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Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
346 PM CDT Sat Apr 19 2014
Short term...(this evening through sunday)
issued at 346 PM CDT Sat Apr 19 2014
Early afternoon water vapor imagery together with 500mb heights and
winds off the 19.12 GFS identified 5 well defined pv anomalies
across North America. Three of these waves were located in the
northern stream along the international border. The one in the
center was over Manitoba...while the other two were equidistant
upstream and downstream. Meanwhile with the remaining two waves were
in the southern stream straddling either coast...with one over the
Baja California peninsula...and the other over Florida.
A closer look at the surface reflection of the northern stream wave
over Manitoba revealed a 1004mb surface low...with a trailing cold
front extending from International Falls...down through the
southwest corner of Minnesota. An area of cool cloud tops was
located ahead of this frontal boundary along the axis of deep
moisture convergence...where with less than 100 j/kg of MUCAPE. This
instability had decreased over the past few hours...with only a few
light sprinkles being reported as of 19z. Therefore have decreased
probability of precipitation as most locations will not see measurable precipitation with the
frontal passage this evening.
Later tonight the shortwave that was located over the Baja California
peninsula will move onshore and cause a trough of low pressure to
form along the Texas/OK panhandles. This will cause the Midwest
frontal boundary to stall out along a line from Omaha...through La
Crosse WI...to Green Bay WI. Confidence is high that precipitation will
develop along that frontal boundary later tonight and persist
through the day on Sunday. Forecast sounding show elevated
instability...so will have thunder as well...and a few locations
should see an inch to perhaps 2 of precipitation as the boundary remains
stationary through Sunday before slowly drifting southeast.
Long term...(sunday night through saturday)
issued at 346 PM CDT Sat Apr 19 2014
Showers and isolated thunderstorms are likely Sunday night along
the frontal boundary meandering from southern Minnesota into west central
WI. Model agreement is high with this scenario with more than an
inch of quantitative precipitation forecast likely just south and east of our forecast area. A
growing concern for Sunday night is how the models handle the
interaction between a northern stream short wave approaching from
the Dakotas and a southern stream shortwave lifting northeast
through the Central Plains. Several runs of the Gem and ec would
suggest having some light showers all the way back into central
Minnesota. The GFS and NAM have been holding tight across the eastern and
southern County Warning Area. We noticed today that the ec was a little too
generous with the showers across central through southwest Minnesota.
With this in mind...held likely probability of precipitation from near Albert Lea to Eau
Claire Sunday night with chance probability of precipitation from Redwood Falls through
the Twin Cities metropolitan to Ladysmith.
The showers end early Monday morning across west central WI and
southeast Minnesota as the shortwave energy pushes east. High pressure
will build in with very pleasant weather through Tuesday. Highs in
the 60s will be common on Monday with middle 50s to lower 60s on
Tuesday. Afternoon humidity will lower to around 35 percent
The threat for showers will return to western Minnesota towards daybreak
on Wednesday. This is ahead of a large storm system pushing
through the western Continental U.S.. showers and isolated thunderstorms will
become more numerous across the forecast area Wednesday and Wednesday night.
As the upper wave pushes into the plains on Thursday it begins to
take on a negative tilt. Model solutions are quite varied at this
time on the track of the surface low pressure system emanating
from the Central Plains on Thursday. The Gem and GFS would favor
moving the low almost due north into the eastern Dakotas while the
ec would have the low reaching southern Minnesota. All of the solutions
show increasing shear and instability...especially across southern
Minnesota. Southerly winds at 500 mb reach or exceed 50 knots over
portions of the forecast area on all three solutions. Depending on how things
evolve...there certainly could be a window of opportunity for
severe weather on Thursday across portions of the forecast area. Thursday
happens to be our severe weather drill day.
The biggest disagreement in the long term is how fast this storm
system exits the region. The ec is the fastest and would have
much of the area dry by Friday afternoon. However...the GFS and
Gem would favor more of a slow moving closed upper low over the
area into Saturday. As the thermal profile cools...it would offer
the chance for some light snow across much of the area Friday
Aviation...(for the 18z tafs through 18z Sunday afternoon)
issued at 1250 PM CDT Sat Apr 19 2014
VFR conditions expected. A line of showers was developing along a
boundary that as of 1pm was located along a line from St cloud to
Ashland WI. Here the elevated instability lined up with the deep
moisture convergence. Southerly winds ahead of this line were
gusting 20 to 30kts...with light westerly winds behind the line.
Over the next 24hrs this boundary will sag southeast...and so to
will the chance for precipitation.
Kmsp...currently the best chance for precipitation will be just north of
kmsp...but could see a few showers this evening. Winds will
decrease as the front approaches...and remain light through the
/Outlook for kmsp/
Monday...VFR. Winds northwest 10-15 kts.
Tuesday...VFR. Winds north 5 to 10 kts.
Wednesday...VFR with MVFR/-ra possible. Winds south-southeast at 15g25kts.