Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
1235 PM CST Sat Dec 20 2014
Short term...(today and tonight)
issued at 417 am CST Sat Dec 20 2014
The short term concern remains the light freezing drizzle threat
through the early morning and then later tonight.
Radar returns lifting across northern periphery of the County Warning Area. Few
stations reporting haze/snow near Brainerd and near Mille Lacs Colorado.
May yet see some light freezing drizzle as this upper wave lifts
northeast. Will likely keep the advisory going over northern
central County Warning Area...but will likely be cancelled early.
Other area of possible freezing drizzle lifting across Iowa and
southeast Minnesota. Not too widespread but arx and dmx radars showing
some light returns. Will have to monitor this but appears most of
this will slide off to the southeast of the area.
High temperatures should warm through the lower and some middle 30s
ahead of the next short wave moving over Montana this morning. This
system rides east today and phases with the upper trough over the
western Great Lakes. We should see another moisture surge to the
northeast across the northern portion of the area later tonight.
Again...this could be a mix of freezing drizzle and light snow.
Isentropic lift does increase to the southeast again as well...ahead
of the trough and could generate more freezing drizzle to the
eastern areas...mainly after 06z Sunday. Uncertain as to how
widespread this will be some will continue with the slight chance
wording for now. Low temperatures are not expected to drop off too
much from the daytime highs...with lower clouds remaining through
Long term...(sunday through friday)
issued at 417 am CST Sat Dec 20 2014
The long range is becoming ever more complex as time GOES on with
uncertainty actually rising in the past day or two. There are three
main features to watch next week - one being the early week upper
low bringing primarily rain...two is the southern stream system
that becomes a monster cyclone somewhere east of the Mississippi
River for middle to late week...and the third being a Panhandle hook
system on the footsteps of the eastern U.S. Cyclone Thursday night
A weak disturbance will rotate through Sunday keeping the light
wintry mix potential going from Saturday night...mainly across eastern
Minnesota and western WI. Any accumulations should be minimal with trace
amounts of precipitation expected.
Feature number one emerges on the northern plains from southern
Canada Sunday night. Consistency with this has decreased...with each
model adverting its own solution. The NAM is furthest north with
the surface low near the Minnesota/Canadian border. It swings a band of
precipitation through Monday morning with Monday night dry as the
region is dry slotted. The GFS is furthest south taking the low
over South Dakota and Iowa...with fairly steady precipitation
continuing all of Monday and Tuesday. The European model (ecmwf) is somewhere
between the two...with the best shot at rain Monday morning...then
favoring northern Minnesota and the Dakotas for wrap around precipitation
Monday night. Think the middle of the Road is probably the best
Route at this point so went with the European model (ecmwf). Temperatures will be
several degrees above freezing Monday and forecast soundings...even
on the southern GFS...show just about all rain. There may be a
period of transition to snow Monday night...but very light quantitative precipitation forecast
means little or no accumulation and it may end up being more of a
drizzle scenario if middle level moisture is lost per the dry
slotting shown on the European model (ecmwf) and NAM.
That brings US to feature number two. Uncertainty with the first
feature compounds the uncertainty for this one. Depending where
the northern upper low stalls...if it does at all...will
ultimately judge where the southern system develops and tracks for
Christmas evening. The NAM...Gem...and dgex stall the northern upper
low over Minnesota. This allows the second trough to dig more
south than east...and bring the southern surface low almost due
north over eastern Iowa and Wisconsin. On the other hand...the
00z operational GFS and European model (ecmwf) keep the northern low tracking
northeast allowing the second trough to dig further east as well.
This will force the surface low to track north northeast over the
state of Michigan or Lake Huron. It should be noted nearly half of
the GFS ensembles are much further west than the operational
run...so this will need to be watched. In fact...the 06z GFS is
coming in as this afd is being typed and has shifted west a bit
with heavy snow and strong winds across Illinois and eastern WI. A storm on
Nov 11 1991 identified by the cips analog which subjectively
identifies closest to the upper pattern...dropped a swath of heavy
snow /in excess of a foot/ across Iowa...southeastern Minnesota...and
western WI. So this one has not been written off for the mpx area
Finally...feature number three. Ridging should build behind the
second feature late week. A trough digging down the West Coast
will eject a system across The Rockies and into the central or
Southern Plains Thursday. Decent baroclinicity and a robust middle
level wave has the potential to spawn a Panhandle hook storm
Friday. Its track and potential impacts will be rather uncertain
for several more days but maintained the chance probability of precipitation during this
Aviation...(for the 18z tafs through 18z Sunday afternoon)
issued at 1151 am CST Sat Dec 20 2014
The MVFR/IFR stratus is here to stay through the taf period and
beyond. We have followed the prevailing trend this month...which
is to raise ceilings and improve visibility slightly during the
day and lower the ceilings/visible at night. There is a weak precipitation signal
late tonight...which would be drizzle/light snow and mainly across
central Minnesota. There is an increase in moisture tomorrow middle to late
morning that could yield light precipitation...but it is difficult to pin
just where and how widespread that will be - we are mainly looking
in eastern Minnesota and western WI for the precipitation tomorrow.
It appears as if the IFR has lifted at the Airport already and may
even improve a bit more this afternoon...however...we typically see
ceilings lower and the visible become worse at night...so that's the
trend we're following over the next 18 hours.
/Outlook for kmsp/
Sun night...MVFR/IFR. Chance -ra. Winds south-southeast 7-10kts.
Monday...IFR. -Ra with -ra/snow mix late. Winds southeast 7-10kts.
Tuesday...MVFR/IFR. Rain/snow mix changing to all snow late. Winds northwest 12
Minnesota...Winter Weather Advisory until noon CST today for mnz041>045-050.