Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
1215 PM CDT Wednesday Oct 7 2015
Updated for 18z aviation discussion below...
Short term...(today through thursday)
issued at 325 am CDT Wednesday Oct 7 2015
The shortwave that has been in question for tonights rainfall
event is evident across the northern rockies and into the
Canadian rockies as of 8z. Over the past couple of days this
shortwave has trended to be faster and slightly weaker along with
a more northern track then previous model runs. In addition...a
very dry atmosphere is noted across most of Minnesota/WI which will
hamper precipitation development across western Minnesota during the
afternoon. Moisture advection is strong later tonight...but initially a
more southeast flow will keep the boundary layer dry until late in the
evening. Therefore...all of mpx County Warning Area is precipitation free until
after 00z. It is likely that most of the region will be dry until
after 3z in mpx far northwest County Warning Area. Have already trended drier during the
afternoon/evening hours. Although the models has trended further north
with the main energy of the shortwave...the moisture advection is
quite impressive late in the evening ahead of the front.
Therefore...this rainfall event may be drier initially...it should
remain favorable for a widespread event toward midnight across
central Minnesota...and spreading rapidly east/southeast across ec Minnesota and wc WI
during the morning hours. Only the far SW/SC parts of Minnesota are in
question as to whether rainfall can reach this area prior to the
frontal passage. I have trended toward a lower chance of widespread
rainfall...especially along the Iowa/Minnesota border...but confidence
remains uncertain for dropping all probability of precipitation at this time. Quantitative precipitation forecast amts
remain the same with the heaviest totals north and east of the
Twin Cities. Although some sprinkles/-shra are possible Thursday
afternoon as the system moves off to the east...cold air advection and drier air may
lead to only cloudy skies.
Long term...(thursday night through tuesday)
issued at 325 am CDT Wednesday Oct 7 2015
Behind the departing low pressure system of Thursday...upper level ridging from
the western Continental U.S. Will build into the central states. In addition...
surface high pressure from The Rockies will also slide eastward. This will make
for deep riding that will last from Thursday night on through the
weekend...suppressing a cutoff low over the Baja California Mexico region
from making any progress northward and making for a prolonged period of
dry weather. In addition...the ridge looks to make its strongest push
northward...and hence highest 500 mb heights...into the region on Sunday.
This will create significant warming to produce unseasonably warm
high temperatures on Sunday ranging from the middle 70s in western WI to the middle
80s in western Minnesota...around 15-20 degrees above climatological norms.
500 mb heights collapse a bit going into Monday as a Canadian low pressure
center looks to drag a cold front along the international border
states. Models indicate plenty of dry air will be associated with
this fnt so have opted to maintain a dry forecast even with this frontal passage
for Sun night into Monday. Surface high pressure then regains control for
early next week under northwest flow aloft...spelling a continuance of
dry weather conds but with a cooling trend in temperatures back closer to
Aviation...(for the 18z tafs through 18z Thursday afternoon)
issued at 1215 PM CDT Wednesday Oct 7 2015
Little change from previous forecast. High confidence of -shra
over the northern and eastern areas. MVFR ceilings should develop over
the northern County Warning Area in the 12z-18z period as well...as cold air advection and
northwest winds increase. Some threat of MVFR ceilings developing in
the krnh earlier but will hold off until 16z. Thunder threat is
there as well as the front moves through. Believe activity will be
fairly scattered/isolated so will leave out of tafs for now. East
to southeast winds ahead of the front into the evening becoming
west/northwest with frontal passage and becoming gusty over Minnesota taf area 12z-18z.
VFR conds through 08z. Still have high level of confidence rain showers will
develop overnight...and continue near the Airport through 12z. Best
window appears 07z-11z. Will mention MVFR visibility with the rain showers and
lower ceilings developing in the 15z-18z period as cold air advection and northwest winds
increase. This may linger into the afternoon as well.
/Outlook for kmsp/
Thursday evening...MVFR ceilings poss. Clearing late. Winds northwest 10-20kts.
Friday...VFR. Winds northwest 7-10kts.
Sat...VFR. Winds SW 15-20g25 kts.