Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 220824

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
324 AM CDT Thu Jun 22 2017

.SHORT TERM...(Today and tonight)
Issued at 330 AM CDT Thu Jun 22 2017

Today and tonight...

Surface analysis early this morning shows a surface low over west-
central Manitoba province with a trailing cold front extending
southeast into north-central MN, curving southwest into southeastern
SD and northern NE. Its associated warm front extends east from a
triple point over southwestern MN into northeastern IA and through
the Ohio River Valley. The surface low is under a deepening H5 low
while upper level flow flattens out considerably over the Upper
Mississippi River Valley, running rather zonal over the region. This
stacked low is expected to drift to the east over the next 24-30
hours, repositioning itself to over south-central Ontario province,
while dragging with it a potent trough axis through the Dakotas into
MN/WI tonight into tomorrow. This movement aloft will help nudge the
cold front eastward while the warm front lifts slightly north,
allowing for some warm-sectoring to occur today into this evening
over eastern MN into western WI.

The rather unstable airmass in advance of the cold front (MUCAPEs in
the 2000-3000 j/kg range and diminishing CINH) plus steep mid-level
lapse rates have contributed and are contributing to scattered
convection overnight through this morning. Some of the storms have
become surface-based and that is expected to continue in mainly
southern MN as the day progresses. In addition, the loss of capping
with the northward-moving warm front plus diurnal heating over an
area that has not been overly worked over will allow for additional
coverage of showers/thunderstorms later today into this evening.
Have indicated as such with pops increasing into the categorical
range for southern and eastern portions of the WFO MPX coverage
area. Aiding the convective development in these southeastern
portions will be highs that climb to near 80 degrees plus dewpoints
into the low-mid 60s. The main hazards continue to be large hail and
damaging winds with storms that will take the form of clusters
and/or MCCs.

The precipitation will steadily wind down and shift off to the east
with the cold frontal passage this evening. This also coincides with
the passage of the potent shortwave aloft. Slightly drier air along
with weak high pressure will fill in behind the front for the
remainder of the overnight hours. This will be reflected in lows for
early Friday morning which will drop to the low-mid 50s along with
dewpoints falling to the upper 40s to lower 50s.

.LONG TERM...(Friday through Wednesday)
Issued at 330 AM CDT Thu Jun 22 2017

The longer term concerns remain the highly amplified pattern with
the cold trough affecting the eastern conus through early next

Northwest flow aloft becomes entrenched across the area Friday.
Cooler with a small chance of showers will be found over the
northeast portion of the cwa. Should see quite a bit of clouds
cover with the cooler air as well. This should limit highs in the
65 to 70 degree ranges. Some 10 to 15 degrees below normal.

Both deterministic long term models drive a couple of short waves
through the region over the weekend. This will affect mainly
about the eastern half of the area. The GFS is farther west with
the initial wave...and seems a bit overdone. Some instability
ahead of this feature so will include slight chance thunder for
Saturday afternoon to the east. This may also occur into Sunday
afternoon as the next wave arrives. This may be even
more isolated with even colder air aloft expected to arrive.

The last wave exits east of the region Monday and this leaves cool
and dry conditions through at least Tuesday. Models do try and
develop a somewhat flatter more zonal upper air pattern to the
area later in the period. The GFS tries and draw warmer air for
the Pacific Northwest while the ECMWF remains not as robust with
the warm air return. We should still see temperatures warm through
the end of the week...closer to or slightly above normal. Along
with the warmer air...another frontal system is expected to
arrive by the end of the work week bringing another chance of
showers and thunderstorms.


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1025 PM CDT Wed Jun 21 2017

Model preference is a combo of the HRRR and NAMnest models, which
feature a squeeze play of showers and thunderstorms moving into
the area overnight from eastern SD and northern IA. Both feature a
fairly rain morning for most of the sites, with embedded
thunderstorm potential as well. Afternoon convective
redevelopment (of stronger storms) still looks to be shifted
south/east of most TAF sites (with the exception of possibly
KEAU).  MVFR cigs/vsbys are possible with thunderstorms, and also
with/behind the frontal passage, but expect to be VFR by 00z
Friday. Winds shift to the northwest behind the front.

There is a small threat for thunder early in the period, but the
more widespread showers (with embedded thunder) holds off until
around/after 10z. The morning looks to have activity around
throughout, and then we scatter out during the mid afternoon.

Fri...VFR. Wind NW 10 kts.
Sat...Mainly VFR. Slight chc -TSRA/MVFR. Wind NW 5-10 kts.
Sun...Mainly VFR. Slight chc -TSRA/MVFR. Wind NW 5-10 kts.




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