Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Indianapolis in
930 am EST Friday Nov 27 2015
the aviation section has been updated below
issued at 239 am EST Friday Nov 27 2015
A front will pass Indiana from the northwest today...then stall a
little to the south of our state. From tonight into Monday the
Hoosier state will stay wedged between the front and high pressure
to our north.
Tuesday and Wednesday low pressure and an associated cold front are
predicted to slowly cross Indiana from the west. A high pressure
system should arrive Thursday.
Near term /today and tonight/...
Issued at 239 am EST Friday Nov 27 2015
All models agree about rain falling over the entire County Warning Area by afternoon
and continuing well into the night. Temperatures are the main
Todays highs will likely be the temperature when rain starts. After
that readings will level off or decline in response to both the rain
and a frontal passage. Using the mav for highs and the superblend
model for timing produces results that look decent based on what is
occurring now. This part of the forecast may need significant
modification with time.
Overnight the guidance lows look OK considering what is upstream.
Short term /Saturday through Sunday night/...
Issued at 239 am EST Friday Nov 27 2015
The main problem is rain chances as a front lingers in the area.
Given where it has the low...the NAM quantitative precipitation forecast fields looks strangely dry
at 12z tomorrow. The GFS is more consistent and the higher mav probability of precipitation
are probably best.
The real uncertainty arrives Saturday night. The models have changed
a lot with every run lately. Given problems coming to a consistent
solution...an an ensemble effect may be best and so a mav met
consensus will be used.
There is significant difference in lows in the northern counties
Saturday night with the mav cooler. This apparently reflects
different handling by the parent models of cooler drier air trying
to infiltrate. That far out its hard to be sure which is right and
a consensus should be the most skillful forecast for now.
Except as mentioned in the previous paragraph statistical guidance
is close for the period and can be used with reasonable confidence.
Long term /Monday through Thursday night/...
Issued at 244 am EST Friday Nov 27 2015
The main focus of the long term period will be rain chances in
association with a potent low pressure system. An upper low will
enter the Central Plains on Monday with a surface low just out
ahead of it. Latest superblend initialization seems to be
handling this system well...highlighting highest rain chances on
Monday and Monday night with passage of cold front. So...will not
deviate from the likely probability of precipitation during that time frame. Precipitation
is still expected to be in the form of rain for the majority of
the event...but there could be a rain/snow mixture Tuesday
night/Wednesday morning across the northern counties when colder
air filters into central Indiana on back side of aforementioned
cold front. High pressure will return on Wednesday...resulting in
dry conditions through the remainder of the extended period.
Aviation /discussion for the 27/1500z taf issuance/...
Issued at 930 am EST Friday Nov 27 2015
Pushed back the timing of MVFR/IFR conditions by a couple of hours.
Previous discussion follows...
Poor flying conditions will prevail for duration of taf period as
a frontal system moves through central Indiana. Rain is currently
beginning to impact taf sites...and conditions are expected to
rapidly deteriorate over the next several hours. MVFR conditions
can be expected by mid-morning...followed by IFR conditions by
late morning. Persistent rain could cause further deterioration to
LIFR category by this afternoon...staying at the IFR/LIFR mark
through the end of the taf period. Meanwhile...winds will start
out southwesterly and gradually veer to the west and finally
north/northeast by this evening. Sustained speeds will range
between 12 to 16 kts with gusts up to 25 kts at times.