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Area forecast discussion 
National Weather Service northern Indiana
839 PM EDT Wednesday may 6 2015

Synopsis...
issued at 431 PM EDT Wednesday may 6 2015

High pressure will maintain warm and mainly dry conditions
through tomorrow. Lows tonight will be around 60 degrees with
highs tomorrow climbing into the middle 80s. A frontal boundary will
then set up over the region on Friday and bring a chance of
showers and thunderstorms through the weekend.

&&

Update...
issued at 802 PM EDT Wednesday may 6 2015

Previous forecast is in good shape this evening with only a couple
of minor tweaks. A few isolated showers have developed early this
evening across southwest lower Michigan. This small area of
showers appears to have been aided by some weak low level
convergence associated with marine influence...which is also
colocated with western fringe of pocket of 500-1000 j/kg MLCAPES.
This instability should be strongerly correlated to diurnal cycle
and with little to no middle/upper forcing...these showers should
dissipate over the next hour or so. Only other tweak was to focus
greatest fog potential across the northeast for the overnight
hours with more favorable crossover temperatures.

&&

Short term...(this evening through thursday)
issued at 414 PM EDT Wednesday may 6 2015

Today's short term forecast can be characterized as generally
benign but very Summer-like. High amplitude ridge will continue to
slowly migrate eastward through tomorrow with deep SW flow
advecting even warmer temperatures into our area. A few extremely
isolated showers have managed to develop in our County Warning Area this afternoon
given modest instability (mlcape around 500 j/kg) and a weak cap.
Lack of synoptic forcing and marginal instability/low level
moisture will keep any activity very isolated through the evening.
Given paltry radar returns and cloud bases of 6-7 kft decided to
remove blanket pop mention and go with a "silent" 14 pop.

Did introduce some patchy fog wording given overnight lows dropping
near cross-over temperatures of upper 50s with very light southeast winds.
Boundary layer got mixed out fairly well today and afternoon
dewpoints are a bit lower. Overnight lows will also be milder given
continued warm air advection so confidence in widespread/dense fog is low. If it
does occur...our eastern counties once again have the highest threat
and will continue to monitor trends overnight.

As alluded to earlier...warm temperatures will be the main story for
tomorrow. Deep mixing...just partly cloudy skies...and warm thermal
profiles aloft will support highs easily in the low to middle 80s. Some
guidance...mav in particular...suggest upper 80s possible and may
not be outside the realm of possibility based on current temperatures just
upstream over central Illinois. Mixing heights at or above 800mb
suggest siding on the warm side of guidance but will hold with
generally middle 80s for now. Some concern for very isolated afternoon
convection to pop up but warm temperatures aloft with surface dewpoints
only in the upper 50s suggests instability will be at a premium.
Forecast soundings also hint at a decent speed bump around 600-700
mb that will likely cap most (if not all) convection. Another
"silent" 14 pop still appears to be the most prudent approach.

&&

Long term...(thursday night through wednesday)
issued at 414 PM EDT Wednesday may 6 2015

Upper ridge over the Ohio Valley/western Great Lakes this afternoon expected to move
to the east of our area by Thursday evening as upper low over western Nebraska shears
out and lifts NE into southwestern Ontario/upper MS valley. Surface low associated
with this feature expected to move through central Ontario overnight
with cold front trailing SW into eastern Iowa by Friday morning. Developing southwesterly flow
ahead of the front will result in gradually incrsg Theta-E overnight.
Many of the 12z models suggest some potential for showers reaching
portions of western County Warning Area early Friday morning as weak shortwave moves
through the moisture plume from the SW. Appears if any showers do
reach the area it would be in the 09z-12z timeframe which is around
dawn this time of year so for now left forecast dry which is also
supported by 12z Gem and hires nmm.

Diurnal heating expected to lead to moderate instability Friday
which should allow scattered thunderstorms to develop as the cold front slowly
approaches from the northwest and possibly weak shortwaves move through the southwesterly
flow aloft over the area. Highest probability of precipitation across the northwest closer to
frontal boundary and within deep moisture plume.

Medium range models suggest the cold front will become stationary across our
area by Saturday as surface low associated with trough digging through western
U.S. Today deepens over western Kansas. Diurnal heating/destabilization
should lead to scattered thunderstorm development once again with axis of highest
probability of precipitation shifting to southeastern 1/2 of County Warning Area along/ahead of front.

Stationary front expected to lift slowly north Sunday as Kansas low ejects NE
into Iowa. Again diurnal heating/destabilization should lead to scattered
thunderstorm development during the day in the vicinity of the front. Appears
to be some potential for locally heavy rainfall over the weekend
given rather moist airmass with precipitation water prognosticated around
1... mbe vectors/potential for training.

Low expected to move NE across the upper Great Lakes Monday-Monday night
with trailing cold front moving through our area. Still appears best chance of
thunderstorms during the long term forecast period will be Monday along/ahead of
the cold front. Stronger winds aloft/increasing shear associated upper
level trough moving through the upper Midwest/Great Lakes suggests potential
for more organized storms Monday if diurnal heating/destabilization
isn't significantly hindered by widespread clouds/showers.

Cold air advection in wake of mondays Great Lakes low should result in considerably
cooler temperatures Tuesday-Wednesday with lingering wrap around strato cumulus and possibly
a few showers Tuesday. High pressure should build into the area Wednesday
providing fair weather with a little more sunshine but temperatures probably will
still be a bit below normal as low level thermal trough moves through
the area.

&&

Aviation...(for the 00z tafs through 00z Thursday evening)
issued at 802 PM EDT Wednesday may 6 2015

Upper ridging to persist across the region through this forecast
period will provide mainly dry conditions. A few isolated showers
have developed early this evening across southwest lower Michigan
where some lake breeze enhancement has aided low level
convergence. Instability will quickly wane this evening and
terminals will remain dry. Higher crossover temperatures exist across
Northeast Indiana/Northwest Ohio where fog potential should be the
greatest tonight. While conditions are not expected to deteriorate
to the level of earlier this morning...at least some IFR visibilities are
possible at kfwa early Thursday morning. Boundary should mix
northward for Thursday with south winds of 10 to 15 knots at
terminals Thursday afternoon.

&&

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

$$

Update...marsili
synopsis...agd
short term...agd
long term...jt
aviation...marsili



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