Scientific Forecaster Discussion
fxus63 kind 171929
Area forecast discussion
National Weather Service Indianapolis in
229 PM EST sun Dec 17 2017
the long term section has been updated below.
issued at 310 am EST sun Dec 17 2017
Mid/upper level trough over the arklatex region on recent
satellite imagery is moving slowly northeast this morning toward
the lower Ohio Valley region. Surface analysis shows a
quasistationary frontal boundary lying east-west across northern in.
Near term /this afternoon/...
Issued at 1000 am EST sun Dec 17 2017
Surface analysis late this morning shows a warm front stretching
across northern Indiana...ahead of low pressure over Iowa. Radar
shows an area of rain fall in the wake of the warm front over SW
Indiana...pushing northeast within the flow. These light rain
showers are expected to push across central Indiana over the next
2-4 hours...producing minimal rainfall amounts. Hrrr also
suggests this propagation. Time heights reveals good moisture and
lift passing across the area near 18z. Thus have fine tuned the
pops a bit to account for rain showers over this time period.
As for temperatures...trended slightly cooler than the previous
forecast with expected clouds and rain through the
afternoon...particularly across the Wabash valley and points
southwest of Indianapolis where the previous forecast appears too
Short term /tonight through Tuesday/...
Issued at 310 am EST sun Dec 17 2017
As weakening low pressure moves across southern in then off to the
east, low clouds and some light rain/drizzle should remain
from cooler air circulating around the backside of the low. Given
the rain producing wet ground and low clouds with light winds,
have collaborated with keeping low clouds, drizzle and fog across
the region for tonight into early Monday morning. Would expect the
possibility of some dense fog especially across urban areas where
the wet comparatively warmer ground is covered by the cooler air
on the backside of the surface system/trough in low levels. This
may impact morning commute on Monday morning before skies
gradually clear by afternoon.
Area will be between systems going into Tuesday as a strong
frontal boundary will be across the Great Lakes westward over
southern WI/northern IL, and a shortwave trough moving in the
southern branch over south central Texas. Southwest surface flow
over the Southern Plains is forecast over are area providing some
clouds but temperatures in the low-mid 50s for Tuesday providing
the best day in the week before the cooler air to the north drops
into the area.
Long term /Wednesday night through Sunday/...
Issued at 229 PM EST sun Dec 17 2017
European model (ecmwf) suggests a warmer than normal pattern during this time
period. A weak ridge of high pressure is expected to develop on
Thursday as a low pressure system exits the Tennessee River
valley. This will keep dry and mild weather across central Indiana
through Thursday. As warm and relatively moist air arrives in the
area ahead of a frontal boundary on Thursday night...superblend
begins to insert pops. This seems overdone as forcing aloft and in
the lower levels is limited. Confidence is low for precip here.
Better chances for precip will be on Friday afternoon through
Saturday morning as a strong cold front works across the states.
Here...better dynamics are in place aloft along with the surface
front. Thus during the Friday and Friday night time
frame...confidence for showers and storms is much higher.
A SW flow aloft is suggested by the European model (ecmwf) to develop by Friday
ahead of a broad trough over the the western United States. This
SW flow will remain in place through next weekend...keeping polar
air at Bay to the north and result in above normal temperatures.
Aviation /discussion for the 171800z tafs/...
Issued at 1255 PM EST sun Dec 17 2017
VFR conditions are expected this afternoon. Overnight...a
deterioration to MVFR and then IFR is expected.
Radar shows rain showers associated with a warm front passing
across the Indianapolis area. These will lift to the north by late
this afternoon. Time heights show best moisture and forcing
leaving the area by this afternoon. However the warm and
relatively moist southwest flow will remain across Indiana and
the Ohio Valley overnight. This will weak flow of warm and moist
air will allow for the development of fog overnight and low
clouds. Forecast soundings and time height sections show saturated
lower levels with minimal forcing aloft through Monday morning.
Thus a trend toward MVFR and IFR will be expected with the
developing inversion overnight.
As heating and mixing resumes on Friday...improvement to MVFR or
better will be expected toward 18z Monday.