949 
fxus63 kmqt 200539 aab 
afdmqt 


Area forecast discussion...updated 
National Weather Service Marquette Michigan 
138 am EDT Wednesday Aug 20 2008 


Updated aviation discussion 06z taf issuance 


Synopsis... 
19z water vapor loop and RUC 500mb height analysis showed upper 
ridging from south central Canada into the upper Midwest...Tropical 
Storm Fay crossing Southeast Florida...a 582 dam low near Wichita Falls 
Texas...and a trough over the NE Pacific into the Pacific northwest. Upper Michigan 
lies on the east side of the upper ridge...which favors subsidence 
and high pressure at the surface. Currently this high is centered along 
the Eastern Lake Superior/Ontario shoreline. A lot of dry air exists 
near this high...noted on tamdar soundings from saw and cmx which 
have 30-40c dewpoint depressions between 850-700mb. Mixing of this 
dry air to the surface has been somewhat troublesome...though...due 
to the cold air that moved in last night. Some locations last night 
dropped into the 30s...such as Chatham which fell to 34. This cold 
air even generated some lake effect clouds over Northern Lake Michigan...but 
these have since dissipated. To our SW...another band of moisture 
noted by clouds extends from dlh to grb. Tamdar sounding from rhi 
shows this with a bit more saturation between 800-900mb. Other low 
clouds exist down near Milwaukee. Farther to the S...upper level 
moisture can be seen streaming northward from Louisiana into 
Missouri on the east side of the upper low. A few storms are also 
noted in Louisiana where dewpoints are in the 70s. Well off to the 
west...storms are marching across the Pacific northwest with the incoming 
upper trough. 


&& 


Short term (tonight through Wednesday night)... 
quiet weather is expected to prevail through this period...thanks to 
the upper ridge over the upper Midwest shifting over Upper Michigan on 
Wednesday...resulting in continued subsidence. However...there are a few 
issues to deal with...mainly clouds and temperatures. This evening should 
generally be clear across the County Warning Area...then some increasing clouds are 
expected over the western u.P. As return flow brings the clouds to 
our SW into the area. Where these clouds move in will also be the 
same area where southerly winds pick up tonight...and therefore 
forecast lows are similar to guidance. Over the eastern half of 
Upper Michigan where skies are clear...the winds are generally light all 
night and precipitable water stays around 0.50 inch...expecting 
temperatures to get chilly again. Went below all guidance given what 
happened last night since similar conditions are present...except 
that the airmass has modified slightly since yesterday. Return flow 
clouds should continue shifting into the central u.P. On Wednesday...but 
not prevent a decent amount of sunshine from occurring. This 
sunshine...combined with 850mb temperatures of 14c east to 16c west will 
bring highs into the 70s and 80s...coolest along the Lake Michigan shore 
with onshore winds and warmest in the western u.P. Where the deepest 
mixing is expected. 


For Wednesday night...the GFS/NAM/UKMET all depict a shortwave moving on top 
of the upper ridge. This shortwave should have little impact given the 
dry air in place...and likely only producing a few clouds. Therefore 
a dry forecast remains. A southerly breeze continues in the western 
u... temperatures will be on the mild side (followed a blend of the 
met/mav guidance). For the eastern u... are indications that 
winds may decouple in the inland areas. However...precipitable water 
values are between 0.75 inches and 1 inch...suggesting the night 
should not be nearly as cold as the last two. Therefore...have lows 
inland dropping below guidance to around 50. 


Long term (thu through next tue)... 
period begins with region still under the upper ridge and influence 
of high pressure centered over the NE U.S. Farther west...longwave 
trough working into the Pacific northwest at 00z Thursday...which will be the 
next weather maker for this area and bring the best chance of rain 
in the extended period. 


