Scientific Forecaster Discussion
Area forecast discussion
National Weather Service northern Indiana
1023 am EDT Friday Oct 31 2014
issued at 510 am EDT Friday Oct 31 2014
A strong storm system across the northern Great Lakes will drop
into the region on today...bringing rain showers along with windy
and colder conditions. As colder air filters into the area
today...some snow is also possible...but little or no snow
accumulation is expected except downstream of Lake Michigan where
1 to 2 inches of snow are possible where a single band sets up.
Snow showers are expected to diminish Friday night as the storm
system pulls off to the east...but unseasonably cool conditions
will persist into the weekend.
issued at 1009 am EDT Friday Oct 31 2014
Area of frontally forced rain showers has filled in across much of
the forecast area this morning. Rainfall rates have generally been
light...in the 0.03-0.08 inch per hour range. Attention for late
this morning through middle afternoon will be second surface trough/cool
front now beginning to work across Southern Lake Michigan. This
surface trough is accompanied by a more pronounced area of surface
pressure rises with wind gusts increasing to 30 to 40 miles per hour
immediately behind this trough. An enhanced area of reflectivity
is noted per radar imagery west of Muskegon at 14z and will be
dropping into far Northwest Indiana toward midday. Precipitation types
will continue to be very challenging through middle afternoon.
Trajectories are still supportive of long residence times over the
lake...with a good deal of boundary layer modification that would
tend to keep low level wet bulbs above freezing supporting mainly
rain. However...continued background low level cold advection and
an increasingly convective nature to precipitation induced by Lake
Michigan modification would be more supportive of snow. Difficult
at this time to make many changes to going forecast with
categorical rain/snow showers this afternoon across the entire
area. Only minor tweak to snow accums this afternoon was to extend
lake effect accumulations eastward a bit as may see the aforementioned
enhanced area of reflectivity curve back southeastward late this
morning in vicinity of low level trough. Will stay with around 1
inch accumulations in association with lake effect/enhanced precipitation
through the remainder of the day...but will need to monitor for
potential of localized higher amounts due to increasing lake
induced instability and localized nature of ptype tendencies. Wind
Advisory headlines will also remain intact...although stronger
gusts may be slightly delayed than headline timing...and follow
the passage of the secondary surface trough.
Short term...(today and tonight)
issued at 501 am EDT Friday Oct 31 2014
A surface low was over Northern Lake Huron early this morning
with a strong cold front extending southwest across lower Michigan
into extreme northern Illinois. Rain was changing to snow farther
northwest behind the front over central Wisconsin where the cold air
was deeper and thermal profiles supported all snow. A very tight
pressure gradient will be over the area this afternoon...with windy
conditions developing. The ongoing timing and location of the Wind
Advisory that was issued earlier appears to be on track and in good
shape...no changes made. Precipitation is expected to develop
rapidly today and spread southeast as the front moves southeast. An
upper level system over Wisconsin will move southeast later today
and continue to help provide a chance for precipitation. Have added
a mention of sleet along with thunder today down stream of Lake
Michigan with wet bulb zero heights hardly off the ground with
extremely cold air aloft. Concern for a faster changeover to
rain/snow or just snow with very cold air in the middle levels...-16c
at 700 mb by late morning with nearly the entire profile below
freezing. The dendritic growth zone was also very favorable for snow
growth in the cloud layer from late morning through the
afternoon...so there may be an even faster changeover from rain to
snow. Kept the mention of accumulating snow over far west areas from
LaPorte County south as a single snow band is likely to develop
along the long axis of Lake Michigan with snowfall amounts up to an
inch possible over western LaPorte County.
Long term...(saturday through thursday)
issued at 501 am EDT Friday Oct 31 2014
Strong shortwave dropping southeast across northern WI this morning will round base
of eastern Continental U.S. Longwave Saturday morning with deepening surface low moving
north-northeast off the NE U.S. Coast the remainder of the weekend. Strong ridge
behind this system will build into our area Saturday. Lingering low
clouds eastern portions of the County Warning Area should gradually dissipate during the
day. Thermal trough over our area in the morning should slide to the
east during the day...but linger long enough to keep temperatures much below
normal with highs only in the u30s/l40s. Surface high expected to move
across the area Sat night resulting in dry airmass... mostly clear
skies... and light winds. These good radiational cooling conditions
should allow temperatures to fall into the m20s over all of the County Warning Area. Latest
MOS guidance a little cooler than previous forecast and did lower mins
slightly but models suggest some low clouds may linger over far western
and eastern portion of County Warning Area for part of the night and a weak vorticity lobe
topping upper ridge over plains may spread some high clouds in late...
so generally stayed on high end of MOS envelope. Southwesterly low level flow
will develop Sunday as surface high moves southeast across the Ohio Valley.
Models continue to suggest considerable middle level moisture will
overspread the area in the afternoon which combined with cold start to
the day will limit the warmup with highs only expected in the
M-u40s. Warm air advection will continue Sunday night with some lingering middle clouds.
Going mins in M-u30s a little above latest MOS guidance but seem
reasonable given expected mixing/cloudiness.
For the extended forecast... upper flow expected to deamplify Monday-Tuesday as
deep trough currently over eastern Pacific moves east across the
plains/upper Great Lakes and becomes increasingly positively tilted and
fractured with cut-off low eventually forming along southwestern U.S./Nwrn
Mexico border by Wednesday. Couple of days of S-SW flow over the Southern
Plains/lower MS valley behind strong departing surface high and ahead of
approaching trough/cold front should allow a fairly substantial plume of Gulf
moisture to advect across our area with precipitation water>1" and surface
dewpoints in the l50s Tuesday. This moist airmass should compensate for
rather weak forcing along trough/cold front supporting likely shower forecast as
it moves slowly east across the County Warning Area around Tuesday. Fast moving shortwave
expected to move east-southeast from southwestern Canada through the Great Lakes Thursday
amplifying the flow a bit. Models have timing/strength differences
but some potential still for light showers in our area with this
system and in its wake with possible lake effect. Temperatures should be a bit
above normal through this period with highs in the 50s and lows in
Aviation...(for the 12z tafs through 12z Saturday morning)
issued at 655 am EDT Friday Oct 31 2014
Strong shortwave dropping southeast across WI this morning resulting in an
area of rain with MVFR conditions over northern Indiana/lower Michigan changing
to snow over southeastern WI. This change in precipitation type should spread southeast
across northern Indiana late this morning and this afternoon. Flying
conditions should be predominantly MVFR with some brief IFR possible
during periods of snow. Northwest-north winds will be very strong today with
gusts over 30kts. Winds will gradually diminish tonight with skies
clearing at ksbn as high pressure builds into the area... although
MVFR conditions will likely persist at kfwa until around 12z.
in...Wind Advisory until 10 PM CDT this evening for inz003.
Lakeshore Flood Advisory until 4 am CDT Saturday for inz003.
Wind Advisory until 8 PM EDT /7 PM CDT/ this evening for inz004-
Michigan...Wind Advisory until 11 PM EDT this evening for miz077.
Lakeshore Flood Advisory until 5 am EDT Saturday for miz077.
Wind Advisory until 8 PM EDT this evening for miz078-079.
Lm...Storm Warning until 8 PM EDT this evening for lmz046.
Gale Warning from 8 PM this evening to 5 am EDT Saturday for
Gale Warning until 5 am EDT Saturday for lmz043.
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