Area forecast discussion 
National Weather Service Indianapolis in 
554 am EST Wednesday Jan 28 2015 


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


&& 


Synopsis... 
issued at 300 am EST Wednesday Jan 28 2015 


A couple of low pressure systems will bring chances of precipitation 
to central Indiana Thursday and again for the second half of the 
weekend into early next week. Temperatures will go from near to 
above normal early in the period to well below average by early next 
week. 


&& 


Near term.../today/ 
issued at 300 am EST Wednesday Jan 28 2015 


Satellite shows some middle and high clouds starting to arrive in 
central Indiana. Expect a gradual increase in middle and high cloud 
today as warm advection and isentropic lift increase aloft. 


Temperatures will start out cold...especially across the northeast 
where some snow cover lingers. However there will be enough sunshine 
today to boost temperatures to in between the met and mav MOS 
numbers. 


&& 


Short term.../tonight through Friday night/ 
issued at 300 am EST Wednesday Jan 28 2015 


Focus is on chances for precipitation tonight into Thursday night. 
Models are close enough that a blend was used. 


Isentropic lift will ramp up this evening with 850mb winds 
increasing to around 50kt. However this lift will have little 
moisture to work with. Will keep the evening dry but increase the 
clouds. 


Overnight...additional forcing will move in as an upper 
trough approaches. However...moisture is still pretty limited in the 
lowest levels. Thus only went slight chance to low chance category 
probability of precipitation starting about 08z. Temperatures will bottom out early in the 
evening then rise overnight with good warm advection. By the time 
any precipitation would start...the atmosphere will be warm enough 
for just rain. 


A couple of upper waves will move through the area Thursday. 
Best combination of forcing and moisture occurs between 12z and 18z 
Thursday. However...even during that period the best moisture 
arrives after forcing has peaked. Thus just went chance probability of precipitation most 
areas...with a thin area of likely probability of precipitation in the far northeast. 


Chances for rain will diminish through Thursday afternoon as forcing 
weakens. Temperatures cool quickly aloft...but surface temperatures 
stay mild for a while. Thus only introduced a mix of snow and rain 
late in the afternoon. 


Kept slight chance probability of precipitation across the eastern half of the area Thursday 
evening as system exits. Continued with slight chance probability of precipitation northeast 
overnight Thursday night to account for any lake effect snow that 
makes it into the area. 


High pressure will then move in and provide dry but cool conditions 
Friday and Friday night. 


&& 


Long term /Saturday through Tuesday/... 
issued at 249 am EST Wednesday Jan 28 2015 


Primary focus for the extended period remains on the growing 
potential for a high impact winter weather system across the Ohio 
Valley for the second half of the weekend. 00z model guidance has 
come in generally with a more phased look to the upper jet structures 
consequently producing a stronger surface wave tracking through the 
region. 


After a dry day Saturday as high pressure moves across the 
area...focus will turn to developing low pressure over Texas early 
Sunday. This system will lift northeast into the Ohio and 
Tennessee valleys as an upper trough amplifies over the Central 
Plains. Variations are present between the different models which 
is to be expected. The ggem and op GFS are particularly aggressive 
in phasing the upper energy over the region by late Sunday... 
consequently producing a deepening low going sub-1000mb Sunday 
night as it passes through the area. European model (ecmwf) is flatter in the upper 
levels initially lending to a faster moving wave with the phasing 
energy aloft not taking place until after the system passes. The 
individual GFS ensemble members have yet to organize into a 
consensus surface low track at this point...showcasing the 
differences with respect to the degree and timing of the polar and 
subtropical jets phasing. 


At this point...the forecast track is in a fairly ideal location 
for snow to be a predominant precipitation type for most of the region. 
As mentioned on Tuesday morning however...the overall handling of 
low level warm intrusions this winter by models have been 
problematic and track of the 850mb low across central Indiana on 
the bulk of the extended guidance does nothing to quell that 
concern at this time. With this storm still 4-5 days out...it remains 
premature to speculate on details until a greater model consensus 
can be achieved. 


The main takeaway at this early stage is that confidence is 
growing in a winter storm to impact the region late Saturday night 
through early Monday. Will carry mainly snow over the northern 
half of the forecast area with a rain/snow mix on Sunday across 
southern counties. Should snow end up as the predominant precipitation 
type...potential exists for several inches of accumulation. Stay 
tuned. 


Much colder air will be drawn south into the region for early next 
week behind this system with potential for coldest temperatures in about 
3 weeks with highs struggling to get out of the teens in some 
locations Monday and Tuesday. Could see lows near or just below 
zero in spots Tuesday morning. 


&& 


Aviation /discussion for 281200z taf issuance/... 
issued at 554 am EST Wednesday Jan 28 2015 


VFR conditions expected throughout the forecast period. 


High pressure centered over the Ohio Valley this morning will 
drift east through the course of the day. Plenty of sunshine is 
anticipated today...with middle and high level clouds slowly 
increasing during the afternoon. Southeast winds will increase to 
10-15kts by the afternoon. 


Skies will become cloudy tonight as low pressure approaches from 
the west. Light rain showers will develop across central Indiana 
after 06z as the low tracks into the lower Great Lakes. Winds will 
veer to southerly by late tonight...increasing to around 15kts 
with gusts 20-25kts. 


&& 


Ind watches/warnings/advisories...none. 


&& 


$$ 


Synopsis...50 
near term...50 
short term...50 
long term...Ryan 
aviation...Ryan 


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