Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
543 am CDT Thursday Oct 30 2014
Short term...(today and tonight)
issued at 353 am CDT Thursday Oct 30 2014
One area of decreasing areal coverage of -ra was across SW Minnesota as of
230 am which produced locally a tenth of an inch of rainfall at
Madison. This area was associated with a departing shortwave moving
quickly southeast across southeast South Dakota. Initial dry air mass across SC/ec Minnesota has
led to only sprinkles at best as the area of -ra moved eastward.
Another area of -ra...mixed with -sn was developing along a weak surface
low near kgfk. Although the surface low will weaken...strong cold air advection evident
just north of the Canadian border will enhance the surface convergence
along this weak low as it moves southeast across Minnesota today. As previously
stated...initial air mass is very dry blw 5k...but moistens
considerably during the morning ahead of this surface low.
Therefore...with the strengthening surface convergence along the leading
edge of cold air...-ra will likely hold together across central/ec
Minnesota and wc WI today. This was also noted in the latest WRF models
forecast reflectivity pattern. The strength of the cold air advection behind this
feature is quite impressive for late October which will lead to
temperatures likely falling behind it during the afternoon. As winds increase
and temperatures fall into the 20s and 30s...wind chill values will likely
fall into the teens.
Long term...(friday through wednesday)
issued at 353 am CDT Thursday Oct 30 2014
The long term forecast issued this morning changed very little
from the previous /day shift/ forecast. There is overall good
model agreement in the long wave pattern and pretty good run-to-
run consistency. A Stout area of high pressure will quickly drop
south into the Dakotas and eventually across Minnesota by Friday morning.
This will bring an impressive surge of cold air and strong winds
with it. Momentum Transfer approximations from the NAM/GFS
forecast soundings suggest peak wind gusts up near 30-35kts in
western Minnesota and 25-30kts across the rest of the forecast area late
Thursday night and Friday morning. The air mass that arrives on
Friday will be the coldest of the season thus far with most of the
guidance forecasting 850mb temperatures between -7c and -11c by Friday
morning across the local area...which will be the coldest air of
the fall season so far. The weekend still looks to bring warmer
temperatures than Friday but will remain cool overall. Minnesota/WI will find
itself under ridging this weekend in between a deep trough off
the northeast coast and an approaching trough from The Rockies. By
06-12z Sunday there are two well-defined pv boots transversing the
Continental U.S. With Minnesota/WI right in the middle. Eventually the system off to
out west on Sunday will move across the High Plains and into
northwest Minnesota and southwest Ontario Monday morning. That puts the
forecast area right in the dry slot on Monday. That is why /even
with an approaching low and cold front/ we really can't go higher
than 30% for precipitation early next week. It looks like convection will
light up a state or two to our south Monday-Monday night. We will
see a quick cool down on Tuesday behind this system. The GFS/European model (ecmwf)
begin to diverge by the middle of next...with the European model (ecmwf)
aggressively bringing back warmer air from the southwest and the
GFS keeping Minnesota/WI in cold northwest flow. There's about a 20c
degree difference in 850mb temperatures between the two next Thursday.
Aviation...(for the 12z tafs through 12z Friday morning)
issued at 530 am CDT Thursday Oct 30 2014
Main aviation concern is timing of cold front and associated MVFR
ceilings developing behind the front.
Based on current trends of satellite imagery of the lower ceilings in
northwest Minnesota and winds...wc Minnesota will see frontal passage around 14-16z.
Across SW/central Minnesota around 16-18z...and through most of ec/SC Minnesota and
wc WI between 19-21z. Initially winds will shift to the north/north-northwest around
10 kts...with stronger winds gusting up to 20-30 kts within an hour
or two. MVFR ceilings seem likely along and behind this front for a
few hours...but confidence remains low on how low the cloud ceilings
become during the afternoon hours. Most of the MVFR ceilings affecting mpx
tafs will be after 18z...so the next set of tafs will have a better
handle on timing and cloud bases. Ceilings should lift to VFR and
scatter out during the late afternoon and evening hours from northwest to southeast.
Frontal passage will be around 18-19z...with some vcsh along it.
However...visibilities will not be a problem on any rain that develops.
Worse conds will occur after 18z so timing on MVFR ceilings will be
updated as needed. Strong north/north-northwest winds will develop an hour or two
after the initial frontal passage with gusts up to 26 kts likely
during the late afternoon/early evening time frame. Winds will slowly
decrease overnight with skies becoming clear.
/Outlook for kmsp/
Friday...VFR. Winds north 10-15 kts.
Sat...VFR. Winds southeast 10-15 kts.
Sun...VFR. Winds south-southeast 10-15 kts.