Thursday looks to be dry with region between the surface low over Canadian 
rockies and warm front stretching east across southern Canada...and upper 
low that has been lingering over the Southern Plains for the last couple 
of days. Disturbances coming out of the upper low will affect the 
region at a couple different times. First wave comes through early 
on Thursday and expected to be dry...due to limited forcing and dry air 
lingering over the area from the existing high. Moisture looks to 
stream into the southern part of the County Warning Area on Thursday afternoon and continue 
across the rest of the County Warning Area on Thursday night. There are some 
differences in the 00z European model (ecmwf) and 00/12z GFS runs...as to light precipitation 
across the southern part of the County Warning Area for Thursday night. The 00z European model (ecmwf)/GFS do 
bring precipitation to the area...as another weak shortwave and h850-700 
q-vector convergence moves across the region. Believe there should 
be enough moisture to squeeze a some -shra out...so have added 
slight chances to the south central part of the County Warning Area. 


For Friday...precipitation chances become a little harder to pinpoint...as 
upper low continues to shear out and lingering energy slides NE 
across the eastern part of the County Warning Area. With the moisture already present 
and weak Omega/qvector forcing on GFS/ECMWF...felt adding slight 
chances to eastern half of County Warning Area was warranted. As for the western 
half...with the area between the wave to the east and approaching 
surface low over Lake Winnipeg and surface cold front stretching S along the 
Red River valley and S to kfsd and into eastern Nebraska between 18z Friday and 
00z Sat...dont really see much chance of precipitation and more likely just 
partly sunny skies. Therefore...added slight chances for the western 
third due to approaching front. Winds will be a little gusty from 
the south ahead of the front on Friday...which may create a few marine 
headlines. Fortunately...Gulf moisture working north with the winds 
should limit any fire weather issues with the dry weather of late. 


Cold front moves through the region fairly quickly on Friday night and 
into Sat. Instability increases on Friday over the western half of the 
County Warning Area...with MLCAPES around 500-700 j/kg by Friday evening. With the 
strong h850 jet...around 40-45kts ahead of the front...and 6-7c 
h700-500 lapse rates...expect some rumbles of thunder as the front 
moves through. 0-6km bulk shear values are expected to be around 
35-40kts...but with cape diminishing during the overnight 
hours...down to 200-400 j/kg and very tall/skinny...dont really 
expect anything severe. Biggest threat will be some gusty winds if 
precipitation loading can bring some of the winds aloft down. Overall...with 
precipitable water values around 1... should see some much needed rain across 
most of the region. 


Sat night through Tuesday...extended models in pretty good agreement on 
high pressure dropping south across region. As the upper low shifts 
across the area on sun...should probably see some low/middle clouds 
across Lake Superior and over land locations near Lake Superior. GFS has 
been hinting that a few showers may develop over the far eastern part of 
the County Warning Area on sun...which wouldnt be surprising given the amount of 
moisture and proximity to upper low...but didnt have enough 
confidence to put it in right now. Drier air then works into the 
area for Sun night through Tuesday...as high moves from The Arrowhead 
of Minnesota on sun...to the NE U.S. On Tuesday. With limited cloud 
cover...subsiding winds...and precipitable water values expected to be about 50 
percent of normal...could see some cold nights under the high on 
sun/Monday night. Have trended the lows down into the middle 40s for 
interior locations...but expect the traditional cold spots to be 
even colder. Future shifts will probably need to adjust the temperatures 
down further. Highs on Monday/Tuesday should be near to slightly below 
normal with h850 temperatures in the 10-12c range. 


&& 


Aviation (for the 06z taf issuance)... 


Expect VFR conditions/light winds to prevail this forecast period with hi pressure 
ridge/dry airmass remaining dominant. 


&& 


Marine (for the 4 PM Lake Superior forecast issuance)... 


High pressure over southeast Quebec will shift east over the northeast U.S. 
On Thursday...allowing winds to shift to the south and increase 
through Friday. This is due to an approaching low pressure system 
over Canada and associated cold front over the northern plains on Friday. 
Winds are expected to get a little gusty on Friday...with gusts to 
25kts over Eastern Lake Superior and Lake Michigan. With the frontal 
passage late Friday night and Saturday...winds will become gusty 
from the west northwest up to 25 knots. High pressure then moves 
over the region for Sunday through Tuesday and keep winds less than 
20kts. 


&& 


MQT watches/warnings/advisories...none. 


&& 


$$ 


Synopsis/short term...aj 
long term...srf 
aviation...kc 
marine...srf 

National Weather Service Glossary of Abbreviations

Non-Expanded Version (with abbreviations)