Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
835 PM CDT Tuesday Oct 21 2014
issued at 835 PM CDT Tuesday Oct 21 2014
The hopwrf...our mpxwrf and the latest RUC all show some showers
and thunderstorms developing across west central Minnesota by 09z with
the activity working east northeast through the morning and
eventually reaching north of the Twin Cities by noon. Even the
sref has some chance probabilities developing in these areas. The
activity is at the leading edge of elevated instability and nose
of a 45 knot low level jet. Therefore...added some small probability of precipitation to
west central through central Minnesota for the late night and morning hours.
Short term...(this evening through Wednesday night)
issued at 310 PM CDT Tuesday Oct 21 2014
Clear skies were widespread across the upper Midwest this afternoon.
Surface high pressure across southern Ontario together with a
developing area of low pressure over southern Saskatchewan led to
southeasterly winds across the Minnesota River Valley. Boundary
layer mixing allowed surface temperatures to climb to near 70 across
western Minnesota...but low clouds limited temperatures to the middle 50s across
Southeasterly winds will continue overnight. An upper level wave
currently located across the Idaho/Montana border will move eastward and
bring precipitation beginning late Wednesday across the west...and
shifting eastward overnight. This well advertised precipitation is now
falling into the time frame of the hires models...so tried to narrow
up the pop window...but increased the percentages as well. Forecast
soundings show some elevated instability...so could see a few
lightning strikes as well. Rainfall totals should range around 0.20
inches for most locations.
Long term...(thursday through tuesday)
issued at 310 PM CDT Tuesday Oct 21 2014
Thursday weather and the departure of the showers in ec Minnesota/wc WI will
be highly dependent on the storm system in the northeastern U.S.
And how it influences/slows the evolution of the upper Midwest
Over the past few model runs...the storm system across the
northeast has remained consistent and holding near or south of
Boston/mass. The storm system across the upper Midwest has slightly
become more negatively tilted leading to a slower/stronger
solution. Due to the storm system in the northeast...it is likely
that the upper Midwest system may slow down further. Current
weather/pop grids reflect a slightly slower solution which may be
slowed more if conds warrant.
Past Thursday...the progressive pattern will remain across The
Rockies/northern plains/upper Midwest. Models have been consistent
in a strong upper ridge building across the southern U.S. With the
extension of this ridge across the upper Midwest. A strong
correlation of abnormally higher heights above 500 mb is evident in the
latest ensembles of the naefs. This will lead to the above normal
temperatures for the next several days past Thursday...with the best
probability of seeing another 70 degree high on both Friday and
Sunday. Depending upon the progressive pattern continuing...this
above normal anomaly of the 20/500 mb will move east by late next
week...with a more unsettled period by late October and early
November. Latest 6-10/8-14 day outlook from CPC has near normal
temperatures by early November. Early November temperatures for the upper
Midwest average around 32 degrees for morning lows and highs in
Aviation...(for the 00z tafs through 00z Wednesday evening)
issued at 701 PM CDT Tuesday Oct 21 2014
Several concerns with the forecast ahead. The first is the
potential for low MVFR ceilings to develop/spread into western Minnesota
near daybreak and lingering through much of the day. At this time...
lamp guidance and sref probabilities point more to the west of
kaxn and krwf. Hence...only carried sct015-020 for these sites in
the morning. Around the end of the period these two sites may see
MVFR ceilings and showers move in. A second concern is the
potential for elevated convection to develop near daybreak between
krwf and kaxn and spread east northeast through kstc and the North
Twin cities metropolitan by late in the morning. This is more plausible
with quite a few cams showing this. Therefore...vcsh was included
for the three aforementioned terminals. The surface pressure
gradient will continue to tighten during the night with gusty southeast
winds for western Minnesota and across all of the taf sites on Wednesday.
Finally...several of the cams are suggesting that thunderstorm
potential is increasing to the south of Minnesota Wednesday evening. This
could impede the moisture flow into our area with the showers for
the Minnesota/WI taf sites being more of a scattered nature.
Kmsp...VFR expected until Wednesday evening. Small threat for
a few showers to pass north of the airfield Wednesday morning.
Showers chances increase Wednesday evening along with the threat
for MVFR ceilings/visibilities.
/Outlook for kmsp/
Thursday...VFR with MVFR/-shra early. Winds south-southeast at 10g20kts.
Friday...VFR. Winds south-southwest at 5-10kts.
Sat...VFR. Winds northwest at 5-10kts.