104 
fxus63 kiwx 231718 
afdiwx 


Area forecast discussion 
National Weather Service northern Indiana 
1218 PM EST Monday Nov 23 2009 


Aviation/18z-18z/ 
stratus shield slowly dissipating while lifting northwest in southeasterly low 
level flow. Expect low clouds will clear at sbn around 19z. Middle 
clouds over southern Indiana expected to lift NE this afternoon and affect 
FWA with VFR ceilings. Skies should clear this evening with light low 
level flow and weak convergence along a weak warm front lifting north 
across the area. This is expected to result in IFR conditions due 
to stratus and fog developing 06z-12z. Low level moisture advecting 
into the area ahead of low approaching from the plains, should 
cause low clouds to persist at least through 18z. 


&& 


Previous discussion... /issued 1136 am EST Monday Nov 23 2009/ 


Update... 


Quick update to remove morning fog wording and reduce high 
temperatures slightly in the SW County Warning Area where low cloud cover this am 
will be replaced by middle clouds this PM with the net result being 
slightly lower high temperatures than forecast. Went between latest GFS lamp 
guidance...which keeps SW County Warning Area in the 40s...and going forecast in the 
middle 50s and expect hedging to be the best bet in this scenario as 
high temperatures will be greatly modulated by any breaks in the cloud 
cover. In NE half of County Warning Area temperatures looking good with little 
adjustment needed. Though forcing looks quite meager...sufficient 
low-middle level moisture warrants retention of low chance pop in the 
afternoon in Ohio counties. Updated grids/zones are out. 




Short term... 


Today through Tuesday night... 


Surface high pressure over New England still holding strong across 
our area this morning. Short wave across middle south is being ejected 
northeast by a weak lead kicker wave moving through the Midwest this 
morning. This wave is ahead of much more potent short wave crossing 
the intermountain west that will begin to affect our area late 
Tuesday. 


Tis the season for fog and stratus and this morning is no exception. 
GOES satellite fog product shows area of stratus that began last 
evening off of Lake Erie has continued to develop and expand across 
just about entire forecast area with high pressure to the east 
providing a weak easterly flow. A few breaks have opened up but 
these will likely fill back in with fog and or stratus through 
daybreak. Have increased sky cover considerably this morning to 
account for cloudy start and added patchy dense fog as few sites 
have been down to one mile or less in fog already. 


Models not doing a good job handling this shallow moisture or the 
low level wind field that is driving it. Ruc13 1000mb winds and relative humidity 
looks to be best and using this to try and forecast movement and 
dissipation this morning. With rather deep dry layer just above 
inversion into middle levels this morning expect these low clouds and 
fog to burn off during the morning hours. However...high thin cirrus 
should be across the area which may inhibit dissipation and also 
provide a partly cloudy day anyway when low clouds dissipate. 
Eastern areas to likely remain mostly cloudy through the day as 
moisture associated with southern wave passing by to the east 
streams over the area. Weak lift still depicted by models on western 
periphery of this wave but sref and MOS probabilities for measurable 
precipitation have dropped considerably since this time last night. Weak 
kicker wave now a little slower to arrive where last night models 
were showing this wave catching up to moisture with ejecting wave. 
Will leave low chance pop in this afternoon and evening in far east 
for consistency but expect any precipitation to be quite light. 


Focus shifts to later part of short term as potent short wave 
crossing the intermountain west this morning deepens and approaches. 
Models coming into better agreement with synoptic evolution which is 
a bit slower than previous forecasts. Much of Tuesday looks to 
remain dry with exception being western areas late in afternoon. 
Sref probabilities showing precipitation chances increasing Tuesday afternoon but 
nearing 100 percent in the west and northwest Tuesday night. Kept 
previous trend in grids of keeping east dry on Tuesday and confined 
highest probability of precipitation to far west in afternoon. Increased probability of precipitation Tuesday night into 
likely category northwest half of area as most sref and mref 
ensemble members agree on precipitation moving through this area. With some 
timing issues amongst models have kept eastern half in high chance 
category but expect precipitation to reach this region either late Tuesday night 
or Wednesday. 


Temperatures through the period will be above normal but a little 
tricky with cloud cover issues. Highs in the 50s today and Tuesday 
still look on target for the most part. Stratus this morning of some 
concern limiting early rises but with expected burn off mixing to 
just 950mb yields temperatures in lower to middle 50s. Mostly cloudy skies 
expected on Tuesday but MOS numbers quite warm with middle to upper 50s. 
These certainly possible with a little sun but prefer to remain 
conservative on lower end of guidance envelop in the lower to middle 
50s with expected clouds thickening during the day and limiting 
afternoon rises. 


Long term /Wednesday through Sunday/... 


Cold and wet for the start of the Holiday weekend... 


Several changes to long term grids as pattern finally becoming 
better established and confidence beginning to increase somewhat. 


Chance for showers will exist through much of Wednesday as closed 
low moves across the area. Have went up to 50 percent with potential 
to go more of a likely mention in later periods. Upper low begins to 
shift east and north somewhat as main push of cold air arrives late 
Wednesday night into Thursday. Combination of several waves in the flow...deep 
synoptic and lake induced moisture and increasingly favorable Delta t's 
all suggest the chance for showers will continue into Friday and 
possibly Friday evening. Models still varying somewhat on timing of 
1300 M 1000-850 mb thickness line but seems reasonable to be here by 
Thursday. Current grids will continue to depict a mix for now. By Thursday 
night into Friday...potential for all snow given surface temperatures approaching 
freezing at night and minimal recovery on Friday. Thursday Evening Lake 
induced eq levels peak out around 10 kft and lake induced cape over 
300 j/kg would suggest that precipitation could a bit aggressive and 
potentially allow for the first light accumulations of snow. 


Temperatures will attempt to moderate towards normal Saturday with drying 
conditions. 


&& 


Iwx watches/warnings/advisories... 
in...none. 
Michigan...none. 
Ohio...none. 
Lm...none. 
&& 


$$ 


Short term...Lashley 
long term...Fisher 
update...Simpson 
aviation...jt 

National Weather Service Glossary of Abbreviations

Non-Expanded Version (with abbreviations)