Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
644 PM CDT Wednesday Jul 30 2014
Short term...(this evening through thursday)
issued at 234 PM CDT Wednesday Jul 30 2014
Tonight and Thursday...surface analysis continues to show extensive
high pressure over much of the north-central states. Aloft...the
pattern continues to be a trough East...Ridge west...with northwest
flow over central North America. Water vapor imagery shows a swath
of moisture rounding the western fringes of the eastern trough...
around a developing cutoff low within the center of the trough over
Ontario. As this moisture drops south into northern Minnesota and
Lake Superior...additional cloud cover can be expected over western
Wisconsin and far eastern Minnesota through the rest of the
afternoon and early evening hours. Going further west into
Minnesota...aside from diurnal pop-up middle-level cumulus clouds... no
significant weather is expected. However...for western Wisconsin...
this additional moisture is in response to another weak shortwave
disturbance aloft. Similar to yesterday...this disturbance will aid
in isolated shower/thunderstorm development for portions of western
Wisconsin. The shortwave for today is not as impressive as the one
experienced yesterday...therefore am expecting lesser coverage and
intensity of any storms that do form. Any and all activity is
expected to dissipate by sunset...allowing for clear skies
overnight. A similar story is then expected for tomorrow as yet
another weak disturbance aloft combined with the heating of the day
will make for isolated afternoon showers and thunderstorms over
western Wisconsin. As for temperatures...more of the same is
expected with no change in airmass. Highs on Thursday will be
similar to today...reaching the upper 70s to lower 80s. Lows tonight
will be similar to what was recorded early this morning...again
dropping to the middle 50s to around 60.
Long term...(thursday night through wednesday)
issued at 234 PM CDT Wednesday Jul 30 2014
The longer term outlook hasn/T changed much with things still
looking to become more active as we head into next week. The
eastern upper trough looks to lift northward as the western ridge
flattens some while expanding eastward over time. Of concern with
respect to active weather... particularly heavy rain potential...
is a cutoff upper low beneath the upper ridge which is prognosticated by
both the European model (ecmwf) and GFS to slide northeast/east into our area
during the first part of the week. This feature looks to be
accompanied by some monsoonal moisture... which helps to boost
precipitable water values over the region that will already be
increasing somewhat in situ from local/regional
evapotranspiration. The main time frame of concern looks to be
from later Monday through late Wednesday as the baroclinic zone
loiters in the area with the surface trough positioned to our
west. The GFS and European model (ecmwf) show the potential for several rounds of
precipitation/convection during that time frame... and produce copious
rainfall in our general vicinity... ranging from 2 to as much as 6
inches or so. The location and timing of each round of precipitation is
highly questionable at this time... and it/S possible the heaviest
activity could be just to our north or south. But... the overall
pattern is looking more favorable for some heavy rainfall in the
region... with confidence increasing a bit with each successive
series of deterministic and ensemble guidance. Prior to that...
we/ll have some occasional chances for scattered lighter precipitation as
shortwaves cruise through the area in the lingering northwest flow
and we maintain sufficient lapse rates for some rain showers and isolated
Aviation...(for the 00z tafs through 00z Thursday evening)
issued at 644 PM CDT Wednesday Jul 30 2014
Quiet weather continues over most of area. Exception will be
chance of fog late tonight around parts of west central Wisconsin.
Scattered afternoon and evening showers the past few days have
moistened the low levels somewhat. Light winds and mostly clear
skies suggest some fog may form late tonight in wisc...especially
in river valleys and other low lying areas.
Thursday weather will be much the same as the past few days. Afternoon
or evening showers in eastern Minnesota and western wisc are possible
as upper low remains parked over James Bay. Thus occasional short
waves rotating southward across Wisconsin will continue. Maybe some
thunder in a couple spots as well tomorrow. Western Minnesota should just have
some afternoon cumulus.
Kmsp...VFR conditions will continue. Light west-northwest wind tonight is
generally unfavorable for fog at kmsp. More cumulus will develop late
tomorrow morning along with increase in northwest winds to 8-10 knots.
/Outlook for kmsp/
Friday...VFR. Slight chance afternoon thunder. Winds northwest 5 kts.
Sat...VFR. Winds variable 5 kts.
Sun...mainly VFR. Slight chance of thunder. Winds SW 5-10 kts.