Weather

487 
fxus63 kmqt 080754 
afdmqt 


Area forecast discussion 
National Weather Service Marquette Michigan 
354 am EDT Monday Sep 8 2008 


Discussion... 
the main concern is with the chance of showers today. 


Water vapor imagery and RUC indiates a longwave trough over Hudson 
Bay. A weak ridge is building over British Columbia. A zonal flow is 
developing from the Dakota trough New England. Weak shortwaves are 
sweeping through the forecast area and Minnesota this morning. An 
upper level jet races from South Dakota through central Wisconsin 
into central lower Michigan. Surface analysis depicts a low over 
James Bay with a cold front draped southwst northern lower Michigan 
then into the Central Plains. A large dome of high pressure 
continues to build over the northern plains. 


Models have come inline and are in fairly good agreement through 72 
hours...except the global Gem which is an outlier keeping activities 
further south then the rest of the models. Plan to go with the 
majority. 


The shortwave over South Dakota will rotate into Wisconsin today. A 
portion of this shortwave will shift into western u.P. By late this 
afternoon increasing some q-vector convergence over the forecast 
area. The cold front will track through lower Michigan as the ridge 
builds into the upper Great Lakes bringing drier air. Forecast 
soundings showing a moist layer around 3k feet (900mb) shifting 
across the area. A strong inversion and drier air will dominate 
conditions above this layer. Therefore...looking for cumulus 
development today...but the cap and dry low levels will prevent any 
preciptiation today. Late in the day low level moisture will wrap 
into the area from the southeast associated with the shortwave. As 
stated in earlier afd's...the lake-850mb Delta-t's of around 14c 
this morning could produce a few isolated lake effect light rain 
showers before the drier air advects into the area. So will keep a 
mention early. Strong northwest winds over the lake will generate 
significant waves and produce an increase risk of rip currents 
especially along the shore between Munising and Grand Marais. Check 
the Lake Shore hazard message for more details. 


A middle level low will develop over Western Lake Superior by early 
evening and sweep across Lake Superior tonight. The surface ridge 
will remain over the area. Due to the shortwave instability...I will 
not rule out completely the chance of rain showers along the Lake 
Michigan shore where a little more precipitable waters  is present. Delta-t's will 
be strong enough to continue low level instabilty...but the low 
level dry air will limit preciptiation and cloud cover. 


The middle level low will slide east early Tuesday while the surface 
ridge shifts across the forecast area. In the morning...the 
shortwave instability along with lake effect enhancement will keep a 
chance of showers over the eastern part of the forecast area in the 
morning. Drier air will invade the area and a warming trend at 850mb 
will limit lake effect rain showers development over the central 
and eastern part of the forecast area in the afternoon...so will 
lower probability of precipitation for eastern u.P. In the afternoon. 


The ridge will remain through Wednesday. Dry air will remain in 
place. Meanwhile...to the west a middle level trough will develop over 
the northern High Plains. Weak shortwaves developing over the 
Dakotas Wednesday morning...will shift over Western Lake Superior 
late on Wednesday. The surface ridge will push through the lower 
Great Lakes while a low develop over the Central Plains with a weak 
trough stretching through the northern plains. Deep moisture will be 
drawn into northern Minnesota by the low. This appears to be a 
little slower than earlier broadcasted by guidance. 


The middle level trough will shift into Manitoba and the northern 
plains Wednesday night. Shortwaves ejected out ahead of the trough 
will navigate through the forecast area Wednesday night. The 
associated surface low will track into southern Minnesota drawing 
the trough into The Arrowhead of Minnesota. Isentropic ascent with 
the front and shortwave energy will generate showers and possible 
thunderstorms through Thursday. With the system appearing to slow a 
little...the preciptation may be a little slower to exit the 
forecast area Thursday night and Friday than ealier projected. Will 
wait to see what the Middle Range models before updating timing on 
these. 


&& 


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


Convection associated with the cold front has exited...with west to 
northwesterly winds remaining. These winds along with cooler air 
aloft and plenty of low level moisture have combined to produce 
light precipitation along the far western counties. Look for light 
precipitation to continue...mainly affecting cmx. Some improvement 
is figured during the daylight hours Monday. 


Towards the end of the period...we will need to keep an eye on 
shower activity coming in from the south. While cmx should remain 
dry...showers could be possible at saw as early as 00z. Will keep 
saw dry for now...with a greater hint at cloud cover. 


&& 


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


Winds will quickly diminish from west to east today as a high pressure ridge 
noses into the area. High pressure will move to the lower lakes Wednesday 
afternoon...resulting in increasing srly winds Wednesday. Srly winds may 
increase into the 15-25mph range Wednesday night/Thursday (mainly over Eastern Lake 
superior) prior to a trough crossing the area Thursday night. This would be 
the next opportunity for stronger winds. No gales seen at this time. 


&& 


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


&& 


$$ 


Discussion...dlg 
aviation...GM 
marine...GM