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Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota
141 am CDT Thursday Apr 17 2014

Update...for 06z aviation discussion below

&&

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 06z tafs through 06z Thursday night)
issued at 116 am CDT Thursday Apr 17 2014

The precipitation has come to an end across most of Minnesota
(except the far east, including msp) and the stratus deck is on
the move. Clear skies have already reached axn had subsidence and
dry air advection continues in that area. The snow/rain intensity
will diminish overnight and come to an end across eastern
Minnesota...then western WI. The tricky aspect of this forecast
package...is how quickly we shed the stratus deck. Hi-res guidance
indicates low level moisture to remain high across eastern Minnesota and
western WI through much of today. Not very confident in this
solution though...as this guidance is overdone with current cloud
cover. The clearing line to the northwest has slowed...but is
still pushing southeast...and may reach the west metropolitan before
halting and even back-filling. Currently excepting MVFR to linger
at most sites (except axn and rwf) winds will generally be northwest
during the period as the surface low pushes off across Wisconsin.

Kmsp...snow will end prior to 08z at msp. Hi-res guidance
indicating MVFR ceilings into the afternoon today...but confidence
in this lacks. Will closely monitor the progression of the stratus
deck...as this actually could go VFR much quicker than currently
advertised in the taf.

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



&&

Mpx watches/warnings/advisories...
Minnesota...Winter Weather Advisory until 4 am CDT early this morning for
mnz062-063.

Winter Storm Warning until 4 am CDT early this morning for
mnz044-045-052-053-060-061.

WI...Winter Weather Advisory until 4 am CDT early this morning for
wiz023.

Winter Storm Warning until 4 am CDT early this morning for
wiz014.

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

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

&&

$$

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