704 
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afdind 


Area forecast discussion 
National Weather Service Indianapolis in 
526 PM EDT Thursday Mar 18 2010 


Aviation... 


Discussion for 19/00z tafs. 


Great flying weather as VFR conditions are expected to continue 
under high pressure. Light west southwest winds tonight will 
increase to near 15 knots from the southwest tomorrow afternoon. 
Huge dew point depressions and persistance favor no visibility 
restrictions tonight. 


&& 


Near term /until 6 am Friday/... 
analysis as of 230 PM this afternoon depicts a large area of high 
pressure centered across the Central Plains. Elsewhere...a trough 
was noted digging into the Pacific northwest...this feature will 
bring precipitation to the forecast area later this weekend. 
Current visible satellite and observations indicate clear 
skies...with only a few scattered high clouds upstream to our 
northwest over northern Illinois. Considering this benign weather 
pattern, tonight's focus will be temperatures...and per good model 
consensus did not stray far from a MOS guidance blend for 
lows...as winds do not completely decouple to allow for maximum 
radiational cooling. Only tweaked down temperatures for a few normally 
cooler lying areas. Lows upper 30s-low 40s. 


&& 


Short term /6 am Friday through Saturday night/... 
the ridge shifts eastward across the Central Plains early Friday to 
a position over the southeast United States by Friday night. More 
benign...beautiful...and seasonably warm weather can be expected for 
Friday under southwest flow. Low level thickness's yield highs once 
again in the middle to upper 60s. Forecast focus then turns to 
precipitation chances this weekend. 


The trough which originated from the Pacific northwest digs across 
the southern states late Friday/early Saturday...scooping 
up energy from the Gulf of Mexico...and develops a closed off low 
over the Missouri River valley. All models are generally in good 
agreement with this scenario with only a few minor differances. Once 
this energy closes off the NAM is showing a somewhat deeper and 
northward solution...while the GFS shows a more southward 
progression. The Euro and UKMET seem to take blend of the two 
extreme NAM/GFS solutions, and this is what was used for the 
forecast. All models seem to slow down the timing of the main slug 
of moisture for later Sunday morning...so tapered back likely probability of precipitation 
Friday night. 


&& 


Long term /Sunday through Thursday/... 
as for the extended...an upper low will push out of the Southern 
Plains on Sunday...spreading clouds and precipitation across 
Indiana and the Ohio Valley. Forecast soundings at the moment 
indicate the lower levels should be above freezing...however 
surface temperatures...especially on Sunday night indicate values in the 
middle 30s are possible. Given this...will include chances from 
snow showers mixed with rain on Sunday night...mainly across the 
northern parts of the forecast area as this area will be most 
likely to be susceptible to cold air. 


Upper ridge returns on Monday through Wednesday. Lingering wrap 
around clouds and cold air will be possible on Monday...but as the 
return flow develops on the backside of the ridge a warming trend is 
expected as the work week progresses. 


By Thursday...GFS and European model (ecmwf) disagree with the strength and timing of 
the approach of the next system. GFS is a bit quicker...while the 
European model (ecmwf) is slower. Like the European model (ecmwf) a better given the ridge that will 
be in place across the regions...which should slow the progression 
of the approaching system. 


&& 


Ind watches/warnings/advisories... 
none. 
&& 


$$ 


Public...smf 
aviation...mk