Weather

943 
fxus63 kmqt 280523 aab 
afdmqt 


Area forecast discussion...updated 
National Weather Service Marquette Michigan 
130 am EDT Thursday Aug 28 2008 


..update for 06z taf issuance... 




Synopsis... 


A broad upper trough over western Canada into the northern US rockies 
will shift east and eventually bump the ridge over the Great Lakes to 
the east. Stronger shortwave within the trough and a decent upper jet 
of 130kt at 250mb come east through Thursday bringing a chance of rain showers 
and thunderstorms and rain to the upper Great Lakes. Primary surface front that is over central 
Minnesota has not moved much today as winds aloft are parallel to the 
front. Expect this to change tonight once the shortwave and height 
falls spread into Minnesota which will kick the surface front to the east. 
Arrival of the stronger dynamics later will combine with the front 
to aid in developing swath of rain showers from Iowa into eastern Minnesota and Western Lake 
Superior. Front and rain chances progress into far West County warning area after 
midnight tonight then slides across rest of the County Warning Area on Thursday. At this time 
best bet for a widespread wetting rainfall is over the western tier from 
Gogebic County into the Keweenaw peninsula. Once the trough moves 
through...a warming trend and dry weather becomes established Friday 
through Labor Day. Next chance of rain arrives Tuesday/Wednesday as a front 
approaches from the northern plains. 


&& 


Short term (tonight and thursday)... 


Not completely sold on widespread rain over all of County Warning Area. Frontal 
boundary pushes into far West County warning area between 06z-12z. Increasing low level 
winds allow for 900-850mb Theta-E advection into the front while 
stronger middle level dynamics (divergence aloft with rrq of jet streak 
and height falls) interacting with the increasing moisture should 
lead to widespread rain showers and a few elevated thunderstorms and rain (si/S around zero) 
shifting into far western Upper Michigan. Into Thursday...expect precipitation to become more 
split as it translates into rest of County Warning Area. Kept highest probability of precipitation during 
the morning on the Keweenaw along track of shortwave as it lifts 
into north Central Lake Superior and Ontario. Otherwise...good deal of clouds 
and isolated-scattered rain showers should linger well into the afternoon over rest of the 
County Warning Area. After 18z...shra/tsra may become more organized over scntrl into 
eastern County Warning Area where 900mb-850mb moisture inflow is maximized due to a south-southwest 
850 mb jet lifting ahead of surface front. Instability anywhere on Thursday 
seems marginal as clouds should hold down heating. Surface based convective available potential energy 
using a T/dew point 75/60 only gives values to around 400j/kg. MLCAPES are 
minimal. Is enough elevated instability with si/S on the negative 
side to keep thunderstorms and rain in the grids...but with lack of heating...does not 
appear to be near enough cape to offset the strong 0-6km shear 
values over 50kt to promote balance for any updrafts. Storm Prediction Center day2 
outlook has the 5 percent contour well to the south over southern WI. 


&& 


Longer term (00z Friday onward)... 


NAM showing a 500 mb trough over the upper Great Lakes 00z Friday which 
pushes east Thursday night and Friday with flow becoming zonal Sat. NAM 
showing moisture and 850-500 mb q-vector convergence moving out Thursday 
night. GFS shows the same thing and will go with a blend for this 
forecast. Kept likely probability of precipitation over the east for Thursday night with some 
strong dynamics moving across that area...jet streak and decent 
moisture then. Kept it dry then for Friday through sun. As for 
temperatures...went pretty close to adjmeh and adjmvr for lows. The 
warmer guidance during the daytime seems to be the way to go with 
warm 850 mb temperatures and cannot see why we would not mix down 
from 850 mb to the surface at this time. Overall...did not make too many 
changes to the going forecast. 


In the extended...GFS...ECMWF and Canadian show a 500 mb ridge in 
control of the weather 00z sun. This ridge then builds into the area 
00z Monday through 00z Tuesday with a trough moving into the northern 
plains then. The trough creeps by to the east slowly 00z Wednesday to the 
northern plains and far upper Great Lakes then. Will continue to 
follow close to the 00z European model (ecmwf) due to its consistency. Went with 
adjmeh for much of the temperatures as it looks pretty warm. Kept 
probability of precipitation in for Tuesday with a weak cold front coming through and 
possibility of lake breeze convection as well. Went with warmest 
guidance which was adjmeh. All other guidance looked way too cold 
for highs with GFS...European model (ecmwf) having 850 mb temperatures around 18c 
which gives ME highs around 90 if mixed to the surface. 


&& 


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


VFR conditions expected through much of the night due to lingering 
low level dry air associated with high pressure exiting the region. 
Strong disturbance and cold front will aprch late tonight...with low level wind shear 
developing at cmx and then saw later with the aprch of the sharper pressure 
gradient. Although rain showers appear likely at cmx during the overnight 
into early Thursday morning...expect low level dry air to maintain 
VFR conditions through 12z with conditions then trending MVFR Thursday 
morning as SW winds advect in additional low level moisture. More 
confident in seeing a MVFR ceiling but there could be some light fog as 
well once rain showers end. Precipitation looks to diminish as it heads toward saw 
with better lifting splitting to the north into Ontario and south 
into Wisconsin. Although a few rain showers could make it/develop near saw 
by midday as front progresses through there as another shortwave catches 
up with the front. 


&& 


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


Expect high pressure over New England drift to the Canadian 
Maritimes into Thursday. A low pressure system taking shape in the 
northern plains will move across the upper Great Lakes on Thursday 
and then through Ontario on Friday while dragging a cold front 
across Lake Superior. South-southeast winds over mainly the east and central 
will increase as high as 25-30 knots tonight into Thursday before 
diminishing later in the day as the low crosses Western Lake 
Superior. A high pressure ridge will then follow into the upper 
Great Lakes on Friday before a weak low pressure trough crosses Lake 
Superior on Friday night. Winds beyond Friday night will remain below 
20 knots. 


&& 


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


&& 


$$ 


Synopsis...jla 
short term...jla 
long term...GM 
aviation...mz 
marine...jla 

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