Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
1249 PM CDT Sat Oct 25 2014
Short term...(today and tonight)
issued at 345 am CDT Sat Oct 25 2014
A very powerful jet stream /150-170 kts/ that was north of the
Canadian border early this morning will continue to carve out
and deepen a surface low near Hudson Bay. The circulation around this
surface low and building high pressure across the High Plains...will
aid in gusty surface winds today...especially in central/ec Minnesota and wc
Initial mild temperatures this morning will not vary too much today as
cold air advection filters south across the upper Midwest. High pressure
overhead tonight will allow for a cool Sunday morning before
another storm system begins to affect the upper Midwest Sunday
Long term...(sunday through friday)
issued at 345 am CDT Sat Oct 25 2014
Sunday and Monday still look to be the warmest days of the
extended forecast period...the warmest days for the rest of
October 2014...ahead of a storm system due to impact the region
Sunday night through Monday night.
A large-scale ridge of high pressure atop the Mississippi River by
daybreak Sunday will continue to shift eastward while a longwave trough
moves across the northern rockies and Great Basin. This trough
will pick up a low pressure center over Alberta province and shift it
eastward. Meanwhile...a more southern stream low pressure center from The Four
Corners region will also be picked up by this trough...but the
models continue to depict both northern and southern stream lows as not
phasing together as they shift eastward sun through Monday. This scenario
will maintain the thinking that precipitation development will be weak
and less widespread across the County warning forecast area. In fact...most of the precipitation
development for Sun night through Monday night looks to be over the eastern
half of the County warning forecast area where moisture columns will be deeper. The southern
Canadian low...over southern Manitoba/Ontario by midday Monday...will
pivot as it is nudged along by a cutoff low within the longwave
trough...forcing the low to become more stacked and weakening its
effects for the mpx County warning forecast area late Monday into Tuesday. Again...the bulk of
the precipitation activity will be in eastern portions of the County warning forecast area.
The trough will open up by early Tuesday and become more
progressive...bringing an effective end to the precipitation by late day
Tuesday...if not early...depending on how fast the system ejects into
the Great Lakes. Once this system exits...the area will get a more
Bona fide feel of fall as colder Canadian air gets a pathway down
to the northern plains and upper miss River Valley for the rest of the
week. Prolonged northwest flow aloft combined with modest cold air advection surges will
drop highs temperatures from the 60s sun-Monday to the 40s and 50s Tue-Fri.
Low temperatures will drop into the 30s by midweek and even to the 20s by
late week. There are some conflicting ideas as to whether a weak
area of low pressure will drop southeastward through the region around Thursday...but
moisture columns are fairly shallow and there is little upper
level support with any systems depicted on the GFS/Gem. The
morning run of the European model (ecmwf) become highly meridional with an upper
low by the end of the week and looks to be quite the outlier so
has much less influence on this forecast pkg. Therefore...have opted
to run with a dry forecast from Tuesday night on through the end of this forecast
Aviation...(for the 18z tafs through 18z Sunday afternoon)
issued at 1222 PM CDT Sat Oct 25 2014
High confidence in tafs this period as high pressure will go from
the central Dakotas to the Ohio River valley over the next 24
hours. Will result in west-northwest winds this afternoon that go light and
vrb overnight before setting up out of the southeast by Sunday morning.
By the end of the taf axn/rwf will likely see those southeast winds
sustained at 15-20 kts by 18z Monday. VFR conds will
dominate...though clouds will start to thicken between 080-120 Sunday
afternoon across eastern Minnesota. Any MVFR ceilings and precipitation will hold off
until after 00z Monday.
Kmsp...high confidence in this taf. Winds will be light and vrb as
they transition from the northwest to the southeast between 3z and 9z tonight.
My Sun afternoon...may see a few gusts up around 20 kts...but the
better wind gusts look to stay off to the west.
/Outlook for kmsp/
Monday...MVFR ceilings likely early. Chance rain showers. Winds becoming west-northwest 5-10 kts.
Tuesday...chance MVFR/shra. Winds west-northwest 15g25 kts.
Wednesday...VFR. Winds SW 5 kts.