241 
fxus63 kdlh 211612 
afddlh 


Area forecast discussion 
National Weather Service Duluth Minnesota 
1012 am CST Sat Nov 21 2009 


Discussion... 
metars...satellite...and webcams all show fog was lifting this 
morning. The visibility has improved to 2sm in kpbh...to 1.5sm in 
kcoq...and to 0.5sm in kmzh. Remaining fog will lift over the next 
couple hours. 


Otherwise...we increased sky cover some today to account for 
cirrus moving in. We also dropped temperatures a couple degrees. 


We also increased clouds tonight to account for increasing low 
level moisture. 


&& 


Previous discussion... /issued 553 am CST Sat Nov 21 2009/ 


Update...for 12z taf set...see discussion below. 


Aviation...12z taf issuance MVFR/IFR visibilities will persist until 15-16z 
with IFR/LIFR at khib with fzfg based on latest observation...stubborn 
high pressure over the lake..and as per NAM/RUC low level 
condensation pressure def forecast. Khyr is on the border of a bank of 
LIFR fog pushing north. Kdlh may see some fog as well with MVFR 
visibilities before 15z before thin cirrus moves in. Anticipate all taf 
sites to be VFR after 16z with cirrus and increasing winds. 


South-southeast winds will pick up today as a pressure gradient forms over the 
area from the departing high and 992 mb low that will push through 
Manitoba. Mixing layer is not very deep...but we do expect some 
gusts in the western terminals especially. 


Late tonight...warm air advection regime will result in MVFR/IFR ceilings...mainly 
after 9z. Models do try to break out precipitation...with the best chance 
at khyr...but slightly deeper saturation will occur after 12z. 


This taf set has introduced low level wind shear at khyr only. A 
strong low level jet will develop late tonight...but shear should 
be mainly speed shear at our western taf sites. Higher confidence 
for lighter winds and some directional shear exists at khyr. 
Future taf sets can monitor this trend to see if it will be added elsewhere. 


Previous discussion... /issued 338 am CST Sat Nov 21 2009/ 


Discussion... 
at this time...an area of shallow fog surrounds and covers Price 
County. Isolated patches of fog...across other areas south of 
Duluth...are having trouble spreading or becoming established due 
to the dryness of the column...especially above the nocturnal 
inversion. A fog advisory rather than a freezing fog advisory has 
been issued since the ground is relatively warm and most frost 
accumulation is restricted to such objects as elevated decks... 
branches and railings rather than roads...walks...or even bridges. 


Deep ridging of Pacific air...both surface and aloft...will 
maintain an axis over the Central Lakes. A pressure gradient to 
the west...over our area...will maintain a brisk south flow just 
above the surface today and especially tonight...where a low-level 
wind shear situation could develop. Falling heights aloft and an 
embedded surface trough will weaken the low level south flow a 
little and bring enough moisture for scattered showers across the 
area Sunday. 


Extended...Sunday night through Friday. 
The models begin the period in fairly good agreement and then 
diverge. A cold front from Mille Lacs up through Duluth and along 
the North Shore will begin to wash out as seen in the wind 
field...but the low level thermal gradient lingers over the area. 
A disturbance will ride along the boundary...triggering 
precipitation into Monday morning. Best moisture transport/low level jet 
along the North Shore and into northwest wisc. After disturbance and 
departing jet cruise off into Canada and merge with the northern 
stream flow...the front then moves north as a warm front as wind 
field becomes more southerly in response to a deepening larger 
amplitude middle level low pushing out of the northern rockies into 
the Central Plains. Probability of precipitation were increased in northeast Minnesota 
accordingly...with an inverted trough axis through our northwest zones. 
Though models agree on evolution...some small differences are seen 
in precipitation fields. Northwest wisc should dry out for a time on Monday with 
drier air filtering in from the east. 


Models then begin to diverge on the surface reflection of this upper 
low as well as the upper low track. General ideas have the GFS/sref 
being the fastest and the furthest north...the NAM and European model (ecmwf) being 
on the slower side...with the Gem in the middle. Have gone closer to 
Gem...though it is interesting of note that the 0z European model (ecmwf) has sped up 
and come further north. The general idea though is that the precipitation 
will linger in northwest Minnesota along the inverted trough axis before the 
upper low swings south and shoves the surface low east of the area. 
On its heels is a fast moving clipper that the GFS moves the best 
forcing south...the European model (ecmwf) further north...with both models pushing a 
cold front through. Temperatures do not get cool enough to support a 
rain/snow mix until Wednesday...so we have removed any snow mention and 
raised temperatures on Tuesday. Either way...conditions will remain 
unsettled through middle-day on Thanksgiving before high pressure 
builds back in. Upper level heights and low level thicknesses 
respond quickly as the upper jet builds back north of the border. 




&& 


Point temps/pops... 
dlh 48 36 49 39 / 0 10 30 30 
inl 49 31 46 29 / 0 10 30 10 
brd 50 36 51 37 / 0 10 20 30 
hyr 51 36 52 40 / 0 10 30 30 
asx 52 37 51 41 / 0 10 30 30 


&& 


Dlh watches/warnings/advisories... 
Minnesota...none. 
WI...none. 
Ls...none. 
&& 


$$ 


Melde/eom/donofrio