Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
414 am CDT Monday Jul 6 2015
Short term...(today and tonight)
issued at 414 am CDT Monday Jul 6 2015
Torrential rains are in progress early this morning from south
central Minnesota through the south/east metropolitan and into west central WI.
Rainfall rates have been around 2 inches an hour overnight in the
heaviest activity. Areas from New Ulm through the south metropolitan and
western WI are on their third round of heavy rain. Hence...we
expanded the flash Flood Advisory earlier this morning to go well into western WI
as well as Goodhue County in southeast Minnesota through 1 PM. Some counties in
central and west central Minnesota were removed as the threat for heavy
rainfall is along and southeast of a cold front that stretches from Lake
Superior through the west metropolitan to Sioux Falls. Two mesoscale convective vortex/S are
noted in the radar imagery across southern Minnesota early this
morning...with one currently near the south metropolitan...with a very
impressive one near kfsd.
Going forward this morning...the heavy rainfall axis will sink
slowly south. The 00z cams and hrrr runs have not had a good
handle on this activity as they have been too far north and a
little slow. Interestingly...the 12z run of the NSSL WRF has a
better depiction at 09z this morning (21 hour fcst). To the rear
of the convective activity is a large mainly stratiform area of
rain with isolated thunder that will continue to stream northeast
across much of the forecast area today ahead of a deepening upper level wave.
Categorical probability of precipitation remain in place with a diminishing trend during
the late afternoon and evening. The threat for renewed strong to
severe thunderstorm development in the afternoon looks like it
will take off just east and south of our forecast area.
Overnight...high pressure will spread with clearing skies along
with dew points dropping back into the middle to upper 40s.
However...with the incoming high is more northwest flow aloft.
National oceanic and atmospheric administration air quality forecast guidance shows more smoke coming into
our Minnesota County Warning Area during the overnight hours. This may cause some
visibility reductions once again across west central into south
central Minnesota. Later shifts will need to decide whether or not it/S
thick enough to mention in the grids.
Long term...(tuesday through sunday)
issued at 414 am CDT Monday Jul 6 2015
No significant changes in thinking during the extended...with cool
and dry Canadian high pressure middle-week eventually giving way to the
return of hot and humid conditions...along with thunderstorm chances
Tuesday and Wednesday...a Canadian high will move across the
area...with dewpoints falling comfortably back into the 40s. 850 mb
temperatures will be back under 10c...which will support highs in the lower
70s...while those lower dewpoints will allow morning lows to drop
back into the 40s/50s. The only drawback to the weather Tuesday and
Wednesday is that this Canadian high will likely bring another round
of smoke with it. This could find its way to the surface...but it/S too
early to tell if this will give US nothing more than a milk colored
sky...or will be able to reduce the visibility and lead to poor air
Not expecting any precipitation until Friday night when a warm front and
tropical air make their return. This warm front will be coming north
in response to a subtropical ridge that will be building across the
Southern Plains...with an upper ridge axis nudging north into the upper
MS valley. This boundary will likely get hung up over/near our area
with the potential for multiple rounds of thunderstorms from
Friday night through Sunday night. 850 mb temperatures also look to warm into
the middle 20s c...which would be supportive of highs in the 90s.
However...with the threat for showers/storms and cloud cover...kept
forecast of highs in the middle/upper 80s going...but if we Don/T have
convection littering the landscape much this weekend...our current
forecast highs for the weekend are likely a good 5 degrees to cold.
Beyond next weekend we will have to watch how far east the ridge
builds across the plains...but certainly both the GFS/European model (ecmwf) are
hinting a significant heat wave building across the plains for the
middle of July.
Aviation...(for the 06z tafs through 06z Monday night)
issued at 1158 PM CDT sun Jul 5 2015
Band of showers and thunderstorms will continue sinking southeast
slowly overnight. Very heavy rain is possible in any of the
thunderstorm cores. A larger...albeit lighter area of rain across
South Dakota will push in behind this line overnight and persist
for much of Monday. Ceilings will deteriorate as winds become north
behind the cold front. Rapidly improving conditions are expected
following the rain late Monday afternoon/evening.
Kmsp...should see rain begin around 06z with the heaviest arriving
between 07-10z. Showers and storms will persist for much of
/Outlook for kmsp/
Tuesday...VFR. Winds north-northwest 5-10 kts.
Wednesday...VFR. Winds S 5-10 kts.
Thursday...VFR. Winds S 5-10 kts.
Minnesota...Flash Flood Watch until 1 PM CDT this afternoon for mnz051>053-
WI...Flash Flood Watch until 1 PM CDT this afternoon for wiz014-015-