986 
fxus63 kapx 061950 
afdapx 


Area forecast discussion 
National Weather Service Gaylord Michigan 
350 PM EDT Sat Sep 6 2008 


Synopsis.../issued at 348 PM/ 


A weak low pressure system will move over Lake Superior 
tonight before exiting into Ontario tomorrow. This feature 
will generate a few light rain showers...over northern Michigan 
through tonight. 


A second storm system...moving over central Canada and the 
upper Midwest...will swing over the Great Lakes Sunday night. 
This system is expected to generate another round of showers... 
over the northern lakes Sunday night and Monday. 


&& 


Short term.../issued at 348 PM/...this evening and tonight 


Latest RUC analysis and visible/IR/WV/radar imagery show weak low 
pressure centered near MQT with an equally as weak surface 
trough/convergence axis bisecting the forecast area from north to 
south. Within a loose low level thetae axis ahead of the 
trough...diurnal heating has contributed to spotty shower 
activity...most prevalent across eastern upper and the far northern 
Lower Lake Huron shoreline. The warm waters of the northern Great 
Lakes have given a boost to these showers as Delta T/S are around 
11c. With the local convergence along the trough and over-water 
instability...a couple waterspouts have been sighted near The 
Straits and Northern Lake Huron shoreline. An additional trough 
extends west from the surface low towards northern Wisconsin...which 
is also supporting shower activity. Farther southwest...a fairly 
potent wave is moving across Nebraska/Iowa which has eyes on the 
southern Great Lakes. Precipitation chances are the main forecast concerns 
tonight. 


Tonight...weak surface low over the north-central u.P. Will shift NE 
across Lake Superior. Loosely defined low level thetae axis 
emanating from this low will exit into Lake Huron by 
mid-evening...ending any spotty shower and waterspout threat across 
northern lower for a period. Things not quite as clear across 
eastern upper where low level convergence is a little better as a 
result of the surface low nearby. There may very well be a break in 
the action across eastern upper during the evening as well...as 
middle-level dry air and isentropic descent arrive for a little while. 
NAM/GFS both point towards a secondary trough dropping southeast across 
Northern Lake Michigan and eastern upper after midnight. If this 
morning was any indication...instability generated by Delta T/S 
around 11c over Northern Lake Michigan may provide a boost to any 
showers that do develop along the trough. Otherwise...decent 
looking shortwave over Nebraska will move into the southern Great 
Lakes by morning. Middle and high clouds will spread across northern 
Michigan ahead of this system during the evening and overnight. 
Deepest moisture from this system will remain to the south but 
probably close enough to warrant an isolated shower along and south 
of M-55 very late. Lows in the middle 40s to low 50s. 


Mpc 


&& 


Long term.../issued at 348 PM/...tonight and beyond 


Interestingly...turn the switch to meteorological fall 
and the weather pattern seems to follow suit...featuring a much more 
active northern stream flow over the northern Continental U.S.. this pattern is 
expected to continue for the foreseeable future...featuring broad 
northern Continental U.S. And western lakes middle level troughiness...which will 
be riddled with relatively fast moving...hard to time shortwaves. 
Although much uncertainty plagues the extended...some useful 
information can be ascertained...namely a continuation of the 
relatively wet pattern and maintenance of the cool early September 
temperatures. 


Although forecast confidence regarding specific shortwave timing 
decreases nearly exponentially farther out in the extended... 
confidence somewhat higher (although still not as high as one would 
like) through Monday night as noam water vapor analysis confirms 
latest model guidance that trifecta of decent shortwaves will affect 
the Great Lakes...one exiting stage right during Sunday morning... 
with progressively stronger ones cutting through the region Sunday 
night and Monday night. Although moisture profiles not overwhelming 
through this period...dynamics should more than compensate... 
bringing periodic rain chances...especially during passage of 
aforementioned waves. Still looking like better dynamics with 
sundays wave will pass south of the region...and have continued to 
focus better potential in our southern zones (still low chance at 
best). Interestingly...farther North...Passage of subtle surface 
trough over Lake Michigan during the morning...augmented with 
possible land breeze convergence axis...moisture flux from the 
relatively Warm Lake waters (delta T/S on the order of 11c to 
12c)...and middle level weak shear axis may be enough to kick off a 
scattered line of showers over the water towards morning...which 
propagate inland as synoptic wind regime overwhelms the land breeze. 
A similar scenario unfolded this past morning...with clear evidence 
of added Lake Michigan support as showers advanced from Wisconsin. 
Otherwise...have removed probability of precipitation for the afternoon hours with some 
semblance of low amplitude ridge axis pivoting into the area. Next 
wave slated to drop southeast Sunday night...this time with better 
dynamics passing over eastern Upper Michigan and points north. Much 
like Sunday...just not overly sold on shower potential with limited 
moisture profiles and better middle level support essentially passing 
north of the area. Will taper chance probability of precipitation from north to south...with 
some west/east timing. Will keep slight chance thunder mention with 
900mb lifted parcels yielding nearly 400 j/kg mean layer cape. 


