272 
fxus63 kapx 181759 
afdapx 


Area forecast discussion 
National Weather Service Gaylord Michigan 
159 PM EDT Friday Jul 18 2008 


Aviation...areas of MVFR SC/cumulus persist is some locales. However... 
with additional daytime heating these clouds should gradually lift 
into a VFR cumulus deck. Daytime heating and approaching weak front... 
however...will also result in spotty shower and thunderstorm 
development. This activity should diminish this evening as weak 
surface front/trough sets up just S of region. Shallow moisture 
behind front is expected to result in low cloud and fog 
development...with IFR conditions possible at tvc/pln/apn after 
about 04z. 


Smith 


&& 


Previous discussion... /issued 1143 am EDT Friday Jul 18 2008/ 


Update...have made few changes to current forecast. Middle morning 
surface map showed an ill-defined cold front extending from 
Central Lake Superior to southern Wisconsin. Plenty of moisture 
still in place out ahead of front...with low clouds and fog in 
many areas (a result of last nights rainfall)...along with dew 
points still in the 60s. 


Front will sag southward this afternoon. As breaks slowly develop in the 
low clouds...expect some destabilization to occur. An 82/66 parcel 
at 21 UTC yields just over 900 j/kg MLCAPE across north central lower. 
This seems reasonable...with an 800 mb Theta-E axis still prognosticated to 
extend across region. Was tempted to remove precipitation farther north 
(across eastern upper). However...with aforementioned 800 mb Theta-E axis 
just S of area and prospects for some lake-breeze induced 
convergence...decided leaving slight chance in was warranted. 


Best chance for showers/storms will be S of a tvc-apn line...where 
frontal convergence and low level moisture should be most favorable 
during peak heating -- after 2 PM. 


Still expecting highs to reach the 70s (ern upper) and 80 to 85 in 
northern lower...though temperature rise will initially be slowed by cloud cover. 


Smith 


Previous discussion... /issued 441 am EDT Friday Jul 18 2008/ 


Active summertime pattern continues under a quasi-zonal middle 
level flow regime...a myriad of short waves traversing the flow 
interacting with a wavy front and plentiful moisture feed across 
the region. Respectable mesoscale convective system that impacted the region last evening 
now well off to the east. However...outflow bisects northern lower 
Michigan back into Wisconsin and 30+ knot low level jet punching across the 
region still triggering showers/storms along this feature. 
Meanwhile upstream...middle level short wave moving along the upper 
Midwest/Canadian border with an associated loosely organized surface 
low and cold front pressing into the western Great Lakes. Other 
than a small area of showers in central Wisconsin...not much 
currently happening with the front itself. 


Today...another day with more uncertainties regarding convective 
evolution...as old outflows/mesoscale features will play a large 
role. But from a synoptic standpoint...aforementioned cold front (by 
name only) expected to slip through northern Michigan this morning 
perhaps getting hung up across central lower Michigan...but 
characterized by little more than a subtle wind shift toward the 
west and perhaps a subtle reduction in dewpoints over northern Michigan 
by later in the day. But little in the way of an outright airmass 
change. Low level jet ahead of the front now pushing across northern lower Michigan 
as well as synoptic support for ascent expected to progress east of 
the area early this morning. This will shift current focus of 
categorical showers/thunderstorms now across the tip of the mitt 
areas into the eastern section of the County Warning Area...then east of the area by 
middle morning. Will thus start the morning with a band of categorical 
rainfall across northern lower Michigan...tapering back to just Chancy 
probability of precipitation for the balance of the morning. 


Then...will likely be quite a bit of lingering cloud cover and low 
stratus in the wake of the convection this morning especially over 
the northern half of the County Warning Area. But as the day progresses we should thin 
out the cloud cover and heat things back up...especially across the 
southern tier of counties. So next question revolves around convective 
potential yet again this afternoon. Slightly drier and cooler air 
appears poised to slip into at least the northern portion of the County Warning Area this 
afternoon leading to the warmest temperatures/best instability across the 
southern half of the County Warning Area with forecast soundings over this region 
yielding 500-1000 j/kg MLCAPE and minimal cinh. So...believe we are 
facing another round of showers/storms this afternoon for areas 
mainly south of M-72...triggering off terrain/old outflows as well 
as any marine boundaries and will have highest probability of precipitation across the high 
terrain and areas east to Lake Huron. Aside from this mornings 
activity may see little in the way of activity north of M-32 but not 
gutsy enough to go with a dry afternoon forecast. 


As far as severe weather GOES...behind this mornings low level 
momentum surge...low level winds forecast to weaken although middle 
level flow remains somewhat robust in the 30-40 knot range. Not 
great...but 0-6km shear values around 30 knots and descent 
instability will support a marginal severe weather threat...mainly 
in the form of strong winds along with continued heavy rain 
potential. 


Tonight...any convection that develops will linger into the middle 
evening timeframe before things quiet down a bit for the balance of 
the night as Hudson Bay high pressure system presses into the northern 
Great Lakes. But still uncertain just how far south the front will 
get later tonight and there may still be some convective activity 
occuring along the boundary through the night from southern Wisconsin 
into Southern Lower Michigan. Will leave low chance probability of precipitation for the 
overnight period for areas south of M-72 in case we do get another 
little surge of moisture/forcing into the area overnight. 


Saturday through Sunday...active weather continues through much of 
the weekend as stalled boundary initially remains situated somewhere 
across central or Southern Lower Michigan. As it stands now...another middle 
level impulse forecast to move out of the northern plains and across the 
Great Lakes later Saturday through Saturday night...which may help 
shove the front back up through northern Michigan Saturday night into 
Sunday bringing a widespread shot of showers and storms to the 
region. At this juncture...exact evolution/timing/placement of probability of precipitation 
difficult to determine at this point but will maintain high Chancy 
probability of precipitation for most areas through the weekend. 


Adam 


&& 


Apx watches/warnings/advisories... 
Michigan...none. 
Lm...none. 
LH...none. 
Ls...none. 
&& 


$$ 

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