Scientific Forecaster Discussion

Return to Local Conditions & Forecast
Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota
429 PM CDT Wednesday Apr 16 2014

Short term...(this evening through thursday)
issued at 352 PM CDT Wednesday Apr 16 2014

Surface analysis puts the surface low over Blue
Earth/Le Sueur/Waseca counties in Minnesota with a warm front snaking northeastward
between klvn/ksyn on to Eau Claire/Clark counties in WI. The cold front
then snakes west-southwestward through kjyg and between kotg/kmjq in southwestern Minnesota. Precipitation
continues to surge northeastward in advance of the low pressure center...with light
rain S of the Twin Cities metropolitan while moderate-heavy snow continues to fall
over much of northern and western portions of the weather forecast office mpx County warning forecast area. Snowfall
rates of 1-2 in/hour can be expected in north-central portions of the area
through the next couple of hours as the low pressure center rotates to the
east-northeast. Not looking for that much warmer air to the S to make much more
of a northward punch than it has already made. Therefore...any areas
currently having snow will stay as snow through the duration of this
event. An areas experiencing rain or a rain/snow mix will then
gradually change over to snow. There are a couple of other key
features evident on satellite imagery and in rap/NAM models that
will play important roles in the precipitation depiction through the early
evening. A dry slot that showed up nicely in eastern South Dakota early today has
shown signs of closing...especially now that it shows up in southwestern Minnesota
on kmpx radar. It still is there...but not as large as
earlier...indicating that the lower levels of the atmos continue to
saturate. This means continued precipitation duration with little breaks
through late evening. In addition...rap/NAM show the upper level trough
nudging the surface low across southern Minnesota has trying to pivot as it swings
through to a more negative position. This would enhance lift with
colder air surging in on the backside of the system...while moisture
still remains fairly deep. This combination would then potentially
create additional bands of heavy snow that will slowly traverse west to
east across much of the mpx County warning forecast area during the evening hours...again potentially
creating 1-2 in/hour bands that much of the County warning forecast area would experience.
Difficult to time it but have maintain high-end probability of precipitation for central-eastern
portions of the County warning forecast area since the overall precipitation shield will be slow to
exit the area. Once the trough moves through late this evening...then the
precipitation will gradually end from west to east across the area...with the vast
majority seeing snow in varying intensities by that point. In
fact...due to the accentuated intensity seen earlier...have added a
few counties into the warning and slightly nudged up snowfall totals
in the west-southwest segments to account for these high-intensity snow bands.
Have also adjusted the end times of the advisory/warning to coincide with
the lowering of probability of precipitation across the County warning forecast area. Temperatures overall will settle into
the lower 20s into the lower 30s late tonight while wet snow accums will
generally top out in the 6-10 inch range in northern portions of the
County warning forecast area...locally upwards of a foot not impossible.

Long term...(thursday night through wednesday)
issued at 352 PM CDT Wednesday Apr 16 2014

While most of the forecaster energy was spent on the short term
with the snow storm...there are a couple items of note in the long
term forecast. The main precipitation event in the extended is a rain
event that looks to largely occur Saturday or Saturday night -
perhaps even a rumble of thunder. That being said no really
significant weather is anticipated through the period...but a
progressive and active pattern is expected. Behind the current
system...a surface high builds in and temperatures but temperatures aloft
either remain steady or slowly moderate. We're still looking at
departures from normal tomorrow close to 20 degrees. More sunshine
and warm advection will allow temperatures to rebound into the 40s and
lower 50s on Friday.

Next chance for precipitation arrives on Saturday when weak isentropic
lift moves into Minnesota. Minnesota/WI will be fighting drier air in the
wake of the high...so...and it looks as if most of the model
guidance has reduced the quantitative precipitation forecast since yesterday's runs - at least in
southern Minnesota where the forcing isn't as strong. The more robust
trough remains north and the resulting forcing is better across
northern and portions of central Minnesota. Nonetheless...a weak short
wave and frontal boundary drop across the forecast area Saturday
night and with the help of conditional symmetric instability or
weak upright instability...we could generate some light showers.
Drying is then expected into early next week with upper level
ridge building into the upper Mississippi River valley.
Temperatures will be mild and above normal with increasing
warm/Theta-E advection returning probability of precipitation Tuesday night into
Wednesday. Look for a warming trend during this period...with
highs in the 60s on Sunday and and even in into the lower 70s by
Tuesday. Continued the trend of bumping highs slightly above
guidance during this period with all models indicating very warm
low and middle level temperatures.

&&

Aviation...(for the 18z tafs through 18z Thursday afternoon)
issued at 106 PM CDT Wednesday Apr 16 2014

Axn/stc/rwf continue to be most affected by moderate/heavy snow this afternoon
as the swath of precipitation within air cold enough to produce
snow rather than rain lingers from southwestern Minnesota into north-central Minnesota.
Msp/rnh/eau have emerged to have little-to-no precipitation at 16/18z
initialization...but within a few hours time the precipitation
area will gradually shift eastward...bringing precipitation back to the eastern
tafs. Precipitation looks to return as -ra for a few hours before a brief
transition to -rasn before all -sn. The concern then becomes
mesoscale banding of precipitation for these eastern sites as the upper level
trough pivots aloft over southern Minnesota this evening...setting the stage for
enhanced localized lift which could produce periods of IFR-worthy
heavy snow this evening. Have used tempo groups to advertised this
at this time. The precipitation looks to be largely away from the terminals by
06z this evening...a little later for the WI sites. The other concern
is the potential for low level stratus overnight with the deep moisture
within the blyr...but am not entirely sold on this idea due to the
strong low level northwest winds expeceted so aside from MVFR ceilings...have left
visibility as improving to VFR.

Kmsp...definitive break in the precipitation has develop over msp...
going mainly S and east from there...while precipitation is not far off at
all going north and west. As the afternoon progresses...this dry period will
come to an end with -ra returning from the west by mid-aftn. Temperatures in
the middle-30s will allow for a p-type of showery -ra when it
resumes. As colder air wraps around the backside of the low pressure
center shifting eastward over southern Minnesota late this afternoon...precipitation will mix
with and eventually change back over to -sn. Some minor snow
accumulation is possible...along with potential bands of moderate-heavy
snow...due to mesoscale effects but its potential is enough to
carry a tempo group this evening. Conds improve late overnight
through the day tmrw to VFR while winds take on a drier northwest flow.

/Outlook for kmsp/
Thursday...mainly VFR. Some MVFR ceilings early. Winds north-northeast 10-15 kts.
Friday...mainly VFR. Chance MVFR Friday night with -ra/-sn. Winds NE 5-10
kts.
Sat...mainly VFR. Chance MVFR with -ra/-sn. Winds east-southeast 10-15 kts.



&&

Mpx watches/warnings/advisories...
Minnesota...Winter Weather Advisory until 10 PM CDT this evening for mnz041-
047-048-054>057-064-065-073.

Winter Storm Warning until 1 am CDT Thursday for mnz042-043-
049>051-058-059.

Winter Storm Warning until 4 am CDT Thursday for mnz044-045-052-
053-061.

Winter Weather Advisory until 4 am CDT Thursday for mnz060-062-
063.

Winter Weather Advisory until 1 am CDT Thursday for mnz066-068.

WI...Winter Storm Warning until 4 am CDT Thursday for wiz014.

Winter Weather Advisory until 4 am CDT Thursday for wiz023.

Winter Storm Warning until 7 am CDT Thursday for wiz015-016.

Winter Weather Advisory until 7 am CDT Thursday for wiz025-027.

&&

$$

Short term...jpc
long term...clf
aviation...jpc