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Area forecast discussion 
National Weather Service Twin Cities/Chanhassen Minnesota
523 am CDT Wednesday Sep 2 2015

Updated for 12z aviation discussion...
issued at 517 am CDT Wednesday Sep 2 2015

&&

Short term...(today and tonight)
issued at 335 am CDT Wednesday Sep 2 2015

The combination of an upper level shortwave together with a
seasonably moist airmass and 2000 j/kg of MUCAPE resulted in an
area of showers and thunderstorms across southern Minnesota this
morning. 15 minute rainfall rates equated out to around 4 inches
per hour under the heaviest cores...and flash 3hr precipitation return
periods were 50 to 100yrs across western Minnesota. Fortunately the
system has picked up a bit of speed so not anticipating any Hydro
problems.

The hires models all are in agreement with weakening the system
throughout the day. The hrrr/devhrrr are doing the best in terms of
timing...so trended this mornings probability of precipitation toward those solutions.
Given that line of thinking...although the timing was sped up
from the previous forecast...may have to shift probability of precipitation northeast even
quicker and dry the region behind this mornings precipitation. Today will
be another muggy day with the same airmass in place. Dewpoints
will once again Hoover around 70 degree...and afternoon highs will be
in the 80s for most locations. Tonight may have to introduce fog
into the forecast if the surface winds decouple more than
currently forecast.

Long term...(thursday through tuesday)
issued at 335 am CDT Wednesday Sep 2 2015

Thu-Fri...a sharp trough/ridge pattern will develop Thursday into Thursday
night over the western-central Continental U.S. Which will prevent any sensible
weather systems from impacting the upper miss River Valley region...
keeping rainfall over the active Pacific northwest and northern rockies along with
the 4-corners region. For the middle-upper miss River Valley...increasing 500 mb
heights along with a prolonged deep plume of moisture from the
Gomex will spell warm/humid conditions for the end of the workweek
as highs increases to the upper 80s to around 90 and heat index values
climb through the 90s.

Sat-sun...the upper ridge will shift east into the Great Lakes/Ohio
Valley/mid-Atlantic regions while a cutoff low swings into the
northern California coast. With all large-scale features shifting
eastward...this puts a transitional meridional flow over the central
Continental U.S....opening the door to a period of active weather for the
weekend. The cutoff low will hold its form and jump over the northern
intermountain region and northern rockies to the northern plains Sat through
sun...helping aid cyclogenesis in advance of its path. With a
developing low pressure system...deep southwesterly flow...plenty of moisture
and support from aloft...periods of showers/thunderstorms can be expected
from early Saturday through Sun night. Not looking for much...if
anything...in the way of severe weather as parameters are not favorable
for such. However...precipitable waters approaching 2 inches within an atmos
capable of promoting high precipitation efficiency may well make for
periods of heavy rain and localized flooding. As for temperatures...
warm/humid conditions will remain in place with highs still in the
80s and heat index values into the 90s.

Mon-Tue...a more vertically stacked low pressure center from both the
aforementioned cutoff upper low and developing surface low will locate
itself over southern Manitoba province by midday Monday...with its
trailing cold front having been pushed through the area. This will allow a
more west-northwest-east-southeast flow aloft to develop...bringing in cooler and more
stable air to the region with surface high pressure. Cooler/drier air will
then take up residence over the area for the early part of next
week with little to no chances for precipitation. Highs will drop
back into the 70s with lows in the 50s.

&&

Aviation...(for the 12z tafs through 12z Thursday morning)
issued at 517 am CDT Wednesday Sep 2 2015

VFR conditions today at the Minnesota sites...with some lingering
MVFR possible at the Wisconsin sites. Precipitation will shift east
today...with afternoon redevelopment possible at Keau. Tonight
winds will decrease...so the potential is there for fog
development after midnight.

Kmsp...
area of rain should be out the door by 12z...with VFR conditions
throughout. Not anticipating redevelopment this afternoon...and
also not expecting fog to cause restrictions Thursday morning at
kmsp.

/Outlook for kmsp/
Friday...VFR. Wind S at 10g20kt.
Sat...VFR with MVFR and rain showers/thunderstorms and rain possible. Wind S at 10g20kt.
Sun...VFR with MVFR/IFR thunderstorms and rain possible early. Wind S at 15g20kt.

&&

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

$$

Short term...jrb
long term...jpc
aviation...jrb

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