Weather

341 
fxus63 kdlh 070158 aab 
afddlh 


Area forecast discussion...updated 
National Weather Service Duluth Minnesota 
858 PM CDT Sat Sep 6 2008 


Update... 
reduced precipitation to isolated category for the rest of the 
evening. We added patchy fog after midnight. 


&& 


Discussion... 
afternoon and evening convection is finally decreasing in coverage 
and...in most areas intensity...clusters of strong thunderstorms 
continue Half Way up the North Shore...south of Bayfield 
peninsula...in the upper saitn croix valley and apparently through 
the Rainy River valley. We ancpt thunder to become less frequent 
and these to weaken into showers toward midnight. An approaching 
trough will spread more showers from west to east across northeast 
Minnesota after midnight. We do not ancpt any more vigorous 
convection late tonight or early Sunday. Holes in the cloud cover 
will result in radiation type fog...we do not ancpt marine fog. 


&& 


Aviation... 




&& 


Previous discussion... /issued 614 PM CDT Sat Sep 6 2008/ 


Update... 
put much more emphasis of showers tongight...especially this 
evening and included thunderstorms this evening. Kept winds up a 
little bit. 


Discussion... 
as has been the case the past few evenings...supposedly diurnal 
showers are continuing to increase in both intensity and coverage. 
This evening will probably be no different than the past two 
evenings...as far as timing of maximum convection between 00z 
and 04z...with showers continuing well past 06z. At this time...a cluster 
of small but rather intense thunderstorms is moving through the 
Iron Range and refusing to weaken...evm has had 40 miles per hour out of the 
outflow. A strong outflow boundary is exiting the Iron Range 
toward the south and beginning to interact with more thunderstorms 
as it moves along. With the low freezing level...small hail is a 
virtual certainty and localized one-hour precipitation is about an inch 
with many thunderstorms...not just in the Iron Range but all 
across our forecast area. We are covering this with strong now 
casts but if anything gets any worse or any reports begin coming 
in...we will begin with the warnings...we are getting 65 dbz 
echoes and...though small in extent...clear evidence of rotation. 


A strong trough is approaching the Red River. We feel that 
intensity will diminish but coverage of showers is apt to begin 
increasing along our western border a few hours after midnight and 
then work east as dawn approaches Sunday. 


If Sunday afternoon bears any similarity to the past several 
afternoons...with a cold column that cools more rapidly aloft and 
strong cyclonic circulation...as indicated...we will have to 
really watch the convection situation. The coming trough is ancpd 
to be quite vigorous Sunday. 


Previous discussion... /issued 321 PM CDT Sat Sep 6 2008/ 


Discussion...main forecast challenge is probability of precipitation through Sunday. 
Upper level flow pattern consists of broad trough across central 
Canada/north central Continental U.S.. diurnally triggered scattered rain showers/ts this 
afternoon should diminish with loss of surface heating this 
evening...and with eastward progression of short wave in trough 
aloft. Possibility of small hail and gusty winds with strongest 
cells will exist through late afternoon...with low freezing 
levels of 6 to 7 kft and steep low level lapse rates per NAM 
soundings. A more potent vorticity maximum now evident on water vapor 
imagery across southern Saskatchewan/Manitoba will approach the 
region late tonight. Stronger forcing per 2-d frontogenesis and 
low level Theta-E advection brings high confidence in raising probability of precipitation 
with this system. Moderate instability...especially across the 
eastern portions of the forecast area Sunday afternoon...along with strong 
low level convergence along the surface trough/cold front 
line...should result in some organized afternoon convection. Cool 
and dry high pressure will then build into the northern plains 
region for Sunday night. 


Still some model differences in placement...however a significant 
frontal system will push across the central Continental U.S. Monday/Monday 
night. GFS brings precipitation shield farthest north...but will 
maintain just small probability of precipitation at this time with dry high pressure expected to 
suppress northward progression of this system. Tuesday into 
Wednesday will be seasonably cool with dry high pressure in 
place...and weak ridging aloft. Should see a warming trend for middle 
next week ahead of next significant northern stream 
trough...looking to pass through Wednesday night and Thursday. 
Strong Theta-E ridge with main baroclinic zone across the 
forecast area...will bring possibility of significant precipitation with this 
system. 


Aviation...mainly broken cumulus-stratocu can be expected across the 
area through early evening...with scattered to numerous 
showers...and a few thunderstorms. Ceilings will generally remain 
at or above 4k feet above ground level...but could occasionally drop to 
MVFR...especially in any heavier showers. As a shortwave passes 
east of the area early this evening...conditions may temporarily 
improve between 00z and 04z...before deteriorating overnight as 
another shortwave pushes across northern Minnesota. Areas of fog 
will also be possible...especially after 09z. For Sunday...a more 
potent shortwave and surface trough will bring continued low end 
VFR-MVFR ceilings and the increased risk for occasional rain 
showers...especially after 14z. Winds will remain 10 kts or less 
through the taf period. 


&& 


Point temps/pops... 
dlh 47 59 44 60 / 20 60 20 10 
inl 41 58 37 59 / 40 60 20 10 
brd 45 63 41 61 / 20 60 10 10 
hyr 41 64 39 61 / 20 60 30 20 
asx 45 64 42 61 / 20 60 40 20 


&& 


Dlh watches/warnings/advisories... 


Minnesota...none. 
WI...none. 
Ls...none. 


$$ 


Eom/tl