Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 171955

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
255 PM CDT Sun Sep 17 2017

.SHORT TERM...(This evening through Monday)
Issued at 255 PM CDT Sun Sep 17 2017

Surface analysis puts the center of high pressure over
southwestern MN this afternoon while an area of low pressure
slowly develops over the TX/OK panhandles. Aloft, a low pressure
center spins over southern Manitoba province, with a trough axis
spinning away on the eastern periphery, with modest WSW-ENE flow
from the western CONUS into the Great Lakes. The high pressure
area will shift off to the east overnight through tomorrow,
resulting in winds going from NW to light/variable to SE tomorrow.
As the surface high exits, the southwestern surface low will be
picked up by a weak shortwave trough moving eastward over the
western half of the lower 48. Though it is progged to remain to
the south of the WFO MPX coverage area, enough isentropic lift to
the north of the warm front extending eastward from the low within
a deeper slug of moisture being brought along by the upper trough
will be sufficient to produce isolated to scattered rain showers
over central and eastern portions of the coverage area during the
day tomorrow. Not looking for much in the way of QPF, generally a
tenth of an inch or rain or less. Cloudy skies will then likely
remain in place going into tomorrow evening. The cool temperatures
of today will also be present tomorrow, with highs only in the
low-to-mid 60s.

.LONG TERM...(Monday night through Sunday)
Issued at 255 PM CDT Sun Sep 17 2017

The extended period can be characterized as becoming very
amplified as a deepening trough develops across the west coast
and the Rockies, with a blocking ridge developing across the Great
Lakes region. This will set the stage for very cool, and
unsettled conditions for the western 1/4 of the nation. Our region
will be abnormally warm with most of the significant and
persistent rainfall developing next weekend, and even this is
uncertain. However, low chances of precipitation can not be ruled
out along a cold front late Tuesday night/Wednesday morning, and
expected embedded short waves riding northeast along the deepening
trough in the southwest late in the week.

Currently the extended forecast has mostly chance percentages, but
this is more of uncertainty in the models, and due to weak short
waves riding northeast along this type of southwest flow aloft.

This type of pattern with a broad trough in the west, and a
blocking ridge over the Great Lakes is very conducive of
abnormally high temperatures for this time of year for the Upper
Midwest. Some of the GEFS members have highs in the 90s or near 90
degrees on Friday for southern Minnesota. I wouldn`t be surprised
to see highs increasing every model run based on these type of
scenarios. In addition to the increasing warmer temperatures which
translates aloft, we could be increasingly capped. Therefore,
chance of precipitation would also go down.

Once the mean trough out west slowly works eastward into the
plains late next weekend, does our chances of precipitation
increase. Again, I wouldn`t be surprised to see the models moving
this trough out faster than expected. Therefore, it could even be
a dry first half of next weekend.

Overall, warmer conditions are likely this week, and into the
first half of the weekend. Chances of precipitation remain
questionable until this trough out west moves out into the plains.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1231 PM CDT Sun Sep 17 2017

Morning cloud deck around 020 is continuing to erode to the north.
Still enough patches of clouds to mention FEW/SCT in parts of
central MN into central WI, with only KAXN having a ceiling at
initialization. The clouds at 025 look to finally dissipate by
this evening, resulting in only high clouds for much of the
overnight. Lowering decks return tomorrow as a weak upper level
wave approaches. Isolated showers are possible late morning into
tomorrow afternoon for mainly the southern TAF sites but
confidence not that great so have gone no further than VCSH. Winds
will continue from the W thru this evening then go light/variable
before swinging to SE overnight thru tomorrow.

KMSP...Enough clearing to not have anything more than FEW025
coverage for this afternoon, and even that may be generous. Clouds
to return overnight and gradually lower during the day tomorrow.
Some showers are possible tomorrow afternoon but coverage is quite
questionable to will run with only VCSH at this point. Growing
potential for MVFR ceilings late tomorrow afternoon as well.

Tue...Mainly VFR. Chance MVFR ceilings. Winds SE 5-10 kts.
Wed...Mainly VFR. Chance TSRA/MVFR early. Winds W 5-10 kts.
Thu...Mainly VFR. Chance MVFR ceilings. Winds SE 5-10 kts.




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