Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
issued by National Weather Service Duluth Minnesota
1031 am CDT Tuesday Jul 22 2014
issued at 1025 am CDT Tuesday Jul 22 2014
|updated to remove probability of precipitation near the Iowa border as prcipitation has
dissipated. Have made minor tweaks to temperatures based on current observation
and trends. Rest of forecast unchanged.
Update issued at 843 am CDT Tuesday Jul 22 2014
Update to extend probability of precipitation through this morning across southern portion
of forecast area north of the Iowa border. Radar indicates a small
area of showers and possible thunderstorms moving through the
area. This is assoicated with a weak surface trough/shortwave
moving through the region. It will dissipate by late morning or
move east into southeast Minnesota. Rst of forecast unchanged.
Short term...(today and tonight)
issued at 352 am CDT Tuesday Jul 22 2014
Severe storms did indeed brush our far northern counties in central
Minnesota overnight. The activity is now in far northern WI and moving
briskly east-northeast. A few showers and isolated thunderstorms have spread
into far west central Minnesota early this morning. The coverage is a
little more widespread to the west of kfsd. A few of the cams
have some light shower activity across SW Minnesota through about 15z.
Therefore...low chance probability of precipitation were included for our southwest
counties. The big change today will be Flushing out the 70+ degree
dew points. A cold front currently stretches from near kdlh through
kstc to kfsd. Dew points have already dropped into the lower 60s in
the wake of the front across west central Minnesota. The front will move
through the Twin Cities during the morning with 75 degree dew points
falling to around 65 degrees by early this afternoon. Dew points
will lower into the upper 60s over south central Minnesota through the Keau
area by late in the afternoon. The southern and eastern forecast area will have
the highest apparent temperatures today with around 90 degrees
forecast. In addition...breezy northwest winds will occur behind the
front today with speeds from 15 to 25 miles per hour. High pressure will build
in tonight from south central Canada. Dew points will continue to
fall with much of the forecast area reaching the lower to middle 50s by
Long term...(wednesday through monday)
issued at 352 am CDT Tuesday Jul 22 2014
Things look fairly unsettled through the remainder of the forecast
period... although there appears to be nothing particularly
significant in the cards. The upper low currently off the British
Columbia coast will be our primary player during this period as it
makes its way eastward. The large scale flow will still be quite
amplified at the start of the period... with the aforementioned
upper low just off the West Coast... ridging from The Four Corners
to Nunavut... and troughing over eastern Canada into the northeast
Continental U.S.. however... the western upper low is expected to push east
through the upper ridge during the latter portion of the week and
into the weekend... then make its way across our area by Sunday
before helping to reinforce the upper trough over eastern North
America by early next week. The GFS and European model (ecmwf) are in good
agreement on this large scale evolution of things... and are even
in reasonable agreement on most of the details... with some timing
differences being the main issues. The ensemble guidance isn/T not
overly dispersive... lending support to the deterministic
solutions... so will generally follow the path of least resistance
and utilize a GFS/European model (ecmwf) consensus approach.
Mild and dry weather should prevail across the area Wednesday
through most of Thursday as northwest upper flow persists and
surface high pressure drifts across the region. Return flow will
start ot setup by late Thursday... with decent warm advection
advertised by Thursday night... along with the return of
convective instability as 850-500mb differential Theta-E values
fall back below zero. Chances for precipitation should steadily increase
from west to east late Thursday afternoon through Thursday night.
The European model (ecmwf) manages to dry things out Friday and Friday night...
while the GFS continues to generate precipitation along the northwest-
southeast oriented baroclinic zone across our area. The GFS has a
somewhat better defined shortwave moving through the northern
plains into our area during that time frame... which is aiding its
more bullish outlook on precipitation. At this point in time... certainly
can/T discount the possibility of a more pronounced lead shortwave
ahead of the main upper trough... so included some low probability of precipitation
through Friday night before allowing for some dry air to work into
the area by Saturday. However... any respite from precipitation should come
to an end by Sunday as the upper trough sinks southeast across the
area... pushing a cold front through as it does so. The middle-upper
level cold pool will then sink into the area from later Sunday
through Monday... setting the stage for additional rain showers and
isolated thunder... particularly during daytime heating period.
Aviation...(for the 12z tafs through 12z Wednesday morning)
issued at 624 am CDT Tuesday Jul 22 2014
A cold front has just passed kmsp and will soon move through krnh.
It will be through Keau by 15z. A band of broken-overcast MVFR ceilings exists
along and ahead of the front where surface dew points are still
in the middle 70s. More MVFR and even some IFR ceilings are occurring
from kaxn on southward to near krwf as well as just north of
kstc. These are in the cold advection behind the front. Short term
guidance would have this moving through the Twin Cities in the
15z-18z time frame. Some showers and isolated thunderstorms will
occur this morning across southwest Minnesota including krwf. This
precipitation is in response to low/middle level frontogenesis holding
over southeast South Dakota and SW Minnesota. This should weaken/dissipate by late in the
morning. VFR conditions expected at all taf sites for the
afternoon and night. Northwest winds today from 14-18 knots with
gusts to around 25 knots. North-northwest winds 10 knots this evening becoming
light north overnight.
Kmsp...gutsy northwest winds today with speeds 16-18 knots gusting
25 knots. Another band of MVFR ceilings (020) should move through
the Twin Cities in the 15z-17z time frame. VFR for the afternoon
/Outlook for kmsp/
Wednesday...VFR. Winds north at 10kts.
Thursday...VFR. Winds southeast at 10kts.
Thursday night...VFR. MVFR conditions/thunderstorms and rain possible. Winds southeast 10 knots.
Friday...VFR. MVFR conditions thunderstorms and rain possible. Winds south-southeast at 10-15kts.