Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Indianapolis in
1158 am EST Tuesday Jan 27 2015
aviation section has been updated below.
issued at 323 am EST Tuesday Jan 27 2015
A couple of low pressure systems will bring chances for
precipitation to central Indiana Thursday and again for the second
half of the weekend. For much of the time temperatures will remain
below average...with the coldest air moving in early next week.
Near term /rest of today/...
Issued at 944 am EST Tuesday Jan 27 2015
freezing drizzle and snow has ended across central Indiana. Mostly
cloudy skies should scatter out this afternoon with highs topping
off in the upper 20s to middle 30s from north to south. Current temperatures
across the area are generally in the middle to upper 20s. Updated grids
have been sent.
today the atmosphere will gradually dry out as high pressure
moves in. Looks like some clearing will occur this afternoon from
northeast to southwest. Mav MOS looks a bit warm...especially
northeast where some snow cover exists. Trimmed it back a bit.
Short term.../tonight through Thursday night/
issued at 323 am EST Tuesday Jan 27 2015
Focus is on chances for precipitation with the next system Wednesday
night into Thursday. Models are close enough that a blend was used.
Clouds should diminish enough tonight that with the light winds
expected...there will be decent radiational cooling. Thus went
closer to the colder mav MOS numbers for lows.
Clouds will increase on Wednesday but there will be enough sun to
warm temperatures to within a couple of degrees of mav MOS.
Isentropic lift begins Wednesday night ahead of an approaching low
pressure system. Clouds will increase/thicken during the
evening...and winds will increase out of the south. These will allow
temperatures to rise during the overnight after reaching lows during
the early evening.
The atmosphere will take a while to moisten up Wednesday night so
only went probability of precipitation after 06z. Moisture still is not great so only went
chance probability of precipitation. Temperatures aloft will be warm so precipitation type
will depend on low levels. Looks like temperatures will be warm
enough to just go rain rather than freezing rain.
Continued chance probability of precipitation on Thursday as the system moves through but
moisture still not that impressive. Temperatures aloft will cool
through the afternoon so kept a mix of rain/snow late afternoon.
Kept slight chance probability of precipitation all areas Thursday evening to account for
any lingering precipitation as the system exits. Went slight chance
probability of precipitation all night across the far north to account for the potential of
some lake effect snow showers getting into the area.
Long term /Friday through Monday/...
issued at 300 am EST Tuesday Jan 27 2015
Northwest flow aloft and strong Canadian high pressure will ensure
a cold start to the extended period on Friday in the wake of the
cold frontal passage on Thursday. The high will drift east through
Saturday maintaining dry chilly conditions across central Indiana.
Highs will generally range from the upper 20s to middle 30s both days.
The main focus for the extended period comes during the second
half of the weekend as a strengthening surface wave tracks from
the western Gulf Sunday morning into New England by Monday. Model
guidance has wavered with the handling of this system over the
last few days ranging from a suppressed system tracking through
the southern states to a more phased solution bringing a greater
impact north into the Ohio Valley. 00z guidance in general has
trended back towards the more phased upper wave with a surface
wave tracking through the Tennessee Valley Sunday into Sunday
night and a broad area of overrunning precipitation spreading
across the entire region.
With cold air lingering across central Indiana and the track to
the south of the forecast area...precipitation would likely fall as snow
as it stands now with possibly a brief period of mixed precipitation on
Sunday depending on the amount of warmth in the boundary layer
that can take place. Still several days out and likely to see
additional changes as we near the weekend. One caveat to keep in
mind...model guidance in general has underdone low level warm
intrusions and caused precipitation type challenges across the forecast
area with surface waves all winter long. Not saying this happens
here if the forecast track through the Tennessee and lower Ohio
valleys holds. It is just something to keep in mind as models hone
in on a consensus solution in the coming days. Should things come
together for a predominant snow event...potential is there for a
few inches of accumulation late Saturday night through Sunday
Once the surface wave passes and deepens off the New England coast
Monday...a fresh batch of Arctic air will spill into the region
for early next week. Highs may struggle to get out of the teens
both Monday/Tuesday across northern counties.
Aviation /discussion for 271800z taf issuance/...
issued at 1158 am EST Tuesday Jan 27 2015
MVFR ceilings possible the first few hours...then VFR rest of the
High pressure ridge was over the western Great Lakes while strong
low pressure was moving up the New England coast. This was producing
a light northeast flow across our area and drier air will spread
west across central Indiana. This will cause improving flight
conditions with most clouds clearing by this evening.
The rest of the forecast will be quiet...although MVFR fog is
possible some areas around sunrise Wednesday. Models indicate
scattered middle clouds and scattered to broken high clouds on
Northeast winds less than 8 knots this afternoon will become light
tonight and southeast up to 8 knots Wednesday.
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