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fxus63 kind 112018 
afdind

Area forecast discussion
National Weather Service Indianapolis in
318 PM EST Mon Nov 11 2019

Update...
the aviation section has been updated below.

&&

Synopsis...
issued at 345 am EST Mon Nov 11 2019

The first accumulating snowfall of the season will impact central
Indiana later today and tonight as a much colder airmass overspreads
the region behind a frontal boundary. Snow will end tonight with the
coldest air of the season so far expected through midweek. Dry and
progressively warmer temperatures come for the second half of the
week with temperatures returning to near normal levels by late
weekend.

&&

Near term /rest of today and tonight/...
issued at 955 am EST Mon Nov 11 2019

The surface low went a little farther north than expected, so
temperatures are running warmer. Have upped temperatures based on
this and updated hourly forecasts with latest trends and model data.
This ends up slowing the transition to all snow a little. This may
lower snow totals a bit, but didn't make major changes to snow
amounts as frontogenetical forcing may make snow briefly heavy
enough to make up the difference. Will continue to monitor closely.

Previous discussion follows...

Clouds continue to press south through central Indiana early this
morning in the wake of a cold front that has shifted into southern
Indiana. Steadier precipitation remains near the Great Lakes
currently in closer proximity to an 850mb front. 08z temperatures
ranged from the upper 30s to the mid 40s.

Focus for today is on the growing potential for the first widespread
snow accumulation for central Indiana and the impacts that will come
along with it. Quiet conditions persist across the forecast area but
beginning to see light precip in the form of rain break out over the
mid Mississippi Valley as moisture is drawn northeast out of the
Southern Plains. Cams have been advertising further expansion of the
light rain over the next few hours into our forecast area and will
introduce chance pops accordingly through daybreak. Any amounts will
be minimal at just a hundredth or two at best. Meanwhile...the axis
of wintry precipitation anchored to our north over the Great Lakes
will pivot into the region through the morning as the 850mb front
drops south. Initially...precipitation will fall as rain but as the
boundary layer cools in response to the deep baroclinic zone diving
into the region...expect a brief axis of mixing with snowflakes
before snow becomes the dominant precip type...commencing later this
morning over northern counties and then shifting south to the I-70
corridor by early afternoon.

The 6-8 hour window from about 18-19z through the first half of the
evening will provide the first snow of the season for the entire
forecast area as boundary layer temps crash and precipitation fully
changes over to snow from northwest to southeast. An axis of low
level convergence and increasing frontogenesis in the 850 to 700mb
layer will accompany the snow band as it tracks southeast through
the afternoon and evening...likely bringing a period with higher and
more impactful snowfall rates that will allow for some accumulation
even as ground and surface temps lag the changeover to snow by a few
hours. Conditions will deteriorate by late afternoon into the
evening as surface temps fall below freezing with potential for
travel difficulties to develop.

The back edge of the steadier snow will track through the forecast
area during the evening with just flurries and scattered lake
induced snow showers left in its wake by late evening into the
overnight. That being said...expect the damage will be done to roads
with a flash freezing component coming into play as well overnight
as temperatures tumble through the 20s and into the teens. Expect 2-
3 inches of snow across much of the forecast area by late tonight
with locally higher amounts focused generally northeast of the indy
Metro.

Have decided to expand the Winter Weather Advisory to encompass the
entire forecast area for a few reasons. Besides bumping up snowfall
totals...feel a headline is warranted to highlight the first
impactful snowfall of the season which is coming earlier than usual.
In addition...the greatest travel impacts from the snow are likely
to coincide with the evening rush hour. Have adjusted the start time
to 18z over the northern half of the forecast area with a 21z start
time further south. Considering the flash freeze potential
overnight...will carry the advisory out through daybreak Tuesday.

Temps...highs ranging from the upper 30s to the mid 40s should be
reached in most areas by midday with falling temps through the
afternoon. Utilized an overall model blend tonight with lows in the
teens.

Potential indy records in jeopardy...
11/12 low: 14 (1911)

&&

Short term /Tuesday through Wednesday night/...
issued at 345 am EST Mon Nov 11 2019

Forecast challenges focus primarily on temperatures through the
period as the coldest weather of the season so far settles over the
Ohio Valley.

May still be a few snow showers and or flurries ongoing over far
eastern counties Tuesday morning with the continuation of a
favorable northwest fetch off Lake Michigan. Low level winds will be
weakening however and with slight backing of the winds by midday
Tuesday...any lingering snow showers will diminish.

Focus then shifts to the unseasonably cold Arctic airmass across the
region with a large deep high pressure ridge building across the
area. Skies will clear rapidly from west to east Tuesday morning
with deep subsidence overspreading the Ohio Valley through early
Wednesday. Mid level clouds will increase from the northwest on
Wednesday as a quick moving clipper-like system tracks across the
northern plains and upper Midwest and then into the Great Lakes
Wednesday night. Model soundings and relative humidity progs show that the dry
airmass through the boundary layer will be stubborn to depart and
with forcing aloft associated with the clipper remaining well north
of the forecast area...do not anticipate any impacts from
precipitation Wednesday night. While surface flow will swing around
to southerly...a sharpening pressure gradient ahead of the system
will bring an increase in wind gusts Wednesday afternoon when
combined with the clouds will make for another chilly day.

Temps...exceptional cold expected through the short term with the
potential for daytime highs to be 30 degrees below normal Tuesday
and only marginally warmer Wednesday. Trended towards warmer metmos
for highs Tuesday which still keeps much of the area in the mid 20s.
Think the record low Max for indy Tuesday is in trouble. Leaned
towards cooler mavmos Wednesday with the clouds as highs should rise
into the lower to mid 30s. Lows will be in the teens Tuesday night
with a recovery into the 20s Wednesday night.

Potential indy records in jeopardy...
11/12 low maximum: 26 (1920)
11/13 low: 10 (1986)

&&



Long term (wednesday night through monday)...
issued at 216 PM EST Mon Nov 11 2019

Models are close enough that the National blend of models
initialization was accepted for most items.

An upper trough will bring some forcing to the area Wednesday night
into Thursday. Best forcing will be north of central Indiana.
Moisture also looks relatively low, with deeper moisture confined to
a southern USA system.

There remains some timing differences in the models with this
system as well. Given the uncertainties with the system, won't
change the intialization's pops of only slight chance across the
extreme north Wednesday night.

Otherwise high pressure should then provide dry conditions through
the weekend. Another upper trough could bring some light rain later
on Monday.

Temperatures will continue to slowly moderate into early next week,
but readings will remain below normal.

&&

Aviation (discussion for the 112100z taf update)...
issued at 318 PM EST Mon Nov 11 2019

Added a tempo lower visibility group based on current conditions and
upstream observations. Precipitation will be all snow now at kind.

Previous discussion follows...

Poor flying conditions expected through much of the first half of
the taf period, then a return to VFR.

Precipitation will continue to increase in coverage early in the
period and will change from rain to snow (from northwest to
southeast) during the first few hours of the taf. IFR or lower
conditions are expected, with brief bursts of heavier snow not out
of the question.

Snow will end from northwest to southeast this evening as much
colder air moves into the area. The drier air will allow clouds to
scatter and for VFR conditions to return overnight. Lake effect snow
bands should remain just east of the taf sites.

Winds will become gusty this afternoon with gusts over 20kt likely.

&&

Ind watches/warnings/advisories...

Winter Weather Advisory from 4 PM this afternoon to 8 am EST
Tuesday for inz051>057-060>065-067>072.

Winter Weather Advisory through 8 am EST Tuesday for
inz021-028>031-035>049.

&&

$$

Synopsis...Ryan

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