Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 220335

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1035 PM CDT Sun May 21 2017

.SHORT TERM...(This evening through Monday)
Issued at 215 PM CDT Sun May 21 2017

The main item of concern in the short term is the possibility of a
few stronger thunderstorms Monday afternoon across the southern
portion of the area. Otherwise, we`ll mainly see a continuation of
mostly cloudy conditions, some light showers and/or drizzle, and
cool temperatures. The surface low to our northeast will continue
its slow northeastward drift away from the area tonight into
Monday. With low-level moisture and cyclonic flow lingering, we`ll
see a few showers into the evening, although there will be a
continued decrease in coverage as the mid-upper level cold pool
pushes a bit east. Some drizzle will remain possible through the
night, but those chances look to be mainly over the northeast
portion of the area.

On Monday, we may see some breaks in the cloud cover during the
later morning and early afternoon, particularly across the
south/southwest portion of the area as the current system shifts
away and the next system starts to approach. A secondary shortwave
trough rotating around the main upper low will work into the area
later tomorrow, helping to enhance a weak surface wave across
southern Minnesota before pushing a reinforcing cold front through
the region. Models are in good agreement with the overall
evolution of things, with timing and the amount of moisture return
having some differences. However, it does appear we`ll see a
window of some instability, with MLCAPE of around 500 J/Kg
developing in the afternoon into early evening, particularly near
and south of I-90. The NAM shows a bit more instability than the
other solutions, but may be too aggressive in its moisture return.
Mid-level winds also look to increase ahead of the shortwave
trough during the afternoon. With the cold pool aloft and low
freezing levels, any stronger storms that are able to develop
would have the potential to produce marginally severe hail, and
perhaps slightly larger than that if they can leverage the deep
layer shear and/or instability is greater than expected. Some
stronger wind gusts could also be a concern with any strong storms
that can develop.

.LONG TERM...(Monday night through Sunday)
Issued at 215 PM CDT Sun May 21 2017

Anything that is able to develop Monday afternoon should quickly
exit out area during the evening, with cold advection and
subsidence initially working into the area. However, on Tuesday
we`ll once again have cold air aloft with the potential for some
shower development. At this point, not anticipating enough
instability for any thunder on Tuesday, but any decent showers
could possibly produce some graupel. After that we will await the
slow but steady arrival of drier air and large scale subsidence to
give us a window of dry and more mild weather. The models are in
fairly good agreement that this will occur during the Wednesday-
Thursday time frame as a shortwave ridge briefly builds over the
region between the eastern trough and a developing western trough.
That western trough then looks to push eastward through the
remainder of the week, bringing chances for precipitation back
into the area Thursday into Friday. The GFS and Canadian have come
around to the somewhat faster solution suggested by the ECMWF and
MPAS runs yesterday. Could see some elevated convection along the
leading edge of the warm advection and theta-e ridge on Thursday,
then a bit of a break before more widespread shower/thunderstorm
chances move west to east across the area later Thursday night and
Friday as the cold front pushes through the region. Another upper
trough looks to work into the region Saturday into Sunday,
bringing additional chances for showers. However, there remains
quite a bit of disagreement on how amplified the pattern will be
at that point, and whether or not we`d get much if any moisture
return into the region. So, for now just covered things with some
chance PoPs.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1034 PM CDT Sun May 21 2017

We have one more batch of rain to work through WI at the start of
the 6z TAF period, then we look to remain dry this period, as
better shower chances stay to our north with the main upper low,
and to our south as a secondary shortwave sparks some TSRA Mon
afternoon from NE SoDak into northern IA. We will have VFR skies
as well and may actually see a descent amount of sun tomorrow
between the two areas of forcing. Monday night we`ll have to
watch for MVFR cigs dropping south out of northern MN. SREF probs
show them reaching AXN by the end of this TAF period, which has
support from an RH time-height cross section for the NAM as well.

KMSP...High confidence in TAFs this period. Only area of
uncertainty is with the last 6 hours. As we hit that point, the
core of the upper trough aloft will be moving overhead. Beside a
return of OVC skies (VFR most likely), there will be a threat for
some -ra as well, but we have lots of time to monitor that
possibility and it looks pretty low impact as well.

Tue...VFR. Chc MVFR/-shra. Wind NW becoming N 5-10 kts.
Wed...VFR. Wind NE 5-10 kts.
Thu...VFR. Wind SE 5-10 kts.




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