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fxus63 kind 211623 
afdind 


Area forecast discussion 
National Weather Service Indianapolis in 
1123 am EST Sat Nov 21 2009 


Aviation...discussion for 21/18z tafs 


High pressure will provide a dry easterly flow which should keep 
most clouds at Bay during the first half of the period...with mainly 
high clouds increasing on Sunday. 


Problem is potential for more fog tonight. Forecasted lows are below 
afternoon dewpoints...but slightly drier air will be working in 
overnight. With light winds overnight though...feel that odds for 
fog development are high enough to put MVFR fog in at most sites 
near Sunrise. East winds should prohibit fog formation at ind due to 
influence of city. Any fog will burn off quickly Sun morning. 


&& 


Update...for rest of today... 
updated forecast to remove mention of fog. Also area of low clouds 
along and north of a kdvn-kgez line was clearing from the south and 
most if not all of our forecast area will be mostly sunny by middle day. 
RUC sounding shows little in the way of Clouds Rest of today. No 
signficant changes made to temperatures for today. 


&& 


Discussion... 
quiet morning in progress as surface high pressure is centered over 
eastern Ohio. Weak upper level shortwave traversing the region early 
this morning. Area of stratocumulus had developed over northern half 
of the forecast area and will likely slip into the indy metropolitan during 
the predawn hours. Where skies were mainly clear...patchy mist/fog 
had developed again this morning. Temperatures at 08z were in the 
30s. 


Forecast challenges today focus on clouds this morning... 
temperatures through Monday...and transition to colder and more 
unsettled pattern by midweek. Models in excellent agreement with 
regards to sensible weather today and Sunday. 


Aforementioned shortwave will continue to progress east through the 
morning as high remains firmly entrenched at the surface. Expect 
lower clouds to persist through daybreak across northern counties 
with mostly clear skies elsewhere. As the shortwave energy shifts 
east into Ohio by late morning however...do anticipate a decrease in 
stratocumulus coverage with plenty of sunshine providing for yet 
another ideal Saturday in November. Ridging aloft will develop this 
afternoon and tonight across the region. Other than cirrus shield 
passing by to the southeast in association with low pressure lifting 
out of the northern Gulf Coast...skies will remain generally clear. 


Model consensus continues to trend away from central Indiana seeing 
any significant impact from said low pressure along the Gulf Coast 
on Sunday. High pressure ridge at the surface extending from New 
England southwest back into the Ohio Valley will keep this low from 
taking a more northerly track into the Tennessee Valley...and 
consequently provide a very pleasant Sunday for the third straight 
week. The only impacts should be a subtle increase in middle and high 
level clouds into the region from the southeast Sunday afternoon and 
night. More significant 285-300k isentropic lift on both NAM/op GFS 
now remain well displaced to the southeast of the forecast area. 
Considering a predominant easterly flow in the lower levels keeping 
boundary layer fairly dry...feel confident in removing 20 probability of precipitation from 
Sunday night forecast. Skies may actually end up being mostly clear 
northwest of the indy metropolitan. 


Weakening upper low associated with the Gulf Coast low will become 
absorbed by significant upper trough as it becomes well established 
over the central and northern plains on Monday. The amplification of 
the trough will spark development of low pressure and a cold front 
Monday night. Specific models differ on how fast the low pressure 
wave spins up and its location by Tuesday morning. Favor more 
conservative and slower 00z NAM/European model (ecmwf) solution...with the low 
pressure near Kansas City by Tuesday morning. 00z op GFS/Gem/GFS 
ensemble mean break down high pressure off the Canadian Maritimes 
faster and consequently progress the low and front further east. 
Warm front lifts north across the forecast area by Monday night with 
southerly flow developing out ahead of the approaching cold front. 
Likely to see an increase in middle level clouds as deeper moisture in 
advects into central Indiana Monday afternoon and night in the 
vicinity of the warm front. 


Adjusted rain chances for Tuesday as cold front likely to not arrive 
until late Tuesday...possibly even Tuesday night should the 00z 
European model (ecmwf) solution be realized. With uncertainty of the timing of the 
frontal passage...will continue with just a mention of rain in the 
forecast Tuesday night. Op GFS/European model (ecmwf) both dropping low level 
thicknesses towards critical values needed for a few wet snowflakes 
to mix in by early Wednesday. The passage of the cold front will 
signal a change to a more unsettled and colder regime for the region 
for the second half of the upcoming week. With upper level low 
progressing slowly across the lower Great Lakes Wednesday and 
Thursday...lower levels do appear to become sufficiently cold enough 
for a few snow showers...especially Wednesday night and Thanksgiving 
day. Will continue with low chances for rain/snow showers through 
the period. 


Temperatures...trended towards warmer mavmos guidance for highs today and 
Sunday. Analysis of low level thicknesses supported leaning towards 
warmer metmos guidance for Monday. Highs in the middle and upper 50s 
will be commonplace over the next three days. Stayed close to MOS 
guidance for lows...with middle and upper 30s largely expected tonight 
and Sunday night. 


&& 


Ind watches/warnings/advisories...none. 


&& 


$$ 


Public...Ryan 
aviation...cs 
update...jh