Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 191809
AFDMPX

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

.SHORT TERM...(Today and tonight)
Issued at 400 AM CDT Wed Apr 19 2017

Two weather concerns in the next 12-24 hrs. First, the onset of
precipitation remains on track for late this morning/early
afternoon across southwest, and south central Minnesota. Current
convection in South Dakota and Nebraska was associated with
strong forcing in advance of the short wave moving out of the
Rockies. Early morning water vapor imagery indicated several
smaller waves embedded in this short wave that will likely enhance
the morning convection across South Dakota and Nebraska.

Initial dry air mass above the boundary layer across Minnesota
will inhibit some of the precipitation from reaching the surface
this morning/early afternoon, or until deeper moisture surges
northward ahead of the short wave in the Rockies. Therefore, most
areas will be dry until noon, especially in eastern Minnesota, and
west central Wisconsin. Once moisture deepens and associated
enhancement of the short wave moves across the Plains, a broad
area of convection will develop.

Between 18-00z precipitation will likely expand rapidly across
southern Minnesota. Current pops/QPF amounts reflect this trend.
Later forecasters can readjust pops/QPF amounts once convection
develops across the region. Model QPF amounts looks to be
associated with the 85h jet and moisture convergence across
Minnesota and South Dakota. Further to the south, most of the
convection will be associated with afternoon instability once the
cap breaks.

The second weather concern is severe thunderstorm potential,
especially in south central/southeast Minnesota where elevated
instability is highest. See the latest SPC outlook for more
information. The latest GFS/EC/MPAS/GEM keep the highest elevated
instability south of the Minnesota border. However, the latest
RAP, which has been consistent over the past several hrs, has this
elevated instability parameter much further north across
Minnesota. If we can tap this higher elevated instability, which
will coincide with high helicity values and wind shear, severe
thunderstorms will be possible. The main threat will be large hail
as all the instability is above the boundary layer. However, this
is something to consider later today as thunderstorms develops.
Overnight convection will centered across central Minnesota where
better moisture convergence remains with the low level jet.

.LONG TERM...(Thursday through Tuesday)
Issued at 400 AM CDT Wed Apr 19 2017

Thursday through Sunday...The period will commence with a potent
low pressure system having moved into central WI by daybreak
Thursday morning. While a trailing NW-SE oriented surface trough
on the backside of the departing low will enhance a wintry mix of
precipitation over NE MN into northern WI, only leftover rain
showers are expected for eastern portions of the WFO MPX coverage
area Thursday into Thursday evening. Any and all precipitation
will end by late Thursday night with surface high pressure
dropping in from the northwest Friday. In addition to the surface
feature, a slow-moving bubble ridge will slide into the Upper
Mississippi River Valley from the Dakotas Friday night, forming a
ridge axis extending off to the NE. The ridge will give way to a
weak cold front dropping through the region late Saturday and
Saturday evening but the system will be fairly devoid of moisture
by the time it drops into central-southern MN and central WI so no
precipitation is expected from this frontal passage. The upper
level ridge will then re-establish itself over the region late
Saturday night through Sunday night, so the overall theme for the
weekend will be generally dry with temperatures right around
normal for mid-April.

Monday and Tuesday...After a tranquil weekend, the pattern looks
to become quite active for the first half of next week. The first
potent upper level pivoting trough will swing through the region
Monday into Monday night, shoving a compact but deeply moist low
pressure system through the region. Periods of showers (and
possibly thunderstorms) are expected for Monday and Monday night.
Once this system exits the area Tuesday, another system is right
on its heels for the latter half of next week and it is this later
system that could bring more prolonged rains to the area as it
looks to become wound up and stacked over southern MN Wednesday
through Friday. Too early to determine rainfall amounts from
either system at this point but safe to say that it`d be beyond
simple spotty rain showers. Temperatures look to remain near
normal through not only the first part of next week but also into
the latter portion of the week as no significant airmass changes
are evident.

&&

.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.

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

&&

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

$$

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



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