Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 221136

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
636 AM CDT Tue May 22 2018

.Updated for 12z Aviation Discussion...
Issued at 628 AM CDT Tue May 22 2018


.SHORT TERM...(Today and tonight)
Issued at 310 AM CDT Tue May 22 2018

Dense fog formed in area that cleared prior to midnight across
southwest/south central Minnesota. Elsewhere, skies were mainly
cloudy which held the formation of dense fog more isolated. Still,
patchy fog continued to develop across southern/central Minnesota,
as well as west central Wisconsin overnight. Based on the enhanced
RGB nighttime satellite imagery, most of the fog in southwest
Minnesota was shallow which indicates that most of the fog should
dissipate shortly after sunrise. Elsewhere, skies were partly to
mostly cloudy in the wake of the disturbance that brought showers
to the area yesterday.

The main forecast change tonight was to hold onto the best chance
of thunderstorms along the Iowa border, and far southwest
Minnesota after midnight. This is where the best enhancement of
the low level jet combines with increasing moisture in the mid
levels of the atmosphere. Most CAMS support convection developing
along the Iowa border, and southwest Minnesota between 3-9z
tonight and spreading this activity to the east-southeast. This is
where the highest percentages remain. There are a few outlier that
form convection across west central-eastward into east central
Minnesota by 12z Wednesday. However, based on the best
instability, will hold onto the better scenario along the Iowa

.LONG TERM...(Wednesday through Monday)
Issued at 330 AM CDT Tue May 22 2018

The first part of the extended period can be characterized as very
warm and humid with afternoon high indices in the 90 to 95 degree
range for Wednesday through Friday. I wouldn`t be surprised to see
heat indices approach 100 degrees on Thursday if most sunshine
occurs. I have already raised temperatures in the inner core of
the Twin Cities due to urban effects for Wednesday, Thursday and
Friday. Outside of the Twin Cities metro area, highs will climb
into the upper 80s. Further to the west in west central Minnesota,
90s will be common. I will highlight the morning HWO with rising
heat indices as this will be the first time this year our region
has experienced this type of heat.

Other than the heat, models support the best chance of widespread
convection Friday morning, and again Friday afternoon as a weak
front moves across the area, and is supported by an upper level
wave. Over the weekend, models are very unorganized in terms of
chances of thunderstorms, especially considering the amount of
instability present. Current forecast has low percentages through
the first part of the weekend, but this again is more related to
instability present than any type of frontal boundary and upper
level waves. The holiday weekend looks to be mainly dry, so don`t
change any plans.

Past this weekend, another upper ridge builds across the Northern
Plains, Upper Midwest, leading to more heat and humidity building.
There is another aspect to next week as a tropical connection
could play a role in our weather. Models have been advertising a
tropical system developing in the Gulf of Mexico next weekend, and
slowly moving this system inland across the southern CONUS, east
of the Rockies. As the upper ridge builds across our region, this
tropical system could get caught up in the weak flow and bring us
a very unsettled week.

As for severe weather aspects this week, wind shear parameters
remain weak, but instability is modest. The best time frame for
any potential of severe thunderstorms will occur in the
afternoon/early evening time period. The other option is the short
wave moving across the Upper Midwest Friday. There could be some
enhancement of wind shear with this wave. So, always continue to
monitor the SPC page for any details.


.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 628 AM CDT Tue May 22 2018

IFR/LIFR conditions to the south this morning should hang on until
around 13/14Z, and then the late May sun should gradually erode
the fog/stratus. There is very light wind in the boundary layer,
so this will keep MVFR conditions around through mid-morning for
many locations. Eventually we should see VFR conditions with light
southerly winds.


MSP is in a clear spot, with IFR conditions surrounding it. For
that reason did go the more optimistic approach for MVFR/VFR
conditions this morning. It is possible clouds fill in later this
morning, and skies go below 1700 ft. Winds will be light and
generally out of the south.

WED...Mainly VFR with -SHRA/TSRA possible. Wind SE 5-10 kts.
THU...Mainly VFR with -SHRA/TSRA possible late. Wind S 10 kts.
FRI...Mainly VFR with -SHRA/TSRA possible. Wind SW 5-10 kts.


MN...Dense Fog Advisory until 9 AM CDT this morning for MNZ047-



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