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Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
251 PM CDT Friday Apr 18 2014
Short term...(this evening through saturday)
issued at 239 PM CDT Friday Apr 18 2014
Early afternoon surface analysis identified an area of low pressure
across the High Plains...with high pressure centered over Ontario.
The north/south pressure gradient across the upper Midwest resulted
in east southeast winds...with higher gusts near the Minnesota/Dakota
border. Over the next 24 hours the upper level pv anomaly driving
this surface low will skirt eastward across the international
border. The surface features will mirror the eastward
propagation...with a trailing cold front forecast to moving down
from the northwest throughout the day on Saturday.
Forecast soundings show middle level saturation...with some elevated
cape...so should see a line of radar returns along the
aforementioned cold front. However...the low level convergence
gradually weakens with time...and the best upper level forcing for
ascent will be focused north of the forecast area. Therefore not
expecting widespread precipitation but should see a few scattered showers
so have continued a chance for precipitation on Saturday. The middle level
clouds that will accompany the front will mitigate afternoon
highs...but the deep boundary layer mixing should raise temperatures near
70 across southern Minnesota...and near 60 across the north. If the middle
level clouds were absent from this forecast...temperatures would
easily climb into the middle 70s across much of the region.
Long term...(saturday night through friday)
issued at 239 PM CDT Friday Apr 18 2014
Zonal flow at the start of the period will amplify by midweek...
but remain fairly progressive through the balance of the forecast
period. This will result in fairly active weather through the
upcoming workweek... although the more significant weather should
be during the second half of the week as a decent surface low and
upper wave make their way into the upper Midwest. The European model (ecmwf) and
GFS are in good agreement on the overall evolution of large scale
features through the week... with the latest GFS more in line
with the European model (ecmwf) in terms of being a bit more progressive than it
was with the system for the second half of the week. However...
neither is exactly fast with that feature... which means we/ll
have an extended period of time with probability of precipitation in the forecast during
that time frame.
The frontal boundary which moves through on Saturday looks to hang
up just to our southeast for an extended period of time from
Saturday night into Monday as the main middle-upper flow shifts a bit
north and is essentially parallel to the old boundary. This will
keep the far east/southeast portion of the area under the gun for
chances of precipitation through Sunday night. Will continue to include a
mention of thunder with 850-500mb differential Theta-E hovering
near/below zero across that area. High pressure should
sufficiently assert itself by Monday to push any lingering precipitation
south/east of the area... with fair and dry weather lingering
through Tuesday. Return flow will setup on the backside of the
high Tuesday night into Wednesday... with decent moisture
transport and warm advection indicated by the GFS and European model (ecmwf) by
Wednesday night into Thursday. This looks to be accompanied by
some convective instability as well... so a mention of thunder
will need to accompany the elevated probability of precipitation. Should we get more
robust southerly flow than expected we might need to think more
about the potential for strong storms... but at this point the
better instability still looks like it will stay south of our
area. We should see a cold front push through by Friday... but the
upper trough and surface low will loiter over the region...
necessitating a continuation of some chance probability of precipitation into Friday.
Aviation...(for the 18z tafs through 18z Saturday afternoon)
issued at 1240 PM CDT Friday Apr 18 2014
a low pressure system will develop and move across northern
Minnesota which will cause the east southeasterly winds to become
southerly later tonight and Saturday morning. A weak cold front
will move through the region which will bring a chance for light
showers. The best chance for rain will be at the northern sites.
Cloud bases have the potential to go down to MVFR during the
rain...but should generally remain above VFR the rest of the time
VFR conditions throughout. The best chance for rain will be north
and west of kmsp...so just have vcsh for now since confidence is
too low to include precipitation in the tafs.
/Outlook for kmsp/
Sat night...chance MVFR with -shra. Winds SW becoming northwest 5-10 kts.
Sun...VFR. Winds north-northeast 5 kts.
Monday...VFR. Winds SW becoming northwest 5-10 kts.