Scientific Forecaster Discussion
fxus63 kmpx 232023
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
323 PM CDT Wed may 23 2018
Short term...(this evening through thursday)
issued at 313 PM CDT Wed may 23 2018
As of this afternoon, the upper level ridge axis is nearly overhead
with a couple subtle waves expected to lift northeast from the
upstream trough across the western Continental U.S.. deep southerly flow has
brought increased moisture north, with dew points in the area now in
the mid 60s. This is the beginning of the trend to warmer and more
humid weather to come.
A very slow moving area of showers and thunderstorms across western
Minnesota has decayed as it's moved east, but not before sending an outflow
boundary southward. A few brief thunderstorms have been able to
initiate along the boundary, which has now essentially stalled out
just north of the Iowa border. Don't expect these storms to
maintain themselves as they run northeast of the best instability.
Speaking of, ample warmth and moisture has pooled to the west, with
3-4k j/kg of mu cape across portions of eastern South Dakota and
Nebraska. For tonight, expecting our forecast area to be primarily
dry, but an isolated shower or storm can't be ruled out.
Undoubtedly, the main activity will be to our west and north. Even
though instability is lacking to our north, the upper level
shortwave will continue northeast from the Dakotas, bringing some
lift to northern Minnesota, so rain chances are much better there.
The latest hrrr solution for the overnight period seems to have a
reasonable expectation of storms continuing overnight across eastern
South Dakota near the nose of the low level jet with a gradual
progressing eastward by tomorrow morning. Did include some chance
pops across western Minnesota for tomorrow morning to account for the
possibility of the storm remnants moving in tomorrow morning.
A warmer day is in store for US tomorrow and the upper ridge will
shift slightly east. Storm Prediction Center has continued a slight risk for western
Minnesota, which makes sense given the 3-5 k j/kg cape, but marginal to
weak shear environment. With additional upper level waves moving
northeast along the backside of the ridge, do expect some
thunderstorms to be set off tomorrow afternoon into the evening
across western Minnesota. Similar to what is occurring now in Nebraska and
South Dakota, expect some severe hail potential given the large
amount of instability. However, expect these storms pulse up and
down during the afternoon. Wind damage could be possible with a
few storms if strong cold pools develop.
Long term...(thursday night through wednesday)
issued at 313 PM CDT Wed may 23 2018
The low-level jet of 25 kts and near 1200-1700 j/kg of MLCAPE will
allow convection to be ongoing during the early overnight hours into
Friday. The eastward progressing storms are expected to weaken by
mid- Friday morning with increasing cin.
The upper-level shortwave trough and surface cold front will
continue progressing eastward through eastern Minnesota and western WI on
Friday. Mostly sunny skies over western WI will allow temperatures
to warm in the upper 80s and lower 90s on the Buffalo Ridge. Remnant
outflow boundaries as well as the main boundary along the cold front
will be the sources of lift for afternoon convection over eastern
Minnesota and western WI. Shear does not appear to be high with only
about 15- 20 kt bulk shear, so there is only a marginal severe
Upper level ridging will commence on Saturday. As mentioned in the
previous long-term discussion, the GFS hints at a "dirty ridge" with
the 12z GFS pushing a shortwave across Minnesota on Sunday into Monday. The
grids indicate slight chances for precipitation, but pops may be
eliminated in the days to come if other guidance continue to show
dry conditions. The European model (ecmwf) is one of the models that indicate dry
conditions though the remainder of Memorial Day weekend before
advecting cyclonic vorticity on Tuesday. This may potentially
bring rain chances on Tuesday to western Minnesota but confidence is low.
Thus, left chance pops in the forecast for Tuesday. Otherwise,
the next best chance for precipitation looks to be Wednesday with
both the GFS and European model (ecmwf) both indicating a short-wave traveling
through the County Warning Area.
Besides rain and storm chances, the other main concern over the long-
term period will be the heat. High temperatures are expected to be
widespread in the upper 80s to lower 90s Saturday through Monday
with the Buffalo Ridge likely reaching into the mid 90s. There is
expected to be an increasing humidity trend throughout the Memorial
Day weekend, so Sunday and Monday will likely be the muggiest
Aviation...(for the 18z tafs through 18z Thursday afternoon)
issued at 100 PM CDT Wed may 23 2018
Decaying showers across south central Minnesota will continue to fall
apart this afternoon, but more thunderstorm development across
western Minnesota will impact axn over the next few hours. Expecting a
pretty quiet night with the precip activity remaining to our north
Kmsp...confidence was high that the showers to our west would fall
apart this afternoon. In addition, those showers have been moving
extremely slow. So, expect VFR conditions throughout.
/Outlook for kmsp/
Friday...mainly VFR chc of shra/tsra. Wind SW 5-10 kts.
Sat...VFR. Wind west-southwest 5-10 kts.
Sun...VFR. Wind west 5 kts.