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Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota
600 am CDT Friday Aug 28 2015

Updated for 12z aviation discussion...
issued at 550 am CDT Friday Aug 28 2015

&&

Short term...(today and tonight)
issued at 356 am CDT Friday Aug 28 2015

Main change in the short term was to shift precipitation chances and
heavy rain axis to the south. Early morning trends on infrared satellite
showed warming cloud tops along the I-90 corridor as the
convection became focused more along the NE/Iowa border where there
was better instability and forcing for ascent.

The reason for this change is due to the fact that the system has
become occluded...but also the lack of an upper level jet. That
means 1) there isnt a speed component to reinforce the absolute
vorticity of the shortwave...and 2) there isnt an upper level
temperature gradient contributing to the potential vorticity. As a
result...the continued diabatic heating is slowly eroding the
potential vorticity...and overall the system should continue to
weaken as forecast by the models. Therefore have shifted the precipitation
chances mainly south and east of the Twin Cities region...which
matches up better with the latest runs of the hires models. Truth be
told...have low confidence that any measurable precipitation will fall
north of I-94...so additional updates may need to continue to adjust
probability of precipitation southward.

The clouds and precipitation will lead to an atypical high temperature
gradient across the region...with afternoon highs only 60s to the
southeast...and 70s across the northwest part of the County Warning Area. Tonight
skies will clear out across the region...and may see some fog
development where winds decouple. Low temperatures will be in the
50s.

Long term...(saturday through thursday)
issued at 356 am CDT Friday Aug 28 2015

The long term forecast period will feature Summer-like weather as
we head into the first week of September. Weather concerns are
minimal...with lack of any notable weather systems in the
foreseeable future.

The weekend ahead looks to be ideal for outdoor
activities...especially on Saturday as temperatures climb to near
or slightly above normal...and couple with light winds. Could
have a thin layer of smoke aloft from the northwest fires...but
low level clouds will be on the decrease.

Temperatures look to moderate a bit on Sunday as middle level heights build
and southerly flow combines with 850 mb temperatures rising to around
+20c to +22c. Should see temperatures respond by warming into the
middle 80s across central Minnesota...with lower 80s across southern Minnesota into
west central WI. Models indicate maybe a degree or two of change
upward in those values through next week...which should translate
to fairly consistent highs in the middle/upper 80s. Dewpoints will
be hanging in the 60s...so low temperatures will be relatively warm as
well.

Models make several attempts to push a front into the area next
week...but it will be tough for any associated precipitation to make it
very far given the better forcing remains to the northwest and
overall we will be starved of deep moisture. Have therefore kept
showers and thunderstorms out of the forecast with the exception
of the evening/nocturnal timeframes when we will be less capped.
Chances still look to be slim through the majority of next week
however...so have kept chances to 20 percent or less.

&&

Aviation...(for the 12z tafs through 12z Saturday morning)
issued at 550 am CDT Friday Aug 28 2015

Main concern today is clouds. Ceilings are bouncing around from
IFR to VFR...but the expansive cirrus shield from the convection
to the south should hold back widespread IFR ceilings. Also...not
anticipating any visby restrictions with the rain since the
heaviest will be south of the taf sites. Later tonight skies will
clear and winds will diminish which should set the stage for some
patchy fog...which will be the main concern heading into Saturday
morning.

Kmsp...
a few light rain showers are possible this morning...but not
anticipating visby restrictions. The main concern will be the
potential for occasional MVFR/IFR ceilings. Not a strong feeling one
way or another...so will have to monitor the trends since the
potential is there for sub 1700ft ceilings.

/Outlook for kmsp/
Sat...VFR. Winds southeast 5-10 kts.
Sun...VFR. Winds S 5-10 kts.
Monday...VFR. Winds S 5-15 kts.

&&

Mpx watches/warnings/advisories...
Minnesota...none.
WI...none.
&&

$$

Short term...jrb
long term...ls
aviation...jrb

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