Scientific Forecaster Discussion
Area forecast discussion
National Weather Service northern Indiana
327 PM EST Thursday Dec 12 2013
issued at 330 PM EST Thursday Dec 12 2013
High pressure will be over the region tonight but temperatures
will not be as cold as last night. Lows will still drop into the
lower and middle teens...with a few single digits possible in
rural areas. Clouds will increase Friday ahead of a strong low
pressure system which will bring accumulating snow to the region
Friday night and Saturday. Current indications are that
accumulations between 2 and 5 inches will be likely.
Short term...(this evening through friday)
issued at 323 PM EST Thursday Dec 12 2013
Few concerns through the short term period as significant weather
ahead of next system will hold off until Friday night.
Satellite showing middle and high clouds exiting southern areas this
afternoon while thermal trough sagging across Lake Michigan was
aiding in stratocu development across Berrien and Cass counties in
Michigan. These low clouds and any lake effect snow showers will be
main challenge tonight. Synoptic scale thermal trough already moving
east but lake induced troughiness and thermal disparity prognosticated to
only slowly warm overnight. Satellite already showing lake clouds
into northern Berrien County despite warm air advection. Hires
guidance suggest trajectories and weak lake aggregate trough may
allow clouds to stream across Michigan counties this evening and
into overnight hours. Previous sky cover grids had this trend
handled well and generally stayed with similar idea. Light snow
showers already near or into extreme northern tip of Berrien County
so will carry scattered flurries or light snow showers through the evening
until warmer air arrives and flow weakens which could lead to weak
mesolow formation over bowl region of Lake. Little or no
accumulation expected given shallow moisture depth in our area.
Otherwise expect mostly clear skies to start the evening with some
middle and high clouds increasing late.
NAM model soundings quite bullish on low level moisture and stratus
development Friday morning. Nam12 has been rather
aggressive with this idea this winter with several instances showing
this with little to no development. Latest hrrr gives some credence
to this solution in the north near weak surface boundary where winds
become light. Have slowly increased clouds across the north
and northwest with potential for some middle and high clouds as well.
This should keep temperatures from falling too much overnight with warm air
advection well underway. Looking for lows in the 10 to 15 degree
range late evening with steady or even slowly rising temperatures late with
any cloud cover development.
Col area associated with weak boundary will lie across northwest forecast
area Friday with generally light winds. Cloud cover remains tricky
depending on how much saturation occurs near boundary with inversion
aloft courtesy of warm air advection. Highs will reach middle to upper
20s most areas with low 30s possible far southwest ahead of next
strong short wave. Bulk of precipitation will hold off until Friday evening
but did allow a slight chance to reside far southwest after 21z with
proximity of increasing moisture and isentropic lift.
Long term...(friday night through thursday)
issued at 323 PM EST Thursday Dec 12 2013
..accumulating snowfall Friday night-Saturday...
Pattern is still supportive of favorable synoptic scale snow event
for the region beginning late Friday night and continuing into the
Northern stream flow will keep the boundary layer cold air in place
and deep enough to favor all snow for the event. The challenge will
be timing the phasing of the southern stream and northern stream
shortwaves across the Great Lakes.
12z runs are generally consistent with the surface low deepening in
the Panhandle region during the day Friday. Continued deepening and
of the surface low over the soruthern plains and lower Mississippi
River valley during the evening Friday into Saturday will usher in
copious moisture and expect to see a pronounced warm layer spreading
northward. This will favor a more dense and wet snow across the
Timing and phasing of the southern and northern stream will
critically affect the durartion of the snow and expect that there
will be a rapid cutoff of precipitation early Saturday.
Snowfall will be heaviest and wetter south of the County warning forecast area and drier
north. Regardless expect to see upwards of 5 inches across most of
As the synoptic driven snow ends...lake effect should continue in
LaPorte...St. Joseph...Berrien and Cass counties for an additional 2
to 4 inches by Saturday night early Sunday morning.
Colder and drier air will settle across the plains Sunday and with
new snow and some clearing...temperatures should bottom out again
Sunday night/Monday morning. Will be making some downward
adjustments to the temperatures for sun/Monday period.
Next clipper system forms in the Great Lakes region monnday/Monday
night/Tuesday and this will bring an increase of clouds and lake
effect to the area. Timing and duration of snowfall is too far out
to make definitive amount forecasts...but it will add to the snow
already on the ground. As that system exits...the cold air returns
in its wake. Starting to see a decent snow pack over the northern
plains...adding to the doubt that any sizable warmup is coming our
Next story on the horizon...European model (ecmwf) prediction of deep and explosive
cyclogensis across the northern and Central Plains Wednesday night
into Thursday. There are hints in the other long range models of a
wave ejecting through The Rockies. This will have to be watched as
the pattern evolves.
Aviation...(for the 18z tafs through 18z Friday afternoon)
issued at 1247 PM EST Thursday Dec 12 2013
VFR conditions to start the period with some uncertainty
regarding ceilings tonight and Friday morning. Middle and high clouds
gradually moving off to southeast with partial clearing occuring
at taf sites early this afternoon. Lake clouds seen on satellite
dropping south toward kbeh at 1730z within thermal trough. This
trough not prognosticated to reach ksbn as it slowly migrates east.
However...low level wind field becomes west-northwest for a period which may
allow clouds to drift toward ksbn. Model soundings also showing
increasing low level moisture around 00z with these trajectories.
For now do not have enough confidence for MVFR or IFR conditions
at ksbn overnight so stayed VFR with introduction of some sct015
clouds. Weak frontal boundary to sag near ksbn Friday am with weak
winds and moisture trapped beneath inversion with warm air
advection aloft. This leads to a little higher confidence in MVFR
ceilings developing during the day along with model guidance so added
MVFR conditions. Kfwa to remain VFR through this period with
deteriorating conditions expected later Friday and especially
Friday night all areas with snow developing.
Lm...Small Craft Advisory until 7 PM EST this evening for lmz043-046.
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