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Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota
745 am CDT sun Apr 19 2015

Update...
issued at 715 am CDT sun Apr 19 2015

Updated to include 12z aviation discussion below.

&&

Short term...(today and tonight)
issued at 300 am CDT sun Apr 19 2015

Surface analysis puts a surface low pressure center near kbdh with a cold front
extending southwestward into the Southern Plains but also a surface trough extending
northward into southern Manitoba. These features are underneath a sharp 500 mb
longwave trough axis over the Dakotas and the Lee of The Rockies
while a weakened cutoff low ejects from the southwestern Continental U.S.. the upper
trough will absorb the southern upper low...aiding in expanding the trough
over the northern-Central Plains and into the Upper- Middle miss River
Valley regions through tonight. Though there is little doubt in these
larger- scale features...the challenge comes in how the dry slot
evident on kmpx radar over the central portions of the County warning forecast area...in
fact even well- place over the I-35 corridor...will play a factor
in the rain shower- distribution over the County warning forecast area through this short-term period.
High confidence remains in much of the County warning forecast area seeing sprinkles to
light rain showers through the first half of the day...but quantitative precipitation forecast
amounts will be much less than anticipated due to the larger area
of dry slotting moving northeastward in conjunction with the surface low.
Hrrr/NAM/hopwrf do try to fill moisture back into the
area...resulting in additional precipitation this aftn/eve...but not
until the cold front has shifted to the Minnesota/WI border which would
confine the bulk of the precipitation to the western WI County portion of the
weather forecast office mpx County warning forecast area. Have structured gridded probability of precipitation as such...dropping probability of precipitation
from west to east through the day today. In addition... the meager
instability...lack of good insolation due to extensive cloud cover
and poorer lapse rates indicate a much lesser chance at convection so
have omitted thunder mention this morning. Precipitation will gradually end
this evening into the early morning hours such that by daybreak Monday
morning...precipitation is no longer expected.

As for temperatures...the cold frontal passage will commence cold air advection for the
area but the expansion of the upper trough...making for northwest flow
aloft... will be the main player in bringing in colder air that
will remain in place going forward. Mild temperatures in the middle 40s to
middle 50s this morning will only range from the middle 50s to middle 60s today.
With deep northwest flow tonight...lows will drop to the middle-upper 30s...which
is near to slightly below normal for late April.

Long term...(monday through saturday)
issued at 300 am CDT sun Apr 19 2015

Water vapor imagery this morning clearly showed two distinct
features of concern for the long term period. The upper level low
pushing from Colorado into western Kansas...and a sharp
shortwave trough extending from the Saskatchewan/Manitoba border
through extreme eastern Montana and Wyoming. The upper low has
been quasi- stationary for days now...but the progressive
shortwave will help it finally gain some steam to the east. By
Monday morning...the shortwave will deepen and become a closed low
at 500mb and the center of it will be over western Ontario. At
850mb and the surface...we'll be squarely within the cold air
advection regime... and strong northwest winds. Deep mixing and a
strong pressure gradient across the area on Monday will persist
into Tuesday as well as low pressure at the surface over the Great
Lakes moves north toward Hudson Bay. A Wind Advisory will be a
possibility for Monday afternoon...but later shifts will make the
call on that. Generally...20 to 30 miles per hour northwest winds with gusts
of 30 to 40 miles per hour are expected on Monday...and about 15 to 25 miles per hour
with gusts to 30 on Tuesday. Temperatures will run about 10 to 15
degrees below normal...so a Stark difference from the recent warm
stretch we've experienced. In terms of precipitation...still
expect showery activity to develop in the cyclonic flow across our
area for Monday and Tuesday. Middle level laps rates look steep
enough to help produce said showers. Surface temperatures will
cool into the low and middle 30s Monday night...so snow showers are
also a possibility during that time.

For Wednesday through Saturday...the main focus is the
aforementioned upper low that will move over the northern Great
Lakes and become quasi-stationary...keeping our region in the
backside of the trough and northwest flow...meaning continued cool
temperatures. Toward the end of the week...the GFS and European model (ecmwf)
really begin to diverge in their handling of this low. The European model (ecmwf)
is more progressive in slowly pushing it east and trying to push
the upper ridge into the upper Midwest by next weekend. The GFS
indicates a secondary upper low to the northwest of the main low
will be pulled south and move through the western Great Lakes
region next weekend...which would keep US cooler and possibly give
US some precipitation. With the disagreement beyond Thursday...not too
confident in either solution so stuck with a broad blend at this
time.

&&

Aviation...(for the 12z tafs through 12z Monday morning)
issued at 715 am CDT sun Apr 19 2015

Low pressure center over western Minnesota with trailing cold front will slowly slide
east across Minnesota into WI today. Significant wind shift and low ceilings
will surround the frontal passage...including ceilings down to IFR levels in
western-central Minnesota and to low-end MVFR ceilings in eastern Minnesota into western
WI. Low chance of IFR ceilings into kmsp and points east but cannot be
ruled out. -Shra associated with the low pressure feature will be
quite light and little to no visibility restrictions are expected.
However...as winds drop off in tune with the wind shift...ceilings
will briefly drop with the decoupling. Once the wind shift occurs
and low level moisture starts to be scoured out...ceilings will
improve and strong northwest winds will persist all through tonight and tmrw.
Strongest winds will come close to daybreak tmrw...although southwestern
Minnesota /including krwf/ will be subject to 15g25kt winds this afternoon.
Trickiest part will be timing the wind shifts through the first half
of the 19/12z taf...so some amendments may well be necessary.

Kmsp...ceilings will bounce close to the 1700ft threshold at the
start of the period then likely remain sub-1700ft for much of the
morning as the cold front approaches. As winds swing around to northwesterly...conds
will start to improve. Not looking for much visibility restrictions
outside of a very brief moderate/heavy shower...but the bulk of the
precipitation will not be east of msp Airport so the chances of reduced visibility
are quite remote.

/Outlook for kmsp/
Monday...VFR with MVFR/-shra possible. Winds northwest at 20g35kts.
Tuesday...VFR. Winds northwest at 15g25kts.
Wednesday...VFR. Winds northwest at 15g25kts.

&&

Mpx watches/warnings/advisories...
Minnesota...none.
WI...none.
&&

$$

Update...jpc
short term...jpc
long term...speed
aviation...jpc

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