Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
1256 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 through monday)
issued at 328 am CDT Tuesday may 21 2013
Cloudy...cool...and scattered to numerous light rain showers or
sprinkles are on tap Wednesday with the low still taking its time
to move across the forecast area. Really think by Tuesday night
the instability will be shoved far enough to the west that we
should just be dealing with the light showers and no thunder. We
are dry by early Thursday morning...but clouds should be slower to
clear. No major forecast changes in the Thursday-Friday time
frame. Went just a bit cooler with temperatures during this time.
The guidance trended that way...but simply think it is more to do
with slight changes in the timing of showers during the day on
Wednesday and clearing of clouds late Thursday night. This should
set the stage for a very cool Friday morning. Upper 30s are
certainly within reason across central Minnesota and west central WI with
the clouds moving out and that high moving in.
Medium to long range guidance continues to forecast troughs along
both west/east coasts and a ridge over the central states and a
closed anticyclone through the weekend into early next
week. Southerly flow ahead of the trough and surface low/warm front
development should focus precipitation over the Central Plains late in
the weekend and into the northern plains/mid-upper MS valley/Great
Lakes early next week where convection is likely as indicated in
the gefs/European model (ecmwf) ensemble members and GFS runs. There are a lot of
probability of precipitation in the extended...but it is difficult to remove them...even
given we have fairly low confidence in the timing and placement
of the showers and thunderstorms late this weekend and early next
week. Here's why its difficult to remove probability of precipitation. Climatology is
right around 25% for a 24 pop forecast this time of year. The
21.00z GFS has a longwave trough approaching from the west and
southwest flow here and the 21.00z European model (ecmwf) is less amplified and
even quasi zonal. Both of these patterns would be fairly active
and would certainly warrant keeping probability of precipitation at least at the
muted/averaged values of climatology.
&&
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...
long term...clf
aviation...
