Area Forecast Discussion
Issued by NWS Twin Cities, MN

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927
FXUS63 KMPX 172333
AFDMPX

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

.UPDATE...For 00z Aviation discussion below

&&

.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 00Z TAFS through 00Z Monday evening)
Issued at 634 PM CDT Sun Sep 17 2017

The first 9 hours of the TAF period look to remain quiet, and
then rain showers with the potential for MVFR conditions expand
north and east across the area on Monday. Starting to see a few
weak radar returns over southeast SD and northwest IA. This area
is expected to blossom late tonight and then spread east and shift
north Monday morning. The main question is how far north the area
will lift, with some hi-res models placing KMSP on the northern
fringes, and other models lifting the area as far north as KSTC
and KAXN. For now have maintained just a VCSH mention for KMSP-
KRNH-KSTC-KAXN, with the more concentrated activity passing across
KRWF-KMKT-KEAU. Will be watching development tonight to see how
things evolve, and whether a prevailing shower mention will be
need farther north. Cigs in the main area of precip look to reduce
to MVFR, although vsbys should be mostly 4-5SM or greater. Light
and variable winds this eve will become prevalent southeasterly,
and gust into the upper teens to lower 20s (knots) at northern
sites (KAXN and KSTC) beginning mid to late Monday morning.

KMSP...
Clouds around 10KFT or slightly above spread in overnight and
lower to low-end VFR or possibly even MVFR tomorrow
afternoon...especially if the main band of showers shifts slightly
farther north and VCSH become prevalent -RA.

/OUTLOOK FOR KMSP/
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.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
&&

$$

SHORT TERM...JPC
LONG TERM...JLT
AVIATION...LS



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