Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Indianapolis in
1009 PM EST Tuesday Jan 27 2015
The near term section has been updated below.
issued at 213 PM EST Tuesday Jan 27 2015
Two separate systems will bring precipitation chances to central
Indiana over the forecast period. The first low pressure system
will result in primarily rain from Wednesday night through
Thursday afternoon before changing to a rain/snow mix early
Thursday evening. After dry conditions on Friday and
Saturday...the second system will track from the lower Mississippi
Valley through the Tennessee Valley on Sunday...bringing snow
chances to the northern portions of central Indiana and a
rain/snow mix to the southern half.
Near term /tonight/...
issued at 1009 PM EST Tuesday Jan 27 2015
No significant changes required as going forecast is in excellent
shape. Did make some tweaks to sky grids for latest satellite trends
but otherwise grids look good. Previous discussion follows.
Issued at 213 PM EST Tuesday Jan 27 2015
Benign weather can be expected across central Indiana tonight with
high pressure in place over the Great Lakes region. Meanwhile...winds
will take on an easterly component as a strong system continues to
work its way up the East Coast.
Strong radiational cooling should take place tonight as clouds
scatter. Overnight lows will dip into the teens over the majority
of the forecast area...except the southwest counties which will be
in the low 20s. As a result...trended toward the slightly cooler
Short term /tomorrow through Friday/...
issued at 213 PM EST Tuesday Jan 27 2015
The main focus of the short term period is precipitation in
association with a low pressure system prognosticated for Wednesday
Ridge of high pressure will result in dry conditions for tomorrow
through most of Wednesday. However...models show ridge breaking
down by Wednesday afternoon as an upper level low approaches from
the upper Midwest. NAM/GFS/Euro are all in agreement with first
wave of energy impacting the northwest portions of central Indiana
around Thursday 09z. Isentropic lift really starts strengthening after
Thursday 12z...making the Thursday 12-18z time frame the best for
precipitation chances. Forecast soundings are above freezing
during that time though...so will go with an all rain forecast.
Cooler air will start filtering in late Thursday afternoon...so
rain will transition to a rain/snow mix over the northern two-
thirds of central Indiana around Thursday 21z. By the time the coldest
air is in place and all precipitation is transitioned to
snow...most of the moisture and best dynamics will be out of the
area. As a result...expect little snow accumulation.
Snow should be out of the area by Thursday night as subsidence
strengthens over the Midwest. Expect dry conditions on Friday.
Temperatures...generally stuck close to a model blend due to the good
model consistency with aforementioned system. Temperatures will be at or
slightly above normal tomorrow and Thursday...then dropping to
slightly below normal late in the period as colder air filters in
on back side of system.
Long term /Friday night through Tuesday/...
issued at 300 am EST Tuesday Jan 27 2015
A northwest flow aloft and a strong Canadian high will ensure a cold
start to the long term. High pressure will be across Ohio Friday
night. Then models swing an upper trough into our region by Sunday.
Both the Canadian and new European model track a surface low across
Kentucky...while the GFS takes a weaker surface low over northern
Indiana on Sunday. Low level thickness from all the models indicate
mixed precipitation is possible across our south...while mostly snow
falls elsewhere. The new European is the wettest as it forecasts
over a half a foot of snow across north and central portions Sunday.
All of this snow will move out by Monday. Tuesday will be
dry...then another weak disturbance will move our way by the middle
of next week.
Undercut MOS temperatures a little Friday night across our northeast
as mostly clear skies there will allow good radiational cooling.
Also cut temperatures a little central and north Sunday on. The
main reason is that all models except for the GFS track the surface
low to our south Sunday and the European brings 850 mb temperatures
as cold as -18 into our northern sections early next week and there
will likely be snow cover in this region as well.
Aviation /discussion for the 280300z kind taf update/...
issued at 922 PM EST Tuesday Jan 27 2015
No significant changes made to the forecast at this time. Previous
Satellite loop indicates the back edge of the MVFR ceilings around
015 progressing to the south. Lower ceilings should clear out of
khuf/kbmg by issuance time.
Still some higher dewpoints lingering in the khuf/kbmg areas...which
is causing some concern for visibility restrictions in fog to
develop later tonight. Short term model guidance and northerly low
level flow suggests dewpoints will fall off in these areas over the
next few hours...so will not include in the forecast at this time
and monitor the trends after dark.
Light surface winds generally at or below 6 kts tonight.
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