Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
520 am CST Friday Dec 19 2014
Short term...(today and tonight)
issued at 406 am CST Friday Dec 19 2014
The short term concern is the light snow threat lifting to the east
this morning. Then the chance of patchy freezing drizzle and light
snow across the area tonight.
Water vapor imagery showing upper trough moving across eastern areas
early this morning. 285 isentropic surface shows band of saturation
moving east this morning. Could see a dusting of snow in the
northeast quadrant of the County Warning Area through about middle morning. Some flurries
may linger over the east into the afternoon but they shouldnt be
significant. Because of the extensive cloud cover...temperatures
should range 25 to 30 for most of the area.
Into tonight...the extension of the trough over western South Dakota
now...digs a bit more to the south and generates a bit more lift
into central and northern Minnesota. Will mention slight chance light snow
again over the far North County warning area into tonight. Lower clouds over the
far south could generate some patchy freezing drizzle or flurries as
the trough passes. At this moment...it is not expected to be
Long term...(saturday through thursday)
issued at 406 am CST Friday Dec 19 2014
Main concerns during the long term remain fzdz potential
Saturday/Saturday night...followed by precipitation chances Sunday
through Wednesday night. Included in the precipitation chance next week
is the issue of p-type Sunday night into Monday night.
Saturday looks dry...one of the only dry periods in the long term.
Little or no lift behind a trough tonight...despite a moist boundary
layer...should prevent drizzle from continuing beyond tonight. Looks
like more of a low ceiling type day. The freezing drizzle appears
to return Saturday night as another wave approaches and provides
modest lift and a deeper moist layer. Does not look widespread...but
patches of drizzle may create some slick spots. As the wave continues
east Sunday...moisture depth will continue to grow and will begin
to intersect the dgz...allowing for a transition from drizzle to
snow. Probability of precipitation remain in the chance range for the eastern County Warning Area Sunday.
The surface low discussed at length lately will emerge from
Alberta Sunday afternoon as it treks southeast into the northern
plains. The trough associated with this low will dig as the low
approaches...causing it to slow and eventually become somewhat cut
off over the upper Mississippi Valley early next week. A thermal
ridge and wetbulb temperatures above freezing will lift North...East of
the center into southern Minnesota and western WI. A mixy scenario should become
mainly rain late Sunday night and Monday...although dry layers
circulating around this low may also allow for a bit of sleet from
time to time. Despite the likely probability of precipitation...several dry hours are
anticipated. However...precipitation should occur at some point
during those 12 hours. Amounts look rather light...between a tenth
and fifteen hundredths each period. The low will push east Monday
night with colder air wrapping around which should bring back
mainly snow. Totals should be less than a couple inches.
A secondary digging of the trough will spawn another low that will
eventually become the stronger...more dominant system for
Christmas evening and day to our east. It is becoming less likely we
will be impacted directly with this system aside from scattered
snow showers or flurries.
Middle level ridging returning for Christmas day will provide the
other dry period before another system organizes over the central
rockies and western High Plains Thursday night and Friday.
Aviation...(for the 12z tafs through 12z Saturday morning)
issued at 508 am CST Friday Dec 19 2014
IFR/LIFR ceilings with some br across the western County Warning Area this morning.
Band of -sn lifting east-northeast and should exit into Wisconsin and
weaken this afternoon. Expect IFR ceilings to remain to the west
through the period...with low end MVFR ceilings with -sn moving
through. Should see ceilings drop this evening to IFR with some br and
possible -sn/-fzdz. The best chance of -sn will be over central Minnesota
with the -fzdz threat limited/patchy to the south. Will leave this
out of tafs for now. Later forecasts may have to include some form
of precipitation depending on the strength of next trough extension
overnight. Southeast to south winds through the period...generally
10kts or less.
Kmsp...expect MVFR ceilings to develop through 14z with critical 1700
feet ceilings by 16z or so. This should remain through the day with IFR
ceilings developing later tonight/03z. Light snow could affect visibilities
down to 4-5sm the next couple of hours. Then some br developing
tonight with -sn or -fzdz possible. Confidence low enough to leave
that out of the taf for now. Will maintain a southeast-S wind less than
10kts through the period.
/Outlook for kmsp/
Sat...MVFR ceilings. Chance -fzdz late. Winds south-southeast 5 kts.
Sun...MVFR/IFR. Chance -fzdz/-ra/-sn. Winds south-southeast 7-10kts.
Monday...IFR. -Ra with chance -pl changing to -sn late. Winds southeast 7-10kts
becoming north-northwest late.