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Area forecast discussion 
National Weather Service northern Indiana
1109 am EDT Wednesday may 6 2015

issued at 1050 am EDT Wednesday may 6 2015

Skies will be sunny for the southern part of the region. Skies
will becoming partly cloudy for the northern part while high
temperatures reach into the upper 70s in southern Michigan to the
middle 80s along the Ohio River. A weak front in the area will
give the far northern part of the region a slight chance for some
showers and thunderstorms. Tonight will be mostly clear with low
temperatures in the upper 50s to around 60.


issued at 1002 am EDT Wednesday may 6 2015

Previous forecast looks on track with only minor changes made on
update. Moved timing of showers up a few hours as weak low level
isent lift and moist airmass has already resulted in isolated
showers developing over northwestern portions of the area this morning.
Significant visibility restrictions due to fog have ended everywhere except
the far NE portion of the area and should be improving there
shortly as diurnal heating continues so have allowed dense fog
advisory to expire.


Short term...(today and tonight)
issued at 402 am EDT Wednesday may 6 2015

Short term issues deal with low clouds and fog this morning followed
by precipitation chances later this afternoon into early evening. Frontal
boundary has sagged well south into central Indiana and has become
quite diffuse overnight. GOES fog/low cloud product showing
extensive shield of stratus north of this boundary and covering all
but extreme southern portion of forecast area. 07z surface observations
confirm with ceilings generally under 1kft and visibilities at or
below 3sm. Hires model soundings show sharp low level inversion and
a few amdar soundings support this. Shallow stratus deck seems to be
keeping visibilities in the 1-3sm range with only a slow drop so
far. There are breaks within the stratus and patchy dense fog will
be possible if/where these cloud free areas persist.

With weak flow through a deep layer mixing will be slow today and
will need to rely more on diurnal heating to aid and eventually
erode cloud deck from south to north. This may take some extra time
and delay clearing until late morning or early afternoon in the far
north as ruc13 low level relative humidity fields do not mix until closer to 18z.
With this in mind have slowed clearing and kept northern areas
mostly cloudy this morning. High temperatures will be tricky as rapid
warming expected once skies clear. Southern areas still expected to
push middle 80s while northern areas may struggle to reach the upper
70s now with delayed clearing. 00z MOS guidance struggling as well
with large disparity between higher resolution met guidance being
much cooler than mav over northern areas while very close in the

Next issue deals with low chances for any afternoon convection.
Rather strong thermal gradient expected to develop with retreating
cloud deck and diffuse front mixing north. NAM 4km develops just a
few isolated cells late afternoon. Lower resolution version develops
very little. Most other guidance packages remain split. Modest cape
values around 1k j/kg expected but shear profiles are
unimpressive given weak flow through column. Slight chance probability of precipitation
remain warranted for any pop up development...mainly after about 20z
and similar to Tuesday night could see a few isolated thunderstorms and rain last through
about 03z far north.


Long term...(thursday through tuesday)
issued at 402 am EDT Wednesday may 6 2015

Upper level ridging will persist into the Great Lakes for the
start of the period...with continued above normal temperatures as
pesky frontal boundary should be north of the area and falling
apart (if not already gone). Upper level trough...currently
dropping south through Washington state will deepen and cut off
over Southern California and then drift slowly east to The Four
Corners area by Saturday night. Several ripples will edge
northeast towards the region starting as early as Friday afternoon
with a surface front drifting slowly southeast into the area.
These...combined with a somewhat unstable atmosphere should allow
for several chances of showers and thunderstorms Friday through
Monday before the main upper low finally ejects and lifts NE away
from the region. Best chance for showers/storms appears to be
Friday night with lead wave and Monday with the main upper low. In
terms of temperatures the rest of the period much will depend on how far
into the area the front gets before stalling out. Likely will end
up a tight gradient from northwest to southeast into the weekend until the main
system passes. Ran with superblend of models being the best


Aviation...(for the 12z tafs through 12z Thursday morning)
issued at 651 am EDT Wednesday may 6 2015

Dense fog which formed over Northwest Ohio has spread westward and
impacting kfwa with vlifr conditions. Wind field remains light
this morning and expect dense fog to persist for a few hours
before weak mixing begins and stalled front over central Indiana
begins to mix north and aids in erosion of low clouds and fog.
This should occur middle to late morning. A slight chance for a
thunderstorm this afternoon but chances remain too low for
inclusion within terminal. Skies clear this evening. Could be some
fog development again tonight depending on location of front and
how much mixing we see this afternoon. For now kept later portion
of tafs VFR.


Iwx watches/warnings/advisories...


short term...Lashley
long term...Fisher

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