Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 230833

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

.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 nite/Fri nite 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 06Z TAFS through 06Z Tuesday night)
Issued at 1058 PM CDT Mon May 22 2017

At 11pm, we are finally starting to see spotty MVFR cigs in
northern MN, though the LAMP and HRRR were both saying this should
be a widespread IFR/MVFR field. As mentioned in 00z discussion,
there was concern the LAMP was overdoing its cig forecast and
certainly trends this evening support that, with forecast
conditions slowly improving in the LAMP. Based on SREF probs, MVFR
cigs are most likely west of MSP, so continued to only have
prevailing MVFR cigs at AXN/STC/RWF. In addition have trends for
these airports more optimistic than what LAMP has. For precip, it
looks to be of the hit- and- miss, on- and- off through the day
Tuesday. Given that expectation, have prolonged periods of VCSH at
all terminals.

KMSP...Confidence is increasing in main MVFR cloud mass remaining
west of MSP this period. Based on HRRR and other CAMs, expect
diurnally driven scattered showers to develop late Tuesday
morning and persist through the rest of the daylight hours.

Wed...VFR. Wind NE 5-10 kts.
Thu...VFR. Wind SE 5-10 kts.
Fri...VFR. Chc MVFR/-SHRA. Wind SW 5-10 kts.




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