Area forecast discussion 
National Weather Service Indianapolis in 
1141 am EST Sat Feb 28 2015 


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


&& 


Synopsis... 
issued at 304 am EST Sat Feb 28 2015 


A frontal system is expected to move through the area tonight and 
Sunday. In the wake of this front...high pressure will build into 
the area by Monday. A stronger low pressure system may affect the 
area towards the middle of next week. 


&& 


Near term /rest of today/... 
issued at 1003 am EST Sat Feb 28 2015 


Satellite indicate lots of middle level clouds over all but the far 
northeast parts of our region. Models soundings indicate some 
breaks may occur across far northeast sections this 
afternoon...otherwise mostly cloudy skies will be the rule. Overall 
current forecast is on track. Will keep low chance probability of precipitation far west 
late today. Highs late this afternoon will range from the lower to 
middle 20s north to near 30 south. 


&& 


Short term /tonight through Monday night/... 
issued at 304 am EST Sat Feb 28 2015 


Main item of interest during this period is a short wave trough that 
is expected to drop southeast across the Great Lakes on Sunday. The 
surface reflection associated with this feature doesn/T look too 
impressive...but models suggest a sustained 35-40 knots low level jet 
across the area from tonight into Sunday evening...indicating a 
rather long duration precipitation event. Will go with high probability of precipitation all 
areas tonight and Sunday...with probability of precipitation tapering off Sunday night as 
low level jet moves off to the east. 


Models are coming into better agreement on the thermal profiles 
during this event...but some of the ensembles are still warmer than 
the operational models. As a result...there is still a possibility 
that the warmer air may get farther north than forecast. At this 
time...the majority of the data suggest mixed precipitation may 
start working its way into the far southern zones during the pre 
dawn hours of Sunday...probably reaching as far north as the central 
zones during the day Sunday. Due to the expected long duration of 
the event...looks like a high end advisory type situation. The lack 
of a good surface feature lends to lower confidence of reaching 
warning criteria over a widespread area at this time. Planning on a 
Winter Weather Advisory for all areas starting this evening and 
lasting through the day Sunday. Model quantitative precipitation forecast and precipitable waters 
flowing into the system suggest 4-6 inches possible over the 
northern half of the forecast area...with progressively lower 
amounts farther south as precipitation becomes more mixed with time. 
Brief period of dry weather expected Monday as surface high pressure 
move through...before lift/precipitation threat moves back into the 
area by late Monday night ahead of the next system. Will continue 
with chance probability of precipitation for mixed precipitation late Monday night. 


Low level thickness forecasts suggest the GFS MOS temperature guidance 
for the rest of the short term doesn/T look too bad...so only minor 
adjustment planned. 


&& 


Long term /Tuesday through Friday/... 
issued at 335 am EST Sat Feb 28 2015 


Active pattern continues through midweek as a broad moist southwest 
flow persists downstream of an amplified upper trough over the 
intermountain west. Confidence remains high in significant weather 
impacts through Wednesday as low pressure tracks through the region 
along a slow moving frontal boundary. 


Model consensus capturing the southwest flow aloft and surface wave 
track into the lower Great Lakes by Tuesday night well. Differences 
however exist with respect to strength of the surface low with the 
op GFS and bulk of the GFS ensemble members offering a much stronger 
feature than the global models. Appears a stronger interaction with 
the northern stream energy may be partially responsible for the 
deeper surface wave. These differences not likely to be ironed out 
for another 24-48 hours but the big picture remains the same as a 
sloppy wintry mix early Tuesday gradually transitions to rain for 
Tuesday afternoon and night before colder air changes precipitation back 
towards snow during the course of the day Wednesday. 


Thermal profiles are strongly suggestive that freezing rain will be 
the main precipitation type Tuesday morning as raw surface temperatures on bulk of 
the 00z models remain subfreezing while warm advection intensifies 
through the boundary layer. The expected snowpack will be a factor 
in near surface warming and as has been discussed...may have to 
wait until snow tonight/Sunday gets down before the models 
accurately Sample impacts. The icing potential looks to make an 
absolute mess for Tuesday morning with surface temperatures warming above 
freezing by late morning/early afternoon. 


Still feel the heavy rain over frozen ground and several inches of 
snow on the ground present a growing and increasingly significant 
flood potential for central Indiana. Precipitation water values remain 
exceptionally high and near the climatological maximum for early March 
between 1.25 and 1.50 inches by Tuesday evening as a strong 65-75kt 
850mb jet moves through the Ohio Valley. Still appears 1-2 inches of 
rain will fall Tuesday afternoon through early Wednesday before the 
front gradually sags south of the Ohio River. In addition...feel 
comfortable in introducing an isolated thunder mention into southern 
portions of central Indiana. Scattered convection will bring 
periodic higher rainfall rates and only exacerbate the flooding 
concerns. Stay tuned. 


Some light snow is possible on the back side of the precipitation shield 
Wednesday and Wednesday evening as colder air spreads south. Much 
colder and drier air then returns for the end of the week. 


&& 


Aviation /discussion for 281800z taf issuance/... 
issued at 1141 am EST Sat Feb 28 2015 


VFR conditions give way to IFR/LIFR around 00z. IFR conditions will 
persist through Sunday. 


VFR deck will gradually lower through the afternoon hours. As a 
system moves into the area this evening...snow will quickly 
overspread the area around 00z lowering conditions to IFR. As snow 
increases late this evening and overnight...LIFR conditions are 
possible all areas. 


However for the moment highest likelihood of LIFR is at kind/huf so 
added a tempo group there. Note there is a chance that LIFR may 
extend past the time indicated in the tempo group. 


Models hint at another surge of snow on Sunday so kept IFR going 
through the taf period Sunday. Winds will diminish this evening and 
remain less than 10kt overnight into Sunday. 


Rain may mix in at kbmg Sunday but feel odds are too low to mention 
in taf at this point. 


&& 


Ind watches/warnings/advisories... 
Winter Weather Advisory from 7 PM this evening to 7 PM EST 
Sunday for inz021-028>031-035>049-051>057-060>065-067>072. 


&& 


$$ 


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


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