Probably the most interesting weather of the extended begins late 
Monday night...continuing through Tuesday morning...as strong 
shortwave makes the turn to the east northeast over the Central 
Plains...with sights set on the Great Lakes region. Latest NAM-WRF 
and GFS guidance have really amplified this system...dropping 
surface pressure to sub 1000mb as it passes through northern 
Michigan. Other guidance remains much less aggressive...and hence 
farther southeast with the surface low (in fact...12z Gem has 
essentially no surface reflection). If American guidance is to be 
believed...rain...locally heavy (over an inch with quantitative precipitation forecast fields) will 
quickly overspread the area late Monday afternoon...continuing 
through Monday night. Looking at middle level height fields...it 
appears both the NAM-WRF and GFS are unrealistically aggressive 
with downstream ridge response (too quickly building heights) after 
passages of late weekend shortwaves. This allows upstream shortwave 
to over-amplify and push farther northeast. In light of the 
above...will side with the more conservative guidance...featuring 
likely probability of precipitation over the south half of the area and much less rainfall. 
Have lingered light shower mention into Tuesday morning as system 
pulls off to the east and weak northwest flow lake effect rain 
showers possibly develop as 850mb temperatures drop to the single 
digits. 


Looking farther out...as mentioned...questions abound later in the 
forecast period. In general...still like the idea of a dry midweek 
period as surface and middle level ridge axes crest the region. Beyond 
this...models hinting at another fairly strong shortwave passing 
through late in the week...bringing another chance of showers. 
However...with Hurricane Ike now slated to pass into the Gulf of 
Mexico (per latest NHC guidance)...would expect this feature to at 
least try to flex its muscle on overall Continental U.S. Flow regime...possibly 
playing some havoc on amplitude and timing of the northern stream 
shortwave. Given uncertainties...felt it would be a forecast 
injustice to try any sort of timing...and have took the simple 
approach of maintaining forecast continuity with pop and weather 
grids and running with HPC guidance all others. 


Temperatures through the extended will remain near to slightly below 
seasonal normals...with highs in the 60s to low 70s and overnight 
lows generally in the 40s and 50s. 


Msb 




&& 


Marine.../issued at 348 PM/ 


Showers and isolated waterspouts continue to form along a 
surface convergence axis...and have been getting a boost from the 
Warm Lake waters of the northern Great Lakes. Shower...along with 
the threat of waterspouts...will be possible along this axis across 
NE lower and far eastern upper until this axis moves over the open 
waters of Lake Huron this evening. Otherwise...no other marine 
hazards are expected since winds will remain light tonight. 


Mpc 


&& 


Aviation.../issued at 100 PM/...valid for 18z tafs 


Challenging forecast over the next 24 hours. Weak 
surface low over central Upper Michigan will track NE over Lake 
Superior with its trailing cool front/surface trough crossing 
northern lower through the afternoon. Showers will remain spotty 
with limited chances of impact on the taf sites. Secondary surface 
trough will pass across the area early tomorrow morning. Hard to 
say if any low clouds/fog will accompany this trough. Certainly is 
possible...judging by what occurred upstream this morning. Best 
chances would appear to be at pln and will trend towards lower visibilities 
and ceilings...but will refrain from going lock/stock/and barrel due to 
poor model guidance. So...will keep VFR going through the taf period 
except at pln. 


Mpc 


&& 


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


&& 


$$ 

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