082 
fxus63 kmqt 192014 
afdmqt 


Area forecast discussion 
National Weather Service Marquette Michigan 
414 PM EDT Friday Mar 19 2010 


Synopsis... 


12z radiosonde observations/latest WV imagery and RUC analysis show upper troffing over 
scntrl can and the northern plains suppressing the persistent upper ridge 
that has dominated the upper Great Lakes for a couple of weeks S into the 
Tennessee River valley. The passage of a cold fnt attendant to shortwave/surface 
low passage through southern Ontario has brought a return of more seasonable 
temperatures to the County Warning Area this afternoon with temperatures mainly in the 30s in the 
chilly northwest flow behind the fnt. 12z 850 mb temperatures upstream are as low as 
-12c at inl and -16c at ypl. The inl/ypl radiosonde observations also show a moist 
atmosphere...with extensive low cloud obsvd upstream from northwest Ontario into 
Minnesota. This low cloud has invaded the northwest half of Upper Michigan early this afternoon. 
Despite the rather deep moisture shown on the inl/ypl radiosonde observations...mainly 
just flurries and lighter -shsn are falling under the SC in Minnesota/ 
adjoining southern Ontario/the County Warning Area due to larger scale upper cnvgc/dnva/ 
cad/h85-5 qvector dvgc in the wake of the shortwave departing to the east. 
The presence of drier low level air shown on the 12z yqd radiosonde observation and the 
aprch of hi pressure in scntrl can has caused the SC to break up in eastern 
ndakota and around Lake Winnipeg. This clearing is edging into northwest Minnesota closer 
to forecast issuance time. 
&& 


Short term discussion /tngt and Sat/... 


Main forecast concerns during this time are cloud trends/impact on temperatures. 


Tonight...confluent upper flow over the upper Great Lakes will allow surface hi pressure 
now moving through scntrl can to build east into the upper Great Lakes...with 
surface ridge axis forecast to extend from the northern plains east-northeastward across the County Warning Area to 
near James Bay. The slow arrival of colder air in the north-northwest flow ahead 
of this ridge as well as the rather extensive moisture obsvd upstream 
should support some light les tonight with the arrival of 850 mb temperatures as low 
as -15c...especially after this evening with the loss of daytime heating 
that often disrupts the les process this late in the season. Any snow 
fall should be on the light side though with arrival of low level drier air 
from the northwest/general anti-cyclonic flow limiting low level cnvgc and causing inversion 
heights to fall to around 4k feet mean sea level. The aprch of the ridge axis/sharper 
anti-cyclonic flow later tonight should also cause a diminishing trend to the 
shsn...especially over the west. Although the extensive low cloud upstream 
would suggest trending toward the hi end of MOS guidance...compromised a 
little lower to account for falling dewpoints upstream of the lake. Still 
tended to keep quite a bit of SC in the forecast tonight despite arrival of 
the drier air and ridge axis/anti-cyclonic flow after 06z. The lowest temperatures are 
most likely over the far west where the aprch of the surface ridge axis is 
most likely to bring some clearing. 


Sat...the surface ridge axis is forecast to drift slowly S across the forecast area. With 
arrival of drier air/sharp anti-cyclonic flow/daytime heating...expect any 
lingering les in the morning to end and the SC to mix out through the day 
to yield more sunshine. Mixing to 800 mb on GFS forecast sdngs yields hi 
temperatures in the 35 to 40 range...so tended toward a blend of the cooler 
NAM/warmer GFS MOS guidance. 


Long term /Saturday night through Friday/... 


Much of this period will be marked by a broad trough...set up from 
Manitoba through Michigan to the New England states...as much of the 
energy remains well to our south. One feature of interest is a 500mb 
trough stretching from Colorado through Minnesota...to the main low 
over northern Hudson Bay. Look for this feature to cut off Saturday 
over northern Texas...and slowly inching to the Carolinas by Monday 
night. Closer to home...as this low exits the Continental states...a 
weak 500mb ridge will form Monday night through Tuesday night. The 
European model (ecmwf) is stronger with this ridge...while the GFS and Canadian would 
keep more zonal flow...to a trough over the upper Great Lakes. By 
daybreak Tuesday the surface low will be over far Western Lake 
Superior...stretching back through The Four Corners region. This 
will allow the weak cold front to swing over the County Warning Area during the day 
Tuesday...before high pressure settles back in Wednesday morning. 


For midweek...the 500mb low to our north will continue to slowly dip 
and swing into northern Quebec 


Overall...decided to stay away from the stronger winds of the 06z 
GFS...and focus on a blend between the ongoing forecast and the 
latest European model (ecmwf) and HPC guidance for Monday and beyond. Since then the 
12z run of the GFS has come back into better agreement with the 
majority of available models. 
&& 


Aviation /for the 18z tafs/... 


MVFR conditions will persist through tonight...especially at kcmx 
where upsloping winds will cause lower ceilings. Winds will diminish 
through the period as a low pressure system continues to move away 
from the area. Winds will be strongest at kcmx due to favorable 
terrain enhancement. Ceilings will likely improve through the day on 
Saturday as high pressure builds into the region. 
&& 


Marine /for the 4 PM Lake Superior forecast/... 


Expect north-northwest winds to 30 kts this evening to diminish with the arrival 
of a hi pressure ridge tonight. Once this ridge shifts to the southeast late 
Sat...SW winds on the northwest flank of this feature will increase to 25 to 
30 kts...highest in the corridor between the Keweenaw and Isle 
Royale where terrain funneling accentuates this flow. Look for these 
winds to diminish Sun night into Monday with the arrival of a hi pressure 
ridge in Ontario. Plan on winds no higher than 20 kts on Tue/Wed. 
&& 


MQT watches/warnings/advisories... 
Upper Michigan... 
none. 
Lake Superior... 
none. 
Lake Michigan... 
none. 
&& 


$$ 


Synopsis...kc 
short term...kc 
long term...kf 
aviation...Titus 
marine...kc 

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