Area Forecast Discussion
Issued by NWS Twin Cities, MN

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280
FXUS63 KMPX 181828
AFDMPX

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
128 PM CDT Fri May 18 2018

.SHORT TERM...(Today and tonight)
Issued at 245 AM CDT Fri May 18 2018

Today will be much like yesterday, but the only difference will be a
bit more high cirrus left over from the convection in the Dakotas.
Early morning IR showed these high level clouds across Minnesota
into western Wisconsin, while the radar showed the precip quickly
dissipating before it reached Minnesota.

This eastward struggle for showers and thunderstorms will continue
today, so have increased temperatures above guidance, especially in
eastern MN and western WI. Southerly winds will be around 10 to 15
mph, and this should allow afternoon highs to reach the 80s once
again. We still have a 20 to 30 percent chance for showers or
thunderstorms overnight, so most locations should stay dry, and
those that do see rainfall will only get around a tenth.

.LONG TERM...(Saturday through Thursday)
Issued at 325 AM CDT Fri May 18 2018

Fairly low confidence in the forecast for this weekend rainfall
potential due to differences in the models, and the split flow
regime which models usually have a difficult time resolving.
Slightly higher confidence past this weekend as the mean flow
aloft begins to amplify with a large ridge building across western
Canadian, and into the Northern Plains/Upper Midwest.

First, a long wave trough in the western CONUS has been persistent
for the past week. Several upper level disturbance continue to
ride north/northeast across the Rockies, and into the high plains
in this long wave trough regime. Between this long wave trough,
slight ridging has dominated the Upper Midwest, with another upper
low, slightly weaker, was meandering across the Mid- Mississippi
River Valley region. This upper low is also causing problems in
the short term with convergent upper level flow across eastern
Minnesota, and Wisconsin. Although a cold front will begin to
move southeast across Minnesota/Wisconsin later today, and into
Saturday, this convergent flow aloft will weaken any energy
sliding southeast across the Upper Midwest. Thus, keeping the bulk
of the energy north of Minnesota, and southwest into
Nebraska/Iowa.

As said before, there is low confidence in the forecast this
weekend for central/southern Minnesota, and west central
Wisconsin. Even though the mean long wave trough in the west does
support some of the energy moving out into the plains this
weekend, model differences and the added drier north/northeasterly
flow developing behind the cold front, will limit any
precipitation. The best potential of widespread precipitation will
occur further to the southwest where the cold front will interact
with stronger forcing aloft as energy moves out into the plains.
The EC is the model outlier which takes much more energy with this
disturbance closer to Minnesota by late Saturday/early Sunday.
This will lead to a much better chance of precipitation across
southern Minnesota, especially along the Iowa border.

Past Sunday, the mean upper level pattern will keep any
significant weather systems to the west and south through the
period. Temperatures under the building ridge will continue the
trend of above average temperatures next week with a general dry
period.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 128 PM CDT Fri May 18 2018

Low confidence on whether or not we`ll see precip this period, as
best forcing for precip looks to go north and south of the MPX
cwa. Last couple of runs of the HRRR have been developing showers
along an advancing cold front across central MN, but will see if
this trend survives a couple of more runs before hitting the
threat for precip any harder than what we currently have with a
VCSH at STC. Beside the threat of showers, there is an expansive
area of IFR/MVFR stratus behind the front across NODAK and there
is broad model support that this stratus will sweep across MN
tonight behind the front, so introduced some MVFR cigs, similar to
what we are seeing with the HRRR/LAV. Beside the NODAK stratus,
there is also stratus down in IL/IN that will head this direction
on the southeast winds. Looks like western edge of these clouds
will make somewhere between Menomonie and Medford in WI, which is
why we introduced the 1k ft cig at EAU at 9z, though these clouds
could end up staying east of EAU.

KMSP...Shra/iso TS threat looks greatest between 6z and 10z, but
not enough confidence in its occurrence to include in the TAF at
this point. Model agreement is strong in low stratus coming in
behind the cold front. Will likely come in under 018, though think
IFR is unlikely.

/OUTLOOK FOR KMSP/
SUN...VFR. Wind ENE 5-10 kt.
MON...MVFR. Chc -SHRA. Wind E 5-10 kt.
TUE...MVFR cigs early, then VFR. Wind lgt and vrb.

&&

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

$$

SHORT TERM...JRB
LONG TERM...JLT
AVIATION...MPG



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