Scientific Forecaster Discussion
fxus63 kmpx 272342
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
642 PM CDT Tue Jun 27 2017
Short term...(this evening through wednesday)
issued at 429 PM CDT Tue Jun 27 2017
The short term concerns are the convective trends/severe weather
threat tonight and Wednesday.
Current mosaic radar showing some isolated convection over the far
northwest cwa. Highly elevated thunder associated with some
waa/layered frontogenesis ahead of a weak short wave/differential
vorticity advection. This is expected to remain over the far
northwest cwa into the early evening and weaken. Redevelopment is
expected farther west in the Dakotas and Nebraska region later this
evening as the western trough advances east along the main
instability axis and the 55kt low level jet develops. This will
translate east into eastern Minnesota by 12z Wed with high pws of around
1.75 forecast...should develop some heavier rainfall with the
organized convection. Severe weather parameters remain best to the
west of the area during the overnight...although strong wind gusts
and hail cannot be ruled out.
The acitivity should be ongoing in the morning mainly across the
central/eastern areas. Again strong winds/hail possible with the
stronger convection as it moves east. Various deterministic and high
res models have been slowing the progression of the front across the
cwa during the day Wednesday. This will have to be monitored for any
clearing to the west will instigate rapid destabilization along the
front and could lead to at least some scattered strong/possibly
severe convection. This looks best across east central Minnesota
after 20z or so and then moving into west central Wisconsin through
the rest of the afternoon/early evening. The current Storm Prediction Center day2
outlook looks good at the moment with marginal risk remaining along
and ahead of the front.
Long term...(wednesday night through tuesday)
issued at 429 PM CDT Tue Jun 27 2017
For the long term, we will have one more deep trough and cool period
to work across the region this weekend before a pattern shift sets
in next week as the western ridge flattens and shifts east. This
pattern shift next week will push the main belt of westerlies to our
north, allowing warmer and more humid air to stream north next week.
We'll be starting the long term Wednesday evening with the remnants
of scattered activity from Wednesday afternoon working across
western WI in a decaying state. After that, Thursday looks dry and
sunny as upper ridging builds over the upper MS River Valley in
response to a trough digging across. Given the mostly sunny
conditions expected, did boost forecast highs Thursday a couple of
degrees above blended guidance given its cool bias during the warm
season in situations like this.
That trough to the west Thursday will come this way Thursday night,
with thunderstorm activity expected to accompany it. How widespread
that activity will be is still at question with the models. What we
are confident in is the cold front that comes through Wednesday will
be stalled out across Iowa, with the greatest potential for storms,
including heavy rain and severe weather down along the I-80
corridor. We'll have an inverted trough swinging through here
Thursday night into Friday, with our best precip chances residing
out ahead of it. The European model (ecmwf)/mpas are most bullish with our precip
potential as they develop a surface low along the boundary in Iowa
Thursday night, with a complex of showers and storms coming across
south central Minnesota toward western WI Thursday night/Friday morning.
The NAM/GFS are not as strong with a wave developing Thursday night
and have considerably less quantitative precipitation forecast in terms of amounts and coverage in
the mpx area. We did increase the pops across the south late
Thursday night night and have high chance/low likely pops working
northeast across the area with the inverted trough Friday.
For the weekend, the best threat for rain looks to be Saturday as an
upper trough and associated pocket of relatively cold mid level air
work through. Precip chances will linger in the east through Sunday
as moist cyclonic flow lingers. With h85 temps dropping back below
10c, we'll see temperatures fall well short of 80 this weekend, but
we will not repeat the fun of highs in the 60s we saw last weekend
as we'll be both warmer at h85, with less shower/cloud coverage as
Next week, as heights build across the Continental U.S. And the main belt of
westerlies retreats into Canada, we'll open ourselves up to warm
emls and strong capping, which will keep US dry Monday and Tuesday.
The next boundary is not expected to arrive until the middle of next
week, but capping issues will continue to impact this boundary.
Though turning warmer next week, it just looks like typical Summer
warmth for US, with warmest air looking to stay locked up to our
west and southwest.
Aviation...(for the 00z tafs through 00z Wednesday evening)
issued at 640 PM CDT Tue Jun 27 2017
Confidence is high that thunderstorms and rain will develop in western Minnesota
late this evening, and move eastward overnight. Currently, timing
is the big concern as models have sped up on the development of
storms an hour or two earlier. This has led to an hour or two
adjustment on the current tafs. Confidence is also high on a
period of moderate to heavy rainfall with cigs lowering to MVFR or
even IFR for short periods. The worst conditions are likely in a 2
to 4 hour window, and this is why a tempo period of 3sm thunderstorms and rain has
been added. I do not think this will be a continuous thunderstorms and rain event,
but a good 1 to 2 hours of lightning is likely with the main band
of storms. After the main band of storms move across the area, a
large area of rain showers and embedded thunderstorms and rain is possible. Will continue
the same with rain showers during the morning, with more development in
the afternoon along the front.
Confidence remains high on the development of thunderstorms and rain after midnight,
with the best time frame between 9-13z with occasional thunderstorms and rain and a
large duration of rain showers. Cigs will likely begin to lower once the
heavier rainfall develops toward sunrise. After 13z, there will
likely be a long period of MVFR cigs with occasional rain showers.
Redevelopment of thunderstorms and rain is also possible during the afternoon before
the cold front moves through.
/Outlook for kmsp/
Fri...VFR. Chance MVFR with thunderstorms and rain. Winds variable 5 kts.
Sat...VFR. Chance MVFR with thunderstorms and rain. Winds west-northwest 5-10 kts.
Sun...VFR. Chance of tsra/shra. Winds light and variable.