Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 251057
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
557 AM CDT Mon Sep 25 2017

.SHORT TERM...(Today and tonight)
Issued at 355 AM CDT Mon Sep 25 2017

As of 3AM this morning, a slug of rain showers with a few embedded
thunderstorms was streaming northeast through southwestern MN and
will continue expanding across most of southern MN.  The actual
front was from near Rice Lake, WI through Albert Lea, MN as of this
writing.

The front will continue very slowly working east today, and with
this system, the cool side of the boundary has been and will
continue to be a focus of widespread precipitation.  Large scale
forcing is best along to the west of the front owing to upper level
vorticity advection with repeat ripples in southwesterly flow and
the strong south to north oriented jet streak from South Dakota
through Ontario and hence strong differential divergence across
Minnesota today and tonight.  Weak instability also exists in the
vicinity of the front, so a few embedded thunderstorms will remain
possible.

There are two main shortwaves to take note of for today.  The first
one is approaching this morning with the aforementioned slug of
rainfall moving through.  There will likely be a period this
afternoon where the precip comes to an end or is very
scattered/isolated.  The next wave pushes in this evening and
delivers round two of widespread rain with embedded thunderstorms.
Hourly pops reflect these two separate waves with a lull in between.
 Expect rain to continue through the overnight hours mainly across
MN.  Western WI won`t see the widespread slug of rain that parts of
MN will as the second wave takes more of a westerly course.

Highs today will be held in the 50s and 60s across most of MN, but
with the front moving slowly, much of western WI and parts of
extreme southern MN will still be within the warmer airmass through
at least a decent portion of today.  Hence highs in the 70s and even
a few 80s near Eau Claire are plausible but highly dependent on the
frontal placement through this afternoon.

.LONG TERM...(Tuesday through Sunday)
Issued at 355 AM CDT Mon Sep 25 2017

Tuesday/Tuesday night weather remains clear as todays system will
quickly move off to the northeast, ending any precipitation
across the area by early Tuesday evening.

Models are more consistent for the system moving southward across
the Upper Midwest Thursday. The earlier outliers are more subtle and
less aggressive with the short wave moving southeast across the
region. Therefore, precipitation chances remain low, but a re-
enforcing shot of colder air remains in the forecast. The
possibility of a frost still looks favorable for portions of west
central Wisconsin Saturday morning as the surface high moves
overhead. Elsewhere, return flow develops and conditions do not look
as favorable of a frost in southern/central Minnesota.

Once Thursday/Friday system departs the area, the combination of
return flow at the surface, and an upper ridge building eastward, a
gradual warm up is expected. However, I don`t see any 80s returning,
but a few 70s are not out of the question by Sunday and early next
week /October 1st week/.

Although the aforementioned upper ridge building across the Rockies,
and into the Northern Plains/Upper Midwest next weekend looks
reasonable based on the ensemble means of the NAEFS/GEFS, there
remains some concern with leftover energy from the departing long
wave trough that has plagued the western half of the nation since
last week. Some of the models have an upper low forming in the
desert southwest this week and slowly moving this upper low
northeast, underneath the developing upper ridge.  The latest run of
the GFS/EC has the upper low merging/absorbing in the mean long wave
trough reforming across the Pacific Northwest. This is roughly late
next weekend. There remains a lot of spread in the ensembles with
the developing long wave trough in the Pacific and the strength of
embedded short waves moving inland across the Pacific Northwest.
This will have a large impact on how the upper low merges/absorbed
into the overall pattern change. Basically this means that next
weekend could be unsettled as this upper low becomes more apparent
in the mean flow.

Past next weekend, the CFS ensemble over the past few runs does
support another warmer period developing the first and second week
of October. This is based on a significant long wave trough
developing across the eastern Pacific, which will lead to ridging
across southern Canadian, and portions of the northern United
States.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 553 AM CDT Mon Sep 25 2017

The front has made it through most of the area by early this
morning, with the first of two main rounds of rain moving through.
Widespread IFR and low MVFR will persist in MN, but KEAU will stay
VFR for a time near the front. Low clouds may lift into MVFR this
afternoon when a lull in the precip is expected. Round two fills
in tonight and IFR is expected once again, possibly LIFR
overnight. Isolated embedded thunder will continue, but its so
isolated that did not include in any TAFs.

KMSP...Will continue to ride the edge of the main precip shield
through the morning, meaning temporary VIS restrictions are
likely.

/OUTLOOK FOR KMSP/
Tue...Chc MVFR/TSRA early. Winds NW 5-10 kts.
Wed...VFR. Winds WNW 5-10 kts.
Thu...VFR. Winds W 5 kts.

&&

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

$$

SHORT TERM...SPD
LONG TERM...JLT
AVIATION...SPD



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