Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 160045 AAA

Area Forecast Discussion...UPDATED
National Weather Service Twin Cities/Chanhassen MN
745 PM CDT Mon May 15 2017

Issued at 745 PM CDT Mon May 15 2017

The WRF-NMM has been handing convection very well today. The
forecast was updated to trend more toward that solution overnight
and Tuesday.

A compact MCS over far northeast Iowa will continue tracking to
the ESE this evening. Little additional activity is expected to
develop until the LLJ strengthens after 10 pm to 50 kts over
eastern Nebraska. Very steep mid level lapse rates over 8C/km are
in place across southern MN with MUCAPE as high as 3500-4000 J/kg
over northern Iowa. Expecting rapid thunderstorm development by
late evening along a line from Redwood Falls to Mankato and the
south metro before activity lifts north and weakens overnight.
There could be some training with these cells given their
orientation to the mean flow contributing to a heavy rain/flood
threat, unless the cells become bowing segments as they mature.
500 mb flow will weaken with time, which could limit the overall
severe threat, however the ample instability and the strong LLJ
should be enough for a somewhat appreciable large hail threat

Most of Tuesday should be dry and firmly in the warm sector. Mid
levels will dry and clouds should scatter by mid morning. Gusty
south southwest winds to 30 mph will result in good mixing and 925
mb temps of +25C should allow many areas over southern MN to reach
the upper 80s or lower 90s.

Updated grids to account for recent trends will be posted


.SHORT TERM...(This evening through Tuesday)
Issued at 315 PM CDT Mon May 15 2017

Surface analysis this afternoon shows a surface low nearly atop
the intersection of I-90 and I-35 in southern MN with a quasi-
stationary front wobbling over and south of the MN/IA border and
extending west through Nebraska and southeast into IL/IN. Aloft, a
deep ridge axis is aligned nearly due N-S from eastern WI through
the middle and lower Mississippi River Valley region. This puts
the WFO MPX coverage area within southwesterly flow and able to
receive plenty of moisture from the deep south. Plenty of
convection slid east over nearly the entire coverage area late
morning through this afternoon due in large part to convergence
along/north of the front which was further north within the MPX
area earlier in the day and due to a few small shortwave buckles
within the larger H7-H5 flow. Though the area was able to avoid
severe weather, a few smaller hail reports came out of the
thunderstorms. In the wake of the storms, a sizable cold pool
developed over eastern SD and NE which has since shifted ENE over
much of the MPX area, helping to produce much cooler temperatures
across the area for the rest of this afternoon. With much more
stable air in place, only scattered showers over southern and
eastern portions of the coverage area will persist going into this
evening. The front to the south is expected to make a better
surge to the north during the early morning hours, aided by the
exiting ridge and additional shortwave disturbances from the
southwest. As the front lifts north, another round of
showers/thunderstorms is expected to develop by around midnight in
southern MN then continue to drift north through the early
morning hours. There is still some potential for these storms to
be strong-to-severe with hail and strong winds in the vicinity of
the low level jet with continued steep lapse rates in place. These
storms are then expected to lift north of the area by late
Tuesday morning, making the area once again worked over,
producing a lull in the action until late afternoon/evening
Tuesday. Even if not severe, storms will still be capable of small
hail, gusty winds and brief heavy downpours (owing to PWATs still
around 1.5 inches). As for temperatures, with the convection
expected to exit by late morning followed by partial afternoon
clearing, the northward movement of the warm front along with the
timing of the convection should allow for better warming. Will
continue to look for highs to hit the upper 70s to lower 80s
tomorrow (just a matter of the hourly path to get to those values
which will be better resolved as the convection trend evolves).

.LONG TERM...(Tuesday night through Monday)
Issued at 315 PM CDT Mon May 15 2017

By tomorrow evening, the cap will be eroding as the 700-800mb
level cools, which will lead to the development of additional
thunderstorms along the frontal zone and in the warm sector from
southwest MN to northeast MN. There is potential for isolated to
scattered severe storms, we do not anticipate widespread severe
potential with this. That is much more likely across parts of
TX/OK/KS tomorrow/tomorrow night, which could limit our
instability. In addition, jet level winds will be stronger in
those areas, where we will be limited by comparatively weaker deep
layer shear. Still, clusters of strong storms with isolated to
scattered severe hail and possibly damaging winds but confidence
is rather low because the activity across the plains could hamper
our instability. So, heavy rainfall then becomes the concern with
the frontal boundary draped across our area and a moist boundary
layer with dew points in the 60s at the surface. Individual storm
cells should be moving but redevelopment along the frontal
convergence zone means that the speed of the front is the more
relevant in terms of flood potential. But, PWATs will be a modest
1.25" or so, and the nose of the low level jet will be primarily
to our south/east hence moisture transport will max out in those

More widespread rains will come Wednesday/Wednesday night as the
actual low finally ejects and moves northeast through the upper
Mississippi Valley. The concern for severe weather is low with
this period with the rainfall amounts being more of a concern.
Widespread 1-2" or rain after the previous couple days of rain
still look to lead to totals in the 2-4" range between today and
Thursday morning. Instability starts shifting off to our east
Wednesday afternoon through the night. We may still have some
showers lingering in cyclonic flow on Thursday morning but should
be dry by the afternoon as dry northerly flow pushes in behind the
departing system.

Another low pressure system across the four corners region by
Thursday will start lifting out towards us and bring chances for
rain for Friday through Sunday. Meanwhile, low level Thursday-
Friday will bring cooler air into the region that will linger
through the weekend.


.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 745 PM CDT Mon May 15 2017

VFR conditions outside of thunderstorms. Dry until about 03Z, then
showers and thunderstorms will begin developing across southern
MN. They will build northward on a low level jet overnight, likely
impacting all the TAF locations. Best chances for strong/severe
thunderstorms will be after 04Z from RWF-MSP-RNH-EAU with
decreasing intensity to the north. South winds will be gusty
Tuesday, possibly up to 35 kt across southern MN and into western

KMSP...Best chance for thunderstorms tonight will be between
04-10Z and a TEMPO has been included to account for that. Tuesday
will be mostly dry and breezy, but additional storms will develop
Tuesday evening.

Wed...Mainly VFR. SHRA/TSRA expected. Occasional MVFR/IFR In
SHRA/TSRA. Wind SE 5-10 kts.
Thu...Mainly VFR. Chc MVFR/-SHRA in the morning. Winds N 10-15
Fri...Mainly VFR. Chance SHRA/TSRA with MVFR. Winds NE 5-10 kts.




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