Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 230931
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
431 AM CDT MON MAY 23 2016

.SHORT TERM...(Today and tonight)
Issued at 431 AM CDT Mon May 23 2016

We expect a couple rounds of showers and storms today. There is a
Slight Risk of severe weather given the threat for gusty straight-
line winds with the strongest storms today, but widespread severe
weather is not expected. In fact, given the marginal wind shear
later on today and due to the fact that the shear vectors will be
mainly parallel to the bands of convection - we think the storms
will be loosely organized and more garden-variety.

Widespread thunderstorms are occurring this morning from the Central
Plains - through western MN - to the US/Canadian border. The storms
are the result of a strong LLJ on the order of 50-60kts and strong
925-700mb moisture advection in the same area. The rain area is also
in a favorable quadrant relative to the upper jet across the
Dakotas. The convection locally is elevated and along the leading
edge of the moisture gradient, which is quite substantial across
the forecast area. The PWAT near the MN/SD border closer to the
surface low and cold front is 1.2"-1.4`, while the PWAT in western
WI is 0.4"-0.5" and much of eastern MN and western WI has morning RH
values in the 40s. Interesting to note, as of 4am, we can see the
leading edge of the moisture off the 0.5 KMPX radar slice, which
shows an eastward propagating fine line of reflectivity. These
storms will continue to the east, but we anticipate a gradual
weakening trend near and after sunrise as they make it into eastern
MN given the diminishing low level wind field to the east and to a
lesser extend the drier air that`s in place.

We do expect more storms to initiate along or ahead of the cold
front this afternoon and this is our best bet for any potential
isolated strong to severe storms. The instability will be limited by
cloud cover, but the BL moisture is on the increase and mid level
lapse rates should steepen with the approaching trough. We should be
able to generate around 1000 J/Kg of MUCAPE by the afternoon. We are
really just advecting everything that is happening in the Dakotas
and western MN farther east. This instability combined with what
we think the shear profile will look like suggest we end up with a
couple storms that produced 30-50mph winds and small hail. If
storms overachieve, perhaps we need a Severe Thunderstorm Warning
or two today for straight-line winds. That is probably the max
potential today.

.LONG TERM...(Tuesday through Sunday)
Issued at 431 AM CDT Mon May 23 2016

Expectations for the long term haven`t changed much.  We should see
several rounds of showers/thunderstorms through the upcoming holiday
weekend with 1-3" of rain area wide through the course of next week
as a more active and humid weather pattern takes hold.  Temperatures
will remain 5 to 10 degrees above normal during the work week, but
look to retreat back closer to normal for the weekend as we get more
and more rounds of clouds and rain.

The reason for the more active pattern is the breaking down of the
persistent east coast trough we have seen over the last couple of
weeks. The demise of the eastern trough will allow the upper ridge
from Texas into the Great Lakes this morning to flatten out during
the first half of the week, which will finally allow energy from the
trough to the west to work out of the central Plains.  Though we
have high confidence in this large scale pattern shift, there is
still low confidence on timing of exact details, as none of the
waves coming at us over the next week look to be particularly strong
as they will result from previous days convection. The only time
where the models are really starting to agree on being relatively
quiet and dry is Tuesday and Tuesday night.  Wednesday, all models
show a wave working across the area, so have likely pops then, but
after that it varies day-to-day with which model is showing precip.
Thursday, the ECMWF is mainly dry, but the GFS brings a sfc low and
heavy precip across the area.  Friday, the GFS is back at again
with sfc low moving across MN, but the ECMWF keeps this low and
associated precip down across Iowa. Saturday, the ECMWF brings up
another surface low and widespread precip, while the GFS
has more scattered activity along a cold front. Given the spread,
persistent 30 to 50 pops can be found Thursday through Saturday.
Sunday...both the GFS and ECMWF are mainly dry, but show a
stationary front hung up across the area, so have low chance pops
continuing through then.  By no means will Wednesday through Sunday
be a washout, but you will find yourself dodging rain drops from
time to time.

Given the variability seen in the models, its too difficult to
really identify much of a severe threat on any one day, but if we
were to see a sfc low work up during an afternoon as at least
one model suggests happening each day Wednesday through Saturday,
then an at least nominal risk for severe weather would exist.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1055 PM CDT Sun May 22 2016

All sites to remain dry thru the early morning hours, then will
expect showers and thunderstorms to develop over far western MN
and gradually shift eastward through daybreak. Have tried to
address latest model thinking that there appears to be two
distinct periods of convection: one around daybreak into late
morning and a second late afternoon into the evening. There may be
some scattered SHRA activity between those two times and the
timing may well need to be adjusted in later TAF issuances.
However, at this point, confidence has increased to start
breaking things out with more detail. Am looking for thunderstorm
activity to bring flight conditions down to MVFR-IFR levels but
have capped ceilings within MVFR while visibility is a blend of
MVFR to IFR. Conditions do look to generally improve late Monday
evening. In addition, have included LLWS at all sites since
gridded TAFs and BUFKIT east indicate 45-50 knots of wind within
the lowest two thousand feet and a directional difference of
around 30 degrees.

KMSP...VFR is expected through the morning push as short-term
models have slowed the progression of the precipitation into
eastern MN. However, just beyond the morning push is when the
first round of convection is expected. The heavier round of
convection is expected for the evening push, roughly 20z-24z
Monday evening, and conditions for this round may well drop into
IFR (which is lower than current thinking). Breezy SSW winds to
continue overnight through tomorrow, plus there is the strong low
level winds overnight into daybreak.

/OUTLOOK FOR KMSP/
TUE...Mainly VFR. Chc TSRA/MVFR. Wind S 5 kts.
WED...Mainly VFR. Chc TSRA/MVFR. Wind light and variable.
THU...Mainly VFR. Chc TSRA/MVFR. Wind south-southwest 5 kts.


&&

.MPX Watches/Warnings/Advisories...
WI...None.
MN...None.
&&

$$

SHORT TERM...CLF
LONG TERM...MPG
AVIATION...JPC


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