Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
640 PM CDT Friday Oct 24 2014
Short term...(this evening through saturday)
issued at 322 PM CDT Friday Oct 24 2014
Surface trough was just east of I-35 at 3pm. 20-30 knots low level jet has developed
out ahead of this trough. However...this has developed beneath the
right exit region of a 150 knots jet up along the international border.
Forecast soundings east of the trough show the subsidence inversion
that has developed within the right exit region. Because of this
inversion...we are seeing no precipitation generation...but are seeing a
stratus deck expand beneath the inversion. These clouds will slowly
work east with the trough...clearing the eastern County Warning Area by midnight. A 1020mb
high will be working across the Dakotas tonight in the wake of the
through...which will help keep any additional fog/stratus at Bay.
With the high coming in...cut back a few degrees on lows for
tonight...though am concerned we may have cut things back a little
too much as surface dewpoints have remained in the
40s/50s...indicating we may not see temperatures drop as aggressively as
we currently have.
Not many concerns for Saturday as high pressure GOES from the
Dakotas and into Minnesota. Will see breezy conditions still along and
north of I-94 as gradient remains tight to the NE. Only change for
Saturday was to boost highs a few degrees...closer to what the
weighted model and bias corrected guidance are showing...which have
been the strongest performers in these sorts of air masses the last
couple of weeks.
Long term...(saturday night through friday)
issued at 322 PM CDT Friday Oct 24 2014
Followed the lead of the short term forecaster and also boosted
high temperatures on Sunday due to the strong warm advection and
high likelihood of partially clear skies through the early
afternoon. By Sunday evening the main occluded front should be
passing into western Minnesota from the Dakotas and the 800-600mb fgen
will be strongest over far eastern Minnesota and western WI. Of the 12z
guidance...the GFS was the fastest in moistening the lower
atmosphere and generating light rain across the eastern half of
the forecast area. The rest of the guidance - NAM/ECMWF/Gem are
all in relatively good agreement in taking most of the rain east
of the forecast area into central and eastern WI. It also appears
there will be a few hundred joules of elevated instability Sunday
night and Monday morning in southern Minnesota and western WI...so we have
included isolated thunder in the forecast. There is a large
difference in the degree of moistening in the forecast soundings
between kmsp and Keau...so the metropolitan may in fact miss out on the
Sunday evening/night rain. Eventually...the surface front and
trough swing through Monday night /about 18 hours after the
initial isentropic band of precip/...so this looks like a better
window for more widespread /albeit still light/ precipitation across the
forecast area. Breezy northwest flow is expected on Tuesday behind
this system and will knock temperatures back into the lower 50s
for highs...which is close to climate normals in Minnesota/WI for late
October. The cooler air mass expected next week is still not as
cold as what we saw in early October when many locations remained
in the 40s for a couple days in a row. The 12z European model (ecmwf) is much more
aggressive with the warming late next week compared to the GFS.
Actually...the previous 24.06z GFS was much more agreeable with
the warmer European model (ecmwf)...but backed off with the morning run.
Aviation...(for the 00z tafs through 00z Saturday evening)
issued at 640 PM CDT Friday Oct 24 2014
Ceilings/visibilities are getting worse this evening instead of
better in west central WI. This is temporary as a surface trough
along the two state border area moves slowly east this evening. It
may take until midnight before Keau is VFR. The Minnesota taf sites are
fine with VFR through the period. Winds will continue to veer to
the northwest during the night and stay there on Saturday. Profile
data suggests low to middle 20 knot gusts likely for kstc...kmsp...
krnh and Keau from late Saturday morning on through much of the
Kmsp...VFR through the period. SW wind early this evening becoming
west and then northwest before daybreak. Raised the sustained wind and gusts
a few knots over the previous forecast for late Saturday morning
/Outlook for kmsp/
sun...VFR early. Chance MVFR/rain showers in evening. Winds southeast 10 kts.
Monday...MVFR ceilings likely. Chance rain showers. Winds becoming west-northwest 5-10 kts.
Tuesday...chance MVFR/shra. Winds west 15g25 kts.