Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 131852

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
152 PM CDT Fri Oct 13 2017

.SHORT TERM...(This evening through Saturday)
Issued at 149 PM CDT Fri Oct 13 2017

Surface analysis this afternoon puts a cold front emanating from
low pressure over Hudson Bay extending south into Lake Superior
then southwest through northwest Wisconsin into southeast
Minnesota and central Iowa. Weak high pressure over the Dakotas is
nudging east behind the front, contributing to clearing skies
slowly spreading east. Aloft, generally ENE-WSW flow is prevailing
while a longwave trough deepens over the Pacific Northwest and
subtropical ridging holds for over the southeastern CONUS. While
the ridge aloft is expected to remain in place through tomorrow
night, the trough will progress eastward over the Rockies and into
the Central Plains by tomorrow evening. The ridge will slow up the
progression of the front, allowing it to stall out from lower
Michigan through northern Missouri overnight. As the trough shifts
east, it will contribute to cyclogenesis over eastern Colorado.
The low is then expected to quickly move northeast along the
stalled front, moving to a position near the IA/MN/WI triple point
by tomorrow evening. A prolonged plume of deep South moisture will
be wrapped around the western periphery of the subtropical ridge
into the Upper Midwest, made available in advance of the
progression of the developing surface low for later tomorrow. This
combination of the approaching upper trough and surface low plus
the additional moisture will make for effective precipitation
generation tomorrow afternoon. Main difference from previous
forecasts is the timing as latest model runs have slowed the
spread of the rainfall from southwest to northeast. That said,
showers are still expected for much of the area by tomorrow
afternoon. As for temperatures, not much difference is expected
for highs tomorrow than from today, in the 50s area-wide. Lows
tonight behind the front will range from the mid 30s to lower 40s.

.LONG TERM...(Saturday through Thursday)
Issued at 408 AM CDT Fri Oct 13 2017

A trough will approach from the Rockies early Saturday and spawn
an area of low pressure over the central Plains. As the system
encounters moistening isentropic upglide over the Midwest, rain is
expected to develop rapidly along a quasi stationary front to the
south along I-80 and along the leading edge of the trough over
the Dakotas Saturday morning. The rain shield will fill in by
Saturday afternoon across southern MN due to these features
phasing and the surface system maturing. The rain shield will lift
northeast before the deformation band reaches maturity, so
amounts will be light. Colder air behind the system Saturday night
could allow for a few snowflakes across western and central MN,
but it appears any steady precip will be well east by that time
with mid level dry air also pushing in.

A chilly Sunday and Sunday night will be followed by a very
tranquil and mild period across the vast majority of the CONUS
for next week. A large ridge will develop across the south,
shifting the storm track to the Pacific Northwest and Canada. This
will prevent any cold air intrusions from reaching this far south
until perhaps next weekend. Southerly surface flow will keep lows
in the 40s and 50s and highs in the 60s and maybe 70s.


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 149 PM CDT Fri Oct 13 2017

VFR to start at all terminals although the clearing line behind
the departing cold front has not quite gotten through KMSP-KMKT
and points east. Any and all precipitation near the front will
remain south of all terminals. The clearing line is expected to
continue moving east, however, resulting in a period of mainly
clear skies (except possible FEW- SCT high clouds) this evening
into the early morning hours. Clouds will fill back in from the
west and south late morning through the day tomorrow. However,
precipitation looks slower to move into the area per latest model
runs so have reflected as such in the TAFs, along with a slower
deterioration of conditions. Winds will swing back from NW to NE
then SE over the next 24 hours with speeds mainly in the 5-10 kt

KMSP...Very few concerns tonight through tomorrow morning with VFR
in place. Only lowering ceilings through the morning push but
everything expected to remain above 5 kft. Tomorrow afternoon has
more concerns as rain is expected to move in from the southwest,
likely to drop ceilings into MVFR range for the start of the
evening push and potentially under 1700ft by the evening with
winds close to 040 direction. Will certainly need to be watched.

Sun...VFR. Wind NW 5-10 kts.
Mon-Thu...VFR. Wind SW 5-10 kts.




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