Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
357 PM CDT Tuesday may 21 2013
Short term...(this evening through wednesday)
issued at 1235 PM CDT Tuesday may 21 2013
Latest water vapor imagery shows our bottled up and stagnant upper
air pattern still in place... with the cutoff low lingering in our
area and another cutoff off the northwest coast. Things are
starting to slowly move eastward with the pattern Delaware-amplifying
some over the upcoming 24 hours or so. Rain showers currently across the
area is taking advantage of what meager instability there is along
with low level forcing arising from the stationary front laced
across the center of the forecast area. More widespread light precipitation
can be found in the middle-level deformation and associated area of
frontogenesis over the north central and northwest County warning forecast area. With
things slowly shifting east through Wednesday... the general look
of activity currently over the area will shift along with the
overall large scale pattern... meaning showers will persist
through the period... with some diurnal enhancement in the pseudo-
warm sector again on Wednesday... although it will be pretty much
east of US at that time. Precipitation north/west of the surface and upper
low will remain fairly consistent over time... along with the
overcast skies. Don/T expect things to dry out or clouds to exit
until we move beyond tomorrow/S daytime hours.
Long term...(wednesday night through tuesday)
issued at 355 PM CDT Tuesday may 21 2013
Omega block remains in place over much of contiguous US for
Wednesday night into Thursday. Deep/dt indicated slower exit
of 500 mb low pressure area into Northern Ohio valley late
Wednesday night into Thursday. Thus have slowed decrease of probability of precipitation
over eastern third of forecast area Wednesday evening...very early Thursday
morning to account for same. Nice surge of Canadian polar
air over forecast area...behind exiting cut off low anticipated for
late Wednesday night into Friday morning. Another warm frontal
boundary expected to impact western forecast area by Friday morning. Broad
area of surface low pressure associated with same will be seen above
northeastern Wyoming by Sat/12z...as 500 mb cut off low noted upstream
over Washington and Oregon. Both gfs40 and European bringing in
decent swath of moisture over region for much of Saturday with
best forcing noted over SW third of forecast area. By sun/12z broad area
of surface low pressure finally treks into western sodak...and
western NE by Sunday/12z time period.
Proximity of warm frontal boundary to or over portions of County Warning Area
Sunday-Monday will determine timing and extent of convective
activity for this time period. Gfs40 much more aggressive with
instability and precipitation chances Sunday into Monday morning as
opposed to European. With that said just tweaked probability of precipitation for
sun-Tuesday period...with highest pop probabilities painted over
SW and west central County Warning Area. Slow moving cold frontal boundary
still prognosticated over far western Minnesota into southeast sodak on Wednesday
afternoon...and should push through much of forecast area next Wednesday night
..and then stall over southern WI into far northern Iowa.
Another much stronger surface cyclone forms on the western
portion of this boundary late Thursday...insuring probable
chances for moisture ending the month of may.
&&
Aviation...(for the 18z tafs through 18z Wednesday afternoon)
issued at 1235 PM CDT Tuesday may 21 2013
Slowly moving surface and upper level lows will drift east through
the forecast period... meaning a continuation of the conditions
we/ve seen for the past few days. Scattered rain showers can be expected
over much of the area this afternoon into this evening... with a
diurnal waning trend later in the evening. However... with the low
sliding east we will find more of the forecast area under the
influence of deeper moisture and persistent/weak forcing later
tonight into Wednesday. Generally overcast conditions with MVFR
ceilings will prevail... with a return to IFR ceilings and some
LIFR tonight. Visibilities look to mainly be VFR... although more
widespread MVFR will occur later tonight into Wednesday morning as
ceilings lower and some persistent light rain or drizzle occurs
across much of the area. Winds will be problematic for locations
near the stationary front... including kmsp... with shifts of
around 180 degrees in direction either side of the boundary...
which will drift a bit north and south through early evening.
Winds will shift and become predominantly north/northeast later
this evening as the surface low shifts to the east.
Kmsp...have decent confidence in the overall trends in the taf...
but lower confidence in some of the details. Ceilings could wind
up lower than forecast from late evening through the overnight
hours when the boundary finally gets permanently south of the
area. Wind direction is tricky this afternoon into early evening
with the front essentially stalled over the area. Went close to
some of the high resolution model guidance which suggests the
current north winds will shift back to the southwest/west for a
time this afternoon before eventually swinging back to the north
for good this evening. Visibilities could certainly be lower for
brief periods of time this afternoon and evening with rain showers... and
there is some potential for longer duration MVFR visibilities
overnight into Wednesday as lower ceilings return.
/Outlook for kmsp/
Wednesday night...MVFR ceilings possible early... otherwise VFR
conditions expected. Northeast wind 10 to 15 knots.
Thursday...VFR conditions expected. Northeast wind 5 to 15 knots.
Thursday night...VFR conditions expected. East wind less than 10
knots becoming southeast.
Friday and Friday night...VFR conditions expected. Southeast wind 5 to
15 knots.
Saturday...MVFR ceilings and visibilities possible with a chance
of showers and thunderstorms. Southeast wind 10 to 20 knots.
&&
Mpx watches/warnings/advisories...
Minnesota...none.
WI...none.
&&
$$
Short term...th
long term...Arizona
aviation...th
