Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 192059

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
359 PM CDT Wed Apr 19 2017

.SHORT TERM...(This evening through Thursday)
Issued at 358 PM CDT Wed Apr 19 2017

Early afternoon water vapor imagery together with RAP13 surface
analysis and obs identified an upper level wave across Nebraska with
an inverted surface trough extending into western Iowa. The warm
front associated with this surface trough was very evident via both
the surface obs and also the GOES16 satellite imagery. This warm
front tilted poleward with height, and an area of elevated showers
and thunderstorms was moving across the forecast area producing a
cool, light to moderate rain.

Expect a few hours of dry weather once this rain moves though, but
another round of precipitation will develop in the form of deep
convection in the warm sector of the aforementioned surface
trough/low. Supercells storms will quickly become severe across
Iowa, and a few of these storms could propagate north of the warm
front and produce a threat for large hail across the southern part
of our forecast area near I-90.

Cold air will rush in on Thursday as the parent cyclone quickly
matures. Forecast soundings show some instability atop the boundary
layer so have included chance of showers through Thursday afternoon
for the eastern part of the forecast area. Highs will struggle to
reach 50 for many locations.

.LONG TERM...(Thursday night through Wednesday)
Issued at 358 PM CDT Wed Apr 19 2017

Looking ahead, the weekend looks dry as high pressure builds across
the region. Precipitable water will drop below a quarter of an
inch. Expect light winds with seasonable temperatures. On Sunday
night an upper level wave will move across the high plains and
develop a compact surface low which will bring showers and
thunderstorms across the region. The mass fields in this system
appear quite similar to the storm system that is moving across
Iowa today, but the major difference is moisture content.

Next weeks storm will have lower dewpoints by about 10 to 15
degrees which means much less available potential energy and a
reduced severe threat. Could see some thunderstorms, but at this
point the instability is very marginal and the LCLs are too high
to merit more than a monitor phase. Cooler weather will follow in
the wake of this system, so could have a freeze concern in the
typical cold parts of the forecast area. &&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 109 PM CDT Wed Apr 19 2017

Band of rain is lifting northeast out of southwest MN this
afternoon is coming in just a tad slower than what we had going
with the TAFs, so minor timing adjustments were made for it.
Otherwise, this forecast leans heavy on a RAP/HRRR solution, with
a shield of showers with embedded TSRA developing in SW MN around
22z that will then race east through 6z. Used the hrrr to time the
thunder threat across all but AXN/STC. For cigs, used a RAP timing
for when to bring low cigs back in, that threat greatly increases
after 3z as the sfc low cross the I-35 corridor in north central
IA. Behind the band of SHRA/TSRA, we will likely see a dry slot
work in that will cut off the heaviest precip and will cut us back
to drizzle at best for a few hours before a deformation band
works in. As for that deformation band, RAP/NAM soundings are cold
enough out toward AXN by 12z Thu to mix in -SN with the -RA as it
is pulling out.

KMSP...Confidence is pretty high on bringing precip in and window
for TS as well, though greatest TS coverage will be south of MSP.
We may see precip end earlier than forecast behind the main TSRA
shield, but we will likely have IFR cigs irregardless of precip
falling tonight into Thu morning. We may see condition improve a
bit faster than what we have, but was more concerned about the
incoming shra/precip threat.

Fri...MVFR ceilings possible early then VFR. Wind NE 5 kts.
Sat...VFR. Wind light and variable.
Sun...VFR. Wind NE-E 5 kts.




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