Weather

540 
fxus63 kdlh 112021 
afddlh 


Area forecast discussion 
National Weather Service Duluth Minnesota 
321 PM CDT Sat Oct 11 2008 


Discussion... 
active synoptic setup with threat of heavy rain 
over the next 72 hours for much of the region. This rainfall...in 
addition to the soggy past few weeks...may result in localized 
flooding problems. No flooding headlines will be issued at this time...but 
this situation will continue to be monitored closely. Main threat 
for heavy rain will be Sunday night through Monday. 


Previous forecast on track with updates to increase probability of precipitation through Monday as 
well as adjusting for slightly slower trend to frontal passage /by 3-6 hours/ 
as portrayed by NAM/ECMWF. Introduced heavy rain wording to Sun 
night and Monday periods. Temperatures/dew points were trended 
upwards through short term closer to met guidance to account for 
strong moisture/warm air advection through sun. 


Models are in good agreement with weekends frontal system and 
Deep Cut-off upper level low that follows. Model of choice for short 
term forecast was the NAM witch has shown run to run consistency over 
the past few days and has good agreement with European model (ecmwf). The outlier 
appears to be the GFS with a faster solution with the frontal 
passage. 


This evening and overnight...surface low pressure in SW Minnesota will 
continue to lift a warm front over the Northland and into southern 
Canada. This will all for the rain showers/thunderstorms and rain that is ongoing this afternoon 
to persist through the evening. Although small hail is 
possible...these storms are not expected to reach severe levels. The 
rain showers will increase in coverage through evening...becoming 
widespread...mainly over the northern 1/3 of the County Warning Area...through the 
night. The forecast area will be situated in the warm sector tonight through 
sun. A developing 40-50 knots low level jet and intense moisture and Theta-E 
advection will allow for dew points and precipitable waters  to rocket near Summer- 
like values by Sun afternoon. The combination of strong forcing and 
abundant moisture will bring a threat for heavy rain along and 
ahead of a slow moving cold front that will sweep east over the 
region Sunday night through Tuesday. NAM bufr forecast soundings agree 
with heavy rain potential with deep saturation...precipitable waters  around 1.5 
in...and a parallel flow to the front allowing for significant 
cell training. 


&& 


Aviation/extended... 


Main inverted surface trough across western County Warning Area with majority of 
precipitation/clouds aligned north and west of this feature. VFR for most 
of County Warning Area this afternoon except inl where low clouds/precipitation remain 
entrenched. Expect worst conditions to prevail near inl through the 
period with MVFR dropping to IFR/LIFR overnight. Farther 
east...latest sref indicates VFR for most of period although 
probability of MVFR ceilings increase slightly through 15z. Have 
opted to lower most terminals to tempo MVFR in early morning time 
frame. 


Extended...Monday through Thursday...majority of model guidance supports timing 
of main frontal system through County Warning Area Monday. GFS is outlier with rapid 
progression of main features so will lean with ec/sref blend.. with 
support from CMC...powerful 140kt upper jet will race north into eastern 
Dakotas by early Monday as large piece of southwestern low ejects towards 
southern Manitoba. Synoptic pattern favors more of a significant rain 
threat as opposed to svrwx. Models agree that a ribbon of 1.5/2" precipitable water 
should advect northward ahead of front. 850 mb moisture transport magnitude 
approaches 250 ktsg/kg. Limiting factor for excessive rain may be 
steady progression of potential heavy rain axis. 
However...considering the tropical contribution from Norbert and the 
amplitude of the middle level trough...will need to monitor north and 
western area of County Warning Area starting late Sunday into Monday. 1/3/6hr ffg 
values high enough initially to limit threat. Clearing occurs Monday 
afternoon from west to east as northern branch ejecting low moves 
eastward. Ec takes remaining southern branch energy and develops second 
area of lift/precipitation which could skirt southeast County Warning Area by Tuesday evening. 
Meanwhile next northern branch system approaches Tuesday night and may 
actually draw southern branch moisture farther north. Temperatures above normal 
through Monday before cold front brings temperatures near/slightly below 
seasonal levels. 


&& 


Point temps/pops... 
dlh 58 53 67 56 / 30 40 40 50 
inl 52 51 62 46 / 60 80 80 80 
brd 63 57 70 55 / 60 60 70 80 
hyr 73 59 76 62 / 20 20 30 40 
asx 71 56 74 59 / 20 30 30 40 


&& 


Dlh watches/warnings/advisories... 


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


$$ 


Graning/Cannon