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Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota
428 am CDT sun may 24 2015

Short term...(today and tonight)
issued at 345 am CDT sun may 24 2015

Today and tonight...surface analysis depicts several weak low pressure
centers over the Southern Plains while a deep upper level low rotates over
the 4-corners region /showing up nicely on WV imagery this mrng/. In
addition...a large subtropical ridge over the southeastern Continental U.S. Will be a
major player in forcing copious amounts of western Gomex moisture into
the upper miss River Valley over the weekend. This deep upper level low
will also help the conglomeration of weak surface lows into an organized
surface low pressure system later today...and help slowly nudge it slowly north-northeast
through tmrw. Isentropic lift heightens greatly this morning in advance of
this system...helping spread precipitation currently moving into far
southwestern Minnesota northward and encompassing much of the weather forecast office mpx County warning forecast area by midday today.
Have gone along with the consensus of the hopwrf/hrrr/sref/arw-E in
slowing down the initiation of the precipitation into the County warning forecast area...more
towards the 12z hour for southern portions and to 17z for the entire County warning forecast area
to be in the likely pop range. Much of this initial precipitation surge
looks to be with a pre-warm-frontal trough which shows up in the 700 mb
through 500 mb pressure levels...indicating a midlvl disturbance riding around
the eastern periphery of the deep low. Once this disturbance moves
through...the models do show a diminishing of the precipitation coverage if
not a temporary break in the action. Have depicted this by a
lowering of probability of precipitation back to the chance category approaching 00z this
evening. More widespread precipitation commences by late this evening into
the overnight hours as the warm front itself pushes into Iowa tonight and
nudges up against the Iowa/Minnesota border by daybreak Monday morning. There is
the potential for pockets of heavy rain as precipitable waters increase to around 1.50
inches later today through tonight and the overall progress of this system
continues to be on a slowing trend. As for convective potential...
the continued lack of instability as evidenced by no Bona fide
periods of sunshine and meager prognosticated convective parameters will
mitigate good thunderstorm potential. Cannot rule it out completely
so have maintained slight chance thunder for this afternoon through tonight but any
thunderstorm development is not expected to be strong/severe. As for
temperatures...have nudged temperatures down slightly from inherited values...especially
over southern Minnesota...due to extensive cloud cover and the lack of
insolation. In some cases...maximum temperatures may well have already been
reached and temperatures may remain steady or even fall a degree or two
throughout the day today. That said...min temperatures early Monday morning are
expected to be warmer than current values this morning due to slight
warm air advection with the approach of the warm front late tonight and deep southwesterly flow from
the upper level pattern. Will look for lows in the 55-60 degree range
Monday morning.

Long term...(monday through saturday)
issued at 345 am CDT sun may 24 2015

Monday will start off wet with the surface low lifting north
through north central Iowa and deformation zone precipitation
expanding across much of the forecast area. At this time...expecting a band
of heaviest precipitation just on the back side of the surface low
through Monday afternoon...but there remains variability in the
guidance on where exactly this band sets up. The 00z runs of the
GFS and NAM came in with good agreement that the area just west of
the Twin Cities through the Mille Lacs Lake area could see the
heaviest amounts on Monday /upwards of an inch/.
However...confidence must be somewhat limited because the
ec...which has been one of the leading models in the handling of
this system as it has come closer in indicating a
surface low track farther east through western Wisconsin and wants
to place that heaviest band of precipitation from Red Wing through New
Richmond. In our forecast area...the most uncertain area for precipitation is
western WI at this time...because if the GFS/NAM solutions end up
being more accurate...that could introduce a dry slot over Eau
Claire and really limit precipitation there. So...much of how Memorial
Day turns out will depend on the track of the surface low. As is
usual with surface lows...areas east of the track will be mainly
limited to the warm air advection precipitation band which typically move
through quickly...then battle the dry slot. Meanwhile...areas
immediately west of the surface low could see several hours of
decent rainfall rates and over an inch is certainly possible.

Strong ascent through Monday morning on the back side of the surface
low is supported by the very strong differential divergence
indicated by the deterministic guidance as we are in a prime region
of right entrance region induced lift of the upper jet. Some
instability and precipitable water values exceeding 1.5" support the idea of
seeing some decent rainfall totals in that deformation band that
will pivot in the vicinity of eastern Minnesota and western WI. Much of the
area will likely dry out Monday afternoon...especially South. West
central Minnesota however may still be plagued by light precipitation right
through the afternoon. By Monday night...the low will have moved off
into the northern Great Lakes and the forecast area may have a few scattered
showers. It looks like a second trough and associated surface low
will then push into the Midwest but most of the precipitation associated
with that feature should remain south of the forecast area. So...cut probability of precipitation back
Monday night.

The track of the second low should remain southeast of our area
through Wednesday...but it may spread light precipitation as far west as
eastern Minnesota and western have included some low probability of precipitation Tuesday
during that time. Expecting a dry day Wednesday before more probability of precipitation
come back Wednesday night through Friday. A messy pattern indeed
for the latter half of the week as a modest feed of moisture and
instability looks to give broad chances for thunderstorm
development during that period.

Little change for the end of the week and next weekend. The ec/GFS
still agree that a Continental polar air mass from the north will
push into the upper Midwest with cooler and drier conditionsexpected.
However...nailing down the exact timing of the frontal passage is tough this
far out.


Aviation...(for the 06z tafs through 06z Sunday night)
issued at 1050 PM CDT Sat may 23 2015

Isolated spits of rain are possible overnight...but the main area
of precipitation will not begin to spread north across the area
until around daybreak Sunday. Said rain will expand north and east
across the area throughout the day Sunday....with ceilings and visibilities
lowering to the MVFR category. The threat for thunder still looks
minimal so have not included a mention in the tafs. Should see a
lull in the rain around 00z Monday...and then it picks up again on
Monday evening

a few passing sprinkles are possible overnight in the vcty of the
field...but the bulk of the showers /with MVFR cigs-vsbys/ should
arrive around/after 17z. MVFR conditions develop during the early
afternoon. Preicp lightens around 23z...with more of a Dr/br
scenario developing.

/Outlook for kmsp/
Monday...VFR. Scattered rain showers/thunderstorms and rain with MVFR or lower conditions. Winds S
10 kts.
Tuesday...VFR. Chance shra/-tsra. Winds SW 10 kts.
Wednesday...VFR. Winds SW 5-10 kts.


Mpx watches/warnings/advisories...


Short term...jpc
long term...speed

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