Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
345 am CDT sun may 3 2015
Short term...(today and tonight)
issued at 330 am CDT sun may 3 2015
Main concern for today is the severe potential late this afternoon
and early this evening from west central Wisconsin to south central
Minnesota. The front expected to kick off thunderstorms this
afternoon was located from north central Minnesota to northestern sodak at 3 am. A
couple clusters of thunderstorms are ongoing this morning ahead of
this front...and have been showing signs of diminishing during the
past couple hours. The impulse responsible will push east across
central/northern Minnesota through early morning and there may not be much
more than a few showers by sunrise north of I-94. Little will focus
additional development through the early afternoon...although cannot
rule out an isolated shower or storm given the presence of left over
boundaries from overnight. As the front approaches and middle level
lapse rates steepen atop a moistening boundary layer this
afternoon...additional development will occur from northwestern WI to far
eastern Minnesota sometime between 19-21z. The best forcing and thus most
widespread activity will be there this afternoon...with more
discrete cells across southern Minnesota where forcing will be weaker initially.
A qlcs should form within a couple hours of initiation and sag
southeast by early evening. A few bowing segments may bring stronger
wind gusts and the more intense cores may be capable of large hail.
Drier and cooler air will push in tonight with clear skies expected
Long term...(monday through saturday)
issued at 330 am CDT sun may 3 2015
Longer term concerns are timing of upper level short wave troughs
and attendant surface frontal passages. Temperatures cool into
early in the week...with Tuesday looking to be the coolest day of
the week. Overall trend is above normal with several chances for
precipitation during the period.
Initially...Monday will be the driest day of the week...with high
pressure dominating in the wake of the cold front. The frontal
boundary that stalls to the south over Iowa...will lift back north
as a warm front Monday night and Tuesday. This should bring in
more clouds and a decent shot of showers and a few thunderstorms
across the southern portion of the County Warning Area. Instability is limited
with this surge of moisture...therefore any significant severe
threat is minimal.
Southwest flow aloft then is the rule through the remainder of the
week. The next significant short wave approached the area later
Wednesday night and Thursday and should drag a frontal boundary
across the area. This will bring another good shot of rain to the
region...as moisture will have increased in the wake of the warm
front. Precipitable water values increase to around 1.50 inches
Wednesday and Thursday. This should be able to generate some more
widespread rainfall for the area. Currently have around one half
to three quarters of an inch of quantitative precipitation forecast from Monday through
Wednesday. Thursday looks to be even a better day for rain for the
County Warning Area.
Some model differences in timing and movement of the front into
Thursday night as flow aloft trends to remain more southwest. We
may be able to trim probability of precipitation Friday into Saturday as high pressure
moves in behind the front. Retained the small chance probability of precipitation for
now...in deference to model trends. Another significant trough
comes ashore over the western Continental U.S. Late in the week...and will
likely affect the weather later into next weekend.
Looking at more sensible weather...the fire weather threat is
lessening with each warm day as Spring Green up continues. Monday
afternoon will see humidity dropping into the lower 20s percent
again but northeasterly flow is not expected to be strong enough.
Frost threat is minimal this week as well with the area seeing
Aviation...(for the 06z tafs through 06z Sunday night)
issued at 1054 PM CDT Sat may 2 2015
A cold front will reach kaxn around daybreak Sunday and then
progress through the Twin Cities around middle afternoon and Keau by
early evening. Confidence remains high on a broken line of strong to
severe thunderstorms developing just east of the Twin Cities
around 21z and progressing across west central WI and southeast Minnesota
through the early evening hours. Indicated a tempo group at Keau
in the 23z-01z period along with wind gusts to 45 knots.
Confidence is not high on what will happen overnight with the
rain showers/thunderstorms and rain heading east from kabr. Short term solutions vary on
dissipating the activity in western Minnesota between kaxn and krwf while
others drive it all the way to the Twin Cities by daybreak.
Hence...held on to vcsh at the Minnesota sites for the overnight hours.
Kmsp...some showers are possible before daybreak along with an
isolated thunderstorm. However...confidence is not high. A cold
front will pass the airfield around 21z on Sunday with winds
switching from SW to northwest. Scattered rain showers/thunderstorms and rain will accompany the front in
the 21z-24z period. Kept the prob30 group as confidence is higher
for more widespread coverage to be east and south of the airfield
in the aforementioned period.
/Outlook for kmsp/
Monday...VFR. Winds north-NE 5-10 kts.
Tuesday...VFR early. Rain showers/thunderstorms and rain afternoon/evening with MVFR/IFR cigs/vsbys.
Winds southeast 10-20 kts.
Wednesday...VFR. Chance MVFR/IFR ceilings/visibilities in shra/tsra.