451 
fxus63 kmqt 211715 aab 
afdmqt 


Area forecast discussion...updated 
National Weather Service Marquette Michigan 
1215 PM EST Sat Nov 21 2009 


Updated for 18z tafs 


Synopsis... 


00z radiosonde observations show ridge aloft building into the western Great Lakes downstream of upper 
troffing along the West Coast. Airmass under this ridge is quite dry aloft... 
with 00z precipitable water as low as a meager 0.11 inch at inl. Since near surface 
moisture is more abundant...fog has developed over the forecast area with light winds 
associated with surface hi pressure building ovhd under the rdging aloft. The fog 
has become locally dense early this morning. To the west...very warm air 
is flooding northward into the northern plains in the southerly flow between the hi pressure 
ridge now ovhd and lower mslp in The Rockies. The 00z 850 mb temperature ranged 
from 4c at grb and inl to 9c at bis and an impressive 14c at Glasgow 
Montana. 


&& 


Discussion... 


Main forecast concerns this forecast period include temperatures this weekend and then 
precipitation chances late sun into the middle of next week as low pressure begins to 
take shape in the plains and moves NE. 


Tday...upper ridge will continue to build over the upper lakes with flood of warm 
air surging into can ahead of deep western trough. With dryness of airmass 
moving ovhd...expect a mosunny day after morning fog Burns off. Issued 
Special Weather Statement to hilight patchy dense fog early this morning. Mixing to h9 on 
forecast sdngs yields hi temperatures topping out as hi as the low 50s. Going 
forecast maximum temperatures seem on track. 


For tonight...as hi pressure ridge shifts to the east...sharper pressure gradient/ 
strengthening southerly flow will develop over the County Warning Area...earliest over the west. 
With this stronger wind...expect relatively little diurnal fall of temperature 
in the downsloping areas near lake supply...especially over the west from iwd- 
p59. Although the sheltered interior ecntrl will see lower temperatures below 
MOS guidance with dry middle levels and weaker winds a bit longer closer 
to departing surface hi...bumped up going forecast min temperatures there a bit 
with both GFS/NAM showing a quicker return of h95-9 specific 
humidity that will favor fog and/or St dvlpment during time of diurnal 
cooling. 


GFS remains the most aggressive model at generating precipitation over the west 
half of the forecast area on Sun afternoon showing moisture return through 700 mb. Although the 
NAM now shows higher specific humidity returning at 700 mb as well...this 
model focuses the axis of higher moisture farther west over Western Lake supply. 
Considering the fairly hi amplitude western trough/eastern ridge pattern that 
would favor a slower west-east progression...tended toward the NAM and 
going forecast. Although the explicit GFS forecast shows precipitation...the GFS MOS 
forecast for iwd shows only a 10 pop for 18z-24z sun...supporting the 
drier NAM and UKMET. Over the east...there will likely be some sunshine 
after morning fog/St Burns off with middle level dry air through the day. More 
persistent cloud cover over the west will limit the diurnal temperature rebound... 
but bumped up forecast hi temperatures farther east away from the moderating 
influence of Lake Michigan with expectation for more afternoon sunshine. 


Tended to follow the less progressive NAM/UKMET/12z European model (ecmwf) again on 
Sun night and cut back on eastward progression of probability of precipitation in previous forecast 
given strength of ridge to the east and lingering middle level dry air. Went 
with hiest probability of precipitation over Western Lake supply where NAM shows axis of higher 850 mb-7 
specific humidity and some weak upper dvgc for a time in rrq of 300 mb jet 
maximum lifting northeastward through northwest Ontario. Over the east...lowered going forecast 
min temperatures below MOS guidance given persistence of dry air aloft and 
where NAM shows rising mslp/weaker gradient flow. Also added some 
fog in these areas where drier air/lighter winds would favor the 
sharper diurnal temperature fall. Raised forecast min temperatures over the west with 
more clouds/stronger winds/downsloping southerly flow. 


With ridge/anti-cyclonic flow tending to strengthen on Monday downstream of 
deepening trough in the plains...trimmed going probability of precipitation to forecast schc probability of precipitation 
only over the far west closer to low pressure trough in NE Minnesota on Monday and Monday 
night. With tendency for drier air...incrsd maximum temperatures on Monday and 
lowered forecast for Monday night mins. Added fog again over the interior 
ecntrl where lowest temperatures are favored under higher mslp. Tended to cut 
probability of precipitation over especially the NE forecast area on Tuesday as well with favored 00z European model (ecmwf) 
still showing tenacious dry air there through 00z Wednesday closer to surface hi 
in Quebec. 


Coordinated with grb. 


&& 


Aviation /for the 18z taf issuance/... 


Morning fog has dissipated with VFR conditions expected at saw and 
cmx through the evening hours. With surface ridge moving east of the 
area and pressure gradient tightening...southerly winds should 
prevent fog from getting as dense as last night. However...with low 
level moisture remaining...do expect some fog to redevelop after 
midnight...especially until southerly winds begin to increase 
towards daybreak. In addition..expect MVFR stratus ceilings to develop 
at both sites late tonight and persist through Sunday morning. 


&& 


Marine /for the 4 am Lake Superior forecast issuance/... 


Winds will remain below 25 knots through this forecast period as 
high pressure remains over the upper Great Lakes and keeps systems 
out of the area. Winds will start to increase Wednesday...possibly to gale 
force...as a storm system comes up from the south. 


&& 


MQT watches/warnings/advisories...none. 


&& 


$$ 


Synopsis/discussion...kc 
aviation...mz 
marine...Pearson 

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