Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota
106 PM 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 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

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 low temperatures will be relatively warm as

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 have kept chances to 20 percent or less.


Aviation...(for the 18z tafs through 18z Saturday afternoon)
issued at 106 PM CDT Friday Aug 28 2015

Rainfall pushed into eau late this morning and this will be the
only terminal impacted by rain this period. Rainfall area is slow kept the 21z end time previous taf had...though it
could be as late as 23z before rain finally ends. Otherwise...main
issue for tonight will be the potential for low stratus/dense fog.
This morning...we saw mainly low stratus form over north central
Minnesota to the northwest of the upper cloud shield associated with the Iowa
system. Tonight...this same region will be centered right on the
mpx County Warning Area. Most models show lows tonight falling 5-10 degrees below
current dense fog is looking pretty likely east of
west central Minnesota...where strong surface winds will keep low levels
mixed and west of where the upper cloud shield with the system to
our south ends up. This would put rwf/stc/msp/rnh in a favored
region for seeing dense fog. For now...hit fog hardest at the
fields fog happens the most climatologically in that list...which
is stc/rnh. Eau could have issues with fog as well...but looks
like they may keep higher clouds through the night...which would
keep visibilities higher. After fog Burns off...Sat looks to bring sky clear
skies and southeast winds of 5 kts or less.

Kmsp...concern is growing that msp may be dealing with LIFR
conditions late tonight into Sat morning. Dense fog is likely at
the satellite airports toward the fringe of the Twin Cities metropolitan.
This will be a radiation fog...which is tough to get at
msp. Instead...current thinking is that 200-300 feet stratus may
develop as fog surrounding the Airport tries to move in...with visible
getting down to 2 or 3 sm. For now just hinted at the possibility
of this happening with the 10z line and will have to monitor this
potential closely tonight.

/Outlook for kmsp/
sun-Tue...VFR. Winds S 5-15 kts.


Mpx watches/warnings/advisories...


Short term...jrb

National Weather Service Glossary of Abbreviations