Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 221155
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
655 AM CDT MON AUG 22 2016

.UPDATE...
Issued at 644 AM CDT Mon Aug 22 2016

Updated to include 12z aviation discussion below.

&&

.SHORT TERM...(Today and tonight)
Issued at 328 AM CDT Mon Aug 22 2016

Today and tonight...Surface analysis this morning shows a large
area of high pressure centered over southern IL/IN, expanding
well westward across the middle and upper Mississippi River valley
regions. Aloft, a ridge axis is located over the central-northern
Plains while a compact upper level low develops over the southern
Canadian Rockies. As the day progresses, this ridge axis will
shift eastward, moving atop MN/WI by daybreak Tuesday morning.
Meanwhile, the surface high will also shift eastward to the Mid-
Atlantic states while a surface low strengthens just north of the
Montana/Canada border. While being on the backside of the surface
high, it will maintain its influence over the area. The lingering
high combined with the incoming ridge will result in warmer
temperatures as highs will range from the lower 80s in western WI
to the upper 80s in western MN. There will be some passing clouds
from time to time in response to an increase in mid-level moisture
and potentially a surface trough reaching into MN from the
Rockies. However, despite a few CAMs showing isolated showers this
afternoon over the region, am not expecting precipitation to
actually develop that would reach the ground because of the deep
dry air that must be overcome. Since this trough will then lift
north into Canada and the low out in the west will not arrive to
influence sensible weather within the next 24 hours, will maintain
a dry forecast with passing clouds. The main influence of the
developing low, especially with respect to lingering high
pressure, will be a tightened pressure gradient over the area
today. This will make for breezy/gusty conditions today with
southerly winds of 15-25 mph and gusts around 30 mph at times this
afternoon. The slight increase in clouds with the strong southerly
flow will make for highs early Tuesday morning about 10 degrees
warmer than this morning.

.LONG TERM...(Tuesday through Sunday)
Issued at 328 AM CDT Mon Aug 22 2016

By Tuesday morning, the thermal ridge will be across the eastern
Dakotas and into western MN, with a surface low advancing northeast
through eastern North Dakota with a cold front trailing to its
west. West of there, a closed low will be advancing east across
southern Canada and will begin to merge with the North Dakota low
during the day on Tuesday. For us, this means Tuesday will again
be a warm one, with stout southerly flow and dew points rising
into the upper 60s and temperatures in the upper 80s and heat
indices into the 90s. Skies will start out partly cloudy but late
in the day a quick increase in cloud cover will signal the
incoming moisture as a shortwave advances through eastern Nebraska
and into Iowa.

The main focus of the long term is the Tuesday night period.  The
previous discussion issued yesterday afternoon greatly described
the possibilities at play Tuesday night and the latest model
guidance latched onto the idea of the heavy rain and MCS potential
being across Iowa in association with the strong low level jet. As
a surface low develops across Kansas, the low level jet evident by
the 850mb winds increasing to 50-60 knots across Kansas through
eastern Nebraska and into southern Iowa will drive the storm
activity and likely MCS development across the greatest
convergence of warm air and moisture transport across Iowa. This
area is the most likely setup for MCS development and with the LLJ
staying to our south, the thunderstorm activity will be limited
across Minnesota and west central Wisconsin. Continued likely pops
along the I-90 corridor for now as scattered storm development is
possible there, but lowered likely pops to chance across the rest
of the forecast area. If this setup is reinforced by todays newest
model guidance, the pops across Minnesota and Wisconsin could be
lowered even more. The HOPWRF-TS forecast reflectivity aligns well
with this thinking as it indicates a very plausible scenario in
which a strong MCS develops along the nose of the LLJ in eastern
Nebraska and moves through central Iowa, and in turn makes it very
difficult to the north of said MCS for much of anything to
develop.

The previously mentioned cold front with this system will push
into western MN Wednesday morning and work through eastern MN
and western WI during the day. Winds will turn northwesterly
behind it and those upper 60s dew points will fall into the 50s by
Wednesday night. Cold air advection will continue and Thursday
will be a lot like yesterday with temperatures in the low 70s and
dew points in the lower 50s. Southerly flow will develop Friday so
we`ll start warming up some but it should be another pleasant day.
This weekend still looks unsettled as two shortwaves look to move
through the Upper Midwest and bring chances for thunderstorms
across the region.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 644 AM CDT Mon Aug 22 2016

VFR conditions will prevail throughout this package with mid-to-
upper level SCT clouds. Some light echoes on KMPX radar this
morning in southern MN will continue drifting E but are not
expected to produce any measurable precipitation due to a deep dry
layer up to about 10 kft. Winds will be the main story as a
tightened pressure gradient will create breezy/gusty southerly
surface winds today. A stronger low level jet will develop this
evening through overnight which will increase 1-2 kft winds to
40-45 kts. The boundary layer direction will be more SW than
surface S winds so it straddles the fence of being LLWS. Currently
thinking is that this is more of a low level turbulence than LLWS
situation so have left mention out of the TAFs at this point.
However, it is something to monitor, particularly if the
directional difference become more prominent.

KMSP...Breezy/gusty surface winds will eventually develop from the
180-190 direction then remain there through tomorrow morning.
Stronger winds in the 1-2 kft level tonight through tomorrow
morning may cause some low level turbulence issues for the morning
push Tuesday morning. Otherwise, no flight condition or
precipitation concerns.

/OUTLOOK FOR KMSP/
Wed...VFR with -TSRA/MVFR possible. Wind SW 5-10 kts becoming W.
Thu...VFR. Wind NW 5-10 kts.
Fri...VFR. Wind SW 5-10 kts.

&&

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

$$

UPDATE...JPC
SHORT TERM...JPC
LONG TERM...SPD
AVIATION...JPC



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