Area Forecast Discussion
Issued by NWS Twin Cities, MN

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797
FXUS63 KMPX 231828
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
128 PM 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 18Z TAFS through 18Z Saturday afternoon)
Issued at 123 PM CDT Fri Sep 23 2016

Elevated instability pushing in is forcing a band of
shra/tsra across MN. The HRRR has had a good handle on it, though
has not been building it far enough southeast. This band of shra
will lift through AXN/MSP/STC/RNH on its way to northern MN and
NW WI. In its wake, we remain north of the surface warm front
tonight, which means more widespread IFR stratus through tonight,
with IFR/MVFR vis developing as well, though that will be closer
to the warm front, so a bigger issue from west central through
south central MN. We may see cigs lift some tomorrow afternoon
ahead of the cold front, with the next chance for TSRA lingering
just outside current TAF period.

KMSP...band of shra with embedded tsra continues to build
southeast as it moves to the northeast and at its current pace
will be to MSP around 20Z. Has become obvious more than a vcsh
was needed, so started shra with a vcts at 20z. Rain shouldn`t
last for much more than an hour, but in it`s wake is extensive
IFR and lower stratus, which is a sign of our future tonight.

/OUTLOOK FOR KMSP/
Sun...MVFR/-SHRA/-TSRA early, bcmg VFR. Wind W 10g20 kts.
Mon...Chc MVFR/-SHRA. Wind WNW 10g15 kts.
Tue...Chc MVFR early then VFR. Wind NW 5-10 kts.

&&

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

$$

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



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