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Office: IND

FXUS63 KIND 151508
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1008 AM EST Fri Dec 15 2017

.UPDATE...
The NEAR TERM and AVIATION Sections has been updated below.

&&

.SYNOPSIS...
Issued at 243 AM EST Fri Dec 15 2017

This period we will see a pattern change from the recent cold
troughing and frequent clipper systems to a milder ridging with
pieces of energy sweeping in from the southwest. Models are in
relatively good agreement with this shift. Below normal
temperatures of the past week will shift to above normal
starting Saturday and remaining so into next Friday.

The last of the clipper systems moves out of the Upper Great
Lakes today. One piece of upper energy in the southwest will eject
northeast to bring light rain to our area Sunday. A more
substantial trough will drop into the Plains Thursday and deepen
as it tracks into the Great Lakes Friday. All models lift this low
up to our northwest keeping us on the milder and showery side
late Thursday into Friday before a shift back to a colder pattern.

&&

.NEAR TERM /This afternoon/...

Issued at 1008 AM EST Fri Dec 15 2017

Surface analysis late this morning shows strong low pressure over
the Great Lakes with cyclonic flow across Indiana. A ridge of
high pressure was found across Oklahoma and western Missouri.
GOES16 shows areas of stratus across Central Indiana as a upper
short wave was exiting the area. Surface flow was from the
southwest.

Forecast soundings and time height sections across the area show
lower level saturation continuing over through the afternoon...and
giving the upstream satellite trends and the weak cyclonic
flow...this appears reasonable. Some breaks in the cloud will be
possible late this afternoon as the lower level flow becomes more
anticyclonic. Given the cloud cover have trended highs slightly
below the forecast builder blend.

&&

.SHORT TERM /Tonight through Sunday night/...

Issued at 243 AM EST Fri Dec 15 2017

Tonight...will be dry with variable cloud cover as heights rise with
the upper trough lifting into New England and a surface
trough/warm front sets up to our northwest. With the periodic
cloud cover and light southwest wind...minimum temperatures will
be a category warmer...in the middle 20s.

Saturday and Saturday night...continued southwest flow and the
surface boundary shifting further north in the Great Lakes will
result in sunnier skies for all areas by Saturday afternoon.
Temperatures top out from 45 to 50...in line with blended
guidance. Saturday night lows will be at or above freezing as
southwest winds continue and high clouds overspread the area after
midnight from the approaching system ejecting this way from the
southern Rockies.

Sunday and Sunday night...the upper trough dampens some as it moves
into the upper ridge over our area. Still, the moisture it pulls
northward will bring overcast skies Sunday. Light rain will also
overspread the area during the morning and continue into the
afternoon. The cloud cover and rain will hold back max
temperatures Sunday in the lower to middle 40s but that will
still feel mild compared to recent days. Rain amounts will be
less than a quarter inch.

Continued southwest flow Sunday night and dewpoints above freezing
will translate to minimal temperature drops Sunday night with
lows in the mid to upper 30s. Some light rain or drizzle will be
possible as more moisture transports into our area from a deep
trough in the southwest US.

&&

.LONG TERM /Monday through Thursday/...
Issued at 235 AM EST Fri Dec 15 2017

Models indicate a zonal upper flow will occur through the middle of
next week...then becoming more amplified late next week as an upper
trough moves into the central U.S. and deepens.  Temperatures will
be quite mild most of this period with a slight cool down towards
Wednesday.

The European and GFS indicate trace precipitation amounts early
Monday as one weak system exits our area.  The GFS indicates another
system may give us low rain chances Monday night as a weak cold
front moves through.  The rest of the long term will be mostly dry
as high pressure moves east across our region. The one exception
will be late Thursday where Superblend indicates slight chance POPS
ahead of the approaching trough.

Stayed close to a MOS Superblend mix on temperatures through the
period.

&&

.AVIATION /Discussion for the 151500Z Tafs/...

VFR Cigs are expected this taf period. GOES16 Satellite trends and
forecast soundings suggest lower level moisture will continue to
linger through the afternoon hours. No significant changes to the
overall TAFs...but VFR CIGS will continue.

Previous discussion below

/Discussion for 151200z TAFS/...

Issued at 617 AM EST Fri Dec 15 2017

An hour period of MVFR decks around 2700 feet should occur
roughly 16Z-18Z today in vicinity of surface trough as winds
switch from WSW to WNW. Otherwise VFR decks to occur most of the
period. Also anticipate gustiness of wind as they swing to WNW
but gusts should lie down by 21z and winds drop below 10kts by
23z.


