Area Forecast Discussion
Issued by NWS Twin Cities, MN

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969
FXUS63 KMPX 231052
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
552 AM CDT FRI SEP 23 2016

.SHORT TERM...(Today and tonight)
Issued at 312 AM CDT Fri Sep 23 2016

An area of elevated instability along the 900-800mb convergence
zone across north central-northeast Iowa, has kept this area
under continuous thunderstorm activity overnight. However, winds
in this layer have shifted slightly across southwest Minnesota and
allowed new thunderstorm development in an area of increasing
instability. This area of thunderstorms is the main concern this
morning as it slowly shifts to the north across southwestern
Minnesota.

Initially instability will be weak and mostly elevated in western
Minnesota, but as winds become more south-southwest above the
boundary layer, expect an increase in thunderstorms through mid-
morning in southwest/west central Minnesota. Usually the typical
diurnal weakening of the thunderstorms in the morning is expected.
However, I am concern that this activity may continue, and spread
to the northeast. Some of the short term models and CAMS
indicate this scenario with thunderstorms re-developing from the
Twin Cities, northwest to Alexandria by the early-mid afternoon
hours. This is where the best coverage of precipitation will occur
with a lower probability south-southwest as a capping inversion
develops this afternoon.

Mid level drying and the main focus of the low level jet occurs
north and east of our region tonight. Therefore, expect only
isolated thunderstorms from Mora, southeast to Rice Lake and Eau
Claire this evening. Elsewhere, it should remain dry.

Boundary layer moisture is high through the afternoon for most of
southern Minnesota and western Wisconsin. This will aid in the
continued cloud cover and temperatures only rising a few degrees
from morning lows. The highest temperatures will occur along the
Iowa border where some breaks in the overcast is possible by the
late afternoon.

.LONG TERM...(Saturday through Thursday)
Issued at 312 AM CDT Fri Sep 23 2016

Saturday through Sunday...The period will commence with a large
ridge axis aloft aligned over the Mississippi River while a deep
cutoff low rotates across the northern Rockies on its way into the
Dakotas. At the surface, a developing surface low will take hold
of the stalled surface front to the south and start lifting it
north. This will allow for a deep warm/moist southwesterly flow
into the region, increasing not only temperatures but also PWATs
for what will be widespread showers/thunderstorms for the entire
area starting Saturday afternoon. Though there are still some
differences as to how far north the warm front will actually lift,
the consensus is to have it shift north into central MN/WI by late
day Saturday, to be followed by its associated cold front
overnight Saturday into Sunday morning. Precipitation coverage is
expected to be fairly widespread but with the front moving fairly
progressively, widespread flooding issues are not expected but
flooding overall cannot be ruled out. QPF is generally in the
0.50-1.00 inch range but locally heavier amounts may well occur.
Any heavy rain atop the recent heavy rainfall may cause or
exacerbate ongoing flooding. In addition, strong low-to-mid level
jetting in advance of the front (including the potential of
35-40kt of bulk shear) may be enough to overcome any lack of
insolation to possibly produce isolated severe thunderstorms
Saturday night. The cold front will pass to the east of the WFO
MPX coverage area by Sunday evening, thus pushing the main swath
of rainfall off into the Great Lakes. As for temperatures, being
in the warm sector of this system will allow highs to hit the
70-80 degree range on Saturday. Behind the cold front for Sunday,
highs will drop back to the 60-70 degree range as flow shifts from
southwest to west-northwest, bringing in modified colder Canadian
air.

Monday through Thursday...The aforementioned upper level low will
slow its progression and slowly rotate eastward over WI and the
Great Lakes Monday into Tuesday. This will result in isolated to
scattered light rain showers for the start of the week with also
noticeably cooler temperatures. Highs will drop into the 50s to
mid 60s while lows bottom out in the 40s. While this low keeps
clouds/showers over the upper Midwest, a large upper level ridge
will develop over much of the western CONUS. This ridge will
spread eastward and become the main feature over the central CONUS
by midweek. With surface high pressure moving in conjunction with
the upper ridge, this will promote clearing skies and a slight
warming trend for the middle to latter portion of the week. Highs
will climb back closer to 70 degrees.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 550 AM CDT Fri Sep 23 2016

Confident that IFR/MVFR ceilings will persist through the morning,
and into the afternoon as boundary layer moisture is high and
observations of the lower ceilings extend into Iowa. Lower
confidence on showers/thunderstorm development this
morning/afternoon as the instability axis moves northward across
Minnesota. Kept VCSH as previous tafs but updates to this are likely
by the late morning as activity becomes more apparent. Ceilings
will likely lower once again tonight with LIFR possible. Winds
will continue from the east-southeast through the period.

KMSP...

Confident that IFR/MVFR ceilings will persist through the late
morning, and possibly through the taf period. Best chance of
ceilings rising above 1.7k is after 18z. Some showers/thunderstorms
are possible after 21z. Otherwise, an east wind will become more
southeast overnight.

/OUTLOOK FOR KMSP/

Sat night...TSRA likely with IFR Cigs. Wind SE 10 kts.
Sun...VFR-MVFR Cigs with Showers. Wind W 10g20 kts.
Mon...Chc MVFR/-SHRA. Wind WNW 5-10 kts.

&&

.MPX Watches/Warnings/Advisories...
WI...None.
MN...None.
&&

$$

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



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