Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Indianapolis in
1242 am EDT Wednesday may 27 2015
the aviation section has been updated below.
issued at 241 PM EDT Tuesday may 26 2015
Unsettled conditions expected into early next week as occasional
upper disturbances move over the area...resulting in periodic
chances for showers and thunderstorms.
Near term /overnight/...
issued at 956 PM EDT Tuesday may 26 2015
Relatively quiet evening ongoing across central Indiana as
widespread convection well off to the east over Ohio. Surge of
drier air has advected into the region from the southwest over the
last few hours...noted nicely on WV satellite and in surface
dewpoints into the upper 50s. 0130z temperatures remain in the 70s.
The Ohio Valley will remain within a southwest flow aloft between
high pressure over the western Atlantic and an upper wave over the
upper Midwest. Low level jet which has been active over the region
today should relax somewhat overnight before increasing again
towards daybreak as another disturbance approaches from the
southwest. Weak energy aloft will drift across the area overnight
but with the drier air through the boundary layer and convective
inhibition across the region...expect a mainly dry night. Hi-res
guidance expanding isolated/scattered convection towards the
Wabash valley by daybreak as storms over the Southern Plains
spread northeast. Outside chance a shower can sneak into western
counties prior to 12z...but keeping dry at this point in time.
Despite decent rainfall for some across the region today...not
really concerned about widespread fog development overnight with
winds staying around 10 miles per hour.
All else in good shape. Zone and grid updates out.
Short term /Wednesday through Friday/...
issued at 241 PM EDT Tuesday may 26 2015
Model data suggest upper flow will flatten out for awhile during
this period before upper ridge reestablishes itself over the eastern
parts of the country by the end of the week.
A weak frontal system will move into the area during the day
Wednesday before washing out later this week. Instability should be
higher on Wednesday as lapse rates steepen quite a bit...although
deep layer shear will be weaker tomorrow compared to today. As a
result...will go with chance probability of precipitation on Wednesday and Wednesday night.
Appears the lowest potential for convection during this period will
be on Thursday and Thursday night as front dissipates and upper
heights begin to build again. Models indicate the instability axis
will be located near the Ohio River on Thursday...so will restrict
the probability of precipitation on Thursday to the southern zones...closed to prognosticated
Will bring chance probability of precipitation back into the area by Friday as models
suggest another upper wave may eject out of The Rockies trough
towards the local area.
Based on prognosticated low level thicknesses...the GFS MOS temperature
guidance looks reasonable for the most part...with the exception of
the lows Wednesday night...which look too cool. Will raise the
guidance 3-5 degrees in that period.
Long term /Friday night through Tuesday/...
Issued at 221 PM EDT Tuesday may 26 2015
The period will begin with a surface low pressure system located
over eastern Canada with a trailing cold front extending from the
upper Midwest and southwestward. This cold front will sweep across
central Indiana Saturday afternoon...causing temperatures to drop
below normal Saturday night through Sunday night before rebounding
back to near normal to close out the period.
Rain shower and thunderstorm chances ahead of the cold front will
turn into likely chances as the front approaches and passes. Then a
slow moving upper level disturbance will approach the five state
region beginning Sunday morning...prolonging the unsettled pattern
through the end of the period.
Aviation /discussion for the 27/0600z tafs/...
Issued at 1240 am EDT Wednesday may 27 2015
Southwesterly flow at low/middle levels is expected to bring an area of
thunderstorms in the vicinity into central Indiana after 12-15z ahead of a cold front that
will be moving in from the northwest. VFR conditions expected with
the exception around vicinity thunderstorms where conditions could
drop to MVFR.
High pressure will build in behind the front Wednesday evening
clearing skies temporarily. Looks like with clear skies and very
light winds...some light fog is expected early Thursday morning.
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