&&

.IND WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SYNOPSIS...Tucek
NEAR TERM...Puma
SHORT TERM...Tucek
LONG TERM...JH
AVIATION...Tucek/JP



Office: IWX FXUS63 KIWX 151131 AFDIWX Area Forecast Discussion National Weather Service Northern Indiana 631 AM EST Fri Dec 15 2017 .SYNOPSIS... Issued at 109 AM EST Fri Dec 15 2017 A weak system will pass across the Great Lakes today bringing scattered to numerous snow showers north of the Toll Road. Some light snow accumulations of an inch or two are possible from today through tonight, especially across southern Lower Michigan where lake effect snow showers are expected to be more numerous. High temperatures this afternoon will range from the mid 20s to lower 30s. Lows tonight will not be as cold, ranging from the mid to upper 20s. The moderating trend will continue into the weekend with highs in the 30s and 40s for Saturday and Sunday. The next chance of rain and snow will arrive by Sunday afternoon. && .SHORT TERM...(Today and Tonight) Issued at 239 AM EST Fri Dec 15 2017 A mid level shortwave will rotate southeast through central/upper Michigan today, with the trailing trough axis swinging through the local area from west to east this morning through early-mid afternoon. Most of the impacts/accums will bypass north given far northerly track of the system sfc reflection, though there will be enough lake enhancement in strengthening westerly flow to generate scattered to numerous snow showers mainly north of Route 6. Steepening lapse rates/mixing into the lower portion of the DGZ could support some stronger snow squalls and light accums in these areas, which when combined with wind gusts of 20-30 mph and snow already on the ground could promote patchy blowing snow and reduced visibilities. Cool/breezy/cloudy with flurries possible elsewhere today. Warm advection regime tonight will likely allow light snow to develop near a trailing baroclinic zone leftover from the Upper Midwest southeast into the Lower Great Lakes. Models are in pretty good agreement in best snow chances (maybe up to an inch) northeast of US 30 mid evening into the overnight. && .LONG TERM...(Saturday through Thursday) Issued at 239 AM EST Fri Dec 15 2017 Positive PNA ridge along the West Coast will break down and allow positive height anomalies to finally overspread the Eastern US this weekend into early next week. The result will be a warming trend and mainly dry conditions, though will have to watch a shearing southern stream shortwave lifting northeast out of Texas for light rain (possibly mixed with some snow) on Sunday. A rather benign, yet still mild, pattern is then expected to persist into the middle of next week as models agree on flatter/split flow downstream of an amplifying Western US trough. This trough does eject east late in the week with a decent mid latitude cyclone likely making a run for the Great Lakes. The northerly track would favor more of a rainer locally followed by colder/drier air in time for next weekend. && .AVIATION...(For the 12Z TAFS through 12Z Saturday Morning) Issued at 625 AM EST Fri Dec 15 2017 Water vapor imagery is clearly depicting the next fast moving upper level short wave that will drop across northern Indiana over the next several hours. The combination of forcing from this wave and some lake enhancement with subtle veering of low level flow should result in a period of scattered snow showers at KSBN from mid morning to early afternoon. Onset of modest low level theta-e positive advection this morning has resulted in an increase in coverage of MVFR 2-3k foot deck and would suspect cigs in this range to persist through much of the day as low level lapse rates steepen in wake of approaching sfc trough. These steeper lapse rates will allow for westerly gusts to around 25 knots later this morning into this afternoon, before decoupling fairly quickly early this evening. Still suspecting a 2nd wave of snow shower activity this evening at KSBN with onset of low/mid level WAA, but after 06Z focus for additional snow showers should lift north of KSBN as thermal trough retreats northward. Will maintain MVFR conditions at KSBN, with confidence too low to go IFR at this time due to more favorable setup for greater snow shower coverage just to the north of the terminal. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...NONE. MI...NONE. OH...NONE. LM...Small Craft Advisory until 5 AM EST Saturday for LMZ043-046. && $$ SYNOPSIS...Marsili SHORT TERM...Steinwedel LONG TERM...Steinwedel AVIATION...Marsili Visit us at www.weather.gov/iwx Follow us on Facebook...Twitter...and YouTube at: www.facebook.com/NWSNorthernIndiana www.twitter.com/nwsiwx www.youtube.com/NWSNorthernIndiana