277 
fxus63 kmqt 182020 
afdmqt 


Area forecast discussion 
National Weather Service Marquette Michigan 
421 PM EDT Friday Jul 18 2008 


Synopsis/short term (tonight and saturday)... 
upper air pattern consists of a 500 mb ridge across the southern 
u... in the Pacific northwest and across Ontario and near zonal 
flow along the northern U.S. There is a shortwave in the Pacific northwest 
embedded in the trough which will affect the weather in the short 
term beginning Sat night. 


NAM showing some 850-500 mb q-vector convergence for Sat afternoon 
along with some moisture along the WI/Michigan border 00z sun. GFS is dry 
while the European model (ecmwf) and UKMET and Canadian show some precipitation right up to 
the border. With this in mind...will push bvack probability of precipitation until late in 
the afternoon and keep slight chance along the border with the next 
shortwave coming in. NAM appears to be affected by convective 
feedback especially Sat night Onward...so its solution is suspect at 
this time. 


For tonight...patchy fog will form again as low level moisture has 
not really had a chance to mix out or scour out very much at all 
today. Light winds and plenty of low level moisture spell patchy fog 
to redevelop again tonight...so put into the forecast. For 
temperatures...did not make any changes to the going forecast except 
for a few tweaks here and there for highs on Saturday. Warmed things 
up a bit along the Lake Superior shoreline as water temperatures are 
now finally starting to warm up a bit even on the Open Lake. 


Long term (saturday night through next friday)... 


Big forecast questions revolve around shortwaves moving through Sat 
night and then again on Sunday. 


Quicker and deeper NAM solution with Sat night shortwave has generally 
been discounted by NCEP as an outlier as its precipitation/surface pressure fields 
look to be contaminated by convective feedback. Generally followed 
along with a blend of the European model (ecmwf)/Canadian and UKMET solutions which have 
been pretty consistent the last few runs in showing increasing upper 
divergence/DPVA/and deep layer qvect conv in left exit region of associated 250 mb 
jet maximum of shortwave moving east across the forecast area. There is still some 
models uncertainty with the timing of the shortwave and associated precipitation 
so have kept in just the 30/40 probability of precipitation of going forecast. Again kept higher 
probability of precipitation along the southern counties closer to 850 mb warm fnt...in line with 
European model (ecmwf) quantitative precipitation forecast fields. 


As the Sat night shortwave departs on sun...another shortwave now over 
southeast British Columbia is forecast to move into the upper Great Lakes and 
maintain upper troffing and cyclonic flow over the region into Monday. Kept in 
chance probability of precipitation from sun into Monday. High temperatures by Monday should cool off into 
the lower 70s under cloudy skies and a cool onshore NE flow off Lake 
Superior. 


12z European model (ecmwf) and GFS both in agreement showing amplified middle-upper ridge 
over the northern plains building toward the upper Great Lakes. Difluent 500 mb 
flow and associated subsidence ahead of the ridge will keep the upper Great 
Lakes dry at least into midweek with perhaps slightly cooler than 
normal temperatures. 


Followed the 12z European model (ecmwf) and GFS ensemble mean which indicates a 
breakdown of the middle-upper ridge by late week as another shortwave 
approaches from southern Canada. Brought chance probability of precipitation back into the forecast area 
for next Friday. 


&& 


Aviation (for the 18z taf issuance)... 


Conditions will continue to improve at kcmx this afternoon and will 
go VFR soon. Kcmx will then drop back to LIFR tonight with light 
winds and plenty of low level moisture around to form fog and ground 
fog before heating in the morning mixes this back out. Ksaw...VFR 
conditions will give way to LIFR conditions again tonight with low 
level moisture and light winds around causing fog/ground fog. 
Heating will mix this back out Sat morning and will go back to VFR 
conditions. 


&& 


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


Expect fog to persist through Saturday morning on the waters due to 
light winds and abundant low level moisture and lack of really 
strong mixing. A bit of drier air pushing across the lake tonight 
should scour out the fog a bit to make it patchier. East 
to northeast winds expected to start the weekend as low pressure 
develops in the plains and a high pressure ridge is present over the 
upper Great Lakes. No strong winds forecasted anytime soon. 


&& 


MQT watches/warnings/advisories...none. 


&& 


$$ 


Synopsis/short term...GM 
long term...Voss 
aviation...GM 
marine...GM