Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
657 PM CDT Wednesday Sep 17 2014
Short term...(this evening through thursday)
issued at 353 PM CDT Wednesday Sep 17 2014
As mentioned in previous discussions...the weather across Minnesota/WI
doesn't become more active until Thursday night and Friday when
the chance for precipitation returns. In the meantime...quiet and
cool weather will once again dominate the short term forecast. The
winds will remain light through tomorrow morning with a baggy
pressure gradient across the region. There is an east-west
orientated cold front stretching from ND...across central Minnesota...and
into northern WI. A decent cumulus field has developed this afternoon
near and south of the boundary...with widespread stratus across
Lake Superior and far northern Minnesota where the air mass is much
cooler. The low level flow is expected to shift more north-NE across
the northern forecast area tonight...which could bring in some of
the cloud cover observed north of here today. There is an area of
middle-level clouds in the western Dakotas this afternoon associated
with an advancing short wave...however...this feature should have
little to no impact on the sensible weather locally - perhaps
adding some cloud cover tonight. Tomorrow shouldn't be too
dissimilar from today aside from increasing southerly winds
tomorrow afternoon...especially in western Minnesota.
Long term...(thursday night through wednesday)
issued at 353 PM CDT Wednesday Sep 17 2014
The primary focus in the long term is between Friday and Saturday
as the potential for widespread showers and thunderstorms returns.
The period will start off with flattening of the western Continental U.S. Middle
level ridge...with more zonal flow becoming prevalent across the
north central Continental U.S.. this will open the door for shortwave energy
to traverse over the area. As is usually the case in this type of
pattern...those waves are relatively difficult to time very far in
advance. Model solutions have slowed a tad with respect to the
arrival of the first wave...with showers and thunderstorms
potentially not reaching central Minnesota until after daybreak Friday.
Did include a 20 pop for western areas after 06z Friday...but it
will most likely not be until Friday morning when activity spreads
across central Minnesota toward WI. The associated cold front is on track
to move across the area on Friday afternoon and night. Ahead of
the front...expect temperatures to easily climb into the upper 70s...with
80s certainly a possibility in areas that see some sun /especially
west central MN/. Regarding the severe potential...the front does look
to have the adequate accompanying forcing and shear to be capable
of producing strong storms. However...whether enough
destabilization will be able to occur during the afternoon/evening
along the front /given the morning convection/...and given the
capping inversion illustrated on the models...development of
strong to severe storms could be hindered.
On Saturday another shortwave trough dives southeast across the
area from Saskatchewan/Manitoba. The most probable area of showers
and thunderstorms associated with the trough will be North/East of
Interstate 94 where the moisture is a bit deeper.
By Sunday...the trough should be far enough east to limit any
additional precipitation...especially as ridging works into the
area. Should then be dry with near normal temperatures into the
middle of the upcoming week as riding prevails. There does look to
be a breaking down of the ridge as a western Continental U.S. Shortwave
trough marches eastward late next week. Model agreement is poor at
this point...but it looks like showers and thunderstorms will
return late next week.
Aviation...(for the 00z tafs through 00z Thursday evening)
issued at 657 PM CDT Wednesday Sep 17 2014
Concern overnight is if low MVFR/IFR ceilings will form and where
is the most likely location. Sref probabilities for low ceilings point
to krwf...kaxn and kstc while the NAM/rap suggest krnh and Keau.
The latter is more of an advection to the southeast of the
current low ceilings around Lake Superior while the former is
associated with the low level Theta-E ridge. At this point put
more stock in the sref probabilities with tempo groups at the
three aforementioned sites. There will likely be MVFR visibilities for 2
to 3 hours around daybreak. Light northeast winds tonight will
turn southeast on Thursday and increase during the late morning
and afternoon hours...especially across western Minnesota with speeds of
10 to 15 knots common with gusts reaching 20 knots at kaxn.
Kmsp...kept a VFR forecast in place with sct008 around daybreak
Thursday. Indicated 6sm br around daybreak with MVFR visibilities likely
at the satellite airports around the Twin Cities. There are some
indications that a low VFR ceiling may form during the middle to
late morning hours (030-035) but confidence is not high enough to
include at this time with only sct030 indicated.
/Outlook for kmsp/
Friday...VFR. Chance rain showers/thunderstorms and rain before 9 PM. More numerous after 9 PM with
MVFR/IFR cigs/vsbys. Winds S-SW 15-25 knots.
Sat...VFR. Morning -shra possibly MVFR ceilings. Winds northwest 10-15 knots.
Sun...VFR. Winds northwest 10-15 kts.