Scientific Forecaster Discussion
fxus63 kind 221142
Area forecast discussion
National Weather Service Indianapolis in
642 am EST Fri Nov 22 2019
the aviation section has been updated below.
issued at 351 am EST Fri Nov 22 2019
Cooler than normal temperatures will be the rule through the
beginning of the forecast period, with some off and on chances for
precipitation with weaker systems moving through the area. A
stronger storm system could impact the area Tuesday into
Near term /early this morning and today/...
Issued at 351 am EST Fri Nov 22 2019
Radar loop shows rain showers continuing to move east across
central Indiana, with coverage generally confined to along and
south of I-70. Over the next few hours these will sink southeast
and away from the forecast area, so that by mid morning the entire
area should be dry. Cool dry air will move in from the northwest
as high pressure builds in from that direction, and this should
keep central Indiana dry for the remainder of the day. Cold
advection throughout the day on northwesterly winds though will
keep temperatures from rising very much, and thus looking at highs
only in the low to mid 40s. There is some uncertainty regarding
cloud cover for the day, with several models indicating clearing
from the north as the high builds in, but currently seeing some
low stratus trapped under an inversion upstream. Kept cloud cover
through at least mid morning before bringing in clearing from the
north, and that may be a little optimistic.
Short term /tonight through Sunday night/...
Issued at 351 am EST Fri Nov 22 2019
Forecast focus is on precip potential/timing/type for Saturday. Current
set of operational runs is bringing the high in from the
northwest a little stronger than previous runs, and this is
resulting in slowing the arrival of precip and leaving much of, if
not the entire forecast area dry for tonight. Kept some low
chance pops in the far southwest before 12z Saturday for
Saturday a surface low is progged to move from the Gulf Coast through
Tennessee Valley as an upper trough approaches from the west.
This combination will bring chances for rain, then changing to a
wintry mix and then snow as cold air moves in as the surface low
moves off to the east. An analysis of soundings over the area
shows the potential for a rain changing to snow mix, but not
seeing a profile that's conducive to freezing rain so took out any
mention for now.
Early Saturday night could see some potential for a little
wraparound snow as the system departs. This will heavily depend
on how quickly the low moves off to the east, but for now at least
a couple of solutions keep the low close enough to merit a snow
mention for eastern parts of the area early Saturday night. On
Sunday, though, an upper ridge will swing through the area
bringing with it dry weather. At this time doesn't look like much
more than a trace, but will continue to monitor. Highs Saturday
may not climb higher than the lower 40s, with Sunday rebounding a
little into the middle 40s.
Long term /Monday through Thursday/...
Issued at 258 am EST Fri Nov 22 2019
Primary focus in long term remains on possible storm system
Tuesday and Tuesday night followed by low pcpn chances around
Models continue to have differences with potent short wave
advertised for Tue into Tue night. 00z trends have moved toward
farther northwest track and a more open wave taking on a negative
tilt as it approaches the Great Lakes. Expect further refinement
and changes to timing/strength/track next few days so will
continue with high chance pops for rain across our area. If we
stay in warm sector would likely see chances for thunderstorms
given dynamics and moisture flux in the warm sector. A lot to
watch for sure.
High pressure builds in behind this system for Wednesday and
likely into Thursday. Nbm kicked out rather high pops for
Thanksgiving day and night. Spectral deterministic models show
little in way of any forcing or pcpn during this period but
ensemble spread quite large with some higher quantitative precipitation forecast totals which led
to increased pops. Confidence quite low but difficult to
collaborate removal of pops so allowed a low chance for the
afternoon and night periods on Thanksgiving.
Aviation /discussion for the 221200z taf issuance/...
Issued at 636 am EST Fri Nov 22 2019
Satellite and surface obs show quite a large area of MVFR cigs
extending well to the west and northwest trapped under strong
inversion. Higher cirrus streaming overtop will initially limit
any mixing from weak November sun. Hires guidance keeps trying to
dissipate upstream cloud cover shortly after each initialization
which points to poor handling of cloud cover and inversion. Have
continued to slow clearing and VFR conditions per latest satellite
images. Still stayed optimistic by late morning and early
afternoon with trends toward VFR once cirrus canopy moves off and
stronger subsidence and dry air with high pressure move in. Pcpn
chances ahead of next wave will not increase until after 12z
Saturday and will be VFR initially but expect trends toward MVFR
as day progresses.