Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
701 PM CDT Tuesday Mar 11 2014
Update...for 00z aviation discussion below
Short term...(this evening through wednesday)
issued at 236 PM CDT Tuesday Mar 11 2014
The rain snow mix has dropped into far south central Minnesota by
middle afternoon. Should exit the area through 6 PM. Forcing wasnt
strong enough to change area over to all snow. There may have been
a band of snow for a time...but BUFKIT profiles indicate the lowest
2-3k feet of the bl remained around freezing.
The main trough aloft will drop southeast and generate a small chance
of light snow over far west central Minnesota overnight and as the
trough swings east...it may generate enough lift into far eastern
area portions of the County Warning Area for a small chance of light snow or flurries.
The 12z NAM was the most vigorous in the development of an inverted
trough that would affect the Minnesota/Wisconsin border region late
tonight into Wednesday morning. As the trough exits the area...we
should see improving conditions during the day. Temperatures area
expected to cool back into the 20s for most of County Warning Area...as The Pocket
of minus 12c to minus 18c 850 mb temperatures moves over the area.
Long term...(wednesday night through tuesday)
issued at 236 PM CDT Tuesday Mar 11 2014
For the most part...the long term period of the forecast looks
fairly quiet. There will be a chance for some light snow Wednesday
night...with the rest of the period looking dry until possibly
Sunday or Tuesday...though by then...models have diverged enough
where it's hard to put much stock in any one outcome.
Over the course of the next week...we will maintain a mean pattern
of a western ridge/eastern trough. However...there will be a series of
shortwave troughs and ridges riding through the northwest flow that will
allow for a bit a variation in temperatures. Model spread remains
fairly negligible through the rest of this work week...but starts to
build considerably over the weekend. Preferred models for the next
week are the NAM/sref/Gem-reg for light snow Wednesday night...with
about a 50/50 split between the European model (ecmwf)/Gem for the weekend and beyond.
The period will start out with a surface ridge axis overhead that will
shift southeast toward the Ohio Valley Wednesday night. As this high shifts
east...the upper MS valley will again get into strong return flow as
a Pacific airmass arrives for Thursday. However...before said
Pacific airmass arrives...it is looking better for some light snow
to impact areas east of the I-35 corridor as a quick burst of
isentropic lift on the 285-290k surface and fgen on a warm front in the
700 mb-h6 layer work south across the area. At this point...favored a
blend of the NAM/sref/Gem-reg for this precipitation...with a quick burst
of snow working across eastern Minnesota/western WI between 6z and 15z Thursday. Not
expecting anything big out of this...with an inch or two possible
before warm air arrives to quickly melt that snow Thursday afternoon.
Behind this warm front...a warm nose...characterized by 925-850 mb
temperatures of +4c east to +9c west will work over the mpx area during the
afternoon. This again will promote highs in the 40s...with highs in
the 50s for parts of Minnesota with no more snow cover. At the
moment...that snow line sits roughly along a Morris...Redwood
Falls...St. James line. Thursday night...a cold front will come
through the area...with Friday expected to be very similar to
today...with temperatures Friday afternoon not rising very far above
their Friday morning values.
Big changes with the models were seen for this weekend beginning
Sunday. Saturday still looks cool as a 1035mb high builds into northern
Minnesota. By Sunday...the 11.12 European model (ecmwf)/Gem show the 500 mb ridge now remaining
farther west...with a clipper greeting US for Sunday/Sunday
night....with temperatures remaining on the cold side of normal into
next week. The 11.12 GFS looks more like the previous run of the
European model (ecmwf)...with return flow quickly kicking in Sunday and another mild
airmass with highs making a run at 50 by the beginning of next week.
At this point...went with an even blend of the current 11.12 models
and the previous forecast.
As for that precipitation chance Tuesday. Models have been a bit all over
the board here...but the GFS/European model (ecmwf) support precipitation Tuesday...but for
different reasons. The GFS has a strong cold front working across
the area Tuesday...with some rain/snow possible with it as it passes.
The European model (ecmwf) would support all snow Tuesday as the area gets into an
inverted trough associated with a surface low over the lower Ohio
Valley. At this point...have just some chance probability of precipitation going for Monday
night/Tuesday with a rain/snow mix...though would need to see some more
consistency with guidance before buying off on a solution.
Aviation...(for the 00z tafs through 00z Wednesday evening)
issued at 700 PM CDT Tuesday Mar 11 2014
Area of low-end VFR clouds over northern Minnesota will continue to shift
south toward the taf area this evening. Could also see some MVFR
level clouds filter in...but have gone more optimistic with ceilings
as compared with deterministic models /that have been overdoing relative humidity
forecasts recently/. Could still see some scattered-broken clouds around 2000 feet
tonight into Wednesday...but that threat is higher over west
central Minnesota /krwf-kaxn/ and over west central WI /krnh-Keau/.
Otherwise...mainly middle/high level clouds are expected through the
day Wednesday. North/northwest flow is expected to prevail into Wednesday
but speeds should diminish to around 5 kts during the afternoon
as the high drops in.
there is a low threat of scattered-broken MVFR clouds developing this evening...but
the best chances exist east of the Airport. North-northwest winds
will prevail through most of the period...but become more west-southwest
later Wednesday afternoon and decrease to at or below 5 kts as the surface ridge
/Outlook for kmsp/
Thursday...VFR. SW wind 5-10 kts.
Friday...VFR. West 10-15 kts.
Sat...VFR. Northwest 5-10 kts.