Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Indianapolis in
427 am EDT Tuesday Jul 22 2014

Update...
the aviation section has been updated below.

&&

Synopsis...
issued at 204 am EDT Tuesday Jul 22 2014

A warm...Summer day is expected today as high pressure east of
Indiana provides warm and humid southerly flow to central Indiana.
This will result in a typical Summer day. Tonight a quick moving
cold front will push central Indiana from the northwest. This will
result in chances for light showers or an isolated thunderstorm
tonight.

The cold front will push south of central Indiana on
Thursday...allowing high pressure to return to central Indiana
from the upper Midwest. The high will bring a return to cooler
than normal temperatures and dry conditions for the rest of the
work week.

Another frontal system will bring more chances for rain during
the weekend.

&&

Near term /today/...

Issued at 204 am EDT Tuesday Jul 22 2014

Surface analysis early this morning shows high pressure in place
over the Middle Atlantic States. Light...southerly return flow was
in place across Indiana and the Ohio Valley. Infrared failed to show any
clouds in the Hoosier state. Dew point temperatures remained in the moist
middle 60s...and some patchy fog was developing across the area.

Main forecast challenge today will be temperatures. GFS and NAM suggest a
ridge axis aloft stretching from broad high pressure over the
Desert Southwest will pivot across Indiana today. This should
result provide good subsidence aloft...diminishing cloud cover.
Time height sections and forecast soundings remain dry through the
day...with the NAM...GFS and European model (ecmwf) all suggesting convective
temperatures in the 90s. Thus it will be hard to produce much cumulus
or clouds today to hamper temperature rises. Forecast soundings
show 850mb temperatures around 18c-19c. Mavmos continues to run too warm.
Models also suggest a thermal axis aloft...northwest of central
Indiana ahead of the approaching cold front over northern
Illinois. Given this will trend temperatures 1-2 degrees cooler than
mavmos at most spots...particularly at ind which has been running
cooler. Look for warmest temperatures across the northwest and southern
parts of central Indiana.

&&

Short term /tonight through Thursday night/...

Issued at 204 am EDT Tuesday Jul 22 2014

Main challenge during this period will be the cold front passage
expected tonight.

NAM and GFS continue to keep a strong ridge in place across the
western United States. This in turn results in a continued Lee
side flow from the northwest spilling into the Great Lakes and
Indiana. Tonight...the GFS and NAM suggest a short waves slides
down the from the Midwest...with the best dynamics a forcing
flowing across the Great Lakes and Michigan. An associated cold
front is expected to accompany this feature and pass across
Indiana...mainly overnight. Essentially the tail of this cold
front is what is left as it passes across Indiana...providing very
limited forcing. Forecast soundings and time height sections fail
to show deep saturation overnight. GFS 310k isentropic surface
shows an axis of high specific humidities pushing across the
state...over 9 g/kg. However no upglide is present. Lower level q
vector convergence is very good across central Indiana as the
front passes tonight. However...low level jet remains weak...with speeds
around 20-25 knts through the night. Thus confidence is low for a
soaking rain...although a few light showers cannot be ruled out.
Will use some low chance probability of precipitation overnight. Given at least the
expected cloud cover will trend low temperatures warmer than mavmos.

Good cold air advection and subsidence then take place across the
area on Wednesday as forecast sounding show a dry column. Surface
high pressure builds into central Indiana...diving southeast out
of south central Canada...bringing a cooler and dry Continental
air mass to our region. This will result in dry and cooler weather
through Thursday night at least. Forecast soundings on Thursday
suggest attainable convective temperatures with a middle level
inversion...once again suggest some harmless...low-topped flat cumulus
during the afternoon hours. Given the good cold air advection in
place on Wednesday and Wednesday night will trend highs and lows
cooler than mavmos. Northerly surface slow continues through
Thursday night. Given this pattern will work a blend of the mavmos
and metmos.

&&

Long term /Friday through Monday/...

Issued at 258 am EDT Tuesday Jul 22 2014

Models are close enough that the allblend initialization was
accepted for most parameters.

Friday looks to remain dry. A front will move into the area and
stall out this weekend. Areas of low pressure will move along the
front. This will keep the threat for showers and thunderstorms in
the forecast for Friday night through Sunday night.

Confidence in which period will have the best threat for rain is low
since timing of the waves of low pressure is uncertain that far out.
Will keep allblend/S chance probability of precipitation.

For Monday an upper trough will dig into the area and bring another
cold front. This will also bring chances for rain to the area.

Temperatures will average near to below normal through the
period...with the coolest readings coming Monday as the upper trough
moves in.

&&

Aviation /discussion for 220900z taf update/...

Issued at 427 am EDT Tuesday Jul 22 2014

Still think some MVFR fog will develop at kind...so no changes made
to taf. IFR fog will continue at the other sites.

Previous discussion follows...
dew points in the middle 60s and calm winds should lead to fog at the
outlying sites again as dew point depressions drop to just a couple
degrees. Expect IFR or worse at times and have included tempo for
this. At kind could see visibilities drop a bit but most likely will
remain in the 5-7sm range. Winds should shift to out of the
southwest Tuesday around 5-10 kts with few to scattered cumulus around 5
kft.

&&

Ind watches/warnings/advisories...
none.
&&

$$

Synopsis...puma
near term...puma
short term...puma
long term....50
aviation...cp/50

Visit US at http://www.Weather.Gov/ind

Follow US on facebook...twitter and youtube at:
www.Facebook.Com/nwsindianapolis
www.Twitter.Com/nwsindianapolis
www.Youtube.Com/nwsindianapolis

National Weather Service Glossary of Abbreviations