014 
fxus63 kmpx 191647 
afdmpx 


Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota 
1147 am CDT Friday Mar 19 2010 


Update... 
updated to include 18z aviation discussion below. 


&& 


Discussion... 
cold advection and cyclonic flow over the area this morning are 
helping to keep temperatures down and cloud cover in place. The 
flow looks to become more anticyclonic during the afternoon into 
the evening hours... so expect somewhat of a decrease in clouds to 
eventually occur... but likely not until tonight. With that in 
mind... and with the 12z radiosonde observation showing a show inversion at the top 
of the mixed layer... do not anticipate much of a rise in 
temperatures today... with readings likely holding steady or going 
down a degree or two through noon then perhaps rising slightly 
during the afternoon. Adjusted forecast highs down a bit to 
account for this. Otherwise... made only minor tweaks to the going 
forecast with respect to probability of precipitation across the south and the chance for 
some scattered flurries. 


&& 


Aviation.../18z taf issuance/ 
widespread MVFR ceilings are in place across the region at the 
current time in the area of cold advection and cyclonic flow 
behind the cold front which moved through. The boundary layer flow 
is expected to become anticyclonic late this afternoon and tonight 
with the boundary layer relative humidity also dropping off as increasing 
subsidence works into the area behind the shortwave trough 
currently over northwest Minnesota. Expect to see the current 
ceilings rise a little bit this afternoon owing to the typical 
diurnal fluctuations... but Don/T expect as much of a rise as 
suggested by the NAM... mainly given the cold advection and lack 
of much temperature rise. The clearing trend tonight should 
generally occur from northwest to southeast... although some 
clouds may hang on a bit longer of the far west and southwest due 
to the lingering layered clouds above the drying boundary layer. 
Some diurnal cumulus can be expected on Saturday... but for now it 
appears this will mainly be scattered or at or above 3k feet. 


Kmsp... main uncertainty/challenge is with the ceiling height in 
the first 6 hours... which looks like it may hang around very 
close to 3k feet before rising again then eventually scattering out 
tonight. Otherwise... fairly confident that conditions will be VFR 
through the period with the gusty winds settling down this evening. 


&& 


Previous discussion... 
/issued 326 am CDT Friday Mar 19 2010/ 


Much cooler...but more seasonable...air is on the way to the 
forecast area today and Saturday with a modest upward trend in 
temperatures from Sunday into the middle of next week. 
Overall...precipitation chances will be minimal through the period though 
there will be chances returning by the middle of next week. Early 
morning water vapor imagery shows an upper circulation spinning 
across north-central Ontario with a low amplitude trough axis 
extending back to the southwest across the Dakotas. A stronger 
circulation is seen on the tail edge of this trough moving into 
western Arizona. This low will track eastward across the Southern 
Plains into Sunday and evolve into a large closed low. This will 
result in a quiet flow pattern for the local area for the weekend 
with surface high pressure in place. 


Some details...approach of aforementioned upper trough axis will be 
the focus in the near term. Middle level baroclinic zone is rather 
tight with the push of cold air. Frontogenetical forcing associated 
with this temperature gradient continues to generate bands of radar 
returns representing sprinkles and spotty light rain from southeast 
sodak across southern Minnesota into western WI with little actually 
reaching the ground thanks to rather dry low level moisture 
profiles. The baroclinic zone will tighten to the southwest as the 
Arizona upper low moves across The Four Corners this morning helping 
push developing surface inverted trough across southeast Colorado eastward into 
the High Plains. Forcing associated with this system may be able to 
be enhanced as far north as the far southern County Warning Area this morning 
resulting in a better chance for rain or snow or a mix of the two. 
Models have been trending further and further south with 
forcing/moisture for precipitation with latest radar trends supporting this 
but the far southern County Warning Area looks to be affected. Will maintain low 
chance mention of rain/snow across the southern two tiers of Minnesota 
counties through the day. Elsewhere...mostly cloudy to partly sunny 
skies will be the rule as colder air settles in. Enough fgen remains 
present to keep the sprinkles going and enough cold air will fill in 
to turn them to flurries in the next few hours. 850 mb temperatures are in the 
process of crashing from +3 to +6 to between -8 and -10 c and 
combined with the cloud cover will only support highs in the lower 
30s west to around 40 east. Steep low level lapse rates will be 
present suggesting additional flurry potential in the colder air for 
much of the area into the afternoon but cyclonic flow becomes 
anticyclonic by early afternoon which should limit development. 
Northwest breezes of 15 to 25 miles per hour will keep things brisk with gusts 
to around 30 miles per hour in the far west. 


High pressure will move southward along the Lee of The Rockies 
tonight bringing a decreased pressure gradient and lighter winds. 
Clouds will remain into the evening but may clear out even before 
daybreak Saturday. The wind should help keep temperatures from bottoming 
out but lows will still fall into the 20s. Saturday will still be 
cold with little change in the temperature profile plus the surface 
ridge axis will be moving overhead. Highs similar to today are 
expected but lighter winds and sunshine will accompany them. The 
main belt of middle/upper level flow will remain to the north of the 
area into Sunday with weak upper ridging nosing in from the west by 
midday Sunday. Saturday night will be quite cold again thanks to the 
surface high ... many sites dropping into the teens but temperatures should 
quickly recover Sunday as warm advection commences. Surface flow will 
still be light which may inhibit mixing which will make temperatures a 
challenge. Guidance shows a range of temperatures but the majority are on 
the warmer end indicating 50 or better for most of the area. Will 
add a few more degrees to the previous forecast pushing highs to the 
upper 40s with a few 50s as well. Wouldn/T take much to have things 
go even warmer but the cold start and the weak surface flow would be the 
limiting factor so will stick with an incremental increase for now. 
Monday looks warmer still with quiet weather continuing and slight 
upper ridging aloft but broad troughing will be developing over the 
western U.S. With surface low pressure developing in the Lee of the 
northern rockies by Monday night. Models begin to diverge here with 
the GFS pushing the low across Minnesota more quickly than the 
European model (ecmwf). A slower approach would likely result in much warmer temperatures 
for Tuesday with the European model (ecmwf) advertising +8 c or better at 850 mb with 
dry weather continuing. Will keep the slight chance probability of precipitation going for 
Tuesday into Wednesday from the previous forecast given the 
difference in solutions. 


&& 


Mpx watches/warnings/advisories... 
Minnesota...none. 
WI...none. 
&& 


$$ 


Trh/mdb 

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