Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
416 PM CST Tuesday Nov 25 2014
Short term...(this evening through wednesday)
issued at 415 PM CST Tuesday Nov 25 2014
The main concern in the short term is a clipper system moving
southeast from the Dakotas to Iowa tonight and Wednesday. There
remains quite a bit of spread in the quantitative precipitation forecast from the various
deterministic solutions today on how far east significant
accumulating snow (3+") will go on Wednesday. Although the 700 mb low
associated with the clipper will basically pass across southwest
Minnesota late tonight...a second short wave is pushing across far
northern Minnesota during this same time. The NAM and the GFS have much more
quantitative precipitation forecast spreading northeast ahead of the northern stream
feature...which if true...would result in much more snow across
eastern Minnesota and west central WI then currently forecast...which is
in the 1 to 2 inch range. The Gem and European model (ecmwf) have more separation
in the quantitative precipitation forecast...with much of the snow focused from west central
through south central Minnesota late tonight and Wednesday. Its
interesting to note that the past five runs of the European model (ecmwf) have
shown the middle level low sinking slowly southward with time which would
keep the heaviest snow to the west and south of the Twin Cities.
The 15z sref is basically in line with this idea...showing the
highest probabilities (60-80 percent) for greater than 0.25 inches
of quantitative precipitation forecast in 12 hours from west central through south central
Minnesota. There is a little bit of a finger of higher
probabilities pointing towards the southwest Twin Cities metropolitan.
Hence...with confidence highest for 3+ inches of snow late tonight
and Wednesday morning from west central through south central
Minnesota...a Winter Weather Advisory was issued for these areas.
With some hint that the heavier snow could get a little more to
the east...the advisory reaches across McLeod and Sibley counties.
Kept the advisory going along the I-35 corridor from Northfield to
Albert Lea during the afternoon where snow will linger.
Low temperatures tonight are a little tricky with the low clouds
trying to diminish some this evening while southerly low level
flow/warm air advection increases. Went on the low side of guidance with
dew points only in the single digits and teens along with some snow
cover. Highs on Wednesday only in the teens across the west with
lower to middle 20s east.
Long term...(wednesday night through tuesday)
issued at 415 PM CST Tuesday Nov 25 2014
The long term continues the push pull weather pattern with brief
warm up/cool Downs. The initial wave exits early Wednesday
night...with cooler high pressure following for Thanksgiving day.
High temperatures expected to remain in the teens once again.
The next wave moves in with warm air advection driving east across the area
Thanksgiving night and Friday. A general 2-3 inch snow is likely
along and northeast of I-94. The warm front lifts north across the
County Warning Area. Depending on sunshine...temperatures could warm through the
30s again...especially in the far south. However...there is some
model timing issues...with the GFS faster with the next cold front.
Will move towards a slower and warmer solution for now...with some
small chance probability of precipitation associated with this front. Better forcing and
baroclinic zone develops along the northern periphery of the area.
The precipitation...if it does develop..could be in the form of
freezing drizzle/light snow or flurries. The GFS is the more robust model
in the overall development across the region.
Arctic high pressure drops south again over the County Warning Area for Saturday and
Saturday night. We should see clouds clear out of the area during
the day Sunday...providing drive Holiday travel for the area. Cold
temperatures return with highs in the teens both Sunday and
Monday...before the next upper trough swings over the western Continental U.S.
And drives warmer air back north and east toward the northern
plains/western Great Lakes for Tuesday.
Aviation...(for the 18z tafs through 18z Wednesday afternoon)
issued at 1159 am CST Tuesday Nov 25 2014
MVFR ceilings at Keau expected to dissipate by 19z as short wave
ridge moves in with the low level flow becoming westerly. To the
west...a patch of VFR clouds from 035-050 will cover the taf sites
for much of the afternoon as well as move into Keau by 20z. This
deck may scatter out this evening but middle level clouds broken-
ovc080-100 will be spreading in ahead of clipper. The heaviest snow
band with this system is down the Minnesota river from Appleton to
Mankato. This will impact krwf Wednesday morning with moderate
snow possible in the morning. Visibility forecast of 3/4sm at this time. Some of
this snow will get pulled eastward across the Twin Cities and west
central WI from middle morning Onward as a short wave passes by to
the north. Overall...MVFR ceilings will follow closely with the
onset of snow later tonight and Wednesday. Winds will back from
southerly to northwest during the taf period.
Kmsp...VFR this afternoon and much of tonight. Ceilings and
visibilities deteriorating between 12z and 15z on Wednesday to
MVFR/IFR respectively as snow moves in. Snow diminishing in the
late afternoon with winds becoming northwest through the evening.
Snow accumulation on Wednesday from 2-3 inches.
/Outlook for kmsp/
Thursday...VFR. Northwest 4-8 kts.
Friday...chance MVFR and -sn. Winds southeast 5 kts.
Sat...chance MVFR. Winds north 10 kts.
Minnesota...Winter Weather Advisory from midnight tonight to noon CST
Wednesday for mnz054-056-064>067-073>075-082-083-091-092.
Winter Weather Advisory from 3 am to 6 PM CST Wednesday for