NWS Forecast Discussion

FXUS63 KMPX 241201

Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
701 AM CDT Sun Jun 24 2018

.Updated for 12Z Aviation Discussion
Issued at 656 AM CDT Sun Jun 24 2018


.SHORT TERM...(Today and tonight)
Issued at 330 AM CDT Sun Jun 24 2018

Today will be partly sunny with scattered showers and thunderstorms.
The best chance for rain is across western Minnesota and the Upper
Minnesota River Valley during the late afternoon and evening. The
threat for severe weather is very low because the wind shear is
light. However storms that do develop will be moving slowly, so
similar to yesterday areas that are under these storms could pick up
a quick couple of inches of rain. WPC has a marginal to slight risk
for excessive rain across southwest Minnesota today and tonight.

Not much change from the previous forecast other than tighten the
gradient of precipitation chances based on the latest runs of the
HiRes models. Early morning water vapor imagery with H500 winds
showed an area of weak, compact positive vorticity across eastern
South Dakota, with another larger area across northern Wyoming.

Over the next 36 hours this first shortwave will weaken as it gets
sheared out, but could still spark a few morning showers and
thunderstorms. There should be a break, but then expect the forcing
with this second wave to redevelop and area of storms in western
Minnesota Sunday afternoon and evening. This precipitation is very
slow to move with the weak steering winds aligned parallel to the
forcing, so could see training thunderstorms along with slow moving
thunderstorms, and this could lead to heavy rain and a flooding
threat late Sunday into Monday and lasting through Tuesday

.LONG TERM...(Monday through Saturday)
Issued at 330 AM CDT Sun Jun 24 2018

The extended period will start with the upper level low drifting
northeast across the Upper Midwest on Monday, and into Tuesday.
During this time frame, precipitable water values are very high
(averaging around 1.7") and the atmosphere will be very efficient
for higher rainfall rates. This will lead to excessive rainfall
amounts, and the possibility of more flooding. The other aspect
is if we get ample instability to generate a few stronger storms
Tuesday. The circulation around the upper low will place the best
divergence and jet max on the east side of the low. Currently,
this upper low is forecast to move over southern Minnesota, with
the best potential of severe storms in eastern Iowa and into
southern Wisconsin (See latest SPC outlook). Any slight deviation
to this track could mean a better chance of stronger storms
Tuesday. However, the main concern will remain the threat of heavy
rainfall and continued flooding, especially considering the
abnormally high river levels in southern Minnesota.

By Tuesday night, this system will quickly depart the Upper Midwest
as strong westerlies develop overhead. There remains a subtle short
wave moving across the region Wednesday. Current low pops seem
warranted as the best moisture and lift is to the east and south.

The heat and humidity will build by the end of the week, with 90s
likely in the forecast. Models have been advertising this upper
ridge building across the central CONUS, and spreading it to the
north/northeast across the Great Lakes, and northeast next weekend.
The main differences in the models is the amplitude and location of
upper ridge. Both the Fv3 (Parallel-GFS), and EC are more
amplified with the upper ridge with the operational GFS and GEM
flatter and weaker. The NAEFS/EC ensembles support the Fv3/
operational EC vs. the GFS/GEM, especially considering run to run
continuity. The more amplified models will lead to a sharper, more
amplified trough across the Northern Rockies/Northern Plains, and
Upper Midwest by the end of the week. This will have a large
impact on where the frontal boundary moves, the strength and
location of the upper jet core, and severity of storms. I wouldn`t
be surprised to see several waves of severe thunderstorms
developing across the Plains, and Upper Midwest next weekend. In
addition, if the upper ridge continues to build further west, this
will lead to more heat and humidity. 90s are still a good
possibility Friday, with 90s still a good bet for the southeastern
1/3 of MPX forecast area Saturday/Sunday. The northwestern
forecast area will likely be in the area of active weather with
several waves of thunderstorms.


.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 656 AM CDT Sun Jun 24 2018

VFR conditions with scattered showers and thunderstorms expected
across western MN which could affect KRWF KAXN and KMKT. Other taf
sites could see a thunderstorm, but chances are lower. Winds will
be southeast.

VFR conditions with scattered afternoon and evening showers and
thunderstorms. Morning thunderstorms should remain west of KMSP,
but should see redevelopment this afternoon, and these storms will
move east and could affect KMSP later this afternoon and evening.

Tue...MVFR/-SHRA/-TSRA likely. Wind SE bcmg NW 5-10 kts.
Wed...VFR. Winds NW 5-10 kts.
Thu...VFR. Winds SE 5-10 kts.





NWS MPX Office Area Forecast Discussion

Script by Ken True @Saratoga-Weather.org