Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 231143

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
643 AM CDT Tue May 23 2017

Issued at 632 AM CDT Tue May 23 2017

Updated to include 12z aviation discussion below.


.SHORT TERM...(Today and tonight)
Issued at 330 AM CDT Tue May 23 2017

Surface analysis early this morning shows a low pressure center
near the MN/WI/IA triple point with a cold front extending
southwest through central IA, southeastern NE into central KS.
Aloft, a large cutoff low is analyzed over central MN within a
large longwave trough encompassing much of the central CONUS. A
potent shortwave axis is rotating southward around the western
periphery of the upper low, and this feature shows up nicely on
both IR and WV imagery, driving nearly due south over the eastern
Dakotas and western MN. Showers currently on KMPX radar are moving
in different directions depending on which part of the coverage
area described: western portions are seeing southeastward-moving
showers while eastern portions are seeing north-northeastward
moving showers. This is owing to the upper level low nearly atop
the coverage area. While the surface low with is associated fronts
are expected to shift slowly off to the south and east, the upper
level low will move nearly due south through MN into IA today and
tonight. While in a deeply moist atmosphere, sporadic rain
showers will rotate through the coverage area all day today then
gradually erode to the east this evening through overnight
tonight. Because of the lack of surface aid to the precipitation
formation, lift will be solely generated by the upper level
feature and, as such, QPF will be reduced to a few hundredths to
possibly a tenth of an inch. Have used coverage wording to
indicate the thinking that showers will come-and-go, rather than
be persistent, and kept pops for most areas capped at 50s percent
to maintain "scattered" wording while far western MN may be more
susceptible to the "numerous" wording with 60 percent pops.
Regardless, showers will be weak and intermittent little rainfall
accumulation. Have also omitted mention of thunder since any
instability will be south and east of the front, thus not
available for this area. That said, a few of the showers could
produce very small hail (i.e. graupel), owing to the cold core
nature of the upper low. The precipitation will come to an end by
daybreak tomorrow morning with mainly cloudy skies in place. As
for temperatures, being behind the front and having cloud/rain
complications underneath the upper level low will promote cooler
conditions than that was experienced yesterday. Highs today will
range 55-60 degrees followed by lows tonight dropping to the low-
mid 40s.

.LONG TERM...(Wednesday through Monday)
Issued at 330 AM CDT Tue May 23 2017

The longer term concerns are timing of the next frontal passage
Thu night/Fri night time frame and development of the long wave
pattern into the holiday weekend.

Initially the upper low pressure trough exits to the east of the
area Wednesday. Drier air and surface ridging moves over the cwa
during the day. This should provide dry conditions along with cool

Timing of the next frontal passage looks to be Friday/Friday night
with initial waa pattern developing into Thursday night over the
west. This will develop a small chance of showers as this upper
trough swings across the Dakotas. As the upper trough moves east,
the front will be driven east Friday/Friday night. Convective
potential appears low at this time the meager moisture and
instability noted on deterministic models. Will hold onto some
slight chance thunder for Friday afternoon/evening to the east.

The GFS and ECMWF diverge some on the overall upper air pattern
over the weekend with the GFS slower and more amplified with the
upper low. We maintained the small chance PoPs for Sunday and
Monday at the moment. Appears temperatures will warm through the
lower to mid 70s into the weekend with a cooling trend into early
next week as the trough exits the area.


.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 632 AM CDT Tue May 23 2017

A large rotating upper level low will slowly sag south over
Minnesota through the day today into tonight, bringing
pockets/periods of MVFR ceilings along with occasional -SHRA to
all TAF sites through this evening. VCSH for most of the day will
actually be a pretty accurate description of today`s events since
any -SHRA that do move across the terminals will be weak and of
short-duration but be fairly frequent around the terminals all
day. Not expecting anything less than 6SM visibility but ceilings
may drop to the 2-3 kft range from time to time. Some sites are
starting out with IFR ceilings but those are not expected to last
long beyond 12z. Conditions will improve during the early morning
hours as the low moves away, allowing ceilings to rise back to VFR
levels then to scatter out around or shortly after 12z tomorrow.

KMSP...VFR ceilings do look to prevail but MVFR ceilings cannot be
ruled out throughout the day today, mainly midday through late
afternoon, but timing/duration will be tricky so will need to
monitor and amend as needed. Precipitation likely to be around the
field (within 10SM) for much of the day but impacts from the
precipitation itself are expected to be minor. MVFR ceilings again
possible around the morning push Wednesday morning then VFR for
the rest of tomorrow.

Thu...VFR. Wind SE 5-10 kts.
Fri...VFR. Chc MVFR/-SHRA. Wind SW 5-10 kts.
Sat...VFR. Wind W 5-10 kts.




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