Scientific Forecaster Discussion
Area forecast discussion
National Weather Service northern Indiana
110 PM EST Tuesday Mar 3 2015
issued at 1038 am EST Tuesday Mar 3 2015
Areas of freezing rain and sleet will changeover to light rain and
drizzle this afternoon and evening in advance of a cold front.
Light ice accumulations will create slick spots on untreated
roads and sidewalks into the early afternoon. Temperatures by late
this afternoon and evening should recover into the middle to upper
30s before falling back into the upper teens and 20s later
tonight into Wednesday behind a cold front.
issued at 1120 am EST Tuesday Mar 3 2015
3 hour extension of advisory primarily for freezing rain persisting
across far northern/northeast County Warning Area. Shallow inversion affording
slower recession across deeper snowpack/more deeply rooted
antecedent Arctic airmass. However...with early March sun peaking
hir altitudes...expect eventual mixout across entire County Warning Area to at or above fzg.
Mar 3 peak solar altitude at kasw for example is 42 degrees which
should also afford rapid improvement of even untreated sfcs in all
but insolation sheltered locales.
Short term...(today and tonight)
issued at 438 am EST Tuesday Mar 3 2015
Radar mosaic early this morning showing increasing returns just
upstream and surface observation indicate lower levels slowly saturating with
mixed precipitation types being reported at observing sites across Illinois and Iowa
as expected. Forecast remains on track though did remove the
inexplicable anomalous rain showers from grids and forecast this
morning where surface temperatures in the middle 20s.
Preference this morning for thermal profiles lies with nam12 and
hires RUC guidance which are both similar through the morning. Only
real issue is with surface temperatures at initialization through about 14z.
All hires guidance has been too cold with falling temperatures early this
morning...seemingly trying to follow some type of climatology based
diurnal curve. Surface observation across the region show steady or slowly
rising temperatures with warm air advection offsetting evap cooling
processes. While temperatures my drop a degree or two...not expecting a 3
to 5 degree drop before rising as most guidance has been showing.
Thus had to manually edit hourly temperature grids through 13z before
model trends seem to latch onto actual warming.
Powt process once again used for weather grid output today using
ruc13 and nam12 as base grids. Results generally as we have been
expecting with a mix of freezing rain...snow and sleet early in the
south and west and light snow initially north and east with a chance
for sleet. As mentioned...did remove rain showers for this morning
where temperatures were below 32f. Transition zone will slowly move from
south to north this morning as precipitation becomes freezing rain all areas
for a few hours. Hires guidance does show a break in precipitation middle to
late morning before secondary batch moves in this afternoon.
Confidence low in trying to time this out but is Worth noting as
radar mosaic shows a weak dry slot but this could easily fill in
Surface temperatures prognosticated to warm near or just above freezing all areas by
early afternoon so rain should be predominant after 18z to 19z.
However...we continue to worry about actual surface temperatures possibly
lagging 2m measured air temperatures by a few hours due to how cold we have
been and frozen ground down to around 10 inches. This is an unknown
factor and one that is nearly impossible to forecast. Thus this
could keep some secondary and less traveled roads icy well into the
afternoon...especially north and east. Ice accumulations still look
to be around a tenth of an inch and no more than 0.15. Snow accums
down a bit in the north with an inch still possible and isolated 2
inches not out of question. These amounts can still vary depending
on exact timing of changeover at different locations. Still well
within going advisory which will continue.
Models have continued to back off on quantitative precipitation forecast totals with this entire
event over our area. Impressive sub tropical moisture plume seen on
water vapor will be taken south and be responsible for impressive
winter storm over the lower Ohio Valley region. Dry slot may work into
our area quicker late this afternoon and evening as system to our
south gets going and steals northward moisture transport. Left
chance probability of precipitation in across central and northwest this evening with low
end likely far southeast. Should be light rain initially with any
precipitation changing to light snow as colder air works in. There is a small
chance for freezing drizzle tonight with drying aloft and
diminishing ice. However...chances look small and will defer to day
shift to evaluate precipitation trends going into the evening.
Long term...(wednesday through monday)
issued at 438 am EST Tuesday Mar 3 2015
Strong cold air advection will be underway Wednesday...helping to
keep temperatures close to 20 degrees below normal. Lake Michigan
has opened up some...with most of the ice on the east side of the
lake per visible satellite from yesterday. Although Delta T values
will be favorable for lake effect snow...low inversion heights
should keep snow amounts light. Kept a chance for lake effect snow
showers over far SW lower Michigan into northern Indiana from
Wednesday through Thursday before inversion heights become too low
to support snow showers. The next system could spread some light
snow on the southeast fringe of the forecast area from Marion to
Lima. Both the NAM and the GFS have trended northwest with this
system. Sufficient isentropic lift for snow still appears marginal
given questionable saturation in the middle levels. Introduced a chance
for snow Thursday night. Otherwise...another round of bitterly cold
air to invade the area yet again. Went above the GFS/mex 13f and the
European model (ecmwf) 14f highs Thursday. Models have been too cold with high
temperatures with clear to partly cloudy skies recently in Arctic
airmasses. So kept highs around 16f Thursday...which would be the
coldest high at feet Wayne for the date.
Aviation...(for the 18z tafs through 18z Wednesday afternoon)
issued at 109 PM EST Tuesday Mar 3 2015
Ample afternoon sun angle and warm air advection should allow ptype to
change to all liquid by 19 UTC at kfwa. Continued moisture flux from
slow melting snowpack and top/down saturation to likely lend long
duration IFR ceilings across northern Indiana through at least middle.Late
eavening. Frontal boundary crtnly across WI into far eastern Iowa to push
eastward through region in 01-03 UTC timeframe and should lead to
mixout inversion trapped moisture for improved visibilities/ceilings through
remainder of forecast period.
in...Winter Weather Advisory until 1 PM EST /noon CST/ this afternoon
Winter Weather Advisory until 4 PM EST this afternoon for inz006-
Michigan...Winter Weather Advisory until 1 PM EST this afternoon for miz077.
Winter Weather Advisory until 4 PM EST this afternoon for
Ohio...Winter Weather Advisory until 1 PM EST this afternoon for ohz004-
Winter Weather Advisory until 4 PM EST this afternoon for ohz001-
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