1.50 inches) within low
level jet immediately downstream of this feature will slowly edge
into northwestern zones middle morning-early afternoon and points east-southeast
thereafter. Support aloft initially will come from weak upper jet
support (rrq of a 80 knots northern lakes 300-200 mb jet) and middle
level uvm/moisture advection surge tied to an embedded vorticity maximum
outrunning trough axis through central lower Michigan. This
forcing/deeper moisture will clip our far northern zones middle-
morning through at least early afternoon where probability of precipitation were
raised...although did opt to drop the thunder mention given
limited instability/middle level lapse rates. Shower coverage will be
more isolated in nature farther southeast through early
afternoon...with areas southeast of the Highway 24 corridor likely
remaining completely dry.

Steady improvement in moisture quality and weak middle level
DCVA/deformation tied to sheared out upper pv filament should keep
scattered showers around into the middle afternoon/evening (best
chances northwest of Highway 24). Any thunderstorm activity with surface
heating/moistening should remain isolated at best given thicker
middle/high cloud canopy and warm column...with convection Happy hi-
res guidance likely overly aggressive regarding surface heating/dewpoints.


Long term...(sunday through friday)
issued at 330 am EDT Sat Aug 29 2015

On Sunday...the upper level pv anomaly tracking across the region
will continue to lose potency and become highly attenuated.
Persistence of this weakening forcing combined with diurnal heating
should yield isolated to scattered afternoon showers and
thunderstorms however. While appreciable moisture should be in place
on Sunday...uncertainty in precise magnitudes of low level moisture
lend some lower confidence into extent of thunder potential given
sensitivity of sbcapes to near surface moisture with continued marginal
middle level lapse rates. Weak forcing with sheared vorticity maximum may
tend to maximize across southeast portions of the forecast
area...although weak lake enhanced low level convergence zone may
also be a secondary focusing area across northwest portions of the
County Warning Area downwind of Lake Michigan. With decaying nature of upper pv
anomaly have maintained low to middle chance probability of precipitation Sunday...peaking in
the afternoon. Slight chance/low chance probability of precipitation were also maintained
into Sunday night following southeast progression of weakening
middle/upper level forcing.

Vorticity filament associated with weakening wave will likely reside
across the region through Tuesday afternoon with the possibility of
weak highly sheared waves lifting northward out of the Lower/Middle MS
River Valley toward middle week. The dominant feature will be
amplifying background upper ridging to affect much of central Continental U.S.
Through the remainder of this forecast period. Medium range models
do point toward possibility of the southern extent of Pacific wave
progressing through mean ridging providing some weak forcing in the
Wednesday-Thursday timeframe...but confidence with any of these embedded waves
is low. The general idea of previous forecast with isolated diurnal
probability of precipitation for the Tuesday-Thursday period was left as is given this pattern.

Building heat for next week could be somewhat tempered by occasional
weak backdoor cool front type features impacting the eastern Great
Lakes...with upper ridge axis likely remaining just west of the
local area through most of the upcoming week which should confine
highs to the middle-upper 80s through much of the Tuesday-Friday period. This
idea is inline with previous gridded forecast and no significant
changes were made to maximum/mins at this time for much of the extended


Aviation...(for the 12z tafs through 12z Sunday morning)
issued at 534 am EDT Sat Aug 29 2015

Mainly VFR with light south-southeast winds can be expected today into
this evening. Chances for showers will increase by later this
morning/afternoon at ksbn and late afternoon/evening at kfwa as
a ribbon of deeper moisture/weak ascent folds in advance of an
approaching shortwave trough. Also could see a rumble of
thunder but chances remain too low for a thunderstorms and rain or thunderstorms in the vicinity mention at this time.
Continued low level moistening along a diffuse low level trough
may support visible or ceiling restrictions toward the end of the taf chances at ksbn.


Iwx watches/warnings/advisories...


short term...steinwedel
long term...marsili

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